MacOS、CMake 和 OpenMP [英] MacOS, CMake and OpenMP

问题描述

我正在使用 Homebrew 的最新 CMake (3.9.3) 以及同样来自 Brew 的 LLVM 5.0.0，因为这里的 Clang 支持 OpenMP.

I am using the newest CMake (3.9.3) from Homebrew along with LLVM 5.0.0 also from Brew, because Clang here has OpenMP support.

这适用于带有 LLVM 5 的 CMake 3.8.2.

This worked in CMake 3.8.2 with LLVM 5.

在我的 CMakeLists.txt 中，我有

find_package( OpenMP )

以后我想做

if( OpenMP_CXX_FOUND )

然而，CMake 似乎没有接受 find_package 指令.

However CMake doesn't seem to pick up on the find_package directive.

我使用 CMake 运行

I run CMake with

cmake .. -DCMAKE_BUILD_TYPE=Debug -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang -DUSE_WERROR=ON

我检查了 clang 和 clang++ 是否正确指向 /usr/local/opt/llvm/bin/clang 和 /usr/local/opt/llvm/bin/clang++

where I have checked that clang and clang++ points correctly to /usr/local/opt/llvm/bin/clang and /usr/local/opt/llvm/bin/clang++

我得到的只有这两行:

-- Could NOT find OpenMP_C (missing: OpenMP_C_FLAGS OpenMP_C_LIB_NAMES) (found version "1.0")
-- Could NOT find OpenMP_CXX (missing: OpenMP_CXX_FLAGS OpenMP_CXX_LIB_NAMES) (found version "1.0")

如果我自己设置 OpenMP_C_FLAGS(使用 -DOpenMP_C_FLAGS=-fopenmp=libomp)，它会将错误更改为

If I set OpenMP_C_FLAGS myself (with -DOpenMP_C_FLAGS=-fopenmp=libomp) it changes the error to

-- Could NOT find OpenMP_C (missing: OpenMP_C_LIB_NAMES) (found version "3.1")

注意到它改变了版本号，所以它一定是在寻找一些东西，对吧?

Notice that it changes the version number, so it must be finding something, right?

我缺少什么才能正常工作?

What am I missing for this to work properly?

好的，似乎在 CMake 提供的 FindOpenMP.cmake 内部我们做了一个 try_compile，它默默地失败了(因为我们做了很多次，而且大部分他们会失败，这是有道理的).但是，使用 Clang 提供了 -Werror 标志，由于未使用的命令行参数而失败.我可以这样补充:

Okay, it seem that inside the FindOpenMP.cmake supplied by CMake we do a try_compile, which fails silently (because we do it a lot of times and most of them will fail, this makes sense). However, with Clang a -Werror flag is supplied, which fails because of an unused command line argument. I can thus add:

if(APPLE)
    if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
        set(OpenMP_C_FLAG "-fopenmp=libomp -Wno-unused-command-line-argument")
    endif()
    if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
        set(OpenMP_CXX_FLAG "-fopenmp=libomp -Wno-unused-command-line-argument")
    endif()
endif()

到我的项目，因为我知道 -fopenmp=libomp 将适用于此 Clang.

to my project because I know that -fopenmp=libomp will work for this Clang.

这是正确的做法吗?

推荐答案

该消息主要是告诉您必须提供库的路径和库的名称.以下示例应该可以解决您的问题(另请参阅 find_package(OpenMP)).请注意，我使用命令brew install llvm"使用 brew 安装.前四行只是为了完整性.

The message basically tells you that you have to provide the path to the libraries and the names of the libraries. The following example should fix your problem (see also find_package(OpenMP)). Note that I use the brew installation using the command "brew install llvm". The first four lines are just for completeness.

set(CMAKE_C_COMPILER "/usr/local/Cellar/llvm/5.0.1/bin/clang")
set(CMAKE_CXX_COMPILER "/usr/local/Cellar/llvm/5.0.1/bin/clang++")
set(OPENMP_LIBRARIES "/usr/local/Cellar/llvm/5.0.1/lib")
set(OPENMP_INCLUDES "/usr/local/Cellar/llvm/5.0.1/include")

OPTION (USE_OpenMP "Use OpenMP to enamble <omp.h>" ON)

# Find OpenMP
if(APPLE AND USE_OpenMP)
    if(CMAKE_C_COMPILER_ID MATCHES "Clang")
        set(OpenMP_C "${CMAKE_C_COMPILER}")
        set(OpenMP_C_FLAGS "-fopenmp=libomp -Wno-unused-command-line-argument")
        set(OpenMP_C_LIB_NAMES "libomp" "libgomp" "libiomp5")
        set(OpenMP_libomp_LIBRARY ${OpenMP_C_LIB_NAMES})
        set(OpenMP_libgomp_LIBRARY ${OpenMP_C_LIB_NAMES})
        set(OpenMP_libiomp5_LIBRARY ${OpenMP_C_LIB_NAMES})
    endif()
    if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
      set(OpenMP_CXX "${CMAKE_CXX_COMPILER}")
      set(OpenMP_CXX_FLAGS "-fopenmp=libomp -Wno-unused-command-line-argument")
      set(OpenMP_CXX_LIB_NAMES "libomp" "libgomp" "libiomp5")
      set(OpenMP_libomp_LIBRARY ${OpenMP_CXX_LIB_NAMES})
      set(OpenMP_libgomp_LIBRARY ${OpenMP_CXX_LIB_NAMES})
      set(OpenMP_libiomp5_LIBRARY ${OpenMP_CXX_LIB_NAMES})
    endif()
endif()

if(USE_OpenMP)
  find_package(OpenMP REQUIRED)
endif(USE_OpenMP)

if (OPENMP_FOUND)
    include_directories("${OPENMP_INCLUDES}")
    link_directories("${OPENMP_LIBRARIES}")
    set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
    # set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}")
endif(OPENMP_FOUND)

您可能想设置例如set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -lpthread") 以便链接器自动检测适当的 pthread 库(参见 pthread 和 wiki).

You might want to set e.g. set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -lpthread") such that the linker automatically detects the appropriate pthread library (see pthread and wiki).

这篇关于MacOS、CMake 和 OpenMP的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！