There's no reference to rel2abs in the IO::File that came with ActivePerl 5.8.8, nor on the latest IO::File in CPAN.

sub open {
    @_ >= 2 && @_ <= 4 or croak 'usage: $fh->open(FILENAME [,MODE [,PE
+RMS]])';
    my ($fh, $file) = @_;
    if (@_ > 2) {
    my ($mode, $perms) = @_[2, 3];
    if ($mode =~ /^\d+$/) {
        defined $perms or $perms = 0666;
        return sysopen($fh, $file, $mode, $perms);
    } elsif ($mode =~ /:/) {
        return open($fh, $mode, $file) if @_ == 3;
        croak 'usage: $fh->open(FILENAME, IOLAYERS)';
    } else {
            return open($fh, IO::Handle::_open_mode_string($mode), $fi
+le);
        }
    }
    open($fh, $file);
}
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rel2abs was used in the past (as late as IO::File 1.13 / IO 1.22), but it isn't anymore (IO::File 1.14 / IO 1.2301). It's noted in changelog as "Performance improvement for IO::File::open".