Building LLVM with CMake¶

Introduction ¶

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

Ifyou are a new contributor, please start with theGetting Started with the LLVM Systempage. This page is geared for existing contributors moving from thelegacy configure/make system.

If you are really anxious about getting a functional LLVM build, go to theQuick start section. If you are a CMake novice, start withBasic CMake usageand then go back to theQuick start section once you know what you are doing. TheOptions and variables section is a reference for customizing your build. Ifyou 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 forinformation about modifying the LLVM CMake build system you may want to see theCMake Primer page. It has a basic overview of the CMake language.

Quick start ¶

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

Download and installCMake. Version 3.20.0 is the minimum required.
Open a shell. Your development tools must be reachable from this shellthrough the PATH environment variable.
Create a build directory. Building LLVM in the sourcedirectory is not supported. cd to this directory:
```
$mkdirmybuilddir$cdmybuilddir
```
Execute this command in the shell replacingpath/to/llvm/source/root withthe path to the root of your LLVM source tree:
```
$cmakepath/to/llvm/source/root
```
CMake will detect your development environment, perform a series of tests, andgenerate the files required for building LLVM. CMake will use default valuesfor all build parameters. See theOptions and variables section fora list of build parameters that you can modify.
This can fail if CMake can’t detect your toolset, or if it thinks that theenvironment is not sane enough. In this case, make sure that the toolset thatyou intend to use is the only one reachable from the shell, and that the shellitself is the correct one for your development environment. CMake will refuseto build MinGW makefiles if you have a POSIX shell reachable through the PATHenvironment variable, for instance. You can force CMake to use a given buildtool; for instructions, see theUsage section, below. You mayalso wish to control which targets LLVM enables, or which LLVMcomponents are built; see theFrequently Used LLVM-relatedvariables below.
After CMake has finished running, proceed to use IDE project files, or startthe build from the build directory:
```
$cmake--build.
```
The--build option tellscmake to invoke the underlying buildtool (make,ninja,xcodebuild,msbuild, etc.)
The underlying build tool can be invoked directly, of course, butthe--build option is portable.
After LLVM has finished building, install it from the build directory:
```
$cmake--build.--targetinstall
```
The--target option withinstall parameter in addition tothe--build option tellscmake to build theinstall target.
It is possible to set a different install prefix at installation timeby invoking thecmake_install.cmake script generated in thebuild directory:
```
$cmake-DCMAKE_INSTALL_PREFIX=/tmp/llvm-Pcmake_install.cmake
```

Basic CMake usage ¶

This section explains basic aspects of CMakewhich you may need in your day-to-day usage.

CMake comes with extensive documentation, in the form of html files, and asonline help accessible via thecmake executable itself. Executecmake--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 whichbuild tool to use, based on your environment. Once it has identified yourbuild tool, CMake uses the correspondingGenerator to create files for yourbuild tool (e.g., Makefiles or Visual Studio or Xcode project files). You canexplicitly specify the generator with the command line option-G"Nameofthegenerator". 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 thecmake--helpoutput, in quotes. For example, to generate project files specifically forVisual Studio 12, you can execute:

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

For a given development platform there can be more than one adequategenerator. If you use Visual Studio, “NMake Makefiles” is a generator you can usefor building with NMake. By default, CMake chooses the most specific generatorsupported by your development environment. If you want an alternative generator,you must tell this to CMake with the-G option.

Options and variables ¶

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

$cmake-DVARIABLE=valuepath/to/llvm/source

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

$cmake-UVARIABLEpath/to/llvm/source

Variables are stored in the CMake cache. This is a file namedCMakeCache.txtstored at the root of your build directory that is generated bycmake.Editing it yourself is not recommended.

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

$cmake-DVARIABLE:TYPE=valuepath/to/llvm/source

Frequently-used CMake variables ¶

Here are some of the CMake variables that are used often, along with abrief explanation. For full documentation, consult the CMake manual,or executecmake--help-variableVARIABLE_NAME. SeeFrequentlyUsed LLVM-related Variables below for information about commonlyused variables that control features of LLVM and enabled subprojects.

