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.

If you are a new contributor, please start with the Getting 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 with Basic CMake usageand then go back to the Quick 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 3.4.3 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:

  1. $ mkdir mybuilddir
  2. $ cd mybuilddir
  • Execute this command in the shell replacing path/to/llvm/source/root withthe path to the root of your LLVM source tree:
  1. $ cmake path/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 the Options 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 the Usage section, below.

  • After CMake has finished running, proceed to use IDE project files, or startthe build from the build directory:
  1. $ cmake --build .

The —build option tells cmake 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:
  1. $ cmake --build . --target install

The —target option with install parameter in addition tothe —build option tells cmake to build the install target.

It is possible to set a different install prefix at installation timeby invoking the cmake_install.cmake script generated in thebuild directory:

  1. $ cmake -DCMAKE_INSTALL_PREFIX=/tmp/llvm -P cmake_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 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 whichbuild tool to use, based on your environment. Once it has identified yourbuild tool, CMake uses the corresponding Generator 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 "Name of thegenerator". To see a list of the available generators on your system, execute

  1. $ 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 —helpoutput, in quotes. For example, to generate project files specifically forVisual Studio 12, you can execute:

  1. $ 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:

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

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

  1. $ cmake -UVARIABLE path/to/llvm/source

Variables are stored in the CMake cache. This is a file named CMakeCache.txtstored 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 withthe variable name and type separated by a colon. You can also specify thevariable and type on the CMake command line:

  1. $ 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 abrief explanation and LLVM-specific notes. For full documentation, consult theCMake manual, or execute cmake —help-variable VARIABLE_NAME.

  • CMAKE_BUILD_TYPE:STRING
  • Sets the build type for make-based generators. Possible values areRelease, Debug, RelWithDebInfo and MinSizeRel. If you are using an IDE such asVisual Studio, you should use the IDE settings to set the build type.Be aware that Release and RelWithDebInfo use different optimization levels onmost platforms.
  • CMAKE_INSTALL_PREFIX:PATH
  • Path where LLVM will be installed if “make install” is invoked or the“install” target is built.
  • 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.
  • CMAKE_C_FLAGS:STRING
  • Extra flags to use when compiling C source files.
  • CMAKE_CXX_FLAGS:STRING
  • Extra flags to use when compiling C++ source files.

Rarely-used CMake variables

Here are some of the CMake variables that are rarely used, along with a briefexplanation and LLVM-specific notes. For full documentation, consult the CMakemanual, or execute cmake —help-variable VARIABLE_NAME.

  • CMAKE_CXX_STANDARD:STRING
  • Sets the C++ standard to conform to when building LLVM. Possible values are14, 17, 20. LLVM Requires C++ 14 or higher. This defaults to 14.

