home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Workbench Add-On
/
Workbench Add-On - Volume 1.iso
/
BBS-Archive
/
Dev
/
gcc-2.6.3-bin.lha
/
GNU
/
info
/
gcc.info-23
(
.txt
)
< prev
next >
Wrap
GNU Info File
|
1995-03-30
|
25KB
|
455 lines
This is Info file gcc.info, produced by Makeinfo-1.55 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, 1994 Free Software Foundation,
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: Misc, Prev: Cross-compilation, Up: Target Macros
Miscellaneous Parameters
========================
Here are several miscellaneous parameters.
`PREDICATE_CODES'
Define this if you have defined special-purpose predicates in the
file `MACHINE.c'. This macro is called within an initializer of an
array of structures. The first field in the structure is the name
of a predicate and the second field is an array of rtl codes. For
each predicate, list all rtl codes that can be in expressions
matched by the predicate. The list should have a trailing comma.
Here is an example of two entries in the list for a typical RISC
machine:
#define PREDICATE_CODES \
{"gen_reg_rtx_operand", {SUBREG, REG}}, \
{"reg_or_short_cint_operand", {SUBREG, REG, CONST_INT}},
Defining this macro does not affect the generated code (however,
incorrect definitions that omit an rtl code that may be matched by
the predicate can cause the compiler to malfunction). Instead, it
allows the table built by `genrecog' to be more compact and
efficient, thus speeding up the compiler. The most important
predicates to include in the list specified by this macro are
thoses used in the most insn patterns.
`CASE_VECTOR_MODE'
An alias for a machine mode name. This is the machine mode that
elements of a jump-table should have.
`CASE_VECTOR_PC_RELATIVE'
Define this macro if jump-tables should contain relative addresses.
`CASE_DROPS_THROUGH'
Define this if control falls through a `case' insn when the index
value is out of range. This means the specified default-label is
actually ignored by the `case' insn proper.
`CASE_VALUES_THRESHOLD'
Define this to be the smallest number of different values for
which it is best to use a jump-table instead of a tree of
conditional branches. The default is four for machines with a
`casesi' instruction and five otherwise. This is best for most
machines.
`WORD_REGISTER_OPERATIONS'
Define this macro if operations between registers with integral
mode smaller than a word are always performed on the entire
register. Most RISC machines have this property and most CISC
machines do not.
`LOAD_EXTEND_OP (MODE)'
Define this macro to be a C expression indicating when insns that
read memory in MODE, an integral mode narrower than a word, set the
bits outside of MODE to be either the sign-extension or the
zero-extension of the data read. Return `SIGN_EXTEND' for values
of MODE for which the insn sign-extends, `ZERO_EXTEND' for which
it zero-extends, and `NIL' for other modes.
This macro is not called with MODE non-integral or with a width
greater than or equal to `BITS_PER_WORD', so you may return any
value in this case. Do not define this macro if it would always
return `NIL'. On machines where this macro is defined, you will
normally define it as the constant `SIGN_EXTEND' or `ZERO_EXTEND'.
`IMPLICIT_FIX_EXPR'
An alias for a tree code that should be used by default for
conversion of floating point values to fixed point. Normally,
`FIX_ROUND_EXPR' is used.
`FIXUNS_TRUNC_LIKE_FIX_TRUNC'
Define this macro if the same instructions that convert a floating
point number to a signed fixed point number also convert validly
to an unsigned one.
`EASY_DIV_EXPR'
An alias for a tree code that is the easiest kind of division to
compile code for in the general case. It may be `TRUNC_DIV_EXPR',
`FLOOR_DIV_EXPR', `CEIL_DIV_EXPR' or `ROUND_DIV_EXPR'. These four
division operators differ in how they round the result to an
integer. `EASY_DIV_EXPR' is used when it is permissible to use
any of those kinds of division and the choice should be made on
the basis of efficiency.
`MOVE_MAX'
The maximum number of bytes that a single instruction can move
quickly from memory to memory.
`MAX_MOVE_MAX'
The maximum number of bytes that a single instruction can move
quickly from memory to memory. If this is undefined, the default
is `MOVE_MAX'. Otherwise, it is the constant value that is the
largest value that `MOVE_MAX' can have at run-time.
