Hmmm. I don't see what went wrong, but here's the output of the filter I get with use Unroll_loop after uncommenting the last print STDERR $source;

my $x;
$x = 0;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;{my $f = fact($x);
    print "factorial($x)=$f\n";} $x++;sub fact {
    $_[0] <= 0 and return 1;
    return $_[0] * fact($_[0] - 1);
}
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And here's the result of Recur_unroll...

my $x;
$x = 0;
while ($x < 8) {
    my $f = fact($x);
    print "factorial($x)=$f\n";
}
continue {
    ++$x
}
sub fact { 
    $_[0] <= 0 and return 1;
    return $_[0] * eval{local @_=$_[0] - 1;
    $_[0] <= 0 and return 1;
    return $_[0] * fact($_[0] - 1);
 };
  }
[download]