By Bansari Mayur Kamdar and Medha Singh (Reuters) -U.S. shares were set to extend gains for the fourth straight session on Wednesday after a turbulent start to the year, as Google-parent Alphabet and chipmaker Advanced Micro Devices’ shares surged following strong quarterly results. Alphabet Inc rose 8.2% after reporting record quarterly sales on Tuesday, and said it plans to undertake a 20-to-one stock split. The stock split should make it more appealing to retail investors, said Neil Wilson, chief market analyst for Markets.com, adding that Alphabet earnings will underpin a return in confide…