objc_msgsend 汇编部分实现

http://yulingtianxia.com/blog/2016/06/15/Objective-C-Message-Sending-and-Forwarding/#回顾-objc-msgSend-伪代码

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cmp

cmp是比较指令， cmp的功能相当于减法指令，只是不保存结果。cmp指令执行后，将对标志寄存器产生影响。其他相关指令通过识别这些被影响的标志寄存器位来得知比较结果。

//判断对象是否存在
cmp x0

CacheLookup NORMAL  //calls imp or objc_msgSend_uncached

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cacheHit

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checkMiss

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MethodTableLookup

https://www.jianshu.com/p/a4c49fecda79

http://blog.zhengdong.me/2013/07/18/a-look-under-the-hood-of-objc-msgsend/

http://www.arigrant.com/blog/2014/2/18/chisels-print-invocation-command

https://www.meiwen.com.cn/subject/gljadftx.html