1@c Copyright (C) 1988-2015 Free Software Foundation, Inc. 2@c This is part of the GCC manual. 3@c For copying conditions, see the file gcc.texi. 4 5@ignore 6@c man begin INCLUDE 7@include gcc-vers.texi 8@c man end 9 10@c man begin COPYRIGHT 11Copyright @copyright{} 1988-2015 Free Software Foundation, Inc. 12 13Permission is granted to copy, distribute and/or modify this document 14under the terms of the GNU Free Documentation License, Version 1.3 or 15any later version published by the Free Software Foundation; with the 16Invariant Sections being ``GNU General Public License'' and ``Funding 17Free Software'', the Front-Cover texts being (a) (see below), and with 18the Back-Cover Texts being (b) (see below). A copy of the license is 19included in the gfdl(7) man page. 20 21(a) The FSF's Front-Cover Text is: 22 23 A GNU Manual 24 25(b) The FSF's Back-Cover Text is: 26 27 You have freedom to copy and modify this GNU Manual, like GNU 28 software. Copies published by the Free Software Foundation raise 29 funds for GNU development. 30@c man end 31@c Set file name and title for the man page. 32@setfilename gcc 33@settitle GNU project C and C++ compiler 34@c man begin SYNOPSIS 35gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] 36 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] 37 [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] 38 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] 39 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] 40 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] 41 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} 42 43Only the most useful options are listed here; see below for the 44remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. 45@c man end 46@c man begin SEEALSO 47gpl(7), gfdl(7), fsf-funding(7), 48cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) 49and the Info entries for @file{gcc}, @file{cpp}, @file{as}, 50@file{ld}, @file{binutils} and @file{gdb}. 51@c man end 52@c man begin BUGS 53For instructions on reporting bugs, see 54@w{@value{BUGURL}}. 55@c man end 56@c man begin AUTHOR 57See the Info entry for @command{gcc}, or 58@w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, 59for contributors to GCC@. 60@c man end 61@end ignore 62 63@node Invoking GCC 64@chapter GCC Command Options 65@cindex GCC command options 66@cindex command options 67@cindex options, GCC command 68 69@c man begin DESCRIPTION 70When you invoke GCC, it normally does preprocessing, compilation, 71assembly and linking. The ``overall options'' allow you to stop this 72process at an intermediate stage. For example, the @option{-c} option 73says not to run the linker. Then the output consists of object files 74output by the assembler. 75 76Other options are passed on to one stage of processing. Some options 77control the preprocessor and others the compiler itself. Yet other 78options control the assembler and linker; most of these are not 79documented here, since you rarely need to use any of them. 80 81@cindex C compilation options 82Most of the command-line options that you can use with GCC are useful 83for C programs; when an option is only useful with another language 84(usually C++), the explanation says so explicitly. If the description 85for a particular option does not mention a source language, you can use 86that option with all supported languages. 87 88@cindex C++ compilation options 89@xref{Invoking G++,,Compiling C++ Programs}, for a summary of special 90options for compiling C++ programs. 91 92@cindex grouping options 93@cindex options, grouping 94The @command{gcc} program accepts options and file names as operands. Many 95options have multi-letter names; therefore multiple single-letter options 96may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d 97-v}}. 98 99@cindex order of options 100@cindex options, order 101You can mix options and other arguments. For the most part, the order 102you use doesn't matter. Order does matter when you use several 103options of the same kind; for example, if you specify @option{-L} more 104than once, the directories are searched in the order specified. Also, 105the placement of the @option{-l} option is significant. 106 107Many options have long names starting with @samp{-f} or with 108@samp{-W}---for example, 109@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of 110these have both positive and negative forms; the negative form of 111@option{-ffoo} is @option{-fno-foo}. This manual documents 112only one of these two forms, whichever one is not the default. 113 114@c man end 115 116@xref{Option Index}, for an index to GCC's options. 117 118@menu 119* Option Summary:: Brief list of all options, without explanations. 120* Overall Options:: Controlling the kind of output: 121 an executable, object files, assembler files, 122 or preprocessed source. 123* Invoking G++:: Compiling C++ programs. 124* C Dialect Options:: Controlling the variant of C language compiled. 125* C++ Dialect Options:: Variations on C++. 126* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C 127 and Objective-C++. 128* Language Independent Options:: Controlling how diagnostics should be 129 formatted. 130* Warning Options:: How picky should the compiler be? 131* Debugging Options:: Symbol tables, measurements, and debugging dumps. 132* Optimize Options:: How much optimization? 133* Preprocessor Options:: Controlling header files and macro definitions. 134 Also, getting dependency information for Make. 135* Assembler Options:: Passing options to the assembler. 136* Link Options:: Specifying libraries and so on. 137* Directory Options:: Where to find header files and libraries. 138 Where to find the compiler executable files. 139* Spec Files:: How to pass switches to sub-processes. 140* Target Options:: Running a cross-compiler, or an old version of GCC. 141* Submodel Options:: Specifying minor hardware or convention variations, 142 such as 68010 vs 68020. 143* Code Gen Options:: Specifying conventions for function calls, data layout 144 and register usage. 145* Environment Variables:: Env vars that affect GCC. 146* Precompiled Headers:: Compiling a header once, and using it many times. 147@end menu 148 149@c man begin OPTIONS 150 151@node Option Summary 152@section Option Summary 153 154Here is a summary of all the options, grouped by type. Explanations are 155in the following sections. 156 157@table @emph 158@item Overall Options 159@xref{Overall Options,,Options Controlling the Kind of Output}. 160@gccoptlist{-c -S -E -o @var{file} -no-canonical-prefixes @gol 161-pipe -pass-exit-codes @gol 162-x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol 163--version -wrapper @@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol 164-fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}} 165 166@item C Language Options 167@xref{C Dialect Options,,Options Controlling C Dialect}. 168@gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol 169-aux-info @var{filename} -fallow-parameterless-variadic-functions @gol 170-fno-asm -fno-builtin -fno-builtin-@var{function} @gol 171-fhosted -ffreestanding -fopenmp -fms-extensions -fplan9-extensions @gol 172-trigraphs -traditional -traditional-cpp @gol 173-fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol 174-fsigned-bitfields -fsigned-char @gol 175-funsigned-bitfields -funsigned-char} 176 177@item C++ Language Options 178@xref{C++ Dialect Options,,Options Controlling C++ Dialect}. 179@gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol 180-fconstexpr-depth=@var{n} -ffriend-injection @gol 181-fno-elide-constructors @gol 182-fno-enforce-eh-specs @gol 183-ffor-scope -fno-for-scope -fno-gnu-keywords @gol 184-fno-implicit-templates @gol 185-fno-implicit-inline-templates @gol 186-fno-implement-inlines -fms-extensions @gol 187-fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol 188-fno-optional-diags -fpermissive @gol 189-fno-pretty-templates @gol 190-frepo -fno-rtti -fstats -ftemplate-backtrace-limit=@var{n} @gol 191-ftemplate-depth=@var{n} @gol 192-fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol 193-fno-default-inline -fvisibility-inlines-hidden @gol 194-fvisibility-ms-compat @gol 195-fext-numeric-literals @gol 196-Wabi -Wconversion-null -Wctor-dtor-privacy @gol 197-Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing @gol 198-Wnoexcept -Wnon-virtual-dtor -Wreorder @gol 199-Weffc++ -Wstrict-null-sentinel @gol 200-Wno-non-template-friend -Wold-style-cast @gol 201-Woverloaded-virtual -Wno-pmf-conversions @gol 202-Wsign-promo} 203 204@item Objective-C and Objective-C++ Language Options 205@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling 206Objective-C and Objective-C++ Dialects}. 207@gccoptlist{-fconstant-string-class=@var{class-name} @gol 208-fgnu-runtime -fnext-runtime @gol 209-fno-nil-receivers @gol 210-fobjc-abi-version=@var{n} @gol 211-fobjc-call-cxx-cdtors @gol 212-fobjc-direct-dispatch @gol 213-fobjc-exceptions @gol 214-fobjc-gc @gol 215-fobjc-nilcheck @gol 216-fobjc-std=objc1 @gol 217-freplace-objc-classes @gol 218-fzero-link @gol 219-gen-decls @gol 220-Wassign-intercept @gol 221-Wno-protocol -Wselector @gol 222-Wstrict-selector-match @gol 223-Wundeclared-selector} 224 225@item Language Independent Options 226@xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. 227@gccoptlist{-fmessage-length=@var{n} @gol 228-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol 229-fno-diagnostics-show-option -fno-diagnostics-show-caret} 230 231@item Warning Options 232@xref{Warning Options,,Options to Request or Suppress Warnings}. 233@gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol 234-pedantic-errors @gol 235-w -Wextra -Wall -Waddress -Waggregate-return @gol 236-Waggressive-loop-optimizations -Warray-bounds @gol 237-Wno-attributes -Wno-builtin-macro-redefined @gol 238-Wc++-compat -Wc++11-compat -Wcast-align -Wcast-qual @gol 239-Wchar-subscripts -Wclobbered -Wcomment @gol 240-Wconversion -Wcoverage-mismatch -Wno-cpp -Wno-deprecated @gol 241-Wno-deprecated-declarations -Wdisabled-optimization @gol 242-Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol 243-Wno-endif-labels -Werror -Werror=* @gol 244-Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol 245-Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol 246-Wformat-security -Wformat-y2k @gol 247-Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol 248-Wignored-qualifiers @gol 249-Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol 250-Winit-self -Winline -Wmaybe-uninitialized @gol 251-Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol 252-Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol 253-Wlogical-op -Wlong-long @gol 254-Wmain -Wmaybe-uninitialized -Wmissing-braces -Wmissing-field-initializers @gol 255-Wmissing-include-dirs @gol 256-Wno-mudflap @gol 257-Wno-multichar -Wnonnull -Wno-overflow @gol 258-Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol 259-Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol 260-Wpointer-arith -Wno-pointer-to-int-cast @gol 261-Wredundant-decls -Wno-return-local-addr @gol 262-Wreturn-type -Wsequence-point -Wshadow @gol 263-Wsign-compare -Wsign-conversion -Wsizeof-pointer-memaccess @gol 264-Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol 265-Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol 266-Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol 267-Wmissing-format-attribute @gol 268-Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol 269-Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef @gol 270-Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol 271-Wunsuffixed-float-constants -Wunused -Wunused-function @gol 272-Wunused-label -Wunused-local-typedefs -Wunused-parameter @gol 273-Wno-unused-result -Wunused-value @gol -Wunused-variable @gol 274-Wunused-but-set-parameter -Wunused-but-set-variable @gol 275-Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol 276-Wvla -Wvolatile-register-var -Wwrite-strings -Wzero-as-null-pointer-constant} 277 278@item C and Objective-C-only Warning Options 279@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol 280-Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol 281-Wold-style-declaration -Wold-style-definition @gol 282-Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol 283-Wdeclaration-after-statement -Wpointer-sign} 284 285@item Debugging Options 286@xref{Debugging Options,,Options for Debugging Your Program or GCC}. 287@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol 288-fsanitize=@var{style} @gol 289-fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol 290-fdisable-ipa-@var{pass_name} @gol 291-fdisable-rtl-@var{pass_name} @gol 292-fdisable-rtl-@var{pass-name}=@var{range-list} @gol 293-fdisable-tree-@var{pass_name} @gol 294-fdisable-tree-@var{pass-name}=@var{range-list} @gol 295-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol 296-fdump-translation-unit@r{[}-@var{n}@r{]} @gol 297-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol 298-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol 299-fdump-passes @gol 300-fdump-statistics @gol 301-fdump-tree-all @gol 302-fdump-tree-original@r{[}-@var{n}@r{]} @gol 303-fdump-tree-optimized@r{[}-@var{n}@r{]} @gol 304-fdump-tree-cfg -fdump-tree-alias @gol 305-fdump-tree-ch @gol 306-fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol 307-fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol 308-fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol 309-fdump-tree-dom@r{[}-@var{n}@r{]} @gol 310-fdump-tree-dse@r{[}-@var{n}@r{]} @gol 311-fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol 312-fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol 313-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol 314-fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol 315-fdump-tree-nrv -fdump-tree-vect @gol 316-fdump-tree-sink @gol 317-fdump-tree-sra@r{[}-@var{n}@r{]} @gol 318-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol 319-fdump-tree-fre@r{[}-@var{n}@r{]} @gol 320-fdump-tree-vrp@r{[}-@var{n}@r{]} @gol 321-ftree-vectorizer-verbose=@var{n} @gol 322-fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol 323-fdump-final-insns=@var{file} @gol 324-fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol 325-feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol 326-feliminate-unused-debug-symbols -femit-class-debug-always @gol 327-fenable-@var{kind}-@var{pass} @gol 328-fenable-@var{kind}-@var{pass}=@var{range-list} @gol 329-fdebug-types-section -fmem-report-wpa @gol 330-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol 331-fopt-info @gol 332-fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol 333-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol 334-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol 335-fstack-usage -ftest-coverage -ftime-report -fvar-tracking @gol 336-fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol 337-g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol 338-ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol 339-gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol 340-gvms -gxcoff -gxcoff+ @gol 341-fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol 342-fdebug-prefix-map=@var{old}=@var{new} @gol 343-femit-struct-debug-baseonly -femit-struct-debug-reduced @gol 344-femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol 345-p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol 346-print-multi-directory -print-multi-lib -print-multi-os-directory @gol 347-print-prog-name=@var{program} -print-search-dirs -Q @gol 348-print-sysroot -print-sysroot-headers-suffix @gol 349-save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} 350 351@item Optimization Options 352@xref{Optimize Options,,Options that Control Optimization}. 353@gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}] @gol 354-falign-jumps[=@var{n}] @gol 355-falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol 356-fassociative-math -fauto-inc-dec -fbranch-probabilities @gol 357-fbranch-target-load-optimize -fbranch-target-load-optimize2 @gol 358-fbtr-bb-exclusive -fcaller-saves @gol 359-fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol 360-fcompare-elim -fcprop-registers -fcrossjumping @gol 361-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol 362-fcx-limited-range @gol 363-fdata-sections -fdce -fdelayed-branch @gol 364-fdelete-null-pointer-checks -fdevirtualize -fdse @gol 365-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol 366-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol 367-fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol 368-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol 369-fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol 370-fif-conversion2 -findirect-inlining @gol 371-finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol 372-finline-small-functions -fipa-cp -fipa-cp-clone @gol 373-fipa-pta -fipa-profile -fipa-pure-const -fipa-reference @gol 374-fira-algorithm=@var{algorithm} @gol 375-fira-region=@var{region} -fira-hoist-pressure @gol 376-fira-loop-pressure -fno-ira-share-save-slots @gol 377-fno-ira-share-spill-slots -fira-verbose=@var{n} @gol 378-fivopts -fkeep-inline-functions -fkeep-static-consts @gol 379-floop-block -floop-interchange -floop-strip-mine -floop-nest-optimize @gol 380-floop-parallelize-all -flto -flto-compression-level @gol 381-flto-partition=@var{alg} -flto-report -fmerge-all-constants @gol 382-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol 383-fmove-loop-invariants fmudflap -fmudflapir -fmudflapth -fno-branch-count-reg @gol 384-fno-default-inline @gol 385-fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol 386-fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol 387-fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol 388-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol 389-fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol 390-fpartial-inlining -fpeel-loops -fpredictive-commoning @gol 391-fprefetch-loop-arrays -fprofile-report @gol 392-fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol 393-fprofile-generate=@var{path} @gol 394-fprofile-use -fprofile-use=@var{path} -fprofile-values @gol 395-freciprocal-math -free -fregmove -frename-registers -freorder-blocks @gol 396-freorder-blocks-and-partition -freorder-functions @gol 397-frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol 398-frounding-math -fsched2-use-superblocks -fsched-pressure @gol 399-fsched-spec-load -fsched-spec-load-dangerous @gol 400-fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol 401-fsched-group-heuristic -fsched-critical-path-heuristic @gol 402-fsched-spec-insn-heuristic -fsched-rank-heuristic @gol 403-fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol 404-fschedule-insns -fschedule-insns2 -fsection-anchors @gol 405-fselective-scheduling -fselective-scheduling2 @gol 406-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol 407-fshrink-wrap -fsignaling-nans -fsingle-precision-constant @gol 408-fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector @gol 409-fstack-protector-all -fstrict-aliasing -fstrict-overflow @gol 410-fthread-jumps -ftracer -ftree-bit-ccp @gol 411-ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol 412-ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop @gol 413-ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse @gol 414-ftree-forwprop -ftree-fre -ftree-loop-if-convert @gol 415-ftree-loop-if-convert-stores -ftree-loop-im @gol 416-ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol 417-ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol 418-ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol 419-ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol 420-ftree-switch-conversion -ftree-tail-merge @gol 421-ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol 422-funit-at-a-time -funroll-all-loops -funroll-loops @gol 423-funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol 424-fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol 425-fwhole-program -fwpa -fuse-ld=@var{linker} -fuse-linker-plugin @gol 426--param @var{name}=@var{value} 427-O -O0 -O1 -O2 -O3 -Os -Ofast -Og} 428 429@item Preprocessor Options 430@xref{Preprocessor Options,,Options Controlling the Preprocessor}. 431@gccoptlist{-A@var{question}=@var{answer} @gol 432-A-@var{question}@r{[}=@var{answer}@r{]} @gol 433-C -dD -dI -dM -dN @gol 434-D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol 435-idirafter @var{dir} @gol 436-include @var{file} -imacros @var{file} @gol 437-iprefix @var{file} -iwithprefix @var{dir} @gol 438-iwithprefixbefore @var{dir} -isystem @var{dir} @gol 439-cxx-isystem @var{dir} @gol 440-imultilib @var{dir} -isysroot @var{dir} @gol 441-M -MM -MF -MG -MP -MQ -MT -nostdinc @gol 442-P -fdebug-cpp -ftrack-macro-expansion -fworking-directory @gol 443-remap -trigraphs -undef -U@var{macro} @gol 444-Wp,@var{option} -Xpreprocessor @var{option} -no-integrated-cpp} 445 446@item Assembler Option 447@xref{Assembler Options,,Passing Options to the Assembler}. 448@gccoptlist{-Wa,@var{option} -Xassembler @var{option}} 449 450@item Linker Options 451@xref{Link Options,,Options for Linking}. 452@gccoptlist{@var{object-file-name} -l@var{library} @gol 453-nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol 454-s -static -static-libgcc -static-libstdc++ @gol 455-static-libasan -static-libtsan @gol 456-shared -shared-libgcc -symbolic @gol 457-T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol 458-u @var{symbol}} 459 460@item Directory Options 461@xref{Directory Options,,Options for Directory Search}. 462@gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} 463-iremap@var{src}:@var{dst} -L@var{dir} 464-specs=@var{file} -I- --sysroot=@var{dir}} 465 466@item Target Options 467@c I wrote this xref this way to avoid overfull hbox. -- rms 468@xref{Target Options}. 469@gccoptlist{-V @var{version} -b @var{machine}} 470@gccoptlist{-B@var{prefix} -I@var{dir} -iplugindir=@var{dir} @gol 471-iquote@var{dir} -L@var{dir} -specs=@var{file} -I- @gol 472--sysroot=@var{dir} --no-sysroot-suffix} 473 474@item Machine Dependent Options 475@xref{Submodel Options,,Hardware Models and Configurations}. 476@c This list is ordered alphanumerically by subsection name. 477@c Try and put the significant identifier (CPU or system) first, 478@c so users have a clue at guessing where the ones they want will be. 479 480@emph{AArch64 Options} 481@gccoptlist{-mbig-endian -mlittle-endian @gol 482-mgeneral-regs-only @gol 483-mcmodel=tiny -mcmodel=small -mcmodel=large @gol 484-mstrict-align @gol 485-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol 486-mtls-dialect=desc -mtls-dialect=traditional @gol 487-mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 @gol 488-march=@var{name} -mcpu=@var{name} -mtune=@var{name}} 489 490@emph{Adapteva Epiphany Options} 491@gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol 492-mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol 493-msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol 494-mround-nearest -mlong-calls -mshort-calls -msmall16 @gol 495-mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol 496-msplit-vecmove-early -m1reg-@var{reg}} 497 498@emph{ARM Options} 499@gccoptlist{-mapcs-frame -mno-apcs-frame @gol 500-mabi=@var{name} @gol 501-mapcs-stack-check -mno-apcs-stack-check @gol 502-mapcs-float -mno-apcs-float @gol 503-mapcs-reentrant -mno-apcs-reentrant @gol 504-msched-prolog -mno-sched-prolog @gol 505-mlittle-endian -mbig-endian -mwords-little-endian @gol 506-mfloat-abi=@var{name} @gol 507-mfp16-format=@var{name} 508-mthumb-interwork -mno-thumb-interwork @gol 509-mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol 510-mstructure-size-boundary=@var{n} @gol 511-mabort-on-noreturn @gol 512-mlong-calls -mno-long-calls @gol 513-msingle-pic-base -mno-single-pic-base @gol 514-mpic-register=@var{reg} @gol 515-mnop-fun-dllimport @gol 516-mpoke-function-name @gol 517-mthumb -marm @gol 518-mtpcs-frame -mtpcs-leaf-frame @gol 519-mcaller-super-interworking -mcallee-super-interworking @gol 520-mtp=@var{name} -mtls-dialect=@var{dialect} @gol 521-mword-relocations @gol 522-mfix-cortex-m3-ldrd @gol 523-munaligned-access} 524 525@emph{AVR Options} 526@gccoptlist{-mmcu=@var{mcu} -maccumulate-args -mbranch-cost=@var{cost} @gol 527-mcall-prologues -mint8 -mno-interrupts -mrelax @gol 528-mstrict-X -mtiny-stack -Waddr-space-convert} 529 530@emph{Blackfin Options} 531@gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol 532-msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol 533-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol 534-mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol 535-mno-id-shared-library -mshared-library-id=@var{n} @gol 536-mleaf-id-shared-library -mno-leaf-id-shared-library @gol 537-msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol 538-mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol 539-micplb} 540 541@emph{C6X Options} 542@gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol 543-msim -msdata=@var{sdata-type}} 544 545@emph{CRIS Options} 546@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol 547-mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol 548-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol 549-mstack-align -mdata-align -mconst-align @gol 550-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol 551-melf -maout -melinux -mlinux -sim -sim2 @gol 552-mmul-bug-workaround -mno-mul-bug-workaround} 553 554@emph{CR16 Options} 555@gccoptlist{-mmac @gol 556-mcr16cplus -mcr16c @gol 557-msim -mint32 -mbit-ops 558-mdata-model=@var{model}} 559 560@emph{Darwin Options} 561@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol 562-arch_only -bind_at_load -bundle -bundle_loader @gol 563-client_name -compatibility_version -current_version @gol 564-dead_strip @gol 565-dependency-file -dylib_file -dylinker_install_name @gol 566-dynamic -dynamiclib -exported_symbols_list @gol 567-filelist -flat_namespace -force_cpusubtype_ALL @gol 568-force_flat_namespace -headerpad_max_install_names @gol 569-iframework @gol 570-image_base -init -install_name -keep_private_externs @gol 571-multi_module -multiply_defined -multiply_defined_unused @gol 572-noall_load -no_dead_strip_inits_and_terms @gol 573-nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol 574-pagezero_size -prebind -prebind_all_twolevel_modules @gol 575-private_bundle -read_only_relocs -sectalign @gol 576-sectobjectsymbols -whyload -seg1addr @gol 577-sectcreate -sectobjectsymbols -sectorder @gol 578-segaddr -segs_read_only_addr -segs_read_write_addr @gol 579-seg_addr_table -seg_addr_table_filename -seglinkedit @gol 580-segprot -segs_read_only_addr -segs_read_write_addr @gol 581-single_module -static -sub_library -sub_umbrella @gol 582-twolevel_namespace -umbrella -undefined @gol 583-unexported_symbols_list -weak_reference_mismatches @gol 584-whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol 585-mkernel -mone-byte-bool} 586 587@emph{DEC Alpha Options} 588@gccoptlist{-mno-fp-regs -msoft-float @gol 589-mieee -mieee-with-inexact -mieee-conformant @gol 590-mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol 591-mtrap-precision=@var{mode} -mbuild-constants @gol 592-mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol 593-mbwx -mmax -mfix -mcix @gol 594-mfloat-vax -mfloat-ieee @gol 595-mexplicit-relocs -msmall-data -mlarge-data @gol 596-msmall-text -mlarge-text @gol 597-mmemory-latency=@var{time}} 598 599@emph{FR30 Options} 600@gccoptlist{-msmall-model -mno-lsim} 601 602@emph{FRV Options} 603@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol 604-mhard-float -msoft-float @gol 605-malloc-cc -mfixed-cc -mdword -mno-dword @gol 606-mdouble -mno-double @gol 607-mmedia -mno-media -mmuladd -mno-muladd @gol 608-mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol 609-mlinked-fp -mlong-calls -malign-labels @gol 610-mlibrary-pic -macc-4 -macc-8 @gol 611-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol 612-moptimize-membar -mno-optimize-membar @gol 613-mscc -mno-scc -mcond-exec -mno-cond-exec @gol 614-mvliw-branch -mno-vliw-branch @gol 615-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol 616-mno-nested-cond-exec -mtomcat-stats @gol 617-mTLS -mtls @gol 618-mcpu=@var{cpu}} 619 620@emph{GNU/Linux Options} 621@gccoptlist{-mglibc -muclibc -mbionic -mandroid @gol 622-tno-android-cc -tno-android-ld} 623 624@emph{H8/300 Options} 625@gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} 626 627@emph{HPPA Options} 628@gccoptlist{-march=@var{architecture-type} @gol 629-mbig-switch -mdisable-fpregs -mdisable-indexing @gol 630-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol 631-mfixed-range=@var{register-range} @gol 632-mjump-in-delay -mlinker-opt -mlong-calls @gol 633-mlong-load-store -mno-big-switch -mno-disable-fpregs @gol 634-mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol 635-mno-jump-in-delay -mno-long-load-store @gol 636-mno-portable-runtime -mno-soft-float @gol 637-mno-space-regs -msoft-float -mpa-risc-1-0 @gol 638-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol 639-mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol 640-munix=@var{unix-std} -nolibdld -static -threads} 641 642@emph{i386 and x86-64 Options} 643@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol 644-mfpmath=@var{unit} @gol 645-masm=@var{dialect} -mno-fancy-math-387 @gol 646-mno-fp-ret-in-387 -msoft-float @gol 647-mno-wide-multiply -mrtd -malign-double @gol 648-mpreferred-stack-boundary=@var{num} @gol 649-mincoming-stack-boundary=@var{num} @gol 650-mcld -mcx16 -msahf -mmovbe -mcrc32 @gol 651-mrecip -mrecip=@var{opt} @gol 652-mvzeroupper -mprefer-avx128 @gol 653-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol 654-mavx2 -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma @gol 655-msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt @gol 656-mbmi2 -mrtm -mlwp -mthreads @gol 657-mno-align-stringops -minline-all-stringops @gol 658-minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol 659-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol 660-m96bit-long-double -mlong-double-64 -mlong-double-80 @gol 661-mregparm=@var{num} -msseregparm @gol 662-mveclibabi=@var{type} -mvect8-ret-in-mem @gol 663-mpc32 -mpc64 -mpc80 -mstackrealign @gol 664-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol 665-mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol 666-m32 -m64 -mx32 -mlarge-data-threshold=@var{num} @gol 667-msse2avx -mfentry -m8bit-idiv @gol 668-mavx256-split-unaligned-load -mavx256-split-unaligned-store} 669 670@emph{i386 and x86-64 Windows Options} 671@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol 672-mnop-fun-dllimport -mthread @gol 673-municode -mwin32 -mwindows -fno-set-stack-executable} 674 675@emph{IA-64 Options} 676@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol 677-mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol 678-mconstant-gp -mauto-pic -mfused-madd @gol 679-minline-float-divide-min-latency @gol 680-minline-float-divide-max-throughput @gol 681-mno-inline-float-divide @gol 682-minline-int-divide-min-latency @gol 683-minline-int-divide-max-throughput @gol 684-mno-inline-int-divide @gol 685-minline-sqrt-min-latency -minline-sqrt-max-throughput @gol 686-mno-inline-sqrt @gol 687-mdwarf2-asm -mearly-stop-bits @gol 688-mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol 689-mtune=@var{cpu-type} -milp32 -mlp64 @gol 690-msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol 691-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol 692-msched-spec-ldc -msched-spec-control-ldc @gol 693-msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol 694-msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol 695-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol 696-msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}} 697 698@emph{LM32 Options} 699@gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol 700-msign-extend-enabled -muser-enabled} 701 702@emph{M32R/D Options} 703@gccoptlist{-m32r2 -m32rx -m32r @gol 704-mdebug @gol 705-malign-loops -mno-align-loops @gol 706-missue-rate=@var{number} @gol 707-mbranch-cost=@var{number} @gol 708-mmodel=@var{code-size-model-type} @gol 709-msdata=@var{sdata-type} @gol 710-mno-flush-func -mflush-func=@var{name} @gol 711-mno-flush-trap -mflush-trap=@var{number} @gol 712-G @var{num}} 713 714@emph{M32C Options} 715@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} 716 717@emph{M680x0 Options} 718@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} 719-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol 720-m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol 721-mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol 722-mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol 723-mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol 724-malign-int -mstrict-align -msep-data -mno-sep-data @gol 725-mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol 726-mxgot -mno-xgot} 727 728@emph{MCore Options} 729@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol 730-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol 731-m4byte-functions -mno-4byte-functions -mcallgraph-data @gol 732-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol 733-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} 734 735@emph{MeP Options} 736@gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol 737-mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol 738-mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol 739-mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol 740-mtiny=@var{n}} 741 742@emph{MicroBlaze Options} 743@gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol 744-mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol 745-mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol 746-mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol 747-mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model}} 748 749@emph{MIPS Options} 750@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol 751-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol 752-mips64 -mips64r2 @gol 753-mips16 -mno-mips16 -mflip-mips16 @gol 754-minterlink-mips16 -mno-interlink-mips16 @gol 755-mabi=@var{abi} -mabicalls -mno-abicalls @gol 756-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol 757-mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol 758-mno-float -msingle-float -mdouble-float @gol 759-mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol 760-mmcu -mmno-mcu @gol 761-mfpu=@var{fpu-type} @gol 762-msmartmips -mno-smartmips @gol 763-mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol 764-mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol 765-mlong64 -mlong32 -msym32 -mno-sym32 @gol 766-G@var{num} -mlocal-sdata -mno-local-sdata @gol 767-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol 768-membedded-data -mno-embedded-data @gol 769-muninit-const-in-rodata -mno-uninit-const-in-rodata @gol 770-mcode-readable=@var{setting} @gol 771-msplit-addresses -mno-split-addresses @gol 772-mexplicit-relocs -mno-explicit-relocs @gol 773-mcheck-zero-division -mno-check-zero-division @gol 774-mdivide-traps -mdivide-breaks @gol 775-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol 776-mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol 777-mfix-24k -mno-fix-24k @gol 778-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol 779-mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol 780-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol 781-mflush-func=@var{func} -mno-flush-func @gol 782-mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol 783-mfp-exceptions -mno-fp-exceptions @gol 784-mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol 785-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address} 786 787@emph{MMIX Options} 788@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol 789-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol 790-melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol 791-mno-base-addresses -msingle-exit -mno-single-exit} 792 793@emph{MN10300 Options} 794@gccoptlist{-mmult-bug -mno-mult-bug @gol 795-mno-am33 -mam33 -mam33-2 -mam34 @gol 796-mtune=@var{cpu-type} @gol 797-mreturn-pointer-on-d0 @gol 798-mno-crt0 -mrelax -mliw -msetlb} 799 800@emph{Moxie Options} 801@gccoptlist{-meb -mel -mno-crt0} 802 803@emph{PDP-11 Options} 804@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol 805-mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol 806-mint16 -mno-int32 -mfloat32 -mno-float64 @gol 807-mfloat64 -mno-float32 -mabshi -mno-abshi @gol 808-mbranch-expensive -mbranch-cheap @gol 809-munix-asm -mdec-asm} 810 811@emph{picoChip Options} 812@gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol 813-msymbol-as-address -mno-inefficient-warnings} 814 815@emph{PowerPC Options} 816See RS/6000 and PowerPC Options. 817 818@emph{RL78 Options} 819@gccoptlist{-msim -mmul=none -mmul=g13 -mmul=rl78} 820 821@emph{RS/6000 and PowerPC Options} 822@gccoptlist{-mcpu=@var{cpu-type} @gol 823-mtune=@var{cpu-type} @gol 824-mcmodel=@var{code-model} @gol 825-mpowerpc64 @gol 826-maltivec -mno-altivec @gol 827-mpowerpc-gpopt -mno-powerpc-gpopt @gol 828-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol 829-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol 830-mfprnd -mno-fprnd @gol 831-mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol 832-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol 833-m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol 834-malign-power -malign-natural @gol 835-msoft-float -mhard-float -mmultiple -mno-multiple @gol 836-msingle-float -mdouble-float -msimple-fpu @gol 837-mstring -mno-string -mupdate -mno-update @gol 838-mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol 839-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol 840-mstrict-align -mno-strict-align -mrelocatable @gol 841-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol 842-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol 843-mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol 844-mprioritize-restricted-insns=@var{priority} @gol 845-msched-costly-dep=@var{dependence_type} @gol 846-minsert-sched-nops=@var{scheme} @gol 847-mcall-sysv -mcall-netbsd @gol 848-maix-struct-return -msvr4-struct-return @gol 849-mabi=@var{abi-type} -msecure-plt -mbss-plt @gol 850-mblock-move-inline-limit=@var{num} @gol 851-misel -mno-isel @gol 852-misel=yes -misel=no @gol 853-mspe -mno-spe @gol 854-mspe=yes -mspe=no @gol 855-mpaired @gol 856-mgen-cell-microcode -mwarn-cell-microcode @gol 857-mvrsave -mno-vrsave @gol 858-mmulhw -mno-mulhw @gol 859-mdlmzb -mno-dlmzb @gol 860-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol 861-mprototype -mno-prototype @gol 862-msim -mmvme -mads -myellowknife -memb -msdata @gol 863-msdata=@var{opt} -mvxworks -G @var{num} -pthread @gol 864-mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol 865-mno-recip-precision @gol 866-mveclibabi=@var{type} -mfriz -mno-friz @gol 867-mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol 868-msave-toc-indirect -mno-save-toc-indirect @gol 869-mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol 870-mcrypto -mno-crypto -mdirect-move -mno-direct-move @gol 871-mquad-memory -mno-quad-memory @gol 872-mquad-memory-atomic -mno-quad-memory-atomic @gol 873-mcompat-align-parm -mno-compat-align-parm} 874 875@emph{RX Options} 876@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol 877-mcpu=@gol 878-mbig-endian-data -mlittle-endian-data @gol 879-msmall-data @gol 880-msim -mno-sim@gol 881-mas100-syntax -mno-as100-syntax@gol 882-mrelax@gol 883-mmax-constant-size=@gol 884-mint-register=@gol 885-mpid@gol 886-mno-warn-multiple-fast-interrupts@gol 887-msave-acc-in-interrupts} 888 889@emph{S/390 and zSeries Options} 890@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol 891-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol 892-mlong-double-64 -mlong-double-128 @gol 893-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol 894-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol 895-m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol 896-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol 897-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol 898-mhotpatch=@var{halfwords},@var{halfwords}} 899 900@emph{Score Options} 901@gccoptlist{-meb -mel @gol 902-mnhwloop @gol 903-muls @gol 904-mmac @gol 905-mscore5 -mscore5u -mscore7 -mscore7d} 906 907@emph{SH Options} 908@gccoptlist{-m1 -m2 -m2e @gol 909-m2a-nofpu -m2a-single-only -m2a-single -m2a @gol 910-m3 -m3e @gol 911-m4-nofpu -m4-single-only -m4-single -m4 @gol 912-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol 913-m5-64media -m5-64media-nofpu @gol 914-m5-32media -m5-32media-nofpu @gol 915-m5-compact -m5-compact-nofpu @gol 916-mb -ml -mdalign -mrelax @gol 917-mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol 918-mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol 919-mspace -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol 920-mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol 921-mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol 922-maccumulate-outgoing-args -minvalid-symbols @gol 923-matomic-model=@var{atomic-model} @gol 924-mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch -mcbranchdi -mcmpeqdi @gol 925-mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol 926-mpretend-cmove -mtas} 927 928@emph{Solaris 2 Options} 929@gccoptlist{-mimpure-text -mno-impure-text @gol 930-pthreads -pthread} 931 932@emph{SPARC Options} 933@gccoptlist{-mcpu=@var{cpu-type} @gol 934-mtune=@var{cpu-type} @gol 935-mcmodel=@var{code-model} @gol 936-mmemory-model=@var{mem-model} @gol 937-m32 -m64 -mapp-regs -mno-app-regs @gol 938-mfaster-structs -mno-faster-structs -mflat -mno-flat @gol 939-mfpu -mno-fpu -mhard-float -msoft-float @gol 940-mhard-quad-float -msoft-quad-float @gol 941-mstack-bias -mno-stack-bias @gol 942-munaligned-doubles -mno-unaligned-doubles @gol 943-muser-mode -mno-user-mode @gol 944-mv8plus -mno-v8plus -mvis -mno-vis @gol 945-mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol 946-mcbcond -mno-cbcond @gol 947-mfmaf -mno-fmaf -mpopc -mno-popc @gol 948-mfix-at697f -mfix-ut699} 949 950@emph{SPU Options} 951@gccoptlist{-mwarn-reloc -merror-reloc @gol 952-msafe-dma -munsafe-dma @gol 953-mbranch-hints @gol 954-msmall-mem -mlarge-mem -mstdmain @gol 955-mfixed-range=@var{register-range} @gol 956-mea32 -mea64 @gol 957-maddress-space-conversion -mno-address-space-conversion @gol 958-mcache-size=@var{cache-size} @gol 959-matomic-updates -mno-atomic-updates} 960 961@emph{System V Options} 962@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} 963 964@emph{TILE-Gx Options} 965@gccoptlist{-mcpu=@var{cpu} -m32 -m64 -mcmodel=@var{code-model}} 966 967@emph{TILEPro Options} 968@gccoptlist{-mcpu=@var{cpu} -m32} 969 970@emph{V850 Options} 971@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol 972-mprolog-function -mno-prolog-function -mspace @gol 973-mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol 974-mapp-regs -mno-app-regs @gol 975-mdisable-callt -mno-disable-callt @gol 976-mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol 977-mv850e -mv850 -mv850e3v5 @gol 978-mloop @gol 979-mrelax @gol 980-mlong-jumps @gol 981-msoft-float @gol 982-mhard-float @gol 983-mgcc-abi @gol 984-mrh850-abi @gol 985-mbig-switch} 986 987@emph{VAX Options} 988@gccoptlist{-mg -mgnu -munix} 989 990@emph{VMS Options} 991@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol 992-mpointer-size=@var{size}} 993 994@emph{VxWorks Options} 995@gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol 996-Xbind-lazy -Xbind-now} 997 998@emph{x86-64 Options} 999See i386 and x86-64 Options. 1000 1001@emph{Xstormy16 Options} 1002@gccoptlist{-msim} 1003 1004@emph{Xtensa Options} 1005@gccoptlist{-mconst16 -mno-const16 @gol 1006-mfused-madd -mno-fused-madd @gol 1007-mforce-no-pic @gol 1008-mserialize-volatile -mno-serialize-volatile @gol 1009-mtext-section-literals -mno-text-section-literals @gol 1010-mtarget-align -mno-target-align @gol 1011-mlongcalls -mno-longcalls} 1012 1013@emph{zSeries Options} 1014See S/390 and zSeries Options. 1015 1016@item Code Generation Options 1017@xref{Code Gen Options,,Options for Code Generation Conventions}. 1018@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol 1019-ffixed-@var{reg} -fexceptions @gol 1020-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol 1021-fasynchronous-unwind-tables @gol 1022-fno-gnu-unique @gol 1023-finhibit-size-directive -finstrument-functions @gol 1024-finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol 1025-finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol 1026-fno-common -fno-ident @gol 1027-fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol 1028-fno-jump-tables @gol 1029-frecord-gcc-switches @gol 1030-freg-struct-return -fshort-enums @gol 1031-fshort-double -fshort-wchar @gol 1032-fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol 1033-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol 1034-fno-stack-limit -fsplit-stack @gol 1035-fleading-underscore -ftls-model=@var{model} @gol 1036-fstack-reuse=@var{reuse_level} @gol 1037-ftrapv -fwrapv -fbounds-check @gol 1038-fvisibility -fstrict-volatile-bitfields -fsync-libcalls} 1039@end table 1040 1041@menu 1042* Overall Options:: Controlling the kind of output: 1043 an executable, object files, assembler files, 1044 or preprocessed source. 1045* C Dialect Options:: Controlling the variant of C language compiled. 1046* C++ Dialect Options:: Variations on C++. 1047* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C 1048 and Objective-C++. 1049* Language Independent Options:: Controlling how diagnostics should be 1050 formatted. 1051* Warning Options:: How picky should the compiler be? 1052* Debugging Options:: Symbol tables, measurements, and debugging dumps. 1053* Optimize Options:: How much optimization? 1054* Preprocessor Options:: Controlling header files and macro definitions. 1055 Also, getting dependency information for Make. 1056* Assembler Options:: Passing options to the assembler. 1057* Link Options:: Specifying libraries and so on. 1058* Directory Options:: Where to find header files and libraries. 1059 Where to find the compiler executable files. 1060* Spec Files:: How to pass switches to sub-processes. 1061* Target Options:: Running a cross-compiler, or an old version of GCC. 1062@end menu 1063 1064@node Overall Options 1065@section Options Controlling the Kind of Output 1066 1067Compilation can involve up to four stages: preprocessing, compilation 1068proper, assembly and linking, always in that order. GCC is capable of 1069preprocessing and compiling several files either into several 1070assembler input files, or into one assembler input file; then each 1071assembler input file produces an object file, and linking combines all 1072the object files (those newly compiled, and those specified as input) 1073into an executable file. 1074 1075@cindex file name suffix 1076For any given input file, the file name suffix determines what kind of 1077compilation is done: 1078 1079@table @gcctabopt 1080@item @var{file}.c 1081C source code that must be preprocessed. 1082 1083@item @var{file}.i 1084C source code that should not be preprocessed. 1085 1086@item @var{file}.ii 1087C++ source code that should not be preprocessed. 1088 1089@item @var{file}.m 1090Objective-C source code. Note that you must link with the @file{libobjc} 1091library to make an Objective-C program work. 1092 1093@item @var{file}.mi 1094Objective-C source code that should not be preprocessed. 1095 1096@item @var{file}.mm 1097@itemx @var{file}.M 1098Objective-C++ source code. Note that you must link with the @file{libobjc} 1099library to make an Objective-C++ program work. Note that @samp{.M} refers 1100to a literal capital M@. 1101 1102@item @var{file}.mii 1103Objective-C++ source code that should not be preprocessed. 1104 1105@item @var{file}.h 1106C, C++, Objective-C or Objective-C++ header file to be turned into a 1107precompiled header (default), or C, C++ header file to be turned into an 1108Ada spec (via the @option{-fdump-ada-spec} switch). 1109 1110@item @var{file}.cc 1111@itemx @var{file}.cp 1112@itemx @var{file}.cxx 1113@itemx @var{file}.cpp 1114@itemx @var{file}.CPP 1115@itemx @var{file}.c++ 1116@itemx @var{file}.C 1117C++ source code that must be preprocessed. Note that in @samp{.cxx}, 1118the last two letters must both be literally @samp{x}. Likewise, 1119@samp{.C} refers to a literal capital C@. 1120 1121@item @var{file}.mm 1122@itemx @var{file}.M 1123Objective-C++ source code that must be preprocessed. 1124 1125@item @var{file}.mii 1126Objective-C++ source code that should not be preprocessed. 1127 1128@item @var{file}.hh 1129@itemx @var{file}.H 1130@itemx @var{file}.hp 1131@itemx @var{file}.hxx 1132@itemx @var{file}.hpp 1133@itemx @var{file}.HPP 1134@itemx @var{file}.h++ 1135@itemx @var{file}.tcc 1136C++ header file to be turned into a precompiled header or Ada spec. 1137 1138@item @var{file}.f 1139@itemx @var{file}.for 1140@itemx @var{file}.ftn 1141Fixed form Fortran source code that should not be preprocessed. 1142 1143@item @var{file}.F 1144@itemx @var{file}.FOR 1145@itemx @var{file}.fpp 1146@itemx @var{file}.FPP 1147@itemx @var{file}.FTN 1148Fixed form Fortran source code that must be preprocessed (with the traditional 1149preprocessor). 1150 1151@item @var{file}.f90 1152@itemx @var{file}.f95 1153@itemx @var{file}.f03 1154@itemx @var{file}.f08 1155Free form Fortran source code that should not be preprocessed. 1156 1157@item @var{file}.F90 1158@itemx @var{file}.F95 1159@itemx @var{file}.F03 1160@itemx @var{file}.F08 1161Free form Fortran source code that must be preprocessed (with the 1162traditional preprocessor). 1163 1164@item @var{file}.go 1165Go source code. 1166 1167@c FIXME: Descriptions of Java file types. 1168@c @var{file}.java 1169@c @var{file}.class 1170@c @var{file}.zip 1171@c @var{file}.jar 1172 1173@item @var{file}.ads 1174Ada source code file that contains a library unit declaration (a 1175declaration of a package, subprogram, or generic, or a generic 1176instantiation), or a library unit renaming declaration (a package, 1177generic, or subprogram renaming declaration). Such files are also 1178called @dfn{specs}. 1179 1180@item @var{file}.adb 1181Ada source code file containing a library unit body (a subprogram or 1182package body). Such files are also called @dfn{bodies}. 1183 1184@c GCC also knows about some suffixes for languages not yet included: 1185@c Pascal: 1186@c @var{file}.p 1187@c @var{file}.pas 1188@c Ratfor: 1189@c @var{file}.r 1190 1191@item @var{file}.s 1192Assembler code. 1193 1194@item @var{file}.S 1195@itemx @var{file}.sx 1196Assembler code that must be preprocessed. 1197 1198@item @var{other} 1199An object file to be fed straight into linking. 1200Any file name with no recognized suffix is treated this way. 1201@end table 1202 1203@opindex x 1204You can specify the input language explicitly with the @option{-x} option: 1205 1206@table @gcctabopt 1207@item -x @var{language} 1208Specify explicitly the @var{language} for the following input files 1209(rather than letting the compiler choose a default based on the file 1210name suffix). This option applies to all following input files until 1211the next @option{-x} option. Possible values for @var{language} are: 1212@smallexample 1213c c-header cpp-output 1214c++ c++-header c++-cpp-output 1215objective-c objective-c-header objective-c-cpp-output 1216objective-c++ objective-c++-header objective-c++-cpp-output 1217assembler assembler-with-cpp 1218ada 1219f77 f77-cpp-input f95 f95-cpp-input 1220go 1221java 1222@end smallexample 1223 1224@item -x none 1225Turn off any specification of a language, so that subsequent files are 1226handled according to their file name suffixes (as they are if @option{-x} 1227has not been used at all). 1228 1229@item -pass-exit-codes 1230@opindex pass-exit-codes 1231Normally the @command{gcc} program exits with the code of 1 if any 1232phase of the compiler returns a non-success return code. If you specify 1233@option{-pass-exit-codes}, the @command{gcc} program instead returns with 1234the numerically highest error produced by any phase returning an error 1235indication. The C, C++, and Fortran front ends return 4 if an internal 1236compiler error is encountered. 1237@end table 1238 1239If you only want some of the stages of compilation, you can use 1240@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and 1241one of the options @option{-c}, @option{-S}, or @option{-E} to say where 1242@command{gcc} is to stop. Note that some combinations (for example, 1243@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. 1244 1245@table @gcctabopt 1246@item -c 1247@opindex c 1248Compile or assemble the source files, but do not link. The linking 1249stage simply is not done. The ultimate output is in the form of an 1250object file for each source file. 1251 1252By default, the object file name for a source file is made by replacing 1253the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. 1254 1255Unrecognized input files, not requiring compilation or assembly, are 1256ignored. 1257 1258@item -S 1259@opindex S 1260Stop after the stage of compilation proper; do not assemble. The output 1261is in the form of an assembler code file for each non-assembler input 1262file specified. 1263 1264By default, the assembler file name for a source file is made by 1265replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. 1266 1267Input files that don't require compilation are ignored. 1268 1269@item -E 1270@opindex E 1271Stop after the preprocessing stage; do not run the compiler proper. The 1272output is in the form of preprocessed source code, which is sent to the 1273standard output. 1274 1275Input files that don't require preprocessing are ignored. 1276 1277@cindex output file option 1278@item -o @var{file} 1279@opindex o 1280Place output in file @var{file}. This applies to whatever 1281sort of output is being produced, whether it be an executable file, 1282an object file, an assembler file or preprocessed C code. 1283 1284If @option{-o} is not specified, the default is to put an executable 1285file in @file{a.out}, the object file for 1286@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its 1287assembler file in @file{@var{source}.s}, a precompiled header file in 1288@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on 1289standard output. 1290 1291@item -v 1292@opindex v 1293Print (on standard error output) the commands executed to run the stages 1294of compilation. Also print the version number of the compiler driver 1295program and of the preprocessor and the compiler proper. 1296 1297@item -### 1298@opindex ### 1299Like @option{-v} except the commands are not executed and arguments 1300are quoted unless they contain only alphanumeric characters or @code{./-_}. 1301This is useful for shell scripts to capture the driver-generated command lines. 1302 1303@item -pipe 1304@opindex pipe 1305Use pipes rather than temporary files for communication between the 1306various stages of compilation. This fails to work on some systems where 1307the assembler is unable to read from a pipe; but the GNU assembler has 1308no trouble. 1309 1310@item --help 1311@opindex help 1312Print (on the standard output) a description of the command-line options 1313understood by @command{gcc}. If the @option{-v} option is also specified 1314then @option{--help} is also passed on to the various processes 1315invoked by @command{gcc}, so that they can display the command-line options 1316they accept. If the @option{-Wextra} option has also been specified 1317(prior to the @option{--help} option), then command-line options that 1318have no documentation associated with them are also displayed. 1319 1320@item --target-help 1321@opindex target-help 1322Print (on the standard output) a description of target-specific command-line 1323options for each tool. For some targets extra target-specific 1324information may also be printed. 1325 1326@item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} 1327Print (on the standard output) a description of the command-line 1328options understood by the compiler that fit into all specified classes 1329and qualifiers. These are the supported classes: 1330 1331@table @asis 1332@item @samp{optimizers} 1333Display all of the optimization options supported by the 1334compiler. 1335 1336@item @samp{warnings} 1337Display all of the options controlling warning messages 1338produced by the compiler. 1339 1340@item @samp{target} 1341Display target-specific options. Unlike the 1342@option{--target-help} option however, target-specific options of the 1343linker and assembler are not displayed. This is because those 1344tools do not currently support the extended @option{--help=} syntax. 1345 1346@item @samp{params} 1347Display the values recognized by the @option{--param} 1348option. 1349 1350@item @var{language} 1351Display the options supported for @var{language}, where 1352@var{language} is the name of one of the languages supported in this 1353version of GCC@. 1354 1355@item @samp{common} 1356Display the options that are common to all languages. 1357@end table 1358 1359These are the supported qualifiers: 1360 1361@table @asis 1362@item @samp{undocumented} 1363Display only those options that are undocumented. 1364 1365@item @samp{joined} 1366Display options taking an argument that appears after an equal 1367sign in the same continuous piece of text, such as: 1368@samp{--help=target}. 1369 1370@item @samp{separate} 1371Display options taking an argument that appears as a separate word 1372following the original option, such as: @samp{-o output-file}. 1373@end table 1374 1375Thus for example to display all the undocumented target-specific 1376switches supported by the compiler, use: 1377 1378@smallexample 1379--help=target,undocumented 1380@end smallexample 1381 1382The sense of a qualifier can be inverted by prefixing it with the 1383@samp{^} character, so for example to display all binary warning 1384options (i.e., ones that are either on or off and that do not take an 1385argument) that have a description, use: 1386 1387@smallexample 1388--help=warnings,^joined,^undocumented 1389@end smallexample 1390 1391The argument to @option{--help=} should not consist solely of inverted 1392qualifiers. 1393 1394Combining several classes is possible, although this usually 1395restricts the output so much that there is nothing to display. One 1396case where it does work, however, is when one of the classes is 1397@var{target}. For example, to display all the target-specific 1398optimization options, use: 1399 1400@smallexample 1401--help=target,optimizers 1402@end smallexample 1403 1404The @option{--help=} option can be repeated on the command line. Each 1405successive use displays its requested class of options, skipping 1406those that have already been displayed. 1407 1408If the @option{-Q} option appears on the command line before the 1409@option{--help=} option, then the descriptive text displayed by 1410@option{--help=} is changed. Instead of describing the displayed 1411options, an indication is given as to whether the option is enabled, 1412disabled or set to a specific value (assuming that the compiler 1413knows this at the point where the @option{--help=} option is used). 1414 1415Here is a truncated example from the ARM port of @command{gcc}: 1416 1417@smallexample 1418 % gcc -Q -mabi=2 --help=target -c 1419 The following options are target specific: 1420 -mabi= 2 1421 -mabort-on-noreturn [disabled] 1422 -mapcs [disabled] 1423@end smallexample 1424 1425The output is sensitive to the effects of previous command-line 1426options, so for example it is possible to find out which optimizations 1427are enabled at @option{-O2} by using: 1428 1429@smallexample 1430-Q -O2 --help=optimizers 1431@end smallexample 1432 1433Alternatively you can discover which binary optimizations are enabled 1434by @option{-O3} by using: 1435 1436@smallexample 1437gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts 1438gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts 1439diff /tmp/O2-opts /tmp/O3-opts | grep enabled 1440@end smallexample 1441 1442@item -no-canonical-prefixes 1443@opindex no-canonical-prefixes 1444Do not expand any symbolic links, resolve references to @samp{/../} 1445or @samp{/./}, or make the path absolute when generating a relative 1446prefix. 1447 1448@item --version 1449@opindex version 1450Display the version number and copyrights of the invoked GCC@. 1451 1452@item -wrapper 1453@opindex wrapper 1454Invoke all subcommands under a wrapper program. The name of the 1455wrapper program and its parameters are passed as a comma separated 1456list. 1457 1458@smallexample 1459gcc -c t.c -wrapper gdb,--args 1460@end smallexample 1461 1462@noindent 1463This invokes all subprograms of @command{gcc} under 1464@samp{gdb --args}, thus the invocation of @command{cc1} is 1465@samp{gdb --args cc1 @dots{}}. 1466 1467@item -fplugin=@var{name}.so 1468Load the plugin code in file @var{name}.so, assumed to be a 1469shared object to be dlopen'd by the compiler. The base name of 1470the shared object file is used to identify the plugin for the 1471purposes of argument parsing (See 1472@option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). 1473Each plugin should define the callback functions specified in the 1474Plugins API. 1475 1476@item -fplugin-arg-@var{name}-@var{key}=@var{value} 1477Define an argument called @var{key} with a value of @var{value} 1478for the plugin called @var{name}. 1479 1480@item -fdump-ada-spec@r{[}-slim@r{]} 1481@opindex fdump-ada-spec 1482For C and C++ source and include files, generate corresponding Ada specs. 1483@xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, 1484GNAT User's Guide}, which provides detailed documentation on this feature. 1485 1486@item -fada-spec-parent=@var{unit} 1487@opindex fada-spec-parent 1488In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate 1489Ada specs as child units of parent @var{unit}. 1490 1491@item -fdump-go-spec=@var{file} 1492@opindex fdump-go-spec 1493For input files in any language, generate corresponding Go 1494declarations in @var{file}. This generates Go @code{const}, 1495@code{type}, @code{var}, and @code{func} declarations which may be a 1496useful way to start writing a Go interface to code written in some 1497other language. 1498 1499@include @value{srcdir}/../libiberty/at-file.texi 1500@end table 1501 1502@node Invoking G++ 1503@section Compiling C++ Programs 1504 1505@cindex suffixes for C++ source 1506@cindex C++ source file suffixes 1507C++ source files conventionally use one of the suffixes @samp{.C}, 1508@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or 1509@samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, 1510@samp{.H}, or (for shared template code) @samp{.tcc}; and 1511preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes 1512files with these names and compiles them as C++ programs even if you 1513call the compiler the same way as for compiling C programs (usually 1514with the name @command{gcc}). 1515 1516@findex g++ 1517@findex c++ 1518However, the use of @command{gcc} does not add the C++ library. 1519@command{g++} is a program that calls GCC and automatically specifies linking 1520against the C++ library. It treats @samp{.c}, 1521@samp{.h} and @samp{.i} files as C++ source files instead of C source 1522files unless @option{-x} is used. This program is also useful when 1523precompiling a C header file with a @samp{.h} extension for use in C++ 1524compilations. On many systems, @command{g++} is also installed with 1525the name @command{c++}. 1526 1527@cindex invoking @command{g++} 1528When you compile C++ programs, you may specify many of the same 1529command-line options that you use for compiling programs in any 1530language; or command-line options meaningful for C and related 1531languages; or options that are meaningful only for C++ programs. 1532@xref{C Dialect Options,,Options Controlling C Dialect}, for 1533explanations of options for languages related to C@. 1534@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for 1535explanations of options that are meaningful only for C++ programs. 1536 1537@node C Dialect Options 1538@section Options Controlling C Dialect 1539@cindex dialect options 1540@cindex language dialect options 1541@cindex options, dialect 1542 1543The following options control the dialect of C (or languages derived 1544from C, such as C++, Objective-C and Objective-C++) that the compiler 1545accepts: 1546 1547@table @gcctabopt 1548@cindex ANSI support 1549@cindex ISO support 1550@item -ansi 1551@opindex ansi 1552In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is 1553equivalent to @option{-std=c++98}. 1554 1555This turns off certain features of GCC that are incompatible with ISO 1556C90 (when compiling C code), or of standard C++ (when compiling C++ code), 1557such as the @code{asm} and @code{typeof} keywords, and 1558predefined macros such as @code{unix} and @code{vax} that identify the 1559type of system you are using. It also enables the undesirable and 1560rarely used ISO trigraph feature. For the C compiler, 1561it disables recognition of C++ style @samp{//} comments as well as 1562the @code{inline} keyword. 1563 1564The alternate keywords @code{__asm__}, @code{__extension__}, 1565@code{__inline__} and @code{__typeof__} continue to work despite 1566@option{-ansi}. You would not want to use them in an ISO C program, of 1567course, but it is useful to put them in header files that might be included 1568in compilations done with @option{-ansi}. Alternate predefined macros 1569such as @code{__unix__} and @code{__vax__} are also available, with or 1570without @option{-ansi}. 1571 1572The @option{-ansi} option does not cause non-ISO programs to be 1573rejected gratuitously. For that, @option{-Wpedantic} is required in 1574addition to @option{-ansi}. @xref{Warning Options}. 1575 1576The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} 1577option is used. Some header files may notice this macro and refrain 1578from declaring certain functions or defining certain macros that the 1579ISO standard doesn't call for; this is to avoid interfering with any 1580programs that might use these names for other things. 1581 1582Functions that are normally built in but do not have semantics 1583defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in 1584functions when @option{-ansi} is used. @xref{Other Builtins,,Other 1585built-in functions provided by GCC}, for details of the functions 1586affected. 1587 1588@item -std= 1589@opindex std 1590Determine the language standard. @xref{Standards,,Language Standards 1591Supported by GCC}, for details of these standard versions. This option 1592is currently only supported when compiling C or C++. 1593 1594The compiler can accept several base standards, such as @samp{c90} or 1595@samp{c++98}, and GNU dialects of those standards, such as 1596@samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the 1597compiler accepts all programs following that standard plus those 1598using GNU extensions that do not contradict it. For example, 1599@option{-std=c90} turns off certain features of GCC that are 1600incompatible with ISO C90, such as the @code{asm} and @code{typeof} 1601keywords, but not other GNU extensions that do not have a meaning in 1602ISO C90, such as omitting the middle term of a @code{?:} 1603expression. On the other hand, when a GNU dialect of a standard is 1604specified, all features supported by the compiler are enabled, even when 1605those features change the meaning of the base standard. As a result, some 1606strict-conforming programs may be rejected. The particular standard 1607is used by @option{-Wpedantic} to identify which features are GNU 1608extensions given that version of the standard. For example 1609@option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} 1610comments, while @option{-std=gnu99 -Wpedantic} does not. 1611 1612A value for this option must be provided; possible values are 1613 1614@table @samp 1615@item c90 1616@itemx c89 1617@itemx iso9899:1990 1618Support all ISO C90 programs (certain GNU extensions that conflict 1619with ISO C90 are disabled). Same as @option{-ansi} for C code. 1620 1621@item iso9899:199409 1622ISO C90 as modified in amendment 1. 1623 1624@item c99 1625@itemx c9x 1626@itemx iso9899:1999 1627@itemx iso9899:199x 1628ISO C99. Note that this standard is not yet fully supported; see 1629@w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The 1630names @samp{c9x} and @samp{iso9899:199x} are deprecated. 1631 1632@item c11 1633@itemx c1x 1634@itemx iso9899:2011 1635ISO C11, the 2011 revision of the ISO C standard. 1636Support is incomplete and experimental. The name @samp{c1x} is 1637deprecated. 1638 1639@item gnu90 1640@itemx gnu89 1641GNU dialect of ISO C90 (including some C99 features). This 1642is the default for C code. 1643 1644@item gnu99 1645@itemx gnu9x 1646GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC, 1647this will become the default. The name @samp{gnu9x} is deprecated. 1648 1649@item gnu11 1650@itemx gnu1x 1651GNU dialect of ISO C11. Support is incomplete and experimental. The 1652name @samp{gnu1x} is deprecated. 1653 1654@item c++98 1655@itemx c++03 1656The 1998 ISO C++ standard plus the 2003 technical corrigendum and some 1657additional defect reports. Same as @option{-ansi} for C++ code. 1658 1659@item gnu++98 1660@itemx gnu++03 1661GNU dialect of @option{-std=c++98}. This is the default for 1662C++ code. 1663 1664@item c++11 1665@itemx c++0x 1666The 2011 ISO C++ standard plus amendments. Support for C++11 is still 1667experimental, and may change in incompatible ways in future releases. 1668The name @samp{c++0x} is deprecated. 1669 1670@item gnu++11 1671@itemx gnu++0x 1672GNU dialect of @option{-std=c++11}. Support for C++11 is still 1673experimental, and may change in incompatible ways in future releases. 1674The name @samp{gnu++0x} is deprecated. 1675 1676@item c++1y 1677The next revision of the ISO C++ standard, tentatively planned for 16782017. Support is highly experimental, and will almost certainly 1679change in incompatible ways in future releases. 1680 1681@item gnu++1y 1682GNU dialect of @option{-std=c++1y}. Support is highly experimental, 1683and will almost certainly change in incompatible ways in future 1684releases. 1685@end table 1686 1687@item -fgnu89-inline 1688@opindex fgnu89-inline 1689The option @option{-fgnu89-inline} tells GCC to use the traditional 1690GNU semantics for @code{inline} functions when in C99 mode. 1691@xref{Inline,,An Inline Function is As Fast As a Macro}. This option 1692is accepted and ignored by GCC versions 4.1.3 up to but not including 16934.3. In GCC versions 4.3 and later it changes the behavior of GCC in 1694C99 mode. Using this option is roughly equivalent to adding the 1695@code{gnu_inline} function attribute to all inline functions 1696(@pxref{Function Attributes}). 1697 1698The option @option{-fno-gnu89-inline} explicitly tells GCC to use the 1699C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it 1700specifies the default behavior). This option was first supported in 1701GCC 4.3. This option is not supported in @option{-std=c90} or 1702@option{-std=gnu90} mode. 1703 1704The preprocessor macros @code{__GNUC_GNU_INLINE__} and 1705@code{__GNUC_STDC_INLINE__} may be used to check which semantics are 1706in effect for @code{inline} functions. @xref{Common Predefined 1707Macros,,,cpp,The C Preprocessor}. 1708 1709@item -aux-info @var{filename} 1710@opindex aux-info 1711Output to the given filename prototyped declarations for all functions 1712declared and/or defined in a translation unit, including those in header 1713files. This option is silently ignored in any language other than C@. 1714 1715Besides declarations, the file indicates, in comments, the origin of 1716each declaration (source file and line), whether the declaration was 1717implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or 1718@samp{O} for old, respectively, in the first character after the line 1719number and the colon), and whether it came from a declaration or a 1720definition (@samp{C} or @samp{F}, respectively, in the following 1721character). In the case of function definitions, a K&R-style list of 1722arguments followed by their declarations is also provided, inside 1723comments, after the declaration. 1724 1725@item -fallow-parameterless-variadic-functions 1726Accept variadic functions without named parameters. 1727 1728Although it is possible to define such a function, this is not very 1729useful as it is not possible to read the arguments. This is only 1730supported for C as this construct is allowed by C++. 1731 1732@item -fno-asm 1733@opindex fno-asm 1734Do not recognize @code{asm}, @code{inline} or @code{typeof} as a 1735keyword, so that code can use these words as identifiers. You can use 1736the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} 1737instead. @option{-ansi} implies @option{-fno-asm}. 1738 1739In C++, this switch only affects the @code{typeof} keyword, since 1740@code{asm} and @code{inline} are standard keywords. You may want to 1741use the @option{-fno-gnu-keywords} flag instead, which has the same 1742effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this 1743switch only affects the @code{asm} and @code{typeof} keywords, since 1744@code{inline} is a standard keyword in ISO C99. 1745 1746@item -fno-builtin 1747@itemx -fno-builtin-@var{function} 1748@opindex fno-builtin 1749@cindex built-in functions 1750Don't recognize built-in functions that do not begin with 1751@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in 1752functions provided by GCC}, for details of the functions affected, 1753including those which are not built-in functions when @option{-ansi} or 1754@option{-std} options for strict ISO C conformance are used because they 1755do not have an ISO standard meaning. 1756 1757GCC normally generates special code to handle certain built-in functions 1758more efficiently; for instance, calls to @code{alloca} may become single 1759instructions which adjust the stack directly, and calls to @code{memcpy} 1760may become inline copy loops. The resulting code is often both smaller 1761and faster, but since the function calls no longer appear as such, you 1762cannot set a breakpoint on those calls, nor can you change the behavior 1763of the functions by linking with a different library. In addition, 1764when a function is recognized as a built-in function, GCC may use 1765information about that function to warn about problems with calls to 1766that function, or to generate more efficient code, even if the 1767resulting code still contains calls to that function. For example, 1768warnings are given with @option{-Wformat} for bad calls to 1769@code{printf} when @code{printf} is built in and @code{strlen} is 1770known not to modify global memory. 1771 1772With the @option{-fno-builtin-@var{function}} option 1773only the built-in function @var{function} is 1774disabled. @var{function} must not begin with @samp{__builtin_}. If a 1775function is named that is not built-in in this version of GCC, this 1776option is ignored. There is no corresponding 1777@option{-fbuiltin-@var{function}} option; if you wish to enable 1778built-in functions selectively when using @option{-fno-builtin} or 1779@option{-ffreestanding}, you may define macros such as: 1780 1781@smallexample 1782#define abs(n) __builtin_abs ((n)) 1783#define strcpy(d, s) __builtin_strcpy ((d), (s)) 1784@end smallexample 1785 1786@item -fhosted 1787@opindex fhosted 1788@cindex hosted environment 1789 1790Assert that compilation targets a hosted environment. This implies 1791@option{-fbuiltin}. A hosted environment is one in which the 1792entire standard library is available, and in which @code{main} has a return 1793type of @code{int}. Examples are nearly everything except a kernel. 1794This is equivalent to @option{-fno-freestanding}. 1795 1796@item -ffreestanding 1797@opindex ffreestanding 1798@cindex hosted environment 1799 1800Assert that compilation targets a freestanding environment. This 1801implies @option{-fno-builtin}. A freestanding environment 1802is one in which the standard library may not exist, and program startup may 1803not necessarily be at @code{main}. The most obvious example is an OS kernel. 1804This is equivalent to @option{-fno-hosted}. 1805 1806@xref{Standards,,Language Standards Supported by GCC}, for details of 1807freestanding and hosted environments. 1808 1809@item -fopenmp 1810@opindex fopenmp 1811@cindex OpenMP parallel 1812Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and 1813@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the 1814compiler generates parallel code according to the OpenMP Application 1815Program Interface v3.0 @w{@uref{http://www.openmp.org/}}. This option 1816implies @option{-pthread}, and thus is only supported on targets that 1817have support for @option{-pthread}. 1818 1819@item -fgnu-tm 1820@opindex fgnu-tm 1821When the option @option{-fgnu-tm} is specified, the compiler 1822generates code for the Linux variant of Intel's current Transactional 1823Memory ABI specification document (Revision 1.1, May 6 2009). This is 1824an experimental feature whose interface may change in future versions 1825of GCC, as the official specification changes. Please note that not 1826all architectures are supported for this feature. 1827 1828For more information on GCC's support for transactional memory, 1829@xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU 1830Transactional Memory Library}. 1831 1832Note that the transactional memory feature is not supported with 1833non-call exceptions (@option{-fnon-call-exceptions}). 1834 1835@item -fms-extensions 1836@opindex fms-extensions 1837Accept some non-standard constructs used in Microsoft header files. 1838 1839In C++ code, this allows member names in structures to be similar 1840to previous types declarations. 1841 1842@smallexample 1843typedef int UOW; 1844struct ABC @{ 1845 UOW UOW; 1846@}; 1847@end smallexample 1848 1849Some cases of unnamed fields in structures and unions are only 1850accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union 1851fields within structs/unions}, for details. 1852 1853@item -fplan9-extensions 1854Accept some non-standard constructs used in Plan 9 code. 1855 1856This enables @option{-fms-extensions}, permits passing pointers to 1857structures with anonymous fields to functions that expect pointers to 1858elements of the type of the field, and permits referring to anonymous 1859fields declared using a typedef. @xref{Unnamed Fields,,Unnamed 1860struct/union fields within structs/unions}, for details. This is only 1861supported for C, not C++. 1862 1863@item -trigraphs 1864@opindex trigraphs 1865Support ISO C trigraphs. The @option{-ansi} option (and @option{-std} 1866options for strict ISO C conformance) implies @option{-trigraphs}. 1867 1868@cindex traditional C language 1869@cindex C language, traditional 1870@item -traditional 1871@itemx -traditional-cpp 1872@opindex traditional-cpp 1873@opindex traditional 1874Formerly, these options caused GCC to attempt to emulate a pre-standard 1875C compiler. They are now only supported with the @option{-E} switch. 1876The preprocessor continues to support a pre-standard mode. See the GNU 1877CPP manual for details. 1878 1879@item -fcond-mismatch 1880@opindex fcond-mismatch 1881Allow conditional expressions with mismatched types in the second and 1882third arguments. The value of such an expression is void. This option 1883is not supported for C++. 1884 1885@item -flax-vector-conversions 1886@opindex flax-vector-conversions 1887Allow implicit conversions between vectors with differing numbers of 1888elements and/or incompatible element types. This option should not be 1889used for new code. 1890 1891@item -funsigned-char 1892@opindex funsigned-char 1893Let the type @code{char} be unsigned, like @code{unsigned char}. 1894 1895Each kind of machine has a default for what @code{char} should 1896be. It is either like @code{unsigned char} by default or like 1897@code{signed char} by default. 1898 1899Ideally, a portable program should always use @code{signed char} or 1900@code{unsigned char} when it depends on the signedness of an object. 1901But many programs have been written to use plain @code{char} and 1902expect it to be signed, or expect it to be unsigned, depending on the 1903machines they were written for. This option, and its inverse, let you 1904make such a program work with the opposite default. 1905 1906The type @code{char} is always a distinct type from each of 1907@code{signed char} or @code{unsigned char}, even though its behavior 1908is always just like one of those two. 1909 1910@item -fsigned-char 1911@opindex fsigned-char 1912Let the type @code{char} be signed, like @code{signed char}. 1913 1914Note that this is equivalent to @option{-fno-unsigned-char}, which is 1915the negative form of @option{-funsigned-char}. Likewise, the option 1916@option{-fno-signed-char} is equivalent to @option{-funsigned-char}. 1917 1918@item -fsigned-bitfields 1919@itemx -funsigned-bitfields 1920@itemx -fno-signed-bitfields 1921@itemx -fno-unsigned-bitfields 1922@opindex fsigned-bitfields 1923@opindex funsigned-bitfields 1924@opindex fno-signed-bitfields 1925@opindex fno-unsigned-bitfields 1926These options control whether a bit-field is signed or unsigned, when the 1927declaration does not use either @code{signed} or @code{unsigned}. By 1928default, such a bit-field is signed, because this is consistent: the 1929basic integer types such as @code{int} are signed types. 1930@end table 1931 1932@node C++ Dialect Options 1933@section Options Controlling C++ Dialect 1934 1935@cindex compiler options, C++ 1936@cindex C++ options, command-line 1937@cindex options, C++ 1938This section describes the command-line options that are only meaningful 1939for C++ programs. You can also use most of the GNU compiler options 1940regardless of what language your program is in. For example, you 1941might compile a file @code{firstClass.C} like this: 1942 1943@smallexample 1944g++ -g -frepo -O -c firstClass.C 1945@end smallexample 1946 1947@noindent 1948In this example, only @option{-frepo} is an option meant 1949only for C++ programs; you can use the other options with any 1950language supported by GCC@. 1951 1952Here is a list of options that are @emph{only} for compiling C++ programs: 1953 1954@table @gcctabopt 1955 1956@item -fabi-version=@var{n} 1957@opindex fabi-version 1958Use version @var{n} of the C++ ABI@. The default is version 2. 1959 1960Version 0 refers to the version conforming most closely to 1961the C++ ABI specification. Therefore, the ABI obtained using version 0 1962will change in different versions of G++ as ABI bugs are fixed. 1963 1964Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. 1965 1966Version 2 is the version of the C++ ABI that first appeared in G++ 3.4. 1967 1968Version 3 corrects an error in mangling a constant address as a 1969template argument. 1970 1971Version 4, which first appeared in G++ 4.5, implements a standard 1972mangling for vector types. 1973 1974Version 5, which first appeared in G++ 4.6, corrects the mangling of 1975attribute const/volatile on function pointer types, decltype of a 1976plain decl, and use of a function parameter in the declaration of 1977another parameter. 1978 1979Version 6, which first appeared in G++ 4.7, corrects the promotion 1980behavior of C++11 scoped enums and the mangling of template argument 1981packs, const/static_cast, prefix ++ and --, and a class scope function 1982used as a template argument. 1983 1984See also @option{-Wabi}. 1985 1986@item -fno-access-control 1987@opindex fno-access-control 1988Turn off all access checking. This switch is mainly useful for working 1989around bugs in the access control code. 1990 1991@item -fcheck-new 1992@opindex fcheck-new 1993Check that the pointer returned by @code{operator new} is non-null 1994before attempting to modify the storage allocated. This check is 1995normally unnecessary because the C++ standard specifies that 1996@code{operator new} only returns @code{0} if it is declared 1997@samp{throw()}, in which case the compiler always checks the 1998return value even without this option. In all other cases, when 1999@code{operator new} has a non-empty exception specification, memory 2000exhaustion is signalled by throwing @code{std::bad_alloc}. See also 2001@samp{new (nothrow)}. 2002 2003@item -fconstexpr-depth=@var{n} 2004@opindex fconstexpr-depth 2005Set the maximum nested evaluation depth for C++11 constexpr functions 2006to @var{n}. A limit is needed to detect endless recursion during 2007constant expression evaluation. The minimum specified by the standard 2008is 512. 2009 2010@item -fdeduce-init-list 2011@opindex fdeduce-init-list 2012Enable deduction of a template type parameter as 2013@code{std::initializer_list} from a brace-enclosed initializer list, i.e.@: 2014 2015@smallexample 2016template <class T> auto forward(T t) -> decltype (realfn (t)) 2017@{ 2018 return realfn (t); 2019@} 2020 2021void f() 2022@{ 2023 forward(@{1,2@}); // call forward<std::initializer_list<int>> 2024@} 2025@end smallexample 2026 2027This deduction was implemented as a possible extension to the 2028originally proposed semantics for the C++11 standard, but was not part 2029of the final standard, so it is disabled by default. This option is 2030deprecated, and may be removed in a future version of G++. 2031 2032@item -ffriend-injection 2033@opindex ffriend-injection 2034Inject friend functions into the enclosing namespace, so that they are 2035visible outside the scope of the class in which they are declared. 2036Friend functions were documented to work this way in the old Annotated 2037C++ Reference Manual, and versions of G++ before 4.1 always worked 2038that way. However, in ISO C++ a friend function that is not declared 2039in an enclosing scope can only be found using argument dependent 2040lookup. This option causes friends to be injected as they were in 2041earlier releases. 2042 2043This option is for compatibility, and may be removed in a future 2044release of G++. 2045 2046@item -fno-elide-constructors 2047@opindex fno-elide-constructors 2048The C++ standard allows an implementation to omit creating a temporary 2049that is only used to initialize another object of the same type. 2050Specifying this option disables that optimization, and forces G++ to 2051call the copy constructor in all cases. 2052 2053@item -fno-enforce-eh-specs 2054@opindex fno-enforce-eh-specs 2055Don't generate code to check for violation of exception specifications 2056at run time. This option violates the C++ standard, but may be useful 2057for reducing code size in production builds, much like defining 2058@samp{NDEBUG}. This does not give user code permission to throw 2059exceptions in violation of the exception specifications; the compiler 2060still optimizes based on the specifications, so throwing an 2061unexpected exception results in undefined behavior at run time. 2062 2063@item -fextern-tls-init 2064@itemx -fno-extern-tls-init 2065@opindex fextern-tls-init 2066@opindex fno-extern-tls-init 2067The C++11 and OpenMP standards allow @samp{thread_local} and 2068@samp{threadprivate} variables to have dynamic (runtime) 2069initialization. To support this, any use of such a variable goes 2070through a wrapper function that performs any necessary initialization. 2071When the use and definition of the variable are in the same 2072translation unit, this overhead can be optimized away, but when the 2073use is in a different translation unit there is significant overhead 2074even if the variable doesn't actually need dynamic initialization. If 2075the programmer can be sure that no use of the variable in a 2076non-defining TU needs to trigger dynamic initialization (either 2077because the variable is statically initialized, or a use of the 2078variable in the defining TU will be executed before any uses in 2079another TU), they can avoid this overhead with the 2080@option{-fno-extern-tls-init} option. 2081 2082On targets that support symbol aliases, the default is 2083@option{-fextern-tls-init}. On targets that do not support symbol 2084aliases, the default is @option{-fno-extern-tls-init}. 2085 2086@item -ffor-scope 2087@itemx -fno-for-scope 2088@opindex ffor-scope 2089@opindex fno-for-scope 2090If @option{-ffor-scope} is specified, the scope of variables declared in 2091a @i{for-init-statement} is limited to the @samp{for} loop itself, 2092as specified by the C++ standard. 2093If @option{-fno-for-scope} is specified, the scope of variables declared in 2094a @i{for-init-statement} extends to the end of the enclosing scope, 2095as was the case in old versions of G++, and other (traditional) 2096implementations of C++. 2097 2098If neither flag is given, the default is to follow the standard, 2099but to allow and give a warning for old-style code that would 2100otherwise be invalid, or have different behavior. 2101 2102@item -fno-gnu-keywords 2103@opindex fno-gnu-keywords 2104Do not recognize @code{typeof} as a keyword, so that code can use this 2105word as an identifier. You can use the keyword @code{__typeof__} instead. 2106@option{-ansi} implies @option{-fno-gnu-keywords}. 2107 2108@item -fno-implicit-templates 2109@opindex fno-implicit-templates 2110Never emit code for non-inline templates that are instantiated 2111implicitly (i.e.@: by use); only emit code for explicit instantiations. 2112@xref{Template Instantiation}, for more information. 2113 2114@item -fno-implicit-inline-templates 2115@opindex fno-implicit-inline-templates 2116Don't emit code for implicit instantiations of inline templates, either. 2117The default is to handle inlines differently so that compiles with and 2118without optimization need the same set of explicit instantiations. 2119 2120@item -fno-implement-inlines 2121@opindex fno-implement-inlines 2122To save space, do not emit out-of-line copies of inline functions 2123controlled by @samp{#pragma implementation}. This causes linker 2124errors if these functions are not inlined everywhere they are called. 2125 2126@item -fms-extensions 2127@opindex fms-extensions 2128Disable Wpedantic warnings about constructs used in MFC, such as implicit 2129int and getting a pointer to member function via non-standard syntax. 2130 2131@item -fno-nonansi-builtins 2132@opindex fno-nonansi-builtins 2133Disable built-in declarations of functions that are not mandated by 2134ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, 2135@code{index}, @code{bzero}, @code{conjf}, and other related functions. 2136 2137@item -fnothrow-opt 2138@opindex fnothrow-opt 2139Treat a @code{throw()} exception specification as if it were a 2140@code{noexcept} specification to reduce or eliminate the text size 2141overhead relative to a function with no exception specification. If 2142the function has local variables of types with non-trivial 2143destructors, the exception specification actually makes the 2144function smaller because the EH cleanups for those variables can be 2145optimized away. The semantic effect is that an exception thrown out of 2146a function with such an exception specification results in a call 2147to @code{terminate} rather than @code{unexpected}. 2148 2149@item -fno-operator-names 2150@opindex fno-operator-names 2151Do not treat the operator name keywords @code{and}, @code{bitand}, 2152@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as 2153synonyms as keywords. 2154 2155@item -fno-optional-diags 2156@opindex fno-optional-diags 2157Disable diagnostics that the standard says a compiler does not need to 2158issue. Currently, the only such diagnostic issued by G++ is the one for 2159a name having multiple meanings within a class. 2160 2161@item -fpermissive 2162@opindex fpermissive 2163Downgrade some diagnostics about nonconformant code from errors to 2164warnings. Thus, using @option{-fpermissive} allows some 2165nonconforming code to compile. 2166 2167@item -fno-pretty-templates 2168@opindex fno-pretty-templates 2169When an error message refers to a specialization of a function 2170template, the compiler normally prints the signature of the 2171template followed by the template arguments and any typedefs or 2172typenames in the signature (e.g. @code{void f(T) [with T = int]} 2173rather than @code{void f(int)}) so that it's clear which template is 2174involved. When an error message refers to a specialization of a class 2175template, the compiler omits any template arguments that match 2176the default template arguments for that template. If either of these 2177behaviors make it harder to understand the error message rather than 2178easier, you can use @option{-fno-pretty-templates} to disable them. 2179 2180@item -frepo 2181@opindex frepo 2182Enable automatic template instantiation at link time. This option also 2183implies @option{-fno-implicit-templates}. @xref{Template 2184Instantiation}, for more information. 2185 2186@item -fno-rtti 2187@opindex fno-rtti 2188Disable generation of information about every class with virtual 2189functions for use by the C++ run-time type identification features 2190(@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts 2191of the language, you can save some space by using this flag. Note that 2192exception handling uses the same information, but G++ generates it as 2193needed. The @samp{dynamic_cast} operator can still be used for casts that 2194do not require run-time type information, i.e.@: casts to @code{void *} or to 2195unambiguous base classes. 2196 2197@item -fstats 2198@opindex fstats 2199Emit statistics about front-end processing at the end of the compilation. 2200This information is generally only useful to the G++ development team. 2201 2202@item -fstrict-enums 2203@opindex fstrict-enums 2204Allow the compiler to optimize using the assumption that a value of 2205enumerated type can only be one of the values of the enumeration (as 2206defined in the C++ standard; basically, a value that can be 2207represented in the minimum number of bits needed to represent all the 2208enumerators). This assumption may not be valid if the program uses a 2209cast to convert an arbitrary integer value to the enumerated type. 2210 2211@item -ftemplate-backtrace-limit=@var{n} 2212@opindex ftemplate-backtrace-limit 2213Set the maximum number of template instantiation notes for a single 2214warning or error to @var{n}. The default value is 10. 2215 2216@item -ftemplate-depth=@var{n} 2217@opindex ftemplate-depth 2218Set the maximum instantiation depth for template classes to @var{n}. 2219A limit on the template instantiation depth is needed to detect 2220endless recursions during template class instantiation. ANSI/ISO C++ 2221conforming programs must not rely on a maximum depth greater than 17 2222(changed to 1024 in C++11). The default value is 900, as the compiler 2223can run out of stack space before hitting 1024 in some situations. 2224 2225@item -fno-threadsafe-statics 2226@opindex fno-threadsafe-statics 2227Do not emit the extra code to use the routines specified in the C++ 2228ABI for thread-safe initialization of local statics. You can use this 2229option to reduce code size slightly in code that doesn't need to be 2230thread-safe. 2231 2232@item -fuse-cxa-atexit 2233@opindex fuse-cxa-atexit 2234Register destructors for objects with static storage duration with the 2235@code{__cxa_atexit} function rather than the @code{atexit} function. 2236This option is required for fully standards-compliant handling of static 2237destructors, but only works if your C library supports 2238@code{__cxa_atexit}. 2239 2240@item -fno-use-cxa-get-exception-ptr 2241@opindex fno-use-cxa-get-exception-ptr 2242Don't use the @code{__cxa_get_exception_ptr} runtime routine. This 2243causes @code{std::uncaught_exception} to be incorrect, but is necessary 2244if the runtime routine is not available. 2245 2246@item -fvisibility-inlines-hidden 2247@opindex fvisibility-inlines-hidden 2248This switch declares that the user does not attempt to compare 2249pointers to inline functions or methods where the addresses of the two functions 2250are taken in different shared objects. 2251 2252The effect of this is that GCC may, effectively, mark inline methods with 2253@code{__attribute__ ((visibility ("hidden")))} so that they do not 2254appear in the export table of a DSO and do not require a PLT indirection 2255when used within the DSO@. Enabling this option can have a dramatic effect 2256on load and link times of a DSO as it massively reduces the size of the 2257dynamic export table when the library makes heavy use of templates. 2258 2259The behavior of this switch is not quite the same as marking the 2260methods as hidden directly, because it does not affect static variables 2261local to the function or cause the compiler to deduce that 2262the function is defined in only one shared object. 2263 2264You may mark a method as having a visibility explicitly to negate the 2265effect of the switch for that method. For example, if you do want to 2266compare pointers to a particular inline method, you might mark it as 2267having default visibility. Marking the enclosing class with explicit 2268visibility has no effect. 2269 2270Explicitly instantiated inline methods are unaffected by this option 2271as their linkage might otherwise cross a shared library boundary. 2272@xref{Template Instantiation}. 2273 2274@item -fvisibility-ms-compat 2275@opindex fvisibility-ms-compat 2276This flag attempts to use visibility settings to make GCC's C++ 2277linkage model compatible with that of Microsoft Visual Studio. 2278 2279The flag makes these changes to GCC's linkage model: 2280 2281@enumerate 2282@item 2283It sets the default visibility to @code{hidden}, like 2284@option{-fvisibility=hidden}. 2285 2286@item 2287Types, but not their members, are not hidden by default. 2288 2289@item 2290The One Definition Rule is relaxed for types without explicit 2291visibility specifications that are defined in more than one 2292shared object: those declarations are permitted if they are 2293permitted when this option is not used. 2294@end enumerate 2295 2296In new code it is better to use @option{-fvisibility=hidden} and 2297export those classes that are intended to be externally visible. 2298Unfortunately it is possible for code to rely, perhaps accidentally, 2299on the Visual Studio behavior. 2300 2301Among the consequences of these changes are that static data members 2302of the same type with the same name but defined in different shared 2303objects are different, so changing one does not change the other; 2304and that pointers to function members defined in different shared 2305objects may not compare equal. When this flag is given, it is a 2306violation of the ODR to define types with the same name differently. 2307 2308@item -fno-weak 2309@opindex fno-weak 2310Do not use weak symbol support, even if it is provided by the linker. 2311By default, G++ uses weak symbols if they are available. This 2312option exists only for testing, and should not be used by end-users; 2313it results in inferior code and has no benefits. This option may 2314be removed in a future release of G++. 2315 2316@item -nostdinc++ 2317@opindex nostdinc++ 2318Do not search for header files in the standard directories specific to 2319C++, but do still search the other standard directories. (This option 2320is used when building the C++ library.) 2321@end table 2322 2323In addition, these optimization, warning, and code generation options 2324have meanings only for C++ programs: 2325 2326@table @gcctabopt 2327@item -fno-default-inline 2328@opindex fno-default-inline 2329Do not assume @samp{inline} for functions defined inside a class scope. 2330@xref{Optimize Options,,Options That Control Optimization}. Note that these 2331functions have linkage like inline functions; they just aren't 2332inlined by default. 2333 2334@item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)} 2335@opindex Wabi 2336@opindex Wno-abi 2337Warn when G++ generates code that is probably not compatible with the 2338vendor-neutral C++ ABI@. Although an effort has been made to warn about 2339all such cases, there are probably some cases that are not warned about, 2340even though G++ is generating incompatible code. There may also be 2341cases where warnings are emitted even though the code that is generated 2342is compatible. 2343 2344You should rewrite your code to avoid these warnings if you are 2345concerned about the fact that code generated by G++ may not be binary 2346compatible with code generated by other compilers. 2347 2348The known incompatibilities in @option{-fabi-version=2} (the default) include: 2349 2350@itemize @bullet 2351 2352@item 2353A template with a non-type template parameter of reference type is 2354mangled incorrectly: 2355@smallexample 2356extern int N; 2357template <int &> struct S @{@}; 2358void n (S<N>) @{2@} 2359@end smallexample 2360 2361This is fixed in @option{-fabi-version=3}. 2362 2363@item 2364SIMD vector types declared using @code{__attribute ((vector_size))} are 2365mangled in a non-standard way that does not allow for overloading of 2366functions taking vectors of different sizes. 2367 2368The mangling is changed in @option{-fabi-version=4}. 2369@end itemize 2370 2371The known incompatibilities in @option{-fabi-version=1} include: 2372 2373@itemize @bullet 2374 2375@item 2376Incorrect handling of tail-padding for bit-fields. G++ may attempt to 2377pack data into the same byte as a base class. For example: 2378 2379@smallexample 2380struct A @{ virtual void f(); int f1 : 1; @}; 2381struct B : public A @{ int f2 : 1; @}; 2382@end smallexample 2383 2384@noindent 2385In this case, G++ places @code{B::f2} into the same byte 2386as @code{A::f1}; other compilers do not. You can avoid this problem 2387by explicitly padding @code{A} so that its size is a multiple of the 2388byte size on your platform; that causes G++ and other compilers to 2389lay out @code{B} identically. 2390 2391@item 2392Incorrect handling of tail-padding for virtual bases. G++ does not use 2393tail padding when laying out virtual bases. For example: 2394 2395@smallexample 2396struct A @{ virtual void f(); char c1; @}; 2397struct B @{ B(); char c2; @}; 2398struct C : public A, public virtual B @{@}; 2399@end smallexample 2400 2401@noindent 2402In this case, G++ does not place @code{B} into the tail-padding for 2403@code{A}; other compilers do. You can avoid this problem by 2404explicitly padding @code{A} so that its size is a multiple of its 2405alignment (ignoring virtual base classes); that causes G++ and other 2406compilers to lay out @code{C} identically. 2407 2408@item 2409Incorrect handling of bit-fields with declared widths greater than that 2410of their underlying types, when the bit-fields appear in a union. For 2411example: 2412 2413@smallexample 2414union U @{ int i : 4096; @}; 2415@end smallexample 2416 2417@noindent 2418Assuming that an @code{int} does not have 4096 bits, G++ makes the 2419union too small by the number of bits in an @code{int}. 2420 2421@item 2422Empty classes can be placed at incorrect offsets. For example: 2423 2424@smallexample 2425struct A @{@}; 2426 2427struct B @{ 2428 A a; 2429 virtual void f (); 2430@}; 2431 2432struct C : public B, public A @{@}; 2433@end smallexample 2434 2435@noindent 2436G++ places the @code{A} base class of @code{C} at a nonzero offset; 2437it should be placed at offset zero. G++ mistakenly believes that the 2438@code{A} data member of @code{B} is already at offset zero. 2439 2440@item 2441Names of template functions whose types involve @code{typename} or 2442template template parameters can be mangled incorrectly. 2443 2444@smallexample 2445template <typename Q> 2446void f(typename Q::X) @{@} 2447 2448template <template <typename> class Q> 2449void f(typename Q<int>::X) @{@} 2450@end smallexample 2451 2452@noindent 2453Instantiations of these templates may be mangled incorrectly. 2454 2455@end itemize 2456 2457It also warns about psABI-related changes. The known psABI changes at this 2458point include: 2459 2460@itemize @bullet 2461 2462@item 2463For SysV/x86-64, unions with @code{long double} members are 2464passed in memory as specified in psABI. For example: 2465 2466@smallexample 2467union U @{ 2468 long double ld; 2469 int i; 2470@}; 2471@end smallexample 2472 2473@noindent 2474@code{union U} is always passed in memory. 2475 2476@end itemize 2477 2478@item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)} 2479@opindex Wctor-dtor-privacy 2480@opindex Wno-ctor-dtor-privacy 2481Warn when a class seems unusable because all the constructors or 2482destructors in that class are private, and it has neither friends nor 2483public static member functions. Also warn if there are no non-private 2484methods, and there's at least one private member function that isn't 2485a constructor or destructor. 2486 2487@item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} 2488@opindex Wdelete-non-virtual-dtor 2489@opindex Wno-delete-non-virtual-dtor 2490Warn when @samp{delete} is used to destroy an instance of a class that 2491has virtual functions and non-virtual destructor. It is unsafe to delete 2492an instance of a derived class through a pointer to a base class if the 2493base class does not have a virtual destructor. This warning is enabled 2494by @option{-Wall}. 2495 2496@item -Wliteral-suffix @r{(C++ and Objective-C++ only)} 2497@opindex Wliteral-suffix 2498@opindex Wno-literal-suffix 2499Warn when a string or character literal is followed by a ud-suffix which does 2500not begin with an underscore. As a conforming extension, GCC treats such 2501suffixes as separate preprocessing tokens in order to maintain backwards 2502compatibility with code that uses formatting macros from @code{<inttypes.h>}. 2503For example: 2504 2505@smallexample 2506#define __STDC_FORMAT_MACROS 2507#include <inttypes.h> 2508#include <stdio.h> 2509 2510int main() @{ 2511 int64_t i64 = 123; 2512 printf("My int64: %"PRId64"\n", i64); 2513@} 2514@end smallexample 2515 2516In this case, @code{PRId64} is treated as a separate preprocessing token. 2517 2518This warning is enabled by default. 2519 2520@item -Wnarrowing @r{(C++ and Objective-C++ only)} 2521@opindex Wnarrowing 2522@opindex Wno-narrowing 2523Warn when a narrowing conversion prohibited by C++11 occurs within 2524@samp{@{ @}}, e.g. 2525 2526@smallexample 2527int i = @{ 2.2 @}; // error: narrowing from double to int 2528@end smallexample 2529 2530This flag is included in @option{-Wall} and @option{-Wc++11-compat}. 2531 2532With @option{-std=c++11}, @option{-Wno-narrowing} suppresses the diagnostic 2533required by the standard. Note that this does not affect the meaning 2534of well-formed code; narrowing conversions are still considered 2535ill-formed in SFINAE context. 2536 2537@item -Wnoexcept @r{(C++ and Objective-C++ only)} 2538@opindex Wnoexcept 2539@opindex Wno-noexcept 2540Warn when a noexcept-expression evaluates to false because of a call 2541to a function that does not have a non-throwing exception 2542specification (i.e. @samp{throw()} or @samp{noexcept}) but is known by 2543the compiler to never throw an exception. 2544 2545@item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)} 2546@opindex Wnon-virtual-dtor 2547@opindex Wno-non-virtual-dtor 2548Warn when a class has virtual functions and an accessible non-virtual 2549destructor, in which case it is possible but unsafe to delete 2550an instance of a derived class through a pointer to the base class. 2551This warning is also enabled if @option{-Weffc++} is specified. 2552 2553@item -Wreorder @r{(C++ and Objective-C++ only)} 2554@opindex Wreorder 2555@opindex Wno-reorder 2556@cindex reordering, warning 2557@cindex warning for reordering of member initializers 2558Warn when the order of member initializers given in the code does not 2559match the order in which they must be executed. For instance: 2560 2561@smallexample 2562struct A @{ 2563 int i; 2564 int j; 2565 A(): j (0), i (1) @{ @} 2566@}; 2567@end smallexample 2568 2569@noindent 2570The compiler rearranges the member initializers for @samp{i} 2571and @samp{j} to match the declaration order of the members, emitting 2572a warning to that effect. This warning is enabled by @option{-Wall}. 2573 2574@item -fext-numeric-literals @r{(C++ and Objective-C++ only)} 2575@opindex fext-numeric-literals 2576@opindex fno-ext-numeric-literals 2577Accept imaginary, fixed-point, or machine-defined 2578literal number suffixes as GNU extensions. 2579When this option is turned off these suffixes are treated 2580as C++11 user-defined literal numeric suffixes. 2581This is on by default for all pre-C++11 dialects and all GNU dialects: 2582@option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11}, 2583@option{-std=gnu++1y}. 2584This option is off by default 2585for ISO C++11 onwards (@option{-std=c++11}, ...). 2586@end table 2587 2588The following @option{-W@dots{}} options are not affected by @option{-Wall}. 2589 2590@table @gcctabopt 2591@item -Weffc++ @r{(C++ and Objective-C++ only)} 2592@opindex Weffc++ 2593@opindex Wno-effc++ 2594Warn about violations of the following style guidelines from Scott Meyers' 2595@cite{Effective C++, Second Edition} book: 2596 2597@itemize @bullet 2598@item 2599Item 11: Define a copy constructor and an assignment operator for classes 2600with dynamically-allocated memory. 2601 2602@item 2603Item 12: Prefer initialization to assignment in constructors. 2604 2605@item 2606Item 14: Make destructors virtual in base classes. 2607 2608@item 2609Item 15: Have @code{operator=} return a reference to @code{*this}. 2610 2611@item 2612Item 23: Don't try to return a reference when you must return an object. 2613 2614@end itemize 2615 2616Also warn about violations of the following style guidelines from 2617Scott Meyers' @cite{More Effective C++} book: 2618 2619@itemize @bullet 2620@item 2621Item 6: Distinguish between prefix and postfix forms of increment and 2622decrement operators. 2623 2624@item 2625Item 7: Never overload @code{&&}, @code{||}, or @code{,}. 2626 2627@end itemize 2628 2629When selecting this option, be aware that the standard library 2630headers do not obey all of these guidelines; use @samp{grep -v} 2631to filter out those warnings. 2632 2633@item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} 2634@opindex Wstrict-null-sentinel 2635@opindex Wno-strict-null-sentinel 2636Warn about the use of an uncasted @code{NULL} as sentinel. When 2637compiling only with GCC this is a valid sentinel, as @code{NULL} is defined 2638to @code{__null}. Although it is a null pointer constant rather than a 2639null pointer, it is guaranteed to be of the same size as a pointer. 2640But this use is not portable across different compilers. 2641 2642@item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} 2643@opindex Wno-non-template-friend 2644@opindex Wnon-template-friend 2645Disable warnings when non-templatized friend functions are declared 2646within a template. Since the advent of explicit template specification 2647support in G++, if the name of the friend is an unqualified-id (i.e., 2648@samp{friend foo(int)}), the C++ language specification demands that the 2649friend declare or define an ordinary, nontemplate function. (Section 265014.5.3). Before G++ implemented explicit specification, unqualified-ids 2651could be interpreted as a particular specialization of a templatized 2652function. Because this non-conforming behavior is no longer the default 2653behavior for G++, @option{-Wnon-template-friend} allows the compiler to 2654check existing code for potential trouble spots and is on by default. 2655This new compiler behavior can be turned off with 2656@option{-Wno-non-template-friend}, which keeps the conformant compiler code 2657but disables the helpful warning. 2658 2659@item -Wold-style-cast @r{(C++ and Objective-C++ only)} 2660@opindex Wold-style-cast 2661@opindex Wno-old-style-cast 2662Warn if an old-style (C-style) cast to a non-void type is used within 2663a C++ program. The new-style casts (@samp{dynamic_cast}, 2664@samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are 2665less vulnerable to unintended effects and much easier to search for. 2666 2667@item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} 2668@opindex Woverloaded-virtual 2669@opindex Wno-overloaded-virtual 2670@cindex overloaded virtual function, warning 2671@cindex warning for overloaded virtual function 2672Warn when a function declaration hides virtual functions from a 2673base class. For example, in: 2674 2675@smallexample 2676struct A @{ 2677 virtual void f(); 2678@}; 2679 2680struct B: public A @{ 2681 void f(int); 2682@}; 2683@end smallexample 2684 2685the @code{A} class version of @code{f} is hidden in @code{B}, and code 2686like: 2687 2688@smallexample 2689B* b; 2690b->f(); 2691@end smallexample 2692 2693@noindent 2694fails to compile. 