[llvm] [LV] Fix FindLastIV reduction for epilogue vectorization. (PR #120395)

[Florian Hahn via llvm-commits]

fhahn wrote:

It would be good to have more runtime test coverage for the FindLastIV logic, could you add some end-to-end test to `llvm-test-suite`, possibly similar to https://github.com/llvm/llvm-test-suite/blob/main/SingleSource/UnitTests/Vectorizer/index-select.cpp

https://github.com/llvm/llvm-project/pull/120395