Some of Hollywood's most powerful stars are re-working their contracts in a way where they could see a huge payoff on the back end of the movie cycle. It is a bit of a gamble, but some movie stars are giving up money upfront for a portion of the money the movie makes. If the movie hits big, they get a bigger pay check and if the movie stinks it up, well, then they just gave up a lot of money on the front end.
For example, Sandra Bullock played it right when she signed her contact for "Gravity". Bullock got paid $20 million upfront which is less than what she usually gets paid. It all paid off because "Gravity" went on to make $710 million.
Another star that scored big by going this route was Cameron Diaz. When she agreed to do "Bad Teacher" she agreed to a million at signing. Lucky for her the movie was a hit and she took in $42 million later.
This course of action doesn't always work out. Just ask John Travolta and the contract he signed for "Battleship Earth". Then you have stars like Jonah Hill who wanted to work with Martin Scorsese and on "The Wolf of Wall Street" so badly he took a huge pay-cut and was paid $60,000.