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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/107095] New: gcc.dg/vect/vect-89.c gets
 miscompiled by DSE
Date: Fri, 30 Sep 2022 10:42:14 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107095

            Bug ID: 107095
           Summary: gcc.dg/vect/vect-89.c gets miscompiled by DSE
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

When fully masked the loop with 256bit vectors gets optimized by FRE4 to

  <bb 2> [local count: 63136016]:
  .MASK_STORE (&tmp, 256B, { 0, -1, -1, -1, -1, -1, -1, -1 }, { 5, 5, 5, 5,=
 5,
5, 5, 5 });
  MEM <vector(8) int> [(int *)&tmp + 32B] =3D { 5, 5, 5, 5, 5, 5, 5, 5 };
  .MASK_STORE (&MEM <struct tmp_struct> [(void *)&tmp + 64B], 256B, { -1, 0=
, 0,
0, 0, 0, 0, 0 }, { 5, 5, 5, 5, 5, 5, 5, 5 });

  <bb 4> [local count: 1010605809]:
  # i_18 =3D PHI <i_8(9), 0(2)>
  # ivtmp_3 =3D PHI <ivtmp_5(9), 16(2)>
  _1 =3D tmp.y[i_18];
  if (_1 !=3D 5)
    goto <bb 5>; [0.00%]
  else
    goto <bb 6>; [100.00%]

  <bb 5> [count: 0]:
  abort ();

  <bb 6> [local count: 1010605809]:
  i_8 =3D i_18 + 1;
  ivtmp_5 =3D ivtmp_3 - 1;
  if (ivtmp_5 !=3D 0)
    goto <bb 9>; [94.12%]
  else
    goto <bb 7>; [5.88%]

  <bb 9> [local count: 951182190]:
  goto <bb 4>; [100.00%]

  <bb 7> [local count: 63136016]:
  tmp =3D{v} {CLOBBER(eol)};
  return 0;

but then DSE comes along and removes the first .MASK_STORE:

  Deleted dead call: .MASK_STORE (&tmp, 256B, { 0, -1, -1, -1, -1, -1, -1, =
-1
}, { 5, 5, 5, 5, 5, 5, 5, 5 });=