# Building LLVM with CMake

## Introduction

CMake is a cross-platform build-generator tool. CMake does not build the project; it generates the files needed by your build tool (GNU make, Visual Studio, etc.) for building LLVM.

If you are a new contributor, please start with the Getting Started with the LLVM System page. This page is geared for existing contributors moving from the legacy configure/make system.

If you are really anxious about getting a functional LLVM build, go to the Quick start section. If you are a CMake novice, start with Basic CMake usage and then go back to the Quick start section once you know what you are doing. The Options and variables section is a reference for customizing your build. If you already have experience with CMake, this is the recommended starting point.

This page is geared towards users of the LLVM CMake build. If you’re looking for information about modifying the LLVM CMake build system, you may want to see the CMake Primer page. It has a basic overview of the CMake language.

## Quick start

We use here the command-line, non-interactive CMake interface.

1. Download and install CMake. Version 3.20.0 is the minimum required.

2. Open a shell. Your development tools must be reachable from this shell through the `PATH` environment variable.

3. Create a build directory. Building LLVM in the source directory is not supported. `cd` to this directory:

       $ mkdir mybuilddir
       $ cd mybuilddir

4. Execute this command in the shell replacing path/to/llvm/source/root with the path to the root of your LLVM source tree:

       $ cmake path/to/llvm/source/root

   CMake will detect your development environment, perform a series of tests, and generate the files required for building LLVM. CMake will use default values for all build parameters. See the Options and variables section for a list of build parameters that you can modify.

   This can fail if CMake can’t detect your toolset, or if it thinks that the environment is not sane enough. In this case, make sure that the toolset that you intend to use is the only one reachable from the shell, and that the shell itself is the correct one for your development environment. CMake will refuse to build MinGW makefiles if you have a POSIX shell reachable through the PATH environment variable, for instance. You can force CMake to use a given build tool; for instructions, see the Usage section, below. You may also wish to control which targets LLVM enables, or which LLVM components are built; see the Frequently Used LLVM-related variables below.

5. After CMake has finished running, use IDE project files, or start the build from the build directory:

       $ cmake --build .

   The `--build` option tells `cmake` to invoke the underlying build tool (`make`, `ninja`, `xcodebuild`, `msbuild`, etc.)

   The underlying build tool can be invoked directly, of course, but the `--build` option is portable.

6. After LLVM has finished building, install it from the build directory:

       $ cmake --build . --target install

   The `--target` option with `install` parameter in addition to the `--build` option tells `cmake` to build the `install` target.

   It is possible to set a different install prefix at installation time by invoking the `cmake_install.cmake` script generated in the build directory:

       $ cmake -DCMAKE_INSTALL_PREFIX=/tmp/llvm -P cmake_install.cmake

## Basic CMake usage

This section explains basic aspects of CMake for daily use.

CMake comes with extensive documentation, in the form of HTML files, and as online help accessible via the `cmake` executable itself. Execute `cmake --help` for further help options.

CMake allows you to specify a build tool (e.g., GNU make, Visual Studio, or Xcode). If not specified on the command line, CMake tries to guess which build tool to use based on your environment. Once it has identified your build tool, CMake uses the corresponding Generator to create files for your build tool (e.g., Makefiles or Visual Studio or Xcode project files). You can explicitly specify the generator with the command line option `-G "Name of the generator"`. To see a list of the available generators on your system, execute:

    $ cmake --help

This will list the generator names at the end of the help text.

Generators’ names are case-sensitive and may contain spaces. For this reason, you should enter them exactly as they are listed in the `cmake --help` output, in quotes. For example, to generate project files specifically for Visual Studio 12, you can execute:

    $ cmake -G "Visual Studio 12" path/to/llvm/source/root

A given development platform can have more than one adequate generator. If you use Visual Studio, “NMake Makefiles” is a generator you can use for building with NMake. By default, CMake chooses the most specific generator supported by your development environment. If you want an alternative generator, you must specify this to CMake with the `-G` option.

## Options and variables

Variables customize how the build will be generated. Options are boolean variables, with possible values ON/OFF. Options and variables are defined on the CMake command line like this:

    $ cmake -DVARIABLE=value path/to/llvm/source

You can set a variable after the initial CMake invocation to change its value. You can also undefine a variable:

    $ cmake -UVARIABLE path/to/llvm/source

Variables are stored in the CMake cache. This is a file named `CMakeCache.txt` stored at the root of your build directory that is generated by `cmake`. Editing it yourself is not recommended.

Variables are listed in the CMake cache and later in this document with the variable name and type separated by a colon. You can also specify the variable and type on the CMake command line:

    $ cmake -DVARIABLE:TYPE=value path/to/llvm/source

### Frequently-used CMake variables

Here are some of the CMake variables that are used often, along with a brief explanation. For full documentation, consult the CMake manual, or execute `cmake --help-variable VARIABLE_NAME`. See Frequently Used LLVM-related Variables below for information about commonly used variables that control features of LLVM and enabled subprojects.

CMAKE_BUILD_TYPE:STRING

  This configures the optimization level for `make` or `ninja` builds.

  Possible values:

  Build Type | Optimizations | Debug Info | Assertions | Best suited for
  --- | --- | --- | --- | ---
  Release | For Speed | No | No | Users of LLVM and Clang
  Debug | None | Yes | Yes | Developers of LLVM
  RelWithDebInfo | For Speed | Yes | No | Users that also need Debug
  MinSizeRel | For Size | No | No | When disk space matters

  - Optimizations make LLVM/Clang run faster but can be an impediment for step-by-step debugging.

  - Builds with debug information can use a lot of RAM and disk space and are usually slower to run. You can improve RAM usage by using `lld`, see the LLVM_USE_LINKER option.

  - Assertions are internal checks to help you find bugs. They typically slow down LLVM and Clang when enabled but can be useful during development. You can manually set LLVM_ENABLE_ASSERTIONS to override the default from CMAKE_BUILD_TYPE.

  If you are using an IDE such as Visual Studio or Xcode, use the IDE settings to set the build type.

