Add test for apparent autodiff bug with nested adds

test/util/all_close.cpp

@@ -90,14 +90,16 @@ template <typename T>
 bool ngraph::test::all_close(const std::vector<T>& a, const std::vector<T>& b, T rtol, T atol)
 {
     assert(a.size() == b.size());
+    bool retval = true;
     for (size_t i = 0; i < a.size(); ++i)
     {
         if (std::abs(a[i] - b[i]) > atol + rtol * std::abs(b[i]))
         {
-            return false;
+            std::cout << "a[" << i << "] = " << a[i] << ", b[" << i << "] = " << b[i] << std::endl;
+            retval = false;
         }
     }
-    return true;
+    return retval;
 }
 
 template bool ngraph::test::all_close<float>(const std::vector<float>& a,

test/util/autodiff.cpp

@@ -65,6 +65,26 @@ TEST(backwards, add)
         manager, backend, make_graph, {x0, x1}, .01f, .01f));
 }
 
+TEST(backwards, add_nested)
+{
+    auto manager = runtime::Manager::get("NGVM");
+    auto backend = manager->allocate_backend();
+
+    test::Uniform<element::Float32> rng(-1.0f, 1.0f);
+    auto shape = Shape{2, 3};
+    auto x0 = rng.initialize(backend->make_parameterized_tensor_view<element::Float32>(shape));
+    auto x1 = rng.initialize(backend->make_parameterized_tensor_view<element::Float32>(shape));
+
+    auto make_graph = [shape]() {
+        auto X0 = make_shared<op::Parameter>(element::Float32::element_type(), shape);
+        auto X1 = make_shared<op::Parameter>(element::Float32::element_type(), shape);
+        return make_shared<Function>(
+            (X0+X1) + (X1+X0), nullptr, std::vector<std::shared_ptr<op::Parameter>>{X0, X1});
+    };
+    EXPECT_TRUE(autodiff_numeric_compare<element::Float32>(
+        manager, backend, make_graph, {x0, x1}, .01f, .01f));
+}
+
 TEST(backwards, broadcast0)
 {
     auto manager = runtime::Manager::get("NGVM");