C LB+ctrlonceonce+mbonceonce
{}
P0(int *x, int *y)
{
int r0;
r0 = READ_ONCE(*x);
if (r0)
WRITE_ONCE(*y, 1);
}
P1(int *x, int *y)
r0 = READ_ONCE(*y);
smp_mb();
WRITE_ONCE(*x, 1);
exists (0:r0=1 /\ 1:r0=1)