[llvm] [InstCombine] Fold `ctpop(X) <u 2` into `ctpop(X) == 1` if X is non-zero (PR #67268)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

ctpop < 2 is better than ctpop == 1 for the backend, and we will no be able to recover from this transform in the backend if it comes from an assume.

https://github.com/llvm/llvm-project/pull/67268