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Initial commit of GCC 2.8.1
2020-09-21 03:06:00 +02:00
This is Info file gcc.info, produced by Makeinfo version 1.67 from the
input file gcc.texi.
This file documents the use and the internals of the GNU compiler.
Published by the Free Software Foundation 59 Temple Place - Suite 330
Boston, MA 02111-1307 USA
Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998
Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the sections entitled "GNU General Public License," "Funding for
Free Software," and "Protect 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 one.
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," "Funding for Free Software," and "Protect Your Freedom--Fight
`Look And Feel'", and this permission notice, may be included in
translations approved by the Free Software Foundation instead of in the
original English.

File: gcc.info, Node: Profiling, Prev: Function Entry, Up: Stack and Calling
Generating Code for Profiling
-----------------------------
These macros will help you generate code for profiling.
`FUNCTION_PROFILER (FILE, LABELNO)'
A C statement or compound statement to output to FILE some
assembler code to call the profiling subroutine `mcount'. Before
calling, the assembler code must load the address of a counter
variable into a register where `mcount' expects to find the
address. The name of this variable is `LP' followed by the number
LABELNO, so you would generate the name using `LP%d' in a
`fprintf'.
The details of how the address should be passed to `mcount' are
determined by your operating system environment, not by GNU CC. To
figure them out, compile a small program for profiling using the
system's installed C compiler and look at the assembler code that
results.
`PROFILE_BEFORE_PROLOGUE'
Define this macro if the code for function profiling should come
before the function prologue. Normally, the profiling code comes
after.
`FUNCTION_BLOCK_PROFILER (FILE, LABELNO)'
A C statement or compound statement to output to FILE some
assembler code to initialize basic-block profiling for the current
object module. The global compile flag `profile_block_flag'
distinguishes two profile modes.
`profile_block_flag != 2'
Output code to call the subroutine `__bb_init_func' once per
object module, passing it as its sole argument the address of
a block allocated in the object module.
The name of the block is a local symbol made with this
statement:
ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 0);
Of course, since you are writing the definition of
`ASM_GENERATE_INTERNAL_LABEL' as well as that of this macro,
you can take a short cut in the definition of this macro and
use the name that you know will result.
The first word of this block is a flag which will be nonzero
if the object module has already been initialized. So test
this word first, and do not call `__bb_init_func' if the flag
is nonzero. BLOCK_OR_LABEL contains a unique number which
may be used to generate a label as a branch destination when
`__bb_init_func' will not be called.
Described in assembler language, the code to be output looks
like:
cmp (LPBX0),0
bne local_label
parameter1 <- LPBX0
call __bb_init_func
local_label:
`profile_block_flag == 2'
Output code to call the subroutine `__bb_init_trace_func' and
pass two parameters to it. The first parameter is the same as
for `__bb_init_func'. The second parameter is the number of
the first basic block of the function as given by
BLOCK_OR_LABEL. Note that `__bb_init_trace_func' has to be
called, even if the object module has been initialized
already.
Described in assembler language, the code to be output looks
like:
parameter1 <- LPBX0
parameter2 <- BLOCK_OR_LABEL
call __bb_init_trace_func
`BLOCK_PROFILER (FILE, BLOCKNO)'
A C statement or compound statement to output to FILE some
assembler code to increment the count associated with the basic
block number BLOCKNO. The global compile flag
`profile_block_flag' distinguishes two profile modes.
`profile_block_flag != 2'
Output code to increment the counter directly. Basic blocks
are numbered separately from zero within each compilation.
The count associated with block number BLOCKNO is at index
BLOCKNO in a vector of words; the name of this array is a
local symbol made with this statement:
ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 2);
Of course, since you are writing the definition of
`ASM_GENERATE_INTERNAL_LABEL' as well as that of this macro,
you can take a short cut in the definition of this macro and
use the name that you know will result.
Described in assembler language, the code to be output looks
like:
inc (LPBX2+4*BLOCKNO)
`profile_block_flag == 2'
Output code to initialize the global structure `__bb' and
call the function `__bb_trace_func', which will increment the
counter.
`__bb' consists of two words. In the first word, the current
basic block number, as given by BLOCKNO, has to be stored. In
the second word, the address of a block allocated in the
object module has to be stored. The address is given by the
label created with this statement:
ASM_GENERATE_INTERNAL_LABEL (BUFFER, "LPBX", 0);
Described in assembler language, the code to be output looks
like:
move BLOCKNO -> (__bb)
move LPBX0 -> (__bb+4)
call __bb_trace_func
`FUNCTION_BLOCK_PROFILER_EXIT (FILE)'
A C statement or compound statement to output to FILE assembler
code to call function `__bb_trace_ret'. The assembler code should
only be output if the global compile flag `profile_block_flag' ==
2. This macro has to be used at every place where code for
returning from a function is generated (e.g. `FUNCTION_EPILOGUE').
