The following code is miscompiled by the current clang trunk (as well as clang 3.3 and 3.2) on x86_64-linux-gnu at -Os and above in both 32-bit and 64-bit modes. 

It is also miscompiled by clang 3.0 and 3.1 at -O3, making it a regression from 2.9.

It also seems to affect MacOS X. 

$ clang-trunk -v
clang version 3.5 (trunk 196634)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.3
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
$ 
$ clang-trunk -O1 small.c; a.out
0
$ clang-trunk -Os small.c; a.out
-1
$ clang-3.3 -Os small.c; a.out
-1
$ clang-3.2 -Os small.c; a.out
-1
$ clang-3.1 -Os small.c; a.out
0
$ clang-3.1 -O3 small.c; a.out
-1
$ clang-3.0 -O3 small.c; a.out
-1
$ clang-2.9 -O3 small.c; a.out
0
$ 
$ gcc-trunk -Os small.c; a.out
0
$ icc -Os small.c; a.out
0
$ 


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


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

struct
{
  int f0;
  int f1;
  int f2;
} a, e;

int b, c = 1, d, f, g, h;

static int
fn1 (unsigned char p)
{
 lbl:
  for (g = 0; g; g++)
    {
      if (c)
	break;
      p && (d |= 1);
    }
  for (e.f1 = 0; e.f1 < 21; e.f1 += 2)
    {
      h = 0;
      if (a.f0)
	goto lbl;
      f |= a.f2 |= p++ || b--;
    }
  return 0;
}

int
main ()
{
  fn1 (128);
  printf ("%d\n", b);
  return 0;
}