1 ====================================
2 Getting Started with the LLVM System
3 ====================================
11 Welcome to LLVM! In order to get started, you first need to know some basic
14 First, LLVM comes in three pieces. The first piece is the LLVM suite. This
15 contains all of the tools, libraries, and header files needed to use LLVM. It
16 contains an assembler, disassembler, bitcode analyzer and bitcode optimizer. It
17 also contains basic regression tests that can be used to test the LLVM tools and
20 The second piece is the `Clang <http://clang.llvm.org/>`_ front end. This
21 component compiles C, C++, Objective C, and Objective C++ code into LLVM
22 bitcode. Once compiled into LLVM bitcode, a program can be manipulated with the
23 LLVM tools from the LLVM suite.
25 There is a third, optional piece called Test Suite. It is a suite of programs
26 with a testing harness that can be used to further test LLVM's functionality
29 Getting Started Quickly (A Summary)
30 ===================================
32 The LLVM Getting Started documentation may be out of date. So, the `Clang
33 Getting Started <http://clang.llvm.org/get_started.html>`_ page might also be a
36 Here's the short story for getting up and running quickly with LLVM:
38 #. Read the documentation.
39 #. Read the documentation.
40 #. Remember that you were warned twice about reading the documentation.
43 * ``cd where-you-want-llvm-to-live``
44 * ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
48 * ``cd where-you-want-llvm-to-live``
50 * ``svn co http://llvm.org/svn/llvm-project/cfe/trunk clang``
52 #. Checkout Compiler-RT (required to build the sanitizers):
54 * ``cd where-you-want-llvm-to-live``
55 * ``cd llvm/projects``
56 * ``svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt``
58 #. Checkout Libomp (required for OpenMP support):
60 * ``cd where-you-want-llvm-to-live``
61 * ``cd llvm/projects``
62 * ``svn co http://llvm.org/svn/llvm-project/openmp/trunk openmp``
64 #. Checkout libcxx and libcxxabi **[Optional]**:
66 * ``cd where-you-want-llvm-to-live``
67 * ``cd llvm/projects``
68 * ``svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx``
69 * ``svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi``
71 #. Get the Test Suite Source Code **[Optional]**
73 * ``cd where-you-want-llvm-to-live``
74 * ``cd llvm/projects``
75 * ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
77 #. Configure and build LLVM and Clang:
79 The usual build uses `CMake <CMake.html>`_. If you would rather use
80 autotools, see `Building LLVM with autotools <BuildingLLVMWithAutotools.html>`_.
82 * ``cd where you want to build llvm``
85 * ``cmake -G <generator> [options] <path to llvm sources>``
87 Some common generators are:
89 * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
90 * ``Ninja`` --- for generating `Ninja <http://martine.github.io/ninja/>`
91 build files. Most llvm developers use Ninja.
92 * ``Visual Studio`` --- for generating Visual Studio projects and
94 * ``Xcode`` --- for generating Xcode projects.
98 * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
99 pathname of where you want the LLVM tools and libraries to be installed
100 (default ``/usr/local``).
102 * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
103 Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
105 * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
106 (default is Yes for Debug builds, No for all other build types).
108 * Run your build tool of choice!
110 * The default target (i.e. ``make``) will build all of LLVM
112 * The ``check-all`` target (i.e. ``make check-all``) will run the
113 regression tests to ensure everything is in working order.
115 * CMake will generate build targets for each tool and library, and most
116 LLVM sub-projects generate their own ``check-<project>`` target.
118 * For more information see `CMake <CMake.html>`_
120 * If you get an "internal compiler error (ICE)" or test failures, see
123 Consult the `Getting Started with LLVM`_ section for detailed information on
124 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
125 that simplify working with the Clang front end and LLVM tools. Go to `Program
126 Layout`_ to learn about the layout of the source code tree.
131 Before you begin to use the LLVM system, review the requirements given below.
132 This may save you some trouble by knowing ahead of time what hardware and
133 software you will need.
138 LLVM is known to work on the following host platforms:
140 ================== ===================== =============
142 ================== ===================== =============
143 Linux x86\ :sup:`1` GCC, Clang
144 Linux amd64 GCC, Clang
145 Linux ARM\ :sup:`4` GCC, Clang
146 Linux PowerPC GCC, Clang
147 Solaris V9 (Ultrasparc) GCC
148 FreeBSD x86\ :sup:`1` GCC, Clang
149 FreeBSD amd64 GCC, Clang
150 MacOS X\ :sup:`2` PowerPC GCC
151 MacOS X x86 GCC, Clang
152 Cygwin/Win32 x86\ :sup:`1, 3` GCC
153 Windows x86\ :sup:`1` Visual Studio
154 Windows x64 x86-64 Visual Studio
155 ================== ===================== =============
159 #. Code generation supported for Pentium processors and up
160 #. Code generation supported for 32-bit ABI only
161 #. To use LLVM modules on Win32-based system, you may configure LLVM
162 with ``-DBUILD_SHARED_LIBS=On`` for CMake builds or ``--enable-shared``
163 for configure builds.
