check if the nodes are reachable before returning the users of a node (#2069)

* - check if the nodes is reachable before returning the users of a node

* address PR comments

* test case fixes

src/ngraph/graph_util.hpp

@@ -179,14 +179,17 @@ namespace ngraph
             result_list.push_back(node_map[independent_node]);
             independent_nodes.pop_front();
 
-            for (auto user_sp : independent_node->get_users())
+            for (auto& output : independent_node->get_outputs())
             {
-                Node* user = user_sp.get();
-                node_dependency_count[user] -= 1;
-                size_t count = node_dependency_count[user];
-                if (count == 0)
+                for (auto& input : output.get_inputs())
                 {
-                    independent_nodes.push_back(user);
+                    auto user = input->get_raw_pointer_node();
+                    node_dependency_count[user] -= 1;
+                    size_t count = node_dependency_count[user];
+                    if (count == 0)
+                    {
+                        independent_nodes.push_back(user);
+                    }
                 }
             }
 

src/ngraph/node.cpp

@@ -21,6 +21,7 @@
 
 #include "ngraph/autodiff/adjoints.hpp"
 #include "ngraph/descriptor/layout/tensor_layout.hpp"
+#include "ngraph/graph_util.hpp"
 #include "ngraph/node.hpp"
 #include "ngraph/op/parameter.hpp"
 #include "ngraph/op/result.hpp"
@@ -382,7 +383,7 @@ descriptor::Output* Node::get_output_to(const shared_ptr<Node>& dst)
     throw ngraph_error("Error: dst is not one of self's output Node");
 }
 
-NodeVector Node::get_users() const
+NodeVector Node::get_users(bool check_is_used) const
 {
     NodeVector result;
 
@@ -390,7 +391,17 @@ NodeVector Node::get_users() const
     {
         for (auto input : get_output_inputs(i))
         {
-            result.push_back(input->get_node());
+            if (check_is_used)
+            {
+                if (is_used(input->get_node().get()))
+                {
+                    result.push_back(input->get_node());
+                }
+            }
+            else
+            {
+                result.push_back(input->get_node());
+            }
         }
     }
 

src/ngraph/node.hpp

@@ -245,7 +245,7 @@ namespace ngraph
         descriptor::Output* get_output_to(const std::shared_ptr<Node>& dst);
 
         /// Get all the nodes that uses the current node
-        NodeVector get_users() const;
+        NodeVector get_users(bool check_is_used = false) const;
 
         virtual std::shared_ptr<Node> get_default_value() const { return nullptr; }
         /// Use instance ids for comparison instead of memory addresses to improve determinism

test/util.cpp

@@ -382,6 +382,7 @@ TEST(graph_util, test_subgraph_topological_sort)
     auto C = make_shared<op::Parameter>(element::f32, shape);
     auto add = A + B;
     auto mul = C * add;
+    auto result = make_shared<op::Result>(mul);
     auto sorted = ngraph::subgraph_topological_sort(NodeVector{mul, add, A});
     std::list<std::shared_ptr<Node>> expected{A, add, mul};
     ASSERT_EQ(expected, sorted);
@@ -399,6 +400,7 @@ TEST(graph_util, test_subgraph_topological_sort_control_dependencies)
     add->add_control_dependency(D);
     add->add_control_dependency(E);
     auto mul = C * add;
+    auto result = make_shared<op::Result>(mul);
     auto sorted = ngraph::subgraph_topological_sort(NodeVector{mul, add, A, D}, true);
     std::list<std::shared_ptr<Node>> expected{A, D, add, mul};
     ASSERT_EQ(expected, sorted);