Use _DefinedFunction.add_to_graph() call inside importer.

Before, Graph._add_function() call was used to import function library from
GraphDef. This private function lacks hash value comparison and importing
the inner function library used by the function gets improted.

PiperOrigin-RevId: 156933480

tensorflow/python/framework/importer.py

@@ -247,7 +247,7 @@ def import_graph_def(graph_def, input_map=None, return_elements=None,
     # not have a scoped name or namespace scheme.
     functions = function._from_library(graph_def.library)
     for f in functions:
-      g._add_function(f)
+      f.add_to_graph(g)
       op_dict[f.name] = f.definition.signature
     # pylint: enable=protected-access
 

tensorflow/python/framework/importer_test.py

@@ -1015,6 +1015,35 @@ class ImportGraphDefTest(test.TestCase):
       z_val = z.eval()
       self.assertEqual(z_val, -2.0)
 
+  def testImportGraphWithFunctionTwice(self):
+    g = ops.Graph()
+    with g.as_default():
+      @function.Defun()
+      def Add2(x, y):
+        return math_ops.add(x, y)
+
+      x = array_ops.placeholder(dtype=dtypes.float32, name="x")
+      y = array_ops.placeholder(dtype=dtypes.float32, name="y")
+      _ = Add2(x, y, name="z")  # pylint: disable=unexpected-keyword-arg
+
+    gdef = g.as_graph_def()
+
+    x = random_ops.random_uniform(dtype=dtypes.float32, shape=())
+    y = random_ops.random_uniform(dtype=dtypes.float32, shape=())
+    input_map = {"x:0": x, "y:0": y}
+
+    with ops.name_scope("first"):
+      z1 = importer.import_graph_def(gdef, return_elements=["z:0"],
+                                     input_map=input_map)[0]
+
+    with ops.name_scope("second"):
+      z2 = importer.import_graph_def(gdef, return_elements=["z:0"],
+                                     input_map=input_map)[0]
+
+    with self.test_session() as sess:
+      z1_val, z2_val = sess.run((z1, z2))
+      self.assertAllEqual(z1_val, z2_val)
+
 
 if __name__ == "__main__":
   test.main()