Last time I checked with the Parrot docs (the tutorial mainly), there was no mention of jumps to computed values (which is what you said you need for implementing call/cc). So the question is: how can one do proper tail recursion without jumps? (Parrot does have jump LABEL though)

Parrot supports jumping (and branching) to locations (and offsets, though they're less useful) stored in registers. Only works with the jump, jsr, branch, and bsr ops though. (Used to work with the conditionals, but that was silly so we yanked that support)