来源：https://twitter.com/stuntpants/status/1346470705446092811

简单来说，苹果想设计出 highly OoO 的架构，但是现有的 ARM32 每条指令都可能影响 control flow，于是需要 predication。但是 predication 会影响 OoO。
> All instructions in A32 were conditional, using predication. However, predication uses bits in the instruction encoding that are already at a premium due to doubling the number of registers in AArch64. Moreover, predication complicates out-of-order execution since it adds an extra input that must be renamed. In A64, the only conditional instructions are branch, comparison and select. While this will slightly increase code size, the simplification is worthwhile.
> Similarly, A32 had an in-line shifter that could be used for ‘free’ with nearly every integer instruction. However, shifts are notorious difficult to implement at high frequency due to the complicated wiring. An implicit shift in every instruction will increase the length of pipeline stages and reduce the overall frequency. A64 instructions can apply a very limited shift to the destination register, and there are new instructions to handle more complicated cases such as variable shifts.
于是 Apple 向 ARM 反馈，并设计出了 ARM64。

果子IP 5S是第一台ARM64的手機
不過ARM早在2011年發表ARMv8就支持64位元了

参与和是的区别能分得清吗？就像富士通参与了sve的开发，但是能说sve就是富士通的吗？

不要非黑即白。