我发现在iOS 13中更改了class_getMethodImplementation方法。

这是iOS 13中的代码：

libobjc.A.dylib`class_getMethodImplementation:
->  0x1b6f70a80 <+0>:  mov    x2,x0
    0x1b6f70a84 <+4>:  mov    x0,#0x0
    0x1b6f70a88 <+8>:  cbz    x2,0x1b6f70ab8           ; <+56>
    0x1b6f70a8c <+12>: cbz    x1,0x1b6f70ab8           ; <+56>
    0x1b6f70a90 <+16>: stp    x29,x30,[sp,#-0x10]!
    0x1b6f70a94 <+20>: mov    x29,sp
    0x1b6f70a98 <+24>: orr    w3,wzr,#0xf
    0x1b6f70a9c <+28>: mov    x0,#0x0
    0x1b6f70aa0 <+32>: bl     0x1b6f80250               ; lookUpImpOrForward
    0x1b6f70aa4 <+36>: adrp   x8,-2
    0x1b6f70aa8 <+40>: add    x8,x8,#0x580            ; =0x580 
    0x1b6f70aac <+44>: cmp    x0,#0x0                  ; =0x0 
    0x1b6f70ab0 <+48>: csel   x0,x0,eq
    0x1b6f70ab4 <+52>: ldp    x29,[sp],#0x10
    0x1b6f70ab8 <+56>: ret    

，其他iOS版本中的代码为：

libobjc.A.dylib`class_getMethodImplementation:
->  0x18457a8c4 <+0>:  mov    x8,#0x0
    0x18457a8c8 <+4>:  cbz    x0,0x18457a900           ; <+60>
    0x18457a8cc <+8>:  cbz    x1,0x18457a900           ; <+60>
    0x18457a8d0 <+12>: stp    x29,#-0x10]!
    0x18457a8d4 <+16>: mov    x29,sp
    0x18457a8d8 <+20>: orr    w3,#0x1
    0x18457a8dc <+24>: orr    w4,#0x1
    0x18457a8e0 <+28>: orr    w5,#0x1
    0x18457a8e4 <+32>: mov    x2,#0x0
    0x18457a8e8 <+36>: bl     0x184585390               ; lookUpImpOrNil
    0x18457a8ec <+40>: adrp   x8,22
    0x18457a8f0 <+44>: add    x8,#0x5e0            ; =0x5e0 
    0x18457a8f4 <+48>: cmp    x0,#0x0                  ; =0x0 
    0x18457a8f8 <+52>: csel   x8,eq
    0x18457a8fc <+56>: ldp    x29,#0x10
    0x18457a900 <+60>: mov    x0,x8
    0x18457a904 <+64>: ret 

，源代码是：

IMP class_getMethodImplementation(Class cls,SEL sel)
{
    IMP imp;
    if (!cls  ||  !sel) return nil;
    imp = lookUpImpOrNil(cls,sel,nil,YES/*initialize*/,YES/*cache*/,YES/*resolver*/);
    // Translate forwarding function to C-callable external version
    if (!imp) {
        return _objc_msgForward;
    }
    return imp;
}

为什么会有这样的变化，从而使运行效率更高？