if (library) {
    // Upgrade nodes in the functions.
    for (FunctionDef& fdef : *library->mutable_function()) {
      auto func_name = fdef.signature().name();
      for (auto& node_def : *fdef.mutable_node_def()) {
        const OpDef* op_def = nullptr;
        // With lazy loading, some functions might not be executed, thus we skip
        // the node if the op is not registered.