Fresh Fish 6/FreshFish_September1994.bin/gnu/info/gcc.info-12

GNU Info File | 1994-09-02 | 51KB | 898 lines

This is Info file gcc.info, produced by Makeinfo-1.54 from the input
file gcc.texi.
   This file documents the use and the internals of the GNU compiler.
   Published by the Free Software Foundation 675 Massachusetts Avenue
Cambridge, MA 02139 USA
   Copyright (C) 1988, 1989, 1992, 1993 Free Software Foundation, Inc.
   Permission is granted to make and distribute verbatim copies of this
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   Permission is granted to copy and distribute modified versions of
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Your Freedom--Fight `Look And Feel'" are included exactly as in the
original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this
   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the sections entitled "GNU General Public
License" and "Protect Your Freedom--Fight `Look And Feel'", and this
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File: gcc.info,  Node: Passes,  Next: RTL,  Prev: Interface,  Up: Top
Passes and Files of the Compiler
********************************
   The overall control structure of the compiler is in `toplev.c'.  This
file is responsible for initialization, decoding arguments, opening and
closing files, and sequencing the passes.
   The parsing pass is invoked only once, to parse the entire input.
The RTL intermediate code for a function is generated as the function
is parsed, a statement at a time.  Each statement is read in as a
syntax tree and then converted to RTL; then the storage for the tree
for the statement is reclaimed.  Storage for types (and the expressions
for their sizes), declarations, and a representation of the binding
contours and how they nest, remain until the function is finished being
compiled; these are all needed to output the debugging information.
   Each time the parsing pass reads a complete function definition or
top-level declaration, it calls either the function
`rest_of_compilation', or the function `rest_of_decl_compilation' in
`toplev.c', which are responsible for all further processing necessary,
ending with output of the assembler language.  All other compiler
passes run, in sequence, within `rest_of_compilation'.  When that
function returns from compiling a function definition, the storage used
for that function definition's compilation is entirely freed, unless it
is an inline function (*note An Inline Function is As Fast As a Macro:
Inline.).
   Here is a list of all the passes of the compiler and their source
files.  Also included is a description of where debugging dumps can be
requested with `-d' options.
   * Parsing.  This pass reads the entire text of a function definition,
     constructing partial syntax trees.  This and RTL generation are no
     longer truly separate passes (formerly they were), but it is
     easier to think of them as separate.
     The tree representation does not entirely follow C syntax, because
     it is intended to support other languages as well.
     Language-specific data type analysis is also done in this pass,
     and every tree node that represents an expression has a data type
     attached.  Variables are represented as declaration nodes.
     Constant folding and some arithmetic simplifications are also done
     during this pass.
     The language-independent source files for parsing are
     `stor-layout.c', `fold-const.c', and `tree.c'.  There are also
     header files `tree.h' and `tree.def' which define the format of
     the tree representation.
     The source files to parse C are `c-parse.in', `c-decl.c',
     `c-typeck.c', `c-aux-info.c', `c-convert.c', and `c-lang.c' along
     with header files `c-lex.h', and `c-tree.h'.
     The source files for parsing C++ are `cp-parse.y', `cp-class.c',
     `cp-cvt.c', `cp-decl.c', `cp-decl2.c', `cp-dem.c', `cp-except.c',
     `cp-expr.c', `cp-init.c', `cp-lex.c', `cp-method.c', `cp-ptree.c',
     `cp-search.c', `cp-tree.c', `cp-type2.c', and `cp-typeck.c', along
     with header files `cp-tree.def', `cp-tree.h', and `cp-decl.h'.
     The special source files for parsing Objective C are
     `objc-parse.y', `objc-actions.c', `objc-tree.def', and
     `objc-actions.h'.  Certain C-specific files are used for this as
     well.
     The file `c-common.c' is also used for all of the above languages.
   * RTL generation.  This is the conversion of syntax tree into RTL
     code.  It is actually done statement-by-statement during parsing,
     but for most purposes it can be thought of as a separate pass.
     This is where the bulk of target-parameter-dependent code is found,
     since often it is necessary for strategies to apply only when
     certain standard kinds of instructions are available.  The purpose
     of named instruction patterns is to provide this information to
     the RTL generation pass.
     Optimization is done in this pass for `if'-conditions that are
     comparisons, boolean operations or conditional expressions.  Tail
     recursion is detected at this time also.  Decisions are made about
     how best to arrange loops and how to output `switch' statements.
     The source files for RTL generation include `stmt.c', `calls.c',
     `expr.c', `explow.c', `expmed.c', `function.c', `optabs.c' and
     `emit-rtl.c'.  Also, the file `insn-emit.c', generated from the
     machine description by the program `genemit', is used in this
     pass.  The header file `expr.h' is used for communication within
     this pass.
     The header files `insn-flags.h' and `insn-codes.h', generated from
     the machine description by the programs `genflags' and `gencodes',
     tell this pass which standard names are available for use and
     which patterns correspond to them.
     Aside from debugging information output, none of the following
     passes refers to the tree structure representation of the function
     (only part of which is saved).
     The decision of whether the function can and should be expanded
     inline in its subsequent callers is made at the end of rtl
     generation.  The function must meet certain criteria, currently
     related to the size of the function and the types and number of
     parameters it has.  Note that this function may contain loops,
     recursive calls to itself (tail-recursive functions can be
     inlined!), gotos, in short, all constructs supported by GNU CC.
     The file `integrate.c' contains the code to save a function's rtl
     for later inlining and to inline that rtl when the function is
     called.  The header file `integrate.h' is also used for this
     purpose.
     The option `-dr' causes a debugging dump of the RTL code after
     this pass.  This dump file's name is made by appending `.rtl' to
     the input file name.
   * Jump optimization.  This pass simplifies jumps to the following
     instruction, jumps across jumps, and jumps to jumps.  It deletes
     unreferenced labels and unreachable code, except that unreachable
     code that contains a loop is not recognized as unreachable in this
     pass.  (Such loops are deleted later in the basic block analysis.)
     It also converts some code originally written with jumps into
     sequences of instructions that directly set values from the
     results of comparisons, if the machine has such instructions.
     Jump optimization is performed two or three times.  The first time
     is immediately following RTL generation.  The second time is after
     CSE, but only if CSE says repeated jump optimization is needed.
     The last time is right before the final pass.  That time,
     cross-jumping and deletion of no-op move instructions are done
     together with the optimizations described above.
     The source file of this pass is `jump.c'.
     The option `-dj' causes a debugging dump of the RTL code after
     this p