164 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
166 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
167 mode, depending on the system (it is so large because of all the debugging
168 information and the fact that the libraries are statically linked into multiple
169 tools). If you do not need many of the tools and you are space-conscious, you
170 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
171 considerably less space.
173 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
174 so. If compilation is successful, the LLVM utilities should be able to
175 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
176 should work as well, although the generated native code may not work on your
182 Compiling LLVM requires that you have several software packages installed. The
183 table below lists those required packages. The Package column is the usual name
184 for the software package that LLVM depends on. The Version column provides
185 "known to work" versions of the package. The Notes column describes how LLVM
186 uses the package and provides other details.
188 =========================================================== ============ ==========================================
189 Package Version Notes
190 =========================================================== ============ ==========================================
191 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
192 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
193 `python <http://www.python.org/>`_ >=2.7 Automated test suite\ :sup:`2`
194 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
195 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
196 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
197 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
198 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
199 =========================================================== ============ ==========================================
203 #. Only the C and C++ languages are needed so there's no need to build the
204 other languages for LLVM's purposes. See `below` for specific version
206 #. Only needed if you want to run the automated test suite in the
207 ``llvm/test`` directory.
208 #. If you want to make changes to the configure scripts, you will need GNU
209 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
210 will also need automake (1.9.6). We only use aclocal from that package.
211 #. Optional, adds compression / uncompression capabilities to selected LLVM
214 Additionally, your compilation host is expected to have the usual plethora of
215 Unix utilities. Specifically:
217 * **ar** --- archive library builder
218 * **bzip2** --- bzip2 command for distribution generation
219 * **bunzip2** --- bunzip2 command for distribution checking
220 * **chmod** --- change permissions on a file
221 * **cat** --- output concatenation utility
222 * **cp** --- copy files
223 * **date** --- print the current date/time
224 * **echo** --- print to standard output
225 * **egrep** --- extended regular expression search utility
226 * **find** --- find files/dirs in a file system
227 * **grep** --- regular expression search utility
228 * **gzip** --- gzip command for distribution generation
229 * **gunzip** --- gunzip command for distribution checking
230 * **install** --- install directories/files
231 * **mkdir** --- create a directory
232 * **mv** --- move (rename) files
233 * **ranlib** --- symbol table builder for archive libraries
234 * **rm** --- remove (delete) files and directories
235 * **sed** --- stream editor for transforming output
236 * **sh** --- Bourne shell for make build scripts
237 * **tar** --- tape archive for distribution generation
238 * **test** --- test things in file system
239 * **unzip** --- unzip command for distribution checking
240 * **zip** --- zip command for distribution generation
245 Host C++ Toolchain, both Compiler and Standard Library
246 ------------------------------------------------------
248 LLVM is very demanding of the host C++ compiler, and as such tends to expose
249 bugs in the compiler. We are also planning to follow improvements and
250 developments in the C++ language and library reasonably closely. As such, we
251 require a modern host C++ toolchain, both compiler and standard library, in
254 For the most popular host toolchains we check for specific minimum versions in
261 Anything older than these toolchains *may* work, but will require forcing the
262 build system with a special option and is not really a supported host platform.
263 Also note that older versions of these compilers have often crashed or
266 For less widely used host toolchains such as ICC or xlC, be aware that a very
267 recent version may be required to support all of the C++ features used in LLVM.
269 We track certain versions of software that are *known* to fail when used as
270 part of the host toolchain. These even include linkers at times.
272 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
273 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
275 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
276 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
277 defined in a discarded section. You can safely ignore these messages as they are
278 erroneous and the linkage is correct. These messages disappear using ld 2.17.
280 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
281 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
282 times (minutes instead of seconds) when building LLVM. We recommend upgrading
283 to a newer version (2.17.50.0.4 or later).
285 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
286 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
287 intermittent failures when building LLVM with position independent code. The
288 symptom is an error about cyclic dependencies. We recommend upgrading to a
289 newer version of Gold.
291 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
292 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
293 3.0 does not implement a few builtins that are used in this library. We
294 recommend using the system GCC to compile LLVM and Clang in this case.
