!11757 Fix do ub fusion with only one node

From: @irmo
Reviewed-by: @zhoufeng54,@kisnwang
Signed-off-by: @jjfeing

mindspore/ccsrc/backend/optimizer/ascend/buffer_fusion/matmul_eltwise_fusion_pass.cc

@@ -1,5 +1,5 @@
 /**
- * Copyright 2020 Huawei Technologies Co., Ltd
+ * Copyright 2020-2021 Huawei Technologies Co., Ltd
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,6 +33,9 @@ void MatmulEltwiseFusionPass::MatchMatmulEltwise(const CNodePtr &cnode, const An
   MS_EXCEPTION_IF_NULL(candidate_fusion);
   auto manager = kernel_graph.manager();
   MS_EXCEPTION_IF_NULL(manager);
+  if (fusion_id_allocator->HasFusionIdAttr(relu_input)) {
+    return;
+  }
   std::vector<int64_t> output_used_num{SizeToLong(manager->node_users()[relu_input].size())};
   AnfAlgo::SetNodeAttr(kAttrOutputUsedNum, MakeValue(output_used_num), relu_input);
   std::unordered_set<AnfNodePtr> record{cnode, relu_input};

mindspore/ccsrc/backend/optimizer/ascend/buffer_fusion/ub_pattern_fusion.cc

@@ -1,5 +1,5 @@
 /**
- * Copyright 2019 Huawei Technologies Co., Ltd
+ * Copyright 2019-2021 Huawei Technologies Co., Ltd
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -405,6 +405,9 @@ bool UbPatternFusion::ReplaceFusionOp(std::unordered_map<int64_t, BufferFusionIn
                                       session::KernelGraph *kernel_graph) const {
   MS_EXCEPTION_IF_NULL(buffer_fusion_infos);
   auto buffer_fusion_info = (*buffer_fusion_infos)[fusion_id];
+  if (buffer_fusion_info.anf_nodes.size() < 2) {
+    return false;
+  }
   TraceGuard guard(std::make_shared<TraceOpt>(buffer_fusion_info.anf_nodes[0]->debug_info()));
   auto buffer_fusion = CreateFusionOp(buffer_fusion_info.inputs_list, buffer_fusion_info.outputs_list,
                                       buffer_fusion_info.anf_nodes, kernel_graph);