// vmerge.vxm vd, vs2, rs1
require_vector;
VI_CHECK_SSS(false);
VI_VVXI_MERGE_LOOP
({
  int midx = i / 64;
  int mpos = i % 64;
  bool use_first = (P.VU.elt<uint64_t>(0, midx) >> mpos) & 0x1;

  vd = use_first ? rs1 : vs2;
})