add backward gradient computation for op argsort (#22203)

* add backward gradient computation for op argsort test=developo

* use pre-commit test=develop

paddle/fluid/operators/argsort_op.cc

@@ -13,6 +13,7 @@ See the License for the specific language governing permissions and
 limitations under the License. */
 
 #include "paddle/fluid/operators/argsort_op.h"
+#include <memory>
 
 namespace paddle {
 namespace operators {
@@ -21,7 +22,7 @@ class ArgsortOp : public framework::OperatorWithKernel {
  public:
   using framework::OperatorWithKernel::OperatorWithKernel;
 
-  void InferShape(framework::InferShapeContext *ctx) const override {
+  void InferShape(framework::InferShapeContext* ctx) const override {
     PADDLE_ENFORCE(ctx->HasInput("X"),
                    "Input(X) of ArgsortOp should not be null.");
     PADDLE_ENFORCE(ctx->HasOutput("Out"),
@@ -49,6 +50,24 @@ class ArgsortOp : public framework::OperatorWithKernel {
   }
 };
 
+class ArgsortGradOp : public framework::OperatorWithKernel {
+ public:
+  using framework::OperatorWithKernel::OperatorWithKernel;
+
+  void InferShape(framework::InferShapeContext* ctx) const override {
+    ctx->SetOutputDim(framework::GradVarName("X"), ctx->GetInputDim("X"));
+    ctx->ShareLoD("X", /*-->*/ framework::GradVarName("X"));
+  }
+
+ protected:
+  framework::OpKernelType GetExpectedKernelType(
+      const framework::ExecutionContext& ctx) const override {
+    return framework::OpKernelType(OperatorWithKernel::IndicateVarDataType(
+                                       ctx, framework::GradVarName("Out")),
+                                   ctx.device_context());
+  }
+};
+
 class ArgsortOpMaker : public framework::OpProtoAndCheckerMaker {
  public:
   void Make() override {
@@ -83,16 +102,42 @@ Output(Indices) gives the sorted order along the given axis Attr(axis).
   }
 };
 
+template <typename T>
+class ArgsortGradOpMaker : public framework::SingleGradOpMaker<T> {
+ public:
+  using framework::SingleGradOpMaker<T>::SingleGradOpMaker;
+
+ protected:
+  std::unique_ptr<T> Apply() const override {
+    std::unique_ptr<T> op(new T());
+    op->SetType("argsort_grad");
+    op->SetInput("Indices", this->Output("Indices"));
+    op->SetInput("X", this->Input("X"));
+    op->SetInput(framework::GradVarName("Out"), this->OutputGrad("Out"));
+    op->SetOutput(framework::GradVarName("X"), this->InputGrad("X"));
+    op->SetAttrMap(this->Attrs());
+    return op;
+  }
+};
+
+DECLARE_NO_NEED_BUFFER_VARS_INFERENCE(ArgsortGradNoNeedBufferVarInference, "X");
+
 }  // namespace operators
 }  // namespace paddle
 
 namespace ops = paddle::operators;
-REGISTER_OPERATOR(
-    argsort, ops::ArgsortOp, ops::ArgsortOpMaker,
-    paddle::framework::EmptyGradOpMaker<paddle::framework::OpDesc>,
-    paddle::framework::EmptyGradOpMaker<paddle::imperative::OpBase>);
+REGISTER_OPERATOR(argsort, ops::ArgsortOp, ops::ArgsortOpMaker,
+                  ops::ArgsortGradOpMaker<paddle::framework::OpDesc>,
+                  ops::ArgsortGradOpMaker<paddle::imperative::OpBase>);
+REGISTER_OPERATOR(argsort_grad, ops::ArgsortGradOp,
+                  ops::ArgsortGradNoNeedBufferVarInference);
 REGISTER_OP_CPU_KERNEL(argsort,
                        ops::ArgsortKernel<paddle::platform::CPUPlace, float>,
                        ops::ArgsortKernel<paddle::platform::CPUPlace, double>,
                        ops::ArgsortKernel<paddle::platform::CPUPlace, int>,
                        ops::ArgsortKernel<paddle::platform::CPUPlace, int64_t>);
+REGISTER_OP_CPU_KERNEL(
+    argsort_grad, ops::ArgsortGradientKernel<paddle::platform::CPUPlace, float>,
+    ops::ArgsortGradientKernel<paddle::platform::CPUPlace, double>,
+    ops::ArgsortGradientKernel<paddle::platform::CPUPlace, int>,
+    ops::ArgsortGradientKernel<paddle::platform::CPUPlace, int64_t>);

paddle/fluid/operators/argsort_op.cu

@@ -58,6 +58,19 @@ static __global__ void FillIndex(T* indices, T num_rows, T num_cols) {
   }
 }
 
