fixed performance regression when B is sparse
fixed performance regression when B is sparse

maxhutch/libxsmm,egeor/libxsmm,egeor/libxsmm,egeor/libxsmm,hfp/libxsmm,hfp/libxsmm,maxhutch/libxsmm,maxhutch/libxsmm,egeor/libxsmm,hfp/libxsmm,egeor/libxsmm,hfp/libxsmm,maxhutch/libxsmm,egeor/libxsmm,hfp/libxsmm,hfp/libxsmm