From 67db9d3521ee3423f9d86004860662e12a601303 Mon Sep 17 00:00:00 2001
From: hedaoyuan <hedaoyuan@github.com>
Date: Wed, 13 Sep 2017 00:11:39 +0800
Subject: [PATCH] Refine the GemmConvKernel.

---
 paddle/operators/gemm_conv_op.h | 47 +++++++++++++++++++--------------
 1 file changed, 27 insertions(+), 20 deletions(-)

diff --git a/paddle/operators/gemm_conv_op.h b/paddle/operators/gemm_conv_op.h
index 6c72362195b..560dfd311f2 100644
--- a/paddle/operators/gemm_conv_op.h
+++ b/paddle/operators/gemm_conv_op.h
@@ -29,61 +29,68 @@ class GemmConvKernel : public framework::OpKernel {
  public:
   void Compute(const framework::ExecutionContext& context) const override {
     const Tensor* input = context.Input<Tensor>("Input");
-    Tensor* filter = const_cast<Tensor*>(context.Input<Tensor>("Filter"));
+    // The filter will be reshaped in the calculations,
+    // so here use an assignment operation,
+    // that avoids modifying the variable in the Scope.
+    Tensor filter = *context.Input<Tensor>("Filter");
     Tensor* output = context.Output<Tensor>("Output");
     output->mutable_data<T>(context.GetPlace());
 
     std::vector<int> strides = context.Attr<std::vector<int>>("strides");
     std::vector<int> paddings = context.Attr<std::vector<int>>("paddings");
-    auto filter_dims = filter->dims();
 
     int batch_size = input->dims()[0];
     int input_channels = input->dims()[1];
-    int filter_height = filter->dims()[filter->dims().size() - 2];
-    int filter_width = filter->dims()[filter->dims().size() - 1];
+    int filter_height = filter.dims()[filter.dims().size() - 2];
+    int filter_width = filter.dims()[filter.dims().size() - 1];
+    int output_channels = output->dims()[1];
     int output_height = output->dims()[2];
     int output_width = output->dims()[3];
 
     paddle::operators::math::Im2ColFunctor<
         paddle::operators::math::ColFormat::kCFO, Place, T>
         im2col;
+    // use col_shape in the im2col calculation
     framework::DDim col_shape = {input_channels, filter_height, filter_width,
                                  output_height, output_width};
+    // use col_matrix_shape in the gemm calculation
+    framework::DDim col_matrix_shape = {
+        input_channels * filter_height * filter_width,
+        output_height * output_width};
     Tensor col;
     col.mutable_data<float>(col_shape, context.GetPlace());
-
-    auto* device_context =
-        const_cast<platform::DeviceContext*>(context.device_context_);
+    // col_matrix shares the same piece of data with col,
+    // but will be reshaped into a two-dimensional matrix shape
+    // to call the matrix multiplication interface.
+    Tensor col_matrix = col;
+    col_matrix.Resize(col_matrix_shape);
 
     framework::DDim input_shape = {input->dims()[1], input->dims()[2],
                                    input->dims()[3]};
     framework::DDim filter_matrix_shape = {
-        filter->dims()[0],
-        filter->dims()[1] * filter->dims()[2] * filter->dims()[3]};
-    framework::DDim col_matrix_shape = {
-        input_channels * filter_height * filter_width,
-        output_height * output_width};
-    framework::DDim output_matrix_shape = {
-        output->dims()[1], output->dims()[2] * output->dims()[3]};
-    filter->Resize(filter_matrix_shape);
+        output_channels, framework::product(filter.dims()) / output_channels};
+    filter.Resize(filter_matrix_shape);
+
+    framework::DDim output_matrix_shape = {output_channels,
+                                           output_height * output_width};
+
+    auto* device_context =
+        const_cast<platform::DeviceContext*>(context.device_context_);
 
     // convolution operator: im2col + gemm
     for (int i = 0; i < batch_size; i++) {
       // im2col
       Tensor in_slice = input->Slice<T>(i, i + 1);
       in_slice.Resize(input_shape);
-      col.Resize(col_shape);
       im2col(in_slice, col, strides[0], strides[1], paddings[0], paddings[1],
              device_context);
 
       // gemm
       Tensor out_slice = output->Slice<T>(i, i + 1);
       out_slice.Resize(output_matrix_shape);
-      col.Resize(col_matrix_shape);
-      math::matmul<Place, T>(*filter, false, col, false, T(1.0), &out_slice,
-                             T(0.0), device_context);
+      math::matmul<Place, T>(filter, false, col_matrix, false, T(1.0),
+                             &out_slice, T(0.0), device_context);
     }
-    filter->Resize(filter_dims);
   }
 };
 
-- 
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