# crindex is char-class-based rindex()
use String::Index 'crindex';

cmpthese(-5, {
  last => sub { my $x = $str; $x =~ s/([A-Z])[^A-Z]*$/$1/ },
  capt_repl => sub { my $x = $str; $x =~ s/(.*[A-Z]).*/$1/ },
  rx_rx => sub { my $x = $str; $x =~ /.*[A-Z]/g and $x =~ s/\G.*// },
  sexeger => sub {
    my $x = $str; ($x = reverse $x) =~ s/^[^A-Z]+//; $x = reverse $x;
  },
  crindex => sub {
    my $x = $str;
    substr($x, crindex($x, "ABCDEFGHIJKLMNOPQRSTUVWXYZ")+1) = "";
  },
});

__END__
             Rate      last capt_repl     rx_rx   sexeger   crindex
last       5581/s        --      -82%      -85%      -86%      -90%
capt_repl 30606/s      448%        --      -20%      -23%      -44%
rx_rx     38194/s      584%       25%        --       -4%      -30%
sexeger   39594/s      609%       29%        4%        --      -28%
crindex   54829/s      882%       79%       44%       38%        --