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

[ubizjak at gmail dot com]

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

--- Comment #3 from Uroš Bizjak <ubizjak at gmail dot com> ---
The master branch has been updated by Uros Bizjak <u...@gcc.gnu.org>:

https://gcc.gnu.org/g:6c2848ad02feef5ac094d1158be3861819b3bb49

commit r11-2140-g6c2848ad02feef5ac094d1158be3861819b3bb49
Author: Uros Bizjak <ubiz...@gmail.com>
Date:   Wed Jul 15 21:27:00 2020 +0200

    i386: Introduce 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:

            movl    %esi, %eax
            lock cmpxchgl   %edx, (%rdi)
            cmpl    %esi, %eax
            sete    %al

    can be optimized by removing the unneeded comparison, since set ZF flag
    signals that no update to EAX happened.

    2020-15-07  Uroš Bizjak  <ubiz...@gmail.com>

    gcc/ChangeLog:
            PR target/95355
            * config/i386/sync.md
            (peephole2 to remove unneded compare after CMPXCHG): New pattern.

    gcc/testsuite/ChangeLog:
            PR target/95355
            * gcc.target/i386/pr96189.c: New test.