  Note: on Windows (building with MSVC or clang-cl), CMake’s RelWithDebInfo setting does not enable the same optimizations as Release. Using the Release build type with LLVM_ENABLE_PDB set may be a better option.

CMAKE_INSTALL_PREFIX:PATH

  Path where LLVM will be installed when the “install” target is built.

CMAKE_{C,CXX}_FLAGS:STRING

  Extra flags to use when compiling C and C++ source files respectively.

CMAKE_{C,CXX}_COMPILER:STRING

  Specify the C and C++ compilers to use. If you have multiple compilers installed, CMake might not default to the one you wish to use.

### Frequently Used LLVM-related variables

The default configuration may not match your requirements. Here are LLVM variables that are frequently used to control that. The full description is in LLVM-related variables below.

LLVM_ENABLE_PROJECTS:STRING

  Control which projects are enabled. For example, you may want to work on clang or lldb by specifying `-DLLVM_ENABLE_PROJECTS="clang;lldb"`.

LLVM_ENABLE_RUNTIMES:STRING

  Control which runtimes are enabled. For example, you may want to work on libc++ or libc++abi by specifying `-DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"`.

LLVM_LIBDIR_SUFFIX:STRING

  Extra suffix to append to the directory where libraries are to be installed. On a 64-bit architecture, one could use `-DLLVM_LIBDIR_SUFFIX=64` to install libraries to `/usr/lib64`.

LLVM_PARALLEL_{COMPILE,LINK}_JOBS:STRING

  Building the llvm toolchain can use a lot of resources, particularly during linking. These options, when you use the Ninja generator, allow you to restrict the parallelism. For example, to avoid OOMs or going into swap, permit only one link job per 15 GB of RAM available on a 32 GB machine, specify `-G Ninja -DLLVM_PARALLEL_LINK_JOBS=2`.

LLVM_TARGETS_TO_BUILD:STRING

  Control which targets are enabled. For example, you may only need to enable your native target with, for example, `-DLLVM_TARGETS_TO_BUILD=X86`.

LLVM_USE_LINKER:STRING

  Override the system’s default linker. For instance, use `lld` with `-DLLVM_USE_LINKER=lld`.

### Rarely-used CMake variables

Here are some of the CMake variables that are rarely used, along with a brief explanation and LLVM-related notes. For full documentation, consult the CMake manual, or execute `cmake --help-variable VARIABLE_NAME`.

CMAKE_CXX_STANDARD:STRING

  Sets the C++ standard to conform to when building LLVM. LLVM requires C++17 or higher. This defaults to 17.

CMAKE_INSTALL_BINDIR:PATH

  The path to install executables, relative to the CMAKE_INSTALL_PREFIX. Defaults to “bin”.

CMAKE_INSTALL_DOCDIR:PATH

  The path to install documentation, relative to the CMAKE_INSTALL_PREFIX. Defaults to “share/doc”.

CMAKE_INSTALL_INCLUDEDIR:PATH

  The path to install header files, relative to the CMAKE_INSTALL_PREFIX. Defaults to “include”.

CMAKE_INSTALL_MANDIR:PATH

  The path to install manpage files, relative to the CMAKE_INSTALL_PREFIX. Defaults to “share/man”.

### LLVM-related variables

These variables provide fine control over the build of LLVM and its enabled sub-projects. Nearly all of these variable names begin with `LLVM_`.

BUILD_SHARED_LIBS:BOOL

  Flag indicating if each LLVM component (e.g. Support) is built as a shared library (ON) or as a static library (OFF). Its default value is OFF. On Windows, shared libraries may be used when building with MinGW, including mingw-w64, but not when building with the Microsoft toolchain.

  Note

  `BUILD_SHARED_LIBS` is only recommended for use by LLVM developers. If you want to build LLVM as a shared library, you should use the `LLVM_BUILD_LLVM_DYLIB` option.

LLVM_ABI_BREAKING_CHECKS:STRING

  Used to decide if LLVM should be built with ABI breaking checks or not. Allowed values are WITH_ASSERTS (default), FORCE_ON and FORCE_OFF. WITH_ASSERTS turns on ABI breaking checks in an assertion-enabled build. FORCE_ON (FORCE_OFF) turns them on (off) irrespective of whether normal (NDEBUG-based) assertions are enabled or not. A version of LLVM built with ABI breaking checks is not ABI compatible with a version built without it.

LLVM_ADDITIONAL_BUILD_TYPES:LIST

  Adding a semicolon-separated list of additional build types to this flag allows for them to be specified as values in `CMAKE_BUILD_TYPE` without encountering a fatal error during the configuration process.

LLVM_APPEND_VC_REV:BOOL

  Embed version control revision info (Git revision id). The version info is provided by the `LLVM_REVISION` macro in `llvm/include/llvm/Support/VCSRevision.h`. Developers using git who don’t need revision info can disable this option to avoid re-linking most binaries after a branch switch. Defaults to ON.

LLVM_FORCE_VC_REPOSITORY:STRING

  Set the git repository to include in version info rather than calling git to determine it.

LLVM_FORCE_VC_REVISION:STRING

  Force a specific Git revision id rather than calling git to determine it. This is useful in environments where git is not available or non-functional but the VC revision is available through other means.

LLVM_BUILD_32_BITS:BOOL

  Build 32-bit executables and libraries on 64-bit systems. This option is available only on some 64-bit Unix systems. Defaults to OFF.

LLVM_BUILD_BENCHMARKS:BOOL

  Adds benchmarks to the list of default targets. Defaults to OFF.

LLVM_BUILD_DOCS:BOOL

  Adds all enabled documentation targets (i.e., Doxygen and Sphinx targets) as dependencies of the default build targets. This results in all of the (enabled) documentation targets being built as part of a normal build. If the `install` target is run, then this also enables all built documentation targets to be installed. Defaults to OFF. To enable a particular documentation target, see `LLVM_ENABLE_SPHINX` and `LLVM_ENABLE_DOXYGEN`.

