[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 #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Note I am not sure `a - a` can be assumed not to include `-0.0` though but at
least the range can be `[-0.0, +INF]` .