[llvm] [InstCombine] Fold expression using basic properties of floor and ceiling function (PR #107107)

[via llvm-commits]

c8ef wrote:

Dear reviewers, is the PR good to go, or does it need further adjustments, or should it be abandoned due to its lack of real-world usefulness? @arsenm @dtcxzyw @nikic

https://github.com/llvm/llvm-project/pull/107107