[llvm] [InstCombine] Handle `ICMP_EQ` when flooring by constant two (PR #73706)

[Nikita Popov via llvm-commits]

nikic wrote:

As far as  I can tell, your optimization is not limited for DivC == 2, but I don't think it's valid for other cases? I've tried to transfer the generic pre-conditions in this proof, maybe I did something wrong: https://alive2.llvm.org/ce/z/XaWD7N

https://github.com/llvm/llvm-project/pull/73706