gcc/treelang/treelang.texi

\input texinfo  @c -*-texinfo-*-

@c NOTE THIS IS NOT A GOOD EXAMPLE OF HOW TO DO A MANUAL. FIXME!!!
@c NOTE THIS IS NOT A GOOD EXAMPLE OF HOW TO DO A MANUAL. FIXME!!!
@c NOTE THIS IS NOT A GOOD EXAMPLE OF HOW TO DO A MANUAL. FIXME!!!


@c %**start of header
@setfilename treelang.info

@include gcc-common.texi

@set version-treelang 1.0

@set last-update 2001-07-30
@set copyrights-treelang 1995,1996,1997,1998,1999,2000,2001,2002

@set email-general gcc@@gcc.gnu.org
@set email-bugs gcc-bugs@@gcc.gnu.org or bug-gcc@@gnu.org
@set email-patches gcc-patches@@gcc.gnu.org
@set path-treelang gcc/gcc/treelang

@set which-treelang GCC-@value{version-GCC}
@set which-GCC GCC

@set email-josling tej@@melbpc.org.au
@set www-josling http://www.geocities.com/timjosling

@c This tells @include'd files that they're part of the overall TREELANG doc
@c set.  (They might be part of a higher-level doc set too.)
@set DOC-TREELANG

@c @setfilename usetreelang.info
@c @setfilename maintaintreelang.info
@c To produce the full manual, use the "treelang.info" setfilename, and
@c make sure the following do NOT begin with '@c' (and the @clear lines DO)
@set INTERNALS
@set USING
@c To produce a user-only manual, use the "usetreelang.info" setfilename, and
@c make sure the following does NOT begin with '@c':
@c @clear INTERNALS
@c To produce a maintainer-only manual, use the "maintaintreelang.info" setfilename,
@c and make sure the following does NOT begin with '@c':
@c @clear USING

@ifset INTERNALS
@ifset USING
@settitle Using and Maintaining GNU Treelang
@end ifset
@end ifset
@c seems reasonable to assume at least one of INTERNALS or USING is set...
@ifclear INTERNALS
@settitle Using GNU Treelang
@end ifclear
@ifclear USING
@settitle Maintaining GNU Treelang
@end ifclear
@c then again, have some fun
@ifclear INTERNALS
@ifclear USING
@settitle Doing Very Little at all with GNU Treelang
@end ifclear
@end ifclear

@syncodeindex fn cp
@syncodeindex vr cp
@c %**end of header

@c Cause even numbered pages to be printed on the left hand side of
@c the page and odd numbered pages to be printed on the right hand
@c side of the page.  Using this, you can print on both sides of a
@c sheet of paper and have the text on the same part of the sheet.

@c The text on right hand pages is pushed towards the right hand
@c margin and the text on left hand pages is pushed toward the left
@c hand margin.
@c (To provide the reverse effect, set bindingoffset to -0.75in.)

@c @tex
@c \global\bindingoffset=0.75in
@c \global\normaloffset =0.75in
@c @end tex

@copying
Copyright @copyright{} @value{copyrights-treelang} Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``GNU General Public License'', the Front-Cover
texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
``GNU Free Documentation License''.

(a) The FSF's Front-Cover Text is:

     A GNU Manual

(b) The FSF's Back-Cover Text is:

     You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development.
@end copying

@ifnottex
@dircategory Programming
@direntry
* treelang: (treelang).                  The GNU Treelang compiler.
@end direntry
@ifset INTERNALS
@ifset USING
This file documents the use and the internals of the GNU Treelang
(@code{treelang}) compiler. At the moment this manual is not
incorporated into the main GCC manual as it is too incomplete. It
corresponds to the @value{which-treelang} version of @code{treelang}.
@end ifset
@end ifset
@ifclear USING
This file documents the internals of the GNU Treelang (@code{treelang}) compiler.
It corresponds to the @value{which-treelang} version of @code{treelang}.
@end ifclear
@ifclear INTERNALS
This file documents the use of the GNU Treelang (@code{treelang}) compiler.
It corresponds to the @value{which-treelang} version of @code{treelang}.
@end ifclear

Published by the Free Software Foundation
59 Temple Place - Suite 330
Boston, MA 02111-1307 USA

@insertcopying
@end ifnottex

treelang was Contributed by Tim Josling (@email{@value{email-josling}}).
Inspired by and based on the 'toy' language, written by Richard Kenner.

This document was written by Tim Josling, based on the GNU C++
documentation.

