GCC 4.7.3 and earlier versions miscompile the following code on x86_64-linux at -Os and above in both 32-bit and 64-bit modes.  But I did not check the latest 4.7 branch. 

It affects neither the current trunk nor 4.8.x. 

$ gcc-4.7.3 -O1 small.c; a.out
1
$ gcc-4.7.3 -Os small.c; a.out
^C
$ gcc-4.6.4 -Os small.c; a.out
^C
$ gcc-4.8.2 -Os small.c; a.out
1
$ gcc-trunk -Os small.c; a.out
1
$ 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 --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 20131117 (experimental) [trunk revision 204920] (GCC) 
$


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


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

int a, *b = &a;

int
main ()
{
  short c = 0;
 lbl:
  ++c;
  *b |= 1;
  if (c)
    goto lbl;
  printf ("%d\n", a);
  return 0;
}