ConvertSubgraphIdxsToFunctionAttrs(tflite::BuiltinOptionsUnion options,
                                   const std::vector<std::string>& func_names,
                                   Builder builder) {
  if (auto* opts = options.AsCallOnceOptions()) {
    uint32_t init_idx = opts->init_subgraph_index;
    if (init_idx >= func_names.size()) {
      return errors::InvalidArgument("subgraph with index not found: ",
                                     init_idx);