@setchapternewpage odd
@c @finalout
@titlepage
@ifset INTERNALS
@ifset USING
@center @titlefont{Using and Maintaining GNU Treelang}

@end ifset
@end ifset
@ifclear INTERNALS
@title Using GNU Treelang
@end ifclear
@ifclear USING
@title Maintaining GNU Treelang
@end ifclear
@sp 2
@center Tim Josling
@sp 3
@center Last updated @value{last-update}
@sp 1
@center for version @value{version-treelang}
@page
@vskip 0pt plus 1filll
For the @value{which-treelang} Version*
@sp 1
Published by the Free Software Foundation @*
59 Temple Place - Suite 330@*
Boston, MA 02111-1307, USA@*
@c Last printed ??ber, 19??.@*
@c Printed copies are available for $? each.@*
@c ISBN ???
@sp 1
@insertcopying
@end titlepage
@page

@ifnottex

@node Top, Copying,, (dir)
@top Introduction
@cindex Introduction

@ifset INTERNALS
@ifset USING
This manual documents how to run, install and maintain @code{treelang},
as well as its new features and incompatibilities,
and how to report bugs.
It corresponds to the @value{which-treelang} version of @code{treelang}.
@end ifset
@end ifset

@ifclear INTERNALS
This manual documents how to run and install @code{treelang},
as well as its new features and incompatibilities, and how to report
bugs.
It corresponds to the @value{which-treelang} version of @code{treelang}.
@end ifclear
@ifclear USING
This manual documents how to maintain @code{treelang}, as well as its
new features and incompatibilities, and how to report bugs.  It
corresponds to the @value{which-treelang} version of @code{treelang}.
@end ifclear

@end ifnottex

@ifset DEVELOPMENT
@emph{Warning:} This document is still under development, and might not
accurately reflect the @code{treelang} code base of which it is a part.
@end ifset

@menu
* Copying::
* Contributors::
* GNU Free Documentation License::
* Funding::
* Getting Started::
* What is GNU Treelang?::
* Lexical Syntax::
* Parsing Syntax::
* Compiler Overview::
* TREELANG and GCC::
* Compiler::
* Other Languages::
* treelang internals::
* Open Questions::
* Bugs::
* Service::
* Projects::
* Index::

@detailmenu
 --- The Detailed Node Listing ---

Other Languages

* Interoperating with C and C++::

treelang internals

* treelang files::
* treelang compiler interfaces::
* Hints and tips::

treelang compiler interfaces

* treelang driver::
* treelang main compiler::

treelang main compiler

* Interfacing to toplev.c::
* Interfacing to the garbage collection::
* Interfacing to the code generation code. ::

Reporting Bugs

* Sending Patches::

@end detailmenu
@end menu

@include gpl.texi

@include fdl.texi

@node Contributors

@unnumbered Contributors to GNU Treelang
@cindex contributors
@cindex credits

Treelang was based on 'toy' by Richard Kenner, and also uses code from
the GCC core code tree. Tim Josling first created the language and
documentation, based on the GCC Fortran compiler's documentation
framework.

@itemize @bullet
@item
The packaging and compiler portions of GNU Treelang are based largely
on the GCC compiler.
@xref{Contributors,,Contributors to GCC,GCC,Using and Maintaining GCC},
for more information.

@item
There is no specific run-time library for treelang, other than the
standard C runtime.

@item
It would have been difficult to build treelang without access to Joachim
Nadler's guide to writing a front end to GCC (written in German). A
translation of this document into English is available via the
CobolForGCC project or via the documentation links from the GCC home
page @uref{http://GCC.gnu.org}.
@end itemize

@include funding.texi

@node Getting Started
@chapter Getting Started
@cindex getting started
@cindex new users
@cindex newbies
@cindex beginners

Treelang is a sample language, useful only to help people understand how
to implement a new language front end to GCC. It is not a useful
language in itself other than as an example or basis for building a new
language. Therefore only language developers are likely to have an
interest in it.

This manual assumes familiarity with GCC, which you can obtain by using
it and by reading the manual @samp{Using and Porting GCC}.

To install treelang, follow the GCC installation instructions,
taking care to ensure you specify treelang in the configure step.

If you're generally curious about the future of
@code{treelang}, see @ref{Projects}.
If you're curious about its past,
see @ref{Contributors}.

To see a few of the questions maintainers of @code{treelang} have,
and that you might be able to answer,
see @ref{Open Questions}.

@ifset USING
@node What is GNU Treelang?, Lexical Syntax, Getting Started, Top
@chapter What is GNU Treelang?
@cindex concepts, basic
@cindex basic concepts

GNU Treelang, or @code{treelang}, is designed initially as a free
replacement for, or alternative to, the 'toy' language, but which is
amenable to inclusion within the GCC source tree.

@code{treelang} is largely a cut down version of C, designed to showcase
the features of the GCC code generation back end. Only those features
that are directly supported by the GCC code generation back end are
implemented. Features are implemented in a manner which is easiest and
clearest to implement. Not all or even most code generation back end
features are implemented. The intention is to add features incrementally
until most features of the GCC back end are implemented in treelang.

