>perl -MO=Concise -e"@b = sort @a"
...
7           <@> sort lK ->8
...

>perl -MO=Concise -e"@b = reverse sort @a"
...
7              <@> sort lK/REV ->8
...

##</code><code>##

if (PL_op->op_private & OPpSORT_REVERSE) {
    SV **p = sorting_av ? AvARRAY(av) : ORIGMARK+1;
    SV **q = p+max-1;
    while (p < q) {
        SV *tmp = *p;
        *p++ = *q;
        *q-- = tmp;
    }
}