CMAKE_BUILD_TYPE:STRING

This configures the optimization level formake orninja 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 forstep-by-step debugging.
Builds with debug information can use a lot of RAM and disk space and isusually slower to run. You can improve RAM usage by usinglld, seetheLLVM_USE_LINKER option.
Assertions are internal checks to help you find bugs. They typically slowdown LLVM and Clang when enabled, but can be useful during development.You can manually setLLVM_ENABLE_ASSERTIONSto override the default fromCMAKE_BUILD_TYPE.

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

Note: on Windows (building with MSVC or clang-cl), CMake’sRelWithDebInfosetting does not enable the same optimizations asRelease. Using theRelease build type withLLVM_ENABLE_PDB setmay 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 multiplecompilers installed, CMake might not default to the one you wish touse.

Frequently Used LLVM-related variables ¶

The default configuration may not match your requirements. Here areLLVM variables that are frequently used to control that. The fulldescription is inLLVM-related variables below.

LLVM_ENABLE_PROJECTS:STRING: Control which projects are enabled. For example you may want to work on clangor lldb by specifying-DLLVM_ENABLE_PROJECTS="clang;lldb".
LLVM_ENABLE_RUNTIMES:STRING: Control which runtimes are enabled. For example you may want to work onlibc++ 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 beinstalled. On a 64-bit architecture, one could use-DLLVM_LIBDIR_SUFFIX=64to install libraries to/usr/lib64.
LLVM_PARALLEL_{COMPILE,LINK}_JOBS:STRING: Building the llvm toolchain can use a lot of resources, particularlylinking. These options, when you use the Ninja generator, allow youto restrict the parallelism. For example, to avoid OOMs or goinginto swap, permit only one link job per 15GB of RAM available on a32GB machine, specify-GNinja-DLLVM_PARALLEL_LINK_JOBS=2.
LLVM_TARGETS_TO_BUILD:STRING: Control which targets are enabled. For example you may only need to enableyour native target with, for example,-DLLVM_TARGETS_TO_BUILD=X86.

LLVM_USE_LINKER:STRING: Override the system’s default linker. For instance uselld with-DLLVM_USE_LINKER=lld.

Rarely-used CMake variables ¶

Here are some of the CMake variables that are rarely used, along with a briefexplanation and LLVM-related notes. For full documentation, consult the CMakemanual, or executecmake--help-variableVARIABLE_NAME.

CMAKE_CXX_STANDARD:STRING: Sets the C++ standard to conform to when building LLVM. Possible values are17 and 20. LLVM Requires C++17 or higher. This defaults to 17.
CMAKE_INSTALL_BINDIR:PATH: The path to install executables, relative to theCMAKE_INSTALL_PREFIX.Defaults to “bin”.
CMAKE_INSTALL_DOCDIR:PATH: The path to install documentation, relative to theCMAKE_INSTALL_PREFIX.Defaults to “share/doc”.
CMAKE_INSTALL_INCLUDEDIR:PATH: The path to install header files, relative to theCMAKE_INSTALL_PREFIX.Defaults to “include”.
CMAKE_INSTALL_MANDIR:PATH: The path to install manpage files, relative to theCMAKE_INSTALL_PREFIX.Defaults to “share/man”.

LLVM-related variables ¶

These variables provide fine control over the build of LLVM andenabled sub-projects. Nearly all of these variable names begin withLLVM_.

