[Experimental] Convert CastLike to Cast when dtype is available | feat(torchlib)

onnxscript/function_libs/torch_lib/graph_building.py

@@ -298,13 +298,25 @@ def eval(self, schema, inputs, attributes):
             if schema.name == "CastLike":
                 assert len(inputs) == 2
                 # Skip CastLike if the input and output types are the same
-                if (
-                    inputs[0] is not None
-                    and inputs[1] is not None
-                    and inputs[0].dtype == inputs[1].dtype
-                    and inputs[1].dtype is not None
-                ):
-                    return inputs[0]
+                src_input = inputs[0]
+                target_input = inputs[1]
+                dtypes_available = (
+                    isinstance(src_input, TorchScriptTensor)
+                    and isinstance(target_input, TorchScriptTensor)
+                    and src_input.dtype is not None
+                    and target_input.dtype is not None
+                )
+                if dtypes_available:
+                    if src_input.dtype == target_input.dtype:
+                        # Same type. No cast needed
+                        return src_input
+                    else:
+                        # Create a Cast node
+                        return self._graph.add_op_call(
+                            onnx.defs.get_schema("Cast"),
+                            (src_input,),
+                            {"to": target_input.onnx_dtype},
+                        )
         return self._graph.add_op_call(schema, inputs, attributes)
 
     @runtime_typing.checked