[Bug middle-end/80815] wrong code because of broken runtime alias check in vectorizer

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815

--- Comment #2 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 19 May 2017, amker at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80815
> 
> --- Comment #1 from amker at gcc dot gnu.org ---
> GCC uses vect_factor as minimal segment length for dr_b when merging alias
> pairs, I think it could be relaxed to vect_factor * abs (DR_STEP (dr_b)). 
> Below test shows this change can merge additional alias checks:

But it would make cases aliasing that are not (that's always a trade off
between more precise result and less runtime checking).