[Bug tree-optimization/57719] New: wrong code at -O3 on x86_64-linux-gnu

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57719

            Bug ID: 57719
           Summary: wrong code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

Current gcc trunk (and 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 20130625 (experimental) [trunk revision 200388] (GCC) 
$ gcc-trunk -O2 reduced.c      
$ a.out
1
$ gcc-4.7 -O3 reduced.c
$ a.out
1
$ gcc-4.8 -O3 reduced.c
$ a.out
0
$ gcc-trunk -O3 reduced.c
$ a.out
0

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

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

int u; 

int a, b, c[2], d, *e, f, g; 

int fn2 ()
{
  int t[1];
  int i;
  i = 0;
  for (; i < 1; i++)
    t[i] = 0;
  for (d = 0; d; d = 1) {
    int *s[1] = {&t[0]};
    g = a = *s[0]; 
  }
  f = g; 
  return 1;
}

void fn1 ()
{
  for (; b < 2; b++) {
    int *p = &u; 
    *p = 0;
    *p = fn2();
    e = &c[b];
    *e = 0;
  }
}

int
main ()
{
  fn1 ();
  printf ("%d\n", u);
  return 0;
}