2695 2696@item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} 2697@opindex Wno-pmf-conversions 2698@opindex Wpmf-conversions 2699Disable the diagnostic for converting a bound pointer to member function 2700to a plain pointer. 2701 2702@item -Wsign-promo @r{(C++ and Objective-C++ only)} 2703@opindex Wsign-promo 2704@opindex Wno-sign-promo 2705Warn when overload resolution chooses a promotion from unsigned or 2706enumerated type to a signed type, over a conversion to an unsigned type of 2707the same size. Previous versions of G++ tried to preserve 2708unsignedness, but the standard mandates the current behavior. 2709@end table 2710 2711@node Objective-C and Objective-C++ Dialect Options 2712@section Options Controlling Objective-C and Objective-C++ Dialects 2713 2714@cindex compiler options, Objective-C and Objective-C++ 2715@cindex Objective-C and Objective-C++ options, command-line 2716@cindex options, Objective-C and Objective-C++ 2717(NOTE: This manual does not describe the Objective-C and Objective-C++ 2718languages themselves. @xref{Standards,,Language Standards 2719Supported by GCC}, for references.) 2720 2721This section describes the command-line options that are only meaningful 2722for Objective-C and Objective-C++ programs. You can also use most of 2723the language-independent GNU compiler options. 2724For example, you might compile a file @code{some_class.m} like this: 2725 2726@smallexample 2727gcc -g -fgnu-runtime -O -c some_class.m 2728@end smallexample 2729 2730@noindent 2731In this example, @option{-fgnu-runtime} is an option meant only for 2732Objective-C and Objective-C++ programs; you can use the other options with 2733any language supported by GCC@. 2734 2735Note that since Objective-C is an extension of the C language, Objective-C 2736compilations may also use options specific to the C front-end (e.g., 2737@option{-Wtraditional}). Similarly, Objective-C++ compilations may use 2738C++-specific options (e.g., @option{-Wabi}). 2739 2740Here is a list of options that are @emph{only} for compiling Objective-C 2741and Objective-C++ programs: 2742 2743@table @gcctabopt 2744@item -fconstant-string-class=@var{class-name} 2745@opindex fconstant-string-class 2746Use @var{class-name} as the name of the class to instantiate for each 2747literal string specified with the syntax @code{@@"@dots{}"}. The default 2748class name is @code{NXConstantString} if the GNU runtime is being used, and 2749@code{NSConstantString} if the NeXT runtime is being used (see below). The 2750@option{-fconstant-cfstrings} option, if also present, overrides the 2751@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals 2752to be laid out as constant CoreFoundation strings. 2753 2754@item -fgnu-runtime 2755@opindex fgnu-runtime 2756Generate object code compatible with the standard GNU Objective-C 2757runtime. This is the default for most types of systems. 2758 2759@item -fnext-runtime 2760@opindex fnext-runtime 2761Generate output compatible with the NeXT runtime. This is the default 2762for NeXT-based systems, including Darwin and Mac OS X@. The macro 2763@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is 2764used. 2765 2766@item -fno-nil-receivers 2767@opindex fno-nil-receivers 2768Assume that all Objective-C message dispatches (@code{[receiver 2769message:arg]}) in this translation unit ensure that the receiver is 2770not @code{nil}. This allows for more efficient entry points in the 2771runtime to be used. This option is only available in conjunction with 2772the NeXT runtime and ABI version 0 or 1. 2773 2774@item -fobjc-abi-version=@var{n} 2775@opindex fobjc-abi-version 2776Use version @var{n} of the Objective-C ABI for the selected runtime. 2777This option is currently supported only for the NeXT runtime. In that 2778case, Version 0 is the traditional (32-bit) ABI without support for 2779properties and other Objective-C 2.0 additions. Version 1 is the 2780traditional (32-bit) ABI with support for properties and other 2781Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If 2782nothing is specified, the default is Version 0 on 32-bit target 2783machines, and Version 2 on 64-bit target machines. 2784 2785@item -fobjc-call-cxx-cdtors 2786@opindex fobjc-call-cxx-cdtors 2787For each Objective-C class, check if any of its instance variables is a 2788C++ object with a non-trivial default constructor. If so, synthesize a 2789special @code{- (id) .cxx_construct} instance method which runs 2790non-trivial default constructors on any such instance variables, in order, 2791and then return @code{self}. Similarly, check if any instance variable 2792is a C++ object with a non-trivial destructor, and if so, synthesize a 2793special @code{- (void) .cxx_destruct} method which runs 2794all such default destructors, in reverse order. 2795 2796The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} 2797methods thusly generated only operate on instance variables 2798declared in the current Objective-C class, and not those inherited 2799from superclasses. It is the responsibility of the Objective-C 2800runtime to invoke all such methods in an object's inheritance 2801hierarchy. The @code{- (id) .cxx_construct} methods are invoked 2802by the runtime immediately after a new object instance is allocated; 2803the @code{- (void) .cxx_destruct} methods are invoked immediately 2804before the runtime deallocates an object instance. 2805 2806As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has 2807support for invoking the @code{- (id) .cxx_construct} and 2808@code{- (void) .cxx_destruct} methods. 2809 2810@item -fobjc-direct-dispatch 2811@opindex fobjc-direct-dispatch 2812Allow fast jumps to the message dispatcher. On Darwin this is 2813accomplished via the comm page. 2814 2815@item -fobjc-exceptions 2816@opindex fobjc-exceptions 2817Enable syntactic support for structured exception handling in 2818Objective-C, similar to what is offered by C++ and Java. This option 2819is required to use the Objective-C keywords @code{@@try}, 2820@code{@@throw}, @code{@@catch}, @code{@@finally} and 2821@code{@@synchronized}. This option is available with both the GNU 2822runtime and the NeXT runtime (but not available in conjunction with 2823the NeXT runtime on Mac OS X 10.2 and earlier). 2824 2825@item -fobjc-gc 2826@opindex fobjc-gc 2827Enable garbage collection (GC) in Objective-C and Objective-C++ 2828programs. This option is only available with the NeXT runtime; the 2829GNU runtime has a different garbage collection implementation that 2830does not require special compiler flags. 2831 2832@item -fobjc-nilcheck 2833@opindex fobjc-nilcheck 2834For the NeXT runtime with version 2 of the ABI, check for a nil 2835receiver in method invocations before doing the actual method call. 2836This is the default and can be disabled using 2837@option{-fno-objc-nilcheck}. Class methods and super calls are never 2838checked for nil in this way no matter what this flag is set to. 2839Currently this flag does nothing when the GNU runtime, or an older 2840version of the NeXT runtime ABI, is used. 2841 2842@item -fobjc-std=objc1 2843@opindex fobjc-std 2844Conform to the language syntax of Objective-C 1.0, the language 2845recognized by GCC 4.0. This only affects the Objective-C additions to 2846the C/C++ language; it does not affect conformance to C/C++ standards, 2847which is controlled by the separate C/C++ dialect option flags. When 2848this option is used with the Objective-C or Objective-C++ compiler, 2849any Objective-C syntax that is not recognized by GCC 4.0 is rejected. 2850This is useful if you need to make sure that your Objective-C code can 2851be compiled with older versions of GCC@. 2852 2853@item -freplace-objc-classes 2854@opindex freplace-objc-classes 2855Emit a special marker instructing @command{ld(1)} not to statically link in 2856the resulting object file, and allow @command{dyld(1)} to load it in at 2857run time instead. This is used in conjunction with the Fix-and-Continue 2858debugging mode, where the object file in question may be recompiled and 2859dynamically reloaded in the course of program execution, without the need 2860to restart the program itself. Currently, Fix-and-Continue functionality 2861is only available in conjunction with the NeXT runtime on Mac OS X 10.3 2862and later. 2863 2864@item -fzero-link 2865@opindex fzero-link 2866When compiling for the NeXT runtime, the compiler ordinarily replaces calls 2867to @code{objc_getClass("@dots{}")} (when the name of the class is known at 2868compile time) with static class references that get initialized at load time, 2869which improves run-time performance. Specifying the @option{-fzero-link} flag 2870suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} 2871to be retained. This is useful in Zero-Link debugging mode, since it allows 2872for individual class implementations to be modified during program execution. 2873The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} 2874regardless of command-line options. 2875 2876@item -gen-decls 2877@opindex gen-decls 2878Dump interface declarations for all classes seen in the source file to a 2879file named @file{@var{sourcename}.decl}. 2880 2881@item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} 2882@opindex Wassign-intercept 2883@opindex Wno-assign-intercept 2884Warn whenever an Objective-C assignment is being intercepted by the 2885garbage collector. 2886 2887@item -Wno-protocol @r{(Objective-C and Objective-C++ only)} 2888@opindex Wno-protocol 2889@opindex Wprotocol 2890If a class is declared to implement a protocol, a warning is issued for 2891every method in the protocol that is not implemented by the class. The 2892default behavior is to issue a warning for every method not explicitly 2893implemented in the class, even if a method implementation is inherited 2894from the superclass. If you use the @option{-Wno-protocol} option, then 2895methods inherited from the superclass are considered to be implemented, 2896and no warning is issued for them. 2897 2898@item -Wselector @r{(Objective-C and Objective-C++ only)} 2899@opindex Wselector 2900@opindex Wno-selector 2901Warn if multiple methods of different types for the same selector are 2902found during compilation. The check is performed on the list of methods 2903in the final stage of compilation. Additionally, a check is performed 2904for each selector appearing in a @code{@@selector(@dots{})} 2905expression, and a corresponding method for that selector has been found 2906during compilation. Because these checks scan the method table only at 2907the end of compilation, these warnings are not produced if the final 2908stage of compilation is not reached, for example because an error is 2909found during compilation, or because the @option{-fsyntax-only} option is 2910being used. 2911 2912@item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)} 2913@opindex Wstrict-selector-match 2914@opindex Wno-strict-selector-match 2915Warn if multiple methods with differing argument and/or return types are 2916found for a given selector when attempting to send a message using this 2917selector to a receiver of type @code{id} or @code{Class}. When this flag 2918is off (which is the default behavior), the compiler omits such warnings 2919if any differences found are confined to types that share the same size 2920and alignment. 2921 2922@item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} 2923@opindex Wundeclared-selector 2924@opindex Wno-undeclared-selector 2925Warn if a @code{@@selector(@dots{})} expression referring to an 2926undeclared selector is found. A selector is considered undeclared if no 2927method with that name has been declared before the 2928@code{@@selector(@dots{})} expression, either explicitly in an 2929@code{@@interface} or @code{@@protocol} declaration, or implicitly in 2930an @code{@@implementation} section. This option always performs its 2931checks as soon as a @code{@@selector(@dots{})} expression is found, 2932while @option{-Wselector} only performs its checks in the final stage of 2933compilation. This also enforces the coding style convention 2934that methods and selectors must be declared before being used. 2935 2936@item -print-objc-runtime-info 2937@opindex print-objc-runtime-info 2938Generate C header describing the largest structure that is passed by 2939value, if any. 2940 2941@end table 2942 2943@node Language Independent Options 2944@section Options to Control Diagnostic Messages Formatting 2945@cindex options to control diagnostics formatting 2946@cindex diagnostic messages 2947@cindex message formatting 2948 2949Traditionally, diagnostic messages have been formatted irrespective of 2950the output device's aspect (e.g.@: its width, @dots{}). You can use the 2951options described below 2952to control the formatting algorithm for diagnostic messages, 2953e.g.@: how many characters per line, how often source location 2954information should be reported. Note that some language front ends may not 2955honor these options. 2956 2957@table @gcctabopt 2958@item -fmessage-length=@var{n} 2959@opindex fmessage-length 2960Try to format error messages so that they fit on lines of about @var{n} 2961characters. The default is 72 characters for @command{g++} and 0 for the rest of 2962the front ends supported by GCC@. If @var{n} is zero, then no 2963line-wrapping is done; each error message appears on a single 2964line. 2965 2966@item -fdiagnostics-show-location=once 2967@opindex fdiagnostics-show-location 2968Only meaningful in line-wrapping mode. Instructs the diagnostic messages 2969reporter to emit source location information @emph{once}; that is, in 2970case the message is too long to fit on a single physical line and has to 2971be wrapped, the source location won't be emitted (as prefix) again, 2972over and over, in subsequent continuation lines. This is the default 2973behavior. 2974 2975@item -fdiagnostics-show-location=every-line 2976Only meaningful in line-wrapping mode. Instructs the diagnostic 2977messages reporter to emit the same source location information (as 2978prefix) for physical lines that result from the process of breaking 2979a message which is too long to fit on a single line. 2980 2981@item -fno-diagnostics-show-option 2982@opindex fno-diagnostics-show-option 2983@opindex fdiagnostics-show-option 2984By default, each diagnostic emitted includes text indicating the 2985command-line option that directly controls the diagnostic (if such an 2986option is known to the diagnostic machinery). Specifying the 2987@option{-fno-diagnostics-show-option} flag suppresses that behavior. 2988 2989@item -fno-diagnostics-show-caret 2990@opindex fno-diagnostics-show-caret 2991@opindex fdiagnostics-show-caret 2992By default, each diagnostic emitted includes the original source line 2993and a caret '^' indicating the column. This option suppresses this 2994information. 2995 2996@end table 2997 2998@node Warning Options 2999@section Options to Request or Suppress Warnings 3000@cindex options to control warnings 3001@cindex warning messages 3002@cindex messages, warning 3003@cindex suppressing warnings 3004 3005Warnings are diagnostic messages that report constructions that 3006are not inherently erroneous but that are risky or suggest there 3007may have been an error. 3008 3009The following language-independent options do not enable specific 3010warnings but control the kinds of diagnostics produced by GCC@. 3011 3012@table @gcctabopt 3013@cindex syntax checking 3014@item -fsyntax-only 3015@opindex fsyntax-only 3016Check the code for syntax errors, but don't do anything beyond that. 3017 3018@item -fmax-errors=@var{n} 3019@opindex fmax-errors 3020Limits the maximum number of error messages to @var{n}, at which point 3021GCC bails out rather than attempting to continue processing the source 3022code. If @var{n} is 0 (the default), there is no limit on the number 3023of error messages produced. If @option{-Wfatal-errors} is also 3024specified, then @option{-Wfatal-errors} takes precedence over this 3025option. 3026 3027@item -w 3028@opindex w 3029Inhibit all warning messages. 3030 3031@item -Werror 3032@opindex Werror 3033@opindex Wno-error 3034Make all warnings into errors. 3035 3036@item -Werror= 3037@opindex Werror= 3038@opindex Wno-error= 3039Make the specified warning into an error. The specifier for a warning 3040is appended; for example @option{-Werror=switch} turns the warnings 3041controlled by @option{-Wswitch} into errors. This switch takes a 3042negative form, to be used to negate @option{-Werror} for specific 3043warnings; for example @option{-Wno-error=switch} makes 3044@option{-Wswitch} warnings not be errors, even when @option{-Werror} 3045is in effect. 3046 3047The warning message for each controllable warning includes the 3048option that controls the warning. That option can then be used with 3049@option{-Werror=} and @option{-Wno-error=} as described above. 3050(Printing of the option in the warning message can be disabled using the 3051@option{-fno-diagnostics-show-option} flag.) 3052 3053Note that specifying @option{-Werror=}@var{foo} automatically implies 3054@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not 3055imply anything. 3056 3057@item -Wfatal-errors 3058@opindex Wfatal-errors 3059@opindex Wno-fatal-errors 3060This option causes the compiler to abort compilation on the first error 3061occurred rather than trying to keep going and printing further error 3062messages. 3063 3064@end table 3065 3066You can request many specific warnings with options beginning with 3067@samp{-W}, for example @option{-Wimplicit} to request warnings on 3068implicit declarations. Each of these specific warning options also 3069has a negative form beginning @samp{-Wno-} to turn off warnings; for 3070example, @option{-Wno-implicit}. This manual lists only one of the 3071two forms, whichever is not the default. For further 3072language-specific options also refer to @ref{C++ Dialect Options} and 3073@ref{Objective-C and Objective-C++ Dialect Options}. 3074 3075When an unrecognized warning option is requested (e.g., 3076@option{-Wunknown-warning}), GCC emits a diagnostic stating 3077that the option is not recognized. However, if the @option{-Wno-} form 3078is used, the behavior is slightly different: no diagnostic is 3079produced for @option{-Wno-unknown-warning} unless other diagnostics 3080are being produced. This allows the use of new @option{-Wno-} options 3081with old compilers, but if something goes wrong, the compiler 3082warns that an unrecognized option is present. 3083 3084@table @gcctabopt 3085@item -Wpedantic 3086@itemx -pedantic 3087@opindex pedantic 3088@opindex Wpedantic 3089Issue all the warnings demanded by strict ISO C and ISO C++; 3090reject all programs that use forbidden extensions, and some other 3091programs that do not follow ISO C and ISO C++. For ISO C, follows the 3092version of the ISO C standard specified by any @option{-std} option used. 3093 3094Valid ISO C and ISO C++ programs should compile properly with or without 3095this option (though a rare few require @option{-ansi} or a 3096@option{-std} option specifying the required version of ISO C)@. However, 3097without this option, certain GNU extensions and traditional C and C++ 3098features are supported as well. With this option, they are rejected. 3099 3100@option{-Wpedantic} does not cause warning messages for use of the 3101alternate keywords whose names begin and end with @samp{__}. Pedantic 3102warnings are also disabled in the expression that follows 3103@code{__extension__}. However, only system header files should use 3104these escape routes; application programs should avoid them. 3105@xref{Alternate Keywords}. 3106 3107Some users try to use @option{-Wpedantic} to check programs for strict ISO 3108C conformance. They soon find that it does not do quite what they want: 3109it finds some non-ISO practices, but not all---only those for which 3110ISO C @emph{requires} a diagnostic, and some others for which 3111diagnostics have been added. 3112 3113A feature to report any failure to conform to ISO C might be useful in 3114some instances, but would require considerable additional work and would 3115be quite different from @option{-Wpedantic}. We don't have plans to 3116support such a feature in the near future. 3117 3118Where the standard specified with @option{-std} represents a GNU 3119extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a 3120corresponding @dfn{base standard}, the version of ISO C on which the GNU 3121extended dialect is based. Warnings from @option{-Wpedantic} are given 3122where they are required by the base standard. (It does not make sense 3123for such warnings to be given only for features not in the specified GNU 3124C dialect, since by definition the GNU dialects of C include all 3125features the compiler supports with the given option, and there would be 3126nothing to warn about.) 3127 3128@item -pedantic-errors 3129@opindex pedantic-errors 3130Like @option{-Wpedantic}, except that errors are produced rather than 3131warnings. 3132 3133@item -Wall 3134@opindex Wall 3135@opindex Wno-all 3136This enables all the warnings about constructions that some users 3137consider questionable, and that are easy to avoid (or modify to 3138prevent the warning), even in conjunction with macros. This also 3139enables some language-specific warnings described in @ref{C++ Dialect 3140Options} and @ref{Objective-C and Objective-C++ Dialect Options}. 3141 3142@option{-Wall} turns on the following warning flags: 3143 3144@gccoptlist{-Waddress @gol 3145-Warray-bounds @r{(only with} @option{-O2}@r{)} @gol 3146-Wc++11-compat @gol 3147-Wchar-subscripts @gol 3148-Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol 3149-Wimplicit-int @r{(C and Objective-C only)} @gol 3150-Wimplicit-function-declaration @r{(C and Objective-C only)} @gol 3151-Wcomment @gol 3152-Wformat @gol 3153-Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol 3154-Wmaybe-uninitialized @gol 3155-Wmissing-braces @r{(only for C/ObjC)} @gol 3156-Wnonnull @gol 3157-Wparentheses @gol 3158-Wpointer-sign @gol 3159-Wreorder @gol 3160-Wreturn-type @gol 3161-Wsequence-point @gol 3162-Wsign-compare @r{(only in C++)} @gol 3163-Wstrict-aliasing @gol 3164-Wstrict-overflow=1 @gol 3165-Wswitch @gol 3166-Wtrigraphs @gol 3167-Wuninitialized @gol 3168-Wunknown-pragmas @gol 3169-Wunused-function @gol 3170-Wunused-label @gol 3171-Wunused-value @gol 3172-Wunused-variable @gol 3173-Wvolatile-register-var @gol 3174} 3175 3176Note that some warning flags are not implied by @option{-Wall}. Some of 3177them warn about constructions that users generally do not consider 3178questionable, but which occasionally you might wish to check for; 3179others warn about constructions that are necessary or hard to avoid in 3180some cases, and there is no simple way to modify the code to suppress 3181the warning. Some of them are enabled by @option{-Wextra} but many of 3182them must be enabled individually. 3183 3184@item -Wextra 3185@opindex W 3186@opindex Wextra 3187@opindex Wno-extra 3188This enables some extra warning flags that are not enabled by 3189@option{-Wall}. (This option used to be called @option{-W}. The older 3190name is still supported, but the newer name is more descriptive.) 3191 3192@gccoptlist{-Wclobbered @gol 3193-Wempty-body @gol 3194-Wignored-qualifiers @gol 3195-Wmissing-field-initializers @gol 3196-Wmissing-parameter-type @r{(C only)} @gol 3197-Wold-style-declaration @r{(C only)} @gol 3198-Woverride-init @gol 3199-Wsign-compare @gol 3200-Wtype-limits @gol 3201-Wuninitialized @gol 3202-Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol 3203-Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol 3204} 3205 3206The option @option{-Wextra} also prints warning messages for the 3207following cases: 3208 3209@itemize @bullet 3210 3211@item 3212A pointer is compared against integer zero with @samp{<}, @samp{<=}, 3213@samp{>}, or @samp{>=}. 3214 3215@item 3216(C++ only) An enumerator and a non-enumerator both appear in a 3217conditional expression. 3218 3219@item 3220(C++ only) Ambiguous virtual bases. 3221 3222@item 3223(C++ only) Subscripting an array that has been declared @samp{register}. 3224 3225@item 3226(C++ only) Taking the address of a variable that has been declared 3227@samp{register}. 3228 3229@item 3230(C++ only) A base class is not initialized in a derived class's copy 3231constructor. 3232 3233@end itemize 3234 3235@item -Wchar-subscripts 3236@opindex Wchar-subscripts 3237@opindex Wno-char-subscripts 3238Warn if an array subscript has type @code{char}. This is a common cause 3239of error, as programmers often forget that this type is signed on some 3240machines. 3241This warning is enabled by @option{-Wall}. 3242 3243@item -Wcomment 3244@opindex Wcomment 3245@opindex Wno-comment 3246Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} 3247comment, or whenever a Backslash-Newline appears in a @samp{//} comment. 3248This warning is enabled by @option{-Wall}. 3249 3250@item -Wno-coverage-mismatch 3251@opindex Wno-coverage-mismatch 3252Warn if feedback profiles do not match when using the 3253@option{-fprofile-use} option. 3254If a source file is changed between compiling with @option{-fprofile-gen} and 3255with @option{-fprofile-use}, the files with the profile feedback can fail 3256to match the source file and GCC cannot use the profile feedback 3257information. By default, this warning is enabled and is treated as an 3258error. @option{-Wno-coverage-mismatch} can be used to disable the 3259warning or @option{-Wno-error=coverage-mismatch} can be used to 3260disable the error. Disabling the error for this warning can result in 3261poorly optimized code and is useful only in the 3262case of very minor changes such as bug fixes to an existing code-base. 3263Completely disabling the warning is not recommended. 3264 3265@item -Wno-cpp 3266@r{(C, Objective-C, C++, Objective-C++ and Fortran only)} 3267 3268Suppress warning messages emitted by @code{#warning} directives. 3269 3270@item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)} 3271@opindex Wdouble-promotion 3272@opindex Wno-double-promotion 3273Give a warning when a value of type @code{float} is implicitly 3274promoted to @code{double}. CPUs with a 32-bit ``single-precision'' 3275floating-point unit implement @code{float} in hardware, but emulate 3276@code{double} in software. On such a machine, doing computations 3277using @code{double} values is much more expensive because of the 3278overhead required for software emulation. 3279 3280It is easy to accidentally do computations with @code{double} because 3281floating-point literals are implicitly of type @code{double}. For 3282example, in: 3283@smallexample 3284@group 3285float area(float radius) 3286@{ 3287 return 3.14159 * radius * radius; 3288@} 3289@end group 3290@end smallexample 3291the compiler performs the entire computation with @code{double} 3292because the floating-point literal is a @code{double}. 3293 3294@item -Wformat 3295@itemx -Wformat=@var{n} 3296@opindex Wformat 3297@opindex Wno-format 3298@opindex ffreestanding 3299@opindex fno-builtin 3300@opindex Wformat= 3301Check calls to @code{printf} and @code{scanf}, etc., to make sure that 3302the arguments supplied have types appropriate to the format string 3303specified, and that the conversions specified in the format string make 3304sense. This includes standard functions, and others specified by format 3305attributes (@pxref{Function Attributes}), in the @code{printf}, 3306@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, 3307not in the C standard) families (or other target-specific families). 3308Which functions are checked without format attributes having been 3309specified depends on the standard version selected, and such checks of 3310functions without the attribute specified are disabled by 3311@option{-ffreestanding} or @option{-fno-builtin}. 3312 3313The formats are checked against the format features supported by GNU 3314libc version 2.2. These include all ISO C90 and C99 features, as well 3315as features from the Single Unix Specification and some BSD and GNU 3316extensions. Other library implementations may not support all these 3317features; GCC does not support warning about features that go beyond a 3318particular library's limitations. However, if @option{-Wpedantic} is used 3319with @option{-Wformat}, warnings are given about format features not 3320in the selected standard version (but not for @code{strfmon} formats, 3321since those are not in any version of the C standard). @xref{C Dialect 3322Options,,Options Controlling C Dialect}. 3323 3324@table @gcctabopt 3325@item -Wformat=1 3326@itemx -Wformat 3327Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and 3328@option{-Wno-format} is equivalent to @option{-Wformat=0}. Since 3329@option{-Wformat} also checks for null format arguments for several 3330functions, @option{-Wformat} also implies @option{-Wnonnull}. Some 3331aspects of this level of format checking can be disabled by the 3332options: @option{-Wno-format-contains-nul}, 3333@option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}. 3334@option{-Wformat} is enabled by @option{-Wall}. 3335 3336@item -Wno-format-contains-nul 3337@opindex Wno-format-contains-nul 3338@opindex Wformat-contains-nul 3339If @option{-Wformat} is specified, do not warn about format strings that 3340contain NUL bytes. 3341 3342@item -Wno-format-extra-args 3343@opindex Wno-format-extra-args 3344@opindex Wformat-extra-args 3345If @option{-Wformat} is specified, do not warn about excess arguments to a 3346@code{printf} or @code{scanf} format function. The C standard specifies 3347that such arguments are ignored. 3348 3349Where the unused arguments lie between used arguments that are 3350specified with @samp{$} operand number specifications, normally 3351warnings are still given, since the implementation could not know what 3352type to pass to @code{va_arg} to skip the unused arguments. However, 3353in the case of @code{scanf} formats, this option suppresses the 3354warning if the unused arguments are all pointers, since the Single 3355Unix Specification says that such unused arguments are allowed. 3356 3357@item -Wno-format-zero-length 3358@opindex Wno-format-zero-length 3359@opindex Wformat-zero-length 3360If @option{-Wformat} is specified, do not warn about zero-length formats. 3361The C standard specifies that zero-length formats are allowed. 3362 3363 3364@item -Wformat=2 3365Enable @option{-Wformat} plus additional format checks. Currently 3366equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security 3367-Wformat-y2k}. 3368 3369@item -Wformat-nonliteral 3370@opindex Wformat-nonliteral 3371@opindex Wno-format-nonliteral 3372If @option{-Wformat} is specified, also warn if the format string is not a 3373string literal and so cannot be checked, unless the format function 3374takes its format arguments as a @code{va_list}. 3375 3376@item -Wformat-security 3377@opindex Wformat-security 3378@opindex Wno-format-security 3379If @option{-Wformat} is specified, also warn about uses of format 3380functions that represent possible security problems. At present, this 3381warns about calls to @code{printf} and @code{scanf} functions where the 3382format string is not a string literal and there are no format arguments, 3383as in @code{printf (foo);}. This may be a security hole if the format 3384string came from untrusted input and contains @samp{%n}. (This is 3385currently a subset of what @option{-Wformat-nonliteral} warns about, but 3386in future warnings may be added to @option{-Wformat-security} that are not 3387included in @option{-Wformat-nonliteral}.) 3388 3389@item -Wformat-y2k 3390@opindex Wformat-y2k 3391@opindex Wno-format-y2k 3392If @option{-Wformat} is specified, also warn about @code{strftime} 3393formats that may yield only a two-digit year. 3394@end table 3395 3396@item -Wnonnull 3397@opindex Wnonnull 3398@opindex Wno-nonnull 3399Warn about passing a null pointer for arguments marked as 3400requiring a non-null value by the @code{nonnull} function attribute. 3401 3402@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It 3403can be disabled with the @option{-Wno-nonnull} option. 3404 3405@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} 3406@opindex Winit-self 3407@opindex Wno-init-self 3408Warn about uninitialized variables that are initialized with themselves. 3409Note this option can only be used with the @option{-Wuninitialized} option. 3410 3411For example, GCC warns about @code{i} being uninitialized in the 3412following snippet only when @option{-Winit-self} has been specified: 3413@smallexample 3414@group 3415int f() 3416@{ 3417 int i = i; 3418 return i; 3419@} 3420@end group 3421@end smallexample 3422 3423This warning is enabled by @option{-Wall} in C++. 3424 3425@item -Wimplicit-int @r{(C and Objective-C only)} 3426@opindex Wimplicit-int 3427@opindex Wno-implicit-int 3428Warn when a declaration does not specify a type. 3429This warning is enabled by @option{-Wall}. 3430 3431@item -Wimplicit-function-declaration @r{(C and Objective-C only)} 3432@opindex Wimplicit-function-declaration 3433@opindex Wno-implicit-function-declaration 3434Give a warning whenever a function is used before being declared. In 3435C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is 3436enabled by default and it is made into an error by 3437@option{-pedantic-errors}. This warning is also enabled by 3438@option{-Wall}. 3439 3440@item -Wimplicit @r{(C and Objective-C only)} 3441@opindex Wimplicit 3442@opindex Wno-implicit 3443Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. 3444This warning is enabled by @option{-Wall}. 3445 3446@item -Wignored-qualifiers @r{(C and C++ only)} 3447@opindex Wignored-qualifiers 3448@opindex Wno-ignored-qualifiers 3449Warn if the return type of a function has a type qualifier 3450such as @code{const}. For ISO C such a type qualifier has no effect, 3451since the value returned by a function is not an lvalue. 3452For C++, the warning is only emitted for scalar types or @code{void}. 3453ISO C prohibits qualified @code{void} return types on function 3454definitions, so such return types always receive a warning 3455even without this option. 3456 3457This warning is also enabled by @option{-Wextra}. 3458 3459@item -Wmain 3460@opindex Wmain 3461@opindex Wno-main 3462Warn if the type of @samp{main} is suspicious. @samp{main} should be 3463a function with external linkage, returning int, taking either zero 3464arguments, two, or three arguments of appropriate types. This warning 3465is enabled by default in C++ and is enabled by either @option{-Wall} 3466or @option{-Wpedantic}. 3467 3468@item -Wmissing-braces 3469@opindex Wmissing-braces 3470@opindex Wno-missing-braces 3471Warn if an aggregate or union initializer is not fully bracketed. In 3472the following example, the initializer for @samp{a} is not fully 3473bracketed, but that for @samp{b} is fully bracketed. This warning is 3474enabled by @option{-Wall} in C. 3475 3476@smallexample 3477int a[2][2] = @{ 0, 1, 2, 3 @}; 3478int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; 3479@end smallexample 3480 3481This warning is enabled by @option{-Wall}. 3482 3483@item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)} 3484@opindex Wmissing-include-dirs 3485@opindex Wno-missing-include-dirs 3486Warn if a user-supplied include directory does not exist. 3487 3488@item -Wparentheses 3489@opindex Wparentheses 3490@opindex Wno-parentheses 3491Warn if parentheses are omitted in certain contexts, such 3492as when there is an assignment in a context where a truth value 3493is expected, or when operators are nested whose precedence people 3494often get confused about. 3495 3496Also warn if a comparison like @samp{x<=y<=z} appears; this is 3497equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different 3498interpretation from that of ordinary mathematical notation. 3499 3500Also warn about constructions where there may be confusion to which 3501@code{if} statement an @code{else} branch belongs. Here is an example of 3502such a case: 3503 3504@smallexample 3505@group 3506@{ 3507 if (a) 3508 if (b) 3509 foo (); 3510 else 3511 bar (); 3512@} 3513@end group 3514@end smallexample 3515 3516In C/C++, every @code{else} branch belongs to the innermost possible 3517@code{if} statement, which in this example is @code{if (b)}. This is 3518often not what the programmer expected, as illustrated in the above 3519example by indentation the programmer chose. When there is the 3520potential for this confusion, GCC issues a warning when this flag 3521is specified. To eliminate the warning, add explicit braces around 3522the innermost @code{if} statement so there is no way the @code{else} 3523can belong to the enclosing @code{if}. The resulting code 3524looks like this: 3525 3526@smallexample 3527@group 3528@{ 3529 if (a) 3530 @{ 3531 if (b) 3532 foo (); 3533 else 3534 bar (); 3535 @} 3536@} 3537@end group 3538@end smallexample 3539 3540Also warn for dangerous uses of the GNU extension to 3541@code{?:} with omitted middle operand. When the condition 3542in the @code{?}: operator is a boolean expression, the omitted value is 3543always 1. Often programmers expect it to be a value computed 3544inside the conditional expression instead. 3545 3546This warning is enabled by @option{-Wall}. 3547 3548@item -Wsequence-point 3549@opindex Wsequence-point 3550@opindex Wno-sequence-point 3551Warn about code that may have undefined semantics because of violations 3552of sequence point rules in the C and C++ standards. 3553 3554The C and C++ standards define the order in which expressions in a C/C++ 3555program are evaluated in terms of @dfn{sequence points}, which represent 3556a partial ordering between the execution of parts of the program: those 3557executed before the sequence point, and those executed after it. These 3558occur after the evaluation of a full expression (one which is not part 3559of a larger expression), after the evaluation of the first operand of a 3560@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a 3561function is called (but after the evaluation of its arguments and the 3562expression denoting the called function), and in certain other places. 3563Other than as expressed by the sequence point rules, the order of 3564evaluation of subexpressions of an expression is not specified. All 3565these rules describe only a partial order rather than a total order, 3566since, for example, if two functions are called within one expression 3567with no sequence point between them, the order in which the functions 3568are called is not specified. However, the standards committee have 3569ruled that function calls do not overlap. 3570 3571It is not specified when between sequence points modifications to the 3572values of objects take effect. Programs whose behavior depends on this 3573have undefined behavior; the C and C++ standards specify that ``Between 3574the previous and next sequence point an object shall have its stored 3575value modified at most once by the evaluation of an expression. 3576Furthermore, the prior value shall be read only to determine the value 3577to be stored.''. If a program breaks these rules, the results on any 3578particular implementation are entirely unpredictable. 3579 3580Examples of code with undefined behavior are @code{a = a++;}, 3581@code{a[n] = b[n++]} and @code{a[i++] = i;}. Some more complicated cases 3582are not diagnosed by this option, and it may give an occasional false 3583positive result, but in general it has been found fairly effective at 3584detecting this sort of problem in programs. 3585 3586The standard is worded confusingly, therefore there is some debate 3587over the precise meaning of the sequence point rules in subtle cases. 3588Links to discussions of the problem, including proposed formal 3589definitions, may be found on the GCC readings page, at 3590@uref{http://gcc.gnu.org/@/readings.html}. 3591 3592This warning is enabled by @option{-Wall} for C and C++. 3593 3594@item -Wno-return-local-addr 3595@opindex Wno-return-local-addr 3596@opindex Wreturn-local-addr 3597Do not warn about returning a pointer (or in C++, a reference) to a 3598variable that goes out of scope after the function returns. 3599 3600@item -Wreturn-type 3601@opindex Wreturn-type 3602@opindex Wno-return-type 3603Warn whenever a function is defined with a return type that defaults 3604to @code{int}. Also warn about any @code{return} statement with no 3605return value in a function whose return type is not @code{void} 3606(falling off the end of the function body is considered returning 3607without a value), and about a @code{return} statement with an 3608expression in a function whose return type is @code{void}. 3609 3610For C++, a function without return type always produces a diagnostic 3611message, even when @option{-Wno-return-type} is specified. The only 3612exceptions are @samp{main} and functions defined in system headers. 3613 3614This warning is enabled by @option{-Wall}. 3615 3616@item -Wswitch 3617@opindex Wswitch 3618@opindex Wno-switch 3619Warn whenever a @code{switch} statement has an index of enumerated type 3620and lacks a @code{case} for one or more of the named codes of that 3621enumeration. (The presence of a @code{default} label prevents this 3622warning.) @code{case} labels outside the enumeration range also 3623provoke warnings when this option is used (even if there is a 3624@code{default} label). 3625This warning is enabled by @option{-Wall}. 3626 3627@item -Wswitch-default 3628@opindex Wswitch-default 3629@opindex Wno-switch-default 3630Warn whenever a @code{switch} statement does not have a @code{default} 3631case. 3632 3633@item -Wswitch-enum 3634@opindex Wswitch-enum 3635@opindex Wno-switch-enum 3636Warn whenever a @code{switch} statement has an index of enumerated type 3637and lacks a @code{case} for one or more of the named codes of that 3638enumeration. @code{case} labels outside the enumeration range also 3639provoke warnings when this option is used. The only difference 3640between @option{-Wswitch} and this option is that this option gives a 3641warning about an omitted enumeration code even if there is a 3642@code{default} label. 3643 3644@item -Wsync-nand @r{(C and C++ only)} 3645@opindex Wsync-nand 3646@opindex Wno-sync-nand 3647Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch} 3648built-in functions are used. These functions changed semantics in GCC 4.4. 3649 3650@item -Wtrigraphs 3651@opindex Wtrigraphs 3652@opindex Wno-trigraphs 3653Warn if any trigraphs are encountered that might change the meaning of 3654the program (trigraphs within comments are not warned about). 3655This warning is enabled by @option{-Wall}. 3656 3657@item -Wunused-but-set-parameter 3658@opindex Wunused-but-set-parameter 3659@opindex Wno-unused-but-set-parameter 3660Warn whenever a function parameter is assigned to, but otherwise unused 3661(aside from its declaration). 3662 3663To suppress this warning use the @samp{unused} attribute 3664(@pxref{Variable Attributes}). 3665 3666This warning is also enabled by @option{-Wunused} together with 3667@option{-Wextra}. 3668 3669@item -Wunused-but-set-variable 3670@opindex Wunused-but-set-variable 3671@opindex Wno-unused-but-set-variable 3672Warn whenever a local variable is assigned to, but otherwise unused 3673(aside from its declaration). 3674This warning is enabled by @option{-Wall}. 3675 3676To suppress this warning use the @samp{unused} attribute 3677(@pxref{Variable Attributes}). 3678 3679This warning is also enabled by @option{-Wunused}, which is enabled 3680by @option{-Wall}. 3681 3682@item -Wunused-function 3683@opindex Wunused-function 3684@opindex Wno-unused-function 3685Warn whenever a static function is declared but not defined or a 3686non-inline static function is unused. 3687This warning is enabled by @option{-Wall}. 3688 3689@item -Wunused-label 3690@opindex Wunused-label 3691@opindex Wno-unused-label 3692Warn whenever a label is declared but not used. 3693This warning is enabled by @option{-Wall}. 3694 3695To suppress this warning use the @samp{unused} attribute 3696(@pxref{Variable Attributes}). 3697 3698@item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)} 3699@opindex Wunused-local-typedefs 3700Warn when a typedef locally defined in a function is not used. 3701This warning is enabled by @option{-Wall}. 3702 3703@item -Wunused-parameter 3704@opindex Wunused-parameter 3705@opindex Wno-unused-parameter 3706Warn whenever a function parameter is unused aside from its declaration. 3707 3708To suppress this warning use the @samp{unused} attribute 3709(@pxref{Variable Attributes}). 3710 3711@item -Wno-unused-result 3712@opindex Wunused-result 3713@opindex Wno-unused-result 3714Do not warn if a caller of a function marked with attribute 3715@code{warn_unused_result} (@pxref{Function Attributes}) does not use 3716its return value. The default is @option{-Wunused-result}. 3717 3718@item -Wunused-variable 3719@opindex Wunused-variable 3720@opindex Wno-unused-variable 3721Warn whenever a local variable or non-constant static variable is unused 3722aside from its declaration. 3723This warning is enabled by @option{-Wall}. 3724 3725To suppress this warning use the @samp{unused} attribute 3726(@pxref{Variable Attributes}). 3727 3728@item -Wunused-value 3729@opindex Wunused-value 3730@opindex Wno-unused-value 3731Warn whenever a statement computes a result that is explicitly not 3732used. To suppress this warning cast the unused expression to 3733@samp{void}. This includes an expression-statement or the left-hand 3734side of a comma expression that contains no side effects. For example, 3735an expression such as @samp{x[i,j]} causes a warning, while 3736@samp{x[(void)i,j]} does not. 3737 3738This warning is enabled by @option{-Wall}. 3739 3740@item -Wunused 3741@opindex Wunused 3742@opindex Wno-unused 3743All the above @option{-Wunused} options combined. 3744 3745In order to get a warning about an unused function parameter, you must 3746either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies 3747@option{-Wunused}), or separately specify @option{-Wunused-parameter}. 3748 3749@item -Wuninitialized 3750@opindex Wuninitialized 3751@opindex Wno-uninitialized 3752Warn if an automatic variable is used without first being initialized 3753or if a variable may be clobbered by a @code{setjmp} call. In C++, 3754warn if a non-static reference or non-static @samp{const} member 3755appears in a class without constructors. 3756 3757If you want to warn about code that uses the uninitialized value of the 3758variable in its own initializer, use the @option{-Winit-self} option. 3759 3760These warnings occur for individual uninitialized or clobbered 3761elements of structure, union or array variables as well as for 3762variables that are uninitialized or clobbered as a whole. They do 3763not occur for variables or elements declared @code{volatile}. Because 3764these warnings depend on optimization, the exact variables or elements 3765for which there are warnings depends on the precise optimization 3766options and version of GCC used. 3767 3768Note that there may be no warning about a variable that is used only 3769to compute a value that itself is never used, because such 3770computations may be deleted by data flow analysis before the warnings 3771are printed. 3772 3773@item -Wmaybe-uninitialized 3774@opindex Wmaybe-uninitialized 3775@opindex Wno-maybe-uninitialized 3776For an automatic variable, if there exists a path from the function 3777entry to a use of the variable that is initialized, but there exist 3778some other paths for which the variable is not initialized, the compiler 3779emits a warning if it cannot prove the uninitialized paths are not 3780executed at run time. These warnings are made optional because GCC is 3781not smart enough to see all the reasons why the code might be correct 3782in spite of appearing to have an error. Here is one example of how 3783this can happen: 3784 3785@smallexample 3786@group 3787@{ 3788 int x; 3789 switch (y) 3790 @{ 3791 case 1: x = 1; 3792 break; 3793 case 2: x = 4; 3794 break; 3795 case 3: x = 5; 3796 @} 3797 foo (x); 3798@} 3799@end group 3800@end smallexample 3801 3802@noindent 3803If the value of @code{y} is always 1, 2 or 3, then @code{x} is 3804always initialized, but GCC doesn't know this. To suppress the 3805warning, you need to provide a default case with assert(0) or 3806similar code. 3807 3808@cindex @code{longjmp} warnings 3809This option also warns when a non-volatile automatic variable might be 3810changed by a call to @code{longjmp}. These warnings as well are possible 3811only in optimizing compilation. 3812 3813The compiler sees only the calls to @code{setjmp}. It cannot know 3814where @code{longjmp} will be called; in fact, a signal handler could 3815call it at any point in the code. As a result, you may get a warning 3816even when there is in fact no problem because @code{longjmp} cannot 3817in fact be called at the place that would cause a problem. 3818 3819Some spurious warnings can be avoided if you declare all the functions 3820you use that never return as @code{noreturn}. @xref{Function 3821Attributes}. 3822 3823This warning is enabled by @option{-Wall} or @option{-Wextra}. 3824 3825@item -Wunknown-pragmas 3826@opindex Wunknown-pragmas 3827@opindex Wno-unknown-pragmas 3828@cindex warning for unknown pragmas 3829@cindex unknown pragmas, warning 3830@cindex pragmas, warning of unknown 3831Warn when a @code{#pragma} directive is encountered that is not understood by 3832GCC@. If this command-line option is used, warnings are even issued 3833for unknown pragmas in system header files. This is not the case if 3834the warnings are only enabled by the @option{-Wall} command-line option. 3835 3836@item -Wno-pragmas 3837@opindex Wno-pragmas 3838@opindex Wpragmas 3839Do not warn about misuses of pragmas, such as incorrect parameters, 3840invalid syntax, or conflicts between pragmas. See also 3841@option{-Wunknown-pragmas}. 3842 3843@item -Wstrict-aliasing 3844@opindex Wstrict-aliasing 3845@opindex Wno-strict-aliasing 3846This option is only active when @option{-fstrict-aliasing} is active. 3847It warns about code that might break the strict aliasing rules that the 3848compiler is using for optimization. The warning does not catch all 3849cases, but does attempt to catch the more common pitfalls. It is 3850included in @option{-Wall}. 3851It is equivalent to @option{-Wstrict-aliasing=3} 3852 3853@item -Wstrict-aliasing=n 3854@opindex Wstrict-aliasing=n 3855This option is only active when @option{-fstrict-aliasing} is active. 3856It warns about code that might break the strict aliasing rules that the 3857compiler is using for optimization. 3858Higher levels correspond to higher accuracy (fewer false positives). 3859Higher levels also correspond to more effort, similar to the way @option{-O} 3860works. 3861@option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}. 3862 3863Level 1: Most aggressive, quick, least accurate. 3864Possibly useful when higher levels 3865do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few 3866false negatives. However, it has many false positives. 3867Warns for all pointer conversions between possibly incompatible types, 3868even if never dereferenced. Runs in the front end only. 3869 3870Level 2: Aggressive, quick, not too precise. 3871May still have many false positives (not as many as level 1 though), 3872and few false negatives (but possibly more than level 1). 3873Unlike level 1, it only warns when an address is taken. Warns about 3874incomplete types. Runs in the front end only. 3875 3876Level 3 (default for @option{-Wstrict-aliasing}): 3877Should have very few false positives and few false 3878negatives. Slightly slower than levels 1 or 2 when optimization is enabled. 3879Takes care of the common pun+dereference pattern in the front end: 3880@code{*(int*)&some_float}. 3881If optimization is enabled, it also runs in the back end, where it deals 3882with multiple statement cases using flow-sensitive points-to information. 3883Only warns when the converted pointer is dereferenced. 3884Does not warn about incomplete types. 3885 3886@item -Wstrict-overflow 3887@itemx -Wstrict-overflow=@var{n} 3888@opindex Wstrict-overflow 3889@opindex Wno-strict-overflow 3890This option is only active when @option{-fstrict-overflow} is active. 3891It warns about cases where the compiler optimizes based on the 3892assumption that signed overflow does not occur. Note that it does not 3893warn about all cases where the code might overflow: it only warns 3894about cases where the compiler implements some optimization. Thus 3895this warning depends on the optimization level. 3896 3897An optimization that assumes that signed overflow does not occur is 3898perfectly safe if the values of the variables involved are such that 3899overflow never does, in fact, occur. Therefore this warning can 3900easily give a false positive: a warning about code that is not 3901actually a problem. To help focus on important issues, several 3902warning levels are defined. No warnings are issued for the use of 3903undefined signed overflow when estimating how many iterations a loop 3904requires, in particular when determining whether a loop will be 3905executed at all. 3906 3907@table @gcctabopt 3908@item -Wstrict-overflow=1 3909Warn about cases that are both questionable and easy to avoid. For 3910example, with @option{-fstrict-overflow}, the compiler simplifies 3911@code{x + 1 > x} to @code{1}. This level of 3912@option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels 3913are not, and must be explicitly requested. 3914 3915@item -Wstrict-overflow=2 3916Also warn about other cases where a comparison is simplified to a 3917constant. For example: @code{abs (x) >= 0}. This can only be 3918simplified when @option{-fstrict-overflow} is in effect, because 3919@code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than 3920zero. @option{-Wstrict-overflow} (with no level) is the same as 3921@option{-Wstrict-overflow=2}. 3922 3923@item -Wstrict-overflow=3 3924Also warn about other cases where a comparison is simplified. For 3925example: @code{x + 1 > 1} is simplified to @code{x > 0}. 3926 3927@item -Wstrict-overflow=4 3928Also warn about other simplifications not covered by the above cases. 3929For example: @code{(x * 10) / 5} is simplified to @code{x * 2}. 3930 3931@item -Wstrict-overflow=5 3932Also warn about cases where the compiler reduces the magnitude of a 3933constant involved in a comparison. For example: @code{x + 2 > y} is 3934simplified to @code{x + 1 >= y}. This is reported only at the 3935highest warning level because this simplification applies to many 3936comparisons, so this warning level gives a very large number of 3937false positives. 3938@end table 3939 3940@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} 3941@opindex Wsuggest-attribute= 3942@opindex Wno-suggest-attribute= 3943Warn for cases where adding an attribute may be beneficial. The 3944attributes currently supported are listed below. 3945 3946@table @gcctabopt 3947@item -Wsuggest-attribute=pure 3948@itemx -Wsuggest-attribute=const 3949@itemx -Wsuggest-attribute=noreturn 3950@opindex Wsuggest-attribute=pure 3951@opindex Wno-suggest-attribute=pure 3952@opindex Wsuggest-attribute=const 3953@opindex Wno-suggest-attribute=const 3954@opindex Wsuggest-attribute=noreturn 3955@opindex Wno-suggest-attribute=noreturn 3956 3957Warn about functions that might be candidates for attributes 3958@code{pure}, @code{const} or @code{noreturn}. The compiler only warns for 3959functions visible in other compilation units or (in the case of @code{pure} and 3960@code{const}) if it cannot prove that the function returns normally. A function 3961returns normally if it doesn't contain an infinite loop or return abnormally 3962by throwing, calling @code{abort()} or trapping. This analysis requires option 3963@option{-fipa-pure-const}, which is enabled by default at @option{-O} and 3964higher. Higher optimization levels improve the accuracy of the analysis. 3965 3966@item -Wsuggest-attribute=format 3967@itemx -Wmissing-format-attribute 3968@opindex Wsuggest-attribute=format 3969@opindex Wmissing-format-attribute 3970@opindex Wno-suggest-attribute=format 3971@opindex Wno-missing-format-attribute 3972@opindex Wformat 3973@opindex Wno-format 3974 3975Warn about function pointers that might be candidates for @code{format} 3976attributes. Note these are only possible candidates, not absolute ones. 3977GCC guesses that function pointers with @code{format} attributes that 3978are used in assignment, initialization, parameter passing or return 3979statements should have a corresponding @code{format} attribute in the 3980resulting type. I.e.@: the left-hand side of the assignment or 3981initialization, the type of the parameter variable, or the return type 3982of the containing function respectively should also have a @code{format} 3983attribute to avoid the warning. 3984 3985GCC also warns about function definitions that might be 3986candidates for @code{format} attributes. Again, these are only 3987possible candidates. GCC guesses that @code{format} attributes 3988might be appropriate for any function that calls a function like 3989@code{vprintf} or @code{vscanf}, but this might not always be the 3990case, and some functions for which @code{format} attributes are 3991appropriate may not be detected. 3992@end table 3993 3994@item -Warray-bounds 3995@opindex Wno-array-bounds 3996@opindex Warray-bounds 3997This option is only active when @option{-ftree-vrp} is active 3998(default for @option{-O2} and above). It warns about subscripts to arrays 3999that are always out of bounds. This warning is enabled by @option{-Wall}. 4000 4001@item -Wno-div-by-zero 4002@opindex Wno-div-by-zero 4003@opindex Wdiv-by-zero 4004Do not warn about compile-time integer division by zero. Floating-point 4005division by zero is not warned about, as it can be a legitimate way of 4006obtaining infinities and NaNs. 4007 4008@item -Wsystem-headers 4009@opindex Wsystem-headers 4010@opindex Wno-system-headers 4011@cindex warnings from system headers 4012@cindex system headers, warnings from 4013Print warning messages for constructs found in system header files. 4014Warnings from system headers are normally suppressed, on the assumption 4015that they usually do not indicate real problems and would only make the 4016compiler output harder to read. Using this command-line option tells 4017GCC to emit warnings from system headers as if they occurred in user 4018code. However, note that using @option{-Wall} in conjunction with this 4019option does @emph{not} warn about unknown pragmas in system 4020headers---for that, @option{-Wunknown-pragmas} must also be used. 4021 4022@item -Wtrampolines 4023@opindex Wtrampolines 4024@opindex Wno-trampolines 4025 Warn about trampolines generated for pointers to nested functions. 4026 4027 A trampoline is a small piece of data or code that is created at run 4028 time on the stack when the address of a nested function is taken, and 4029 is used to call the nested function indirectly. For some targets, it 4030 is made up of data only and thus requires no special treatment. But, 4031 for most targets, it is made up of code and thus requires the stack 4032 to be made executable in order for the program to work properly. 4033 4034@item -Wfloat-equal 4035@opindex Wfloat-equal 4036@opindex Wno-float-equal 4037Warn if floating-point values are used in equality comparisons. 4038 4039The idea behind this is that sometimes it is convenient (for the 4040programmer) to consider floating-point values as approximations to 4041infinitely precise real numbers. If you are doing this, then you need 4042to compute (by analyzing the code, or in some other way) the maximum or 4043likely maximum error that the computation introduces, and allow for it 4044when performing comparisons (and when producing output, but that's a 4045different problem). In particular, instead of testing for equality, you 4046should check to see whether the two values have ranges that overlap; and 4047this is done with the relational operators, so equality comparisons are 4048probably mistaken. 4049 4050@item -Wtraditional @r{(C and Objective-C only)} 4051@opindex Wtraditional 4052@opindex Wno-traditional 4053Warn about certain constructs that behave differently in traditional and 4054ISO C@. Also warn about ISO C constructs that have no traditional C 4055equivalent, and/or problematic constructs that should be avoided. 4056 4057@itemize @bullet 4058@item 4059Macro parameters that appear within string literals in the macro body. 4060In traditional C macro replacement takes place within string literals, 4061but in ISO C it does not. 4062 4063@item 4064In traditional C, some preprocessor directives did not exist. 4065Traditional preprocessors only considered a line to be a directive 4066if the @samp{#} appeared in column 1 on the line. Therefore 4067@option{-Wtraditional} warns about directives that traditional C 4068understands but ignores because the @samp{#} does not appear as the 4069first character on the line. It also suggests you hide directives like 4070@samp{#pragma} not understood by traditional C by indenting them. Some 4071traditional implementations do not recognize @samp{#elif}, so this option 4072suggests avoiding it altogether. 4073 4074@item 4075A function-like macro that appears without arguments. 4076 4077@item 4078The unary plus operator. 4079 4080@item 4081The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point 4082constant suffixes. (Traditional C does support the @samp{L} suffix on integer 4083constants.) Note, these suffixes appear in macros defined in the system 4084headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}. 4085Use of these macros in user code might normally lead to spurious 4086warnings, however GCC's integrated preprocessor has enough context to 4087avoid warning in these cases. 4088 4089@item 4090A function declared external in one block and then used after the end of 4091the block. 4092 4093@item 4094A @code{switch} statement has an operand of type @code{long}. 4095 4096@item 4097A non-@code{static} function declaration follows a @code{static} one. 4098This construct is not accepted by some traditional C compilers. 4099 4100@item 4101The ISO type of an integer constant has a different width or 4102signedness from its traditional type. This warning is only issued if 4103the base of the constant is ten. I.e.@: hexadecimal or octal values, which 4104typically represent bit patterns, are not warned about. 4105 4106@item 4107Usage of ISO string concatenation is detected. 4108 4109@item 4110Initialization of automatic aggregates. 4111 4112@item 4113Identifier conflicts with labels. Traditional C lacks a separate 4114namespace for labels. 4115 4116@item 4117Initialization of unions. If the initializer is zero, the warning is 4118omitted. This is done under the assumption that the zero initializer in 4119user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing 4120initializer warnings and relies on default initialization to zero in the 4121traditional C case. 4122 4123@item 4124Conversions by prototypes between fixed/floating-point values and vice 4125versa. The absence of these prototypes when compiling with traditional 4126C causes serious problems. This is a subset of the possible 4127conversion warnings; for the full set use @option{-Wtraditional-conversion}. 4128 4129@item 4130Use of ISO C style function definitions. This warning intentionally is 4131@emph{not} issued for prototype declarations or variadic functions 4132because these ISO C features appear in your code when using 4133libiberty's traditional C compatibility macros, @code{PARAMS} and 4134@code{VPARAMS}. This warning is also bypassed for nested functions 4135because that feature is already a GCC extension and thus not relevant to 4136traditional C compatibility. 4137@end itemize 4138 4139@item -Wtraditional-conversion @r{(C and Objective-C only)} 4140@opindex Wtraditional-conversion 4141@opindex Wno-traditional-conversion 4142Warn if a prototype causes a type conversion that is different from what 4143would happen to the same argument in the absence of a prototype. This 4144includes conversions of fixed point to floating and vice versa, and 4145conversions changing the width or signedness of a fixed-point argument 4146except when the same as the default promotion. 4147 4148@item -Wdeclaration-after-statement @r{(C and Objective-C only)} 4149@opindex Wdeclaration-after-statement 4150@opindex Wno-declaration-after-statement 4151Warn when a declaration is found after a statement in a block. This 4152construct, known from C++, was introduced with ISO C99 and is by default 4153allowed in GCC@. It is not supported by ISO C90 and was not supported by 4154GCC versions before GCC 3.0. @xref{Mixed Declarations}. 4155 4156@item -Wundef 4157@opindex Wundef 4158@opindex Wno-undef 4159Warn if an undefined identifier is evaluated in an @samp{#if} directive. 4160 4161@item -Wno-endif-labels 4162@opindex Wno-endif-labels 4163@opindex Wendif-labels 4164Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text. 4165 4166@item -Wshadow 4167@opindex Wshadow 4168@opindex Wno-shadow 4169Warn whenever a local variable or type declaration shadows another variable, 4170parameter, type, or class member (in C++), or whenever a built-in function 4171is shadowed. Note that in C++, the compiler warns if a local variable 4172shadows an explicit typedef, but not if it shadows a struct/class/enum. 4173 4174@item -Wlarger-than=@var{len} 4175@opindex Wlarger-than=@var{len} 4176@opindex Wlarger-than-@var{len} 4177Warn whenever an object of larger than @var{len} bytes is defined. 4178 4179@item -Wframe-larger-than=@var{len} 4180@opindex Wframe-larger-than 4181Warn if the size of a function frame is larger than @var{len} bytes. 4182The computation done to determine the stack frame size is approximate 4183and not conservative. 4184The actual requirements may be somewhat greater than @var{len} 4185even if you do not get a warning. In addition, any space allocated 4186via @code{alloca}, variable-length arrays, or related constructs 4187is not included by the compiler when determining 4188whether or not to issue a warning. 4189 4190@item -Wno-free-nonheap-object 4191@opindex Wno-free-nonheap-object 4192@opindex Wfree-nonheap-object 4193Do not warn when attempting to free an object that was not allocated 4194on the heap. 4195 4196@item -Wstack-usage=@var{len} 4197@opindex Wstack-usage 4198Warn if the stack usage of a function might be larger than @var{len} bytes. 4199The computation done to determine the stack usage is conservative. 4200Any space allocated via @code{alloca}, variable-length arrays, or related 4201constructs is included by the compiler when determining whether or not to 4202issue a warning. 4203 4204The message is in keeping with the output of @option{-fstack-usage}. 4205 4206@itemize 4207@item 4208If the stack usage is fully static but exceeds the specified amount, it's: 4209 4210@smallexample 4211 warning: stack usage is 1120 bytes 4212@end smallexample 4213@item 4214If the stack usage is (partly) dynamic but bounded, it's: 4215 4216@smallexample 4217 warning: stack usage might be 1648 bytes 4218@end smallexample 4219@item 4220If the stack usage is (partly) dynamic and not bounded, it's: 4221 4222@smallexample 4223 warning: stack usage might be unbounded 4224@end smallexample 4225@end itemize 4226 4227@item -Wunsafe-loop-optimizations 4228@opindex Wunsafe-loop-optimizations 4229@opindex Wno-unsafe-loop-optimizations 4230Warn if the loop cannot be optimized because the compiler cannot 4231assume anything on the bounds of the loop indices. With 4232@option{-funsafe-loop-optimizations} warn if the compiler makes 4233such assumptions. 4234 4235@item -Wno-pedantic-ms-format @r{(MinGW targets only)} 4236@opindex Wno-pedantic-ms-format 4237@opindex Wpedantic-ms-format 4238When used in combination with @option{-Wformat} 4239and @option{-pedantic} without GNU extensions, this option 4240disables the warnings about non-ISO @code{printf} / @code{scanf} format 4241width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, 4242which depend on the MS runtime. 4243 4244@item -Wpointer-arith 4245@opindex Wpointer-arith 4246@opindex Wno-pointer-arith 4247Warn about anything that depends on the ``size of'' a function type or 4248of @code{void}. GNU C assigns these types a size of 1, for 4249convenience in calculations with @code{void *} pointers and pointers 4250to functions. In C++, warn also when an arithmetic operation involves 4251@code{NULL}. This warning is also enabled by @option{-Wpedantic}. 4252 4253@item -Wtype-limits 4254@opindex Wtype-limits 4255@opindex Wno-type-limits 4256Warn if a comparison is always true or always false due to the limited 4257range of the data type, but do not warn for constant expressions. For 4258example, warn if an unsigned variable is compared against zero with 4259@samp{<} or @samp{>=}. This warning is also enabled by 4260@option{-Wextra}. 4261 4262@item -Wbad-function-cast @r{(C and Objective-C only)} 4263@opindex Wbad-function-cast 4264@opindex Wno-bad-function-cast 4265Warn whenever a function call is cast to a non-matching type. 4266For example, warn if @code{int malloc()} is cast to @code{anything *}. 4267 4268@item -Wc++-compat @r{(C and Objective-C only)} 4269Warn about ISO C constructs that are outside of the common subset of 4270ISO C and ISO C++, e.g.@: request for implicit conversion from 4271@code{void *} to a pointer to non-@code{void} type. 4272 4273@item -Wc++11-compat @r{(C++ and Objective-C++ only)} 4274Warn about C++ constructs whose meaning differs between ISO C++ 1998 4275and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords 4276in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is 4277enabled by @option{-Wall}. 4278 4279@item -Wcast-qual 4280@opindex Wcast-qual 4281@opindex Wno-cast-qual 4282Warn whenever a pointer is cast so as to remove a type qualifier from 4283the target type. For example, warn if a @code{const char *} is cast 4284to an ordinary @code{char *}. 4285 4286Also warn when making a cast that introduces a type qualifier in an 4287unsafe way. For example, casting @code{char **} to @code{const char **} 4288is unsafe, as in this example: 4289 4290@smallexample 4291 /* p is char ** value. */ 4292 const char **q = (const char **) p; 4293 /* Assignment of readonly string to const char * is OK. */ 4294 *q = "string"; 4295 /* Now char** pointer points to read-only memory. */ 4296 **p = 'b'; 4297@end smallexample 4298 4299@item -Wcast-align 4300@opindex Wcast-align 4301@opindex Wno-cast-align 4302Warn whenever a pointer is cast such that the required alignment of the 4303target is increased. For example, warn if a @code{char *} is cast to 4304an @code{int *} on machines where integers can only be accessed at 4305two- or four-byte boundaries. 4306 4307@item -Wwrite-strings 4308@opindex Wwrite-strings 4309@opindex Wno-write-strings 4310When compiling C, give string constants the type @code{const 4311char[@var{length}]} so that copying the address of one into a 4312non-@code{const} @code{char *} pointer produces a warning. These 4313warnings help you find at compile time code that can try to write 4314into a string constant, but only if you have been very careful about 4315using @code{const} in declarations and prototypes. Otherwise, it is 4316just a nuisance. This is why we did not make @option{-Wall} request 4317these warnings. 4318 4319When compiling C++, warn about the deprecated conversion from string 4320literals to @code{char *}. This warning is enabled by default for C++ 4321programs. 4322 4323@item -Wclobbered 4324@opindex Wclobbered 4325@opindex Wno-clobbered 4326Warn for variables that might be changed by @samp{longjmp} or 4327@samp{vfork}. This warning is also enabled by @option{-Wextra}. 4328 4329@item -Wconversion 4330@opindex Wconversion 4331@opindex Wno-conversion 4332Warn for implicit conversions that may alter a value. This includes 4333conversions between real and integer, like @code{abs (x)} when 4334@code{x} is @code{double}; conversions between signed and unsigned, 4335like @code{unsigned ui = -1}; and conversions to smaller types, like 4336@code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs 4337((int) x)} and @code{ui = (unsigned) -1}, or if the value is not 4338changed by the conversion like in @code{abs (2.0)}. Warnings about 4339conversions between signed and unsigned integers can be disabled by 4340using @option{-Wno-sign-conversion}. 4341 4342For C++, also warn for confusing overload resolution for user-defined 4343conversions; and conversions that never use a type conversion 4344operator: conversions to @code{void}, the same type, a base class or a 4345reference to them. Warnings about conversions between signed and 4346unsigned integers are disabled by default in C++ unless 4347@option{-Wsign-conversion} is explicitly enabled. 4348 4349@item -Wno-conversion-null @r{(C++ and Objective-C++ only)} 4350@opindex Wconversion-null 4351@opindex Wno-conversion-null 4352Do not warn for conversions between @code{NULL} and non-pointer 4353types. @option{-Wconversion-null} is enabled by default. 4354 4355@item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)} 4356@opindex Wzero-as-null-pointer-constant 4357@opindex Wno-zero-as-null-pointer-constant 4358Warn when a literal '0' is used as null pointer constant. This can 4359be useful to facilitate the conversion to @code{nullptr} in C++11. 4360 4361@item -Wuseless-cast @r{(C++ and Objective-C++ only)} 4362@opindex Wuseless-cast 4363@opindex Wno-useless-cast 4364Warn when an expression is casted to its own type. 4365 4366@item -Wempty-body 4367@opindex Wempty-body 4368@opindex Wno-empty-body 4369Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do 4370while} statement. This warning is also enabled by @option{-Wextra}. 4371 4372@item -Wenum-compare 4373@opindex Wenum-compare 4374@opindex Wno-enum-compare 4375Warn about a comparison between values of different enumerated types. 4376In C++ enumeral mismatches in conditional expressions are also 4377diagnosed and the warning is enabled by default. In C this warning is 4378enabled by @option{-Wall}. 4379 4380@item -Wjump-misses-init @r{(C, Objective-C only)} 4381@opindex Wjump-misses-init 4382@opindex Wno-jump-misses-init 4383Warn if a @code{goto} statement or a @code{switch} statement jumps 4384forward across the initialization of a variable, or jumps backward to a 4385label after the variable has been initialized. This only warns about 4386variables that are initialized when they are declared. This warning is 4387only supported for C and Objective-C; in C++ this sort of branch is an 4388error in any case. 4389 4390@option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It 4391can be disabled with the @option{-Wno-jump-misses-init} option. 4392 4393@item -Wsign-compare 4394@opindex Wsign-compare 4395@opindex Wno-sign-compare 4396@cindex warning for comparison of signed and unsigned values 4397@cindex comparison of signed and unsigned values, warning 4398@cindex signed and unsigned values, comparison warning 4399Warn when a comparison between signed and unsigned values could produce 4400an incorrect result when the signed value is converted to unsigned. 4401This warning is also enabled by @option{-Wextra}; to get the other warnings 4402of @option{-Wextra} without this warning, use @option{-Wextra -Wno-sign-compare}. 4403 4404@item -Wsign-conversion 4405@opindex Wsign-conversion 4406@opindex Wno-sign-conversion 4407Warn for implicit conversions that may change the sign of an integer 4408value, like assigning a signed integer expression to an unsigned 4409integer variable. An explicit cast silences the warning. In C, this 4410option is enabled also by @option{-Wconversion}. 4411 4412@item -Wsizeof-pointer-memaccess 4413@opindex Wsizeof-pointer-memaccess 4414@opindex Wno-sizeof-pointer-memaccess 4415Warn for suspicious length parameters to certain string and memory built-in 4416functions if the argument uses @code{sizeof}. This warning warns e.g.@: 4417about @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not an array, 4418but a pointer, and suggests a possible fix, or about 4419@code{memcpy (&foo, ptr, sizeof (&foo));}. This warning is enabled by 4420@option{-Wall}. 4421 4422@item -Waddress 4423@opindex Waddress 4424@opindex Wno-address 4425Warn about suspicious uses of memory addresses. These include using 4426the address of a function in a conditional expression, such as 4427@code{void func(void); if (func)}, and comparisons against the memory 4428address of a string literal, such as @code{if (x == "abc")}. Such 4429uses typically indicate a programmer error: the address of a function 4430always evaluates to true, so their use in a conditional usually 4431indicate that the programmer forgot the parentheses in a function 4432call; and comparisons against string literals result in unspecified 4433behavior and are not portable in C, so they usually indicate that the 4434programmer intended to use @code{strcmp}. This warning is enabled by 4435@option{-Wall}. 4436 4437@item -Wlogical-op 4438@opindex Wlogical-op 4439@opindex Wno-logical-op 4440Warn about suspicious uses of logical operators in expressions. 4441This includes using logical operators in contexts where a 4442bit-wise operator is likely to be expected. 4443 4444@item -Waggregate-return 4445@opindex Waggregate-return 4446@opindex Wno-aggregate-return 4447Warn if any functions that return structures or unions are defined or 4448called. (In languages where you can return an array, this also elicits 4449a warning.) 4450 4451@item -Wno-aggressive-loop-optimizations 4452@opindex Wno-aggressive-loop-optimizations 4453@opindex Waggressive-loop-optimizations 4454Warn if in a loop with constant number of iterations the compiler detects 4455undefined behavior in some statement during one or more of the iterations. 4456 4457@item -Wno-attributes 4458@opindex Wno-attributes 4459@opindex Wattributes 4460Do not warn if an unexpected @code{__attribute__} is used, such as 4461unrecognized attributes, function attributes applied to variables, 4462etc. This does not stop errors for incorrect use of supported 4463attributes. 4464 4465@item -Wno-builtin-macro-redefined 4466@opindex Wno-builtin-macro-redefined 4467@opindex Wbuiltin-macro-redefined 4468Do not warn if certain built-in macros are redefined. This suppresses 4469warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__}, 4470@code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}. 4471 4472@item -Wstrict-prototypes @r{(C and Objective-C only)} 4473@opindex Wstrict-prototypes 4474@opindex Wno-strict-prototypes 4475Warn if a function is declared or defined without specifying the 4476argument types. (An old-style function definition is permitted without 4477a warning if preceded by a declaration that specifies the argument 4478types.) 4479 4480@item -Wold-style-declaration @r{(C and Objective-C only)} 4481@opindex Wold-style-declaration 4482@opindex Wno-old-style-declaration 4483Warn for obsolescent usages, according to the C Standard, in a 4484declaration. For example, warn if storage-class specifiers like 4485@code{static} are not the first things in a declaration. This warning 4486is also enabled by @option{-Wextra}. 4487 4488@item -Wold-style-definition @r{(C and Objective-C only)} 4489@opindex Wold-style-definition 4490@opindex Wno-old-style-definition 4491Warn if an old-style function definition is used. A warning is given 4492even if there is a previous prototype. 4493 4494@item -Wmissing-parameter-type @r{(C and Objective-C only)} 4495@opindex Wmissing-parameter-type 4496@opindex Wno-missing-parameter-type 4497A function parameter is declared without a type specifier in K&R-style 4498functions: 4499 4500@smallexample 4501void foo(bar) @{ @} 4502@end smallexample 4503 4504This warning is also enabled by @option{-Wextra}. 4505 4506@item -Wmissing-prototypes @r{(C and Objective-C only)} 4507@opindex Wmissing-prototypes 4508@opindex Wno-missing-prototypes 4509Warn if a global function is defined without a previous prototype 4510declaration. This warning is issued even if the definition itself 4511provides a prototype. Use this option to detect global functions 4512that do not have a matching prototype declaration in a header file. 4513This option is not valid for C++ because all function declarations 4514provide prototypes and a non-matching declaration will declare an 4515overload rather than conflict with an earlier declaration. 4516Use @option{-Wmissing-declarations} to detect missing declarations in C++. 4517 4518@item -Wmissing-declarations 4519@opindex Wmissing-declarations 4520@opindex Wno-missing-declarations 4521Warn if a global function is defined without a previous declaration. 4522Do so even if the definition itself provides a prototype. 4523Use this option to detect global functions that are not declared in 4524header files. In C, no warnings are issued for functions with previous 4525non-prototype declarations; use @option{-Wmissing-prototype} to detect 4526missing prototypes. In C++, no warnings are issued for function templates, 4527or for inline functions, or for functions in anonymous namespaces. 4528 4529@item -Wmissing-field-initializers 4530@opindex Wmissing-field-initializers 4531@opindex Wno-missing-field-initializers 4532@opindex W 4533@opindex Wextra 4534@opindex Wno-extra 4535Warn if a structure's initializer has some fields missing. For 4536example, the following code causes such a warning, because 4537@code{x.h} is implicitly zero: 4538 4539@smallexample 4540struct s @{ int f, g, h; @}; 4541struct s x = @{ 3, 4 @}; 4542@end smallexample 4543 4544This option does not warn about designated initializers, so the following 4545modification does not trigger a warning: 4546 4547@smallexample 4548struct s @{ int f, g, h; @}; 4549struct s x = @{ .f = 3, .g = 4 @}; 4550@end smallexample 4551 4552This warning is included in @option{-Wextra}. To get other @option{-Wextra} 4553warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}. 4554 4555@item -Wno-multichar 4556@opindex Wno-multichar 4557@opindex Wmultichar 4558Do not warn if a multicharacter constant (@samp{'FOOF'}) is used. 4559Usually they indicate a typo in the user's code, as they have 4560implementation-defined values, and should not be used in portable code. 4561 4562@item -Wnormalized=<none|id|nfc|nfkc> 4563@opindex Wnormalized= 4564@cindex NFC 4565@cindex NFKC 4566@cindex character set, input normalization 4567In ISO C and ISO C++, two identifiers are different if they are 4568different sequences of characters. However, sometimes when characters 4569outside the basic ASCII character set are used, you can have two 4570different character sequences that look the same. To avoid confusion, 4571the ISO 10646 standard sets out some @dfn{normalization rules} which 4572when applied ensure that two sequences that look the same are turned into 4573the same sequence. GCC can warn you if you are using identifiers that 4574have not been normalized; this option controls that warning. 4575 4576There are four levels of warning supported by GCC@. The default is 4577@option{-Wnormalized=nfc}, which warns about any identifier that is 4578not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the 4579recommended form for most uses. 4580 4581Unfortunately, there are some characters allowed in identifiers by 4582ISO C and ISO C++ that, when turned into NFC, are not allowed in 4583identifiers. That is, there's no way to use these symbols in portable 4584ISO C or C++ and have all your identifiers in NFC@. 4585@option{-Wnormalized=id} suppresses the warning for these characters. 4586It is hoped that future versions of the standards involved will correct 4587this, which is why this option is not the default. 4588 4589You can switch the warning off for all characters by writing 4590@option{-Wnormalized=none}. You should only do this if you 4591are using some other normalization scheme (like ``D''), because 4592otherwise you can easily create bugs that are literally impossible to see. 4593 4594Some characters in ISO 10646 have distinct meanings but look identical 4595in some fonts or display methodologies, especially once formatting has 4596been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL 4597LETTER N'', displays just like a regular @code{n} that has been 4598placed in a superscript. ISO 10646 defines the @dfn{NFKC} 4599normalization scheme to convert all these into a standard form as 4600well, and GCC warns if your code is not in NFKC if you use 4601@option{-Wnormalized=nfkc}. This warning is comparable to warning 4602about every identifier that contains the letter O because it might be 4603confused with the digit 0, and so is not the default, but may be 4604useful as a local coding convention if the programming environment 4605cannot be fixed to display these characters distinctly. 4606 4607@item -Wno-deprecated 4608@opindex Wno-deprecated 4609@opindex Wdeprecated 4610Do not warn about usage of deprecated features. @xref{Deprecated Features}. 4611 4612@item -Wno-deprecated-declarations 4613@opindex Wno-deprecated-declarations 4614@opindex Wdeprecated-declarations 4615Do not warn about uses of functions (@pxref{Function Attributes}), 4616variables (@pxref{Variable Attributes}), and types (@pxref{Type 4617Attributes}) marked as deprecated by using the @code{deprecated} 4618attribute. 4619 4620@item -Wno-overflow 4621@opindex Wno-overflow 4622@opindex Woverflow 4623Do not warn about compile-time overflow in constant expressions. 4624 4625@item -Woverride-init @r{(C and Objective-C only)} 4626@opindex Woverride-init 4627@opindex Wno-override-init 4628@opindex W 4629@opindex Wextra 4630@opindex Wno-extra 4631Warn if an initialized field without side effects is overridden when 4632using designated initializers (@pxref{Designated Inits, , Designated 4633Initializers}). 4634 4635This warning is included in @option{-Wextra}. To get other 4636@option{-Wextra} warnings without this one, use @option{-Wextra 4637-Wno-override-init}. 4638 4639@item -Wpacked 4640@opindex Wpacked 4641@opindex Wno-packed 4642Warn if a structure is given the packed attribute, but the packed 4643attribute has no effect on the layout or size of the structure. 4644Such structures may be mis-aligned for little benefit. For 4645instance, in this code, the variable @code{f.x} in @code{struct bar} 4646is misaligned even though @code{struct bar} does not itself 4647have the packed attribute: 4648 4649@smallexample 4650@group 4651struct foo @{ 4652 int x; 4653 char a, b, c, d; 4654@} __attribute__((packed)); 4655struct bar @{ 4656 char z; 4657 struct foo f; 4658@}; 4659@end group 4660@end smallexample 4661 4662@item -Wpacked-bitfield-compat 4663@opindex Wpacked-bitfield-compat 4664@opindex Wno-packed-bitfield-compat 4665The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute 4666on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but 4667the change can lead to differences in the structure layout. GCC 4668informs you when the offset of such a field has changed in GCC 4.4. 4669For example there is no longer a 4-bit padding between field @code{a} 4670and @code{b} in this structure: 4671 4672@smallexample 4673struct foo 4674@{ 4675 char a:4; 4676 char b:8; 4677@} __attribute__ ((packed)); 4678@end smallexample 4679 4680This warning is enabled by default. Use 4681@option{-Wno-packed-bitfield-compat} to disable this warning. 4682 4683@item -Wpadded 4684@opindex Wpadded 4685@opindex Wno-padded 4686Warn if padding is included in a structure, either to align an element 4687of the structure or to align the whole structure. Sometimes when this 4688happens it is possible to rearrange the fields of the structure to 4689reduce the padding and so make the structure smaller. 4690 4691@item -Wredundant-decls 4692@opindex Wredundant-decls 4693@opindex Wno-redundant-decls 4694Warn if anything is declared more than once in the same scope, even in 4695cases where multiple declaration is valid and changes nothing. 4696 4697@item -Wnested-externs @r{(C and Objective-C only)} 4698@opindex Wnested-externs 4699@opindex Wno-nested-externs 4700Warn if an @code{extern} declaration is encountered within a function. 4701 4702@item -Wno-inherited-variadic-ctor 4703@opindex Winherited-variadic-ctor 4704@opindex Wno-inherited-variadic-ctor 4705Suppress warnings about use of C++11 inheriting constructors when the 4706base class inherited from has a C variadic constructor; the warning is 4707on by default because the ellipsis is not inherited. 4708 4709@item -Winline 4710@opindex Winline 4711@opindex Wno-inline 4712Warn if a function that is declared as inline cannot be inlined. 4713Even with this option, the compiler does not warn about failures to 4714inline functions declared in system headers. 4715 4716The compiler uses a variety of heuristics to determine whether or not 4717to inline a function. For example, the compiler takes into account 4718the size of the function being inlined and the amount of inlining 4719that has already been done in the current function. Therefore, 4720seemingly insignificant changes in the source program can cause the 4721warnings produced by @option{-Winline} to appear or disappear. 4722 4723@item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} 4724@opindex Wno-invalid-offsetof 4725@opindex Winvalid-offsetof 4726Suppress warnings from applying the @samp{offsetof} macro to a non-POD 4727type. According to the 1998 ISO C++ standard, applying @samp{offsetof} 4728to a non-POD type is undefined. In existing C++ implementations, 4729however, @samp{offsetof} typically gives meaningful results even when 4730applied to certain kinds of non-POD types (such as a simple 4731@samp{struct} that fails to be a POD type only by virtue of having a 4732constructor). This flag is for users who are aware that they are 4733writing nonportable code and who have deliberately chosen to ignore the 4734warning about it. 4735 4736The restrictions on @samp{offsetof} may be relaxed in a future version 4737of the C++ standard. 4738 4739@item -Wno-int-to-pointer-cast 4740@opindex Wno-int-to-pointer-cast 4741@opindex Wint-to-pointer-cast 4742Suppress warnings from casts to pointer type of an integer of a 4743different size. In C++, casting to a pointer type of smaller size is 4744an error. @option{Wint-to-pointer-cast} is enabled by default. 4745 4746 4747@item -Wno-pointer-to-int-cast @r{(C and Objective-C only)} 4748@opindex Wno-pointer-to-int-cast 4749@opindex Wpointer-to-int-cast 4750Suppress warnings from casts from a pointer to an integer type of a 4751different size. 4752 4753@item -Winvalid-pch 4754@opindex Winvalid-pch 4755@opindex Wno-invalid-pch 4756Warn if a precompiled header (@pxref{Precompiled Headers}) is found in 4757the search path but can't be used. 4758 4759@item -Wlong-long 4760@opindex Wlong-long 4761@opindex Wno-long-long 4762Warn if @samp{long long} type is used. This is enabled by either 4763@option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98 4764modes. To inhibit the warning messages, use @option{-Wno-long-long}. 4765 4766@item -Wvariadic-macros 4767@opindex Wvariadic-macros 4768@opindex Wno-variadic-macros 4769Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU 4770alternate syntax when in pedantic ISO C99 mode. This is default. 4771To inhibit the warning messages, use @option{-Wno-variadic-macros}. 4772 4773@item -Wvarargs 4774@opindex Wvarargs 4775@opindex Wno-varargs 4776Warn upon questionable usage of the macros used to handle variable 4777arguments like @samp{va_start}. This is default. To inhibit the 4778warning messages, use @option{-Wno-varargs}. 4779 4780@item -Wvector-operation-performance 4781@opindex Wvector-operation-performance 4782@opindex Wno-vector-operation-performance 4783Warn if vector operation is not implemented via SIMD capabilities of the 4784architecture. Mainly useful for the performance tuning. 4785Vector operation can be implemented @code{piecewise}, which means that the 4786scalar operation is performed on every vector element; 4787@code{in parallel}, which means that the vector operation is implemented 4788using scalars of wider type, which normally is more performance efficient; 4789and @code{as a single scalar}, which means that vector fits into a 4790scalar type. 4791 4792@item -Wno-virtual-move-assign 4793@opindex Wvirtual-move-assign 4794@opindex Wno-virtual-move-assign 4795Suppress warnings about inheriting from a virtual base with a 4796non-trivial C++11 move assignment operator. This is dangerous because 4797if the virtual base is reachable along more than one path, it will be 4798moved multiple times, which can mean both objects end up in the 4799moved-from state. If the move assignment operator is written to avoid 4800moving from a moved-from object, this warning can be disabled. 4801 4802@item -Wvla 4803@opindex Wvla 4804@opindex Wno-vla 4805Warn if variable length array is used in the code. 4806@option{-Wno-vla} prevents the @option{-Wpedantic} warning of 4807the variable length array. 4808 4809@item -Wvolatile-register-var 4810@opindex Wvolatile-register-var 4811@opindex Wno-volatile-register-var 4812Warn if a register variable is declared volatile. The volatile 4813modifier does not inhibit all optimizations that may eliminate reads 4814and/or writes to register variables. This warning is enabled by 4815@option{-Wall}. 4816 4817@item -Wdisabled-optimization 4818@opindex Wdisabled-optimization 4819@opindex Wno-disabled-optimization 4820Warn if a requested optimization pass is disabled. This warning does 4821not generally indicate that there is anything wrong with your code; it 4822merely indicates that GCC's optimizers are unable to handle the code 4823effectively. Often, the problem is that your code is too big or too 4824complex; GCC refuses to optimize programs when the optimization 4825itself is likely to take inordinate amounts of time. 4826 4827@item -Wpointer-sign @r{(C and Objective-C only)} 4828@opindex Wpointer-sign 4829@opindex Wno-pointer-sign 4830Warn for pointer argument passing or assignment with different signedness. 4831This option is only supported for C and Objective-C@. It is implied by 4832@option{-Wall} and by @option{-Wpedantic}, which can be disabled with 4833@option{-Wno-pointer-sign}. 4834 4835@item -Wstack-protector 4836@opindex Wstack-protector 4837@opindex Wno-stack-protector 4838This option is only active when @option{-fstack-protector} is active. It 4839warns about functions that are not protected against stack smashing. 4840 4841@item -Wno-mudflap 4842@opindex Wno-mudflap 4843Suppress warnings about constructs that cannot be instrumented by 4844@option{-fmudflap}. 4845 4846@item -Woverlength-strings 4847@opindex Woverlength-strings 4848@opindex Wno-overlength-strings 4849Warn about string constants that are longer than the ``minimum 4850maximum'' length specified in the C standard. Modern compilers 4851generally allow string constants that are much longer than the 4852standard's minimum limit, but very portable programs should avoid 4853using longer strings. 4854 4855The limit applies @emph{after} string constant concatenation, and does 4856not count the trailing NUL@. In C90, the limit was 509 characters; in 4857C99, it was raised to 4095. C++98 does not specify a normative 4858minimum maximum, so we do not diagnose overlength strings in C++@. 4859 4860This option is implied by @option{-Wpedantic}, and can be disabled with 4861@option{-Wno-overlength-strings}. 4862 4863@item -Wunsuffixed-float-constants @r{(C and Objective-C only)} 4864@opindex Wunsuffixed-float-constants 4865 4866Issue a warning for any floating constant that does not have 4867a suffix. When used together with @option{-Wsystem-headers} it 4868warns about such constants in system header files. This can be useful 4869when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma 4870from the decimal floating-point extension to C99. 4871@end table 4872 4873@node Debugging Options 4874@section Options for Debugging Your Program or GCC 4875@cindex options, debugging 4876@cindex debugging information options 4877 4878GCC has various special options that are used for debugging 4879either your program or GCC: 4880 4881@table @gcctabopt 4882@item -g 4883@opindex g 4884Produce debugging information in the operating system's native format 4885(stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging 4886information. 4887 4888On most systems that use stabs format, @option{-g} enables use of extra 4889debugging information that only GDB can use; this extra information 4890makes debugging work better in GDB but probably makes other debuggers 4891crash or 4892refuse to read the program. If you want to control for certain whether 4893to generate the extra information, use @option{-gstabs+}, @option{-gstabs}, 4894@option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below). 4895 4896GCC allows you to use @option{-g} with 4897@option{-O}. The shortcuts taken by optimized code may occasionally 4898produce surprising results: some variables you declared may not exist 4899at all; flow of control may briefly move where you did not expect it; 4900some statements may not be executed because they compute constant 4901results or their values are already at hand; some statements may 4902execute in different places because they have been moved out of loops. 4903 4904Nevertheless it proves possible to debug optimized output. This makes 4905it reasonable to use the optimizer for programs that might have bugs. 4906 4907The following options are useful when GCC is generated with the 4908capability for more than one debugging format. 4909 4910@item -gsplit-dwarf 4911@opindex gsplit-dwarf 4912Separate as much dwarf debugging information as possible into a 4913separate output file with the extension .dwo. This option allows 4914the build system to avoid linking files with debug information. To 4915be useful, this option requires a debugger capable of reading .dwo 4916files. 4917 4918@item -ggdb 4919@opindex ggdb 4920Produce debugging information for use by GDB@. This means to use the 4921most expressive format available (DWARF 2, stabs, or the native format 4922if neither of those are supported), including GDB extensions if at all 4923possible. 4924 4925@item -gpubnames 4926@opindex gpubnames 4927Generate dwarf .debug_pubnames and .debug_pubtypes sections. 4928 4929@item -gstabs 4930@opindex gstabs 4931Produce debugging information in stabs format (if that is supported), 4932without GDB extensions. This is the format used by DBX on most BSD 4933systems. On MIPS, Alpha and System V Release 4 systems this option 4934produces stabs debugging output that is not understood by DBX or SDB@. 4935On System V Release 4 systems this option requires the GNU assembler. 4936 4937@item -feliminate-unused-debug-symbols 4938@opindex feliminate-unused-debug-symbols 4939Produce debugging information in stabs format (if that is supported), 4940for only symbols that are actually used. 4941 4942@item -femit-class-debug-always 4943Instead of emitting debugging information for a C++ class in only one 4944object file, emit it in all object files using the class. This option 4945should be used only with debuggers that are unable to handle the way GCC 4946normally emits debugging information for classes because using this 4947option increases the size of debugging information by as much as a 4948factor of two. 4949 4950@item -fdebug-types-section 4951@opindex fdebug-types-section 4952@opindex fno-debug-types-section 4953When using DWARF Version 4 or higher, type DIEs can be put into 4954their own @code{.debug_types} section instead of making them part of the 4955@code{.debug_info} section. It is more efficient to put them in a separate 4956comdat sections since the linker can then remove duplicates. 4957But not all DWARF consumers support @code{.debug_types} sections yet 4958and on some objects @code{.debug_types} produces larger instead of smaller 4959debugging information. 4960 4961@item -gstabs+ 4962@opindex gstabs+ 4963Produce debugging information in stabs format (if that is supported), 4964using GNU extensions understood only by the GNU debugger (GDB)@. The 4965use of these extensions is likely to make other debuggers crash or 4966refuse to read the program. 4967 4968@item -gcoff 4969@opindex gcoff 4970Produce debugging information in COFF format (if that is supported). 4971This is the format used by SDB on most System V systems prior to 4972System V Release 4. 4973 4974@item -gxcoff 4975@opindex gxcoff 4976Produce debugging information in XCOFF format (if that is supported). 4977This is the format used by the DBX debugger on IBM RS/6000 systems. 4978 4979@item -gxcoff+ 4980@opindex gxcoff+ 4981Produce debugging information in XCOFF format (if that is supported), 4982using GNU extensions understood only by the GNU debugger (GDB)@. The 4983use of these extensions is likely to make other debuggers crash or 4984refuse to read the program, and may cause assemblers other than the GNU 4985assembler (GAS) to fail with an error. 4986 4987@item -gdwarf-@var{version} 4988@opindex gdwarf-@var{version} 4989Produce debugging information in DWARF format (if that is supported). 4990The value of @var{version} may be either 2, 3 or 4; the default version 4991for most targets is 4. 4992 4993Note that with DWARF Version 2, some ports require and always 4994use some non-conflicting DWARF 3 extensions in the unwind tables. 4995 4996Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments} 4997for maximum benefit. 4998 4999@item -grecord-gcc-switches 5000@opindex grecord-gcc-switches 5001This switch causes the command-line options used to invoke the 5002compiler that may affect code generation to be appended to the 5003DW_AT_producer attribute in DWARF debugging information. The options 5004are concatenated with spaces separating them from each other and from 5005the compiler version. See also @option{-frecord-gcc-switches} for another 5006way of storing compiler options into the object file. This is the default. 5007 5008@item -gno-record-gcc-switches 5009@opindex gno-record-gcc-switches 5010Disallow appending command-line options to the DW_AT_producer attribute 5011in DWARF debugging information. 5012 5013@item -gstrict-dwarf 5014@opindex gstrict-dwarf 5015Disallow using extensions of later DWARF standard version than selected 5016with @option{-gdwarf-@var{version}}. On most targets using non-conflicting 5017DWARF extensions from later standard versions is allowed. 5018 5019@item -gno-strict-dwarf 5020@opindex gno-strict-dwarf 5021Allow using extensions of later DWARF standard version than selected with 5022@option{-gdwarf-@var{version}}. 5023 5024@item -gvms 5025@opindex gvms 5026Produce debugging information in Alpha/VMS debug format (if that is 5027supported). This is the format used by DEBUG on Alpha/VMS systems. 5028 5029@item -g@var{level} 5030@itemx -ggdb@var{level} 5031@itemx -gstabs@var{level} 5032@itemx -gcoff@var{level} 5033@itemx -gxcoff@var{level} 5034@itemx -gvms@var{level} 5035Request debugging information and also use @var{level} to specify how 5036much information. The default level is 2. 5037 5038Level 0 produces no debug information at all. Thus, @option{-g0} negates 5039@option{-g}. 5040 5041Level 1 produces minimal information, enough for making backtraces in 5042parts of the program that you don't plan to debug. This includes 5043descriptions of functions and external variables, but no information 5044about local variables and no line numbers. 5045 5046Level 3 includes extra information, such as all the macro definitions 5047present in the program. Some debuggers support macro expansion when 5048you use @option{-g3}. 5049 5050@option{-gdwarf-2} does not accept a concatenated debug level, because 5051GCC used to support an option @option{-gdwarf} that meant to generate 5052debug information in version 1 of the DWARF format (which is very 5053different from version 2), and it would have been too confusing. That 5054debug format is long obsolete, but the option cannot be changed now. 5055Instead use an additional @option{-g@var{level}} option to change the 5056debug level for DWARF. 5057 5058@item -gtoggle 5059@opindex gtoggle 5060Turn off generation of debug info, if leaving out this option 5061generates it, or turn it on at level 2 otherwise. The position of this 5062argument in the command line does not matter; it takes effect after all 5063other options are processed, and it does so only once, no matter how 5064many times it is given. This is mainly intended to be used with 5065@option{-fcompare-debug}. 5066 5067@item -fsanitize=address 5068Enable AddressSanitizer, a fast memory error detector. 5069Memory access instructions will be instrumented to detect 5070out-of-bounds and use-after-free bugs. 5071See @uref{http://code.google.com/p/address-sanitizer/} for more details. 5072 5073@item -fsanitize=thread 5074Enable ThreadSanitizer, a fast data race detector. 5075Memory access instructions will be instrumented to detect 5076data race bugs. 5077See @uref{http://code.google.com/p/data-race-test/wiki/ThreadSanitizer} for more details. 5078 5079@item -fdump-final-insns@r{[}=@var{file}@r{]} 5080@opindex fdump-final-insns 5081Dump the final internal representation (RTL) to @var{file}. If the 5082optional argument is omitted (or if @var{file} is @code{.}), the name 5083of the dump file is determined by appending @code{.gkd} to the 5084compilation output file name. 5085 5086@item -fcompare-debug@r{[}=@var{opts}@r{]} 5087@opindex fcompare-debug 5088@opindex fno-compare-debug 5089If no error occurs during compilation, run the compiler a second time, 5090adding @var{opts} and @option{-fcompare-debug-second} to the arguments 5091passed to the second compilation. Dump the final internal 5092representation in both compilations, and print an error if they differ. 5093 5094If the equal sign is omitted, the default @option{-gtoggle} is used. 5095 5096The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty 5097and nonzero, implicitly enables @option{-fcompare-debug}. If 5098@env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash, 5099then it is used for @var{opts}, otherwise the default @option{-gtoggle} 5100is used. 5101 5102@option{-fcompare-debug=}, with the equal sign but without @var{opts}, 5103is equivalent to @option{-fno-compare-debug}, which disables the dumping 5104of the final representation and the second compilation, preventing even 5105@env{GCC_COMPARE_DEBUG} from taking effect. 5106 5107To verify full coverage during @option{-fcompare-debug} testing, set 5108@env{GCC_COMPARE_DEBUG} to say @samp{-fcompare-debug-not-overridden}, 5109which GCC rejects as an invalid option in any actual compilation 5110(rather than preprocessing, assembly or linking). To get just a 5111warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug 5112not overridden} will do. 5113 5114@item -fcompare-debug-second 5115@opindex fcompare-debug-second 5116This option is implicitly passed to the compiler for the second 5117compilation requested by @option{-fcompare-debug}, along with options to 5118silence warnings, and omitting other options that would cause 5119side-effect compiler outputs to files or to the standard output. Dump 5120files and preserved temporary files are renamed so as to contain the 5121@code{.gk} additional extension during the second compilation, to avoid 5122overwriting those generated by the first. 5123 5124When this option is passed to the compiler driver, it causes the 5125@emph{first} compilation to be skipped, which makes it useful for little 5126other than debugging the compiler proper. 5127 5128@item -feliminate-dwarf2-dups 5129@opindex feliminate-dwarf2-dups 5130Compress DWARF 2 debugging information by eliminating duplicated 5131information about each symbol. This option only makes sense when 5132generating DWARF 2 debugging information with @option{-gdwarf-2}. 5133 5134@item -femit-struct-debug-baseonly 5135Emit debug information for struct-like types 5136only when the base name of the compilation source file 5137matches the base name of file in which the struct is defined. 5138 5139This option substantially reduces the size of debugging information, 5140but at significant potential loss in type information to the debugger. 5141See @option{-femit-struct-debug-reduced} for a less aggressive option. 5142See @option{-femit-struct-debug-detailed} for more detailed control. 5143 5144This option works only with DWARF 2. 5145 5146@item -femit-struct-debug-reduced 5147Emit debug information for struct-like types 5148only when the base name of the compilation source file 5149matches the base name of file in which the type is defined, 5150unless the struct is a template or defined in a system header. 5151 5152This option significantly reduces the size of debugging information, 5153with some potential loss in type information to the debugger. 5154See @option{-femit-struct-debug-baseonly} for a more aggressive option. 5155See @option{-femit-struct-debug-detailed} for more detailed control. 5156 5157This option works only with DWARF 2. 5158 5159@item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} 5160Specify the struct-like types 5161for which the compiler generates debug information. 5162The intent is to reduce duplicate struct debug information 5163between different object files within the same program. 5164 5165This option is a detailed version of 5166@option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly}, 5167which serves for most needs. 5168 5169A specification has the syntax@* 5170[@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none}) 5171 5172The optional first word limits the specification to 5173structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}). 5174A struct type is used directly when it is the type of a variable, member. 5175Indirect uses arise through pointers to structs. 5176That is, when use of an incomplete struct is valid, the use is indirect. 5177An example is 5178@samp{struct one direct; struct two * indirect;}. 5179 5180The optional second word limits the specification to 5181ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}). 5182Generic structs are a bit complicated to explain. 5183For C++, these are non-explicit specializations of template classes, 5184or non-template classes within the above. 5185Other programming languages have generics, 5186but @option{-femit-struct-debug-detailed} does not yet implement them. 5187 5188The third word specifies the source files for those 5189structs for which the compiler should emit debug information. 5190The values @samp{none} and @samp{any} have the normal meaning. 5191The value @samp{base} means that 5192the base of name of the file in which the type declaration appears 5193must match the base of the name of the main compilation file. 5194In practice, this means that when compiling @file{foo.c}, debug information 5195is generated for types declared in that file and @file{foo.h}, 5196but not other header files. 5197The value @samp{sys} means those types satisfying @samp{base} 5198or declared in system or compiler headers. 5199 5200You may need to experiment to determine the best settings for your application. 5201 5202The default is @option{-femit-struct-debug-detailed=all}. 5203 5204This option works only with DWARF 2. 5205 5206@item -fno-merge-debug-strings 5207@opindex fmerge-debug-strings 5208@opindex fno-merge-debug-strings 5209Direct the linker to not merge together strings in the debugging 5210information that are identical in different object files. Merging is 5211not supported by all assemblers or linkers. Merging decreases the size 5212of the debug information in the output file at the cost of increasing 5213link processing time. Merging is enabled by default. 5214 5215@item -fdebug-prefix-map=@var{old}=@var{new} 5216@opindex fdebug-prefix-map 5217When compiling files in directory @file{@var{old}}, record debugging 5218information describing them as in @file{@var{new}} instead. 5219 5220@item -fno-dwarf2-cfi-asm 5221@opindex fdwarf2-cfi-asm 5222@opindex fno-dwarf2-cfi-asm 5223Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section 5224instead of using GAS @code{.cfi_*} directives. 5225 5226@cindex @command{prof} 5227@item -p 5228@opindex p 5229Generate extra code to write profile information suitable for the 5230analysis program @command{prof}. You must use this option when compiling 5231the source files you want data about, and you must also use it when 5232linking. 