mirror of
git://gcc.gnu.org/git/gcc.git
synced 2025-03-25 07:40:25 +08:00
cc1ef413a8
CMPXCHG instruction sets ZF flag if the values in the destination operand
and EAX register are equal; otherwise the ZF flag is cleared and value
from destination operand is loaded to EAX. Following assembly:
xorl %eax, %eax
lock cmpxchgl %edx, (%rdi)
testl %eax, %eax
sete %al
can be optimized by removing the unneeded comparison, since set ZF flag
signals that no update to EAX happened. This patch adds peephole2
pattern to also handle XOR zeroing and load of -1 by OR.
2020-07-16 Uroš Bizjak <ubizjak@gmail.com>
gcc/ChangeLog:
PR target/96189
* config/i386/sync.md
(peephole2 to remove unneded compare after CMPXCHG):
New pattern, also handle XOR zeroing and load of -1 by OR.
gcc/testsuite/ChangeLog:
PR target/96189
* gcc.target/i386/pr96189-1.c: New test.
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.