TF_EXPECT_OK(root.ToGraphDef(&graph_def));
  for (auto& node : *graph_def.mutable_node()) {
    node.set_device("/cpu:0");
  }
  SessionOptions sess_options;
  sess_options.config.mutable_graph_options()->set_build_cost_model(1);
  std::unique_ptr<Session> session(NewSession(sess_options));

  TF_CHECK_OK(session->Create(graph_def));

  QueueRunnerDef queue_runner_def =