296 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
297 least some (``cxxabi.h``) libstdc++ headers.
299 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
300 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
301 causes Clang to refuse to compile condition_variable header file. At the time
302 of writing, this breaks LLD build.
304 Getting a Modern Host C++ Toolchain
305 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
307 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
308 have a sufficiently modern Xcode, or you will likely need to upgrade until you
309 do. On Windows, just use Visual Studio 2013 as the host compiler, it is
310 explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
311 Clang as the system compiler.
313 However, some Linux distributions and some other or older BSDs sometimes have
314 extremely old versions of GCC. These steps attempt to help you upgrade you
315 compiler even on such a system. However, if at all possible, we encourage you
316 to use a recent version of a distribution with a modern system compiler that
317 meets these requirements. Note that it is tempting to to install a prior
318 version of Clang and libc++ to be the host compiler, however libc++ was not
319 well tested or set up to build on Linux until relatively recently. As
320 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
321 initial host in a bootstrap, and then using Clang (and potentially libc++).
323 The first step is to get a recent GCC toolchain installed. The most common
324 distribution on which users have struggled with the version requirements is
325 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
326 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
327 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
328 not all users can use PPAs and there are many other distributions, so it may be
329 necessary (or just useful, if you're here you *are* doing compiler development
330 after all) to build and install GCC from source. It is also quite easy to do
333 .. _toolchain testing PPA:
334 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
335 .. _ask ubuntu stack exchange:
336 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
338 Easy steps for installing GCC 4.8.2:
340 .. code-block:: console
342 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
343 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2.sig
344 % wget https://ftp.gnu.org/gnu/gnu-keyring.gpg
345 % signature_invalid=`gpg --verify --no-default-keyring --keyring ./gnu-keyring.gpg gcc-4.8.2.tar.bz2.sig`
346 % if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
347 % tar -xvjf gcc-4.8.2.tar.bz2
349 % ./contrib/download_prerequisites
351 % mkdir gcc-4.8.2-build
353 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
357 For more details, check out the excellent `GCC wiki entry`_, where I got most
358 of this information from.
361 http://gcc.gnu.org/wiki/InstallingGCC
363 Once you have a GCC toolchain, configure your build of LLVM to use the new
364 toolchain for your host compiler and C++ standard library. Because the new
365 version of libstdc++ is not on the system library search path, you need to pass
366 extra linker flags so that it can be found at link time (``-L``) and at runtime
367 (``-rpath``). If you are using CMake, this invocation should produce working
370 .. code-block:: console
374 % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
375 cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
377 If you fail to set rpath, most LLVM binaries will fail on startup with a message
378 from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
379 found``. This means you need to tweak the -rpath linker flag.
381 When you build Clang, you will need to give *it* access to modern C++11
382 standard library in order to use it as your new host in part of a bootstrap.
383 There are two easy ways to do this, either build (and install) libc++ along
384 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
385 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
386 Clang will look within its own prefix for libstdc++ and use it if found. You
387 can also add an explicit prefix for Clang to look in for a GCC toolchain with
388 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
389 link commands when using your just-built-Clang to bootstrap.
391 .. _Getting Started with LLVM:
393 Getting Started with LLVM
394 =========================
396 The remainder of this guide is meant to get you up and running with LLVM and to
397 give you some basic information about the LLVM environment.
399 The later sections of this guide describe the `general layout`_ of the LLVM
400 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
401 more information about LLVM or to get help via e-mail.
403 Terminology and Notation
404 ------------------------
406 Throughout this manual, the following names are used to denote paths specific to
407 the local system and working environment. *These are not environment variables
408 you need to set but just strings used in the rest of this document below*. In
409 any of the examples below, simply replace each of these names with the
410 appropriate pathname on your local system. All these paths are absolute:
414 This is the top level directory of the LLVM source tree.
418 This is the top level directory of the LLVM object tree (i.e. the tree where
419 object files and compiled programs will be placed. It can be the same as
422 .. _Setting Up Your Environment:
424 Setting Up Your Environment
425 ---------------------------
427 In order to compile and use LLVM, you may need to set some environment
430 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
432 [Optional] This environment variable helps LLVM linking tools find the
433 locations of your bitcode libraries. It is provided only as a convenience
434 since you can specify the paths using the -L options of the tools and the
435 C/C++ front-end will automatically use the bitcode files installed in its
438 Unpacking the LLVM Archives
439 ---------------------------
441 If you have the LLVM distribution, you will need to unpack it before you can
442 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
443 and the LLVM GCC front end compiled for your platform. There is an additional
444 test suite that is optional. Each file is a TAR archive that is compressed with
447 The files are as follows, with *x.y* marking the version number:
451 Source release for the LLVM libraries and tools.
453 ``llvm-test-x.y.tar.gz``
455 Source release for the LLVM test-suite.
459 Checkout LLVM from Subversion
460 -----------------------------
462 If you have access to our Subversion repository, you can get a fresh copy of the
463 entire source code. All you need to do is check it out from Subversion as
466 * ``cd where-you-want-llvm-to-live``
467 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
468 * Read-Write: ``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
470 This will create an '``llvm``' directory in the current directory and fully
471 populate it with the LLVM source code, Makefiles, test directories, and local
472 copies of documentation files.
