!14855 fix a allreduce bug in pynative mode

From: @lvchangquan
Reviewed-by: @zhoufeng54,@jjfeing
Signed-off-by: @jjfeing

mindspore/ccsrc/backend/session/session_basic.cc

@@ -2294,6 +2294,7 @@ std::vector<uint32_t> GenerateBucketSizeList(const KernelGraphPtr &graph, const
 }
 
 void PreProcessOnSplitIndex(const KernelGraphPtr &graph, vector<uint32_t> *split_index) {
+  MS_EXCEPTION_IF_NULL(split_index);
   if (split_index->empty()) {
     return;
   }
@@ -2313,6 +2314,15 @@ void PreProcessOnSplitIndex(const KernelGraphPtr &graph, vector<uint32_t> *split
 void SessionBasic::InitAllBucket(const KernelGraphPtr &graph) {
   MS_EXCEPTION_IF_NULL(graph);
   MS_LOG(INFO) << "Init Bucket start, graph_id:" << graph->graph_id();
+  auto ms_context = MsContext::GetInstance();
+  MS_EXCEPTION_IF_NULL(ms_context);
+  const bool pynative_mode = (ms_context->get_param<int>(MS_CTX_EXECUTION_MODE) == kPynativeMode);
+  auto parallel_context = parallel::ParallelContext::GetInstance();
+  MS_EXCEPTION_IF_NULL(parallel_context);
+  auto parallel_mode = parallel_context->parallel_mode();
+  if (!pynative_mode || parallel_mode != parallel::DATA_PARALLEL) {
+    return;
+  }
   SetGraphBpropAttr(graph);
 
   if (!graph->is_bprop()) {