LLVM_BUILD_EXAMPLES:BOOL

  Include LLVM examples in the ‘all’ build target and install them as part of the `install` target. Defaults to OFF. Targets for building examples are still generated, this is controlled by LLVM_INCLUDE_EXAMPLES. Note that some examples might still be built as dependencies for tests.

LLVM_BUILD_INSTRUMENTED_COVERAGE:BOOL

  If enabled, source-based code coverage instrumentation is enabled while building llvm. If CMake can locate the code coverage scripts and the llvm-cov and llvm-profdata tools that pair with your compiler, the build will also generate the generate-coverage-report target to generate the code coverage report for LLVM, and the clear-profile-data utility target to delete captured profile data. See documentation for LLVM_CODE_COVERAGE_TARGETS and LLVM_COVERAGE_SOURCE_DIRS for more information on configuring code coverage reports.

LLVM_BUILD_LLVM_DYLIB:BOOL

  If enabled, the target for building the libLLVM shared library is added. This library contains all of LLVM’s components in a single shared library. Defaults to OFF. This cannot be used in conjunction with `BUILD_SHARED_LIBS`. Tools will only be linked to the libLLVM shared library if `LLVM_LINK_LLVM_DYLIB` is also ON. The components in the library can be customised by setting `LLVM_DYLIB_COMPONENTS` to a list of the desired components. This option is not available on Windows.

LLVM_BUILD_TESTS:BOOL

  Include LLVM unit tests in the ‘all’ build target. Defaults to OFF. Targets for building each unit test are generated in any case. You can build a specific unit test using the targets defined under unittests, such as ADTTests, IRTests, SupportTests, etc. (Search for `add_llvm_unittest` in the subdirectories of unittests for a complete list of unit tests.) It is possible to build all unit tests with the target UnitTests.

LLVM_BUILD_TOOLS:BOOL

  Build LLVM tools. Defaults to ON. Targets for building each tool are generated in any case. You can build a tool separately by invoking its target. For example, you can build llvm-as with a Makefile-based system by executing make llvm-as at the root of your build directory.

LLVM_CCACHE_BUILD:BOOL

  If enabled and the `ccache` program is available, then LLVM will be built using `ccache` to speed up rebuilds of LLVM and its components. Defaults to OFF. The size and location of the cache maintained by `ccache` can be adjusted via the `LLVM_CCACHE_MAXSIZE` and `LLVM_CCACHE_DIR` options, which are passed to the `CCACHE_MAXSIZE` and `CCACHE_DIR` environment variables, respectively.

LLVM_CODE_COVERAGE_TARGETS:STRING

  If set to a semicolon-separated list of targets, those targets will be used to drive the code coverage reports. If unset, the target list will be constructed using the LLVM build’s CMake export list.

LLVM_COVERAGE_SOURCE_DIRS:STRING

  If set to a semicolon-separated list of directories, the coverage reports will limit code coverage summaries to just the listed directories. If unset, coverage reports will include all sources identified by the tooling.

LLVM_CREATE_XCODE_TOOLCHAIN:BOOL

  macOS only: If enabled, CMake will generate a target named ‘install-xcode-toolchain’. This target will create a directory at `$CMAKE_INSTALL_PREFIX/Toolchains` containing an xctoolchain directory which can be used to override the default system tools.

LLVM_DEFAULT_TARGET_TRIPLE:STRING

  LLVM target to use for code generation when no target is explicitly specified. It defaults to “host”, meaning that it shall pick the architecture of the machine where LLVM is being built. If you are building a cross-compiler, set it to the target triple of your desired architecture.

LLVM_DOXYGEN_QCH_FILENAME:STRING

  The filename of the Qt Compressed Help file that will be generated when `-DLLVM_ENABLE_DOXYGEN=ON` and `-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON` are given. Defaults to `org.llvm.qch`. This option is only useful in combination with `-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON`; otherwise it has no effect.

LLVM_DOXYGEN_QHELPGENERATOR_PATH:STRING

  The path to the `qhelpgenerator` executable. Defaults to whatever CMake’s `find_program()` can find. This option is only useful in combination with `-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON`; otherwise it has no effect.

LLVM_DOXYGEN_QHP_CUST_FILTER_NAME:STRING

  See Qt Help Project for more information. Defaults to the CMake variable `${PACKAGE_STRING}` which is a combination of the package name and version string. This filter can then be used in Qt Creator to select only documentation from LLVM when browsing through all the help files that you might have loaded. This option is only useful in combination with `-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON`; otherwise it has no effect.

LLVM_DOXYGEN_QHP_NAMESPACE:STRING

  Namespace under which the intermediate Qt Help Project file lives. See Qt Help Project for more information. Defaults to “org.llvm”. This option is only useful in combination with `-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON`; otherwise it has no effect.

LLVM_ENABLE_ASSERTIONS:BOOL

  Enables code assertions. Defaults to ON if and only if `CMAKE_BUILD_TYPE` is Debug.

LLVM_ENABLE_BINDINGS:BOOL

  If disabled, do not try to build the OCaml bindings.

LLVM_ENABLE_CURL:

  Used to decide if LLVM tools, should support downloading information (particularly debug info from `llvm-debuginfod`) over HTTP. Allowed values are `OFF` (default), `ON`, and `FORCE_ON` (error if libcurl is not found).

LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING:STRING

  Enhances Debugify’s ability to detect line number errors by storing extra information inside Instructions, removing false positives from Debugify’s results at the cost of performance. Allowed values are DISABLED (default), COVERAGE, and COVERAGE_AND_ORIGIN. COVERAGE tracks whether and why a line number was intentionally dropped or not generated for an instruction, allowing Debugify to avoid reporting these as errors; this comes with a small performance cost of ~0.1%. COVERAGE_AND_ORIGIN additionally stores a stacktrace of the point where each DebugLoc is unintentionally dropped, allowing for much easier bug triaging at the cost of a ~10x performance slowdown. COVERAGE and COVERAGE_AND_ORIGIN are ABI-breaking options.

