concat support data as input

paddle/fluid/operators/concat_op.h

@@ -60,34 +60,45 @@ template <typename DeviceContext, typename T>
 class ConcatGradKernel : public framework::OpKernel<T> {
  public:
   void Compute(const framework::ExecutionContext& ctx) const {
-    auto* in = ctx.Input<framework::Tensor>(framework::GradVarName("Out"));
+    auto* out_grad =
+        ctx.Input<framework::Tensor>(framework::GradVarName("Out"));
+    auto ins = ctx.MultiInput<framework::Tensor>("X");
+    auto out_var_names = ctx.Outputs(framework::GradVarName("X"));
     auto outs = ctx.MultiOutput<framework::Tensor>(framework::GradVarName("X"));
     int64_t axis = static_cast<int64_t>(ctx.Attr<int>("axis"));
 
+    // get output tensor that the name is not kEmptyVarName
+    std::vector<framework::Tensor*> outputs;
+    for (size_t j = 0; j < outs.size(); ++j) {
+      if (out_var_names[j] != framework::kEmptyVarName) {
+        outs[j]->mutable_data<T>(ctx.GetPlace());
+        outputs.push_back(outs[j]);
+      } else {
+        outputs.push_back(nullptr);
+      }
+    }
+
     // Sometimes direct copies will be faster, this maybe need deeply analysis.
     if (axis == 0 && outs.size() < 10) {
       size_t input_offset = 0;
-      auto in_stride = framework::stride_numel(in->dims());
+      const auto in_stride = framework::stride_numel(out_grad->dims());
 
-      for (auto& out : outs) {
-        out->mutable_data<T>(ctx.GetPlace());
-        auto out_stride = framework::stride_numel(out->dims());
-        StridedNumelCopyWithAxis<T>(ctx.device_context(), axis, out->data<T>(),
-                                    out_stride, in->data<T>() + input_offset,
-                                    in_stride, out_stride[axis]);
+      for (size_t i = 0; i < outs.size(); ++i) {
+        auto out_stride = framework::stride_numel(ins[i]->dims());
+        auto* out = outputs[i];
+        if (out != nullptr) {
+          StridedNumelCopyWithAxis<T>(
+              ctx.device_context(), axis, out->data<T>(), out_stride,
+              out_grad->data<T>() + input_offset, in_stride, out_stride[axis]);
+        }
         input_offset += out_stride[axis];
       }
     } else {
-      std::vector<framework::Tensor> outputs(outs.size());
-      for (size_t j = 0; j < outs.size(); ++j) {
-        outs[j]->mutable_data<T>(ctx.GetPlace());
-        outputs[j] = *outs[j];
-      }
-
       auto& dev_ctx = ctx.template device_context<DeviceContext>();
       paddle::operators::math::ConcatGradFunctor<DeviceContext, T>
           concat_grad_functor;
-      concat_grad_functor(dev_ctx, *in, static_cast<int>(axis), &outputs);
+      concat_grad_functor(dev_ctx, *out_grad, ins, static_cast<int>(axis),
+                          &outputs);
     }
   }
 };

paddle/fluid/operators/math/concat.cc

@@ -70,35 +70,40 @@ template <typename T>
 class ConcatGradFunctor<platform::CPUDeviceContext, T> {
  public:
   void operator()(const platform::CPUDeviceContext& context,
-                  const framework::Tensor& input, const int axis,
-                  std::vector<framework::Tensor>* outputs) {
+                  const framework::Tensor& input,
+                  const std::vector<const framework::Tensor*>& ref_inputs,
+                  const int axis, std::vector<framework::Tensor*>* outputs) {
     // TODO(zcd): Add input data validity checking
-    int num = outputs->size();
+    size_t num = outputs->size();
 
     int input_rows = 1;
-    auto dim_0 = outputs->at(0).dims();
+    auto dim_0 = ref_inputs[0]->dims();
     for (int i = 0; i < axis; ++i) {
       input_rows *= dim_0[i];
     }
+
     int input_cols = 0;
 
     std::vector<int64_t> output_cols(outputs->size());
-    for (int i = 0; i < num; ++i) {
-      int t_cols = outputs->at(i).numel() / input_rows;
+    for (size_t i = 0; i < num; ++i) {
+      int t_cols = ref_inputs[i]->numel() / input_rows;
       input_cols += t_cols;
       output_cols[i] = t_cols;
     }
     auto cpu_place = boost::get<platform::CPUPlace>(context.GetPlace());
 
     // computation
-    for (int k = 0; k < input_rows; ++k) {
+    for (size_t k = 0; k < input_rows; ++k) {
       const T* src_ptr = input.data<T>() + k * input_cols;
       int col_idx = 0;
       for (int j = 0; j < num; ++j) {
         int col_len = output_cols[j];
-        T* dst_ptr = outputs->at(j).data<T>() + k * col_len;
+        auto* out_tensor = (*outputs)[j];
+        if (out_tensor != nullptr) {
+          T* dst_ptr = out_tensor->data<T>() + k * col_len;
           memory::Copy(cpu_place, dst_ptr, cpu_place, src_ptr + col_idx,
                        sizeof(T) * col_len);
+        }
         col_idx += col_len;
       }
     }

paddle/fluid/operators/math/concat.h

@@ -57,7 +57,8 @@ template <typename DeviceContext, typename T>
 class ConcatGradFunctor {
  public:
   void operator()(const DeviceContext& context, const framework::Tensor& input,
-                  const int axis, std::vector<framework::Tensor>* outputs);
+                  const std::vector<const framework::Tensor*>& ref_inputs,
+                  const int axis, std::vector<framework::Tensor*>* outputs);
 };
 
 }  // namespace math