update MergeAdd for selected_rows_functor.cu

paddle/fluid/operators/math/selected_rows_functor.cu

@@ -296,6 +296,52 @@ struct MergeAdd<platform::CUDADeviceContext, T> {
         out.mutable_rows()->CUDAMutableData(context.GetPlace()),
         out.rows().size(), input_width);
   }
+
+  void operator()(const platform::CUDADeviceContext& context,
+                  const std::vector<const framework::SelectedRows*>& inputs,
+                  framework::SelectedRows* output) {
+    PADDLE_ENFORCE_GT(inputs.size(), 0, "should have at least one input");
+    auto input_width = inputs[0]->value().dims()[1];
+    auto input_height = inputs[0]->height();
+    framework::SelectedRows& out = *output;
+    std::set<int64_t> merged_row_set;
+    for (auto* input : inputs) {
+      PADDLE_ENFORCE_EQ(input_width, input->value().dims()[1],
+                        "all input should have same "
+                        "dimension except for the first one");
+      PADDLE_ENFORCE_EQ(input_height, input->height(),
+                        "all input should have same height");
+      merged_row_set.insert(input->rows().begin(), input->rows().end());
+    }
+    std::vector<int64_t> merge_rows(merged_row_set.begin(),
+                                    merged_row_set.end());
+
+    out.set_rows(merge_rows);
+    out.set_height(input_height);
+    out.mutable_value()->mutable_data<T>(
+        framework::make_ddim(
+            {static_cast<int64_t>(merge_rows.size()), input_width}),
+        context.GetPlace());
+
+    math::SetConstant<platform::CPUDeviceContext, T> constant_functor;
+    constant_functor(context, out.mutable_value(), 0.0);
+
+    auto* out_data = out.mutable_value()->data<T>();
+
+    const int block_size = 256;
+    dim3 threads(block_size, 1);
+
+    for (auto* input : inputs) {
+      auto* input_data = input->value().data<T>();
+      auto& input_rows = input->rows();
+      dim3 grid1(input_rows.size(), 1);
+
+      MergeAddKernel<T, 256><<<grid1, threads, 0, context.stream()>>>(
+          input_data, input_rows.CUDAData(context.GetPlace()), out_data,
+          out.mutable_rows()->CUDAMutableData(context.GetPlace()),
+          out.rows().size(), input_width);
+    }
+  }
 };
 
 template struct MergeAdd<platform::CUDADeviceContext, float>;