From the perlrun manpage:

-u

causes Perl to dump core after compiling your script. You can then in theory take this core dump and turn it into an executable file by using the undump program (not supplied). This speeds startup at the expense of some disk space (which you can minimize by stripping the executable). (Still, a ``hello world'' executable comes out to about 200K on my machine.) If you want to execute a portion of your script before dumping, use the dump() operator instead. Note: availability of undump is platform specific and may not be available for a specific port of Perl. It has been superseded by the new perl-to-C compiler, which is more portable, even though it's still only considered beta.

This is probably useles on windows, but: where can I get this "undump" program? I can't find it on my debian machine..