[Bug target/96189] Failure to use eflags from cmpxchg on x86

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96189

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Uros Bizjak <u...@gcc.gnu.org>:

https://gcc.gnu.org/g:cc1ef413a859433a8313fa9c15aaff41bdc837dc

commit r11-2181-gcc1ef413a859433a8313fa9c15aaff41bdc837dc
Author: Uros Bizjak <ubiz...@gmail.com>
Date:   Thu Jul 16 20:11:43 2020 +0200

    i386: Additional peephole2 to use flags from CMPXCHG more [PR96189]

    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  <ubiz...@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.