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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/56766] Fails to combine (vec_select (vec_concat ...)) to (vec_merge ...)
Date: Tue, 12 May 2015 14:20:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56766

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-05-12
                 CC|                            |uros at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
The vectorizer patch is now in (I added a testcase for addsubps because for
that
it happens to work).

We still need to fixup the sse3_addsubv2df3 pattern or fix combine to try
multiple "canonical" forms of vec_merge vs. (vec_select (vec_concat ...)).
Or decide which one is canonical (I'd prefer simply dropping vec_merge - with
AVX512 we've run out of bits for the CONST_INT selector....)

One issue with the vec_select form is that it requires an intermediate mode of
double-size while vec_merge avoids this.

Eventually one can also teach combine that certain (vec_select (vec_concat ..))
can be treated as (vec_merge ...).

void testd (double * __restrict__ p, double * __restrict q)
{
  p[0] = p[0] - q[0];
  p[1] = p[1] + q[1];
}

should vectorize to addsubpd with -msse3.