[llvm] [InstCombine] Add handling for (or (zext x), (shl (zext (ashr x, bw-1))), bw) -> (sext x) fold (PR #130316)

[Yingwei Zheng via llvm-commits]

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

LGTM w/ some nits.


https://github.com/llvm/llvm-project/pull/130316