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 CAE933AA88FD; Thu, 17 Nov 2022 14:58:20 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org CAE933AA88FD
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1668697100;
	bh=OI8w8wZNX990Bv6sAx+ZGJyT4S9RwI6rUrkOkscvuhI=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=pXxDLwgSd/IIQeZ9w5+irqXYmp8eFgsia8OAXQ825ByfamULiJv1ORNUB/jsR0Zh/
	 jM+CR8eNpo9tAc8ajjeHyvSbr0tOwqEdL8PI5bzWY5Mdfbq/KnMuL9Ojm4QfMvYIdm
	 MyynJVzW+Yw0C6KTRDf5sVNWj1XyGSRnqDtZblts=
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107451] [11/12/13 Regression] Segmentation
 fault with vectorized code since r11-6434
Date: Thu, 17 Nov 2022 14:58:20 +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: 11.3.1
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: rguenth at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 11.4
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-107451-4-OOJwZA6XRv@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-107451-4@http.gcc.gnu.org/bugzilla/>
References: <bug-107451-4@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
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107451

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Interestingly the following variant of the testcase falls back to
VMAT_ELEMENTWISE but does have the same problem there fixed up by later
folding, but it will segfault when using -O2 -mavx2 -fno-vect-cost-model
-fdisable-tree-vrp2 -fdisable-free-forwprop4 which then keeps the bogus

  _62 =3D *ivtmp_64;
  _61 =3D MEM[(const double *)ivtmp_64 + 8B];
  ivtmp_60 =3D ivtmp_64 + _65;
  _59 =3D *ivtmp_60;
  _58 =3D MEM[(const double *)ivtmp_60 + 8B];
  ivtmp_57 =3D ivtmp_60 + _65;
  vect_cst__56 =3D {_62, _61, _59, _58};
  vect__4.7_55 =3D VEC_PERM_EXPR <vect_cst__56, vect_cst__56, { 0, 1, 0, 1 =
}>;

that problem should be present even before the r11-6434 change.  In fact
this segfaults on the GCC 10 branch with just -O2 -ftree-loop-vectorize -ma=
vx2
generating the same load/permute as trunk for the reduction (so there's some
half-way "fix" on the later branches).  Also broken with GCC 9.5.

static void __attribute__((noipa))
setdot(int n, const double *x, int inc_x, const double *y, double * __restr=
ict
dot)
{
  int i, ix =3D 0;

  for(i =3D 0; i < n; i++) {
      dot[i*4+0] =3D x[ix]          * y[ix]   ;
      dot[i*4+1] =3D x[ix+1] * y[ix+1] ;
      dot[i*4+2] =3D x[ix]          * y[ix+1] ;
      dot[i*4+3] =3D x[ix+1] * y[ix]   ;
      ix +=3D inc_x ;
  }
}

int main(void)
{
  double x[2] =3D {0, 0}, y[2] =3D {0, 0};
  double dot[4];
  setdot(1, x, 4096*4096, y, dot);
  return 0;
}=