[llvm] [ValueTracking] Teach isGuaranteedNotToBeUndefOrPoison about splats (PR #163570)

[Yingwei Zheng via llvm-commits]

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

LGTM. Perhaps we can also teach this function with single-source shufflevectors.


https://github.com/llvm/llvm-project/pull/163570