[llvm] [PowerPC] improve performance on the isNan and !isNan function in case of -ffp-model=strict" (PR #215587)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

You haven't addressed my high level point. I think this is just adding code for no practical benefit. This is adding optimizations for *non-canonical IR* and duplicating an optimization the IR already does for you. This needs concrete justification with a case where an IS_FPCLASS with a nan mask appears as a result of legalization 

https://github.com/llvm/llvm-project/pull/215587