Although you have to write the definition of `FUNCTION_EPILOGUE'
as well, you have to define this macro to tell the compiler, that
the proper call to `__bb_trace_ret' is produced.
`MACHINE_STATE_SAVE (ID)'
A C statement or compound statement to save all registers, which
may be clobbered by a function call, including condition codes.
The `asm' statement will be mostly likely needed to handle this
task. Local labels in the assembler code can be concatenated with
the string ID, to obtain a unique lable name.
Registers or condition codes clobbered by `FUNCTION_PROLOGUE' or
`FUNCTION_EPILOGUE' must be saved in the macros
`FUNCTION_BLOCK_PROFILER', `FUNCTION_BLOCK_PROFILER_EXIT' and
`BLOCK_PROFILER' prior calling `__bb_init_trace_func',
`__bb_trace_ret' and `__bb_trace_func' respectively.
`MACHINE_STATE_RESTORE (ID)'
A C statement or compound statement to restore all registers,
including condition codes, saved by `MACHINE_STATE_SAVE'.
Registers or condition codes clobbered by `FUNCTION_PROLOGUE' or
`FUNCTION_EPILOGUE' must be restored in the macros
`FUNCTION_BLOCK_PROFILER', `FUNCTION_BLOCK_PROFILER_EXIT' and
`BLOCK_PROFILER' after calling `__bb_init_trace_func',
`__bb_trace_ret' and `__bb_trace_func' respectively.
`BLOCK_PROFILER_CODE'
A C function or functions which are needed in the library to
support block profiling.

File: gcc.info, Node: Varargs, Next: Trampolines, Prev: Stack and Calling, Up: Target Macros
Implementing the Varargs Macros
===============================
GNU CC comes with an implementation of `varargs.h' and `stdarg.h'
that work without change on machines that pass arguments on the stack.
Other machines require their own implementations of varargs, and the
two machine independent header files must have conditionals to include
it.
ANSI `stdarg.h' differs from traditional `varargs.h' mainly in the
calling convention for `va_start'. The traditional implementation
takes just one argument, which is the variable in which to store the
argument pointer. The ANSI implementation of `va_start' takes an
additional second argument. The user is supposed to write the last
named argument of the function here.
However, `va_start' should not use this argument. The way to find
the end of the named arguments is with the built-in functions described
below.
`__builtin_saveregs ()'
Use this built-in function to save the argument registers in
memory so that the varargs mechanism can access them. Both ANSI
and traditional versions of `va_start' must use
`__builtin_saveregs', unless you use `SETUP_INCOMING_VARARGS' (see
below) instead.
On some machines, `__builtin_saveregs' is open-coded under the
control of the macro `EXPAND_BUILTIN_SAVEREGS'. On other machines,
it calls a routine written in assembler language, found in
`libgcc2.c'.
Code generated for the call to `__builtin_saveregs' appears at the
beginning of the function, as opposed to where the call to
`__builtin_saveregs' is written, regardless of what the code is.
This is because the registers must be saved before the function
starts to use them for its own purposes.
`__builtin_args_info (CATEGORY)'
Use this built-in function to find the first anonymous arguments in
registers.
In general, a machine may have several categories of registers
used for arguments, each for a particular category of data types.
(For example, on some machines, floating-point registers are used
for floating-point arguments while other arguments are passed in
the general registers.) To make non-varargs functions use the
proper calling convention, you have defined the `CUMULATIVE_ARGS'
data type to record how many registers in each category have been
used so far
`__builtin_args_info' accesses the same data structure of type
`CUMULATIVE_ARGS' after the ordinary argument layout is finished
with it, with CATEGORY specifying which word to access. Thus, the
value indicates the first unused register in a given category.
Normally, you would use `__builtin_args_info' in the implementation
of `va_start', accessing each category just once and storing the
value in the `va_list' object. This is because `va_list' will
have to update the values, and there is no way to alter the values
accessed by `__builtin_args_info'.
`__builtin_next_arg (LASTARG)'
This is the equivalent of `__builtin_args_info', for stack
arguments. It returns the address of the first anonymous stack
argument, as type `void *'. If `ARGS_GROW_DOWNWARD', it returns
the address of the location above the first anonymous stack
argument. Use it in `va_start' to initialize the pointer for
fetching arguments from the stack. Also use it in `va_start' to
verify that the second parameter LASTARG is the last named argument
of the current function.
