[llvm-branch-commits] [SLP]Drop samesign of narrowed bit test compares (PR #235287)

[Alexey Bataev via llvm-branch-commits]

https://github.com/alexey-bataev created https://github.com/llvm/llvm-project/pull/235287

The bit tests compare and L, R, which sign-extends from the narrow type only
if both L and R do, so its sign may change after narrowing.

Fixes https://github.com/llvm/llvm-project/pull/233124#issuecomment-6382644843

Assisted-by: Cursor