flags/metadata/attributes on phi nodes

I recently made a change that would allow fast-math-flags to appear on phi nodes of floating-point values in IR:
https://reviews.llvm.org/D67564 (r372878)

As noted there, the patch is an extension of allowing FMF on select-of-FP, and the underlying motivation is to clean up semantics of FMF as described in:
https://bugs.llvm.org/show_bug.cgi?id=38086
…and related bugs.

Does allowing these flags or other metadata/attributes on phi nodes raise any concerns?