}
  }
  return errors::InvalidArgument(
      "Multiple NextIteration inputs to merge node ",
      FormatNodeForError(*merge), ": \n", absl::StrJoin(backedges, "\n"),
      "\nMerge nodes can have at most one incoming NextIteration edge.");
}

Status FindUniqueBackedge(Node* merge, const Edge** result) {
  *result = nullptr;
  CHECK(merge->IsMerge());

                           latch.output_false);
  Output iv_next = ops::Add(root.WithOpName(prefix + "/ivnext"),
                            latch.output_true, increment_by);
  Output next_iteration =
      ops::NextIteration(root.WithOpName(prefix + "/next_iteration"), iv_next);

  CHECK(root.graph()
            ->UpdateEdge(next_iteration.node(), 0, iv.output.node(), 1)
            .ok());

  auto b = ops::Placeholder(root.WithOpName("B"), DT_FLOAT);
  auto c = ops::Add(root.WithOpName("C"), a, b);
  auto enter = ops::internal::Enter(root, c, "aframe");
  auto next_iter = ops::NextIteration(root, enter);
  auto exit = ops::internal::Exit(root, next_iter);
  auto d = ops::Add(root.WithOpName("D"), c, exit);

  std::unique_ptr<Graph> graph(new Graph(OpRegistry::Global()));

    // and only disallow these Identities to go into the cluster with nodes from
    // the loop body but still consider them candidates.
    //
    // LoopCond ->
    // Merge    -> Switch -> Identity -> i++ -> ... -> NextIteration
    //                               ..> Const -> LoopBody
    //                            (control edge)
    TF_ASSIGN_OR_RETURN(bool is_identity_driving_consts_in_loop,