C cmpxchg-fail-unordered-2

(*
 * Result: Sometimes
 *
 * Demonstrate that a failing cmpxchg() operation does not act as either
 * an acquire release operation.  (In contrast, a successful cmpxchg()
 * does act as both an acquire and a release operation.)
 *)

{}

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

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

P1(int *x, int *y)
{
	int r1;
	int r2;

	r1 = cmpxchg(y, 0, 1);
	r2 = READ_ONCE(*x);
}

exists (0:r1=0 /\ 1:r1=1 /\ 1:r2=0)