474 If you want to get a specific release (as opposed to the most recent revision),
475 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
476 following releases are located in the following subdirectories of the '``tags``'
479 * Release 3.4: **RELEASE_34/final**
480 * Release 3.3: **RELEASE_33/final**
481 * Release 3.2: **RELEASE_32/final**
482 * Release 3.1: **RELEASE_31/final**
483 * Release 3.0: **RELEASE_30/final**
484 * Release 2.9: **RELEASE_29/final**
485 * Release 2.8: **RELEASE_28**
486 * Release 2.7: **RELEASE_27**
487 * Release 2.6: **RELEASE_26**
488 * Release 2.5: **RELEASE_25**
489 * Release 2.4: **RELEASE_24**
490 * Release 2.3: **RELEASE_23**
491 * Release 2.2: **RELEASE_22**
492 * Release 2.1: **RELEASE_21**
493 * Release 2.0: **RELEASE_20**
494 * Release 1.9: **RELEASE_19**
495 * Release 1.8: **RELEASE_18**
496 * Release 1.7: **RELEASE_17**
497 * Release 1.6: **RELEASE_16**
498 * Release 1.5: **RELEASE_15**
499 * Release 1.4: **RELEASE_14**
500 * Release 1.3: **RELEASE_13**
501 * Release 1.2: **RELEASE_12**
502 * Release 1.1: **RELEASE_11**
503 * Release 1.0: **RELEASE_1**
505 If you would like to get the LLVM test suite (a separate package as of 1.4), you
506 get it from the Subversion repository:
508 .. code-block:: console
511 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
513 By placing it in the ``llvm/projects``, it will be automatically configured by
514 the LLVM configure script as well as automatically updated when you run ``svn
520 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
521 automatically with each Subversion commit and contain all necessary git-svn
522 marks (so, you can recreate git-svn metadata locally). Note that right now
523 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
526 .. code-block:: console
528 % git clone http://llvm.org/git/llvm.git
530 If you want to check out clang too, run:
532 .. code-block:: console
535 % git clone http://llvm.org/git/clang.git
537 If you want to check out compiler-rt (required to build the sanitizers), run:
539 .. code-block:: console
542 % git clone http://llvm.org/git/compiler-rt.git
544 If you want to check out libomp (required for OpenMP support), run:
546 .. code-block:: console
549 % git clone http://llvm.org/git/openmp.git
551 If you want to check out libcxx and libcxxabi (optional), run:
553 .. code-block:: console
556 % git clone http://llvm.org/git/libcxx.git
557 % git clone http://llvm.org/git/libcxxabi.git
559 If you want to check out the Test Suite Source Code (optional), run:
561 .. code-block:: console
564 % git clone http://llvm.org/git/test-suite.git
566 Since the upstream repository is in Subversion, you should use ``git
567 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
568 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
569 master branch, run the following command:
571 .. code-block:: console
573 % git config branch.master.rebase true
575 Sending patches with Git
576 ^^^^^^^^^^^^^^^^^^^^^^^^
578 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
580 Assume ``master`` points the upstream and ``mybranch`` points your working
581 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
582 sanity of whitespaces:
584 .. code-block:: console
586 % git diff --check master..mybranch
588 The easiest way to generate a patch is as below:
590 .. code-block:: console
592 % git diff master..mybranch > /path/to/mybranch.diff
594 It is a little different from svn-generated diff. git-diff-generated diff has
595 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
596 could be accepted with ``patch -p1 -N``.
598 But you may generate patchset with git-format-patch. It generates by-each-commit
599 patchset. To generate patch files to attach to your article:
601 .. code-block:: console
603 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
605 If you would like to send patches directly, you may use git-send-email or
606 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
608 .. code-block:: console
610 % git format-patch --attach master..mybranch --stdout | git imap-send
612 Then, your .git/config should have [imap] sections.
617 host = imaps://imap.gmail.com
618 user = your.gmail.account@gmail.com
623 folder = "[Gmail]/Drafts"
624 ; example for Japanese, "Modified UTF-7" encoded.
