[llvm] [InstCombine] Try optimizing with knownbits which determined from Cond (PR #91762)

[via llvm-commits]

goldsteinn wrote:

> I have very little experience sending PRs, is this the right way to write commit messages for tests related to a patch?
please let me know if I'm wrong

1) It would be nice if the commit messages explained the tests in question. I.e "add tests" or "modify the test..." don't really explain the tests in question.
2) Commits 4-5 should be merged. Basically the `check-all` target should pass at every commit in your PR.

https://github.com/llvm/llvm-project/pull/91762