gtl::ArraySlice<Gradient*> output_gradients, absl::Span<Gradient*> result,
    bool build_default_zeros_grads) {
  std::unordered_set<int64_t> sources_set(source_tensor_ids.begin(),
                                          source_tensor_ids.end());
  BackpropInitialState<BackwardFunction, TapeTensor> state = PrepareBackprop(
      target_tensor_ids, tensor_tape_, &op_tape_, sources_set, persistent_);