The main features missing are structures, arrays and pointers.

A sample program follows:

@example
// function prototypes
// function 'add' taking two ints and returning an int
external_definition int add(int arg1, int arg2);
external_definition int subtract(int arg3, int arg4);
external_definition int first_nonzero(int arg5, int arg6);
external_definition int double_plus_one(int arg7);

// function definition
add
@{
// return the sum of arg1 and arg2
  return arg1 + arg2;
@}


subtract
@{
  return arg3 - arg4;
@}

double_plus_one
@{
// aaa is a variable, of type integer and allocated at the start of the function
  automatic int aaa;
// set aaa to the value returned from aaa, when passed arg7 and arg7 as the two parameters
  aaa=add(arg7, arg7);
  aaa=add(aaa, aaa);
  aaa=subtract(subtract(aaa, arg7), arg7) + 1;
  return aaa;
@}

first_nonzero
@{
// C-like if statement
  if (arg5)
    @{
      return arg5;
    @}
  else
    @{
    @}
  return arg6;
@}
@end example

@node Lexical Syntax, Parsing Syntax, What is GNU Treelang?, Top
@chapter Lexical Syntax
@cindex Lexical Syntax

Treelang programs consist of whitespace, comments, keywords and names.
@itemize @bullet

@item
Whitespace consists of the space character and the end of line
character. Tabs are not allowed. Line terminations are as defined by the
standard C library. Whitespace is ignored except within comments,
and where it separates parts of the program. In the example below, A and
B are two separate names separated by whitespace.

@smallexample
A B
@end smallexample

@item
Comments consist of @samp{//} followed by any characters up to the end
of the line. C style comments (/* */) are not supported. For example,
the assignment below is followed by a not very helpful comment.

@smallexample
x=1; // Set X to 1
@end smallexample

@item
Keywords consist of any reserved words or symbols as described
later. The list of keywords follows:

@smallexample
@{ - used to start the statements in a function
@} - used to end the statements in a function
( - start list of function arguments, or to change the precedence of operators in an expression
) - end list or prioritized operators in expression
, - used to separate parameters in a function prototype or in a function call
; - used to end a statement
+ - addition
- - subtraction
= - assignment
== - equality test
if - begin IF statement
else - begin 'else' portion of IF statement
static - indicate variable is permanent, or function has file scope only
automatic - indicate that variable is allocated for the life of the function
external_reference - indicate that variable or function is defined in another file
external_definition - indicate that variable or function is to be accessible from other files
int - variable is an integer (same as C int)
char - variable is a character (same as C char)
unsigned - variable is unsigned. If this is not present, the variable is signed
return - start function return statement
void - used as function type to indicate function returns nothing
@end smallexample


@item
Names consist of any letter or "_" followed by any number of letters or
numbers or "_". "$" is not allowed in a name. All names must be globally
unique - the same name may not be used twice in any context - and must
not be a keyword. Names and keywords are case sensitive. For example:

@smallexample
a A _a a_ IF_X
@end smallexample

are all different names.

@end itemize

@node Parsing Syntax, Compiler Overview, Lexical Syntax, Top
@chapter Parsing Syntax
@cindex Parsing Syntax

Declarations are built up from the lexical elements described above. A
file may contain one of more declarations.

@itemize @bullet

@item
declaration: variable declaration OR function prototype OR function declaration

@item
Function Prototype: storage type NAME ( parameter_list )

@smallexample
static int add (int a, int b)
@end smallexample

@item
variable_declaration: storage type NAME initial;

Example:

@smallexample
int temp1=1;
@end smallexample

A variable declaration can be outside a function, or at the start of a function.

@item
storage: automatic OR static OR external_reference OR external_definition

This defines the scope, duration and visibility of a function or variable

@enumerate 1

@item
automatic: This means a variable is allocated at start of function and
released when the function returns. This can only be used for variables
within functions. It cannot be used for functions.

@item
static: This means a variable is allocated at start of program and
remains allocated until the program as a whole ends. For a function, it
means that the function is only visible within the current file.

@item
external_definition: For a variable, which must be defined outside a
function, it means that the variable is visible from other files. For a
function, it means that the function is visible from another file.

@item
external_reference: For a variable, which must be defined outside a
function, it means that the variable is defined in another file. For a
function, it means that the function is defined in another file.

@end enumerate

@item
type: int OR unsigned int OR char OR unsigned char OR void

This defines the data type of a variable or the return type of a function.

@enumerate a

@item
int: The variable is a signed integer. The function returns a signed integer.

@item
unsigned int: The variable is an unsigned integer. The function returns an unsigned integer.

@item
char: The variable is a signed character. The function returns a signed character.

