Building LLVM with CMake

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

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

Download and install CMake. Version 2.6.2 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.

TODO

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.

CMAKE_BUILD_TYPE:STRING: Sets the build type for make based generators. Possible values are Release, Debug, RelWithDebInfo and MiniSizeRel. On systems like Visual Studio the user sets the build type with the IDE settings.
CMAKE_INSTALL_PREFIX:PATH: Path where LLVM will be installed if "make install" is invoked or the "INSTALL" target is built.
BUILD_SHARED_LIBS:BOOL: Flag indicating is shared libraries will be built. Its default value is OFF. Shared libraries are not supported on Windows and not recommended in the other OSes.

LLVM_TARGETS_TO_BUILD:STRING: Semicolon-separated list of targets to build, or all for building all targets. Case-sensitive. For Visual C++ defaults to X86. On the other cases defaults to all. Example: -DLLVM_TARGETS_TO_BUILD="X86;PowerPC;Alpha".
LLVM_ENABLE_THREADS:BOOL: Build with threads support, if available. Defaults to ON.
LLVM_ENABLE_PIC:BOOL: Add the -fPIC flag to the compiler command-line, if the compiler supports this flag. Some systems, like Windows, does not need this flag. Defaults to OFF.
LLVM_BUILD_32_BITS:BOOL: 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_PLO_FLAGS:STRING: Extra flags for creating partially linked objects. Visual C++ does not use this.
LLVM_TABLEGEN:STRING: Full path to a native TableGen executable (usually named tblgen). This is intented for cross-compiling: if the user sets this variable, no native TableGen will be created.

TODO