<< (queue_set_.count(fn) ? "already inserted" : "newly inserted")
               << ")\n");
    if (queue_set_.insert(fn).second) queue_.push(fn);
  }

  // Enqueues callers on functions.
  void EnqueueCallers(func::FuncOp fn);

  // Returns the function at the front of the queue.
  func::FuncOp front() { return queue_.front(); }

  // Returns whether work queue is empty.