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
(see 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.
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.
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 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 pass is run for the first time. This dump file's name is made by
appending `.jump
' to the input file name.
regclass.c
'.
threaded
' through
the second conditional test. The source code for this pass is in
`jump.c
'. This optimization is only performed if
`-fthread-jumps
' is enabled.
cse.c
'. If constant
propagation causes conditional jumps to become unconditional or to
become no-ops, jump optimization is run again when CSE is finished.
The option `-ds
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.cse
' to
the input file name.
loop.c
' and `unroll.c
', plus the header
`loop.h
' used for communication between them. Loop unrolling uses
some functions in `integrate.c
' and the header `integrate.h
'.
The option `-dL
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.loop
' to
the input file name.
-frerun-cse-after-loop
' was enabled, a second common
subexpression elimination pass is performed after the loop optimization
pass. Jump threading is also done again at this time if it was specified.
The option `-dt
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.cse2
' to
the input file name.
stupid.c
'.
flow.c
'). This pass divides the program
into basic blocks (and in the process deletes unreachable loops); then
it computes which pseudo-registers are live at each point in the
program, and makes the first instruction that uses a value point at
the instruction that computed the value.
This pass also deletes computations whose results are never used, and combines memory references with add or subtract instructions to make autoincrement or autodecrement addressing.
The option `-df
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.flow
' to
the input file name. If stupid register allocation is in use, this
dump file reflects the full results of such allocation.
combine.c
'). This pass attempts to
combine groups of two or three instructions that are related by data
flow into single instructions. It combines the RTL expressions for
the instructions by substitution, simplifies the result using algebra,
and then attempts to match the result against the machine description.
The option `-dc
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.combine
'
to the input file name.
sched.c
'). This pass looks for
instructions whose output will not be available by the time that it is
used in subsequent instructions. (Memory loads and floating point
instructions often have this behavior on RISC machines). It re-orders
instructions within a basic block to try to separate the definition and
use of items that otherwise would cause pipeline stalls.
Instruction scheduling is performed twice. The first time is immediately after instruction combination and the second is immediately after reload.
The option `-dS
' causes a debugging dump of the RTL code after this
pass is run for the first time. The dump file's name is made by
appending `.sched
' to the input file name.
regclass.c
'.
local-alloc.c
'). This pass allocates
hard registers to pseudo registers that are used only within one basic
block. Because the basic block is linear, it can use fast and
powerful techniques to do a very good job.
The option `-dl
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.lreg
' to
the input file name.
global.c
'). This pass
allocates hard registers for the remaining pseudo registers (those
whose life spans are not contained in one basic block).
The reload pass also optionally eliminates the frame pointer and inserts instructions to save and restore call-clobbered registers around calls.
Source files are `reload.c
' and `reload1.c
', plus the header
`reload.h
' used for communication between them.
The option `-dg
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.greg
' to
the input file name.
The option `-dR
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.sched2
'
to the input file name.
The option `-dJ
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.jump2
'
to the input file name.
reorg.c
'.
The option `-dd
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.dbr
'
to the input file name.
reg-stack.c
'.
The options `-dk
' causes a debugging dump of the RTL code after
this pass. This dump file's name is made by appending `.stack
'
to the input file name.
The source files are `final.c
' plus `insn-output.c
'; the
latter is generated automatically from the machine description by the
tool `genoutput
'. The header file `conditions.h
' is used
for communication between these files.
dbxout.c
' for DBX symbol table
format, `sdbout.c
' for SDB symbol table format, and
`dwarfout.c
' for DWARF symbol table format.
Some additional files are used by all or many passes:
machmode.def
' and `machmode.h
' which define
the machine modes.
real.h
', which defines the default
representation of floating point constants and how to operate on them.
rtl.h
'
and `rtl.def
', and subroutines in file `rtl.c
'. The tools
gen*
also use these files to read and work with the machine
description RTL.
insn-config.h
' which
contains a few parameters (C macro definitions) generated
automatically from the machine description RTL by the tool
genconfig
.
recog.c
' and `recog.h
', plus the files `insn-recog.c
'
and `insn-extract.c
' that are generated automatically from the
machine description by the tools `genrecog
' and
`genextract
'.
regs.h
' which defines the
information recorded about pseudo register usage, and `basic-block.h
'
which defines the information recorded about basic blocks.
hard-reg-set.h
' defines the type HARD_REG_SET
, a bit-vector
with a bit for each hard register, and some macros to manipulate it.
This type is just int
if the machine has few enough hard registers;
otherwise it is an array of int
and some of the macros expand
into loops.
insn-attr.h
', which is generated from the machine description by
the program `genattr
'. The file `insn-attrtab.c
' contains
subroutines to obtain the attribute values for insns. It is generated
from the machine description by the program `genattrtab
'.