::flatbuffers::uoffset_t start_;
  void add_opcode_index(uint32_t opcode_index) {
    fbb_.AddElement<uint32_t>(Operator::VT_OPCODE_INDEX, opcode_index, 0);
  }
  void add_inputs(::flatbuffers::Offset<::flatbuffers::Vector<int32_t>> inputs) {
    fbb_.AddOffset(Operator::VT_INPUTS, inputs);
  }
  void add_outputs(::flatbuffers::Offset<::flatbuffers::Vector<int32_t>> outputs) {

    auto signature_key_buf =
        builder_.CreateString(signature_def_data.signature_key);
    tflite::SignatureDefBuilder sig_def_builder(builder_);
    sig_def_builder.add_inputs(inputs_buf);
    sig_def_builder.add_outputs(outputs_buf);
    sig_def_builder.add_signature_key(signature_key_buf);
    sig_def_builder.add_subgraph_index(signature_def_data.subgraph_index);

    TFL_StatefulTensor:$fw_input_cell_state,
    TFL_StatefulTensor:$bw_input_activation_state,
    TFL_StatefulTensor:$bw_input_cell_state,

    // Auxiliary input & weights.
    TFL_TensorOfOrNone<[F32, I8]>:$aux_input,
    // Auxiliary fw weights.
    TFL_TensorOfOrNone<[F32, I8]>:$fw_aux_input_to_input_weights,
    TFL_TensorOfOrNone<[F32, I8]>:$fw_aux_input_to_forget_weights,

             llvm::enumerate(block.getArgumentTypes())) {
          TensorType updated_ty =
              UpdateElementTypeTo(original_ty, element_types[block_idx]);
          signature.addInputs(block_idx, {updated_ty});
        }
        rewriter.applySignatureConversion(&region.front(), signature);
      }
    }

    // Replace all uses of `op` results with the newly created op.