Add a conditional branch in order to only optimize performance.
Add a conditional branch in order to only optimize performance.

chainer/chainer,wkentaro/chainer,ktnyt/chainer,wkentaro/chainer,ktnyt/chainer,jnishi/chainer,niboshi/chainer,wkentaro/chainer,ktnyt/chainer,keisuke-umezawa/chainer,jnishi/chainer,keisuke-umezawa/chainer,hvy/chainer,niboshi/chainer,ronekko/chainer,keisuke-umezawa/chainer,hvy/chainer,okuta/chainer,chainer/chainer,wkentaro/chainer,jnishi/chainer,jnishi/chainer,hvy/chainer,okuta/chainer,pfnet/chainer,okuta/chainer,keisuke-umezawa/chainer,okuta/chainer,niboshi/chainer,rezoo/chainer,niboshi/chainer,chainer/chainer,anaruse/chainer,hvy/chainer,chainer/chainer,tkerola/chainer,ktnyt/chainer