add prefetch in nce

paddle/fluid/operators/nce_op.h

@@ -26,6 +26,10 @@ limitations under the License. */
 #include "paddle/fluid/operators/math/sampler.h"
 #include "unsupported/Eigen/CXX11/Tensor"
 
+#ifdef PADDLE_WITH_DISTRIBUTE
+#include "paddle/fluid/operators/distributed/parameter_prefetch.h"
+#endif
+
 namespace paddle {
 namespace operators {
 
@@ -166,8 +170,8 @@ class NCEKernel : public framework::OpKernel<T> {
       auto height_sections = context.Attr<std::vector<int>>("height_sections");
       auto table_names = context.Attr<std::vector<std::string>>("table_names");
 
-      framework::Variable *ids = local_scope.Var("Ids");
-      framework::Variable *weight = local_scope.Var("Weight");
+      local_scope.Var("Ids");
+      local_scope.Var("Weight");
 
 #ifdef PADDLE_WITH_DISTRIBUTE
       operators::distributed::prefetch("Ids", "Weight", table_names, epmap,