`__builtin_classify_type (OBJECT)'
Since each machine has its own conventions for which data types are
passed in which kind of register, your implementation of `va_arg'
has to embody these conventions. The easiest way to categorize the
specified data type is to use `__builtin_classify_type' together
with `sizeof' and `__alignof__'.
`__builtin_classify_type' ignores the value of OBJECT, considering
only its data type. It returns an integer describing what kind of
type that is--integer, floating, pointer, structure, and so on.
The file `typeclass.h' defines an enumeration that you can use to
interpret the values of `__builtin_classify_type'.
These machine description macros help implement varargs:
`EXPAND_BUILTIN_SAVEREGS (ARGS)'
If defined, is a C expression that produces the machine-specific
code for a call to `__builtin_saveregs'. This code will be moved
to the very beginning of the function, before any parameter access
are made. The return value of this function should be an RTX that
contains the value to use as the return of `__builtin_saveregs'.
The argument ARGS is a `tree_list' containing the arguments that
were passed to `__builtin_saveregs'.
If this macro is not defined, the compiler will output an ordinary
call to the library function `__builtin_saveregs'.
`SETUP_INCOMING_VARARGS (ARGS_SO_FAR, MODE, TYPE,'
PRETEND_ARGS_SIZE, SECOND_TIME) This macro offers an alternative
to using `__builtin_saveregs' and defining the macro
`EXPAND_BUILTIN_SAVEREGS'. Use it to store the anonymous register
arguments into the stack so that all the arguments appear to have
been passed consecutively on the stack. Once this is done, you
can use the standard implementation of varargs that works for
machines that pass all their arguments on the stack.
The argument ARGS_SO_FAR is the `CUMULATIVE_ARGS' data structure,
containing the values that obtain after processing of the named
arguments. The arguments MODE and TYPE describe the last named
argument--its machine mode and its data type as a tree node.
The macro implementation should do two things: first, push onto the
stack all the argument registers *not* used for the named
arguments, and second, store the size of the data thus pushed into
the `int'-valued variable whose name is supplied as the argument
PRETEND_ARGS_SIZE. The value that you store here will serve as
additional offset for setting up the stack frame.
Because you must generate code to push the anonymous arguments at
compile time without knowing their data types,
`SETUP_INCOMING_VARARGS' is only useful on machines that have just
a single category of argument register and use it uniformly for
all data types.
If the argument SECOND_TIME is nonzero, it means that the
arguments of the function are being analyzed for the second time.
This happens for an inline function, which is not actually
compiled until the end of the source file. The macro
`SETUP_INCOMING_VARARGS' should not generate any instructions in
this case.
`STRICT_ARGUMENT_NAMING'
Define this macro if the location where a function argument is
passed depends on whether or not it is a named argument.
This macro controls how the NAMED argument to `FUNCTION_ARG' is
set for varargs and stdarg functions. With this macro defined,
the NAMED argument is always true for named arguments, and false
for unnamed arguments. If this is not defined, but
`SETUP_INCOMING_VARARGS' is defined, then all arguments are
treated as named. Otherwise, all named arguments except the last
are treated as named.

File: gcc.info, Node: Trampolines, Next: Library Calls, Prev: Varargs, Up: Target Macros
Trampolines for Nested Functions
================================
A "trampoline" is a small piece of code that is created at run time
when the address of a nested function is taken. It normally resides on
the stack, in the stack frame of the containing function. These macros
tell GNU CC how to generate code to allocate and initialize a
trampoline.
The instructions in the trampoline must do two things: load a
constant address into the static chain register, and jump to the real
address of the nested function. On CISC machines such as the m68k,
this requires two instructions, a move immediate and a jump. Then the
two addresses exist in the trampoline as word-long immediate operands.
On RISC machines, it is often necessary to load each address into a
register in two parts. Then pieces of each address form separate
immediate operands.
The code generated to initialize the trampoline must store the
variable parts--the static chain value and the function address--into
the immediate operands of the instructions. On a CISC machine, this is
simply a matter of copying each address to a memory reference at the
proper offset from the start of the trampoline. On a RISC machine, it
may be necessary to take out pieces of the address and store them
separately.
`TRAMPOLINE_TEMPLATE (FILE)'
A C statement to output, on the stream FILE, assembler code for a
block of data that contains the constant parts of a trampoline.
