fix dump ir (#2235)

python/tvm/build_module.py

@@ -5,8 +5,8 @@ LoweredFunc and compiled Module.
 """
 from __future__ import absolute_import as _abs
 import warnings
-import types
 
+from ._ffi.function import Function
 from ._ffi.node import NodeBase, register_node
 from . import api
 from . import _api_internal
@@ -69,7 +69,7 @@ class DumpIR(object):
             vset[k] = v
         for k, v in vset.items():
             self._recover_list.append(recover)
-            vset[k] = self.decorate(v) if isinstance(v, types.FunctionType) else v
+            vset[k] = self.decorate(v) if isinstance(v, Function) else v
 
     def decorate_custompass(self, custom_pass):
         """decorate given list of custom passes, and return decorated passes"""