[llvm] [CodeGen] Mark mem intrinsic loads and stores as dereferenceable (PR #80184)

[Jay Foad via llvm-commits]

https://github.com/jayfoad requested changes to this pull request.

Unconditionally marking these loads/stores as dereferenceable does not seem justified to me, any more than it would for a regular load/store.

(Having said that, I don't understand the point of the MODereferenceable flag. In IR `derefenceable` metadata is applied to the thing that creates the pointer, so you get UB at that point if it is _not_ dereferenceable. Applying it to the load/store that uses the pointer seems redundant, since they would always give UB anyway if the pointer is not dereferenceable.)

https://github.com/llvm/llvm-project/pull/80184