Someone

  /* FIXME: We should get gcc to allocate one of the condition  */
  /* registers.  I always got "impossible constraint" when I    */
  /* tried the "y" constraint.                                  */
  __asm__ __volatile__ (
    "lwz %0,%1\n"
    "cmpw cr7,%0,%0\n"
    "bne- cr7,1f\n"
    "1: isync\n"
    : "=r" (result)
    : "m"(*addr) : "memory", "cc");
  return result;