625 folder = "[Gmail]/&Tgtm+DBN-"
626 ; example for Traditional Chinese
627 folder = "[Gmail]/&g0l6Pw-"
629 For developers to work with git-svn
630 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
632 To set up clone from which you can submit code using ``git-svn``, run:
634 .. code-block:: console
636 % git clone http://llvm.org/git/llvm.git
638 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
639 % git config svn-remote.svn.fetch :refs/remotes/origin/master
640 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
642 # If you have clang too:
644 % git clone http://llvm.org/git/clang.git
646 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
647 % git config svn-remote.svn.fetch :refs/remotes/origin/master
650 Likewise for compiler-rt, libomp and test-suite.
652 To update this clone without generating git-svn tags that conflict with the
653 upstream Git repo, run:
655 .. code-block:: console
657 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
658 % git checkout master
661 git checkout master &&
664 Likewise for compiler-rt, libomp and test-suite.
666 This leaves your working directories on their master branches, so you'll need to
667 ``checkout`` each working branch individually and ``rebase`` it on top of its
670 For those who wish to be able to update an llvm repo/revert patches easily using
671 git-svn, please look in the directory for the scripts ``git-svnup`` and
674 To perform the aforementioned update steps go into your source directory and
675 just type ``git-svnup`` or ``git svnup`` and everything will just work.
677 If one wishes to revert a commit with git-svn, but do not want the git hash to
678 escape into the commit message, one can use the script ``git-svnrevert`` or
679 ``git svnrevert`` which will take in the git hash for the commit you want to
680 revert, look up the appropriate svn revision, and output a message where all
681 references to the git hash have been replaced with the svn revision.
683 To commit back changes via git-svn, use ``git svn dcommit``:
685 .. code-block:: console
689 Note that git-svn will create one SVN commit for each Git commit you have pending,
690 so squash and edit each commit before executing ``dcommit`` to make sure they all
691 conform to the coding standards and the developers' policy.
693 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
694 please make sure your current branch is up-to-date (via fetch/rebase) before
697 The git-svn metadata can get out of sync after you mess around with branches and
698 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
699 about files with uncommitted changes. The fix is to rebuild the metadata:
701 .. code-block:: console
706 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
708 Local LLVM Configuration
709 ------------------------
711 Once checked out from the Subversion repository, the LLVM suite source code must
712 be configured before being built. For instructions using autotools please see
713 `Building LLVM With Autotools <BuildingLLVMWithAutotools.html>`_. The
714 recommended process uses CMake. Unlinke the normal ``configure`` script, CMake
715 generates the build files in whatever format you request as well as various
716 ``*.inc`` files, and ``llvm/include/Config/config.h``.
718 Variables are passed to ``cmake`` on the command line using the format
719 ``-D<variable name>=<value>``. The following variables are some common options
720 used by people developing LLVM.
722 +-------------------------+----------------------------------------------------+
723 | Variable | Purpose |
724 +=========================+====================================================+
725 | CMAKE_C_COMPILER | Tells ``cmake`` which C compiler to use. By |
726 | | default, this will be /usr/bin/cc. |
727 +-------------------------+----------------------------------------------------+
728 | CMAKE_CXX_COMPILER | Tells ``cmake`` which C++ compiler to use. By |
729 | | default, this will be /usr/bin/c++. |
730 +-------------------------+----------------------------------------------------+
731 | CMAKE_BUILD_TYPE | Tells ``cmake`` what type of build you are trying |
732 | | to generate files for. Valid options are Debug, |
733 | | Release, RelWithDebInfo, and MinSizeRel. Default |
735 +-------------------------+----------------------------------------------------+
736 | CMAKE_INSTALL_PREFIX | Specifies the install directory to target when |
737 | | running the install action of the build files. |
738 +-------------------------+----------------------------------------------------+
739 | LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
740 | | targets will be built and linked into llc. This is |
741 | | equivalent to the ``--enable-targets`` option in |
742 | | the configure script. The default list is defined |
743 | | as ``LLVM_ALL_TARGETS``, and can be set to include |
744 | | out-of-tree targets. The default value includes: |
745 | | ``AArch64, AMDGPU, ARM, BPF, CppBackend, Hexagon, |
746 | | Mips, MSP430, NVPTX, PowerPC, Sparc, SystemZ |
748 +-------------------------+----------------------------------------------------+
749 | LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
750 | | code This is disabled by default because it is |
751 | | slow and generates a lot of output. |
752 +-------------------------+----------------------------------------------------+
753 | LLVM_ENABLE_SPHINX | Build sphinx-based documentation from the source |
754 | | code. This is disabled by default because it is |
755 | | slow and generates a lot of output. |
756 +-------------------------+----------------------------------------------------+
757 | LLVM_BUILD_LLVM_DYLIB | Generate libLLVM.so. This library contains a |
758 | | default set of LLVM components that can be |
759 | | overridden with ``LLVM_DYLIB_COMPONENTS``. The |
760 | | default contains most of LLVM and is defined in |
761 | | ``tools/llvm-shlib/CMakelists.txt``. |
762 +-------------------------+----------------------------------------------------+
763 | LLVM_OPTIMIZED_TABLEGEN | Builds a release tablegen that gets used during |
764 | | the LLVM build. This can dramatically speed up |
766 +-------------------------+----------------------------------------------------+
768 To configure LLVM, follow these steps:
770 #. Change directory into the object root directory:
772 .. code-block:: console
776 #. Run the ``cmake``:
778 .. code-block:: console
780 % cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=prefix=/install/path