5233 5234@cindex @command{gprof} 5235@item -pg 5236@opindex pg 5237Generate extra code to write profile information suitable for the 5238analysis program @command{gprof}. You must use this option when compiling 5239the source files you want data about, and you must also use it when 5240linking. 5241 5242@item -Q 5243@opindex Q 5244Makes the compiler print out each function name as it is compiled, and 5245print some statistics about each pass when it finishes. 5246 5247@item -ftime-report 5248@opindex ftime-report 5249Makes the compiler print some statistics about the time consumed by each 5250pass when it finishes. 5251 5252@item -fmem-report 5253@opindex fmem-report 5254Makes the compiler print some statistics about permanent memory 5255allocation when it finishes. 5256 5257@item -fmem-report-wpa 5258@opindex fmem-report-wpa 5259Makes the compiler print some statistics about permanent memory 5260allocation for the WPA phase only. 5261 5262@item -fpre-ipa-mem-report 5263@opindex fpre-ipa-mem-report 5264@item -fpost-ipa-mem-report 5265@opindex fpost-ipa-mem-report 5266Makes the compiler print some statistics about permanent memory 5267allocation before or after interprocedural optimization. 5268 5269@item -fprofile-report 5270@opindex fprofile-report 5271Makes the compiler print some statistics about consistency of the 5272(estimated) profile and effect of individual passes. 5273 5274@item -fstack-usage 5275@opindex fstack-usage 5276Makes the compiler output stack usage information for the program, on a 5277per-function basis. The filename for the dump is made by appending 5278@file{.su} to the @var{auxname}. @var{auxname} is generated from the name of 5279the output file, if explicitly specified and it is not an executable, 5280otherwise it is the basename of the source file. An entry is made up 5281of three fields: 5282 5283@itemize 5284@item 5285The name of the function. 5286@item 5287A number of bytes. 5288@item 5289One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. 5290@end itemize 5291 5292The qualifier @code{static} means that the function manipulates the stack 5293statically: a fixed number of bytes are allocated for the frame on function 5294entry and released on function exit; no stack adjustments are otherwise made 5295in the function. The second field is this fixed number of bytes. 5296 5297The qualifier @code{dynamic} means that the function manipulates the stack 5298dynamically: in addition to the static allocation described above, stack 5299adjustments are made in the body of the function, for example to push/pop 5300arguments around function calls. If the qualifier @code{bounded} is also 5301present, the amount of these adjustments is bounded at compile time and 5302the second field is an upper bound of the total amount of stack used by 5303the function. If it is not present, the amount of these adjustments is 5304not bounded at compile time and the second field only represents the 5305bounded part. 5306 5307@item -fprofile-arcs 5308@opindex fprofile-arcs 5309Add code so that program flow @dfn{arcs} are instrumented. During 5310execution the program records how many times each branch and call is 5311executed and how many times it is taken or returns. When the compiled 5312program exits it saves this data to a file called 5313@file{@var{auxname}.gcda} for each source file. The data may be used for 5314profile-directed optimizations (@option{-fbranch-probabilities}), or for 5315test coverage analysis (@option{-ftest-coverage}). Each object file's 5316@var{auxname} is generated from the name of the output file, if 5317explicitly specified and it is not the final executable, otherwise it is 5318the basename of the source file. In both cases any suffix is removed 5319(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or 5320@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). 5321@xref{Cross-profiling}. 5322 5323@cindex @command{gcov} 5324@item --coverage 5325@opindex coverage 5326 5327This option is used to compile and link code instrumented for coverage 5328analysis. The option is a synonym for @option{-fprofile-arcs} 5329@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when 5330linking). See the documentation for those options for more details. 5331 5332@itemize 5333 5334@item 5335Compile the source files with @option{-fprofile-arcs} plus optimization 5336and code generation options. For test coverage analysis, use the 5337additional @option{-ftest-coverage} option. You do not need to profile 5338every source file in a program. 5339 5340@item 5341Link your object files with @option{-lgcov} or @option{-fprofile-arcs} 5342(the latter implies the former). 5343 5344@item 5345Run the program on a representative workload to generate the arc profile 5346information. This may be repeated any number of times. You can run 5347concurrent instances of your program, and provided that the file system 5348supports locking, the data files will be correctly updated. Also 5349@code{fork} calls are detected and correctly handled (double counting 5350will not happen). 5351 5352@item 5353For profile-directed optimizations, compile the source files again with 5354the same optimization and code generation options plus 5355@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that 5356Control Optimization}). 5357 5358@item 5359For test coverage analysis, use @command{gcov} to produce human readable 5360information from the @file{.gcno} and @file{.gcda} files. Refer to the 5361@command{gcov} documentation for further information. 5362 5363@end itemize 5364 5365With @option{-fprofile-arcs}, for each function of your program GCC 5366creates a program flow graph, then finds a spanning tree for the graph. 5367Only arcs that are not on the spanning tree have to be instrumented: the 5368compiler adds code to count the number of times that these arcs are 5369executed. When an arc is the only exit or only entrance to a block, the 5370instrumentation code can be added to the block; otherwise, a new basic 5371block must be created to hold the instrumentation code. 5372 5373@need 2000 5374@item -ftest-coverage 5375@opindex ftest-coverage 5376Produce a notes file that the @command{gcov} code-coverage utility 5377(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to 5378show program coverage. Each source file's note file is called 5379@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option 5380above for a description of @var{auxname} and instructions on how to 5381generate test coverage data. Coverage data matches the source files 5382more closely if you do not optimize. 5383 5384@item -fdbg-cnt-list 5385@opindex fdbg-cnt-list 5386Print the name and the counter upper bound for all debug counters. 5387 5388 5389@item -fdbg-cnt=@var{counter-value-list} 5390@opindex fdbg-cnt 5391Set the internal debug counter upper bound. @var{counter-value-list} 5392is a comma-separated list of @var{name}:@var{value} pairs 5393which sets the upper bound of each debug counter @var{name} to @var{value}. 5394All debug counters have the initial upper bound of @code{UINT_MAX}; 5395thus @code{dbg_cnt()} returns true always unless the upper bound 5396is set by this option. 5397For example, with @option{-fdbg-cnt=dce:10,tail_call:0}, 5398@code{dbg_cnt(dce)} returns true only for first 10 invocations. 5399 5400@item -fenable-@var{kind}-@var{pass} 5401@itemx -fdisable-@var{kind}-@var{pass}=@var{range-list} 5402@opindex fdisable- 5403@opindex fenable- 5404 5405This is a set of options that are used to explicitly disable/enable 5406optimization passes. These options are intended for use for debugging GCC. 5407Compiler users should use regular options for enabling/disabling 5408passes instead. 5409 5410@table @gcctabopt 5411 5412@item -fdisable-ipa-@var{pass} 5413Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is 5414statically invoked in the compiler multiple times, the pass name should be 5415appended with a sequential number starting from 1. 5416 5417@item -fdisable-rtl-@var{pass} 5418@itemx -fdisable-rtl-@var{pass}=@var{range-list} 5419Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is 5420statically invoked in the compiler multiple times, the pass name should be 5421appended with a sequential number starting from 1. @var{range-list} is a 5422comma-separated list of function ranges or assembler names. Each range is a number 5423pair separated by a colon. The range is inclusive in both ends. If the range 5424is trivial, the number pair can be simplified as a single number. If the 5425function's call graph node's @var{uid} falls within one of the specified ranges, 5426the @var{pass} is disabled for that function. The @var{uid} is shown in the 5427function header of a dump file, and the pass names can be dumped by using 5428option @option{-fdump-passes}. 5429 5430@item -fdisable-tree-@var{pass} 5431@itemx -fdisable-tree-@var{pass}=@var{range-list} 5432Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of 5433option arguments. 5434 5435@item -fenable-ipa-@var{pass} 5436Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is 5437statically invoked in the compiler multiple times, the pass name should be 5438appended with a sequential number starting from 1. 5439 5440@item -fenable-rtl-@var{pass} 5441@itemx -fenable-rtl-@var{pass}=@var{range-list} 5442Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument 5443description and examples. 5444 5445@item -fenable-tree-@var{pass} 5446@itemx -fenable-tree-@var{pass}=@var{range-list} 5447Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description 5448of option arguments. 5449 5450@end table 5451 5452Here are some examples showing uses of these options. 5453 5454@smallexample 5455 5456# disable ccp1 for all functions 5457 -fdisable-tree-ccp1 5458# disable complete unroll for function whose cgraph node uid is 1 5459 -fenable-tree-cunroll=1 5460# disable gcse2 for functions at the following ranges [1,1], 5461# [300,400], and [400,1000] 5462# disable gcse2 for functions foo and foo2 5463 -fdisable-rtl-gcse2=foo,foo2 5464# disable early inlining 5465 -fdisable-tree-einline 5466# disable ipa inlining 5467 -fdisable-ipa-inline 5468# enable tree full unroll 5469 -fenable-tree-unroll 5470 5471@end smallexample 5472 5473@item -d@var{letters} 5474@itemx -fdump-rtl-@var{pass} 5475@itemx -fdump-rtl-@var{pass}=@var{filename} 5476@opindex d 5477Says to make debugging dumps during compilation at times specified by 5478@var{letters}. This is used for debugging the RTL-based passes of the 5479compiler. The file names for most of the dumps are made by appending 5480a pass number and a word to the @var{dumpname}, and the files are 5481created in the directory of the output file. In case of 5482@option{=@var{filename}} option, the dump is output on the given file 5483instead of the pass numbered dump files. Note that the pass number is 5484computed statically as passes get registered into the pass manager. 5485Thus the numbering is not related to the dynamic order of execution of 5486passes. In particular, a pass installed by a plugin could have a 5487number over 200 even if it executed quite early. @var{dumpname} is 5488generated from the name of the output file, if explicitly specified 5489and it is not an executable, otherwise it is the basename of the 5490source file. These switches may have different effects when 5491@option{-E} is used for preprocessing. 5492 5493Debug dumps can be enabled with a @option{-fdump-rtl} switch or some 5494@option{-d} option @var{letters}. Here are the possible 5495letters for use in @var{pass} and @var{letters}, and their meanings: 5496 5497@table @gcctabopt 5498 5499@item -fdump-rtl-alignments 5500@opindex fdump-rtl-alignments 5501Dump after branch alignments have been computed. 5502 5503@item -fdump-rtl-asmcons 5504@opindex fdump-rtl-asmcons 5505Dump after fixing rtl statements that have unsatisfied in/out constraints. 5506 5507@item -fdump-rtl-auto_inc_dec 5508@opindex fdump-rtl-auto_inc_dec 5509Dump after auto-inc-dec discovery. This pass is only run on 5510architectures that have auto inc or auto dec instructions. 5511 5512@item -fdump-rtl-barriers 5513@opindex fdump-rtl-barriers 5514Dump after cleaning up the barrier instructions. 5515 5516@item -fdump-rtl-bbpart 5517@opindex fdump-rtl-bbpart 5518Dump after partitioning hot and cold basic blocks. 5519 5520@item -fdump-rtl-bbro 5521@opindex fdump-rtl-bbro 5522Dump after block reordering. 5523 5524@item -fdump-rtl-btl1 5525@itemx -fdump-rtl-btl2 5526@opindex fdump-rtl-btl2 5527@opindex fdump-rtl-btl2 5528@option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping 5529after the two branch 5530target load optimization passes. 5531 5532@item -fdump-rtl-bypass 5533@opindex fdump-rtl-bypass 5534Dump after jump bypassing and control flow optimizations. 5535 5536@item -fdump-rtl-combine 5537@opindex fdump-rtl-combine 5538Dump after the RTL instruction combination pass. 5539 5540@item -fdump-rtl-compgotos 5541@opindex fdump-rtl-compgotos 5542Dump after duplicating the computed gotos. 5543 5544@item -fdump-rtl-ce1 5545@itemx -fdump-rtl-ce2 5546@itemx -fdump-rtl-ce3 5547@opindex fdump-rtl-ce1 5548@opindex fdump-rtl-ce2 5549@opindex fdump-rtl-ce3 5550@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and 5551@option{-fdump-rtl-ce3} enable dumping after the three 5552if conversion passes. 5553 5554@item -fdump-rtl-cprop_hardreg 5555@opindex fdump-rtl-cprop_hardreg 5556Dump after hard register copy propagation. 5557 5558@item -fdump-rtl-csa 5559@opindex fdump-rtl-csa 5560Dump after combining stack adjustments. 5561 5562@item -fdump-rtl-cse1 5563@itemx -fdump-rtl-cse2 5564@opindex fdump-rtl-cse1 5565@opindex fdump-rtl-cse2 5566@option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after 5567the two common subexpression elimination passes. 5568 5569@item -fdump-rtl-dce 5570@opindex fdump-rtl-dce 5571Dump after the standalone dead code elimination passes. 5572 5573@item -fdump-rtl-dbr 5574@opindex fdump-rtl-dbr 5575Dump after delayed branch scheduling. 5576 5577@item -fdump-rtl-dce1 5578@itemx -fdump-rtl-dce2 5579@opindex fdump-rtl-dce1 5580@opindex fdump-rtl-dce2 5581@option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after 5582the two dead store elimination passes. 5583 5584@item -fdump-rtl-eh 5585@opindex fdump-rtl-eh 5586Dump after finalization of EH handling code. 5587 5588@item -fdump-rtl-eh_ranges 5589@opindex fdump-rtl-eh_ranges 5590Dump after conversion of EH handling range regions. 5591 5592@item -fdump-rtl-expand 5593@opindex fdump-rtl-expand 5594Dump after RTL generation. 5595 5596@item -fdump-rtl-fwprop1 5597@itemx -fdump-rtl-fwprop2 5598@opindex fdump-rtl-fwprop1 5599@opindex fdump-rtl-fwprop2 5600@option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable 5601dumping after the two forward propagation passes. 5602 5603@item -fdump-rtl-gcse1 5604@itemx -fdump-rtl-gcse2 5605@opindex fdump-rtl-gcse1 5606@opindex fdump-rtl-gcse2 5607@option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping 5608after global common subexpression elimination. 5609 5610@item -fdump-rtl-init-regs 5611@opindex fdump-rtl-init-regs 5612Dump after the initialization of the registers. 5613 5614@item -fdump-rtl-initvals 5615@opindex fdump-rtl-initvals 5616Dump after the computation of the initial value sets. 5617 5618@item -fdump-rtl-into_cfglayout 5619@opindex fdump-rtl-into_cfglayout 5620Dump after converting to cfglayout mode. 5621 5622@item -fdump-rtl-ira 5623@opindex fdump-rtl-ira 5624Dump after iterated register allocation. 5625 5626@item -fdump-rtl-jump 5627@opindex fdump-rtl-jump 5628Dump after the second jump optimization. 5629 5630@item -fdump-rtl-loop2 5631@opindex fdump-rtl-loop2 5632@option{-fdump-rtl-loop2} enables dumping after the rtl 5633loop optimization passes. 5634 5635@item -fdump-rtl-mach 5636@opindex fdump-rtl-mach 5637Dump after performing the machine dependent reorganization pass, if that 5638pass exists. 5639 5640@item -fdump-rtl-mode_sw 5641@opindex fdump-rtl-mode_sw 5642Dump after removing redundant mode switches. 5643 5644@item -fdump-rtl-rnreg 5645@opindex fdump-rtl-rnreg 5646Dump after register renumbering. 5647 5648@item -fdump-rtl-outof_cfglayout 5649@opindex fdump-rtl-outof_cfglayout 5650Dump after converting from cfglayout mode. 5651 5652@item -fdump-rtl-peephole2 5653@opindex fdump-rtl-peephole2 5654Dump after the peephole pass. 5655 5656@item -fdump-rtl-postreload 5657@opindex fdump-rtl-postreload 5658Dump after post-reload optimizations. 5659 5660@item -fdump-rtl-pro_and_epilogue 5661@opindex fdump-rtl-pro_and_epilogue 5662Dump after generating the function prologues and epilogues. 5663 5664@item -fdump-rtl-regmove 5665@opindex fdump-rtl-regmove 5666Dump after the register move pass. 5667 5668@item -fdump-rtl-sched1 5669@itemx -fdump-rtl-sched2 5670@opindex fdump-rtl-sched1 5671@opindex fdump-rtl-sched2 5672@option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping 5673after the basic block scheduling passes. 5674 5675@item -fdump-rtl-see 5676@opindex fdump-rtl-see 5677Dump after sign extension elimination. 5678 5679@item -fdump-rtl-seqabstr 5680@opindex fdump-rtl-seqabstr 5681Dump after common sequence discovery. 5682 5683@item -fdump-rtl-shorten 5684@opindex fdump-rtl-shorten 5685Dump after shortening branches. 5686 5687@item -fdump-rtl-sibling 5688@opindex fdump-rtl-sibling 5689Dump after sibling call optimizations. 5690 5691@item -fdump-rtl-split1 5692@itemx -fdump-rtl-split2 5693@itemx -fdump-rtl-split3 5694@itemx -fdump-rtl-split4 5695@itemx -fdump-rtl-split5 5696@opindex fdump-rtl-split1 5697@opindex fdump-rtl-split2 5698@opindex fdump-rtl-split3 5699@opindex fdump-rtl-split4 5700@opindex fdump-rtl-split5 5701@option{-fdump-rtl-split1}, @option{-fdump-rtl-split2}, 5702@option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and 5703@option{-fdump-rtl-split5} enable dumping after five rounds of 5704instruction splitting. 5705 5706@item -fdump-rtl-sms 5707@opindex fdump-rtl-sms 5708Dump after modulo scheduling. This pass is only run on some 5709architectures. 5710 5711@item -fdump-rtl-stack 5712@opindex fdump-rtl-stack 5713Dump after conversion from GCC's ``flat register file'' registers to the 5714x87's stack-like registers. This pass is only run on x86 variants. 5715 5716@item -fdump-rtl-subreg1 5717@itemx -fdump-rtl-subreg2 5718@opindex fdump-rtl-subreg1 5719@opindex fdump-rtl-subreg2 5720@option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after 5721the two subreg expansion passes. 5722 5723@item -fdump-rtl-unshare 5724@opindex fdump-rtl-unshare 5725Dump after all rtl has been unshared. 5726 5727@item -fdump-rtl-vartrack 5728@opindex fdump-rtl-vartrack 5729Dump after variable tracking. 5730 5731@item -fdump-rtl-vregs 5732@opindex fdump-rtl-vregs 5733Dump after converting virtual registers to hard registers. 5734 5735@item -fdump-rtl-web 5736@opindex fdump-rtl-web 5737Dump after live range splitting. 5738 5739@item -fdump-rtl-regclass 5740@itemx -fdump-rtl-subregs_of_mode_init 5741@itemx -fdump-rtl-subregs_of_mode_finish 5742@itemx -fdump-rtl-dfinit 5743@itemx -fdump-rtl-dfinish 5744@opindex fdump-rtl-regclass 5745@opindex fdump-rtl-subregs_of_mode_init 5746@opindex fdump-rtl-subregs_of_mode_finish 5747@opindex fdump-rtl-dfinit 5748@opindex fdump-rtl-dfinish 5749These dumps are defined but always produce empty files. 5750 5751@item -da 5752@itemx -fdump-rtl-all 5753@opindex da 5754@opindex fdump-rtl-all 5755Produce all the dumps listed above. 5756 5757@item -dA 5758@opindex dA 5759Annotate the assembler output with miscellaneous debugging information. 5760 5761@item -dD 5762@opindex dD 5763Dump all macro definitions, at the end of preprocessing, in addition to 5764normal output. 5765 5766@item -dH 5767@opindex dH 5768Produce a core dump whenever an error occurs. 5769 5770@item -dp 5771@opindex dp 5772Annotate the assembler output with a comment indicating which 5773pattern and alternative is used. The length of each instruction is 5774also printed. 5775 5776@item -dP 5777@opindex dP 5778Dump the RTL in the assembler output as a comment before each instruction. 5779Also turns on @option{-dp} annotation. 5780 5781@item -dx 5782@opindex dx 5783Just generate RTL for a function instead of compiling it. Usually used 5784with @option{-fdump-rtl-expand}. 5785@end table 5786 5787@item -fdump-noaddr 5788@opindex fdump-noaddr 5789When doing debugging dumps, suppress address output. This makes it more 5790feasible to use diff on debugging dumps for compiler invocations with 5791different compiler binaries and/or different 5792text / bss / data / heap / stack / dso start locations. 5793 5794@item -fdump-unnumbered 5795@opindex fdump-unnumbered 5796When doing debugging dumps, suppress instruction numbers and address output. 5797This makes it more feasible to use diff on debugging dumps for compiler 5798invocations with different options, in particular with and without 5799@option{-g}. 5800 5801@item -fdump-unnumbered-links 5802@opindex fdump-unnumbered-links 5803When doing debugging dumps (see @option{-d} option above), suppress 5804instruction numbers for the links to the previous and next instructions 5805in a sequence. 5806 5807@item -fdump-translation-unit @r{(C++ only)} 5808@itemx -fdump-translation-unit-@var{options} @r{(C++ only)} 5809@opindex fdump-translation-unit 5810Dump a representation of the tree structure for the entire translation 5811unit to a file. The file name is made by appending @file{.tu} to the 5812source file name, and the file is created in the same directory as the 5813output file. If the @samp{-@var{options}} form is used, @var{options} 5814controls the details of the dump as described for the 5815@option{-fdump-tree} options. 5816 5817@item -fdump-class-hierarchy @r{(C++ only)} 5818@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)} 5819@opindex fdump-class-hierarchy 5820Dump a representation of each class's hierarchy and virtual function 5821table layout to a file. The file name is made by appending 5822@file{.class} to the source file name, and the file is created in the 5823same directory as the output file. If the @samp{-@var{options}} form 5824is used, @var{options} controls the details of the dump as described 5825for the @option{-fdump-tree} options. 5826 5827@item -fdump-ipa-@var{switch} 5828@opindex fdump-ipa 5829Control the dumping at various stages of inter-procedural analysis 5830language tree to a file. The file name is generated by appending a 5831switch specific suffix to the source file name, and the file is created 5832in the same directory as the output file. The following dumps are 5833possible: 5834 5835@table @samp 5836@item all 5837Enables all inter-procedural analysis dumps. 5838 5839@item cgraph 5840Dumps information about call-graph optimization, unused function removal, 5841and inlining decisions. 5842 5843@item inline 5844Dump after function inlining. 5845 5846@end table 5847 5848@item -fdump-passes 5849@opindex fdump-passes 5850Dump the list of optimization passes that are turned on and off by 5851the current command-line options. 5852 5853@item -fdump-statistics-@var{option} 5854@opindex fdump-statistics 5855Enable and control dumping of pass statistics in a separate file. The 5856file name is generated by appending a suffix ending in 5857@samp{.statistics} to the source file name, and the file is created in 5858the same directory as the output file. If the @samp{-@var{option}} 5859form is used, @samp{-stats} causes counters to be summed over the 5860whole compilation unit while @samp{-details} dumps every event as 5861the passes generate them. The default with no option is to sum 5862counters for each function compiled. 5863 5864@item -fdump-tree-@var{switch} 5865@itemx -fdump-tree-@var{switch}-@var{options} 5866@itemx -fdump-tree-@var{switch}-@var{options}=@var{filename} 5867@opindex fdump-tree 5868Control the dumping at various stages of processing the intermediate 5869language tree to a file. The file name is generated by appending a 5870switch-specific suffix to the source file name, and the file is 5871created in the same directory as the output file. In case of 5872@option{=@var{filename}} option, the dump is output on the given file 5873instead of the auto named dump files. If the @samp{-@var{options}} 5874form is used, @var{options} is a list of @samp{-} separated options 5875which control the details of the dump. Not all options are applicable 5876to all dumps; those that are not meaningful are ignored. The 5877following options are available 5878 5879@table @samp 5880@item address 5881Print the address of each node. Usually this is not meaningful as it 5882changes according to the environment and source file. Its primary use 5883is for tying up a dump file with a debug environment. 5884@item asmname 5885If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that 5886in the dump instead of @code{DECL_NAME}. Its primary use is ease of 5887use working backward from mangled names in the assembly file. 5888@item slim 5889When dumping front-end intermediate representations, inhibit dumping 5890of members of a scope or body of a function merely because that scope 5891has been reached. Only dump such items when they are directly reachable 5892by some other path. 5893 5894When dumping pretty-printed trees, this option inhibits dumping the 5895bodies of control structures. 5896 5897When dumping RTL, print the RTL in slim (condensed) form instead of 5898the default LISP-like representation. 5899@item raw 5900Print a raw representation of the tree. By default, trees are 5901pretty-printed into a C-like representation. 5902@item details 5903Enable more detailed dumps (not honored by every dump option). Also 5904include information from the optimization passes. 5905@item stats 5906Enable dumping various statistics about the pass (not honored by every dump 5907option). 5908@item blocks 5909Enable showing basic block boundaries (disabled in raw dumps). 5910@item graph 5911For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}), 5912dump a representation of the control flow graph suitable for viewing with 5913GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in 5914the file is pretty-printed as a subgraph, so that GraphViz can render them 5915all in a single plot. 5916 5917This option currently only works for RTL dumps, and the RTL is always 5918dumped in slim form. 5919@item vops 5920Enable showing virtual operands for every statement. 5921@item lineno 5922Enable showing line numbers for statements. 5923@item uid 5924Enable showing the unique ID (@code{DECL_UID}) for each variable. 5925@item verbose 5926Enable showing the tree dump for each statement. 5927@item eh 5928Enable showing the EH region number holding each statement. 5929@item scev 5930Enable showing scalar evolution analysis details. 5931@item optimized 5932Enable showing optimization information (only available in certain 5933passes). 5934@item missed 5935Enable showing missed optimization information (only available in certain 5936passes). 5937@item notes 5938Enable other detailed optimization information (only available in 5939certain passes). 5940@item =@var{filename} 5941Instead of an auto named dump file, output into the given file 5942name. The file names @file{stdout} and @file{stderr} are treated 5943specially and are considered already open standard streams. For 5944example, 5945 5946@smallexample 5947gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump 5948 -fdump-tree-pre=stderr file.c 5949@end smallexample 5950 5951outputs vectorizer dump into @file{foo.dump}, while the PRE dump is 5952output on to @file{stderr}. If two conflicting dump filenames are 5953given for the same pass, then the latter option overrides the earlier 5954one. 5955 5956@item all 5957Turn on all options, except @option{raw}, @option{slim}, @option{verbose} 5958and @option{lineno}. 5959 5960@item optall 5961Turn on all optimization options, i.e., @option{optimized}, 5962@option{missed}, and @option{note}. 5963@end table 5964 5965The following tree dumps are possible: 5966@table @samp 5967 5968@item original 5969@opindex fdump-tree-original 5970Dump before any tree based optimization, to @file{@var{file}.original}. 5971 5972@item optimized 5973@opindex fdump-tree-optimized 5974Dump after all tree based optimization, to @file{@var{file}.optimized}. 5975 5976@item gimple 5977@opindex fdump-tree-gimple 5978Dump each function before and after the gimplification pass to a file. The 5979file name is made by appending @file{.gimple} to the source file name. 5980 5981@item cfg 5982@opindex fdump-tree-cfg 5983Dump the control flow graph of each function to a file. The file name is 5984made by appending @file{.cfg} to the source file name. 5985 5986@item ch 5987@opindex fdump-tree-ch 5988Dump each function after copying loop headers. The file name is made by 5989appending @file{.ch} to the source file name. 5990 5991@item ssa 5992@opindex fdump-tree-ssa 5993Dump SSA related information to a file. The file name is made by appending 5994@file{.ssa} to the source file name. 5995 5996@item alias 5997@opindex fdump-tree-alias 5998Dump aliasing information for each function. The file name is made by 5999appending @file{.alias} to the source file name. 6000 6001@item ccp 6002@opindex fdump-tree-ccp 6003Dump each function after CCP@. The file name is made by appending 6004@file{.ccp} to the source file name. 6005 6006@item storeccp 6007@opindex fdump-tree-storeccp 6008Dump each function after STORE-CCP@. The file name is made by appending 6009@file{.storeccp} to the source file name. 6010 6011@item pre 6012@opindex fdump-tree-pre 6013Dump trees after partial redundancy elimination. The file name is made 6014by appending @file{.pre} to the source file name. 6015 6016@item fre 6017@opindex fdump-tree-fre 6018Dump trees after full redundancy elimination. The file name is made 6019by appending @file{.fre} to the source file name. 6020 6021@item copyprop 6022@opindex fdump-tree-copyprop 6023Dump trees after copy propagation. The file name is made 6024by appending @file{.copyprop} to the source file name. 6025 6026@item store_copyprop 6027@opindex fdump-tree-store_copyprop 6028Dump trees after store copy-propagation. The file name is made 6029by appending @file{.store_copyprop} to the source file name. 6030 6031@item dce 6032@opindex fdump-tree-dce 6033Dump each function after dead code elimination. The file name is made by 6034appending @file{.dce} to the source file name. 6035 6036@item mudflap 6037@opindex fdump-tree-mudflap 6038Dump each function after adding mudflap instrumentation. The file name is 6039made by appending @file{.mudflap} to the source file name. 6040 6041@item sra 6042@opindex fdump-tree-sra 6043Dump each function after performing scalar replacement of aggregates. The 6044file name is made by appending @file{.sra} to the source file name. 6045 6046@item sink 6047@opindex fdump-tree-sink 6048Dump each function after performing code sinking. The file name is made 6049by appending @file{.sink} to the source file name. 6050 6051@item dom 6052@opindex fdump-tree-dom 6053Dump each function after applying dominator tree optimizations. The file 6054name is made by appending @file{.dom} to the source file name. 6055 6056@item dse 6057@opindex fdump-tree-dse 6058Dump each function after applying dead store elimination. The file 6059name is made by appending @file{.dse} to the source file name. 6060 6061@item phiopt 6062@opindex fdump-tree-phiopt 6063Dump each function after optimizing PHI nodes into straightline code. The file 6064name is made by appending @file{.phiopt} to the source file name. 6065 6066@item forwprop 6067@opindex fdump-tree-forwprop 6068Dump each function after forward propagating single use variables. The file 6069name is made by appending @file{.forwprop} to the source file name. 6070 6071@item copyrename 6072@opindex fdump-tree-copyrename 6073Dump each function after applying the copy rename optimization. The file 6074name is made by appending @file{.copyrename} to the source file name. 6075 6076@item nrv 6077@opindex fdump-tree-nrv 6078Dump each function after applying the named return value optimization on 6079generic trees. The file name is made by appending @file{.nrv} to the source 6080file name. 6081 6082@item vect 6083@opindex fdump-tree-vect 6084Dump each function after applying vectorization of loops. The file name is 6085made by appending @file{.vect} to the source file name. 6086 6087@item slp 6088@opindex fdump-tree-slp 6089Dump each function after applying vectorization of basic blocks. The file name 6090is made by appending @file{.slp} to the source file name. 6091 6092@item vrp 6093@opindex fdump-tree-vrp 6094Dump each function after Value Range Propagation (VRP). The file name 6095is made by appending @file{.vrp} to the source file name. 6096 6097@item all 6098@opindex fdump-tree-all 6099Enable all the available tree dumps with the flags provided in this option. 6100@end table 6101 6102@item -fopt-info 6103@itemx -fopt-info-@var{options} 6104@itemx -fopt-info-@var{options}=@var{filename} 6105@opindex fopt-info 6106Controls optimization dumps from various optimization passes. If the 6107@samp{-@var{options}} form is used, @var{options} is a list of 6108@samp{-} separated options to select the dump details and 6109optimizations. If @var{options} is not specified, it defaults to 6110@option{all} for details and @option{optall} for optimization 6111groups. If the @var{filename} is not specified, it defaults to 6112@file{stderr}. Note that the output @var{filename} will be overwritten 6113in case of multiple translation units. If a combined output from 6114multiple translation units is desired, @file{stderr} should be used 6115instead. 6116 6117The options can be divided into two groups, 1) options describing the 6118verbosity of the dump, and 2) options describing which optimizations 6119should be included. The options from both the groups can be freely 6120mixed as they are non-overlapping. However, in case of any conflicts, 6121the latter options override the earlier options on the command 6122line. Though multiple -fopt-info options are accepted, only one of 6123them can have @option{=filename}. If other filenames are provided then 6124all but the first one are ignored. 6125 6126The dump verbosity has the following options 6127 6128@table @samp 6129@item optimized 6130Print information when an optimization is successfully applied. It is 6131up to a pass to decide which information is relevant. For example, the 6132vectorizer passes print the source location of loops which got 6133successfully vectorized. 6134@item missed 6135Print information about missed optimizations. Individual passes 6136control which information to include in the output. For example, 6137 6138@smallexample 6139gcc -O2 -ftree-vectorize -fopt-info-vec-missed 6140@end smallexample 6141 6142will print information about missed optimization opportunities from 6143vectorization passes on stderr. 6144@item note 6145Print verbose information about optimizations, such as certain 6146transformations, more detailed messages about decisions etc. 6147@item all 6148Print detailed optimization information. This includes 6149@var{optimized}, @var{missed}, and @var{note}. 6150@end table 6151 6152The second set of options describes a group of optimizations and may 6153include one or more of the following. 6154 6155@table @samp 6156@item ipa 6157Enable dumps from all interprocedural optimizations. 6158@item loop 6159Enable dumps from all loop optimizations. 6160@item inline 6161Enable dumps from all inlining optimizations. 6162@item vec 6163Enable dumps from all vectorization optimizations. 6164@end table 6165 6166For example, 6167@smallexample 6168gcc -O3 -fopt-info-missed=missed.all 6169@end smallexample 6170 6171outputs missed optimization report from all the passes into 6172@file{missed.all}. 6173 6174As another example, 6175@smallexample 6176gcc -O3 -fopt-info-inline-optimized-missed=inline.txt 6177@end smallexample 6178 6179will output information about missed optimizations as well as 6180optimized locations from all the inlining passes into 6181@file{inline.txt}. 6182 6183If the @var{filename} is provided, then the dumps from all the 6184applicable optimizations are concatenated into the @file{filename}. 6185Otherwise the dump is output onto @file{stderr}. If @var{options} is 6186omitted, it defaults to @option{all-optall}, which means dump all 6187available optimization info from all the passes. In the following 6188example, all optimization info is output on to @file{stderr}. 6189 6190@smallexample 6191gcc -O3 -fopt-info 6192@end smallexample 6193 6194Note that @option{-fopt-info-vec-missed} behaves the same as 6195@option{-fopt-info-missed-vec}. 6196 6197As another example, consider 6198 6199@smallexample 6200gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt 6201@end smallexample 6202 6203Here the two output filenames @file{vec.miss} and @file{loop.opt} are 6204in conflict since only one output file is allowed. In this case, only 6205the first option takes effect and the subsequent options are 6206ignored. Thus only the @file{vec.miss} is produced which cotaints 6207dumps from the vectorizer about missed opportunities. 6208 6209@item -ftree-vectorizer-verbose=@var{n} 6210@opindex ftree-vectorizer-verbose 6211This option is deprecated and is implemented in terms of 6212@option{-fopt-info}. Please use @option{-fopt-info-@var{kind}} form 6213instead, where @var{kind} is one of the valid opt-info options. It 6214prints additional optimization information. For @var{n}=0 no 6215diagnostic information is reported. If @var{n}=1 the vectorizer 6216reports each loop that got vectorized, and the total number of loops 6217that got vectorized. If @var{n}=2 the vectorizer reports locations 6218which could not be vectorized and the reasons for those. For any 6219higher verbosity levels all the analysis and transformation 6220information from the vectorizer is reported. 6221 6222Note that the information output by @option{-ftree-vectorizer-verbose} 6223option is sent to @file{stderr}. If the equivalent form 6224@option{-fopt-info-@var{options}=@var{filename}} is used then the 6225output is sent into @var{filename} instead. 6226 6227@item -frandom-seed=@var{string} 6228@opindex frandom-seed 6229This option provides a seed that GCC uses in place of 6230random numbers in generating certain symbol names 6231that have to be different in every compiled file. It is also used to 6232place unique stamps in coverage data files and the object files that 6233produce them. You can use the @option{-frandom-seed} option to produce 6234reproducibly identical object files. 6235 6236The @var{string} should be different for every file you compile. 6237 6238@item -fsched-verbose=@var{n} 6239@opindex fsched-verbose 6240On targets that use instruction scheduling, this option controls the 6241amount of debugging output the scheduler prints. This information is 6242written to standard error, unless @option{-fdump-rtl-sched1} or 6243@option{-fdump-rtl-sched2} is specified, in which case it is output 6244to the usual dump listing file, @file{.sched1} or @file{.sched2} 6245respectively. However for @var{n} greater than nine, the output is 6246always printed to standard error. 6247 6248For @var{n} greater than zero, @option{-fsched-verbose} outputs the 6249same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}. 6250For @var{n} greater than one, it also output basic block probabilities, 6251detailed ready list information and unit/insn info. For @var{n} greater 6252than two, it includes RTL at abort point, control-flow and regions info. 6253And for @var{n} over four, @option{-fsched-verbose} also includes 6254dependence info. 6255 6256@item -save-temps 6257@itemx -save-temps=cwd 6258@opindex save-temps 6259Store the usual ``temporary'' intermediate files permanently; place them 6260in the current directory and name them based on the source file. Thus, 6261compiling @file{foo.c} with @option{-c -save-temps} produces files 6262@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a 6263preprocessed @file{foo.i} output file even though the compiler now 6264normally uses an integrated preprocessor. 6265 6266When used in combination with the @option{-x} command-line option, 6267@option{-save-temps} is sensible enough to avoid over writing an 6268input source file with the same extension as an intermediate file. 6269The corresponding intermediate file may be obtained by renaming the 6270source file before using @option{-save-temps}. 6271 6272If you invoke GCC in parallel, compiling several different source 6273files that share a common base name in different subdirectories or the 6274same source file compiled for multiple output destinations, it is 6275likely that the different parallel compilers will interfere with each 6276other, and overwrite the temporary files. For instance: 6277 6278@smallexample 6279gcc -save-temps -o outdir1/foo.o indir1/foo.c& 6280gcc -save-temps -o outdir2/foo.o indir2/foo.c& 6281@end smallexample 6282 6283may result in @file{foo.i} and @file{foo.o} being written to 6284simultaneously by both compilers. 6285 6286@item -save-temps=obj 6287@opindex save-temps=obj 6288Store the usual ``temporary'' intermediate files permanently. If the 6289@option{-o} option is used, the temporary files are based on the 6290object file. If the @option{-o} option is not used, the 6291@option{-save-temps=obj} switch behaves like @option{-save-temps}. 6292 6293For example: 6294 6295@smallexample 6296gcc -save-temps=obj -c foo.c 6297gcc -save-temps=obj -c bar.c -o dir/xbar.o 6298gcc -save-temps=obj foobar.c -o dir2/yfoobar 6299@end smallexample 6300 6301@noindent 6302creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i}, 6303@file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and 6304@file{dir2/yfoobar.o}. 6305 6306@item -time@r{[}=@var{file}@r{]} 6307@opindex time 6308Report the CPU time taken by each subprocess in the compilation 6309sequence. For C source files, this is the compiler proper and assembler 6310(plus the linker if linking is done). 6311 6312Without the specification of an output file, the output looks like this: 6313 6314@smallexample 6315# cc1 0.12 0.01 6316# as 0.00 0.01 6317@end smallexample 6318 6319The first number on each line is the ``user time'', that is time spent 6320executing the program itself. The second number is ``system time'', 6321time spent executing operating system routines on behalf of the program. 6322Both numbers are in seconds. 6323 6324With the specification of an output file, the output is appended to the 6325named file, and it looks like this: 6326 6327@smallexample 63280.12 0.01 cc1 @var{options} 63290.00 0.01 as @var{options} 6330@end smallexample 6331 6332The ``user time'' and the ``system time'' are moved before the program 6333name, and the options passed to the program are displayed, so that one 6334can later tell what file was being compiled, and with which options. 6335 6336@item -fvar-tracking 6337@opindex fvar-tracking 6338Run variable tracking pass. It computes where variables are stored at each 6339position in code. Better debugging information is then generated 6340(if the debugging information format supports this information). 6341 6342It is enabled by default when compiling with optimization (@option{-Os}, 6343@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and 6344the debug info format supports it. 6345 6346@item -fvar-tracking-assignments 6347@opindex fvar-tracking-assignments 6348@opindex fno-var-tracking-assignments 6349Annotate assignments to user variables early in the compilation and 6350attempt to carry the annotations over throughout the compilation all the 6351way to the end, in an attempt to improve debug information while 6352optimizing. Use of @option{-gdwarf-4} is recommended along with it. 6353 6354It can be enabled even if var-tracking is disabled, in which case 6355annotations are created and maintained, but discarded at the end. 6356 6357@item -fvar-tracking-assignments-toggle 6358@opindex fvar-tracking-assignments-toggle 6359@opindex fno-var-tracking-assignments-toggle 6360Toggle @option{-fvar-tracking-assignments}, in the same way that 6361@option{-gtoggle} toggles @option{-g}. 6362 6363@item -print-file-name=@var{library} 6364@opindex print-file-name 6365Print the full absolute name of the library file @var{library} that 6366would be used when linking---and don't do anything else. With this 6367option, GCC does not compile or link anything; it just prints the 6368file name. 6369 6370@item -print-multi-directory 6371@opindex print-multi-directory 6372Print the directory name corresponding to the multilib selected by any 6373other switches present in the command line. This directory is supposed 6374to exist in @env{GCC_EXEC_PREFIX}. 6375 6376@item -print-multi-lib 6377@opindex print-multi-lib 6378Print the mapping from multilib directory names to compiler switches 6379that enable them. The directory name is separated from the switches by 6380@samp{;}, and each switch starts with an @samp{@@} instead of the 6381@samp{-}, without spaces between multiple switches. This is supposed to 6382ease shell processing. 6383 6384@item -print-multi-os-directory 6385@opindex print-multi-os-directory 6386Print the path to OS libraries for the selected 6387multilib, relative to some @file{lib} subdirectory. If OS libraries are 6388present in the @file{lib} subdirectory and no multilibs are used, this is 6389usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}} 6390sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or 6391@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}} 6392subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}. 6393 6394@item -print-multiarch 6395@opindex print-multiarch 6396Print the path to OS libraries for the selected multiarch, 6397relative to some @file{lib} subdirectory. 6398 6399@item -print-prog-name=@var{program} 6400@opindex print-prog-name 6401Like @option{-print-file-name}, but searches for a program such as @samp{cpp}. 6402 6403@item -print-libgcc-file-name 6404@opindex print-libgcc-file-name 6405Same as @option{-print-file-name=libgcc.a}. 6406 6407This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} 6408but you do want to link with @file{libgcc.a}. You can do: 6409 6410@smallexample 6411gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` 6412@end smallexample 6413 6414@item -print-search-dirs 6415@opindex print-search-dirs 6416Print the name of the configured installation directory and a list of 6417program and library directories @command{gcc} searches---and don't do anything else. 6418 6419This is useful when @command{gcc} prints the error message 6420@samp{installation problem, cannot exec cpp0: No such file or directory}. 6421To resolve this you either need to put @file{cpp0} and the other compiler 6422components where @command{gcc} expects to find them, or you can set the environment 6423variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. 6424Don't forget the trailing @samp{/}. 6425@xref{Environment Variables}. 6426 6427@item -print-sysroot 6428@opindex print-sysroot 6429Print the target sysroot directory that is used during 6430compilation. This is the target sysroot specified either at configure 6431time or using the @option{--sysroot} option, possibly with an extra 6432suffix that depends on compilation options. If no target sysroot is 6433specified, the option prints nothing. 6434 6435@item -print-sysroot-headers-suffix 6436@opindex print-sysroot-headers-suffix 6437Print the suffix added to the target sysroot when searching for 6438headers, or give an error if the compiler is not configured with such 6439a suffix---and don't do anything else. 6440 6441@item -dumpmachine 6442@opindex dumpmachine 6443Print the compiler's target machine (for example, 6444@samp{i686-pc-linux-gnu})---and don't do anything else. 6445 6446@item -dumpversion 6447@opindex dumpversion 6448Print the compiler version (for example, @samp{3.0})---and don't do 6449anything else. 6450 6451@item -dumpspecs 6452@opindex dumpspecs 6453Print the compiler's built-in specs---and don't do anything else. (This 6454is used when GCC itself is being built.) @xref{Spec Files}. 6455 6456@item -fno-eliminate-unused-debug-types 6457@opindex feliminate-unused-debug-types 6458@opindex fno-eliminate-unused-debug-types 6459Normally, when producing DWARF 2 output, GCC avoids producing debug symbol 6460output for types that are nowhere used in the source file being compiled. 6461Sometimes it is useful to have GCC emit debugging 6462information for all types declared in a compilation 6463unit, regardless of whether or not they are actually used 6464in that compilation unit, for example 6465if, in the debugger, you want to cast a value to a type that is 6466not actually used in your program (but is declared). More often, 6467however, this results in a significant amount of wasted space. 6468@end table 6469 6470@node Optimize Options 6471@section Options That Control Optimization 6472@cindex optimize options 6473@cindex options, optimization 6474 6475These options control various sorts of optimizations. 6476 6477Without any optimization option, the compiler's goal is to reduce the 6478cost of compilation and to make debugging produce the expected 6479results. Statements are independent: if you stop the program with a 6480breakpoint between statements, you can then assign a new value to any 6481variable or change the program counter to any other statement in the 6482function and get exactly the results you expect from the source 6483code. 6484 6485Turning on optimization flags makes the compiler attempt to improve 6486the performance and/or code size at the expense of compilation time 6487and possibly the ability to debug the program. 6488 6489The compiler performs optimization based on the knowledge it has of the 6490program. Compiling multiple files at once to a single output file mode allows 6491the compiler to use information gained from all of the files when compiling 6492each of them. 6493 6494Not all optimizations are controlled directly by a flag. Only 6495optimizations that have a flag are listed in this section. 6496 6497Most optimizations are only enabled if an @option{-O} level is set on 6498the command line. Otherwise they are disabled, even if individual 6499optimization flags are specified. 6500 6501Depending on the target and how GCC was configured, a slightly different 6502set of optimizations may be enabled at each @option{-O} level than 6503those listed here. You can invoke GCC with @option{-Q --help=optimizers} 6504to find out the exact set of optimizations that are enabled at each level. 6505@xref{Overall Options}, for examples. 6506 6507@table @gcctabopt 6508@item -O 6509@itemx -O1 6510@opindex O 6511@opindex O1 6512Optimize. Optimizing compilation takes somewhat more time, and a lot 6513more memory for a large function. 6514 6515With @option{-O}, the compiler tries to reduce code size and execution 6516time, without performing any optimizations that take a great deal of 6517compilation time. 6518 6519@option{-O} turns on the following optimization flags: 6520@gccoptlist{ 6521-fauto-inc-dec @gol 6522-fcompare-elim @gol 6523-fcprop-registers @gol 6524-fdce @gol 6525-fdefer-pop @gol 6526-fdelayed-branch @gol 6527-fdse @gol 6528-fguess-branch-probability @gol 6529-fif-conversion2 @gol 6530-fif-conversion @gol 6531-fipa-pure-const @gol 6532-fipa-profile @gol 6533-fipa-reference @gol 6534-fmerge-constants 6535-fsplit-wide-types @gol 6536-ftree-bit-ccp @gol 6537-ftree-builtin-call-dce @gol 6538-ftree-ccp @gol 6539-ftree-ch @gol 6540-ftree-copyrename @gol 6541-ftree-dce @gol 6542-ftree-dominator-opts @gol 6543-ftree-dse @gol 6544-ftree-forwprop @gol 6545-ftree-fre @gol 6546-ftree-phiprop @gol 6547-ftree-slsr @gol 6548-ftree-sra @gol 6549-ftree-pta @gol 6550-ftree-ter @gol 6551-funit-at-a-time} 6552 6553@option{-O} also turns on @option{-fomit-frame-pointer} on machines 6554where doing so does not interfere with debugging. 6555 6556@item -O2 6557@opindex O2 6558Optimize even more. GCC performs nearly all supported optimizations 6559that do not involve a space-speed tradeoff. 6560As compared to @option{-O}, this option increases both compilation time 6561and the performance of the generated code. 6562 6563@option{-O2} turns on all optimization flags specified by @option{-O}. It 6564also turns on the following optimization flags: 6565@gccoptlist{-fthread-jumps @gol 6566-falign-functions -falign-jumps @gol 6567-falign-loops -falign-labels @gol 6568-fcaller-saves @gol 6569-fcrossjumping @gol 6570-fcse-follow-jumps -fcse-skip-blocks @gol 6571-fdelete-null-pointer-checks @gol 6572-fdevirtualize @gol 6573-fexpensive-optimizations @gol 6574-fgcse -fgcse-lm @gol 6575-fhoist-adjacent-loads @gol 6576-finline-small-functions @gol 6577-findirect-inlining @gol 6578-fipa-sra @gol 6579-foptimize-sibling-calls @gol 6580-fpartial-inlining @gol 6581-fpeephole2 @gol 6582-fregmove @gol 6583-freorder-blocks -freorder-functions @gol 6584-frerun-cse-after-loop @gol 6585-fsched-interblock -fsched-spec @gol 6586-fschedule-insns -fschedule-insns2 @gol 6587-fstrict-aliasing -fstrict-overflow @gol 6588-ftree-switch-conversion -ftree-tail-merge @gol 6589-ftree-pre @gol 6590-ftree-vrp} 6591 6592Please note the warning under @option{-fgcse} about 6593invoking @option{-O2} on programs that use computed gotos. 6594 6595@item -O3 6596@opindex O3 6597Optimize yet more. @option{-O3} turns on all optimizations specified 6598by @option{-O2} and also turns on the @option{-finline-functions}, 6599@option{-funswitch-loops}, @option{-fpredictive-commoning}, 6600@option{-fgcse-after-reload}, @option{-ftree-vectorize}, 6601@option{-fvect-cost-model}, 6602@option{-ftree-partial-pre} and @option{-fipa-cp-clone} options. 6603 6604@item -O0 6605@opindex O0 6606Reduce compilation time and make debugging produce the expected 6607results. This is the default. 6608 6609@item -Os 6610@opindex Os 6611Optimize for size. @option{-Os} enables all @option{-O2} optimizations that 6612do not typically increase code size. It also performs further 6613optimizations designed to reduce code size. 6614 6615@option{-Os} disables the following optimization flags: 6616@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol 6617-falign-labels -freorder-blocks -freorder-blocks-and-partition @gol 6618-fprefetch-loop-arrays -ftree-vect-loop-version} 6619 6620@item -Ofast 6621@opindex Ofast 6622Disregard strict standards compliance. @option{-Ofast} enables all 6623@option{-O3} optimizations. It also enables optimizations that are not 6624valid for all standard-compliant programs. 6625It turns on @option{-ffast-math} and the Fortran-specific 6626@option{-fno-protect-parens} and @option{-fstack-arrays}. 6627 6628@item -Og 6629@opindex Og 6630Optimize debugging experience. @option{-Og} enables optimizations 6631that do not interfere with debugging. It should be the optimization 6632level of choice for the standard edit-compile-debug cycle, offering 6633a reasonable level of optimization while maintaining fast compilation 6634and a good debugging experience. 6635 6636If you use multiple @option{-O} options, with or without level numbers, 6637the last such option is the one that is effective. 6638@end table 6639 6640Options of the form @option{-f@var{flag}} specify machine-independent 6641flags. Most flags have both positive and negative forms; the negative 6642form of @option{-ffoo} is @option{-fno-foo}. In the table 6643below, only one of the forms is listed---the one you typically 6644use. You can figure out the other form by either removing @samp{no-} 6645or adding it. 6646 6647The following options control specific optimizations. They are either 6648activated by @option{-O} options or are related to ones that are. You 6649can use the following flags in the rare cases when ``fine-tuning'' of 6650optimizations to be performed is desired. 6651 6652@table @gcctabopt 6653@item -fno-default-inline 6654@opindex fno-default-inline 6655Do not make member functions inline by default merely because they are 6656defined inside the class scope (C++ only). Otherwise, when you specify 6657@w{@option{-O}}, member functions defined inside class scope are compiled 6658inline by default; i.e., you don't need to add @samp{inline} in front of 6659the member function name. 6660 6661@item -fno-defer-pop 6662@opindex fno-defer-pop 6663Always pop the arguments to each function call as soon as that function 6664returns. For machines that must pop arguments after a function call, 6665the compiler normally lets arguments accumulate on the stack for several 6666function calls and pops them all at once. 6667 6668Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 6669 6670@item -fforward-propagate 6671@opindex fforward-propagate 6672Perform a forward propagation pass on RTL@. The pass tries to combine two 6673instructions and checks if the result can be simplified. If loop unrolling 6674is active, two passes are performed and the second is scheduled after 6675loop unrolling. 6676 6677This option is enabled by default at optimization levels @option{-O}, 6678@option{-O2}, @option{-O3}, @option{-Os}. 6679 6680@item -ffp-contract=@var{style} 6681@opindex ffp-contract 6682@option{-ffp-contract=off} disables floating-point expression contraction. 6683@option{-ffp-contract=fast} enables floating-point expression contraction 6684such as forming of fused multiply-add operations if the target has 6685native support for them. 6686@option{-ffp-contract=on} enables floating-point expression contraction 6687if allowed by the language standard. This is currently not implemented 6688and treated equal to @option{-ffp-contract=off}. 6689 6690The default is @option{-ffp-contract=fast}. 6691 6692@item -fomit-frame-pointer 6693@opindex fomit-frame-pointer 6694Don't keep the frame pointer in a register for functions that 6695don't need one. This avoids the instructions to save, set up and 6696restore frame pointers; it also makes an extra register available 6697in many functions. @strong{It also makes debugging impossible on 6698some machines.} 6699 6700On some machines, such as the VAX, this flag has no effect, because 6701the standard calling sequence automatically handles the frame pointer 6702and nothing is saved by pretending it doesn't exist. The 6703machine-description macro @code{FRAME_POINTER_REQUIRED} controls 6704whether a target machine supports this flag. @xref{Registers,,Register 6705Usage, gccint, GNU Compiler Collection (GCC) Internals}. 6706 6707Starting with GCC version 4.6, the default setting (when not optimizing for 6708size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets has been changed to 6709@option{-fomit-frame-pointer}. The default can be reverted to 6710@option{-fno-omit-frame-pointer} by configuring GCC with the 6711@option{--enable-frame-pointer} configure option. 6712 6713Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 6714 6715@item -foptimize-sibling-calls 6716@opindex foptimize-sibling-calls 6717Optimize sibling and tail recursive calls. 6718 6719Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 6720 6721@item -fno-inline 6722@opindex fno-inline 6723Do not expand any functions inline apart from those marked with 6724the @code{always_inline} attribute. This is the default when not 6725optimizing. 6726 6727Single functions can be exempted from inlining by marking them 6728with the @code{noinline} attribute. 6729 6730@item -finline-small-functions 6731@opindex finline-small-functions 6732Integrate functions into their callers when their body is smaller than expected 6733function call code (so overall size of program gets smaller). The compiler 6734heuristically decides which functions are simple enough to be worth integrating 6735in this way. This inlining applies to all functions, even those not declared 6736inline. 6737 6738Enabled at level @option{-O2}. 6739 6740@item -findirect-inlining 6741@opindex findirect-inlining 6742Inline also indirect calls that are discovered to be known at compile 6743time thanks to previous inlining. This option has any effect only 6744when inlining itself is turned on by the @option{-finline-functions} 6745or @option{-finline-small-functions} options. 6746 6747Enabled at level @option{-O2}. 6748 6749@item -finline-functions 6750@opindex finline-functions 6751Consider all functions for inlining, even if they are not declared inline. 6752The compiler heuristically decides which functions are worth integrating 6753in this way. 6754 6755If all calls to a given function are integrated, and the function is 6756declared @code{static}, then the function is normally not output as 6757assembler code in its own right. 6758 6759Enabled at level @option{-O3}. 6760 6761@item -finline-functions-called-once 6762@opindex finline-functions-called-once 6763Consider all @code{static} functions called once for inlining into their 6764caller even if they are not marked @code{inline}. If a call to a given 6765function is integrated, then the function is not output as assembler code 6766in its own right. 6767 6768Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}. 6769 6770@item -fearly-inlining 6771@opindex fearly-inlining 6772Inline functions marked by @code{always_inline} and functions whose body seems 6773smaller than the function call overhead early before doing 6774@option{-fprofile-generate} instrumentation and real inlining pass. Doing so 6775makes profiling significantly cheaper and usually inlining faster on programs 6776having large chains of nested wrapper functions. 6777 6778Enabled by default. 6779 6780@item -fipa-sra 6781@opindex fipa-sra 6782Perform interprocedural scalar replacement of aggregates, removal of 6783unused parameters and replacement of parameters passed by reference 6784by parameters passed by value. 6785 6786Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}. 6787 6788@item -finline-limit=@var{n} 6789@opindex finline-limit 6790By default, GCC limits the size of functions that can be inlined. This flag 6791allows coarse control of this limit. @var{n} is the size of functions that 6792can be inlined in number of pseudo instructions. 6793 6794Inlining is actually controlled by a number of parameters, which may be 6795specified individually by using @option{--param @var{name}=@var{value}}. 6796The @option{-finline-limit=@var{n}} option sets some of these parameters 6797as follows: 6798 6799@table @gcctabopt 6800@item max-inline-insns-single 6801is set to @var{n}/2. 6802@item max-inline-insns-auto 6803is set to @var{n}/2. 6804@end table 6805 6806See below for a documentation of the individual 6807parameters controlling inlining and for the defaults of these parameters. 6808 6809@emph{Note:} there may be no value to @option{-finline-limit} that results 6810in default behavior. 6811 6812@emph{Note:} pseudo instruction represents, in this particular context, an 6813abstract measurement of function's size. In no way does it represent a count 6814of assembly instructions and as such its exact meaning might change from one 6815release to an another. 6816 6817@item -fno-keep-inline-dllexport 6818@opindex -fno-keep-inline-dllexport 6819This is a more fine-grained version of @option{-fkeep-inline-functions}, 6820which applies only to functions that are declared using the @code{dllexport} 6821attribute or declspec (@xref{Function Attributes,,Declaring Attributes of 6822Functions}.) 6823 6824@item -fkeep-inline-functions 6825@opindex fkeep-inline-functions 6826In C, emit @code{static} functions that are declared @code{inline} 6827into the object file, even if the function has been inlined into all 6828of its callers. This switch does not affect functions using the 6829@code{extern inline} extension in GNU C90@. In C++, emit any and all 6830inline functions into the object file. 6831 6832@item -fkeep-static-consts 6833@opindex fkeep-static-consts 6834Emit variables declared @code{static const} when optimization isn't turned 6835on, even if the variables aren't referenced. 6836 6837GCC enables this option by default. If you want to force the compiler to 6838check if a variable is referenced, regardless of whether or not 6839optimization is turned on, use the @option{-fno-keep-static-consts} option. 6840 6841@item -fmerge-constants 6842@opindex fmerge-constants 6843Attempt to merge identical constants (string constants and floating-point 6844constants) across compilation units. 6845 6846This option is the default for optimized compilation if the assembler and 6847linker support it. Use @option{-fno-merge-constants} to inhibit this 6848behavior. 6849 6850Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 6851 6852@item -fmerge-all-constants 6853@opindex fmerge-all-constants 6854Attempt to merge identical constants and identical variables. 6855 6856This option implies @option{-fmerge-constants}. In addition to 6857@option{-fmerge-constants} this considers e.g.@: even constant initialized 6858arrays or initialized constant variables with integral or floating-point 6859types. Languages like C or C++ require each variable, including multiple 6860instances of the same variable in recursive calls, to have distinct locations, 6861so using this option results in non-conforming 6862behavior. 6863 6864@item -fmodulo-sched 6865@opindex fmodulo-sched 6866Perform swing modulo scheduling immediately before the first scheduling 6867pass. This pass looks at innermost loops and reorders their 6868instructions by overlapping different iterations. 6869 6870@item -fmodulo-sched-allow-regmoves 6871@opindex fmodulo-sched-allow-regmoves 6872Perform more aggressive SMS-based modulo scheduling with register moves 6873allowed. By setting this flag certain anti-dependences edges are 6874deleted, which triggers the generation of reg-moves based on the 6875life-range analysis. This option is effective only with 6876@option{-fmodulo-sched} enabled. 6877 6878@item -fno-branch-count-reg 6879@opindex fno-branch-count-reg 6880Do not use ``decrement and branch'' instructions on a count register, 6881but instead generate a sequence of instructions that decrement a 6882register, compare it against zero, then branch based upon the result. 6883This option is only meaningful on architectures that support such 6884instructions, which include x86, PowerPC, IA-64 and S/390. 6885 6886The default is @option{-fbranch-count-reg}. 6887 6888@item -fno-function-cse 6889@opindex fno-function-cse 6890Do not put function addresses in registers; make each instruction that 6891calls a constant function contain the function's address explicitly. 6892 6893This option results in less efficient code, but some strange hacks 6894that alter the assembler output may be confused by the optimizations 6895performed when this option is not used. 6896 6897The default is @option{-ffunction-cse} 6898 6899@item -fno-zero-initialized-in-bss 6900@opindex fno-zero-initialized-in-bss 6901If the target supports a BSS section, GCC by default puts variables that 6902are initialized to zero into BSS@. This can save space in the resulting 6903code. 6904 6905This option turns off this behavior because some programs explicitly 6906rely on variables going to the data section---e.g., so that the 6907resulting executable can find the beginning of that section and/or make 6908assumptions based on that. 6909 6910The default is @option{-fzero-initialized-in-bss}. 6911 6912@item -fmudflap -fmudflapth -fmudflapir 6913@opindex fmudflap 6914@opindex fmudflapth 6915@opindex fmudflapir 6916@cindex bounds checking 6917@cindex mudflap 6918For front-ends that support it (C and C++), instrument all risky 6919pointer/array dereferencing operations, some standard library 6920string/heap functions, and some other associated constructs with 6921range/validity tests. Modules so instrumented should be immune to 6922buffer overflows, invalid heap use, and some other classes of C/C++ 6923programming errors. The instrumentation relies on a separate runtime 6924library (@file{libmudflap}), which is linked into a program if 6925@option{-fmudflap} is given at link time. Run-time behavior of the 6926instrumented program is controlled by the @env{MUDFLAP_OPTIONS} 6927environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out} 6928for its options. 6929 6930Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to 6931link if your program is multi-threaded. Use @option{-fmudflapir}, in 6932addition to @option{-fmudflap} or @option{-fmudflapth}, if 6933instrumentation should ignore pointer reads. This produces less 6934instrumentation (and therefore faster execution) and still provides 6935some protection against outright memory corrupting writes, but allows 6936erroneously read data to propagate within a program. 6937 6938@item -fthread-jumps 6939@opindex fthread-jumps 6940Perform optimizations that check to see if a jump branches to a 6941location where another comparison subsumed by the first is found. If 6942so, the first branch is redirected to either the destination of the 6943second branch or a point immediately following it, depending on whether 6944the condition is known to be true or false. 6945 6946Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 6947 6948@item -fsplit-wide-types 6949@opindex fsplit-wide-types 6950When using a type that occupies multiple registers, such as @code{long 6951long} on a 32-bit system, split the registers apart and allocate them 6952independently. This normally generates better code for those types, 6953but may make debugging more difficult. 6954 6955Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, 6956@option{-Os}. 6957 6958@item -fcse-follow-jumps 6959@opindex fcse-follow-jumps 6960In common subexpression elimination (CSE), scan through jump instructions 6961when the target of the jump is not reached by any other path. For 6962example, when CSE encounters an @code{if} statement with an 6963@code{else} clause, CSE follows the jump when the condition 6964tested is false. 6965 6966Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 6967 6968@item -fcse-skip-blocks 6969@opindex fcse-skip-blocks 6970This is similar to @option{-fcse-follow-jumps}, but causes CSE to 6971follow jumps that conditionally skip over blocks. When CSE 6972encounters a simple @code{if} statement with no else clause, 6973@option{-fcse-skip-blocks} causes CSE to follow the jump around the 6974body of the @code{if}. 6975 6976Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 6977 6978@item -frerun-cse-after-loop 6979@opindex frerun-cse-after-loop 6980Re-run common subexpression elimination after loop optimizations are 6981performed. 6982 6983Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 6984 6985@item -fgcse 6986@opindex fgcse 6987Perform a global common subexpression elimination pass. 6988This pass also performs global constant and copy propagation. 6989 6990@emph{Note:} When compiling a program using computed gotos, a GCC 6991extension, you may get better run-time performance if you disable 6992the global common subexpression elimination pass by adding 6993@option{-fno-gcse} to the command line. 6994 6995Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 6996 6997@item -fgcse-lm 6998@opindex fgcse-lm 6999When @option{-fgcse-lm} is enabled, global common subexpression elimination 7000attempts to move loads that are only killed by stores into themselves. This 7001allows a loop containing a load/store sequence to be changed to a load outside 7002the loop, and a copy/store within the loop. 7003 7004Enabled by default when @option{-fgcse} is enabled. 7005 7006@item -fgcse-sm 7007@opindex fgcse-sm 7008When @option{-fgcse-sm} is enabled, a store motion pass is run after 7009global common subexpression elimination. This pass attempts to move 7010stores out of loops. When used in conjunction with @option{-fgcse-lm}, 7011loops containing a load/store sequence can be changed to a load before 7012the loop and a store after the loop. 7013 7014Not enabled at any optimization level. 7015 7016@item -fgcse-las 7017@opindex fgcse-las 7018When @option{-fgcse-las} is enabled, the global common subexpression 7019elimination pass eliminates redundant loads that come after stores to the 7020same memory location (both partial and full redundancies). 7021 7022Not enabled at any optimization level. 7023 7024@item -fgcse-after-reload 7025@opindex fgcse-after-reload 7026When @option{-fgcse-after-reload} is enabled, a redundant load elimination 7027pass is performed after reload. The purpose of this pass is to clean up 7028redundant spilling. 7029 7030@item -faggressive-loop-optimizations 7031@opindex faggressive-loop-optimizations 7032This option tells the loop optimizer to use language constraints to 7033derive bounds for the number of iterations of a loop. This assumes that 7034loop code does not invoke undefined behavior by for example causing signed 7035integer overflows or out-of-bound array accesses. The bounds for the 7036number of iterations of a loop are used to guide loop unrolling and peeling 7037and loop exit test optimizations. 7038This option is enabled by default. 7039 7040@item -funsafe-loop-optimizations 7041@opindex funsafe-loop-optimizations 7042This option tells the loop optimizer to assume that loop indices do not 7043overflow, and that loops with nontrivial exit condition are not 7044infinite. This enables a wider range of loop optimizations even if 7045the loop optimizer itself cannot prove that these assumptions are valid. 7046If you use @option{-Wunsafe-loop-optimizations}, the compiler warns you 7047if it finds this kind of loop. 7048 7049@item -fcrossjumping 7050@opindex fcrossjumping 7051Perform cross-jumping transformation. 7052This transformation unifies equivalent code and saves code size. The 7053resulting code may or may not perform better than without cross-jumping. 7054 7055Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 7056 7057@item -fauto-inc-dec 7058@opindex fauto-inc-dec 7059Combine increments or decrements of addresses with memory accesses. 7060This pass is always skipped on architectures that do not have 7061instructions to support this. Enabled by default at @option{-O} and 7062higher on architectures that support this. 7063 7064@item -fdce 7065@opindex fdce 7066Perform dead code elimination (DCE) on RTL@. 7067Enabled by default at @option{-O} and higher. 7068 7069@item -fdse 7070@opindex fdse 7071Perform dead store elimination (DSE) on RTL@. 7072Enabled by default at @option{-O} and higher. 7073 7074@item -fif-conversion 7075@opindex fif-conversion 7076Attempt to transform conditional jumps into branch-less equivalents. This 7077includes use of conditional moves, min, max, set flags and abs instructions, and 7078some tricks doable by standard arithmetics. The use of conditional execution 7079on chips where it is available is controlled by @code{if-conversion2}. 7080 7081Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 7082 7083@item -fif-conversion2 7084@opindex fif-conversion2 7085Use conditional execution (where available) to transform conditional jumps into 7086branch-less equivalents. 7087 7088Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 7089 7090@item -fdelete-null-pointer-checks 7091@opindex fdelete-null-pointer-checks 7092Assume that programs cannot safely dereference null pointers, and that 7093no code or data element resides there. This enables simple constant 7094folding optimizations at all optimization levels. In addition, other 7095optimization passes in GCC use this flag to control global dataflow 7096analyses that eliminate useless checks for null pointers; these assume 7097that if a pointer is checked after it has already been dereferenced, 7098it cannot be null. 7099 7100Note however that in some environments this assumption is not true. 7101Use @option{-fno-delete-null-pointer-checks} to disable this optimization 7102for programs that depend on that behavior. 7103 7104Some targets, especially embedded ones, disable this option at all levels. 7105Otherwise it is enabled at all levels: @option{-O0}, @option{-O1}, 7106@option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information 7107are enabled independently at different optimization levels. 7108 7109@item -fdevirtualize 7110@opindex fdevirtualize 7111Attempt to convert calls to virtual functions to direct calls. This 7112is done both within a procedure and interprocedurally as part of 7113indirect inlining (@code{-findirect-inlining}) and interprocedural constant 7114propagation (@option{-fipa-cp}). 7115Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 7116 7117@item -fexpensive-optimizations 7118@opindex fexpensive-optimizations 7119Perform a number of minor optimizations that are relatively expensive. 7120 7121Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 7122 7123@item -free 7124@opindex free 7125Attempt to remove redundant extension instructions. This is especially 7126helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit 7127registers after writing to their lower 32-bit half. 7128 7129Enabled for x86 at levels @option{-O2}, @option{-O3}. 7130 7131@item -foptimize-register-move 7132@itemx -fregmove 7133@opindex foptimize-register-move 7134@opindex fregmove 7135Attempt to reassign register numbers in move instructions and as 7136operands of other simple instructions in order to maximize the amount of 7137register tying. This is especially helpful on machines with two-operand 7138instructions. 7139 7140Note @option{-fregmove} and @option{-foptimize-register-move} are the same 7141optimization. 7142 7143Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 7144 7145@item -fira-algorithm=@var{algorithm} 7146Use the specified coloring algorithm for the integrated register 7147allocator. The @var{algorithm} argument can be @samp{priority}, which 7148specifies Chow's priority coloring, or @samp{CB}, which specifies 7149Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented 7150for all architectures, but for those targets that do support it, it is 7151the default because it generates better code. 7152 7153@item -fira-region=@var{region} 7154Use specified regions for the integrated register allocator. The 7155@var{region} argument should be one of the following: 7156 7157@table @samp 7158 7159@item all 7160Use all loops as register allocation regions. 7161This can give the best results for machines with a small and/or 7162irregular register set. 7163 7164@item mixed 7165Use all loops except for loops with small register pressure 7166as the regions. This value usually gives 7167the best results in most cases and for most architectures, 7168and is enabled by default when compiling with optimization for speed 7169(@option{-O}, @option{-O2}, @dots{}). 7170 7171@item one 7172Use all functions as a single region. 7173This typically results in the smallest code size, and is enabled by default for 7174@option{-Os} or @option{-O0}. 7175 7176@end table 7177 7178@item -fira-hoist-pressure 7179@opindex fira-hoist-pressure 7180Use IRA to evaluate register pressure in the code hoisting pass for 7181decisions to hoist expressions. This option usually results in smaller 7182code, but it can slow the compiler down. 7183 7184This option is enabled at level @option{-Os} for all targets. 7185 7186@item -fira-loop-pressure 7187@opindex fira-loop-pressure 7188Use IRA to evaluate register pressure in loops for decisions to move 7189loop invariants. This option usually results in generation 7190of faster and smaller code on machines with large register files (>= 32 7191registers), but it can slow the compiler down. 7192 7193This option is enabled at level @option{-O3} for some targets. 7194 7195@item -fno-ira-share-save-slots 7196@opindex fno-ira-share-save-slots 7197Disable sharing of stack slots used for saving call-used hard 7198registers living through a call. Each hard register gets a 7199separate stack slot, and as a result function stack frames are 7200larger. 7201 7202@item -fno-ira-share-spill-slots 7203@opindex fno-ira-share-spill-slots 7204Disable sharing of stack slots allocated for pseudo-registers. Each 7205pseudo-register that does not get a hard register gets a separate 7206stack slot, and as a result function stack frames are larger. 7207 7208@item -fira-verbose=@var{n} 7209@opindex fira-verbose 7210Control the verbosity of the dump file for the integrated register allocator. 7211The default value is 5. If the value @var{n} is greater or equal to 10, 7212the dump output is sent to stderr using the same format as @var{n} minus 10. 7213 7214@item -fdelayed-branch 7215@opindex fdelayed-branch 7216If supported for the target machine, attempt to reorder instructions 7217to exploit instruction slots available after delayed branch 7218instructions. 7219 7220Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 7221 7222@item -fschedule-insns 7223@opindex fschedule-insns 7224If supported for the target machine, attempt to reorder instructions to 7225eliminate execution stalls due to required data being unavailable. This 7226helps machines that have slow floating point or memory load instructions 7227by allowing other instructions to be issued until the result of the load 7228or floating-point instruction is required. 7229 7230Enabled at levels @option{-O2}, @option{-O3}. 7231 7232@item -fschedule-insns2 7233@opindex fschedule-insns2 7234Similar to @option{-fschedule-insns}, but requests an additional pass of 7235instruction scheduling after register allocation has been done. This is 7236especially useful on machines with a relatively small number of 7237registers and where memory load instructions take more than one cycle. 7238 7239Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 7240 7241@item -fno-sched-interblock 7242@opindex fno-sched-interblock 7243Don't schedule instructions across basic blocks. This is normally 7244enabled by default when scheduling before register allocation, i.e.@: 7245with @option{-fschedule-insns} or at @option{-O2} or higher. 7246 7247@item -fno-sched-spec 7248@opindex fno-sched-spec 7249Don't allow speculative motion of non-load instructions. This is normally 7250enabled by default when scheduling before register allocation, i.e.@: 7251with @option{-fschedule-insns} or at @option{-O2} or higher. 7252 7253@item -fsched-pressure 7254@opindex fsched-pressure 7255Enable register pressure sensitive insn scheduling before register 7256allocation. This only makes sense when scheduling before register 7257allocation is enabled, i.e.@: with @option{-fschedule-insns} or at 7258@option{-O2} or higher. Usage of this option can improve the 7259generated code and decrease its size by preventing register pressure 7260increase above the number of available hard registers and subsequent 7261spills in register allocation. 7262 7263@item -fsched-spec-load 7264@opindex fsched-spec-load 7265Allow speculative motion of some load instructions. This only makes 7266sense when scheduling before register allocation, i.e.@: with 7267@option{-fschedule-insns} or at @option{-O2} or higher. 7268 7269@item -fsched-spec-load-dangerous 7270@opindex fsched-spec-load-dangerous 7271Allow speculative motion of more load instructions. This only makes 7272sense when scheduling before register allocation, i.e.@: with 7273@option{-fschedule-insns} or at @option{-O2} or higher. 7274 7275@item -fsched-stalled-insns 7276@itemx -fsched-stalled-insns=@var{n} 7277@opindex fsched-stalled-insns 7278Define how many insns (if any) can be moved prematurely from the queue 7279of stalled insns into the ready list during the second scheduling pass. 7280@option{-fno-sched-stalled-insns} means that no insns are moved 7281prematurely, @option{-fsched-stalled-insns=0} means there is no limit 7282on how many queued insns can be moved prematurely. 7283@option{-fsched-stalled-insns} without a value is equivalent to 7284@option{-fsched-stalled-insns=1}. 7285 7286@item -fsched-stalled-insns-dep 7287@itemx -fsched-stalled-insns-dep=@var{n} 7288@opindex fsched-stalled-insns-dep 7289Define how many insn groups (cycles) are examined for a dependency 7290on a stalled insn that is a candidate for premature removal from the queue 7291of stalled insns. This has an effect only during the second scheduling pass, 7292and only if @option{-fsched-stalled-insns} is used. 7293@option{-fno-sched-stalled-insns-dep} is equivalent to 7294@option{-fsched-stalled-insns-dep=0}. 7295@option{-fsched-stalled-insns-dep} without a value is equivalent to 7296@option{-fsched-stalled-insns-dep=1}. 7297 7298@item -fsched2-use-superblocks 7299@opindex fsched2-use-superblocks 7300When scheduling after register allocation, use superblock scheduling. 7301This allows motion across basic block boundaries, 7302resulting in faster schedules. This option is experimental, as not all machine 7303descriptions used by GCC model the CPU closely enough to avoid unreliable 7304results from the algorithm. 7305 7306This only makes sense when scheduling after register allocation, i.e.@: with 7307@option{-fschedule-insns2} or at @option{-O2} or higher. 7308 7309@item -fsched-group-heuristic 7310@opindex fsched-group-heuristic 7311Enable the group heuristic in the scheduler. This heuristic favors 7312the instruction that belongs to a schedule group. This is enabled 7313by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} 7314or @option{-fschedule-insns2} or at @option{-O2} or higher. 7315 7316@item -fsched-critical-path-heuristic 7317@opindex fsched-critical-path-heuristic 7318Enable the critical-path heuristic in the scheduler. This heuristic favors 7319instructions on the critical path. This is enabled by default when 7320scheduling is enabled, i.e.@: with @option{-fschedule-insns} 7321or @option{-fschedule-insns2} or at @option{-O2} or higher. 7322 7323@item -fsched-spec-insn-heuristic 7324@opindex fsched-spec-insn-heuristic 7325Enable the speculative instruction heuristic in the scheduler. This 7326heuristic favors speculative instructions with greater dependency weakness. 7327This is enabled by default when scheduling is enabled, i.e.@: 7328with @option{-fschedule-insns} or @option{-fschedule-insns2} 7329or at @option{-O2} or higher. 7330 7331@item -fsched-rank-heuristic 7332@opindex fsched-rank-heuristic 7333Enable the rank heuristic in the scheduler. This heuristic favors 7334the instruction belonging to a basic block with greater size or frequency. 7335This is enabled by default when scheduling is enabled, i.e.@: 7336with @option{-fschedule-insns} or @option{-fschedule-insns2} or 7337at @option{-O2} or higher. 7338 7339@item -fsched-last-insn-heuristic 7340@opindex fsched-last-insn-heuristic 7341Enable the last-instruction heuristic in the scheduler. This heuristic 7342favors the instruction that is less dependent on the last instruction 7343scheduled. This is enabled by default when scheduling is enabled, 7344i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or 7345at @option{-O2} or higher. 7346 7347@item -fsched-dep-count-heuristic 7348@opindex fsched-dep-count-heuristic 7349Enable the dependent-count heuristic in the scheduler. This heuristic 7350favors the instruction that has more instructions depending on it. 7351This is enabled by default when scheduling is enabled, i.e.@: 7352with @option{-fschedule-insns} or @option{-fschedule-insns2} or 7353at @option{-O2} or higher. 7354 7355@item -freschedule-modulo-scheduled-loops 7356@opindex freschedule-modulo-scheduled-loops 7357Modulo scheduling is performed before traditional scheduling. If a loop 7358is modulo scheduled, later scheduling passes may change its schedule. 7359Use this option to control that behavior. 7360 7361@item -fselective-scheduling 7362@opindex fselective-scheduling 7363Schedule instructions using selective scheduling algorithm. Selective 7364scheduling runs instead of the first scheduler pass. 7365 7366@item -fselective-scheduling2 7367@opindex fselective-scheduling2 7368Schedule instructions using selective scheduling algorithm. Selective 7369scheduling runs instead of the second scheduler pass. 7370 7371@item -fsel-sched-pipelining 7372@opindex fsel-sched-pipelining 7373Enable software pipelining of innermost loops during selective scheduling. 7374This option has no effect unless one of @option{-fselective-scheduling} or 7375@option{-fselective-scheduling2} is turned on. 7376 7377@item -fsel-sched-pipelining-outer-loops 7378@opindex fsel-sched-pipelining-outer-loops 7379When pipelining loops during selective scheduling, also pipeline outer loops. 7380This option has no effect unless @option{-fsel-sched-pipelining} is turned on. 7381 7382@item -fshrink-wrap 7383@opindex fshrink-wrap 7384Emit function prologues only before parts of the function that need it, 7385rather than at the top of the function. This flag is enabled by default at 7386@option{-O} and higher. 7387 7388@item -fcaller-saves 7389@opindex fcaller-saves 7390Enable allocation of values to registers that are clobbered by 7391function calls, by emitting extra instructions to save and restore the 7392registers around such calls. Such allocation is done only when it 7393seems to result in better code. 7394 7395This option is always enabled by default on certain machines, usually 7396those which have no call-preserved registers to use instead. 7397 7398Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 7399 7400@item -fcombine-stack-adjustments 7401@opindex fcombine-stack-adjustments 7402Tracks stack adjustments (pushes and pops) and stack memory references 7403and then tries to find ways to combine them. 7404 7405Enabled by default at @option{-O1} and higher. 7406 7407@item -fconserve-stack 7408@opindex fconserve-stack 7409Attempt to minimize stack usage. The compiler attempts to use less 7410stack space, even if that makes the program slower. This option 7411implies setting the @option{large-stack-frame} parameter to 100 7412and the @option{large-stack-frame-growth} parameter to 400. 7413 7414@item -ftree-reassoc 7415@opindex ftree-reassoc 7416Perform reassociation on trees. This flag is enabled by default 7417at @option{-O} and higher. 7418 7419@item -ftree-pre 7420@opindex ftree-pre 7421Perform partial redundancy elimination (PRE) on trees. This flag is 7422enabled by default at @option{-O2} and @option{-O3}. 7423 7424@item -ftree-partial-pre 7425@opindex ftree-partial-pre 7426Make partial redundancy elimination (PRE) more aggressive. This flag is 7427enabled by default at @option{-O3}. 7428 7429@item -ftree-forwprop 7430@opindex ftree-forwprop 7431Perform forward propagation on trees. This flag is enabled by default 7432at @option{-O} and higher. 7433 7434@item -ftree-fre 7435@opindex ftree-fre 7436Perform full redundancy elimination (FRE) on trees. The difference 7437between FRE and PRE is that FRE only considers expressions 7438that are computed on all paths leading to the redundant computation. 7439This analysis is faster than PRE, though it exposes fewer redundancies. 7440This flag is enabled by default at @option{-O} and higher. 7441 7442@item -ftree-phiprop 7443@opindex ftree-phiprop 7444Perform hoisting of loads from conditional pointers on trees. This 7445pass is enabled by default at @option{-O} and higher. 7446 7447@item -fhoist-adjacent-loads 7448@opindex hoist-adjacent-loads 7449Speculatively hoist loads from both branches of an if-then-else if the 7450loads are from adjacent locations in the same structure and the target 7451architecture has a conditional move instruction. This flag is enabled 7452by default at @option{-O2} and higher. 7453 7454@item -ftree-copy-prop 7455@opindex ftree-copy-prop 7456Perform copy propagation on trees. This pass eliminates unnecessary 7457copy operations. This flag is enabled by default at @option{-O} and 7458higher. 7459 7460@item -fipa-pure-const 7461@opindex fipa-pure-const 7462Discover which functions are pure or constant. 7463Enabled by default at @option{-O} and higher. 7464 7465@item -fipa-reference 7466@opindex fipa-reference 7467Discover which static variables do not escape the 7468compilation unit. 7469Enabled by default at @option{-O} and higher. 7470 7471@item -fipa-pta 7472@opindex fipa-pta 7473Perform interprocedural pointer analysis and interprocedural modification 7474and reference analysis. This option can cause excessive memory and 7475compile-time usage on large compilation units. It is not enabled by 7476default at any optimization level. 7477 7478@item -fipa-profile 7479@opindex fipa-profile 7480Perform interprocedural profile propagation. The functions called only from 7481cold functions are marked as cold. Also functions executed once (such as 7482@code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold 7483functions and loop less parts of functions executed once are then optimized for 7484size. 7485Enabled by default at @option{-O} and higher. 7486 7487@item -fipa-cp 7488@opindex fipa-cp 7489Perform interprocedural constant propagation. 7490This optimization analyzes the program to determine when values passed 7491to functions are constants and then optimizes accordingly. 7492This optimization can substantially increase performance 7493if the application has constants passed to functions. 7494This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}. 7495 7496@item -fipa-cp-clone 7497@opindex fipa-cp-clone 7498Perform function cloning to make interprocedural constant propagation stronger. 7499When enabled, interprocedural constant propagation performs function cloning 7500when externally visible function can be called with constant arguments. 7501Because this optimization can create multiple copies of functions, 7502it may significantly increase code size 7503(see @option{--param ipcp-unit-growth=@var{value}}). 7504This flag is enabled by default at @option{-O3}. 7505 7506@item -ftree-sink 7507@opindex ftree-sink 7508Perform forward store motion on trees. This flag is 7509enabled by default at @option{-O} and higher. 7510 7511@item -ftree-bit-ccp 7512@opindex ftree-bit-ccp 7513Perform sparse conditional bit constant propagation on trees and propagate 7514pointer alignment information. 7515This pass only operates on local scalar variables and is enabled by default 7516at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled. 7517 7518@item -ftree-ccp 7519@opindex ftree-ccp 7520Perform sparse conditional constant propagation (CCP) on trees. This 7521pass only operates on local scalar variables and is enabled by default 7522at @option{-O} and higher. 7523 7524@item -ftree-switch-conversion 7525Perform conversion of simple initializations in a switch to 7526initializations from a scalar array. This flag is enabled by default 7527at @option{-O2} and higher. 7528 7529@item -ftree-tail-merge 7530Look for identical code sequences. When found, replace one with a jump to the 7531other. This optimization is known as tail merging or cross jumping. This flag 7532is enabled by default at @option{-O2} and higher. The compilation time 7533in this pass can 7534be limited using @option{max-tail-merge-comparisons} parameter and 7535@option{max-tail-merge-iterations} parameter. 7536 7537@item -ftree-dce 7538@opindex ftree-dce 7539Perform dead code elimination (DCE) on trees. This flag is enabled by 7540default at @option{-O} and higher. 7541 7542@item -ftree-builtin-call-dce 7543@opindex ftree-builtin-call-dce 7544Perform conditional dead code elimination (DCE) for calls to built-in functions 7545that may set @code{errno} but are otherwise side-effect free. This flag is 7546enabled by default at @option{-O2} and higher if @option{-Os} is not also 7547specified. 7548 7549@item -ftree-dominator-opts 7550@opindex ftree-dominator-opts 7551Perform a variety of simple scalar cleanups (constant/copy 7552propagation, redundancy elimination, range propagation and expression 7553simplification) based on a dominator tree traversal. This also 7554performs jump threading (to reduce jumps to jumps). This flag is 7555enabled by default at @option{-O} and higher. 7556 7557@item -ftree-dse 7558@opindex ftree-dse 7559Perform dead store elimination (DSE) on trees. A dead store is a store into 7560a memory location that is later overwritten by another store without 7561any intervening loads. In this case the earlier store can be deleted. This 7562flag is enabled by default at @option{-O} and higher. 7563 7564@item -ftree-ch 7565@opindex ftree-ch 7566Perform loop header copying on trees. This is beneficial since it increases 7567effectiveness of code motion optimizations. It also saves one jump. This flag 7568is enabled by default at @option{-O} and higher. It is not enabled 7569for @option{-Os}, since it usually increases code size. 7570 7571@item -ftree-loop-optimize 7572@opindex ftree-loop-optimize 7573Perform loop optimizations on trees. This flag is enabled by default 7574at @option{-O} and higher. 7575 7576@item -ftree-loop-linear 7577@opindex ftree-loop-linear 7578Perform loop interchange transformations on tree. Same as 7579@option{-floop-interchange}. To use this code transformation, GCC has 7580to be configured with @option{--with-ppl} and @option{--with-cloog} to 7581enable the Graphite loop transformation infrastructure. 7582 7583@item -floop-interchange 7584@opindex floop-interchange 7585Perform loop interchange transformations on loops. Interchanging two 7586nested loops switches the inner and outer loops. For example, given a 7587loop like: 7588@smallexample 7589DO J = 1, M 7590 DO I = 1, N 7591 A(J, I) = A(J, I) * C 7592 ENDDO 7593ENDDO 7594@end smallexample 7595loop interchange transforms the loop as if it were written: 7596@smallexample 7597DO I = 1, N 7598 DO J = 1, M 7599 A(J, I) = A(J, I) * C 7600 ENDDO 7601ENDDO 7602@end smallexample 7603which can be beneficial when @code{N} is larger than the caches, 7604because in Fortran, the elements of an array are stored in memory 7605contiguously by column, and the original loop iterates over rows, 7606potentially creating at each access a cache miss. This optimization 7607applies to all the languages supported by GCC and is not limited to 7608Fortran. To use this code transformation, GCC has to be configured 7609with @option{--with-ppl} and @option{--with-cloog} to enable the 7610Graphite loop transformation infrastructure. 7611 7612@item -floop-strip-mine 7613@opindex floop-strip-mine 7614Perform loop strip mining transformations on loops. Strip mining 7615splits a loop into two nested loops. The outer loop has strides 7616equal to the strip size and the inner loop has strides of the 7617original loop within a strip. The strip length can be changed 7618using the @option{loop-block-tile-size} parameter. For example, 7619given a loop like: 7620@smallexample 7621DO I = 1, N 7622 A(I) = A(I) + C 7623ENDDO 7624@end smallexample 7625loop strip mining transforms the loop as if it were written: 7626@smallexample 7627DO II = 1, N, 51 7628 DO I = II, min (II + 50, N) 7629 A(I) = A(I) + C 7630 ENDDO 7631ENDDO 7632@end smallexample 7633This optimization applies to all the languages supported by GCC and is 7634not limited to Fortran. To use this code transformation, GCC has to 7635be configured with @option{--with-ppl} and @option{--with-cloog} to 7636enable the Graphite loop transformation infrastructure. 7637 7638@item -floop-block 7639@opindex floop-block 7640Perform loop blocking transformations on loops. Blocking strip mines 7641each loop in the loop nest such that the memory accesses of the 7642element loops fit inside caches. The strip length can be changed 7643using the @option{loop-block-tile-size} parameter. For example, given 7644a loop like: 7645@smallexample 7646DO I = 1, N 7647 DO J = 1, M 7648 A(J, I) = B(I) + C(J) 7649 ENDDO 7650ENDDO 7651@end smallexample 7652loop blocking transforms the loop as if it were written: 7653@smallexample 7654DO II = 1, N, 51 7655 DO JJ = 1, M, 51 7656 DO I = II, min (II + 50, N) 7657 DO J = JJ, min (JJ + 50, M) 7658 A(J, I) = B(I) + C(J) 7659 ENDDO 7660 ENDDO 7661 ENDDO 7662ENDDO 7663@end smallexample 7664which can be beneficial when @code{M} is larger than the caches, 7665because the innermost loop iterates over a smaller amount of data 7666which can be kept in the caches. This optimization applies to all the 7667languages supported by GCC and is not limited to Fortran. To use this 7668code transformation, GCC has to be configured with @option{--with-ppl} 7669and @option{--with-cloog} to enable the Graphite loop transformation 7670infrastructure. 7671 7672@item -fgraphite-identity 7673@opindex fgraphite-identity 7674Enable the identity transformation for graphite. For every SCoP we generate 7675the polyhedral representation and transform it back to gimple. Using 7676@option{-fgraphite-identity} we can check the costs or benefits of the 7677GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations 7678are also performed by the code generator CLooG, like index splitting and 7679dead code elimination in loops. 7680 7681@item -floop-nest-optimize 7682@opindex floop-nest-optimize 7683Enable the ISL based loop nest optimizer. This is a generic loop nest 7684optimizer based on the Pluto optimization algorithms. It calculates a loop 7685structure optimized for data-locality and parallelism. This option 7686is experimental. 7687 7688@item -floop-parallelize-all 7689@opindex floop-parallelize-all 7690Use the Graphite data dependence analysis to identify loops that can 7691be parallelized. Parallelize all the loops that can be analyzed to 7692not contain loop carried dependences without checking that it is 7693profitable to parallelize the loops. 7694 7695@item -fcheck-data-deps 7696@opindex fcheck-data-deps 7697Compare the results of several data dependence analyzers. This option 7698is used for debugging the data dependence analyzers. 7699 7700@item -ftree-loop-if-convert 7701Attempt to transform conditional jumps in the innermost loops to 7702branch-less equivalents. The intent is to remove control-flow from 7703the innermost loops in order to improve the ability of the 7704vectorization pass to handle these loops. This is enabled by default 7705if vectorization is enabled. 7706 7707@item -ftree-loop-if-convert-stores 7708Attempt to also if-convert conditional jumps containing memory writes. 7709This transformation can be unsafe for multi-threaded programs as it 7710transforms conditional memory writes into unconditional memory writes. 7711For example, 7712@smallexample 7713for (i = 0; i < N; i++) 7714 if (cond) 7715 A[i] = expr; 7716@end smallexample 7717is transformed to 7718@smallexample 7719for (i = 0; i < N; i++) 7720 A[i] = cond ? expr : A[i]; 7721@end smallexample 7722potentially producing data races. 7723 7724@item -ftree-loop-distribution 7725Perform loop distribution. This flag can improve cache performance on 7726big loop bodies and allow further loop optimizations, like 7727parallelization or vectorization, to take place. For example, the loop 7728@smallexample 7729DO I = 1, N 7730 A(I) = B(I) + C 7731 D(I) = E(I) * F 7732ENDDO 7733@end smallexample 7734is transformed to 7735@smallexample 7736DO I = 1, N 7737 A(I) = B(I) + C 7738ENDDO 7739DO I = 1, N 7740 D(I) = E(I) * F 7741ENDDO 7742@end smallexample 7743 7744@item -ftree-loop-distribute-patterns 7745Perform loop distribution of patterns that can be code generated with 7746calls to a library. This flag is enabled by default at @option{-O3}. 7747 7748This pass distributes the initialization loops and generates a call to 7749memset zero. For example, the loop 7750@smallexample 7751DO I = 1, N 7752 A(I) = 0 7753 B(I) = A(I) + I 7754ENDDO 7755@end smallexample 7756is transformed to 7757@smallexample 7758DO I = 1, N 7759 A(I) = 0 7760ENDDO 7761DO I = 1, N 7762 B(I) = A(I) + I 7763ENDDO 7764@end smallexample 7765and the initialization loop is transformed into a call to memset zero. 7766 7767@item -ftree-loop-im 7768@opindex ftree-loop-im 7769Perform loop invariant motion on trees. This pass moves only invariants that 7770are hard to handle at RTL level (function calls, operations that expand to 7771nontrivial sequences of insns). With @option{-funswitch-loops} it also moves 7772operands of conditions that are invariant out of the loop, so that we can use 7773just trivial invariantness analysis in loop unswitching. The pass also includes 7774store motion. 7775 7776@item -ftree-loop-ivcanon 7777@opindex ftree-loop-ivcanon 7778Create a canonical counter for number of iterations in loops for which 7779determining number of iterations requires complicated analysis. Later 7780optimizations then may determine the number easily. Useful especially 7781in connection with unrolling. 7782 7783@item -fivopts 7784@opindex fivopts 7785Perform induction variable optimizations (strength reduction, induction 7786variable merging and induction variable elimination) on trees. 7787 7788@item -ftree-parallelize-loops=n 7789@opindex ftree-parallelize-loops 7790Parallelize loops, i.e., split their iteration space to run in n threads. 7791This is only possible for loops whose iterations are independent 7792and can be arbitrarily reordered. The optimization is only 7793profitable on multiprocessor machines, for loops that are CPU-intensive, 7794rather than constrained e.g.@: by memory bandwidth. This option 7795implies @option{-pthread}, and thus is only supported on targets 7796that have support for @option{-pthread}. 7797 7798@item -ftree-pta 7799@opindex ftree-pta 7800Perform function-local points-to analysis on trees. This flag is 7801enabled by default at @option{-O} and higher. 7802 7803@item -ftree-sra 7804@opindex ftree-sra 7805Perform scalar replacement of aggregates. This pass replaces structure 7806references with scalars to prevent committing structures to memory too 7807early. This flag is enabled by default at @option{-O} and higher. 7808 7809@item -ftree-copyrename 7810@opindex ftree-copyrename 7811Perform copy renaming on trees. This pass attempts to rename compiler 7812temporaries to other variables at copy locations, usually resulting in 7813variable names which more closely resemble the original variables. This flag 7814is enabled by default at @option{-O} and higher. 7815 7816@item -ftree-coalesce-inlined-vars 7817Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to 7818combine small user-defined variables too, but only if they were inlined 7819from other functions. It is a more limited form of 7820@option{-ftree-coalesce-vars}. This may harm debug information of such 7821inlined variables, but it will keep variables of the inlined-into 7822function apart from each other, such that they are more likely to 7823contain the expected values in a debugging session. This was the 7824default in GCC versions older than 4.7. 7825 7826@item -ftree-coalesce-vars 7827Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to 7828combine small user-defined variables too, instead of just compiler 7829temporaries. This may severely limit the ability to debug an optimized 7830program compiled with @option{-fno-var-tracking-assignments}. In the 7831negated form, this flag prevents SSA coalescing of user variables, 7832including inlined ones. This option is enabled by default. 7833 7834@item -ftree-ter 7835@opindex ftree-ter 7836Perform temporary expression replacement during the SSA->normal phase. Single 7837use/single def temporaries are replaced at their use location with their 7838defining expression. This results in non-GIMPLE code, but gives the expanders 7839much more complex trees to work on resulting in better RTL generation. This is 7840enabled by default at @option{-O} and higher. 7841 7842@item -ftree-slsr 7843@opindex ftree-slsr 7844Perform straight-line strength reduction on trees. This recognizes related 7845expressions involving multiplications and replaces them by less expensive 7846calculations when possible. This is enabled by default at @option{-O} and 7847higher. 7848 7849@item -ftree-vectorize 7850@opindex ftree-vectorize 7851Perform loop vectorization on trees. This flag is enabled by default at 7852@option{-O3}. 7853 7854@item -ftree-slp-vectorize 7855@opindex ftree-slp-vectorize 7856Perform basic block vectorization on trees. This flag is enabled by default at 7857@option{-O3} and when @option{-ftree-vectorize} is enabled. 7858 7859@item -ftree-vect-loop-version 7860@opindex ftree-vect-loop-version 7861Perform loop versioning when doing loop vectorization on trees. When a loop 7862appears to be vectorizable except that data alignment or data dependence cannot 7863be determined at compile time, then vectorized and non-vectorized versions of 7864the loop are generated along with run-time checks for alignment or dependence 7865to control which version is executed. This option is enabled by default 7866except at level @option{-Os} where it is disabled. 7867 7868@item -fvect-cost-model 7869@opindex fvect-cost-model 7870Enable cost model for vectorization. This option is enabled by default at 7871@option{-O3}. 7872 7873@item -ftree-vrp 7874@opindex ftree-vrp 7875Perform Value Range Propagation on trees. This is similar to the 7876constant propagation pass, but instead of values, ranges of values are 7877propagated. This allows the optimizers to remove unnecessary range 7878checks like array bound checks and null pointer checks. This is 7879enabled by default at @option{-O2} and higher. Null pointer check 7880elimination is only done if @option{-fdelete-null-pointer-checks} is 7881enabled. 7882 7883@item -ftracer 7884@opindex ftracer 7885Perform tail duplication to enlarge superblock size. This transformation 7886simplifies the control flow of the function allowing other optimizations to do 7887a better job. 7888 7889@item -funroll-loops 7890@opindex funroll-loops 7891Unroll loops whose number of iterations can be determined at compile 7892time or upon entry to the loop. @option{-funroll-loops} implies 7893@option{-frerun-cse-after-loop}. This option makes code larger, 7894and may or may not make it run faster. 7895 7896@item -funroll-all-loops 7897@opindex funroll-all-loops 7898Unroll all loops, even if their number of iterations is uncertain when 7899the loop is entered. This usually makes programs run more slowly. 7900@option{-funroll-all-loops} implies the same options as 7901@option{-funroll-loops}, 7902 7903@item -fsplit-ivs-in-unroller 7904@opindex fsplit-ivs-in-unroller 7905Enables expression of values of induction variables in later iterations 7906of the unrolled loop using the value in the first iteration. This breaks 7907long dependency chains, thus improving efficiency of the scheduling passes. 7908 7909A combination of @option{-fweb} and CSE is often sufficient to obtain the 7910same effect. However, that is not reliable in cases where the loop body 7911is more complicated than a single basic block. It also does not work at all 7912on some architectures due to restrictions in the CSE pass. 7913 7914This optimization is enabled by default. 7915 7916@item -fvariable-expansion-in-unroller 7917@opindex fvariable-expansion-in-unroller 7918With this option, the compiler creates multiple copies of some 7919local variables when unrolling a loop, which can result in superior code. 7920 7921@item -fpartial-inlining 7922@opindex fpartial-inlining 7923Inline parts of functions. This option has any effect only 7924when inlining itself is turned on by the @option{-finline-functions} 7925or @option{-finline-small-functions} options. 7926 7927Enabled at level @option{-O2}. 7928 7929@item -fpredictive-commoning 7930@opindex fpredictive-commoning 7931Perform predictive commoning optimization, i.e., reusing computations 7932(especially memory loads and stores) performed in previous 7933iterations of loops. 7934 7935This option is enabled at level @option{-O3}. 7936 7937@item -fprefetch-loop-arrays 7938@opindex fprefetch-loop-arrays 7939If supported by the target machine, generate instructions to prefetch 7940memory to improve the performance of loops that access large arrays. 7941 7942This option may generate better or worse code; results are highly 7943dependent on the structure of loops within the source code. 7944 7945Disabled at level @option{-Os}. 7946 7947@item -fno-peephole 7948@itemx -fno-peephole2 7949@opindex fno-peephole 7950@opindex fno-peephole2 7951Disable any machine-specific peephole optimizations. The difference 7952between @option{-fno-peephole} and @option{-fno-peephole2} is in how they 7953are implemented in the compiler; some targets use one, some use the 7954other, a few use both. 7955 7956@option{-fpeephole} is enabled by default. 7957@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 7958 7959@item -fno-guess-branch-probability 7960@opindex fno-guess-branch-probability 7961Do not guess branch probabilities using heuristics. 