1/* Definitions for the branch prediction routines in the GNU compiler. 2 Copyright (C) 2001-2017 Free Software Foundation, Inc. 3 4This file is part of GCC. 5 6GCC is free software; you can redistribute it and/or modify it under 7the terms of the GNU General Public License as published by the Free 8Software Foundation; either version 3, or (at your option) any later 9version. 10 11GCC is distributed in the hope that it will be useful, but WITHOUT ANY 12WARRANTY; without even the implied warranty of MERCHANTABILITY or 13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14for more details. 15 16You should have received a copy of the GNU General Public License 17along with GCC; see the file COPYING3. If not see 18<http://www.gnu.org/licenses/>. */ 19 20/* Before including this file, you should define a macro: 21 22 DEF_PREDICTOR (ENUM, NAME, HITRATE) 23 24 This macro will be called once for each predictor. The ENUM will 25 be of type `enum predictor', and will enumerate all supported 26 predictors. The order of DEF_PREDICTOR calls is important, as 27 in the first match combining heuristics, the predictor appearing 28 first in this file will win. 29 30 NAME is used in the debugging output to determine predictor type. 31 32 HITRATE is the probability that edge predicted by predictor as taken 33 will be really taken (so it should be always above 34 REG_BR_PROB_BASE / 2). */ 35 36 37/* A value used as final outcome of all heuristics. */ 38DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) 39 40/* An outcome estimated by Dempster-Shaffer theory. */ 41DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0) 42 43/* A combined heuristics using probability determined by first 44 matching heuristics from this list. */ 45DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) 46 47/* Heuristic applying when no heuristic below applies. */ 48DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) 49 50/* Mark unconditional jump as taken. */ 51DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, 52 PRED_FLAG_FIRST_MATCH) 53 54/* Use number of loop iterations determined by # of iterations 55 analysis to set probability. We don't want to use Dempster-Shaffer 56 theory here, as the predictions is exact. */ 57DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS, 58 PRED_FLAG_FIRST_MATCH) 59 60/* Assume that any given atomic operation has low contention, 61 and thus the compare-and-swap operation succeeds. */ 62DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY, 63 PRED_FLAG_FIRST_MATCH) 64 65/* Hints dropped by user via __builtin_expect feature. Note: the 66 probability of PROB_VERY_LIKELY is now overwritten by param 67 builtin_expect_probability with a default value of HITRATE(90). 68 Refer to param.def for details. */ 69DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, 70 PRED_FLAG_FIRST_MATCH) 71 72/* Use number of loop iterations guessed by the contents of the loop. */ 73DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", 74 PROB_ALWAYS, PRED_FLAG_FIRST_MATCH) 75 76/* Use number of loop iterations guessed by the contents of the loop. */ 77DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations", 78 PROB_ALWAYS, PRED_FLAG_FIRST_MATCH) 79 80/* Branch containing goto is probably not taken. */ 81DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0) 82 83/* Branch to basic block containing call marked by noreturn attribute. */ 84DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, 85 PRED_FLAG_FIRST_MATCH) 86 87/* Branch to basic block containing call marked by cold function attribute. */ 88DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, 89 PRED_FLAG_FIRST_MATCH) 90 91/* Edge causing loop to terminate is probably not taken. */ 92DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (85), 93 PRED_FLAG_FIRST_MATCH) 94 95/* Same as LOOP_EXIT but for loops containing recursive call. */ 96DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion", 97 HITRATE (72), PRED_FLAG_FIRST_MATCH) 98 99/* Edge causing loop to terminate by computing value used by later 100 conditional. */ 101DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (83), 102 PRED_FLAG_FIRST_MATCH) 103 104/* Pointers are usually not NULL. */ 105DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0) 106DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0) 107 108/* NE is probable, EQ not etc... */ 109DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (64), 0) 110DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0) 111DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) 112DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", 113 HITRATE (64), 0) 114DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", 115 HITRATE (66), 0) 116DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) 117 118/* Branch guarding call is probably taken. */ 119DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0) 120 121/* PRED_CALL is not very reliable predictor and it turns out to be even 122 less reliable for indirect calls and polymorphic calls. For spec2k6 123 the predictio nis slightly in the direction of taking the call. */ 124DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", HITRATE (86), 0) 125DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", HITRATE (59), 0) 126 127/* Recursive calls are usually not taken or the function will recurse 128 indefinitely. */ 129DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", HITRATE (75), 0) 130 131/* Branch causing function to terminate is probably not taken. 