[Bug tree-optimization/91734] gcc skip an if statement with "-O1 -ffast-math"

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91734

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So two things:
-funsafe-math-optimizations
assumes there are no denormals (subnormals) or they are flushed to zero.

-ffinite-math-only
assumes that infinite and nans don't exists (IIRC).