std::unique_ptr<Graph> graph_out;
  FunctionLibraryDefinition* const library = options.flib_def;

  // Constant folding below might need to run part of the function to compute
  // constants. Create an FunctionLibraryRuntime with a single CPU device
  // that can run the part of the function.
  // NOTE: If this turns out to be slow, we can cache the FLRs keyed by
  // `options`.
  SessionOptions session_options;

  std::unique_ptr<ProcessFunctionLibraryRuntime> pflr(
      new ProcessFunctionLibraryRuntime(nullptr, env_, /*config=*/nullptr,
                                        TF_GRAPH_DEF_VERSION, flib_def_, opts));
  FunctionLibraryRuntime* lib_runtime =
      pflr->GetFLR(ProcessFunctionLibraryRuntime::kDefaultFLRDevice);
  std::vector<bool> compile_time_const_nodes(graph_->num_node_ids(), false);
  TF_RETURN_IF_ERROR(BackwardsConstAnalysis(