* previously we use rtl_andi(s0, s1, 0xfffffffful), but 0xffffffff can
  not be loaded correctly by load_imm() in the rv64 engine

* this may write $0, so reset $0 when reading from $0, and do not check
  $0 during difftest
* also do not write dsrc1/dsrc2, and be careful about dsrc1/dsrc2 ==
  ddest