[llvm] [Local] Only intersect llvm.access.group metadata if instr moves. (PR #115868)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Before we start relying on this in one way or the other, I'd like to have it spelled out that this is UB (rather than poison) in LangRef, so we don't have to guess next time.

https://github.com/llvm/llvm-project/pull/115868