How to build LLVM, libclang, and liblld from source

Windows

Alternate Options to Building from Source

• pre-built binaries
• cross-compile using the bootstrap repository

Setup

Install CMake, version 3.17 or newer.

Download llvm, clang, and lld and unzip each to their own directory. Ensure no directories have spaces in them. For example:

• C:\Users\Andy\llvm-14.0.6.src
• C:\Users\Andy\clang-14.0.6.src
• C:\Users\Andy\lld-14.0.6.src

Install Build Tools for Visual Studio 2019. Be sure to select "C++ build tools" when prompted.

• You must additionally check the optional component labeled C++ ATL for v142 build tools.
• Full list of supported MSVC versions:
  • 2017 (version 15.8)
  • 2019 (version 16)

Install Python 3.9.4. Tick the box to add python to your PATH environment variable.

LLVM

Using the start menu, run x64 Native Tools Command Prompt for VS 2019 and execute these commands, replacing C:\Users\Andy with the correct value.

Release Mode

mkdir C:\Users\Andy\llvm-14.0.6.src\build-release
cd C:\Users\Andy\llvm-14.0.6.src\build-release
"c:\Program Files\CMake\bin\cmake.exe" .. -Thost=x64 -G "Visual Studio 16 2019" -A x64 -DCMAKE_INSTALL_PREFIX=C:\Users\Andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-release-mt -DCMAKE_PREFIX_PATH=C:\Users\Andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-release-mt -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_LIBXML2=OFF -DLLVM_USE_CRT_RELEASE=MT
msbuild /m -p:Configuration=Release INSTALL.vcxproj

Debug Mode

mkdir C:\Users\Andy\llvm-14.0.6.src\build-debug
cd C:\Users\Andy\llvm-14.0.6.src\build-debug
"c:\Program Files\CMake\bin\cmake.exe" .. -Thost=x64 -G "Visual Studio 16 2019" -A x64 -DCMAKE_INSTALL_PREFIX=C:\Users\andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-debug -DCMAKE_PREFIX_PATH=C:\Users\andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-debug -DCMAKE_BUILD_TYPE=Debug -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD="AVR" -DLLVM_ENABLE_LIBXML2=OFF -DLLVM_USE_CRT_DEBUG=MTd
msbuild /m INSTALL.vcxproj

LLD

Using the start menu, run x64 Native Tools Command Prompt for VS 2019 and execute these commands, replacing C:\Users\Andy with the correct value.

Release Mode

mkdir C:\Users\Andy\lld-14.0.6.src\build-release
cd C:\Users\Andy\lld-14.0.6.src\build-release
"c:\Program Files\CMake\bin\cmake.exe" .. -Thost=x64 -G "Visual Studio 16 2019" -A x64 -DCMAKE_INSTALL_PREFIX=C:\Users\Andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-release-mt -DCMAKE_PREFIX_PATH=C:\Users\Andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-release-mt -DCMAKE_BUILD_TYPE=Release -DLLVM_USE_CRT_RELEASE=MT
msbuild /m -p:Configuration=Release INSTALL.vcxproj

Debug Mode

mkdir C:\Users\Andy\lld-14.0.6.src\build-debug
cd C:\Users\Andy\lld-14.0.6.src\build-debug
"c:\Program Files\CMake\bin\cmake.exe" .. -Thost=x64 -G "Visual Studio 16 2019" -A x64 -DCMAKE_INSTALL_PREFIX=C:\Users\andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-debug -DCMAKE_PREFIX_PATH=C:\Users\andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-debug -DCMAKE_BUILD_TYPE=Debug -DLLVM_USE_CRT_DEBUG=MTd
msbuild /m INSTALL.vcxproj

Clang

Using the start menu, run x64 Native Tools Command Prompt for VS 2019 and execute these commands, replacing C:\Users\Andy with the correct value.

Release Mode

mkdir C:\Users\Andy\clang-14.0.6.src\build-release
cd C:\Users\Andy\clang-14.0.6.src\build-release
"c:\Program Files\CMake\bin\cmake.exe" .. -Thost=x64 -G "Visual Studio 16 2019" -A x64 -DCMAKE_INSTALL_PREFIX=C:\Users\Andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-release-mt -DCMAKE_PREFIX_PATH=C:\Users\Andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-release-mt -DCMAKE_BUILD_TYPE=Release -DLLVM_USE_CRT_RELEASE=MT
msbuild /m -p:Configuration=Release INSTALL.vcxproj

Debug Mode

mkdir C:\Users\Andy\clang-14.0.6.src\build-debug
cd C:\Users\Andy\clang-14.0.6.src\build-debug
"c:\Program Files\CMake\bin\cmake.exe" .. -Thost=x64 -G "Visual Studio 16 2019" -A x64 -DCMAKE_INSTALL_PREFIX=C:\Users\andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-debug -DCMAKE_PREFIX_PATH=C:\Users\andy\llvm+clang+lld-14.0.6-x86_64-windows-msvc-debug -DCMAKE_BUILD_TYPE=Debug -DLLVM_USE_CRT_DEBUG=MTd
msbuild /m INSTALL.vcxproj

Posix

This guide will get you both a Debug build of LLVM, and/or a Release build of LLVM. It intentionally does not require privileged access, using a prefix inside your home directory instead of a global installation.

Release

This is the generally recommended approach.

cd ~/Downloads
git clone --depth 1 --branch release/14.x https://github.com/llvm/llvm-project llvm-project-14
cd llvm-project-14
git checkout release/14.x

# LLVM
cd llvm
mkdir build-release
cd build-release
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-release -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-release -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_LIBXML2=OFF -DLLVM_ENABLE_TERMINFO=OFF -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1
ninja install
cd ../..

# LLD
cd lld
mkdir build-release
cd build-release
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-release -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-release -DCMAKE_BUILD_TYPE=Release  -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1 -DCMAKE_CXX_STANDARD=17
ninja install
cd ../..

# Clang
cd clang
mkdir build-release
cd build-release
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-release -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-release -DCMAKE_BUILD_TYPE=Release  -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1
ninja install
cd ../..

Debug

This is occasionally needed when debugging Zig's LLVM backend.

# Skip this step if you already did it for Release above.
cd ~/Downloads
git clone --depth 1 --branch release/14.x https://github.com/llvm/llvm-project llvm-project-14
cd llvm-project-14
git checkout release/14.x

# LLVM
cd llvm
mkdir build-debug
cd build-debug
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-debug -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-debug -DCMAKE_BUILD_TYPE=Debug -DLLVM_ENABLE_LIBXML2=OFF -DLLVM_ENABLE_TERMINFO=OFF -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1
ninja install
cd ../..

# LLD
cd lld
mkdir build-debug
cd build-debug
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-debug -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-debug -DCMAKE_BUILD_TYPE= Release  -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1 -DCMAKE_CXX_STANDARD=17
ninja install
cd ../..

# Clang
cd clang
mkdir build-debug
cd build-debug
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME/local/llvm14-debug -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-debug -DCMAKE_BUILD_TYPE=Release  -G Ninja -DLLVM_PARALLEL_LINK_JOBS=1
ninja install
cd ../..

Then add to your Zig CMake line that you got from the README.md: -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-debug or -DCMAKE_PREFIX_PATH=$HOME/local/llvm14-release depending on whether you want Debug or Release LLVM.