def match(self, files):
        """Given a set of files in this directory, returns all the files that
        match the :class:`Pattern` instances which match this directory."""
        if not files:
            return set()

        if (self.matched_inherit.all_files()
                or self.matched_and_subdir.all_files()
                or self.matched_no_subdir.all_files()):
            # Optimization: one of the matched patterns matches everything
            # So simply return it
            return set(files)

        unmatched = set(files)
        matched = set()
        for pattern_set in self._matching_pattern_sets():
            pattern_set.match_files(matched, unmatched)
            if not unmatched:
                # Optimization: If we have matched all files already
                # simply return at this point - nothing else to do
                break

        return matched