[llvm] [InstCombine] Simplify fractions when there is no overflow (PR #92949)

[via llvm-commits]

goldsteinn wrote:

In your proofs please don't arbitrarily use `noundef`, and particularly there should never be a reason to `noundef` the return value. It hides bugs. In this case a bug with `sdiv INT_MIN, -1` that can result if `C1 == -C2` in the `sdiv` case:
https://alive2.llvm.org/ce/z/95jbW3

Its okay to `noundef` what can't be undef (mostly constants in your impl).


https://github.com/llvm/llvm-project/pull/92949