[llvm] [InstCombine] Use the select condition to try to constant fold binops into select (PR #84696)

[via llvm-commits]

goldsteinn wrote:

> This PR seems to be doing multiple things at the same time. Can you please split this up, and for example first only do the multi-use relaxation for div of select by constant rhs, before layering more things on top of it?

Hmm? Im not really sure how to split this up further. We already support multi-use `foldOpIntoSelect` for div/rem. What this patch is doing is enabling `foldOpIntoSelect` when we don't have all constant operands.

https://github.com/llvm/llvm-project/pull/84696