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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/112736] [14 Regression] vectorizer is
 introducing out of bounds memory access
Date: Tue, 28 Nov 2023 12:10:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112736

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot =
gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
The vectorizer sees

  <bb 3> [local count: 214748368]:
  # a.3_5 =3D PHI <_2(5), 2(2)>
  # ivtmp_9 =3D PHI <ivtmp_3(5), 3(2)>
  _14 =3D b[a.3_5];
  c[a.3_5][0] =3D _14;
  c[a.3_5][1] =3D _14;
  c[a.3_5][2] =3D _14;
  c[a.3_5][3] =3D _14;
  _2 =3D a.3_5 + -1;
  ivtmp_3 =3D ivtmp_9 - 1;
  if (ivtmp_3 !=3D 0)
    goto <bb 5>; [89.00%]
  else
    goto <bb 4>; [11.00%]

  <bb 5> [local count: 191126048]:
  goto <bb 3>; [100.00%]

and uses SLP, this is likely caused by my patch to allow non-grouped-loads
there.

t.c:7:17: note:   node 0x4637048 (max_nunits=3D4, refcnt=3D1) vector(4) int
t.c:7:17: note:   op template: _14 =3D b[a.3_5];
t.c:7:17: note:         stmt 0 _14 =3D b[a.3_5];
t.c:7:17: note:         stmt 1 _14 =3D b[a.3_5];
t.c:7:17: note:         stmt 2 _14 =3D b[a.3_5];
t.c:7:17: note:         stmt 3 _14 =3D b[a.3_5];
t.c:7:17: note:         load permutation { 0 0 0 0 }

I think we need to force strided-SLP for them.=