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

[via llvm-commits]

SingleAccretion wrote:

It would be nice to resurrect this change... is only the `getObjectPtrOffset` part enough for the address mode folding?

I am currently working around this in a frontend, and it's a bit painful, since you need to 'unroll' your memset/memcpy using `ptrtoint + add nuw + inttoptr` (otherwise your unrolling folded back into intrinsics, which then get suboptimally expanded).

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