+template <typename T, typename IndType>
+static __global__ void FillGrad(const T* dO, const IndType* indices, T* dX,
+                                IndType num_rows, IndType num_cols) {
+  int col_id = threadIdx.x;
+  int row_id = blockIdx.x;
+
+  for (IndType j = row_id; j < num_rows; j += gridDim.x) {
+    for (IndType i = col_id; i < num_cols; i += blockDim.x) {
+      dX[j * num_cols + indices[j * num_cols + i]] = dO[j * num_cols + i];
+    }
+  }
+}
+
 // Sort by flag descending, True: descending. False: Ascending.
 // Default is false.
 template <typename T, typename IndType>
@@ -160,6 +173,35 @@ void ArgFullSort(const platform::CUDADeviceContext& ctx, const Tensor* input,
       temp_storage_bytes, cudaGetErrorString(err));
 }
 
+template <typename T, typename IndType>
+void ArgFullAssign(const platform::CUDADeviceContext& ctx, const Tensor* dO,
+                   const Tensor* indices, Tensor* dX, const IndType num_rows,
+                   const IndType num_cols) {
+  auto cu_stream = ctx.stream();
+
+  auto ComputeBlockSize = [](IndType col) {
+    if (col > 512)
+      return 1024;
+    else if (col > 256 && col <= 512)
+      return 512;
+    else if (col > 128 && col <= 256)
+      return 256;
+    else if (col > 64 && col <= 128)
+      return 128;
+    else
+      return 64;
+  };
+
+  int block_size = ComputeBlockSize(num_cols);
+
+  int maxGridDimX = ctx.GetCUDAMaxGridDimSize().x;
+  // actually, int num_rows < max_grid_size
+  int grid_size = num_rows < maxGridDimX ? num_rows : maxGridDimX;
+  FillGrad<<<grid_size, block_size, 0, cu_stream>>>(
+      dO->data<T>(), indices->data<IndType>(), dX->data<T>(), num_rows,
+      num_cols);
+}
+
 template <typename T>
 class ArgsortOpCUDAKernel : public framework::OpKernel<T> {
  public:
@@ -234,6 +276,81 @@ class ArgsortOpCUDAKernel : public framework::OpKernel<T> {
   }
 };
 
