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Merging r214077:
------------------------------------------------------------------------ r214077 | delcypher | 2014-07-28 14:36:37 +0100 (Mon, 28 Jul 2014) | 2 lines Document the new LLVM CMake interface for building against LLVM libraries. With many contributions from Brad King. ------------------------------------------------------------------------ git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_35@214079 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Liew
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docs/CMake.rst
151
docs/CMake.rst
@ -392,66 +392,112 @@ cross-compiling.
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Embedding LLVM in your project
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==============================
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The most difficult part of adding LLVM to the build of a project is to determine
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the set of LLVM libraries corresponding to the set of required LLVM
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features. What follows is an example of how to obtain this information:
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From LLVM 3.5 onwards both the CMake and autoconf/Makefile build systems export
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LLVM libraries as importable CMake targets. This means that clients of LLVM can
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now reliably use CMake to develop their own LLVM based projects against an
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installed version of LLVM regardless of how it was built.
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Here is a simple example of CMakeLists.txt file that imports the LLVM libraries
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and uses them to build a simple application ``simple-tool``.
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.. code-block:: cmake
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# A convenience variable:
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set(LLVM_ROOT "" CACHE PATH "Root of LLVM install.")
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cmake_minimum_required(VERSION 2.8.8)
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project(SimpleProject)
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# A bit of a sanity check:
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if( NOT EXISTS ${LLVM_ROOT}/include/llvm )
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message(FATAL_ERROR "LLVM_ROOT (${LLVM_ROOT}) is not a valid LLVM install")
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endif()
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find_package(LLVM REQUIRED CONFIG)
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# We incorporate the CMake features provided by LLVM:
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set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${LLVM_ROOT}/share/llvm/cmake")
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include(LLVMConfig)
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message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
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message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
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# Now set the header and library paths:
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include_directories( ${LLVM_INCLUDE_DIRS} )
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link_directories( ${LLVM_LIBRARY_DIRS} )
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add_definitions( ${LLVM_DEFINITIONS} )
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# Set your project compile flags.
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# E.g. if using the C++ header files
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# you will need to enable C++11 support
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# for your compiler.
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# Let's suppose we want to build a JIT compiler with support for
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# binary code (no interpreter):
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llvm_map_components_to_libraries(REQ_LLVM_LIBRARIES jit native)
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include_directories(${LLVM_INCLUDE_DIRS})
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add_definitions(${LLVM_DEFINITIONS})
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# Finally, we link the LLVM libraries to our executable:
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target_link_libraries(mycompiler ${REQ_LLVM_LIBRARIES})
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# Now build our tools
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add_excutable(simple-tool tool.cpp)
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This assumes that LLVM_ROOT points to an install of LLVM. The procedure works
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too for uninstalled builds although we need to take care to add an
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`include_directories` for the location of the headers on the LLVM source
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directory (if we are building out-of-source.)
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# Find the libraries that correspond to the LLVM components
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# that we wish to use
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llvm_map_components_to_libnames(llvm_libs support core irreader)
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Alternativaly, you can utilize CMake's ``find_package`` functionality. Here is
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an equivalent variant of snippet shown above:
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# Link against LLVM libraries
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target_link_libraries(simple-tool ${llvm_libs})
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.. code-block:: cmake
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The ``find_package(...)`` directive when used in CONFIG mode (as in the above
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example) will look for the ``LLVMConfig.cmake`` file in various locations (see
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cmake manual for details). It creates a ``LLVM_DIR`` cache entry to save the
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directory where ``LLVMConfig.cmake`` is found or allows the user to specify the
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directory (e.g. by passing ``-DLLVM_DIR=/usr/share/llvm/cmake`` to
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the ``cmake`` command or by setting it directly in ``ccmake`` or ``cmake-gui``).
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find_package(LLVM)
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This file is available in two different locations.
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if( NOT LLVM_FOUND )
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message(FATAL_ERROR "LLVM package can't be found. Set CMAKE_PREFIX_PATH variable to LLVM's installation prefix.")
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endif()
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* ``<INSTALL_PREFIX>/share/llvm/cmake/LLVMConfig.cmake`` where
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``<INSTALL_PREFIX>`` is the install prefix of an installed version of LLVM.
