size_t frame_start = 0;
  while (frame_start < topo.size()) {
    // Batching nodes who have the same root frame.
    absl::string_view cur_frame_name;
    TF_RETURN_IF_ERROR(
        GetRootFrame(topo[frame_start], control_flow_info_, &cur_frame_name));
    size_t frame_end = frame_start;
    for (size_t i = frame_start + 1; i < topo.size(); ++i) {
      absl::string_view i_frame_name;