`SHIFT_COUNT_TRUNCATED'
A C expression that is nonzero if on this machine the number of
bits actually used for the count of a shift operation is equal to
the number of bits needed to represent the size of the object
being shifted. When this macro is non-zero, the compiler will
assume that it is safe to omit a sign-extend, zero-extend, and
certain bitwise `and' instructions that truncates the count of a
shift operation. On machines that have instructions that act on
bitfields at variable positions, which may include `bit test'
instructions, a nonzero `SHIFT_COUNT_TRUNCATED' also enables
deletion of truncations of the values that serve as arguments to
bitfield instructions.
If both types of instructions truncate the count (for shifts) and
position (for bitfield operations), or if no variable-position
bitfield instructions exist, you should define this macro.
However, on some machines, such as the 80386 and the 680x0,
truncation only applies to shift operations and not the (real or
pretended) bitfield operations. Define `SHIFT_COUNT_TRUNCATED' to
be zero on such machines. Instead, add patterns to the `md' file
that include the implied truncation of the shift instructions.
You need not define this macro if it would always have the value
of zero.
`TRULY_NOOP_TRUNCATION (OUTPREC, INPREC)'
A C expression which is nonzero if on this machine it is safe to
"convert" an integer of INPREC bits to one of OUTPREC bits (where
OUTPREC is smaller than INPREC) by merely operating on it as if it
had only OUTPREC bits.
On many machines, this expression can be 1.
When `TRULY_NOOP_TRUNCATION' returns 1 for a pair of sizes for
modes for which `MODES_TIEABLE_P' is 0, suboptimal code can result.
If this is the case, making `TRULY_NOOP_TRUNCATION' return 0 in
such cases may improve things.
`STORE_FLAG_VALUE'
A C expression describing the value returned by a comparison
operator with an integral mode and stored by a store-flag
instruction (`sCOND') when the condition is true. This
description must apply to *all* the `sCOND' patterns and all the
comparison operators whose results have a `MODE_INT' mode.
A value of 1 or -1 means that the instruction implementing the
comparison operator returns exactly 1 or -1 when the comparison is
true and 0 when the comparison is false. Otherwise, the value
indicates which bits of the result are guaranteed to be 1 when the
comparison is true. This value is interpreted in the mode of the
comparison operation, which is given by the mode of the first
operand in the `sCOND' pattern. Either the low bit or the sign
bit of `STORE_FLAG_VALUE' be on. Presently, only those bits are
used by the compiler.
If `STORE_FLAG_VALUE' is neither 1 or -1, the compiler will
generate code that depends only on the specified bits. It can also
replace comparison operators with equivalent operations if they
cause the required bits to be set, even if the remaining bits are
undefined. For example, on a machine whose comparison operators
return an `SImode' value and where `STORE_FLAG_VALUE' is defined as
`0x80000000', saying that just the sign bit is relevant, the
expression
(ne:SI (and:SI X (const_int POWER-OF-2)) (const_int 0))
can be converted to
(ashift:SI X (const_int N))
where N is the appropriate shift count to move the bit being
tested into the sign bit.
There is no way to describe a machine that always sets the
low-order bit for a true value, but does not guarantee the value
of any other bits, but we do not know of any machine that has such
an instruction. If you are trying to port GNU CC to such a
machine, include an instruction to perform a logical-and of the
result with 1 in the pattern for the comparison operators and let
us know (*note How to Report Bugs: Bug Reporting.).
Often, a machine will have multiple instructions that obtain a
value from a comparison (or the condition codes). Here are rules
to guide the choice of value for `STORE_FLAG_VALUE', and hence the
instructions to be used:
* Use the shortest sequence that yields a valid definition for
`STORE_FLAG_VALUE'. It is more efficient for the compiler to
"normalize" the value (convert it to, e.g., 1 or 0) than for
the comparison operators to do so because there may be
opportunities to combine the normalization with other
operations.
* For equal-length sequences, use a value of 1 or -1, with -1
being slightly preferred on machines with expensive jumps and
1 preferred on other machines.
