[Bug target/85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write) instructions on x86[_64]

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Wed May 30 07:19:24 2018
New Revision: 260915

URL: https://gcc.gnu.org/viewcvs?rev=260915&root=gcc&view=rev
Log:
        Backported from mainline
        2018-05-08  Jakub Jelinek  <jakub@redhat.com>

        PR target/85683
        * config/i386/i386.md: Add peepholes for mem {+,-,&,|,^}= x; mem != 0
        after cmpelim optimization.

        * gcc.target/i386/pr49095.c: Add -masm=att to dg-options.  Add
        scan-assembler-times checking that except for [fh]*xor other functions
        don't use any load instructions.

Modified:
    branches/gcc-8-branch/gcc/ChangeLog
    branches/gcc-8-branch/gcc/config/i386/i386.md
    branches/gcc-8-branch/gcc/testsuite/ChangeLog
    branches/gcc-8-branch/gcc/testsuite/gcc.target/i386/pr49095.c