[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@gcc.gnu.org>]

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)