781 [other options] SRC_ROOT
783 Compiling the LLVM Suite Source Code
784 ------------------------------------
786 Unlike with autotools, with CMake your build type is defined at configuration.
787 If you want to change your build type, you can re-run cmake with the following
790 .. code-block:: console
792 % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=type SRC_ROOT
794 Between runs, CMake preserves the values set for all options. CMake has the
795 following build types defined:
799 These builds are the default. The build system will compile the tools and
800 libraries unoptimized, with debugging information, and asserts enabled.
804 For these builds, the build system will compile the tools and libraries
805 with optimizations enabled and not generate debug info. CMakes default
806 optimization level is -O3. This can be configured by setting the
807 ``CMAKE_CXX_FLAGS_RELEASE`` variable on the CMake command line.
811 These builds are useful when debugging. They generate optimized binaries with
812 debug information. CMakes default optimization level is -O2. This can be
813 configured by setting the ``CMAKE_CXX_FLAGS_RELWITHDEBINFO`` variable on the
816 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
817 directory and issuing the following command:
819 .. code-block:: console
823 If the build fails, please `check here`_ to see if you are using a version of
824 GCC that is known not to compile LLVM.
826 If you have multiple processors in your machine, you may wish to use some of the
827 parallel build options provided by GNU Make. For example, you could use the
830 .. code-block:: console
834 There are several special targets which are useful when working with the LLVM
839 Removes all files generated by the build. This includes object files,
840 generated C/C++ files, libraries, and executables.
844 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
845 under ``$PREFIX``, specified with ``CMAKE_INSTALL_PREFIX``, which
846 defaults to ``/usr/local``.
848 ``make docs-llvm-html``
850 If configured with ``-DLLVM_ENABLE_SPHINX=On``, this will generate a directory
851 at ``OBJ_ROOT/docs/html`` which contains the HTML formatted documentation.
856 It is possible to cross-compile LLVM itself. That is, you can create LLVM
857 executables and libraries to be hosted on a platform different from the platform
858 where they are built (a Canadian Cross build). To generate build files for
859 cross-compiling CMake provides a variable ``CMAKE_TOOLCHAIN_FILE`` which can
860 define compiler flags and variables used during the CMake test operations.
862 The result of such a build is executables that are not runnable on on the build
863 host but can be executed on the target. As an example the following CMake
864 invocation can generate build files targeting iOS. This will work on Mac OS X
865 with the latest Xcode:
867 .. code-block:: console
869 % cmake -G "Ninja" -DCMAKE_OSX_ARCHITECTURES="armv7;armv7s;arm64"
870 -DCMAKE_TOOLCHAIN_FILE=<PATH_TO_LLVM>/cmake/platforms/iOS.cmake
871 -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_RUNTIME=Off -DLLVM_INCLUDE_TESTS=Off
872 -DLLVM_INCLUDE_EXAMPLES=Off -DLLVM_ENABLE_BACKTRACES=Off [options]
875 Note: There are some additional flags that need to be passed when building for
876 iOS due to limitations in the iOS SDK.
878 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
879 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
880 about cross-compiling.
882 The Location of LLVM Object Files
883 ---------------------------------
885 The LLVM build system is capable of sharing a single LLVM source tree among
886 several LLVM builds. Hence, it is possible to build LLVM for several different
887 platforms or configurations using the same source tree.