BUILD_SHARED_LIBS:BOOL: Flag indicating if each LLVM component (e.g. Support) is built as a sharedlibrary (ON) or as a static library (OFF). Its default value is OFF. OnWindows, shared libraries may be used when building with MinGW, includingmingw-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 theLLVM_BUILD_LLVM_DYLIB option.
LLVM_ABI_BREAKING_CHECKS:STRING: Used to decide if LLVM should be built with ABI breaking checks ornot. Allowed values areWITH_ASSERTS (default),FORCE_ON andFORCE_OFF.WITH_ASSERTS turns on ABI breaking checks in anassertion enabled build.FORCE_ON (FORCE_OFF) turns them on(off) irrespective of whether normal (NDEBUG-based) assertions areenabled or not. A version of LLVM built with ABI breaking checksis 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 flagallows for them to be specified as values in CMAKE_BUILD_TYPE withoutencountering 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 theLLVM_REVISION macro inllvm/include/llvm/Support/VCSRevision.h. Developers using git who don’tneed revision info can disable this option to avoid re-linking most binariesafter a branch switch. Defaults to ON.
LLVM_FORCE_VC_REPOSITORY:STRING: Set the git repository to include in version info rather than calling git todetermine it.
LLVM_FORCE_VC_REVISION:STRING: Force a specific Git revision id rather than calling to git to determine it.This is useful in environments where git is not available or non-functionalbut 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 isavailable 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 allenabled documentation targets (i.e. Doxgyen and Sphinx targets) asdependencies of the default build targets. This results in all of the (enabled)documentation targets being as part of a normal build. If theinstalltarget is run then this also enables all built documentation targets to beinstalled. Defaults to OFF. To enable a particular documentation target, seeLLVM_ENABLE_SPHINX and LLVM_ENABLE_DOXYGEN.
LLVM_BUILD_EXAMPLES:BOOL: Build LLVM examples. Defaults to OFF. Targets for building each example aregenerated in any case. See documentation forLLVM_BUILD_TOOLS above for moredetails.
LLVM_BUILD_INSTRUMENTED_COVERAGE:BOOL: If enabled,source-based code coverage instrumentationis enabled while building llvm. If CMake can locate the code coveragescripts and the llvm-cov and llvm-profdata tools that pair to your compiler,the build will also generate thegenerate-coverage-report target to generatethe code coverage report for LLVM, and theclear-profile-data utility targetto delete captured profile data. See documentation forLLVM_CODE_COVERAGE_TARGETS andLLVM_COVERAGE_SOURCE_DIRS for moreinformation 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_DYLIBis also ON.The components in the library can be customised by setting LLVM_DYLIB_COMPONENTSto 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. Targetsfor building each unit test are generated in any case. You can build aspecific unit test using the targets defined underunittests, such asADTTests, IRTests, SupportTests, etc. (Search foradd_llvm_unittest inthe subdirectories ofunittests for a complete list of unit tests.) It ispossible to build all unit tests with the targetUnitTests.
LLVM_BUILD_TOOLS:BOOL: Build LLVM tools. Defaults to ON. Targets for building each tool are generatedin any case. You can build a tool separately by invoking its target. Forexample, you can buildllvm-as with a Makefile-based system by executingmakellvm-as at the root of your build directory.
LLVM_CCACHE_BUILD:BOOL: If enabled and theccache program is available, then LLVM will bebuilt usingccache to speed up rebuilds of LLVM and its components.Defaults to OFF. The size and location of the cache maintainedbyccache can be adjusted via the LLVM_CCACHE_MAXSIZE and LLVM_CCACHE_DIRoptions, which are passed to the CCACHE_MAXSIZE and CCACHE_DIR environmentvariables, respectively.
LLVM_CODE_COVERAGE_TARGETS:STRING: If set to a semicolon separated list of targets, those targets will be usedto drive the code coverage reports. If unset, the target list will beconstructed using the LLVM build’s CMake export list.
LLVM_COVERAGE_SOURCE_DIRS:STRING: If set to a semicolon separated list of directories, the coverage reportswill 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$CMAKE_INSTALL_PREFIX/Toolchains containing an xctoolchain directory which canbe used to override the default system tools.
LLVM_DEFAULT_TARGET_TRIPLE:STRING: LLVM target to use for code generation when no target is explicitly specified.It defaults to “host”, meaning that it shall pick the architectureof the machine where LLVM is being built. If you are building a cross-compiler,set it to the target triple of your desired architecture.
LLVM_DOXYGEN_QCH_FILENAME:STRING: The filename of the Qt Compressed Help file that will be generated when-DLLVM_ENABLE_DOXYGEN=ON and-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON are given. Defaults toorg.llvm.qch.This option is only useful in combination with-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON;otherwise it has no effect.
LLVM_DOXYGEN_QHELPGENERATOR_PATH:STRING: The path to theqhelpgenerator executable. Defaults to whatever CMake’sfind_program() can find. This option is only useful in combination with-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON; otherwise it has noeffect.
LLVM_DOXYGEN_QHP_CUST_FILTER_NAME:STRING: SeeQt Help Project formore information. Defaults to the CMake variable${PACKAGE_STRING} whichis a combination of the package name and version string. This filter can thenbe used in Qt Creator to select only documentation from LLVM when browsingthrough all the help files that you might have loaded. This option is onlyuseful 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. SeeQtHelp Projectfor more information. Defaults to “org.llvm”. This option is only useful incombination with-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON; otherwiseit has no effect.

