Clang是LLVM(Low Level Virtual Machine)项目提供的工具链中的编译器的前端部分
LLVM项目是模块化和可重用的编译器和工具链技术的集合,LLVM的一大特色就是，有着独立的、完善的、严格约束的中间代码表示。这种中间代码，就是LLVM的字节码，是LLVM抽象的精髓，前端生成这种中间代码，后端自动进行各类优化分析，让用LLVM开发的编译器，都能用上最先见的后端优化技术。
编译器编译流程如下
来自《编译原理》
编译器分成前端与后端两部分
前端负责处理源代码，后端负责生成目标代码
来自参考链接3
macOS Hign Sierra 10.13.6
Xcode10.1
获取llvm源代码
% git clone https://git.llvm.org/git/llvm.git/获取Clang源代码
% cd llvm/tools% git clone https://git.llvm.org/git/clang.git/获取compiler-rt源代码
## 定位到llvm工程目录下% cd llvm% git clone https://git.llvm.org/git/compiler-rt.git/获取libomp源代码
% cd llvm% git clone https://git.llvm.org/git/openmp.git/获取libcxx和libcxxabi源代码
% cd llvm% git clone https://git.llvm.org/git/libcxx.git/% git clone https://git.llvm.org/git/libcxxabi.git/获取测试用例
% cd llvm% git clone https://git.llvm.org/git/test-suite.git/Clang 使用CMake(一个用于构建，测试和打包软件的开源跨平台工具系列)进行构建
# LLVM 禁止源码内编译(in-tree build is not supported),创建一个与llvm工程同级的build目录% cd src/% mkdir build% cd build ## 安装cmake% brew install cmake## -G <generator-name>## Specify a build system generator.## cmake [{-D <var>=<value>}...] -P <cmake-script-file>## Create or update a cmake cache entry.## When cmake is first run in an empty build tree, it ## creates a CMakeCache.txt file and populates it with customizable settings for## the project. This option may be used to specify a setting that takes priority over the projectas default value. The option may## be repeated for as many cache entries as desired.## 会被存在build目录下的CMakeCache.txt中## -Wno-dev 忽略开发警告% cmake -G Ninja ../llvm/ -DCMAKE_INSTALL_PREFIX=/opt/llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_FFI=ON -DLLVM_BUILD_LLVM_DYLIB=ON -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DLLVM_TARGETS_TO_BUILD="host;AMDGPU" -Wno-dev## 安装 ninja## Ninja is a small build system with a focus on speed. ## It differs from other build systems in two major respects: it is designed to have its input files generated by a higher-level build system, and it is designed to run builds as fast as possible.% brew install ninja## -j N run N jobs in parallel [default=6, derived from CPUs available]## CMake Error at cmake_install.cmake:36 (file):## file INSTALL cannot set permissions on "/opt/llvm/include/llvm"## 加上sudo% sudo ninja -j4 install 替换Clang ## 查看系统的Clang的位置~% which clang/usr/清新的樱桃/clang~% clang -v Apple LLVM version 10.0.0 (clang-1000.11.45.5)Target: x86_64-apple-darwin17.7.0Thread model: posixInstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/清新的樱桃根据参考链接7
新建Xcode工程
创建用户自定义配置CC,并设置DEBUG时的值为编译完成后Clang二进制的位置。
⌘ B 编译,查看编译输出的日志,证明已经使用了编译的Clang
错误原因:
Unknown argument: '-index-store-path'根据参考链接10,在Build Setting 中搜索index并将Enable Index-While-Building Functionality选项设置为NO
⌘ B
错误原因:
fatal error: error in backend: No available targets are compatible with triple "arm64-apple-ios9.0.0"clang-8: error: clang frontend command failed with exit code 70 (use -v to see invocation)clang version 8.0.0 (https://git.llvm.org/git/clang.git/ a6eb16ed631365f3bbadd0450ab52746c151794d) (https://git.llvm.org/git/llvm.git/ 1c98a2b870d058132698ae4d67ef954b13dc41b4)Target: aarch64-apple-darwin17.7.0Thread model: posixInstalledDir: /opt/llvm/清新的樱桃分析: 因为该手机架构是arm64而cmake编译时指定的是 -DLLVM_TARGETS_TO_BUILD="host;AMDGPU",并没有对应的架构
HowToBuildOnARM
cmake $LLVM_SRC_DIR -DCMAKE_BUILD_TYPE=Release
-DLLVM_TARGETS_TO_BUILD=“ARM;X86;AArch64”
操作
## 重新编译% cmake -G Ninja ../llvm/ -DCMAKE_INSTALL_PREFIX=/opt/llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_FFI=ON -DLLVM_BUILD_LLVM_DYLIB=ON -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DLLVM_TARGETS_TO_BUILD="host;ARM;X86;AArch64" -Wno-dev## 确认% grep -r "LLVM_TARGETS_TO_BUILD" CMakeCache.txtCMakeCache.txt:LLVM_TARGETS_TO_BUILD:STRING=host;ARM;X86;AArch64## 安装 只会处理有变更的部分% sudo ninja -j4 install⌘ B 成功
代码TryLLVM
参考 llvm.org结构化编译器前端 Clang 介绍编译器架构的王者LLVMcmake.orgwiki-XcodeVersionInfo下载标准库libcxx出现svn: E000104: Error running context: Connection reset by peer的解决方案安装 LLVM + Clang如何让Xcode使用clang的替代版本Why can’t I create a directory under /opt without sudocompilation-error-when-using-xcode-9-0-with-clang-cannot-specify-o-when-genera