Hack to help MKLDNN avoid ref convolution (#669)

src/ngraph/runtime/cpu/cpu_emitter.cpp

@@ -2197,6 +2197,11 @@ namespace ngraph
                         runtime::cpu::mkldnn_utils::get_input_mkldnn_format(node, 0);
                     auto weights_format =
                         runtime::cpu::mkldnn_utils::get_input_mkldnn_format(node, 1);
+                    // HACK to help MKLDNN pick the right implementation
+                    if (weights_format == mkldnn::memory::format::nchw)
+                    {
+                        weights_format = mkldnn::memory::format::oihw;
+                    }
                     auto output_format =
                         runtime::cpu::mkldnn_utils::get_output_mkldnn_format(node, 0);
 
@@ -2341,8 +2346,15 @@ namespace ngraph
                     }
 
                     auto& mkldnn_emitter = external_function->get_mkldnn_emitter();
-                    auto weights_desc = mkldnn_emitter->build_memory_descriptor(
-                        args[0], runtime::cpu::mkldnn_utils::get_input_mkldnn_format(node, 0));
+                    // HACK to help MKLDNN pick the right implementation
+                    auto weights_format =
+                        runtime::cpu::mkldnn_utils::get_input_mkldnn_format(node, 0);
+                    if (weights_format == mkldnn::memory::format::nchw)
+                    {
+                        weights_format = mkldnn::memory::format::oihw;
+                    }
+                    auto weights_desc =
+                        mkldnn_emitter->build_memory_descriptor(args[0], weights_format);
                     auto delta_desc = mkldnn_emitter->build_memory_descriptor(
                         args[1], runtime::cpu::mkldnn_utils::get_input_mkldnn_format(node, 1));
                     auto result_desc = mkldnn_emitter->build_memory_descriptor(