LLVM_ENABLE_ASSERTIONS:BOOL: Enables code assertions. Defaults to ON if and only ifCMAKE_BUILD_TYPEisDebug.
LLVM_ENABLE_BINDINGS:BOOL: If disabled, do not try to build the OCaml bindings.
LLVM_ENABLE_DEBUGLOC_COVERAGE_TRACKING:STRING: Enhances Debugify’s ability to detect line number errors by storing extrainformation inside Instructions, removing false positives from Debugify’sresults at the cost of performance. Allowed values areDISABLED (default),COVERAGE, andCOVERAGE_AND_ORIGIN.COVERAGE tracks whether and why aline number was intentionally dropped or not generated for an instruction,allowing Debugify to avoid reporting these as errors; this comes with a smallperformance cost of ~0.1%.COVERAGE_AND_ORIGIN additionally stores astacktrace of the point where each DebugLoc is unintentionally dropped,allowing for much easier bug triaging at the cost of a ~10x performanceslowdown.COVERAGE andCOVERAGE_AND_ORIGIN are ABI-breaking options.
LLVM_ENABLE_DIA_SDK:BOOL: Enable building with MSVC DIA SDK for PDB debugging support. Availableonly 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 targetdoxygen-llvm. When enabled, apart fromthe normal HTML output generated by doxygen, this will produce a QCH filenamedorg.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 tolink against LLVM libraries and make use of C++ exceptions in your own codethat 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 FunctionInterface library (libffi) in order to enable calling external functions.If the library or its headers are installed in a customlocation, you can also set the variables FFI_INCLUDE_DIR andFFI_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-debuginfodto serve debug info over HTTP.cpp-httplibmust be installed, orhttplib_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 thecreation of certain convenience build system targets, such as the variousinstall-* andcheck-* targets, since IDEs don’t always deal well witha large number of targets. This is usually autodetected, but it can beconfigured manually to explicitly control the generation of those targets.
LLVM_ENABLE_LIBCXX:BOOL: If the host compiler and linker supports the stdlib flag, -stdlib=libc++ ispassed 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 historyin LLVM tools. WhenON, forces libedit support to be enabled and will cause aCMake configuration error if libedit cannot be found. WhenOFF, disableslibedit support entirely. If not specified, LLVM will auto-detect libeditavailability. Defaults to auto-detection.
LLVM_ENABLE_LIBPFM:BOOL: Enable building with libpfm to support hardware counter measurements in LLVMtools.Defaults to ON.
LLVM_ENABLE_LLD:BOOL: This option is equivalent to-DLLVM_USE_LINKER=lld, except during a 2-stagebuild where a dependency is added from the first stage to the second ensuringthat lld is built before stage2 begins.
LLVM_ENABLE_LLVM_LIBC: BOOL: If the LLVM libc overlay is installed in a location where the host linkercan access it, all built executables will be linked against the LLVM libcoverlay before linking against the system libc. Defaults to OFF.
LLVM_ENABLE_LTO:STRING: Add-flto or-flto= flags to the compile and link commandlines, enabling link-time optimization. Possible values areOff,On,Thin andFull. Defaults to OFF.
LLVM_ENABLE_MODULES:BOOL: Compile withClang Header Modules.

