[llvm] [InstCombine] Evaluate zext nneg as sext where possible (PR #212230)

[Valeriy Savchenko via llvm-commits]

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SavchenkoValeriy wrote:

I'm a bit concerned that we effectively do two traversals for `nonneg` zexts. Here and the newly added check. Can we hoist the check up here and remove the predicate for `canEvaluateZExtd` if `EvaluateAsSigned` is true?

https://github.com/llvm/llvm-project/pull/212230