LLVM_ENABLE_DIA_SDK:BOOL

  Enable building with MSVC DIA SDK for PDB debugging support. Available only with MSVC. Defaults to ON.

LLVM_ENABLE_DOXYGEN:BOOL

  Enables the generation of browsable HTML documentation using doxygen. Defaults to OFF.

LLVM_ENABLE_DOXYGEN_QT_HELP:BOOL

  Enables the generation of a Qt Compressed Help file. Defaults to OFF. This affects the make target `doxygen-llvm`. When enabled, apart from the normal HTML output generated by doxygen, this will produce a QCH file named `org.llvm.qch`. You can then load this file into Qt Creator. This option is only useful in combination with `-DLLVM_ENABLE_DOXYGEN=ON`; otherwise this has no effect.

LLVM_ENABLE_EH:BOOL

  Build LLVM with exception-handling support. This is necessary if you wish to link against LLVM libraries and make use of C++ exceptions in your own code that need to propagate through LLVM code. Defaults to OFF.

LLVM_ENABLE_EXPENSIVE_CHECKS:BOOL

  Enable additional time/memory expensive checking. Defaults to OFF.

LLVM_ENABLE_FFI:BOOL

  Indicates whether the LLVM Interpreter will be linked with the Foreign Function Interface library (libffi) in order to enable calling external functions. If the library or its headers are installed in a custom location, you can also set the variables `FFI_INCLUDE_DIR` and `FFI_LIBRARY_DIR` to the directories where `ffi.h` and `libffi.so` can be found, respectively. Defaults to OFF.

LLVM_ENABLE_HTTPLIB:BOOL

  Enables the optional cpp-httplib dependency which is used by llvm-debuginfod to serve debug info over HTTP. cpp-httplib must be installed, or httplib_ROOT must be set. Defaults to OFF.

LLVM_ENABLE_IDE:BOOL

  Tell the build system that an IDE is being used. This in turn disables the creation of certain convenience build system targets, such as the various `install-*` and `check-*` targets, since IDEs don’t always deal well with a large number of targets. This is usually autodetected, but it can be configured manually to explicitly control the generation of those targets.

LLVM_ENABLE_LIBCXX:BOOL

  If the host compiler and linker support the stdlib flag, `-stdlib=libc++` is passed to invocations of both so that the project is built using libc++ instead of stdlibc++. Defaults to OFF.

LLVM_ENABLE_LIBEDIT:BOOL

  Controls whether to enable libedit support for command-line editing and history in LLVM tools. When `ON`, forces libedit support to be enabled and will cause a CMake configuration error if libedit cannot be found. When `OFF`, disables libedit support entirely. If not specified, LLVM will auto-detect libedit availability. Defaults to auto-detection.

LLVM_ENABLE_LIBPFM:BOOL

  Enable building with libpfm to support hardware counter measurements in LLVM tools. Defaults to ON.

LLVM_ENABLE_LLD:BOOL

  This option is equivalent to -DLLVM_USE_LINKER=lld, except during a 2-stage build where a dependency is added from the first stage to the second ensuring that lld is built before stage2 begins.

LLVM_ENABLE_LLVM_LIBC: BOOL

  If the LLVM libc overlay is installed in a location where the host linker can access it, all built executables will be linked against the LLVM libc overlay before linking against the system libc. Defaults to OFF.

LLVM_ENABLE_LTO:STRING

  Add `-flto` or `-flto=` flags to the compile and link command lines, enabling link-time optimization. Possible values are `Off`, `On`, `Thin` and `Full`. Defaults to OFF.

LLVM_ENABLE_MODULES:BOOL

  Compile with Clang Header Modules.

LLVM_ENABLE_PDB:BOOL

  For Windows builds using MSVC or clang-cl, generate PDB files when CMAKE_BUILD_TYPE is set to Release.

LLVM_ENABLE_PEDANTIC:BOOL

  Enable pedantic mode. This disables compiler-specific extensions, if possible. Defaults to ON.

LLVM_ENABLE_PIC:BOOL

  Add the `-fPIC` flag to the compiler command-line, if the compiler supports this flag. Some systems, like Windows, do not need this flag. Defaults to ON.

LLVM_ENABLE_PROJECTS:STRING

  Semicolon-separated list of projects to build, or all for building all (clang, lldb, lld, polly, etc) projects. This flag assumes that projects are checked out side-by-side and not nested, i.e. clang needs to be in parallel to llvm instead of nested in `llvm/tools`. This feature allows having one build for only LLVM and another for clang+llvm using the same source checkout.

  The full list is:

  `bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libc;libclc;lld;lldb;mlir;openmp;polly`

  Note

  Some projects listed here can also go in `LLVM_ENABLE_RUNTIMES`. They should only appear in one of the two lists. If a project is a valid possibility for both, prefer putting it in `LLVM_ENABLE_RUNTIMES`.

LLVM_ENABLE_RTTI:BOOL

  Build LLVM with run-time type information. Defaults to OFF.

LLVM_ENABLE_RUNTIMES:STRING

  Build libc++, libc++abi, libunwind or compiler-rt using the just-built compiler. This is the correct way to build runtimes when putting together a toolchain. It will build the builtins separately from the other runtimes to preserve correct dependency ordering. If you want to build the runtimes using a system compiler, see the libc++ documentation.

  Note

  The list should not have duplicates with `LLVM_ENABLE_PROJECTS`.

  To list all possible runtimes, include an invalid name. For example `-DLLVM_ENABLE_RUNTIMES=notaruntime`. The resulting CMake error will list the possible runtime names.

  To enable all of the runtimes, use:

  `LLVM_ENABLE_RUNTIMES=all`

LLVM_ENABLE_SPHINX:BOOL

  If specified, CMake will search for the `sphinx-build` executable and will make the `SPHINX_OUTPUT_HTML` and `SPHINX_OUTPUT_MAN` CMake options available. Defaults to OFF.

LLVM_ENABLE_THREADS:BOOL

  Build with threads support, if available. Defaults to ON.

