[llvm] [Vectorizer] precommit test for miscompilation (PR #120731)

[Florian Hahn via llvm-commits]

https://github.com/fhahn approved this pull request.

LGTM, thanks!

Some more suggestions inline

As for the test name, `vplan-...` is usually only used when the test checks the printed VPlans. maybe `drop-inbounds-flags-for-reverse-vector-pointer.ll`

https://github.com/llvm/llvm-project/pull/120731