See either the GNU General Public License or the Artistic License for more details. If not, you can get one from the Perl distribution. Subs which use the AutoLoader module are forcibly loaded at compile-time. Slightly faster compilation.
Minor bug fixes.
One or two of the programs in perl's own test suite do this. The patch is in file op.patch. The compiler declares all OPs as static structures and uses that magic sequence number. PL to write a personalised Makefile for your system. Your C compiler may need to be able to cope with Standard C for this.