之后，是两个加法指令，第一个是普通相加，第二个是带进位相加。

Then comes two add instructions. The first is a normal add and the second one is add with carry.

youdao

因此，si_a (a, b)会强制使用a指令做加法运算。

So, si_a (a, b) forces the instruction a to be used for addition.

youdao

可以看到test1()中每次加法都需要读取和存储全局变量errs，而在test2()中，localerrs分配在寄存器上，只需要一条指令。

Note that test1 must load and store the global errs value each time it is incremented, whereas test2 stores localerrs in a register and needs only a single instruction.

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