Create NodeArg for all initializers if IR version is > 3. (#742)

Previously all initializers had to have matching graph inputs and the NodeArg was guaranteed to be created via graph input processing.

onnxruntime/core/graph/graph.cc

@@ -658,6 +658,18 @@ Graph::Graph(GraphProto* graph_proto,
     // Copy initial tensors to a map.
     for (auto& tensor : graph_proto_->initializer()) {
       name_to_initial_tensor_[tensor.name()] = &tensor;
+
+      // v4 does not require initializers to be inputs, so we need to ensure there is a NodeArg created for all
+      // initializers in that case
+      if (ir_version > 3) {
+        TypeProto t;
+        t.mutable_tensor_type()->set_elem_type(tensor.data_type());
+        auto shape = t.mutable_tensor_type()->mutable_shape();
+        for (auto dim : tensor.dims())
+          shape->add_dim()->set_dim_value(dim);
+
+        GetOrCreateNodeArg(tensor.name(), &t);
+      }
     }
 
     // Collect all node arg name, type, shape information in the graph.

onnxruntime/test/ir/onnx_model_test.cc

@@ -146,5 +146,15 @@ INSTANTIATE_TEST_CASE_P(ONNXModelsTests,
                         ::testing::Values("bvlc_alexnet", "bvlc_googlenet", "bvlc_reference_caffenet", "bvlc_reference_rcnn_ilsvrc13", "densenet121", "emotion_ferplus", "inception_v1", "inception_v2", "mnist", "resnet50", "shufflenet", "squeezenet", "tiny_yolov2", "vgg19", "zfnet512"));
 
 #endif
+
+// test a model that conforms to ONNX IR v4 where there are initializers that are not graph inputs.
+// a NodeArg should be created for all initializers in this case.
+// the test model contains initializers that are used as implicit inputs in a subgraph, and the NodeArg is required
+// for Graph::Resolve to succeed when processing the subgraph.
+TEST(ONNXModelsTest, TestIRv4NonInputInitializers) {
+  std::shared_ptr<Model> model;
+  ASSERT_TRUE(Model::Load("testdata/subgraph_implicit_input_from_initializer.onnx", model).IsOK());
+  EXPECT_TRUE(model->MainGraph().Resolve().IsOK());
+}
 }  // namespace test
 }  // namespace onnxruntime