only compute the first max value in backward
only compute the first max value in backward

tensor-tang/Paddle,PaddlePaddle/Paddle,QiJune/Paddle,putcn/Paddle,putcn/Paddle,chengduoZH/Paddle,pengli09/Paddle,baidu/Paddle,jacquesqiao/Paddle,tensor-tang/Paddle,QiJune/Paddle,QiJune/Paddle,luotao1/Paddle,lcy-seso/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,reyoung/Paddle,jacquesqiao/Paddle,pkuyym/Paddle,PaddlePaddle/Paddle,Canpio/Paddle,pkuyym/Paddle,lcy-seso/Paddle,luotao1/Paddle,luotao1/Paddle,luotao1/Paddle,jacquesqiao/Paddle,jacquesqiao/Paddle,pengli09/Paddle,Canpio/Paddle,pengli09/Paddle,chengduoZH/Paddle,pengli09/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,tensor-tang/Paddle,lcy-seso/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,baidu/Paddle,pkuyym/Paddle,luotao1/Paddle,QiJune/Paddle,reyoung/Paddle,baidu/Paddle,pengli09/Paddle,luotao1/Paddle,putcn/Paddle,jacquesqiao/Paddle,chengduoZH/Paddle,pkuyym/Paddle,pengli09/Paddle,jacquesqiao/Paddle,tensor-tang/Paddle,pengli09/Paddle,putcn/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,baidu/Paddle,lcy-seso/Paddle,Canpio/Paddle,chengduoZH/Paddle,chengduoZH/Paddle,PaddlePaddle/Paddle,QiJune/Paddle,pkuyym/Paddle,putcn/Paddle,tensor-tang/Paddle,QiJune/Paddle,Canpio/Paddle,Canpio/Paddle,lcy-seso/Paddle,pengli09/Paddle,Canpio/Paddle,Canpio/Paddle,lcy-seso/Paddle,Canpio/Paddle,baidu/Paddle,luotao1/Paddle,pkuyym/Paddle,putcn/Paddle