[llvm] [InstSimplify] Discard unnecessary `select` when the conditions are `ICmps` with EQ (PR #179183)

[Gábor Spaits via llvm-commits]

spaits wrote:

I have updated the PR to build on top of #183291 (The currently draft PR with the non refining select ops). Sadly that PR in itself didn't bring any improvemnet.

I have restructured the tesing (Alive2 proofs: https://alive2.llvm.org/ce/z/G-w2Xf).
I know that there are more tests to be written, but first I would like to ask @dtcxzyw and @nikic whether this is the good direction to solve the issue.

This patch, and the predecessor patch, that introduces a recursive function with the recursion limit of 2, may be too expensive, when considering what we can gain from it. Also this would raise the recursion limit to 3 in `directlyImpliesPoison` (needed for the motivating case to work).

Are these costs too much?

Thank you for checking it out in advance!

https://github.com/llvm/llvm-project/pull/179183