Show types in VisualizeTree (#1733)

* show types in visualize_tree

* fix a warning

* address Bob's feedback

src/ngraph/pass/visualize_tree.cpp

@@ -103,7 +103,7 @@ std::string pass::VisualizeTree::get_attributes(shared_ptr<Node> node)
 
     ss << " label=\"" << node->get_name();
 
-    static const auto nvtos = std::getenv("NGRAPH_VISUALIZE_TREE_OUTPUT_SHAPES");
+    static const char* nvtos = std::getenv("NGRAPH_VISUALIZE_TREE_OUTPUT_SHAPES");
     if (nvtos != nullptr)
     {
         // The shapes of the Outputs of a multi-output op
@@ -112,6 +112,15 @@ std::string pass::VisualizeTree::get_attributes(shared_ptr<Node> node)
                                                       : vector_to_string(node->get_shape()));
     }
 
+    static const char* nvtot = std::getenv("NGRAPH_VISUALIZE_TREE_OUTPUT_TYPES");
+    if (nvtot != nullptr)
+    {
+        // The types of the Outputs of a multi-output op
+        // will be printed for its corresponding `GetOutputElement`s
+        ss << " " << ((node->get_outputs().size() != 1) ? std::string("[skipped]")
+                                                        : node->get_element_type().c_type_string());
+    }
+
     const Node& n = *node;
     auto eh = m_ops_to_details.find(TI(n));
     if (eh != m_ops_to_details.end())