889 This is accomplished in the typical autoconf manner:
891 * Change directory to where the LLVM object files should live:
893 .. code-block:: console
899 .. code-block:: console
901 % cmake -G "Unix Makefiles" SRC_ROOT
903 The LLVM build will create a structure underneath *OBJ_ROOT* that matches the
904 LLVM source tree. At each level where source files are present in the source
905 tree there will be a corresponding ``CMakeFiles`` directory in the *OBJ_ROOT*.
906 Underneath that directory there is another directory with a name ending in
907 ``.dir`` under which you'll find object files for each source.
911 .. code-block:: console
914 % find lib/Support/ -name APFloat*
915 lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
917 Optional Configuration Items
918 ----------------------------
920 If you're running on a Linux system that supports the `binfmt_misc
921 <http://en.wikipedia.org/wiki/binfmt_misc>`_
922 module, and you have root access on the system, you can set your system up to
923 execute LLVM bitcode files directly. To do this, use commands like this (the
924 first command may not be required if you are already using the module):
926 .. code-block:: console
928 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
929 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
930 % chmod u+x hello.bc (if needed)
933 This allows you to execute LLVM bitcode files directly. On Debian, you can also
934 use this command instead of the 'echo' command above:
936 .. code-block:: console
938 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
946 One useful source of information about the LLVM source base is the LLVM `doxygen
947 <http://www.doxygen.org/>`_ documentation available at
948 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
954 This directory contains some simple examples of how to use the LLVM IR and JIT.
959 This directory contains public header files exported from the LLVM library. The
960 three main subdirectories of this directory are:
962 ``llvm/include/llvm``
964 This directory contains all of the LLVM specific header files. This directory
965 also has subdirectories for different portions of LLVM: ``Analysis``,
966 ``CodeGen``, ``Target``, ``Transforms``, etc...
968 ``llvm/include/llvm/Support``
970 This directory contains generic support libraries that are provided with LLVM
971 but not necessarily specific to LLVM. For example, some C++ STL utilities and
972 a Command Line option processing library store their header files here.
974 ``llvm/include/llvm/Config``
976 This directory contains header files configured by the ``configure`` script.
977 They wrap "standard" UNIX and C header files. Source code can include these
978 header files which automatically take care of the conditional #includes that
979 the ``configure`` script generates.
984 This directory contains most of the source files of the LLVM system. In LLVM,
985 almost all code exists in libraries, making it very easy to share code among the
990 This directory holds the core LLVM source files that implement core classes
991 like Instruction and BasicBlock.
993 ``llvm/lib/AsmParser/``
995 This directory holds the source code for the LLVM assembly language parser
998 ``llvm/lib/Bitcode/``
1000 This directory holds code for reading and write LLVM bitcode.
1002 ``llvm/lib/Analysis/``
1004 This directory contains a variety of different program analyses, such as
1005 Dominator Information, Call Graphs, Induction Variables, Interval
1006 Identification, Natural Loop Identification, etc.
1008 ``llvm/lib/Transforms/``
1010 This directory contains the source code for the LLVM to LLVM program
1011 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1012 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1013 Elimination, and many others.
1015 ``llvm/lib/Target/``
1017 This directory contains files that describe various target architectures for
1018 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1019 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1022 ``llvm/lib/CodeGen/``
1024 This directory contains the major parts of the code generator: Instruction
1025 Selector, Instruction Scheduling, and Register Allocation.
1031 ``llvm/lib/Debugger/``
1033 This directory contains the source level debugger library that makes it
1034 possible to instrument LLVM programs so that a debugger could identify source
1035 code locations at which the program is executing.
1037 ``llvm/lib/ExecutionEngine/``
1039 This directory contains libraries for executing LLVM bitcode directly at
1040 runtime in both interpreted and JIT compiled fashions.
1042 ``llvm/lib/Support/``
1044 This directory contains the source code that corresponds to the header files
1045 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1050 This directory contains projects that are not strictly part of LLVM but are
1051 shipped with LLVM. This is also the directory where you should create your own
1052 LLVM-based projects.
1057 This directory contains libraries which are compiled into LLVM bitcode and used
1058 when linking programs with the Clang front end. Most of these libraries are
1059 skeleton versions of real libraries; for example, libc is a stripped down
1062 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1068 This directory contains feature and regression tests and other basic sanity
1069 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1070 lot of territory without being exhaustive.
1075 This is not a directory in the normal llvm module; it is a separate Subversion
1076 module that must be checked out (usually to ``projects/test-suite``). This
1077 module contains a comprehensive correctness, performance, and benchmarking test
1078 suite for LLVM. It is a separate Subversion module because not every LLVM user
1079 is interested in downloading or building such a comprehensive test suite. For
1080 further details on this test suite, please see the :doc:`Testing Guide
1081 <TestingGuide>` document.
