ASM_FMT_B1
op = ASM_OP_BR_COND, fmt = ASM_FMT_B1;
op = ASM_OP_BR_WEXIT, fmt = ASM_FMT_B1;
op = ASM_OP_BR_WTOP, fmt = ASM_FMT_B1;
case ASM_FMT_B1: /* 0 dst */