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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/98513] [10/11 Regression] Wrong code with -O3
 since r10-2804-gbf05a3bbb58b3558
Date: Mon, 04 Jan 2021 15:41:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98513

Martin Li=C5=A1ka <marxin at gcc dot gnu.org> changed:

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

--- Comment #1 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
A cleaner test-case:

$ cat combined.cc
extern unsigned long long var_20;
extern unsigned short arr_8[][26][1][1][11];
const int &max(int &a, const int &b) { return a > b ? a : b; }
int test___trans_tmp_1, var_5 =3D -1, var_6 =3D -2;
void test(int var_5, int var_6,
          signed char arr_1[1][1][1]) {
  for (unsigned i_0 =3D 0; i_0 < 21; i_0 +=3D 2)
    for (int i_2 =3D 0; i_2 < 8; i_2 +=3D 82) {
      for (int i_3 =3D 0; i_3 < test___trans_tmp_1; i_3++)
        for (short i_4 =3D 0; i_4 < 20; i_4 +=3D 4)
          var_20 =3D max(var_5, 0);
      for (int i_5 =3D 0; i_5 < 19;
           i_5 +=3D 20)
        for (int i_6 =3D var_6 + 2; i_6 < var_5 + 3; i_6++)
          arr_8[3][2][i_2][i_5][i_6] =3D arr_1[0][0][0];
    }
}
unsigned long long var_20;
signed char arr_1[1][1][1];
unsigned short arr_8[22][26][1][1][11];
int main() { test(var_5, var_6, arr_1); }

Optimized dump contains:

  <bb 11> [local count: 17523394]:
  _93 =3D MEM[(signed char[26][19] *)arr_1_31(D) + 1482B][2][0];
  _94 =3D (short unsigned int) _93;
  arr_8[3][2][0][0][-2147483648] =3D _94; <---- HERE
  if (i_6_103 > _131)
    goto <bb 9>; [11.00%]
  else
    goto <bb 12>; [89.00%]

which is instruction that causes the segfault. I'm going to take a look.=