bool IsKeyPlaceholderNode(const Node& n) {
  return n.type_string() == "Placeholder" &&
         absl::EndsWith(n.name(), "_key_placeholder");
}

// Returns nodes with given type.
std::vector<Node*> GatherNodesWithType(const Graph& g, const string& type) {
  std::vector<Node*> result;
  for (Node* n : g.nodes()) {
    if (n->type_string() == type) {
      result.push_back(n);
    }
  }
  return result;
}