+template <typename T>
+class ArgsortGradOpCUDAKernel : public framework::OpKernel<T> {
+ public:
+  void Compute(const framework::ExecutionContext& ctx) const override {
+    auto* indices = ctx.Input<Tensor>("Indices");
+    auto* dX = ctx.Output<Tensor>(framework::GradVarName("X"));
+    auto* dO = ctx.Input<Tensor>(framework::GradVarName("Out"));
+    int axis = ctx.Attr<int>("axis");
+
+    dX->mutable_data<T>(ctx.GetPlace());
+    auto dxt = framework::EigenVector<T>::Flatten(*dX);
+    auto& place = *ctx.template device_context<platform::CUDADeviceContext>()
+                       .eigen_device();
+    dxt.device(place) = dxt.constant(static_cast<T>(0));
+    if (dO->numel() == 0) return;
+
+    auto in_dims = indices->dims();
+    axis = (axis < 0) ? (in_dims.size() + axis) : axis;
+
+    int64_t numel = indices->numel();
+
+    // Special case for full sort, speedup ~190x.
+    if (axis == -1 || axis + 1 == in_dims.size()) {
+      const int64_t input_height = framework::product(
+          framework::slice_ddim(in_dims, 0, in_dims.size() - 1));
+      const int64_t input_width = in_dims[in_dims.size() - 1];
+      const auto& dev_ctx = ctx.cuda_device_context();
+      ArgFullAssign<T, int64_t>(dev_ctx, dO, indices, dX, input_height,
+                                input_width);
+    } else {
+      // if not full sort, do transpose first
+      std::vector<int> trans;
+      for (int i = 0; i < axis; i++) {
+        trans.push_back(i);
+      }
+      trans.push_back(in_dims.size() - 1);
+      for (int i = axis + 1; i < in_dims.size() - 1; i++) {
+        trans.push_back(i);
+      }
+      trans.push_back(axis);
+      framework::DDim trans_dims(in_dims);
+      for (int i = 0; i < trans.size(); i++) {
+        trans_dims[i] = in_dims[trans[i]];
+      }
+
+      Tensor trans_dO;
+      trans_dO.mutable_data<T>(trans_dims, ctx.GetPlace());
+      Tensor trans_ind;
+      trans_ind.mutable_data<int64_t>(trans_dims, ctx.GetPlace());
+      int ndims = trans.size();
+      const auto& dev_ctx = ctx.cuda_device_context();
+      // Do transpose
+      TransCompute<platform::CUDADeviceContext, T>(ndims, dev_ctx, *dO,
+                                                   &trans_dO, trans);
+      TransCompute<platform::CUDADeviceContext, int64_t>(
+          ndims, dev_ctx, *indices, &trans_ind, trans);
+
+      const int64_t input_height = framework::product(
+          framework::slice_ddim(trans_dims, 0, trans_dims.size() - 1));
+      const int64_t input_width = trans_dims[trans_dims.size() - 1];
+
+      Tensor tmp_out;
+      tmp_out.mutable_data<T>(trans_dims, ctx.GetPlace());
+
+      ArgFullAssign<T, int64_t>(dev_ctx, &trans_dO, &trans_ind, &tmp_out,
+                                input_height, input_width);
+
+      // transpose back
+      TransCompute<platform::CUDADeviceContext, T>(ndims, dev_ctx, tmp_out, dX,
+                                                   trans);
+      return;
+    }
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle
 
@@ -243,3 +360,9 @@ REGISTER_OP_CUDA_KERNEL(
     paddle::operators::ArgsortOpCUDAKernel<int>,
     paddle::operators::ArgsortOpCUDAKernel<int64_t>,
     paddle::operators::ArgsortOpCUDAKernel<paddle::platform::float16>);
+REGISTER_OP_CUDA_KERNEL(
+    argsort_grad, paddle::operators::ArgsortGradOpCUDAKernel<float>,
+    paddle::operators::ArgsortGradOpCUDAKernel<double>,
+    paddle::operators::ArgsortGradOpCUDAKernel<int>,
+    paddle::operators::ArgsortGradOpCUDAKernel<int64_t>,
+    paddle::operators::ArgsortGradOpCUDAKernel<paddle::platform::float16>);

paddle/fluid/operators/argsort_op.h

@@ -68,6 +68,31 @@ static void FullSort(Type input_height, Type input_width, int input_dim,
     }
   }
 }
+
+template <typename T, typename Type>
+static void FullAssign(Type input_height, Type input_width, int input_dim,
+                       const framework::Tensor* input,
+                       const framework::Tensor* indices, T* t_out) {
+#ifdef PADDLE_WITH_MKLML
+#pragma omp parallel for
+#endif
+  for (Type i = 0; i < input_height; ++i) {
+    if (input_dim == 1) {
+      auto e_input = EigenVector<T>::Flatten(*input);
+      auto e_indices = EigenVector<Type>::Flatten(*indices);
+      for (Type j = 0; j < input_width; ++j) {
+        t_out[i * input_width + e_indices(j)] = e_input(e_indices(j));
+      }
+    } else {
+      auto e_input = EigenMatrix<T>::Reshape(*input, input_dim - 1);
+      auto e_indices = EigenMatrix<Type>::Reshape(*indices, input_dim - 1);
+      for (Type j = 0; j < input_width; ++j) {
+        t_out[i * input_width + e_indices(i, j)] = e_input(i, e_indices(i, j));
+      }
+    }
+  }
+}
+
 template <typename DeviceContext, typename T>
 class ArgsortKernel : public framework::OpKernel<T> {
  public:
@@ -142,5 +167,77 @@ class ArgsortKernel : public framework::OpKernel<T> {
   }
 };
 
