Method FoldNode

tensorflow/core/grappler/optimizers/constant_folding.cc:1441–1564

}

Status ConstantFolding::FoldNode(NodeDef* node, GraphDef* output_graph,
                                 bool* result_too_large) {
  *result_too_large = false;
  if (IsMerge(*node)) {
    return FoldMergeNode(node, output_graph);
  }

  std::vector<NodeDef> const_nodes;
  TF_RETURN_IF_ERROR(
      EvaluateOneFoldable(*node, &const_nodes, result_too_large));
  VLOG(2) << "Folded node: " << SummarizeNodeDef(*node);

  NodeDef* constant_output = nullptr;
  for (int i = 0; i < const_nodes.size(); i++) {
    NodeDef* const_node = &const_nodes[i];
    VLOG(3) << "Generated constant node: " << SummarizeNodeDef(*const_node);
    if (const_node->name().empty()) {
      // Dead output: we can't create a constant to encode its value, so we'll
      // just skip it. We'll preserve the edges that originate from that
      // output below to preserve the overall behavior of the graph wrt dead
      // edges.
      continue;
    }

    // Returns `true` iff `const_node` already has control input named `input`.
    const auto is_duplicate_control_input = [&](const string& input) -> bool {
      auto it = absl::c_find(const_node->input(), input);
      return it != const_node->input().end();
    };

    // Forward control dependencies.
    for (const string& input : node->input()) {
      // Forward control dependencies from folded node.
      if (IsControlInput(input)) {
        if (!is_duplicate_control_input(input)) {
          *const_node->add_input() = input;
        }
      }

      // Forward control dependencies from constant inputs to folded node.
      if (!IsControlInput(input)) {
        NodeDef* input_node = node_map_->GetNode(input);
        for (const string& fanin_of_input : input_node->input()) {
          if (!is_duplicate_control_input(fanin_of_input)) {
            *const_node->add_input() = fanin_of_input;
          }
        }
      }
    }

    // We rewrite the existing node if it only has a single output, and
    // create new nodes otherwise.
    if (const_nodes.size() == 1) {
      node->set_op("Const");
      // Note we need to clear the inputs in NodeMap before we clear the inputs
      // in the node, otherwise NodeMap would see empty inputs and effectively
      // does nothing.
      node_map_->RemoveInputs(node->name());