[Bug target/54087] __atomic_fetch_add does not use xadd instruction

[drepper.fsp+rhbz at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54087

Ulrich Drepper <drepper.fsp+rhbz at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |drepper.fsp+rhbz at gmail dot com

--- Comment #11 from Ulrich Drepper <drepper.fsp+rhbz at gmail dot com> ---
Yes, although there still in an oddity.  The code from comment #3 is compiled
as:

0000000000000000 <a>:
   0:    ba fb ff ff ff           mov    $0xfffffffb,%edx
   5:    89 d0                    mov    %edx,%eax
   7:    f0 0f c1 05 00 00 00     lock xadd %eax,0x0(%rip)        # f <a+0xf>
   e:    00 
            b: R_X86_64_PC32    v-0x4
   f:    01 d0                    add    %edx,%eax
  11:    c3                       retq   
  12:    66 66 66 66 66 2e 0f     data32 data32 data32 data32 nopw
%cs:0x0(%rax,%rax,1)
  19:    1f 84 00 00 00 00 00 

0000000000000020 <b>:
  20:    b8 fb ff ff ff           mov    $0xfffffffb,%eax
  25:    f0 0f c1 05 00 00 00     lock xadd %eax,0x0(%rip)        # 2d <b+0xd>
  2c:    00 
            29: R_X86_64_PC32    v-0x4
  2d:    83 e8 05                 sub    $0x5,%eax
  30:    c3                       retq   



There is no reason for the difference.  In both cases the latter sequence
should be generated.