C cmpxchg-fail-unordered-1

(*
 * Result: Sometimes
 *
 * Demonstrate that a failing cmpxchg() operation does not act as a
 * full barrier.  (In contrast, a successful cmpxchg() does act as a
 * full barrier.)
 *)

{}

P0(int *x, int *y, int *z)
{
	int r0;
	int r1;

	WRITE_ONCE(*x, 1);
	r1 = cmpxchg(z, 1, 0);
	r0 = READ_ONCE(*y);
}

P1(int *x, int *y, int *z)
{
	int r0;
	int r1;

	WRITE_ONCE(*y, 1);
	r1 = cmpxchg(z, 1, 0);
	r0 = READ_ONCE(*x);
}

locations[0:r1;1:r1]
exists (0:r0=0 /\ 1:r0=0)