if (EmptyParams(params)) {
        *changed |= false;
        break;
      }
      // propagate this params to all the quantizable ports.
      if (failed(PropagateQuantParams(op, params, new_items, changed))) {
        return failure();
      }
      break;
    }
    default: {
      // TODO(fengliuai): implement the other types.
      llvm_unreachable("no implementation.");

  // so they can be added to the working queue. `changed` is set to true if
  // there are any new elements being added to `new_items`.
  LogicalResult PropagateQuantParams(Operation *op, const QuantParams params,
                                     AdjacentOperations *new_items,
                                     bool *changed);

 private:
  class StatesManager {
   public: