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From: "thiago at kde dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/102566] [i386] GCC should emit LOCK BTS for simple
 bit-test-and-set operations with std::atomic
Date: Mon, 04 Oct 2021 16:10:27 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102566

--- Comment #8 from Thiago Macieira <thiago at kde dot org> ---
$ cat /tmp/test.cpp=20=20
#include <atomic>
bool tbit(std::atomic<int> &i)
{
   return i.fetch_or(1, std::memory_order_relaxed) & 1;
}
$ ~/dev/gcc/bin/gcc -S -o - -O2 /tmp/test.cpp=20=20
       .file   "test.cpp"
       .text
       .p2align 4
       .globl  _Z4tbitRSt6atomicIiE
       .type   _Z4tbitRSt6atomicIiE, @function
_Z4tbitRSt6atomicIiE:
.LFB339:
       .cfi_startproc
       lock btsl       $0, (%rdi)
       setc    %al
       ret
       .cfi_endproc
.LFE339:
       .size   _Z4tbitRSt6atomicIiE, .-_Z4tbitRSt6atomicIiE
       .ident  "GCC: (GNU) 12.0.0 20211004 (experimental)"
       .section        .note.GNU-stack,"",@progbits

+1=