Check if circle exists in a graph.

mindspore/core/ir/graph_utils.cc

@@ -58,14 +58,32 @@ std::vector<AnfNodePtr> TopoSort(const AnfNodePtr &root, const SuccFunc &succ, c
       node->extra_seen_ = seen;
       continue;
     }
-    if (node->seen_ == seen && node->extra_seen_ != seen) {
-      MS_LOG(EXCEPTION) << "Graph exists cycle, node " << node->DebugString(2);
-    }
     node->seen_ = seen;
     if (incl == FOLLOW) {
       auto succs = succ(node);
-      (void)std::copy_if(succs.begin(), succs.end(), std::back_inserter(todo),
-                         [seen](const AnfNodePtr &next) { return next != nullptr && next->seen_ != seen; });
+      (void)std::copy_if(succs.begin(), succs.end(), std::back_inserter(todo), [seen, todo](const AnfNodePtr &next) {
+        if (next == nullptr || next->extra_seen_ == seen) {
+          return false;
+        }
+        if (next->seen_ != seen) {
+          return true;
+        }
+        if (next->func_graph()->get_return() == next) {
+          return false;
+        }
+        // To dump all nodes in a circle.
+        MS_LOG(ERROR) << "Graph cycle exists. Circle is: ";
+        size_t pos = 0;
+        auto circle_node_it = std::find(todo.begin(), todo.end(), next);
+        for (; circle_node_it != todo.end(); circle_node_it++) {
+          auto circle_node = *circle_node_it;
+          if (circle_node->seen_) {
+            MS_LOG(ERROR) << "#" << pos << ": " << circle_node->DebugString();
+            pos++;
+          }
+        }
+        MS_LOG(EXCEPTION) << "Graph cycle exists, node " << next->DebugString(2);
+      });
     } else if (incl > EXCLUDE) {  // Not NOFOLLOW or EXCLUDE
       MS_LOG(EXCEPTION) << "The result of include(node) must be one of: \"follow\", \"nofollow\", \"exclude\"";
     }
@@ -138,10 +156,6 @@ std::vector<AnfNodePtr> SuccDeeper(const AnfNodePtr &node) {
       auto &inputs = node->cast<CNodePtr>()->inputs();
       (void)vecs.insert(vecs.end(), inputs.begin(), inputs.end());
     }
-    auto graph = node->func_graph();
-    if (graph->get_return() != nullptr) {
-      vecs.push_back(graph->get_return());
-    }
     return vecs;
   }