如何防止VC ++ 9链接器链接不必要的全局变量? [英] How to prevent VC++ 9 linker from linking unnecessary global variables?

问题描述

我正在玩函数级链接在VC ++中.我已启用/OPT:REF和/OPT:ICF，链接器很高兴消除所有未使用的功能.变量不是这样.

I'm playing with function-level linking in VC++. I've enabled /OPT:REF and /OPT:ICF and the linker is happy to eliminate all unused functions. Not so with variables.

以下代码仅用于演示问题，我完全理解，实际上以这种方式构造代码是次优的.

The following code is to demonstrate the problem only, I fully understand that actually having code structured that way is suboptimal.

//A.cpp
SomeType variable1;

//B.cpp
extern SomeType variable1;
SomeType variable2;
class ClassInB {
 //actually uses variable1
};

//C.cpp
extern SomeType variable2;
class ClassInC {
 //actually uses variable2;
};

所有这些文件都被编译成静态库.消费者项目仅使用 ClassInC 并链接到静态库.现在出现了VC ++ 9链接器.

All those files are compiled into a static lib. The consumer project only uses ClassInC and links to the static library. Now comes the VC++ 9 linker.

首先，链接程序会看到 C.obj 引用了 variable2 ，并包含了 B.obj . B.obj 引用 variable1 ，因此它包含 A.obj .然后未引用的东西消除阶段开始.它删除 A.obj 和 B.obj 中的所有函数，但不删除变量. variable 和 variable2 都与它们的静态初始化程序和反初始化程序一起保存.这会放大图像的大小，并会导致运行初始化程序和取消初始化的延迟.

First the linker sees that C.obj references variable2 and includes B.obj. B.obj references variable1, so it includes A.obj. Then the unreferenced stuff elimination phase starts. It removes all functions in A.obj and B.obj, but not the variables. Both variable and variable2 are preserved together with their static initializers and deinitializers. That inflates the image size and introduces a delay for running the initializers and deinitializes.

上面的代码过于简单，在实际代码中，我真的不能轻易地将 variable2 移到 C.cpp 中.我可以将其放入一个单独的.cpp文件中，但这看起来真是愚蠢.有没有更好的选择来解决Visual C ++ 9的问题?

The code above is oversimplified, in actual code I really can't move variable2 into C.cpp easily. I could put it into a separate .cpp file, but that looks really dumb. Is there any better option to resolve the problem with Visual C++ 9?

推荐答案

MSDN (请参见 Arguments 部分， REF | NOREF 参数，第4段)指定您必须显式将数据标记为COMDAT；使用__declspec(selectany).链接器可以在使用/OPT:REF 时删除未使用的数据.

The MSDN (see the Arguments section, REF | NOREF arguments, 4th paragraph) specifies that You have to explicitly mark data as a COMDAT; use __declspec(selectany). for the linker to remove said unused data when using /OPT:REF.

您是否尝试过并有机会使用 __declspec(selectany)?

Have you tried and had any chance with __declspec(selectany) ?

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