Whether the analysis seems sound or not, I'd probably not want to return to v5.004. If you configured perl with -DDEBUGGING, and you chose to use the perl malloc, then try this script:

#!/usr/bin/perl 

use strict;
use warnings;

warn('!');
do 'lib/auto/POSIX/autosplit.ix';
warn('!!! "after"');
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Run it like this:

perl -Dm script.pl
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I ran it with -Dm, but if you want other options, run it with -D for a complete list of options.