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Building LLVM with CMake
.. contents::
`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 really anxious about getting a functional LLVM build, go to the
`Quick start`_ section. If you are a CMake novice, start on `Basic CMake usage`_
and then go back to the `Quick start`_ 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.
.. _Quick start:
Quick start
We use here the command-line, non-interactive CMake interface.
#. `Download <>`_ and install
CMake. Version 2.8.8 is the minimum required.
#. Open a shell. Your development tools must be reachable from this shell
through the PATH environment variable.
#. Create a directory for containing the build. It is not supported to build
LLVM on the source directory. cd to this directory:
.. code-block:: console
$ mkdir mybuilddir
$ cd mybuilddir
#. Execute this command on the shell replacing `path/to/llvm/source/root` with
the path to the root of your LLVM source tree:
.. code-block:: console
$ cmake path/to/llvm/source/root
CMake will detect your development environment, perform a series of test and
generate the files required for building LLVM. CMake will use default values
for all build parameters. See the `Options and variables`_ section for
fine-tuning your build
This can fail if CMake can't detect your toolset, or if it thinks that the
environment is not sane enough. On 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 you 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, see the `Usage`_ section.
#. After CMake has finished running, proceed to use IDE project files or start
the build from the build directory:
.. code-block:: console
$ 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 either of course, but
the ``--build`` option is portable.
#. After LLVM has finished building, install it from the build directory:
.. code-block:: console
$ 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:
.. code-block:: console
$ cmake -DCMAKE_INSTALL_PREFIX=/tmp/llvm -P cmake_install.cmake
.. _Basic CMake usage:
.. _Usage:
Basic CMake usage
This section explains basic aspects of CMake, mostly for explaining those
options which you may need on your day-to-day usage.
CMake comes with extensive documentation in the form of html files and on the
cmake executable itself. Execute ``cmake --help`` for further help options.
CMake requires to know for which build tool it shall generate files (GNU make,
Visual Studio, Xcode, etc). If not specified on the command line, it tries to
guess it based on you environment. Once identified the build tool, CMake uses
the corresponding *Generator* for creating files for your build tool. You can
explicitly specify the generator with the command line option ``-G "Name of the
generator"``. For knowing the available generators on your platform, execute
.. code-block:: console
$ cmake --help
This will list the generator's names at the end of the help text. Generator's
names are case-sensitive. Example:
.. code-block:: console
$ cmake -G "Visual Studio 11" path/to/llvm/source/root
For a given development platform there can be 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 more specific generator
supported by your development environment. If you want an alternative generator,
you must tell this to CMake with the ``-G`` option.
.. todo::
Explain variables and cache. Move explanation here from #options section.
.. _Options and variables:
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:
.. code-block:: console
$ cmake -DVARIABLE=value path/to/llvm/source
You can set a variable after the initial CMake invocation for changing its
value. You can also undefine a variable:
.. code-block:: console
$ cmake -UVARIABLE path/to/llvm/source
Variables are stored on the CMake cache. This is a file named ``CMakeCache.txt``
on the root of the build directory. Do not hand-edit it.
Variables are listed here appending its type after a colon. It is correct to
write the variable and the type on the CMake command line:
.. code-block:: console
$ 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 and LLVM-specific notes. For full documentation, check the
CMake docs or execute ``cmake --help-variable VARIABLE_NAME``.
Sets the build type for ``make`` based generators. Possible values are
Release, Debug, RelWithDebInfo and MinSizeRel. On systems like Visual Studio
the user sets the build type with the IDE settings.
Path where LLVM will be installed if "make install" is invoked or the
"INSTALL" target is built.
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``.
Extra flags to use when compiling C source files.
Extra flags to use when compiling C++ source files.
Flag indicating if shared libraries will be built. Its default value is
OFF. Shared libraries are not supported on Windows and not recommended on the
other OSes.
.. _LLVM-specific variables:
LLVM-specific variables
Semicolon-separated list of targets to build, or *all* for building all
targets. Case-sensitive. Defaults to *all*. Example:
Build LLVM tools. Defaults to ON. Targets for building each tool are generated
in any case. You can build an tool separately by invoking its target. For
example, you can build *llvm-as* with a makefile-based system executing *make
llvm-as* on the root of your build directory.
Generate build targets for the LLVM tools. Defaults to ON. You can use that
option for disabling the generation of build targets for the LLVM tools.
Build LLVM examples. Defaults to OFF. Targets for building each example are
generated in any case. See documentation for *LLVM_BUILD_TOOLS* above for more
Generate build targets for the LLVM examples. Defaults to ON. You can use that
option for disabling the generation of build targets for the LLVM examples.
Build LLVM unit tests. Defaults to OFF. Targets for building each unit test
are generated in any case. You can build a specific unit test with the target
*UnitTestNameTests* (where at this time *UnitTestName* can be ADT, Analysis,
ExecutionEngine, JIT, Support, Transform, VMCore; see the subdirectories of
*unittests* for an updated list.) It is possible to build all unit tests with
the target *UnitTests*.
Generate build targets for the LLVM unit tests. Defaults to ON. You can use
that option for disabling the generation of build targets for the LLVM unit
Append version control revision info (svn revision number or Git revision id)
to LLVM version string (stored in the PACKAGE_VERSION macro). For this to work
cmake must be invoked before the build. Defaults to OFF.
Build with threads support, if available. Defaults to ON.
Build in C++1y mode, if available. Defaults to OFF.
