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From: "krebbel at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/98736] New: Wrong partition order generated
 in loop distribution pass
Date: Mon, 18 Jan 2021 19:40:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98736

            Bug ID: 98736
           Summary: Wrong partition order generated in loop distribution
                    pass
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: krebbel at gcc dot gnu.org
  Target Milestone: ---

int a[6];
char b, c;
int main() {
  int d[4] =3D {0, 0, 0, 0};
  for (c =3D 0; c <=3D 5; c++) {
    for (b =3D 2; b !=3D 0; b++)
      a[c] =3D 8;
    a[c] =3D d[3];
  }
  if (a[0] !=3D 0)
    __builtin_abort();
}

Aborts when compiled with:
gcc -Os -march=3Dz13 t.c -o t

Succeeds with:
gcc -O3 -march=3Dz13 t.c -o t

The outer loop is recognized as clearmem. Unfortunately it is generated bef=
ore
the inner loop body.=