[llvm] [InstCombineCompares] Try to "strengthen" compares based on known bits. (PR #79405)

[Mikhail Gudim via llvm-commits]

mgudim wrote:

@dtcxzyw @nikic Actually, now I don't think it's such a good idea. If the comparison is used in a branch an we "strengthen" then if the branch is taken, we can deduce more. BUT on the other hand, we have actually "weakend" the opposite inequality: if the branch is not taken we can deduce less. Maybe a better way to express this would be to insert `assume` intrinsics?

https://github.com/llvm/llvm-project/pull/79405