+template <typename DeviceContext, typename T>
+class ArgsortGradientKernel : public framework::OpKernel<T> {
+ public:
+  void Compute(const framework::ExecutionContext& ctx) const override {
+    auto* indices = ctx.Input<Tensor>("Indices");
+    auto* dX = ctx.Output<Tensor>(framework::GradVarName("X"));
+    auto* dO = ctx.Input<Tensor>(framework::GradVarName("Out"));
+    int axis = ctx.Attr<int>("axis");
+
+    auto in_dims = indices->dims();
+    axis = (axis < 0) ? (in_dims.size() + axis) : axis;
+
+    dX->mutable_data<T>(ctx.GetPlace());
+    auto dxt = framework::EigenVector<T>::Flatten(*dX);
+    auto& place = *ctx.template device_context<platform::CPUDeviceContext>()
+                       .eigen_device();
+    dxt.device(place) = dxt.constant(static_cast<T>(0));
+    if (dO->numel() == 0) return;
+
+    // Do full assign
+    if (axis == -1 || axis + 1 == in_dims.size()) {
+      const int64_t input_height = framework::product(
+          framework::slice_ddim(in_dims, 0, in_dims.size() - 1));
+      const int64_t input_width = in_dims[in_dims.size() - 1];
+
+      FullAssign<T, int64_t>(input_height, input_width, in_dims.size(), dO,
+                             indices, dX->data<T>());
+    } else {
+      // If not full assign do transpose
+      std::vector<int> trans;
+      for (int i = 0; i < axis; i++) {
+        trans.push_back(i);
+      }
+      trans.push_back(in_dims.size() - 1);
+      for (int i = axis + 1; i < in_dims.size() - 1; i++) {
+        trans.push_back(i);
+      }
+      trans.push_back(axis);
+      framework::DDim trans_dims(in_dims);
+      for (size_t i = 0; i < trans.size(); i++) {
+        trans_dims[i] = in_dims[trans[i]];
+      }
+
+      Tensor trans_dO;
+      trans_dO.mutable_data<T>(trans_dims, ctx.GetPlace());
+      Tensor trans_ind;
+      trans_ind.mutable_data<int64_t>(trans_dims, ctx.GetPlace());
+      int ndims = trans.size();
+      auto& dev_ctx = ctx.template device_context<platform::CPUDeviceContext>();
+      // Do transpose
+      TransCompute<platform::CPUDeviceContext, T>(ndims, dev_ctx, *dO,
+                                                  &trans_dO, trans);
+      TransCompute<platform::CPUDeviceContext, int64_t>(
+          ndims, dev_ctx, *indices, &trans_ind, trans);
+
+      const int64_t input_height = framework::product(
+          framework::slice_ddim(trans_dims, 0, trans_dims.size() - 1));
+      const int64_t input_width = trans_dims[trans_dims.size() - 1];
+
+      Tensor tmp_out;
+      T* t_out = tmp_out.mutable_data<T>(trans_dims, ctx.GetPlace());
+
+      FullAssign<T, int64_t>(input_height, input_width, in_dims.size(),
+                             &trans_dO, &trans_ind, t_out);
+
+      // transpose back
+      TransCompute<platform::CPUDeviceContext, T>(ndims, dev_ctx, tmp_out, dX,
+                                                  trans);
+    }
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle

python/paddle/fluid/tests/unittests/test_argsort_op.py

@@ -48,7 +48,7 @@ class TestArgsortOp(OpTest):
         self.axis = -1
 
     def init_datatype(self):
-        self.dtype = "float32"
+        self.dtype = "float64"
 
     def init_direction(self):
         self.descending = False
@@ -56,6 +56,9 @@ class TestArgsortOp(OpTest):
     def test_check_output(self):
         self.check_output()
 
+    def test_check_grad(self):
+        self.check_grad(['X'], 'Out')
+
 
 class TestArgsortOpAxis0(TestArgsortOp):
     def init_axis(self):
@@ -146,5 +149,18 @@ class TestArgsortOpDescendingAxisNeg2(TestArgsortOpAxisNeg2):
         self.descending = True
 
 
+class TestArgsortOpFP32Axis(TestArgsortOp):
+    def init_datatype(self):
+        self.dtype = "float32"
+
+
+class TestArgsortOpFP32DescendingAxis(TestArgsortOp):
+    def init_datatype(self):
+        self.dtype = "float32"
+
+    def init_direction(self):
+        self.descending = True
+
+
 if __name__ == "__main__":
     unittest.main()