Enables code assertions. Defaults to ON if and only if ``CMAKE_BUILD_TYPE``
is *Debug*.
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.
Add the ``-fPIC`` flag for the compiler command-line, if the compiler supports
this flag. Some systems, like Windows, do not need this flag. Defaults to ON.
Build LLVM with run time type information. Defaults to OFF.
Enable all compiler warnings. Defaults to ON.
Enable pedantic mode. This disables compiler specific extensions, if
possible. Defaults to ON.
Stop and fail build, if a compiler warning is triggered. Defaults to OFF.
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.
Build 32-bits executables and libraries on 64-bits systems. This option is
available only on some 64-bits unix systems. Defaults to OFF.
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.
Full path to a native TableGen executable (usually named ``tblgen``). This is
intended for cross-compiling: if the user sets this variable, no native
TableGen will be created.
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
The path to GnuWin32 tools for tests. Valid on Windows host. Defaults to "",
then Lit seeks tools according to %PATH%. Lit can find tools(eg. grep, sort,
&c) on LLVM_LIT_TOOLS_DIR at first, without specifying GnuWin32 to %PATH%.
Indicates whether LLVM Interpreter will be linked with Foreign Function
Interface library. If the library or its headers are installed on a custom
location, you can set the variables FFI_INCLUDE_DIR and
Path to ``{Clang,lld,Polly}``\'s source directory. Defaults to
``tools/{clang,lld,polly}``. ``{Clang,lld,Polly}`` will not be built when it
is empty or it does not point to a valid path.
Enable building OProfile JIT support. Defaults to OFF
Enable building support for Intel JIT Events API. Defaults to OFF
Build with zlib to support compression/uncompression in LLVM tools.
Defaults to ON.
Define the sanitizer used to build LLVM binaries and tests. Possible values
are ``Address``, ``Memory``, ``MemoryWithOrigins``, ``Undefined``, ``Thread``,
and ``Address;Undefined``. Defaults to empty string.
Define the maximum number of concurrent compilation jobs.
Define the maximum number of concurrent link jobs.
Enables all enabled documentation targets (i.e. Doxgyen and Sphinx targets) to
be built as part of the normal build. If the ``install`` target is run then
this also enables all built documentation targets to be installed. Defaults to
Enables the generation of browsable HTML documentation using doxygen.
Defaults to OFF.
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.
The filename of the Qt Compressed Help file that will be generated when
``-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON`` are given. Defaults to
This option is only useful in combination with
otherwise this has no effect.
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
this has no effect.
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 this has no effect.
.. _Qt Help Project:
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 this has no
Uses .svg files instead of .png files for graphs in the Doxygen output.
Defaults to OFF.
If enabled 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.
The path to the ``sphinx-build`` executable detected by CMake.
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.
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.
If enabled then sphinx documentation warnings will be treated as
errors. Defaults to ON.
Executing the test suite
Testing is performed when the *check* target is built. For instance, if you are
using makefiles, execute this command while on the top level of your build
.. code-block:: console
$ make check
On Visual Studio, you may run tests to build the project "check".
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. On the wiki page there are
several examples including toolchain files. Go directly to `this section
for a quick solution.
Also see the `LLVM-specific variables`_ section for variables used when
Embedding LLVM in your project
From LLVM 3.5 onwards both the CMake and autoconf/Makefile build systems export
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 CMakeLists.txt file that imports the LLVM libraries
and uses them to build a simple application ``simple-tool``.
.. code-block:: cmake
cmake_minimum_required(VERSION 2.8.8)
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.
# 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 a ``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/share/llvm/cmake`` to
the ``cmake`` command or by setting it directly in ``ccmake`` or ``cmake-gui``).
This file is available in two different locations.
* ``<INSTALL_PREFIX>/share/llvm/cmake/LLVMConfig.cmake`` where
``<INSTALL_PREFIX>`` is the install prefix of an installed version of LLVM.
On Linux typically this is ``/usr/share/llvm/cmake/LLVMConfig.cmake``.
* ``<LLVM_BUILD_ROOT>/share/llvm/cmake/LLVMConfig.cmake`` where
``<LLVM_BUILD_ROOT>`` is the root of the LLVM build tree. **Note this 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
The path to the LLVM CMake directory (i.e. the directory containing
A list of preprocessor defines that should be used when building against LLVM.
This is set to ON if LLVM was built with assertions, otherwise OFF.
This is set to ON if LLVM was built with exception handling (EH) enabled,
otherwise OFF.
This is set to ON if LLVM was built with run time type information (RTTI),
otherwise OFF.
A list of include paths to directories containing LLVM header files.
The LLVM version. This string can be used with CMake conditionals. E.g. ``if
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.
.. _cmake-out-of-source-pass:
Developing LLVM passes out of source
It is possible to 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.
.. code-block:: none
<project dir>/
<pass name>/
Contents of ``<project dir>/CMakeLists.txt``:
.. code-block:: cmake
add_subdirectory(<pass name>)
Contents of ``<project dir>/<pass name>/CMakeLists.txt``:
.. code-block:: cmake
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_loadable_module function instead by...
Adding the following to ``<project dir>/CMakeLists.txt`` (after
``find_package(LLVM ...)``)
.. code-block:: cmake
And then changing ``<project dir>/<pass name>/CMakeLists.txt`` to
.. code-block:: cmake
When you are done developing your pass, you may wish to integrate it
into 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++
Specifies the maximum number of parallell 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.