[llvm] [CodeGen] Treat hasOrderedMemoryRef as implying arbitrary loads or stores (PR #182000)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Alternatively, we could mark fences as mayLoad mayStore, and remove hasSideEffects. That would also satisfy hasOrderedMemRef, since there will be no MMO

Right. I was hoping the discussion would reach some kind of consensus on this. Some downsides of marking MIR fences as mayLoad/mayStore are (a) they don't really load or store anything and (b) tablegen complains because the corresponding fence DAG node is not mayLoad/mayStore.

https://github.com/llvm/llvm-project/pull/182000