Intel Advanced Performance Extensions (APX) introduce new instructions, including PUSH2 and POP2, which allow for the simultaneous transfer of two register values to and from memory in a single instruction. This is an optimization aimed at improving performance, particularly in scenarios like function prologues and epilogues, by reducing the number of individual push and pop operations.

The PUSH2/POP2 instructions in APX require the stack to be aligned to a 16-byte boundary.