Minor performance optimizations
Minor performance optimizations

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