Indexing can have a lot of overhead (30x in one pseudo-benchmark) even when we don't use the Int index. Ideally it would be almost free for right-biased traversals.
Is this solved in the presence of the new conjoined machinery?
Well, conjoined makes it so you don't pay for Indexing if you don't use it, which is good. But I assume that it's still as slow as before if you do.
I just tested it again and even when you do use indexing it looks like the performance is much better than I remembered -- maybe ~2x rather than ~30x, though I didn't try very hard. No idea what happened in the last six months.
I still think we could generate better Core but I'm not sure how. We can open this issue again if we find a place where Indexing makes a big difference.