有时，语义上等同但采用两种不同方式编写的代码可能会使优化器在执行良好的寄存器分配上所花费的时间相差巨大。

At times, semantically equivalent code, written in two different ways, might cause the optimizer to have a more difficult time performing good register allocation.

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使用其他模式无法进行的内存访问(地址可以通过其他方式进行计算，并存储到寄存器中，然后就使用这个值来访问内存)。

Any memory access that is not available by other modes (the address can be calculated by other means and stored in the register, which is then used for the access).

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全局变量不会被分配在寄存器上，修改全局变量需要通过指针或者调用函数的方式间接进行。

Global variables are never allocated to registers. Global variables can be changed by assigning them indirectly using a pointer, or by a function call.

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