!3969 benchmark cannot find output node bug add error log

Merge pull request !3969 from cjh9368/fix_benchmark_inf_bug

mindspore/lite/tools/benchmark/benchmark.cc

@@ -230,17 +230,25 @@ int Benchmark::CompareOutput() {
   for (const auto &calibTensor : calibData) {
     std::string nodeName = calibTensor.first;
     auto tensors = session->GetOutputsByName(nodeName);
-    for (auto tensor : tensors) {
-      MS_ASSERT(tensor->GetDataType() == DataType_DT_FLOAT);
-      MS_ASSERT(tensor->GetData() != nullptr);
-      float bias = CompareData(nodeName, tensor->shape(), static_cast<float *>(tensor->MutableData()));
-      if (bias >= 0) {
-        totalBias += bias;
-        totalSize++;
-      } else {
-        hasError = true;
-        break;
-      }
+    if (tensors.empty()) {
+      MS_LOG(ERROR) << "Cannot find output node: " << nodeName.c_str() << " , compare output data fail.";
+      return RET_ERROR;
+    }
+    // make sure tensor size is 1
+    if (tensors.size() != 1) {
+      MS_LOG(ERROR) << "Only support 1 tensor with a name now.";
+      return RET_ERROR;
+    }
+    auto &tensor = tensors.front();
+    MS_ASSERT(tensor->GetDataType() == DataType_DT_FLOAT);
+    MS_ASSERT(tensor->GetData() != nullptr);
+    float bias = CompareData(nodeName, tensor->shape(), static_cast<float *>(tensor->MutableData()));
+    if (bias >= 0) {
+      totalBias += bias;
+      totalSize++;
+    } else {
+      hasError = true;
+      break;
     }
   }