@item
unsigned char: The variable is an unsigned character. The function returns an unsigned character.

@end enumerate

@item
parameter_list OR parameter [, parameter]...

@item
parameter: variable_declaration ,

The variable declarations must not have initialisations.

@item
initial: = value

@item
value: integer_constant

@smallexample
eg 1 +2 -3
@end smallexample

@item
function_declaration: name @{variable_declarations statements @}

A function consists of the function name then the declarations (if any)
and statements (if any) within one pair of braces.

The details of the function arguments come from the function
prototype. The function prototype must precede the function declaration
in the file.

@item
statement: if_statement OR expression_statement OR return_statement

@item
if_statement: if (expression) @{ statements @} else @{ statements @}

The first lot of statements is executed if the expression is
nonzero. Otherwise the second lot of statements is executed. Either
list of statements may be empty, but both sets of braces and the else must be present.

@smallexample
if (a==b)
@{
// nothing
@}
else
@{
a=b;
@}
@end smallexample

@item
expression_statement: expression;

The expression is executed and any side effects, such

@item
return_statement: return expression_opt;

Returns from the function. If the function is void, the expression must
be absent, and if the function is not void the expression must be
present.

@item
expression: variable OR integer_constant OR expression+expression OR expression-expression
 OR expression==expression OR (expression) OR variable=expression OR function_call

An expression can be a constant or a variable reference or a
function_call. Expressions can be combined as a sum of two expressions
or the difference of two expressions, or an equality test of two
expresions. An assignment is also an expression. Expresions and operator
precedence work as in C.

@item
function_call: function_name (comma_separated_expressions)

This invokes the function, passing to it the values of the expressions
as actual parameters.

@end itemize

@cindex compilers
@node Compiler Overview, TREELANG and GCC, Parsing Syntax, Top
@chapter Compiler Overview
treelang is run as part of the GCC compiler.

@itemize @bullet
@cindex source code
@cindex file, source
@cindex code, source
@cindex source file
@item
It reads a user's program, stored in a file and containing instructions
written in the appropriate language (Treelang, C, and so on).  This file
contains @dfn{source code}.

@cindex translation of user programs
@cindex machine code
@cindex code, machine
@cindex mistakes
@item
It translates the user's program into instructions a computer can carry
out more quickly than it takes to translate the instructions in the
first place.  These instructions are called @dfn{machine code}---code
designed to be efficiently translated and processed by a machine such as
a computer.  Humans usually aren't as good writing machine code as they
are at writing Treelang or C, because it is easy to make tiny mistakes
writing machine code.  When writing Treelang or C, it is easy to make
big mistakes. But you can only make one mistake, because the compiler
stops after it finds any problem.

@cindex debugger
@cindex bugs, finding
@cindex @code{gdb}, command
@cindex commands, @code{gdb}
@item
It provides information in the generated machine code
that can make it easier to find bugs in the program
(using a debugging tool, called a @dfn{debugger},
such as @code{gdb}).

@cindex libraries
@cindex linking
@cindex @code{ld} command
@cindex commands, @code{ld}
@item
It locates and gathers machine code already generated to perform actions
requested by statements in the user's program.  This machine code is
organized into @dfn{libraries} and is located and gathered during the
@dfn{link} phase of the compilation process.  (Linking often is thought
of as a separate step, because it can be directly invoked via the
@code{ld} command.  However, the @code{gcc} command, as with most
compiler commands, automatically performs the linking step by calling on
@code{ld} directly, unless asked to not do so by the user.)

@cindex language, incorrect use of
@cindex incorrect use of language
@item
It attempts to diagnose cases where the user's program contains
incorrect usages of the language.  The @dfn{diagnostics} produced by the
compiler indicate the problem and the location in the user's source file
where the problem was first noticed.  The user can use this information
to locate and fix the problem.

The compiler stops after the first error. There are no plans to fix
this, ever, as it would vastly complicate the implementation of treelang
to little or no benefit.

@cindex diagnostics, incorrect
@cindex incorrect diagnostics
@cindex error messages, incorrect
@cindex incorrect error messages
(Sometimes an incorrect usage of the language leads to a situation where
the compiler can not make any sense of what it reads---while a human
might be able to---and thus ends up complaining about an incorrect
``problem'' it encounters that, in fact, reflects a misunderstanding of
the programmer's intention.)

@cindex warnings
@cindex questionable instructions
@item
There are no warnings in treelang. A program is either correct or in
error.
@end itemize

@cindex components of treelang
@cindex @code{treelang}, components of
@code{treelang} consists of several components:

@cindex @code{gcc}, command
@cindex commands, @code{gcc}
@itemize @bullet
@item
A modified version of the @code{gcc} command, which also might be
installed as the system's @code{cc} command.
(In many cases, @code{cc} refers to the
system's ``native'' C compiler, which
might be a non-GNU compiler, or an older version
of @code{GCC} considered more stable or that is
used to build the operating system kernel.)