LLVM_ENABLE_PDB:BOOL

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

LLVM_ENABLE_PEDANTIC:BOOL

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

LLVM_ENABLE_PIC:BOOL

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

LLVM_ENABLE_PROJECTS:STRING

Semicolon-separated list of projects to build, orall for building all(clang, lldb, lld, polly, etc) projects. This flag assumes that projectsare checked out side-by-side and not nested, i.e. clang needs to be inparallel of llvm instead of nested inllvm/tools. This feature allowsto have one build for only LLVM and another for clang+llvm using the samesource 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 inLLVM_ENABLE_RUNTIMES. Theyshould only appear in one of the two lists. If a project is a valid possibilityfor both, prefer putting it inLLVM_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 preservecorrect dependency ordering. If you want to build the runtimes using a systemcompiler, see thelibc++ documentation.

Note

The list should not have duplicates withLLVM_ENABLE_PROJECTS.

The full list is:

libc;libunwind;libcxxabi;libcxx;compiler-rt;openmp;llvm-libgcc;offload

To enable all of them, use:

LLVM_ENABLE_RUNTIMES=all

LLVM_ENABLE_SPHINX:BOOL

If specified, CMake will search for thesphinx-build executable and will maketheSPHINX_OUTPUT_HTML andSPHINX_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 thesize 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 needs to be available on the system.

LLVM_ENABLE_ZLIB:STRING

Used to decide if LLVM tools should support compression/decompression withzlib. Allowed values areOFF,ON (default, enable if zlib is found),andFORCE_ON (error if zlib is not found).

LLVM_ENABLE_ZSTD:STRING

Used to decide if LLVM tools should support compression/decompression withzstd. Allowed values areOFF,ON (default, enable if zstd is found),andFORCE_ON (error if zstd is not found).

LLVM_EXPERIMENTAL_TARGETS_TO_BUILD:STRING

Semicolon-separated list of experimental targets to build and linked intollvm. This will build the experimental target without needing it to add to thelist 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 ofllvm. For each project LLVM_EXTERNAL_<NAME>_SOURCE_DIR have to be specifiedwith 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 externalLLVM projects Clang, lld, and Polly, respectively, relative to the top-levelsource directory. If the in-tree subdirectory for an external projectexists (e.g., llvm/tools/clang for Clang), then the corresponding variablewill not be used. If the variable for an external project does not pointto 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 allexecutables (Darwin Only).

LLVM_FORCE_USE_OLD_TOOLCHAIN:BOOL

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

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 thisoption 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 usethis option to disable the generation of build targets for the LLVM unittests.

LLVM_INCLUDE_TOOLS:BOOL

Generate build targets for the LLVM tools. Defaults to ON. You can use thisoption 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 foreach test case will be generated and stored in a separate directory under theconfig.test_exec_root path. This feature allows code coverage analysis of eachindividual 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 caneither 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 caneither be absolute or relative to the CMAKE_INSTALL_PREFIX. Defaults to${CMAKE_INSTALL_DOCDIR}/llvm/html.

LLVM_INSTALL_UTILS:BOOL

If enabled, utility binaries likeFileCheck andnot will be installedto CMAKE_INSTALL_PREFIX.

