The chipmaker’s shares are down 24% from a December record, well underperforming the S&P 500 Index. The selloff is part of investors’ broader rotation away from the largest technology companies due to fears about the sustainability of the hundreds of billions of dollars committed to developing artificial intelligence capabilities. Broadcom, which is the seventh-most valuable company in the S&P 500 at $1.5 trillion, is a chipmaking partner with Alphabet Inc. and other AI giants, making it a beneficiary of that largesse.