I'm curious which comparison routines get optimized.
No block, $a <=> $b, $b <=> $a, $a cmp $b and $b cmp $a.
I don't see why you'd be surprised that creating a single hash would be faster than creating a ton of tiny anonymous arrays.
No lookup would even be faster. With a GRT you don't use block with sort, and hence, no array or hash lookup. 
use Benchmark "cmpthese";

our @files = glob "/bin/*";

our (@o, @s, @g);

cmpthese -1 => {
    ordinary   => '@o = sort {-s $a <=> -s $b} @files',
    st         => '@s = map   $_ -> [0],
                        sort {$a -> [1] <=> $b -> [1]}
                        map  [$_ => -s], @files',
    grt        => '@g = map  substr ($_, 8),
                        sort
                        map  sprintf ("%08d%s", -s, $_), @files',
};

die unless "@o" eq "@s" && "@o" eq "@g";
__END__


           Rate ordinary       st      grt
ordinary  684/s       --     -54%     -63%
st       1492/s     118%       --     -20%
grt      1864/s     172%      25%       --

[download]

In reply to Re^3: Benchmark, -s versus schwartzian (vs hash) by Anonymous Monk
in thread Benchmark, -s versus schwartzian by Darby

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