LLVM_INSTALL_DOXYGEN_HTML_DIR:STRING

The path to install Doxygen-generated HTML documentation to. This path caneither be absolute or relative to theCMAKE_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 LLVMtools and libraries. Using a lock-free allocator such as the ones listed belowgreatly decreases ThinLTO link time by about an order of magnitude. It alsomildly improves Clang build times, by about 5-10%. At the moment, rpmalloc,snmalloc and mimalloc are supported. Use the path togit clone to selectthe respective allocator, for example:

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

This option needs to be used along with the static CRT, ie. if building theRelease 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 thehost toolchain as a C runtime allocator. The version currently used isrpmalloc 1.4.5. This option also implies linking with the static CRT, there’sno need to provide CMAKE_MSVC_RUNTIME_LIBRARY.

LLVM_LINK_LLVM_DYLIB:BOOL

If enabled, tools will be linked with the libLLVM shared library. Defaultsto OFF. Setting LLVM_LINK_LLVM_DYLIB to ON also sets LLVM_BUILD_LLVM_DYLIBto 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.makecheck andmakeclang-test are affected.By default,'-sv--no-progress-bar' on Visual C++ and Xcode,'-sv' onothers.

LLVM_LIT_TOOLS_DIR:PATH

The path to GnuWin32 tools for tests. Valid on Windows host. Defaults tothe 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 thatlit 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 asllvm-tblgen andclang-tblgen). This isintended for cross-compiling: if the user sets this variable and thedirectory contains executables with the expected names, no separatenative versions of those executables will be built.

LLVM_NO_INSTALL_NAME_DIR_FOR_BUILD_TREE:BOOL

Defaults toOFF. If set toON, CMake’s default logic for library IDson Darwin in the build tree will be used. Otherwise the install-time libraryIDs will be used in the build tree as well. Mainly useful when other CMakelibrary ID control variables (e.g.,CMAKE_INSTALL_NAME_DIR) are beingset to non-standard values.

LLVM_OPTIMIZED_TABLEGEN:BOOL

If enabled and building a debug or asserts build the CMake build system willgenerate a Release build tree to build a fully optimized tablegen for useduring the build. Enabling this option can significantly speed up build timesespecially when building LLVM in Debug configurations.

LLVM_PARALLEL_{COMPILE,LINK,TABLEGEN}_JOBS:STRING

Limit the maximum number of concurrent compilation, link ortablegen jobs respectively. The default total number of parallel jobs isdetermined by the number of logical CPUs.

LLVM_PROFDATA_FILE:PATH

Path to a profdata file to pass into clang’s -fprofile-instr-use flag. Thiscan 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 jobsrespectively, depending on available physical memory. The valuespecified is in MB. The respectiveLLVM_PARALLEL_{COMPILE,LINK,TABLEGEN}_JOBS variable isoverwritten by computing the memory size divided by thespecified value. The largest memory user is linking, but rememberthat jobs in the other categories might run in parallel to the linkjobs, and you need to consider their memory requirements whenin a memory-limited environment. Using a-DLLVM_RAM_PER_LINK_JOB=10000 is a good approximation. On ELFplatforms debug builds can reduce link-time memory pressure by alsousingLLVM_USE_SPLIT_DWARF.

LLVM_REVERSE_ITERATION:BOOL

If enabled, all supported unordered llvm containers would be iterated inreverse order. This is useful for uncovering non-determinism caused byiteration 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 theLLVM_ENABLE_LIBCXX flag. Defaults to OFF.

LLVM_TABLEGEN:STRING

Full path to a native TableGen executable (usually namedllvm-tblgen). This isintended for cross-compiling: if the user sets this variable, no nativeTableGen will be created.

LLVM_TARGET_ARCH:STRING

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

LLVM_TARGETS_TO_BUILD:STRING

Semicolon-separated list of targets to build, orall for building alltargets. Case-sensitive. Defaults toall. Example:-DLLVM_TARGETS_TO_BUILD="X86;PowerPC".The full list, as of March 2023, is:AArch64;AMDGPU;ARM;AVR;BPF;Hexagon;Lanai;LoongArch;Mips;MSP430;NVPTX;PowerPC;RISCV;Sparc;SystemZ;VE;WebAssembly;X86;XCore

You can also specifyhost orNative to automatically detect andinclude the target corresponding to the host machine’s architecture, oruseall to include all available targets.For example, on an x86_64 machine, specifying-DLLVM_TARGETS_TO_BUILD=hostwill include theX86 target.

LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN:BOOL

If enabled, the compiler version check will only warn when using a toolchainwhich 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 ifLLVM_USE_SANITIZER containsUndefined. This can be used to overridethe default set of UBSan flags.

LLVM_UNREACHABLE_OPTIMIZE:BOOL

This flag controls the behavior ofllvm_unreachable() in release build(when assertions are disabled in general). When ON (default) thenllvm_unreachable() is considered “undefined behavior” and optimized assuch. 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 value depend onyour compiler, for clang the value can be an absolute path to your customlinker, otherwise clang will prefix the name withld. and apply its usualsearch. For example to link LLVM with the Gold linker, cmake can be invokedwith-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. Thesource 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 prefixcan be adjusted via the LLVM_SOURCE_PREFIX variable.

LLVM_USE_SANITIZER:STRING

Define the sanitizer used to build LLVM binaries and tests. Possible valuesareAddress,Memory,MemoryWithOrigins,Undefined,Thread,DataFlow, andAddress;Undefined. Defaults to empty string.

LLVM_USE_SPLIT_DWARF:BOOL

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

SPHINX_EXECUTABLE:STRING

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

SPHINX_OUTPUT_HTML:BOOL

If enabled (andLLVM_ENABLE_SPHINX is enabled) then the targets forbuilding the documentation as html are added (but not built by default unlessLLVM_BUILD_DOCS is enabled). There is a target for each project in thesource tree that uses sphinx (e.g.docs-llvm-html,docs-clang-htmlanddocs-lld-html). Defaults to ON.

SPHINX_OUTPUT_MAN:BOOL

If enabled (andLLVM_ENABLE_SPHINX is enabled) the targets for buildingthe man pages are added (but not built by default unlessLLVM_BUILD_DOCSis enabled). Currently the only target added isdocs-llvm-man. Defaultsto ON.

SPHINX_WARNINGS_AS_ERRORS:BOOL

If enabled then sphinx documentation warnings will be treated aserrors. Defaults to ON.

Advanced variables ¶

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

LLVM_EXAMPLES_INSTALL_DIR:STRING: The path for examples of using LLVM, relative to theCMAKE_INSTALL_PREFIX.Only matters ifLLVM_BUILD_EXAMPLES is enabled.Defaults to “examples”.
LLVM_TOOLS_INSTALL_DIR:STRING: The path to install the main LLVM tools, relative to theCMAKE_INSTALL_PREFIX.Defaults toCMAKE_INSTALL_BINDIR.
LLVM_UTILS_INSTALL_DIR:STRING: The path to install auxiliary LLVM utilities, relative to theCMAKE_INSTALL_PREFIX.Only matters ifLLVM_INSTALL_UTILS is enabled.Defaults toLLVM_TOOLS_INSTALL_DIR.

CMake Caches ¶

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

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

$cmake-C<pathtocachefile><pathtosources>

CMake cache scripts are processed in an isolated scope, only cached variablesremain set when the main configuration runs. CMake cached variables do not resetvariables 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 andcan be read inside the cache file
- -D arguments specified after -C are set after the cache is processed andare 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 commandline arguments
It is recommended that all -D options should be specifiedbefore -C

For more information about some of the advanced build configurations supportedvia Cache files seeAdvanced Build Configurations.

Executing the Tests ¶

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

$makecheck-all

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

Cross compiling ¶

Seethis wiki page forgeneric instructions on how to cross-compile with CMake. It goes into detailedexplanations and may seem daunting, but it is not. On the wiki page there areseveral examples including toolchain files. Go directly to theInformationhowtosetupvariouscrosscompilingtoolchains sectionfor a quick solution.