This code should not include a label--the label is taken care of
automatically.
If you do not define this macro, it means no template is needed
for the target. Do not define this macro on systems where the
block move code to copy the trampoline into place would be larger
than the code to generate it on the spot.
`TRAMPOLINE_SECTION'
The name of a subroutine to switch to the section in which the
trampoline template is to be placed (*note Sections::.). The
default is a value of `readonly_data_section', which places the
trampoline in the section containing read-only data.
`TRAMPOLINE_SIZE'
A C expression for the size in bytes of the trampoline, as an
integer.
`TRAMPOLINE_ALIGNMENT'
Alignment required for trampolines, in bits.
If you don't define this macro, the value of `BIGGEST_ALIGNMENT'
is used for aligning trampolines.
`INITIALIZE_TRAMPOLINE (ADDR, FNADDR, STATIC_CHAIN)'
A C statement to initialize the variable parts of a trampoline.
ADDR is an RTX for the address of the trampoline; FNADDR is an RTX
for the address of the nested function; STATIC_CHAIN is an RTX for
the static chain value that should be passed to the function when
it is called.
`ALLOCATE_TRAMPOLINE (FP)'
A C expression to allocate run-time space for a trampoline. The
expression value should be an RTX representing a memory reference
to the space for the trampoline.
If this macro is not defined, by default the trampoline is
allocated as a stack slot. This default is right for most
machines. The exceptions are machines where it is impossible to
execute instructions in the stack area. On such machines, you may
have to implement a separate stack, using this macro in
conjunction with `FUNCTION_PROLOGUE' and `FUNCTION_EPILOGUE'.
FP points to a data structure, a `struct function', which
describes the compilation status of the immediate containing
function of the function which the trampoline is for. Normally
(when `ALLOCATE_TRAMPOLINE' is not defined), the stack slot for the
trampoline is in the stack frame of this containing function.
Other allocation strategies probably must do something analogous
with this information.
Implementing trampolines is difficult on many machines because they
have separate instruction and data caches. Writing into a stack
location fails to clear the memory in the instruction cache, so when
the program jumps to that location, it executes the old contents.
Here are two possible solutions. One is to clear the relevant parts
of the instruction cache whenever a trampoline is set up. The other is
to make all trampolines identical, by having them jump to a standard
subroutine. The former technique makes trampoline execution faster; the
latter makes initialization faster.
To clear the instruction cache when a trampoline is initialized,
define the following macros which describe the shape of the cache.
`INSN_CACHE_SIZE'
The total size in bytes of the cache.
`INSN_CACHE_LINE_WIDTH'
The length in bytes of each cache line. The cache is divided into
cache lines which are disjoint slots, each holding a contiguous
chunk of data fetched from memory. Each time data is brought into
the cache, an entire line is read at once. The data loaded into a
cache line is always aligned on a boundary equal to the line size.
`INSN_CACHE_DEPTH'
The number of alternative cache lines that can hold any particular
memory location.
Alternatively, if the machine has system calls or instructions to
clear the instruction cache directly, you can define the following
macro.
`CLEAR_INSN_CACHE (BEG, END)'
If defined, expands to a C expression clearing the *instruction
cache* in the specified interval. If it is not defined, and the
macro INSN_CACHE_SIZE is defined, some generic code is generated
to clear the cache. The definition of this macro would typically
be a series of `asm' statements. Both BEG and END are both pointer
expressions.
To use a standard subroutine, define the following macro. In
addition, you must make sure that the instructions in a trampoline fill
an entire cache line with identical instructions, or else ensure that
the beginning of the trampoline code is always aligned at the same
point in its cache line. Look in `m68k.h' as a guide.
`TRANSFER_FROM_TRAMPOLINE'
Define this macro if trampolines need a special subroutine to do
their work. The macro should expand to a series of `asm'
statements which will be compiled with GNU CC. They go in a
library function named `__transfer_from_trampoline'.
If you need to avoid executing the ordinary prologue code of a
compiled C function when you jump to the subroutine, you can do so
by placing a special label of your own in the assembler code. Use
one `asm' statement to generate an assembler label, and another to
make the label global. Then trampolines can use that label to
jump directly to your special assembler code.

File: gcc.info, Node: Library Calls, Next: Addressing Modes, Prev: Trampolines, Up: Target Macros
Implicit Calls to Library Routines
==================================
Here is an explanation of implicit calls to library routines.
`MULSI3_LIBCALL'
A C string constant giving the name of the function to call for
multiplication of one signed full-word by another. If you do not
define this macro, the default name is used, which is `__mulsi3',
a function defined in `libgcc.a'.
