Eliminate all useless nodes related to UpdateStates.

mindspore/ccsrc/backend/session/session_basic.cc

@@ -1875,10 +1875,9 @@ bool CNodeFirstInputIsPrimitive(const AnfNodePtr &node) {
 
 std::vector<AnfNodePtr> ExtendNodeUsers(const FuncGraphManagerPtr &front_func_graph_manager,
                                         const AnfNodePtr &front_node) {
-  auto node_users = front_func_graph_manager->node_users();
-  auto users = node_users[front_node];
+  auto &users = front_func_graph_manager->node_users()[front_node];
   std::vector<AnfNodePtr> result;
-  for (auto user : users) {
+  for (auto &user : users) {
     if (IsPrimitiveCNode(user.first, prim::kPrimControlDepend)) {
       continue;
     }

mindspore/ccsrc/frontend/optimizer/irpass/incorporate_getitem.h

@@ -433,12 +433,12 @@ class IncorporateGetitemSwitch : public AnfVisitor {
     MS_EXCEPTION_IF_NULL(switch_call_cnode);
     auto manager = fg->manager();
     MS_EXCEPTION_IF_NULL(manager);
-    auto node_users_map = manager->node_users();
+    auto &node_users_map = manager->node_users();
     auto it = node_users_map.find(switch_call);
     if (it == node_users_map.end()) {
       return false;
     }
-    auto node_users = it->second;
+    auto &node_users = it->second;
     // If switch was used by more than 1 tuple_getitem nodes, this pass shouldn't be execute.s
     auto tuple_getitem_num = std::count_if(node_users.begin(), node_users.end(), [](std::pair<AnfNodePtr, int> &user) {
       return IsPrimitiveCNode(user.first, prim::kPrimTupleGetItem);

mindspore/ccsrc/frontend/optimizer/irpass/updatestate_eliminate.cc

@@ -291,6 +291,50 @@ AnfNodePtr MakeTupleForSameNodes(const FuncGraphPtr &fg, const CNodePtr &old_upd
   return make_tuple;
 }
 
+// Remove all nodes related to UpdateStates, if they're redundant.
+void EliminateUselessNodesForUpdateStates(const std::vector<CNodePtr> &update_states) {
+  if (update_states.empty()) {
+    return;
+  }
+  auto mgr = GetManager(update_states[0]);
+
+  // 1. Remove the use of UpdateState nodes, except the last one.
+  for (auto i = update_states.size() - 1; i > 0; i--) {
+    auto &us = update_states[i];
+    mgr->Replace(us, us->input(kInputIndex));
+  }
+
+  // 2. Remove the Depend users of last UpdateState node.
+  auto &node_users = mgr->node_users();
+  auto iter = node_users.find(update_states[0]);
+  if (iter == node_users.end()) {
+    return;
+  }
+  auto &us_users = iter->second;
+  if (us_users.size() < 2) {
+    return;
+  }
+  std::vector<AnfNodePtr> depend_nodes;
+  for (auto &user : us_users) {
+    if (IsPrimitiveCNode(user.first, prim::kPrimDepend) && user.second == kAttachIndex) {
+      depend_nodes.emplace_back(user.first);
+    }
+  }
+  if (depend_nodes.empty()) {
+    return;
+  }
+  ssize_t end = 0;
+  // If all users are Depend CNode.
+  if (depend_nodes.size() == us_users.size()) {
+    end = 1;
+  }
+  for (ssize_t i = depend_nodes.size() - 1; i >= end; i--) {
+    const auto &depend_node = depend_nodes[i];
+    const auto &depend_cnode = depend_node->cast<CNodePtr>();
+    mgr->Replace(depend_cnode, depend_cnode->input(kInputIndex));
+  }
+}
+
 // Eliminate UpdateStates for consecutive Loads.
 // Convert:
 //    x1 = Load(x1, u)
@@ -336,10 +380,9 @@ AnfNodePtr EliminateUpdateStateForLoads(const CNodePtr &old_update_state, const
       mgr->SetEdge(load, kAttachIndex, input_monad);
     }
   }
-  for (auto i = update_states.size() - 1; i > 0; i--) {
-    auto &us = update_states[i];
-    mgr->Replace(us, us->input(kInputIndex));
-  }
+
+  EliminateUselessNodesForUpdateStates(update_states);
+
   if (make_tuple_inputs.size() == 1) {
     // This should not happen.
     MS_LOG(WARNING) << "No loads for " << old_update_state->DebugString(2);

mindspore/ccsrc/frontend/parallel/pipeline_transformer/pipeline_transformer.cc

@@ -52,25 +52,24 @@ static bool IsInWhiteList(const CNodePtr &cnode) {
   return false;
 }
 
-static void SetGradTag(const AnfNodePtr &node, NodeUsersMap node_users_map) {
-  auto node_users = node_users_map[node];
+static void SetGradTag(const AnfNodePtr &node, const FuncGraphManagerPtr &manager) {
+  const auto &node_users = manager->node_users()[node];
   for (auto &user_pair : node_users) {
     auto user_node = user_pair.first;
     if (!user_node->grad()) {
       user_node->set_grad(true);
-      SetGradTag(user_node, node_users_map);
+      SetGradTag(user_node, manager);
     }
   }
 }
 
 void PipelineTransformer::LabelRequiredGradCNode() {
   auto parameters = root_->parameters();
-  auto node_users_map = manager_->node_users();
   for (auto parameter : parameters) {
     if (!ParameterRequireGrad(parameter)) {
       continue;
     }
-    SetGradTag(parameter, node_users_map);
+    SetGradTag(parameter, manager_);
   }
 }
 
@@ -243,7 +242,7 @@ void PipelineTransformer::DoBroadCast(const FuncGraphPtr &func) {
   while (need_coloring) {
     need_coloring = false;
     auto all_nodes = func->nodes();
-    auto node_users = manager_->node_users();
+    auto &node_users = manager_->node_users();
     for (auto &node : all_nodes) {
       if (node->isa<CNode>() || node->stage() == -1) {
         continue;

mindspore/ccsrc/runtime/device/ascend/tasksink/task_generator.cc

@@ -58,7 +58,7 @@ void TaskGenerator::LaunchAddrCleanAkgKernel(const CNodePtr &anf_node_ptr, Addre
     MS_EXCEPTION_IF_NULL(graph);
     auto manager = graph->manager();
     MS_EXCEPTION_IF_NULL(manager);
-    auto node_users = manager->node_users();
+    auto &node_users = manager->node_users();
     if (node_users[anf_node_ptr].empty()) {
       MS_LOG(EXCEPTION) << "Node users of " << anf_node_ptr->ToString() << " is empty.";
     }

tests/ut/cpp/ir/manager_test.cc

@@ -391,7 +391,7 @@ TEST_F(TestManager, test_nested_manual) {
   ASSERT_EQ(2, f->nodes().size());
   ASSERT_EQ(1, g->nodes().size());
 
-  auto users = mng->node_users();
+  auto &users = mng->node_users();
   for (auto& iter : users) {
     ASSERT_EQ(1, iter.second.size());
   }