What was the Horcrux Voldemort used to regenerate in Goblet of Fire?

Voldemort didn't use a Horcrux to be regenerated. That was a spell to get his body back, it didn't take up an actual Horcrux, this is in the chapter Flesh, Blood and Bones. The only Horcrux that got around to being used was the one in the Diary but as we know that got destroyed before he could properly be brought back. It was dark magic that had him attach to Quirrel.