7962 7963GCC uses heuristics to guess branch probabilities if they are 7964not provided by profiling feedback (@option{-fprofile-arcs}). These 7965heuristics are based on the control flow graph. If some branch probabilities 7966are specified by @samp{__builtin_expect}, then the heuristics are 7967used to guess branch probabilities for the rest of the control flow graph, 7968taking the @samp{__builtin_expect} info into account. The interactions 7969between the heuristics and @samp{__builtin_expect} can be complex, and in 7970some cases, it may be useful to disable the heuristics so that the effects 7971of @samp{__builtin_expect} are easier to understand. 7972 7973The default is @option{-fguess-branch-probability} at levels 7974@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 7975 7976@item -freorder-blocks 7977@opindex freorder-blocks 7978Reorder basic blocks in the compiled function in order to reduce number of 7979taken branches and improve code locality. 7980 7981Enabled at levels @option{-O2}, @option{-O3}. 7982 7983@item -freorder-blocks-and-partition 7984@opindex freorder-blocks-and-partition 7985In addition to reordering basic blocks in the compiled function, in order 7986to reduce number of taken branches, partitions hot and cold basic blocks 7987into separate sections of the assembly and .o files, to improve 7988paging and cache locality performance. 7989 7990This optimization is automatically turned off in the presence of 7991exception handling, for linkonce sections, for functions with a user-defined 7992section attribute and on any architecture that does not support named 7993sections. 7994 7995@item -freorder-functions 7996@opindex freorder-functions 7997Reorder functions in the object file in order to 7998improve code locality. This is implemented by using special 7999subsections @code{.text.hot} for most frequently executed functions and 8000@code{.text.unlikely} for unlikely executed functions. Reordering is done by 8001the linker so object file format must support named sections and linker must 8002place them in a reasonable way. 8003 8004Also profile feedback must be available to make this option effective. See 8005@option{-fprofile-arcs} for details. 8006 8007Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. 8008 8009@item -fstrict-aliasing 8010@opindex fstrict-aliasing 8011Allow the compiler to assume the strictest aliasing rules applicable to 8012the language being compiled. For C (and C++), this activates 8013optimizations based on the type of expressions. In particular, an 8014object of one type is assumed never to reside at the same address as an 8015object of a different type, unless the types are almost the same. For 8016example, an @code{unsigned int} can alias an @code{int}, but not a 8017@code{void*} or a @code{double}. A character type may alias any other 8018type. 8019 8020@anchor{Type-punning}Pay special attention to code like this: 8021@smallexample 8022union a_union @{ 8023 int i; 8024 double d; 8025@}; 8026 8027int f() @{ 8028 union a_union t; 8029 t.d = 3.0; 8030 return t.i; 8031@} 8032@end smallexample 8033The practice of reading from a different union member than the one most 8034recently written to (called ``type-punning'') is common. Even with 8035@option{-fstrict-aliasing}, type-punning is allowed, provided the memory 8036is accessed through the union type. So, the code above works as 8037expected. @xref{Structures unions enumerations and bit-fields 8038implementation}. However, this code might not: 8039@smallexample 8040int f() @{ 8041 union a_union t; 8042 int* ip; 8043 t.d = 3.0; 8044 ip = &t.i; 8045 return *ip; 8046@} 8047@end smallexample 8048 8049Similarly, access by taking the address, casting the resulting pointer 8050and dereferencing the result has undefined behavior, even if the cast 8051uses a union type, e.g.: 8052@smallexample 8053int f() @{ 8054 double d = 3.0; 8055 return ((union a_union *) &d)->i; 8056@} 8057@end smallexample 8058 8059The @option{-fstrict-aliasing} option is enabled at levels 8060@option{-O2}, @option{-O3}, @option{-Os}. 8061 8062@item -fstrict-overflow 8063@opindex fstrict-overflow 8064Allow the compiler to assume strict signed overflow rules, depending 8065on the language being compiled. For C (and C++) this means that 8066overflow when doing arithmetic with signed numbers is undefined, which 8067means that the compiler may assume that it does not happen. This 8068permits various optimizations. For example, the compiler assumes 8069that an expression like @code{i + 10 > i} is always true for 8070signed @code{i}. This assumption is only valid if signed overflow is 8071undefined, as the expression is false if @code{i + 10} overflows when 8072using twos complement arithmetic. When this option is in effect any 8073attempt to determine whether an operation on signed numbers 8074overflows must be written carefully to not actually involve overflow. 8075 8076This option also allows the compiler to assume strict pointer 8077semantics: given a pointer to an object, if adding an offset to that 8078pointer does not produce a pointer to the same object, the addition is 8079undefined. This permits the compiler to conclude that @code{p + u > 8080p} is always true for a pointer @code{p} and unsigned integer 8081@code{u}. This assumption is only valid because pointer wraparound is 8082undefined, as the expression is false if @code{p + u} overflows using 8083twos complement arithmetic. 8084 8085See also the @option{-fwrapv} option. Using @option{-fwrapv} means 8086that integer signed overflow is fully defined: it wraps. When 8087@option{-fwrapv} is used, there is no difference between 8088@option{-fstrict-overflow} and @option{-fno-strict-overflow} for 8089integers. With @option{-fwrapv} certain types of overflow are 8090permitted. For example, if the compiler gets an overflow when doing 8091arithmetic on constants, the overflowed value can still be used with 8092@option{-fwrapv}, but not otherwise. 8093 8094The @option{-fstrict-overflow} option is enabled at levels 8095@option{-O2}, @option{-O3}, @option{-Os}. 8096 8097@item -falign-functions 8098@itemx -falign-functions=@var{n} 8099@opindex falign-functions 8100Align the start of functions to the next power-of-two greater than 8101@var{n}, skipping up to @var{n} bytes. For instance, 8102@option{-falign-functions=32} aligns functions to the next 32-byte 8103boundary, but @option{-falign-functions=24} aligns to the next 810432-byte boundary only if this can be done by skipping 23 bytes or less. 8105 8106@option{-fno-align-functions} and @option{-falign-functions=1} are 8107equivalent and mean that functions are not aligned. 8108 8109Some assemblers only support this flag when @var{n} is a power of two; 8110in that case, it is rounded up. 8111 8112If @var{n} is not specified or is zero, use a machine-dependent default. 8113 8114Enabled at levels @option{-O2}, @option{-O3}. 8115 8116@item -falign-labels 8117@itemx -falign-labels=@var{n} 8118@opindex falign-labels 8119Align all branch targets to a power-of-two boundary, skipping up to 8120@var{n} bytes like @option{-falign-functions}. This option can easily 8121make code slower, because it must insert dummy operations for when the 8122branch target is reached in the usual flow of the code. 8123 8124@option{-fno-align-labels} and @option{-falign-labels=1} are 8125equivalent and mean that labels are not aligned. 8126 8127If @option{-falign-loops} or @option{-falign-jumps} are applicable and 8128are greater than this value, then their values are used instead. 8129 8130If @var{n} is not specified or is zero, use a machine-dependent default 8131which is very likely to be @samp{1}, meaning no alignment. 8132 8133Enabled at levels @option{-O2}, @option{-O3}. 8134 8135@item -falign-loops 8136@itemx -falign-loops=@var{n} 8137@opindex falign-loops 8138Align loops to a power-of-two boundary, skipping up to @var{n} bytes 8139like @option{-falign-functions}. If the loops are 8140executed many times, this makes up for any execution of the dummy 8141operations. 8142 8143@option{-fno-align-loops} and @option{-falign-loops=1} are 8144equivalent and mean that loops are not aligned. 8145 8146If @var{n} is not specified or is zero, use a machine-dependent default. 8147 8148Enabled at levels @option{-O2}, @option{-O3}. 8149 8150@item -falign-jumps 8151@itemx -falign-jumps=@var{n} 8152@opindex falign-jumps 8153Align branch targets to a power-of-two boundary, for branch targets 8154where the targets can only be reached by jumping, skipping up to @var{n} 8155bytes like @option{-falign-functions}. In this case, no dummy operations 8156need be executed. 8157 8158@option{-fno-align-jumps} and @option{-falign-jumps=1} are 8159equivalent and mean that loops are not aligned. 8160 8161If @var{n} is not specified or is zero, use a machine-dependent default. 8162 8163Enabled at levels @option{-O2}, @option{-O3}. 8164 8165@item -funit-at-a-time 8166@opindex funit-at-a-time 8167This option is left for compatibility reasons. @option{-funit-at-a-time} 8168has no effect, while @option{-fno-unit-at-a-time} implies 8169@option{-fno-toplevel-reorder} and @option{-fno-section-anchors}. 8170 8171Enabled by default. 8172 8173@item -fno-toplevel-reorder 8174@opindex fno-toplevel-reorder 8175Do not reorder top-level functions, variables, and @code{asm} 8176statements. Output them in the same order that they appear in the 8177input file. When this option is used, unreferenced static variables 8178are not removed. This option is intended to support existing code 8179that relies on a particular ordering. For new code, it is better to 8180use attributes. 8181 8182Enabled at level @option{-O0}. When disabled explicitly, it also implies 8183@option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some 8184targets. 8185 8186@item -fweb 8187@opindex fweb 8188Constructs webs as commonly used for register allocation purposes and assign 8189each web individual pseudo register. This allows the register allocation pass 8190to operate on pseudos directly, but also strengthens several other optimization 8191passes, such as CSE, loop optimizer and trivial dead code remover. It can, 8192however, make debugging impossible, since variables no longer stay in a 8193``home register''. 8194 8195Enabled by default with @option{-funroll-loops}. 8196 8197@item -fwhole-program 8198@opindex fwhole-program 8199Assume that the current compilation unit represents the whole program being 8200compiled. All public functions and variables with the exception of @code{main} 8201and those merged by attribute @code{externally_visible} become static functions 8202and in effect are optimized more aggressively by interprocedural optimizers. 8203 8204This option should not be used in combination with @code{-flto}. 8205Instead relying on a linker plugin should provide safer and more precise 8206information. 8207 8208@item -flto[=@var{n}] 8209@opindex flto 8210This option runs the standard link-time optimizer. When invoked 8211with source code, it generates GIMPLE (one of GCC's internal 8212representations) and writes it to special ELF sections in the object 8213file. When the object files are linked together, all the function 8214bodies are read from these ELF sections and instantiated as if they 8215had been part of the same translation unit. 8216 8217To use the link-time optimizer, @option{-flto} needs to be specified at 8218compile time and during the final link. For example: 8219 8220@smallexample 8221gcc -c -O2 -flto foo.c 8222gcc -c -O2 -flto bar.c 8223gcc -o myprog -flto -O2 foo.o bar.o 8224@end smallexample 8225 8226The first two invocations to GCC save a bytecode representation 8227of GIMPLE into special ELF sections inside @file{foo.o} and 8228@file{bar.o}. The final invocation reads the GIMPLE bytecode from 8229@file{foo.o} and @file{bar.o}, merges the two files into a single 8230internal image, and compiles the result as usual. Since both 8231@file{foo.o} and @file{bar.o} are merged into a single image, this 8232causes all the interprocedural analyses and optimizations in GCC to 8233work across the two files as if they were a single one. This means, 8234for example, that the inliner is able to inline functions in 8235@file{bar.o} into functions in @file{foo.o} and vice-versa. 8236 8237Another (simpler) way to enable link-time optimization is: 8238 8239@smallexample 8240gcc -o myprog -flto -O2 foo.c bar.c 8241@end smallexample 8242 8243The above generates bytecode for @file{foo.c} and @file{bar.c}, 8244merges them together into a single GIMPLE representation and optimizes 8245them as usual to produce @file{myprog}. 8246 8247The only important thing to keep in mind is that to enable link-time 8248optimizations the @option{-flto} flag needs to be passed to both the 8249compile and the link commands. 8250 8251To make whole program optimization effective, it is necessary to make 8252certain whole program assumptions. The compiler needs to know 8253what functions and variables can be accessed by libraries and runtime 8254outside of the link-time optimized unit. When supported by the linker, 8255the linker plugin (see @option{-fuse-linker-plugin}) passes information 8256to the compiler about used and externally visible symbols. When 8257the linker plugin is not available, @option{-fwhole-program} should be 8258used to allow the compiler to make these assumptions, which leads 8259to more aggressive optimization decisions. 8260 8261Note that when a file is compiled with @option{-flto}, the generated 8262object file is larger than a regular object file because it 8263contains GIMPLE bytecodes and the usual final code. This means that 8264object files with LTO information can be linked as normal object 8265files; if @option{-flto} is not passed to the linker, no 8266interprocedural optimizations are applied. 8267 8268Additionally, the optimization flags used to compile individual files 8269are not necessarily related to those used at link time. For instance, 8270 8271@smallexample 8272gcc -c -O0 -flto foo.c 8273gcc -c -O0 -flto bar.c 8274gcc -o myprog -flto -O3 foo.o bar.o 8275@end smallexample 8276 8277This produces individual object files with unoptimized assembler 8278code, but the resulting binary @file{myprog} is optimized at 8279@option{-O3}. If, instead, the final binary is generated without 8280@option{-flto}, then @file{myprog} is not optimized. 8281 8282When producing the final binary with @option{-flto}, GCC only 8283applies link-time optimizations to those files that contain bytecode. 8284Therefore, you can mix and match object files and libraries with 8285GIMPLE bytecodes and final object code. GCC automatically selects 8286which files to optimize in LTO mode and which files to link without 8287further processing. 8288 8289There are some code generation flags preserved by GCC when 8290generating bytecodes, as they need to be used during the final link 8291stage. Currently, the following options are saved into the GIMPLE 8292bytecode files: @option{-fPIC}, @option{-fcommon} and all the 8293@option{-m} target flags. 8294 8295At link time, these options are read in and reapplied. Note that the 8296current implementation makes no attempt to recognize conflicting 8297values for these options. If different files have conflicting option 8298values (e.g., one file is compiled with @option{-fPIC} and another 8299isn't), the compiler simply uses the last value read from the 8300bytecode files. It is recommended, then, that you compile all the files 8301participating in the same link with the same options. 8302 8303If LTO encounters objects with C linkage declared with incompatible 8304types in separate translation units to be linked together (undefined 8305behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be 8306issued. The behavior is still undefined at run time. 8307 8308Another feature of LTO is that it is possible to apply interprocedural 8309optimizations on files written in different languages. This requires 8310support in the language front end. Currently, the C, C++ and 8311Fortran front ends are capable of emitting GIMPLE bytecodes, so 8312something like this should work: 8313 8314@smallexample 8315gcc -c -flto foo.c 8316g++ -c -flto bar.cc 8317gfortran -c -flto baz.f90 8318g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran 8319@end smallexample 8320 8321Notice that the final link is done with @command{g++} to get the C++ 8322runtime libraries and @option{-lgfortran} is added to get the Fortran 8323runtime libraries. In general, when mixing languages in LTO mode, you 8324should use the same link command options as when mixing languages in a 8325regular (non-LTO) compilation; all you need to add is @option{-flto} to 8326all the compile and link commands. 8327 8328If object files containing GIMPLE bytecode are stored in a library archive, say 8329@file{libfoo.a}, it is possible to extract and use them in an LTO link if you 8330are using a linker with plugin support. To enable this feature, use 8331the flag @option{-fuse-linker-plugin} at link time: 8332 8333@smallexample 8334gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo 8335@end smallexample 8336 8337With the linker plugin enabled, the linker extracts the needed 8338GIMPLE files from @file{libfoo.a} and passes them on to the running GCC 8339to make them part of the aggregated GIMPLE image to be optimized. 8340 8341If you are not using a linker with plugin support and/or do not 8342enable the linker plugin, then the objects inside @file{libfoo.a} 8343are extracted and linked as usual, but they do not participate 8344in the LTO optimization process. 8345 8346Link-time optimizations do not require the presence of the whole program to 8347operate. If the program does not require any symbols to be exported, it is 8348possible to combine @option{-flto} and @option{-fwhole-program} to allow 8349the interprocedural optimizers to use more aggressive assumptions which may 8350lead to improved optimization opportunities. 8351Use of @option{-fwhole-program} is not needed when linker plugin is 8352active (see @option{-fuse-linker-plugin}). 8353 8354The current implementation of LTO makes no 8355attempt to generate bytecode that is portable between different 8356types of hosts. The bytecode files are versioned and there is a 8357strict version check, so bytecode files generated in one version of 8358GCC will not work with an older/newer version of GCC@. 8359 8360Link-time optimization does not work well with generation of debugging 8361information. Combining @option{-flto} with 8362@option{-g} is currently experimental and expected to produce wrong 8363results. 8364 8365If you specify the optional @var{n}, the optimization and code 8366generation done at link time is executed in parallel using @var{n} 8367parallel jobs by utilizing an installed @command{make} program. The 8368environment variable @env{MAKE} may be used to override the program 8369used. The default value for @var{n} is 1. 8370 8371You can also specify @option{-flto=jobserver} to use GNU make's 8372job server mode to determine the number of parallel jobs. This 8373is useful when the Makefile calling GCC is already executing in parallel. 8374You must prepend a @samp{+} to the command recipe in the parent Makefile 8375for this to work. This option likely only works if @env{MAKE} is 8376GNU make. 8377 8378This option is disabled by default. 8379 8380@item -flto-partition=@var{alg} 8381@opindex flto-partition 8382Specify the partitioning algorithm used by the link-time optimizer. 8383The value is either @code{1to1} to specify a partitioning mirroring 8384the original source files or @code{balanced} to specify partitioning 8385into equally sized chunks (whenever possible) or @code{max} to create 8386new partition for every symbol where possible. Specifying @code{none} 8387as an algorithm disables partitioning and streaming completely. 8388The default value is @code{balanced}. While @code{1to1} can be used 8389as an workaround for various code ordering issues, the @code{max} 8390partitioning is intended for internal testing only. 8391 8392@item -flto-compression-level=@var{n} 8393This option specifies the level of compression used for intermediate 8394language written to LTO object files, and is only meaningful in 8395conjunction with LTO mode (@option{-flto}). Valid 8396values are 0 (no compression) to 9 (maximum compression). Values 8397outside this range are clamped to either 0 or 9. If the option is not 8398given, a default balanced compression setting is used. 8399 8400@item -flto-report 8401Prints a report with internal details on the workings of the link-time 8402optimizer. The contents of this report vary from version to version. 8403It is meant to be useful to GCC developers when processing object 8404files in LTO mode (via @option{-flto}). 8405 8406Disabled by default. 8407 8408@item -fuse-linker-plugin 8409Enables the use of a linker plugin during link-time optimization. This 8410option relies on plugin support in the linker, which is available in gold 8411or in GNU ld 2.21 or newer. 8412 8413This option enables the extraction of object files with GIMPLE bytecode out 8414of library archives. This improves the quality of optimization by exposing 8415more code to the link-time optimizer. This information specifies what 8416symbols can be accessed externally (by non-LTO object or during dynamic 8417linking). Resulting code quality improvements on binaries (and shared 8418libraries that use hidden visibility) are similar to @code{-fwhole-program}. 8419See @option{-flto} for a description of the effect of this flag and how to 8420use it. 8421 8422This option is enabled by default when LTO support in GCC is enabled 8423and GCC was configured for use with 8424a linker supporting plugins (GNU ld 2.21 or newer or gold). 8425 8426@item -ffat-lto-objects 8427@opindex ffat-lto-objects 8428Fat LTO objects are object files that contain both the intermediate language 8429and the object code. This makes them usable for both LTO linking and normal 8430linking. This option is effective only when compiling with @option{-flto} 8431and is ignored at link time. 8432 8433@option{-fno-fat-lto-objects} improves compilation time over plain LTO, but 8434requires the complete toolchain to be aware of LTO. It requires a linker with 8435linker plugin support for basic functionality. Additionally, 8436@command{nm}, @command{ar} and @command{ranlib} 8437need to support linker plugins to allow a full-featured build environment 8438(capable of building static libraries etc). GCC provides the @command{gcc-ar}, 8439@command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options 8440to these tools. With non fat LTO makefiles need to be modified to use them. 8441 8442The default is @option{-ffat-lto-objects} but this default is intended to 8443change in future releases when linker plugin enabled environments become more 8444common. 8445 8446@item -fcompare-elim 8447@opindex fcompare-elim 8448After register allocation and post-register allocation instruction splitting, 8449identify arithmetic instructions that compute processor flags similar to a 8450comparison operation based on that arithmetic. If possible, eliminate the 8451explicit comparison operation. 8452 8453This pass only applies to certain targets that cannot explicitly represent 8454the comparison operation before register allocation is complete. 8455 8456Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 8457 8458@item -fuse-ld=bfd 8459Use the @command{bfd} linker instead of the default linker. 8460 8461@item -fuse-ld=gold 8462Use the @command{gold} linker instead of the default linker. 8463 8464@item -fcprop-registers 8465@opindex fcprop-registers 8466After register allocation and post-register allocation instruction splitting, 8467perform a copy-propagation pass to try to reduce scheduling dependencies 8468and occasionally eliminate the copy. 8469 8470Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. 8471 8472@item -fprofile-correction 8473@opindex fprofile-correction 8474Profiles collected using an instrumented binary for multi-threaded programs may 8475be inconsistent due to missed counter updates. When this option is specified, 8476GCC uses heuristics to correct or smooth out such inconsistencies. By 8477default, GCC emits an error message when an inconsistent profile is detected. 8478 8479@item -fprofile-dir=@var{path} 8480@opindex fprofile-dir 8481 8482Set the directory to search for the profile data files in to @var{path}. 8483This option affects only the profile data generated by 8484@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs} 8485and used by @option{-fprofile-use} and @option{-fbranch-probabilities} 8486and its related options. Both absolute and relative paths can be used. 8487By default, GCC uses the current directory as @var{path}, thus the 8488profile data file appears in the same directory as the object file. 8489 8490@item -fprofile-generate 8491@itemx -fprofile-generate=@var{path} 8492@opindex fprofile-generate 8493 8494Enable options usually used for instrumenting application to produce 8495profile useful for later recompilation with profile feedback based 8496optimization. You must use @option{-fprofile-generate} both when 8497compiling and when linking your program. 8498 8499The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}. 8500 8501If @var{path} is specified, GCC looks at the @var{path} to find 8502the profile feedback data files. See @option{-fprofile-dir}. 8503 8504@item -fprofile-use 8505@itemx -fprofile-use=@var{path} 8506@opindex fprofile-use 8507Enable profile feedback directed optimizations, and optimizations 8508generally profitable only with profile feedback available. 8509 8510The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt}, 8511@code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}, @code{-ftree-vectorize}, 8512@code{ftree-loop-distribute-patterns} 8513 8514By default, GCC emits an error message if the feedback profiles do not 8515match the source code. This error can be turned into a warning by using 8516@option{-Wcoverage-mismatch}. Note this may result in poorly optimized 8517code. 8518 8519If @var{path} is specified, GCC looks at the @var{path} to find 8520the profile feedback data files. See @option{-fprofile-dir}. 8521@end table 8522 8523The following options control compiler behavior regarding floating-point 8524arithmetic. These options trade off between speed and 8525correctness. All must be specifically enabled. 8526 8527@table @gcctabopt 8528@item -ffloat-store 8529@opindex ffloat-store 8530Do not store floating-point variables in registers, and inhibit other 8531options that might change whether a floating-point value is taken from a 8532register or memory. 8533 8534@cindex floating-point precision 8535This option prevents undesirable excess precision on machines such as 8536the 68000 where the floating registers (of the 68881) keep more 8537precision than a @code{double} is supposed to have. Similarly for the 8538x86 architecture. For most programs, the excess precision does only 8539good, but a few programs rely on the precise definition of IEEE floating 8540point. Use @option{-ffloat-store} for such programs, after modifying 8541them to store all pertinent intermediate computations into variables. 8542 8543@item -fexcess-precision=@var{style} 8544@opindex fexcess-precision 8545This option allows further control over excess precision on machines 8546where floating-point registers have more precision than the IEEE 8547@code{float} and @code{double} types and the processor does not 8548support operations rounding to those types. By default, 8549@option{-fexcess-precision=fast} is in effect; this means that 8550operations are carried out in the precision of the registers and that 8551it is unpredictable when rounding to the types specified in the source 8552code takes place. When compiling C, if 8553@option{-fexcess-precision=standard} is specified then excess 8554precision follows the rules specified in ISO C99; in particular, 8555both casts and assignments cause values to be rounded to their 8556semantic types (whereas @option{-ffloat-store} only affects 8557assignments). This option is enabled by default for C if a strict 8558conformance option such as @option{-std=c99} is used. 8559 8560@opindex mfpmath 8561@option{-fexcess-precision=standard} is not implemented for languages 8562other than C, and has no effect if 8563@option{-funsafe-math-optimizations} or @option{-ffast-math} is 8564specified. On the x86, it also has no effect if @option{-mfpmath=sse} 8565or @option{-mfpmath=sse+387} is specified; in the former case, IEEE 8566semantics apply without excess precision, and in the latter, rounding 8567is unpredictable. 8568 8569@item -ffast-math 8570@opindex ffast-math 8571Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, 8572@option{-ffinite-math-only}, @option{-fno-rounding-math}, 8573@option{-fno-signaling-nans} and @option{-fcx-limited-range}. 8574 8575This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. 8576 8577This option is not turned on by any @option{-O} option besides 8578@option{-Ofast} since it can result in incorrect output for programs 8579that depend on an exact implementation of IEEE or ISO rules/specifications 8580for math functions. It may, however, yield faster code for programs 8581that do not require the guarantees of these specifications. 8582 8583@item -fno-math-errno 8584@opindex fno-math-errno 8585Do not set @code{errno} after calling math functions that are executed 8586with a single instruction, e.g., @code{sqrt}. A program that relies on 8587IEEE exceptions for math error handling may want to use this flag 8588for speed while maintaining IEEE arithmetic compatibility. 8589 8590This option is not turned on by any @option{-O} option since 8591it can result in incorrect output for programs that depend on 8592an exact implementation of IEEE or ISO rules/specifications for 8593math functions. It may, however, yield faster code for programs 8594that do not require the guarantees of these specifications. 8595 8596The default is @option{-fmath-errno}. 8597 8598On Darwin systems, the math library never sets @code{errno}. There is 8599therefore no reason for the compiler to consider the possibility that 8600it might, and @option{-fno-math-errno} is the default. 8601 8602@item -funsafe-math-optimizations 8603@opindex funsafe-math-optimizations 8604 8605Allow optimizations for floating-point arithmetic that (a) assume 8606that arguments and results are valid and (b) may violate IEEE or 8607ANSI standards. When used at link-time, it may include libraries 8608or startup files that change the default FPU control word or other 8609similar optimizations. 8610 8611This option is not turned on by any @option{-O} option since 8612it can result in incorrect output for programs that depend on 8613an exact implementation of IEEE or ISO rules/specifications for 8614math functions. It may, however, yield faster code for programs 8615that do not require the guarantees of these specifications. 8616Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math}, 8617@option{-fassociative-math} and @option{-freciprocal-math}. 8618 8619The default is @option{-fno-unsafe-math-optimizations}. 8620 8621@item -fassociative-math 8622@opindex fassociative-math 8623 8624Allow re-association of operands in series of floating-point operations. 8625This violates the ISO C and C++ language standard by possibly changing 8626computation result. NOTE: re-ordering may change the sign of zero as 8627well as ignore NaNs and inhibit or create underflow or overflow (and 8628thus cannot be used on code that relies on rounding behavior like 8629@code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons 8630and thus may not be used when ordered comparisons are required. 8631This option requires that both @option{-fno-signed-zeros} and 8632@option{-fno-trapping-math} be in effect. Moreover, it doesn't make 8633much sense with @option{-frounding-math}. For Fortran the option 8634is automatically enabled when both @option{-fno-signed-zeros} and 8635@option{-fno-trapping-math} are in effect. 8636 8637The default is @option{-fno-associative-math}. 8638 8639@item -freciprocal-math 8640@opindex freciprocal-math 8641 8642Allow the reciprocal of a value to be used instead of dividing by 8643the value if this enables optimizations. For example @code{x / y} 8644can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)} 8645is subject to common subexpression elimination. Note that this loses 8646precision and increases the number of flops operating on the value. 8647 8648The default is @option{-fno-reciprocal-math}. 8649 8650@item -ffinite-math-only 8651@opindex ffinite-math-only 8652Allow optimizations for floating-point arithmetic that assume 8653that arguments and results are not NaNs or +-Infs. 8654 8655This option is not turned on by any @option{-O} option since 8656it can result in incorrect output for programs that depend on 8657an exact implementation of IEEE or ISO rules/specifications for 8658math functions. It may, however, yield faster code for programs 8659that do not require the guarantees of these specifications. 8660 8661The default is @option{-fno-finite-math-only}. 8662 8663@item -fno-signed-zeros 8664@opindex fno-signed-zeros 8665Allow optimizations for floating-point arithmetic that ignore the 8666signedness of zero. IEEE arithmetic specifies the behavior of 8667distinct +0.0 and @minus{}0.0 values, which then prohibits simplification 8668of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}). 8669This option implies that the sign of a zero result isn't significant. 8670 8671The default is @option{-fsigned-zeros}. 8672 8673@item -fno-trapping-math 8674@opindex fno-trapping-math 8675Compile code assuming that floating-point operations cannot generate 8676user-visible traps. These traps include division by zero, overflow, 8677underflow, inexact result and invalid operation. This option requires 8678that @option{-fno-signaling-nans} be in effect. Setting this option may 8679allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. 8680 8681This option should never be turned on by any @option{-O} option since 8682it can result in incorrect output for programs that depend on 8683an exact implementation of IEEE or ISO rules/specifications for 8684math functions. 8685 8686The default is @option{-ftrapping-math}. 8687 8688@item -frounding-math 8689@opindex frounding-math 8690Disable transformations and optimizations that assume default floating-point 8691rounding behavior. This is round-to-zero for all floating point 8692to integer conversions, and round-to-nearest for all other arithmetic 8693truncations. This option should be specified for programs that change 8694the FP rounding mode dynamically, or that may be executed with a 8695non-default rounding mode. This option disables constant folding of 8696floating-point expressions at compile time (which may be affected by 8697rounding mode) and arithmetic transformations that are unsafe in the 8698presence of sign-dependent rounding modes. 8699 8700The default is @option{-fno-rounding-math}. 8701 8702This option is experimental and does not currently guarantee to 8703disable all GCC optimizations that are affected by rounding mode. 8704Future versions of GCC may provide finer control of this setting 8705using C99's @code{FENV_ACCESS} pragma. This command-line option 8706will be used to specify the default state for @code{FENV_ACCESS}. 8707 8708@item -fsignaling-nans 8709@opindex fsignaling-nans 8710Compile code assuming that IEEE signaling NaNs may generate user-visible 8711traps during floating-point operations. Setting this option disables 8712optimizations that may change the number of exceptions visible with 8713signaling NaNs. This option implies @option{-ftrapping-math}. 8714 8715This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to 8716be defined. 8717 8718The default is @option{-fno-signaling-nans}. 8719 8720This option is experimental and does not currently guarantee to 8721disable all GCC optimizations that affect signaling NaN behavior. 8722 8723@item -fsingle-precision-constant 8724@opindex fsingle-precision-constant 8725Treat floating-point constants as single precision instead of 8726implicitly converting them to double-precision constants. 8727 8728@item -fcx-limited-range 8729@opindex fcx-limited-range 8730When enabled, this option states that a range reduction step is not 8731needed when performing complex division. Also, there is no checking 8732whether the result of a complex multiplication or division is @code{NaN 8733+ I*NaN}, with an attempt to rescue the situation in that case. The 8734default is @option{-fno-cx-limited-range}, but is enabled by 8735@option{-ffast-math}. 8736 8737This option controls the default setting of the ISO C99 8738@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to 8739all languages. 8740 8741@item -fcx-fortran-rules 8742@opindex fcx-fortran-rules 8743Complex multiplication and division follow Fortran rules. Range 8744reduction is done as part of complex division, but there is no checking 8745whether the result of a complex multiplication or division is @code{NaN 8746+ I*NaN}, with an attempt to rescue the situation in that case. 8747 8748The default is @option{-fno-cx-fortran-rules}. 8749 8750@end table 8751 8752The following options control optimizations that may improve 8753performance, but are not enabled by any @option{-O} options. This 8754section includes experimental options that may produce broken code. 8755 8756@table @gcctabopt 8757@item -fbranch-probabilities 8758@opindex fbranch-probabilities 8759After running a program compiled with @option{-fprofile-arcs} 8760(@pxref{Debugging Options,, Options for Debugging Your Program or 8761@command{gcc}}), you can compile it a second time using 8762@option{-fbranch-probabilities}, to improve optimizations based on 8763the number of times each branch was taken. When a program 8764compiled with @option{-fprofile-arcs} exits, it saves arc execution 8765counts to a file called @file{@var{sourcename}.gcda} for each source 8766file. The information in this data file is very dependent on the 8767structure of the generated code, so you must use the same source code 8768and the same optimization options for both compilations. 8769 8770With @option{-fbranch-probabilities}, GCC puts a 8771@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. 8772These can be used to improve optimization. Currently, they are only 8773used in one place: in @file{reorg.c}, instead of guessing which path a 8774branch is most likely to take, the @samp{REG_BR_PROB} values are used to 8775exactly determine which path is taken more often. 8776 8777@item -fprofile-values 8778@opindex fprofile-values 8779If combined with @option{-fprofile-arcs}, it adds code so that some 8780data about values of expressions in the program is gathered. 8781 8782With @option{-fbranch-probabilities}, it reads back the data gathered 8783from profiling values of expressions for usage in optimizations. 8784 8785Enabled with @option{-fprofile-generate} and @option{-fprofile-use}. 8786 8787@item -fvpt 8788@opindex fvpt 8789If combined with @option{-fprofile-arcs}, this option instructs the compiler 8790to add code to gather information about values of expressions. 8791 8792With @option{-fbranch-probabilities}, it reads back the data gathered 8793and actually performs the optimizations based on them. 8794Currently the optimizations include specialization of division operations 8795using the knowledge about the value of the denominator. 8796 8797@item -frename-registers 8798@opindex frename-registers 8799Attempt to avoid false dependencies in scheduled code by making use 8800of registers left over after register allocation. This optimization 8801most benefits processors with lots of registers. Depending on the 8802debug information format adopted by the target, however, it can 8803make debugging impossible, since variables no longer stay in 8804a ``home register''. 8805 8806Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}. 8807 8808@item -ftracer 8809@opindex ftracer 8810Perform tail duplication to enlarge superblock size. This transformation 8811simplifies the control flow of the function allowing other optimizations to do 8812a better job. 8813 8814Enabled with @option{-fprofile-use}. 8815 8816@item -funroll-loops 8817@opindex funroll-loops 8818Unroll loops whose number of iterations can be determined at compile time or 8819upon entry to the loop. @option{-funroll-loops} implies 8820@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. 8821It also turns on complete loop peeling (i.e.@: complete removal of loops with 8822a small constant number of iterations). This option makes code larger, and may 8823or may not make it run faster. 8824 8825Enabled with @option{-fprofile-use}. 8826 8827@item -funroll-all-loops 8828@opindex funroll-all-loops 8829Unroll all loops, even if their number of iterations is uncertain when 8830the loop is entered. This usually makes programs run more slowly. 8831@option{-funroll-all-loops} implies the same options as 8832@option{-funroll-loops}. 8833 8834@item -fpeel-loops 8835@opindex fpeel-loops 8836Peels loops for which there is enough information that they do not 8837roll much (from profile feedback). It also turns on complete loop peeling 8838(i.e.@: complete removal of loops with small constant number of iterations). 8839 8840Enabled with @option{-fprofile-use}. 8841 8842@item -fmove-loop-invariants 8843@opindex fmove-loop-invariants 8844Enables the loop invariant motion pass in the RTL loop optimizer. Enabled 8845at level @option{-O1} 8846 8847@item -funswitch-loops 8848@opindex funswitch-loops 8849Move branches with loop invariant conditions out of the loop, with duplicates 8850of the loop on both branches (modified according to result of the condition). 8851 8852@item -ffunction-sections 8853@itemx -fdata-sections 8854@opindex ffunction-sections 8855@opindex fdata-sections 8856Place each function or data item into its own section in the output 8857file if the target supports arbitrary sections. The name of the 8858function or the name of the data item determines the section's name 8859in the output file. 8860 8861Use these options on systems where the linker can perform optimizations 8862to improve locality of reference in the instruction space. Most systems 8863using the ELF object format and SPARC processors running Solaris 2 have 8864linkers with such optimizations. AIX may have these optimizations in 8865the future. 8866 8867Only use these options when there are significant benefits from doing 8868so. When you specify these options, the assembler and linker 8869create larger object and executable files and are also slower. 8870You cannot use @code{gprof} on all systems if you 8871specify this option, and you may have problems with debugging if 8872you specify both this option and @option{-g}. 8873 8874@item -fbranch-target-load-optimize 8875@opindex fbranch-target-load-optimize 8876Perform branch target register load optimization before prologue / epilogue 8877threading. 8878The use of target registers can typically be exposed only during reload, 8879thus hoisting loads out of loops and doing inter-block scheduling needs 8880a separate optimization pass. 8881 8882@item -fbranch-target-load-optimize2 8883@opindex fbranch-target-load-optimize2 8884Perform branch target register load optimization after prologue / epilogue 8885threading. 8886 8887@item -fbtr-bb-exclusive 8888@opindex fbtr-bb-exclusive 8889When performing branch target register load optimization, don't reuse 8890branch target registers within any basic block. 8891 8892@item -fstack-protector 8893@opindex fstack-protector 8894Emit extra code to check for buffer overflows, such as stack smashing 8895attacks. This is done by adding a guard variable to functions with 8896vulnerable objects. This includes functions that call @code{alloca}, and 8897functions with buffers larger than 8 bytes. The guards are initialized 8898when a function is entered and then checked when the function exits. 8899If a guard check fails, an error message is printed and the program exits. 8900 8901@item -fstack-protector-all 8902@opindex fstack-protector-all 8903Like @option{-fstack-protector} except that all functions are protected. 8904 8905@item -fsection-anchors 8906@opindex fsection-anchors 8907Try to reduce the number of symbolic address calculations by using 8908shared ``anchor'' symbols to address nearby objects. This transformation 8909can help to reduce the number of GOT entries and GOT accesses on some 8910targets. 8911 8912For example, the implementation of the following function @code{foo}: 8913 8914@smallexample 8915static int a, b, c; 8916int foo (void) @{ return a + b + c; @} 8917@end smallexample 8918 8919@noindent 8920usually calculates the addresses of all three variables, but if you 8921compile it with @option{-fsection-anchors}, it accesses the variables 8922from a common anchor point instead. The effect is similar to the 8923following pseudocode (which isn't valid C): 8924 8925@smallexample 8926int foo (void) 8927@{ 8928 register int *xr = &x; 8929 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; 8930@} 8931@end smallexample 8932 8933Not all targets support this option. 8934 8935@item --param @var{name}=@var{value} 8936@opindex param 8937In some places, GCC uses various constants to control the amount of 8938optimization that is done. For example, GCC does not inline functions 8939that contain more than a certain number of instructions. You can 8940control some of these constants on the command line using the 8941@option{--param} option. 8942 8943The names of specific parameters, and the meaning of the values, are 8944tied to the internals of the compiler, and are subject to change 8945without notice in future releases. 8946 8947In each case, the @var{value} is an integer. The allowable choices for 8948@var{name} are: 8949 8950@table @gcctabopt 8951@item predictable-branch-outcome 8952When branch is predicted to be taken with probability lower than this threshold 8953(in percent), then it is considered well predictable. The default is 10. 8954 8955@item max-crossjump-edges 8956The maximum number of incoming edges to consider for cross-jumping. 8957The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in 8958the number of edges incoming to each block. Increasing values mean 8959more aggressive optimization, making the compilation time increase with 8960probably small improvement in executable size. 8961 8962@item min-crossjump-insns 8963The minimum number of instructions that must be matched at the end 8964of two blocks before cross-jumping is performed on them. This 8965value is ignored in the case where all instructions in the block being 8966cross-jumped from are matched. The default value is 5. 8967 8968@item max-grow-copy-bb-insns 8969The maximum code size expansion factor when copying basic blocks 8970instead of jumping. The expansion is relative to a jump instruction. 8971The default value is 8. 8972 8973@item max-goto-duplication-insns 8974The maximum number of instructions to duplicate to a block that jumps 8975to a computed goto. To avoid @math{O(N^2)} behavior in a number of 8976passes, GCC factors computed gotos early in the compilation process, 8977and unfactors them as late as possible. Only computed jumps at the 8978end of a basic blocks with no more than max-goto-duplication-insns are 8979unfactored. The default value is 8. 8980 8981@item max-delay-slot-insn-search 8982The maximum number of instructions to consider when looking for an 8983instruction to fill a delay slot. If more than this arbitrary number of 8984instructions are searched, the time savings from filling the delay slot 8985are minimal, so stop searching. Increasing values mean more 8986aggressive optimization, making the compilation time increase with probably 8987small improvement in execution time. 8988 8989@item max-delay-slot-live-search 8990When trying to fill delay slots, the maximum number of instructions to 8991consider when searching for a block with valid live register 8992information. Increasing this arbitrarily chosen value means more 8993aggressive optimization, increasing the compilation time. This parameter 8994should be removed when the delay slot code is rewritten to maintain the 8995control-flow graph. 8996 8997@item max-gcse-memory 8998The approximate maximum amount of memory that can be allocated in 8999order to perform the global common subexpression elimination 9000optimization. If more memory than specified is required, the 9001optimization is not done. 9002 9003@item max-gcse-insertion-ratio 9004If the ratio of expression insertions to deletions is larger than this value 9005for any expression, then RTL PRE inserts or removes the expression and thus 9006leaves partially redundant computations in the instruction stream. The default value is 20. 9007 9008@item max-pending-list-length 9009The maximum number of pending dependencies scheduling allows 9010before flushing the current state and starting over. Large functions 9011with few branches or calls can create excessively large lists which 9012needlessly consume memory and resources. 9013 9014@item max-modulo-backtrack-attempts 9015The maximum number of backtrack attempts the scheduler should make 9016when modulo scheduling a loop. Larger values can exponentially increase 9017compilation time. 9018 9019@item max-inline-insns-single 9020Several parameters control the tree inliner used in GCC@. 9021This number sets the maximum number of instructions (counted in GCC's 9022internal representation) in a single function that the tree inliner 9023considers for inlining. This only affects functions declared 9024inline and methods implemented in a class declaration (C++). 9025The default value is 400. 9026 9027@item max-inline-insns-auto 9028When you use @option{-finline-functions} (included in @option{-O3}), 9029a lot of functions that would otherwise not be considered for inlining 9030by the compiler are investigated. To those functions, a different 9031(more restrictive) limit compared to functions declared inline can 9032be applied. 9033The default value is 40. 9034 9035@item inline-min-speedup 9036When estimated performance improvement of caller + callee runtime exceeds this 9037threshold (in precent), the function can be inlined regardless the limit on 9038@option{--param max-inline-insns-single} and @option{--param 9039max-inline-insns-auto}. 9040 9041@item large-function-insns 9042The limit specifying really large functions. For functions larger than this 9043limit after inlining, inlining is constrained by 9044@option{--param large-function-growth}. This parameter is useful primarily 9045to avoid extreme compilation time caused by non-linear algorithms used by the 9046back end. 9047The default value is 2700. 9048 9049@item large-function-growth 9050Specifies maximal growth of large function caused by inlining in percents. 9051The default value is 100 which limits large function growth to 2.0 times 9052the original size. 9053 9054@item large-unit-insns 9055The limit specifying large translation unit. Growth caused by inlining of 9056units larger than this limit is limited by @option{--param inline-unit-growth}. 9057For small units this might be too tight. 9058For example, consider a unit consisting of function A 9059that is inline and B that just calls A three times. If B is small relative to 9060A, the growth of unit is 300\% and yet such inlining is very sane. For very 9061large units consisting of small inlineable functions, however, the overall unit 9062growth limit is needed to avoid exponential explosion of code size. Thus for 9063smaller units, the size is increased to @option{--param large-unit-insns} 9064before applying @option{--param inline-unit-growth}. The default is 10000. 9065 9066@item inline-unit-growth 9067Specifies maximal overall growth of the compilation unit caused by inlining. 9068The default value is 30 which limits unit growth to 1.3 times the original 9069size. 9070 9071@item ipcp-unit-growth 9072Specifies maximal overall growth of the compilation unit caused by 9073interprocedural constant propagation. The default value is 10 which limits 9074unit growth to 1.1 times the original size. 9075 9076@item large-stack-frame 9077The limit specifying large stack frames. While inlining the algorithm is trying 9078to not grow past this limit too much. The default value is 256 bytes. 9079 9080@item large-stack-frame-growth 9081Specifies maximal growth of large stack frames caused by inlining in percents. 9082The default value is 1000 which limits large stack frame growth to 11 times 9083the original size. 9084 9085@item max-inline-insns-recursive 9086@itemx max-inline-insns-recursive-auto 9087Specifies the maximum number of instructions an out-of-line copy of a 9088self-recursive inline 9089function can grow into by performing recursive inlining. 9090 9091For functions declared inline, @option{--param max-inline-insns-recursive} is 9092taken into account. For functions not declared inline, recursive inlining 9093happens only when @option{-finline-functions} (included in @option{-O3}) is 9094enabled and @option{--param max-inline-insns-recursive-auto} is used. The 9095default value is 450. 9096 9097@item max-inline-recursive-depth 9098@itemx max-inline-recursive-depth-auto 9099Specifies the maximum recursion depth used for recursive inlining. 9100 9101For functions declared inline, @option{--param max-inline-recursive-depth} is 9102taken into account. For functions not declared inline, recursive inlining 9103happens only when @option{-finline-functions} (included in @option{-O3}) is 9104enabled and @option{--param max-inline-recursive-depth-auto} is used. The 9105default value is 8. 9106 9107@item min-inline-recursive-probability 9108Recursive inlining is profitable only for function having deep recursion 9109in average and can hurt for function having little recursion depth by 9110increasing the prologue size or complexity of function body to other 9111optimizers. 9112 9113When profile feedback is available (see @option{-fprofile-generate}) the actual 9114recursion depth can be guessed from probability that function recurses via a 9115given call expression. This parameter limits inlining only to call expressions 9116whose probability exceeds the given threshold (in percents). 9117The default value is 10. 9118 9119@item early-inlining-insns 9120Specify growth that the early inliner can make. In effect it increases 9121the amount of inlining for code having a large abstraction penalty. 9122The default value is 10. 9123 9124@item max-early-inliner-iterations 9125@itemx max-early-inliner-iterations 9126Limit of iterations of the early inliner. This basically bounds 9127the number of nested indirect calls the early inliner can resolve. 9128Deeper chains are still handled by late inlining. 9129 9130@item comdat-sharing-probability 9131@itemx comdat-sharing-probability 9132Probability (in percent) that C++ inline function with comdat visibility 9133are shared across multiple compilation units. The default value is 20. 9134 9135@item min-vect-loop-bound 9136The minimum number of iterations under which loops are not vectorized 9137when @option{-ftree-vectorize} is used. The number of iterations after 9138vectorization needs to be greater than the value specified by this option 9139to allow vectorization. The default value is 0. 9140 9141@item gcse-cost-distance-ratio 9142Scaling factor in calculation of maximum distance an expression 9143can be moved by GCSE optimizations. This is currently supported only in the 9144code hoisting pass. The bigger the ratio, the more aggressive code hoisting 9145is with simple expressions, i.e., the expressions that have cost 9146less than @option{gcse-unrestricted-cost}. Specifying 0 disables 9147hoisting of simple expressions. The default value is 10. 9148 9149@item gcse-unrestricted-cost 9150Cost, roughly measured as the cost of a single typical machine 9151instruction, at which GCSE optimizations do not constrain 9152the distance an expression can travel. This is currently 9153supported only in the code hoisting pass. The lesser the cost, 9154the more aggressive code hoisting is. Specifying 0 9155allows all expressions to travel unrestricted distances. 9156The default value is 3. 9157 9158@item max-hoist-depth 9159The depth of search in the dominator tree for expressions to hoist. 9160This is used to avoid quadratic behavior in hoisting algorithm. 9161The value of 0 does not limit on the search, but may slow down compilation 9162of huge functions. The default value is 30. 9163 9164@item max-tail-merge-comparisons 9165The maximum amount of similar bbs to compare a bb with. This is used to 9166avoid quadratic behavior in tree tail merging. The default value is 10. 9167 9168@item max-tail-merge-iterations 9169The maximum amount of iterations of the pass over the function. This is used to 9170limit compilation time in tree tail merging. The default value is 2. 9171 9172@item max-unrolled-insns 9173The maximum number of instructions that a loop may have to be unrolled. 9174If a loop is unrolled, this parameter also determines how many times 9175the loop code is unrolled. 9176 9177@item max-average-unrolled-insns 9178The maximum number of instructions biased by probabilities of their execution 9179that a loop may have to be unrolled. If a loop is unrolled, 9180this parameter also determines how many times the loop code is unrolled. 9181 9182@item max-unroll-times 9183The maximum number of unrollings of a single loop. 9184 9185@item max-peeled-insns 9186The maximum number of instructions that a loop may have to be peeled. 9187If a loop is peeled, this parameter also determines how many times 9188the loop code is peeled. 9189 9190@item max-peel-times 9191The maximum number of peelings of a single loop. 9192 9193@item max-peel-branches 9194The maximum number of branches on the hot path through the peeled sequence. 9195 9196@item max-completely-peeled-insns 9197The maximum number of insns of a completely peeled loop. 9198 9199@item max-completely-peel-times 9200The maximum number of iterations of a loop to be suitable for complete peeling. 9201 9202@item max-completely-peel-loop-nest-depth 9203The maximum depth of a loop nest suitable for complete peeling. 9204 9205@item max-unswitch-insns 9206The maximum number of insns of an unswitched loop. 9207 9208@item max-unswitch-level 9209The maximum number of branches unswitched in a single loop. 9210 9211@item lim-expensive 9212The minimum cost of an expensive expression in the loop invariant motion. 9213 9214@item iv-consider-all-candidates-bound 9215Bound on number of candidates for induction variables, below which 9216all candidates are considered for each use in induction variable 9217optimizations. If there are more candidates than this, 9218only the most relevant ones are considered to avoid quadratic time complexity. 9219 9220@item iv-max-considered-uses 9221The induction variable optimizations give up on loops that contain more 9222induction variable uses. 9223 9224@item iv-always-prune-cand-set-bound 9225If the number of candidates in the set is smaller than this value, 9226always try to remove unnecessary ivs from the set 9227when adding a new one. 9228 9229@item scev-max-expr-size 9230Bound on size of expressions used in the scalar evolutions analyzer. 9231Large expressions slow the analyzer. 9232 9233@item scev-max-expr-complexity 9234Bound on the complexity of the expressions in the scalar evolutions analyzer. 9235Complex expressions slow the analyzer. 9236 9237@item omega-max-vars 9238The maximum number of variables in an Omega constraint system. 9239The default value is 128. 9240 9241@item omega-max-geqs 9242The maximum number of inequalities in an Omega constraint system. 9243The default value is 256. 9244 9245@item omega-max-eqs 9246The maximum number of equalities in an Omega constraint system. 9247The default value is 128. 9248 9249@item omega-max-wild-cards 9250The maximum number of wildcard variables that the Omega solver is 9251able to insert. The default value is 18. 9252 9253@item omega-hash-table-size 9254The size of the hash table in the Omega solver. The default value is 9255550. 9256 9257@item omega-max-keys 9258The maximal number of keys used by the Omega solver. The default 9259value is 500. 9260 9261@item omega-eliminate-redundant-constraints 9262When set to 1, use expensive methods to eliminate all redundant 9263constraints. The default value is 0. 9264 9265@item vect-max-version-for-alignment-checks 9266The maximum number of run-time checks that can be performed when 9267doing loop versioning for alignment in the vectorizer. See option 9268@option{-ftree-vect-loop-version} for more information. 9269 9270@item vect-max-version-for-alias-checks 9271The maximum number of run-time checks that can be performed when 9272doing loop versioning for alias in the vectorizer. See option 9273@option{-ftree-vect-loop-version} for more information. 9274 9275@item max-iterations-to-track 9276The maximum number of iterations of a loop the brute-force algorithm 9277for analysis of the number of iterations of the loop tries to evaluate. 9278 9279@item hot-bb-count-ws-permille 9280A basic block profile count is considered hot if it contributes to 9281the given permillage (i.e. 0...1000) of the entire profiled execution. 9282 9283@item hot-bb-frequency-fraction 9284Select fraction of the entry block frequency of executions of basic block in 9285function given basic block needs to have to be considered hot. 9286 9287@item max-predicted-iterations 9288The maximum number of loop iterations we predict statically. This is useful 9289in cases where a function contains a single loop with known bound and 9290another loop with unknown bound. 9291The known number of iterations is predicted correctly, while 9292the unknown number of iterations average to roughly 10. This means that the 9293loop without bounds appears artificially cold relative to the other one. 9294 9295@item align-threshold 9296 9297Select fraction of the maximal frequency of executions of a basic block in 9298a function to align the basic block. 9299 9300@item align-loop-iterations 9301 9302A loop expected to iterate at least the selected number of iterations is 9303aligned. 9304 9305@item tracer-dynamic-coverage 9306@itemx tracer-dynamic-coverage-feedback 9307 9308This value is used to limit superblock formation once the given percentage of 9309executed instructions is covered. This limits unnecessary code size 9310expansion. 9311 9312The @option{tracer-dynamic-coverage-feedback} is used only when profile 9313feedback is available. The real profiles (as opposed to statically estimated 9314ones) are much less balanced allowing the threshold to be larger value. 9315 9316@item tracer-max-code-growth 9317Stop tail duplication once code growth has reached given percentage. This is 9318a rather artificial limit, as most of the duplicates are eliminated later in 9319cross jumping, so it may be set to much higher values than is the desired code 9320growth. 9321 9322@item tracer-min-branch-ratio 9323 9324Stop reverse growth when the reverse probability of best edge is less than this 9325threshold (in percent). 9326 9327@item tracer-min-branch-ratio 9328@itemx tracer-min-branch-ratio-feedback 9329 9330Stop forward growth if the best edge has probability lower than this 9331threshold. 9332 9333Similarly to @option{tracer-dynamic-coverage} two values are present, one for 9334compilation for profile feedback and one for compilation without. The value 9335for compilation with profile feedback needs to be more conservative (higher) in 9336order to make tracer effective. 9337 9338@item max-cse-path-length 9339 9340The maximum number of basic blocks on path that CSE considers. 9341The default is 10. 9342 9343@item max-cse-insns 9344The maximum number of instructions CSE processes before flushing. 9345The default is 1000. 9346 9347@item ggc-min-expand 9348 9349GCC uses a garbage collector to manage its own memory allocation. This 9350parameter specifies the minimum percentage by which the garbage 9351collector's heap should be allowed to expand between collections. 9352Tuning this may improve compilation speed; it has no effect on code 9353generation. 9354 9355The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when 9356RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is 9357the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If 9358GCC is not able to calculate RAM on a particular platform, the lower 9359bound of 30% is used. Setting this parameter and 9360@option{ggc-min-heapsize} to zero causes a full collection to occur at 9361every opportunity. This is extremely slow, but can be useful for 9362debugging. 9363 9364@item ggc-min-heapsize 9365 9366Minimum size of the garbage collector's heap before it begins bothering 9367to collect garbage. The first collection occurs after the heap expands 9368by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, 9369tuning this may improve compilation speed, and has no effect on code 9370generation. 9371 9372The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that 9373tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but 9374with a lower bound of 4096 (four megabytes) and an upper bound of 9375131072 (128 megabytes). If GCC is not able to calculate RAM on a 9376particular platform, the lower bound is used. Setting this parameter 9377very large effectively disables garbage collection. Setting this 9378parameter and @option{ggc-min-expand} to zero causes a full collection 9379to occur at every opportunity. 9380 9381@item max-reload-search-insns 9382The maximum number of instruction reload should look backward for equivalent 9383register. Increasing values mean more aggressive optimization, making the 9384compilation time increase with probably slightly better performance. 9385The default value is 100. 9386 9387@item max-cselib-memory-locations 9388The maximum number of memory locations cselib should take into account. 9389Increasing values mean more aggressive optimization, making the compilation time 9390increase with probably slightly better performance. The default value is 500. 9391 9392@item reorder-blocks-duplicate 9393@itemx reorder-blocks-duplicate-feedback 9394 9395Used by the basic block reordering pass to decide whether to use unconditional 9396branch or duplicate the code on its destination. Code is duplicated when its 9397estimated size is smaller than this value multiplied by the estimated size of 9398unconditional jump in the hot spots of the program. 9399 9400The @option{reorder-block-duplicate-feedback} is used only when profile 9401feedback is available. It may be set to higher values than 9402@option{reorder-block-duplicate} since information about the hot spots is more 9403accurate. 9404 9405@item max-sched-ready-insns 9406The maximum number of instructions ready to be issued the scheduler should 9407consider at any given time during the first scheduling pass. Increasing 9408values mean more thorough searches, making the compilation time increase 9409with probably little benefit. The default value is 100. 9410 9411@item max-sched-region-blocks 9412The maximum number of blocks in a region to be considered for 9413interblock scheduling. The default value is 10. 9414 9415@item max-pipeline-region-blocks 9416The maximum number of blocks in a region to be considered for 9417pipelining in the selective scheduler. The default value is 15. 9418 9419@item max-sched-region-insns 9420The maximum number of insns in a region to be considered for 9421interblock scheduling. The default value is 100. 9422 9423@item max-pipeline-region-insns 9424The maximum number of insns in a region to be considered for 9425pipelining in the selective scheduler. The default value is 200. 9426 9427@item min-spec-prob 9428The minimum probability (in percents) of reaching a source block 9429for interblock speculative scheduling. The default value is 40. 9430 9431@item max-sched-extend-regions-iters 9432The maximum number of iterations through CFG to extend regions. 9433A value of 0 (the default) disables region extensions. 9434 9435@item max-sched-insn-conflict-delay 9436The maximum conflict delay for an insn to be considered for speculative motion. 9437The default value is 3. 9438 9439@item sched-spec-prob-cutoff 9440The minimal probability of speculation success (in percents), so that 9441speculative insns are scheduled. 9442The default value is 40. 9443 9444@item sched-spec-state-edge-prob-cutoff 9445The minimum probability an edge must have for the scheduler to save its 9446state across it. 9447The default value is 10. 9448 9449@item sched-mem-true-dep-cost 9450Minimal distance (in CPU cycles) between store and load targeting same 9451memory locations. The default value is 1. 9452 9453@item selsched-max-lookahead 9454The maximum size of the lookahead window of selective scheduling. It is a 9455depth of search for available instructions. 9456The default value is 50. 9457 9458@item selsched-max-sched-times 9459The maximum number of times that an instruction is scheduled during 9460selective scheduling. This is the limit on the number of iterations 9461through which the instruction may be pipelined. The default value is 2. 9462 9463@item selsched-max-insns-to-rename 9464The maximum number of best instructions in the ready list that are considered 9465for renaming in the selective scheduler. The default value is 2. 9466 9467@item sms-min-sc 9468The minimum value of stage count that swing modulo scheduler 9469generates. The default value is 2. 9470 9471@item max-last-value-rtl 9472The maximum size measured as number of RTLs that can be recorded in an expression 9473in combiner for a pseudo register as last known value of that register. The default 9474is 10000. 9475 9476@item integer-share-limit 9477Small integer constants can use a shared data structure, reducing the 9478compiler's memory usage and increasing its speed. This sets the maximum 9479value of a shared integer constant. The default value is 256. 9480 9481@item ssp-buffer-size 9482The minimum size of buffers (i.e.@: arrays) that receive stack smashing 9483protection when @option{-fstack-protection} is used. 9484 9485@item max-jump-thread-duplication-stmts 9486Maximum number of statements allowed in a block that needs to be 9487duplicated when threading jumps. 9488 9489@item max-fields-for-field-sensitive 9490Maximum number of fields in a structure treated in 9491a field sensitive manner during pointer analysis. The default is zero 9492for @option{-O0} and @option{-O1}, 9493and 100 for @option{-Os}, @option{-O2}, and @option{-O3}. 9494 9495@item prefetch-latency 9496Estimate on average number of instructions that are executed before 9497prefetch finishes. The distance prefetched ahead is proportional 9498to this constant. Increasing this number may also lead to less 9499streams being prefetched (see @option{simultaneous-prefetches}). 9500 9501@item simultaneous-prefetches 9502Maximum number of prefetches that can run at the same time. 9503 9504@item l1-cache-line-size 9505The size of cache line in L1 cache, in bytes. 9506 9507@item l1-cache-size 9508The size of L1 cache, in kilobytes. 9509 9510@item l2-cache-size 9511The size of L2 cache, in kilobytes. 9512 9513@item min-insn-to-prefetch-ratio 9514The minimum ratio between the number of instructions and the 9515number of prefetches to enable prefetching in a loop. 9516 9517@item prefetch-min-insn-to-mem-ratio 9518The minimum ratio between the number of instructions and the 9519number of memory references to enable prefetching in a loop. 9520 9521@item use-canonical-types 9522Whether the compiler should use the ``canonical'' type system. By 9523default, this should always be 1, which uses a more efficient internal 9524mechanism for comparing types in C++ and Objective-C++. However, if 9525bugs in the canonical type system are causing compilation failures, 9526set this value to 0 to disable canonical types. 9527 9528@item switch-conversion-max-branch-ratio 9529Switch initialization conversion refuses to create arrays that are 9530bigger than @option{switch-conversion-max-branch-ratio} times the number of 9531branches in the switch. 9532 9533@item max-partial-antic-length 9534Maximum length of the partial antic set computed during the tree 9535partial redundancy elimination optimization (@option{-ftree-pre}) when 9536optimizing at @option{-O3} and above. For some sorts of source code 9537the enhanced partial redundancy elimination optimization can run away, 9538consuming all of the memory available on the host machine. This 9539parameter sets a limit on the length of the sets that are computed, 9540which prevents the runaway behavior. Setting a value of 0 for 9541this parameter allows an unlimited set length. 9542 9543@item sccvn-max-scc-size 9544Maximum size of a strongly connected component (SCC) during SCCVN 9545processing. If this limit is hit, SCCVN processing for the whole 9546function is not done and optimizations depending on it are 9547disabled. The default maximum SCC size is 10000. 9548 9549@item sccvn-max-alias-queries-per-access 9550Maximum number of alias-oracle queries we perform when looking for 9551redundancies for loads and stores. If this limit is hit the search 9552is aborted and the load or store is not considered redundant. The 9553number of queries is algorithmically limited to the number of 9554stores on all paths from the load to the function entry. 9555The default maxmimum number of queries is 1000. 9556 9557@item ira-max-loops-num 9558IRA uses regional register allocation by default. If a function 9559contains more loops than the number given by this parameter, only at most 9560the given number of the most frequently-executed loops form regions 9561for regional register allocation. The default value of the 9562parameter is 100. 9563 9564@item ira-max-conflict-table-size 9565Although IRA uses a sophisticated algorithm to compress the conflict 9566table, the table can still require excessive amounts of memory for 9567huge functions. If the conflict table for a function could be more 9568than the size in MB given by this parameter, the register allocator 9569instead uses a faster, simpler, and lower-quality 9570algorithm that does not require building a pseudo-register conflict table. 9571The default value of the parameter is 2000. 9572 9573@item ira-loop-reserved-regs 9574IRA can be used to evaluate more accurate register pressure in loops 9575for decisions to move loop invariants (see @option{-O3}). The number 9576of available registers reserved for some other purposes is given 9577by this parameter. The default value of the parameter is 2, which is 9578the minimal number of registers needed by typical instructions. 9579This value is the best found from numerous experiments. 9580 9581@item loop-invariant-max-bbs-in-loop 9582Loop invariant motion can be very expensive, both in compilation time and 9583in amount of needed compile-time memory, with very large loops. Loops 9584with more basic blocks than this parameter won't have loop invariant 9585motion optimization performed on them. The default value of the 9586parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above. 9587 9588@item loop-max-datarefs-for-datadeps 9589Building data dapendencies is expensive for very large loops. This 9590parameter limits the number of data references in loops that are 9591considered for data dependence analysis. These large loops are no 9592handled by the optimizations using loop data dependencies. 9593The default value is 1000. 9594 9595@item max-vartrack-size 9596Sets a maximum number of hash table slots to use during variable 9597tracking dataflow analysis of any function. If this limit is exceeded 9598with variable tracking at assignments enabled, analysis for that 9599function is retried without it, after removing all debug insns from 9600the function. If the limit is exceeded even without debug insns, var 9601tracking analysis is completely disabled for the function. Setting 9602the parameter to zero makes it unlimited. 9603 9604@item max-vartrack-expr-depth 9605Sets a maximum number of recursion levels when attempting to map 9606variable names or debug temporaries to value expressions. This trades 9607compilation time for more complete debug information. If this is set too 9608low, value expressions that are available and could be represented in 9609debug information may end up not being used; setting this higher may 9610enable the compiler to find more complex debug expressions, but compile 9611time and memory use may grow. The default is 12. 9612 9613@item min-nondebug-insn-uid 9614Use uids starting at this parameter for nondebug insns. The range below 9615the parameter is reserved exclusively for debug insns created by 9616@option{-fvar-tracking-assignments}, but debug insns may get 9617(non-overlapping) uids above it if the reserved range is exhausted. 9618 9619@item ipa-sra-ptr-growth-factor 9620IPA-SRA replaces a pointer to an aggregate with one or more new 9621parameters only when their cumulative size is less or equal to 9622@option{ipa-sra-ptr-growth-factor} times the size of the original 9623pointer parameter. 9624 9625@item tm-max-aggregate-size 9626When making copies of thread-local variables in a transaction, this 9627parameter specifies the size in bytes after which variables are 9628saved with the logging functions as opposed to save/restore code 9629sequence pairs. This option only applies when using 9630@option{-fgnu-tm}. 9631 9632@item graphite-max-nb-scop-params 9633To avoid exponential effects in the Graphite loop transforms, the 9634number of parameters in a Static Control Part (SCoP) is bounded. The 9635default value is 10 parameters. A variable whose value is unknown at 9636compilation time and defined outside a SCoP is a parameter of the SCoP. 9637 9638@item graphite-max-bbs-per-function 9639To avoid exponential effects in the detection of SCoPs, the size of 9640the functions analyzed by Graphite is bounded. The default value is 9641100 basic blocks. 9642 9643@item loop-block-tile-size 9644Loop blocking or strip mining transforms, enabled with 9645@option{-floop-block} or @option{-floop-strip-mine}, strip mine each 9646loop in the loop nest by a given number of iterations. The strip 9647length can be changed using the @option{loop-block-tile-size} 9648parameter. The default value is 51 iterations. 9649 9650@item ipa-cp-value-list-size 9651IPA-CP attempts to track all possible values and types passed to a function's 9652parameter in order to propagate them and perform devirtualization. 9653@option{ipa-cp-value-list-size} is the maximum number of values and types it 9654stores per one formal parameter of a function. 9655 9656@item lto-partitions 9657Specify desired number of partitions produced during WHOPR compilation. 9658The number of partitions should exceed the number of CPUs used for compilation. 9659The default value is 32. 9660 9661@item lto-minpartition 9662Size of minimal partition for WHOPR (in estimated instructions). 9663This prevents expenses of splitting very small programs into too many 9664partitions. 9665 9666@item cxx-max-namespaces-for-diagnostic-help 9667The maximum number of namespaces to consult for suggestions when C++ 9668name lookup fails for an identifier. The default is 1000. 9669 9670@item sink-frequency-threshold 9671The maximum relative execution frequency (in percents) of the target block 9672relative to a statement's original block to allow statement sinking of a 9673statement. Larger numbers result in more aggressive statement sinking. 9674The default value is 75. A small positive adjustment is applied for 9675statements with memory operands as those are even more profitable so sink. 9676 9677@item max-stores-to-sink 9678The maximum number of conditional stores paires that can be sunk. Set to 0 9679if either vectorization (@option{-ftree-vectorize}) or if-conversion 9680(@option{-ftree-loop-if-convert}) is disabled. The default is 2. 9681 9682@item allow-load-data-races 9683Allow optimizers to introduce new data races on loads. 9684Set to 1 to allow, otherwise to 0. This option is enabled by default 9685unless implicitly set by the @option{-fmemory-model=} option. 9686 9687@item allow-store-data-races 9688Allow optimizers to introduce new data races on stores. 9689Set to 1 to allow, otherwise to 0. This option is enabled by default 9690unless implicitly set by the @option{-fmemory-model=} option. 9691 9692@item allow-packed-load-data-races 9693Allow optimizers to introduce new data races on packed data loads. 9694Set to 1 to allow, otherwise to 0. This option is enabled by default 9695unless implicitly set by the @option{-fmemory-model=} option. 9696 9697@item allow-packed-store-data-races 9698Allow optimizers to introduce new data races on packed data stores. 9699Set to 1 to allow, otherwise to 0. This option is enabled by default 9700unless implicitly set by the @option{-fmemory-model=} option. 9701 9702@item case-values-threshold 9703The smallest number of different values for which it is best to use a 9704jump-table instead of a tree of conditional branches. If the value is 97050, use the default for the machine. The default is 0. 9706 9707@item tree-reassoc-width 9708Set the maximum number of instructions executed in parallel in 9709reassociated tree. This parameter overrides target dependent 9710heuristics used by default if has non zero value. 9711 9712@item sched-pressure-algorithm 9713Choose between the two available implementations of 9714@option{-fsched-pressure}. Algorithm 1 is the original implementation 9715and is the more likely to prevent instructions from being reordered. 9716Algorithm 2 was designed to be a compromise between the relatively 9717conservative approach taken by algorithm 1 and the rather aggressive 9718approach taken by the default scheduler. It relies more heavily on 9719having a regular register file and accurate register pressure classes. 9720See @file{haifa-sched.c} in the GCC sources for more details. 9721 9722The default choice depends on the target. 9723 9724@item max-slsr-cand-scan 9725Set the maximum number of existing candidates that will be considered when 9726seeking a basis for a new straight-line strength reduction candidate. 9727 9728@end table 9729@end table 9730 9731@node Preprocessor Options 9732@section Options Controlling the Preprocessor 9733@cindex preprocessor options 9734@cindex options, preprocessor 9735 9736These options control the C preprocessor, which is run on each C source 9737file before actual compilation. 9738 9739If you use the @option{-E} option, nothing is done except preprocessing. 9740Some of these options make sense only together with @option{-E} because 9741they cause the preprocessor output to be unsuitable for actual 9742compilation. 9743 9744@table @gcctabopt 9745@item -Wp,@var{option} 9746@opindex Wp 9747You can use @option{-Wp,@var{option}} to bypass the compiler driver 9748and pass @var{option} directly through to the preprocessor. If 9749@var{option} contains commas, it is split into multiple options at the 9750commas. However, many options are modified, translated or interpreted 9751by the compiler driver before being passed to the preprocessor, and 9752@option{-Wp} forcibly bypasses this phase. The preprocessor's direct 9753interface is undocumented and subject to change, so whenever possible 9754you should avoid using @option{-Wp} and let the driver handle the 9755options instead. 9756 9757@item -Xpreprocessor @var{option} 9758@opindex Xpreprocessor 9759Pass @var{option} as an option to the preprocessor. You can use this to 9760supply system-specific preprocessor options that GCC does not 9761recognize. 9762 9763If you want to pass an option that takes an argument, you must use 9764@option{-Xpreprocessor} twice, once for the option and once for the argument. 9765 9766@item -no-integrated-cpp 9767@opindex no-integrated-cpp 9768Perform preprocessing as a separate pass before compilation. 9769By default, GCC performs preprocessing as an integrated part of 9770input tokenization and parsing. 9771If this option is provided, the appropriate language front end 9772(@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++, 9773and Objective-C, respectively) is instead invoked twice, 9774once for preprocessing only and once for actual compilation 9775of the preprocessed input. 9776This option may be useful in conjunction with the @option{-B} or 9777@option{-wrapper} options to specify an alternate preprocessor or 9778perform additional processing of the program source between 9779normal preprocessing and compilation. 9780@end table 9781 9782@include cppopts.texi 9783 9784@node Assembler Options 9785@section Passing Options to the Assembler 9786 9787@c prevent bad page break with this line 9788You can pass options to the assembler. 9789 9790@table @gcctabopt 9791@item -Wa,@var{option} 9792@opindex Wa 9793Pass @var{option} as an option to the assembler. If @var{option} 9794contains commas, it is split into multiple options at the commas. 9795 9796@item -Xassembler @var{option} 9797@opindex Xassembler 9798Pass @var{option} as an option to the assembler. You can use this to 9799supply system-specific assembler options that GCC does not 9800recognize. 9801 9802If you want to pass an option that takes an argument, you must use 9803@option{-Xassembler} twice, once for the option and once for the argument. 9804 9805@end table 9806 9807@node Link Options 9808@section Options for Linking 9809@cindex link options 9810@cindex options, linking 9811 9812These options come into play when the compiler links object files into 9813an executable output file. They are meaningless if the compiler is 9814not doing a link step. 9815 9816@table @gcctabopt 9817@cindex file names 9818@item @var{object-file-name} 9819A file name that does not end in a special recognized suffix is 9820considered to name an object file or library. (Object files are 9821distinguished from libraries by the linker according to the file 9822contents.) If linking is done, these object files are used as input 9823to the linker. 9824 9825@item -c 9826@itemx -S 9827@itemx -E 9828@opindex c 9829@opindex S 9830@opindex E 9831If any of these options is used, then the linker is not run, and 9832object file names should not be used as arguments. @xref{Overall 9833Options}. 9834 9835@cindex Libraries 9836@item -l@var{library} 9837@itemx -l @var{library} 9838@opindex l 9839Search the library named @var{library} when linking. (The second 9840alternative with the library as a separate argument is only for 9841POSIX compliance and is not recommended.) 9842 9843It makes a difference where in the command you write this option; the 9844linker searches and processes libraries and object files in the order they 9845are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} 9846after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers 9847to functions in @samp{z}, those functions may not be loaded. 9848 9849The linker searches a standard list of directories for the library, 9850which is actually a file named @file{lib@var{library}.a}. The linker 9851then uses this file as if it had been specified precisely by name. 9852 9853The directories searched include several standard system directories 9854plus any that you specify with @option{-L}. 9855 9856Normally the files found this way are library files---archive files 9857whose members are object files. The linker handles an archive file by 9858scanning through it for members which define symbols that have so far 9859been referenced but not defined. But if the file that is found is an 9860ordinary object file, it is linked in the usual fashion. The only 9861difference between using an @option{-l} option and specifying a file name 9862is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a} 9863and searches several directories. 9864 9865@item -lobjc 9866@opindex lobjc 9867You need this special case of the @option{-l} option in order to 9868link an Objective-C or Objective-C++ program. 9869 9870@item -nostartfiles 9871@opindex nostartfiles 9872Do not use the standard system startup files when linking. 9873The standard system libraries are used normally, unless @option{-nostdlib} 9874or @option{-nodefaultlibs} is used. 9875 9876@item -nodefaultlibs 9877@opindex nodefaultlibs 9878Do not use the standard system libraries when linking. 9879Only the libraries you specify are passed to the linker, and options 9880specifying linkage of the system libraries, such as @code{-static-libgcc} 9881or @code{-shared-libgcc}, are ignored. 9882The standard startup files are used normally, unless @option{-nostartfiles} 9883is used. 9884 9885The compiler may generate calls to @code{memcmp}, 9886@code{memset}, @code{memcpy} and @code{memmove}. 9887These entries are usually resolved by entries in 9888libc. These entry points should be supplied through some other 9889mechanism when this option is specified. 9890 9891@item -nostdlib 9892@opindex nostdlib 9893Do not use the standard system startup files or libraries when linking. 9894No startup files and only the libraries you specify are passed to 9895the linker, and options specifying linkage of the system libraries, such as 9896@code{-static-libgcc} or @code{-shared-libgcc}, are ignored. 9897 9898The compiler may generate calls to @code{memcmp}, @code{memset}, 9899@code{memcpy} and @code{memmove}. 9900These entries are usually resolved by entries in 9901libc. These entry points should be supplied through some other 9902mechanism when this option is specified. 9903 9904@cindex @option{-lgcc}, use with @option{-nostdlib} 9905@cindex @option{-nostdlib} and unresolved references 9906@cindex unresolved references and @option{-nostdlib} 9907@cindex @option{-lgcc}, use with @option{-nodefaultlibs} 9908@cindex @option{-nodefaultlibs} and unresolved references 9909@cindex unresolved references and @option{-nodefaultlibs} 9910One of the standard libraries bypassed by @option{-nostdlib} and 9911@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines 9912which GCC uses to overcome shortcomings of particular machines, or special 9913needs for some languages. 9914(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler 9915Collection (GCC) Internals}, 9916for more discussion of @file{libgcc.a}.) 9917In most cases, you need @file{libgcc.a} even when you want to avoid 9918other standard libraries. In other words, when you specify @option{-nostdlib} 9919or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. 9920This ensures that you have no unresolved references to internal GCC 9921library subroutines. 9922(An example of such an internal subroutine is @samp{__main}, used to ensure C++ 9923constructors are called; @pxref{Collect2,,@code{collect2}, gccint, 9924GNU Compiler Collection (GCC) Internals}.) 9925 9926@item -pie 9927@opindex pie 9928Produce a position independent executable on targets that support it. 9929For predictable results, you must also specify the same set of options 9930used for compilation (@option{-fpie}, @option{-fPIE}, 9931or model suboptions) when you specify this linker option. 9932 9933@item -rdynamic 9934@opindex rdynamic 9935Pass the flag @option{-export-dynamic} to the ELF linker, on targets 9936that support it. This instructs the linker to add all symbols, not 9937only used ones, to the dynamic symbol table. This option is needed 9938for some uses of @code{dlopen} or to allow obtaining backtraces 9939from within a program. 9940 9941@item -s 9942@opindex s 9943Remove all symbol table and relocation information from the executable. 9944 9945@item -static 9946@opindex static 9947On systems that support dynamic linking, this prevents linking with the shared 9948libraries. On other systems, this option has no effect. 9949 9950@item -shared 9951@opindex shared 9952Produce a shared object which can then be linked with other objects to 9953form an executable. Not all systems support this option. For predictable 9954results, you must also specify the same set of options used for compilation 9955(@option{-fpic}, @option{-fPIC}, or model suboptions) when 9956you specify this linker option.@footnote{On some systems, @samp{gcc -shared} 9957needs to build supplementary stub code for constructors to work. On 9958multi-libbed systems, @samp{gcc -shared} must select the correct support 9959libraries to link against. Failing to supply the correct flags may lead 9960to subtle defects. Supplying them in cases where they are not necessary 9961is innocuous.} 9962 9963@item -shared-libgcc 9964@itemx -static-libgcc 9965@opindex shared-libgcc 9966@opindex static-libgcc 9967On systems that provide @file{libgcc} as a shared library, these options 9968force the use of either the shared or static version, respectively. 9969If no shared version of @file{libgcc} was built when the compiler was 9970configured, these options have no effect. 9971 9972There are several situations in which an application should use the 9973shared @file{libgcc} instead of the static version. The most common 9974of these is when the application wishes to throw and catch exceptions 9975across different shared libraries. In that case, each of the libraries 9976as well as the application itself should use the shared @file{libgcc}. 9977 9978Therefore, the G++ and GCJ drivers automatically add 9979@option{-shared-libgcc} whenever you build a shared library or a main 9980executable, because C++ and Java programs typically use exceptions, so 9981this is the right thing to do. 9982 9983If, instead, you use the GCC driver to create shared libraries, you may 9984find that they are not always linked with the shared @file{libgcc}. 9985If GCC finds, at its configuration time, that you have a non-GNU linker 9986or a GNU linker that does not support option @option{--eh-frame-hdr}, 9987it links the shared version of @file{libgcc} into shared libraries 9988by default. Otherwise, it takes advantage of the linker and optimizes 9989away the linking with the shared version of @file{libgcc}, linking with 9990the static version of libgcc by default. This allows exceptions to 9991propagate through such shared libraries, without incurring relocation 9992costs at library load time. 9993 9994However, if a library or main executable is supposed to throw or catch 9995exceptions, you must link it using the G++ or GCJ driver, as appropriate 9996for the languages used in the program, or using the option 9997@option{-shared-libgcc}, such that it is linked with the shared 9998@file{libgcc}. 9999 10000@item -static-libasan 10001When the @option{-fsanitize=address} option is used to link a program, 10002the GCC driver automatically links against @option{libasan}. If 10003@file{libasan} is available as a shared library, and the @option{-static} 10004option is not used, then this links against the shared version of 10005@file{libasan}. The @option{-static-libasan} option directs the GCC 10006driver to link @file{libasan} statically, without necessarily linking 10007other libraries statically. 10008 10009@item -static-libtsan 10010When the @option{-fsanitize=thread} option is used to link a program, 10011the GCC driver automatically links against @option{libtsan}. If 10012@file{libtsan} is available as a shared library, and the @option{-static} 10013option is not used, then this links against the shared version of 10014@file{libtsan}. The @option{-static-libtsan} option directs the GCC 10015driver to link @file{libtsan} statically, without necessarily linking 10016other libraries statically. 10017 10018@item -static-libstdc++ 10019When the @command{g++} program is used to link a C++ program, it 10020normally automatically links against @option{libstdc++}. If 10021@file{libstdc++} is available as a shared library, and the 10022@option{-static} option is not used, then this links against the 10023shared version of @file{libstdc++}. That is normally fine. However, it 10024is sometimes useful to freeze the version of @file{libstdc++} used by 10025the program without going all the way to a fully static link. The 10026@option{-static-libstdc++} option directs the @command{g++} driver to 10027link @file{libstdc++} statically, without necessarily linking other 10028libraries statically. 10029 10030@item -symbolic 10031@opindex symbolic 10032Bind references to global symbols when building a shared object. Warn 10033about any unresolved references (unless overridden by the link editor 10034option @option{-Xlinker -z -Xlinker defs}). Only a few systems support 10035this option. 10036 10037@item -T @var{script} 10038@opindex T 10039@cindex linker script 10040Use @var{script} as the linker script. This option is supported by most 10041systems using the GNU linker. On some targets, such as bare-board 10042targets without an operating system, the @option{-T} option may be required 10043when linking to avoid references to undefined symbols. 10044 10045@item -Xlinker @var{option} 10046@opindex Xlinker 10047Pass @var{option} as an option to the linker. You can use this to 10048supply system-specific linker options that GCC does not recognize. 10049 10050If you want to pass an option that takes a separate argument, you must use 10051@option{-Xlinker} twice, once for the option and once for the argument. 10052For example, to pass @option{-assert definitions}, you must write 10053@option{-Xlinker -assert -Xlinker definitions}. It does not work to write 10054@option{-Xlinker "-assert definitions"}, because this passes the entire 10055string as a single argument, which is not what the linker expects. 10056 10057When using the GNU linker, it is usually more convenient to pass 10058arguments to linker options using the @option{@var{option}=@var{value}} 10059syntax than as separate arguments. For example, you can specify 10060@option{-Xlinker -Map=output.map} rather than 10061@option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support 10062this syntax for command-line options. 10063 10064@item -Wl,@var{option} 10065@opindex Wl 10066Pass @var{option} as an option to the linker. If @var{option} contains 10067commas, it is split into multiple options at the commas. You can use this 10068syntax to pass an argument to the option. 10069For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the 10070linker. When using the GNU linker, you can also get the same effect with 10071@option{-Wl,-Map=output.map}. 10072 10073@item -u @var{symbol} 10074@opindex u 10075Pretend the symbol @var{symbol} is undefined, to force linking of 10076library modules to define it. You can use @option{-u} multiple times with 10077different symbols to force loading of additional library modules. 10078@end table 10079 10080@node Directory Options 10081@section Options for Directory Search 10082@cindex directory options 10083@cindex options, directory search 10084@cindex search path 10085 10086These options specify directories to search for header files, for 10087libraries and for parts of the compiler: 10088 10089@table @gcctabopt 10090@item -I@var{dir} 10091@opindex I 10092Add the directory @var{dir} to the head of the list of directories to be 10093searched for header files. This can be used to override a system header 10094file, substituting your own version, since these directories are 10095searched before the system header file directories. However, you should 10096not use this option to add directories that contain vendor-supplied 10097system header files (use @option{-isystem} for that). If you use more than 10098one @option{-I} option, the directories are scanned in left-to-right 10099order; the standard system directories come after. 10100 10101If a standard system include directory, or a directory specified with 10102@option{-isystem}, is also specified with @option{-I}, the @option{-I} 10103option is ignored. The directory is still searched but as a 10104system directory at its normal position in the system include chain. 10105This is to ensure that GCC's procedure to fix buggy system headers and 10106the ordering for the @code{include_next} directive are not inadvertently changed. 10107If you really need to change the search order for system directories, 10108use the @option{-nostdinc} and/or @option{-isystem} options. 10109 10110@item -iplugindir=@var{dir} 10111Set the directory to search for plugins that are passed 10112by @option{-fplugin=@var{name}} instead of 10113@option{-fplugin=@var{path}/@var{name}.so}. This option is not meant 10114to be used by the user, but only passed by the driver. 10115 10116@item -iquote@var{dir} 10117@opindex iquote 10118Add the directory @var{dir} to the head of the list of directories to 10119be searched for header files only for the case of @samp{#include 10120"@var{file}"}; they are not searched for @samp{#include <@var{file}>}, 10121otherwise just like @option{-I}. 10122 10123@item -iremap @var{src}:@var{dst} 10124@opindex iremap 10125Replace the prefix @var{src} in __FILE__ with @var{dst} at expansion time. 10126This option can be specified more than once. Processing stops at the first 10127match. 10128 10129@item -L@var{dir} 10130@opindex L 10131Add directory @var{dir} to the list of directories to be searched 10132for @option{-l}. 10133 10134@item -B@var{prefix} 10135@opindex B 10136This option specifies where to find the executables, libraries, 10137include files, and data files of the compiler itself. 10138 10139The compiler driver program runs one or more of the subprograms 10140@command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries 10141@var{prefix} as a prefix for each program it tries to run, both with and 10142without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). 10143 10144For each subprogram to be run, the compiler driver first tries the 10145@option{-B} prefix, if any. If that name is not found, or if @option{-B} 10146is not specified, the driver tries two standard prefixes, 10147@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of 10148those results in a file name that is found, the unmodified program 10149name is searched for using the directories specified in your 10150@env{PATH} environment variable. 10151 10152The compiler checks to see if the path provided by the @option{-B} 10153refers to a directory, and if necessary it adds a directory 10154separator character at the end of the path. 10155 10156@option{-B} prefixes that effectively specify directory names also apply 10157to libraries in the linker, because the compiler translates these 10158options into @option{-L} options for the linker. They also apply to 10159includes files in the preprocessor, because the compiler translates these 10160options into @option{-isystem} options for the preprocessor. In this case, 10161the compiler appends @samp{include} to the prefix. 10162 10163The runtime support file @file{libgcc.a} can also be searched for using 10164the @option{-B} prefix, if needed. If it is not found there, the two 10165standard prefixes above are tried, and that is all. The file is left 10166out of the link if it is not found by those means. 10167 10168Another way to specify a prefix much like the @option{-B} prefix is to use 10169the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment 10170Variables}. 10171 10172As a special kludge, if the path provided by @option{-B} is 10173@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to 101749, then it is replaced by @file{[dir/]include}. This is to help 10175with boot-strapping the compiler. 10176 10177@item -specs=@var{file} 10178@opindex specs 10179Process @var{file} after the compiler reads in the standard @file{specs} 10180file, in order to override the defaults which the @command{gcc} driver 10181program uses when determining what switches to pass to @command{cc1}, 10182@command{cc1plus}, @command{as}, @command{ld}, etc. More than one 10183@option{-specs=@var{file}} can be specified on the command line, and they 10184are processed in order, from left to right. 10185 10186@item --sysroot=@var{dir} 10187@opindex sysroot 10188Use @var{dir} as the logical root directory for headers and libraries. 10189For example, if the compiler normally searches for headers in 10190@file{/usr/include} and libraries in @file{/usr/lib}, it instead 10191searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. 10192 10193If you use both this option and the @option{-isysroot} option, then 10194the @option{--sysroot} option applies to libraries, but the 10195@option{-isysroot} option applies to header files. 10196 10197The GNU linker (beginning with version 2.16) has the necessary support 10198for this option. If your linker does not support this option, the 10199header file aspect of @option{--sysroot} still works, but the 10200library aspect does not. 10201 10202@item --no-sysroot-suffix 10203@opindex no-sysroot-suffix 10204For some targets, a suffix is added to the root directory specified 10205with @option{--sysroot}, depending on the other options used, so that 10206headers may for example be found in 10207@file{@var{dir}/@var{suffix}/usr/include} instead of 10208@file{@var{dir}/usr/include}. This option disables the addition of 10209such a suffix. 10210 10211@item -I- 10212@opindex I- 10213This option has been deprecated. Please use @option{-iquote} instead for 10214@option{-I} directories before the @option{-I-} and remove the @option{-I-}. 10215Any directories you specify with @option{-I} options before the @option{-I-} 10216option are searched only for the case of @samp{#include "@var{file}"}; 10217they are not searched for @samp{#include <@var{file}>}. 10218 10219If additional directories are specified with @option{-I} options after 10220the @option{-I-}, these directories are searched for all @samp{#include} 10221directives. (Ordinarily @emph{all} @option{-I} directories are used 10222this way.) 10223 10224In addition, the @option{-I-} option inhibits the use of the current 10225directory (where the current input file came from) as the first search 10226directory for @samp{#include "@var{file}"}. There is no way to 10227override this effect of @option{-I-}. With @option{-I.} you can specify 10228searching the directory that is current when the compiler is 10229invoked. That is not exactly the same as what the preprocessor does 10230by default, but it is often satisfactory. 10231 10232@option{-I-} does not inhibit the use of the standard system directories 10233for header files. Thus, @option{-I-} and @option{-nostdinc} are 10234independent. 10235@end table 10236 10237@c man end 10238 10239@node Spec Files 10240@section Specifying subprocesses and the switches to pass to them 10241@cindex Spec Files 10242 10243@command{gcc} is a driver program. It performs its job by invoking a 10244sequence of other programs to do the work of compiling, assembling and 10245linking. GCC interprets its command-line parameters and uses these to 10246deduce which programs it should invoke, and which command-line options 10247it ought to place on their command lines. This behavior is controlled 10248by @dfn{spec strings}. In most cases there is one spec string for each 10249program that GCC can invoke, but a few programs have multiple spec 10250strings to control their behavior. The spec strings built into GCC can 10251be overridden by using the @option{-specs=} command-line switch to specify 10252a spec file. 10253 10254@dfn{Spec files} are plaintext files that are used to construct spec 10255strings. They consist of a sequence of directives separated by blank 10256lines. The type of directive is determined by the first non-whitespace 10257character on the line, which can be one of the following: 10258 10259@table @code 10260@item %@var{command} 10261Issues a @var{command} to the spec file processor. The commands that can 10262appear here are: 10263 10264@table @code 10265@item %include <@var{file}> 10266@cindex @code{%include} 10267Search for @var{file} and insert its text at the current point in the 10268specs file. 10269 10270@item %include_noerr <@var{file}> 10271@cindex @code{%include_noerr} 10272Just like @samp{%include}, but do not generate an error message if the include 10273file cannot be found. 10274 10275@item %rename @var{old_name} @var{new_name} 10276@cindex @code{%rename} 10277Rename the spec string @var{old_name} to @var{new_name}. 10278 10279@end table 10280 10281@item *[@var{spec_name}]: 10282This tells the compiler to create, override or delete the named spec 10283string. All lines after this directive up to the next directive or 10284blank line are considered to be the text for the spec string. If this 10285results in an empty string then the spec is deleted. (Or, if the 10286spec did not exist, then nothing happens.) Otherwise, if the spec 10287does not currently exist a new spec is created. If the spec does 10288exist then its contents are overridden by the text of this 10289directive, unless the first character of that text is the @samp{+} 10290character, in which case the text is appended to the spec. 10291 10292@item [@var{suffix}]: 10293Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive 10294and up to the next directive or blank line are considered to make up the 10295spec string for the indicated suffix. When the compiler encounters an 10296input file with the named suffix, it processes the spec string in 10297order to work out how to compile that file. For example: 10298 10299@smallexample 10300.ZZ: 10301z-compile -input %i 10302@end smallexample 10303 10304This says that any input file whose name ends in @samp{.ZZ} should be 10305passed to the program @samp{z-compile}, which should be invoked with the 10306command-line switch @option{-input} and with the result of performing the 10307@samp{%i} substitution. (See below.) 10308 10309As an alternative to providing a spec string, the text following a 10310suffix directive can be one of the following: 10311 10312@table @code 10313@item @@@var{language} 10314This says that the suffix is an alias for a known @var{language}. This is 10315similar to using the @option{-x} command-line switch to GCC to specify a 10316language explicitly. For example: 10317 10318@smallexample 10319.ZZ: 10320@@c++ 10321@end smallexample 10322 10323Says that .ZZ files are, in fact, C++ source files. 10324 10325@item #@var{name} 10326This causes an error messages saying: 10327 10328@smallexample 10329@var{name} compiler not installed on this system. 10330@end smallexample 10331@end table 10332 10333GCC already has an extensive list of suffixes built into it. 10334This directive adds an entry to the end of the list of suffixes, but 10335since the list is searched from the end backwards, it is effectively 10336possible to override earlier entries using this technique. 10337 10338@end table 10339 10340GCC has the following spec strings built into it. Spec files can 10341override these strings or create their own. Note that individual 10342targets can also add their own spec strings to this list. 10343 10344@smallexample 10345asm Options to pass to the assembler 10346asm_final Options to pass to the assembler post-processor 10347cpp Options to pass to the C preprocessor 10348cc1 Options to pass to the C compiler 10349cc1plus Options to pass to the C++ compiler 10350endfile Object files to include at the end of the link 10351link Options to pass to the linker 10352lib Libraries to include on the command line to the linker 10353libgcc Decides which GCC support library to pass to the linker 10354linker Sets the name of the linker 10355predefines Defines to be passed to the C preprocessor 10356signed_char Defines to pass to CPP to say whether @code{char} is signed 10357 by default 10358startfile Object files to include at the start of the link 10359@end smallexample 10360 10361Here is a small example of a spec file: 10362 10363@smallexample 10364%rename lib old_lib 10365 10366*lib: 10367--start-group -lgcc -lc -leval1 --end-group %(old_lib) 10368@end smallexample 10369 10370This example renames the spec called @samp{lib} to @samp{old_lib} and 10371then overrides the previous definition of @samp{lib} with a new one. 10372The new definition adds in some extra command-line options before 10373including the text of the old definition. 10374 10375@dfn{Spec strings} are a list of command-line options to be passed to their 10376corresponding program. In addition, the spec strings can contain 10377@samp{%}-prefixed sequences to substitute variable text or to 10378conditionally insert text into the command line. Using these constructs 10379it is possible to generate quite complex command lines. 10380 10381Here is a table of all defined @samp{%}-sequences for spec 10382strings. Note that spaces are not generated automatically around the 10383results of expanding these sequences. Therefore you can concatenate them 10384together or combine them with constant text in a single argument. 