consume obviously doesn't need a barrier on arm or x86, but it still needs a source level annotation. relaxed is not enough as the compiler could otherwise brea

consume obviously doesn't need a barrier on arm or x86, but it still needs a source level annotation. relaxed is not enough as the compiler could otherwise break the required dependency (for example by introducing a speculation). In fact consume is in practice not implemented optimally by compilers because it is very very hard to guarantee that the data dependency is not broken in all cases. I.e. the quirks of Alpha have no bearing on the existence of consume. A different annotation between relaxed and acquire would still needed to specifically capture the semantics of data dependencies (that's the theory at least, in practice even consume and the [[carries_dependency]] annotations are not enough).