JDK-8351994 introduced Assembler::emit_eevex_or_demote, which has:

  if (is_demotable(no_flags, dst_enc, nds_enc)) {
    int encode = is_prefixq ? prefixq_and_encode(src_enc, dst_enc, is_map1) : prefix_and_encode(src_enc, dst_enc, is_map1);

The `src_enc` and `dst_enc` seem to be swapped here. prefixq_and_encode is:

  int prefixq_and_encode(int dst_enc, int src_enc, bool is_map1 = false);

There are other patterns in the same file, like:

    if (swap) {
      encode = is_prefixq ? prefixq_and_encode(dst_enc, src_enc, is_map1) : prefix_and_encode(dst_enc, src_enc, is_map1);
    } else {
      encode = is_prefixq ? prefixq_and_encode(src_enc, dst_enc, is_map1) : prefix_and_encode(src_enc, dst_enc, is_map1);
    }

...which are also questionable. The "original" order is `dst_enc, src_enc`, yet we do it when `swap == true`?

Please check if this makes sense.