例如，C code，在拆装演示动荡？ [英] Example C code that demonstrates volatile in disassembly?

问题描述

什么是演示在拆卸挥发性和非挥发性的区别很短的说明C程序？

What is a short illustrative C program that demonstrates the difference between volatile and non-volatile in the disassembly?

即

int main()
{
    volatile int x;

    ???
}

VS

int main()
{
    int x;

    ???
}

我们可以更换两个 ??? 这样所产生的code是不同的？

What can we replace both ??? with such that the generated code is different?

推荐答案

例如：

x = 0;

如果 X 不是挥发性，编译器会看到，它不使用，将可能消除（无论是 X = 0; 完全从产生code作为一个优化的语句，甚至变量本身）

If x is not volatile, the compiler will see that it's unused and will probably eliminate it (either the x = 0; statement or even the variable itself) completely from the generated code as an optimization.

但是，挥发性关键字正好为$ P $从这样pventing编译器。基本上，它告诉code发电机不管你认为这个变量是/不，不要再次猜测，我需要它。所以，那么编译器将把volatile变量的访问，它会发出相应的前pression实际code。

However, the volatile keyword is exactly for preventing the compiler from doing this. It basically tells the code generator "whatever you think this variable is/does, don't second guess me, I need it." So then the compiler will treat the volatile variable as accessed and it will emit the actual code corresponding to the expression.

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