@cindex @code{treelang}, command
@cindex commands, @code{treelang}
@item
The @code{treelang} command itself.

@item
The @code{libc} run-time library.  This library contains the machine
code needed to support capabilities of the Treelang language that are
not directly provided by the machine code generated by the
@code{treelang} compilation phase. This is the same library that the
main c compiler uses (libc).

@cindex @code{tree1}, program
@cindex programs, @code{tree1}
@cindex assembler
@cindex @code{as} command
@cindex commands, @code{as}
@cindex assembly code
@cindex code, assembly
@item
The compiler itself, is internally named @code{tree1}.

Note that @code{tree1} does not generate machine code directly---it
generates @dfn{assembly code} that is a more readable form
of machine code, leaving the conversion to actual machine code
to an @dfn{assembler}, usually named @code{as}.
@end itemize

@code{GCC} is often thought of as ``the C compiler'' only,
but it does more than that.
Based on command-line options and the names given for files
on the command line, @code{gcc} determines which actions to perform, including
preprocessing, compiling (in a variety of possible languages), assembling,
and linking.

@cindex driver, gcc command as
@cindex @code{gcc}, command as driver
@cindex executable file
@cindex files, executable
@cindex cc1 program
@cindex programs, cc1
@cindex preprocessor
@cindex cpp program
@cindex programs, cpp
For example, the command @samp{gcc foo.c} @dfn{drives} the file
@file{foo.c} through the preprocessor @code{cpp}, then
the C compiler (internally named
@code{cc1}), then the assembler (usually @code{as}), then the linker
(@code{ld}), producing an executable program named @file{a.out} (on
UNIX systems).

@cindex treelang program
@cindex programs, treelang
As another example, the command @samp{gcc foo.tree} would do much the
same as @samp{gcc foo.c}, but instead of using the C compiler named
@code{cc1}, @code{gcc} would use the treelang compiler (named
@code{tree1}). However there is no preprocessor for treelang.

@cindex @code{tree1}, program
@cindex programs, @code{tree1}
In a GNU Treelang installation, @code{gcc} recognizes Treelang source
files by name just like it does C and C++ source files.  It knows to use
the Treelang compiler named @code{tree1}, instead of @code{cc1} or
@code{cc1plus}, to compile Treelang files. If a file's name ends in
@code{.tree} then GCC knows that the program is written in treelang. You
can also manually override the language.

@cindex @code{gcc}, not recognizing Treelang source
@cindex unrecognized file format
@cindex file format not recognized
Non-Treelang-related operation of @code{gcc} is generally
unaffected by installing the GNU Treelang version of @code{gcc}.
However, without the installed version of @code{gcc} being the
GNU Treelang version, @code{gcc} will not be able to compile
and link Treelang programs.

@cindex printing version information
@cindex version information, printing
The command @samp{gcc -v x.tree} where @samp{x.tree} is a file which
must exist but whose contents are ignored, is a quick way to display
version information for the various programs used to compile a typical
Treelang source file.

The @code{tree1} program represents most of what is unique to GNU
Treelang; @code{tree1} is a combination of two rather large chunks of
code.

@cindex GCC Back End (GBE)
@cindex GBE
@cindex @code{GCC}, back end
@cindex back end, GCC
@cindex code generator
One chunk is the so-called @dfn{GNU Back End}, or GBE,
which knows how to generate fast code for a wide variety of processors.
The same GBE is used by the C, C++, and Treelang compiler programs @code{cc1},
@code{cc1plus}, and @code{tree1}, plus others.
Often the GBE is referred to as the ``GCC back end'' or
even just ``GCC''---in this manual, the term GBE is used
whenever the distinction is important.

@cindex GNU Treelang Front End (TFE)
@cindex tree1
@cindex @code{treelang}, front end
@cindex front end, @code{treelang}
The other chunk of @code{tree1} is the majority of what is unique about
GNU Treelang---the code that knows how to interpret Treelang programs to
determine what they are intending to do, and then communicate that
knowledge to the GBE for actual compilation of those programs.  This
chunk is called the @dfn{Treelang Front End} (TFE).  The @code{cc1} and
@code{cc1plus} programs have their own front ends, for the C and C++
languages, respectively.  These fronts ends are responsible for
diagnosing incorrect usage of their respective languages by the programs
the process, and are responsible for most of the warnings about
questionable constructs as well.  (The GBE in principle handles
producing some warnings, like those concerning possible references to
undefined variables, but these warnings should not occur in treelang
programs as the front end is meant to pick them up first).

