https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65697
--- Comment #18 from Andrew Haley <aph at gcc dot gnu.org> ---
(In reply to mwahab from comment #17)
> ----
> int cas(int* barf, int* expected, int* desired)
> {
> return __atomic_compare_exchange_n(barf, expected, desired, 0,
> __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
> }
> ----
> cas:
> ldr w3, [x1]
> .L3:
> ldaxr w4, [x0]
> cmp w4, w3
> bne .L4
> stlxr w5, w2, [x0] ; store-release
> cbnz w5, .L3
> .L4:
> cset w0, eq
> cbz w0, .L6
> ret
> .p2align 3
> .L6:
> str w4, [x1] ; store, no barrier.
> ret
> ----
>
> This looks odd to me but I'd need look into it more.
That looks fine to me: if the CAS fails, the prev value -> *expected.
