Hmmm, Charybde and Scylla. There's no solution I suppose, or maybe just go by what RMS wants: produce a data structure for the necessary data for the simplest possible improvement, then define a more involved data structure for a more ambitious feature, and reiterate again and again, until the data structure becomes isomorphic to what Gcc deals with. No need to actually code all these steps, just specifying them should help RMS understand that it's inevitable at some point.