PepsiCo Inc PEP.O raised its full-year revenue forecast, helped by sustained demand for its sodas and snacks, sending the company's shares up 0.5%. By Amruta Khandekar July 12 (Reuters) - The S&P 500 and the Nasdaq fell on Tuesday as investors fretted about an economic downturn from aggressive interest rate hikes around the world to tamp down inflation. Adding to worries of slowing global growth, several cities in China are adopting fresh COVID-19 curbs from this week to rein in new infections after finding a highly transmissible Omicron subvariant.