如何在CLang C ++下编译/使用头单元模块? [英] How to compile/use header unit modules under CLang C++?
问题描述
在文档中说CLang中的模块支持是部分的.我正在使用LLVM 12.0的最新版本在Windows 64位下使用CLang.
我成功地设法使用了常规模块(通过 import modulename; 导入).
但是我还没有创建和使用标头单元模块，即您通过 import" header.hpp"; 导入的模块.您可以通过示例建议如何做到这一点吗?
为尝试头单元，我创建了下一个玩具文件:
hello.hpp :
#include< vector> use.cpp :
import"hello.hpp";int main(){std :: vector< int>v(123);} 然后，我成功(希望)将标头单元 hello.hpp 编译为PCM文件:
clang ++ -std = c ++ 20 -Xclang -emit-header-module -I.hello.hpp -o hello.pcm 命令运行没有错误，并生成了 hello.pcm .如果运行上面的命令时没有 -o 标志，则文件 hello.hpp.gch 已创建.
然后我尝试编译 use.cpp ，但是没有成功，它以某种方式无法识别我的标头单元和/或找不到对应的 hello.pcm .我认为我缺少一些特殊的标志，这些标志向编译器表明它是标头单元.使用了下一条命令:
clang ++ -std = c ++ 20 -fprebuilt-module-path =.-fmodule-file = hello.hpp = hello.pcm -I.use.cpp 哪个给出了编译错误:
use.cpp:1:8:错误:头文件"hello.hpp"(aka'./hello.hpp')无法导入，因为它不知道是标头单元导入"hello.hpp"；^ 在MSVC下，我成功地设法使用了常规模块和标头单元模块.但不是在CLang中.你能帮我吗?或者告诉我，也许尚不支持CLang标头单元.
最后，我设法解决了上面的几乎所有任务.
Finally I managed to solve almost task above.
Instructions below are for Windows 64-bit, most recent CLang from LLVM 12.0 release (which you can get here) and most recent MSVC Community Build Tools 2019 v16.9.4 (which you can get from here).
I solved task not exactly for header units but for header modules, which behave almost same, there is no difference in their usage.
Toy example files below:
module.modulemap:
module mod {
requires cplusplus17
header "mod.hpp"
export *
}
mod.hpp:
#include <iostream>
use.cpp:
import mod;
int main() {
std::cout << "Hello, world!" << std::endl;
}
I used next 3 commands:
clang++.exe -cc1 module.modulemap -o prebuilt/mod.pcm -emit-module -fmodules -fmodule-name=mod -std=c++20 ^
-internal-isystem "d:\\bin2\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.28.29910\\include" ^
-internal-isystem "C:\\Program Files (x86)\\Windows Kits\\10\\Include\\10.0.19041.0\\ucrt" ^
-debug-info-kind=limited -fms-extensions -fms-compatibility -fms-compatibility-version=19.28 -xc++ ^
-fmath-errno -fexceptions -fcxx-exceptions -triple x86_64-pc-windows-msvc || exit /b
clang++.exe -cc1 -emit-obj use.cpp -fmodule-file=prebuilt/mod.pcm -std=c++20 ^
-internal-isystem "d:\\bin2\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.28.29910\\include" ^
-internal-isystem "C:\\Program Files (x86)\\Windows Kits\\10\\Include\\10.0.19041.0\\ucrt" ^
-debug-info-kind=limited -fms-extensions -fms-compatibility -fms-compatibility-version=19.28 -xc++ ^
-fmath-errno -fexceptions -fcxx-exceptions -triple x86_64-pc-windows-msvc || exit /b
clang++.exe use.o -o use.exe || exit /b
which all worked without errors. You can see that there are full paths to include directories of standard library, these paths are specific to my system. This is needed because in commands I used -cc1 option which enabled to use low level CLang front end instead of simplified driver, this front end needs a lot of low-level options to work.
You can get all options just by doing clang++ -### use.cpp, this will dump to console all options that are needed for your system.
Commands above can be used with -cc1 front end only, driver doesn't support module map file.
Actually among those 3 commands above second command can be simplified, compiling object file doesn't need low-level front-end. But it can be simplified only in the case if 1st command has default params obtained by clang -### command, then 2nd command can be short-written as clang++ use.cpp -o use.o -c -std=c++20 -fmodule-file=prebuilt/mod.pcm.
Result of these commands is that use.o is compiled within a fraction of a second. It is known that iostream takes a lot of time to compile. Very fast compilation of use.o means that we used modules correctly and boosted our speed.
Why I wanted header units in the first place? To be able to upgrade my old code, just by automated replacing regular old-style includes with imports, to greatly improve compilation time. This replacement is only possible with header units or header modules. Regular modules can't export other full header as I know.
For further instructions regarding modules see CLang's Modules Doc and CommandLine Doc.
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