disable ctrl edge for MdUpdt task in prediction (#1006)

Former-commit-id: b2d088d4

oneflow/core/graph/task_node.cpp

@@ -141,7 +141,11 @@ int64_t TaskNode::MemZoneId121() const {
 }
 
 void TaskNode::BuildCtrlRegstDescIfNeed(TaskNode* dst_node) {
-  if (IsMeaningLess() || dst_node->IsMeaningLess()) return;
+  if (IsMeaningLess() || dst_node->IsMeaningLess()) { return; }
+  if (!Global<JobDesc>::Get()->IsTrain() && GetTaskType() == kNormalMdUpdt
+      && dst_node->GetTaskType() == kNormalMdUpdt) {
+    return;
+  }
   const auto& dst_ancestors = dst_node->ancestors();
   if (dst_ancestors.find(this) != dst_ancestors.end()) return;
   RegstDescTypeProto regst_desc_type;