Combine fcmp + select to fminnum / fmaxnum if no nans and legal

Also require unsafe FP math for no since there isn't a way to
test for signed zeros.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225744 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed