[Bug tree-optimization/58570] New: wrong code at -Os and above on x86_64-linux-gnu (both 32-bit and 64-bit modes)

[su at cs dot ucdavis.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58570

            Bug ID: 58570
           Summary: wrong code at -Os and above on x86_64-linux-gnu (both
                    32-bit and 64-bit modes)
           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

The current gcc trunk mis-compiles the following code on x86_64-linux at -Os
and above in both 32-bit and 64-bit modes.

This is a regression from 4.8.x.

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure
--enable-languages=c,c++,objc,obj-c++,fortran,lto --disable-werror
--enable-checking=release --with-gmp=/usr/local/gcc-trunk
--with-mpfr=/usr/local/gcc-trunk --with-mpc=/usr/local/gcc-trunk
--with-cloog=/usr/local/gcc-trunk --prefix=/usr/local/gcc-trunk
Thread model: posix
gcc version 4.9.0 20130928 (experimental) [trunk revision 203003] (GCC) 
$ 
$ gcc-trunk -O1 small.c
$ a.out
1
$ gcc-4.8 -O3 small.c
$ a.out
1
$ gcc-trunk -O3 small.c
$ a.out
0
$ gcc-trunk -O2 small.c
$ a.out
0
$ gcc-trunk -Os small.c
$ a.out
0
$



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


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

#pragma pack(1)
struct S
{
  int f0:15;
  int f1:29;
};

int a, b, c, e = 1, g;
static struct S d[6];
long long f;

static short
foo (int p)
{
  for (b = 0; b < 1; b++)
    {
      g |= 1;
      for (; a < 1; a++)
    {
      int i;
      if (p < c - 1)
        return 4;
      if (p)
        for (i = 0; i < 6; i++)
          {
        struct S j = {1, 1};
        d[i] = j;
          }
      continue;
    }
    }
  return 0;
}

int
main ()
{
  if (e)
    foo (!f);
  printf ("%d\n", d[0].f1);
  return 0;
}