As usually, if speed is your concern, you can trade it for space. 
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

warn "start\n";
my $tstart1 = time;
my (%by_count, %by_word);
while (<>) {
    chomp;
    my ($k, $v) = split /\t/, $_, 2;
    if (exists $by_word{$k}) {
        $v += $by_word{$k};
        delete $by_count{ $by_word{$k} }{$k};
    }
    undef $by_count{$v}{$k};
    $by_word{$k} = $v;
}

my $tend1   = time;
warn "get properties: ", $tend1 - $tstart1, " secs\n";

my $tstart2 = time;
for my $count (sort { $b <=> $a } keys %by_count) {
    say "$_\t$count" for sort keys %{ $by_count{$count} };
}
my $tend2 = time;
warn "sort + output: ", $tend2 - $tstart2, " secs\n";
warn "total: ", $tend2 - $tstart1, " secs\n";

[download]

Comparison? 

llil start
get_properties : 13 secs
sort + output  : 85 secs
total          : 98 secs

start
get properties: 21 secs
sort + output: 25 secs
total: 46 secs

[download]
The output is identical.

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: Rosetta Code: Long List is Long by choroba
in thread Rosetta Code: Long List is Long by eyepopslikeamosquito

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