for (const auto& edge : back_edge_helper_.RemovedEdges()) {
    if (back_edge_node_output_.find(edge.src) != back_edge_node_output_.end() &&
        back_edge_node_output_[edge.src] != edge.src_output) {
      return errors::FailedPrecondition(
          "More than one of the src node outputs are backedges!");
    }
    back_edge_node_output_[edge.src] = edge.src_output;