有符号乘法运算

Signed Multiply Long multiplies two 32-bit register values, and writes the result to the 64-bit destination register.

将两个32位寄存器值相乘，并将结果写入64位目标寄存器。

64-bit variant
    SMULL <Xd>, <Wn>, <Wm>
    is equivalent to
    SMADDL <Xd>, <Wn>, <Wm>, XZR

  403f34:    528cccfc     mov    w28, #0x6667                    // #26215
  403f38:    529999b7     mov    w23, #0xcccd                    // #52429
  403f3c:    72acccdc     movk    w28, #0x6666, lsl #16
  403f40:    72b99997     movk    w23, #0xcccc, lsl #16
  403f44:    d503201f     nop
  403f48:    1adb0f42     sdiv    w2, w26, w27
  403f4c:    9b3c7c40     smull    x0, w2, w28