// directly.
      auto iter = merge_to_next_iteration.find(n);
      if (iter != merge_to_next_iteration.end()) {
        const Node *next_iter = iter->second, *node = next_iter;
        do {
          TF_RETURN_IF_ERROR(node->input_node(0, &node));
        } while (node->IsIdentity());
        const Node* switch_input;
        bool is_loop_invariant = node->IsSwitch() &&