[llvm] [InstCombine] Improve coverage of `foldSelectValueEquivalence` (PR #88298)

[via llvm-commits]

goldsteinn wrote:

> > > If not any suggestions for simplifying to make it reviewable?
> > 
> > 
> > I guess I can provide some suggestions after the ir diff is available :)
> 
> See https://alive2.llvm.org/ce/z/EUTKhF. I think we can do this simplification iff `simplifyWithOpReplaced` returns a constant.

Looking at the diff, it seems we get some benefit from the non-const simplification.
Ill split to multiple commits. If that doesn't simplify review ill split to multiple PRs.

https://github.com/llvm/llvm-project/pull/88298