LLVM_ENABLE_UNWIND_TABLES:BOOL

  Enable unwind tables in the binary. Disabling unwind tables can reduce the size of the libraries. Defaults to ON.

LLVM_ENABLE_WARNINGS:BOOL

  Enable all compiler warnings. Defaults to ON.

LLVM_ENABLE_WERROR:BOOL

  Stop and fail the build, if a compiler warning is triggered. Defaults to OFF.

LLVM_ENABLE_Z3_SOLVER:BOOL

  If enabled, the Z3 constraint solver is activated for the Clang static analyzer. A recent version of the z3 library must be available on the system.

LLVM_ENABLE_ZLIB:STRING

  Used to decide if LLVM tools should support compression/decompression with zlib. Allowed values are `OFF`, `ON` (default, enable if zlib is found), and `FORCE_ON` (error if zlib is not found).

LLVM_ENABLE_ZSTD:STRING

  Used to decide if LLVM tools should support compression/decompression with zstd. Allowed values are `OFF`, `ON` (default, enable if zstd is found), and `FORCE_ON` (error if zstd is not found).

LLVM_EXPERIMENTAL_TARGETS_TO_BUILD:STRING

  Semicolon-separated list of experimental targets to build and linked into llvm. This will build the experimental target without needing it to add to the list of all the targets available in the LLVM’s main `CMakeLists.txt`.

LLVM_EXTERNAL_PROJECTS:STRING

  Semicolon-separated list of additional external projects to build as part of llvm. For each project, `LLVM_EXTERNAL_<NAME>_SOURCE_DIR` has to be specified with the path for the source code of the project. Example: `-DLLVM_EXTERNAL_PROJECTS="Foo;Bar" -DLLVM_EXTERNAL_FOO_SOURCE_DIR=/src/foo -DLLVM_EXTERNAL_BAR_SOURCE_DIR=/src/bar`.

LLVM_EXTERNAL_{CLANG,LLD,POLLY}_SOURCE_DIR:PATH

  These variables specify the path to the source directory for the external LLVM projects Clang, lld, and Polly, respectively, relative to the top-level source directory. If the in-tree subdirectory for an external project exists (e.g., `llvm/tools/clang` for Clang), then the corresponding variable will not be used. If the variable for an external project does not point to a valid path, then that project will not be built.

LLVM_EXTERNALIZE_DEBUGINFO:BOOL

  Generate dSYM files and strip executables and libraries (Darwin only). Defaults to OFF.

LLVM_ENABLE_EXPORTED_SYMBOLS_IN_EXECUTABLES:BOOL

  When building executables, preserve symbol exports. Defaults to ON. You can use this option to disable exported symbols from all executables (Darwin Only).

LLVM_FORCE_USE_OLD_TOOLCHAIN:BOOL

  If enabled, the compiler and standard library versions won’t be checked. LLVM may not compile at all, or might fail at runtime due to known bugs in these toolchains.

LLVM_INCLUDE_BENCHMARKS:BOOL

  Generate build targets for the LLVM benchmarks. Defaults to ON.

LLVM_INCLUDE_EXAMPLES:BOOL

  Generate build targets for the LLVM examples. Defaults to ON. You can use this option to disable the generation of build targets for the LLVM examples.

LLVM_INCLUDE_TESTS:BOOL

  Generate build targets for the LLVM unit tests. Defaults to ON. You can use this option to disable the generation of build targets for the LLVM unit tests.

LLVM_INCLUDE_TOOLS:BOOL

  Generate build targets for the LLVM tools. Defaults to ON. You can use this option to disable the generation of build targets for the LLVM tools.

LLVM_INDIVIDUAL_TEST_COVERAGE:BOOL

  Enable individual test case coverage. When set to ON, code coverage data for each test case will be generated and stored in a separate directory under the config.test_exec_root path. This feature allows code coverage analysis of each individual test case. Defaults to OFF.

LLVM_INSTALL_BINUTILS_SYMLINKS:BOOL

  Install symlinks from the binutils tool names to the corresponding LLVM tools. For example, ar will be symlinked to llvm-ar.

LLVM_INSTALL_CCTOOLS_SYMLINKS:BOOL

  Install symlinks from the cctools tool names to the corresponding LLVM tools. For example, lipo will be symlinked to llvm-lipo.

LLVM_INSTALL_OCAMLDOC_HTML_DIR:STRING

  The path to install OCamldoc-generated HTML documentation to. This path can either be absolute or relative to the `CMAKE_INSTALL_PREFIX`. Defaults to `${CMAKE_INSTALL_DOCDIR}/llvm/ocaml-html`.

LLVM_INSTALL_SPHINX_HTML_DIR:STRING

  The path to install Sphinx-generated HTML documentation to. This path can either be absolute or relative to the `CMAKE_INSTALL_PREFIX`. Defaults to `${CMAKE_INSTALL_DOCDIR}/llvm/html`.

LLVM_INSTALL_UTILS:BOOL

  If enabled, utility binaries like `FileCheck` and `not` will be installed to `CMAKE_INSTALL_PREFIX`.

LLVM_INSTALL_DOXYGEN_HTML_DIR:STRING

  The path to install Doxygen-generated HTML documentation to. This path can either be absolute or relative to the CMAKE_INSTALL_PREFIX. Defaults to `${CMAKE_INSTALL_DOCDIR}/llvm/doxygen-html`.

LLVM_INTEGRATED_CRT_ALLOC:PATH

  On Windows, allows embedding a different C runtime allocator into the LLVM tools and libraries. Using a lock-free allocator such as the ones listed below greatly decreases ThinLTO link time by about an order of magnitude. It also mildly improves Clang build times, by about 5-10%. At the moment, rpmalloc, snmalloc and mimalloc are supported. Use the path to git clone to select the respective allocator, for example:

      $ D:\git> git clone https://github.com/mjansson/rpmalloc
      $ D:\llvm-project> cmake ... -DLLVM_INTEGRATED_CRT_ALLOC=D:\git\rpmalloc

  This option needs to be used along with the static CRT, i.e., if building the Release target, add `-DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded`. Note that rpmalloc is also supported natively in-tree, see option below.