`DIVSI3_LIBCALL'
A C string constant giving the name of the function to call for
division of one signed full-word by another. If you do not define
this macro, the default name is used, which is `__divsi3', a
function defined in `libgcc.a'.
`UDIVSI3_LIBCALL'
A C string constant giving the name of the function to call for
division of one unsigned full-word by another. If you do not
define this macro, the default name is used, which is `__udivsi3',
a function defined in `libgcc.a'.
`MODSI3_LIBCALL'
A C string constant giving the name of the function to call for the
remainder in division of one signed full-word by another. If you
do not define this macro, the default name is used, which is
`__modsi3', a function defined in `libgcc.a'.
`UMODSI3_LIBCALL'
A C string constant giving the name of the function to call for the
remainder in division of one unsigned full-word by another. If
you do not define this macro, the default name is used, which is
`__umodsi3', a function defined in `libgcc.a'.
`MULDI3_LIBCALL'
A C string constant giving the name of the function to call for
multiplication of one signed double-word by another. If you do not
define this macro, the default name is used, which is `__muldi3',
a function defined in `libgcc.a'.
`DIVDI3_LIBCALL'
A C string constant giving the name of the function to call for
division of one signed double-word by another. If you do not
define this macro, the default name is used, which is `__divdi3', a
function defined in `libgcc.a'.
`UDIVDI3_LIBCALL'
A C string constant giving the name of the function to call for
division of one unsigned full-word by another. If you do not
define this macro, the default name is used, which is `__udivdi3',
a function defined in `libgcc.a'.
`MODDI3_LIBCALL'
A C string constant giving the name of the function to call for the
remainder in division of one signed double-word by another. If
you do not define this macro, the default name is used, which is
`__moddi3', a function defined in `libgcc.a'.
`UMODDI3_LIBCALL'
A C string constant giving the name of the function to call for the
remainder in division of one unsigned full-word by another. If
you do not define this macro, the default name is used, which is
`__umoddi3', a function defined in `libgcc.a'.
`INIT_TARGET_OPTABS'
Define this macro as a C statement that declares additional library
routines renames existing ones. `init_optabs' calls this macro
after initializing all the normal library routines.
`TARGET_EDOM'
The value of `EDOM' on the target machine, as a C integer constant
expression. If you don't define this macro, GNU CC does not
attempt to deposit the value of `EDOM' into `errno' directly.
Look in `/usr/include/errno.h' to find the value of `EDOM' on your
system.
If you do not define `TARGET_EDOM', then compiled code reports
domain errors by calling the library function and letting it
report the error. If mathematical functions on your system use
`matherr' when there is an error, then you should leave
`TARGET_EDOM' undefined so that `matherr' is used normally.
`GEN_ERRNO_RTX'
Define this macro as a C expression to create an rtl expression
that refers to the global "variable" `errno'. (On certain systems,
`errno' may not actually be a variable.) If you don't define this
macro, a reasonable default is used.
`TARGET_MEM_FUNCTIONS'
Define this macro if GNU CC should generate calls to the System V
(and ANSI C) library functions `memcpy' and `memset' rather than
the BSD functions `bcopy' and `bzero'.
`LIBGCC_NEEDS_DOUBLE'
Define this macro if only `float' arguments cannot be passed to
library routines (so they must be converted to `double'). This
macro affects both how library calls are generated and how the
library routines in `libgcc1.c' accept their arguments. It is
useful on machines where floating and fixed point arguments are
passed differently, such as the i860.
`FLOAT_ARG_TYPE'
Define this macro to override the type used by the library
routines to pick up arguments of type `float'. (By default, they
use a union of `float' and `int'.)
The obvious choice would be `float'--but that won't work with
traditional C compilers that expect all arguments declared as
`float' to arrive as `double'. To avoid this conversion, the
library routines ask for the value as some other type and then
treat it as a `float'.
On some systems, no other type will work for this. For these
systems, you must use `LIBGCC_NEEDS_DOUBLE' instead, to force
conversion of the values `double' before they are passed.
`FLOATIFY (PASSED-VALUE)'
Define this macro to override the way library routines redesignate
a `float' argument as a `float' instead of the type it was passed
as. The default is an expression which takes the `float' field of
the union.
`FLOAT_VALUE_TYPE'
Define this macro to override the type used by the library
routines to return values that ought to have type `float'. (By
default, they use `int'.)
The obvious choice would be `float'--but that won't work with
traditional C compilers gratuitously convert values declared as
`float' into `double'.
