test=develop, fix cpu running error

paddle/fluid/operators/distributed/parameter_prefetch.h

@@ -39,9 +39,6 @@ void prefetch_with_reconstruct(const std::string& id_name,
                                const framework::ExecutionContext& context,
                                const framework::Scope& scope,
                                framework::LoDTensor* original) {
-  platform::DeviceContextPool& pool = platform::DeviceContextPool::Instance();
-  auto& actual_ctx = *pool.Get(context.GetPlace());
-
   prefetch(id_name, out_name, table_names, epmap, height_sections, context,
            scope);
   auto& out = scope.FindVar(out_name)->Get<framework::LoDTensor>();
@@ -54,23 +51,30 @@ void prefetch_with_reconstruct(const std::string& id_name,
   if (!platform::is_cpu_place(ids.place())) {
     is_on_cpu_place = false;
   }
-
-  for (int64_t i = 0; i < ids.numel(); i++) {
-    const T* out_rows = out_value + original_width * i;
-    T* original_row = original_value + original_width * ids.data<int64_t>()[i];
-    if (is_on_cpu_place) {
+  if (is_on_cpu_place) {
+    for (int64_t i = 0; i < ids.numel(); i++) {
+      const T* out_rows = out_value + original_width * i;
+      T* original_row =
+          original_value + original_width * ids.data<int64_t>()[i];
       std::memcpy(original_row, out_rows, original_width * sizeof(T));
-    } else {
+    }
+  } else {
 #ifndef PADDLE_WITH_CUDA
-      PADDLE_THROW("paddle is not compiled with CUDA!");
+    PADDLE_THROW("paddle is not compiled with CUDA!");
 #else
+    platform::DeviceContextPool& pool = platform::DeviceContextPool::Instance();
+    auto& actual_ctx = *pool.Get(context.GetPlace());
+    for (int64_t i = 0; i < ids.numel(); i++) {
+      const T* out_rows = out_value + original_width * i;
+      T* original_row =
+          original_value + original_width * ids.data<int64_t>()[i];
       auto stream =
           static_cast<platform::CUDADeviceContext*>(&actual_ctx)->stream();
       memory::Copy(boost::get<platform::CUDAPlace>(ids.place()), original_row,
                    platform::CPUPlace(), out_rows, original_width * sizeof(T),
                    stream);
-#endif
     }
+#endif
   }
 }