[ONNX] Change default broadcast dim value, gemm improvement (#2638)

* [ONNX] Change default broadcast dim value, gemm improvement

* update comments: ones -> zeros

src/ngraph/frontend/onnx_import/op/gemm.cpp

@@ -19,7 +19,6 @@
 #include "ngraph/frontend/onnx_import/utils/broadcasting.hpp"
 #include "ngraph/frontend/onnx_import/utils/reshape.hpp"
 #include "ngraph/op/add.hpp"
-#include "ngraph/op/broadcast.hpp"
 #include "ngraph/op/constant.hpp"
 #include "ngraph/op/dot.hpp"
 #include "ngraph/op/multiply.hpp"

src/ngraph/frontend/onnx_import/utils/broadcasting.cpp

@@ -44,10 +44,10 @@ ngraph::Shape calculate_broadcast_shape(ngraph::Shape left_shape, ngraph::Shape
     auto right_rank = right_shape.size();
     auto max_rank = std::max(left_rank, right_rank);
 
-    // left-pad the left_shape with ones
-    left_shape.insert(std::begin(left_shape), max_rank - left_rank, 1);
-    // left-pad the right_shape with ones
-    right_shape.insert(std::begin(right_shape), max_rank - right_rank, 1);
+    // left-pad the left_shape with zeros
+    left_shape.insert(std::begin(left_shape), max_rank - left_rank, 0);
+    // left-pad the right_shape with zeros
+    right_shape.insert(std::begin(right_shape), max_rank - right_rank, 0);
 
     for (std::size_t index = 0; index < max_rank; ++index)
     {