[Bug tree-optimization/56933] [4.9 Regression] Vectorizer missing read-write dependency for interleaved accesses

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56933

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Bernd Edlinger from comment #7)
> Created attachment 30712 [details]
> fixed test case
> 
> Looking deeper into the matter it seems like this an example
> where vectorisation is not supposed to happen.
> But this is still vectorized and causes the crash here:
> 
>    for (i = 0; i < 2*1024; i++)
>      d[i] = 1.;

That loop is initialization only and can be vectorized.  I have committed
a fix (hopefully), so you may want to check again.

> 
> So this is my proposed fix for the test case:
> - added check_vect() to prevent invalid instruction as Jakub suggested
> - addeded scan-tree-dump to detect the READ_WRITE depencency
>   to make sure that the vectorization in foo() did not happen
>   for the right reason.