Greenlight Capital's plan to split up General Motors' stock, as well as its challenge to the company's board of directors, will come to a head on Tuesday, as the U.S. automaker's shareholders cast their votes on the hedge fund's proposals. Greenlight's proxy contest comes during a major overhaul at GM as Chief Executive Mary Barra seeks to jolt the company's lagging stock price and sales by slashing costs and refocusing on the most profitable markets.