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Building LLVM With Autotools
.. contents::
This document details how to use the LLVM autotools based build system to
configure and build LLVM from source. The normal developer process using CMake
is detailed `here <GettingStarted.html#check-here>`_.
A Quick Summary
#. Configure and build LLVM and Clang:
* ``cd where-you-want-to-build-llvm``
* ``mkdir build`` (for building without polluting the source dir)
* ``cd build``
* ``../llvm/configure [options]``
Some common options:
* ``--prefix=directory`` --- Specify for *directory* the full pathname of
where you want the LLVM tools and libraries to be installed (default
* ``--enable-optimized`` --- Compile with optimizations enabled (default
is NO).
* ``--enable-assertions`` --- Compile with assertion checks enabled
(default is YES).
* ``make [-j]`` --- The ``-j`` specifies the number of jobs (commands) to run
simultaneously. This builds both LLVM and Clang for Debug+Asserts mode.
The ``--enable-optimized`` configure option is used to specify a Release
* ``make check-all`` --- This run the regression tests to ensure everything
is in working order.
* If you get an "internal compiler error (ICE)" or test failures, see
`here <GettingStarted.html#check-here>`_.
Local LLVM Configuration
Once checked out from the Subversion repository, the LLVM suite source code must
be configured via the ``configure`` script. This script sets variables in the
various ``*.in`` files, most notably ``llvm/Makefile.config`` and
``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
Makefiles needed to begin building LLVM.
The following environment variables are used by the ``configure`` script to
configure the build system:
| Variable | Purpose |
| CC | Tells ``configure`` which C compiler to use. By default, |
| | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
| | compilers (in this order). Use this variable to override |
| | ``configure``\'s default behavior. |
| CXX | Tells ``configure`` which C++ compiler to use. By |
| | default, ``configure`` will check ``PATH`` for |
| | ``clang++`` and GCC C++ compilers (in this order). Use |
| | this variable to override ``configure``'s default |
| | behavior. |
The following options can be used to set or enable LLVM specific options:
Enables optimized compilation (debugging symbols are removed and GCC
optimization flags are enabled). Note that this is the default setting if you
are using the LLVM distribution. The default behavior of a Subversion
checkout is to use an unoptimized build (also known as a debug build).
Enables debug symbols in the runtime libraries. The default is to strip debug
symbols from the runtime libraries.
Compile the Just In Time (JIT) compiler functionality. This is not available
on all platforms. The default is dependent on platform, so it is best to
explicitly enable it if you want it.
Controls which targets will be built and linked into llc. The default value
for ``target_options`` is "all" which builds and links all available targets.
The "host" target is selected as the target of the build host. You can also
specify a comma separated list of target names that you want available in llc.
The target names use all lower case. The current set of targets is:
``aarch64, arm, arm64, cpp, hexagon, mips, mipsel, mips64, mips64el, msp430,
powerpc, nvptx, r600, sparc, systemz, x86, x86_64, xcore``.
Look for the doxygen program and enable construction of doxygen based
documentation from the source code. This is disabled by default because
generating the documentation can take a long time and producess 100s of
megabytes of output.
To configure LLVM, follow these steps:
#. Change directory into the object root directory:
.. code-block:: console
#. Run the ``configure`` script located in the LLVM source tree:
.. code-block:: console
% $LLVM_SRC_DIR/configure --prefix=/install/path [other options]
Compiling the LLVM Suite Source Code
Once you have configured LLVM, you can build it. There are three types of
Debug Builds
These builds are the default when one is using a Subversion checkout and
types ``gmake`` (unless the ``--enable-optimized`` option was used during
configuration). The build system will compile the tools and libraries with
debugging information. To get a Debug Build using the LLVM distribution the
``--disable-optimized`` option must be passed to ``configure``.
Release (Optimized) Builds
These builds are enabled with the ``--enable-optimized`` option to
``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
line. For these builds, the build system will compile the tools and libraries
with GCC optimizations enabled and strip debugging information from the
libraries and executables it generates. Note that Release Builds are default
when using an LLVM distribution.
