Do not recreate tf.function on different calls to the same layer

PiperOrigin-RevId: 297366158

official/nlp/modeling/layers/transformer.py

@@ -195,11 +195,13 @@ class Transformer(tf.keras.layers.Layer):
 
   def call(self, inputs):
     # TODO(b/150147476, b/150024785): Fix tf.function in TF1 crash.
-    call_impl = self.call_impl
+    if not hasattr(self, "_call_impl"):
+      self._call_impl = self.call_impl
       if not hasattr(tf.compat.v1, "executing_eagerly_outside_functions"
                     ) or tf.compat.v1.executing_eagerly_outside_functions():
-      call_impl = tf.function(experimental_compile=True)(call_impl)
-    return call_impl(inputs)
+        self._call_impl = tf.function(experimental_compile=True)(
+            self._call_impl)
+    return self._call_impl(inputs)
 
   def call_impl(self, inputs):
     if isinstance(inputs, (list, tuple)) and len(inputs) == 2: