// Note: we avoid this path for deadChange-only iterations, to fix #51639.
			if states == nil {
				states = make(map[string]bool)
			}
			h := f.rewriteHash()
			if _, ok := states[h]; ok {
				// We've found a cycle.
				// To diagnose it, set debug to 2 and start again,
				// so that we'll print all rules applied until we complete another cycle.