Toyota Motor Corp is hitching its future to green cars, investing billions of dollars in gasoline-electric hybrids and fuel-cell vehicles, but for now its record profit performance is being powered largely by a gas-guzzling U.S. market. In the United States, relatively cheap gasoline prices helped to spur brisk 9 percent growth in industry-wide light truck sales in the first half of the year, making that one of the fastest-growing major global market segments - accounting for about one-tenth of global vehicle sales. Toyota outperformed the overall U.S. market, moreover, with its fresh model line-up - the Highlander SUV was redesigned in February and the Tundra pick-up got a facelift last September - powering a 10 percent rise in its January-June U.S. light truck sales to nearly half a million vehicles. That success is feeding the nearly $40 billion cash pile that Toyota will tap for future green car investments. "The U.S. is one of the few bright spots contributing to year-o