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builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi pattern.

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* builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi
	pattern.
	* doc/md.texi (cmpstrn): Note that the comparison stops if both
	fetched bytes are zero.
	(cmpstr): Likewise.
	(cmpmem): Note that the comparison does not stop if both of the
	fetched bytes are zero.

From-SVN: r177701
This commit is contained in:
Nick Clifton 2011-08-12 16:26:11 +00:00 • committed by Nick Clifton
parent c49b1a299e
commit 9b0f6f5e51
3 changed files with 29 additions and 27 deletions
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10
gcc/ChangeLog
View file

@ -1,3 +1,13 @@
2011-08-12 Nick Clifton <nickc@redhat.com>
* builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi
pattern.
* doc/md.texi (cmpstrn): Note that the comparison stops if both
fetched bytes are zero.
(cmpstr): Likewise.
(cmpmem): Note that the comparison does not stop if both of the
fetched bytes are zero.
2011-08-12 Uros Bizjak <ubizjak@gmail.com>
* builtins.def (BUILT_IN_ICEIL{,F,L}, BUILT_IN_IFLOOR{,F,L}

28
gcc/builtins.c
View file

@ -3635,9 +3635,9 @@ expand_builtin_bzero (tree exp)
}
/* Expand expression EXP, which is a call to the memcmp built-in function.
Return NULL_RTX if we failed and the
caller should emit a normal call, otherwise try to get the result in
TARGET, if convenient (and in mode MODE, if that's convenient). */
Return NULL_RTX if we failed and the caller should emit a normal call,
otherwise try to get the result in TARGET, if convenient (and in mode
MODE, if that's convenient). */
static rtx
expand_builtin_memcmp (tree exp, ATTRIBUTE_UNUSED rtx target,
@ -3649,7 +3649,10 @@ expand_builtin_memcmp (tree exp, ATTRIBUTE_UNUSED rtx target,
POINTER_TYPE, POINTER_TYPE, INTEGER_TYPE, VOID_TYPE))
return NULL_RTX;
#if defined HAVE_cmpmemsi || defined HAVE_cmpstrnsi
/* Note: The cmpstrnsi pattern, if it exists, is not suitable for
implementing memcmp because it will stop if it encounters two
zero bytes. */
#if defined HAVE_cmpmemsi
{
rtx arg1_rtx, arg2_rtx, arg3_rtx;
rtx result;
@ -3662,16 +3665,9 @@ expand_builtin_memcmp (tree exp, ATTRIBUTE_UNUSED rtx target,
unsigned int arg2_align = get_pointer_alignment (arg2) / BITS_PER_UNIT;
enum machine_mode insn_mode;
#ifdef HAVE_cmpmemsi
if (HAVE_cmpmemsi)
insn_mode = insn_data[(int) CODE_FOR_cmpmemsi].operand[0].mode;
else
#endif
#ifdef HAVE_cmpstrnsi
if (HAVE_cmpstrnsi)
insn_mode = insn_data[(int) CODE_FOR_cmpstrnsi].operand[0].mode;
else
#endif
return NULL_RTX;
/* If we don't have POINTER_TYPE, call the function. */
@ -3696,18 +3692,10 @@ expand_builtin_memcmp (tree exp, ATTRIBUTE_UNUSED rtx target,
set_mem_size (arg2_rtx, INTVAL (arg3_rtx));
}
#ifdef HAVE_cmpmemsi
if (HAVE_cmpmemsi)
insn = gen_cmpmemsi (result, arg1_rtx, arg2_rtx, arg3_rtx,
GEN_INT (MIN (arg1_align, arg2_align)));
else
#endif
#ifdef HAVE_cmpstrnsi
if (HAVE_cmpstrnsi)
insn = gen_cmpstrnsi (result, arg1_rtx, arg2_rtx, arg3_rtx,
GEN_INT (MIN (arg1_align, arg2_align)));
else
#endif
gcc_unreachable ();
if (insn)
@ -3733,7 +3721,7 @@ expand_builtin_memcmp (tree exp, ATTRIBUTE_UNUSED rtx target,
else
return convert_to_mode (mode, result, 0);
}
#endif
#endif /* HAVE_cmpmemsi. */
return NULL_RTX;
}

18
gcc/doc/md.texi
View file

@ -4680,8 +4680,9 @@ byte by byte in lexicographic order starting at the beginning of each
string. The instruction is not allowed to prefetch more than one byte
at a time since either string may end in the first byte and reading past
that may access an invalid page or segment and cause a fault. The
effect of the instruction is to store a value in operand 0 whose sign
indicates the result of the comparison.
comparison terminates early if the fetched bytes are different or if
they are equal to zero. The effect of the instruction is to store a
value in operand 0 whose sign indicates the result of the comparison.
@cindex @code{cmpstr@var{m}} instruction pattern
@item @samp{cmpstr@var{m}}
@ -4699,8 +4700,10 @@ The two memory blocks specified are compared byte by byte in lexicographic
order starting at the beginning of each string. The instruction is not allowed
to prefetch more than one byte at a time since either string may end in the
first byte and reading past that may access an invalid page or segment and
cause a fault. The effect of the instruction is to store a value in operand 0
whose sign indicates the result of the comparison.
cause a fault. The comparison will terminate when the fetched bytes
are different or if they are equal to zero. The effect of the
instruction is to store a value in operand 0 whose sign indicates the
result of the comparison.
@cindex @code{cmpmem@var{m}} instruction pattern
@item @samp{cmpmem@var{m}}
@ -4708,9 +4711,10 @@ Block compare instruction, with five operands like the operands
of @samp{cmpstr@var{m}}. The two memory blocks specified are compared
byte by byte in lexicographic order starting at the beginning of each
block. Unlike @samp{cmpstr@var{m}} the instruction can prefetch
any bytes in the two memory blocks. The effect of the instruction is
to store a value in operand 0 whose sign indicates the result of the
comparison.
any bytes in the two memory blocks. Also unlike @samp{cmpstr@var{m}}
the comparison will not stop if both bytes are zero. The effect of
the instruction is to store a value in operand 0 whose sign indicates
the result of the comparison.
@cindex @code{strlen@var{m}} instruction pattern
@item @samp{strlen@var{m}}