132 FIXME: early return currently predicts code: 133 int foo (int a) 134 { 135 if (a) 136 bar(); 137 else 138 bar2(); 139 } 140 even though there is no return statement involved. We probably want to track 141 this from FE or retire the predictor. */ 142DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (54), 0) 143 144/* Branch containing goto is probably not taken. 145 FIXME: Currently not used. */ 146DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0) 147 148/* Branch ending with return constant is probably not taken. */ 149DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (69), 0) 150 151/* Branch ending with return negative constant is probably not taken. */ 152DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0) 153 154/* Branch ending with return; is probably not taken */ 155DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (91), 0) 156 157/* Branches to compare induction variable to a loop bound is 158 extremely likely. */ 159DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare", 160 HITRATE (98), 0) 161 162/* Use number of loop iterations determined by # of iterations analysis 163 to set probability of branches that compares IV to loop bound variable. */ 164DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY, 165 PRED_FLAG_FIRST_MATCH) 166 167/* In the following code 168 for (loop1) 169 if (cond) 170 for (loop2) 171 body; 172 guess that cond is unlikely. */ 173DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (66), 0) 174 175/* Same but for loops containing recursion. */ 176DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion", 177 HITRATE (85), 0) 178 179/* Branches to hot labels are likely. */ 180DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0) 181 182/* Branches to cold labels are extremely unlikely. */ 183DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY, 184 PRED_FLAG_FIRST_MATCH) 185 186 187/* The following predictors are used in Fortran. */ 188 189/* Branch leading to an integer overflow are extremely unlikely. */ 190DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS, 191 PRED_FLAG_FIRST_MATCH) 192 193/* Branch leading to a failure status are unlikely. This can occur for out 194 of memory. This predictor only occurs when the user explicitly asked 195 for a return status. By default, the code aborts, 196 which is handled via PRED_NORETURN. */ 197DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc", PROB_VERY_LIKELY, 0) 198 199/* Predictor is used for an allocation of an already allocated memory or 200 deallocating an already deallocated allocatable. */ 201DEF_PREDICTOR (PRED_FORTRAN_REALLOC, \ 202 "Fortran repeated allocation/deallocation", PROB_LIKELY, 0) 203 204/* Branch leading to an I/O failure status are unlikely. This predictor is 205 used for I/O failures such as for invalid unit numbers. This predictor 206 only occurs when the user explicitly asked for a return status. By default, 207 the code aborts, which is handled via PRED_NORETURN. */ 208DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0) 209 210/* Branch leading to a run-time warning message which is printed only once 211 are unlikely. The print-warning branch itself can be likely or unlikely. */ 212DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0) 213 214/* Branch belonging to a zero-sized array. */ 215DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \ 216 HITRATE (99), 0) 217 218/* Branch belonging to an invalid bound index, in a context where it is 219 standard conform and well defined but rather pointless and, hence, rather 220 unlikely to occur. */ 221DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \ 222 HITRATE (90), 0) 223 224/* Branch belonging to the handling of absent optional arguments. This 225 predictor is used when an optional dummy argument, associated with an 226 absent argument, is passed on as actual argument to another procedure, 227 which in turn has an optional argument. */ 228DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \ 229 HITRATE (60), 0) 230 231/* Fortran DO statement generates a pre-header guard: 232 empty = (step > 0 ? to < from : to > from), which can be predicted 233 to be very likely. */ 234DEF_PREDICTOR (PRED_FORTRAN_LOOP_PREHEADER, "Fortran loop preheader", \ 235 HITRATE (99), 0) 236