LLVM-specific variables

  • LLVM_TARGETS_TO_BUILD:STRING
  • Semicolon-separated list of targets to build, or all for building alltargets. Case-sensitive. Defaults to all. Example:-DLLVM_TARGETS_TO_BUILD="X86;PowerPC".
  • 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 build llvm-as with a Makefile-based system by executing makellvm-as at the root of your build directory.
  • 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_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 symliks from the cctools tool names to the corresponding LLVM tools.For example, lipo will be symlinked to llvm-lipo.
  • LLVM_BUILD_EXAMPLES:BOOL
  • Build LLVM examples. Defaults to OFF. Targets for building each example aregenerated in any case. See documentation for LLVM_BUILD_TOOLS above for moredetails.
  • 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_BUILD_TESTS:BOOL
  • Build LLVM unit tests. Defaults to OFF. Targets for building each unit testare generated in any case. You can build a specific unit test using thetargets defined under unittests, such as ADTTests, IRTests, SupportTests,etc. (Search for addllvm_unittest in the subdirectories of _unittests_for a complete list of unit tests.) It is possible to build all unit testswith the target _UnitTests.
  • 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_BUILD_BENCHMARKS:BOOL
  • Adds benchmarks to the list of default targets. Defaults to OFF.
  • LLVM_INCLUDE_BENCHMARKS:BOOL
  • Generate build targets for the LLVM benchmarks. Defaults to ON.
  • LLVM_APPEND_VC_REV:BOOL
  • Embed version control revision info (Git revision id).The version info is provided by the LLVM_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_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_ASSERTIONS:BOOL
  • Enables code assertions. Defaults to ON if and only if CMAKEBUILD_TYPEis _Debug.
  • 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_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- and check- 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. Onescenario where a manual override may be desirable is when using Visual Studio2017’s CMake integration, which would not be detected as an IDE otherwise.
  • 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_RTTI:BOOL
  • Build LLVM with run-time type information. Defaults to OFF.
  • LLVM_ENABLE_WARNINGS:BOOL
  • Enable all compiler warnings. Defaults to ON.
  • LLVM_ENABLE_PEDANTIC:BOOL
  • Enable pedantic mode. This disables compiler-specific extensions, ifpossible. Defaults to ON.
  • LLVM_ENABLE_WERROR:BOOL
  • Stop and fail the build, if a compiler warning is triggered. Defaults to OFF.
  • LLVM_ABI_BREAKING_CHECKS:STRING
  • Used to decide if LLVM should be built with ABI breaking checks ornot. Allowed values are WITH_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_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_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_TABLEGEN:STRING
  • Full path to a native TableGen executable (usually named llvm-tblgen). This isintended for cross-compiling: if the user sets this variable, no nativeTableGen will be created.
  • 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' 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_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.
  • LLVMEXTERNAL{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_ENABLE_PROJECTS:STRING
  • Semicolon-separated list of projects to build, or all for building all(clang, libcxx, libcxxabi, lldb, compiler-rt, 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 of llvm instead of nested in llvm/tools.This feature allows to have one build for only LLVM and another for clang+llvmusing the same source checkout.The full list is:clang;clang-tools-extra;compiler-rt;debuginfo-tests;libc;libclc;libcxx;libcxxabi;libunwind;lld;lldb;openmp;parallel-libs;polly;pstl
  • LLVM_EXTERNAL_PROJECTS:STRING
  • Semicolon-separated list of additional external projects to build as part ofllvm. For each project LLVMEXTERNAL_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_USE_OPROFILE:BOOL
  • Enable building OProfile JIT support. Defaults to OFF.
  • 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_USE_INTEL_JITEVENTS:BOOL
  • Enable building support for Intel JIT Events API. Defaults to OFF.
  • LLVM_ENABLE_LIBPFM:BOOL
  • Enable building with libpfm to support hardware counter measurements in LLVMtools.Defaults to ON.
  • LLVM_USE_PERF:BOOL
  • Enable building support for Perf (linux profiling tool) JIT support. Defaults to OFF.
  • LLVM_ENABLE_ZLIB:BOOL
  • Enable building with zlib to support compression/uncompression in LLVM tools.Defaults to ON.
  • LLVM_ENABLE_DIA_SDK:BOOL
  • Enable building with MSVC DIA SDK for PDB debugging support. Availableonly with MSVC. Defaults to ON.
  • LLVM_USE_SANITIZER:STRING
  • Define the sanitizer used to build LLVM binaries and tests. Possible valuesare Address, Memory, MemoryWithOrigins, Undefined, Thread,and Address;Undefined. Defaults to empty string.
  • LLVM_ENABLE_LTO:STRING
  • Add -flto or -flto= flags to the compile and link commandlines, enabling link-time optimization. Possible values are Off,On, Thin and Full. 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 with ld. and apply its usualsearch. For example to link LLVM with the Gold linker, cmake can be invokedwith -DLLVM_USE_LINKER=gold.
  • 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_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 conjuction with the LLVM_ENABLE_LIBCXX flag. Defaults to OFF.
  • 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_PARALLEL_COMPILE_JOBS:STRING
  • Define the maximum number of concurrent compilation jobs.
  • LLVM_PARALLEL_LINK_JOBS:STRING
  • Define the maximum number of concurrent link jobs.
  • LLVM_BUILD_DOCS:BOOL
  • Adds all enabled 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 the installtarget is run then this also enables all built documentation targets to beinstalled. Defaults to OFF. To enable a particular documentation target, seesee LLVM_ENABLE_SPHINX and LLVM_ENABLE_DOXYGEN.
  • 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 fromthe normal HTML output generated by doxygen, this will produce a QCH filenamed 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_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_QHP_NAMESPACE:STRING
  • Namespace under which the intermediate Qt Help Project file lives. See QtHelp 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_DOXYGEN_QHP_CUST_FILTER_NAME:STRING

  • See Qt 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_QHELPGENERATOR_PATH:STRING

