This is another step towards having FMF apply only to FP values rather than those + fcmp. See PR38086 for one of the original discussions/motivations:
And the test here is derived from PR39535:
Currently, we lose FMF when converting any phi to select in SimplifyCFG. There are a small number of similar changes needed to correct within SimplifyCFG, so it should be quick to patch this pass up.