[Bug c/103406] gcc -O0 behaves differently on "DBL_MAX related operations" than gcc -O1 and above

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103406

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
We are folding

(1.79769313486231570814527423731704356798070567525844996599e+308 * 2.0e+0) -
(1.79769313486231570814527423731704356798070567525844996599e+308 * 2.0e+0)

to 0.0 via

(simplify
 (minus @0 @0)
 (if (!FLOAT_TYPE_P (type) || !tree_expr_maybe_nan_p (@0))
  { build_zero_cst (type); }))

but appearantly even Inf - Inf is not zero.