void* thr2(void* arg) { //reader
  __VERIFIER_atomic_r();
  y = x;
  assert(y == x);
  r = r-1;

  return 0;
}
void* thr2(void* arg) { //reader
  __VERIFIER_atomic_r();
  y = x;
  /* assert not proved */
  assert(y == x);
  /* reachable */
  r = r-1;

  return 0;
}