const tensorflow::OpDef* op_def = nullptr;
  status->status =
      tensorflow::OpRegistry::Global()->LookUpOpDef(op_name, &op_def);
  if (!status->status.ok()) return nullptr;

  if (input_index >= op_def->input_arg_size() || input_index < 0) {
    status->status = tensorflow::errors::InvalidArgument(
        input_index, " out of range for ", op_name);
    return nullptr;
  }

  }

  void VerifyFDefInputs(const tensorflow::FunctionDef& fdef,
                        const std::vector<IOSpec>& inputs) {
    const OpDef& signature = fdef.signature();
    ASSERT_EQ(inputs.size(), signature.input_arg_size());
    for (int i = 0; i < inputs.size(); ++i) {
      const OpDef::ArgDef& arg = signature.input_arg(i);
      const IOSpec& in = inputs[i];
      if (in.second != DT_INVALID) {