Because so much is shared among the compilers for various languages,
much of the behavior and many of the user-selectable options for these
compilers are similar.
For example, diagnostics (error messages and
warnings) are similar in appearance; command-line
options like @samp{-Wall} have generally similar effects; and the quality
of generated code (in terms of speed and size) is roughly similar
(since that work is done by the shared GBE).

@node TREELANG and GCC, Compiler, Compiler Overview, Top
@chapter Compile Treelang, C, or Other Programs
@cindex compiling programs
@cindex programs, compiling

@cindex @code{gcc}, command
@cindex commands, @code{gcc}
A GNU Treelang installation includes a modified version of the @code{gcc}
command.

In a non-Treelang installation, @code{gcc} recognizes C, C++,
and Objective-C source files.

In a GNU Treelang installation, @code{gcc} also recognizes Treelang source
files and accepts Treelang-specific command-line options, plus some
command-line options that are designed to cater to Treelang users
but apply to other languages as well.

@xref{G++ and GCC,,Compile C; C++; or Objective-C,GCC,Using and Porting GCC},
for information on the way different languages are handled
by the GCC compiler (@code{gcc}).

You can use this, combined with the output of the @samp{GCC -v x.tree}
command to get the options applicable to treelang. Treelang programs
must end with the suffix @samp{.tree}.

@cindex preprocessor

Treelang programs are not by default run through the C
preprocessor by @code{gcc}. There is no reason why they cannot be run through the
preprocessor manually, but you would need to prevent the preprocessor
from generating #line directives, using the @samp{-P} option, otherwise
tree1 will not accept the input.

@node Compiler, Other Languages, TREELANG and GCC, Top
@chapter The GNU Treelang Compiler

The GNU Treelang compiler, @code{treelang}, supports programs written
in the GNU Treelang language.

@node Other Languages, treelang internals, Compiler, Top
@chapter Other Languages

@menu
* Interoperating with C and C++::
@end menu

@node Interoperating with C and C++,  , Other Languages, Other Languages
@section Tools and advice for interoperating with C and C++

The output of treelang programs looks like C program code to the linker
and everybody else, so you should be able to freely mix treelang and C
(and C++) code, with one proviso.

C promotes small integer types to 'int' when used as function parameters and
return values. The treelang compiler does not do this, so if you want to interface
to C, you need to specify the promoted value, not the nominal value.

@ifset INTERNALS
@node treelang internals, Open Questions, Other Languages, Top
@chapter treelang internals

@menu
* treelang files::
* treelang compiler interfaces::
* Hints and tips::
@end menu

@node treelang files, treelang compiler interfaces, treelang internals, treelang internals
@section treelang files

To create a compiler that integrates into GCC, you need create many
files. Some of the files are integrated into the main GCC makefile, to
build the various parts of the compiler and to run the test
suite. Others are incorporated into various GCC programs such as
GCC.c. Finally you must provide the actual programs comprising your
compiler.

@cindex files

The files are:

@enumerate 1

@item
COPYING. This is the copyright file, assuming you are going to use the
GNU General Public Licence. You probably need to use the GPL because if
you use the GCC back end your program and the back end are one program,
and the back end is GPLed.

This need not be present if the language is incorporated into the main
GCC tree, as the main GCC directory has this file.

@item
COPYING.LIB. This is the copyright file for those parts of your program
that are not to be covered by the GPL, but are instead to be covered by
the LGPL (Library or Lesser GPL). This licence may be appropriate for
the library routines associated with your compiler. These are the
routines that are linked with the @emph{output} of the compiler. Using
the LGPL for these programs allows programs written using your compiler
to be closed source. For example LIBC is under the LGPL.

This need not be present if the language is incorporated into the main
GCC tree, as the main GCC directory has this file.

@item
ChangeLog. Record all the changes to your compiler. Use the same format
as used in treelang as it is supported by an emacs editing mode and is
part of the FSF coding standard. Normally each directory has its own
changelog. The FSF standard allows but does not require a meaningful
comment on why the changes were made, above and beyond @emph{why} they
were made. In the author's opinion it is useful to provide this
information.

@item
treelang.texi. The manual, written in texinfo. Your manual would have a
different file name. You need not write it in texinfo if you don't want
do, but a lot of GNU software does use texinfo.

@cindex Make-lang.in
@item
Make-lang.in. This file is part of the make file which in incorporated
with the GCC make file skeleton (Makefile.in in the GCC directory) to
make Makefile, as part of the configuration process.

Makefile in turn is the main instruction to actually build
everything. The build instructions are held in the main GCC manual and
web site so they are not repeated here.

There are some comments at the top which will help you understand what
you need to do.

There are make commands to build things, remove generated files with
various degrees of thoroughness, count the lines of code (so you know
how much progress you are making), build info and html files from the
texinfo source, run the tests etc.

