https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58790
--- Comment #4 from Matthias Kretz (Vir) <kretz at kde dot org> ---
I'm still not familiar with this part of GCC, but isn't `_2 == { -1, -1, -1, -1
}` equivalent to _1, i.e. it reverses VEC_COND_EXPR? However, if the `==` is
supposed to return a scalar boolean instead of a vector boolean, then that's
the expression which most generally describes all_equal1.