`INTIFY (FLOAT-VALUE)'
Define this macro to override the way the value of a
`float'-returning library routine should be packaged in order to
return it. These functions are actually declared to return type
`FLOAT_VALUE_TYPE' (normally `int').
These values can't be returned as type `float' because traditional
C compilers would gratuitously convert the value to a `double'.
A local variable named `intify' is always available when the macro
`INTIFY' is used. It is a union of a `float' field named `f' and
a field named `i' whose type is `FLOAT_VALUE_TYPE' or `int'.
If you don't define this macro, the default definition works by
copying the value through that union.
`nongcc_SI_type'
Define this macro as the name of the data type corresponding to
`SImode' in the system's own C compiler.
You need not define this macro if that type is `long int', as it
usually is.
`nongcc_word_type'
Define this macro as the name of the data type corresponding to the
word_mode in the system's own C compiler.
You need not define this macro if that type is `long int', as it
usually is.
`perform_...'
Define these macros to supply explicit C statements to carry out
various arithmetic operations on types `float' and `double' in the
library routines in `libgcc1.c'. See that file for a full list of
these macros and their arguments.
On most machines, you don't need to define any of these macros,
because the C compiler that comes with the system takes care of
doing them.
`NEXT_OBJC_RUNTIME'
Define this macro to generate code for Objective C message sending
using the calling convention of the NeXT system. This calling
convention involves passing the object, the selector and the
method arguments all at once to the method-lookup library function.
The default calling convention passes just the object and the
selector to the lookup function, which returns a pointer to the
method.

File: gcc.info, Node: Addressing Modes, Next: Condition Code, Prev: Library Calls, Up: Target Macros
Addressing Modes
================
This is about addressing modes.
`HAVE_POST_INCREMENT'
Define this macro if the machine supports post-increment
addressing.
`HAVE_PRE_INCREMENT'
`HAVE_POST_DECREMENT'
`HAVE_PRE_DECREMENT'
Similar for other kinds of addressing.
`CONSTANT_ADDRESS_P (X)'
A C expression that is 1 if the RTX X is a constant which is a
valid address. On most machines, this can be defined as
`CONSTANT_P (X)', but a few machines are more restrictive in which
constant addresses are supported.
`CONSTANT_P' accepts integer-values expressions whose values are
not explicitly known, such as `symbol_ref', `label_ref', and
`high' expressions and `const' arithmetic expressions, in addition
to `const_int' and `const_double' expressions.
`MAX_REGS_PER_ADDRESS'
A number, the maximum number of registers that can appear in a
valid memory address. Note that it is up to you to specify a
value equal to the maximum number that `GO_IF_LEGITIMATE_ADDRESS'
would ever accept.
`GO_IF_LEGITIMATE_ADDRESS (MODE, X, LABEL)'
A C compound statement with a conditional `goto LABEL;' executed
if X (an RTX) is a legitimate memory address on the target machine
for a memory operand of mode MODE.
It usually pays to define several simpler macros to serve as
subroutines for this one. Otherwise it may be too complicated to
understand.
This macro must exist in two variants: a strict variant and a
non-strict one. The strict variant is used in the reload pass. It
must be defined so that any pseudo-register that has not been
allocated a hard register is considered a memory reference. In
contexts where some kind of register is required, a pseudo-register
with no hard register must be rejected.
The non-strict variant is used in other passes. It must be
defined to accept all pseudo-registers in every context where some
kind of register is required.
Compiler source files that want to use the strict variant of this
macro define the macro `REG_OK_STRICT'. You should use an `#ifdef
REG_OK_STRICT' conditional to define the strict variant in that
case and the non-strict variant otherwise.
Subroutines to check for acceptable registers for various purposes
(one for base registers, one for index registers, and so on) are
typically among the subroutines used to define
`GO_IF_LEGITIMATE_ADDRESS'. Then only these subroutine macros
need have two variants; the higher levels of macros may be the
same whether strict or not.
Normally, constant addresses which are the sum of a `symbol_ref'
and an integer are stored inside a `const' RTX to mark them as
constant. Therefore, there is no need to recognize such sums
specifically as legitimate addresses. Normally you would simply
recognize any `const' as legitimate.
Usually `PRINT_OPERAND_ADDRESS' is not prepared to handle constant
sums that are not marked with `const'. It assumes that a naked
`plus' indicates indexing. If so, then you *must* reject such
naked constant sums as illegitimate addresses, so that none of
them will be given to `PRINT_OPERAND_ADDRESS'.