10385 10386@table @code 10387@item %% 10388Substitute one @samp{%} into the program name or argument. 10389 10390@item %i 10391Substitute the name of the input file being processed. 10392 10393@item %b 10394Substitute the basename of the input file being processed. 10395This is the substring up to (and not including) the last period 10396and not including the directory. 10397 10398@item %B 10399This is the same as @samp{%b}, but include the file suffix (text after 10400the last period). 10401 10402@item %d 10403Marks the argument containing or following the @samp{%d} as a 10404temporary file name, so that that file is deleted if GCC exits 10405successfully. Unlike @samp{%g}, this contributes no text to the 10406argument. 10407 10408@item %g@var{suffix} 10409Substitute a file name that has suffix @var{suffix} and is chosen 10410once per compilation, and mark the argument in the same way as 10411@samp{%d}. To reduce exposure to denial-of-service attacks, the file 10412name is now chosen in a way that is hard to predict even when previously 10413chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} 10414might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches 10415the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is 10416treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} 10417was simply substituted with a file name chosen once per compilation, 10418without regard to any appended suffix (which was therefore treated 10419just like ordinary text), making such attacks more likely to succeed. 10420 10421@item %u@var{suffix} 10422Like @samp{%g}, but generates a new temporary file name 10423each time it appears instead of once per compilation. 10424 10425@item %U@var{suffix} 10426Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a 10427new one if there is no such last file name. In the absence of any 10428@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share 10429the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} 10430involves the generation of two distinct file names, one 10431for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was 10432simply substituted with a file name chosen for the previous @samp{%u}, 10433without regard to any appended suffix. 10434 10435@item %j@var{suffix} 10436Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is 10437writable, and if @option{-save-temps} is not used; 10438otherwise, substitute the name 10439of a temporary file, just like @samp{%u}. This temporary file is not 10440meant for communication between processes, but rather as a junk 10441disposal mechanism. 10442 10443@item %|@var{suffix} 10444@itemx %m@var{suffix} 10445Like @samp{%g}, except if @option{-pipe} is in effect. In that case 10446@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at 10447all. These are the two most common ways to instruct a program that it 10448should read from standard input or write to standard output. If you 10449need something more elaborate you can use an @samp{%@{pipe:@code{X}@}} 10450construct: see for example @file{f/lang-specs.h}. 10451 10452@item %.@var{SUFFIX} 10453Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args 10454when it is subsequently output with @samp{%*}. @var{SUFFIX} is 10455terminated by the next space or %. 10456 10457@item %w 10458Marks the argument containing or following the @samp{%w} as the 10459designated output file of this compilation. This puts the argument 10460into the sequence of arguments that @samp{%o} substitutes. 10461 10462@item %o 10463Substitutes the names of all the output files, with spaces 10464automatically placed around them. You should write spaces 10465around the @samp{%o} as well or the results are undefined. 10466@samp{%o} is for use in the specs for running the linker. 10467Input files whose names have no recognized suffix are not compiled 10468at all, but they are included among the output files, so they are 10469linked. 10470 10471@item %O 10472Substitutes the suffix for object files. Note that this is 10473handled specially when it immediately follows @samp{%g, %u, or %U}, 10474because of the need for those to form complete file names. The 10475handling is such that @samp{%O} is treated exactly as if it had already 10476been substituted, except that @samp{%g, %u, and %U} do not currently 10477support additional @var{suffix} characters following @samp{%O} as they do 10478following, for example, @samp{.o}. 10479 10480@item %p 10481Substitutes the standard macro predefinitions for the 10482current target machine. Use this when running @code{cpp}. 10483 10484@item %P 10485Like @samp{%p}, but puts @samp{__} before and after the name of each 10486predefined macro, except for macros that start with @samp{__} or with 10487@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO 10488C@. 10489 10490@item %I 10491Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}), 10492@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), 10493@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options) 10494and @option{-imultilib} as necessary. 10495 10496@item %s 10497Current argument is the name of a library or startup file of some sort. 10498Search for that file in a standard list of directories and substitute 10499the full name found. The current working directory is included in the 10500list of directories scanned. 10501 10502@item %T 10503Current argument is the name of a linker script. Search for that file 10504in the current list of directories to scan for libraries. If the file 10505is located insert a @option{--script} option into the command line 10506followed by the full path name found. If the file is not found then 10507generate an error message. Note: the current working directory is not 10508searched. 10509 10510@item %e@var{str} 10511Print @var{str} as an error message. @var{str} is terminated by a newline. 10512Use this when inconsistent options are detected. 10513 10514@item %(@var{name}) 10515Substitute the contents of spec string @var{name} at this point. 10516 10517@item %x@{@var{option}@} 10518Accumulate an option for @samp{%X}. 10519 10520@item %X 10521Output the accumulated linker options specified by @option{-Wl} or a @samp{%x} 10522spec string. 10523 10524@item %Y 10525Output the accumulated assembler options specified by @option{-Wa}. 10526 10527@item %Z 10528Output the accumulated preprocessor options specified by @option{-Wp}. 10529 10530@item %a 10531Process the @code{asm} spec. This is used to compute the 10532switches to be passed to the assembler. 10533 10534@item %A 10535Process the @code{asm_final} spec. This is a spec string for 10536passing switches to an assembler post-processor, if such a program is 10537needed. 10538 10539@item %l 10540Process the @code{link} spec. This is the spec for computing the 10541command line passed to the linker. Typically it makes use of the 10542@samp{%L %G %S %D and %E} sequences. 10543 10544@item %D 10545Dump out a @option{-L} option for each directory that GCC believes might 10546contain startup files. If the target supports multilibs then the 10547current multilib directory is prepended to each of these paths. 10548 10549@item %L 10550Process the @code{lib} spec. This is a spec string for deciding which 10551libraries are included on the command line to the linker. 10552 10553@item %G 10554Process the @code{libgcc} spec. This is a spec string for deciding 10555which GCC support library is included on the command line to the linker. 10556 10557@item %S 10558Process the @code{startfile} spec. This is a spec for deciding which 10559object files are the first ones passed to the linker. Typically 10560this might be a file named @file{crt0.o}. 10561 10562@item %E 10563Process the @code{endfile} spec. This is a spec string that specifies 10564the last object files that are passed to the linker. 10565 10566@item %C 10567Process the @code{cpp} spec. This is used to construct the arguments 10568to be passed to the C preprocessor. 10569 10570@item %1 10571Process the @code{cc1} spec. This is used to construct the options to be 10572passed to the actual C compiler (@samp{cc1}). 10573 10574@item %2 10575Process the @code{cc1plus} spec. This is used to construct the options to be 10576passed to the actual C++ compiler (@samp{cc1plus}). 10577 10578@item %* 10579Substitute the variable part of a matched option. See below. 10580Note that each comma in the substituted string is replaced by 10581a single space. 10582 10583@item %<@code{S} 10584Remove all occurrences of @code{-S} from the command line. Note---this 10585command is position dependent. @samp{%} commands in the spec string 10586before this one see @code{-S}, @samp{%} commands in the spec string 10587after this one do not. 10588 10589@item %:@var{function}(@var{args}) 10590Call the named function @var{function}, passing it @var{args}. 10591@var{args} is first processed as a nested spec string, then split 10592into an argument vector in the usual fashion. The function returns 10593a string which is processed as if it had appeared literally as part 10594of the current spec. 10595 10596The following built-in spec functions are provided: 10597 10598@table @code 10599@item @code{getenv} 10600The @code{getenv} spec function takes two arguments: an environment 10601variable name and a string. If the environment variable is not 10602defined, a fatal error is issued. Otherwise, the return value is the 10603value of the environment variable concatenated with the string. For 10604example, if @env{TOPDIR} is defined as @file{/path/to/top}, then: 10605 10606@smallexample 10607%:getenv(TOPDIR /include) 10608@end smallexample 10609 10610expands to @file{/path/to/top/include}. 10611 10612@item @code{if-exists} 10613The @code{if-exists} spec function takes one argument, an absolute 10614pathname to a file. If the file exists, @code{if-exists} returns the 10615pathname. Here is a small example of its usage: 10616 10617@smallexample 10618*startfile: 10619crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s 10620@end smallexample 10621 10622@item @code{if-exists-else} 10623The @code{if-exists-else} spec function is similar to the @code{if-exists} 10624spec function, except that it takes two arguments. The first argument is 10625an absolute pathname to a file. If the file exists, @code{if-exists-else} 10626returns the pathname. If it does not exist, it returns the second argument. 10627This way, @code{if-exists-else} can be used to select one file or another, 10628based on the existence of the first. Here is a small example of its usage: 10629 10630@smallexample 10631*startfile: 10632crt0%O%s %:if-exists(crti%O%s) \ 10633%:if-exists-else(crtbeginT%O%s crtbegin%O%s) 10634@end smallexample 10635 10636@item @code{replace-outfile} 10637The @code{replace-outfile} spec function takes two arguments. It looks for the 10638first argument in the outfiles array and replaces it with the second argument. Here 10639is a small example of its usage: 10640 10641@smallexample 10642%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@} 10643@end smallexample 10644 10645@item @code{remove-outfile} 10646The @code{remove-outfile} spec function takes one argument. It looks for the 10647first argument in the outfiles array and removes it. Here is a small example 10648its usage: 10649 10650@smallexample 10651%:remove-outfile(-lm) 10652@end smallexample 10653 10654@item @code{pass-through-libs} 10655The @code{pass-through-libs} spec function takes any number of arguments. It 10656finds any @option{-l} options and any non-options ending in @file{.a} (which it 10657assumes are the names of linker input library archive files) and returns a 10658result containing all the found arguments each prepended by 10659@option{-plugin-opt=-pass-through=} and joined by spaces. This list is 10660intended to be passed to the LTO linker plugin. 10661 10662@smallexample 10663%:pass-through-libs(%G %L %G) 10664@end smallexample 10665 10666@item @code{print-asm-header} 10667The @code{print-asm-header} function takes no arguments and simply 10668prints a banner like: 10669 10670@smallexample 10671Assembler options 10672================= 10673 10674Use "-Wa,OPTION" to pass "OPTION" to the assembler. 10675@end smallexample 10676 10677It is used to separate compiler options from assembler options 10678in the @option{--target-help} output. 10679@end table 10680 10681@item %@{@code{S}@} 10682Substitutes the @code{-S} switch, if that switch is given to GCC@. 10683If that switch is not specified, this substitutes nothing. Note that 10684the leading dash is omitted when specifying this option, and it is 10685automatically inserted if the substitution is performed. Thus the spec 10686string @samp{%@{foo@}} matches the command-line option @option{-foo} 10687and outputs the command-line option @option{-foo}. 10688 10689@item %W@{@code{S}@} 10690Like %@{@code{S}@} but mark last argument supplied within as a file to be 10691deleted on failure. 10692 10693@item %@{@code{S}*@} 10694Substitutes all the switches specified to GCC whose names start 10695with @code{-S}, but which also take an argument. This is used for 10696switches like @option{-o}, @option{-D}, @option{-I}, etc. 10697GCC considers @option{-o foo} as being 10698one switch whose name starts with @samp{o}. %@{o*@} substitutes this 10699text, including the space. Thus two arguments are generated. 10700 10701@item %@{@code{S}*&@code{T}*@} 10702Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options 10703(the order of @code{S} and @code{T} in the spec is not significant). 10704There can be any number of ampersand-separated variables; for each the 10705wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. 10706 10707@item %@{@code{S}:@code{X}@} 10708Substitutes @code{X}, if the @option{-S} switch is given to GCC@. 10709 10710@item %@{!@code{S}:@code{X}@} 10711Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@. 10712 10713@item %@{@code{S}*:@code{X}@} 10714Substitutes @code{X} if one or more switches whose names start with 10715@code{-S} are specified to GCC@. Normally @code{X} is substituted only 10716once, no matter how many such switches appeared. However, if @code{%*} 10717appears somewhere in @code{X}, then @code{X} is substituted once 10718for each matching switch, with the @code{%*} replaced by the part of 10719that switch matching the @code{*}. 10720 10721@item %@{.@code{S}:@code{X}@} 10722Substitutes @code{X}, if processing a file with suffix @code{S}. 10723 10724@item %@{!.@code{S}:@code{X}@} 10725Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}. 10726 10727@item %@{,@code{S}:@code{X}@} 10728Substitutes @code{X}, if processing a file for language @code{S}. 10729 10730@item %@{!,@code{S}:@code{X}@} 10731Substitutes @code{X}, if not processing a file for language @code{S}. 10732 10733@item %@{@code{S}|@code{P}:@code{X}@} 10734Substitutes @code{X} if either @code{-S} or @code{-P} is given to 10735GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and 10736@code{*} sequences as well, although they have a stronger binding than 10737the @samp{|}. If @code{%*} appears in @code{X}, all of the 10738alternatives must be starred, and only the first matching alternative 10739is substituted. 10740 10741For example, a spec string like this: 10742 10743@smallexample 10744%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} 10745@end smallexample 10746 10747@noindent 10748outputs the following command-line options from the following input 10749command-line options: 10750 10751@smallexample 10752fred.c -foo -baz 10753jim.d -bar -boggle 10754-d fred.c -foo -baz -boggle 10755-d jim.d -bar -baz -boggle 10756@end smallexample 10757 10758@item %@{S:X; T:Y; :D@} 10759 10760If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is 10761given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can 10762be as many clauses as you need. This may be combined with @code{.}, 10763@code{,}, @code{!}, @code{|}, and @code{*} as needed. 10764 10765 10766@end table 10767 10768The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar 10769construct may contain other nested @samp{%} constructs or spaces, or 10770even newlines. They are processed as usual, as described above. 10771Trailing white space in @code{X} is ignored. White space may also 10772appear anywhere on the left side of the colon in these constructs, 10773except between @code{.} or @code{*} and the corresponding word. 10774 10775The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are 10776handled specifically in these constructs. If another value of 10777@option{-O} or the negated form of a @option{-f}, @option{-m}, or 10778@option{-W} switch is found later in the command line, the earlier 10779switch value is ignored, except with @{@code{S}*@} where @code{S} is 10780just one letter, which passes all matching options. 10781 10782The character @samp{|} at the beginning of the predicate text is used to 10783indicate that a command should be piped to the following command, but 10784only if @option{-pipe} is specified. 10785 10786It is built into GCC which switches take arguments and which do not. 10787(You might think it would be useful to generalize this to allow each 10788compiler's spec to say which switches take arguments. But this cannot 10789be done in a consistent fashion. GCC cannot even decide which input 10790files have been specified without knowing which switches take arguments, 10791and it must know which input files to compile in order to tell which 10792compilers to run). 10793 10794GCC also knows implicitly that arguments starting in @option{-l} are to be 10795treated as compiler output files, and passed to the linker in their 10796proper position among the other output files. 10797 10798@c man begin OPTIONS 10799 10800@node Target Options 10801@section Specifying Target Machine and Compiler Version 10802@cindex target options 10803@cindex cross compiling 10804@cindex specifying machine version 10805@cindex specifying compiler version and target machine 10806@cindex compiler version, specifying 10807@cindex target machine, specifying 10808 10809The usual way to run GCC is to run the executable called @command{gcc}, or 10810@command{@var{machine}-gcc} when cross-compiling, or 10811@command{@var{machine}-gcc-@var{version}} to run a version other than the 10812one that was installed last. 10813 10814@node Submodel Options 10815@section Hardware Models and Configurations 10816@cindex submodel options 10817@cindex specifying hardware config 10818@cindex hardware models and configurations, specifying 10819@cindex machine dependent options 10820 10821Each target machine types can have its own 10822special options, starting with @samp{-m}, to choose among various 10823hardware models or configurations---for example, 68010 vs 68020, 10824floating coprocessor or none. A single installed version of the 10825compiler can compile for any model or configuration, according to the 10826options specified. 10827 10828Some configurations of the compiler also support additional special 10829options, usually for compatibility with other compilers on the same 10830platform. 10831 10832@c This list is ordered alphanumerically by subsection name. 10833@c It should be the same order and spelling as these options are listed 10834@c in Machine Dependent Options 10835 10836@menu 10837* AArch64 Options:: 10838* Adapteva Epiphany Options:: 10839* ARM Options:: 10840* AVR Options:: 10841* Blackfin Options:: 10842* C6X Options:: 10843* CRIS Options:: 10844* CR16 Options:: 10845* Darwin Options:: 10846* DEC Alpha Options:: 10847* FR30 Options:: 10848* FRV Options:: 10849* GNU/Linux Options:: 10850* H8/300 Options:: 10851* HPPA Options:: 10852* i386 and x86-64 Options:: 10853* i386 and x86-64 Windows Options:: 10854* IA-64 Options:: 10855* LM32 Options:: 10856* M32C Options:: 10857* M32R/D Options:: 10858* M680x0 Options:: 10859* MCore Options:: 10860* MeP Options:: 10861* MicroBlaze Options:: 10862* MIPS Options:: 10863* MMIX Options:: 10864* MN10300 Options:: 10865* Moxie Options:: 10866* PDP-11 Options:: 10867* picoChip Options:: 10868* PowerPC Options:: 10869* RL78 Options:: 10870* RS/6000 and PowerPC Options:: 10871* RX Options:: 10872* S/390 and zSeries Options:: 10873* Score Options:: 10874* SH Options:: 10875* Solaris 2 Options:: 10876* SPARC Options:: 10877* SPU Options:: 10878* System V Options:: 10879* TILE-Gx Options:: 10880* TILEPro Options:: 10881* V850 Options:: 10882* VAX Options:: 10883* VMS Options:: 10884* VxWorks Options:: 10885* x86-64 Options:: 10886* Xstormy16 Options:: 10887* Xtensa Options:: 10888* zSeries Options:: 10889@end menu 10890 10891@node AArch64 Options 10892@subsection AArch64 Options 10893@cindex AArch64 Options 10894 10895These options are defined for AArch64 implementations: 10896 10897@table @gcctabopt 10898 10899@item -mbig-endian 10900@opindex mbig-endian 10901Generate big-endian code. This is the default when GCC is configured for an 10902@samp{aarch64_be-*-*} target. 10903 10904@item -mgeneral-regs-only 10905@opindex mgeneral-regs-only 10906Generate code which uses only the general registers. 10907 10908@item -mlittle-endian 10909@opindex mlittle-endian 10910Generate little-endian code. This is the default when GCC is configured for an 10911@samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target. 10912 10913@item -mcmodel=tiny 10914@opindex mcmodel=tiny 10915Generate code for the tiny code model. The program and its statically defined 10916symbols must be within 1GB of each other. Pointers are 64 bits. Programs can 10917be statically or dynamically linked. This model is not fully implemented and 10918mostly treated as @samp{small}. 10919 10920@item -mcmodel=small 10921@opindex mcmodel=small 10922Generate code for the small code model. The program and its statically defined 10923symbols must be within 4GB of each other. Pointers are 64 bits. Programs can 10924be statically or dynamically linked. This is the default code model. 10925 10926@item -mcmodel=large 10927@opindex mcmodel=large 10928Generate code for the large code model. This makes no assumptions about 10929addresses and sizes of sections. Pointers are 64 bits. Programs can be 10930statically linked only. 10931 10932@item -mstrict-align 10933@opindex mstrict-align 10934Do not assume that unaligned memory references will be handled by the system. 10935 10936@item -momit-leaf-frame-pointer 10937@itemx -mno-omit-leaf-frame-pointer 10938@opindex momit-leaf-frame-pointer 10939@opindex mno-omit-leaf-frame-pointer 10940Omit or keep the frame pointer in leaf functions. The former behaviour is the 10941default. 10942 10943@item -mtls-dialect=desc 10944@opindex mtls-dialect=desc 10945Use TLS descriptors as the thread-local storage mechanism for dynamic accesses 10946of TLS variables. This is the default. 10947 10948@item -mtls-dialect=traditional 10949@opindex mtls-dialect=traditional 10950Use traditional TLS as the thread-local storage mechanism for dynamic accesses 10951of TLS variables. 10952 10953@item -mfix-cortex-a53-835769 10954@itemx -mno-fix-cortex-a53-835769 10955@opindex -mfix-cortex-a53-835769 10956@opindex -mno-fix-cortex-a53-835769 10957Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. 10958This will involve inserting a NOP instruction between memory instructions and 1095964-bit integer multiply-accumulate instructions. 10960 10961@item -march=@var{name} 10962@opindex march 10963Specify the name of the target architecture, optionally suffixed by one or 10964more feature modifiers. This option has the form 10965@option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the 10966only value for @var{arch} is @samp{armv8-a}. The possible values for 10967@var{feature} are documented in the sub-section below. 10968 10969Where conflicting feature modifiers are specified, the right-most feature is 10970used. 10971 10972GCC uses this name to determine what kind of instructions it can emit when 10973generating assembly code. This option can be used in conjunction with or 10974instead of the @option{-mcpu=} option. 10975 10976@item -mcpu=@var{name} 10977@opindex mcpu 10978Specify the name of the target processor, optionally suffixed by one or more 10979feature modifiers. This option has the form 10980@option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the 10981possible values for @var{cpu} are @samp{generic}, @samp{large}. The 10982possible values for @var{feature} are documented in the sub-section 10983below. 10984 10985Where conflicting feature modifiers are specified, the right-most feature is 10986used. 10987 10988GCC uses this name to determine what kind of instructions it can emit when 10989generating assembly code. 10990 10991@item -mtune=@var{name} 10992@opindex mtune 10993Specify the name of the processor to tune the performance for. The code will 10994be tuned as if the target processor were of the type specified in this option, 10995but still using instructions compatible with the target processor specified 10996by a @option{-mcpu=} option. This option cannot be suffixed by feature 10997modifiers. 10998 10999@end table 11000 11001@subsubsection @option{-march} and @option{-mcpu} feature modifiers 11002@cindex @option{-march} feature modifiers 11003@cindex @option{-mcpu} feature modifiers 11004Feature modifiers used with @option{-march} and @option{-mcpu} can be one 11005the following: 11006 11007@table @samp 11008@item crypto 11009Enable Crypto extension. This implies Advanced SIMD is enabled. 11010@item fp 11011Enable floating-point instructions. 11012@item simd 11013Enable Advanced SIMD instructions. This implies floating-point instructions 11014are enabled. This is the default for all current possible values for options 11015@option{-march} and @option{-mcpu=}. 11016@end table 11017 11018@node Adapteva Epiphany Options 11019@subsection Adapteva Epiphany Options 11020 11021These @samp{-m} options are defined for Adapteva Epiphany: 11022 11023@table @gcctabopt 11024@item -mhalf-reg-file 11025@opindex mhalf-reg-file 11026Don't allocate any register in the range @code{r32}@dots{}@code{r63}. 11027That allows code to run on hardware variants that lack these registers. 11028 11029@item -mprefer-short-insn-regs 11030@opindex mprefer-short-insn-regs 11031Preferrentially allocate registers that allow short instruction generation. 11032This can result in increased instruction count, so this may either reduce or 11033increase overall code size. 11034 11035@item -mbranch-cost=@var{num} 11036@opindex mbranch-cost 11037Set the cost of branches to roughly @var{num} ``simple'' instructions. 11038This cost is only a heuristic and is not guaranteed to produce 11039consistent results across releases. 11040 11041@item -mcmove 11042@opindex mcmove 11043Enable the generation of conditional moves. 11044 11045@item -mnops=@var{num} 11046@opindex mnops 11047Emit @var{num} NOPs before every other generated instruction. 11048 11049@item -mno-soft-cmpsf 11050@opindex mno-soft-cmpsf 11051For single-precision floating-point comparisons, emit an @code{fsub} instruction 11052and test the flags. This is faster than a software comparison, but can 11053get incorrect results in the presence of NaNs, or when two different small 11054numbers are compared such that their difference is calculated as zero. 11055The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant, 11056software comparisons. 11057 11058@item -mstack-offset=@var{num} 11059@opindex mstack-offset 11060Set the offset between the top of the stack and the stack pointer. 11061E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7} 11062can be used by leaf functions without stack allocation. 11063Values other than @samp{8} or @samp{16} are untested and unlikely to work. 11064Note also that this option changes the ABI; compiling a program with a 11065different stack offset than the libraries have been compiled with 11066generally does not work. 11067This option can be useful if you want to evaluate if a different stack 11068offset would give you better code, but to actually use a different stack 11069offset to build working programs, it is recommended to configure the 11070toolchain with the appropriate @option{--with-stack-offset=@var{num}} option. 11071 11072@item -mno-round-nearest 11073@opindex mno-round-nearest 11074Make the scheduler assume that the rounding mode has been set to 11075truncating. The default is @option{-mround-nearest}. 11076 11077@item -mlong-calls 11078@opindex mlong-calls 11079If not otherwise specified by an attribute, assume all calls might be beyond 11080the offset range of the @code{b} / @code{bl} instructions, and therefore load the 11081function address into a register before performing a (otherwise direct) call. 11082This is the default. 11083 11084@item -mshort-calls 11085@opindex short-calls 11086If not otherwise specified by an attribute, assume all direct calls are 11087in the range of the @code{b} / @code{bl} instructions, so use these instructions 11088for direct calls. The default is @option{-mlong-calls}. 11089 11090@item -msmall16 11091@opindex msmall16 11092Assume addresses can be loaded as 16-bit unsigned values. This does not 11093apply to function addresses for which @option{-mlong-calls} semantics 11094are in effect. 11095 11096@item -mfp-mode=@var{mode} 11097@opindex mfp-mode 11098Set the prevailing mode of the floating-point unit. 11099This determines the floating-point mode that is provided and expected 11100at function call and return time. Making this mode match the mode you 11101predominantly need at function start can make your programs smaller and 11102faster by avoiding unnecessary mode switches. 11103 11104@var{mode} can be set to one the following values: 11105 11106@table @samp 11107@item caller 11108Any mode at function entry is valid, and retained or restored when 11109the function returns, and when it calls other functions. 11110This mode is useful for compiling libraries or other compilation units 11111you might want to incorporate into different programs with different 11112prevailing FPU modes, and the convenience of being able to use a single 11113object file outweighs the size and speed overhead for any extra 11114mode switching that might be needed, compared with what would be needed 11115with a more specific choice of prevailing FPU mode. 11116 11117@item truncate 11118This is the mode used for floating-point calculations with 11119truncating (i.e.@: round towards zero) rounding mode. That includes 11120conversion from floating point to integer. 11121 11122@item round-nearest 11123This is the mode used for floating-point calculations with 11124round-to-nearest-or-even rounding mode. 11125 11126@item int 11127This is the mode used to perform integer calculations in the FPU, e.g.@: 11128integer multiply, or integer multiply-and-accumulate. 11129@end table 11130 11131The default is @option{-mfp-mode=caller} 11132 11133@item -mnosplit-lohi 11134@itemx -mno-postinc 11135@itemx -mno-postmodify 11136@opindex mnosplit-lohi 11137@opindex mno-postinc 11138@opindex mno-postmodify 11139Code generation tweaks that disable, respectively, splitting of 32-bit 11140loads, generation of post-increment addresses, and generation of 11141post-modify addresses. The defaults are @option{msplit-lohi}, 11142@option{-mpost-inc}, and @option{-mpost-modify}. 11143 11144@item -mnovect-double 11145@opindex mno-vect-double 11146Change the preferred SIMD mode to SImode. The default is 11147@option{-mvect-double}, which uses DImode as preferred SIMD mode. 11148 11149@item -max-vect-align=@var{num} 11150@opindex max-vect-align 11151The maximum alignment for SIMD vector mode types. 11152@var{num} may be 4 or 8. The default is 8. 11153Note that this is an ABI change, even though many library function 11154interfaces are unaffected if they don't use SIMD vector modes 11155in places that affect size and/or alignment of relevant types. 11156 11157@item -msplit-vecmove-early 11158@opindex msplit-vecmove-early 11159Split vector moves into single word moves before reload. In theory this 11160can give better register allocation, but so far the reverse seems to be 11161generally the case. 11162 11163@item -m1reg-@var{reg} 11164@opindex m1reg- 11165Specify a register to hold the constant @minus{}1, which makes loading small negative 11166constants and certain bitmasks faster. 11167Allowable values for @var{reg} are @samp{r43} and @samp{r63}, 11168which specify use of that register as a fixed register, 11169and @samp{none}, which means that no register is used for this 11170purpose. The default is @option{-m1reg-none}. 11171 11172@end table 11173 11174@node ARM Options 11175@subsection ARM Options 11176@cindex ARM options 11177 11178These @samp{-m} options are defined for Advanced RISC Machines (ARM) 11179architectures: 11180 11181@table @gcctabopt 11182@item -mabi=@var{name} 11183@opindex mabi 11184Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, 11185@samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. 11186 11187@item -mapcs-frame 11188@opindex mapcs-frame 11189Generate a stack frame that is compliant with the ARM Procedure Call 11190Standard for all functions, even if this is not strictly necessary for 11191correct execution of the code. Specifying @option{-fomit-frame-pointer} 11192with this option causes the stack frames not to be generated for 11193leaf functions. The default is @option{-mno-apcs-frame}. 11194 11195@item -mapcs 11196@opindex mapcs 11197This is a synonym for @option{-mapcs-frame}. 11198 11199@ignore 11200@c not currently implemented 11201@item -mapcs-stack-check 11202@opindex mapcs-stack-check 11203Generate code to check the amount of stack space available upon entry to 11204every function (that actually uses some stack space). If there is 11205insufficient space available then either the function 11206@samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} is 11207called, depending upon the amount of stack space required. The runtime 11208system is required to provide these functions. The default is 11209@option{-mno-apcs-stack-check}, since this produces smaller code. 11210 11211@c not currently implemented 11212@item -mapcs-float 11213@opindex mapcs-float 11214Pass floating-point arguments using the floating-point registers. This is 11215one of the variants of the APCS@. This option is recommended if the 11216target hardware has a floating-point unit or if a lot of floating-point 11217arithmetic is going to be performed by the code. The default is 11218@option{-mno-apcs-float}, since the size of integer-only code is 11219slightly increased if @option{-mapcs-float} is used. 11220 11221@c not currently implemented 11222@item -mapcs-reentrant 11223@opindex mapcs-reentrant 11224Generate reentrant, position-independent code. The default is 11225@option{-mno-apcs-reentrant}. 11226@end ignore 11227 11228@item -mthumb-interwork 11229@opindex mthumb-interwork 11230Generate code that supports calling between the ARM and Thumb 11231instruction sets. Without this option, on pre-v5 architectures, the 11232two instruction sets cannot be reliably used inside one program. The 11233default is @option{-mno-thumb-interwork}, since slightly larger code 11234is generated when @option{-mthumb-interwork} is specified. In AAPCS 11235configurations this option is meaningless. 11236 11237@item -mno-sched-prolog 11238@opindex mno-sched-prolog 11239Prevent the reordering of instructions in the function prologue, or the 11240merging of those instruction with the instructions in the function's 11241body. This means that all functions start with a recognizable set 11242of instructions (or in fact one of a choice from a small set of 11243different function prologues), and this information can be used to 11244locate the start of functions inside an executable piece of code. The 11245default is @option{-msched-prolog}. 11246 11247@item -mfloat-abi=@var{name} 11248@opindex mfloat-abi 11249Specifies which floating-point ABI to use. Permissible values 11250are: @samp{soft}, @samp{softfp} and @samp{hard}. 11251 11252Specifying @samp{soft} causes GCC to generate output containing 11253library calls for floating-point operations. 11254@samp{softfp} allows the generation of code using hardware floating-point 11255instructions, but still uses the soft-float calling conventions. 11256@samp{hard} allows generation of floating-point instructions 11257and uses FPU-specific calling conventions. 11258 11259The default depends on the specific target configuration. Note that 11260the hard-float and soft-float ABIs are not link-compatible; you must 11261compile your entire program with the same ABI, and link with a 11262compatible set of libraries. 11263 11264@item -mlittle-endian 11265@opindex mlittle-endian 11266Generate code for a processor running in little-endian mode. This is 11267the default for all standard configurations. 11268 11269@item -mbig-endian 11270@opindex mbig-endian 11271Generate code for a processor running in big-endian mode; the default is 11272to compile code for a little-endian processor. 11273 11274@item -mwords-little-endian 11275@opindex mwords-little-endian 11276This option only applies when generating code for big-endian processors. 11277Generate code for a little-endian word order but a big-endian byte 11278order. That is, a byte order of the form @samp{32107654}. Note: this 11279option should only be used if you require compatibility with code for 11280big-endian ARM processors generated by versions of the compiler prior to 112812.8. This option is now deprecated. 11282 11283@item -march=@var{name} 11284@opindex march 11285This specifies the name of the target ARM architecture. GCC uses this 11286name to determine what kind of instructions it can emit when generating 11287assembly code. This option can be used in conjunction with or instead 11288of the @option{-mcpu=} option. Permissible names are: @samp{armv2}, 11289@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t}, 11290@samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te}, 11291@samp{armv6}, @samp{armv6j}, 11292@samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m}, 11293@samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, @samp{armv7e-m} 11294@samp{armv8-a}, 11295@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}. 11296 11297@option{-march=native} causes the compiler to auto-detect the architecture 11298of the build computer. At present, this feature is only supported on 11299GNU/Linux, and not all architectures are recognized. If the auto-detect 11300is unsuccessful the option has no effect. 11301 11302@item -mtune=@var{name} 11303@opindex mtune 11304This option specifies the name of the target ARM processor for 11305which GCC should tune the performance of the code. 11306For some ARM implementations better performance can be obtained by using 11307this option. 11308Permissible names are: @samp{arm2}, @samp{arm250}, 11309@samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610}, 11310@samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm}, 11311@samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700}, 11312@samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100}, 11313@samp{arm720}, 11314@samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s}, 11315@samp{arm710t}, @samp{arm720t}, @samp{arm740t}, 11316@samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100}, 11317@samp{strongarm1110}, 11318@samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920}, 11319@samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s}, 11320@samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi}, 11321@samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s}, 11322@samp{arm10e}, @samp{arm1020e}, @samp{arm1022e}, 11323@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp}, 11324@samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s}, 11325@samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8}, @samp{cortex-a9}, 11326@samp{cortex-a15}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-r5}, 11327@samp{cortex-m4}, @samp{cortex-m3}, 11328@samp{cortex-m1}, 11329@samp{cortex-m0}, 11330@samp{cortex-m0plus}, 11331@samp{marvell-pj4}, 11332@samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}, 11333@samp{fa526}, @samp{fa626}, 11334@samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te}. 11335 11336@option{-mtune=generic-@var{arch}} specifies that GCC should tune the 11337performance for a blend of processors within architecture @var{arch}. 11338The aim is to generate code that run well on the current most popular 11339processors, balancing between optimizations that benefit some CPUs in the 11340range, and avoiding performance pitfalls of other CPUs. The effects of 11341this option may change in future GCC versions as CPU models come and go. 11342 11343@option{-mtune=native} causes the compiler to auto-detect the CPU 11344of the build computer. At present, this feature is only supported on 11345GNU/Linux, and not all architectures are recognized. If the auto-detect is 11346unsuccessful the option has no effect. 11347 11348@item -mcpu=@var{name} 11349@opindex mcpu 11350This specifies the name of the target ARM processor. GCC uses this name 11351to derive the name of the target ARM architecture (as if specified 11352by @option{-march}) and the ARM processor type for which to tune for 11353performance (as if specified by @option{-mtune}). Where this option 11354is used in conjunction with @option{-march} or @option{-mtune}, 11355those options take precedence over the appropriate part of this option. 11356 11357Permissible names for this option are the same as those for 11358@option{-mtune}. 11359 11360@option{-mcpu=generic-@var{arch}} is also permissible, and is 11361equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}. 11362See @option{-mtune} for more information. 11363 11364@option{-mcpu=native} causes the compiler to auto-detect the CPU 11365of the build computer. At present, this feature is only supported on 11366GNU/Linux, and not all architectures are recognized. If the auto-detect 11367is unsuccessful the option has no effect. 11368 11369@item -mfpu=@var{name} 11370@opindex mfpu 11371This specifies what floating-point hardware (or hardware emulation) is 11372available on the target. Permissible names are: @samp{vfp}, @samp{vfpv3}, 11373@samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, 11374@samp{vfpv3xd-fp16}, @samp{neon}, @samp{neon-fp16}, @samp{vfpv4}, 11375@samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4}, 11376@samp{fp-armv8}, @samp{neon-fp-armv8}, and @samp{crypto-neon-fp-armv8}. 11377 11378If @option{-msoft-float} is specified this specifies the format of 11379floating-point values. 11380 11381If the selected floating-point hardware includes the NEON extension 11382(e.g. @option{-mfpu}=@samp{neon}), note that floating-point 11383operations are not generated by GCC's auto-vectorization pass unless 11384@option{-funsafe-math-optimizations} is also specified. This is 11385because NEON hardware does not fully implement the IEEE 754 standard for 11386floating-point arithmetic (in particular denormal values are treated as 11387zero), so the use of NEON instructions may lead to a loss of precision. 11388 11389@item -mfp16-format=@var{name} 11390@opindex mfp16-format 11391Specify the format of the @code{__fp16} half-precision floating-point type. 11392Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative}; 11393the default is @samp{none}, in which case the @code{__fp16} type is not 11394defined. @xref{Half-Precision}, for more information. 11395 11396@item -mstructure-size-boundary=@var{n} 11397@opindex mstructure-size-boundary 11398The sizes of all structures and unions are rounded up to a multiple 11399of the number of bits set by this option. Permissible values are 8, 32 11400and 64. The default value varies for different toolchains. For the COFF 11401targeted toolchain the default value is 8. A value of 64 is only allowed 11402if the underlying ABI supports it. 11403 11404Specifying a larger number can produce faster, more efficient code, but 11405can also increase the size of the program. Different values are potentially 11406incompatible. Code compiled with one value cannot necessarily expect to 11407work with code or libraries compiled with another value, if they exchange 11408information using structures or unions. 11409 11410@item -mabort-on-noreturn 11411@opindex mabort-on-noreturn 11412Generate a call to the function @code{abort} at the end of a 11413@code{noreturn} function. It is executed if the function tries to 11414return. 11415 11416@item -mlong-calls 11417@itemx -mno-long-calls 11418@opindex mlong-calls 11419@opindex mno-long-calls 11420Tells the compiler to perform function calls by first loading the 11421address of the function into a register and then performing a subroutine 11422call on this register. This switch is needed if the target function 11423lies outside of the 64-megabyte addressing range of the offset-based 11424version of subroutine call instruction. 11425 11426Even if this switch is enabled, not all function calls are turned 11427into long calls. The heuristic is that static functions, functions 11428that have the @samp{short-call} attribute, functions that are inside 11429the scope of a @samp{#pragma no_long_calls} directive, and functions whose 11430definitions have already been compiled within the current compilation 11431unit are not turned into long calls. The exceptions to this rule are 11432that weak function definitions, functions with the @samp{long-call} 11433attribute or the @samp{section} attribute, and functions that are within 11434the scope of a @samp{#pragma long_calls} directive are always 11435turned into long calls. 11436 11437This feature is not enabled by default. Specifying 11438@option{-mno-long-calls} restores the default behavior, as does 11439placing the function calls within the scope of a @samp{#pragma 11440long_calls_off} directive. Note these switches have no effect on how 11441the compiler generates code to handle function calls via function 11442pointers. 11443 11444@item -msingle-pic-base 11445@opindex msingle-pic-base 11446Treat the register used for PIC addressing as read-only, rather than 11447loading it in the prologue for each function. The runtime system is 11448responsible for initializing this register with an appropriate value 11449before execution begins. 11450 11451@item -mpic-register=@var{reg} 11452@opindex mpic-register 11453Specify the register to be used for PIC addressing. 11454For standard PIC base case, the default will be any suitable register 11455determined by compiler. For single PIC base case, the default is 11456@samp{R9} if target is EABI based or stack-checking is enabled, 11457otherwise the default is @samp{R10}. 11458 11459@item -mpoke-function-name 11460@opindex mpoke-function-name 11461Write the name of each function into the text section, directly 11462preceding the function prologue. The generated code is similar to this: 11463 11464@smallexample 11465 t0 11466 .ascii "arm_poke_function_name", 0 11467 .align 11468 t1 11469 .word 0xff000000 + (t1 - t0) 11470 arm_poke_function_name 11471 mov ip, sp 11472 stmfd sp!, @{fp, ip, lr, pc@} 11473 sub fp, ip, #4 11474@end smallexample 11475 11476When performing a stack backtrace, code can inspect the value of 11477@code{pc} stored at @code{fp + 0}. If the trace function then looks at 11478location @code{pc - 12} and the top 8 bits are set, then we know that 11479there is a function name embedded immediately preceding this location 11480and has length @code{((pc[-3]) & 0xff000000)}. 11481 11482@item -mthumb 11483@itemx -marm 11484@opindex marm 11485@opindex mthumb 11486 11487Select between generating code that executes in ARM and Thumb 11488states. The default for most configurations is to generate code 11489that executes in ARM state, but the default can be changed by 11490configuring GCC with the @option{--with-mode=}@var{state} 11491configure option. 11492 11493@item -mtpcs-frame 11494@opindex mtpcs-frame 11495Generate a stack frame that is compliant with the Thumb Procedure Call 11496Standard for all non-leaf functions. (A leaf function is one that does 11497not call any other functions.) The default is @option{-mno-tpcs-frame}. 11498 11499@item -mtpcs-leaf-frame 11500@opindex mtpcs-leaf-frame 11501Generate a stack frame that is compliant with the Thumb Procedure Call 11502Standard for all leaf functions. (A leaf function is one that does 11503not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. 11504 11505@item -mcallee-super-interworking 11506@opindex mcallee-super-interworking 11507Gives all externally visible functions in the file being compiled an ARM 11508instruction set header which switches to Thumb mode before executing the 11509rest of the function. This allows these functions to be called from 11510non-interworking code. This option is not valid in AAPCS configurations 11511because interworking is enabled by default. 11512 11513@item -mcaller-super-interworking 11514@opindex mcaller-super-interworking 11515Allows calls via function pointers (including virtual functions) to 11516execute correctly regardless of whether the target code has been 11517compiled for interworking or not. There is a small overhead in the cost 11518of executing a function pointer if this option is enabled. This option 11519is not valid in AAPCS configurations because interworking is enabled 11520by default. 11521 11522@item -mtp=@var{name} 11523@opindex mtp 11524Specify the access model for the thread local storage pointer. The valid 11525models are @option{soft}, which generates calls to @code{__aeabi_read_tp}, 11526@option{cp15}, which fetches the thread pointer from @code{cp15} directly 11527(supported in the arm6k architecture), and @option{auto}, which uses the 11528best available method for the selected processor. The default setting is 11529@option{auto}. 11530 11531@item -mtls-dialect=@var{dialect} 11532@opindex mtls-dialect 11533Specify the dialect to use for accessing thread local storage. Two 11534@var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The 11535@samp{gnu} dialect selects the original GNU scheme for supporting 11536local and global dynamic TLS models. The @samp{gnu2} dialect 11537selects the GNU descriptor scheme, which provides better performance 11538for shared libraries. The GNU descriptor scheme is compatible with 11539the original scheme, but does require new assembler, linker and 11540library support. Initial and local exec TLS models are unaffected by 11541this option and always use the original scheme. 11542 11543@item -mword-relocations 11544@opindex mword-relocations 11545Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). 11546This is enabled by default on targets (uClinux, SymbianOS) where the runtime 11547loader imposes this restriction, and when @option{-fpic} or @option{-fPIC} 11548is specified. 11549 11550@item -mfix-cortex-m3-ldrd 11551@opindex mfix-cortex-m3-ldrd 11552Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions 11553with overlapping destination and base registers are used. This option avoids 11554generating these instructions. This option is enabled by default when 11555@option{-mcpu=cortex-m3} is specified. 11556 11557@item -munaligned-access 11558@itemx -mno-unaligned-access 11559@opindex munaligned-access 11560@opindex mno-unaligned-access 11561Enables (or disables) reading and writing of 16- and 32- bit values 11562from addresses that are not 16- or 32- bit aligned. By default 11563unaligned access is disabled for all pre-ARMv6 and all ARMv6-M 11564architectures, and enabled for all other architectures. If unaligned 11565access is not enabled then words in packed data structures will be 11566accessed a byte at a time. 11567 11568The ARM attribute @code{Tag_CPU_unaligned_access} will be set in the 11569generated object file to either true or false, depending upon the 11570setting of this option. If unaligned access is enabled then the 11571preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} will also be 11572defined. 11573 11574@end table 11575 11576@node AVR Options 11577@subsection AVR Options 11578@cindex AVR Options 11579 11580These options are defined for AVR implementations: 11581 11582@table @gcctabopt 11583@item -mmcu=@var{mcu} 11584@opindex mmcu 11585Specify Atmel AVR instruction set architectures (ISA) or MCU type. 11586 11587The default for this option is@tie{}@code{avr2}. 11588 11589GCC supports the following AVR devices and ISAs: 11590 11591@include avr-mmcu.texi 11592 11593@item -maccumulate-args 11594@opindex maccumulate-args 11595Accumulate outgoing function arguments and acquire/release the needed 11596stack space for outgoing function arguments once in function 11597prologue/epilogue. Without this option, outgoing arguments are pushed 11598before calling a function and popped afterwards. 11599 11600Popping the arguments after the function call can be expensive on 11601AVR so that accumulating the stack space might lead to smaller 11602executables because arguments need not to be removed from the 11603stack after such a function call. 11604 11605This option can lead to reduced code size for functions that perform 11606several calls to functions that get their arguments on the stack like 11607calls to printf-like functions. 11608 11609@item -mbranch-cost=@var{cost} 11610@opindex mbranch-cost 11611Set the branch costs for conditional branch instructions to 11612@var{cost}. Reasonable values for @var{cost} are small, non-negative 11613integers. The default branch cost is 0. 11614 11615@item -mcall-prologues 11616@opindex mcall-prologues 11617Functions prologues/epilogues are expanded as calls to appropriate 11618subroutines. Code size is smaller. 11619 11620@item -mint8 11621@opindex mint8 11622Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a 11623@code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes, 11624and @code{long long} is 4 bytes. Please note that this option does not 11625conform to the C standards, but it results in smaller code 11626size. 11627 11628@item -mno-interrupts 11629@opindex mno-interrupts 11630Generated code is not compatible with hardware interrupts. 11631Code size is smaller. 11632 11633@item -mrelax 11634@opindex mrelax 11635Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter 11636@code{RCALL} resp.@: @code{RJMP} instruction if applicable. 11637Setting @code{-mrelax} just adds the @code{--relax} option to the 11638linker command line when the linker is called. 11639 11640Jump relaxing is performed by the linker because jump offsets are not 11641known before code is located. Therefore, the assembler code generated by the 11642compiler is the same, but the instructions in the executable may 11643differ from instructions in the assembler code. 11644 11645Relaxing must be turned on if linker stubs are needed, see the 11646section on @code{EIND} and linker stubs below. 11647 11648@item -msp8 11649@opindex msp8 11650Treat the stack pointer register as an 8-bit register, 11651i.e.@: assume the high byte of the stack pointer is zero. 11652In general, you don't need to set this option by hand. 11653 11654This option is used internally by the compiler to select and 11655build multilibs for architectures @code{avr2} and @code{avr25}. 11656These architectures mix devices with and without @code{SPH}. 11657For any setting other than @code{-mmcu=avr2} or @code{-mmcu=avr25} 11658the compiler driver will add or remove this option from the compiler 11659proper's command line, because the compiler then knows if the device 11660or architecture has an 8-bit stack pointer and thus no @code{SPH} 11661register or not. 11662 11663@item -mstrict-X 11664@opindex mstrict-X 11665Use address register @code{X} in a way proposed by the hardware. This means 11666that @code{X} is only used in indirect, post-increment or 11667pre-decrement addressing. 11668 11669Without this option, the @code{X} register may be used in the same way 11670as @code{Y} or @code{Z} which then is emulated by additional 11671instructions. 11672For example, loading a value with @code{X+const} addressing with a 11673small non-negative @code{const < 64} to a register @var{Rn} is 11674performed as 11675 11676@example 11677adiw r26, const ; X += const 11678ld @var{Rn}, X ; @var{Rn} = *X 11679sbiw r26, const ; X -= const 11680@end example 11681 11682@item -mtiny-stack 11683@opindex mtiny-stack 11684Only change the lower 8@tie{}bits of the stack pointer. 11685 11686@item -Waddr-space-convert 11687@opindex Waddr-space-convert 11688Warn about conversions between address spaces in the case where the 11689resulting address space is not contained in the incoming address space. 11690@end table 11691 11692@subsubsection @code{EIND} and Devices with more than 128 Ki Bytes of Flash 11693@cindex @code{EIND} 11694Pointers in the implementation are 16@tie{}bits wide. 11695The address of a function or label is represented as word address so 11696that indirect jumps and calls can target any code address in the 11697range of 64@tie{}Ki words. 11698 11699In order to facilitate indirect jump on devices with more than 128@tie{}Ki 11700bytes of program memory space, there is a special function register called 11701@code{EIND} that serves as most significant part of the target address 11702when @code{EICALL} or @code{EIJMP} instructions are used. 11703 11704Indirect jumps and calls on these devices are handled as follows by 11705the compiler and are subject to some limitations: 11706 11707@itemize @bullet 11708 11709@item 11710The compiler never sets @code{EIND}. 11711 11712@item 11713The compiler uses @code{EIND} implicitely in @code{EICALL}/@code{EIJMP} 11714instructions or might read @code{EIND} directly in order to emulate an 11715indirect call/jump by means of a @code{RET} instruction. 11716 11717@item 11718The compiler assumes that @code{EIND} never changes during the startup 11719code or during the application. In particular, @code{EIND} is not 11720saved/restored in function or interrupt service routine 11721prologue/epilogue. 11722 11723@item 11724For indirect calls to functions and computed goto, the linker 11725generates @emph{stubs}. Stubs are jump pads sometimes also called 11726@emph{trampolines}. Thus, the indirect call/jump jumps to such a stub. 11727The stub contains a direct jump to the desired address. 11728 11729@item 11730Linker relaxation must be turned on so that the linker will generate 11731the stubs correctly an all situaltion. See the compiler option 11732@code{-mrelax} and the linler option @code{--relax}. 11733There are corner cases where the linker is supposed to generate stubs 11734but aborts without relaxation and without a helpful error message. 11735 11736@item 11737The default linker script is arranged for code with @code{EIND = 0}. 11738If code is supposed to work for a setup with @code{EIND != 0}, a custom 11739linker script has to be used in order to place the sections whose 11740name start with @code{.trampolines} into the segment where @code{EIND} 11741points to. 11742 11743@item 11744The startup code from libgcc never sets @code{EIND}. 11745Notice that startup code is a blend of code from libgcc and AVR-LibC. 11746For the impact of AVR-LibC on @code{EIND}, see the 11747@w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}. 11748 11749@item 11750It is legitimate for user-specific startup code to set up @code{EIND} 11751early, for example by means of initialization code located in 11752section @code{.init3}. Such code runs prior to general startup code 11753that initializes RAM and calls constructors, but after the bit 11754of startup code from AVR-LibC that sets @code{EIND} to the segment 11755where the vector table is located. 11756@example 11757#include <avr/io.h> 11758 11759static void 11760__attribute__((section(".init3"),naked,used,no_instrument_function)) 11761init3_set_eind (void) 11762@{ 11763 __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" 11764 "out %i0,r24" :: "n" (&EIND) : "r24","memory"); 11765@} 11766@end example 11767 11768@noindent 11769The @code{__trampolines_start} symbol is defined in the linker script. 11770 11771@item 11772Stubs are generated automatically by the linker if 11773the following two conditions are met: 11774@itemize @minus 11775 11776@item The address of a label is taken by means of the @code{gs} modifier 11777(short for @emph{generate stubs}) like so: 11778@example 11779LDI r24, lo8(gs(@var{func})) 11780LDI r25, hi8(gs(@var{func})) 11781@end example 11782@item The final location of that label is in a code segment 11783@emph{outside} the segment where the stubs are located. 11784@end itemize 11785 11786@item 11787The compiler emits such @code{gs} modifiers for code labels in the 11788following situations: 11789@itemize @minus 11790@item Taking address of a function or code label. 11791@item Computed goto. 11792@item If prologue-save function is used, see @option{-mcall-prologues} 11793command-line option. 11794@item Switch/case dispatch tables. If you do not want such dispatch 11795tables you can specify the @option{-fno-jump-tables} command-line option. 11796@item C and C++ constructors/destructors called during startup/shutdown. 11797@item If the tools hit a @code{gs()} modifier explained above. 11798@end itemize 11799 11800@item 11801Jumping to non-symbolic addresses like so is @emph{not} supported: 11802 11803@example 11804int main (void) 11805@{ 11806 /* Call function at word address 0x2 */ 11807 return ((int(*)(void)) 0x2)(); 11808@} 11809@end example 11810 11811Instead, a stub has to be set up, i.e.@: the function has to be called 11812through a symbol (@code{func_4} in the example): 11813 11814@example 11815int main (void) 11816@{ 11817 extern int func_4 (void); 11818 11819 /* Call function at byte address 0x4 */ 11820 return func_4(); 11821@} 11822@end example 11823 11824and the application be linked with @code{-Wl,--defsym,func_4=0x4}. 11825Alternatively, @code{func_4} can be defined in the linker script. 11826@end itemize 11827 11828@subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers 11829@cindex @code{RAMPD} 11830@cindex @code{RAMPX} 11831@cindex @code{RAMPY} 11832@cindex @code{RAMPZ} 11833Some AVR devices support memories larger than the 64@tie{}KiB range 11834that can be accessed with 16-bit pointers. To access memory locations 11835outside this 64@tie{}KiB range, the contentent of a @code{RAMP} 11836register is used as high part of the address: 11837The @code{X}, @code{Y}, @code{Z} address register is concatenated 11838with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function 11839register, respectively, to get a wide address. Similarly, 11840@code{RAMPD} is used together with direct addressing. 11841 11842@itemize 11843@item 11844The startup code initializes the @code{RAMP} special function 11845registers with zero. 11846 11847@item 11848If a @ref{AVR Named Address Spaces,named address space} other than 11849generic or @code{__flash} is used, then @code{RAMPZ} is set 11850as needed before the operation. 11851 11852@item 11853If the device supports RAM larger than 64@tie{KiB} and the compiler 11854needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ} 11855is reset to zero after the operation. 11856 11857@item 11858If the device comes with a specific @code{RAMP} register, the ISR 11859prologue/epilogue saves/restores that SFR and initializes it with 11860zero in case the ISR code might (implicitly) use it. 11861 11862@item 11863RAM larger than 64@tie{KiB} is not supported by GCC for AVR targets. 11864If you use inline assembler to read from locations outside the 1186516-bit address range and change one of the @code{RAMP} registers, 11866you must reset it to zero after the access. 11867 11868@end itemize 11869 11870@subsubsection AVR Built-in Macros 11871 11872GCC defines several built-in macros so that the user code can test 11873for the presence or absence of features. Almost any of the following 11874built-in macros are deduced from device capabilities and thus 11875triggered by the @code{-mmcu=} command-line option. 11876 11877For even more AVR-specific built-in macros see 11878@ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}. 11879 11880@table @code 11881 11882@item __AVR_ARCH__ 11883Build-in macro that resolves to a decimal number that identifies the 11884architecture and depends on the @code{-mmcu=@var{mcu}} option. 11885Possible values are: 11886 11887@code{2}, @code{25}, @code{3}, @code{31}, @code{35}, 11888@code{4}, @code{5}, @code{51}, @code{6}, @code{102}, @code{104}, 11889@code{105}, @code{106}, @code{107} 11890 11891for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, 11892@code{avr31}, @code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, 11893@code{avr6}, @code{avrxmega2}, @code{avrxmega4}, @code{avrxmega5}, 11894@code{avrxmega6}, @code{avrxmega7}, respectively. 11895If @var{mcu} specifies a device, this built-in macro is set 11896accordingly. For example, with @code{-mmcu=atmega8} the macro will be 11897defined to @code{4}. 11898 11899@item __AVR_@var{Device}__ 11900Setting @code{-mmcu=@var{device}} defines this built-in macro which reflects 11901the device's name. For example, @code{-mmcu=atmega8} defines the 11902built-in macro @code{__AVR_ATmega8__}, @code{-mmcu=attiny261a} defines 11903@code{__AVR_ATtiny261A__}, etc. 11904 11905The built-in macros' names follow 11906the scheme @code{__AVR_@var{Device}__} where @var{Device} is 11907the device name as from the AVR user manual. The difference between 11908@var{Device} in the built-in macro and @var{device} in 11909@code{-mmcu=@var{device}} is that the latter is always lowercase. 11910 11911If @var{device} is not a device but only a core architecture like 11912@code{avr51}, this macro will not be defined. 11913 11914@item __AVR_XMEGA__ 11915The device / architecture belongs to the XMEGA family of devices. 11916 11917@item __AVR_HAVE_ELPM__ 11918The device has the the @code{ELPM} instruction. 11919 11920@item __AVR_HAVE_ELPMX__ 11921The device has the @code{ELPM R@var{n},Z} and @code{ELPM 11922R@var{n},Z+} instructions. 11923 11924@item __AVR_HAVE_MOVW__ 11925The device has the @code{MOVW} instruction to perform 16-bit 11926register-register moves. 11927 11928@item __AVR_HAVE_LPMX__ 11929The device has the @code{LPM R@var{n},Z} and 11930@code{LPM R@var{n},Z+} instructions. 11931 11932@item __AVR_HAVE_MUL__ 11933The device has a hardware multiplier. 11934 11935@item __AVR_HAVE_JMP_CALL__ 11936The device has the @code{JMP} and @code{CALL} instructions. 11937This is the case for devices with at least 16@tie{}KiB of program 11938memory. 11939 11940@item __AVR_HAVE_EIJMP_EICALL__ 11941@itemx __AVR_3_BYTE_PC__ 11942The device has the @code{EIJMP} and @code{EICALL} instructions. 11943This is the case for devices with more than 128@tie{}KiB of program memory. 11944This also means that the program counter 11945(PC) is 3@tie{}bytes wide. 11946 11947@item __AVR_2_BYTE_PC__ 11948The program counter (PC) is 2@tie{}bytes wide. This is the case for devices 11949with up to 128@tie{}KiB of program memory. 11950 11951@item __AVR_HAVE_8BIT_SP__ 11952@itemx __AVR_HAVE_16BIT_SP__ 11953The stack pointer (SP) register is treated as 8-bit respectively 1195416-bit register by the compiler. 11955The definition of these macros is affected by @code{-mtiny-stack}. 11956 11957@item __AVR_HAVE_SPH__ 11958@itemx __AVR_SP8__ 11959The device has the SPH (high part of stack pointer) special function 11960register or has an 8-bit stack pointer, respectively. 11961The definition of these macros is affected by @code{-mmcu=} and 11962in the cases of @code{-mmcu=avr2} and @code{-mmcu=avr25} also 11963by @code{-msp8}. 11964 11965@item __AVR_HAVE_RAMPD__ 11966@itemx __AVR_HAVE_RAMPX__ 11967@itemx __AVR_HAVE_RAMPY__ 11968@itemx __AVR_HAVE_RAMPZ__ 11969The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY}, 11970@code{RAMPZ} special function register, respectively. 11971 11972@item __NO_INTERRUPTS__ 11973This macro reflects the @code{-mno-interrupts} command line option. 11974 11975@item __AVR_ERRATA_SKIP__ 11976@itemx __AVR_ERRATA_SKIP_JMP_CALL__ 11977Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit 11978instructions because of a hardware erratum. Skip instructions are 11979@code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}. 11980The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also 11981set. 11982 11983@item __AVR_SFR_OFFSET__=@var{offset} 11984Instructions that can address I/O special function registers directly 11985like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different 11986address as if addressed by an instruction to access RAM like @code{LD} 11987or @code{STS}. This offset depends on the device architecture and has 11988to be subtracted from the RAM address in order to get the 11989respective I/O@tie{}address. 11990 11991@item __WITH_AVRLIBC__ 11992The compiler is configured to be used together with AVR-Libc. 11993See the @code{--with-avrlibc} configure option. 11994 11995@end table 11996 11997@node Blackfin Options 11998@subsection Blackfin Options 11999@cindex Blackfin Options 12000 12001@table @gcctabopt 12002@item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} 12003@opindex mcpu= 12004Specifies the name of the target Blackfin processor. Currently, @var{cpu} 12005can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518}, 12006@samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526}, 12007@samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533}, 12008@samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539}, 12009@samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549}, 12010@samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m}, 12011@samp{bf561}, @samp{bf592}. 12012 12013The optional @var{sirevision} specifies the silicon revision of the target 12014Blackfin processor. Any workarounds available for the targeted silicon revision 12015are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled. 12016If @var{sirevision} is @samp{any}, all workarounds for the targeted processor 12017are enabled. The @code{__SILICON_REVISION__} macro is defined to two 12018hexadecimal digits representing the major and minor numbers in the silicon 12019revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__} 12020is not defined. If @var{sirevision} is @samp{any}, the 12021@code{__SILICON_REVISION__} is defined to be @code{0xffff}. 12022If this optional @var{sirevision} is not used, GCC assumes the latest known 12023silicon revision of the targeted Blackfin processor. 12024 12025GCC defines a preprocessor macro for the specified @var{cpu}. 12026For the @samp{bfin-elf} toolchain, this option causes the hardware BSP 12027provided by libgloss to be linked in if @option{-msim} is not given. 12028 12029Without this option, @samp{bf532} is used as the processor by default. 12030 12031Note that support for @samp{bf561} is incomplete. For @samp{bf561}, 12032only the preprocessor macro is defined. 12033 12034@item -msim 12035@opindex msim 12036Specifies that the program will be run on the simulator. This causes 12037the simulator BSP provided by libgloss to be linked in. This option 12038has effect only for @samp{bfin-elf} toolchain. 12039Certain other options, such as @option{-mid-shared-library} and 12040@option{-mfdpic}, imply @option{-msim}. 12041 12042@item -momit-leaf-frame-pointer 12043@opindex momit-leaf-frame-pointer 12044Don't keep the frame pointer in a register for leaf functions. This 12045avoids the instructions to save, set up and restore frame pointers and 12046makes an extra register available in leaf functions. The option 12047@option{-fomit-frame-pointer} removes the frame pointer for all functions, 12048which might make debugging harder. 12049 12050@item -mspecld-anomaly 12051@opindex mspecld-anomaly 12052When enabled, the compiler ensures that the generated code does not 12053contain speculative loads after jump instructions. If this option is used, 12054@code{__WORKAROUND_SPECULATIVE_LOADS} is defined. 12055 12056@item -mno-specld-anomaly 12057@opindex mno-specld-anomaly 12058Don't generate extra code to prevent speculative loads from occurring. 12059 12060@item -mcsync-anomaly 12061@opindex mcsync-anomaly 12062When enabled, the compiler ensures that the generated code does not 12063contain CSYNC or SSYNC instructions too soon after conditional branches. 12064If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined. 12065 12066@item -mno-csync-anomaly 12067@opindex mno-csync-anomaly 12068Don't generate extra code to prevent CSYNC or SSYNC instructions from 12069occurring too soon after a conditional branch. 12070 12071@item -mlow-64k 12072@opindex mlow-64k 12073When enabled, the compiler is free to take advantage of the knowledge that 12074the entire program fits into the low 64k of memory. 12075 12076@item -mno-low-64k 12077@opindex mno-low-64k 12078Assume that the program is arbitrarily large. This is the default. 12079 12080@item -mstack-check-l1 12081@opindex mstack-check-l1 12082Do stack checking using information placed into L1 scratchpad memory by the 12083uClinux kernel. 12084 12085@item -mid-shared-library 12086@opindex mid-shared-library 12087Generate code that supports shared libraries via the library ID method. 12088This allows for execute in place and shared libraries in an environment 12089without virtual memory management. This option implies @option{-fPIC}. 12090With a @samp{bfin-elf} target, this option implies @option{-msim}. 12091 12092@item -mno-id-shared-library 12093@opindex mno-id-shared-library 12094Generate code that doesn't assume ID-based shared libraries are being used. 12095This is the default. 12096 12097@item -mleaf-id-shared-library 12098@opindex mleaf-id-shared-library 12099Generate code that supports shared libraries via the library ID method, 12100but assumes that this library or executable won't link against any other 12101ID shared libraries. That allows the compiler to use faster code for jumps 12102and calls. 12103 12104@item -mno-leaf-id-shared-library 12105@opindex mno-leaf-id-shared-library 12106Do not assume that the code being compiled won't link against any ID shared 12107libraries. Slower code is generated for jump and call insns. 12108 12109@item -mshared-library-id=n 12110@opindex mshared-library-id 12111Specifies the identification number of the ID-based shared library being 12112compiled. Specifying a value of 0 generates more compact code; specifying 12113other values forces the allocation of that number to the current 12114library but is no more space- or time-efficient than omitting this option. 12115 12116@item -msep-data 12117@opindex msep-data 12118Generate code that allows the data segment to be located in a different 12119area of memory from the text segment. This allows for execute in place in 12120an environment without virtual memory management by eliminating relocations 12121against the text section. 12122 12123@item -mno-sep-data 12124@opindex mno-sep-data 12125Generate code that assumes that the data segment follows the text segment. 12126This is the default. 12127 12128@item -mlong-calls 12129@itemx -mno-long-calls 12130@opindex mlong-calls 12131@opindex mno-long-calls 12132Tells the compiler to perform function calls by first loading the 12133address of the function into a register and then performing a subroutine 12134call on this register. This switch is needed if the target function 12135lies outside of the 24-bit addressing range of the offset-based 12136version of subroutine call instruction. 12137 12138This feature is not enabled by default. Specifying 12139@option{-mno-long-calls} restores the default behavior. Note these 12140switches have no effect on how the compiler generates code to handle 12141function calls via function pointers. 12142 12143@item -mfast-fp 12144@opindex mfast-fp 12145Link with the fast floating-point library. This library relaxes some of 12146the IEEE floating-point standard's rules for checking inputs against 12147Not-a-Number (NAN), in the interest of performance. 12148 12149@item -minline-plt 12150@opindex minline-plt 12151Enable inlining of PLT entries in function calls to functions that are 12152not known to bind locally. It has no effect without @option{-mfdpic}. 12153 12154@item -mmulticore 12155@opindex mmulticore 12156Build a standalone application for multicore Blackfin processors. 12157This option causes proper start files and link scripts supporting 12158multicore to be used, and defines the macro @code{__BFIN_MULTICORE}. 12159It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. 12160 12161This option can be used with @option{-mcorea} or @option{-mcoreb}, which 12162selects the one-application-per-core programming model. Without 12163@option{-mcorea} or @option{-mcoreb}, the single-application/dual-core 12164programming model is used. In this model, the main function of Core B 12165should be named as @code{coreb_main}. 12166 12167If this option is not used, the single-core application programming 12168model is used. 12169 12170@item -mcorea 12171@opindex mcorea 12172Build a standalone application for Core A of BF561 when using 12173the one-application-per-core programming model. Proper start files 12174and link scripts are used to support Core A, and the macro 12175@code{__BFIN_COREA} is defined. 12176This option can only be used in conjunction with @option{-mmulticore}. 12177 12178@item -mcoreb 12179@opindex mcoreb 12180Build a standalone application for Core B of BF561 when using 12181the one-application-per-core programming model. Proper start files 12182and link scripts are used to support Core B, and the macro 12183@code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main} 12184should be used instead of @code{main}. 12185This option can only be used in conjunction with @option{-mmulticore}. 12186 12187@item -msdram 12188@opindex msdram 12189Build a standalone application for SDRAM. Proper start files and 12190link scripts are used to put the application into SDRAM, and the macro 12191@code{__BFIN_SDRAM} is defined. 12192The loader should initialize SDRAM before loading the application. 12193 12194@item -micplb 12195@opindex micplb 12196Assume that ICPLBs are enabled at run time. This has an effect on certain 12197anomaly workarounds. For Linux targets, the default is to assume ICPLBs 12198are enabled; for standalone applications the default is off. 12199@end table 12200 12201@node C6X Options 12202@subsection C6X Options 12203@cindex C6X Options 12204 12205@table @gcctabopt 12206@item -march=@var{name} 12207@opindex march 12208This specifies the name of the target architecture. GCC uses this 12209name to determine what kind of instructions it can emit when generating 12210assembly code. Permissible names are: @samp{c62x}, 12211@samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}. 12212 12213@item -mbig-endian 12214@opindex mbig-endian 12215Generate code for a big-endian target. 12216 12217@item -mlittle-endian 12218@opindex mlittle-endian 12219Generate code for a little-endian target. This is the default. 12220 12221@item -msim 12222@opindex msim 12223Choose startup files and linker script suitable for the simulator. 12224 12225@item -msdata=default 12226@opindex msdata=default 12227Put small global and static data in the @samp{.neardata} section, 12228which is pointed to by register @code{B14}. Put small uninitialized 12229global and static data in the @samp{.bss} section, which is adjacent 12230to the @samp{.neardata} section. Put small read-only data into the 12231@samp{.rodata} section. The corresponding sections used for large 12232pieces of data are @samp{.fardata}, @samp{.far} and @samp{.const}. 12233 12234@item -msdata=all 12235@opindex msdata=all 12236Put all data, not just small objects, into the sections reserved for 12237small data, and use addressing relative to the @code{B14} register to 12238access them. 12239 12240@item -msdata=none 12241@opindex msdata=none 12242Make no use of the sections reserved for small data, and use absolute 12243addresses to access all data. Put all initialized global and static 12244data in the @samp{.fardata} section, and all uninitialized data in the 12245@samp{.far} section. Put all constant data into the @samp{.const} 12246section. 12247@end table 12248 12249@node CRIS Options 12250@subsection CRIS Options 12251@cindex CRIS Options 12252 12253These options are defined specifically for the CRIS ports. 12254 12255@table @gcctabopt 12256@item -march=@var{architecture-type} 12257@itemx -mcpu=@var{architecture-type} 12258@opindex march 12259@opindex mcpu 12260Generate code for the specified architecture. The choices for 12261@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for 12262respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@. 12263Default is @samp{v0} except for cris-axis-linux-gnu, where the default is 12264@samp{v10}. 12265 12266@item -mtune=@var{architecture-type} 12267@opindex mtune 12268Tune to @var{architecture-type} everything applicable about the generated 12269code, except for the ABI and the set of available instructions. The 12270choices for @var{architecture-type} are the same as for 12271@option{-march=@var{architecture-type}}. 12272 12273@item -mmax-stack-frame=@var{n} 12274@opindex mmax-stack-frame 12275Warn when the stack frame of a function exceeds @var{n} bytes. 12276 12277@item -metrax4 12278@itemx -metrax100 12279@opindex metrax4 12280@opindex metrax100 12281The options @option{-metrax4} and @option{-metrax100} are synonyms for 12282@option{-march=v3} and @option{-march=v8} respectively. 12283 12284@item -mmul-bug-workaround 12285@itemx -mno-mul-bug-workaround 12286@opindex mmul-bug-workaround 12287@opindex mno-mul-bug-workaround 12288Work around a bug in the @code{muls} and @code{mulu} instructions for CPU 12289models where it applies. This option is active by default. 12290 12291@item -mpdebug 12292@opindex mpdebug 12293Enable CRIS-specific verbose debug-related information in the assembly 12294code. This option also has the effect of turning off the @samp{#NO_APP} 12295formatted-code indicator to the assembler at the beginning of the 12296assembly file. 12297 12298@item -mcc-init 12299@opindex mcc-init 12300Do not use condition-code results from previous instruction; always emit 12301compare and test instructions before use of condition codes. 12302 12303@item -mno-side-effects 12304@opindex mno-side-effects 12305Do not emit instructions with side effects in addressing modes other than 12306post-increment. 12307 12308@item -mstack-align 12309@itemx -mno-stack-align 12310@itemx -mdata-align 12311@itemx -mno-data-align 12312@itemx -mconst-align 12313@itemx -mno-const-align 12314@opindex mstack-align 12315@opindex mno-stack-align 12316@opindex mdata-align 12317@opindex mno-data-align 12318@opindex mconst-align 12319@opindex mno-const-align 12320These options (@samp{no-} options) arrange (eliminate arrangements) for the 12321stack frame, individual data and constants to be aligned for the maximum 12322single data access size for the chosen CPU model. The default is to 12323arrange for 32-bit alignment. ABI details such as structure layout are 12324not affected by these options. 12325 12326@item -m32-bit 12327@itemx -m16-bit 12328@itemx -m8-bit 12329@opindex m32-bit 12330@opindex m16-bit 12331@opindex m8-bit 12332Similar to the stack- data- and const-align options above, these options 12333arrange for stack frame, writable data and constants to all be 32-bit, 1233416-bit or 8-bit aligned. The default is 32-bit alignment. 12335 12336@item -mno-prologue-epilogue 12337@itemx -mprologue-epilogue 12338@opindex mno-prologue-epilogue 12339@opindex mprologue-epilogue 12340With @option{-mno-prologue-epilogue}, the normal function prologue and 12341epilogue which set up the stack frame are omitted and no return 12342instructions or return sequences are generated in the code. Use this 12343option only together with visual inspection of the compiled code: no 12344warnings or errors are generated when call-saved registers must be saved, 12345or storage for local variables needs to be allocated. 12346 12347@item -mno-gotplt 12348@itemx -mgotplt 12349@opindex mno-gotplt 12350@opindex mgotplt 12351With @option{-fpic} and @option{-fPIC}, don't generate (do generate) 12352instruction sequences that load addresses for functions from the PLT part 12353of the GOT rather than (traditional on other architectures) calls to the 12354PLT@. The default is @option{-mgotplt}. 12355 12356@item -melf 12357@opindex melf 12358Legacy no-op option only recognized with the cris-axis-elf and 12359cris-axis-linux-gnu targets. 12360 12361@item -mlinux 12362@opindex mlinux 12363Legacy no-op option only recognized with the cris-axis-linux-gnu target. 12364 12365@item -sim 12366@opindex sim 12367This option, recognized for the cris-axis-elf, arranges 12368to link with input-output functions from a simulator library. Code, 12369initialized data and zero-initialized data are allocated consecutively. 12370 12371@item -sim2 12372@opindex sim2 12373Like @option{-sim}, but pass linker options to locate initialized data at 123740x40000000 and zero-initialized data at 0x80000000. 12375@end table 12376 12377@node CR16 Options 12378@subsection CR16 Options 12379@cindex CR16 Options 12380 12381These options are defined specifically for the CR16 ports. 12382 12383@table @gcctabopt 12384 12385@item -mmac 12386@opindex mmac 12387Enable the use of multiply-accumulate instructions. Disabled by default. 12388 12389@item -mcr16cplus 12390@itemx -mcr16c 12391@opindex mcr16cplus 12392@opindex mcr16c 12393Generate code for CR16C or CR16C+ architecture. CR16C+ architecture 12394is default. 12395 12396@item -msim 12397@opindex msim 12398Links the library libsim.a which is in compatible with simulator. Applicable 12399to ELF compiler only. 12400 12401@item -mint32 12402@opindex mint32 12403Choose integer type as 32-bit wide. 12404 12405@item -mbit-ops 12406@opindex mbit-ops 12407Generates @code{sbit}/@code{cbit} instructions for bit manipulations. 12408 12409@item -mdata-model=@var{model} 12410@opindex mdata-model 12411Choose a data model. The choices for @var{model} are @samp{near}, 12412@samp{far} or @samp{medium}. @samp{medium} is default. 12413However, @samp{far} is not valid with @option{-mcr16c}, as the 12414CR16C architecture does not support the far data model. 12415@end table 12416 12417@node Darwin Options 12418@subsection Darwin Options 12419@cindex Darwin options 12420 12421These options are defined for all architectures running the Darwin operating 12422system. 12423 12424FSF GCC on Darwin does not create ``fat'' object files; it creates 12425an object file for the single architecture that GCC was built to 12426target. Apple's GCC on Darwin does create ``fat'' files if multiple 12427@option{-arch} options are used; it does so by running the compiler or 12428linker multiple times and joining the results together with 12429@file{lipo}. 12430 12431The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or 12432@samp{i686}) is determined by the flags that specify the ISA 12433that GCC is targeting, like @option{-mcpu} or @option{-march}. The 12434@option{-force_cpusubtype_ALL} option can be used to override this. 12435 12436The Darwin tools vary in their behavior when presented with an ISA 12437mismatch. The assembler, @file{as}, only permits instructions to 12438be used that are valid for the subtype of the file it is generating, 12439so you cannot put 64-bit instructions in a @samp{ppc750} object file. 12440The linker for shared libraries, @file{/usr/bin/libtool}, fails 12441and prints an error if asked to create a shared library with a less 12442restrictive subtype than its input files (for instance, trying to put 12443a @samp{ppc970} object file in a @samp{ppc7400} library). The linker 12444for executables, @command{ld}, quietly gives the executable the most 12445restrictive subtype of any of its input files. 12446 12447@table @gcctabopt 12448@item -F@var{dir} 12449@opindex F 12450Add the framework directory @var{dir} to the head of the list of 12451directories to be searched for header files. These directories are 12452interleaved with those specified by @option{-I} options and are 12453scanned in a left-to-right order. 12454 12455A framework directory is a directory with frameworks in it. A 12456framework is a directory with a @file{Headers} and/or 12457@file{PrivateHeaders} directory contained directly in it that ends 12458in @file{.framework}. The name of a framework is the name of this 12459directory excluding the @file{.framework}. Headers associated with 12460the framework are found in one of those two directories, with 12461@file{Headers} being searched first. A subframework is a framework 12462directory that is in a framework's @file{Frameworks} directory. 12463Includes of subframework headers can only appear in a header of a 12464framework that contains the subframework, or in a sibling subframework 12465header. Two subframeworks are siblings if they occur in the same 12466framework. A subframework should not have the same name as a 12467framework; a warning is issued if this is violated. Currently a 12468subframework cannot have subframeworks; in the future, the mechanism 12469may be extended to support this. The standard frameworks can be found 12470in @file{/System/Library/Frameworks} and 12471@file{/Library/Frameworks}. An example include looks like 12472@code{#include <Framework/header.h>}, where @file{Framework} denotes 12473the name of the framework and @file{header.h} is found in the 12474@file{PrivateHeaders} or @file{Headers} directory. 12475 12476@item -iframework@var{dir} 12477@opindex iframework 12478Like @option{-F} except the directory is a treated as a system 12479directory. The main difference between this @option{-iframework} and 12480@option{-F} is that with @option{-iframework} the compiler does not 12481warn about constructs contained within header files found via 12482@var{dir}. This option is valid only for the C family of languages. 12483 12484@item -gused 12485@opindex gused 12486Emit debugging information for symbols that are used. For stabs 12487debugging format, this enables @option{-feliminate-unused-debug-symbols}. 12488This is by default ON@. 12489 12490@item -gfull 12491@opindex gfull 12492Emit debugging information for all symbols and types. 12493 12494@item -mmacosx-version-min=@var{version} 12495The earliest version of MacOS X that this executable will run on 12496is @var{version}. Typical values of @var{version} include @code{10.1}, 12497@code{10.2}, and @code{10.3.9}. 12498 12499If the compiler was built to use the system's headers by default, 12500then the default for this option is the system version on which the 12501compiler is running, otherwise the default is to make choices that 12502are compatible with as many systems and code bases as possible. 12503 12504@item -mkernel 12505@opindex mkernel 12506Enable kernel development mode. The @option{-mkernel} option sets 12507@option{-static}, @option{-fno-common}, @option{-fno-use-cxa-atexit}, 12508@option{-fno-exceptions}, @option{-fno-non-call-exceptions}, 12509@option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where 12510applicable. This mode also sets @option{-mno-altivec}, 12511@option{-msoft-float}, @option{-fno-builtin} and 12512@option{-mlong-branch} for PowerPC targets. 12513 12514@item -mone-byte-bool 12515@opindex mone-byte-bool 12516Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}. 12517By default @samp{sizeof(bool)} is @samp{4} when compiling for 12518Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this 12519option has no effect on x86. 12520 12521@strong{Warning:} The @option{-mone-byte-bool} switch causes GCC 12522to generate code that is not binary compatible with code generated 12523without that switch. Using this switch may require recompiling all 12524other modules in a program, including system libraries. Use this 12525switch to conform to a non-default data model. 12526 12527@item -mfix-and-continue 12528@itemx -ffix-and-continue 12529@itemx -findirect-data 12530@opindex mfix-and-continue 12531@opindex ffix-and-continue 12532@opindex findirect-data 12533Generate code suitable for fast turnaround development, such as to 12534allow GDB to dynamically load @code{.o} files into already-running 12535programs. @option{-findirect-data} and @option{-ffix-and-continue} 12536are provided for backwards compatibility. 12537 12538@item -all_load 12539@opindex all_load 12540Loads all members of static archive libraries. 12541See man ld(1) for more information. 12542 12543@item -arch_errors_fatal 12544@opindex arch_errors_fatal 12545Cause the errors having to do with files that have the wrong architecture 12546to be fatal. 12547 12548@item -bind_at_load 12549@opindex bind_at_load 12550Causes the output file to be marked such that the dynamic linker will 12551bind all undefined references when the file is loaded or launched. 12552 12553@item -bundle 12554@opindex bundle 12555Produce a Mach-o bundle format file. 12556See man ld(1) for more information. 12557 12558@item -bundle_loader @var{executable} 12559@opindex bundle_loader 12560This option specifies the @var{executable} that will load the build 12561output file being linked. See man ld(1) for more information. 12562 12563@item -dynamiclib 12564@opindex dynamiclib 12565When passed this option, GCC produces a dynamic library instead of 12566an executable when linking, using the Darwin @file{libtool} command. 12567 12568@item -force_cpusubtype_ALL 12569@opindex force_cpusubtype_ALL 12570This causes GCC's output file to have the @var{ALL} subtype, instead of 12571one controlled by the @option{-mcpu} or @option{-march} option. 12572 12573@item -allowable_client @var{client_name} 12574@itemx -client_name 12575@itemx -compatibility_version 12576@itemx -current_version 12577@itemx -dead_strip 12578@itemx -dependency-file 12579@itemx -dylib_file 12580@itemx -dylinker_install_name 12581@itemx -dynamic 12582@itemx -exported_symbols_list 12583@itemx -filelist 12584@need 800 12585@itemx -flat_namespace 12586@itemx -force_flat_namespace 12587@itemx -headerpad_max_install_names 12588@itemx -image_base 12589@itemx -init 12590@itemx -install_name 12591@itemx -keep_private_externs 12592@itemx -multi_module 12593@itemx -multiply_defined 12594@itemx -multiply_defined_unused 12595@need 800 12596@itemx -noall_load 12597@itemx -no_dead_strip_inits_and_terms 12598@itemx -nofixprebinding 12599@itemx -nomultidefs 12600@itemx -noprebind 12601@itemx -noseglinkedit 12602@itemx -pagezero_size 12603@itemx -prebind 12604@itemx -prebind_all_twolevel_modules 12605@itemx -private_bundle 12606@need 800 12607@itemx -read_only_relocs 12608@itemx -sectalign 12609@itemx -sectobjectsymbols 12610@itemx -whyload 12611@itemx -seg1addr 12612@itemx -sectcreate 12613@itemx -sectobjectsymbols 12614@itemx -sectorder 12615@itemx -segaddr 12616@itemx -segs_read_only_addr 12617@need 800 12618@itemx -segs_read_write_addr 12619@itemx -seg_addr_table 12620@itemx -seg_addr_table_filename 12621@itemx -seglinkedit 12622@itemx -segprot 12623@itemx -segs_read_only_addr 12624@itemx -segs_read_write_addr 12625@itemx -single_module 12626@itemx -static 12627@itemx -sub_library 12628@need 800 12629@itemx -sub_umbrella 12630@itemx -twolevel_namespace 12631@itemx -umbrella 12632@itemx -undefined 12633@itemx -unexported_symbols_list 12634@itemx -weak_reference_mismatches 12635@itemx -whatsloaded 12636@opindex allowable_client 12637@opindex client_name 12638@opindex compatibility_version 12639@opindex current_version 12640@opindex dead_strip 12641@opindex dependency-file 12642@opindex dylib_file 12643@opindex dylinker_install_name 12644@opindex dynamic 12645@opindex exported_symbols_list 12646@opindex filelist 12647@opindex flat_namespace 12648@opindex force_flat_namespace 12649@opindex headerpad_max_install_names 12650@opindex image_base 12651@opindex init 12652@opindex install_name 12653@opindex keep_private_externs 12654@opindex multi_module 12655@opindex multiply_defined 12656@opindex multiply_defined_unused 12657@opindex noall_load 12658@opindex no_dead_strip_inits_and_terms 12659@opindex nofixprebinding 12660@opindex nomultidefs 12661@opindex noprebind 12662@opindex noseglinkedit 12663@opindex pagezero_size 12664@opindex prebind 12665@opindex prebind_all_twolevel_modules 12666@opindex private_bundle 12667@opindex read_only_relocs 12668@opindex sectalign 12669@opindex sectobjectsymbols 12670@opindex whyload 12671@opindex seg1addr 12672@opindex sectcreate 12673@opindex sectobjectsymbols 12674@opindex sectorder 12675@opindex segaddr 12676@opindex segs_read_only_addr 12677@opindex segs_read_write_addr 12678@opindex seg_addr_table 12679@opindex seg_addr_table_filename 12680@opindex seglinkedit 12681@opindex segprot 12682@opindex segs_read_only_addr 12683@opindex segs_read_write_addr 12684@opindex single_module 12685@opindex static 12686@opindex sub_library 12687@opindex sub_umbrella 12688@opindex twolevel_namespace 12689@opindex umbrella 12690@opindex undefined 12691@opindex unexported_symbols_list 12692@opindex weak_reference_mismatches 12693@opindex whatsloaded 12694These options are passed to the Darwin linker. The Darwin linker man page 12695describes them in detail. 12696@end table 12697 12698@node DEC Alpha Options 12699@subsection DEC Alpha Options 12700 12701These @samp{-m} options are defined for the DEC Alpha implementations: 12702 12703@table @gcctabopt 12704@item -mno-soft-float 12705@itemx -msoft-float 12706@opindex mno-soft-float 12707@opindex msoft-float 12708Use (do not use) the hardware floating-point instructions for 12709floating-point operations. When @option{-msoft-float} is specified, 12710functions in @file{libgcc.a} are used to perform floating-point 12711operations. Unless they are replaced by routines that emulate the 12712floating-point operations, or compiled in such a way as to call such 12713emulations routines, these routines issue floating-point 12714operations. If you are compiling for an Alpha without floating-point 12715operations, you must ensure that the library is built so as not to call 12716them. 12717 12718Note that Alpha implementations without floating-point operations are 12719required to have floating-point registers. 12720 12721@item -mfp-reg 12722@itemx -mno-fp-regs 12723@opindex mfp-reg 12724@opindex mno-fp-regs 12725Generate code that uses (does not use) the floating-point register set. 12726@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point 12727register set is not used, floating-point operands are passed in integer 12728registers as if they were integers and floating-point results are passed 12729in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, 12730so any function with a floating-point argument or return value called by code 12731compiled with @option{-mno-fp-regs} must also be compiled with that 12732option. 12733 12734A typical use of this option is building a kernel that does not use, 12735and hence need not save and restore, any floating-point registers. 12736 12737@item -mieee 12738@opindex mieee 12739The Alpha architecture implements floating-point hardware optimized for 12740maximum performance. It is mostly compliant with the IEEE floating-point 12741standard. However, for full compliance, software assistance is 12742required. This option generates code fully IEEE-compliant code 12743@emph{except} that the @var{inexact-flag} is not maintained (see below). 12744If this option is turned on, the preprocessor macro @code{_IEEE_FP} is 12745defined during compilation. The resulting code is less efficient but is 12746able to correctly support denormalized numbers and exceptional IEEE 12747values such as not-a-number and plus/minus infinity. Other Alpha 12748compilers call this option @option{-ieee_with_no_inexact}. 12749 12750@item -mieee-with-inexact 12751@opindex mieee-with-inexact 12752This is like @option{-mieee} except the generated code also maintains 12753the IEEE @var{inexact-flag}. Turning on this option causes the 12754generated code to implement fully-compliant IEEE math. In addition to 12755@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor 12756macro. On some Alpha implementations the resulting code may execute 12757significantly slower than the code generated by default. Since there is 12758very little code that depends on the @var{inexact-flag}, you should 12759normally not specify this option. Other Alpha compilers call this 12760option @option{-ieee_with_inexact}. 12761 12762@item -mfp-trap-mode=@var{trap-mode} 12763@opindex mfp-trap-mode 12764This option controls what floating-point related traps are enabled. 12765Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. 12766The trap mode can be set to one of four values: 12767 12768@table @samp 12769@item n 12770This is the default (normal) setting. The only traps that are enabled 12771are the ones that cannot be disabled in software (e.g., division by zero 12772trap). 12773 12774@item u 12775In addition to the traps enabled by @samp{n}, underflow traps are enabled 12776as well. 12777 12778@item su 12779Like @samp{u}, but the instructions are marked to be safe for software 12780completion (see Alpha architecture manual for details). 12781 12782@item sui 12783Like @samp{su}, but inexact traps are enabled as well. 12784@end table 12785 12786@item -mfp-rounding-mode=@var{rounding-mode} 12787@opindex mfp-rounding-mode 12788Selects the IEEE rounding mode. Other Alpha compilers call this option 12789@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one 12790of: 12791 12792@table @samp 12793@item n 12794Normal IEEE rounding mode. Floating-point numbers are rounded towards 12795the nearest machine number or towards the even machine number in case 12796of a tie. 12797 12798@item m 12799Round towards minus infinity. 12800 12801@item c 12802Chopped rounding mode. Floating-point numbers are rounded towards zero. 12803 12804@item d 12805Dynamic rounding mode. A field in the floating-point control register 12806(@var{fpcr}, see Alpha architecture reference manual) controls the 12807rounding mode in effect. The C library initializes this register for 12808rounding towards plus infinity. Thus, unless your program modifies the 12809@var{fpcr}, @samp{d} corresponds to round towards plus infinity. 12810@end table 12811 12812@item -mtrap-precision=@var{trap-precision} 12813@opindex mtrap-precision 12814In the Alpha architecture, floating-point traps are imprecise. This 12815means without software assistance it is impossible to recover from a 12816floating trap and program execution normally needs to be terminated. 12817GCC can generate code that can assist operating system trap handlers 12818in determining the exact location that caused a floating-point trap. 12819Depending on the requirements of an application, different levels of 12820precisions can be selected: 12821 12822@table @samp 12823@item p 12824Program precision. This option is the default and means a trap handler 12825can only identify which program caused a floating-point exception. 12826 12827@item f 12828Function precision. The trap handler can determine the function that 12829caused a floating-point exception. 12830 12831@item i 12832Instruction precision. The trap handler can determine the exact 12833instruction that caused a floating-point exception. 12834@end table 12835 12836Other Alpha compilers provide the equivalent options called 12837@option{-scope_safe} and @option{-resumption_safe}. 12838 12839@item -mieee-conformant 12840@opindex mieee-conformant 12841This option marks the generated code as IEEE conformant. You must not 12842use this option unless you also specify @option{-mtrap-precision=i} and either 12843@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect 12844is to emit the line @samp{.eflag 48} in the function prologue of the 12845generated assembly file. 12846 12847@item -mbuild-constants 12848@opindex mbuild-constants 12849Normally GCC examines a 32- or 64-bit integer constant to 12850see if it can construct it from smaller constants in two or three 12851instructions. If it cannot, it outputs the constant as a literal and 12852generates code to load it from the data segment at run time. 12853 12854Use this option to require GCC to construct @emph{all} integer constants 12855using code, even if it takes more instructions (the maximum is six). 12856 12857You typically use this option to build a shared library dynamic 12858loader. Itself a shared library, it must relocate itself in memory 12859before it can find the variables and constants in its own data segment. 12860 12861@item -mbwx 12862@itemx -mno-bwx 12863@itemx -mcix 12864@itemx -mno-cix 12865@itemx -mfix 12866@itemx -mno-fix 12867@itemx -mmax 12868@itemx -mno-max 12869@opindex mbwx 12870@opindex mno-bwx 12871@opindex mcix 12872@opindex mno-cix 12873@opindex mfix 12874@opindex mno-fix 12875@opindex mmax 12876@opindex mno-max 12877Indicate whether GCC should generate code to use the optional BWX, 12878CIX, FIX and MAX instruction sets. The default is to use the instruction 12879sets supported by the CPU type specified via @option{-mcpu=} option or that 12880of the CPU on which GCC was built if none is specified. 12881 12882@item -mfloat-vax 12883@itemx -mfloat-ieee 12884@opindex mfloat-vax 12885@opindex mfloat-ieee 12886Generate code that uses (does not use) VAX F and G floating-point 12887arithmetic instead of IEEE single and double precision. 12888 12889@item -mexplicit-relocs 12890@itemx -mno-explicit-relocs 12891@opindex mexplicit-relocs 12892@opindex mno-explicit-relocs 12893Older Alpha assemblers provided no way to generate symbol relocations 12894except via assembler macros. Use of these macros does not allow 12895optimal instruction scheduling. GNU binutils as of version 2.12 12896supports a new syntax that allows the compiler to explicitly mark 12897which relocations should apply to which instructions. This option 12898is mostly useful for debugging, as GCC detects the capabilities of 12899the assembler when it is built and sets the default accordingly. 12900 12901@item -msmall-data 12902@itemx -mlarge-data 12903@opindex msmall-data 12904@opindex mlarge-data 12905When @option{-mexplicit-relocs} is in effect, static data is 12906accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} 12907is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} 12908(the @code{.sdata} and @code{.sbss} sections) and are accessed via 1290916-bit relocations off of the @code{$gp} register. This limits the 12910size of the small data area to 64KB, but allows the variables to be 12911directly accessed via a single instruction. 12912 12913The default is @option{-mlarge-data}. With this option the data area 12914is limited to just below 2GB@. Programs that require more than 2GB of 12915data must use @code{malloc} or @code{mmap} to allocate the data in the 12916heap instead of in the program's data segment. 12917 12918When generating code for shared libraries, @option{-fpic} implies 12919@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. 12920 12921@item -msmall-text 12922@itemx -mlarge-text 12923@opindex msmall-text 12924@opindex mlarge-text 12925When @option{-msmall-text} is used, the compiler assumes that the 12926code of the entire program (or shared library) fits in 4MB, and is 12927thus reachable with a branch instruction. When @option{-msmall-data} 12928is used, the compiler can assume that all local symbols share the 12929same @code{$gp} value, and thus reduce the number of instructions 12930required for a function call from 4 to 1. 12931 12932The default is @option{-mlarge-text}. 12933 12934@item -mcpu=@var{cpu_type} 12935@opindex mcpu 12936Set the instruction set and instruction scheduling parameters for 12937machine type @var{cpu_type}. You can specify either the @samp{EV} 12938style name or the corresponding chip number. GCC supports scheduling 12939parameters for the EV4, EV5 and EV6 family of processors and 12940chooses the default values for the instruction set from the processor 12941you specify. If you do not specify a processor type, GCC defaults 12942to the processor on which the compiler was built. 12943 12944Supported values for @var{cpu_type} are 12945 12946@table @samp 12947@item ev4 12948@itemx ev45 12949@itemx 21064 12950Schedules as an EV4 and has no instruction set extensions. 12951 12952@item ev5 12953@itemx 21164 12954Schedules as an EV5 and has no instruction set extensions. 12955 12956@item ev56 12957@itemx 21164a 12958Schedules as an EV5 and supports the BWX extension. 12959 12960@item pca56 12961@itemx 21164pc 12962@itemx 21164PC 12963Schedules as an EV5 and supports the BWX and MAX extensions. 12964 12965@item ev6 12966@itemx 21264 12967Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. 12968 12969@item ev67 12970@itemx 21264a 12971Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. 12972@end table 12973 12974Native toolchains also support the value @samp{native}, 12975which selects the best architecture option for the host processor. 12976@option{-mcpu=native} has no effect if GCC does not recognize 12977the processor. 12978 12979@item -mtune=@var{cpu_type} 12980@opindex mtune 12981Set only the instruction scheduling parameters for machine type 12982@var{cpu_type}. The instruction set is not changed. 12983 12984Native toolchains also support the value @samp{native}, 12985which selects the best architecture option for the host processor. 12986@option{-mtune=native} has no effect if GCC does not recognize 12987the processor. 12988 12989@item -mmemory-latency=@var{time} 12990@opindex mmemory-latency 12991Sets the latency the scheduler should assume for typical memory 12992references as seen by the application. This number is highly 12993dependent on the memory access patterns used by the application 12994and the size of the external cache on the machine. 12995 12996Valid options for @var{time} are 12997 12998@table @samp 12999@item @var{number} 13000A decimal number representing clock cycles. 13001 13002@item L1 13003@itemx L2 13004@itemx L3 13005@itemx main 13006The compiler contains estimates of the number of clock cycles for 13007``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches 13008(also called Dcache, Scache, and Bcache), as well as to main memory. 13009Note that L3 is only valid for EV5. 13010 13011@end table 13012@end table 13013 13014@node FR30 Options 13015@subsection FR30 Options 13016@cindex FR30 Options 13017 13018These options are defined specifically for the FR30 port. 13019 13020@table @gcctabopt 13021 13022@item -msmall-model 13023@opindex msmall-model 13024Use the small address space model. This can produce smaller code, but 13025it does assume that all symbolic values and addresses fit into a 1302620-bit range. 13027 13028@item -mno-lsim 13029@opindex mno-lsim 13030Assume that runtime support has been provided and so there is no need 13031to include the simulator library (@file{libsim.a}) on the linker 13032command line. 13033 13034@end table 13035 13036@node FRV Options 13037@subsection FRV Options 13038@cindex FRV Options 13039 13040@table @gcctabopt 13041@item -mgpr-32 13042@opindex mgpr-32 13043 13044Only use the first 32 general-purpose registers. 13045 13046@item -mgpr-64 13047@opindex mgpr-64 13048 13049Use all 64 general-purpose registers. 13050 13051@item -mfpr-32 13052@opindex mfpr-32 13053 13054Use only the first 32 floating-point registers. 13055 13056@item -mfpr-64 13057@opindex mfpr-64 13058 13059Use all 64 floating-point registers. 13060 13061@item -mhard-float 13062@opindex mhard-float 13063 13064Use hardware instructions for floating-point operations. 13065 13066@item -msoft-float 13067@opindex msoft-float 13068 13069Use library routines for floating-point operations. 13070 13071@item -malloc-cc 13072@opindex malloc-cc 13073 13074Dynamically allocate condition code registers. 13075 13076@item -mfixed-cc 13077@opindex mfixed-cc 13078 13079Do not try to dynamically allocate condition code registers, only 13080use @code{icc0} and @code{fcc0}. 13081 13082@item -mdword 13083@opindex mdword 13084 13085Change ABI to use double word insns. 13086 13087@item -mno-dword 13088@opindex mno-dword 13089 13090Do not use double word instructions. 13091 13092@item -mdouble 13093@opindex mdouble 13094 13095Use floating-point double instructions. 13096 13097@item -mno-double 13098@opindex mno-double 13099 13100Do not use floating-point double instructions. 13101 13102@item -mmedia 13103@opindex mmedia 13104 13105Use media instructions. 13106 13107@item -mno-media 13108@opindex mno-media 13109 13110Do not use media instructions. 13111 13112@item -mmuladd 13113@opindex mmuladd 13114 13115Use multiply and add/subtract instructions. 13116 13117@item -mno-muladd 13118@opindex mno-muladd 13119 13120Do not use multiply and add/subtract instructions. 