[Bug testsuite/63175] [4.9/5 regression] FAIL: gcc.dg/vect/costmodel/ppc/costmodel-bb-slp-9a.c scan-tree-dump-times slp2" basic block vectorized using SLP" 1

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63175

--- Comment #19 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 2 Mar 2015, rguenther at suse dot de wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63175
> 
> --- Comment #18 from rguenther at suse dot de <rguenther at suse dot de> ---
> On Mon, 2 Mar 2015, msebor at gcc dot gnu.org wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63175
> > 
> > --- Comment #17 from Martin Sebor <msebor at gcc dot gnu.org> ---
> > Following up on my comment #14, and as requested on gcc-patches, the test case
> > below is vectorized with GCC 4.8.2 for T being either 32 bits wide (e.g., int)
> > or 64-bits wide (e.g., long or long long) but not with the fix referenced in
> > comment #13.  The difference between the test in costmodel-bb-slp-9a.c and the
> > code here is that unlike the source, the destination of the copy isn't aligned
> > on an even element boundary.
> > 
> > const T a [] = { 1, 2, 3, 4, 5 };
> > extern T b[sizeof a / sizeof *a];
> > 
> > void g (void)
> > {
> >     const T *p = a;
> >     T *q = b + 1;
> > 
> >     *q++ = *p++;
> >     *q++ = *p++;
> >     *q++ = *p++;
> >     *q++ = *p++;
> > }
> > 
> > In addition to this failure (mentioned on the list) the latest trunk also fails
> > to vectorize the following code which is successfully vectorized by 4.8.2.  The
> > difference is that the arrays are only declared here while in
> > costmodel-bb-slp-9a.c they are defined.  I only noticed this now, and so it's
> > not being exercised in the proposed enhanced test submitted to gcc-patches last
> > Friday,
> > 
> > extern const T a [];
> > extern T b[];
> > 
> > void g (void)
> > {
> >     const T *p = a + 1;
> >     T *q = b;
> > 
> >     *q++ = *p++;
> >     *q++ = *p++;
> >     *q++ = *p++;
> >     *q++ = *p++;
> > }
> 
> Both is because powerpc simply cannot handle unaligned stores and
> in neither testcase we can force its alignemnt (it's "extern", and
> for the first case aligning the first element won't align the
> vector store)

How does GCC 4.8 generated vectorized code look like?