@item
README. Just a brief informative text file saying what is in this
directory.

@cindex config-lang.in
@item
config-lang.in. This file is read by the configuration progress and must
be present. You specify the name of your language, the name(s) of the
compiler(s) incouding preprocessors you are going to build, whether any,
usually generated, files should be excluded from diffs (ie when making
diff files to send in patches). Whether the equate 'stagestuff' is used
is unknown (???).

@cindex lang-options
@item
lang-options. This file is included into GCC.c, the main GCC driver, and
tells it what options your language supports. This is only used to
display help (is this true ???).

@cindex lang-specs
@item
lang-specs. This file is also included in GCC.c. It tells GCC.c when to
call your programs and what options to send them. The mini-language
'specs' is documented in the source of GCC.c. Do not attempt to write a
specs file from scratch - use an existing one as the base and enhance
it.

@item
Your texi files. Texinfo can be used to build documentation in HTML,
info, dvi and postscript formats. It is a tagged language, is documented
in its own manual, and has its own emacs mode.

@item
Your programs. The relationships between all the programs are explained
in the next section. You need to write or use the following programs:

@itemize @bullet

@item
lexer. This breaks the input into words and passes these to the
parser. This is lex.l in treelang, which is passed through flex, a lex
variant, to produce C code lex.c. Note there is a school of thought that
says real men hand code their own lexers, however you may prefer to
write far less code and use flex, as was done with treelang.

@item
parser. This breaks the program into recognizable constructs such as
expressions, statements etc. This is parse.y in treelang, which is
passed through bison, which is a yacc variant, to produce C code parse.c.

@item
back end interface. This interfaces to the code generation back end. In
treelang, this is tree1.c which mainly interfaces to toplev.c and
treetree.c which mainly interfaces to everything else. Many languages
mix up the back end interface with the parser, as in the C compiler for
example. It is a matter of taste which way to do it, but with treelang
it is separated out to make the back end interface cleaner and easier to
understand.

@item
header files. For function prototypes and common data items. One point
to note here is that bison can generate a header files with all the
numbers is has assigned to the keywords and symbols, and you can include
the same header in your lexer. This technique is demonstrated in
treelang.

@item
compiler main file. GCC comes with a program toplev.c which is a
perfectly serviceable main program for your compiler. treelang uses
toplev.c but other languages have been known to replace it with their
own main program. Again this is a matter of taste and how much code you
want to write.

@end itemize

@end enumerate

@node treelang compiler interfaces, Hints and tips, treelang files, treelang internals
@section treelang compiler interfaces

@cindex driver
@cindex toplev.c

@menu
* treelang driver::
* treelang main compiler::
@end menu

@node treelang driver, treelang main compiler, treelang compiler interfaces, treelang compiler interfaces
@subsection treelang driver

The GCC compiler consists of a driver, which then executes the various
compiler phases based on the instructions in the specs files.

Typically a program's language will be identified from its suffix (eg
.tree) for treelang programs.

The driver (gcc.c) will then drive (exec) in turn a preprocessor, the main
compiler, the assembler and the link editor. Options to GCC allow you to
override all of this. In the case of treelang programs there is no
preprocessor, and mostly these days the C preprocessor is run within the
main C compiler rather than as a separate process, apparently for reasons of speed.

You will be using the standard assembler and linkage editor so these are
ignored from now on.

You have to write your own preprocessor if you want one. This is usually
totally language specific. The main point to be aware of is to ensure
that you find some way to pass file name and line number information
through to the main compiler so that it can tell the back end this
information and so the debugger can find the right source line for each
piece of code. That is all there is to say about the preprocessor except
that the preprocessor will probably not be the slowest part of the
compiler and will probably not use the most memory so don't waste too
much time tuning it until you know you need to do so.

@node treelang main compiler,  , treelang driver, treelang compiler interfaces
@subsection treelang main compiler

The main compiler for treelang consists of toplev.c from the main GCC
compiler, the parser, lexer and back end interface routines, and the
back end routines themselves, of which there are many.

toplev.c does a lot of work for you and you should almost certainly use it,

Writing this code is the hard part of creating a compiler using GCC. The
back end interface documentation is incomplete and the interface is
complex.

There are three main aspects to interfacing to the other GCC code.

@menu
* Interfacing to toplev.c::
* Interfacing to the garbage collection::
* Interfacing to the code generation code. ::
@end menu

@node Interfacing to toplev.c, Interfacing to the garbage collection, treelang main compiler, treelang main compiler
@subsubsection Interfacing to toplev.c

In treelang this is handled mainly in tree1.c
and partly in treetree.c. Peruse toplev.c for details of what you need
to do.

