[llvm] [InstCombine] Fix ninf propagation for fcmp+sel -> minmax (PR #136433)

[Nikita Popov via llvm-commits]

nikic wrote:

I'm a bit confused here. What are the semantics of ninf on select supposed to be? Normally it means that both the inputs and outputs have to be ninf. But if I understand correctly, for select we interpret this as only the output (and thus the chosen input) having to be ninf?

This makes some sense to me (esp as these are the only possible semantics for phis) but I can't find any wording to that effect in LangRef.

https://github.com/llvm/llvm-project/pull/136433