It'd be helpful to know more of the specifics. For example, if the keys are limited to alphanumeric labels, the simplification could provide further speedup. Anyway, here's one regex-convoluted aka "adding problems to problems" version for your perusal:
sub uhuu {
my $keys = join "|", map "\Q$_\E", ($match_list =~ m{([^/,]+)/[^,]
+*}g);
my %R;
return unless $attrs =~ m{
\A \Q$tag\E \s+
(?: ($keys)=(\S+) (?(?{ defined $R{$1} || ($R{$1}=$2, 0) })(?!
+)) \s* )*+
\z }x;
$markup =~ s[X{($keys)}][ $R{$1} // $& ]ger
}
A side-note to benchmarkers: localize the globals that you modify. ("On the importance of testing your testing.")
