OperationState op_state(loc, op_name);

  for (auto input_num : op.inputs) {
    if (input_num == -1) {
      assert(optional_arg_marker != nullptr);
      op_state.addOperands({optional_arg_marker});
    } else {
      op_state.addOperands({vals_map.at(input_num)});
    }
  }

  for (auto output_num : op.outputs) {
    auto& tensor = *tensors.at(output_num);

  // Retrieve the regression signature from meta graph def.
  const auto signature_def_map = metagraph_def.signature_def();
  const auto signature_def = signature_def_map.at("regress_x_to_y");

  const string input_name =
      signature_def.inputs().at(tensorflow::kRegressInputs).name();
  const string output_name =
      signature_def.outputs().at(tensorflow::kRegressOutputs).name();