Disconnected inputs like comment pointed out, added basic test

Author: NikolasMarkou

tests/test_optimizers.py

@@ -1177,6 +1177,25 @@ def test_cast_back_to_back_non_const_mixed_types(self):
         self.run_and_compare(["res", "res2", "res3"], {"u": np.random.randn(1, 2, 3).astype(np.float32)}, model_proto,
                              "Cast", 5)
 
+    def test_upsample_all_ones_removed(self):
+        node1 = helper.make_node("Upsample", ["X"], ["Y"], scales=[1, 1, 1, 1], name="upsample1")
+
+        graph = helper.make_graph(
+            [node1],
+            "test_upsample_all_ones",
+            [helper.make_tensor_value_info("X", TensorProto.FLOAT, (32, 16))],
+            [helper.make_tensor_value_info("Y", TensorProto.FLOAT, (32, 16))],
+        )
+
+        model_proto = self.make_model(graph, producer_name="onnx-tests")
+
+        self.run_and_compare(
+            ["Y"],
+            {"X": np.random.randn(32, 16).astype(np.float32)},
+            model_proto,
+            "Upsample",
+            0)
+
 
 if __name__ == "__main__":
     unittest_main()

tf2onnx/optimizer/upsample_optimizer.py

@@ -10,7 +10,7 @@
 
 
 class UpsampleOptimizer(GraphOptimizerBase):
-    """Resize Optimizer."""
+    """Upsample Optimizer."""
 
     def __init__(self):  # pylint: disable=useless-super-delegation
         super(UpsampleOptimizer, self).__init__()
@@ -21,12 +21,14 @@ def _optimize(self, graph):
             self._optimize_at_current_graph_level)
 
     def _optimize_at_current_graph_level(self, graph):
-        # replace resize operations with all ones in scale with Identity nodes
+        # replace upsample node with all ones in scale with identity node
         for n in graph.get_nodes():
             if n.type == "Upsample":
                 scales = n.get_attr_value("scales")
                 if all([s == 1 for s in scales]):
                     n.type = "Identity"
+                    if len(n.input) > 0:
+                        n.input = [n.input[0]]
                     self.logger.debug("replacing " + n.name +
                                       " with Identity operation")
         return graph