[llvm] [LV] Fix handleFirstArgMinOrMax to use 0 as identity element for UMax/SMax (PR #192054)

[Florian Hahn via llvm-commits]

fhahn wrote:

> We have confirmed this is causing wrong-code generation in a real-world signal processing benchmark (argmax with strict > predicate, returning 0 instead of the correct index). This PR fixes the issue

If you have a loop that reproduces the issue  end-to-end, it would be great if you could add it here

https://github.com/llvm/llvm-test-suite/blob/main/SingleSource/UnitTests/Vectorizer/argmin-argmax-int.cpp

https://github.com/llvm/llvm-project/pull/192054