* As a second choice, choose a value of `0x80000001' if
instructions exist that set both the sign and low-order bits
but do not define the others.
* Otherwise, use a value of `0x80000000'.
Many machines can produce both the value chosen for
`STORE_FLAG_VALUE' and its negation in the same number of
instructions. On those machines, you should also define a pattern
for those cases, e.g., one matching
(set A (neg:M (ne:M B C)))
Some machines can also perform `and' or `plus' operations on
condition code values with less instructions than the corresponding
`sCOND' insn followed by `and' or `plus'. On those machines,
define the appropriate patterns. Use the names `incscc' and
`decscc', respectively, for the the patterns which perform `plus'
or `minus' operations on condition code values. See `rs6000.md'
for some examples. The GNU Superoptizer can be used to find such
instruction sequences on other machines.
You need not define `STORE_FLAG_VALUE' if the machine has no
store-flag instructions.
`FLOAT_STORE_FLAG_VALUE'
A C expression that gives a non-zero floating point value that is
returned when comparison operators with floating-point results are
true. Define this macro on machine that have comparison
operations that return floating-point values. If there are no
such operations, do not define this macro.
`Pmode'
An alias for the machine mode for pointers. Normally the
definition can be
#define Pmode SImode
`FUNCTION_MODE'
An alias for the machine mode used for memory references to
functions being called, in `call' RTL expressions. On most
machines this should be `QImode'.
`INTEGRATE_THRESHOLD (DECL)'
A C expression for the maximum number of instructions above which
the function DECL should not be inlined. DECL is a
`FUNCTION_DECL' node.
The default definition of this macro is 64 plus 8 times the number
of arguments that the function accepts. Some people think a larger
threshold should be used on RISC machines.
`SCCS_DIRECTIVE'
Define this if the preprocessor should ignore `#sccs' directives
and print no error message.
`NO_IMPLICIT_EXTERN_C'
Define this macro if the system header files support C++ as well
as C. This macro inhibits the usual method of using system header
files in C++, which is to pretend that the file's contents are
enclosed in `extern "C" {...}'.
`HANDLE_PRAGMA (STREAM)'
Define this macro if you want to implement any pragmas. If
defined, it should be a C statement to be executed when `#pragma'
is seen. The argument STREAM is the stdio input stream from which
the source text can be read.
It is generally a bad idea to implement new uses of `#pragma'. The
only reason to define this macro is for compatibility with other
compilers that do support `#pragma' for the sake of any user
programs which already use it.
`VALID_MACHINE_ATTRIBUTE (TYPE, ATTRIBUTES, IDENTIFIER)'
Define this macro if you want to support machine specific
attributes for types. If defined, it should be a C statement
whose value is nonzero if IDENTIFIER is an attribute that is valid
for TYPE. The attributes in ATTRIBUTES have previously been
assigned to TYPE.
`COMP_TYPE_ATTRIBUTES (TYPE1, TYPE2)'
Define this macro if type attributes must be checked for
compatibility. If defined, it should be a C statement that
returns zero if the attributes on TYPE1 and TYPE2 are
incompatible, one if they are compatible, and two if they are
nearly compatible (which causes a warning to be generated).
`SET_DEFAULT_TYPE_ATTRIBUTES (TYPE)'
Define this macro if you want to give the newly defined TYPE some
default attributes.
`DOLLARS_IN_IDENTIFIERS'
Define this macro to control use of the character `$' in identifier
names. The value should be 0, 1, or 2. 0 means `$' is not allowed
by default; 1 means it is allowed by default if `-traditional' is
used; 2 means it is allowed by default provided `-ansi' is not
used. 1 is the default; there is no need to define this macro in
that case.
`NO_DOLLAR_IN_LABEL'
Define this macro if the assembler does not accept the character
`$' in label names. By default constructors and destructors in
G++ have `$' in the identifiers. If this macro is defined, `.' is
used instead.
`NO_DOT_IN_LABEL'
Define this macro if the assembler does not accept the character
`.' in label names. By default constructors and destructors in G++
have names that use `.'. If this macro is defined, these names
are rewritten to avoid `.'.