LLVM_ENABLE_RPMALLOC:BOOL

  Similar to LLVM_INTEGRATED_CRT_ALLOC, embeds the in-tree rpmalloc into the host toolchain as a C runtime allocator. The version currently used is rpmalloc 1.4.5. This option also implies linking with the static CRT, there’s no need to provide CMAKE_MSVC_RUNTIME_LIBRARY.

LLVM_LINK_LLVM_DYLIB:BOOL

  If enabled, tools will be linked with the libLLVM shared library. Defaults to OFF. Setting `LLVM_LINK_LLVM_DYLIB` to ON also sets `LLVM_BUILD_LLVM_DYLIB` to ON. This option is not available on Windows.

LLVM_<target>_LINKER_FLAGS:STRING

  Defines the set of linker flags that should be applied to a <target>.

LLVM_LIT_ARGS:STRING

  Arguments given to lit. `make check` and `make clang-test` are affected. By default, `'-sv --no-progress-bar'` on Visual C++ and Xcode, `'-sv'` on others.

LLVM_LIT_TOOLS_DIR:PATH

  The path to GnuWin32 tools for tests. Valid on Windows host. Defaults to the empty string, in which case lit will look for tools needed for tests (e.g., `grep`, `sort`, etc.) in your `%PATH%`. If GnuWin32 is not in your `%PATH%`, then you can set this variable to the GnuWin32 directory so that lit can find tools needed for tests in that directory.

LLVM_NATIVE_TOOL_DIR:STRING

  Full path to a directory containing executables for the build host (containing binaries such as `llvm-tblgen` and `clang-tblgen`). This is intended for cross-compiling: if the user sets this variable and the directory contains executables with the expected names, no separate native versions of those executables will be built.

LLVM_NO_INSTALL_NAME_DIR_FOR_BUILD_TREE:BOOL

  Defaults to `OFF`. If set to `ON`, CMake’s default logic for library IDs on Darwin in the build tree will be used. Otherwise the install-time library IDs will be used in the build tree as well. Mainly useful when other CMake library ID control variables (e.g., `CMAKE_INSTALL_NAME_DIR`) are being set to non-standard values.

LLVM_OPTIMIZED_TABLEGEN:BOOL

  If enabled and building a debug or assert build, the CMake build system will generate a Release build tree to build a fully optimized tablegen for use during the build. Enabling this option can significantly speed up build times, especially when building LLVM in Debug configurations.

LLVM_PARALLEL_{COMPILE,LINK,TABLEGEN}_JOBS:STRING

  Limit the maximum number of concurrent compilation, link or tablegen jobs respectively. The default total number of parallel jobs is determined by the number of logical CPUs.

LLVM_PROFDATA_FILE:PATH

  Path to a profdata file to pass into clang’s `-fprofile-instr-use` flag. This can only be specified if you’re building with clang.

LLVM_RAM_PER_{COMPILE,LINK,TABLEGEN}_JOB:STRING

  Limit the number of concurrent compile, link or tablegen jobs respectively, depending on available physical memory. The value specified is in MB. The respective `LLVM_PARALLEL_{COMPILE,LINK,TABLEGEN}_JOBS` variable is overwritten by computing the memory size divided by the specified value. The largest memory user is linking, but remember that jobs in the other categories might run in parallel with the link jobs, and you need to consider their memory requirements when in a memory-limited environment. Using a `-DLLVM_RAM_PER_LINK_JOB=10000` is a good approximation. On ELF platforms debug builds can reduce link-time memory pressure by also using `LLVM_USE_SPLIT_DWARF`.

LLVM_REVERSE_ITERATION:BOOL

  If enabled, all supported unordered llvm containers would be iterated in reverse order. This is useful for uncovering non-determinism caused by iteration of unordered containers.

LLVM_STATIC_LINK_CXX_STDLIB:BOOL

  Statically link to the C++ standard library if possible. This uses the flag `-static-libstdc++`, but a Clang host compiler will statically link to libc++ if used in conjunction with the LLVM_ENABLE_LIBCXX flag. Defaults to OFF.

LLVM_TABLEGEN:STRING

  Full path to a native TableGen executable (usually named `llvm-tblgen`). This is intended for cross-compiling: if the user sets this variable, no native TableGen will be created.

LLVM_TARGET_ARCH:STRING

  LLVM target to use for native code generation. This is required for JIT generation. It defaults to “host”, meaning that it shall pick the architecture of the machine where LLVM is being built. If you are cross-compiling, set it to the target architecture name.

LLVM_TARGETS_TO_BUILD:STRING

  Semicolon-separated list of targets to build, or all for building all targets. Case-sensitive. Defaults to all. Example: `-DLLVM_TARGETS_TO_BUILD="X86;PowerPC"`. The full list, as of August 2025, is: `AArch64;AMDGPU;ARM;AVR;BPF;Hexagon;Lanai;LoongArch;Mips;MSP430;NVPTX;PowerPC;RISCV;Sparc;SPIRV;SystemZ;VE;WebAssembly;X86;XCore`

  You can also specify `host` or `Native` to automatically detect and include the target corresponding to the host machine’s architecture, or use `all` to include all available targets. For example, on an x86_64 machine, specifying `-DLLVM_TARGETS_TO_BUILD=host` will include the `X86` target.

LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN:BOOL

  If enabled, the compiler version check will only warn when using a toolchain which is about to be deprecated, instead of emitting an error.

LLVM_UBSAN_FLAGS:STRING

  Defines the set of compile flags used to enable UBSan. Only used if `LLVM_USE_SANITIZER` contains `Undefined`. This can be used to override the default set of UBSan flags.

LLVM_UNREACHABLE_OPTIMIZE:BOOL

  This flag controls the behavior of `llvm_unreachable()` in a release build (when assertions are disabled in general). When ON (default) then `llvm_unreachable()` is considered “undefined behavior” and optimized as such. When OFF it is instead replaced with a guaranteed “trap”.

