US STOCKS-Wall St rebounds from losses as oil prices move up
* S&P 500 gains after falling below 200-day moving average
* China slowdown fears drag commodities towards 2015 lows
* U.S. oil prices reverse losses
* AMD revenue warning weighs on semiconductor companies
* Indexes: Dow up 0.41 pct, S&P up 0.51 pct, Nasdaq down 0.04 pct (Updates with market gains, comment, updates prices)
By Noel Randewich
July 7 (Reuters) - U.S. stocks reversed early losses and moved higher in choppy trade on Tuesday, as a rebound in U.S. oil prices offset concerns of a slowdown in China and the Greek debt crisis.
The S&P energy index reversed course to trade up 1.13 percent as U.S. crude rose 0.7 percent after trading as much as 3.7 percent lower earlier in the day.
Oil markets have been keeping a close eye on negotiations between Iran and six major powers over a nuclear deal. A source close to the talks said on Tuesday that the negoations cannot continue indefinitely and there must be an agreement soon if there is to be an accord to end sanctions in exchange for curbs on Tehran's atomic program. Continuación...