[llvm] [LV] Don't simplify wide binops to constants if non-uniform (PR #121898)

[Shih-Po Hung via llvm-commits]

arcbbb wrote:

I was pondering this: replace the reduction-phi with a constant, then the vector operation wouldn't be necessary.
like this https://github.com/arcbbb/llvm-project/commit/fix-reduc-opt/

https://github.com/llvm/llvm-project/pull/121898