13121 13122@item -mfdpic 13123@opindex mfdpic 13124 13125Select the FDPIC ABI, which uses function descriptors to represent 13126pointers to functions. Without any PIC/PIE-related options, it 13127implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it 13128assumes GOT entries and small data are within a 12-bit range from the 13129GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets 13130are computed with 32 bits. 13131With a @samp{bfin-elf} target, this option implies @option{-msim}. 13132 13133@item -minline-plt 13134@opindex minline-plt 13135 13136Enable inlining of PLT entries in function calls to functions that are 13137not known to bind locally. It has no effect without @option{-mfdpic}. 13138It's enabled by default if optimizing for speed and compiling for 13139shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an 13140optimization option such as @option{-O3} or above is present in the 13141command line. 13142 13143@item -mTLS 13144@opindex mTLS 13145 13146Assume a large TLS segment when generating thread-local code. 13147 13148@item -mtls 13149@opindex mtls 13150 13151Do not assume a large TLS segment when generating thread-local code. 13152 13153@item -mgprel-ro 13154@opindex mgprel-ro 13155 13156Enable the use of @code{GPREL} relocations in the FDPIC ABI for data 13157that is known to be in read-only sections. It's enabled by default, 13158except for @option{-fpic} or @option{-fpie}: even though it may help 13159make the global offset table smaller, it trades 1 instruction for 4. 13160With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4, 13161one of which may be shared by multiple symbols, and it avoids the need 13162for a GOT entry for the referenced symbol, so it's more likely to be a 13163win. If it is not, @option{-mno-gprel-ro} can be used to disable it. 13164 13165@item -multilib-library-pic 13166@opindex multilib-library-pic 13167 13168Link with the (library, not FD) pic libraries. It's implied by 13169@option{-mlibrary-pic}, as well as by @option{-fPIC} and 13170@option{-fpic} without @option{-mfdpic}. You should never have to use 13171it explicitly. 13172 13173@item -mlinked-fp 13174@opindex mlinked-fp 13175 13176Follow the EABI requirement of always creating a frame pointer whenever 13177a stack frame is allocated. This option is enabled by default and can 13178be disabled with @option{-mno-linked-fp}. 13179 13180@item -mlong-calls 13181@opindex mlong-calls 13182 13183Use indirect addressing to call functions outside the current 13184compilation unit. This allows the functions to be placed anywhere 13185within the 32-bit address space. 13186 13187@item -malign-labels 13188@opindex malign-labels 13189 13190Try to align labels to an 8-byte boundary by inserting NOPs into the 13191previous packet. This option only has an effect when VLIW packing 13192is enabled. It doesn't create new packets; it merely adds NOPs to 13193existing ones. 13194 13195@item -mlibrary-pic 13196@opindex mlibrary-pic 13197 13198Generate position-independent EABI code. 13199 13200@item -macc-4 13201@opindex macc-4 13202 13203Use only the first four media accumulator registers. 13204 13205@item -macc-8 13206@opindex macc-8 13207 13208Use all eight media accumulator registers. 13209 13210@item -mpack 13211@opindex mpack 13212 13213Pack VLIW instructions. 13214 13215@item -mno-pack 13216@opindex mno-pack 13217 13218Do not pack VLIW instructions. 13219 13220@item -mno-eflags 13221@opindex mno-eflags 13222 13223Do not mark ABI switches in e_flags. 13224 13225@item -mcond-move 13226@opindex mcond-move 13227 13228Enable the use of conditional-move instructions (default). 13229 13230This switch is mainly for debugging the compiler and will likely be removed 13231in a future version. 13232 13233@item -mno-cond-move 13234@opindex mno-cond-move 13235 13236Disable the use of conditional-move instructions. 13237 13238This switch is mainly for debugging the compiler and will likely be removed 13239in a future version. 13240 13241@item -mscc 13242@opindex mscc 13243 13244Enable the use of conditional set instructions (default). 13245 13246This switch is mainly for debugging the compiler and will likely be removed 13247in a future version. 13248 13249@item -mno-scc 13250@opindex mno-scc 13251 13252Disable the use of conditional set instructions. 13253 13254This switch is mainly for debugging the compiler and will likely be removed 13255in a future version. 13256 13257@item -mcond-exec 13258@opindex mcond-exec 13259 13260Enable the use of conditional execution (default). 13261 13262This switch is mainly for debugging the compiler and will likely be removed 13263in a future version. 13264 13265@item -mno-cond-exec 13266@opindex mno-cond-exec 13267 13268Disable the use of conditional execution. 13269 13270This switch is mainly for debugging the compiler and will likely be removed 13271in a future version. 13272 13273@item -mvliw-branch 13274@opindex mvliw-branch 13275 13276Run a pass to pack branches into VLIW instructions (default). 13277 13278This switch is mainly for debugging the compiler and will likely be removed 13279in a future version. 13280 13281@item -mno-vliw-branch 13282@opindex mno-vliw-branch 13283 13284Do not run a pass to pack branches into VLIW instructions. 13285 13286This switch is mainly for debugging the compiler and will likely be removed 13287in a future version. 13288 13289@item -mmulti-cond-exec 13290@opindex mmulti-cond-exec 13291 13292Enable optimization of @code{&&} and @code{||} in conditional execution 13293(default). 13294 13295This switch is mainly for debugging the compiler and will likely be removed 13296in a future version. 13297 13298@item -mno-multi-cond-exec 13299@opindex mno-multi-cond-exec 13300 13301Disable optimization of @code{&&} and @code{||} in conditional execution. 13302 13303This switch is mainly for debugging the compiler and will likely be removed 13304in a future version. 13305 13306@item -mnested-cond-exec 13307@opindex mnested-cond-exec 13308 13309Enable nested conditional execution optimizations (default). 13310 13311This switch is mainly for debugging the compiler and will likely be removed 13312in a future version. 13313 13314@item -mno-nested-cond-exec 13315@opindex mno-nested-cond-exec 13316 13317Disable nested conditional execution optimizations. 13318 13319This switch is mainly for debugging the compiler and will likely be removed 13320in a future version. 13321 13322@item -moptimize-membar 13323@opindex moptimize-membar 13324 13325This switch removes redundant @code{membar} instructions from the 13326compiler-generated code. It is enabled by default. 13327 13328@item -mno-optimize-membar 13329@opindex mno-optimize-membar 13330 13331This switch disables the automatic removal of redundant @code{membar} 13332instructions from the generated code. 13333 13334@item -mtomcat-stats 13335@opindex mtomcat-stats 13336 13337Cause gas to print out tomcat statistics. 13338 13339@item -mcpu=@var{cpu} 13340@opindex mcpu 13341 13342Select the processor type for which to generate code. Possible values are 13343@samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450}, 13344@samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}. 13345 13346@end table 13347 13348@node GNU/Linux Options 13349@subsection GNU/Linux Options 13350 13351These @samp{-m} options are defined for GNU/Linux targets: 13352 13353@table @gcctabopt 13354@item -mglibc 13355@opindex mglibc 13356Use the GNU C library. This is the default except 13357on @samp{*-*-linux-*uclibc*} and @samp{*-*-linux-*android*} targets. 13358 13359@item -muclibc 13360@opindex muclibc 13361Use uClibc C library. This is the default on 13362@samp{*-*-linux-*uclibc*} targets. 13363 13364@item -mbionic 13365@opindex mbionic 13366Use Bionic C library. This is the default on 13367@samp{*-*-linux-*android*} targets. 13368 13369@item -mandroid 13370@opindex mandroid 13371Compile code compatible with Android platform. This is the default on 13372@samp{*-*-linux-*android*} targets. 13373 13374When compiling, this option enables @option{-mbionic}, @option{-fPIC}, 13375@option{-fno-exceptions} and @option{-fno-rtti} by default. When linking, 13376this option makes the GCC driver pass Android-specific options to the linker. 13377Finally, this option causes the preprocessor macro @code{__ANDROID__} 13378to be defined. 13379 13380@item -tno-android-cc 13381@opindex tno-android-cc 13382Disable compilation effects of @option{-mandroid}, i.e., do not enable 13383@option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and 13384@option{-fno-rtti} by default. 13385 13386@item -tno-android-ld 13387@opindex tno-android-ld 13388Disable linking effects of @option{-mandroid}, i.e., pass standard Linux 13389linking options to the linker. 13390 13391@end table 13392 13393@node H8/300 Options 13394@subsection H8/300 Options 13395 13396These @samp{-m} options are defined for the H8/300 implementations: 13397 13398@table @gcctabopt 13399@item -mrelax 13400@opindex mrelax 13401Shorten some address references at link time, when possible; uses the 13402linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, 13403ld, Using ld}, for a fuller description. 13404 13405@item -mh 13406@opindex mh 13407Generate code for the H8/300H@. 13408 13409@item -ms 13410@opindex ms 13411Generate code for the H8S@. 13412 13413@item -mn 13414@opindex mn 13415Generate code for the H8S and H8/300H in the normal mode. This switch 13416must be used either with @option{-mh} or @option{-ms}. 13417 13418@item -ms2600 13419@opindex ms2600 13420Generate code for the H8S/2600. This switch must be used with @option{-ms}. 13421 13422@item -mexr 13423@opindex mexr 13424Extended registers are stored on stack before execution of function 13425with monitor attribute. Default option is @option{-mexr}. 13426This option is valid only for H8S targets. 13427 13428@item -mno-exr 13429@opindex mno-exr 13430Extended registers are not stored on stack before execution of function 13431with monitor attribute. Default option is @option{-mno-exr}. 13432This option is valid only for H8S targets. 13433 13434@item -mint32 13435@opindex mint32 13436Make @code{int} data 32 bits by default. 13437 13438@item -malign-300 13439@opindex malign-300 13440On the H8/300H and H8S, use the same alignment rules as for the H8/300. 13441The default for the H8/300H and H8S is to align longs and floats on 134424-byte boundaries. 13443@option{-malign-300} causes them to be aligned on 2-byte boundaries. 13444This option has no effect on the H8/300. 13445@end table 13446 13447@node HPPA Options 13448@subsection HPPA Options 13449@cindex HPPA Options 13450 13451These @samp{-m} options are defined for the HPPA family of computers: 13452 13453@table @gcctabopt 13454@item -march=@var{architecture-type} 13455@opindex march 13456Generate code for the specified architecture. The choices for 13457@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA 134581.1, and @samp{2.0} for PA 2.0 processors. Refer to 13459@file{/usr/lib/sched.models} on an HP-UX system to determine the proper 13460architecture option for your machine. Code compiled for lower numbered 13461architectures runs on higher numbered architectures, but not the 13462other way around. 13463 13464@item -mpa-risc-1-0 13465@itemx -mpa-risc-1-1 13466@itemx -mpa-risc-2-0 13467@opindex mpa-risc-1-0 13468@opindex mpa-risc-1-1 13469@opindex mpa-risc-2-0 13470Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. 13471 13472@item -mbig-switch 13473@opindex mbig-switch 13474Generate code suitable for big switch tables. Use this option only if 13475the assembler/linker complain about out-of-range branches within a switch 13476table. 13477 13478@item -mjump-in-delay 13479@opindex mjump-in-delay 13480Fill delay slots of function calls with unconditional jump instructions 13481by modifying the return pointer for the function call to be the target 13482of the conditional jump. 13483 13484@item -mdisable-fpregs 13485@opindex mdisable-fpregs 13486Prevent floating-point registers from being used in any manner. This is 13487necessary for compiling kernels that perform lazy context switching of 13488floating-point registers. If you use this option and attempt to perform 13489floating-point operations, the compiler aborts. 13490 13491@item -mdisable-indexing 13492@opindex mdisable-indexing 13493Prevent the compiler from using indexing address modes. This avoids some 13494rather obscure problems when compiling MIG generated code under MACH@. 13495 13496@item -mno-space-regs 13497@opindex mno-space-regs 13498Generate code that assumes the target has no space registers. This allows 13499GCC to generate faster indirect calls and use unscaled index address modes. 13500 13501Such code is suitable for level 0 PA systems and kernels. 13502 13503@item -mfast-indirect-calls 13504@opindex mfast-indirect-calls 13505Generate code that assumes calls never cross space boundaries. This 13506allows GCC to emit code that performs faster indirect calls. 13507 13508This option does not work in the presence of shared libraries or nested 13509functions. 13510 13511@item -mfixed-range=@var{register-range} 13512@opindex mfixed-range 13513Generate code treating the given register range as fixed registers. 13514A fixed register is one that the register allocator cannot use. This is 13515useful when compiling kernel code. A register range is specified as 13516two registers separated by a dash. Multiple register ranges can be 13517specified separated by a comma. 13518 13519@item -mlong-load-store 13520@opindex mlong-load-store 13521Generate 3-instruction load and store sequences as sometimes required by 13522the HP-UX 10 linker. This is equivalent to the @samp{+k} option to 13523the HP compilers. 13524 13525@item -mportable-runtime 13526@opindex mportable-runtime 13527Use the portable calling conventions proposed by HP for ELF systems. 13528 13529@item -mgas 13530@opindex mgas 13531Enable the use of assembler directives only GAS understands. 13532 13533@item -mschedule=@var{cpu-type} 13534@opindex mschedule 13535Schedule code according to the constraints for the machine type 13536@var{cpu-type}. The choices for @var{cpu-type} are @samp{700} 13537@samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer 13538to @file{/usr/lib/sched.models} on an HP-UX system to determine the 13539proper scheduling option for your machine. The default scheduling is 13540@samp{8000}. 13541 13542@item -mlinker-opt 13543@opindex mlinker-opt 13544Enable the optimization pass in the HP-UX linker. Note this makes symbolic 13545debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 13546linkers in which they give bogus error messages when linking some programs. 13547 13548@item -msoft-float 13549@opindex msoft-float 13550Generate output containing library calls for floating point. 13551@strong{Warning:} the requisite libraries are not available for all HPPA 13552targets. Normally the facilities of the machine's usual C compiler are 13553used, but this cannot be done directly in cross-compilation. You must make 13554your own arrangements to provide suitable library functions for 13555cross-compilation. 13556 13557@option{-msoft-float} changes the calling convention in the output file; 13558therefore, it is only useful if you compile @emph{all} of a program with 13559this option. In particular, you need to compile @file{libgcc.a}, the 13560library that comes with GCC, with @option{-msoft-float} in order for 13561this to work. 13562 13563@item -msio 13564@opindex msio 13565Generate the predefine, @code{_SIO}, for server IO@. The default is 13566@option{-mwsio}. This generates the predefines, @code{__hp9000s700}, 13567@code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These 13568options are available under HP-UX and HI-UX@. 13569 13570@item -mgnu-ld 13571@opindex mgnu-ld 13572Use options specific to GNU @command{ld}. 13573This passes @option{-shared} to @command{ld} when 13574building a shared library. It is the default when GCC is configured, 13575explicitly or implicitly, with the GNU linker. This option does not 13576affect which @command{ld} is called; it only changes what parameters 13577are passed to that @command{ld}. 13578The @command{ld} that is called is determined by the 13579@option{--with-ld} configure option, GCC's program search path, and 13580finally by the user's @env{PATH}. The linker used by GCC can be printed 13581using @samp{which `gcc -print-prog-name=ld`}. This option is only available 13582on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. 13583 13584@item -mhp-ld 13585@opindex mhp-ld 13586Use options specific to HP @command{ld}. 13587This passes @option{-b} to @command{ld} when building 13588a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all 13589links. It is the default when GCC is configured, explicitly or 13590implicitly, with the HP linker. This option does not affect 13591which @command{ld} is called; it only changes what parameters are passed to that 13592@command{ld}. 13593The @command{ld} that is called is determined by the @option{--with-ld} 13594configure option, GCC's program search path, and finally by the user's 13595@env{PATH}. The linker used by GCC can be printed using @samp{which 13596`gcc -print-prog-name=ld`}. This option is only available on the 64-bit 13597HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. 13598 13599@item -mlong-calls 13600@opindex mno-long-calls 13601Generate code that uses long call sequences. This ensures that a call 13602is always able to reach linker generated stubs. The default is to generate 13603long calls only when the distance from the call site to the beginning 13604of the function or translation unit, as the case may be, exceeds a 13605predefined limit set by the branch type being used. The limits for 13606normal calls are 7,600,000 and 240,000 bytes, respectively for the 13607PA 2.0 and PA 1.X architectures. Sibcalls are always limited at 13608240,000 bytes. 13609 13610Distances are measured from the beginning of functions when using the 13611@option{-ffunction-sections} option, or when using the @option{-mgas} 13612and @option{-mno-portable-runtime} options together under HP-UX with 13613the SOM linker. 13614 13615It is normally not desirable to use this option as it degrades 13616performance. However, it may be useful in large applications, 13617particularly when partial linking is used to build the application. 13618 13619The types of long calls used depends on the capabilities of the 13620assembler and linker, and the type of code being generated. The 13621impact on systems that support long absolute calls, and long pic 13622symbol-difference or pc-relative calls should be relatively small. 13623However, an indirect call is used on 32-bit ELF systems in pic code 13624and it is quite long. 13625 13626@item -munix=@var{unix-std} 13627@opindex march 13628Generate compiler predefines and select a startfile for the specified 13629UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95} 13630and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95} 13631is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX 1363211.11 and later. The default values are @samp{93} for HP-UX 10.00, 13633@samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11 13634and later. 13635 13636@option{-munix=93} provides the same predefines as GCC 3.3 and 3.4. 13637@option{-munix=95} provides additional predefines for @code{XOPEN_UNIX} 13638and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}. 13639@option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX}, 13640@code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and 13641@code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}. 13642 13643It is @emph{important} to note that this option changes the interfaces 13644for various library routines. It also affects the operational behavior 13645of the C library. Thus, @emph{extreme} care is needed in using this 13646option. 13647 13648Library code that is intended to operate with more than one UNIX 13649standard must test, set and restore the variable @var{__xpg4_extended_mask} 13650as appropriate. Most GNU software doesn't provide this capability. 13651 13652@item -nolibdld 13653@opindex nolibdld 13654Suppress the generation of link options to search libdld.sl when the 13655@option{-static} option is specified on HP-UX 10 and later. 13656 13657@item -static 13658@opindex static 13659The HP-UX implementation of setlocale in libc has a dependency on 13660libdld.sl. There isn't an archive version of libdld.sl. Thus, 13661when the @option{-static} option is specified, special link options 13662are needed to resolve this dependency. 13663 13664On HP-UX 10 and later, the GCC driver adds the necessary options to 13665link with libdld.sl when the @option{-static} option is specified. 13666This causes the resulting binary to be dynamic. On the 64-bit port, 13667the linkers generate dynamic binaries by default in any case. The 13668@option{-nolibdld} option can be used to prevent the GCC driver from 13669adding these link options. 13670 13671@item -threads 13672@opindex threads 13673Add support for multithreading with the @dfn{dce thread} library 13674under HP-UX@. This option sets flags for both the preprocessor and 13675linker. 13676@end table 13677 13678@node i386 and x86-64 Options 13679@subsection Intel 386 and AMD x86-64 Options 13680@cindex i386 Options 13681@cindex x86-64 Options 13682@cindex Intel 386 Options 13683@cindex AMD x86-64 Options 13684 13685These @samp{-m} options are defined for the i386 and x86-64 family of 13686computers: 13687 13688@table @gcctabopt 13689 13690@item -march=@var{cpu-type} 13691@opindex march 13692Generate instructions for the machine type @var{cpu-type}. In contrast to 13693@option{-mtune=@var{cpu-type}}, which merely tunes the generated code 13694for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC 13695to generate code that may not run at all on processors other than the one 13696indicated. Specifying @option{-march=@var{cpu-type}} implies 13697@option{-mtune=@var{cpu-type}}. 13698 13699The choices for @var{cpu-type} are: 13700 13701@table @samp 13702@item native 13703This selects the CPU to generate code for at compilation time by determining 13704the processor type of the compiling machine. Using @option{-march=native} 13705enables all instruction subsets supported by the local machine (hence 13706the result might not run on different machines). Using @option{-mtune=native} 13707produces code optimized for the local machine under the constraints 13708of the selected instruction set. 13709 13710@item i386 13711Original Intel i386 CPU@. 13712 13713@item i486 13714Intel i486 CPU@. (No scheduling is implemented for this chip.) 13715 13716@item i586 13717@itemx pentium 13718Intel Pentium CPU with no MMX support. 13719 13720@item pentium-mmx 13721Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. 13722 13723@item pentiumpro 13724Intel Pentium Pro CPU@. 13725 13726@item i686 13727When used with @option{-march}, the Pentium Pro 13728instruction set is used, so the code runs on all i686 family chips. 13729When used with @option{-mtune}, it has the same meaning as @samp{generic}. 13730 13731@item pentium2 13732Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set 13733support. 13734 13735@item pentium3 13736@itemx pentium3m 13737Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction 13738set support. 13739 13740@item pentium-m 13741Intel Pentium M; low-power version of Intel Pentium III CPU 13742with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks. 13743 13744@item pentium4 13745@itemx pentium4m 13746Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support. 13747 13748@item prescott 13749Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction 13750set support. 13751 13752@item nocona 13753Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, 13754SSE2 and SSE3 instruction set support. 13755 13756@item core2 13757Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 13758instruction set support. 13759 13760@item corei7 13761Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1 13762and SSE4.2 instruction set support. 13763 13764@item corei7-avx 13765Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, 13766SSE4.1, SSE4.2, AVX, AES and PCLMUL instruction set support. 13767 13768@item core-avx-i 13769Intel Core CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, 13770SSE4.1, SSE4.2, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C instruction 13771set support. 13772 13773@item core-avx2 13774Intel Core CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, 13775SSE4.1, SSE4.2, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 13776and F16C instruction set support. 13777 13778@item atom 13779Intel Atom CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3 13780instruction set support. 13781 13782@item k6 13783AMD K6 CPU with MMX instruction set support. 13784 13785@item k6-2 13786@itemx k6-3 13787Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support. 13788 13789@item athlon 13790@itemx athlon-tbird 13791AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions 13792support. 13793 13794@item athlon-4 13795@itemx athlon-xp 13796@itemx athlon-mp 13797Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE 13798instruction set support. 13799 13800@item k8 13801@itemx opteron 13802@itemx athlon64 13803@itemx athlon-fx 13804Processors based on the AMD K8 core with x86-64 instruction set support, 13805including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. 13806(This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit 13807instruction set extensions.) 13808 13809@item k8-sse3 13810@itemx opteron-sse3 13811@itemx athlon64-sse3 13812Improved versions of AMD K8 cores with SSE3 instruction set support. 13813 13814@item amdfam10 13815@itemx barcelona 13816CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This 13817supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit 13818instruction set extensions.) 13819 13820@item bdver1 13821CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This 13822supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, 13823SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) 13824@item bdver2 13825AMD Family 15h core based CPUs with x86-64 instruction set support. (This 13826supersets BMI, TBM, F16C, FMA, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, 13827SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set 13828extensions.) 13829@item bdver3 13830AMD Family 15h core based CPUs with x86-64 instruction set support. (This 13831supersets BMI, TBM, F16C, FMA, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, 13832SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set 13833extensions. 13834 13835@item btver1 13836CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This 13837supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit 13838instruction set extensions.) 13839 13840@item btver2 13841CPUs based on AMD Family 16h cores with x86-64 instruction set support. This 13842includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM, 13843SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions. 13844 13845@item winchip-c6 13846IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction 13847set support. 13848 13849@item winchip2 13850IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@: 13851instruction set support. 13852 13853@item c3 13854VIA C3 CPU with MMX and 3DNow!@: instruction set support. (No scheduling is 13855implemented for this chip.) 13856 13857@item c3-2 13858VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. 13859(No scheduling is 13860implemented for this chip.) 13861 13862@item geode 13863AMD Geode embedded processor with MMX and 3DNow!@: instruction set support. 13864@end table 13865 13866@item -mtune=@var{cpu-type} 13867@opindex mtune 13868Tune to @var{cpu-type} everything applicable about the generated code, except 13869for the ABI and the set of available instructions. 13870While picking a specific @var{cpu-type} schedules things appropriately 13871for that particular chip, the compiler does not generate any code that 13872cannot run on the default machine type unless you use a 13873@option{-march=@var{cpu-type}} option. 13874For example, if GCC is configured for i686-pc-linux-gnu 13875then @option{-mtune=pentium4} generates code that is tuned for Pentium 4 13876but still runs on i686 machines. 13877 13878The choices for @var{cpu-type} are the same as for @option{-march}. 13879In addition, @option{-mtune} supports an extra choice for @var{cpu-type}: 13880 13881@table @samp 13882@item generic 13883Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors. 13884If you know the CPU on which your code will run, then you should use 13885the corresponding @option{-mtune} or @option{-march} option instead of 13886@option{-mtune=generic}. But, if you do not know exactly what CPU users 13887of your application will have, then you should use this option. 13888 13889As new processors are deployed in the marketplace, the behavior of this 13890option will change. Therefore, if you upgrade to a newer version of 13891GCC, code generation controlled by this option will change to reflect 13892the processors 13893that are most common at the time that version of GCC is released. 13894 13895There is no @option{-march=generic} option because @option{-march} 13896indicates the instruction set the compiler can use, and there is no 13897generic instruction set applicable to all processors. In contrast, 13898@option{-mtune} indicates the processor (or, in this case, collection of 13899processors) for which the code is optimized. 13900@end table 13901 13902@item -mcpu=@var{cpu-type} 13903@opindex mcpu 13904A deprecated synonym for @option{-mtune}. 13905 13906@item -mfpmath=@var{unit} 13907@opindex mfpmath 13908Generate floating-point arithmetic for selected unit @var{unit}. The choices 13909for @var{unit} are: 13910 13911@table @samp 13912@item 387 13913Use the standard 387 floating-point coprocessor present on the majority of chips and 13914emulated otherwise. Code compiled with this option runs almost everywhere. 13915The temporary results are computed in 80-bit precision instead of the precision 13916specified by the type, resulting in slightly different results compared to most 13917of other chips. See @option{-ffloat-store} for more detailed description. 13918 13919This is the default choice for i386 compiler. 13920 13921@item sse 13922Use scalar floating-point instructions present in the SSE instruction set. 13923This instruction set is supported by Pentium III and newer chips, 13924and in the AMD line 13925by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE 13926instruction set supports only single-precision arithmetic, thus the double and 13927extended-precision arithmetic are still done using 387. A later version, present 13928only in Pentium 4 and AMD x86-64 chips, supports double-precision 13929arithmetic too. 13930 13931For the i386 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse} 13932or @option{-msse2} switches to enable SSE extensions and make this option 13933effective. For the x86-64 compiler, these extensions are enabled by default. 13934 13935The resulting code should be considerably faster in the majority of cases and avoid 13936the numerical instability problems of 387 code, but may break some existing 13937code that expects temporaries to be 80 bits. 13938 13939This is the default choice for the x86-64 compiler. 13940 13941@item sse,387 13942@itemx sse+387 13943@itemx both 13944Attempt to utilize both instruction sets at once. This effectively doubles the 13945amount of available registers, and on chips with separate execution units for 13946387 and SSE the execution resources too. Use this option with care, as it is 13947still experimental, because the GCC register allocator does not model separate 13948functional units well, resulting in unstable performance. 13949@end table 13950 13951@item -masm=@var{dialect} 13952@opindex masm=@var{dialect} 13953Output assembly instructions using selected @var{dialect}. Supported 13954choices are @samp{intel} or @samp{att} (the default). Darwin does 13955not support @samp{intel}. 13956 13957@item -mieee-fp 13958@itemx -mno-ieee-fp 13959@opindex mieee-fp 13960@opindex mno-ieee-fp 13961Control whether or not the compiler uses IEEE floating-point 13962comparisons. These correctly handle the case where the result of a 13963comparison is unordered. 13964 13965@item -msoft-float 13966@opindex msoft-float 13967Generate output containing library calls for floating point. 13968 13969@strong{Warning:} the requisite libraries are not part of GCC@. 13970Normally the facilities of the machine's usual C compiler are used, but 13971this can't be done directly in cross-compilation. You must make your 13972own arrangements to provide suitable library functions for 13973cross-compilation. 13974 13975On machines where a function returns floating-point results in the 80387 13976register stack, some floating-point opcodes may be emitted even if 13977@option{-msoft-float} is used. 13978 13979@item -mno-fp-ret-in-387 13980@opindex mno-fp-ret-in-387 13981Do not use the FPU registers for return values of functions. 13982 13983The usual calling convention has functions return values of types 13984@code{float} and @code{double} in an FPU register, even if there 13985is no FPU@. The idea is that the operating system should emulate 13986an FPU@. 13987 13988The option @option{-mno-fp-ret-in-387} causes such values to be returned 13989in ordinary CPU registers instead. 13990 13991@item -mno-fancy-math-387 13992@opindex mno-fancy-math-387 13993Some 387 emulators do not support the @code{sin}, @code{cos} and 13994@code{sqrt} instructions for the 387. Specify this option to avoid 13995generating those instructions. This option is the default on FreeBSD, 13996OpenBSD and NetBSD@. This option is overridden when @option{-march} 13997indicates that the target CPU always has an FPU and so the 13998instruction does not need emulation. These 13999instructions are not generated unless you also use the 14000@option{-funsafe-math-optimizations} switch. 14001 14002@item -malign-double 14003@itemx -mno-align-double 14004@opindex malign-double 14005@opindex mno-align-double 14006Control whether GCC aligns @code{double}, @code{long double}, and 14007@code{long long} variables on a two-word boundary or a one-word 14008boundary. Aligning @code{double} variables on a two-word boundary 14009produces code that runs somewhat faster on a Pentium at the 14010expense of more memory. 14011 14012On x86-64, @option{-malign-double} is enabled by default. 14013 14014@strong{Warning:} if you use the @option{-malign-double} switch, 14015structures containing the above types are aligned differently than 14016the published application binary interface specifications for the 386 14017and are not binary compatible with structures in code compiled 14018without that switch. 14019 14020@item -m96bit-long-double 14021@itemx -m128bit-long-double 14022@opindex m96bit-long-double 14023@opindex m128bit-long-double 14024These switches control the size of @code{long double} type. The i386 14025application binary interface specifies the size to be 96 bits, 14026so @option{-m96bit-long-double} is the default in 32-bit mode. 14027 14028Modern architectures (Pentium and newer) prefer @code{long double} 14029to be aligned to an 8- or 16-byte boundary. In arrays or structures 14030conforming to the ABI, this is not possible. So specifying 14031@option{-m128bit-long-double} aligns @code{long double} 14032to a 16-byte boundary by padding the @code{long double} with an additional 1403332-bit zero. 14034 14035In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as 14036its ABI specifies that @code{long double} is aligned on 16-byte boundary. 14037 14038Notice that neither of these options enable any extra precision over the x87 14039standard of 80 bits for a @code{long double}. 14040 14041@strong{Warning:} if you override the default value for your target ABI, this 14042changes the size of 14043structures and arrays containing @code{long double} variables, 14044as well as modifying the function calling convention for functions taking 14045@code{long double}. Hence they are not binary-compatible 14046with code compiled without that switch. 14047 14048@item -mlong-double-64 14049@itemx -mlong-double-80 14050@opindex mlong-double-64 14051@opindex mlong-double-80 14052These switches control the size of @code{long double} type. A size 14053of 64 bits makes the @code{long double} type equivalent to the @code{double} 14054type. This is the default for Bionic C library. 14055 14056@strong{Warning:} if you override the default value for your target ABI, this 14057changes the size of 14058structures and arrays containing @code{long double} variables, 14059as well as modifying the function calling convention for functions taking 14060@code{long double}. Hence they are not binary-compatible 14061with code compiled without that switch. 14062 14063@item -mlarge-data-threshold=@var{threshold} 14064@opindex mlarge-data-threshold 14065When @option{-mcmodel=medium} is specified, data objects larger than 14066@var{threshold} are placed in the large data section. This value must be the 14067same across all objects linked into the binary, and defaults to 65535. 14068 14069@item -mrtd 14070@opindex mrtd 14071Use a different function-calling convention, in which functions that 14072take a fixed number of arguments return with the @code{ret @var{num}} 14073instruction, which pops their arguments while returning. This saves one 14074instruction in the caller since there is no need to pop the arguments 14075there. 14076 14077You can specify that an individual function is called with this calling 14078sequence with the function attribute @samp{stdcall}. You can also 14079override the @option{-mrtd} option by using the function attribute 14080@samp{cdecl}. @xref{Function Attributes}. 14081 14082@strong{Warning:} this calling convention is incompatible with the one 14083normally used on Unix, so you cannot use it if you need to call 14084libraries compiled with the Unix compiler. 14085 14086Also, you must provide function prototypes for all functions that 14087take variable numbers of arguments (including @code{printf}); 14088otherwise incorrect code is generated for calls to those 14089functions. 14090 14091In addition, seriously incorrect code results if you call a 14092function with too many arguments. (Normally, extra arguments are 14093harmlessly ignored.) 14094 14095@item -mregparm=@var{num} 14096@opindex mregparm 14097Control how many registers are used to pass integer arguments. By 14098default, no registers are used to pass arguments, and at most 3 14099registers can be used. You can control this behavior for a specific 14100function by using the function attribute @samp{regparm}. 14101@xref{Function Attributes}. 14102 14103@strong{Warning:} if you use this switch, and 14104@var{num} is nonzero, then you must build all modules with the same 14105value, including any libraries. This includes the system libraries and 14106startup modules. 14107 14108@item -msseregparm 14109@opindex msseregparm 14110Use SSE register passing conventions for float and double arguments 14111and return values. You can control this behavior for a specific 14112function by using the function attribute @samp{sseregparm}. 14113@xref{Function Attributes}. 14114 14115@strong{Warning:} if you use this switch then you must build all 14116modules with the same value, including any libraries. This includes 14117the system libraries and startup modules. 14118 14119@item -mvect8-ret-in-mem 14120@opindex mvect8-ret-in-mem 14121Return 8-byte vectors in memory instead of MMX registers. This is the 14122default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun 14123Studio compilers until version 12. Later compiler versions (starting 14124with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which 14125is the default on Solaris@tie{}10 and later. @emph{Only} use this option if 14126you need to remain compatible with existing code produced by those 14127previous compiler versions or older versions of GCC@. 14128 14129@item -mpc32 14130@itemx -mpc64 14131@itemx -mpc80 14132@opindex mpc32 14133@opindex mpc64 14134@opindex mpc80 14135 14136Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32} 14137is specified, the significands of results of floating-point operations are 14138rounded to 24 bits (single precision); @option{-mpc64} rounds the 14139significands of results of floating-point operations to 53 bits (double 14140precision) and @option{-mpc80} rounds the significands of results of 14141floating-point operations to 64 bits (extended double precision), which is 14142the default. When this option is used, floating-point operations in higher 14143precisions are not available to the programmer without setting the FPU 14144control word explicitly. 14145 14146Setting the rounding of floating-point operations to less than the default 1414780 bits can speed some programs by 2% or more. Note that some mathematical 14148libraries assume that extended-precision (80-bit) floating-point operations 14149are enabled by default; routines in such libraries could suffer significant 14150loss of accuracy, typically through so-called ``catastrophic cancellation'', 14151when this option is used to set the precision to less than extended precision. 14152 14153@item -mstackrealign 14154@opindex mstackrealign 14155Realign the stack at entry. On the Intel x86, the @option{-mstackrealign} 14156option generates an alternate prologue and epilogue that realigns the 14157run-time stack if necessary. This supports mixing legacy codes that keep 141584-byte stack alignment with modern codes that keep 16-byte stack alignment for 14159SSE compatibility. See also the attribute @code{force_align_arg_pointer}, 14160applicable to individual functions. 14161 14162@item -mpreferred-stack-boundary=@var{num} 14163@opindex mpreferred-stack-boundary 14164Attempt to keep the stack boundary aligned to a 2 raised to @var{num} 14165byte boundary. If @option{-mpreferred-stack-boundary} is not specified, 14166the default is 4 (16 bytes or 128 bits). 14167 14168@strong{Warning:} When generating code for the x86-64 architecture with 14169SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be 14170used to keep the stack boundary aligned to 8 byte boundary. Since 14171x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and 14172intended to be used in controlled environment where stack space is 14173important limitation. This option will lead to wrong code when functions 14174compiled with 16 byte stack alignment (such as functions from a standard 14175library) are called with misaligned stack. In this case, SSE 14176instructions may lead to misaligned memory access traps. In addition, 14177variable arguments will be handled incorrectly for 16 byte aligned 14178objects (including x87 long double and __int128), leading to wrong 14179results. You must build all modules with 14180@option{-mpreferred-stack-boundary=3}, including any libraries. This 14181includes the system libraries and startup modules. 14182 14183@item -mincoming-stack-boundary=@var{num} 14184@opindex mincoming-stack-boundary 14185Assume the incoming stack is aligned to a 2 raised to @var{num} byte 14186boundary. If @option{-mincoming-stack-boundary} is not specified, 14187the one specified by @option{-mpreferred-stack-boundary} is used. 14188 14189On Pentium and Pentium Pro, @code{double} and @code{long double} values 14190should be aligned to an 8-byte boundary (see @option{-malign-double}) or 14191suffer significant run time performance penalties. On Pentium III, the 14192Streaming SIMD Extension (SSE) data type @code{__m128} may not work 14193properly if it is not 16-byte aligned. 14194 14195To ensure proper alignment of these values on the stack, the stack boundary 14196must be as aligned as that required by any value stored on the stack. 14197Further, every function must be generated such that it keeps the stack 14198aligned. Thus calling a function compiled with a higher preferred 14199stack boundary from a function compiled with a lower preferred stack 14200boundary most likely misaligns the stack. It is recommended that 14201libraries that use callbacks always use the default setting. 14202 14203This extra alignment does consume extra stack space, and generally 14204increases code size. Code that is sensitive to stack space usage, such 14205as embedded systems and operating system kernels, may want to reduce the 14206preferred alignment to @option{-mpreferred-stack-boundary=2}. 14207 14208@item -mmmx 14209@itemx -mno-mmx 14210@itemx -msse 14211@itemx -mno-sse 14212@itemx -msse2 14213@itemx -mno-sse2 14214@itemx -msse3 14215@itemx -mno-sse3 14216@itemx -mssse3 14217@itemx -mno-ssse3 14218@itemx -msse4.1 14219@need 800 14220@itemx -mno-sse4.1 14221@itemx -msse4.2 14222@itemx -mno-sse4.2 14223@itemx -msse4 14224@itemx -mno-sse4 14225@itemx -mavx 14226@itemx -mno-avx 14227@itemx -mavx2 14228@itemx -mno-avx2 14229@itemx -maes 14230@itemx -mno-aes 14231@itemx -mpclmul 14232@need 800 14233@itemx -mno-pclmul 14234@itemx -mfsgsbase 14235@itemx -mno-fsgsbase 14236@itemx -mrdrnd 14237@itemx -mno-rdrnd 14238@itemx -mf16c 14239@itemx -mno-f16c 14240@itemx -mfma 14241@itemx -mno-fma 14242@itemx -msse4a 14243@itemx -mno-sse4a 14244@itemx -mfma4 14245@need 800 14246@itemx -mno-fma4 14247@itemx -mxop 14248@itemx -mno-xop 14249@itemx -mlwp 14250@itemx -mno-lwp 14251@itemx -m3dnow 14252@itemx -mno-3dnow 14253@itemx -mpopcnt 14254@itemx -mno-popcnt 14255@itemx -mabm 14256@itemx -mno-abm 14257@itemx -mbmi 14258@itemx -mbmi2 14259@itemx -mno-bmi 14260@itemx -mno-bmi2 14261@itemx -mlzcnt 14262@itemx -mno-lzcnt 14263@itemx -mrtm 14264@itemx -mtbm 14265@itemx -mno-tbm 14266@opindex mmmx 14267@opindex mno-mmx 14268@opindex msse 14269@opindex mno-sse 14270@opindex m3dnow 14271@opindex mno-3dnow 14272These switches enable or disable the use of instructions in the MMX, SSE, 14273SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, F16C, 14274FMA, SSE4A, FMA4, XOP, LWP, ABM, BMI, BMI2, LZCNT, RTM or 3DNow!@: 14275extended instruction sets. 14276These extensions are also available as built-in functions: see 14277@ref{X86 Built-in Functions}, for details of the functions enabled and 14278disabled by these switches. 14279 14280To generate SSE/SSE2 instructions automatically from floating-point 14281code (as opposed to 387 instructions), see @option{-mfpmath=sse}. 14282 14283GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it 14284generates new AVX instructions or AVX equivalence for all SSEx instructions 14285when needed. 14286 14287These options enable GCC to use these extended instructions in 14288generated code, even without @option{-mfpmath=sse}. Applications that 14289perform run-time CPU detection must compile separate files for each 14290supported architecture, using the appropriate flags. In particular, 14291the file containing the CPU detection code should be compiled without 14292these options. 14293 14294@item -mcld 14295@opindex mcld 14296This option instructs GCC to emit a @code{cld} instruction in the prologue 14297of functions that use string instructions. String instructions depend on 14298the DF flag to select between autoincrement or autodecrement mode. While the 14299ABI specifies the DF flag to be cleared on function entry, some operating 14300systems violate this specification by not clearing the DF flag in their 14301exception dispatchers. The exception handler can be invoked with the DF flag 14302set, which leads to wrong direction mode when string instructions are used. 14303This option can be enabled by default on 32-bit x86 targets by configuring 14304GCC with the @option{--enable-cld} configure option. Generation of @code{cld} 14305instructions can be suppressed with the @option{-mno-cld} compiler option 14306in this case. 14307 14308@item -mvzeroupper 14309@opindex mvzeroupper 14310This option instructs GCC to emit a @code{vzeroupper} instruction 14311before a transfer of control flow out of the function to minimize 14312the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper} 14313intrinsics. 14314 14315@item -mprefer-avx128 14316@opindex mprefer-avx128 14317This option instructs GCC to use 128-bit AVX instructions instead of 14318256-bit AVX instructions in the auto-vectorizer. 14319 14320@item -mcx16 14321@opindex mcx16 14322This option enables GCC to generate @code{CMPXCHG16B} instructions. 14323@code{CMPXCHG16B} allows for atomic operations on 128-bit double quadword 14324(or oword) data types. 14325This is useful for high-resolution counters that can be updated 14326by multiple processors (or cores). This instruction is generated as part of 14327atomic built-in functions: see @ref{__sync Builtins} or 14328@ref{__atomic Builtins} for details. 14329 14330@item -msahf 14331@opindex msahf 14332This option enables generation of @code{SAHF} instructions in 64-bit code. 14333Early Intel Pentium 4 CPUs with Intel 64 support, 14334prior to the introduction of Pentium 4 G1 step in December 2005, 14335lacked the @code{LAHF} and @code{SAHF} instructions 14336which were supported by AMD64. 14337These are load and store instructions, respectively, for certain status flags. 14338In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod}, 14339@code{drem}, and @code{remainder} built-in functions; 14340see @ref{Other Builtins} for details. 14341 14342@item -mmovbe 14343@opindex mmovbe 14344This option enables use of the @code{movbe} instruction to implement 14345@code{__builtin_bswap32} and @code{__builtin_bswap64}. 14346 14347@item -mcrc32 14348@opindex mcrc32 14349This option enables built-in functions @code{__builtin_ia32_crc32qi}, 14350@code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and 14351@code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction. 14352 14353@item -mrecip 14354@opindex mrecip 14355This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions 14356(and their vectorized variants @code{RCPPS} and @code{RSQRTPS}) 14357with an additional Newton-Raphson step 14358to increase precision instead of @code{DIVSS} and @code{SQRTSS} 14359(and their vectorized 14360variants) for single-precision floating-point arguments. These instructions 14361are generated only when @option{-funsafe-math-optimizations} is enabled 14362together with @option{-finite-math-only} and @option{-fno-trapping-math}. 14363Note that while the throughput of the sequence is higher than the throughput 14364of the non-reciprocal instruction, the precision of the sequence can be 14365decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994). 14366 14367Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS} 14368(or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option 14369combination), and doesn't need @option{-mrecip}. 14370 14371Also note that GCC emits the above sequence with additional Newton-Raphson step 14372for vectorized single-float division and vectorized @code{sqrtf(@var{x})} 14373already with @option{-ffast-math} (or the above option combination), and 14374doesn't need @option{-mrecip}. 14375 14376@item -mrecip=@var{opt} 14377@opindex mrecip=opt 14378This option controls which reciprocal estimate instructions 14379may be used. @var{opt} is a comma-separated list of options, which may 14380be preceded by a @samp{!} to invert the option: 14381 14382@table @samp 14383@item all 14384Enable all estimate instructions. 14385 14386@item default 14387Enable the default instructions, equivalent to @option{-mrecip}. 14388 14389@item none 14390Disable all estimate instructions, equivalent to @option{-mno-recip}. 14391 14392@item div 14393Enable the approximation for scalar division. 14394 14395@item vec-div 14396Enable the approximation for vectorized division. 14397 14398@item sqrt 14399Enable the approximation for scalar square root. 14400 14401@item vec-sqrt 14402Enable the approximation for vectorized square root. 14403@end table 14404 14405So, for example, @option{-mrecip=all,!sqrt} enables 14406all of the reciprocal approximations, except for square root. 14407 14408@item -mveclibabi=@var{type} 14409@opindex mveclibabi 14410Specifies the ABI type to use for vectorizing intrinsics using an 14411external library. Supported values for @var{type} are @samp{svml} 14412for the Intel short 14413vector math library and @samp{acml} for the AMD math core library. 14414To use this option, both @option{-ftree-vectorize} and 14415@option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML 14416ABI-compatible library must be specified at link time. 14417 14418GCC currently emits calls to @code{vmldExp2}, 14419@code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2}, 14420@code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2}, 14421@code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2}, 14422@code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2}, 14423@code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104}, 14424@code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4}, 14425@code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4}, 14426@code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4}, 14427@code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding 14428function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin}, 14429@code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2}, 14430@code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf}, 14431@code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f}, 14432@code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type 14433when @option{-mveclibabi=acml} is used. 14434 14435@item -mabi=@var{name} 14436@opindex mabi 14437Generate code for the specified calling convention. Permissible values 14438are @samp{sysv} for the ABI used on GNU/Linux and other systems, and 14439@samp{ms} for the Microsoft ABI. The default is to use the Microsoft 14440ABI when targeting Microsoft Windows and the SysV ABI on all other systems. 14441You can control this behavior for a specific function by 14442using the function attribute @samp{ms_abi}/@samp{sysv_abi}. 14443@xref{Function Attributes}. 14444 14445@item -mtls-dialect=@var{type} 14446@opindex mtls-dialect 14447Generate code to access thread-local storage using the @samp{gnu} or 14448@samp{gnu2} conventions. @samp{gnu} is the conservative default; 14449@samp{gnu2} is more efficient, but it may add compile- and run-time 14450requirements that cannot be satisfied on all systems. 14451 14452@item -mpush-args 14453@itemx -mno-push-args 14454@opindex mpush-args 14455@opindex mno-push-args 14456Use PUSH operations to store outgoing parameters. This method is shorter 14457and usually equally fast as method using SUB/MOV operations and is enabled 14458by default. In some cases disabling it may improve performance because of 14459improved scheduling and reduced dependencies. 14460 14461@item -maccumulate-outgoing-args 14462@opindex maccumulate-outgoing-args 14463If enabled, the maximum amount of space required for outgoing arguments is 14464computed in the function prologue. This is faster on most modern CPUs 14465because of reduced dependencies, improved scheduling and reduced stack usage 14466when the preferred stack boundary is not equal to 2. The drawback is a notable 14467increase in code size. This switch implies @option{-mno-push-args}. 14468 14469@item -mthreads 14470@opindex mthreads 14471Support thread-safe exception handling on MinGW. Programs that rely 14472on thread-safe exception handling must compile and link all code with the 14473@option{-mthreads} option. When compiling, @option{-mthreads} defines 14474@code{-D_MT}; when linking, it links in a special thread helper library 14475@option{-lmingwthrd} which cleans up per-thread exception-handling data. 14476 14477@item -mno-align-stringops 14478@opindex mno-align-stringops 14479Do not align the destination of inlined string operations. This switch reduces 14480code size and improves performance in case the destination is already aligned, 14481but GCC doesn't know about it. 14482 14483@item -minline-all-stringops 14484@opindex minline-all-stringops 14485By default GCC inlines string operations only when the destination is 14486known to be aligned to least a 4-byte boundary. 14487This enables more inlining and increases code 14488size, but may improve performance of code that depends on fast 14489@code{memcpy}, @code{strlen}, 14490and @code{memset} for short lengths. 14491 14492@item -minline-stringops-dynamically 14493@opindex minline-stringops-dynamically 14494For string operations of unknown size, use run-time checks with 14495inline code for small blocks and a library call for large blocks. 14496 14497@item -mstringop-strategy=@var{alg} 14498@opindex mstringop-strategy=@var{alg} 14499Override the internal decision heuristic for the particular algorithm to use 14500for inlining string operations. The allowed values for @var{alg} are: 14501 14502@table @samp 14503@item rep_byte 14504@itemx rep_4byte 14505@itemx rep_8byte 14506Expand using i386 @code{rep} prefix of the specified size. 14507 14508@item byte_loop 14509@itemx loop 14510@itemx unrolled_loop 14511Expand into an inline loop. 14512 14513@item libcall 14514Always use a library call. 14515@end table 14516 14517@item -momit-leaf-frame-pointer 14518@opindex momit-leaf-frame-pointer 14519Don't keep the frame pointer in a register for leaf functions. This 14520avoids the instructions to save, set up, and restore frame pointers and 14521makes an extra register available in leaf functions. The option 14522@option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions, 14523which might make debugging harder. 14524 14525@item -mtls-direct-seg-refs 14526@itemx -mno-tls-direct-seg-refs 14527@opindex mtls-direct-seg-refs 14528Controls whether TLS variables may be accessed with offsets from the 14529TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit), 14530or whether the thread base pointer must be added. Whether or not this 14531is valid depends on the operating system, and whether it maps the 14532segment to cover the entire TLS area. 14533 14534For systems that use the GNU C Library, the default is on. 14535 14536@item -msse2avx 14537@itemx -mno-sse2avx 14538@opindex msse2avx 14539Specify that the assembler should encode SSE instructions with VEX 14540prefix. The option @option{-mavx} turns this on by default. 14541 14542@item -mfentry 14543@itemx -mno-fentry 14544@opindex mfentry 14545If profiling is active (@option{-pg}), put the profiling 14546counter call before the prologue. 14547Note: On x86 architectures the attribute @code{ms_hook_prologue} 14548isn't possible at the moment for @option{-mfentry} and @option{-pg}. 14549 14550@item -m8bit-idiv 14551@itemx -mno-8bit-idiv 14552@opindex 8bit-idiv 14553On some processors, like Intel Atom, 8-bit unsigned integer divide is 14554much faster than 32-bit/64-bit integer divide. This option generates a 14555run-time check. If both dividend and divisor are within range of 0 14556to 255, 8-bit unsigned integer divide is used instead of 1455732-bit/64-bit integer divide. 14558 14559@item -mavx256-split-unaligned-load 14560@itemx -mavx256-split-unaligned-store 14561@opindex avx256-split-unaligned-load 14562@opindex avx256-split-unaligned-store 14563Split 32-byte AVX unaligned load and store. 14564 14565@end table 14566 14567These @samp{-m} switches are supported in addition to the above 14568on x86-64 processors in 64-bit environments. 14569 14570@table @gcctabopt 14571@item -m32 14572@itemx -m64 14573@itemx -mx32 14574@opindex m32 14575@opindex m64 14576@opindex mx32 14577Generate code for a 32-bit or 64-bit environment. 14578The @option{-m32} option sets @code{int}, @code{long}, and pointer types 14579to 32 bits, and 14580generates code that runs on any i386 system. 14581 14582The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer 14583types to 64 bits, and generates code for the x86-64 architecture. 14584For Darwin only the @option{-m64} option also turns off the @option{-fno-pic} 14585and @option{-mdynamic-no-pic} options. 14586 14587The @option{-mx32} option sets @code{int}, @code{long}, and pointer types 14588to 32 bits, and 14589generates code for the x86-64 architecture. 14590 14591@item -mno-red-zone 14592@opindex mno-red-zone 14593Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated 14594by the x86-64 ABI; it is a 128-byte area beyond the location of the 14595stack pointer that is not modified by signal or interrupt handlers 14596and therefore can be used for temporary data without adjusting the stack 14597pointer. The flag @option{-mno-red-zone} disables this red zone. 14598 14599@item -mcmodel=small 14600@opindex mcmodel=small 14601Generate code for the small code model: the program and its symbols must 14602be linked in the lower 2 GB of the address space. Pointers are 64 bits. 14603Programs can be statically or dynamically linked. This is the default 14604code model. 14605 14606@item -mcmodel=kernel 14607@opindex mcmodel=kernel 14608Generate code for the kernel code model. The kernel runs in the 14609negative 2 GB of the address space. 14610This model has to be used for Linux kernel code. 14611 14612@item -mcmodel=medium 14613@opindex mcmodel=medium 14614Generate code for the medium model: the program is linked in the lower 2 14615GB of the address space. Small symbols are also placed there. Symbols 14616with sizes larger than @option{-mlarge-data-threshold} are put into 14617large data or BSS sections and can be located above 2GB. Programs can 14618be statically or dynamically linked. 14619 14620@item -mcmodel=large 14621@opindex mcmodel=large 14622Generate code for the large model. This model makes no assumptions 14623about addresses and sizes of sections. 14624 14625@item -maddress-mode=long 14626@opindex maddress-mode=long 14627Generate code for long address mode. This is only supported for 64-bit 14628and x32 environments. It is the default address mode for 64-bit 14629environments. 14630 14631@item -maddress-mode=short 14632@opindex maddress-mode=short 14633Generate code for short address mode. This is only supported for 32-bit 14634and x32 environments. It is the default address mode for 32-bit and 14635x32 environments. 14636@end table 14637 14638@node i386 and x86-64 Windows Options 14639@subsection i386 and x86-64 Windows Options 14640@cindex i386 and x86-64 Windows Options 14641 14642These additional options are available for Microsoft Windows targets: 14643 14644@table @gcctabopt 14645@item -mconsole 14646@opindex mconsole 14647This option 14648specifies that a console application is to be generated, by 14649instructing the linker to set the PE header subsystem type 14650required for console applications. 14651This option is available for Cygwin and MinGW targets and is 14652enabled by default on those targets. 14653 14654@item -mdll 14655@opindex mdll 14656This option is available for Cygwin and MinGW targets. It 14657specifies that a DLL---a dynamic link library---is to be 14658generated, enabling the selection of the required runtime 14659startup object and entry point. 14660 14661@item -mnop-fun-dllimport 14662@opindex mnop-fun-dllimport 14663This option is available for Cygwin and MinGW targets. It 14664specifies that the @code{dllimport} attribute should be ignored. 14665 14666@item -mthread 14667@opindex mthread 14668This option is available for MinGW targets. It specifies 14669that MinGW-specific thread support is to be used. 14670 14671@item -municode 14672@opindex municode 14673This option is available for MinGW-w64 targets. It causes 14674the @code{UNICODE} preprocessor macro to be predefined, and 14675chooses Unicode-capable runtime startup code. 14676 14677@item -mwin32 14678@opindex mwin32 14679This option is available for Cygwin and MinGW targets. It 14680specifies that the typical Microsoft Windows predefined macros are to 14681be set in the pre-processor, but does not influence the choice 14682of runtime library/startup code. 14683 14684@item -mwindows 14685@opindex mwindows 14686This option is available for Cygwin and MinGW targets. It 14687specifies that a GUI application is to be generated by 14688instructing the linker to set the PE header subsystem type 14689appropriately. 14690 14691@item -fno-set-stack-executable 14692@opindex fno-set-stack-executable 14693This option is available for MinGW targets. It specifies that 14694the executable flag for the stack used by nested functions isn't 14695set. This is necessary for binaries running in kernel mode of 14696Microsoft Windows, as there the User32 API, which is used to set executable 14697privileges, isn't available. 14698 14699@item -fwritable-relocated-rdata 14700@opindex fno-writable-relocated-rdata 14701This option is available for MinGW and Cygwin targets. It specifies 14702that relocated-data in read-only section is put into .data 14703section. This is a necessary for older runtimes not supporting 14704modification of .rdata sections for pseudo-relocation. 14705 14706@item -mpe-aligned-commons 14707@opindex mpe-aligned-commons 14708This option is available for Cygwin and MinGW targets. It 14709specifies that the GNU extension to the PE file format that 14710permits the correct alignment of COMMON variables should be 14711used when generating code. It is enabled by default if 14712GCC detects that the target assembler found during configuration 14713supports the feature. 14714@end table 14715 14716See also under @ref{i386 and x86-64 Options} for standard options. 14717 14718@node IA-64 Options 14719@subsection IA-64 Options 14720@cindex IA-64 Options 14721 14722These are the @samp{-m} options defined for the Intel IA-64 architecture. 14723 14724@table @gcctabopt 14725@item -mbig-endian 14726@opindex mbig-endian 14727Generate code for a big-endian target. This is the default for HP-UX@. 14728 14729@item -mlittle-endian 14730@opindex mlittle-endian 14731Generate code for a little-endian target. This is the default for AIX5 14732and GNU/Linux. 14733 14734@item -mgnu-as 14735@itemx -mno-gnu-as 14736@opindex mgnu-as 14737@opindex mno-gnu-as 14738Generate (or don't) code for the GNU assembler. This is the default. 14739@c Also, this is the default if the configure option @option{--with-gnu-as} 14740@c is used. 14741 14742@item -mgnu-ld 14743@itemx -mno-gnu-ld 14744@opindex mgnu-ld 14745@opindex mno-gnu-ld 14746Generate (or don't) code for the GNU linker. This is the default. 14747@c Also, this is the default if the configure option @option{--with-gnu-ld} 14748@c is used. 14749 14750@item -mno-pic 14751@opindex mno-pic 14752Generate code that does not use a global pointer register. The result 14753is not position independent code, and violates the IA-64 ABI@. 14754 14755@item -mvolatile-asm-stop 14756@itemx -mno-volatile-asm-stop 14757@opindex mvolatile-asm-stop 14758@opindex mno-volatile-asm-stop 14759Generate (or don't) a stop bit immediately before and after volatile asm 14760statements. 14761 14762@item -mregister-names 14763@itemx -mno-register-names 14764@opindex mregister-names 14765@opindex mno-register-names 14766Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for 14767the stacked registers. This may make assembler output more readable. 14768 14769@item -mno-sdata 14770@itemx -msdata 14771@opindex mno-sdata 14772@opindex msdata 14773Disable (or enable) optimizations that use the small data section. This may 14774be useful for working around optimizer bugs. 14775 14776@item -mconstant-gp 14777@opindex mconstant-gp 14778Generate code that uses a single constant global pointer value. This is 14779useful when compiling kernel code. 14780 14781@item -mauto-pic 14782@opindex mauto-pic 14783Generate code that is self-relocatable. This implies @option{-mconstant-gp}. 14784This is useful when compiling firmware code. 14785 14786@item -minline-float-divide-min-latency 14787@opindex minline-float-divide-min-latency 14788Generate code for inline divides of floating-point values 14789using the minimum latency algorithm. 14790 14791@item -minline-float-divide-max-throughput 14792@opindex minline-float-divide-max-throughput 14793Generate code for inline divides of floating-point values 14794using the maximum throughput algorithm. 14795 14796@item -mno-inline-float-divide 14797@opindex mno-inline-float-divide 14798Do not generate inline code for divides of floating-point values. 14799 14800@item -minline-int-divide-min-latency 14801@opindex minline-int-divide-min-latency 14802Generate code for inline divides of integer values 14803using the minimum latency algorithm. 14804 14805@item -minline-int-divide-max-throughput 14806@opindex minline-int-divide-max-throughput 14807Generate code for inline divides of integer values 14808using the maximum throughput algorithm. 14809 14810@item -mno-inline-int-divide 14811@opindex mno-inline-int-divide 14812Do not generate inline code for divides of integer values. 14813 14814@item -minline-sqrt-min-latency 14815@opindex minline-sqrt-min-latency 14816Generate code for inline square roots 14817using the minimum latency algorithm. 14818 14819@item -minline-sqrt-max-throughput 14820@opindex minline-sqrt-max-throughput 14821Generate code for inline square roots 14822using the maximum throughput algorithm. 14823 14824@item -mno-inline-sqrt 14825@opindex mno-inline-sqrt 14826Do not generate inline code for @code{sqrt}. 14827 14828@item -mfused-madd 14829@itemx -mno-fused-madd 14830@opindex mfused-madd 14831@opindex mno-fused-madd 14832Do (don't) generate code that uses the fused multiply/add or multiply/subtract 14833instructions. The default is to use these instructions. 14834 14835@item -mno-dwarf2-asm 14836@itemx -mdwarf2-asm 14837@opindex mno-dwarf2-asm 14838@opindex mdwarf2-asm 14839Don't (or do) generate assembler code for the DWARF 2 line number debugging 14840info. This may be useful when not using the GNU assembler. 14841 14842@item -mearly-stop-bits 14843@itemx -mno-early-stop-bits 14844@opindex mearly-stop-bits 14845@opindex mno-early-stop-bits 14846Allow stop bits to be placed earlier than immediately preceding the 14847instruction that triggered the stop bit. This can improve instruction 14848scheduling, but does not always do so. 14849 14850@item -mfixed-range=@var{register-range} 14851@opindex mfixed-range 14852Generate code treating the given register range as fixed registers. 14853A fixed register is one that the register allocator cannot use. This is 14854useful when compiling kernel code. A register range is specified as 14855two registers separated by a dash. Multiple register ranges can be 14856specified separated by a comma. 14857 14858@item -mtls-size=@var{tls-size} 14859@opindex mtls-size 14860Specify bit size of immediate TLS offsets. Valid values are 14, 22, and 1486164. 14862 14863@item -mtune=@var{cpu-type} 14864@opindex mtune 14865Tune the instruction scheduling for a particular CPU, Valid values are 14866@samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2}, 14867and @samp{mckinley}. 14868 14869@item -milp32 14870@itemx -mlp64 14871@opindex milp32 14872@opindex mlp64 14873Generate code for a 32-bit or 64-bit environment. 14874The 32-bit environment sets int, long and pointer to 32 bits. 14875The 64-bit environment sets int to 32 bits and long and pointer 14876to 64 bits. These are HP-UX specific flags. 14877 14878@item -mno-sched-br-data-spec 14879@itemx -msched-br-data-spec 14880@opindex mno-sched-br-data-spec 14881@opindex msched-br-data-spec 14882(Dis/En)able data speculative scheduling before reload. 14883This results in generation of @code{ld.a} instructions and 14884the corresponding check instructions (@code{ld.c} / @code{chk.a}). 14885The default is 'disable'. 14886 14887@item -msched-ar-data-spec 14888@itemx -mno-sched-ar-data-spec 14889@opindex msched-ar-data-spec 14890@opindex mno-sched-ar-data-spec 14891(En/Dis)able data speculative scheduling after reload. 14892This results in generation of @code{ld.a} instructions and 14893the corresponding check instructions (@code{ld.c} / @code{chk.a}). 14894The default is 'enable'. 14895 14896@item -mno-sched-control-spec 14897@itemx -msched-control-spec 14898@opindex mno-sched-control-spec 14899@opindex msched-control-spec 14900(Dis/En)able control speculative scheduling. This feature is 14901available only during region scheduling (i.e.@: before reload). 14902This results in generation of the @code{ld.s} instructions and 14903the corresponding check instructions @code{chk.s}. 14904The default is 'disable'. 14905 14906@item -msched-br-in-data-spec 14907@itemx -mno-sched-br-in-data-spec 14908@opindex msched-br-in-data-spec 14909@opindex mno-sched-br-in-data-spec 14910(En/Dis)able speculative scheduling of the instructions that 14911are dependent on the data speculative loads before reload. 14912This is effective only with @option{-msched-br-data-spec} enabled. 14913The default is 'enable'. 14914 14915@item -msched-ar-in-data-spec 14916@itemx -mno-sched-ar-in-data-spec 14917@opindex msched-ar-in-data-spec 14918@opindex mno-sched-ar-in-data-spec 14919(En/Dis)able speculative scheduling of the instructions that 14920are dependent on the data speculative loads after reload. 14921This is effective only with @option{-msched-ar-data-spec} enabled. 14922The default is 'enable'. 14923 14924@item -msched-in-control-spec 14925@itemx -mno-sched-in-control-spec 14926@opindex msched-in-control-spec 14927@opindex mno-sched-in-control-spec 14928(En/Dis)able speculative scheduling of the instructions that 14929are dependent on the control speculative loads. 14930This is effective only with @option{-msched-control-spec} enabled. 14931The default is 'enable'. 14932 14933@item -mno-sched-prefer-non-data-spec-insns 14934@itemx -msched-prefer-non-data-spec-insns 14935@opindex mno-sched-prefer-non-data-spec-insns 14936@opindex msched-prefer-non-data-spec-insns 14937If enabled, data-speculative instructions are chosen for schedule 14938only if there are no other choices at the moment. This makes 14939the use of the data speculation much more conservative. 14940The default is 'disable'. 14941 14942@item -mno-sched-prefer-non-control-spec-insns 14943@itemx -msched-prefer-non-control-spec-insns 14944@opindex mno-sched-prefer-non-control-spec-insns 14945@opindex msched-prefer-non-control-spec-insns 14946If enabled, control-speculative instructions are chosen for schedule 14947only if there are no other choices at the moment. This makes 14948the use of the control speculation much more conservative. 14949The default is 'disable'. 14950 14951@item -mno-sched-count-spec-in-critical-path 14952@itemx -msched-count-spec-in-critical-path 14953@opindex mno-sched-count-spec-in-critical-path 14954@opindex msched-count-spec-in-critical-path 14955If enabled, speculative dependencies are considered during 14956computation of the instructions priorities. This makes the use of the 14957speculation a bit more conservative. 14958The default is 'disable'. 14959 14960@item -msched-spec-ldc 14961@opindex msched-spec-ldc 14962Use a simple data speculation check. This option is on by default. 14963 14964@item -msched-control-spec-ldc 14965@opindex msched-spec-ldc 14966Use a simple check for control speculation. This option is on by default. 14967 14968@item -msched-stop-bits-after-every-cycle 14969@opindex msched-stop-bits-after-every-cycle 14970Place a stop bit after every cycle when scheduling. This option is on 14971by default. 14972 14973@item -msched-fp-mem-deps-zero-cost 14974@opindex msched-fp-mem-deps-zero-cost 14975Assume that floating-point stores and loads are not likely to cause a conflict 14976when placed into the same instruction group. This option is disabled by 14977default. 14978 14979@item -msel-sched-dont-check-control-spec 14980@opindex msel-sched-dont-check-control-spec 14981Generate checks for control speculation in selective scheduling. 14982This flag is disabled by default. 14983 14984@item -msched-max-memory-insns=@var{max-insns} 14985@opindex msched-max-memory-insns 14986Limit on the number of memory insns per instruction group, giving lower 14987priority to subsequent memory insns attempting to schedule in the same 14988instruction group. Frequently useful to prevent cache bank conflicts. 14989The default value is 1. 14990 14991@item -msched-max-memory-insns-hard-limit 14992@opindex msched-max-memory-insns-hard-limit 14993Makes the limit specified by @option{msched-max-memory-insns} a hard limit, 14994disallowing more than that number in an instruction group. 14995Otherwise, the limit is ``soft'', meaning that non-memory operations 14996are preferred when the limit is reached, but memory operations may still 14997be scheduled. 14998 14999@end table 15000 15001@node LM32 Options 15002@subsection LM32 Options 15003@cindex LM32 options 15004 15005These @option{-m} options are defined for the LatticeMico32 architecture: 15006 15007@table @gcctabopt 15008@item -mbarrel-shift-enabled 15009@opindex mbarrel-shift-enabled 15010Enable barrel-shift instructions. 15011 15012@item -mdivide-enabled 15013@opindex mdivide-enabled 15014Enable divide and modulus instructions. 15015 15016@item -mmultiply-enabled 15017@opindex multiply-enabled 15018Enable multiply instructions. 15019 15020@item -msign-extend-enabled 15021@opindex msign-extend-enabled 15022Enable sign extend instructions. 15023 15024@item -muser-enabled 15025@opindex muser-enabled 15026Enable user-defined instructions. 15027 15028@end table 15029 15030@node M32C Options 15031@subsection M32C Options 15032@cindex M32C options 15033 15034@table @gcctabopt 15035@item -mcpu=@var{name} 15036@opindex mcpu= 15037Select the CPU for which code is generated. @var{name} may be one of 15038@samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to 15039/60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for 15040the M32C/80 series. 15041 15042@item -msim 15043@opindex msim 15044Specifies that the program will be run on the simulator. This causes 15045an alternate runtime library to be linked in which supports, for 15046example, file I/O@. You must not use this option when generating 15047programs that will run on real hardware; you must provide your own 15048runtime library for whatever I/O functions are needed. 15049 15050@item -memregs=@var{number} 15051@opindex memregs= 15052Specifies the number of memory-based pseudo-registers GCC uses 15053during code generation. These pseudo-registers are used like real 15054registers, so there is a tradeoff between GCC's ability to fit the 15055code into available registers, and the performance penalty of using 15056memory instead of registers. Note that all modules in a program must 15057be compiled with the same value for this option. Because of that, you 15058must not use this option with GCC's default runtime libraries. 15059 15060@end table 15061 15062@node M32R/D Options 15063@subsection M32R/D Options 15064@cindex M32R/D options 15065 15066These @option{-m} options are defined for Renesas M32R/D architectures: 15067 15068@table @gcctabopt 15069@item -m32r2 15070@opindex m32r2 15071Generate code for the M32R/2@. 15072 15073@item -m32rx 15074@opindex m32rx 15075Generate code for the M32R/X@. 15076 15077@item -m32r 15078@opindex m32r 15079Generate code for the M32R@. This is the default. 15080 15081@item -mmodel=small 15082@opindex mmodel=small 15083Assume all objects live in the lower 16MB of memory (so that their addresses 15084can be loaded with the @code{ld24} instruction), and assume all subroutines 15085are reachable with the @code{bl} instruction. 15086This is the default. 15087 15088The addressability of a particular object can be set with the 15089@code{model} attribute. 15090 15091@item -mmodel=medium 15092@opindex mmodel=medium 15093Assume objects may be anywhere in the 32-bit address space (the compiler 15094generates @code{seth/add3} instructions to load their addresses), and 15095assume all subroutines are reachable with the @code{bl} instruction. 15096 15097@item -mmodel=large 15098@opindex mmodel=large 15099Assume objects may be anywhere in the 32-bit address space (the compiler 15100generates @code{seth/add3} instructions to load their addresses), and 15101assume subroutines may not be reachable with the @code{bl} instruction 15102(the compiler generates the much slower @code{seth/add3/jl} 15103instruction sequence). 15104 15105@item -msdata=none 15106@opindex msdata=none 15107Disable use of the small data area. Variables are put into 15108one of @samp{.data}, @samp{.bss}, or @samp{.rodata} (unless the 15109@code{section} attribute has been specified). 15110This is the default. 15111 15112The small data area consists of sections @samp{.sdata} and @samp{.sbss}. 15113Objects may be explicitly put in the small data area with the 15114@code{section} attribute using one of these sections. 15115 15116@item -msdata=sdata 15117@opindex msdata=sdata 15118Put small global and static data in the small data area, but do not 15119generate special code to reference them. 15120 15121@item -msdata=use 15122@opindex msdata=use 15123Put small global and static data in the small data area, and generate 15124special instructions to reference them. 15125 15126@item -G @var{num} 15127@opindex G 15128@cindex smaller data references 15129Put global and static objects less than or equal to @var{num} bytes 15130into the small data or BSS sections instead of the normal data or BSS 15131sections. The default value of @var{num} is 8. 15132The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} 15133for this option to have any effect. 15134 15135All modules should be compiled with the same @option{-G @var{num}} value. 15136Compiling with different values of @var{num} may or may not work; if it 15137doesn't the linker gives an error message---incorrect code is not 15138generated. 15139 15140@item -mdebug 15141@opindex mdebug 15142Makes the M32R-specific code in the compiler display some statistics 15143that might help in debugging programs. 15144 15145@item -malign-loops 15146@opindex malign-loops 15147Align all loops to a 32-byte boundary. 15148 15149@item -mno-align-loops 15150@opindex mno-align-loops 15151Do not enforce a 32-byte alignment for loops. This is the default. 15152 15153@item -missue-rate=@var{number} 15154@opindex missue-rate=@var{number} 15155Issue @var{number} instructions per cycle. @var{number} can only be 1 15156or 2. 15157 15158@item -mbranch-cost=@var{number} 15159@opindex mbranch-cost=@var{number} 15160@var{number} can only be 1 or 2. If it is 1 then branches are 15161preferred over conditional code, if it is 2, then the opposite applies. 15162 15163@item -mflush-trap=@var{number} 15164@opindex mflush-trap=@var{number} 15165Specifies the trap number to use to flush the cache. The default is 1516612. Valid numbers are between 0 and 15 inclusive. 15167 15168@item -mno-flush-trap 15169@opindex mno-flush-trap 15170Specifies that the cache cannot be flushed by using a trap. 15171 15172@item -mflush-func=@var{name} 15173@opindex mflush-func=@var{name} 15174Specifies the name of the operating system function to call to flush 15175the cache. The default is @emph{_flush_cache}, but a function call 15176is only used if a trap is not available. 15177 15178@item -mno-flush-func 15179@opindex mno-flush-func 15180Indicates that there is no OS function for flushing the cache. 15181 15182@end table 15183 15184@node M680x0 Options 15185@subsection M680x0 Options 15186@cindex M680x0 options 15187 15188These are the @samp{-m} options defined for M680x0 and ColdFire processors. 15189The default settings depend on which architecture was selected when 15190the compiler was configured; the defaults for the most common choices 15191are given below. 15192 15193@table @gcctabopt 15194@item -march=@var{arch} 15195@opindex march 15196Generate code for a specific M680x0 or ColdFire instruction set 15197architecture. Permissible values of @var{arch} for M680x0 15198architectures are: @samp{68000}, @samp{68010}, @samp{68020}, 15199@samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire 15200architectures are selected according to Freescale's ISA classification 15201and the permissible values are: @samp{isaa}, @samp{isaaplus}, 15202@samp{isab} and @samp{isac}. 15203 15204GCC defines a macro @samp{__mcf@var{arch}__} whenever it is generating 15205code for a ColdFire target. The @var{arch} in this macro is one of the 15206@option{-march} arguments given above. 15207 15208When used together, @option{-march} and @option{-mtune} select code 15209that runs on a family of similar processors but that is optimized 15210for a particular microarchitecture. 15211 15212@item -mcpu=@var{cpu} 15213@opindex mcpu 15214Generate code for a specific M680x0 or ColdFire processor. 15215The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020}, 15216@samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332} 15217and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table 15218below, which also classifies the CPUs into families: 15219 15220@multitable @columnfractions 0.20 0.80 15221@item @strong{Family} @tab @strong{@samp{-mcpu} arguments} 15222@item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm} 15223@item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206} 15224@item @samp{5206e} @tab @samp{5206e} 15225@item @samp{5208} @tab @samp{5207} @samp{5208} 15226@item @samp{5211a} @tab @samp{5210a} @samp{5211a} 15227@item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213} 15228@item @samp{5216} @tab @samp{5214} @samp{5216} 15229@item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235} 15230@item @samp{5225} @tab @samp{5224} @samp{5225} 15231@item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259} 15232@item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x} 15233@item @samp{5249} @tab @samp{5249} 15234@item @samp{5250} @tab @samp{5250} 15235@item @samp{5271} @tab @samp{5270} @samp{5271} 15236@item @samp{5272} @tab @samp{5272} 15237@item @samp{5275} @tab @samp{5274} @samp{5275} 15238@item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x} 15239@item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017} 15240@item @samp{5307} @tab @samp{5307} 15241@item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x} 15242@item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x} 15243@item @samp{5407} @tab @samp{5407} 15244@item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485} 15245@end multitable 15246 15247@option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if 15248@var{arch} is compatible with @var{cpu}. Other combinations of 15249@option{-mcpu} and @option{-march} are rejected. 15250 15251GCC defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target 15252@var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}}, 15253where the value of @var{family} is given by the table above. 15254 15255@item -mtune=@var{tune} 15256@opindex mtune 15257Tune the code for a particular microarchitecture within the 15258constraints set by @option{-march} and @option{-mcpu}. 15259The M680x0 microarchitectures are: @samp{68000}, @samp{68010}, 15260@samp{68020}, @samp{68030}, @samp{68040}, @samp{68060} 15261and @samp{cpu32}. The ColdFire microarchitectures 15262are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}. 15263 15264You can also use @option{-mtune=68020-40} for code that needs 15265to run relatively well on 68020, 68030 and 68040 targets. 15266@option{-mtune=68020-60} is similar but includes 68060 targets 15267as well. These two options select the same tuning decisions as 15268@option{-m68020-40} and @option{-m68020-60} respectively. 15269 15270GCC defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__} 15271when tuning for 680x0 architecture @var{arch}. It also defines 15272@samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std} 15273option is used. If GCC is tuning for a range of architectures, 15274as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60}, 15275it defines the macros for every architecture in the range. 15276 15277GCC also defines the macro @samp{__m@var{uarch}__} when tuning for 15278ColdFire microarchitecture @var{uarch}, where @var{uarch} is one 15279of the arguments given above. 15280 15281@item -m68000 15282@itemx -mc68000 15283@opindex m68000 15284@opindex mc68000 15285Generate output for a 68000. This is the default 15286when the compiler is configured for 68000-based systems. 15287It is equivalent to @option{-march=68000}. 15288 15289Use this option for microcontrollers with a 68000 or EC000 core, 15290including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. 15291 15292@item -m68010 15293@opindex m68010 15294Generate output for a 68010. This is the default 15295when the compiler is configured for 68010-based systems. 15296It is equivalent to @option{-march=68010}. 15297 15298@item -m68020 15299@itemx -mc68020 15300@opindex m68020 15301@opindex mc68020 15302Generate output for a 68020. This is the default 15303when the compiler is configured for 68020-based systems. 15304It is equivalent to @option{-march=68020}. 15305 15306@item -m68030 15307@opindex m68030 15308Generate output for a 68030. This is the default when the compiler is 15309configured for 68030-based systems. It is equivalent to 15310@option{-march=68030}. 15311 15312@item -m68040 15313@opindex m68040 15314Generate output for a 68040. This is the default when the compiler is 15315configured for 68040-based systems. It is equivalent to 15316@option{-march=68040}. 15317 15318This option inhibits the use of 68881/68882 instructions that have to be 15319emulated by software on the 68040. Use this option if your 68040 does not 15320have code to emulate those instructions. 15321 15322@item -m68060 15323@opindex m68060 15324Generate output for a 68060. This is the default when the compiler is 15325configured for 68060-based systems. It is equivalent to 15326@option{-march=68060}. 15327 15328This option inhibits the use of 68020 and 68881/68882 instructions that 15329have to be emulated by software on the 68060. Use this option if your 68060 15330does not have code to emulate those instructions. 15331 15332@item -mcpu32 15333@opindex mcpu32 15334Generate output for a CPU32. This is the default 15335when the compiler is configured for CPU32-based systems. 15336It is equivalent to @option{-march=cpu32}. 15337 15338Use this option for microcontrollers with a 15339CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, 1534068336, 68340, 68341, 68349 and 68360. 15341 15342@item -m5200 15343@opindex m5200 15344Generate output for a 520X ColdFire CPU@. This is the default 15345when the compiler is configured for 520X-based systems. 15346It is equivalent to @option{-mcpu=5206}, and is now deprecated 15347in favor of that option. 15348 15349Use this option for microcontroller with a 5200 core, including 15350the MCF5202, MCF5203, MCF5204 and MCF5206. 15351 15352@item -m5206e 15353@opindex m5206e 15354Generate output for a 5206e ColdFire CPU@. The option is now 15355deprecated in favor of the equivalent @option{-mcpu=5206e}. 15356 15357@item -m528x 15358@opindex m528x 15359Generate output for a member of the ColdFire 528X family. 15360The option is now deprecated in favor of the equivalent 15361@option{-mcpu=528x}. 15362 15363@item -m5307 15364@opindex m5307 15365Generate output for a ColdFire 5307 CPU@. The option is now deprecated 15366in favor of the equivalent @option{-mcpu=5307}. 15367 15368@item -m5407 15369@opindex m5407 15370Generate output for a ColdFire 5407 CPU@. The option is now deprecated 15371in favor of the equivalent @option{-mcpu=5407}. 15372 15373@item -mcfv4e 15374@opindex mcfv4e 15375Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x). 15376This includes use of hardware floating-point instructions. 15377The option is equivalent to @option{-mcpu=547x}, and is now 15378deprecated in favor of that option. 15379 15380@item -m68020-40 15381@opindex m68020-40 15382Generate output for a 68040, without using any of the new instructions. 15383This results in code that can run relatively efficiently on either a 1538468020/68881 or a 68030 or a 68040. The generated code does use the 1538568881 instructions that are emulated on the 68040. 15386 15387The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}. 15388 15389@item -m68020-60 15390@opindex m68020-60 15391Generate output for a 68060, without using any of the new instructions. 15392This results in code that can run relatively efficiently on either a 1539368020/68881 or a 68030 or a 68040. The generated code does use the 1539468881 instructions that are emulated on the 68060. 15395 15396The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}. 15397 15398@item -mhard-float 15399@itemx -m68881 15400@opindex mhard-float 15401@opindex m68881 15402Generate floating-point instructions. This is the default for 68020 15403and above, and for ColdFire devices that have an FPU@. It defines the 15404macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__} 15405on ColdFire targets. 15406 15407@item -msoft-float 15408@opindex msoft-float 15409Do not generate floating-point instructions; use library calls instead. 15410This is the default for 68000, 68010, and 68832 targets. It is also 15411the default for ColdFire devices that have no FPU. 15412 15413@item -mdiv 15414@itemx -mno-div 15415@opindex mdiv 15416@opindex mno-div 15417Generate (do not generate) ColdFire hardware divide and remainder 15418instructions. If @option{-march} is used without @option{-mcpu}, 15419the default is ``on'' for ColdFire architectures and ``off'' for M680x0 15420architectures. Otherwise, the default is taken from the target CPU 15421(either the default CPU, or the one specified by @option{-mcpu}). For 15422example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for 15423@option{-mcpu=5206e}. 15424 15425GCC defines the macro @samp{__mcfhwdiv__} when this option is enabled. 15426 15427@item -mshort 15428@opindex mshort 15429Consider type @code{int} to be 16 bits wide, like @code{short int}. 15430Additionally, parameters passed on the stack are also aligned to a 1543116-bit boundary even on targets whose API mandates promotion to 32-bit. 15432 15433@item -mno-short 15434@opindex mno-short 15435Do not consider type @code{int} to be 16 bits wide. This is the default. 15436 15437@item -mnobitfield 15438@itemx -mno-bitfield 15439@opindex mnobitfield 15440@opindex mno-bitfield 15441Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} 15442and @option{-m5200} options imply @w{@option{-mnobitfield}}. 15443 15444@item -mbitfield 15445@opindex mbitfield 15446Do use the bit-field instructions. The @option{-m68020} option implies 15447@option{-mbitfield}. This is the default if you use a configuration 15448designed for a 68020. 15449 15450@item -mrtd 15451@opindex mrtd 15452Use a different function-calling convention, in which functions 15453that take a fixed number of arguments return with the @code{rtd} 15454instruction, which pops their arguments while returning. This 15455saves one instruction in the caller since there is no need to pop 15456the arguments there. 15457 15458This calling convention is incompatible with the one normally 15459used on Unix, so you cannot use it if you need to call libraries 15460compiled with the Unix compiler. 15461 15462Also, you must provide function prototypes for all functions that 15463take variable numbers of arguments (including @code{printf}); 15464otherwise incorrect code is generated for calls to those 15465functions. 15466 15467In addition, seriously incorrect code results if you call a 15468function with too many arguments. (Normally, extra arguments are 15469harmlessly ignored.) 15470 15471The @code{rtd} instruction is supported by the 68010, 68020, 68030, 1547268040, 68060 and CPU32 processors, but not by the 68000 or 5200. 15473 15474@item -mno-rtd 15475@opindex mno-rtd 15476Do not use the calling conventions selected by @option{-mrtd}. 15477This is the default. 15478 15479@item -malign-int 15480@itemx -mno-align-int 15481@opindex malign-int 15482@opindex mno-align-int 15483Control whether GCC aligns @code{int}, @code{long}, @code{long long}, 15484@code{float}, @code{double}, and @code{long double} variables on a 32-bit 15485boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). 15486Aligning variables on 32-bit boundaries produces code that runs somewhat 15487faster on processors with 32-bit busses at the expense of more memory. 15488 15489@strong{Warning:} if you use the @option{-malign-int} switch, GCC 15490aligns structures containing the above types differently than 15491most published application binary interface specifications for the m68k. 15492 15493@item -mpcrel 15494@opindex mpcrel 15495Use the pc-relative addressing mode of the 68000 directly, instead of 15496using a global offset table. At present, this option implies @option{-fpic}, 15497allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is 15498not presently supported with @option{-mpcrel}, though this could be supported for 1549968020 and higher processors. 15500 15501@item -mno-strict-align 15502@itemx -mstrict-align 15503@opindex mno-strict-align 15504@opindex mstrict-align 15505Do not (do) assume that unaligned memory references are handled by 15506the system. 15507 15508@item -msep-data 15509Generate code that allows the data segment to be located in a different 15510area of memory from the text segment. This allows for execute-in-place in 15511an environment without virtual memory management. This option implies 15512@option{-fPIC}. 15513 15514@item -mno-sep-data 15515Generate code that assumes that the data segment follows the text segment. 15516This is the default. 15517 15518@item -mid-shared-library 15519Generate code that supports shared libraries via the library ID method. 15520This allows for execute-in-place and shared libraries in an environment 15521without virtual memory management. This option implies @option{-fPIC}. 15522 15523@item -mno-id-shared-library 15524Generate code that doesn't assume ID-based shared libraries are being used. 15525This is the default. 15526 15527@item -mshared-library-id=n 15528Specifies the identification number of the ID-based shared library being 15529compiled. Specifying a value of 0 generates more compact code; specifying 15530other values forces the allocation of that number to the current 15531library, but is no more space- or time-efficient than omitting this option. 15532 15533@item -mxgot 15534@itemx -mno-xgot 15535@opindex mxgot 15536@opindex mno-xgot 15537When generating position-independent code for ColdFire, generate code 15538that works if the GOT has more than 8192 entries. This code is 15539larger and slower than code generated without this option. On M680x0 15540processors, this option is not needed; @option{-fPIC} suffices. 15541 15542GCC normally uses a single instruction to load values from the GOT@. 15543While this is relatively efficient, it only works if the GOT 15544is smaller than about 64k. Anything larger causes the linker 15545to report an error such as: 15546 15547@cindex relocation truncated to fit (ColdFire) 15548@smallexample 15549relocation truncated to fit: R_68K_GOT16O foobar 15550@end smallexample 15551 15552If this happens, you should recompile your code with @option{-mxgot}. 15553It should then work with very large GOTs. However, code generated with 15554@option{-mxgot} is less efficient, since it takes 4 instructions to fetch 15555the value of a global symbol. 15556 15557Note that some linkers, including newer versions of the GNU linker, 15558can create multiple GOTs and sort GOT entries. If you have such a linker, 15559you should only need to use @option{-mxgot} when compiling a single 15560object file that accesses more than 8192 GOT entries. Very few do. 15561 15562These options have no effect unless GCC is generating 15563position-independent code. 15564 15565@end table 15566 15567@node MCore Options 15568@subsection MCore Options 15569@cindex MCore options 15570 15571These are the @samp{-m} options defined for the Motorola M*Core 15572processors. 15573 15574@table @gcctabopt 15575 15576@item -mhardlit 15577@itemx -mno-hardlit 15578@opindex mhardlit 15579@opindex mno-hardlit 15580Inline constants into the code stream if it can be done in two 15581instructions or less. 15582 15583@item -mdiv 15584@itemx -mno-div 15585@opindex mdiv 15586@opindex mno-div 15587Use the divide instruction. (Enabled by default). 15588 15589@item -mrelax-immediate 15590@itemx -mno-relax-immediate 15591@opindex mrelax-immediate 15592@opindex mno-relax-immediate 15593Allow arbitrary-sized immediates in bit operations. 15594 15595@item -mwide-bitfields 15596@itemx -mno-wide-bitfields 15597@opindex mwide-bitfields 15598@opindex mno-wide-bitfields 15599Always treat bit-fields as @code{int}-sized. 15600 15601@item -m4byte-functions 15602@itemx -mno-4byte-functions 15603@opindex m4byte-functions 15604@opindex mno-4byte-functions 15605Force all functions to be aligned to a 4-byte boundary. 15606 15607@item -mcallgraph-data 15608@itemx -mno-callgraph-data 15609@opindex mcallgraph-data 15610@opindex mno-callgraph-data 15611Emit callgraph information. 15612 15613@item -mslow-bytes 15614@itemx -mno-slow-bytes 15615@opindex mslow-bytes 15616@opindex mno-slow-bytes 15617Prefer word access when reading byte quantities. 15618 15619@item -mlittle-endian 15620@itemx -mbig-endian 15621@opindex mlittle-endian 15622@opindex mbig-endian 15623Generate code for a little-endian target. 15624 15625@item -m210 15626@itemx -m340 15627@opindex m210 15628@opindex m340 15629Generate code for the 210 processor. 15630 15631@item -mno-lsim 15632@opindex mno-lsim 15633Assume that runtime support has been provided and so omit the 15634simulator library (@file{libsim.a)} from the linker command line. 15635 15636@item -mstack-increment=@var{size} 15637@opindex mstack-increment 15638Set the maximum amount for a single stack increment operation. Large 15639values can increase the speed of programs that contain functions 15640that need a large amount of stack space, but they can also trigger a 15641segmentation fault if the stack is extended too much. The default 15642value is 0x1000. 15643 15644@end table 15645 15646@node MeP Options 15647@subsection MeP Options 15648@cindex MeP options 15649 15650@table @gcctabopt 15651 15652@item -mabsdiff 15653@opindex mabsdiff 15654Enables the @code{abs} instruction, which is the absolute difference 15655between two registers. 15656 15657@item -mall-opts 15658@opindex mall-opts 15659Enables all the optional instructions---average, multiply, divide, bit 15660operations, leading zero, absolute difference, min/max, clip, and 15661saturation. 15662 15663 15664@item -maverage 15665@opindex maverage 15666Enables the @code{ave} instruction, which computes the average of two 15667registers. 15668 15669@item -mbased=@var{n} 15670@opindex mbased= 15671Variables of size @var{n} bytes or smaller are placed in the 15672@code{.based} section by default. Based variables use the @code{$tp} 15673register as a base register, and there is a 128-byte limit to the 15674@code{.based} section. 15675 15676@item -mbitops 15677@opindex mbitops 15678Enables the bit operation instructions---bit test (@code{btstm}), set 15679(@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and 15680test-and-set (@code{tas}). 15681 15682@item -mc=@var{name} 15683@opindex mc= 15684Selects which section constant data is placed in. @var{name} may 15685be @code{tiny}, @code{near}, or @code{far}. 15686 15687@item -mclip 15688@opindex mclip 15689Enables the @code{clip} instruction. Note that @code{-mclip} is not 15690useful unless you also provide @code{-mminmax}. 15691 15692@item -mconfig=@var{name} 15693@opindex mconfig= 15694Selects one of the built-in core configurations. Each MeP chip has 15695one or more modules in it; each module has a core CPU and a variety of 15696coprocessors, optional instructions, and peripherals. The 15697@code{MeP-Integrator} tool, not part of GCC, provides these 15698configurations through this option; using this option is the same as 15699using all the corresponding command-line options. The default 15700configuration is @code{default}. 15701 15702@item -mcop 15703@opindex mcop 15704Enables the coprocessor instructions. By default, this is a 32-bit 15705coprocessor. Note that the coprocessor is normally enabled via the 15706@code{-mconfig=} option. 15707 15708@item -mcop32 15709@opindex mcop32 15710Enables the 32-bit coprocessor's instructions. 15711 15712@item -mcop64 15713@opindex mcop64 15714Enables the 64-bit coprocessor's instructions. 15715 15716@item -mivc2 15717@opindex mivc2 15718Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor. 15719 15720@item -mdc 15721@opindex mdc 15722Causes constant variables to be placed in the @code{.near} section. 15723 15724@item -mdiv 15725@opindex mdiv 15726Enables the @code{div} and @code{divu} instructions. 15727 15728@item -meb 15729@opindex meb 15730Generate big-endian code. 15731 15732@item -mel 15733@opindex mel 15734Generate little-endian code. 15735 15736@item -mio-volatile 15737@opindex mio-volatile 15738Tells the compiler that any variable marked with the @code{io} 15739attribute is to be considered volatile. 15740 15741@item -ml 15742@opindex ml 15743Causes variables to be assigned to the @code{.far} section by default. 15744 15745@item -mleadz 15746@opindex mleadz 15747Enables the @code{leadz} (leading zero) instruction. 15748 15749@item -mm 15750@opindex mm 15751Causes variables to be assigned to the @code{.near} section by default. 15752 15753@item -mminmax 15754@opindex mminmax 15755Enables the @code{min} and @code{max} instructions. 15756 15757@item -mmult 15758@opindex mmult 15759Enables the multiplication and multiply-accumulate instructions. 15760 15761@item -mno-opts 15762@opindex mno-opts 15763Disables all the optional instructions enabled by @code{-mall-opts}. 15764 15765@item -mrepeat 15766@opindex mrepeat 15767Enables the @code{repeat} and @code{erepeat} instructions, used for 15768low-overhead looping. 15769 15770@item -ms 15771@opindex ms 15772Causes all variables to default to the @code{.tiny} section. Note 15773that there is a 65536-byte limit to this section. Accesses to these 15774variables use the @code{%gp} base register. 15775 15776@item -msatur 15777@opindex msatur 15778Enables the saturation instructions. Note that the compiler does not 15779currently generate these itself, but this option is included for 15780compatibility with other tools, like @code{as}. 15781 15782@item -msdram 15783@opindex msdram 15784Link the SDRAM-based runtime instead of the default ROM-based runtime. 15785 15786@item -msim 15787@opindex msim 15788Link the simulator runtime libraries. 15789 15790@item -msimnovec 15791@opindex msimnovec 15792Link the simulator runtime libraries, excluding built-in support 15793for reset and exception vectors and tables. 15794 15795@item -mtf 15796@opindex mtf 15797Causes all functions to default to the @code{.far} section. Without 15798this option, functions default to the @code{.near} section. 15799 15800@item -mtiny=@var{n} 15801@opindex mtiny= 15802Variables that are @var{n} bytes or smaller are allocated to the 15803@code{.tiny} section. These variables use the @code{$gp} base 15804register. The default for this option is 4, but note that there's a 1580565536-byte limit to the @code{.tiny} section. 15806 15807@end table 15808 15809@node MicroBlaze Options 15810@subsection MicroBlaze Options 15811@cindex MicroBlaze Options 15812 15813@table @gcctabopt 15814 15815@item -msoft-float 15816@opindex msoft-float 15817Use software emulation for floating point (default). 15818 15819@item -mhard-float 15820@opindex mhard-float 15821Use hardware floating-point instructions. 15822 15823@item -mmemcpy 15824@opindex mmemcpy 15825Do not optimize block moves, use @code{memcpy}. 15826 15827@item -mno-clearbss 15828@opindex mno-clearbss 15829This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead. 15830 15831@item -mcpu=@var{cpu-type} 15832@opindex mcpu= 15833Use features of, and schedule code for, the given CPU. 15834Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}}, 15835where @var{X} is a major version, @var{YY} is the minor version, and 15836@var{Z} is compatibility code. Example values are @samp{v3.00.a}, 15837@samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}. 15838 15839@item -mxl-soft-mul 15840@opindex mxl-soft-mul 15841Use software multiply emulation (default). 15842 15843@item -mxl-soft-div 15844@opindex mxl-soft-div 15845Use software emulation for divides (default). 15846 15847@item -mxl-barrel-shift 15848@opindex mxl-barrel-shift 15849Use the hardware barrel shifter. 15850 15851@item -mxl-pattern-compare 15852@opindex mxl-pattern-compare 15853Use pattern compare instructions. 15854 15855@item -msmall-divides 15856@opindex msmall-divides 15857Use table lookup optimization for small signed integer divisions. 15858 15859@item -mxl-stack-check 15860@opindex mxl-stack-check 15861This option is deprecated. Use @option{-fstack-check} instead. 15862 15863@item -mxl-gp-opt 15864@opindex mxl-gp-opt 15865Use GP-relative @code{.sdata}/@code{.sbss} sections. 15866 15867@item -mxl-multiply-high 15868@opindex mxl-multiply-high 15869Use multiply high instructions for high part of 32x32 multiply. 15870 15871@item -mxl-float-convert 15872@opindex mxl-float-convert 15873Use hardware floating-point conversion instructions. 15874 15875@item -mxl-float-sqrt 15876@opindex mxl-float-sqrt 15877Use hardware floating-point square root instruction. 15878 15879@item -mbig-endian 15880@opindex mbig-endian 15881Generate code for a big-endian target. 15882 15883@item -mlittle-endian 15884@opindex mlittle-endian 15885Generate code for a little-endian target. 15886 15887@item -mxl-reorder 15888@opindex mxl-reorder 15889Use reorder instructions (swap and byte reversed load/store). 15890 15891@item -mxl-mode-@var{app-model} 15892Select application model @var{app-model}. Valid models are 15893@table @samp 15894@item executable 15895normal executable (default), uses startup code @file{crt0.o}. 15896 15897@item xmdstub 15898for use with Xilinx Microprocessor Debugger (XMD) based 15899software intrusive debug agent called xmdstub. This uses startup file 15900@file{crt1.o} and sets the start address of the program to 0x800. 15901 15902@item bootstrap 15903for applications that are loaded using a bootloader. 15904This model uses startup file @file{crt2.o} which does not contain a processor 15905reset vector handler. This is suitable for transferring control on a 15906processor reset to the bootloader rather than the application. 15907 15908@item novectors 15909for applications that do not require any of the 15910MicroBlaze vectors. This option may be useful for applications running 15911within a monitoring application. This model uses @file{crt3.o} as a startup file. 15912@end table 15913 15914Option @option{-xl-mode-@var{app-model}} is a deprecated alias for 15915@option{-mxl-mode-@var{app-model}}. 15916 15917@end table 15918 15919@node MIPS Options 15920@subsection MIPS Options 15921@cindex MIPS options 15922 15923@table @gcctabopt 15924 15925@item -EB 15926@opindex EB 15927Generate big-endian code. 15928 15929@item -EL 15930@opindex EL 15931Generate little-endian code. This is the default for @samp{mips*el-*-*} 15932configurations. 15933 15934@item -march=@var{arch} 15935@opindex march 15936Generate code that runs on @var{arch}, which can be the name of a 15937generic MIPS ISA, or the name of a particular processor. 15938The ISA names are: 15939@samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, 15940@samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}. 15941The processor names are: 15942@samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc}, 15943@samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd}, 15944@samp{5kc}, @samp{5kf}, 15945@samp{20kc}, 15946@samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1}, 15947@samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1}, 15948@samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn}, 15949@samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2}, 15950@samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1}, 15951@samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a}, 15952@samp{m4k}, 15953@samp{octeon}, @samp{octeon+}, @samp{octeon2}, 15954@samp{orion}, 15955@samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, 15956@samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r6000}, @samp{r8000}, 15957@samp{rm7000}, @samp{rm9000}, 15958@samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000}, 15959@samp{sb1}, 15960@samp{sr71000}, 15961@samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300}, 15962@samp{vr5000}, @samp{vr5400}, @samp{vr5500}, 15963@samp{xlr} and @samp{xlp}. 15964The special value @samp{from-abi} selects the 15965most compatible architecture for the selected ABI (that is, 15966@samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@. 