  • The path to the qhelpgenerator 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_SVG:BOOL
  • Uses .svg files instead of .png files for graphs in the Doxygen output.Defaults to OFF.
  • LLVM_INSTALL_DOXYGEN_HTML_DIR:STRING
  • The path to install Doxygen-generated HTML documentation to. This path caneither be absolute or relative to the CMAKEINSTALL_PREFIX. Defaults to_share/doc/llvm/doxygen-html.
  • LLVM_ENABLE_SPHINX:BOOL
  • If specified, CMake will search for the sphinx-build executable and will makethe SPHINX_OUTPUT_HTML and SPHINX_OUTPUT_MAN CMake options available.Defaults to OFF.
  • SPHINX_EXECUTABLE:STRING
  • The path to the sphinx-build executable detected by CMake.For installation instructions, seehttp://www.sphinx-doc.org/en/latest/usage/installation.html
  • SPHINX_OUTPUT_HTML:BOOL
  • If enabled (and LLVM_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-htmland docs-lld-html). Defaults to ON.
  • SPHINX_OUTPUT_MAN:BOOL
  • If enabled (and LLVM_ENABLE_SPHINX is enabled) the targets for buildingthe man pages are added (but not built by default unless LLVM_BUILD_DOCSis enabled). Currently the only target added is docs-llvm-man. Defaultsto ON.
  • SPHINX_WARNINGS_AS_ERRORS:BOOL
  • If enabled then sphinx documentation warnings will be treated aserrors. Defaults to ON.
  • LLVM_INSTALL_SPHINX_HTML_DIR:STRING
  • The path to install Sphinx-generated HTML documentation to. This path caneither be absolute or relative to the CMAKEINSTALL_PREFIX. Defaults to_share/doc/llvm/html.
  • LLVM_INSTALL_OCAMLDOC_HTML_DIR:STRING
  • The path to install OCamldoc-generated HTML documentation to. This path caneither be absolute or relative to the CMAKEINSTALL_PREFIX. Defaults to_share/doc/llvm/ocaml-html.
  • 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_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_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.
  • 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_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_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_BUILD_INSTRUMENTED_COVERAGE:BOOL
  • If enabled, source-based code coverage instrumentationis enabled while building llvm.
  • LLVM_CCACHE_BUILD:BOOL
  • If enabled and the ccache program is available, then LLVM will bebuilt using ccache to speed up rebuilds of LLVM and its components.Defaults to OFF. The size and location of the cache maintainedby ccache 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_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_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_USE_NEWPM:BOOL
  • If enabled, use the experimental new pass manager.
  • LLVM_ENABLE_BINDINGS:BOOL
  • If disabled, do not try to build the OCaml and go bindings.
  • 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_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_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.

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:

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

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 specified before -C

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

Executing the Tests

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

  1. $ 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 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 this sectionfor a quick solution.

Also see the LLVM-specific 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 application simple-tool.

  1. cmake_minimum_required(VERSION 3.4.3)
  2. project(SimpleProject)
  3.  
  4. find_package(LLVM REQUIRED CONFIG)
  5.  
  6. message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
  7. message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
  8.  
  9. # Set your project compile flags.
  10. # E.g. if using the C++ header files
  11. # you will need to enable C++11 support
  12. # for your compiler.
  13.  
  14. include_directories(${LLVM_INCLUDE_DIRS})
  15. add_definitions(${LLVM_DEFINITIONS})
  16.  
  17. # Now build our tools
  18. add_executable(simple-tool tool.cpp)
  19.  
  20. # Find the libraries that correspond to the LLVM components
  21. # that we wish to use
  22. llvm_map_components_to_libnames(llvm_libs support core irreader)
  23.  
  24. # Link against LLVM libraries
  25. target_link_libraries(simple-tool ${llvm_libs})

The find_package(…) directive when used in CONFIG mode (as in the aboveexample) will look for the LLVMConfig.cmake file in various locations (seecmake manual for details). It creates a LLVM_DIR cache entry to save thedirectory where LLVMConfig.cmake is found or allows the user to specify thedirectory (e.g. by passing -DLLVM_DIR=/usr/lib/cmake/llvm tothe cmake command or by setting it directly in ccmake or cmake-gui).

This file is available in two different locations.

  • <INSTALL_PREFIX>/lib/cmake/llvm/LLVMConfig.cmake where<INSTALL_PREFIX> is the install prefix of an installed version of LLVM.On Linux typically this is /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.

The LLVMConfig.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 link simple-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 running llvm-config —components.

Note that for LLVM < 3.5 llvm_map_components_to_libraries() wasused instead of llvm_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.

  1. <project dir>/
  2.     |
  3.     CMakeLists.txt
  4.     <pass name>/
  5.         |
  6.         CMakeLists.txt
  7.         Pass.cpp
  8.         ...

Contents of <project dir>/CMakeLists.txt:

  1. find_package(LLVM REQUIRED CONFIG)
  2.  
  3. add_definitions(${LLVM_DEFINITIONS})
  4. include_directories(${LLVM_INCLUDE_DIRS})
  5.  
  6. add_subdirectory(<pass name>)

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

  1. add_library(LLVMPassname MODULE Pass.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 <project dir>/CMakeLists.txt (afterfind_package(LLVM …))

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

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

  1. add_llvm_library(LLVMPassname MODULE
  2.   Pass.cpp
  3.   )

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 <pass name> folder into <LLVM root>/lib/Transform directory.
  • Adding add_subdirectory(<pass name>) line into<LLVM root>/lib/Transform/CMakeLists.txt.

Compiler/Platform-specific topics

Notes for specific compilers and/or platforms.

Microsoft Visual C++

  • 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.