From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 1B17F3851C01; Tue, 26 Jan 2021 13:24:08 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 1B17F3851C01
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/98563] [10/11 Regression] vectorization fails
 while it worked on gcc 9 and earlier since since
 r10-2271-gd81ab49d0586fca0
Date: Tue, 26 Jan 2021 13:24:08 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 10.1.0
X-Bugzilla-Keywords: missed-optimization, openmp
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 10.3
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-98563-4-YQ10dHXRV7@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-98563-4@http.gcc.gnu.org/bugzilla/>
References: <bug-98563-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Tue, 26 Jan 2021 13:24:08 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98563

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #7)
> I'm afraid no.
> The vectorization can handle addresses into the simd arrays, but right now
> only if it accesses the whole element, i.e. when we can turn the simd arr=
ay
> into a vector register (or set thereof) that hold the variable.
> In this case that is not the case, as in the end it uses the real and imag
> parts separately.
> So, either it can be handled in SRA, or we'd need to teach the vectorizer=
 to
> permute those fur us.

Hmm, I see.  The vectorizer can in theory handle "existing" vectors (curren=
tly
only enabled for basic-block SLP though).  But of course the first hurdle is
to not treat those as memory accesses (thus ignore the data-ref analysis
failure or somehow make that treat the SIMD_LANE indexing "nicely").

When we see

  _13 =3D .GOMP_SIMD_LANE (simduid.0_12(D), 0);

can we compute how _13 evolves with loop iteration?  Thus, can we
SCEV analyze it?  Isn't it sth like { .GOMP_SIMD_LANE_START (simduid.0_12(D=
),
.GOMP_SIMD_LANE_STEP (simduid.0_12(D), 0) } thus an affine evolution
in the end?

Simplified C testcase:

typedef _Complex double cplx;
void foo (cplx *);
void test(cplx* __restrict__ a, const cplx* b, double c, int N)
{
  cplx tem;
#pragma omp simd private (tem)
  for (int i=3D0; i<8*N; i++) {
      __real tem =3D __real b[i];
      __imag tem =3D __imag b[i];
      __real a[i] =3D __real tem;
      __imag a[i] =3D __imag tem;
  }
  foo (&tem);
}

which we miscompile (well, I guess I did sth wrong with the use after
the loop but to trigger GOMP_SIMD_LANE the temporary seems to need to
have its address taken).=