`DEFAULT_MAIN_RETURN'
Define this macro if the target system expects every program's
`main' function to return a standard "success" value by default
(if no other value is explicitly returned).
The definition should be a C statement (sans semicolon) to
generate the appropriate rtl instructions. It is used only when
compiling the end of `main'.
`HAVE_ATEXIT'
Define this if the target system supports the function `atexit'
from the ANSI C standard. If this is not defined, and
`INIT_SECTION_ASM_OP' is not defined, a default `exit' function
will be provided to support C++.
`EXIT_BODY'
Define this if your `exit' function needs to do something besides
calling an external function `_cleanup' before terminating with
`_exit'. The `EXIT_BODY' macro is only needed if netiher
`HAVE_ATEXIT' nor `INIT_SECTION_ASM_OP' are defined.
`INSN_SETS_ARE_DELAYED (INSN)'
Define this macro as a C expression that is nonzero if it is safe
for the delay slot scheduler to place instructions in the delay
slot of INSN, even if they appear to use a resource set or
clobbered in INSN. INSN is always a `jump_insn' or an `insn'; GNU
CC knows that every `call_insn' has this behavior. On machines
where some `insn' or `jump_insn' is really a function call and
hence has this behavior, you should define this macro.
You need not define this macro if it would always return zero.
`INSN_REFERENCES_ARE_DELAYED (INSN)'
Define this macro as a C expression that is nonzero if it is safe
for the delay slot scheduler to place instructions in the delay
slot of INSN, even if they appear to set or clobber a resource
referenced in INSN. INSN is always a `jump_insn' or an `insn'.
On machines where some `insn' or `jump_insn' is really a function
call and its operands are registers whose use is actually in the
subroutine it calls, you should define this macro. Doing so
allows the delay slot scheduler to move instructions which copy
arguments into the argument registers into the delay slot of INSN.
You need not define this macro if it would always return zero.
`MACHINE_DEPENDENT_REORG (INSN)'
In rare cases, correct code generation requires extra machine
dependent processing between the second jump optimization pass and
delayed branch scheduling. On those machines, define this macro
as a C statement to act on the code starting at INSN.
File: gcc.info, Node: Config, Next: Index, Prev: Target Macros, Up: Top
The Configuration File
**********************
The configuration file `xm-MACHINE.h' contains macro definitions
that describe the machine and system on which the compiler is running,
unlike the definitions in `MACHINE.h', which describe the machine for
which the compiler is producing output. Most of the values in
`xm-MACHINE.h' are actually the same on all machines that GNU CC runs
on, so large parts of all configuration files are identical. But there
are some macros that vary:
`USG'
Define this macro if the host system is System V.
`VMS'
Define this macro if the host system is VMS.
`FAILURE_EXIT_CODE'
A C expression for the status code to be returned when the compiler
exits after serious errors.
`SUCCESS_EXIT_CODE'
A C expression for the status code to be returned when the compiler
exits without serious errors.
`HOST_WORDS_BIG_ENDIAN'
Defined if the host machine stores words of multi-word values in
big-endian order. (GNU CC does not depend on the host byte
ordering within a word.)
`HOST_FLOAT_WORDS_BIG_ENDIAN'
Define this macro to be 1 if the host machine stores `DFmode',
`XFmode' or `TFmode' floating point numbers in memory with the
word containing the sign bit at the lowest address; otherwise,
define it to be zero.
This macro need not be defined if the ordering is the same as for
multi-word integers.
`HOST_FLOAT_FORMAT'
A numeric code distinguishing the floating point format for the
host machine. See `TARGET_FLOAT_FORMAT' in *Note Storage Layout::
for the alternatives and default.
`HOST_BITS_PER_CHAR'
A C expression for the number of bits in `char' on the host
machine.
`HOST_BITS_PER_SHORT'
A C expression for the number of bits in `short' on the host
machine.
`HOST_BITS_PER_INT'
A C expression for the number of bits in `int' on the host machine.
`HOST_BITS_PER_LONG'
A C expression for the number of bits in `long' on the host
machine.
