Node* b = Input(b2.opts().WithName("B"));
    Node* control = Input(b2.opts().WithName("Control"));

    NodeBuilder nb("F1", "F1", lib_def.get());
    nb.Input(a).ControlInput(control);
    Node* call1 = b2.opts().FinalizeBuilder(&nb);

    NodeBuilder nb2("F2", "F2", lib_def.get());
    nb2.Input(b).Input(call1).ControlInput(control);
    Node* call2 = b2.opts().FinalizeBuilder(&nb2);

using tensorflow::GraphDef;
using tensorflow::mutex_lock;
using tensorflow::NameRangeMap;
using tensorflow::NameRangesForNode;
using tensorflow::NewSession;
using tensorflow::Node;
using tensorflow::NodeBuilder;
using tensorflow::OpDef;
using tensorflow::PartialTensorShape;
using tensorflow::RunMetadata;
using tensorflow::RunOptions;
using tensorflow::Session;
using tensorflow::Status;
using tensorflow::string;

  std::string new_node_name =
      update_inplace ? node->name()
                     : GetUniqueNodeName(node->name(), index, node_name_map);

  Node* placeholder_node;
  NodeBuilder builder(new_node_name, "Placeholder");
  builder.Attr("shape", shape);
  builder.Attr("dtype", dtype);
  TF_RETURN_IF_ERROR(builder.Finalize(graph_.get(), &placeholder_node));