Hi Mathieu,
Tested on godbolt.org with:
int a;
void fct(void)
{
(void) __atomic_add_fetch(&a, 1, __ATOMIC_RELAXED);
__atomic_thread_fence(__ATOMIC_SEQ_CST);
}
x86-64 gcc 12.2 -O2 -std=c11:
fct:
lock add DWORD PTR a[rip], 1
lock or QWORD PTR [rsp], 0
ret
a:
.zero 4
that's disappointing. It's the same if both use __ATOMIC_SEQ_CST:
int a;
void fct(void)
{
(void) __atomic_add_fetch(&a, 1, __ATOMIC_SEQ_CST);
__atomic_thread_fence(__ATOMIC_SEQ_CST);
}
->
fct():
lock add DWORD PTR a[rip], 1
lock or QWORD PTR [rsp], 0
ret
a:
.zero 4
on x86-64 gcc 12.2 -O2 -std=c11. Clang also doesn't optimize the fence away.
Best wishes, Duncan.
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