Configuration

Reference for the most-used CMake variables when configuring an LLVM build. The full list lives in llvm/CMakeLists.txt and the per-subproject CMakeLists.txt files; this page covers the ones a contributor reaches for daily.

Subproject selection

Variable	Purpose	Typical values
LLVM_ENABLE_PROJECTS	Compiler/tool subprojects to build	clang;lld;lldb;mlir;flang;bolt;clang-tools-extra;polly
LLVM_ENABLE_RUNTIMES	Runtime libraries to build	compiler-rt;libcxx;libcxxabi;libunwind;openmp;libc;flang-rt;orc-rt;offload;llvm-libgcc
LLVM_TARGETS_TO_BUILD	Backend targets to enable	host, X86;AArch64;RISCV, all
LLVM_EXPERIMENTAL_TARGETS_TO_BUILD	Experimental targets	(per-target)

Build-type controls

Variable	Purpose	Typical values
CMAKE_BUILD_TYPE	Optimization/debug level	Release, RelWithDebInfo, Debug, MinSizeRel
LLVM_ENABLE_ASSERTIONS	Enable internal assert()s	ON (recommended for development), OFF (default in Release)
LLVM_USE_LINKER	Override the linker	lld, gold, ld
LLVM_ENABLE_LTO	Build LLVM itself with LTO	OFF, Thin, Full
LLVM_USE_SANITIZER	Build LLVM under a sanitizer	Address, Thread, Memory, Undefined
LLVM_BUILD_TESTS	Enable lit/unit-test targets	ON (default)
LLVM_INCLUDE_TESTS	Include test directories in build	ON
LLVM_INCLUDE_BENCHMARKS	Include benchmarks	OFF
LLVM_INCLUDE_EXAMPLES	Include the examples/ directory	ON/OFF
LLVM_BUILD_EXAMPLES	Actually build them	OFF (default)
LLVM_PARALLEL_LINK_JOBS	Cap simultaneous link jobs	1 for low-RAM machines

Compiler / cache

Variable	Purpose
CMAKE_C_COMPILER / CMAKE_CXX_COMPILER	Override host compiler
LLVM_CCACHE_BUILD	Wrap compiles with ccache
LLVM_USE_SPLIT_DWARF	Emit split-dwarf debug info to speed up debug-build links
LLVM_BUILD_LLVM_DYLIB	Build a single shared libLLVM rather than per-component statics
BUILD_SHARED_LIBS	Produce shared libraries for the per-component build

Toolchain integration

Variable	Purpose
LLVM_DEFAULT_TARGET_TRIPLE	Default target triple Clang uses
LLVM_HOST_TRIPLE	Override the host triple
LLVM_INSTALL_TOOLCHAIN_ONLY	When installing, ship just the toolchain (no internal headers)
LLVM_DISTRIBUTION_COMPONENTS	Which install components ship in the install-distribution target

Runtime-build specifics

Variable	Purpose
COMPILER_RT_BUILD_BUILTINS	Build the builtins library
COMPILER_RT_BUILD_SANITIZERS	Build the sanitizer runtimes
COMPILER_RT_BUILD_PROFILE	Build the profile runtime
COMPILER_RT_BUILD_XRAY	Build XRay
LIBCXX_USE_COMPILER_RT	Use compiler-rt instead of libgcc for libc++
LIBCXXABI_USE_LLVM_UNWINDER	Use libunwind rather than the system unwinder
LIBC_TARGETS	Targets that LLVM-libc should produce overlays for

CMake presets

llvm/CMakePresets.json bundles common configurations. Useful entry points:

cmake --list-presets
cmake --preset stage1
cmake --preset bootstrap

The presets are a moving target — read the current contents of CMakePresets.json rather than memorizing this list.

Useful CMake invocations

# Iterate quickly on Clang
cmake -G Ninja -S llvm -B build \
    -DCMAKE_BUILD_TYPE=RelWithDebInfo \
    -DLLVM_ENABLE_ASSERTIONS=ON \
    -DLLVM_USE_LINKER=lld \
    -DLLVM_CCACHE_BUILD=ON \
    -DLLVM_TARGETS_TO_BUILD=Native \
    -DLLVM_ENABLE_PROJECTS="clang;lld"

# Build a runtime-side change against a built clang
cmake -G Ninja -S runtimes -B build-rt \
    -DCMAKE_C_COMPILER=$PWD/build/bin/clang \
    -DCMAKE_CXX_COMPILER=$PWD/build/bin/clang++ \
    -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind"

# Two-stage bootstrap (stage-1 builds Clang, stage-2 uses it)
cmake -G Ninja -S llvm -B stage1 \
    -DCMAKE_BUILD_TYPE=Release \
    -DLLVM_ENABLE_PROJECTS="clang;lld" \
    -DLLVM_TARGETS_TO_BUILD=host
ninja -C stage1
cmake -G Ninja -S llvm -B stage2 \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_C_COMPILER=$PWD/stage1/bin/clang \
    -DCMAKE_CXX_COMPILER=$PWD/stage1/bin/clang++ \
    -DLLVM_USE_LINKER=lld \
    -DLLVM_ENABLE_PROJECTS="clang;lld" \
    -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind"
ninja -C stage2

Reference

• Building LLVM with CMake
• Getting started — the abbreviated practical guide