[llvm] [IR][NFC] Introduce Constant::containsMatchingVectorElement and corresponding matcher (PR #200502)

[Sean Clarke via llvm-commits]

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xarkenz wrote:

I think checking the splat would be a good change, but I'm not convinced it would be NFC. I went ahead and just added the checks that used to be in `maskContainsAllOneOrUndef` at the call site.

https://github.com/llvm/llvm-project/pull/200502