[llvm] [X86] Check MinMax has NaN and replace with NewX for minimumnum/maximumnum (PR #164546)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

> LGTM. This logic is a bit hard to follow; hope it can be simplified using early returns to reduce complexity from line 29496 for `IsNum=true` in the future.

Simplified :)

https://github.com/llvm/llvm-project/pull/164546