for (int i = 0, e = op.getNumOperands(); i != e; ++i) {
      auto &state = states_manager_.GetOperandQuantState(op, i);
      auto &requantize = states_manager_.GetOperandRequantizeState(op, i);
      if (state.IsEmpty() && requantize.pos == RequantizeState::NO_REQUANTIZE) {
        input_specs.push_back(original_input_specs[i]);
      } else if (requantize.pos == RequantizeState::ON_OUTPUT) {

    QuantState &GetResultQuantState(Operation *op, int index) {
      return states_[result_states_[{op, index}]];
    }

    // Returns the state of the index-th operand of the op.
    RequantizeState &GetOperandRequantizeState(Operation *op, int index) {
      return rescale_states_[operand_states_[{op, index}]];
    }

    // Returns the state of the index-th result of the op.