@node Interfacing to the garbage collection, Interfacing to the code generation code. , Interfacing to toplev.c, treelang main compiler
@subsubsection Interfacing to the garbage collection

Interfacing to the garbage collection. In treelang this is mainly in
tree1.c.

Memory allocation in the compiler should be done using the ggc_alloc and
kindred routines in ggc*.*. At the end of every 'function' in your language, toplev.c calls
the garbage collection several times. The garbage collection calls mark
routines which go through the memory which is still used, telling the
garbage collection not to free it. Then all the memory not used is
freed.

What this means is that you need a way to hook into this marking
process. This is done by calling ggc_add_root. This provides the address
of a callback routine which will be called duing garbage collection and
which can call ggc_mark to save the storage. If storage is only
used within the parsing of a function, you do not need to provide a way
to mark it.

Note that you can also call ggc_mark_tree to mark any of the back end
internal 'tree' nodes. This routine will follow the branches of the
trees and mark all the subordinate structures. This is useful for
example when you have created a variable declaaration that will be used
across multiple functions, or for a function declaration (from a
prototype) that may be used later on. See the next item for more on the
tree nodes.

@node Interfacing to the code generation code. ,  , Interfacing to the garbage collection, treelang main compiler
@subsubsection Interfacing to the code generation code.

In treelang this is done in treetree.c. A typedef called 'tree' which is
defined in tree.h and tree.def in the GCC directory and largely
implemented in tree.c and stmt.c forms the basic interface to the
compiler back end.

In general you call various tree routines to generate code, either
directly or through toplev.c. You build up data structures and
expressions in similar ways.

You can read some documentation on this which can be found via the GCC
main web page. In particular, the documentation produced by Joachim
Nadler and translated by Tim Josling can be quite useful. the C compiler
also has documentation in the main GCC manual (particularly the current
CVS version) which is useful on a lot of the details.

In time it is hoped to enhance this document to provide a more
comprehensive overview of this topic. The main gap is in explaining how
it all works together.

@node Hints and tips,  , treelang compiler interfaces, treelang internals
@section Hints and tips

@itemize @bullet

@item
TAGS: Use the make ETAGS commands to create TAGS files which can be used in
emacs to jump to any symbol quickly.

@item
GREP: grep is also a useful way to find all uses of a symbol.

@item
TREE: The main routines to look at are tree.h and tree.def. You will
probably want a hardcopy of these.

@item
SAMPLE: look at the sample interfacing code in treetree.c. You can use
gdb to trace through the code and learn about how it all works.

@item
GDB: the GCC back end works well with gdb. It traps abort() and allows
you to trace back what went wrong.

@item
Error Checking: The compiler back end does some error and consistency
checking. Often the result of an error is just no code being
generated. You will then need to trace through and find out what is
going wrong. The rtl dump files can help here also.

@item
rtl dump files: The main compiler documents these files which are dumps
of the rtl (intermediate code) which is manipulated doing the code
generation process. This can provide useful clues about what is going
wrong. The rtl 'language' is documented in the main GCC manual.

@end itemize

@end ifset

@node Open Questions, Bugs, treelang internals, Top
@chapter Open Questions

If you know GCC well, please consider looking at the file treetree.c and
resolving any questions marked "???".

@node Bugs, Service, Open Questions, Top
@chapter Reporting Bugs
@cindex bugs
@cindex reporting bugs

You can report bugs to @email{@value{email-bugs}}. Please make
sure bugs are real before reporting them. Follow the guidelines in the
main GCC manual for submitting bug reports.

@menu
* Sending Patches::
@end menu

@node Sending Patches,  , Bugs, Bugs
@section Sending Patches for GNU Treelang

If you would like to write bug fixes or improvements for the GNU
Treelang compiler, that is very helpful.  Send suggested fixes to
@email{@value{email-patches}}.

@node Service, Projects, Bugs, Top
@chapter How To Get Help with GNU Treelang

If you need help installing, using or changing GNU Treelang, there are two
ways to find it:

@itemize @bullet

@item
Look in the service directory for someone who might help you for a fee.
The service directory is found in the file named @file{SERVICE} in the
GCC distribution.

@item
Send a message to @email{@value{email-general}}.

@end itemize

@end ifset
@ifset INTERNALS

@node Projects, Index, Service, Top
@chapter Projects
@cindex projects

If you want to contribute to @code{treelang} by doing research,
design, specification, documentation, coding, or testing,
the following information should give you some ideas.

Send a message to @email{@value{email-general}} if you plan to add a
feature.

The main requirement for treelang is to add features and to add
documentation. Features are things that the GCC back end can do but
which are not reflected in treelang. Examples include structures,
unions, pointers, arrays.

@end ifset

@node Index,  , Projects, Top
@unnumbered Index

@printindex cp
@summarycontents
@contents
@bye