Graph *host_graph = host_fbody->graph;
  Node *key_placeholder = nullptr, *sequencer = nullptr;
  for (Node *n : host_graph->nodes()) {
    if (n->type_string() == "Placeholder" &&
        absl::EndsWith(n->name(), "_key_placeholder")) {
      EXPECT_EQ(key_placeholder, nullptr);
      key_placeholder = n;
    } else if (HasNodeAttr(n->def(), "_xla_host_transfer_sequencer")) {

  Graph* g = fbody->graph;

  // Find or create the key placeholder node.
  Node* key_placeholder = nullptr;
  for (Node* n : g->nodes()) {
    if (IsKeyPlaceholderNode(*n)) {
      key_placeholder = n;
      break;
    }
  }
  if (!key_placeholder) {
    TF_ASSIGN_OR_RETURN(key_placeholder,
                        AddHostComputeKeyPlaceholder(xla_cluster_name, g));
  }

Node* KeyPlaceholderShape(const GraphDefBuilder::Options& opts) {
  return KnownShapeBase(DT_STRING, {2}, opts);
}

Node* KeyPlaceholder(const string& call_node,
                     const GraphDefBuilder::Options& opts) {
  if (opts.HaveError()) return nullptr;
  NodeBuilder node_builder(absl::StrCat(call_node, "_key_placeholder"),
                           "Placeholder", opts.op_registry());
  TensorShapeProto shape;