Build libclang on Windows

Download source

The LLVM Project is a collection of modular and reusable compiler and toolchain technologies, including Clang and libclang. It can be obtained by cloning its source with Git:

git clone https://github.com/llvm/llvm-project.git

Configure + build

The LLVM Project already offers configure and build instructions for Windows here. The steps outlined under "Using Ninja alongside Visual Studio" are recommended.

Notes:

• Visual Studio 2019 and 2022 are also supported.
• Skip steps 5. and 6. if you want to build with MinGW GCC instead of MSVC (or set the values accordingly).
• Add

  -DCMAKE_BUILD_TYPE=Debug
  

  to your configure command if you need a debug build of libclang, e.g.,

  cmake -GNinja -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_BUILD_TYPE=Debug ..\llvm
  

• It is recommended to add an install prefix to your configure command, e.g.,

  cmake -GNinja -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_INSTALL_PREFIX=C:\libclang\ ..\llvm
  

  . Run

  cmake -- install .
  

  after the build to install libclang to the directory you provided through the install prefix.

Intel Compiler

Currently llvm requires some tweaks to compile with icl (https://software.intel.com/en-us/forums/intel-c-compiler/topic/759252 may solve some of them).

Profile-guided builds extra configuration

MSVC

* First build round:
  CMAKE_C_FLAGS and CMAKE_CXX_FLAGS: /GL
  CMAKE_EXE_LINKER_FLAGS and CMAKE_SHARED_LINKER_FLAGS: /LTCG and /GENPROFILE:PGD=pgd\files\path
* Training
  Just run parsing/completion
* Second build round:
  CMAKE_C_FLAGS and CMAKE_CXX_FLAGS: /GL
  CMAKE_EXE_LINKER_FLAGS and CMAKE_SHARED_LINKER_FLAGS: /LTCG and /USEPROFILE:PGD=same\pgd\files\path

MinGW

* First build round:
  CMAKE_C_FLAGS and CMAKE_CXX_FLAGS: -fprofile-generate=path\to\profile\files
* Training
  Just run parsing/completion
* Second build round:
  CMAKE_C_FLAGS and CMAKE_CXX_FLAGS: -fprofile-use=path\to\profile\files

Clang

Clang requires compiler-rt to build llvm with -fprofile-instr-generate flag Follow the https://compiler-rt.llvm.org/ to build it. You need additional configuration though: -DCMAKE_INSTALL_PREFIX=<path\to\llvm\install>\lib\clang\5.0.0 and a proper -DCMAKE_BUILD_TYPE

* First build round:
  cmake -G "NMake Makefiles JOM" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RTTI=1 -DCMAKE_C_COMPILER=clang-cl -DCMAKE_CXX_COMPILER=clang-cl -DCMAKE_INSTALL_PREFIX=path\to\install -DCMAKE_C_FLAGS="-fms-compatibility-version=19.0 -fprofile-instr-generate=path\llvm-%p.profraw" -DCMAKE_CXX_FLAGS="-fms-compatibility-version=19.0 -fprofile-instr-generate=path\llvm-%p.profraw" -DMSVC=1 -DCMAKE_CL_64=<1|0> -DCMAKE_EXE_LINKER_FLAGS="<path\to\llvm\install>\lib\clang\5.0.0\lib\windows\clang_rt.profile-x86_64.lib /FORCE:MULTIPLE" path\to\llvm
* Training
* Merging train data
  llvm-profdata merge -output= llvm.profdata llvm-*.profraw
* Second build round:
  cmake -G "NMake Makefiles JOM" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RTTI=1 -DCMAKE_C_COMPILER=clang-cl -DCMAKE_CXX_COMPILER=clang-cl -DCMAKE_INSTALL_PREFIX=path\to\install -DCMAKE_C_FLAGS="-fms-compatibility-version=19.0 -fprofile-instr-use=path\llvm.prodata" -DCMAKE_CXX_FLAGS="-fms-compatibility-version=19.0 -fprofile-instr-use=path\llvm.prodata" -DMSVC=1 -DCMAKE_CL_64=<1|0> path\to\llvm

Intel Compiler

* First build round:
cmake -G "Ninja" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RTTI=1 -DCMAKE_C_COMPILER=icl -DCMAKE_CXX_COMPILER=icl -DCMAKE_INSTALL_PREFIX=path\to\install -DLLVM_ENABLE_WARNINGS=0 -DCMAKE_CXX_FLAGS="/Qvc14.1 /Qprof-gen /Qprof-dirc:\icl_profiled" -DCMAKE_C_FLAGS="/Qvc14.1 /Qprof-gen /Qprof-dirc:\icl_profiled" path\to\llvm
* Training
* Second build round:
cmake -G "Ninja" -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RTTI=1 -DCMAKE_C_COMPILER=icl -DCMAKE_CXX_COMPILER=icl -DCMAKE_INSTALL_PREFIX=path\to\install -DLLVM_ENABLE_WARNINGS=0 -DCMAKE_CXX_FLAGS="/Qvc14.1 /Qprof-use /O2 /Qip /Qprof-dirc:\icl_profiled" -DCMAKE_C_FLAGS="/Qvc14.1 /Qprof-use /O2 /Qip /Qprof-dirc:\icl_profiled" path\to\llvm

Performance

We have measurements comparison between different llvm builds. The most important there are parse and re-parse times.

This is the comparison for sample file that was done for our llvm builds (all compilers are 64-bit):

action	LLVM 5.0 mingw PGO	LLVM 5.0 intel compiler PGO	LLVM 3.9 mingw PGO	LLVM 3.9 msvc2015	LLVM 3.9 msvc2017 PGO	LLVM 3.9 clang PGO	LLVM 3.9 mingw	LLVM 3.9 clang	LLVM 3.9 msvc2017
Parsing	1.306	1.5426	1.2874	2.7482	1.473	1.5015	1.5797	1.7486	1.8487
Reparsing	1.9258	2.2318	2.3362	2.9665	2.5521	2.6727	3.183	2.8431	3.0255

That means that currently the fastest build is mingw with applied profile-guided optimization.