Bug fix to graph control logic to always compute output tensors (#1053)

* Bug fix to graph control logic to always compute output tensors

* Remove stale comments

src/ngraph/descriptor/input.cpp

@@ -44,7 +44,7 @@ void Input::replace_output(std::shared_ptr<Node> node, size_t i)
     replace_output(node->m_outputs.at(i));
 }
 
-std::shared_ptr<Node> Input::get_node()
+std::shared_ptr<Node> Input::get_node() const
 {
     return m_node->shared_from_this();
 }

src/ngraph/descriptor/input.hpp

@@ -41,7 +41,7 @@ namespace ngraph
             Input(Node* node, size_t index, Output& output);
 
             /// @return the node that this is an input of
-            std::shared_ptr<Node> get_node();
+            std::shared_ptr<Node> get_node() const;
 
             /// @return the position within all supplied tensors of this input
             size_t get_index() const { return m_index; }

src/ngraph/runtime/cpu/cpu_external_function.cpp

@@ -794,6 +794,32 @@ using namespace ngraph::runtime;
                         writer << " || t_en[" << tensor_index_map[input_name] << "]";
                     }
                 }
+
+                auto computes_output = [&]() {
+                    if (std::dynamic_pointer_cast<ngraph::op::Result>(node))
+                    {
+                        return true;
+                    }
+                    // Check if node feeds a result node that has been copy eliminated
+                    for (const descriptor::Output& output : node->get_outputs())
+                    {
+                        for (const descriptor::Input* input : output.get_inputs())
+                        {
+                            auto res =
+                                std::dynamic_pointer_cast<ngraph::op::Result>(input->get_node());
+                            if (res && !res->needs_copy())
+                            {
+                                return true;
+                            }
+                        }
+                    }
+                    return false;
+                };
+                // Always enable nodes computing output tensors
+                if (computes_output())
+                {
+                    writer << " || 1";
+                }
                 writer << ") {\n";
                 writer.indent++;
             }

test/backend_test.in.cpp

@@ -1498,6 +1498,21 @@ NGRAPH_TEST(${BACKEND_NAME}, tensor_constant_with_op)
     EXPECT_EQ((vector<float>{1, 2, 3, 4, 5, 6, 7, 8}), read_vector<float>(result));
 }
 
+NGRAPH_TEST(${BACKEND_NAME}, constant_multi_use)
+{
+    auto A = make_shared<op::Constant>(element::i32, Shape{}, std::vector<std::string>{"388"});
+    auto f = make_shared<Function>(A, op::ParameterVector{});
+    auto backend = runtime::Backend::create("${BACKEND_NAME}");
+
+    std::shared_ptr<runtime::TensorView> r1 = backend->create_tensor(element::i32, Shape{});
+    backend->call(f, {r1}, std::vector<std::shared_ptr<runtime::TensorView>>{});
+    EXPECT_EQ(read_vector<int>(r1), std::vector<int>{388});
+
+    std::shared_ptr<runtime::TensorView> r2 = backend->create_tensor(element::i32, Shape{});
+    backend->call(f, {r2}, std::vector<std::shared_ptr<runtime::TensorView>>{});
+    EXPECT_EQ(read_vector<int>(r2), std::vector<int>{388});
+}
+
 NGRAPH_TEST(${BACKEND_NAME}, constant_broadcast)
 {
     const string js =