15967 15968The native Linux/GNU toolchain also supports the value @samp{native}, 15969which selects the best architecture option for the host processor. 15970@option{-march=native} has no effect if GCC does not recognize 15971the processor. 15972 15973In processor names, a final @samp{000} can be abbreviated as @samp{k} 15974(for example, @option{-march=r2k}). Prefixes are optional, and 15975@samp{vr} may be written @samp{r}. 15976 15977Names of the form @samp{@var{n}f2_1} refer to processors with 15978FPUs clocked at half the rate of the core, names of the form 15979@samp{@var{n}f1_1} refer to processors with FPUs clocked at the same 15980rate as the core, and names of the form @samp{@var{n}f3_2} refer to 15981processors with FPUs clocked a ratio of 3:2 with respect to the core. 15982For compatibility reasons, @samp{@var{n}f} is accepted as a synonym 15983for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are 15984accepted as synonyms for @samp{@var{n}f1_1}. 15985 15986GCC defines two macros based on the value of this option. The first 15987is @samp{_MIPS_ARCH}, which gives the name of target architecture, as 15988a string. The second has the form @samp{_MIPS_ARCH_@var{foo}}, 15989where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@. 15990For example, @option{-march=r2000} sets @samp{_MIPS_ARCH} 15991to @samp{"r2000"} and defines the macro @samp{_MIPS_ARCH_R2000}. 15992 15993Note that the @samp{_MIPS_ARCH} macro uses the processor names given 15994above. In other words, it has the full prefix and does not 15995abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi}, 15996the macro names the resolved architecture (either @samp{"mips1"} or 15997@samp{"mips3"}). It names the default architecture when no 15998@option{-march} option is given. 15999 16000@item -mtune=@var{arch} 16001@opindex mtune 16002Optimize for @var{arch}. Among other things, this option controls 16003the way instructions are scheduled, and the perceived cost of arithmetic 16004operations. The list of @var{arch} values is the same as for 16005@option{-march}. 16006 16007When this option is not used, GCC optimizes for the processor 16008specified by @option{-march}. By using @option{-march} and 16009@option{-mtune} together, it is possible to generate code that 16010runs on a family of processors, but optimize the code for one 16011particular member of that family. 16012 16013@option{-mtune} defines the macros @samp{_MIPS_TUNE} and 16014@samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the 16015@option{-march} ones described above. 16016 16017@item -mips1 16018@opindex mips1 16019Equivalent to @option{-march=mips1}. 16020 16021@item -mips2 16022@opindex mips2 16023Equivalent to @option{-march=mips2}. 16024 16025@item -mips3 16026@opindex mips3 16027Equivalent to @option{-march=mips3}. 16028 16029@item -mips4 16030@opindex mips4 16031Equivalent to @option{-march=mips4}. 16032 16033@item -mips32 16034@opindex mips32 16035Equivalent to @option{-march=mips32}. 16036 16037@item -mips32r2 16038@opindex mips32r2 16039Equivalent to @option{-march=mips32r2}. 16040 16041@item -mips64 16042@opindex mips64 16043Equivalent to @option{-march=mips64}. 16044 16045@item -mips64r2 16046@opindex mips64r2 16047Equivalent to @option{-march=mips64r2}. 16048 16049@item -mips16 16050@itemx -mno-mips16 16051@opindex mips16 16052@opindex mno-mips16 16053Generate (do not generate) MIPS16 code. If GCC is targeting a 16054MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@. 16055 16056MIPS16 code generation can also be controlled on a per-function basis 16057by means of @code{mips16} and @code{nomips16} attributes. 16058@xref{Function Attributes}, for more information. 16059 16060@item -mflip-mips16 16061@opindex mflip-mips16 16062Generate MIPS16 code on alternating functions. This option is provided 16063for regression testing of mixed MIPS16/non-MIPS16 code generation, and is 16064not intended for ordinary use in compiling user code. 16065 16066@item -minterlink-mips16 16067@itemx -mno-interlink-mips16 16068@opindex minterlink-mips16 16069@opindex mno-interlink-mips16 16070Require (do not require) that non-MIPS16 code be link-compatible with 16071MIPS16 code. 16072 16073For example, non-MIPS16 code cannot jump directly to MIPS16 code; 16074it must either use a call or an indirect jump. @option{-minterlink-mips16} 16075therefore disables direct jumps unless GCC knows that the target of the 16076jump is not MIPS16. 16077 16078@item -mabi=32 16079@itemx -mabi=o64 16080@itemx -mabi=n32 16081@itemx -mabi=64 16082@itemx -mabi=eabi 16083@opindex mabi=32 16084@opindex mabi=o64 16085@opindex mabi=n32 16086@opindex mabi=64 16087@opindex mabi=eabi 16088Generate code for the given ABI@. 16089 16090Note that the EABI has a 32-bit and a 64-bit variant. GCC normally 16091generates 64-bit code when you select a 64-bit architecture, but you 16092can use @option{-mgp32} to get 32-bit code instead. 16093 16094For information about the O64 ABI, see 16095@uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}. 16096 16097GCC supports a variant of the o32 ABI in which floating-point registers 16098are 64 rather than 32 bits wide. You can select this combination with 16099@option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1} 16100and @code{mfhc1} instructions and is therefore only supported for 16101MIPS32R2 processors. 16102 16103The register assignments for arguments and return values remain the 16104same, but each scalar value is passed in a single 64-bit register 16105rather than a pair of 32-bit registers. For example, scalar 16106floating-point values are returned in @samp{$f0} only, not a 16107@samp{$f0}/@samp{$f1} pair. The set of call-saved registers also 16108remains the same, but all 64 bits are saved. 16109 16110@item -mabicalls 16111@itemx -mno-abicalls 16112@opindex mabicalls 16113@opindex mno-abicalls 16114Generate (do not generate) code that is suitable for SVR4-style 16115dynamic objects. @option{-mabicalls} is the default for SVR4-based 16116systems. 16117 16118@item -mshared 16119@itemx -mno-shared 16120Generate (do not generate) code that is fully position-independent, 16121and that can therefore be linked into shared libraries. This option 16122only affects @option{-mabicalls}. 16123 16124All @option{-mabicalls} code has traditionally been position-independent, 16125regardless of options like @option{-fPIC} and @option{-fpic}. However, 16126as an extension, the GNU toolchain allows executables to use absolute 16127accesses for locally-binding symbols. It can also use shorter GP 16128initialization sequences and generate direct calls to locally-defined 16129functions. This mode is selected by @option{-mno-shared}. 16130 16131@option{-mno-shared} depends on binutils 2.16 or higher and generates 16132objects that can only be linked by the GNU linker. However, the option 16133does not affect the ABI of the final executable; it only affects the ABI 16134of relocatable objects. Using @option{-mno-shared} generally makes 16135executables both smaller and quicker. 16136 16137@option{-mshared} is the default. 16138 16139@item -mplt 16140@itemx -mno-plt 16141@opindex mplt 16142@opindex mno-plt 16143Assume (do not assume) that the static and dynamic linkers 16144support PLTs and copy relocations. This option only affects 16145@option{-mno-shared -mabicalls}. For the n64 ABI, this option 16146has no effect without @option{-msym32}. 16147 16148You can make @option{-mplt} the default by configuring 16149GCC with @option{--with-mips-plt}. The default is 16150@option{-mno-plt} otherwise. 16151 16152@item -mxgot 16153@itemx -mno-xgot 16154@opindex mxgot 16155@opindex mno-xgot 16156Lift (do not lift) the usual restrictions on the size of the global 16157offset table. 16158 16159GCC normally uses a single instruction to load values from the GOT@. 16160While this is relatively efficient, it only works if the GOT 16161is smaller than about 64k. Anything larger causes the linker 16162to report an error such as: 16163 16164@cindex relocation truncated to fit (MIPS) 16165@smallexample 16166relocation truncated to fit: R_MIPS_GOT16 foobar 16167@end smallexample 16168 16169If this happens, you should recompile your code with @option{-mxgot}. 16170This works with very large GOTs, although the code is also 16171less efficient, since it takes three instructions to fetch the 16172value of a global symbol. 16173 16174Note that some linkers can create multiple GOTs. If you have such a 16175linker, you should only need to use @option{-mxgot} when a single object 16176file accesses more than 64k's worth of GOT entries. Very few do. 16177 16178These options have no effect unless GCC is generating position 16179independent code. 16180 16181@item -mgp32 16182@opindex mgp32 16183Assume that general-purpose registers are 32 bits wide. 16184 16185@item -mgp64 16186@opindex mgp64 16187Assume that general-purpose registers are 64 bits wide. 16188 16189@item -mfp32 16190@opindex mfp32 16191Assume that floating-point registers are 32 bits wide. 16192 16193@item -mfp64 16194@opindex mfp64 16195Assume that floating-point registers are 64 bits wide. 16196 16197@item -mhard-float 16198@opindex mhard-float 16199Use floating-point coprocessor instructions. 16200 16201@item -msoft-float 16202@opindex msoft-float 16203Do not use floating-point coprocessor instructions. Implement 16204floating-point calculations using library calls instead. 16205 16206@item -mno-float 16207@opindex mno-float 16208Equivalent to @option{-msoft-float}, but additionally asserts that the 16209program being compiled does not perform any floating-point operations. 16210This option is presently supported only by some bare-metal MIPS 16211configurations, where it may select a special set of libraries 16212that lack all floating-point support (including, for example, the 16213floating-point @code{printf} formats). 16214If code compiled with @code{-mno-float} accidentally contains 16215floating-point operations, it is likely to suffer a link-time 16216or run-time failure. 16217 16218@item -msingle-float 16219@opindex msingle-float 16220Assume that the floating-point coprocessor only supports single-precision 16221operations. 16222 16223@item -mdouble-float 16224@opindex mdouble-float 16225Assume that the floating-point coprocessor supports double-precision 16226operations. This is the default. 16227 16228@item -mllsc 16229@itemx -mno-llsc 16230@opindex mllsc 16231@opindex mno-llsc 16232Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to 16233implement atomic memory built-in functions. When neither option is 16234specified, GCC uses the instructions if the target architecture 16235supports them. 16236 16237@option{-mllsc} is useful if the runtime environment can emulate the 16238instructions and @option{-mno-llsc} can be useful when compiling for 16239nonstandard ISAs. You can make either option the default by 16240configuring GCC with @option{--with-llsc} and @option{--without-llsc} 16241respectively. @option{--with-llsc} is the default for some 16242configurations; see the installation documentation for details. 16243 16244@item -mdsp 16245@itemx -mno-dsp 16246@opindex mdsp 16247@opindex mno-dsp 16248Use (do not use) revision 1 of the MIPS DSP ASE@. 16249@xref{MIPS DSP Built-in Functions}. This option defines the 16250preprocessor macro @samp{__mips_dsp}. It also defines 16251@samp{__mips_dsp_rev} to 1. 16252 16253@item -mdspr2 16254@itemx -mno-dspr2 16255@opindex mdspr2 16256@opindex mno-dspr2 16257Use (do not use) revision 2 of the MIPS DSP ASE@. 16258@xref{MIPS DSP Built-in Functions}. This option defines the 16259preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}. 16260It also defines @samp{__mips_dsp_rev} to 2. 16261 16262@item -msmartmips 16263@itemx -mno-smartmips 16264@opindex msmartmips 16265@opindex mno-smartmips 16266Use (do not use) the MIPS SmartMIPS ASE. 16267 16268@item -mpaired-single 16269@itemx -mno-paired-single 16270@opindex mpaired-single 16271@opindex mno-paired-single 16272Use (do not use) paired-single floating-point instructions. 16273@xref{MIPS Paired-Single Support}. This option requires 16274hardware floating-point support to be enabled. 16275 16276@item -mdmx 16277@itemx -mno-mdmx 16278@opindex mdmx 16279@opindex mno-mdmx 16280Use (do not use) MIPS Digital Media Extension instructions. 16281This option can only be used when generating 64-bit code and requires 16282hardware floating-point support to be enabled. 16283 16284@item -mips3d 16285@itemx -mno-mips3d 16286@opindex mips3d 16287@opindex mno-mips3d 16288Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}. 16289The option @option{-mips3d} implies @option{-mpaired-single}. 16290 16291@item -mmt 16292@itemx -mno-mt 16293@opindex mmt 16294@opindex mno-mt 16295Use (do not use) MT Multithreading instructions. 16296 16297@item -mmcu 16298@itemx -mno-mcu 16299@opindex mmcu 16300@opindex mno-mcu 16301Use (do not use) the MIPS MCU ASE instructions. 16302 16303@item -mlong64 16304@opindex mlong64 16305Force @code{long} types to be 64 bits wide. See @option{-mlong32} for 16306an explanation of the default and the way that the pointer size is 16307determined. 16308 16309@item -mlong32 16310@opindex mlong32 16311Force @code{long}, @code{int}, and pointer types to be 32 bits wide. 16312 16313The default size of @code{int}s, @code{long}s and pointers depends on 16314the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI 16315uses 64-bit @code{long}s, as does the 64-bit EABI; the others use 1631632-bit @code{long}s. Pointers are the same size as @code{long}s, 16317or the same size as integer registers, whichever is smaller. 16318 16319@item -msym32 16320@itemx -mno-sym32 16321@opindex msym32 16322@opindex mno-sym32 16323Assume (do not assume) that all symbols have 32-bit values, regardless 16324of the selected ABI@. This option is useful in combination with 16325@option{-mabi=64} and @option{-mno-abicalls} because it allows GCC 16326to generate shorter and faster references to symbolic addresses. 16327 16328@item -G @var{num} 16329@opindex G 16330Put definitions of externally-visible data in a small data section 16331if that data is no bigger than @var{num} bytes. GCC can then generate 16332more efficient accesses to the data; see @option{-mgpopt} for details. 16333 16334The default @option{-G} option depends on the configuration. 16335 16336@item -mlocal-sdata 16337@itemx -mno-local-sdata 16338@opindex mlocal-sdata 16339@opindex mno-local-sdata 16340Extend (do not extend) the @option{-G} behavior to local data too, 16341such as to static variables in C@. @option{-mlocal-sdata} is the 16342default for all configurations. 16343 16344If the linker complains that an application is using too much small data, 16345you might want to try rebuilding the less performance-critical parts with 16346@option{-mno-local-sdata}. You might also want to build large 16347libraries with @option{-mno-local-sdata}, so that the libraries leave 16348more room for the main program. 16349 16350@item -mextern-sdata 16351@itemx -mno-extern-sdata 16352@opindex mextern-sdata 16353@opindex mno-extern-sdata 16354Assume (do not assume) that externally-defined data is in 16355a small data section if the size of that data is within the @option{-G} limit. 16356@option{-mextern-sdata} is the default for all configurations. 16357 16358If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G 16359@var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var} 16360that is no bigger than @var{num} bytes, you must make sure that @var{Var} 16361is placed in a small data section. If @var{Var} is defined by another 16362module, you must either compile that module with a high-enough 16363@option{-G} setting or attach a @code{section} attribute to @var{Var}'s 16364definition. If @var{Var} is common, you must link the application 16365with a high-enough @option{-G} setting. 16366 16367The easiest way of satisfying these restrictions is to compile 16368and link every module with the same @option{-G} option. However, 16369you may wish to build a library that supports several different 16370small data limits. You can do this by compiling the library with 16371the highest supported @option{-G} setting and additionally using 16372@option{-mno-extern-sdata} to stop the library from making assumptions 16373about externally-defined data. 16374 16375@item -mgpopt 16376@itemx -mno-gpopt 16377@opindex mgpopt 16378@opindex mno-gpopt 16379Use (do not use) GP-relative accesses for symbols that are known to be 16380in a small data section; see @option{-G}, @option{-mlocal-sdata} and 16381@option{-mextern-sdata}. @option{-mgpopt} is the default for all 16382configurations. 16383 16384@option{-mno-gpopt} is useful for cases where the @code{$gp} register 16385might not hold the value of @code{_gp}. For example, if the code is 16386part of a library that might be used in a boot monitor, programs that 16387call boot monitor routines pass an unknown value in @code{$gp}. 16388(In such situations, the boot monitor itself is usually compiled 16389with @option{-G0}.) 16390 16391@option{-mno-gpopt} implies @option{-mno-local-sdata} and 16392@option{-mno-extern-sdata}. 16393 16394@item -membedded-data 16395@itemx -mno-embedded-data 16396@opindex membedded-data 16397@opindex mno-embedded-data 16398Allocate variables to the read-only data section first if possible, then 16399next in the small data section if possible, otherwise in data. This gives 16400slightly slower code than the default, but reduces the amount of RAM required 16401when executing, and thus may be preferred for some embedded systems. 16402 16403@item -muninit-const-in-rodata 16404@itemx -mno-uninit-const-in-rodata 16405@opindex muninit-const-in-rodata 16406@opindex mno-uninit-const-in-rodata 16407Put uninitialized @code{const} variables in the read-only data section. 16408This option is only meaningful in conjunction with @option{-membedded-data}. 16409 16410@item -mcode-readable=@var{setting} 16411@opindex mcode-readable 16412Specify whether GCC may generate code that reads from executable sections. 16413There are three possible settings: 16414 16415@table @gcctabopt 16416@item -mcode-readable=yes 16417Instructions may freely access executable sections. This is the 16418default setting. 16419 16420@item -mcode-readable=pcrel 16421MIPS16 PC-relative load instructions can access executable sections, 16422but other instructions must not do so. This option is useful on 4KSc 16423and 4KSd processors when the code TLBs have the Read Inhibit bit set. 16424It is also useful on processors that can be configured to have a dual 16425instruction/data SRAM interface and that, like the M4K, automatically 16426redirect PC-relative loads to the instruction RAM. 16427 16428@item -mcode-readable=no 16429Instructions must not access executable sections. This option can be 16430useful on targets that are configured to have a dual instruction/data 16431SRAM interface but that (unlike the M4K) do not automatically redirect 16432PC-relative loads to the instruction RAM. 16433@end table 16434 16435@item -msplit-addresses 16436@itemx -mno-split-addresses 16437@opindex msplit-addresses 16438@opindex mno-split-addresses 16439Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler 16440relocation operators. This option has been superseded by 16441@option{-mexplicit-relocs} but is retained for backwards compatibility. 16442 16443@item -mexplicit-relocs 16444@itemx -mno-explicit-relocs 16445@opindex mexplicit-relocs 16446@opindex mno-explicit-relocs 16447Use (do not use) assembler relocation operators when dealing with symbolic 16448addresses. The alternative, selected by @option{-mno-explicit-relocs}, 16449is to use assembler macros instead. 16450 16451@option{-mexplicit-relocs} is the default if GCC was configured 16452to use an assembler that supports relocation operators. 16453 16454@item -mcheck-zero-division 16455@itemx -mno-check-zero-division 16456@opindex mcheck-zero-division 16457@opindex mno-check-zero-division 16458Trap (do not trap) on integer division by zero. 16459 16460The default is @option{-mcheck-zero-division}. 16461 16462@item -mdivide-traps 16463@itemx -mdivide-breaks 16464@opindex mdivide-traps 16465@opindex mdivide-breaks 16466MIPS systems check for division by zero by generating either a 16467conditional trap or a break instruction. Using traps results in 16468smaller code, but is only supported on MIPS II and later. Also, some 16469versions of the Linux kernel have a bug that prevents trap from 16470generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to 16471allow conditional traps on architectures that support them and 16472@option{-mdivide-breaks} to force the use of breaks. 16473 16474The default is usually @option{-mdivide-traps}, but this can be 16475overridden at configure time using @option{--with-divide=breaks}. 16476Divide-by-zero checks can be completely disabled using 16477@option{-mno-check-zero-division}. 16478 16479@item -mmemcpy 16480@itemx -mno-memcpy 16481@opindex mmemcpy 16482@opindex mno-memcpy 16483Force (do not force) the use of @code{memcpy()} for non-trivial block 16484moves. The default is @option{-mno-memcpy}, which allows GCC to inline 16485most constant-sized copies. 16486 16487@item -mlong-calls 16488@itemx -mno-long-calls 16489@opindex mlong-calls 16490@opindex mno-long-calls 16491Disable (do not disable) use of the @code{jal} instruction. Calling 16492functions using @code{jal} is more efficient but requires the caller 16493and callee to be in the same 256 megabyte segment. 16494 16495This option has no effect on abicalls code. The default is 16496@option{-mno-long-calls}. 16497 16498@item -mmad 16499@itemx -mno-mad 16500@opindex mmad 16501@opindex mno-mad 16502Enable (disable) use of the @code{mad}, @code{madu} and @code{mul} 16503instructions, as provided by the R4650 ISA@. 16504 16505@item -mfused-madd 16506@itemx -mno-fused-madd 16507@opindex mfused-madd 16508@opindex mno-fused-madd 16509Enable (disable) use of the floating-point multiply-accumulate 16510instructions, when they are available. The default is 16511@option{-mfused-madd}. 16512 16513On the R8000 CPU when multiply-accumulate instructions are used, 16514the intermediate product is calculated to infinite precision 16515and is not subject to the FCSR Flush to Zero bit. This may be 16516undesirable in some circumstances. On other processors the result 16517is numerically identical to the equivalent computation using 16518separate multiply, add, subtract and negate instructions. 16519 16520@item -nocpp 16521@opindex nocpp 16522Tell the MIPS assembler to not run its preprocessor over user 16523assembler files (with a @samp{.s} suffix) when assembling them. 16524 16525@item -mfix-24k 16526@item -mno-fix-24k 16527@opindex mfix-24k 16528@opindex mno-fix-24k 16529Work around the 24K E48 (lost data on stores during refill) errata. 16530The workarounds are implemented by the assembler rather than by GCC@. 16531 16532@item -mfix-r4000 16533@itemx -mno-fix-r4000 16534@opindex mfix-r4000 16535@opindex mno-fix-r4000 16536Work around certain R4000 CPU errata: 16537@itemize @minus 16538@item 16539A double-word or a variable shift may give an incorrect result if executed 16540immediately after starting an integer division. 16541@item 16542A double-word or a variable shift may give an incorrect result if executed 16543while an integer multiplication is in progress. 16544@item 16545An integer division may give an incorrect result if started in a delay slot 16546of a taken branch or a jump. 16547@end itemize 16548 16549@item -mfix-r4400 16550@itemx -mno-fix-r4400 16551@opindex mfix-r4400 16552@opindex mno-fix-r4400 16553Work around certain R4400 CPU errata: 16554@itemize @minus 16555@item 16556A double-word or a variable shift may give an incorrect result if executed 16557immediately after starting an integer division. 16558@end itemize 16559 16560@item -mfix-r10000 16561@itemx -mno-fix-r10000 16562@opindex mfix-r10000 16563@opindex mno-fix-r10000 16564Work around certain R10000 errata: 16565@itemize @minus 16566@item 16567@code{ll}/@code{sc} sequences may not behave atomically on revisions 16568prior to 3.0. They may deadlock on revisions 2.6 and earlier. 16569@end itemize 16570 16571This option can only be used if the target architecture supports 16572branch-likely instructions. @option{-mfix-r10000} is the default when 16573@option{-march=r10000} is used; @option{-mno-fix-r10000} is the default 16574otherwise. 16575 16576@item -mfix-vr4120 16577@itemx -mno-fix-vr4120 16578@opindex mfix-vr4120 16579Work around certain VR4120 errata: 16580@itemize @minus 16581@item 16582@code{dmultu} does not always produce the correct result. 16583@item 16584@code{div} and @code{ddiv} do not always produce the correct result if one 16585of the operands is negative. 16586@end itemize 16587The workarounds for the division errata rely on special functions in 16588@file{libgcc.a}. At present, these functions are only provided by 16589the @code{mips64vr*-elf} configurations. 16590 16591Other VR4120 errata require a NOP to be inserted between certain pairs of 16592instructions. These errata are handled by the assembler, not by GCC itself. 16593 16594@item -mfix-vr4130 16595@opindex mfix-vr4130 16596Work around the VR4130 @code{mflo}/@code{mfhi} errata. The 16597workarounds are implemented by the assembler rather than by GCC, 16598although GCC avoids using @code{mflo} and @code{mfhi} if the 16599VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi} 16600instructions are available instead. 16601 16602@item -mfix-sb1 16603@itemx -mno-fix-sb1 16604@opindex mfix-sb1 16605Work around certain SB-1 CPU core errata. 16606(This flag currently works around the SB-1 revision 2 16607``F1'' and ``F2'' floating-point errata.) 16608 16609@item -mr10k-cache-barrier=@var{setting} 16610@opindex mr10k-cache-barrier 16611Specify whether GCC should insert cache barriers to avoid the 16612side-effects of speculation on R10K processors. 16613 16614In common with many processors, the R10K tries to predict the outcome 16615of a conditional branch and speculatively executes instructions from 16616the ``taken'' branch. It later aborts these instructions if the 16617predicted outcome is wrong. However, on the R10K, even aborted 16618instructions can have side effects. 16619 16620This problem only affects kernel stores and, depending on the system, 16621kernel loads. As an example, a speculatively-executed store may load 16622the target memory into cache and mark the cache line as dirty, even if 16623the store itself is later aborted. If a DMA operation writes to the 16624same area of memory before the ``dirty'' line is flushed, the cached 16625data overwrites the DMA-ed data. See the R10K processor manual 16626for a full description, including other potential problems. 16627 16628One workaround is to insert cache barrier instructions before every memory 16629access that might be speculatively executed and that might have side 16630effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}} 16631controls GCC's implementation of this workaround. It assumes that 16632aborted accesses to any byte in the following regions does not have 16633side effects: 16634 16635@enumerate 16636@item 16637the memory occupied by the current function's stack frame; 16638 16639@item 16640the memory occupied by an incoming stack argument; 16641 16642@item 16643the memory occupied by an object with a link-time-constant address. 16644@end enumerate 16645 16646It is the kernel's responsibility to ensure that speculative 16647accesses to these regions are indeed safe. 16648 16649If the input program contains a function declaration such as: 16650 16651@smallexample 16652void foo (void); 16653@end smallexample 16654 16655then the implementation of @code{foo} must allow @code{j foo} and 16656@code{jal foo} to be executed speculatively. GCC honors this 16657restriction for functions it compiles itself. It expects non-GCC 16658functions (such as hand-written assembly code) to do the same. 16659 16660The option has three forms: 16661 16662@table @gcctabopt 16663@item -mr10k-cache-barrier=load-store 16664Insert a cache barrier before a load or store that might be 16665speculatively executed and that might have side effects even 16666if aborted. 16667 16668@item -mr10k-cache-barrier=store 16669Insert a cache barrier before a store that might be speculatively 16670executed and that might have side effects even if aborted. 16671 16672@item -mr10k-cache-barrier=none 16673Disable the insertion of cache barriers. This is the default setting. 16674@end table 16675 16676@item -mflush-func=@var{func} 16677@itemx -mno-flush-func 16678@opindex mflush-func 16679Specifies the function to call to flush the I and D caches, or to not 16680call any such function. If called, the function must take the same 16681arguments as the common @code{_flush_func()}, that is, the address of the 16682memory range for which the cache is being flushed, the size of the 16683memory range, and the number 3 (to flush both caches). The default 16684depends on the target GCC was configured for, but commonly is either 16685@samp{_flush_func} or @samp{__cpu_flush}. 16686 16687@item mbranch-cost=@var{num} 16688@opindex mbranch-cost 16689Set the cost of branches to roughly @var{num} ``simple'' instructions. 16690This cost is only a heuristic and is not guaranteed to produce 16691consistent results across releases. A zero cost redundantly selects 16692the default, which is based on the @option{-mtune} setting. 16693 16694@item -mbranch-likely 16695@itemx -mno-branch-likely 16696@opindex mbranch-likely 16697@opindex mno-branch-likely 16698Enable or disable use of Branch Likely instructions, regardless of the 16699default for the selected architecture. By default, Branch Likely 16700instructions may be generated if they are supported by the selected 16701architecture. An exception is for the MIPS32 and MIPS64 architectures 16702and processors that implement those architectures; for those, Branch 16703Likely instructions are not be generated by default because the MIPS32 16704and MIPS64 architectures specifically deprecate their use. 16705 16706@item -mfp-exceptions 16707@itemx -mno-fp-exceptions 16708@opindex mfp-exceptions 16709Specifies whether FP exceptions are enabled. This affects how 16710FP instructions are scheduled for some processors. 16711The default is that FP exceptions are 16712enabled. 16713 16714For instance, on the SB-1, if FP exceptions are disabled, and we are emitting 1671564-bit code, then we can use both FP pipes. Otherwise, we can only use one 16716FP pipe. 16717 16718@item -mvr4130-align 16719@itemx -mno-vr4130-align 16720@opindex mvr4130-align 16721The VR4130 pipeline is two-way superscalar, but can only issue two 16722instructions together if the first one is 8-byte aligned. When this 16723option is enabled, GCC aligns pairs of instructions that it 16724thinks should execute in parallel. 16725 16726This option only has an effect when optimizing for the VR4130. 16727It normally makes code faster, but at the expense of making it bigger. 16728It is enabled by default at optimization level @option{-O3}. 16729 16730@item -msynci 16731@itemx -mno-synci 16732@opindex msynci 16733Enable (disable) generation of @code{synci} instructions on 16734architectures that support it. The @code{synci} instructions (if 16735enabled) are generated when @code{__builtin___clear_cache()} is 16736compiled. 16737 16738This option defaults to @code{-mno-synci}, but the default can be 16739overridden by configuring with @code{--with-synci}. 16740 16741When compiling code for single processor systems, it is generally safe 16742to use @code{synci}. However, on many multi-core (SMP) systems, it 16743does not invalidate the instruction caches on all cores and may lead 16744to undefined behavior. 16745 16746@item -mrelax-pic-calls 16747@itemx -mno-relax-pic-calls 16748@opindex mrelax-pic-calls 16749Try to turn PIC calls that are normally dispatched via register 16750@code{$25} into direct calls. This is only possible if the linker can 16751resolve the destination at link-time and if the destination is within 16752range for a direct call. 16753 16754@option{-mrelax-pic-calls} is the default if GCC was configured to use 16755an assembler and a linker that support the @code{.reloc} assembly 16756directive and @code{-mexplicit-relocs} is in effect. With 16757@code{-mno-explicit-relocs}, this optimization can be performed by the 16758assembler and the linker alone without help from the compiler. 16759 16760@item -mmcount-ra-address 16761@itemx -mno-mcount-ra-address 16762@opindex mmcount-ra-address 16763@opindex mno-mcount-ra-address 16764Emit (do not emit) code that allows @code{_mcount} to modify the 16765calling function's return address. When enabled, this option extends 16766the usual @code{_mcount} interface with a new @var{ra-address} 16767parameter, which has type @code{intptr_t *} and is passed in register 16768@code{$12}. @code{_mcount} can then modify the return address by 16769doing both of the following: 16770@itemize 16771@item 16772Returning the new address in register @code{$31}. 16773@item 16774Storing the new address in @code{*@var{ra-address}}, 16775if @var{ra-address} is nonnull. 16776@end itemize 16777 16778The default is @option{-mno-mcount-ra-address}. 16779 16780@end table 16781 16782@node MMIX Options 16783@subsection MMIX Options 16784@cindex MMIX Options 16785 16786These options are defined for the MMIX: 16787 16788@table @gcctabopt 16789@item -mlibfuncs 16790@itemx -mno-libfuncs 16791@opindex mlibfuncs 16792@opindex mno-libfuncs 16793Specify that intrinsic library functions are being compiled, passing all 16794values in registers, no matter the size. 16795 16796@item -mepsilon 16797@itemx -mno-epsilon 16798@opindex mepsilon 16799@opindex mno-epsilon 16800Generate floating-point comparison instructions that compare with respect 16801to the @code{rE} epsilon register. 16802 16803@item -mabi=mmixware 16804@itemx -mabi=gnu 16805@opindex mabi=mmixware 16806@opindex mabi=gnu 16807Generate code that passes function parameters and return values that (in 16808the called function) are seen as registers @code{$0} and up, as opposed to 16809the GNU ABI which uses global registers @code{$231} and up. 16810 16811@item -mzero-extend 16812@itemx -mno-zero-extend 16813@opindex mzero-extend 16814@opindex mno-zero-extend 16815When reading data from memory in sizes shorter than 64 bits, use (do not 16816use) zero-extending load instructions by default, rather than 16817sign-extending ones. 16818 16819@item -mknuthdiv 16820@itemx -mno-knuthdiv 16821@opindex mknuthdiv 16822@opindex mno-knuthdiv 16823Make the result of a division yielding a remainder have the same sign as 16824the divisor. With the default, @option{-mno-knuthdiv}, the sign of the 16825remainder follows the sign of the dividend. Both methods are 16826arithmetically valid, the latter being almost exclusively used. 16827 16828@item -mtoplevel-symbols 16829@itemx -mno-toplevel-symbols 16830@opindex mtoplevel-symbols 16831@opindex mno-toplevel-symbols 16832Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly 16833code can be used with the @code{PREFIX} assembly directive. 16834 16835@item -melf 16836@opindex melf 16837Generate an executable in the ELF format, rather than the default 16838@samp{mmo} format used by the @command{mmix} simulator. 16839 16840@item -mbranch-predict 16841@itemx -mno-branch-predict 16842@opindex mbranch-predict 16843@opindex mno-branch-predict 16844Use (do not use) the probable-branch instructions, when static branch 16845prediction indicates a probable branch. 16846 16847@item -mbase-addresses 16848@itemx -mno-base-addresses 16849@opindex mbase-addresses 16850@opindex mno-base-addresses 16851Generate (do not generate) code that uses @emph{base addresses}. Using a 16852base address automatically generates a request (handled by the assembler 16853and the linker) for a constant to be set up in a global register. The 16854register is used for one or more base address requests within the range 0 16855to 255 from the value held in the register. The generally leads to short 16856and fast code, but the number of different data items that can be 16857addressed is limited. This means that a program that uses lots of static 16858data may require @option{-mno-base-addresses}. 16859 16860@item -msingle-exit 16861@itemx -mno-single-exit 16862@opindex msingle-exit 16863@opindex mno-single-exit 16864Force (do not force) generated code to have a single exit point in each 16865function. 16866@end table 16867 16868@node MN10300 Options 16869@subsection MN10300 Options 16870@cindex MN10300 options 16871 16872These @option{-m} options are defined for Matsushita MN10300 architectures: 16873 16874@table @gcctabopt 16875@item -mmult-bug 16876@opindex mmult-bug 16877Generate code to avoid bugs in the multiply instructions for the MN10300 16878processors. This is the default. 16879 16880@item -mno-mult-bug 16881@opindex mno-mult-bug 16882Do not generate code to avoid bugs in the multiply instructions for the 16883MN10300 processors. 16884 16885@item -mam33 16886@opindex mam33 16887Generate code using features specific to the AM33 processor. 16888 16889@item -mno-am33 16890@opindex mno-am33 16891Do not generate code using features specific to the AM33 processor. This 16892is the default. 16893 16894@item -mam33-2 16895@opindex mam33-2 16896Generate code using features specific to the AM33/2.0 processor. 16897 16898@item -mam34 16899@opindex mam34 16900Generate code using features specific to the AM34 processor. 16901 16902@item -mtune=@var{cpu-type} 16903@opindex mtune 16904Use the timing characteristics of the indicated CPU type when 16905scheduling instructions. This does not change the targeted processor 16906type. The CPU type must be one of @samp{mn10300}, @samp{am33}, 16907@samp{am33-2} or @samp{am34}. 16908 16909@item -mreturn-pointer-on-d0 16910@opindex mreturn-pointer-on-d0 16911When generating a function that returns a pointer, return the pointer 16912in both @code{a0} and @code{d0}. Otherwise, the pointer is returned 16913only in @code{a0}, and attempts to call such functions without a prototype 16914result in errors. Note that this option is on by default; use 16915@option{-mno-return-pointer-on-d0} to disable it. 16916 16917@item -mno-crt0 16918@opindex mno-crt0 16919Do not link in the C run-time initialization object file. 16920 16921@item -mrelax 16922@opindex mrelax 16923Indicate to the linker that it should perform a relaxation optimization pass 16924to shorten branches, calls and absolute memory addresses. This option only 16925has an effect when used on the command line for the final link step. 16926 16927This option makes symbolic debugging impossible. 16928 16929@item -mliw 16930@opindex mliw 16931Allow the compiler to generate @emph{Long Instruction Word} 16932instructions if the target is the @samp{AM33} or later. This is the 16933default. This option defines the preprocessor macro @samp{__LIW__}. 16934 16935@item -mnoliw 16936@opindex mnoliw 16937Do not allow the compiler to generate @emph{Long Instruction Word} 16938instructions. This option defines the preprocessor macro 16939@samp{__NO_LIW__}. 16940 16941@item -msetlb 16942@opindex msetlb 16943Allow the compiler to generate the @emph{SETLB} and @emph{Lcc} 16944instructions if the target is the @samp{AM33} or later. This is the 16945default. This option defines the preprocessor macro @samp{__SETLB__}. 16946 16947@item -mnosetlb 16948@opindex mnosetlb 16949Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc} 16950instructions. This option defines the preprocessor macro 16951@samp{__NO_SETLB__}. 16952 16953@end table 16954 16955@node Moxie Options 16956@subsection Moxie Options 16957@cindex Moxie Options 16958 16959@table @gcctabopt 16960 16961@item -meb 16962@opindex meb 16963Generate big-endian code. This is the default for @samp{moxie-*-*} 16964configurations. 16965 16966@item -mel 16967@opindex mel 16968Generate little-endian code. 16969 16970@item -mno-crt0 16971@opindex mno-crt0 16972Do not link in the C run-time initialization object file. 16973 16974@end table 16975 16976@node PDP-11 Options 16977@subsection PDP-11 Options 16978@cindex PDP-11 Options 16979 16980These options are defined for the PDP-11: 16981 16982@table @gcctabopt 16983@item -mfpu 16984@opindex mfpu 16985Use hardware FPP floating point. This is the default. (FIS floating 16986point on the PDP-11/40 is not supported.) 16987 16988@item -msoft-float 16989@opindex msoft-float 16990Do not use hardware floating point. 16991 16992@item -mac0 16993@opindex mac0 16994Return floating-point results in ac0 (fr0 in Unix assembler syntax). 16995 16996@item -mno-ac0 16997@opindex mno-ac0 16998Return floating-point results in memory. This is the default. 16999 17000@item -m40 17001@opindex m40 17002Generate code for a PDP-11/40. 17003 17004@item -m45 17005@opindex m45 17006Generate code for a PDP-11/45. This is the default. 17007 17008@item -m10 17009@opindex m10 17010Generate code for a PDP-11/10. 17011 17012@item -mbcopy-builtin 17013@opindex mbcopy-builtin 17014Use inline @code{movmemhi} patterns for copying memory. This is the 17015default. 17016 17017@item -mbcopy 17018@opindex mbcopy 17019Do not use inline @code{movmemhi} patterns for copying memory. 17020 17021@item -mint16 17022@itemx -mno-int32 17023@opindex mint16 17024@opindex mno-int32 17025Use 16-bit @code{int}. This is the default. 17026 17027@item -mint32 17028@itemx -mno-int16 17029@opindex mint32 17030@opindex mno-int16 17031Use 32-bit @code{int}. 17032 17033@item -mfloat64 17034@itemx -mno-float32 17035@opindex mfloat64 17036@opindex mno-float32 17037Use 64-bit @code{float}. This is the default. 17038 17039@item -mfloat32 17040@itemx -mno-float64 17041@opindex mfloat32 17042@opindex mno-float64 17043Use 32-bit @code{float}. 17044 17045@item -mabshi 17046@opindex mabshi 17047Use @code{abshi2} pattern. This is the default. 17048 17049@item -mno-abshi 17050@opindex mno-abshi 17051Do not use @code{abshi2} pattern. 17052 17053@item -mbranch-expensive 17054@opindex mbranch-expensive 17055Pretend that branches are expensive. This is for experimenting with 17056code generation only. 17057 17058@item -mbranch-cheap 17059@opindex mbranch-cheap 17060Do not pretend that branches are expensive. This is the default. 17061 17062@item -munix-asm 17063@opindex munix-asm 17064Use Unix assembler syntax. This is the default when configured for 17065@samp{pdp11-*-bsd}. 17066 17067@item -mdec-asm 17068@opindex mdec-asm 17069Use DEC assembler syntax. This is the default when configured for any 17070PDP-11 target other than @samp{pdp11-*-bsd}. 17071@end table 17072 17073@node picoChip Options 17074@subsection picoChip Options 17075@cindex picoChip options 17076 17077These @samp{-m} options are defined for picoChip implementations: 17078 17079@table @gcctabopt 17080 17081@item -mae=@var{ae_type} 17082@opindex mcpu 17083Set the instruction set, register set, and instruction scheduling 17084parameters for array element type @var{ae_type}. Supported values 17085for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}. 17086 17087@option{-mae=ANY} selects a completely generic AE type. Code 17088generated with this option runs on any of the other AE types. The 17089code is not as efficient as it would be if compiled for a specific 17090AE type, and some types of operation (e.g., multiplication) do not 17091work properly on all types of AE. 17092 17093@option{-mae=MUL} selects a MUL AE type. This is the most useful AE type 17094for compiled code, and is the default. 17095 17096@option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this 17097option may suffer from poor performance of byte (char) manipulation, 17098since the DSP AE does not provide hardware support for byte load/stores. 17099 17100@item -msymbol-as-address 17101Enable the compiler to directly use a symbol name as an address in a 17102load/store instruction, without first loading it into a 17103register. Typically, the use of this option generates larger 17104programs, which run faster than when the option isn't used. However, the 17105results vary from program to program, so it is left as a user option, 17106rather than being permanently enabled. 17107 17108@item -mno-inefficient-warnings 17109Disables warnings about the generation of inefficient code. These 17110warnings can be generated, for example, when compiling code that 17111performs byte-level memory operations on the MAC AE type. The MAC AE has 17112no hardware support for byte-level memory operations, so all byte 17113load/stores must be synthesized from word load/store operations. This is 17114inefficient and a warning is generated to indicate 17115that you should rewrite the code to avoid byte operations, or to target 17116an AE type that has the necessary hardware support. This option disables 17117these warnings. 17118 17119@end table 17120 17121@node PowerPC Options 17122@subsection PowerPC Options 17123@cindex PowerPC options 17124 17125These are listed under @xref{RS/6000 and PowerPC Options}. 17126 17127@node RL78 Options 17128@subsection RL78 Options 17129@cindex RL78 Options 17130 17131@table @gcctabopt 17132 17133@item -msim 17134@opindex msim 17135Links in additional target libraries to support operation within a 17136simulator. 17137 17138@item -mmul=none 17139@itemx -mmul=g13 17140@itemx -mmul=rl78 17141@opindex mmul 17142Specifies the type of hardware multiplication support to be used. The 17143default is @code{none}, which uses software multiplication functions. 17144The @code{g13} option is for the hardware multiply/divide peripheral 17145only on the RL78/G13 targets. The @code{rl78} option is for the 17146standard hardware multiplication defined in the RL78 software manual. 17147 17148@end table 17149 17150@node RS/6000 and PowerPC Options 17151@subsection IBM RS/6000 and PowerPC Options 17152@cindex RS/6000 and PowerPC Options 17153@cindex IBM RS/6000 and PowerPC Options 17154 17155These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: 17156@table @gcctabopt 17157@item -mpowerpc-gpopt 17158@itemx -mno-powerpc-gpopt 17159@itemx -mpowerpc-gfxopt 17160@itemx -mno-powerpc-gfxopt 17161@need 800 17162@itemx -mpowerpc64 17163@itemx -mno-powerpc64 17164@itemx -mmfcrf 17165@itemx -mno-mfcrf 17166@itemx -mpopcntb 17167@itemx -mno-popcntb 17168@itemx -mpopcntd 17169@itemx -mno-popcntd 17170@itemx -mfprnd 17171@itemx -mno-fprnd 17172@need 800 17173@itemx -mcmpb 17174@itemx -mno-cmpb 17175@itemx -mmfpgpr 17176@itemx -mno-mfpgpr 17177@itemx -mhard-dfp 17178@itemx -mno-hard-dfp 17179@opindex mpowerpc-gpopt 17180@opindex mno-powerpc-gpopt 17181@opindex mpowerpc-gfxopt 17182@opindex mno-powerpc-gfxopt 17183@opindex mpowerpc64 17184@opindex mno-powerpc64 17185@opindex mmfcrf 17186@opindex mno-mfcrf 17187@opindex mpopcntb 17188@opindex mno-popcntb 17189@opindex mpopcntd 17190@opindex mno-popcntd 17191@opindex mfprnd 17192@opindex mno-fprnd 17193@opindex mcmpb 17194@opindex mno-cmpb 17195@opindex mmfpgpr 17196@opindex mno-mfpgpr 17197@opindex mhard-dfp 17198@opindex mno-hard-dfp 17199You use these options to specify which instructions are available on the 17200processor you are using. The default value of these options is 17201determined when configuring GCC@. Specifying the 17202@option{-mcpu=@var{cpu_type}} overrides the specification of these 17203options. We recommend you use the @option{-mcpu=@var{cpu_type}} option 17204rather than the options listed above. 17205 17206Specifying @option{-mpowerpc-gpopt} allows 17207GCC to use the optional PowerPC architecture instructions in the 17208General Purpose group, including floating-point square root. Specifying 17209@option{-mpowerpc-gfxopt} allows GCC to 17210use the optional PowerPC architecture instructions in the Graphics 17211group, including floating-point select. 17212 17213The @option{-mmfcrf} option allows GCC to generate the move from 17214condition register field instruction implemented on the POWER4 17215processor and other processors that support the PowerPC V2.01 17216architecture. 17217The @option{-mpopcntb} option allows GCC to generate the popcount and 17218double-precision FP reciprocal estimate instruction implemented on the 17219POWER5 processor and other processors that support the PowerPC V2.02 17220architecture. 17221The @option{-mpopcntd} option allows GCC to generate the popcount 17222instruction implemented on the POWER7 processor and other processors 17223that support the PowerPC V2.06 architecture. 17224The @option{-mfprnd} option allows GCC to generate the FP round to 17225integer instructions implemented on the POWER5+ processor and other 17226processors that support the PowerPC V2.03 architecture. 17227The @option{-mcmpb} option allows GCC to generate the compare bytes 17228instruction implemented on the POWER6 processor and other processors 17229that support the PowerPC V2.05 architecture. 17230The @option{-mmfpgpr} option allows GCC to generate the FP move to/from 17231general-purpose register instructions implemented on the POWER6X 17232processor and other processors that support the extended PowerPC V2.05 17233architecture. 17234The @option{-mhard-dfp} option allows GCC to generate the decimal 17235floating-point instructions implemented on some POWER processors. 17236 17237The @option{-mpowerpc64} option allows GCC to generate the additional 1723864-bit instructions that are found in the full PowerPC64 architecture 17239and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to 17240@option{-mno-powerpc64}. 17241 17242@item -mcpu=@var{cpu_type} 17243@opindex mcpu 17244Set architecture type, register usage, and 17245instruction scheduling parameters for machine type @var{cpu_type}. 17246Supported values for @var{cpu_type} are @samp{401}, @samp{403}, 17247@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp}, 17248@samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603}, 17249@samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740}, 17250@samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823}, 17251@samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2}, 17252@samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500}, 17253@samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5}, 17254@samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+}, 17255@samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8}, @samp{powerpc}, 17256@samp{powerpc64}, @samp{powerpc64le}, and @samp{rs64}. 17257 17258@option{-mcpu=powerpc}, @option{-mcpu=powerpc64}, and 17259@option{-mcpu=powerpc64le} specify pure 32-bit PowerPC (either 17260endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC 17261architecture machine types, with an appropriate, generic processor 17262model assumed for scheduling purposes. 17263 17264The other options specify a specific processor. Code generated under 17265those options runs best on that processor, and may not run at all on 17266others. 17267 17268The @option{-mcpu} options automatically enable or disable the 17269following options: 17270 17271@gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol 17272-mpopcntb -mpopcntd -mpowerpc64 @gol 17273-mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol 17274-msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx @gol 17275-mcrypto -mdirect-move -mpower8-fusion -mpower8-vector @gol 17276-mquad-memory -mquad-memory-atomic} 17277 17278The particular options set for any particular CPU varies between 17279compiler versions, depending on what setting seems to produce optimal 17280code for that CPU; it doesn't necessarily reflect the actual hardware's 17281capabilities. If you wish to set an individual option to a particular 17282value, you may specify it after the @option{-mcpu} option, like 17283@option{-mcpu=970 -mno-altivec}. 17284 17285On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are 17286not enabled or disabled by the @option{-mcpu} option at present because 17287AIX does not have full support for these options. You may still 17288enable or disable them individually if you're sure it'll work in your 17289environment. 17290 17291@item -mtune=@var{cpu_type} 17292@opindex mtune 17293Set the instruction scheduling parameters for machine type 17294@var{cpu_type}, but do not set the architecture type or register usage, 17295as @option{-mcpu=@var{cpu_type}} does. The same 17296values for @var{cpu_type} are used for @option{-mtune} as for 17297@option{-mcpu}. If both are specified, the code generated uses the 17298architecture and registers set by @option{-mcpu}, but the 17299scheduling parameters set by @option{-mtune}. 17300 17301@item -mcmodel=small 17302@opindex mcmodel=small 17303Generate PowerPC64 code for the small model: The TOC is limited to 1730464k. 17305 17306@item -mcmodel=medium 17307@opindex mcmodel=medium 17308Generate PowerPC64 code for the medium model: The TOC and other static 17309data may be up to a total of 4G in size. 17310 17311@item -mcmodel=large 17312@opindex mcmodel=large 17313Generate PowerPC64 code for the large model: The TOC may be up to 4G 17314in size. Other data and code is only limited by the 64-bit address 17315space. 17316 17317@item -maltivec 17318@itemx -mno-altivec 17319@opindex maltivec 17320@opindex mno-altivec 17321Generate code that uses (does not use) AltiVec instructions, and also 17322enable the use of built-in functions that allow more direct access to 17323the AltiVec instruction set. You may also need to set 17324@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI 17325enhancements. 17326 17327When @option{-maltivec} is used, rather than @option{-maltivec=le} or 17328@option{-maltivec=be}, the element order for Altivec intrinsics such 17329as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert} will 17330match array element order corresponding to the endianness of the 17331target. That is, element zero identifies the leftmost element in a 17332vector register when targeting a big-endian platform, and identifies 17333the rightmost element in a vector register when targeting a 17334little-endian platform. 17335 17336@item -maltivec=be 17337@opindex maltivec=be 17338Generate Altivec instructions using big-endian element order, 17339regardless of whether the target is big- or little-endian. This is 17340the default when targeting a big-endian platform. 17341 17342The element order is used to interpret element numbers in Altivec 17343intrinsics such as @code{vec_splat}, @code{vec_extract}, and 17344@code{vec_insert}. By default, these will match array element order 17345corresponding to the endianness for the target. 17346 17347@item -maltivec=le 17348@opindex maltivec=le 17349Generate Altivec instructions using little-endian element order, 17350regardless of whether the target is big- or little-endian. This is 17351the default when targeting a little-endian platform. This option is 17352currently ignored when targeting a big-endian platform. 17353 17354The element order is used to interpret element numbers in Altivec 17355intrinsics such as @code{vec_splat}, @code{vec_extract}, and 17356@code{vec_insert}. By default, these will match array element order 17357corresponding to the endianness for the target. 17358 17359@item -mvrsave 17360@itemx -mno-vrsave 17361@opindex mvrsave 17362@opindex mno-vrsave 17363Generate VRSAVE instructions when generating AltiVec code. 17364 17365@item -mgen-cell-microcode 17366@opindex mgen-cell-microcode 17367Generate Cell microcode instructions. 17368 17369@item -mwarn-cell-microcode 17370@opindex mwarn-cell-microcode 17371Warn when a Cell microcode instruction is emitted. An example 17372of a Cell microcode instruction is a variable shift. 17373 17374@item -msecure-plt 17375@opindex msecure-plt 17376Generate code that allows @command{ld} and @command{ld.so} 17377to build executables and shared 17378libraries with non-executable @code{.plt} and @code{.got} sections. 17379This is a PowerPC 1738032-bit SYSV ABI option. 17381 17382@item -mbss-plt 17383@opindex mbss-plt 17384Generate code that uses a BSS @code{.plt} section that @command{ld.so} 17385fills in, and 17386requires @code{.plt} and @code{.got} 17387sections that are both writable and executable. 17388This is a PowerPC 32-bit SYSV ABI option. 17389 17390@item -misel 17391@itemx -mno-isel 17392@opindex misel 17393@opindex mno-isel 17394This switch enables or disables the generation of ISEL instructions. 17395 17396@item -misel=@var{yes/no} 17397This switch has been deprecated. Use @option{-misel} and 17398@option{-mno-isel} instead. 17399 17400@item -mspe 17401@itemx -mno-spe 17402@opindex mspe 17403@opindex mno-spe 17404This switch enables or disables the generation of SPE simd 17405instructions. 17406 17407@item -mpaired 17408@itemx -mno-paired 17409@opindex mpaired 17410@opindex mno-paired 17411This switch enables or disables the generation of PAIRED simd 17412instructions. 17413 17414@item -mspe=@var{yes/no} 17415This option has been deprecated. Use @option{-mspe} and 17416@option{-mno-spe} instead. 17417 17418@item -mvsx 17419@itemx -mno-vsx 17420@opindex mvsx 17421@opindex mno-vsx 17422Generate code that uses (does not use) vector/scalar (VSX) 17423instructions, and also enable the use of built-in functions that allow 17424more direct access to the VSX instruction set. 17425 17426@item -mcrypto 17427@itemx -mno-crypto 17428@opindex mcrypto 17429@opindex mno-crypto 17430Enable the use (disable) of the built-in functions that allow direct 17431access to the cryptographic instructions that were added in version 174322.07 of the PowerPC ISA. 17433 17434@item -mdirect-move 17435@itemx -mno-direct-move 17436@opindex mdirect-move 17437@opindex mno-direct-move 17438Generate code that uses (does not use) the instructions to move data 17439between the general purpose registers and the vector/scalar (VSX) 17440registers that were added in version 2.07 of the PowerPC ISA. 17441 17442@item -mpower8-fusion 17443@itemx -mno-power8-fusion 17444@opindex mpower8-fusion 17445@opindex mno-power8-fusion 17446Generate code that keeps (does not keeps) some integer operations 17447adjacent so that the instructions can be fused together on power8 and 17448later processors. 17449 17450@item -mpower8-vector 17451@itemx -mno-power8-vector 17452@opindex mpower8-vector 17453@opindex mno-power8-vector 17454Generate code that uses (does not use) the vector and scalar 17455instructions that were added in version 2.07 of the PowerPC ISA. Also 17456enable the use of built-in functions that allow more direct access to 17457the vector instructions. 17458 17459@item -mquad-memory 17460@itemx -mno-quad-memory 17461@opindex mquad-memory 17462@opindex mno-quad-memory 17463Generate code that uses (does not use) the non-atomic quad word memory 17464instructions. The @option{-mquad-memory} option requires use of 1746564-bit mode. 17466 17467@item -mquad-memory-atomic 17468@itemx -mno-quad-memory-atomic 17469@opindex mquad-memory-atomic 17470@opindex mno-quad-memory-atomic 17471Generate code that uses (does not use) the atomic quad word memory 17472instructions. The @option{-mquad-memory-atomic} option requires use of 1747364-bit mode. 17474 17475@item -mfloat-gprs=@var{yes/single/double/no} 17476@itemx -mfloat-gprs 17477@opindex mfloat-gprs 17478This switch enables or disables the generation of floating-point 17479operations on the general-purpose registers for architectures that 17480support it. 17481 17482The argument @var{yes} or @var{single} enables the use of 17483single-precision floating-point operations. 17484 17485The argument @var{double} enables the use of single and 17486double-precision floating-point operations. 17487 17488The argument @var{no} disables floating-point operations on the 17489general-purpose registers. 17490 17491This option is currently only available on the MPC854x. 17492 17493@item -m32 17494@itemx -m64 17495@opindex m32 17496@opindex m64 17497Generate code for 32-bit or 64-bit environments of Darwin and SVR4 17498targets (including GNU/Linux). The 32-bit environment sets int, long 17499and pointer to 32 bits and generates code that runs on any PowerPC 17500variant. The 64-bit environment sets int to 32 bits and long and 17501pointer to 64 bits, and generates code for PowerPC64, as for 17502@option{-mpowerpc64}. 17503 17504@item -mfull-toc 17505@itemx -mno-fp-in-toc 17506@itemx -mno-sum-in-toc 17507@itemx -mminimal-toc 17508@opindex mfull-toc 17509@opindex mno-fp-in-toc 17510@opindex mno-sum-in-toc 17511@opindex mminimal-toc 17512Modify generation of the TOC (Table Of Contents), which is created for 17513every executable file. The @option{-mfull-toc} option is selected by 17514default. In that case, GCC allocates at least one TOC entry for 17515each unique non-automatic variable reference in your program. GCC 17516also places floating-point constants in the TOC@. However, only 1751716,384 entries are available in the TOC@. 17518 17519If you receive a linker error message that saying you have overflowed 17520the available TOC space, you can reduce the amount of TOC space used 17521with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. 17522@option{-mno-fp-in-toc} prevents GCC from putting floating-point 17523constants in the TOC and @option{-mno-sum-in-toc} forces GCC to 17524generate code to calculate the sum of an address and a constant at 17525run time instead of putting that sum into the TOC@. You may specify one 17526or both of these options. Each causes GCC to produce very slightly 17527slower and larger code at the expense of conserving TOC space. 17528 17529If you still run out of space in the TOC even when you specify both of 17530these options, specify @option{-mminimal-toc} instead. This option causes 17531GCC to make only one TOC entry for every file. When you specify this 17532option, GCC produces code that is slower and larger but which 17533uses extremely little TOC space. You may wish to use this option 17534only on files that contain less frequently-executed code. 17535 17536@item -maix64 17537@itemx -maix32 17538@opindex maix64 17539@opindex maix32 17540Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit 17541@code{long} type, and the infrastructure needed to support them. 17542Specifying @option{-maix64} implies @option{-mpowerpc64}, 17543while @option{-maix32} disables the 64-bit ABI and 17544implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. 17545 17546@item -mxl-compat 17547@itemx -mno-xl-compat 17548@opindex mxl-compat 17549@opindex mno-xl-compat 17550Produce code that conforms more closely to IBM XL compiler semantics 17551when using AIX-compatible ABI@. Pass floating-point arguments to 17552prototyped functions beyond the register save area (RSA) on the stack 17553in addition to argument FPRs. Do not assume that most significant 17554double in 128-bit long double value is properly rounded when comparing 17555values and converting to double. Use XL symbol names for long double 17556support routines. 17557 17558The AIX calling convention was extended but not initially documented to 17559handle an obscure K&R C case of calling a function that takes the 17560address of its arguments with fewer arguments than declared. IBM XL 17561compilers access floating-point arguments that do not fit in the 17562RSA from the stack when a subroutine is compiled without 17563optimization. Because always storing floating-point arguments on the 17564stack is inefficient and rarely needed, this option is not enabled by 17565default and only is necessary when calling subroutines compiled by IBM 17566XL compilers without optimization. 17567 17568@item -mpe 17569@opindex mpe 17570Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an 17571application written to use message passing with special startup code to 17572enable the application to run. The system must have PE installed in the 17573standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file 17574must be overridden with the @option{-specs=} option to specify the 17575appropriate directory location. The Parallel Environment does not 17576support threads, so the @option{-mpe} option and the @option{-pthread} 17577option are incompatible. 17578 17579@item -malign-natural 17580@itemx -malign-power 17581@opindex malign-natural 17582@opindex malign-power 17583On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option 17584@option{-malign-natural} overrides the ABI-defined alignment of larger 17585types, such as floating-point doubles, on their natural size-based boundary. 17586The option @option{-malign-power} instructs GCC to follow the ABI-specified 17587alignment rules. GCC defaults to the standard alignment defined in the ABI@. 17588 17589On 64-bit Darwin, natural alignment is the default, and @option{-malign-power} 17590is not supported. 17591 17592@item -msoft-float 17593@itemx -mhard-float 17594@opindex msoft-float 17595@opindex mhard-float 17596Generate code that does not use (uses) the floating-point register set. 17597Software floating-point emulation is provided if you use the 17598@option{-msoft-float} option, and pass the option to GCC when linking. 17599 17600@item -msingle-float 17601@itemx -mdouble-float 17602@opindex msingle-float 17603@opindex mdouble-float 17604Generate code for single- or double-precision floating-point operations. 17605@option{-mdouble-float} implies @option{-msingle-float}. 17606 17607@item -msimple-fpu 17608@opindex msimple-fpu 17609Do not generate @code{sqrt} and @code{div} instructions for hardware 17610floating-point unit. 17611 17612@item -mfpu=@var{name} 17613@opindex mfpu 17614Specify type of floating-point unit. Valid values for @var{name} are 17615@samp{sp_lite} (equivalent to @option{-msingle-float -msimple-fpu}), 17616@samp{dp_lite} (equivalent to @option{-mdouble-float -msimple-fpu}), 17617@samp{sp_full} (equivalent to @option{-msingle-float}), 17618and @samp{dp_full} (equivalent to @option{-mdouble-float}). 17619 17620@item -mxilinx-fpu 17621@opindex mxilinx-fpu 17622Perform optimizations for the floating-point unit on Xilinx PPC 405/440. 17623 17624@item -mmultiple 17625@itemx -mno-multiple 17626@opindex mmultiple 17627@opindex mno-multiple 17628Generate code that uses (does not use) the load multiple word 17629instructions and the store multiple word instructions. These 17630instructions are generated by default on POWER systems, and not 17631generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian 17632PowerPC systems, since those instructions do not work when the 17633processor is in little-endian mode. The exceptions are PPC740 and 17634PPC750 which permit these instructions in little-endian mode. 17635 17636@item -mstring 17637@itemx -mno-string 17638@opindex mstring 17639@opindex mno-string 17640Generate code that uses (does not use) the load string instructions 17641and the store string word instructions to save multiple registers and 17642do small block moves. These instructions are generated by default on 17643POWER systems, and not generated on PowerPC systems. Do not use 17644@option{-mstring} on little-endian PowerPC systems, since those 17645instructions do not work when the processor is in little-endian mode. 17646The exceptions are PPC740 and PPC750 which permit these instructions 17647in little-endian mode. 17648 17649@item -mupdate 17650@itemx -mno-update 17651@opindex mupdate 17652@opindex mno-update 17653Generate code that uses (does not use) the load or store instructions 17654that update the base register to the address of the calculated memory 17655location. These instructions are generated by default. If you use 17656@option{-mno-update}, there is a small window between the time that the 17657stack pointer is updated and the address of the previous frame is 17658stored, which means code that walks the stack frame across interrupts or 17659signals may get corrupted data. 17660 17661@item -mavoid-indexed-addresses 17662@itemx -mno-avoid-indexed-addresses 17663@opindex mavoid-indexed-addresses 17664@opindex mno-avoid-indexed-addresses 17665Generate code that tries to avoid (not avoid) the use of indexed load 17666or store instructions. These instructions can incur a performance 17667penalty on Power6 processors in certain situations, such as when 17668stepping through large arrays that cross a 16M boundary. This option 17669is enabled by default when targeting Power6 and disabled otherwise. 17670 17671@item -mfused-madd 17672@itemx -mno-fused-madd 17673@opindex mfused-madd 17674@opindex mno-fused-madd 17675Generate code that uses (does not use) the floating-point multiply and 17676accumulate instructions. These instructions are generated by default 17677if hardware floating point is used. The machine-dependent 17678@option{-mfused-madd} option is now mapped to the machine-independent 17679@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is 17680mapped to @option{-ffp-contract=off}. 17681 17682@item -mmulhw 17683@itemx -mno-mulhw 17684@opindex mmulhw 17685@opindex mno-mulhw 17686Generate code that uses (does not use) the half-word multiply and 17687multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. 17688These instructions are generated by default when targeting those 17689processors. 17690 17691@item -mdlmzb 17692@itemx -mno-dlmzb 17693@opindex mdlmzb 17694@opindex mno-dlmzb 17695Generate code that uses (does not use) the string-search @samp{dlmzb} 17696instruction on the IBM 405, 440, 464 and 476 processors. This instruction is 17697generated by default when targeting those processors. 17698 17699@item -mno-bit-align 17700@itemx -mbit-align 17701@opindex mno-bit-align 17702@opindex mbit-align 17703On System V.4 and embedded PowerPC systems do not (do) force structures 17704and unions that contain bit-fields to be aligned to the base type of the 17705bit-field. 17706 17707For example, by default a structure containing nothing but 8 17708@code{unsigned} bit-fields of length 1 is aligned to a 4-byte 17709boundary and has a size of 4 bytes. By using @option{-mno-bit-align}, 17710the structure is aligned to a 1-byte boundary and is 1 byte in 17711size. 17712 17713@item -mno-strict-align 17714@itemx -mstrict-align 17715@opindex mno-strict-align 17716@opindex mstrict-align 17717On System V.4 and embedded PowerPC systems do not (do) assume that 17718unaligned memory references are handled by the system. 17719 17720@item -mrelocatable 17721@itemx -mno-relocatable 17722@opindex mrelocatable 17723@opindex mno-relocatable 17724Generate code that allows (does not allow) a static executable to be 17725relocated to a different address at run time. A simple embedded 17726PowerPC system loader should relocate the entire contents of 17727@code{.got2} and 4-byte locations listed in the @code{.fixup} section, 17728a table of 32-bit addresses generated by this option. For this to 17729work, all objects linked together must be compiled with 17730@option{-mrelocatable} or @option{-mrelocatable-lib}. 17731@option{-mrelocatable} code aligns the stack to an 8-byte boundary. 17732 17733@item -mrelocatable-lib 17734@itemx -mno-relocatable-lib 17735@opindex mrelocatable-lib 17736@opindex mno-relocatable-lib 17737Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a 17738@code{.fixup} section to allow static executables to be relocated at 17739run time, but @option{-mrelocatable-lib} does not use the smaller stack 17740alignment of @option{-mrelocatable}. Objects compiled with 17741@option{-mrelocatable-lib} may be linked with objects compiled with 17742any combination of the @option{-mrelocatable} options. 17743 17744@item -mno-toc 17745@itemx -mtoc 17746@opindex mno-toc 17747@opindex mtoc 17748On System V.4 and embedded PowerPC systems do not (do) assume that 17749register 2 contains a pointer to a global area pointing to the addresses 17750used in the program. 17751 17752@item -mlittle 17753@itemx -mlittle-endian 17754@opindex mlittle 17755@opindex mlittle-endian 17756On System V.4 and embedded PowerPC systems compile code for the 17757processor in little-endian mode. The @option{-mlittle-endian} option is 17758the same as @option{-mlittle}. 17759 17760@item -mbig 17761@itemx -mbig-endian 17762@opindex mbig 17763@opindex mbig-endian 17764On System V.4 and embedded PowerPC systems compile code for the 17765processor in big-endian mode. The @option{-mbig-endian} option is 17766the same as @option{-mbig}. 17767 17768@item -mdynamic-no-pic 17769@opindex mdynamic-no-pic 17770On Darwin and Mac OS X systems, compile code so that it is not 17771relocatable, but that its external references are relocatable. The 17772resulting code is suitable for applications, but not shared 17773libraries. 17774 17775@item -msingle-pic-base 17776@opindex msingle-pic-base 17777Treat the register used for PIC addressing as read-only, rather than 17778loading it in the prologue for each function. The runtime system is 17779responsible for initializing this register with an appropriate value 17780before execution begins. 17781 17782@item -mprioritize-restricted-insns=@var{priority} 17783@opindex mprioritize-restricted-insns 17784This option controls the priority that is assigned to 17785dispatch-slot restricted instructions during the second scheduling 17786pass. The argument @var{priority} takes the value @samp{0}, @samp{1}, 17787or @samp{2} to assign no, highest, or second-highest (respectively) 17788priority to dispatch-slot restricted 17789instructions. 17790 17791@item -msched-costly-dep=@var{dependence_type} 17792@opindex msched-costly-dep 17793This option controls which dependences are considered costly 17794by the target during instruction scheduling. The argument 17795@var{dependence_type} takes one of the following values: 17796 17797@table @asis 17798@item @samp{no} 17799No dependence is costly. 17800 17801@item @samp{all} 17802All dependences are costly. 17803 17804@item @samp{true_store_to_load} 17805A true dependence from store to load is costly. 17806 17807@item @samp{store_to_load} 17808Any dependence from store to load is costly. 17809 17810@item @var{number} 17811Any dependence for which the latency is greater than or equal to 17812@var{number} is costly. 17813@end table 17814 17815@item -minsert-sched-nops=@var{scheme} 17816@opindex minsert-sched-nops 17817This option controls which NOP insertion scheme is used during 17818the second scheduling pass. The argument @var{scheme} takes one of the 17819following values: 17820 17821@table @asis 17822@item @samp{no} 17823Don't insert NOPs. 17824 17825@item @samp{pad} 17826Pad with NOPs any dispatch group that has vacant issue slots, 17827according to the scheduler's grouping. 17828 17829@item @samp{regroup_exact} 17830Insert NOPs to force costly dependent insns into 17831separate groups. Insert exactly as many NOPs as needed to force an insn 17832to a new group, according to the estimated processor grouping. 17833 17834@item @var{number} 17835Insert NOPs to force costly dependent insns into 17836separate groups. Insert @var{number} NOPs to force an insn to a new group. 17837@end table 17838 17839@item -mcall-sysv 17840@opindex mcall-sysv 17841On System V.4 and embedded PowerPC systems compile code using calling 17842conventions that adhere to the March 1995 draft of the System V 17843Application Binary Interface, PowerPC processor supplement. This is the 17844default unless you configured GCC using @samp{powerpc-*-eabiaix}. 17845 17846@item -mcall-sysv-eabi 17847@itemx -mcall-eabi 17848@opindex mcall-sysv-eabi 17849@opindex mcall-eabi 17850Specify both @option{-mcall-sysv} and @option{-meabi} options. 17851 17852@item -mcall-sysv-noeabi 17853@opindex mcall-sysv-noeabi 17854Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. 17855 17856@item -mcall-aixdesc 17857@opindex m 17858On System V.4 and embedded PowerPC systems compile code for the AIX 17859operating system. 17860 17861@item -mcall-linux 17862@opindex mcall-linux 17863On System V.4 and embedded PowerPC systems compile code for the 17864Linux-based GNU system. 17865 17866@item -mcall-freebsd 17867@opindex mcall-freebsd 17868On System V.4 and embedded PowerPC systems compile code for the 17869FreeBSD operating system. 17870 17871@item -mcall-netbsd 17872@opindex mcall-netbsd 17873On System V.4 and embedded PowerPC systems compile code for the 17874NetBSD operating system. 17875 17876@item -mcall-openbsd 17877@opindex mcall-netbsd 17878On System V.4 and embedded PowerPC systems compile code for the 17879OpenBSD operating system. 17880 17881@item -maix-struct-return 17882@opindex maix-struct-return 17883Return all structures in memory (as specified by the AIX ABI)@. 17884 17885@item -msvr4-struct-return 17886@opindex msvr4-struct-return 17887Return structures smaller than 8 bytes in registers (as specified by the 17888SVR4 ABI)@. 17889 17890@item -mabi=@var{abi-type} 17891@opindex mabi 17892Extend the current ABI with a particular extension, or remove such extension. 17893Valid values are @var{altivec}, @var{no-altivec}, @var{spe}, 17894@var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}, 17895@var{elfv1}, @var{elfv2}@. 17896 17897@item -mabi=spe 17898@opindex mabi=spe 17899Extend the current ABI with SPE ABI extensions. This does not change 17900the default ABI, instead it adds the SPE ABI extensions to the current 17901ABI@. 17902 17903@item -mabi=no-spe 17904@opindex mabi=no-spe 17905Disable Book-E SPE ABI extensions for the current ABI@. 17906 17907@item -mabi=ibmlongdouble 17908@opindex mabi=ibmlongdouble 17909Change the current ABI to use IBM extended-precision long double. 17910This is a PowerPC 32-bit SYSV ABI option. 17911 17912@item -mabi=ieeelongdouble 17913@opindex mabi=ieeelongdouble 17914Change the current ABI to use IEEE extended-precision long double. 17915This is a PowerPC 32-bit Linux ABI option. 17916 17917@item -mabi=elfv1 17918@opindex mabi=elfv1 17919Change the current ABI to use the ELFv1 ABI. 17920This is the default ABI for big-endian PowerPC 64-bit Linux. 17921Overriding the default ABI requires special system support and is 17922likely to fail in spectacular ways. 17923 17924@item -mabi=elfv2 17925@opindex mabi=elfv2 17926Change the current ABI to use the ELFv2 ABI. 17927This is the default ABI for little-endian PowerPC 64-bit Linux. 17928Overriding the default ABI requires special system support and is 17929likely to fail in spectacular ways. 17930 17931@item -mprototype 17932@itemx -mno-prototype 17933@opindex mprototype 17934@opindex mno-prototype 17935On System V.4 and embedded PowerPC systems assume that all calls to 17936variable argument functions are properly prototyped. Otherwise, the 17937compiler must insert an instruction before every non-prototyped call to 17938set or clear bit 6 of the condition code register (@var{CR}) to 17939indicate whether floating-point values are passed in the floating-point 17940registers in case the function takes variable arguments. With 17941@option{-mprototype}, only calls to prototyped variable argument functions 17942set or clear the bit. 17943 17944@item -msim 17945@opindex msim 17946On embedded PowerPC systems, assume that the startup module is called 17947@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and 17948@file{libc.a}. This is the default for @samp{powerpc-*-eabisim} 17949configurations. 17950 17951@item -mmvme 17952@opindex mmvme 17953On embedded PowerPC systems, assume that the startup module is called 17954@file{crt0.o} and the standard C libraries are @file{libmvme.a} and 17955@file{libc.a}. 17956 17957@item -mads 17958@opindex mads 17959On embedded PowerPC systems, assume that the startup module is called 17960@file{crt0.o} and the standard C libraries are @file{libads.a} and 17961@file{libc.a}. 17962 17963@item -myellowknife 17964@opindex myellowknife 17965On embedded PowerPC systems, assume that the startup module is called 17966@file{crt0.o} and the standard C libraries are @file{libyk.a} and 17967@file{libc.a}. 17968 17969@item -mvxworks 17970@opindex mvxworks 17971On System V.4 and embedded PowerPC systems, specify that you are 17972compiling for a VxWorks system. 17973 17974@item -memb 17975@opindex memb 17976On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags 17977header to indicate that @samp{eabi} extended relocations are used. 17978 17979@item -meabi 17980@itemx -mno-eabi 17981@opindex meabi 17982@opindex mno-eabi 17983On System V.4 and embedded PowerPC systems do (do not) adhere to the 17984Embedded Applications Binary Interface (EABI), which is a set of 17985modifications to the System V.4 specifications. Selecting @option{-meabi} 17986means that the stack is aligned to an 8-byte boundary, a function 17987@code{__eabi} is called from @code{main} to set up the EABI 17988environment, and the @option{-msdata} option can use both @code{r2} and 17989@code{r13} to point to two separate small data areas. Selecting 17990@option{-mno-eabi} means that the stack is aligned to a 16-byte boundary, 17991no EABI initialization function is called from @code{main}, and the 17992@option{-msdata} option only uses @code{r13} to point to a single 17993small data area. The @option{-meabi} option is on by default if you 17994configured GCC using one of the @samp{powerpc*-*-eabi*} options. 17995 17996@item -msdata=eabi 17997@opindex msdata=eabi 17998On System V.4 and embedded PowerPC systems, put small initialized 17999@code{const} global and static data in the @samp{.sdata2} section, which 18000is pointed to by register @code{r2}. Put small initialized 18001non-@code{const} global and static data in the @samp{.sdata} section, 18002which is pointed to by register @code{r13}. Put small uninitialized 18003global and static data in the @samp{.sbss} section, which is adjacent to 18004the @samp{.sdata} section. The @option{-msdata=eabi} option is 18005incompatible with the @option{-mrelocatable} option. The 18006@option{-msdata=eabi} option also sets the @option{-memb} option. 18007 18008@item -msdata=sysv 18009@opindex msdata=sysv 18010On System V.4 and embedded PowerPC systems, put small global and static 18011data in the @samp{.sdata} section, which is pointed to by register 18012@code{r13}. Put small uninitialized global and static data in the 18013@samp{.sbss} section, which is adjacent to the @samp{.sdata} section. 18014The @option{-msdata=sysv} option is incompatible with the 18015@option{-mrelocatable} option. 18016 18017@item -msdata=default 18018@itemx -msdata 18019@opindex msdata=default 18020@opindex msdata 18021On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, 18022compile code the same as @option{-msdata=eabi}, otherwise compile code the 18023same as @option{-msdata=sysv}. 18024 18025@item -msdata=data 18026@opindex msdata=data 18027On System V.4 and embedded PowerPC systems, put small global 18028data in the @samp{.sdata} section. Put small uninitialized global 18029data in the @samp{.sbss} section. Do not use register @code{r13} 18030to address small data however. This is the default behavior unless 18031other @option{-msdata} options are used. 18032 18033@item -msdata=none 18034@itemx -mno-sdata 18035@opindex msdata=none 18036@opindex mno-sdata 18037On embedded PowerPC systems, put all initialized global and static data 18038in the @samp{.data} section, and all uninitialized data in the 18039@samp{.bss} section. 18040 18041@item -mblock-move-inline-limit=@var{num} 18042@opindex mblock-move-inline-limit 18043Inline all block moves (such as calls to @code{memcpy} or structure 18044copies) less than or equal to @var{num} bytes. The minimum value for 18045@var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit 18046targets. The default value is target-specific. 18047 18048@item -G @var{num} 18049@opindex G 18050@cindex smaller data references (PowerPC) 18051@cindex .sdata/.sdata2 references (PowerPC) 18052On embedded PowerPC systems, put global and static items less than or 18053equal to @var{num} bytes into the small data or BSS sections instead of 18054the normal data or BSS section. By default, @var{num} is 8. The 18055@option{-G @var{num}} switch is also passed to the linker. 18056All modules should be compiled with the same @option{-G @var{num}} value. 18057 18058@item -mregnames 18059@itemx -mno-regnames 18060@opindex mregnames 18061@opindex mno-regnames 18062On System V.4 and embedded PowerPC systems do (do not) emit register 18063names in the assembly language output using symbolic forms. 18064 18065@item -mlongcall 18066@itemx -mno-longcall 18067@opindex mlongcall 18068@opindex mno-longcall 18069By default assume that all calls are far away so that a longer and more 18070expensive calling sequence is required. This is required for calls 18071farther than 32 megabytes (33,554,432 bytes) from the current location. 18072A short call is generated if the compiler knows 18073the call cannot be that far away. This setting can be overridden by 18074the @code{shortcall} function attribute, or by @code{#pragma 18075longcall(0)}. 18076 18077Some linkers are capable of detecting out-of-range calls and generating 18078glue code on the fly. On these systems, long calls are unnecessary and 18079generate slower code. As of this writing, the AIX linker can do this, 18080as can the GNU linker for PowerPC/64. It is planned to add this feature 18081to the GNU linker for 32-bit PowerPC systems as well. 18082 18083On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr 18084callee, L42}, plus a @dfn{branch island} (glue code). The two target 18085addresses represent the callee and the branch island. The 18086Darwin/PPC linker prefers the first address and generates a @code{bl 18087callee} if the PPC @code{bl} instruction reaches the callee directly; 18088otherwise, the linker generates @code{bl L42} to call the branch 18089island. The branch island is appended to the body of the 18090calling function; it computes the full 32-bit address of the callee 18091and jumps to it. 18092 18093On Mach-O (Darwin) systems, this option directs the compiler emit to 18094the glue for every direct call, and the Darwin linker decides whether 18095to use or discard it. 18096 18097In the future, GCC may ignore all longcall specifications 18098when the linker is known to generate glue. 18099 18100@item -mtls-markers 18101@itemx -mno-tls-markers 18102@opindex mtls-markers 18103@opindex mno-tls-markers 18104Mark (do not mark) calls to @code{__tls_get_addr} with a relocation 18105specifying the function argument. The relocation allows the linker to 18106reliably associate function call with argument setup instructions for 18107TLS optimization, which in turn allows GCC to better schedule the 18108sequence. 18109 18110@item -pthread 18111@opindex pthread 18112Adds support for multithreading with the @dfn{pthreads} library. 18113This option sets flags for both the preprocessor and linker. 18114 18115@item -mrecip 18116@itemx -mno-recip 18117@opindex mrecip 18118This option enables use of the reciprocal estimate and 18119reciprocal square root estimate instructions with additional 18120Newton-Raphson steps to increase precision instead of doing a divide or 18121square root and divide for floating-point arguments. You should use 18122the @option{-ffast-math} option when using @option{-mrecip} (or at 18123least @option{-funsafe-math-optimizations}, 18124@option{-finite-math-only}, @option{-freciprocal-math} and 18125@option{-fno-trapping-math}). Note that while the throughput of the 18126sequence is generally higher than the throughput of the non-reciprocal 18127instruction, the precision of the sequence can be decreased by up to 2 18128ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square 18129roots. 18130 18131@item -mrecip=@var{opt} 18132@opindex mrecip=opt 18133This option controls which reciprocal estimate instructions 18134may be used. @var{opt} is a comma-separated list of options, which may 18135be preceded by a @code{!} to invert the option: 18136@code{all}: enable all estimate instructions, 18137@code{default}: enable the default instructions, equivalent to @option{-mrecip}, 18138@code{none}: disable all estimate instructions, equivalent to @option{-mno-recip}; 18139@code{div}: enable the reciprocal approximation instructions for both single and double precision; 18140@code{divf}: enable the single-precision reciprocal approximation instructions; 18141@code{divd}: enable the double-precision reciprocal approximation instructions; 18142@code{rsqrt}: enable the reciprocal square root approximation instructions for both single and double precision; 18143@code{rsqrtf}: enable the single-precision reciprocal square root approximation instructions; 18144@code{rsqrtd}: enable the double-precision reciprocal square root approximation instructions; 18145 18146So, for example, @option{-mrecip=all,!rsqrtd} enables 18147all of the reciprocal estimate instructions, except for the 18148@code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions 18149which handle the double-precision reciprocal square root calculations. 18150 18151@item -mrecip-precision 18152@itemx -mno-recip-precision 18153@opindex mrecip-precision 18154Assume (do not assume) that the reciprocal estimate instructions 18155provide higher-precision estimates than is mandated by the PowerPC 18156ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or 18157@option{-mcpu=power8} automatically selects @option{-mrecip-precision}. 18158The double-precision square root estimate instructions are not generated by 18159default on low-precision machines, since they do not provide an 18160estimate that converges after three steps. 18161 18162@item -mveclibabi=@var{type} 18163@opindex mveclibabi 18164Specifies the ABI type to use for vectorizing intrinsics using an 18165external library. The only type supported at present is @code{mass}, 18166which specifies to use IBM's Mathematical Acceleration Subsystem 18167(MASS) libraries for vectorizing intrinsics using external libraries. 18168GCC currently emits calls to @code{acosd2}, @code{acosf4}, 18169@code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4}, 18170@code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4}, 18171@code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4}, 18172@code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4}, 18173@code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4}, 18174@code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4}, 18175@code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4}, 18176@code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4}, 18177@code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4}, 18178@code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4}, 18179@code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2}, 18180@code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2}, 18181@code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code 18182for power7. Both @option{-ftree-vectorize} and 18183@option{-funsafe-math-optimizations} must also be enabled. The MASS 18184libraries must be specified at link time. 18185 18186@item -mfriz 18187@itemx -mno-friz 18188@opindex mfriz 18189Generate (do not generate) the @code{friz} instruction when the 18190@option{-funsafe-math-optimizations} option is used to optimize 18191rounding of floating-point values to 64-bit integer and back to floating 18192point. The @code{friz} instruction does not return the same value if 18193the floating-point number is too large to fit in an integer. 18194 18195@item -mpointers-to-nested-functions 18196@itemx -mno-pointers-to-nested-functions 18197@opindex mpointers-to-nested-functions 18198Generate (do not generate) code to load up the static chain register 18199(@var{r11}) when calling through a pointer on AIX and 64-bit Linux 18200systems where a function pointer points to a 3-word descriptor giving 18201the function address, TOC value to be loaded in register @var{r2}, and 18202static chain value to be loaded in register @var{r11}. The 18203@option{-mpointers-to-nested-functions} is on by default. You cannot 18204call through pointers to nested functions or pointers 18205to functions compiled in other languages that use the static chain if 18206you use the @option{-mno-pointers-to-nested-functions}. 18207 18208@item -msave-toc-indirect 18209@itemx -mno-save-toc-indirect 18210@opindex msave-toc-indirect 18211Generate (do not generate) code to save the TOC value in the reserved 18212stack location in the function prologue if the function calls through 18213a pointer on AIX and 64-bit Linux systems. If the TOC value is not 18214saved in the prologue, it is saved just before the call through the 18215pointer. The @option{-mno-save-toc-indirect} option is the default. 18216 18217@item -mcompat-align-parm 18218@itemx -mno-compat-align-parm 18219@opindex mcompat-align-parm 18220Generate (do not generate) code to pass structure parameters with a 18221maximum alignment of 64 bits, for compatibility with older versions 18222of GCC. 18223 18224Older versions of GCC (prior to 4.9.0) incorrectly did not align a 18225structure parameter on a 128-bit boundary when that structure contained 18226a member requiring 128-bit alignment. This is corrected in more 18227recent versions of GCC. This option may be used to generate code 18228that is compatible with functions compiled with older versions of 18229GCC. 18230 18231In this version of the compiler, the @option{-mcompat-align-parm} 18232is the default, except when using the Linux ELFv2 ABI. 18233@end table 18234 18235@node RX Options 18236@subsection RX Options 18237@cindex RX Options 18238 18239These command-line options are defined for RX targets: 18240 18241@table @gcctabopt 18242@item -m64bit-doubles 18243@itemx -m32bit-doubles 18244@opindex m64bit-doubles 18245@opindex m32bit-doubles 18246Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) 18247or 32 bits (@option{-m32bit-doubles}) in size. The default is 18248@option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only 18249works on 32-bit values, which is why the default is 18250@option{-m32bit-doubles}. 18251 18252@item -fpu 18253@itemx -nofpu 18254@opindex fpu 18255@opindex nofpu 18256Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX 18257floating-point hardware. The default is enabled for the @var{RX600} 18258series and disabled for the @var{RX200} series. 18259 18260Floating-point instructions are only generated for 32-bit floating-point 18261values, however, so the FPU hardware is not used for doubles if the 18262@option{-m64bit-doubles} option is used. 18263 18264@emph{Note} If the @option{-fpu} option is enabled then 18265@option{-funsafe-math-optimizations} is also enabled automatically. 18266This is because the RX FPU instructions are themselves unsafe. 18267 18268@item -mcpu=@var{name} 18269@opindex -mcpu 18270Selects the type of RX CPU to be targeted. Currently three types are 18271supported, the generic @var{RX600} and @var{RX200} series hardware and 18272the specific @var{RX610} CPU. The default is @var{RX600}. 18273 18274The only difference between @var{RX600} and @var{RX610} is that the 18275@var{RX610} does not support the @code{MVTIPL} instruction. 18276 18277The @var{RX200} series does not have a hardware floating-point unit 18278and so @option{-nofpu} is enabled by default when this type is 18279selected. 18280 18281@item -mbig-endian-data 18282@itemx -mlittle-endian-data 18283@opindex mbig-endian-data 18284@opindex mlittle-endian-data 18285Store data (but not code) in the big-endian format. The default is 18286@option{-mlittle-endian-data}, i.e.@: to store data in the little-endian 18287format. 18288 18289@item -msmall-data-limit=@var{N} 18290@opindex msmall-data-limit 18291Specifies the maximum size in bytes of global and static variables 18292which can be placed into the small data area. Using the small data 18293area can lead to smaller and faster code, but the size of area is 18294limited and it is up to the programmer to ensure that the area does 18295not overflow. Also when the small data area is used one of the RX's 18296registers (usually @code{r13}) is reserved for use pointing to this 18297area, so it is no longer available for use by the compiler. This 18298could result in slower and/or larger code if variables are pushed onto 18299the stack instead of being held in this register. 18300 18301Note, common variables (variables that have not been initialized) and 18302constants are not placed into the small data area as they are assigned 18303to other sections in the output executable. 18304 18305The default value is zero, which disables this feature. Note, this 18306feature is not enabled by default with higher optimization levels 18307(@option{-O2} etc) because of the potentially detrimental effects of 18308reserving a register. It is up to the programmer to experiment and 18309discover whether this feature is of benefit to their program. See the 18310description of the @option{-mpid} option for a description of how the 18311actual register to hold the small data area pointer is chosen. 18312 18313@item -msim 18314@itemx -mno-sim 18315@opindex msim 18316@opindex mno-sim 18317Use the simulator runtime. The default is to use the libgloss 18318board-specific runtime. 18319 18320@item -mas100-syntax 18321@itemx -mno-as100-syntax 18322@opindex mas100-syntax 18323@opindex mno-as100-syntax 18324When generating assembler output use a syntax that is compatible with 18325Renesas's AS100 assembler. This syntax can also be handled by the GAS 18326assembler, but it has some restrictions so it is not generated by default. 18327 18328@item -mmax-constant-size=@var{N} 18329@opindex mmax-constant-size 18330Specifies the maximum size, in bytes, of a constant that can be used as 18331an operand in a RX instruction. Although the RX instruction set does 18332allow constants of up to 4 bytes in length to be used in instructions, 18333a longer value equates to a longer instruction. Thus in some 18334circumstances it can be beneficial to restrict the size of constants 18335that are used in instructions. Constants that are too big are instead 18336placed into a constant pool and referenced via register indirection. 18337 18338The value @var{N} can be between 0 and 4. A value of 0 (the default) 18339or 4 means that constants of any size are allowed. 18340 18341@item -mrelax 18342@opindex mrelax 18343Enable linker relaxation. Linker relaxation is a process whereby the 18344linker attempts to reduce the size of a program by finding shorter 18345versions of various instructions. Disabled by default. 18346 18347@item -mint-register=@var{N} 18348@opindex mint-register 18349Specify the number of registers to reserve for fast interrupt handler 18350functions. The value @var{N} can be between 0 and 4. A value of 1 18351means that register @code{r13} is reserved for the exclusive use 18352of fast interrupt handlers. A value of 2 reserves @code{r13} and 18353@code{r12}. A value of 3 reserves @code{r13}, @code{r12} and 18354@code{r11}, and a value of 4 reserves @code{r13} through @code{r10}. 18355A value of 0, the default, does not reserve any registers. 18356 18357@item -msave-acc-in-interrupts 18358@opindex msave-acc-in-interrupts 18359Specifies that interrupt handler functions should preserve the 18360accumulator register. This is only necessary if normal code might use 18361the accumulator register, for example because it performs 64-bit 18362multiplications. The default is to ignore the accumulator as this 18363makes the interrupt handlers faster. 18364 18365@item -mpid 18366@itemx -mno-pid 18367@opindex mpid 18368@opindex mno-pid 18369Enables the generation of position independent data. When enabled any 18370access to constant data is done via an offset from a base address 18371held in a register. This allows the location of constant data to be 18372determined at run time without requiring the executable to be 18373relocated, which is a benefit to embedded applications with tight 18374memory constraints. Data that can be modified is not affected by this 18375option. 18376 18377Note, using this feature reserves a register, usually @code{r13}, for 18378the constant data base address. This can result in slower and/or 18379larger code, especially in complicated functions. 18380 18381The actual register chosen to hold the constant data base address 18382depends upon whether the @option{-msmall-data-limit} and/or the 18383@option{-mint-register} command-line options are enabled. Starting 18384with register @code{r13} and proceeding downwards, registers are 18385allocated first to satisfy the requirements of @option{-mint-register}, 18386then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it 18387is possible for the small data area register to be @code{r8} if both 18388@option{-mint-register=4} and @option{-mpid} are specified on the 18389command line. 18390 18391By default this feature is not enabled. The default can be restored 18392via the @option{-mno-pid} command-line option. 18393 18394@item -mno-warn-multiple-fast-interrupts 18395@itemx -mwarn-multiple-fast-interrupts 18396@opindex mno-warn-multiple-fast-interrupts 18397@opindex mwarn-multiple-fast-interrupts 18398Prevents GCC from issuing a warning message if it finds more than one 18399fast interrupt handler when it is compiling a file. The default is to 18400issue a warning for each extra fast interrupt handler found, as the RX 18401only supports one such interrupt. 18402 18403@end table 18404 18405@emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}} 18406has special significance to the RX port when used with the 18407@code{interrupt} function attribute. This attribute indicates a 18408function intended to process fast interrupts. GCC ensures 18409that it only uses the registers @code{r10}, @code{r11}, @code{r12} 18410and/or @code{r13} and only provided that the normal use of the 18411corresponding registers have been restricted via the 18412@option{-ffixed-@var{reg}} or @option{-mint-register} command-line 18413options. 18414 18415@node S/390 and zSeries Options 18416@subsection S/390 and zSeries Options 18417@cindex S/390 and zSeries Options 18418 18419These are the @samp{-m} options defined for the S/390 and zSeries architecture. 18420 18421@table @gcctabopt 18422@item -mhard-float 18423@itemx -msoft-float 18424@opindex mhard-float 18425@opindex msoft-float 18426Use (do not use) the hardware floating-point instructions and registers 18427for floating-point operations. When @option{-msoft-float} is specified, 18428functions in @file{libgcc.a} are used to perform floating-point 18429operations. When @option{-mhard-float} is specified, the compiler 18430generates IEEE floating-point instructions. This is the default. 18431 18432@item -mhard-dfp 18433@itemx -mno-hard-dfp 18434@opindex mhard-dfp 18435@opindex mno-hard-dfp 18436Use (do not use) the hardware decimal-floating-point instructions for 18437decimal-floating-point operations. When @option{-mno-hard-dfp} is 18438specified, functions in @file{libgcc.a} are used to perform 18439decimal-floating-point operations. When @option{-mhard-dfp} is 18440specified, the compiler generates decimal-floating-point hardware 18441instructions. This is the default for @option{-march=z9-ec} or higher. 18442 18443@item -mlong-double-64 18444@itemx -mlong-double-128 18445@opindex mlong-double-64 18446@opindex mlong-double-128 18447These switches control the size of @code{long double} type. A size 18448of 64 bits makes the @code{long double} type equivalent to the @code{double} 18449type. This is the default. 18450 18451@item -mbackchain 18452@itemx -mno-backchain 18453@opindex mbackchain 18454@opindex mno-backchain 18455Store (do not store) the address of the caller's frame as backchain pointer 18456into the callee's stack frame. 18457A backchain may be needed to allow debugging using tools that do not understand 18458DWARF 2 call frame information. 18459When @option{-mno-packed-stack} is in effect, the backchain pointer is stored 18460at the bottom of the stack frame; when @option{-mpacked-stack} is in effect, 18461the backchain is placed into the topmost word of the 96/160 byte register 18462save area. 18463 18464In general, code compiled with @option{-mbackchain} is call-compatible with 18465code compiled with @option{-mmo-backchain}; however, use of the backchain 18466for debugging purposes usually requires that the whole binary is built with 18467@option{-mbackchain}. Note that the combination of @option{-mbackchain}, 18468@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order 18469to build a linux kernel use @option{-msoft-float}. 18470 18471The default is to not maintain the backchain. 18472 18473@item -mpacked-stack 18474@itemx -mno-packed-stack 18475@opindex mpacked-stack 18476@opindex mno-packed-stack 18477Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is 18478specified, the compiler uses the all fields of the 96/160 byte register save 18479area only for their default purpose; unused fields still take up stack space. 18480When @option{-mpacked-stack} is specified, register save slots are densely 18481packed at the top of the register save area; unused space is reused for other 18482purposes, allowing for more efficient use of the available stack space. 18483However, when @option{-mbackchain} is also in effect, the topmost word of 18484the save area is always used to store the backchain, and the return address 18485register is always saved two words below the backchain. 18486 18487As long as the stack frame backchain is not used, code generated with 18488@option{-mpacked-stack} is call-compatible with code generated with 18489@option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for 18490S/390 or zSeries generated code that uses the stack frame backchain at run 18491time, not just for debugging purposes. Such code is not call-compatible 18492with code compiled with @option{-mpacked-stack}. Also, note that the 18493combination of @option{-mbackchain}, 18494@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order 18495to build a linux kernel use @option{-msoft-float}. 18496 18497The default is to not use the packed stack layout. 18498 18499@item -msmall-exec 18500@itemx -mno-small-exec 18501@opindex msmall-exec 18502@opindex mno-small-exec 18503Generate (or do not generate) code using the @code{bras} instruction 18504to do subroutine calls. 18505This only works reliably if the total executable size does not 18506exceed 64k. The default is to use the @code{basr} instruction instead, 18507which does not have this limitation. 18508 18509@item -m64 18510@itemx -m31 18511@opindex m64 18512@opindex m31 18513When @option{-m31} is specified, generate code compliant to the 18514GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate 18515code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in 18516particular to generate 64-bit instructions. For the @samp{s390} 18517targets, the default is @option{-m31}, while the @samp{s390x} 18518targets default to @option{-m64}. 18519 18520@item -mzarch 18521@itemx -mesa 18522@opindex mzarch 18523@opindex mesa 18524When @option{-mzarch} is specified, generate code using the 18525instructions available on z/Architecture. 18526When @option{-mesa} is specified, generate code using the 18527instructions available on ESA/390. Note that @option{-mesa} is 18528not possible with @option{-m64}. 18529When generating code compliant to the GNU/Linux for S/390 ABI, 18530the default is @option{-mesa}. When generating code compliant 18531to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}. 18532 18533@item -mmvcle 18534@itemx -mno-mvcle 18535@opindex mmvcle 18536@opindex mno-mvcle 18537Generate (or do not generate) code using the @code{mvcle} instruction 18538to perform block moves. When @option{-mno-mvcle} is specified, 18539use a @code{mvc} loop instead. This is the default unless optimizing for 18540size. 18541 18542@item -mdebug 18543@itemx -mno-debug 18544@opindex mdebug 18545@opindex mno-debug 18546Print (or do not print) additional debug information when compiling. 18547The default is to not print debug information. 18548 18549@item -march=@var{cpu-type} 18550@opindex march 18551Generate code that runs on @var{cpu-type}, which is the name of a system 18552representing a certain processor type. Possible values for 18553@var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990}, 18554@samp{z9-109}, @samp{z9-ec}, @samp{z10}, @samp{z196}, and @samp{zEC12}. 18555When generating code using the instructions available on z/Architecture, 18556the default is @option{-march=z900}. Otherwise, the default is 18557@option{-march=g5}. 18558 18559@item -mtune=@var{cpu-type} 18560@opindex mtune 18561Tune to @var{cpu-type} everything applicable about the generated code, 18562except for the ABI and the set of available instructions. 18563The list of @var{cpu-type} values is the same as for @option{-march}. 18564The default is the value used for @option{-march}. 18565 18566@item -mtpf-trace 18567@itemx -mno-tpf-trace 18568@opindex mtpf-trace 18569@opindex mno-tpf-trace 18570Generate code that adds (does not add) in TPF OS specific branches to trace 18571routines in the operating system. This option is off by default, even 18572when compiling for the TPF OS@. 18573 18574@item -mfused-madd 18575@itemx -mno-fused-madd 18576@opindex mfused-madd 18577@opindex mno-fused-madd 18578Generate code that uses (does not use) the floating-point multiply and 18579accumulate instructions. These instructions are generated by default if 18580hardware floating point is used. 18581 18582@item -mwarn-framesize=@var{framesize} 18583@opindex mwarn-framesize 18584Emit a warning if the current function exceeds the given frame size. Because 18585this is a compile-time check it doesn't need to be a real problem when the program 18586runs. It is intended to identify functions that most probably cause 18587a stack overflow. It is useful to be used in an environment with limited stack 18588size e.g.@: the linux kernel. 18589 18590@item -mwarn-dynamicstack 18591@opindex mwarn-dynamicstack 18592Emit a warning if the function calls @code{alloca} or uses dynamically-sized 18593arrays. This is generally a bad idea with a limited stack size. 18594 18595@item -mstack-guard=@var{stack-guard} 18596@itemx -mstack-size=@var{stack-size} 18597@opindex mstack-guard 18598@opindex mstack-size 18599If these options are provided the S/390 back end emits additional instructions in 18600the function prologue that trigger a trap if the stack size is @var{stack-guard} 18601bytes above the @var{stack-size} (remember that the stack on S/390 grows downward). 18602If the @var{stack-guard} option is omitted the smallest power of 2 larger than 18603the frame size of the compiled function is chosen. 18604These options are intended to be used to help debugging stack overflow problems. 18605The additionally emitted code causes only little overhead and hence can also be 18606used in production-like systems without greater performance degradation. The given 18607values have to be exact powers of 2 and @var{stack-size} has to be greater than 18608@var{stack-guard} without exceeding 64k. 18609In order to be efficient the extra code makes the assumption that the stack starts 18610at an address aligned to the value given by @var{stack-size}. 18611The @var{stack-guard} option can only be used in conjunction with @var{stack-size}. 18612 18613@item -mhotpatch=@var{pre-halfwords},@var{post-halfwords} 18614@opindex mhotpatch 18615If the hotpatch option is enabled, a ``hot-patching'' function 18616prologue is generated for all functions in the compilation unit. 18617The funtion label is prepended with the given number of two-byte 18618NOP instructions (@var{pre-halfwords}, maximum 1000000). After 18619the label, 2 * @var{post-halfwords} bytes are appended, using the 18620largest NOP like instructions the architecture allows (maximum 186211000000). 18622 18623If both arguments are zero, hotpatching is disabled. 18624 18625This option can be overridden for individual functions with the 18626@code{hotpatch} attribute. 18627@end table 18628 18629@node Score Options 18630@subsection Score Options 18631@cindex Score Options 18632 18633These options are defined for Score implementations: 18634 18635@table @gcctabopt 18636@item -meb 18637@opindex meb 18638Compile code for big-endian mode. This is the default. 18639 18640@item -mel 18641@opindex mel 18642Compile code for little-endian mode. 18643 18644@item -mnhwloop 18645@opindex mnhwloop 18646Disable generation of @code{bcnz} instructions. 18647 18648@item -muls 18649@opindex muls 18650Enable generation of unaligned load and store instructions. 18651 18652@item -mmac 18653@opindex mmac 18654Enable the use of multiply-accumulate instructions. Disabled by default. 18655 18656@item -mscore5 18657@opindex mscore5 18658Specify the SCORE5 as the target architecture. 18659 18660@item -mscore5u 18661@opindex mscore5u 18662Specify the SCORE5U of the target architecture. 