Fix bug

paddle/framework/backward.cc

@@ -158,8 +158,7 @@ static std::unique_ptr<OperatorBase> BackwardRecursive(
         }
         insert_position.push_back(
             {dup_op.back(),
-             OpRegistry::CreateOp(
-                 "sum", {{"X", {insert_add_x}}, {"X", {insert_add_y}}},
+             OpRegistry::CreateOp("sum", {{"X", {insert_add_x, insert_add_y}}},
                                   {{"Out", {insert_add_out}}}, {})});
       }
     }
@@ -200,7 +199,8 @@ static std::unique_ptr<OperatorBase> BackwardRecursive(
 
     // process recurrent gradient op as a special operator.
     if (forwardOp.Type() == "recurrent") {
-      // NOTE clean up cycle call somewhere (RNN's stepnet constains itself), or
+      // NOTE clean up cycle call somewhere (RNN's stepnet constains itself),
+      // or
       // this will result in infinite loop.
       const auto& rnnop =
           *static_cast<const operators::RecurrentOp*>(&forwardOp);