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.
We use here the command-line, non-interactive CMake interface
Download and install CMake. Version 2.8 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:
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:
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.
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
cmake --help
This will list the generator's names at the end of the help text. Generator's names are case-sensitive. Example:
cmake -G "Visual Studio 8 2005" 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.
Variables customize how the build will be generated. Options are boolean variables, with possible values ON/OFF. Options and variables are defined on the CMake command line like this:
cmake -DVARIABLE=value path/to/llvm/source
You can set a variable after the initial CMake invocation for changing its value. You can also undefine a variable:
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:
cmake -DVARIABLE:TYPE=value path/to/llvm/source
Here are listed 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.
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 directory:
make check
On Visual Studio, you may run tests to build the project "check".
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 cross-compiling.
The most difficult part of adding LLVM to the build of a project is to determine the set of LLVM libraries corresponding to the set of required LLVM features. What follows is an example of how to obtain this information:
# A convenience variable:
set(LLVM_ROOT "" CACHE PATH "Root of LLVM install.")
# A bit of a sanity check:
if( NOT EXISTS ${LLVM_ROOT}/include/llvm )
message(FATAL_ERROR "LLVM_ROOT (${LLVM_ROOT}) is not a valid LLVM install")
endif()
# We incorporate the CMake features provided by LLVM:
set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${LLVM_ROOT}/share/llvm/cmake")
include(LLVMConfig)
# Now set the header and library paths:
include_directories( ${LLVM_INCLUDE_DIRS} )
link_directories( ${LLVM_LIBRARY_DIRS} )
add_definitions( ${LLVM_DEFINITIONS} )
# Let's suppose we want to build a JIT compiler with support for
# binary code (no interpreter):
llvm_map_components_to_libraries(REQ_LLVM_LIBRARIES jit native)
# Finally, we link the LLVM libraries to our executable:
target_link_libraries(mycompiler ${REQ_LLVM_LIBRARIES})
This assumes that LLVM_ROOT points to an install of LLVM. The procedure works too for uninstalled builds although we need to take care to add an include_directories for the location of the headers on the LLVM source directory (if we are building out-of-source.)
Alternativaly, you can utilize CMake's find_package functionality. Here is an equivalent variant of snippet shown above:
find_package(LLVM)
if( NOT LLVM_FOUND )
message(FATAL_ERROR "LLVM package can't be found. Set CMAKE_PREFIX_PATH variable to LLVM's installation prefix.")
endif()
include_directories( ${LLVM_INCLUDE_DIRS} )
link_directories( ${LLVM_LIBRARY_DIRS} )
llvm_map_components_to_libraries(REQ_LLVM_LIBRARIES jit native)
target_link_libraries(mycompiler ${REQ_LLVM_LIBRARIES})
It is possible to develop LLVM passes against installed LLVM. An example of project layout provided below:
<project dir>/
|
CMakeLists.txt
<pass name>/
|
CMakeLists.txt
Pass.cpp
...
Contents of <project dir>/CMakeLists.txt:
find_package(LLVM)
# Define add_llvm_* macro's.
include(AddLLVM)
add_definitions(${LLVM_DEFINITIONS})
include_directories(${LLVM_INCLUDE_DIRS})
link_directories(${LLVM_LIBRARY_DIRS})
add_subdirectory(<pass name>)
Contents of <project dir>/<pass name>/CMakeLists.txt:
add_llvm_loadable_module(LLVMPassname
Pass.cpp
)
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:
1. Copying <pass name> folder into <LLVM root>/lib/Transform directory.
2. Adding "add_subdirectory(<pass name>)" line into <LLVM root>/lib/Transform/CMakeLists.txt
Notes for specific compilers and/or platforms.