990117-1.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

static void
__bb_init_prg ()
{
  const char *p;

      {
	unsigned long l;

	(__extension__ (__builtin_constant_p (p) && __builtin_constant_p (l)
			? 5 : 2));
      }

}