reinterpret_cast转换费用 [英] reinterpret_cast cast cost

问题描述

我的理解是C ++ reinterpret_cast和C指针强制转换只是
a的编译时功能，根本没有性能成本。

My understanding is that C++ reinterpret_cast and C pointer cast is a just a compile-time functionality and that it has no performance cost at all.

是

推荐答案

这是一个很好的假设。但是，在存在 reinterpret_cast<> 或C指针强制转换的情况下，优化器可能会受到限制。然后，即使强制类型转换本身没有关联的指令，生成的代码也会变慢。

It's a good assumption to start with. However, the optimizer may be restricted in what it can assume in the presence of a reinterpret_cast<> or C pointer cast. Then, even though the cast itself has no associated instructions, the resulting code is slower.

例如，如果将int强制转换为指针，则优化器可能会具有不知道该指针可能指向什么。结果，可能必须假设通过该指针进行的写操作可以更改任何变量。优于非常常见的优化方法，例如将变量存储在寄存器中。

For instance, if you cast an int to a pointer, the optimizer likely will have no idea what that pointer could be pointing to. As a result, it probably has to assume that a write through that pointer can change any variable. That beats very common optimizations such as storing variables in registers.

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