optimization for about 2x speedup (#2036)

* optimization for about 2x speedup

* more optimizations

src/ngraph/coordinate_transform.cpp

@@ -45,6 +45,7 @@ CoordinateTransform::CoordinateTransform(const Shape& source_shape,
     , m_target_padding_below(target_padding_below)
     , m_target_padding_above(target_padding_above)
     , m_target_dilation_strides(target_dilation_strides)
+    , m_end_iterator(Shape(), true)
 {
     m_n_axes = source_shape.size();
 

src/ngraph/coordinate_transform.hpp

@@ -93,8 +93,7 @@ namespace ngraph
         };
 
         Iterator begin() noexcept { return Iterator(m_target_shape); }
-        Iterator end() noexcept { return Iterator(m_target_shape, true); }
-    private:
+        Iterator end() noexcept { return m_end_iterator; }
         size_t index_source(const Coordinate& c) const;
         static Strides default_strides(size_t n_axes);
         static CoordinateDiff default_padding(size_t n_axes);
@@ -113,5 +112,6 @@ namespace ngraph
 
         Shape m_target_shape;
         size_t m_n_axes;
+        Iterator m_end_iterator;
     };
 }

src/ngraph/runtime/reference/convolution.hpp

@@ -59,7 +59,7 @@ namespace ngraph
                 // At the outermost level we will walk over every output coordinate O.
                 CoordinateTransform output_transform(out_shape);
 
-                for (Coordinate out_coord : output_transform)
+                for (const Coordinate& out_coord : output_transform)
                 {
                     // Our output coordinate O will have the form:
                     //
@@ -169,9 +169,10 @@ namespace ngraph
 
                     CoordinateTransform::Iterator input_it = input_batch_transform.begin();
                     CoordinateTransform::Iterator filter_it = filter_transform.begin();
+                    CoordinateTransform::Iterator input_it_end = input_batch_transform.end();
+                    CoordinateTransform::Iterator filter_it_end = filter_transform.end();
 
-                    while (input_it != input_batch_transform.end() &&
-                           filter_it != filter_transform.end())
+                    while (input_it != input_it_end && filter_it != filter_it_end)
                     {
                         const Coordinate& input_batch_coord = *input_it;
                         Coordinate filter_coord = *filter_it;