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

[jsm28 at gcc dot gnu.org via Gcc-bugs]

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

--- Comment #4 from Joseph S. Myers <jsm28 at gcc dot gnu.org> ---
NaN < 0 and -0.0 < 0 are both false, so it does always return 0; it's just
exceptions that are lost in the Inf - Inf case.