[llvm] [InstCombine] Fold `(op x, ({z,s}ext (icmp eq x, C)))` to select (PR #89020)

[via llvm-commits]

goldsteinn wrote:

@dtcxzyw can you re-run this. If we don't hit any non `add` patterns ill close this and post nikic's simplification.

https://github.com/llvm/llvm-project/pull/89020