refine force syncbn (#52860)

paddle/fluid/eager/backward.cc

@@ -372,32 +372,31 @@ std::vector<paddle::Tensor> RunBackward(
 
         auto add_next_node_func = [&node_in_degree_map,
                                    &queue](GradNodeBase* next_node) {
-          if (node_in_degree_map[next_node] == 0) {
-            if (dynamic_cast<egr::GradNodeAccumulation*>(next_node)) {
-              queue.push_front(std::move(next_node));
-            } else {
-              queue.push_back(std::move(next_node));
-            }
+          if (dynamic_cast<egr::GradNodeAccumulation*>(next_node)) {
+            queue.push_front(std::move(next_node));
+          } else {
+            queue.push_back(std::move(next_node));
           }
         };
-
-        if (force_sequential_nodes_set.count(next_node)) {
-          if (force_sequential_nodes_queue.front() == next_node) {
-            force_sequential_nodes_queue.pop_front();
-            add_next_node_func(next_node);
-            while (ready_force_sequential_nodes.count(
-                force_sequential_nodes_queue.front())) {
-              ready_force_sequential_nodes.erase(
-                  force_sequential_nodes_queue.front());
-              add_next_node_func(force_sequential_nodes_queue.front());
+        if (node_in_degree_map[next_node] == 0) {
+          if (force_sequential_nodes_set.count(next_node)) {
+            if (force_sequential_nodes_queue.front() == next_node) {
               force_sequential_nodes_queue.pop_front();
+              add_next_node_func(next_node);
+              while (ready_force_sequential_nodes.count(
+                  force_sequential_nodes_queue.front())) {
+                ready_force_sequential_nodes.erase(
+                    force_sequential_nodes_queue.front());
+                add_next_node_func(force_sequential_nodes_queue.front());
+                force_sequential_nodes_queue.pop_front();
+              }
+            } else {
+              ready_force_sequential_nodes.insert(next_node);
+              continue;
             }
           } else {
-            ready_force_sequential_nodes.insert(next_node);
-            continue;
+            add_next_node_func(next_node);
           }
-        } else {
-          add_next_node_func(next_node);
         }
       }
     }