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On Linux typically this is ``/usr/share/llvm/cmake/LLVMConfig.cmake``.
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include_directories( ${LLVM_INCLUDE_DIRS} )
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link_directories( ${LLVM_LIBRARY_DIRS} )
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* ``<LLVM_BUILD_ROOT>/share/llvm/cmake/LLVMConfig.cmake`` where
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``<LLVM_BUILD_ROOT>`` is the root of the LLVM build tree. **Note this only
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available when building LLVM with CMake**
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llvm_map_components_to_libraries(REQ_LLVM_LIBRARIES jit native)
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If LLVM is installed in your operating system's normal installation prefix (e.g.
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on Linux this is usually ``/usr/``) ``find_package(LLVM ...)`` will
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automatically find LLVM if it is installed correctly. If LLVM is not installed
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or you wish to build directly against the LLVM build tree you can use
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``LLVM_DIR`` as previously mentioned.
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target_link_libraries(mycompiler ${REQ_LLVM_LIBRARIES})
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The ``LLVMConfig.cmake`` file sets various useful variables. Notable variables
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include
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``LLVM_CMAKE_DIR``
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The path to the LLVM CMake directory (i.e. the directory containing
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LLVMConfig.cmake).
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``LLVM_DEFINITIONS``
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A list of preprocessor defines that should be used when building against LLVM.
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``LLVM_ENABLE_ASSERTIONS``
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This is set to ON if LLVM was built with assertions, otherwise OFF.
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``LLVM_ENABLE_EH``
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This is set to ON if LLVM was built with exception handling (EH) enabled,
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otherwise OFF.
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``LLVM_ENABLE_RTTI``
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This is set to ON if LLVM was built with run time type information (RTTI),
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otherwise OFF.
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``LLVM_INCLUDE_DIRS``
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A list of include paths to directories containing LLVM header files.
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``LLVM_PACKAGE_VERSION``
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The LLVM version. This string can be used with CMake conditionals. E.g. ``if
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(${LLVM_PACKAGE_VERSION} VERSION_LESS "3.5")``.
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``LLVM_TOOLS_BINARY_DIR``
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The path to the directory containing the LLVM tools (e.g. ``llvm-as``).
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Notice that in the above example we link ``simple-tool`` against several LLVM
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libraries. The list of libraries is determined by using the
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``llvm_map_components_to_libnames()`` CMake function. For a list of available
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components look at the output of running ``llvm-config --components``.
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Note that for LLVM < 3.5 ``llvm_map_components_to_libraries()`` was
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used instead of ``llvm_map_components_to_libnames()``. This is now deprecated
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and will be removed in a future version of LLVM.
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.. _cmake-out-of-source-pass:
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Developing LLVM pass out of source
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----------------------------------
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Developing LLVM passes out of source
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------------------------------------
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It is possible to develop LLVM passes against installed LLVM. An example of
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project layout provided below:
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It is possible to develop LLVM passes out of LLVM's source tree (i.e. against an
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installed or built LLVM). An example of a project layout is provided below.
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.. code-block:: none
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@ -468,19 +514,34 @@ Contents of ``<project dir>/CMakeLists.txt``:
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.. code-block:: cmake
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find_package(LLVM)
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# Define add_llvm_* macro's.
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include(AddLLVM)
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find_package(LLVM REQUIRED CONFIG)
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add_definitions(${LLVM_DEFINITIONS})
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include_directories(${LLVM_INCLUDE_DIRS})
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link_directories(${LLVM_LIBRARY_DIRS})
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add_subdirectory(<pass name>)
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Contents of ``<project dir>/<pass name>/CMakeLists.txt``:
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.. code-block:: cmake
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add_library(LLVMPassname MODULE Pass.cpp)
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Note if you intend for this pass to be merged into the LLVM source tree at some
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point in the future it might make more sense to use LLVM's internal
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add_llvm_loadable_module function instead by...
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Adding the following to ``<project dir>/CMakeLists.txt`` (after
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``find_package(LLVM ...)``)
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.. code-block:: cmake
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list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_DIR}")
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include(AddLLVM)
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And then changing ``<project dir>/<pass name>/CMakeLists.txt`` to
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.. code-block:: cmake
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add_llvm_loadable_module(LLVMPassname
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