[llvm] [InstCombine] Avoid breaking SPF by `foldICmpUsingKnownBits` (PR #82472)

[Nikita Popov via llvm-commits]

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

Based on the test diffs, we're clearly missing a `umax(smax)` -> `smax` fold. But that should be addressed by adding the fold. Please add some test coverage for the benefit that this is supposed to produce.

https://github.com/llvm/llvm-project/pull/82472