[Bug other/63387] Optimize pairs of isnan() calls into a single isunordered()

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63387

--- Comment #7 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Tobias Burnus from comment #4)
>   _Bool foo(float x, float y) { return x != x || y != y; }

This testcase is not optimized (even with -fno-trapping-math or with |) because
x != x is not canonicalized to x unord x (or the reverse, but we should not
keep both).