The Prestige
I'm pretty sure this was the movie that touched on this topic. This was an outstanding movie with Hugh Jackman and Christian Bale where two stage magicians engage in a battle to create the ultimate illusion while sacrificing everything they have to outwit each other.
In the end Jackman's character creates a duplicate of himself at the end of every performance, but he must kill himself for the duplicate to appear. He never knows if his duplicate is still himself or another with all his memories.