`ONLY_INT_FIELDS'
Define this macro to indicate that the host compiler only supports
`int' bit fields, rather than other integral types, including
`enum', as do most C compilers.
`EXECUTABLE_SUFFIX'
Define this macro if the host system uses a naming convention for
executable files that involves a common suffix (such as, in some
systems, `.exe') that must be mentioned explicitly when you run
the program.
`OBSTACK_CHUNK_SIZE'
A C expression for the size of ordinary obstack chunks. If you
don't define this, a usually-reasonable default is used.
`OBSTACK_CHUNK_ALLOC'
The function used to allocate obstack chunks. If you don't define
this, `xmalloc' is used.
`OBSTACK_CHUNK_FREE'
The function used to free obstack chunks. If you don't define
this, `free' is used.
`USE_C_ALLOCA'
Define this macro to indicate that the compiler is running with the
`alloca' implemented in C. This version of `alloca' can be found
in the file `alloca.c'; to use it, you must also alter the
`Makefile' variable `ALLOCA'. (This is done automatically for the
systems on which we know it is needed.)
If you do define this macro, you should probably do it as follows:
#ifndef __GNUC__
#define USE_C_ALLOCA
#else
#define alloca __builtin_alloca
#endif
so that when the compiler is compiled with GNU CC it uses the more
efficient built-in `alloca' function.
`FUNCTION_CONVERSION_BUG'
Define this macro to indicate that the host compiler does not
properly handle converting a function value to a
pointer-to-function when it is used in an expression.
`HAVE_VPRINTF'
Define this if the library function `vprintf' is available on your
system.
`MULTIBYTE_CHARS'
Define this macro to enable support for multibyte characters in the
input to GNU CC. This requires that the host system support the
ANSI C library functions for converting multibyte characters to
wide characters.
`HAVE_PUTENV'
Define this if the library function `putenv' is available on your
system.
`NO_SYS_SIGLIST'
Define this if your system *does not* provide the variable
`sys_siglist'.
`DONT_DECLARE_SYS_SIGLIST'
Define this if your system has the variable `sys_siglist', and
there is already a declaration of it in the system header files.
`USE_PROTOTYPES'
Define this to be 1 if you know that the host compiler supports
prototypes, even if it doesn't define __STDC__, or define it to be
0 if you do not want any prototypes used in compiling GNU CC. If
`USE_PROTOTYPES' is not defined, it will be determined
automatically whether your compiler supports prototypes by
checking if `__STDC__' is defined.
`NO_MD_PROTOTYPES'
Define this if you wish suppression of prototypes generated from
the machine description file, but to use other prototypes within
GNU CC. If `USE_PROTOTYPES' is defined to be 0, or the host
compiler does not support prototypes, this macro has no effect.
`MD_CALL_PROTOTYPES'
Define this if you wish to generate prototypes for the `gen_call'
or `gen_call_value' functions generated from the machine
description file. If `USE_PROTOTYPES' is defined to be 0, or the
host compiler does not support prototypes, or `NO_MD_PROTOTYPES'
is defined, this macro has no effect. As soon as all of the
machine descriptions are modified to have the appropriate number
of arguments, this macro will be removed.
Some systems do provide this variable, but with a different name
such as `_sys_siglist'. On these systems, you can define
`sys_siglist' as a macro which expands into the name actually
provided.
`NO_STAB_H'
Define this if your system does not have the include file
`stab.h'. If `USG' is defined, `NO_STAB_H' is assumed.
`PATH_SEPARATOR'
Define this macro to be a C character constant representing the
character used to separate components in paths. The default value
is. the colon character
`DIR_SEPARATOR'
If your system uses some character other than slash to separate
directory names within a file specification, define this macro to
be a C character constant specifying that character. When GNU CC
displays file names, the character you specify will be used. GNU
CC will test for both slash and the character you specify when
parsing filenames.
In addition, configuration files for system V define `bcopy',
`bzero' and `bcmp' as aliases. Some files define `alloca' as a macro
when compiled with GNU CC, in order to take advantage of the benefit of
GNU CC's built-in `alloca'.