[llvm] [LAA] Fix off-by-EltSize in negative-step deref bounds check (PR #211964)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

I think with this we now also vectorize reverse counting loops, could you add a LoopVectorize test to confirm and to make sure LV handles this correctly?

https://github.com/llvm/llvm-project/pull/211964