[llvm] [InstCombine] Add an additional nnan constraint for xfrm fcmp + sel => fmax/fmin (PR #117977)

[Rajat Bajpai via llvm-commits]

rajatbajpai wrote:

Right now we try to preserve it even if `fcmp` doesn't have that flag. https://godbolt.org/z/5vPjrWT95

https://github.com/llvm/llvm-project/pull/117977