[Bug tree-optimization/58223] New: wrong code at -O3 on x86_64-linux-gnu

["su at cs dot ucdavis.edu" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58223

            Bug ID: 58223
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk (as well as gcc 4.8) produces wrong code for the
following testcase on x86_64-linux when compiled at -O3 in both 32-bit and
64-bit modes. This is a regression from 4.7.x.

$ gcc-trunk -v
gcc version 4.9.0 20130822 (experimental) [trunk revision 201915] (GCC) 
$ gcc-4.7 -O3 reduced.c
$ a.out
1
$ gcc-trunk -O2 reduced.c
$ a.out
1
$ gcc-trunk -O3 reduced.c
$ a.out
0
$ gcc-4.8 -O3 reduced.c
$ a.out
0
$ 

-------------------------------------------

int printf (const char *, ...);

int a[2], b;

int main ()
{
  for (b = 0; b < 2; b++)
    {
      a[0] = 1;
      a[b] = 0;
    }
  printf ("%d\n", a[0]);
  return 0;
}