!1698 bugfix:get nullptr from graph manager

Merge pull request !1698 from zyli2020/r0.3

mindspore/ccsrc/pre_activate/mem_reuse/mem_swap_manager.cc

@@ -65,6 +65,7 @@ void MemSwapManager::Init(const mindspore::session::KernelGraph *kernel_graph) {
 void MemSwapManager::SaveUserKernelTopoOrder(const mindspore::session::KernelGraph *kernel_graph) {
   MS_EXCEPTION_IF_NULL(kernel_graph);
   FuncGraphManagerPtr manager = kernel_graph->manager();
+  MS_EXCEPTION_IF_NULL(manager);
   NodeUsersMap user_map = manager->node_users();
   for (const auto &kernel : execution_order_) {
     auto iter = user_map.find(kernel);

mindspore/ccsrc/session/session_basic.cc

@@ -590,6 +590,7 @@ KernelGraphPtr SessionBasic::ConstructKernelGraph(const AnfNodePtrList &lst, con
   graph->set_output(ConstructOutput(outputs, graph));
   MS_EXCEPTION_IF_NULL(context_);
   FuncGraphManagerPtr manager = MakeManager({graph});
+  context_->AddManager(manager);
   if (manager) {
     manager->AddFuncGraph(graph);
     graph->set_manager(manager);

mindspore/ccsrc/session/session_context.h

@@ -37,8 +37,10 @@ class Context : public pipeline::ResourceBase {
 
   uint32_t device_id() const { return device_id_; }
   static std::shared_ptr<Context> GetInstance();
+  void AddManager(const FuncGraphManagerPtr &m) { manager_list_.push_back(m); }
 
  private:
+  std::vector<FuncGraphManagerPtr> manager_list_;
   std::string target_;
   uint32_t device_id_;
 };