LLVM_USE_INTEL_JITEVENTS:BOOL

  Enable building support for Intel JIT Events API. Defaults to OFF.

LLVM_USE_LINKER:STRING

  Add `-fuse-ld={name}` to the link invocation. The possible values depend on your compiler. For clang, the value can be an absolute path to your custom linker, otherwise clang will prefix the name with `ld.` and apply its usual search. For example, to link LLVM with the Gold linker, cmake can be invoked with `-DLLVM_USE_LINKER=gold`.

LLVM_USE_OPROFILE:BOOL

  Enable building OProfile JIT support. Defaults to OFF.

LLVM_USE_PERF:BOOL

  Enable building support for Perf (linux profiling tool) JIT support. Defaults to OFF.

LLVM_USE_RELATIVE_PATHS_IN_FILES:BOOL

  Rewrite absolute source paths in sources and debug info to relative ones. The source prefix can be adjusted via the `LLVM_SOURCE_PREFIX` variable.

LLVM_USE_RELATIVE_PATHS_IN_DEBUG_INFO:BOOL

  Rewrite absolute source paths in debug info to relative ones. The source prefix can be adjusted via the `LLVM_SOURCE_PREFIX` variable.

LLVM_USE_SANITIZER:STRING

  Define the sanitizer used to build LLVM binaries and tests. Possible values are `Address`, `Memory`, `MemoryWithOrigins`, `Undefined`, `Thread`, `DataFlow`, and `Address;Undefined`. Defaults to empty string.

LLVM_USE_SPLIT_DWARF:BOOL

  If enabled CMake will pass `-gsplit-dwarf` to the compiler. This option reduces link-time memory usage by reducing the amount of debug information that the linker needs to resolve. It is recommended for platforms using the ELF object format, like Linux systems when linker memory usage is too high.

SPHINX_EXECUTABLE:STRING

  The path to the `sphinx-build` executable detected by CMake. For installation instructions, see https://www.sphinx-doc.org/en/master/usage/installation.html

SPHINX_OUTPUT_HTML:BOOL

  If enabled (and `LLVM_ENABLE_SPHINX` is enabled) then the targets for building the documentation as HTML are added (but not built by default unless `LLVM_BUILD_DOCS` is enabled). There is a target for each project in the source tree that uses sphinx (e.g., `docs-llvm-html`, `docs-clang-html` and `docs-lld-html`). Defaults to ON.

SPHINX_OUTPUT_MAN:BOOL

  If enabled (and `LLVM_ENABLE_SPHINX` is enabled) the targets for building the man pages are added (but not built by default unless `LLVM_BUILD_DOCS` is enabled). Currently the only target added is `docs-llvm-man`. Defaults to ON.

SPHINX_WARNINGS_AS_ERRORS:BOOL

  If enabled, then sphinx documentation warnings will be treated as errors. Defaults to ON.

#### Advanced variables

These are niche, and changing them from their defaults is more likely to cause things to go wrong. They are also unstable across LLVM versions.

LLVM_EXAMPLES_INSTALL_DIR:STRING

  The path for examples of using LLVM, relative to the CMAKE_INSTALL_PREFIX. Only matters if LLVM_BUILD_EXAMPLES is enabled. Defaults to “examples”.

LLVM_TOOLS_INSTALL_DIR:STRING

  The path to install the main LLVM tools, relative to the CMAKE_INSTALL_PREFIX. Defaults to CMAKE_INSTALL_BINDIR.

LLVM_UTILS_INSTALL_DIR:STRING

  The path to install auxiliary LLVM utilities, relative to the CMAKE_INSTALL_PREFIX. Only matters if LLVM_INSTALL_UTILS is enabled. Defaults to LLVM_TOOLS_INSTALL_DIR.

## CMake Caches

Recently, LLVM and Clang have been adding some more complicated build system features. Utilizing these new features often involves a complicated chain of CMake variables passed on the command line. Clang provides a collection of CMake cache scripts to make these features more approachable.

CMake cache files are utilized using CMake’s `-C` flag:

    $ cmake -C <path to cache file> <path to sources>

CMake cache scripts are processed in an isolated scope, only cached variables remain set when the main configuration runs. CMake cached variables do not reset variables that are already set unless the FORCE option is specified.

A few notes about CMake Caches:

- Order of command line arguments is important

  - `-D` arguments specified before `-C` are set before the cache is processed and can be read inside the cache file

  - `-D` arguments specified after `-C` are set after the cache is processed and are unset inside the cache file

- All `-D` arguments will override cache file settings

- CMAKE_TOOLCHAIN_FILE is evaluated after both the cache file and the command line arguments

- It is recommended that all `-D` options be specified before `-C`

For more information about some of the advanced build configurations supported via Cache files see Advanced Build Configurations.

## Executing the Tests

Testing is performed when the check-all target is built. For instance, if you are using Makefiles, execute this command in the root of your build directory:

    $ make check-all

On Visual Studio, you may run tests by building the project “check-all”. For more information about testing, see the LLVM Testing Infrastructure Guide.

## Cross compiling

See this wiki page for generic instructions on how to cross-compile with CMake. It goes into detailed explanations and may seem daunting, but it is not. The wiki page has several examples including toolchain files. Go directly to the `Information how to set up various cross compiling toolchains` section for a quick solution.

Also see the LLVM-related variables section for variables used when cross-compiling.

## Embedding LLVM in your project

From LLVM 3.5 onward, the CMake build system exports LLVM libraries as importable CMake targets. This means that clients of LLVM can now reliably use CMake to develop their own LLVM-based projects against an installed version of LLVM regardless of how it was built.

