// Grow autotmpnames, if needed.
	if n >= len(autotmpnames) {
		autotmpnames = append(autotmpnames, make([]string, n+1-len(autotmpnames))...)
		autotmpnames = autotmpnames[:cap(autotmpnames)]
	}

	s := autotmpnames[n]
	if s == "" {
		// Give each tmp a different name so that they can be registerized.
		// Add a preceding . to avoid clashing with legal names.
		prefix := ".autotmp_%d"