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Subject: [Bug tree-optimization/55079] [4.8 regression] false positive -Warray-bounds (also seen at -O3 bootstrap)
Date: Thu, 15 Nov 2012 01:01:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D55079

--- Comment #9 from Jan Hubicka <hubicka at gcc dot gnu.org> 2012-11-15 01:=
01:30 UTC ---
This is reduced testcase from gcov.c
int a[8];
int
t (void)
{
  int ix =3D 0;
  int k;
  int b =3D 0;
  int curr =3D 0;
  for (k =3D 0; k < 2; k++)
    {
      b =3D ix * 32;
      curr =3D a[ix++];
      if (!(ix <=3D 8))
        abort ();

      while (curr)
        {
          b =3D ix * 32;
          curr =3D a[ix++];
          if (!(ix <=3D 8))
            abort ();
        }
    }
  return curr + b;
}

jan@linux-e0ml:~/trunk/build/gcc> ./xgcc -B ./ -O2 -fprofile-use t.c
-Warray-bounds -S -S -fdump-tree-cunroll-details  -fdump-tree-all-details=
=20=20
t.c: In function =E2=80=98t=E2=80=99:
t.c:14:2: warning: incompatible implicit declaration of built-in function
=E2=80=98abort=E2=80=99 [enabled by default]
  abort ();
  ^
t.c:25:1: note: file /home/jan/trunk/build/gcc/t.gcda not found, execution
counts estimated
 }
 ^
t.c:19:15: warning: array subscript is above array bounds [-Warray-bounds]
       curr =3D a[ix++];
               ^
t.c:19:15: warning: array subscript is above array bounds [-Warray-bounds]

Obivously here unroller does not know that bv_ix is at least 1