tnum_and
struct tnum tnum_and(struct tnum a, struct tnum b);
dst_reg->var_off = tnum_and(dst_reg->var_off, src_reg.var_off);
t = tnum_and(tnum_subreg(reg1->var_off), tnum_const(~val));
reg1->var_off = tnum_and(reg1->var_off, tnum_const(~val));