sub splice_unique2 {
    my @sorted = sort qw{q w e r t y q w e r t y};
    my $last = '';
    my @unique = @sorted;
    my $removed = 0;

    for (0 .. $#sorted) {
        if ($sorted[$_] eq $last) {
            splice @unique, $_ - $removed++, 1;
        }
        else {
            $last = $sorted[$_];
        }
    }
}

##</code><code>##

                   Rate splice_unique2 splice_unique  shift_unique    map_unique
splice_unique2  83836/s             --          -10%          -15%          -28%
splice_unique   92839/s            11%            --           -6%          -20%
shift_unique    99211/s            18%            7%            --          -14%
map_unique     115924/s            38%           25%           17%            --