On some machines, whether a symbolic address is legitimate depends
on the section that the address refers to. On these machines,
define the macro `ENCODE_SECTION_INFO' to store the information
into the `symbol_ref', and then check for it here. When you see a
`const', you will have to look inside it to find the `symbol_ref'
in order to determine the section. *Note Assembler Format::.
The best way to modify the name string is by adding text to the
beginning, with suitable punctuation to prevent any ambiguity.
Allocate the new name in `saveable_obstack'. You will have to
modify `ASM_OUTPUT_LABELREF' to remove and decode the added text
and output the name accordingly, and define `STRIP_NAME_ENCODING'
to access the original name string.
You can check the information stored here into the `symbol_ref' in
the definitions of the macros `GO_IF_LEGITIMATE_ADDRESS' and
`PRINT_OPERAND_ADDRESS'.
`REG_OK_FOR_BASE_P (X)'
A C expression that is nonzero if X (assumed to be a `reg' RTX) is
valid for use as a base register. For hard registers, it should
always accept those which the hardware permits and reject the
others. Whether the macro accepts or rejects pseudo registers
must be controlled by `REG_OK_STRICT' as described above. This
usually requires two variant definitions, of which `REG_OK_STRICT'
controls the one actually used.
`REG_MODE_OK_FOR_BASE_P (X, MODE)'
A C expression that is just like `REG_OK_FOR_BASE_P', except that
that expression may examine the mode of the memory reference in
MODE. You should define this macro if the mode of the memory
reference affects whether a register may be used as a base
register. If you define this macro, the compiler will use it
instead of `REG_OK_FOR_BASE_P'.
`REG_OK_FOR_INDEX_P (X)'
A C expression that is nonzero if X (assumed to be a `reg' RTX) is
valid for use as an index register.
The difference between an index register and a base register is
that the index register may be scaled. If an address involves the
sum of two registers, neither one of them scaled, then either one
may be labeled the "base" and the other the "index"; but whichever
labeling is used must fit the machine's constraints of which
registers may serve in each capacity. The compiler will try both
labelings, looking for one that is valid, and will reload one or
both registers only if neither labeling works.
`LEGITIMIZE_ADDRESS (X, OLDX, MODE, WIN)'
A C compound statement that attempts to replace X with a valid
memory address for an operand of mode MODE. WIN will be a C
statement label elsewhere in the code; the macro definition may use
GO_IF_LEGITIMATE_ADDRESS (MODE, X, WIN);
to avoid further processing if the address has become legitimate.
X will always be the result of a call to `break_out_memory_refs',
and OLDX will be the operand that was given to that function to
produce X.
The code generated by this macro should not alter the substructure
of X. If it transforms X into a more legitimate form, it should
assign X (which will always be a C variable) a new value.
It is not necessary for this macro to come up with a legitimate
address. The compiler has standard ways of doing so in all cases.
In fact, it is safe for this macro to do nothing. But often a
machine-dependent strategy can generate better code.
`GO_IF_MODE_DEPENDENT_ADDRESS (ADDR, LABEL)'
A C statement or compound statement with a conditional `goto
LABEL;' executed if memory address X (an RTX) can have different
meanings depending on the machine mode of the memory reference it
is used for or if the address is valid for some modes but not
others.
Autoincrement and autodecrement addresses typically have
mode-dependent effects because the amount of the increment or
decrement is the size of the operand being addressed. Some
machines have other mode-dependent addresses. Many RISC machines
have no mode-dependent addresses.
You may assume that ADDR is a valid address for the machine.
`LEGITIMATE_CONSTANT_P (X)'
A C expression that is nonzero if X is a legitimate constant for
an immediate operand on the target machine. You can assume that X
satisfies `CONSTANT_P', so you need not check this. In fact, `1'
is a suitable definition for this macro on machines where anything
`CONSTANT_P' is valid.

File: gcc.info, Node: Condition Code, Next: Costs, Prev: Addressing Modes, Up: Target Macros
Condition Code Status
=====================
This describes the condition code status.
The file `conditions.h' defines a variable `cc_status' to describe
how the condition code was computed (in case the interpretation of the
condition code depends on the instruction that it was set by). This
variable contains the RTL expressions on which the condition code is
currently based, and several standard flags.
Sometimes additional machine-specific flags must be defined in the
machine description header file. It can also add additional
machine-specific information by defining `CC_STATUS_MDEP'.
`CC_STATUS_MDEP'
C code for a data type which is used for declaring the `mdep'
component of `cc_status'. It defaults to `int'.
