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Subject: [Bug target/103066]
 __sync_val_compare_and_swap/__sync_bool_compare_and_swap aren't optimized
Date: Fri, 05 Nov 2021 12:33:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103066

--- Comment #4 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Jakub Jelinek from comment #3)
> If by fail you mean that it doesn't update the memory if the memory isn't
> equal to expected, sure, but do you mean it can fail spuriously, not upda=
te
> the memory even if the memory is equal to expected?
> Neither __sync_{bool,val}_compare_and_swap nor __atomic_compare_exchange_n
> with weak set to false can fail spuriously, __atomic_compare_exchange_n w=
ith
> weak set to true can.

If we generate

        movl m(%rip), %eax
        cmpl  %edi, %eax
        jne  .L1
        movl    %edi, %eax
        lock cmpxchgl   %esi, m(%rip)
.L1:
        ret

is it a valid implementation of atomic_compare_exchange_strong?=