18663 18664@item -mscore7 18665@opindex mscore7 18666Specify the SCORE7 as the target architecture. This is the default. 18667 18668@item -mscore7d 18669@opindex mscore7d 18670Specify the SCORE7D as the target architecture. 18671@end table 18672 18673@node SH Options 18674@subsection SH Options 18675 18676These @samp{-m} options are defined for the SH implementations: 18677 18678@table @gcctabopt 18679@item -m1 18680@opindex m1 18681Generate code for the SH1. 18682 18683@item -m2 18684@opindex m2 18685Generate code for the SH2. 18686 18687@item -m2e 18688Generate code for the SH2e. 18689 18690@item -m2a-nofpu 18691@opindex m2a-nofpu 18692Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way 18693that the floating-point unit is not used. 18694 18695@item -m2a-single-only 18696@opindex m2a-single-only 18697Generate code for the SH2a-FPU, in such a way that no double-precision 18698floating-point operations are used. 18699 18700@item -m2a-single 18701@opindex m2a-single 18702Generate code for the SH2a-FPU assuming the floating-point unit is in 18703single-precision mode by default. 18704 18705@item -m2a 18706@opindex m2a 18707Generate code for the SH2a-FPU assuming the floating-point unit is in 18708double-precision mode by default. 18709 18710@item -m3 18711@opindex m3 18712Generate code for the SH3. 18713 18714@item -m3e 18715@opindex m3e 18716Generate code for the SH3e. 18717 18718@item -m4-nofpu 18719@opindex m4-nofpu 18720Generate code for the SH4 without a floating-point unit. 18721 18722@item -m4-single-only 18723@opindex m4-single-only 18724Generate code for the SH4 with a floating-point unit that only 18725supports single-precision arithmetic. 18726 18727@item -m4-single 18728@opindex m4-single 18729Generate code for the SH4 assuming the floating-point unit is in 18730single-precision mode by default. 18731 18732@item -m4 18733@opindex m4 18734Generate code for the SH4. 18735 18736@item -m4-100 18737@opindex m4-100 18738Generate code for SH4-100. 18739 18740@item -m4-100-nofpu 18741@opindex m4-100-nofpu 18742Generate code for SH4-100 in such a way that the 18743floating-point unit is not used. 18744 18745@item -m4-100-single 18746@opindex m4-100-single 18747Generate code for SH4-100 assuming the floating-point unit is in 18748single-precision mode by default. 18749 18750@item -m4-100-single-only 18751@opindex m4-100-single-only 18752Generate code for SH4-100 in such a way that no double-precision 18753floating-point operations are used. 18754 18755@item -m4-200 18756@opindex m4-200 18757Generate code for SH4-200. 18758 18759@item -m4-200-nofpu 18760@opindex m4-200-nofpu 18761Generate code for SH4-200 without in such a way that the 18762floating-point unit is not used. 18763 18764@item -m4-200-single 18765@opindex m4-200-single 18766Generate code for SH4-200 assuming the floating-point unit is in 18767single-precision mode by default. 18768 18769@item -m4-200-single-only 18770@opindex m4-200-single-only 18771Generate code for SH4-200 in such a way that no double-precision 18772floating-point operations are used. 18773 18774@item -m4-300 18775@opindex m4-300 18776Generate code for SH4-300. 18777 18778@item -m4-300-nofpu 18779@opindex m4-300-nofpu 18780Generate code for SH4-300 without in such a way that the 18781floating-point unit is not used. 18782 18783@item -m4-300-single 18784@opindex m4-300-single 18785Generate code for SH4-300 in such a way that no double-precision 18786floating-point operations are used. 18787 18788@item -m4-300-single-only 18789@opindex m4-300-single-only 18790Generate code for SH4-300 in such a way that no double-precision 18791floating-point operations are used. 18792 18793@item -m4-340 18794@opindex m4-340 18795Generate code for SH4-340 (no MMU, no FPU). 18796 18797@item -m4-500 18798@opindex m4-500 18799Generate code for SH4-500 (no FPU). Passes @option{-isa=sh4-nofpu} to the 18800assembler. 18801 18802@item -m4a-nofpu 18803@opindex m4a-nofpu 18804Generate code for the SH4al-dsp, or for a SH4a in such a way that the 18805floating-point unit is not used. 18806 18807@item -m4a-single-only 18808@opindex m4a-single-only 18809Generate code for the SH4a, in such a way that no double-precision 18810floating-point operations are used. 18811 18812@item -m4a-single 18813@opindex m4a-single 18814Generate code for the SH4a assuming the floating-point unit is in 18815single-precision mode by default. 18816 18817@item -m4a 18818@opindex m4a 18819Generate code for the SH4a. 18820 18821@item -m4al 18822@opindex m4al 18823Same as @option{-m4a-nofpu}, except that it implicitly passes 18824@option{-dsp} to the assembler. GCC doesn't generate any DSP 18825instructions at the moment. 18826 18827@item -m5-32media 18828@opindex m5-32media 18829Generate 32-bit code for SHmedia. 18830 18831@item -m5-32media-nofpu 18832@opindex m5-32media-nofpu 18833Generate 32-bit code for SHmedia in such a way that the 18834floating-point unit is not used. 18835 18836@item -m5-64media 18837@opindex m5-64media 18838Generate 64-bit code for SHmedia. 18839 18840@item -m5-64media-nofpu 18841@opindex m5-64media-nofpu 18842Generate 64-bit code for SHmedia in such a way that the 18843floating-point unit is not used. 18844 18845@item -m5-compact 18846@opindex m5-compact 18847Generate code for SHcompact. 18848 18849@item -m5-compact-nofpu 18850@opindex m5-compact-nofpu 18851Generate code for SHcompact in such a way that the 18852floating-point unit is not used. 18853 18854@item -mb 18855@opindex mb 18856Compile code for the processor in big-endian mode. 18857 18858@item -ml 18859@opindex ml 18860Compile code for the processor in little-endian mode. 18861 18862@item -mdalign 18863@opindex mdalign 18864Align doubles at 64-bit boundaries. Note that this changes the calling 18865conventions, and thus some functions from the standard C library do 18866not work unless you recompile it first with @option{-mdalign}. 18867 18868@item -mrelax 18869@opindex mrelax 18870Shorten some address references at link time, when possible; uses the 18871linker option @option{-relax}. 18872 18873@item -mbigtable 18874@opindex mbigtable 18875Use 32-bit offsets in @code{switch} tables. The default is to use 1887616-bit offsets. 18877 18878@item -mbitops 18879@opindex mbitops 18880Enable the use of bit manipulation instructions on SH2A. 18881 18882@item -mfmovd 18883@opindex mfmovd 18884Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for 18885alignment constraints. 18886 18887@item -mrenesas 18888@opindex mrenesas 18889Comply with the calling conventions defined by Renesas. 18890 18891@item -mno-renesas 18892@opindex mno-renesas 18893Comply with the calling conventions defined for GCC before the Renesas 18894conventions were available. This option is the default for all 18895targets of the SH toolchain. 18896 18897@item -mnomacsave 18898@opindex mnomacsave 18899Mark the @code{MAC} register as call-clobbered, even if 18900@option{-mrenesas} is given. 18901 18902@item -mieee 18903@itemx -mno-ieee 18904@opindex mieee 18905@opindex mno-ieee 18906Control the IEEE compliance of floating-point comparisons, which affects the 18907handling of cases where the result of a comparison is unordered. By default 18908@option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is 18909enabled @option{-mno-ieee} is implicitly set, which results in faster 18910floating-point greater-equal and less-equal comparisons. The implcit settings 18911can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}. 18912 18913@item -minline-ic_invalidate 18914@opindex minline-ic_invalidate 18915Inline code to invalidate instruction cache entries after setting up 18916nested function trampolines. 18917This option has no effect if @option{-musermode} is in effect and the selected 18918code generation option (e.g. @option{-m4}) does not allow the use of the @code{icbi} 18919instruction. 18920If the selected code generation option does not allow the use of the @code{icbi} 18921instruction, and @option{-musermode} is not in effect, the inlined code 18922manipulates the instruction cache address array directly with an associative 18923write. This not only requires privileged mode at run time, but it also 18924fails if the cache line had been mapped via the TLB and has become unmapped. 18925 18926@item -misize 18927@opindex misize 18928Dump instruction size and location in the assembly code. 18929 18930@item -mpadstruct 18931@opindex mpadstruct 18932This option is deprecated. It pads structures to multiple of 4 bytes, 18933which is incompatible with the SH ABI@. 18934 18935@item -matomic-model=@var{model} 18936@opindex matomic-model=@var{model} 18937Sets the model of atomic operations and additional parameters as a comma 18938separated list. For details on the atomic built-in functions see 18939@ref{__atomic Builtins}. The following models and parameters are supported: 18940 18941@table @samp 18942 18943@item none 18944Disable compiler generated atomic sequences and emit library calls for atomic 18945operations. This is the default if the target is not @code{sh*-*-linux*}. 18946 18947@item soft-gusa 18948Generate GNU/Linux compatible gUSA software atomic sequences for the atomic 18949built-in functions. The generated atomic sequences require additional support 18950from the interrupt/exception handling code of the system and are only suitable 18951for SH3* and SH4* single-core systems. This option is enabled by default when 18952the target is @code{sh*-*-linux*} and SH3* or SH4*. When the target is SH4A, 18953this option will also partially utilize the hardware atomic instructions 18954@code{movli.l} and @code{movco.l} to create more efficient code, unless 18955@samp{strict} is specified. 18956 18957@item soft-tcb 18958Generate software atomic sequences that use a variable in the thread control 18959block. This is a variation of the gUSA sequences which can also be used on 18960SH1* and SH2* targets. The generated atomic sequences require additional 18961support from the interrupt/exception handling code of the system and are only 18962suitable for single-core systems. When using this model, the @samp{gbr-offset=} 18963parameter has to be specified as well. 18964 18965@item soft-imask 18966Generate software atomic sequences that temporarily disable interrupts by 18967setting @code{SR.IMASK = 1111}. This model works only when the program runs 18968in privileged mode and is only suitable for single-core systems. Additional 18969support from the interrupt/exception handling code of the system is not 18970required. This model is enabled by default when the target is 18971@code{sh*-*-linux*} and SH1* or SH2*. 18972 18973@item hard-llcs 18974Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l} 18975instructions only. This is only available on SH4A and is suitable for 18976multi-core systems. Since the hardware instructions support only 32 bit atomic 18977variables access to 8 or 16 bit variables is emulated with 32 bit accesses. 18978Code compiled with this option will also be compatible with other software 18979atomic model interrupt/exception handling systems if executed on an SH4A 18980system. Additional support from the interrupt/exception handling code of the 18981system is not required for this model. 18982 18983@item gbr-offset= 18984This parameter specifies the offset in bytes of the variable in the thread 18985control block structure that should be used by the generated atomic sequences 18986when the @samp{soft-tcb} model has been selected. For other models this 18987parameter is ignored. The specified value must be an integer multiple of four 18988and in the range 0-1020. 18989 18990@item strict 18991This parameter prevents mixed usage of multiple atomic models, even though they 18992would be compatible, and will make the compiler generate atomic sequences of the 18993specified model only. 18994 18995@end table 18996 18997@item -mtas 18998@opindex mtas 18999Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}. 19000Notice that depending on the particular hardware and software configuration 19001this can degrade overall performance due to the operand cache line flushes 19002that are implied by the @code{tas.b} instruction. On multi-core SH4A 19003processors the @code{tas.b} instruction must be used with caution since it 19004can result in data corruption for certain cache configurations. 19005 19006@item -mprefergot 19007@opindex mprefergot 19008When generating position-independent code, emit function calls using 19009the Global Offset Table instead of the Procedure Linkage Table. 19010 19011@item -musermode 19012@itemx -mno-usermode 19013@opindex musermode 19014@opindex mno-usermode 19015Don't allow (allow) the compiler generating privileged mode code. Specifying 19016@option{-musermode} also implies @option{-mno-inline-ic_invalidate} if the 19017inlined code would not work in user mode. @option{-musermode} is the default 19018when the target is @code{sh*-*-linux*}. If the target is SH1* or SH2* 19019@option{-musermode} has no effect, since there is no user mode. 19020 19021@item -multcost=@var{number} 19022@opindex multcost=@var{number} 19023Set the cost to assume for a multiply insn. 19024 19025@item -mdiv=@var{strategy} 19026@opindex mdiv=@var{strategy} 19027Set the division strategy to be used for integer division operations. 19028For SHmedia @var{strategy} can be one of: 19029 19030@table @samp 19031 19032@item fp 19033Performs the operation in floating point. This has a very high latency, 19034but needs only a few instructions, so it might be a good choice if 19035your code has enough easily-exploitable ILP to allow the compiler to 19036schedule the floating-point instructions together with other instructions. 19037Division by zero causes a floating-point exception. 19038 19039@item inv 19040Uses integer operations to calculate the inverse of the divisor, 19041and then multiplies the dividend with the inverse. This strategy allows 19042CSE and hoisting of the inverse calculation. Division by zero calculates 19043an unspecified result, but does not trap. 19044 19045@item inv:minlat 19046A variant of @samp{inv} where, if no CSE or hoisting opportunities 19047have been found, or if the entire operation has been hoisted to the same 19048place, the last stages of the inverse calculation are intertwined with the 19049final multiply to reduce the overall latency, at the expense of using a few 19050more instructions, and thus offering fewer scheduling opportunities with 19051other code. 19052 19053@item call 19054Calls a library function that usually implements the @samp{inv:minlat} 19055strategy. 19056This gives high code density for @code{m5-*media-nofpu} compilations. 19057 19058@item call2 19059Uses a different entry point of the same library function, where it 19060assumes that a pointer to a lookup table has already been set up, which 19061exposes the pointer load to CSE and code hoisting optimizations. 19062 19063@item inv:call 19064@itemx inv:call2 19065@itemx inv:fp 19066Use the @samp{inv} algorithm for initial 19067code generation, but if the code stays unoptimized, revert to the @samp{call}, 19068@samp{call2}, or @samp{fp} strategies, respectively. Note that the 19069potentially-trapping side effect of division by zero is carried by a 19070separate instruction, so it is possible that all the integer instructions 19071are hoisted out, but the marker for the side effect stays where it is. 19072A recombination to floating-point operations or a call is not possible 19073in that case. 19074 19075@item inv20u 19076@itemx inv20l 19077Variants of the @samp{inv:minlat} strategy. In the case 19078that the inverse calculation is not separated from the multiply, they speed 19079up division where the dividend fits into 20 bits (plus sign where applicable) 19080by inserting a test to skip a number of operations in this case; this test 19081slows down the case of larger dividends. @samp{inv20u} assumes the case of a such 19082a small dividend to be unlikely, and @samp{inv20l} assumes it to be likely. 19083 19084@end table 19085 19086For targets other than SHmedia @var{strategy} can be one of: 19087 19088@table @samp 19089 19090@item call-div1 19091Calls a library function that uses the single-step division instruction 19092@code{div1} to perform the operation. Division by zero calculates an 19093unspecified result and does not trap. This is the default except for SH4, 19094SH2A and SHcompact. 19095 19096@item call-fp 19097Calls a library function that performs the operation in double precision 19098floating point. Division by zero causes a floating-point exception. This is 19099the default for SHcompact with FPU. Specifying this for targets that do not 19100have a double precision FPU will default to @code{call-div1}. 19101 19102@item call-table 19103Calls a library function that uses a lookup table for small divisors and 19104the @code{div1} instruction with case distinction for larger divisors. Division 19105by zero calculates an unspecified result and does not trap. This is the default 19106for SH4. Specifying this for targets that do not have dynamic shift 19107instructions will default to @code{call-div1}. 19108 19109@end table 19110 19111When a division strategy has not been specified the default strategy will be 19112selected based on the current target. For SH2A the default strategy is to 19113use the @code{divs} and @code{divu} instructions instead of library function 19114calls. 19115 19116@item -maccumulate-outgoing-args 19117@opindex maccumulate-outgoing-args 19118Reserve space once for outgoing arguments in the function prologue rather 19119than around each call. Generally beneficial for performance and size. Also 19120needed for unwinding to avoid changing the stack frame around conditional code. 19121 19122@item -mdivsi3_libfunc=@var{name} 19123@opindex mdivsi3_libfunc=@var{name} 19124Set the name of the library function used for 32-bit signed division to 19125@var{name}. 19126This only affects the name used in the @samp{call} and @samp{inv:call} 19127division strategies, and the compiler still expects the same 19128sets of input/output/clobbered registers as if this option were not present. 19129 19130@item -mfixed-range=@var{register-range} 19131@opindex mfixed-range 19132Generate code treating the given register range as fixed registers. 19133A fixed register is one that the register allocator can not use. This is 19134useful when compiling kernel code. A register range is specified as 19135two registers separated by a dash. Multiple register ranges can be 19136specified separated by a comma. 19137 19138@item -mindexed-addressing 19139@opindex mindexed-addressing 19140Enable the use of the indexed addressing mode for SHmedia32/SHcompact. 19141This is only safe if the hardware and/or OS implement 32-bit wrap-around 19142semantics for the indexed addressing mode. The architecture allows the 19143implementation of processors with 64-bit MMU, which the OS could use to 19144get 32-bit addressing, but since no current hardware implementation supports 19145this or any other way to make the indexed addressing mode safe to use in 19146the 32-bit ABI, the default is @option{-mno-indexed-addressing}. 19147 19148@item -mgettrcost=@var{number} 19149@opindex mgettrcost=@var{number} 19150Set the cost assumed for the @code{gettr} instruction to @var{number}. 19151The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise. 19152 19153@item -mpt-fixed 19154@opindex mpt-fixed 19155Assume @code{pt*} instructions won't trap. This generally generates 19156better-scheduled code, but is unsafe on current hardware. 19157The current architecture 19158definition says that @code{ptabs} and @code{ptrel} trap when the target 19159anded with 3 is 3. 19160This has the unintentional effect of making it unsafe to schedule these 19161instructions before a branch, or hoist them out of a loop. For example, 19162@code{__do_global_ctors}, a part of @file{libgcc} 19163that runs constructors at program 19164startup, calls functions in a list which is delimited by @minus{}1. With the 19165@option{-mpt-fixed} option, the @code{ptabs} is done before testing against @minus{}1. 19166That means that all the constructors run a bit more quickly, but when 19167the loop comes to the end of the list, the program crashes because @code{ptabs} 19168loads @minus{}1 into a target register. 19169 19170Since this option is unsafe for any 19171hardware implementing the current architecture specification, the default 19172is @option{-mno-pt-fixed}. Unless specified explicitly with 19173@option{-mgettrcost}, @option{-mno-pt-fixed} also implies @option{-mgettrcost=100}; 19174this deters register allocation from using target registers for storing 19175ordinary integers. 19176 19177@item -minvalid-symbols 19178@opindex minvalid-symbols 19179Assume symbols might be invalid. Ordinary function symbols generated by 19180the compiler are always valid to load with 19181@code{movi}/@code{shori}/@code{ptabs} or 19182@code{movi}/@code{shori}/@code{ptrel}, 19183but with assembler and/or linker tricks it is possible 19184to generate symbols that cause @code{ptabs} or @code{ptrel} to trap. 19185This option is only meaningful when @option{-mno-pt-fixed} is in effect. 19186It prevents cross-basic-block CSE, hoisting and most scheduling 19187of symbol loads. The default is @option{-mno-invalid-symbols}. 19188 19189@item -mbranch-cost=@var{num} 19190@opindex mbranch-cost=@var{num} 19191Assume @var{num} to be the cost for a branch instruction. Higher numbers 19192make the compiler try to generate more branch-free code if possible. 19193If not specified the value is selected depending on the processor type that 19194is being compiled for. 19195 19196@item -mzdcbranch 19197@itemx -mno-zdcbranch 19198@opindex mzdcbranch 19199@opindex mno-zdcbranch 19200Assume (do not assume) that zero displacement conditional branch instructions 19201@code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the 19202compiler will try to prefer zero displacement branch code sequences. This is 19203enabled by default when generating code for SH4 and SH4A. It can be explicitly 19204disabled by specifying @option{-mno-zdcbranch}. 19205 19206@item -mcbranchdi 19207@opindex mcbranchdi 19208Enable the @code{cbranchdi4} instruction pattern. 19209 19210@item -mcmpeqdi 19211@opindex mcmpeqdi 19212Emit the @code{cmpeqdi_t} instruction pattern even when @option{-mcbranchdi} 19213is in effect. 19214 19215@item -mfused-madd 19216@itemx -mno-fused-madd 19217@opindex mfused-madd 19218@opindex mno-fused-madd 19219Generate code that uses (does not use) the floating-point multiply and 19220accumulate instructions. These instructions are generated by default 19221if hardware floating point is used. The machine-dependent 19222@option{-mfused-madd} option is now mapped to the machine-independent 19223@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is 19224mapped to @option{-ffp-contract=off}. 19225 19226@item -mfsca 19227@itemx -mno-fsca 19228@opindex mfsca 19229@opindex mno-fsca 19230Allow or disallow the compiler to emit the @code{fsca} instruction for sine 19231and cosine approximations. The option @code{-mfsca} must be used in 19232combination with @code{-funsafe-math-optimizations}. It is enabled by default 19233when generating code for SH4A. Using @code{-mno-fsca} disables sine and cosine 19234approximations even if @code{-funsafe-math-optimizations} is in effect. 19235 19236@item -mfsrra 19237@itemx -mno-fsrra 19238@opindex mfsrra 19239@opindex mno-fsrra 19240Allow or disallow the compiler to emit the @code{fsrra} instruction for 19241reciprocal square root approximations. The option @code{-mfsrra} must be used 19242in combination with @code{-funsafe-math-optimizations} and 19243@code{-ffinite-math-only}. It is enabled by default when generating code for 19244SH4A. Using @code{-mno-fsrra} disables reciprocal square root approximations 19245even if @code{-funsafe-math-optimizations} and @code{-ffinite-math-only} are 19246in effect. 19247 19248@item -mpretend-cmove 19249@opindex mpretend-cmove 19250Prefer zero-displacement conditional branches for conditional move instruction 19251patterns. This can result in faster code on the SH4 processor. 19252 19253@end table 19254 19255@node Solaris 2 Options 19256@subsection Solaris 2 Options 19257@cindex Solaris 2 options 19258 19259These @samp{-m} options are supported on Solaris 2: 19260 19261@table @gcctabopt 19262@item -mimpure-text 19263@opindex mimpure-text 19264@option{-mimpure-text}, used in addition to @option{-shared}, tells 19265the compiler to not pass @option{-z text} to the linker when linking a 19266shared object. Using this option, you can link position-dependent 19267code into a shared object. 19268 19269@option{-mimpure-text} suppresses the ``relocations remain against 19270allocatable but non-writable sections'' linker error message. 19271However, the necessary relocations trigger copy-on-write, and the 19272shared object is not actually shared across processes. Instead of 19273using @option{-mimpure-text}, you should compile all source code with 19274@option{-fpic} or @option{-fPIC}. 19275 19276@end table 19277 19278These switches are supported in addition to the above on Solaris 2: 19279 19280@table @gcctabopt 19281@item -pthreads 19282@opindex pthreads 19283Add support for multithreading using the POSIX threads library. This 19284option sets flags for both the preprocessor and linker. This option does 19285not affect the thread safety of object code produced by the compiler or 19286that of libraries supplied with it. 19287 19288@item -pthread 19289@opindex pthread 19290This is a synonym for @option{-pthreads}. 19291@end table 19292 19293@node SPARC Options 19294@subsection SPARC Options 19295@cindex SPARC options 19296 19297These @samp{-m} options are supported on the SPARC: 19298 19299@table @gcctabopt 19300@item -mno-app-regs 19301@itemx -mapp-regs 19302@opindex mno-app-regs 19303@opindex mapp-regs 19304Specify @option{-mapp-regs} to generate output using the global registers 193052 through 4, which the SPARC SVR4 ABI reserves for applications. Like the 19306global register 1, each global register 2 through 4 is then treated as an 19307allocable register that is clobbered by function calls. This is the default. 19308 19309To be fully SVR4 ABI-compliant at the cost of some performance loss, 19310specify @option{-mno-app-regs}. You should compile libraries and system 19311software with this option. 19312 19313@item -mflat 19314@itemx -mno-flat 19315@opindex mflat 19316@opindex mno-flat 19317With @option{-mflat}, the compiler does not generate save/restore instructions 19318and uses a ``flat'' or single register window model. This model is compatible 19319with the regular register window model. The local registers and the input 19320registers (0--5) are still treated as ``call-saved'' registers and are 19321saved on the stack as needed. 19322 19323With @option{-mno-flat} (the default), the compiler generates save/restore 19324instructions (except for leaf functions). This is the normal operating mode. 19325 19326@item -mfpu 19327@itemx -mhard-float 19328@opindex mfpu 19329@opindex mhard-float 19330Generate output containing floating-point instructions. This is the 19331default. 19332 19333@item -mno-fpu 19334@itemx -msoft-float 19335@opindex mno-fpu 19336@opindex msoft-float 19337Generate output containing library calls for floating point. 19338@strong{Warning:} the requisite libraries are not available for all SPARC 19339targets. Normally the facilities of the machine's usual C compiler are 19340used, but this cannot be done directly in cross-compilation. You must make 19341your own arrangements to provide suitable library functions for 19342cross-compilation. The embedded targets @samp{sparc-*-aout} and 19343@samp{sparclite-*-*} do provide software floating-point support. 19344 19345@option{-msoft-float} changes the calling convention in the output file; 19346therefore, it is only useful if you compile @emph{all} of a program with 19347this option. In particular, you need to compile @file{libgcc.a}, the 19348library that comes with GCC, with @option{-msoft-float} in order for 19349this to work. 19350 19351@item -mhard-quad-float 19352@opindex mhard-quad-float 19353Generate output containing quad-word (long double) floating-point 19354instructions. 19355 19356@item -msoft-quad-float 19357@opindex msoft-quad-float 19358Generate output containing library calls for quad-word (long double) 19359floating-point instructions. The functions called are those specified 19360in the SPARC ABI@. This is the default. 19361 19362As of this writing, there are no SPARC implementations that have hardware 19363support for the quad-word floating-point instructions. They all invoke 19364a trap handler for one of these instructions, and then the trap handler 19365emulates the effect of the instruction. Because of the trap handler overhead, 19366this is much slower than calling the ABI library routines. Thus the 19367@option{-msoft-quad-float} option is the default. 19368 19369@item -mno-unaligned-doubles 19370@itemx -munaligned-doubles 19371@opindex mno-unaligned-doubles 19372@opindex munaligned-doubles 19373Assume that doubles have 8-byte alignment. This is the default. 19374 19375With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte 19376alignment only if they are contained in another type, or if they have an 19377absolute address. Otherwise, it assumes they have 4-byte alignment. 19378Specifying this option avoids some rare compatibility problems with code 19379generated by other compilers. It is not the default because it results 19380in a performance loss, especially for floating-point code. 19381 19382@item -muser-mode 19383@itemx -mno-user-mode 19384@opindex muser-mode 19385@opindex mno-user-mode 19386Do not generate code that can only run in supervisor mode. This is relevant 19387only for the @code{casa} instruction emitted for the LEON3 processor. The 19388default is @option{-mno-user-mode}. 19389 19390@item -mno-faster-structs 19391@itemx -mfaster-structs 19392@opindex mno-faster-structs 19393@opindex mfaster-structs 19394With @option{-mfaster-structs}, the compiler assumes that structures 19395should have 8-byte alignment. This enables the use of pairs of 19396@code{ldd} and @code{std} instructions for copies in structure 19397assignment, in place of twice as many @code{ld} and @code{st} pairs. 19398However, the use of this changed alignment directly violates the SPARC 19399ABI@. Thus, it's intended only for use on targets where the developer 19400acknowledges that their resulting code is not directly in line with 19401the rules of the ABI@. 19402 19403@item -mcpu=@var{cpu_type} 19404@opindex mcpu 19405Set the instruction set, register set, and instruction scheduling parameters 19406for machine type @var{cpu_type}. Supported values for @var{cpu_type} are 19407@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc}, 19408@samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{sparclite}, @samp{f930}, 19409@samp{f934}, @samp{sparclite86x}, @samp{sparclet}, @samp{tsc701}, @samp{v9}, 19410@samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, 19411@samp{niagara3} and @samp{niagara4}. 19412 19413Native Solaris and GNU/Linux toolchains also support the value @samp{native}, 19414which selects the best architecture option for the host processor. 19415@option{-mcpu=native} has no effect if GCC does not recognize 19416the processor. 19417 19418Default instruction scheduling parameters are used for values that select 19419an architecture and not an implementation. These are @samp{v7}, @samp{v8}, 19420@samp{sparclite}, @samp{sparclet}, @samp{v9}. 19421 19422Here is a list of each supported architecture and their supported 19423implementations. 19424 19425@table @asis 19426@item v7 19427cypress, leon3v7 19428 19429@item v8 19430supersparc, hypersparc, leon, leon3 19431 19432@item sparclite 19433f930, f934, sparclite86x 19434 19435@item sparclet 19436tsc701 19437 19438@item v9 19439ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4 19440@end table 19441 19442By default (unless configured otherwise), GCC generates code for the V7 19443variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler 19444additionally optimizes it for the Cypress CY7C602 chip, as used in the 19445SPARCStation/SPARCServer 3xx series. This is also appropriate for the older 19446SPARCStation 1, 2, IPX etc. 19447 19448With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC 19449architecture. The only difference from V7 code is that the compiler emits 19450the integer multiply and integer divide instructions which exist in SPARC-V8 19451but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally 19452optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 194532000 series. 19454 19455With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of 19456the SPARC architecture. This adds the integer multiply, integer divide step 19457and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7. 19458With @option{-mcpu=f930}, the compiler additionally optimizes it for the 19459Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With 19460@option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu 19461MB86934 chip, which is the more recent SPARClite with FPU@. 19462 19463With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of 19464the SPARC architecture. This adds the integer multiply, multiply/accumulate, 19465integer divide step and scan (@code{ffs}) instructions which exist in SPARClet 19466but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally 19467optimizes it for the TEMIC SPARClet chip. 19468 19469With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC 19470architecture. This adds 64-bit integer and floating-point move instructions, 194713 additional floating-point condition code registers and conditional move 19472instructions. With @option{-mcpu=ultrasparc}, the compiler additionally 19473optimizes it for the Sun UltraSPARC I/II/IIi chips. With 19474@option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the 19475Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With 19476@option{-mcpu=niagara}, the compiler additionally optimizes it for 19477Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler 19478additionally optimizes it for Sun UltraSPARC T2 chips. With 19479@option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun 19480UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler 19481additionally optimizes it for Sun UltraSPARC T4 chips. 19482 19483@item -mtune=@var{cpu_type} 19484@opindex mtune 19485Set the instruction scheduling parameters for machine type 19486@var{cpu_type}, but do not set the instruction set or register set that the 19487option @option{-mcpu=@var{cpu_type}} does. 19488 19489The same values for @option{-mcpu=@var{cpu_type}} can be used for 19490@option{-mtune=@var{cpu_type}}, but the only useful values are those 19491that select a particular CPU implementation. Those are @samp{cypress}, 19492@samp{supersparc}, @samp{hypersparc}, @samp{leon}, @samp{leon3}, 19493@samp{leon3v7}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, @samp{tsc701}, 19494@samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, 19495@samp{niagara3} and @samp{niagara4}. With native Solaris and GNU/Linux 19496toolchains, @samp{native} can also be used. 19497 19498@item -mv8plus 19499@itemx -mno-v8plus 19500@opindex mv8plus 19501@opindex mno-v8plus 19502With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The 19503difference from the V8 ABI is that the global and out registers are 19504considered 64 bits wide. This is enabled by default on Solaris in 32-bit 19505mode for all SPARC-V9 processors. 19506 19507@item -mvis 19508@itemx -mno-vis 19509@opindex mvis 19510@opindex mno-vis 19511With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC 19512Visual Instruction Set extensions. The default is @option{-mno-vis}. 19513 19514@item -mvis2 19515@itemx -mno-vis2 19516@opindex mvis2 19517@opindex mno-vis2 19518With @option{-mvis2}, GCC generates code that takes advantage of 19519version 2.0 of the UltraSPARC Visual Instruction Set extensions. The 19520default is @option{-mvis2} when targeting a cpu that supports such 19521instructions, such as UltraSPARC-III and later. Setting @option{-mvis2} 19522also sets @option{-mvis}. 19523 19524@item -mvis3 19525@itemx -mno-vis3 19526@opindex mvis3 19527@opindex mno-vis3 19528With @option{-mvis3}, GCC generates code that takes advantage of 19529version 3.0 of the UltraSPARC Visual Instruction Set extensions. The 19530default is @option{-mvis3} when targeting a cpu that supports such 19531instructions, such as niagara-3 and later. Setting @option{-mvis3} 19532also sets @option{-mvis2} and @option{-mvis}. 19533 19534@item -mcbcond 19535@itemx -mno-cbcond 19536@opindex mcbcond 19537@opindex mno-cbcond 19538With @option{-mcbcond}, GCC generates code that takes advantage of 19539compare-and-branch instructions, as defined in the Sparc Architecture 2011. 19540The default is @option{-mcbcond} when targeting a cpu that supports such 19541instructions, such as niagara-4 and later. 19542 19543@item -mpopc 19544@itemx -mno-popc 19545@opindex mpopc 19546@opindex mno-popc 19547With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC 19548population count instruction. The default is @option{-mpopc} 19549when targeting a cpu that supports such instructions, such as Niagara-2 and 19550later. 19551 19552@item -mfmaf 19553@itemx -mno-fmaf 19554@opindex mfmaf 19555@opindex mno-fmaf 19556With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC 19557Fused Multiply-Add Floating-point extensions. The default is @option{-mfmaf} 19558when targeting a cpu that supports such instructions, such as Niagara-3 and 19559later. 19560 19561@item -mfix-at697f 19562@opindex mfix-at697f 19563Enable the documented workaround for the single erratum of the Atmel AT697F 19564processor (which corresponds to erratum #13 of the AT697E processor). 19565 19566@item -mfix-ut699 19567@opindex mfix-ut699 19568Enable the documented workarounds for the floating-point errata and the data 19569cache nullify errata of the UT699 processor. 19570@end table 19571 19572These @samp{-m} options are supported in addition to the above 19573on SPARC-V9 processors in 64-bit environments: 19574 19575@table @gcctabopt 19576@item -m32 19577@itemx -m64 19578@opindex m32 19579@opindex m64 19580Generate code for a 32-bit or 64-bit environment. 19581The 32-bit environment sets int, long and pointer to 32 bits. 19582The 64-bit environment sets int to 32 bits and long and pointer 19583to 64 bits. 19584 19585@item -mcmodel=@var{which} 19586@opindex mcmodel 19587Set the code model to one of 19588 19589@table @samp 19590@item medlow 19591The Medium/Low code model: 64-bit addresses, programs 19592must be linked in the low 32 bits of memory. Programs can be statically 19593or dynamically linked. 19594 19595@item medmid 19596The Medium/Middle code model: 64-bit addresses, programs 19597must be linked in the low 44 bits of memory, the text and data segments must 19598be less than 2GB in size and the data segment must be located within 2GB of 19599the text segment. 19600 19601@item medany 19602The Medium/Anywhere code model: 64-bit addresses, programs 19603may be linked anywhere in memory, the text and data segments must be less 19604than 2GB in size and the data segment must be located within 2GB of the 19605text segment. 19606 19607@item embmedany 19608The Medium/Anywhere code model for embedded systems: 1960964-bit addresses, the text and data segments must be less than 2GB in 19610size, both starting anywhere in memory (determined at link time). The 19611global register %g4 points to the base of the data segment. Programs 19612are statically linked and PIC is not supported. 19613@end table 19614 19615@item -mmemory-model=@var{mem-model} 19616@opindex mmemory-model 19617Set the memory model in force on the processor to one of 19618 19619@table @samp 19620@item default 19621The default memory model for the processor and operating system. 19622 19623@item rmo 19624Relaxed Memory Order 19625 19626@item pso 19627Partial Store Order 19628 19629@item tso 19630Total Store Order 19631 19632@item sc 19633Sequential Consistency 19634@end table 19635 19636These memory models are formally defined in Appendix D of the Sparc V9 19637architecture manual, as set in the processor's @code{PSTATE.MM} field. 19638 19639@item -mstack-bias 19640@itemx -mno-stack-bias 19641@opindex mstack-bias 19642@opindex mno-stack-bias 19643With @option{-mstack-bias}, GCC assumes that the stack pointer, and 19644frame pointer if present, are offset by @minus{}2047 which must be added back 19645when making stack frame references. This is the default in 64-bit mode. 19646Otherwise, assume no such offset is present. 19647@end table 19648 19649@node SPU Options 19650@subsection SPU Options 19651@cindex SPU options 19652 19653These @samp{-m} options are supported on the SPU: 19654 19655@table @gcctabopt 19656@item -mwarn-reloc 19657@itemx -merror-reloc 19658@opindex mwarn-reloc 19659@opindex merror-reloc 19660 19661The loader for SPU does not handle dynamic relocations. By default, GCC 19662gives an error when it generates code that requires a dynamic 19663relocation. @option{-mno-error-reloc} disables the error, 19664@option{-mwarn-reloc} generates a warning instead. 19665 19666@item -msafe-dma 19667@itemx -munsafe-dma 19668@opindex msafe-dma 19669@opindex munsafe-dma 19670 19671Instructions that initiate or test completion of DMA must not be 19672reordered with respect to loads and stores of the memory that is being 19673accessed. 19674With @option{-munsafe-dma} you must use the @code{volatile} keyword to protect 19675memory accesses, but that can lead to inefficient code in places where the 19676memory is known to not change. Rather than mark the memory as volatile, 19677you can use @option{-msafe-dma} to tell the compiler to treat 19678the DMA instructions as potentially affecting all memory. 19679 19680@item -mbranch-hints 19681@opindex mbranch-hints 19682 19683By default, GCC generates a branch hint instruction to avoid 19684pipeline stalls for always-taken or probably-taken branches. A hint 19685is not generated closer than 8 instructions away from its branch. 19686There is little reason to disable them, except for debugging purposes, 19687or to make an object a little bit smaller. 19688 19689@item -msmall-mem 19690@itemx -mlarge-mem 19691@opindex msmall-mem 19692@opindex mlarge-mem 19693 19694By default, GCC generates code assuming that addresses are never larger 19695than 18 bits. With @option{-mlarge-mem} code is generated that assumes 19696a full 32-bit address. 19697 19698@item -mstdmain 19699@opindex mstdmain 19700 19701By default, GCC links against startup code that assumes the SPU-style 19702main function interface (which has an unconventional parameter list). 19703With @option{-mstdmain}, GCC links your program against startup 19704code that assumes a C99-style interface to @code{main}, including a 19705local copy of @code{argv} strings. 19706 19707@item -mfixed-range=@var{register-range} 19708@opindex mfixed-range 19709Generate code treating the given register range as fixed registers. 19710A fixed register is one that the register allocator cannot use. This is 19711useful when compiling kernel code. A register range is specified as 19712two registers separated by a dash. Multiple register ranges can be 19713specified separated by a comma. 19714 19715@item -mea32 19716@itemx -mea64 19717@opindex mea32 19718@opindex mea64 19719Compile code assuming that pointers to the PPU address space accessed 19720via the @code{__ea} named address space qualifier are either 32 or 64 19721bits wide. The default is 32 bits. As this is an ABI-changing option, 19722all object code in an executable must be compiled with the same setting. 19723 19724@item -maddress-space-conversion 19725@itemx -mno-address-space-conversion 19726@opindex maddress-space-conversion 19727@opindex mno-address-space-conversion 19728Allow/disallow treating the @code{__ea} address space as superset 19729of the generic address space. This enables explicit type casts 19730between @code{__ea} and generic pointer as well as implicit 19731conversions of generic pointers to @code{__ea} pointers. The 19732default is to allow address space pointer conversions. 19733 19734@item -mcache-size=@var{cache-size} 19735@opindex mcache-size 19736This option controls the version of libgcc that the compiler links to an 19737executable and selects a software-managed cache for accessing variables 19738in the @code{__ea} address space with a particular cache size. Possible 19739options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64} 19740and @samp{128}. The default cache size is 64KB. 19741 19742@item -matomic-updates 19743@itemx -mno-atomic-updates 19744@opindex matomic-updates 19745@opindex mno-atomic-updates 19746This option controls the version of libgcc that the compiler links to an 19747executable and selects whether atomic updates to the software-managed 19748cache of PPU-side variables are used. If you use atomic updates, changes 19749to a PPU variable from SPU code using the @code{__ea} named address space 19750qualifier do not interfere with changes to other PPU variables residing 19751in the same cache line from PPU code. If you do not use atomic updates, 19752such interference may occur; however, writing back cache lines is 19753more efficient. The default behavior is to use atomic updates. 19754 19755@item -mdual-nops 19756@itemx -mdual-nops=@var{n} 19757@opindex mdual-nops 19758By default, GCC inserts nops to increase dual issue when it expects 19759it to increase performance. @var{n} can be a value from 0 to 10. A 19760smaller @var{n} inserts fewer nops. 10 is the default, 0 is the 19761same as @option{-mno-dual-nops}. Disabled with @option{-Os}. 19762 19763@item -mhint-max-nops=@var{n} 19764@opindex mhint-max-nops 19765Maximum number of nops to insert for a branch hint. A branch hint must 19766be at least 8 instructions away from the branch it is affecting. GCC 19767inserts up to @var{n} nops to enforce this, otherwise it does not 19768generate the branch hint. 19769 19770@item -mhint-max-distance=@var{n} 19771@opindex mhint-max-distance 19772The encoding of the branch hint instruction limits the hint to be within 19773256 instructions of the branch it is affecting. By default, GCC makes 19774sure it is within 125. 19775 19776@item -msafe-hints 19777@opindex msafe-hints 19778Work around a hardware bug that causes the SPU to stall indefinitely. 19779By default, GCC inserts the @code{hbrp} instruction to make sure 19780this stall won't happen. 19781 19782@end table 19783 19784@node System V Options 19785@subsection Options for System V 19786 19787These additional options are available on System V Release 4 for 19788compatibility with other compilers on those systems: 19789 19790@table @gcctabopt 19791@item -G 19792@opindex G 19793Create a shared object. 19794It is recommended that @option{-symbolic} or @option{-shared} be used instead. 19795 19796@item -Qy 19797@opindex Qy 19798Identify the versions of each tool used by the compiler, in a 19799@code{.ident} assembler directive in the output. 19800 19801@item -Qn 19802@opindex Qn 19803Refrain from adding @code{.ident} directives to the output file (this is 19804the default). 19805 19806@item -YP,@var{dirs} 19807@opindex YP 19808Search the directories @var{dirs}, and no others, for libraries 19809specified with @option{-l}. 19810 19811@item -Ym,@var{dir} 19812@opindex Ym 19813Look in the directory @var{dir} to find the M4 preprocessor. 19814The assembler uses this option. 19815@c This is supposed to go with a -Yd for predefined M4 macro files, but 19816@c the generic assembler that comes with Solaris takes just -Ym. 19817@end table 19818 19819@node TILE-Gx Options 19820@subsection TILE-Gx Options 19821@cindex TILE-Gx options 19822 19823These @samp{-m} options are supported on the TILE-Gx: 19824 19825@table @gcctabopt 19826@item -mcmodel=small 19827@opindex mcmodel=small 19828Generate code for the small model. The distance for direct calls is 19829limited to 500M in either direction. PC-relative addresses are 32 19830bits. Absolute addresses support the full address range. 19831 19832@item -mcmodel=large 19833@opindex mcmodel=large 19834Generate code for the large model. There is no limitation on call 19835distance, pc-relative addresses, or absolute addresses. 19836 19837@item -mcpu=@var{name} 19838@opindex mcpu 19839Selects the type of CPU to be targeted. Currently the only supported 19840type is @samp{tilegx}. 19841 19842@item -m32 19843@itemx -m64 19844@opindex m32 19845@opindex m64 19846Generate code for a 32-bit or 64-bit environment. The 32-bit 19847environment sets int, long, and pointer to 32 bits. The 64-bit 19848environment sets int to 32 bits and long and pointer to 64 bits. 19849@end table 19850 19851@node TILEPro Options 19852@subsection TILEPro Options 19853@cindex TILEPro options 19854 19855These @samp{-m} options are supported on the TILEPro: 19856 19857@table @gcctabopt 19858@item -mcpu=@var{name} 19859@opindex mcpu 19860Selects the type of CPU to be targeted. Currently the only supported 19861type is @samp{tilepro}. 19862 19863@item -m32 19864@opindex m32 19865Generate code for a 32-bit environment, which sets int, long, and 19866pointer to 32 bits. This is the only supported behavior so the flag 19867is essentially ignored. 19868@end table 19869 19870@node V850 Options 19871@subsection V850 Options 19872@cindex V850 Options 19873 19874These @samp{-m} options are defined for V850 implementations: 19875 19876@table @gcctabopt 19877@item -mlong-calls 19878@itemx -mno-long-calls 19879@opindex mlong-calls 19880@opindex mno-long-calls 19881Treat all calls as being far away (near). If calls are assumed to be 19882far away, the compiler always loads the function's address into a 19883register, and calls indirect through the pointer. 19884 19885@item -mno-ep 19886@itemx -mep 19887@opindex mno-ep 19888@opindex mep 19889Do not optimize (do optimize) basic blocks that use the same index 19890pointer 4 or more times to copy pointer into the @code{ep} register, and 19891use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} 19892option is on by default if you optimize. 19893 19894@item -mno-prolog-function 19895@itemx -mprolog-function 19896@opindex mno-prolog-function 19897@opindex mprolog-function 19898Do not use (do use) external functions to save and restore registers 19899at the prologue and epilogue of a function. The external functions 19900are slower, but use less code space if more than one function saves 19901the same number of registers. The @option{-mprolog-function} option 19902is on by default if you optimize. 19903 19904@item -mspace 19905@opindex mspace 19906Try to make the code as small as possible. At present, this just turns 19907on the @option{-mep} and @option{-mprolog-function} options. 19908 19909@item -mtda=@var{n} 19910@opindex mtda 19911Put static or global variables whose size is @var{n} bytes or less into 19912the tiny data area that register @code{ep} points to. The tiny data 19913area can hold up to 256 bytes in total (128 bytes for byte references). 19914 19915@item -msda=@var{n} 19916@opindex msda 19917Put static or global variables whose size is @var{n} bytes or less into 19918the small data area that register @code{gp} points to. The small data 19919area can hold up to 64 kilobytes. 19920 19921@item -mzda=@var{n} 19922@opindex mzda 19923Put static or global variables whose size is @var{n} bytes or less into 19924the first 32 kilobytes of memory. 19925 19926@item -mv850 19927@opindex mv850 19928Specify that the target processor is the V850. 19929 19930@item -mv850e3v5 19931@opindex mv850e3v5 19932Specify that the target processor is the V850E3V5. The preprocessor 19933constant @samp{__v850e3v5__} is defined if this option is used. 19934 19935@item -mv850e2v4 19936@opindex mv850e2v4 19937Specify that the target processor is the V850E3V5. This is an alias for 19938the @option{-mv850e3v5} option. 19939 19940@item -mv850e2v3 19941@opindex mv850e2v3 19942Specify that the target processor is the V850E2V3. The preprocessor 19943constant @samp{__v850e2v3__} is defined if this option is used. 19944 19945@item -mv850e2 19946@opindex mv850e2 19947Specify that the target processor is the V850E2. The preprocessor 19948constant @samp{__v850e2__} is defined if this option is used. 19949 19950@item -mv850e1 19951@opindex mv850e1 19952Specify that the target processor is the V850E1. The preprocessor 19953constants @samp{__v850e1__} and @samp{__v850e__} are defined if 19954this option is used. 19955 19956@item -mv850es 19957@opindex mv850es 19958Specify that the target processor is the V850ES. This is an alias for 19959the @option{-mv850e1} option. 19960 19961@item -mv850e 19962@opindex mv850e 19963Specify that the target processor is the V850E@. The preprocessor 19964constant @samp{__v850e__} is defined if this option is used. 19965 19966If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1} 19967nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5} 19968are defined then a default target processor is chosen and the 19969relevant @samp{__v850*__} preprocessor constant is defined. 19970 19971The preprocessor constants @samp{__v850} and @samp{__v851__} are always 19972defined, regardless of which processor variant is the target. 19973 19974@item -mdisable-callt 19975@itemx -mno-disable-callt 19976@opindex mdisable-callt 19977@opindex mno-disable-callt 19978This option suppresses generation of the @code{CALLT} instruction for the 19979v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 19980architecture. 19981 19982This option is enabled by default when the RH850 ABI is 19983in use (see @option{-mrh850-abi}), and disabled by default when the 19984GCC ABI is in use. If @code{CALLT} instructions are being generated 19985then the C preprocessor symbol @code{__V850_CALLT__} will be defined. 19986 19987@item -mrelax 19988@itemx -mno-relax 19989@opindex mrelax 19990@opindex mno-relax 19991Pass on (or do not pass on) the @option{-mrelax} command line option 19992to the assembler. 19993 19994@item -mlong-jumps 19995@itemx -mno-long-jumps 19996@opindex mlong-jumps 19997@opindex mno-long-jumps 19998Disable (or re-enable) the generation of PC-relative jump instructions. 19999 20000@item -msoft-float 20001@itemx -mhard-float 20002@opindex msoft-float 20003@opindex mhard-float 20004Disable (or re-enable) the generation of hardware floating point 20005instructions. This option is only significant when the target 20006architecture is @samp{V850E2V3} or higher. If hardware floating point 20007instructions are being generated then the C preprocessor symbol 20008@code{__FPU_OK__} will be defined, otherwise the symbol 20009@code{__NO_FPU__} will be defined. 20010 20011@item -mloop 20012@opindex mloop 20013Enables the use of the e3v5 LOOP instruction. The use of this 20014instruction is not enabled by default when the e3v5 architecture is 20015selected because its use is still experimental. 20016 20017@item -mrh850-abi 20018@itemx -mghs 20019@opindex mrh850-abi 20020@opindex mghs 20021Enables support for the RH850 version of the V850 ABI. This is the 20022default. With this version of the ABI the following rules apply: 20023 20024@itemize 20025@item 20026Integer sized structures and unions are returned via a memory pointer 20027rather than a register. 20028 20029@item 20030Large structures and unions (more than 8 bytes in size) are passed by 20031value. 20032 20033@item 20034Functions are aligned to 16-bit boundaries. 20035 20036@item 20037The @option{-m8byte-align} command line option is supported. 20038 20039@item 20040The @option{-mdisable-callt} command line option is enabled by 20041default. The @option{-mno-disable-callt} command line option is not 20042supported. 20043@end itemize 20044 20045When this version of the ABI is enabled the C preprocessor symbol 20046@code{__V850_RH850_ABI__} is defined. 20047 20048@item -mgcc-abi 20049@opindex mgcc-abi 20050Enables support for the old GCC version of the V850 ABI. With this 20051version of the ABI the following rules apply: 20052 20053@itemize 20054@item 20055Integer sized structures and unions are returned in register @code{r10}. 20056 20057@item 20058Large structures and unions (more than 8 bytes in size) are passed by 20059reference. 20060 20061@item 20062Functions are aligned to 32-bit boundaries, unless optimizing for 20063size. 20064 20065@item 20066The @option{-m8byte-align} command line option is not supported. 20067 20068@item 20069The @option{-mdisable-callt} command line option is supported but not 20070enabled by default. 20071@end itemize 20072 20073When this version of the ABI is enabled the C preprocessor symbol 20074@code{__V850_GCC_ABI__} is defined. 20075 20076@item -m8byte-align 20077@itemx -mno-8byte-align 20078@opindex m8byte-align 20079@opindex mno-8byte-align 20080Enables support for @code{doubles} and @code{long long} types to be 20081aligned on 8-byte boundaries. The default is to restrict the 20082alignment of all objects to at most 4-bytes. When 20083@option{-m8byte-align} is in effect the C preprocessor symbol 20084@code{__V850_8BYTE_ALIGN__} will be defined. 20085 20086@item -mbig-switch 20087@opindex mbig-switch 20088Generate code suitable for big switch tables. Use this option only if 20089the assembler/linker complain about out of range branches within a switch 20090table. 20091 20092@item -mapp-regs 20093@opindex mapp-regs 20094This option causes r2 and r5 to be used in the code generated by 20095the compiler. This setting is the default. 20096 20097@item -mno-app-regs 20098@opindex mno-app-regs 20099This option causes r2 and r5 to be treated as fixed registers. 20100 20101@end table 20102 20103@node VAX Options 20104@subsection VAX Options 20105@cindex VAX options 20106 20107These @samp{-m} options are defined for the VAX: 20108 20109@table @gcctabopt 20110@item -munix 20111@opindex munix 20112Do not output certain jump instructions (@code{aobleq} and so on) 20113that the Unix assembler for the VAX cannot handle across long 20114ranges. 20115 20116@item -mgnu 20117@opindex mgnu 20118Do output those jump instructions, on the assumption that the 20119GNU assembler is being used. 20120 20121@item -mg 20122@opindex mg 20123Output code for G-format floating-point numbers instead of D-format. 20124@end table 20125 20126@node VMS Options 20127@subsection VMS Options 20128 20129These @samp{-m} options are defined for the VMS implementations: 20130 20131@table @gcctabopt 20132@item -mvms-return-codes 20133@opindex mvms-return-codes 20134Return VMS condition codes from @code{main}. The default is to return POSIX-style 20135condition (e.g.@ error) codes. 20136 20137@item -mdebug-main=@var{prefix} 20138@opindex mdebug-main=@var{prefix} 20139Flag the first routine whose name starts with @var{prefix} as the main 20140routine for the debugger. 20141 20142@item -mmalloc64 20143@opindex mmalloc64 20144Default to 64-bit memory allocation routines. 20145 20146@item -mpointer-size=@var{size} 20147@opindex -mpointer-size=@var{size} 20148Set the default size of pointers. Possible options for @var{size} are 20149@samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long} 20150for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers. 20151The later option disables @code{pragma pointer_size}. 20152@end table 20153 20154@node VxWorks Options 20155@subsection VxWorks Options 20156@cindex VxWorks Options 20157 20158The options in this section are defined for all VxWorks targets. 20159Options specific to the target hardware are listed with the other 20160options for that target. 20161 20162@table @gcctabopt 20163@item -mrtp 20164@opindex mrtp 20165GCC can generate code for both VxWorks kernels and real time processes 20166(RTPs). This option switches from the former to the latter. It also 20167defines the preprocessor macro @code{__RTP__}. 20168 20169@item -non-static 20170@opindex non-static 20171Link an RTP executable against shared libraries rather than static 20172libraries. The options @option{-static} and @option{-shared} can 20173also be used for RTPs (@pxref{Link Options}); @option{-static} 20174is the default. 20175 20176@item -Bstatic 20177@itemx -Bdynamic 20178@opindex Bstatic 20179@opindex Bdynamic 20180These options are passed down to the linker. They are defined for 20181compatibility with Diab. 20182 20183@item -Xbind-lazy 20184@opindex Xbind-lazy 20185Enable lazy binding of function calls. This option is equivalent to 20186@option{-Wl,-z,now} and is defined for compatibility with Diab. 20187 20188@item -Xbind-now 20189@opindex Xbind-now 20190Disable lazy binding of function calls. This option is the default and 20191is defined for compatibility with Diab. 20192@end table 20193 20194@node x86-64 Options 20195@subsection x86-64 Options 20196@cindex x86-64 options 20197 20198These are listed under @xref{i386 and x86-64 Options}. 20199 20200@node Xstormy16 Options 20201@subsection Xstormy16 Options 20202@cindex Xstormy16 Options 20203 20204These options are defined for Xstormy16: 20205 20206@table @gcctabopt 20207@item -msim 20208@opindex msim 20209Choose startup files and linker script suitable for the simulator. 20210@end table 20211 20212@node Xtensa Options 20213@subsection Xtensa Options 20214@cindex Xtensa Options 20215 20216These options are supported for Xtensa targets: 20217 20218@table @gcctabopt 20219@item -mconst16 20220@itemx -mno-const16 20221@opindex mconst16 20222@opindex mno-const16 20223Enable or disable use of @code{CONST16} instructions for loading 20224constant values. The @code{CONST16} instruction is currently not a 20225standard option from Tensilica. When enabled, @code{CONST16} 20226instructions are always used in place of the standard @code{L32R} 20227instructions. The use of @code{CONST16} is enabled by default only if 20228the @code{L32R} instruction is not available. 20229 20230@item -mfused-madd 20231@itemx -mno-fused-madd 20232@opindex mfused-madd 20233@opindex mno-fused-madd 20234Enable or disable use of fused multiply/add and multiply/subtract 20235instructions in the floating-point option. This has no effect if the 20236floating-point option is not also enabled. Disabling fused multiply/add 20237and multiply/subtract instructions forces the compiler to use separate 20238instructions for the multiply and add/subtract operations. This may be 20239desirable in some cases where strict IEEE 754-compliant results are 20240required: the fused multiply add/subtract instructions do not round the 20241intermediate result, thereby producing results with @emph{more} bits of 20242precision than specified by the IEEE standard. Disabling fused multiply 20243add/subtract instructions also ensures that the program output is not 20244sensitive to the compiler's ability to combine multiply and add/subtract 20245operations. 20246 20247@item -mserialize-volatile 20248@itemx -mno-serialize-volatile 20249@opindex mserialize-volatile 20250@opindex mno-serialize-volatile 20251When this option is enabled, GCC inserts @code{MEMW} instructions before 20252@code{volatile} memory references to guarantee sequential consistency. 20253The default is @option{-mserialize-volatile}. Use 20254@option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. 20255 20256@item -mforce-no-pic 20257@opindex mforce-no-pic 20258For targets, like GNU/Linux, where all user-mode Xtensa code must be 20259position-independent code (PIC), this option disables PIC for compiling 20260kernel code. 20261 20262@item -mtext-section-literals 20263@itemx -mno-text-section-literals 20264@opindex mtext-section-literals 20265@opindex mno-text-section-literals 20266Control the treatment of literal pools. The default is 20267@option{-mno-text-section-literals}, which places literals in a separate 20268section in the output file. This allows the literal pool to be placed 20269in a data RAM/ROM, and it also allows the linker to combine literal 20270pools from separate object files to remove redundant literals and 20271improve code size. With @option{-mtext-section-literals}, the literals 20272are interspersed in the text section in order to keep them as close as 20273possible to their references. This may be necessary for large assembly 20274files. 20275 20276@item -mtarget-align 20277@itemx -mno-target-align 20278@opindex mtarget-align 20279@opindex mno-target-align 20280When this option is enabled, GCC instructs the assembler to 20281automatically align instructions to reduce branch penalties at the 20282expense of some code density. The assembler attempts to widen density 20283instructions to align branch targets and the instructions following call 20284instructions. If there are not enough preceding safe density 20285instructions to align a target, no widening is performed. The 20286default is @option{-mtarget-align}. These options do not affect the 20287treatment of auto-aligned instructions like @code{LOOP}, which the 20288assembler always aligns, either by widening density instructions or 20289by inserting NOP instructions. 20290 20291@item -mlongcalls 20292@itemx -mno-longcalls 20293@opindex mlongcalls 20294@opindex mno-longcalls 20295When this option is enabled, GCC instructs the assembler to translate 20296direct calls to indirect calls unless it can determine that the target 20297of a direct call is in the range allowed by the call instruction. This 20298translation typically occurs for calls to functions in other source 20299files. Specifically, the assembler translates a direct @code{CALL} 20300instruction into an @code{L32R} followed by a @code{CALLX} instruction. 20301The default is @option{-mno-longcalls}. This option should be used in 20302programs where the call target can potentially be out of range. This 20303option is implemented in the assembler, not the compiler, so the 20304assembly code generated by GCC still shows direct call 20305instructions---look at the disassembled object code to see the actual 20306instructions. Note that the assembler uses an indirect call for 20307every cross-file call, not just those that really are out of range. 20308@end table 20309 20310@node zSeries Options 20311@subsection zSeries Options 20312@cindex zSeries options 20313 20314These are listed under @xref{S/390 and zSeries Options}. 20315 20316@node Code Gen Options 20317@section Options for Code Generation Conventions 20318@cindex code generation conventions 20319@cindex options, code generation 20320@cindex run-time options 20321 20322These machine-independent options control the interface conventions 20323used in code generation. 20324 20325Most of them have both positive and negative forms; the negative form 20326of @option{-ffoo} is @option{-fno-foo}. In the table below, only 20327one of the forms is listed---the one that is not the default. You 20328can figure out the other form by either removing @samp{no-} or adding 20329it. 20330 20331@table @gcctabopt 20332@item -fbounds-check 20333@opindex fbounds-check 20334For front ends that support it, generate additional code to check that 20335indices used to access arrays are within the declared range. This is 20336currently only supported by the Java and Fortran front ends, where 20337this option defaults to true and false respectively. 20338 20339@item -fstack-reuse=@var{reuse-level} 20340@opindex fstack_reuse 20341This option controls stack space reuse for user declared local/auto variables 20342and compiler generated temporaries. @var{reuse_level} can be @samp{all}, 20343@samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all 20344local variables and temporaries, @samp{named_vars} enables the reuse only for 20345user defined local variables with names, and @samp{none} disables stack reuse 20346completely. The default value is @samp{all}. The option is needed when the 20347program extends the lifetime of a scoped local variable or a compiler generated 20348temporary beyond the end point defined by the language. When a lifetime of 20349a variable ends, and if the variable lives in memory, the optimizing compiler 20350has the freedom to reuse its stack space with other temporaries or scoped 20351local variables whose live range does not overlap with it. Legacy code extending 20352local lifetime will likely to break with the stack reuse optimization. 20353 20354For example, 20355 20356@smallexample 20357 int *p; 20358 @{ 20359 int local1; 20360 20361 p = &local1; 20362 local1 = 10; 20363 .... 20364 @} 20365 @{ 20366 int local2; 20367 local2 = 20; 20368 ... 20369 @} 20370 20371 if (*p == 10) // out of scope use of local1 20372 @{ 20373 20374 @} 20375@end smallexample 20376 20377Another example: 20378@smallexample 20379 20380 struct A 20381 @{ 20382 A(int k) : i(k), j(k) @{ @} 20383 int i; 20384 int j; 20385 @}; 20386 20387 A *ap; 20388 20389 void foo(const A& ar) 20390 @{ 20391 ap = &ar; 20392 @} 20393 20394 void bar() 20395 @{ 20396 foo(A(10)); // temp object's lifetime ends when foo returns 20397 20398 @{ 20399 A a(20); 20400 .... 20401 @} 20402 ap->i+= 10; // ap references out of scope temp whose space 20403 // is reused with a. What is the value of ap->i? 20404 @} 20405 20406@end smallexample 20407 20408The lifetime of a compiler generated temporary is well defined by the C++ 20409standard. When a lifetime of a temporary ends, and if the temporary lives 20410in memory, the optimizing compiler has the freedom to reuse its stack 20411space with other temporaries or scoped local variables whose live range 20412does not overlap with it. However some of the legacy code relies on 20413the behavior of older compilers in which temporaries' stack space is 20414not reused, the aggressive stack reuse can lead to runtime errors. This 20415option is used to control the temporary stack reuse optimization. 20416 20417@item -ftrapv 20418@opindex ftrapv 20419This option generates traps for signed overflow on addition, subtraction, 20420multiplication operations. 20421 20422@item -fwrapv 20423@opindex fwrapv 20424This option instructs the compiler to assume that signed arithmetic 20425overflow of addition, subtraction and multiplication wraps around 20426using twos-complement representation. This flag enables some optimizations 20427and disables others. This option is enabled by default for the Java 20428front end, as required by the Java language specification. 20429 20430@item -fexceptions 20431@opindex fexceptions 20432Enable exception handling. Generates extra code needed to propagate 20433exceptions. For some targets, this implies GCC generates frame 20434unwind information for all functions, which can produce significant data 20435size overhead, although it does not affect execution. If you do not 20436specify this option, GCC enables it by default for languages like 20437C++ that normally require exception handling, and disables it for 20438languages like C that do not normally require it. However, you may need 20439to enable this option when compiling C code that needs to interoperate 20440properly with exception handlers written in C++. You may also wish to 20441disable this option if you are compiling older C++ programs that don't 20442use exception handling. 20443 20444@item -fnon-call-exceptions 20445@opindex fnon-call-exceptions 20446Generate code that allows trapping instructions to throw exceptions. 20447Note that this requires platform-specific runtime support that does 20448not exist everywhere. Moreover, it only allows @emph{trapping} 20449instructions to throw exceptions, i.e.@: memory references or floating-point 20450instructions. It does not allow exceptions to be thrown from 20451arbitrary signal handlers such as @code{SIGALRM}. 20452 20453@item -fdelete-dead-exceptions 20454@opindex fdelete-dead-exceptions 20455Consider that instructions that may throw exceptions but don't otherwise 20456contribute to the execution of the program can be optimized away. 20457This option is enabled by default for the Ada front end, as permitted by 20458the Ada language specification. 20459Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. 20460 20461@item -funwind-tables 20462@opindex funwind-tables 20463Similar to @option{-fexceptions}, except that it just generates any needed 20464static data, but does not affect the generated code in any other way. 20465You normally do not need to enable this option; instead, a language processor 20466that needs this handling enables it on your behalf. 20467 20468@item -fasynchronous-unwind-tables 20469@opindex fasynchronous-unwind-tables 20470Generate unwind table in DWARF 2 format, if supported by target machine. The 20471table is exact at each instruction boundary, so it can be used for stack 20472unwinding from asynchronous events (such as debugger or garbage collector). 20473 20474@item -fno-gnu-unique 20475@opindex fno-gnu-unique 20476On systems with recent GNU assembler and C library, the C++ compiler 20477uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions 20478of template static data members and static local variables in inline 20479functions are unique even in the presence of @code{RTLD_LOCAL}; this 20480is necessary to avoid problems with a library used by two different 20481@code{RTLD_LOCAL} plugins depending on a definition in one of them and 20482therefore disagreeing with the other one about the binding of the 20483symbol. But this causes @code{dlclose} to be ignored for affected 20484DSOs; if your program relies on reinitialization of a DSO via 20485@code{dlclose} and @code{dlopen}, you can use 20486@option{-fno-gnu-unique}. 20487 20488@item -fpcc-struct-return 20489@opindex fpcc-struct-return 20490Return ``short'' @code{struct} and @code{union} values in memory like 20491longer ones, rather than in registers. This convention is less 20492efficient, but it has the advantage of allowing intercallability between 20493GCC-compiled files and files compiled with other compilers, particularly 20494the Portable C Compiler (pcc). 20495 20496The precise convention for returning structures in memory depends 20497on the target configuration macros. 20498 20499Short structures and unions are those whose size and alignment match 20500that of some integer type. 20501 20502@strong{Warning:} code compiled with the @option{-fpcc-struct-return} 20503switch is not binary compatible with code compiled with the 20504@option{-freg-struct-return} switch. 20505Use it to conform to a non-default application binary interface. 20506 20507@item -freg-struct-return 20508@opindex freg-struct-return 20509Return @code{struct} and @code{union} values in registers when possible. 20510This is more efficient for small structures than 20511@option{-fpcc-struct-return}. 20512 20513If you specify neither @option{-fpcc-struct-return} nor 20514@option{-freg-struct-return}, GCC defaults to whichever convention is 20515standard for the target. If there is no standard convention, GCC 20516defaults to @option{-fpcc-struct-return}, except on targets where GCC is 20517the principal compiler. In those cases, we can choose the standard, and 20518we chose the more efficient register return alternative. 20519 20520@strong{Warning:} code compiled with the @option{-freg-struct-return} 20521switch is not binary compatible with code compiled with the 20522@option{-fpcc-struct-return} switch. 20523Use it to conform to a non-default application binary interface. 20524 20525@item -fshort-enums 20526@opindex fshort-enums 20527Allocate to an @code{enum} type only as many bytes as it needs for the 20528declared range of possible values. Specifically, the @code{enum} type 20529is equivalent to the smallest integer type that has enough room. 20530 20531@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate 20532code that is not binary compatible with code generated without that switch. 20533Use it to conform to a non-default application binary interface. 20534 20535@item -fshort-double 20536@opindex fshort-double 20537Use the same size for @code{double} as for @code{float}. 20538 20539@strong{Warning:} the @option{-fshort-double} switch causes GCC to generate 20540code that is not binary compatible with code generated without that switch. 20541Use it to conform to a non-default application binary interface. 20542 20543@item -fshort-wchar 20544@opindex fshort-wchar 20545Override the underlying type for @samp{wchar_t} to be @samp{short 20546unsigned int} instead of the default for the target. This option is 20547useful for building programs to run under WINE@. 20548 20549@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate 20550code that is not binary compatible with code generated without that switch. 20551Use it to conform to a non-default application binary interface. 20552 20553@item -fno-common 20554@opindex fno-common 20555In C code, controls the placement of uninitialized global variables. 20556Unix C compilers have traditionally permitted multiple definitions of 20557such variables in different compilation units by placing the variables 20558in a common block. 20559This is the behavior specified by @option{-fcommon}, and is the default 20560for GCC on most targets. 20561On the other hand, this behavior is not required by ISO C, and on some 20562targets may carry a speed or code size penalty on variable references. 20563The @option{-fno-common} option specifies that the compiler should place 20564uninitialized global variables in the data section of the object file, 20565rather than generating them as common blocks. 20566This has the effect that if the same variable is declared 20567(without @code{extern}) in two different compilations, 20568you get a multiple-definition error when you link them. 20569In this case, you must compile with @option{-fcommon} instead. 20570Compiling with @option{-fno-common} is useful on targets for which 20571it provides better performance, or if you wish to verify that the 20572program will work on other systems that always treat uninitialized 20573variable declarations this way. 20574 20575@item -fno-ident 20576@opindex fno-ident 20577Ignore the @samp{#ident} directive. 20578 20579@item -finhibit-size-directive 20580@opindex finhibit-size-directive 20581Don't output a @code{.size} assembler directive, or anything else that 20582would cause trouble if the function is split in the middle, and the 20583two halves are placed at locations far apart in memory. This option is 20584used when compiling @file{crtstuff.c}; you should not need to use it 20585for anything else. 20586 20587@item -fverbose-asm 20588@opindex fverbose-asm 20589Put extra commentary information in the generated assembly code to 20590make it more readable. This option is generally only of use to those 20591who actually need to read the generated assembly code (perhaps while 20592debugging the compiler itself). 20593 20594@option{-fno-verbose-asm}, the default, causes the 20595extra information to be omitted and is useful when comparing two assembler 20596files. 20597 20598@item -frecord-gcc-switches 20599@opindex frecord-gcc-switches 20600This switch causes the command line used to invoke the 20601compiler to be recorded into the object file that is being created. 20602This switch is only implemented on some targets and the exact format 20603of the recording is target and binary file format dependent, but it 20604usually takes the form of a section containing ASCII text. This 20605switch is related to the @option{-fverbose-asm} switch, but that 20606switch only records information in the assembler output file as 20607comments, so it never reaches the object file. 20608See also @option{-grecord-gcc-switches} for another 20609way of storing compiler options into the object file. 20610 20611@item -fpic 20612@opindex fpic 20613@cindex global offset table 20614@cindex PIC 20615Generate position-independent code (PIC) suitable for use in a shared 20616library, if supported for the target machine. Such code accesses all 20617constant addresses through a global offset table (GOT)@. The dynamic 20618loader resolves the GOT entries when the program starts (the dynamic 20619loader is not part of GCC; it is part of the operating system). If 20620the GOT size for the linked executable exceeds a machine-specific 20621maximum size, you get an error message from the linker indicating that 20622@option{-fpic} does not work; in that case, recompile with @option{-fPIC} 20623instead. (These maximums are 8k on the SPARC and 32k 20624on the m68k and RS/6000. The 386 has no such limit.) 20625 20626Position-independent code requires special support, and therefore works 20627only on certain machines. For the 386, GCC supports PIC for System V 20628but not for the Sun 386i. Code generated for the IBM RS/6000 is always 20629position-independent. 20630 20631When this flag is set, the macros @code{__pic__} and @code{__PIC__} 20632are defined to 1. 20633 20634@item -fPIC 20635@opindex fPIC 20636If supported for the target machine, emit position-independent code, 20637suitable for dynamic linking and avoiding any limit on the size of the 20638global offset table. This option makes a difference on the m68k, 20639PowerPC and SPARC@. 20640 20641Position-independent code requires special support, and therefore works 20642only on certain machines. 20643 20644When this flag is set, the macros @code{__pic__} and @code{__PIC__} 20645are defined to 2. 20646 20647@item -fpie 20648@itemx -fPIE 20649@opindex fpie 20650@opindex fPIE 20651These options are similar to @option{-fpic} and @option{-fPIC}, but 20652generated position independent code can be only linked into executables. 20653Usually these options are used when @option{-pie} GCC option is 20654used during linking. 20655 20656@option{-fpie} and @option{-fPIE} both define the macros 20657@code{__pie__} and @code{__PIE__}. The macros have the value 1 20658for @option{-fpie} and 2 for @option{-fPIE}. 20659 20660@item -fno-jump-tables 20661@opindex fno-jump-tables 20662Do not use jump tables for switch statements even where it would be 20663more efficient than other code generation strategies. This option is 20664of use in conjunction with @option{-fpic} or @option{-fPIC} for 20665building code that forms part of a dynamic linker and cannot 20666reference the address of a jump table. On some targets, jump tables 20667do not require a GOT and this option is not needed. 20668 20669@item -ffixed-@var{reg} 20670@opindex ffixed 20671Treat the register named @var{reg} as a fixed register; generated code 20672should never refer to it (except perhaps as a stack pointer, frame 20673pointer or in some other fixed role). 20674 20675@var{reg} must be the name of a register. The register names accepted 20676are machine-specific and are defined in the @code{REGISTER_NAMES} 20677macro in the machine description macro file. 20678 20679This flag does not have a negative form, because it specifies a 20680three-way choice. 20681 20682@item -fcall-used-@var{reg} 20683@opindex fcall-used 20684Treat the register named @var{reg} as an allocable register that is 20685clobbered by function calls. It may be allocated for temporaries or 20686variables that do not live across a call. Functions compiled this way 20687do not save and restore the register @var{reg}. 20688 20689It is an error to use this flag with the frame pointer or stack pointer. 20690Use of this flag for other registers that have fixed pervasive roles in 20691the machine's execution model produces disastrous results. 20692 20693This flag does not have a negative form, because it specifies a 20694three-way choice. 20695 20696@item -fcall-saved-@var{reg} 20697@opindex fcall-saved 20698Treat the register named @var{reg} as an allocable register saved by 20699functions. It may be allocated even for temporaries or variables that 20700live across a call. Functions compiled this way save and restore 20701the register @var{reg} if they use it. 20702 20703It is an error to use this flag with the frame pointer or stack pointer. 20704Use of this flag for other registers that have fixed pervasive roles in 20705the machine's execution model produces disastrous results. 20706 20707A different sort of disaster results from the use of this flag for 20708a register in which function values may be returned. 20709 20710This flag does not have a negative form, because it specifies a 20711three-way choice. 20712 20713@item -fpack-struct[=@var{n}] 20714@opindex fpack-struct 20715Without a value specified, pack all structure members together without 20716holes. When a value is specified (which must be a small power of two), pack 20717structure members according to this value, representing the maximum 20718alignment (that is, objects with default alignment requirements larger than 20719this are output potentially unaligned at the next fitting location. 20720 20721@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate 20722code that is not binary compatible with code generated without that switch. 20723Additionally, it makes the code suboptimal. 20724Use it to conform to a non-default application binary interface. 20725 20726@item -finstrument-functions 20727@opindex finstrument-functions 20728Generate instrumentation calls for entry and exit to functions. Just 20729after function entry and just before function exit, the following 20730profiling functions are called with the address of the current 20731function and its call site. (On some platforms, 20732@code{__builtin_return_address} does not work beyond the current 20733function, so the call site information may not be available to the 20734profiling functions otherwise.) 20735 20736@smallexample 20737void __cyg_profile_func_enter (void *this_fn, 20738 void *call_site); 20739void __cyg_profile_func_exit (void *this_fn, 20740 void *call_site); 20741@end smallexample 20742 20743The first argument is the address of the start of the current function, 20744which may be looked up exactly in the symbol table. 20745 20746This instrumentation is also done for functions expanded inline in other 20747functions. The profiling calls indicate where, conceptually, the 20748inline function is entered and exited. This means that addressable 20749versions of such functions must be available. If all your uses of a 20750function are expanded inline, this may mean an additional expansion of 20751code size. If you use @samp{extern inline} in your C code, an 20752addressable version of such functions must be provided. (This is 20753normally the case anyway, but if you get lucky and the optimizer always 20754expands the functions inline, you might have gotten away without 20755providing static copies.) 20756 20757A function may be given the attribute @code{no_instrument_function}, in 20758which case this instrumentation is not done. This can be used, for 20759example, for the profiling functions listed above, high-priority 20760interrupt routines, and any functions from which the profiling functions 20761cannot safely be called (perhaps signal handlers, if the profiling 20762routines generate output or allocate memory). 20763 20764@item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} 20765@opindex finstrument-functions-exclude-file-list 20766 20767Set the list of functions that are excluded from instrumentation (see 20768the description of @code{-finstrument-functions}). If the file that 20769contains a function definition matches with one of @var{file}, then 20770that function is not instrumented. The match is done on substrings: 20771if the @var{file} parameter is a substring of the file name, it is 20772considered to be a match. 20773 20774For example: 20775 20776@smallexample 20777-finstrument-functions-exclude-file-list=/bits/stl,include/sys 20778@end smallexample 20779 20780@noindent 20781excludes any inline function defined in files whose pathnames 20782contain @code{/bits/stl} or @code{include/sys}. 20783 20784If, for some reason, you want to include letter @code{','} in one of 20785@var{sym}, write @code{'\,'}. For example, 20786@code{-finstrument-functions-exclude-file-list='\,\,tmp'} 20787(note the single quote surrounding the option). 20788 20789@item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} 20790@opindex finstrument-functions-exclude-function-list 20791 20792This is similar to @code{-finstrument-functions-exclude-file-list}, 20793but this option sets the list of function names to be excluded from 20794instrumentation. The function name to be matched is its user-visible 20795name, such as @code{vector<int> blah(const vector<int> &)}, not the 20796internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The 20797match is done on substrings: if the @var{sym} parameter is a substring 20798of the function name, it is considered to be a match. For C99 and C++ 20799extended identifiers, the function name must be given in UTF-8, not 20800using universal character names. 20801 20802@item -fstack-check 20803@opindex fstack-check 20804Generate code to verify that you do not go beyond the boundary of the 20805stack. You should specify this flag if you are running in an 20806environment with multiple threads, but you only rarely need to specify it in 20807a single-threaded environment since stack overflow is automatically 20808detected on nearly all systems if there is only one stack. 20809 20810Note that this switch does not actually cause checking to be done; the 20811operating system or the language runtime must do that. The switch causes 20812generation of code to ensure that they see the stack being extended. 20813 20814You can additionally specify a string parameter: @code{no} means no 20815checking, @code{generic} means force the use of old-style checking, 20816@code{specific} means use the best checking method and is equivalent 20817to bare @option{-fstack-check}. 20818 20819Old-style checking is a generic mechanism that requires no specific 20820target support in the compiler but comes with the following drawbacks: 20821 20822@enumerate 20823@item 20824Modified allocation strategy for large objects: they are always 20825allocated dynamically if their size exceeds a fixed threshold. 20826 20827@item 20828Fixed limit on the size of the static frame of functions: when it is 20829topped by a particular function, stack checking is not reliable and 20830a warning is issued by the compiler. 20831 20832@item 20833Inefficiency: because of both the modified allocation strategy and the 20834generic implementation, code performance is hampered. 20835@end enumerate 20836 20837Note that old-style stack checking is also the fallback method for 20838@code{specific} if no target support has been added in the compiler. 20839 20840@item -fstack-limit-register=@var{reg} 20841@itemx -fstack-limit-symbol=@var{sym} 20842@itemx -fno-stack-limit 20843@opindex fstack-limit-register 20844@opindex fstack-limit-symbol 20845@opindex fno-stack-limit 20846Generate code to ensure that the stack does not grow beyond a certain value, 20847either the value of a register or the address of a symbol. If a larger 20848stack is required, a signal is raised at run time. For most targets, 20849the signal is raised before the stack overruns the boundary, so 20850it is possible to catch the signal without taking special precautions. 20851 20852For instance, if the stack starts at absolute address @samp{0x80000000} 20853and grows downwards, you can use the flags 20854@option{-fstack-limit-symbol=__stack_limit} and 20855@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit 20856of 128KB@. Note that this may only work with the GNU linker. 20857 20858@item -fsplit-stack 20859@opindex fsplit-stack 20860Generate code to automatically split the stack before it overflows. 20861The resulting program has a discontiguous stack which can only 20862overflow if the program is unable to allocate any more memory. This 20863is most useful when running threaded programs, as it is no longer 20864necessary to calculate a good stack size to use for each thread. This 20865is currently only implemented for the i386 and x86_64 back ends running 20866GNU/Linux. 20867 20868When code compiled with @option{-fsplit-stack} calls code compiled 20869without @option{-fsplit-stack}, there may not be much stack space 20870available for the latter code to run. If compiling all code, 20871including library code, with @option{-fsplit-stack} is not an option, 20872then the linker can fix up these calls so that the code compiled 20873without @option{-fsplit-stack} always has a large stack. Support for 20874this is implemented in the gold linker in GNU binutils release 2.21 20875and later. 20876 20877@item -fleading-underscore 20878@opindex fleading-underscore 20879This option and its counterpart, @option{-fno-leading-underscore}, forcibly 20880change the way C symbols are represented in the object file. One use 20881is to help link with legacy assembly code. 20882 20883@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to 20884generate code that is not binary compatible with code generated without that 20885switch. Use it to conform to a non-default application binary interface. 20886Not all targets provide complete support for this switch. 20887 20888@item -ftls-model=@var{model} 20889@opindex ftls-model 20890Alter the thread-local storage model to be used (@pxref{Thread-Local}). 20891The @var{model} argument should be one of @code{global-dynamic}, 20892@code{local-dynamic}, @code{initial-exec} or @code{local-exec}. 20893 20894The default without @option{-fpic} is @code{initial-exec}; with 20895@option{-fpic} the default is @code{global-dynamic}. 20896 20897@item -fvisibility=@var{default|internal|hidden|protected} 20898@opindex fvisibility 20899Set the default ELF image symbol visibility to the specified option---all 20900symbols are marked with this unless overridden within the code. 20901Using this feature can very substantially improve linking and 20902load times of shared object libraries, produce more optimized 20903code, provide near-perfect API export and prevent symbol clashes. 20904It is @strong{strongly} recommended that you use this in any shared objects 20905you distribute. 20906 20907Despite the nomenclature, @code{default} always means public; i.e., 20908available to be linked against from outside the shared object. 20909@code{protected} and @code{internal} are pretty useless in real-world 20910usage so the only other commonly used option is @code{hidden}. 20911The default if @option{-fvisibility} isn't specified is 20912@code{default}, i.e., make every 20913symbol public---this causes the same behavior as previous versions of 20914GCC@. 20915 20916A good explanation of the benefits offered by ensuring ELF 20917symbols have the correct visibility is given by ``How To Write 20918Shared Libraries'' by Ulrich Drepper (which can be found at 20919@w{@uref{http://people.redhat.com/~drepper/}})---however a superior 20920solution made possible by this option to marking things hidden when 20921the default is public is to make the default hidden and mark things 20922public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden} 20923and @code{__attribute__ ((visibility("default")))} instead of 20924@code{__declspec(dllexport)} you get almost identical semantics with 20925identical syntax. This is a great boon to those working with 20926cross-platform projects. 20927 20928For those adding visibility support to existing code, you may find 20929@samp{#pragma GCC visibility} of use. This works by you enclosing 20930the declarations you wish to set visibility for with (for example) 20931@samp{#pragma GCC visibility push(hidden)} and 20932@samp{#pragma GCC visibility pop}. 20933Bear in mind that symbol visibility should be viewed @strong{as 20934part of the API interface contract} and thus all new code should 20935always specify visibility when it is not the default; i.e., declarations 20936only for use within the local DSO should @strong{always} be marked explicitly 20937as hidden as so to avoid PLT indirection overheads---making this 20938abundantly clear also aids readability and self-documentation of the code. 20939Note that due to ISO C++ specification requirements, @code{operator new} and 20940@code{operator delete} must always be of default visibility. 20941 20942Be aware that headers from outside your project, in particular system 20943headers and headers from any other library you use, may not be 20944expecting to be compiled with visibility other than the default. You 20945may need to explicitly say @samp{#pragma GCC visibility push(default)} 20946before including any such headers. 20947 20948@samp{extern} declarations are not affected by @option{-fvisibility}, so 20949a lot of code can be recompiled with @option{-fvisibility=hidden} with 20950no modifications. However, this means that calls to @code{extern} 20951functions with no explicit visibility use the PLT, so it is more 20952effective to use @code{__attribute ((visibility))} and/or 20953@code{#pragma GCC visibility} to tell the compiler which @code{extern} 20954declarations should be treated as hidden. 20955 20956Note that @option{-fvisibility} does affect C++ vague linkage 20957entities. This means that, for instance, an exception class that is 20958be thrown between DSOs must be explicitly marked with default 20959visibility so that the @samp{type_info} nodes are unified between 20960the DSOs. 20961 20962An overview of these techniques, their benefits and how to use them 20963is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}. 20964 20965@item -fstrict-volatile-bitfields 20966@opindex fstrict-volatile-bitfields 20967This option should be used if accesses to volatile bit-fields (or other 20968structure fields, although the compiler usually honors those types 20969anyway) should use a single access of the width of the 20970field's type, aligned to a natural alignment if possible. For 20971example, targets with memory-mapped peripheral registers might require 20972all such accesses to be 16 bits wide; with this flag you can 20973declare all peripheral bit-fields as @code{unsigned short} (assuming short 20974is 16 bits on these targets) to force GCC to use 16-bit accesses 20975instead of, perhaps, a more efficient 32-bit access. 20976 20977If this option is disabled, the compiler uses the most efficient 20978instruction. In the previous example, that might be a 32-bit load 20979instruction, even though that accesses bytes that do not contain 20980any portion of the bit-field, or memory-mapped registers unrelated to 20981the one being updated. 20982 20983If the target requires strict alignment, and honoring the field 20984type would require violating this alignment, a warning is issued. 20985If the field has @code{packed} attribute, the access is done without 20986honoring the field type. If the field doesn't have @code{packed} 20987attribute, the access is done honoring the field type. In both cases, 20988GCC assumes that the user knows something about the target hardware 20989that it is unaware of. 20990 20991The default value of this option is determined by the application binary 20992interface for the target processor. 20993 20994@item -fsync-libcalls 20995@opindex fsync-libcalls 20996This option controls whether any out-of-line instance of the @code{__sync} 20997family of functions may be used to implement the C++11 @code{__atomic} 20998family of functions. 20999 21000The default value of this option is enabled, thus the only useful form 21001of the option is @option{-fno-sync-libcalls}. This option is used in 21002the implementation of the @file{libatomic} runtime library. 21003 21004@end table 21005 21006@c man end 21007 21008@node Environment Variables 21009@section Environment Variables Affecting GCC 21010@cindex environment variables 21011 21012@c man begin ENVIRONMENT 21013This section describes several environment variables that affect how GCC 21014operates. Some of them work by specifying directories or prefixes to use 21015when searching for various kinds of files. Some are used to specify other 21016aspects of the compilation environment. 21017 21018Note that you can also specify places to search using options such as 21019@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These 21020take precedence over places specified using environment variables, which 21021in turn take precedence over those specified by the configuration of GCC@. 21022@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, 21023GNU Compiler Collection (GCC) Internals}. 21024 21025@table @env 21026@item LANG 21027@itemx LC_CTYPE 21028@c @itemx LC_COLLATE 21029@itemx LC_MESSAGES 21030@c @itemx LC_MONETARY 21031@c @itemx LC_NUMERIC 21032@c @itemx LC_TIME 21033@itemx LC_ALL 21034@findex LANG 21035@findex LC_CTYPE 21036@c @findex LC_COLLATE 21037@findex LC_MESSAGES 21038@c @findex LC_MONETARY 21039@c @findex LC_NUMERIC 21040@c @findex LC_TIME 21041@findex LC_ALL 21042@cindex locale 21043These environment variables control the way that GCC uses 21044localization information which allows GCC to work with different 21045national conventions. GCC inspects the locale categories 21046@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do 21047so. These locale categories can be set to any value supported by your 21048installation. A typical value is @samp{en_GB.UTF-8} for English in the United 21049Kingdom encoded in UTF-8. 21050 21051The @env{LC_CTYPE} environment variable specifies character 21052classification. GCC uses it to determine the character boundaries in 21053a string; this is needed for some multibyte encodings that contain quote 21054and escape characters that are otherwise interpreted as a string 21055end or escape. 21056 21057The @env{LC_MESSAGES} environment variable specifies the language to 21058use in diagnostic messages. 21059 21060If the @env{LC_ALL} environment variable is set, it overrides the value 21061of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} 21062and @env{LC_MESSAGES} default to the value of the @env{LANG} 21063environment variable. If none of these variables are set, GCC 21064defaults to traditional C English behavior. 21065 21066@item TMPDIR 21067@findex TMPDIR 21068If @env{TMPDIR} is set, it specifies the directory to use for temporary 21069files. GCC uses temporary files to hold the output of one stage of 21070compilation which is to be used as input to the next stage: for example, 21071the output of the preprocessor, which is the input to the compiler 21072proper. 21073 21074@item GCC_COMPARE_DEBUG 21075@findex GCC_COMPARE_DEBUG 21076Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing 21077@option{-fcompare-debug} to the compiler driver. See the documentation 21078of this option for more details. 21079 21080@item GCC_EXEC_PREFIX 21081@findex GCC_EXEC_PREFIX 21082If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the 21083names of the subprograms executed by the compiler. No slash is added 21084when this prefix is combined with the name of a subprogram, but you can 21085specify a prefix that ends with a slash if you wish. 21086 21087If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out 21088an appropriate prefix to use based on the pathname it is invoked with. 21089 21090If GCC cannot find the subprogram using the specified prefix, it 21091tries looking in the usual places for the subprogram. 21092 21093The default value of @env{GCC_EXEC_PREFIX} is 21094@file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to 21095the installed compiler. In many cases @var{prefix} is the value 21096of @code{prefix} when you ran the @file{configure} script. 21097 21098Other prefixes specified with @option{-B} take precedence over this prefix. 21099 21100This prefix is also used for finding files such as @file{crt0.o} that are 21101used for linking. 21102 21103In addition, the prefix is used in an unusual way in finding the 21104directories to search for header files. For each of the standard 21105directories whose name normally begins with @samp{/usr/local/lib/gcc} 21106(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries 21107replacing that beginning with the specified prefix to produce an 21108alternate directory name. Thus, with @option{-Bfoo/}, GCC searches 21109@file{foo/bar} just before it searches the standard directory 21110@file{/usr/local/lib/bar}. 21111If a standard directory begins with the configured 21112@var{prefix} then the value of @var{prefix} is replaced by 21113@env{GCC_EXEC_PREFIX} when looking for header files. 21114 21115@item COMPILER_PATH 21116@findex COMPILER_PATH 21117The value of @env{COMPILER_PATH} is a colon-separated list of 21118directories, much like @env{PATH}. GCC tries the directories thus 21119specified when searching for subprograms, if it can't find the 21120subprograms using @env{GCC_EXEC_PREFIX}. 21121 21122@item LIBRARY_PATH 21123@findex LIBRARY_PATH 21124The value of @env{LIBRARY_PATH} is a colon-separated list of 21125directories, much like @env{PATH}. When configured as a native compiler, 21126GCC tries the directories thus specified when searching for special 21127linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking 21128using GCC also uses these directories when searching for ordinary 21129libraries for the @option{-l} option (but directories specified with 21130@option{-L} come first). 21131 21132@item LANG 21133@findex LANG 21134@cindex locale definition 21135This variable is used to pass locale information to the compiler. One way in 21136which this information is used is to determine the character set to be used 21137when character literals, string literals and comments are parsed in C and C++. 21138When the compiler is configured to allow multibyte characters, 21139the following values for @env{LANG} are recognized: 21140 21141@table @samp 21142@item C-JIS 21143Recognize JIS characters. 21144@item C-SJIS 21145Recognize SJIS characters. 21146@item C-EUCJP 21147Recognize EUCJP characters. 21148@end table 21149 21150If @env{LANG} is not defined, or if it has some other value, then the 21151compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to 21152recognize and translate multibyte characters. 21153@end table 21154 21155@noindent 21156Some additional environment variables affect the behavior of the 21157preprocessor. 21158 21159@include cppenv.texi 21160 21161@c man end 21162 21163@node Precompiled Headers 21164@section Using Precompiled Headers 21165@cindex precompiled headers 21166@cindex speed of compilation 21167 21168Often large projects have many header files that are included in every 21169source file. The time the compiler takes to process these header files 21170over and over again can account for nearly all of the time required to 21171build the project. To make builds faster, GCC allows you to 21172@dfn{precompile} a header file. 21173 21174To create a precompiled header file, simply compile it as you would any 21175other file, if necessary using the @option{-x} option to make the driver 21176treat it as a C or C++ header file. You may want to use a 21177tool like @command{make} to keep the precompiled header up-to-date when 21178the headers it contains change. 21179 21180A precompiled header file is searched for when @code{#include} is 21181seen in the compilation. As it searches for the included file 21182(@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the 21183compiler looks for a precompiled header in each directory just before it 21184looks for the include file in that directory. The name searched for is 21185the name specified in the @code{#include} with @samp{.gch} appended. If 21186the precompiled header file can't be used, it is ignored. 21187 21188For instance, if you have @code{#include "all.h"}, and you have 21189@file{all.h.gch} in the same directory as @file{all.h}, then the 21190precompiled header file is used if possible, and the original 21191header is used otherwise. 21192 21193Alternatively, you might decide to put the precompiled header file in a 21194directory and use @option{-I} to ensure that directory is searched 21195before (or instead of) the directory containing the original header. 21196Then, if you want to check that the precompiled header file is always 21197used, you can put a file of the same name as the original header in this 21198directory containing an @code{#error} command. 21199 21200This also works with @option{-include}. So yet another way to use 21201precompiled headers, good for projects not designed with precompiled 21202header files in mind, is to simply take most of the header files used by 21203a project, include them from another header file, precompile that header 21204file, and @option{-include} the precompiled header. If the header files 21205have guards against multiple inclusion, they are skipped because 21206they've already been included (in the precompiled header). 21207 21208If you need to precompile the same header file for different 21209languages, targets, or compiler options, you can instead make a 21210@emph{directory} named like @file{all.h.gch}, and put each precompiled 21211header in the directory, perhaps using @option{-o}. It doesn't matter 21212what you call the files in the directory; every precompiled header in 21213the directory is considered. The first precompiled header 21214encountered in the directory that is valid for this compilation is 21215used; they're searched in no particular order. 21216 21217There are many other possibilities, limited only by your imagination, 21218good sense, and the constraints of your build system. 21219 21220A precompiled header file can be used only when these conditions apply: 21221 21222@itemize 21223@item 21224Only one precompiled header can be used in a particular compilation. 21225 21226@item 21227A precompiled header can't be used once the first C token is seen. You 21228can have preprocessor directives before a precompiled header; you cannot 21229include a precompiled header from inside another header. 21230 21231@item 21232The precompiled header file must be produced for the same language as 21233the current compilation. You can't use a C precompiled header for a C++ 21234compilation. 21235 21236@item 21237The precompiled header file must have been produced by the same compiler 21238binary as the current compilation is using. 21239 21240@item 21241Any macros defined before the precompiled header is included must 21242either be defined in the same way as when the precompiled header was 21243generated, or must not affect the precompiled header, which usually 21244means that they don't appear in the precompiled header at all. 21245 21246The @option{-D} option is one way to define a macro before a 21247precompiled header is included; using a @code{#define} can also do it. 21248There are also some options that define macros implicitly, like 21249@option{-O} and @option{-Wdeprecated}; the same rule applies to macros 21250defined this way. 21251 21252@item If debugging information is output when using the precompiled 21253header, using @option{-g} or similar, the same kind of debugging information 21254must have been output when building the precompiled header. However, 21255a precompiled header built using @option{-g} can be used in a compilation 21256when no debugging information is being output. 21257 21258@item The same @option{-m} options must generally be used when building 21259and using the precompiled header. @xref{Submodel Options}, 21260for any cases where this rule is relaxed. 21261 21262@item Each of the following options must be the same when building and using 21263the precompiled header: 21264 21265@gccoptlist{-fexceptions} 21266 21267@item 21268Some other command-line options starting with @option{-f}, 21269@option{-p}, or @option{-O} must be defined in the same way as when 21270the precompiled header was generated. At present, it's not clear 21271which options are safe to change and which are not; the safest choice 21272is to use exactly the same options when generating and using the 21273precompiled header. The following are known to be safe: 21274 21275@gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol 21276-fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol 21277-fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol 21278-pedantic-errors} 21279 21280@end itemize 21281 21282For all of these except the last, the compiler automatically 21283ignores the precompiled header if the conditions aren't met. If you 21284find an option combination that doesn't work and doesn't cause the 21285precompiled header to be ignored, please consider filing a bug report, 21286see @ref{Bugs}. 21287 21288If you do use differing options when generating and using the 21289precompiled header, the actual behavior is a mixture of the 21290behavior for the options. For instance, if you use @option{-g} to 21291generate the precompiled header but not when using it, you may or may 21292not get debugging information for routines in the precompiled header. 21293