[llvm] [InstCombine] Make the `(icmp eq/ne (and X, Y), X)` canonicalization work for non-const operands (PR #84688)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

The first two commits LGTM. I don't think we need the last one -- the cases it improves look very artificial to me. If you do want to have that one, I think it's best to make a separate PR so @dtcxzyw can check whether the problematic patterns occur in the wild. But in the meantime I don't mind regressing them.

https://github.com/llvm/llvm-project/pull/84688