return WalkResult::interrupt();
      host_device = host_device_value;
    }
    cluster_to_host[tpu_cluster.getOperation()] = host_device;
    return tpu_cluster.walk([&](Operation* op) {
      insert_pending_op(op, tpu_cluster);
      return callback(op, tpu_cluster,
                      cluster_to_host[tpu_cluster.getOperation()]);
    });
  });
  if (result.wasInterrupted()) return failure();