[Bug tree-optimization/128306] `a - a` for real types where a is not a NaN can be assumed to be >= 0

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128306

--- Comment #3 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Note llvm optimizes this testcase to 0.