Remove redundant process of keeping roots.

mindspore/ccsrc/ir/func_graph_cloner.h

@@ -59,7 +59,7 @@ class Cloner {
 
   // Map of replicate nodes and graphs
   std::unordered_map<AnfNodePtr, AnfNodePtr> *cloned_node() { return &repl_node_; }
-  std::unordered_map<FuncGraphPtr, FuncGraphPtr> cloned_func_graph() { return repl_func_graph_; }
+  std::unordered_map<FuncGraphPtr, FuncGraphPtr> &cloned_func_graph() { return repl_func_graph_; }
 
   // Scope of cloned graphs
   void set_scope(const ScopePtr &scope) { scope_ = scope; }

mindspore/ccsrc/optimizer/optimizer.h

@@ -185,13 +185,6 @@ class Optimizer : public std::enable_shared_from_this<Optimizer> {
         break;
       }
     }
-
-    auto keep_root = [&func_graph, this]() {
-      std::vector<FuncGraphPtr> func_graphs;
-      func_graphs.push_back(func_graph);
-      resource_->manager()->KeepRoots(func_graphs);
-    };
-    use_profile ? WITH(MsProfile::GetProfile()->Step("keep_roots")) keep_root : keep_root();
     return func_graph;
   }