core.stdc.stdatomic

[IGotD-]

On Friday, 17 November 2023 at 10:25:31 UTC, claptrap wrote:
>
> What instructions the compiler inserts around the CAS 
> instruction are irrelevant, none of what they do can break the 
> CAS.

It is not irrelevant. You cannot break the CAS itself as it is 
usually implemented according to the SW ABI of the architecture. 
However, you must instruct the compiler so that reordering 
optimizations don't spill over the CAS implementations. If 
optimizations make instructions spill over to the wrong side of 
the CAS, then you possibly will end up in a non working algorithm.

So you not only perhaps need to insert a memory barrier 
instruction depending on ISA, you also need to instruct the 
compiler not to trespass the atomic instructions. This is usually 
implicit as atomic operations are implemented as intrinsics which 
automatically do this for you.