$ cat deb.pl
#!/usr/bin/perl

use strict;
use warnings;
use Getopt::Long;

my $FOO_DEBUG_MODE;
BEGIN { GetOptions("debug", \$FOO_DEBUG_MODE) }
use constant FOO_DEBUG_MODE => $FOO_DEBUG_MODE;

print "debug statment\n" if FOO_DEBUG_MODE;
print "done!\n";

##</code><code>##

$ perl -MO=Deparse deb.pl
use Getopt::Long;
BEGIN {${^WARNING_BITS} = "UUUUUUUUUUUU"}
use strict 'refs';
my $FOO_DEBUG_MODE;
sub BEGIN {
    GetOptions 'debug', \$FOO_DEBUG_MODE;
}
use constant ('FOO_DEBUG_MODE', $FOO_DEBUG_MODE);
'???';
print "done!\n";
deb.pl syntax OK

##</code><code>##

$ perl -MO=Deparse deb.pl -debug
use Getopt::Long;
BEGIN {${^WARNING_BITS} = "UUUUUUUUUUUU"}
use strict 'refs';
my $FOO_DEBUG_MODE;
sub BEGIN {
    GetOptions 'debug', \$FOO_DEBUG_MODE;
}
use constant ('FOO_DEBUG_MODE', $FOO_DEBUG_MODE);
print "debug statment\n";
print "done!\n";
deb.pl syntax OK