[llvm] [Loads] Check loop-varying pointer in isDereferenceableAndAlignedInLoop. (PR #120962)

[Philip Reames via llvm-commits]

preames wrote:

> We have a flag UseDerefAtPointSemantics to enable those, but the implementation never got to a usable point. Part of the reason is that we never got a consensus on some key semantics questions, in particular relating to the interaction of noalias, nofree and nosync.
> 
> But in any case, I think that for dereferenceable _assumptions_ we do need to use deref-at-point semantics, otherwise it's too easy for things to go wrong.

I agree that deref-at-point semantics are the only sane ones for the assumptions.  

https://github.com/llvm/llvm-project/pull/120962