1088 The **tools** directory contains the executables built out of the libraries
1089 above, which form the main part of the user interface. You can always get help
1090 for a tool by typing ``tool_name -help``. The following is a brief introduction
1091 to the most important tools. More detailed information is in
1092 the `Command Guide <CommandGuide/index.html>`_.
1096 ``bugpoint`` is used to debug optimization passes or code generation backends
1097 by narrowing down the given test case to the minimum number of passes and/or
1098 instructions that still cause a problem, whether it is a crash or
1099 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1104 The archiver produces an archive containing the given LLVM bitcode files,
1105 optionally with an index for faster lookup.
1109 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1113 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1117 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1122 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1123 (although very slowly...). For architectures that support it (currently x86,
1124 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1125 compiler (if the functionality was compiled in), and will execute the code
1126 *much* faster than the interpreter.
1130 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1131 native code assembly file or to C code (with the ``-march=c`` option).
1135 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1136 (which are specified on the command line), and then outputs the resultant
1137 bitcode. The '``opt -help``' command is a good way to get a list of the
1138 program transformations available in LLVM.
1140 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1141 file and print out the results. It is primarily useful for debugging
1142 analyses, or familiarizing yourself with what an analysis does.
1147 This directory contains utilities for working with LLVM source code, and some of
1148 the utilities are actually required as part of the build process because they
1149 are code generators for parts of LLVM infrastructure.
1154 ``codegen-diff`` is a script that finds differences between code that LLC
1155 generates and code that LLI generates. This is a useful tool if you are
1156 debugging one of them, assuming that the other generates correct output. For
1157 the full user manual, run ```perldoc codegen-diff'``.
1161 The ``emacs`` directory contains syntax-highlighting files which will work
1162 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1163 assembly files and TableGen description files. For information on how to use
1164 the syntax files, consult the ``README`` file in that directory.
1168 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1169 which is useful if one wishes to do a lot of development across directories
1170 and does not want to individually find each file. One way to use it is to run,
1171 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1176 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1177 passes to it a regular expression provided on ``llvmgrep``'s command
1178 line. This is a very efficient way of searching the source base for a
1179 particular regular expression.
1183 The ``makellvm`` script compiles all files in the current directory and then
1184 compiles and links the tool that is the first argument. For example, assuming
1185 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1186 path, simply running ``makellvm llc`` will make a build of the current
1187 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1192 The ``TableGen`` directory contains the tool used to generate register
1193 descriptions, instruction set descriptions, and even assemblers from common
1194 TableGen description files.
1198 The ``vim`` directory contains syntax-highlighting files which will work with
1199 the VIM editor, providing syntax highlighting support for LLVM assembly files
1200 and TableGen description files. For information on how to use the syntax
1201 files, consult the ``README`` file in that directory.
1205 An Example Using the LLVM Tool Chain
1206 ====================================
1208 This section gives an example of using LLVM with the Clang front end.
1213 #. First, create a simple C file, name it 'hello.c':
1220 printf("hello world\n");
1224 #. Next, compile the C file into a native executable:
1226 .. code-block:: console
1228 % clang hello.c -o hello
1232 Clang works just like GCC by default. The standard -S and -c arguments
1233 work as usual (producing a native .s or .o file, respectively).
1235 #. Next, compile the C file into an LLVM bitcode file:
1237 .. code-block:: console
1239 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1241 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1242 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1243 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1245 #. Run the program in both forms. To run the program, use:
1247 .. code-block:: console
1253 .. code-block:: console
1257 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1258 <CommandGuide/lli>`.
1260 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1262 .. code-block:: console
1264 % llvm-dis < hello.bc | less
1266 #. Compile the program to native assembly using the LLC code generator:
1268 .. code-block:: console
1270 % llc hello.bc -o hello.s
1272 #. Assemble the native assembly language file into a program:
1274 .. code-block:: console
1276 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1278 % gcc hello.s -o hello.native # On others
1280 #. Execute the native code program:
1282 .. code-block:: console
1286 Note that using clang to compile directly to native code (i.e. when the
1287 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1292 If you are having problems building or using LLVM, or if you have any other
1293 general questions about LLVM, please consult the `Frequently Asked
1294 Questions <FAQ.html>`_ page.
1301 This document is just an **introduction** on how to use LLVM to do some simple
1302 things... there are many more interesting and complicated things that you can do
1303 that aren't documented here (but we'll gladly accept a patch if you want to
1304 write something up!). For more information about LLVM, check out:
1306 * `LLVM Homepage <http://llvm.org/>`_
1307 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1308 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_