[Bug tree-optimization/65961] [6 Regression] ice in vect_is_simple_use_1 with -O3

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65961

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmpf, so we have an operand that is both part of a regular SLP node _and_ is
part
of a SLP node that gets its operand built up from scalars.  So obviously
looking at STMT_VINFO_VECTORIZABLE (def-of-op) isn't giving the correct answer
(it depends on context).

I tried to avoid passing down the SLP node to vect_is_simple_use[_1], but that
is what it would take to fix this (well, or reject the SLP build while we
compute
STMT_VINFO_VECTORIZABLE ()).

I have to think more about what refactoring would make sense here.