Method UpdateFanoutsInternal

tensorflow/core/grappler/mutable_graph_view.cc:749–844

}

Status MutableGraphView::UpdateFanoutsInternal(NodeDef* from_node,
                                               NodeDef* to_node) {
  VLOG(2) << absl::Substitute("Update fanouts from '$0' to '$1'.",
                              from_node->name(), to_node->name());
  if (from_node == to_node) {
    return Status::OK();
  }

  // Update internal state with the new output_port->input_port edge.
  const auto add_edge = [this](const OutputPort& output_port,
                               const InputPort& input_port) {
    fanouts()[output_port].insert(input_port);
  };

  // Remove invalidated edge from the internal state.
  const auto remove_edge = [this](const OutputPort& output_port,
                                  const InputPort& input_port) {
    fanouts()[output_port].erase(input_port);
  };

  // For the control fanouts we do not know the input index in a NodeDef,
  // so we have to traverse all control inputs.

  auto control_fanouts =
      GetFanout(GraphView::OutputPort(from_node, Graph::kControlSlot));

  bool to_node_is_switch = IsSwitch(*to_node);
  for (const InputPort& control_port : control_fanouts) {
    // Node can't be control dependency of itself.
    if (control_port.node == to_node) continue;

    // Can't add Switch node as a control dependency.
    if (to_node_is_switch) {
      // Trying to add a Switch as a control dependency, which if allowed will
      // make the graph invalid.
      return UpdateFanoutsError(from_node->name(), to_node->name())(
          absl::Substitute("can't update fanouts to node '$0' as it will "
                           "become a Switch control dependency",
                           to_node->name()));
    }

    NodeDef* node = control_port.node;
    RemoveControllingFaninInternal(node, from_node);
    AddFaninInternal(node, {to_node, Graph::kControlSlot});
  }

  // First we update regular fanouts. For the regular fanouts
  // `input_port:port_id` is the input index in NodeDef.

  auto regular_edges =
      GetFanoutEdges(*from_node, /*include_controlled_edges=*/false);

  // Maximum index of the `from_node` output tensor that is still used as an
  // input to some other node.
  int keep_max_regular_output_port = -1;

  for (const Edge& edge : regular_edges) {
    const OutputPort output_port = edge.src;