Here is a simple example of a `CMakeLists.txt` file that imports the LLVM libraries and uses them to build a simple application `simple-tool`.

    cmake_minimum_required(VERSION 3.20.0)
    project(SimpleProject)

    find_package(LLVM REQUIRED CONFIG)

    message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
    message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")

    # Set your project compile flags.
    # E.g. if using the C++ header files
    # you will need to enable C++11 support
    # for your compiler.

    include_directories(${LLVM_INCLUDE_DIRS})
    separate_arguments(LLVM_DEFINITIONS_LIST NATIVE_COMMAND ${LLVM_DEFINITIONS})
    add_definitions(${LLVM_DEFINITIONS_LIST})

    # Now build our tools
    add_executable(simple-tool tool.cpp)

    # Find the libraries that correspond to the LLVM components
    # that we wish to use
    llvm_map_components_to_libnames(llvm_libs support core irreader)

    # Link against LLVM libraries
    target_link_libraries(simple-tool ${llvm_libs})

The `find_package(...)` directive when used in CONFIG mode (as in the above example) will look for the `LLVMConfig.cmake` file in various locations (see CMake manual for details). It creates an `LLVM_DIR` cache entry to save the directory where `LLVMConfig.cmake` is found or allows the user to specify the directory (e.g., by passing `-DLLVM_DIR=/usr/lib/cmake/llvm` to the `cmake` command or by setting it directly in `ccmake` or `cmake-gui`).

This file is available in two different locations.

- `<LLVM_INSTALL_PACKAGE_DIR>/LLVMConfig.cmake` where `<LLVM_INSTALL_PACKAGE_DIR>` is the location where LLVM CMake modules are installed as part of an installed version of LLVM. This is typically `cmake/llvm/` within the lib directory. On Linux, this is typically `/usr/lib/cmake/llvm/LLVMConfig.cmake`.

- `<LLVM_BUILD_ROOT>/lib/cmake/llvm/LLVMConfig.cmake` where `<LLVM_BUILD_ROOT>` is the root of the LLVM build tree. Note: this is only available when building LLVM with CMake.

If LLVM is installed in your operating system’s normal installation prefix (e.g. on Linux this is usually `/usr/`) `find_package(LLVM ...)` will automatically find LLVM if it is installed correctly. If LLVM is not installed or you wish to build directly against the LLVM build tree you can use `LLVM_DIR` as previously mentioned.

The `LLVMConfig.cmake` file sets various useful variables. Notable variables include:

`LLVM_CMAKE_DIR`

  The path to the LLVM CMake directory (i.e., the directory containing `LLVMConfig.cmake`).

`LLVM_DEFINITIONS`

  A list of preprocessor defines that should be used when building against LLVM.

`LLVM_ENABLE_ASSERTIONS`

  This is set to ON if LLVM was built with assertions, otherwise OFF.

`LLVM_ENABLE_EH`

  This is set to ON if LLVM was built with exception handling (EH) enabled, otherwise OFF.

`LLVM_ENABLE_RTTI`

  This is set to ON if LLVM was built with run time type information (RTTI), otherwise OFF.

`LLVM_INCLUDE_DIRS`

  A list of include paths to directories containing LLVM header files.

`LLVM_PACKAGE_VERSION`

  The LLVM version. This string can be used with CMake conditionals, e.g., `if (${LLVM_PACKAGE_VERSION} VERSION_LESS "3.5")`.

`LLVM_TOOLS_BINARY_DIR`

  The path to the directory containing the LLVM tools (e.g., `llvm-as`).

Notice that in the above example we link `simple-tool` against several LLVM libraries. The list of libraries is determined by using the `llvm_map_components_to_libnames()` CMake function. For a list of available components look at the output of running `llvm-config --components`.

Note that for LLVM < 3.5 `llvm_map_components_to_libraries()` was used instead of `llvm_map_components_to_libnames()`. This is now deprecated and will be removed in a future version of LLVM.

### Developing LLVM passes out of source

You can develop LLVM passes out of LLVM’s source tree (i.e., against an installed or built LLVM). An example of a project layout is provided below.

    <project dir>/
        |
        CMakeLists.txt
        <pass name>/
            |
            CMakeLists.txt
            Pass.cpp
            ...

Contents of `<project dir>/CMakeLists.txt`:

    find_package(LLVM REQUIRED CONFIG)

    separate_arguments(LLVM_DEFINITIONS_LIST NATIVE_COMMAND ${LLVM_DEFINITIONS})
    add_definitions(${LLVM_DEFINITIONS_LIST})
    include_directories(${LLVM_INCLUDE_DIRS})

    add_subdirectory(<pass name>)

Contents of `<project dir>/<pass name>/CMakeLists.txt`:

    add_library(LLVMPassname MODULE Pass.cpp)

Note if you intend for this pass to be merged into the LLVM source tree at some point in the future it might make more sense to use LLVM’s internal `add_llvm_library` function with the MODULE argument instead by…

Adding the following to `<project dir>/CMakeLists.txt` (after `find_package(LLVM ...)`)

    list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_DIR}")
    include(AddLLVM)

And then changing `<project dir>/<pass name>/CMakeLists.txt` to

    add_llvm_library(LLVMPassname MODULE
      Pass.cpp
      )

When you are done developing your pass, you may wish to integrate it into the LLVM source tree. You can achieve it in two easy steps:

1. Copying `<pass name>` folder into `<LLVM root>/lib/Transforms` directory.

2. Adding `add_subdirectory(<pass name>)` line into `<LLVM root>/lib/Transforms/CMakeLists.txt`.

## Compiler/Platform-specific topics

Notes for specific compilers and/or platforms.

### Windows

LLVM_COMPILER_JOBS:STRING

  Specifies the maximum number of parallel compiler jobs to use per project when building with msbuild or Visual Studio. Only supported for the Visual Studio 2010 CMake generator. 0 means use all processors. Default is 0.

CMAKE_MT:STRING

  When compiling with clang-cl, CMake may use `llvm-mt` as the Manifest Tool when available. ``llvm-mt`` is only present when libxml2 is found at build-time. To ensure using Microsoft’s Manifest Tool set CMAKE_MT=mt.

### Apple/OSX

CMAKE_OSX_SYSROOT:STRING

  When compiling for OSX, in order for the test suite to find libSystem to link dylib tests you’ll need to run CMake with ``xcrun --show-sdk-path`` as the string to pass in so that the testsuite can find your os libraries.

  This will show up as ``ld: library not found for -lSystem`` when running tests.