Also see theLLVM-related variables section for variables used whencross-compiling.

Embedding LLVM in your project ¶

From LLVM 3.5 onwards the CMake build system exports LLVM libraries asimportable CMake targets. This means that clients of LLVM can now reliably useCMake to develop their own LLVM-based projects against an installed version ofLLVM regardless of how it was built.

Here is a simple example of a CMakeLists.txt file that imports the LLVM librariesand uses them to build a simple applicationsimple-tool.

cmake_minimum_required(VERSION3.20.0)project(SimpleProject)find_package(LLVMREQUIREDCONFIG)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_LISTNATIVE_COMMAND${LLVM_DEFINITIONS})add_definitions(${LLVM_DEFINITIONS_LIST})# Now build our toolsadd_executable(simple-tooltool.cpp)# Find the libraries that correspond to the LLVM components# that we wish to usellvm_map_components_to_libnames(llvm_libssupportcoreirreader)# Link against LLVM librariestarget_link_libraries(simple-tool${llvm_libs})

Thefind_package(...) directive when used in CONFIG mode (as in the aboveexample) will look for theLLVMConfig.cmake file in various locations (seecmake manual for details). It creates aLLVM_DIR cache entry to save thedirectory whereLLVMConfig.cmake is found or allows the user to specify thedirectory (e.g. by passing-DLLVM_DIR=/usr/lib/cmake/llvm tothecmake command or by setting it directly inccmake orcmake-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 areinstalled as part of an installed version of LLVM. This is typicallycmake/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 onlyavailable 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...) willautomatically find LLVM if it is installed correctly. If LLVM is not installedor you wish to build directly against the LLVM build tree you can useLLVM_DIR as previously mentioned.

TheLLVMConfig.cmake file sets various useful variables. Notable variablesinclude

LLVM_CMAKE_DIR: The path to the LLVM CMake directory (i.e. the directory containingLLVMConfig.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 linksimple-tool against several LLVMlibraries. The list of libraries is determined by using thellvm_map_components_to_libnames() CMake function. For a list of availablecomponents look at the output of runningllvm-config--components.

Note that for LLVM < 3.5llvm_map_components_to_libraries() wasused instead ofllvm_map_components_to_libnames(). This is now deprecatedand will be removed in a future version of LLVM.

Developing LLVM passes out of source ¶

It is possible to develop LLVM passes out of LLVM’s source tree (i.e. against aninstalled or built LLVM). An example of a project layout is provided below.

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

Contents of<projectdir>/CMakeLists.txt:

find_package(LLVMREQUIREDCONFIG)separate_arguments(LLVM_DEFINITIONS_LISTNATIVE_COMMAND${LLVM_DEFINITIONS})add_definitions(${LLVM_DEFINITIONS_LIST})include_directories(${LLVM_INCLUDE_DIRS})add_subdirectory(<passname>)

Contents of<projectdir>/<passname>/CMakeLists.txt:

add_library(LLVMPassnameMODULEPass.cpp)

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

Adding the following to<projectdir>/CMakeLists.txt (afterfind_package(LLVM...))

list(APPENDCMAKE_MODULE_PATH"${LLVM_CMAKE_DIR}")include(AddLLVM)

And then changing<projectdir>/<passname>/CMakeLists.txt to

add_llvm_library(LLVMPassnameMODULEPass.cpp)

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

Copying<passname> folder into<LLVMroot>/lib/Transforms directory.
Addingadd_subdirectory(<passname>) line into<LLVMroot>/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 projectwhen building with msbuild or Visual Studio. Only supported for the VisualStudio 2010 CMake generator. 0 means use all processors. Default is 0.
CMAKE_MT:STRING: When compiling with clang-cl, CMake may usellvm-mt as the Manifest Toolwhen available.llvm-mt is only present when libxml2 is found at build-time.To ensure using Microsoft’s Manifest Tool setCMAKE_MT=mt.

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