This macro is not used on machines that do not use `cc0'.
`CC_STATUS_MDEP_INIT'
A C expression to initialize the `mdep' field to "empty". The
default definition does nothing, since most machines don't use the
field anyway. If you want to use the field, you should probably
define this macro to initialize it.
This macro is not used on machines that do not use `cc0'.
`NOTICE_UPDATE_CC (EXP, INSN)'
A C compound statement to set the components of `cc_status'
appropriately for an insn INSN whose body is EXP. It is this
macro's responsibility to recognize insns that set the condition
code as a byproduct of other activity as well as those that
explicitly set `(cc0)'.
This macro is not used on machines that do not use `cc0'.
If there are insns that do not set the condition code but do alter
other machine registers, this macro must check to see whether they
invalidate the expressions that the condition code is recorded as
reflecting. For example, on the 68000, insns that store in address
registers do not set the condition code, which means that usually
`NOTICE_UPDATE_CC' can leave `cc_status' unaltered for such insns.
But suppose that the previous insn set the condition code based
on location `a4@(102)' and the current insn stores a new value in
`a4'. Although the condition code is not changed by this, it will
no longer be true that it reflects the contents of `a4@(102)'.
Therefore, `NOTICE_UPDATE_CC' must alter `cc_status' in this case
to say that nothing is known about the condition code value.
The definition of `NOTICE_UPDATE_CC' must be prepared to deal with
the results of peephole optimization: insns whose patterns are
`parallel' RTXs containing various `reg', `mem' or constants which
are just the operands. The RTL structure of these insns is not
sufficient to indicate what the insns actually do. What
`NOTICE_UPDATE_CC' should do when it sees one is just to run
`CC_STATUS_INIT'.
A possible definition of `NOTICE_UPDATE_CC' is to call a function
that looks at an attribute (*note Insn Attributes::.) named, for
example, `cc'. This avoids having detailed information about
patterns in two places, the `md' file and in `NOTICE_UPDATE_CC'.
`EXTRA_CC_MODES'
A list of names to be used for additional modes for condition code
values in registers (*note Jump Patterns::.). These names are
added to `enum machine_mode' and all have class `MODE_CC'. By
convention, they should start with `CC' and end with `mode'.
You should only define this macro if your machine does not use
`cc0' and only if additional modes are required.
`EXTRA_CC_NAMES'
A list of C strings giving the names for the modes listed in
`EXTRA_CC_MODES'. For example, the Sparc defines this macro and
`EXTRA_CC_MODES' as
#define EXTRA_CC_MODES CC_NOOVmode, CCFPmode, CCFPEmode
#define EXTRA_CC_NAMES "CC_NOOV", "CCFP", "CCFPE"
This macro is not required if `EXTRA_CC_MODES' is not defined.
`SELECT_CC_MODE (OP, X, Y)'
Returns a mode from class `MODE_CC' to be used when comparison
operation code OP is applied to rtx X and Y. For example, on the
Sparc, `SELECT_CC_MODE' is defined as (see *note Jump Patterns::.
for a description of the reason for this definition)
#define SELECT_CC_MODE(OP,X,Y) \
(GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \
: ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
|| GET_CODE (X) == NEG) \
? CC_NOOVmode : CCmode))
You need not define this macro if `EXTRA_CC_MODES' is not defined.
`CANONICALIZE_COMPARISON (CODE, OP0, OP1)'
One some machines not all possible comparisons are defined, but
you can convert an invalid comparison into a valid one. For
example, the Alpha does not have a `GT' comparison, but you can
use an `LT' comparison instead and swap the order of the operands.
On such machines, define this macro to be a C statement to do any
required conversions. CODE is the initial comparison code and OP0
and OP1 are the left and right operands of the comparison,
respectively. You should modify CODE, OP0, and OP1 as required.
GNU CC will not assume that the comparison resulting from this
macro is valid but will see if the resulting insn matches a
pattern in the `md' file.
You need not define this macro if it would never change the
comparison code or operands.
`REVERSIBLE_CC_MODE (MODE)'
A C expression whose value is one if it is always safe to reverse a
comparison whose mode is MODE. If `SELECT_CC_MODE' can ever
return MODE for a floating-point inequality comparison, then
`REVERSIBLE_CC_MODE (MODE)' must be zero.
You need not define this macro if it would always returns zero or
if the floating-point format is anything other than
`IEEE_FLOAT_FORMAT'. For example, here is the definition used on
the Sparc, where floating-point inequality comparisons are always
given `CCFPEmode':
#define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode)
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