“abc167338a99f1b644e1a5d4bb324a566d2fd87f”上不存在“develop/doc/howto/rnn/recurrent_group_en.html”
* add sparse support for sum op * typo fix * fix gpu build error * fix unittest error * typo fix * infer var type and shape in op_test * follow comments * fix build error * bypass some unittests depend on NetOp