https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102178
--- Comment #9 from Hongtao.liu <crazylht at gmail dot com> --- 1703 : 401cb1: vmovq %xmm1,%r9 (*) 834 : 401cb6: vmovq %r8,%xmm1 1719 : 401cbb: vmovq %r9,%xmm0 (*) Look like %r9 is dead after the second (*), and it can be optimized to 1703 : 401cb1: vmovq %xmm1,%xmm0 834 : 401cb6: vmovq %r8,%xmm1