// ordered.
void SortControlInputs(GraphDef* gdef) {
  int64_t num_nodes = gdef->node_size();
  for (int64_t i = 0; i < num_nodes; ++i) {
    NodeDef* node = gdef->mutable_node(i);
    // Stable sort control inputs and leave the order of data inputs unchanged.
    std::stable_sort(node->mutable_input()->begin(),
                     node->mutable_input()->end(),