sum op support empty selected rows as input

paddle/fluid/operators/math/selected_rows_functor.cc

@@ -195,6 +195,10 @@ struct SelectedRowsAddToTensor<platform::CPUDeviceContext, T> {
   void operator()(const platform::CPUDeviceContext& context,
                   const framework::SelectedRows& input1,
                   framework::Tensor* input2) {
+    if (input1.rows().size() == 0) {
+      LOG(WARNING) << "input selected rows is empty!";
+      return;
+    }
     auto in1_height = input1.height();
     auto in2_dims = input2->dims();
     PADDLE_ENFORCE_EQ(in1_height, in2_dims[0]);

paddle/fluid/operators/sum_op.cc

@@ -41,7 +41,9 @@ class SumOp : public framework::OperatorWithKernel {
       return;  // skip runtime infershape when is tensor array;
     }
 
+    auto x_var_types = ctx->GetInputsVarType("X");
     auto x_dims = ctx->GetInputsDim("X");
+
     size_t N = x_dims.size();
     PADDLE_ENFORCE_GT(N, 0, "Input tensors count should > 0.");
     if (N == 1) {
@@ -49,7 +51,11 @@ class SumOp : public framework::OperatorWithKernel {
     }
 
     framework::DDim in_dim({0});
-    for (auto& x_dim : x_dims) {
+    for (size_t i = 0; i < x_dims.size(); ++i) {
+      if (x_var_types[i] == framework::proto::VarType::SELECTED_ROWS) {
+        continue;
+      }
+      auto& x_dim = x_dims[i];
       if (framework::product(x_dim) == 0) {
         continue;
       }