void checkOverride(JCTree tree, Type site, ClassSymbol origin, MethodSymbol m) {
        TypeSymbol c = site.tsym;
        Scope.Entry e = c.members().lookup(m.name);
        while (e.scope != null) {
            if (m.overrides(e.sym, origin, types, false)) {
                if ((e.sym.flags() & ABSTRACT) == 0) {
                    checkOverride(tree, m, (MethodSymbol)e.sym, origin);
                }
            }
            e = e.next();
        }
    }