How big can a rocky planet get?
Giant planets have an abundance of H and He. Hydrogen burning occurs at relatively low temperatures. Rocky planets, on the other hand, don't have much hydrogen and even less helium. For them, the first relevant process would be C burning, which occurs at about 8 solar masses.

But this is valid only as a thought experiment. Rocky planets loose or don't accrete H/He mainly because of insufficient mass. If they were massive, they would consist of H/He and therefore "ignite" at 17 Jupiter masses.