// deadlock in a graph containing a while loop.
  Scope root = Scope::NewRootScope().ExitOnError();
  auto a = ops::Placeholder(root.WithOpName("A"), DT_FLOAT);
  auto enter_0 = ops::internal::Enter(root.WithOpName("enter_a"), a, "frame");
  auto exit_0 = ops::internal::Exit(root.WithOpName("exit_a"), enter_0);
  auto tanh = ops::Tanh(root.WithOpName("tanh"), exit_0);
  auto enter_1 =