raw_ostream& print(raw_ostream& os) const {
    if (auto* op = producer.dyn_cast<Operation*>())
      os << "op " << op->getName();
    if (auto ba = producer.dyn_cast<BlockArgument>())
      os << "block_arg " << ba.getArgNumber();
    os << formatv(" [{0}]", llvm::make_range(port.begin(), port.end()));
    return os;
  }

  bool IsValid() const { return !producer.isNull(); }
};

struct ValuePortHasher {