C++11/C11 are not implementable on Alpha CPUs that don't have BWX extensions, BTW.
This is because it requires individual bytes to be accessible in atomic way between multiple threads, which without BWX is not possible on Alpha, which started out with minimum 32bit read/writes.
yes, but even beyond that, I think think there were changes and/or clarifications to the semantics of releaxed atomics that made the straightforward no-barriers-at-all implementation on alpha non-conformant strictly speaking. But I might be misremembering.
This is because it requires individual bytes to be accessible in atomic way between multiple threads, which without BWX is not possible on Alpha, which started out with minimum 32bit read/writes.