[Bug rtl-optimization/57569] New: wrong code for struct copy at -O3 on x86_64-linux

[dhazeghi at yahoo dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57569

            Bug ID: 57569
           Summary: wrong code for struct copy at -O3 on x86_64-linux
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dhazeghi at yahoo dot com

The following code is miscompiled with current gcc-trunk on x86_64-linux at -O3
optimization level in 32-bit mode, outputting garbage (rather than 0).  This is
a regression from 4.7.

$ gcc-trunk -v
gcc version 4.9.0 20130608 (experimental) [trunk revision 199849] (GCC) 
$ gcc-trunk -O2 -m32 reduced.c 
$ ./a.out 
0
$ gcc-4.7 -O3 -m32 reduced.c 
$ ./a.out 
0
$ gcc-trunk -O3 -m32 reduced.c 
$ ./a.out 
134519796
----------------------------
int printf (const char *, ...);

struct S { int f0; } a; 

int b, e, *d = &b, f;

void 
fn1 ()
{
  int **g[9][6];
  int ***h = &g[6][3];
  for (; e < 9; e++) {
    f = 0;
    for (; f < 6; f++)
      g[e][f] = &d;
  }
  ***h = 0;
}

void
fn2 ()
{
  fn1 ();
  struct S c[4][10] = {};
  a = c[3][9];
}

int
main ()
{
  fn2 ();
  printf ("%d\n", a.f0);
  return 0;
}