Fix some ClangTidy warnings in Grappler's dependency optimizer on a boring Friday afternoon.

PiperOrigin-RevId: 452882239
diff --git a/tensorflow/core/grappler/optimizers/BUILD b/tensorflow/core/grappler/optimizers/BUILD
index 1e628bc..b879ab0 100644
--- a/tensorflow/core/grappler/optimizers/BUILD
+++ b/tensorflow/core/grappler/optimizers/BUILD
@@ -416,6 +416,8 @@
         "//tensorflow/core/grappler/costs:graph_properties",
         "//tensorflow/core/grappler/utils:topological_sort",
         "@com_google_absl//absl/container:flat_hash_map",
+        "@com_google_absl//absl/container:flat_hash_set",
+        "@com_google_absl//absl/strings",
     ],
 )
 
diff --git a/tensorflow/core/grappler/optimizers/dependency_optimizer.cc b/tensorflow/core/grappler/optimizers/dependency_optimizer.cc
index 88f1bd5..f2b2608 100644
--- a/tensorflow/core/grappler/optimizers/dependency_optimizer.cc
+++ b/tensorflow/core/grappler/optimizers/dependency_optimizer.cc
@@ -18,6 +18,7 @@
 #include <unordered_set>
 
 #include "absl/container/flat_hash_map.h"
+#include "absl/strings/match.h"
 #include "tensorflow/core/framework/node_def.pb.h"
 #include "tensorflow/core/framework/node_def_util.h"
 #include "tensorflow/core/framework/op.h"
@@ -134,7 +135,7 @@
             << " to NoOp. Node has side effect.";
     return false;
   }
-  if (node.op().rfind("Submodel", 0) == 0) {
+  if (absl::EndsWith(node.op(), "Submodel")) {
     return false;
   }
   const OpDef* op_def = nullptr;
@@ -142,11 +143,12 @@
   if (!status.ok() || op_def->output_arg_size() == 0) {
     return false;
   }
-  const std::unordered_set<string> do_not_rewrite_ops{
-      "Assert",     "CheckNumerics",         "_Retval",
-      "_Arg",       "_ParallelConcatUpdate", "TPUExecute",
-      "TPUCompile", "ControlTrigger"};
-  if (do_not_rewrite_ops.find(node.op()) != do_not_rewrite_ops.end()) {
+  static const absl::flat_hash_set<string>* do_not_rewrite_ops =
+      new absl::flat_hash_set<string>{
+          "Assert",     "CheckNumerics",         "_Retval",
+          "_Arg",       "_ParallelConcatUpdate", "TPUExecute",
+          "TPUCompile", "ControlTrigger"};
+  if (do_not_rewrite_ops->find(node.op()) != do_not_rewrite_ops->end()) {
     return false;
   }
   if (!SafeToRemoveIdentity(node)) {
@@ -750,7 +752,8 @@
                                      GraphDef* optimized_graph) {
   optimized_graph_ = optimized_graph;
   *optimized_graph_ = item.graph;
-  nodes_to_preserve_ = item.NodesToPreserve();
+  nodes_to_preserve_ = absl::flat_hash_set<string>(
+      item.NodesToPreserve().begin(), item.NodesToPreserve().end());
   fetch_nodes_known_ = !item.fetch.empty();
   CleanControlInputs();
 
diff --git a/tensorflow/core/grappler/optimizers/dependency_optimizer.h b/tensorflow/core/grappler/optimizers/dependency_optimizer.h
index 4251a4a..4f37204 100644
--- a/tensorflow/core/grappler/optimizers/dependency_optimizer.h
+++ b/tensorflow/core/grappler/optimizers/dependency_optimizer.h
@@ -16,7 +16,8 @@
 #ifndef TENSORFLOW_CORE_GRAPPLER_OPTIMIZERS_DEPENDENCY_OPTIMIZER_H_
 #define TENSORFLOW_CORE_GRAPPLER_OPTIMIZERS_DEPENDENCY_OPTIMIZER_H_
 
-#include <unordered_set>
+#include "absl/container/flat_hash_map.h"
+#include "absl/container/flat_hash_set.h"
 #include "tensorflow/core/grappler/optimizers/graph_optimizer.h"
 #include "tensorflow/core/grappler/utils.h"
 #include "tensorflow/core/protobuf/rewriter_config.pb.h"
@@ -73,9 +74,9 @@
   void GroupCrossDeviceControlEdges(bool host_granularity);
 
   bool fetch_nodes_known_;
-  std::unordered_set<string> nodes_to_preserve_;
+  absl::flat_hash_set<string> nodes_to_preserve_;
   std::unique_ptr<NodeMap> node_map_;
-  std::unordered_map<const NodeDef*, int> node_to_idx_;
+  absl::flat_hash_map<const NodeDef*, int> node_to_idx_;
   GraphDef* optimized_graph_;  // Not owned.
 };
 
diff --git a/tensorflow/core/grappler/optimizers/graph_optimizer_stage.h b/tensorflow/core/grappler/optimizers/graph_optimizer_stage.h
index c958e4e..266e8c4 100644
--- a/tensorflow/core/grappler/optimizers/graph_optimizer_stage.h
+++ b/tensorflow/core/grappler/optimizers/graph_optimizer_stage.h
@@ -295,9 +295,11 @@
 
   std::vector<string> StageNames() {
     std::vector<string> names;
-    for (const auto& stage : stages_) {
-      names.push_back(stage->stage_name());
-    }
+    std::transform(
+        stages_.begin(), stages_.end(), std::back_inserter(names),
+        [](const std::unique_ptr<GraphOptimizerStage<Result>>& stage) {
+          return stage->stage_name();
+        });
     return names;
   }