Profile Builds
These builds are for use with profiling. They compile profiling information
into the code for use with programs like ``gprof``. Profile builds must be
started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
directory and issuing the following command:
.. code-block:: console
% gmake
If the build fails, please `check here <GettingStarted.html#check-here>`_
to see if you are using a version of GCC that is known not to compile LLVM.
If you have multiple processors in your machine, you may wish to use some of the
parallel build options provided by GNU Make. For example, you could use the
.. code-block:: console
% gmake -j2
There are several special targets which are useful when working with the LLVM
source code:
``gmake clean``
Removes all files generated by the build. This includes object files,
generated C/C++ files, libraries, and executables.
``gmake dist-clean``
Removes everything that ``gmake clean`` does, but also removes files generated
by ``configure``. It attempts to return the source tree to the original state
in which it was shipped.
``gmake install``
Installs LLVM header files, libraries, tools, and documentation in a hierarchy
under ``$PREFIX``, specified with ``$LLVM_SRC_DIR/configure --prefix=[dir]``, which
defaults to ``/usr/local``.
``gmake -C runtime install-bytecode``
Assuming you built LLVM into $OBJDIR, when this command is run, it will
install bitcode libraries into the GCC front end's bitcode library directory.
If you need to update your bitcode libraries, this is the target to use once
you've built them.
Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
these ``make`` targets and descriptions of other targets available.
It is also possible to override default values from ``configure`` by declaring
variables on the command line. The following are some examples:
Perform a Release (Optimized) build.
Perform a Release (Optimized) build without assertions enabled.
Perform a Debug build.
Perform a Profiling build.
``gmake VERBOSE=1``
Print what ``gmake`` is doing on standard output.
``gmake TOOL_VERBOSE=1``
Ask each tool invoked by the makefiles to print out what it is doing on
the standard output. This also implies ``VERBOSE=1``.
Every directory in the LLVM object tree includes a ``Makefile`` to build it and
any subdirectories that it contains. Entering any directory inside the LLVM
object tree and typing ``gmake`` should rebuild anything in or below that
directory that is out of date.
This does not apply to building the documentation.
LLVM's (non-Doxygen) documentation is produced with the
`Sphinx <>`_ documentation generation system.
There are some HTML documents that have not yet been converted to the new
system (which uses the easy-to-read and easy-to-write
`reStructuredText <>`_ plaintext markup
The generated documentation is built in the ``$LLVM_SRC_DIR/docs`` directory using
a special makefile.
For instructions on how to install Sphinx, see
`Sphinx Introduction for LLVM Developers
After following the instructions there for installing Sphinx, build the LLVM
HTML documentation by doing the following:
.. code-block:: console
$ cd $LLVM_SRC_DIR/docs
$ make -f Makefile.sphinx
This creates a ``_build/html`` sub-directory with all of the HTML files, not
just the generated ones.
This directory corresponds to ````.
For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
Cross-Compiling LLVM
It is possible to cross-compile LLVM itself. That is, you can create LLVM
executables and libraries to be hosted on a platform different from the platform
where they are built (a Canadian Cross build). To configure a cross-compile,
supply the configure script with ``--build`` and ``--host`` options that are
different. The values of these options must be legal target triples that your
GCC compiler supports.
The result of such a build is executables that are not runnable on on the build
host (--build option) but can be executed on the compile host (--host option).
Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
<>`_ for more information
about cross-compiling.
The Location of LLVM Object Files
The LLVM build system is capable of sharing a single LLVM source tree among
several LLVM builds. Hence, it is possible to build LLVM for several different
platforms or configurations using the same source tree.
This is accomplished in the typical autoconf manner:
* Change directory to where the LLVM object files should live:
.. code-block:: console
* Run the ``configure`` script found in the LLVM source directory:
.. code-block:: console
% $LLVM_SRC_DIR/configure
The LLVM build will place files underneath *OBJ_ROOT* in directories named after
the build type:
Debug Builds with assertions enabled (the default)
Release Builds
Profile Builds