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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106247] GCC12 warning in Eigen: array
 subscript is partly outside array bounds
Date: Sun, 10 Jul 2022 19:26:27 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106247

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
the warning is correct in the sense the load is there in IR, though it looks
like it is dead (but only because b and a are unused):
  array.7_137 =3D (long unsigned int) &MEM <double[6]> [(void *)&b + 8B];
  _139 =3D array.7_137 >> 3;
  _140 =3D -_139;
  _141 =3D _140 & 3;
  first_142 =3D (long int) _141;
  _143 =3D MIN_EXPR <first_142, 2>;
  _145 =3D 2 - _143;
  alignedEnd_148 =3D _143;
  goto <bb 4>; [100.00%]

  <bb 3> [local count: 8655976563]:
  index.12_166 =3D (long unsigned int) index_165;
  _167 =3D index.12_166 * 8;
  _168 =3D &MEM <double[4]> [(void *)&a + 16B] + _167;
  _171 =3D &MEM <double[6]> [(void *)&b + 8B] + _167;
  _172 =3D *_168;
  MEM[(double &)_171] =3D _172;
  index_173 =3D index_165 + 1;

  <bb 4> [local count: 9725816346]:
  # index_165 =3D PHI <0(2), index_173(3)>
  if (_143 > index_165)
    goto <bb 3>; [89.00%]
  else
    goto <bb 6>; [11.00%]

  <bb 5> [local count: 8655976563]:
  index.10_152 =3D (long unsigned int) index_151;
  _153 =3D index.10_152 * 8;
  _154 =3D &MEM <double[4]> [(void *)&a + 16B] + _153;
  _155 =3D MEM[(__m256d_u * {ref-all})_154];
  _158 =3D &MEM <double[6]> [(void *)&b + 8B] + _153;
  MEM[(__m256d * {ref-all})_158] =3D _155;
  index_159 =3D index_151 + 4;

  <bb 6> [local count: 9725816346]:
  # index_151 =3D PHI <_143(4), index_159(5)>
  if (alignedEnd_148 > index_151)
    goto <bb 5>; [89.00%]
  else
    goto <bb 8>; [11.00%]=