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32 The LLVM Getting Started documentation may be out of date.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>`_.
81 Although the build is known to work with CMake >= 2.8.8, we recommend CMake
82 >= v3.2, especially if you're generating Ninja build files.
84 * ``cd where you want to build llvm``
87 * ``cmake -G <generator> [options] <path to llvm sources>``
89 Some common generators are:
91 * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
92 * ``Ninja`` --- for generating `Ninja <http://martine.github.io/ninja/>`
93 build files. Most llvm developers use Ninja.
94 * ``Visual Studio`` --- for generating Visual Studio projects and
96 * ``Xcode`` --- for generating Xcode projects.
100 * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
101 pathname of where you want the LLVM tools and libraries to be installed
102 (default ``/usr/local``).
104 * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
105 Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
107 * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
108 (default is Yes for Debug builds, No for all other build types).
110 * Run your build tool of choice!
112 * The default target (i.e. ``make``) will build all of LLVM
114 * The ``check-all`` target (i.e. ``make check-all``) will run the
115 regression tests to ensure everything is in working order.
117 * CMake will generate build targets for each tool and library, and most
118 LLVM sub-projects generate their own ``check-<project>`` target.
120 * For more information see `CMake <CMake.html>`_
122 * If you get an "internal compiler error (ICE)" or test failures, see
125 Consult the `Getting Started with LLVM`_ section for detailed information on
126 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
127 that simplify working with the Clang front end and LLVM tools. Go to `Program
128 Layout`_ to learn about the layout of the source code tree.
133 Before you begin to use the LLVM system, review the requirements given below.
134 This may save you some trouble by knowing ahead of time what hardware and
135 software you will need.
140 LLVM is known to work on the following host platforms:
142 ================== ===================== =============
144 ================== ===================== =============
145 Linux x86\ :sup:`1` GCC, Clang
146 Linux amd64 GCC, Clang
147 Linux ARM\ :sup:`4` GCC, Clang
148 Linux PowerPC GCC, Clang
149 Solaris V9 (Ultrasparc) GCC
150 FreeBSD x86\ :sup:`1` GCC, Clang
151 FreeBSD amd64 GCC, Clang
152 MacOS X\ :sup:`2` PowerPC GCC
153 MacOS X x86 GCC, Clang
154 Cygwin/Win32 x86\ :sup:`1, 3` GCC
155 Windows x86\ :sup:`1` Visual Studio
156 Windows x64 x86-64 Visual Studio
157 ================== ===================== =============
161 #. Code generation supported for Pentium processors and up
162 #. Code generation supported for 32-bit ABI only
163 #. To use LLVM modules on Win32-based system, you may configure LLVM
164 with ``-DBUILD_SHARED_LIBS=On`` for CMake builds or ``--enable-shared``
165 for configure builds.
166 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
168 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
169 mode, depending on the system (it is so large because of all the debugging
170 information and the fact that the libraries are statically linked into multiple
171 tools). If you do not need many of the tools and you are space-conscious, you
172 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
173 considerably less space.
175 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
176 so. If compilation is successful, the LLVM utilities should be able to
177 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
178 should work as well, although the generated native code may not work on your
184 Compiling LLVM requires that you have several software packages installed. The
185 table below lists those required packages. The Package column is the usual name
186 for the software package that LLVM depends on. The Version column provides
187 "known to work" versions of the package. The Notes column describes how LLVM
188 uses the package and provides other details.
190 =========================================================== ============ ==========================================
191 Package Version Notes
192 =========================================================== ============ ==========================================
193 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
194 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
195 `python <http://www.python.org/>`_ >=2.7 Automated test suite\ :sup:`2`
196 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
197 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
198 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
199 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
200 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
201 =========================================================== ============ ==========================================
205 #. Only the C and C++ languages are needed so there's no need to build the
206 other languages for LLVM's purposes. See `below` for specific version
208 #. Only needed if you want to run the automated test suite in the
209 ``llvm/test`` directory.
210 #. If you want to make changes to the configure scripts, you will need GNU
211 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
212 will also need automake (1.9.6). We only use aclocal from that package.
213 #. Optional, adds compression / uncompression capabilities to selected LLVM
216 Additionally, your compilation host is expected to have the usual plethora of
217 Unix utilities. Specifically:
219 * **ar** --- archive library builder
220 * **bzip2** --- bzip2 command for distribution generation
221 * **bunzip2** --- bunzip2 command for distribution checking
222 * **chmod** --- change permissions on a file
223 * **cat** --- output concatenation utility
224 * **cp** --- copy files
225 * **date** --- print the current date/time
226 * **echo** --- print to standard output
227 * **egrep** --- extended regular expression search utility
228 * **find** --- find files/dirs in a file system
229 * **grep** --- regular expression search utility
230 * **gzip** --- gzip command for distribution generation
231 * **gunzip** --- gunzip command for distribution checking
232 * **install** --- install directories/files
233 * **mkdir** --- create a directory
234 * **mv** --- move (rename) files
235 * **ranlib** --- symbol table builder for archive libraries
236 * **rm** --- remove (delete) files and directories
237 * **sed** --- stream editor for transforming output
238 * **sh** --- Bourne shell for make build scripts
239 * **tar** --- tape archive for distribution generation
240 * **test** --- test things in file system
241 * **unzip** --- unzip command for distribution checking
242 * **zip** --- zip command for distribution generation
247 Host C++ Toolchain, both Compiler and Standard Library
248 ------------------------------------------------------
250 LLVM is very demanding of the host C++ compiler, and as such tends to expose
251 bugs in the compiler. We are also planning to follow improvements and
252 developments in the C++ language and library reasonably closely. As such, we
253 require a modern host C++ toolchain, both compiler and standard library, in
256 For the most popular host toolchains we check for specific minimum versions in
263 Anything older than these toolchains *may* work, but will require forcing the
264 build system with a special option and is not really a supported host platform.
265 Also note that older versions of these compilers have often crashed or
268 For less widely used host toolchains such as ICC or xlC, be aware that a very
269 recent version may be required to support all of the C++ features used in LLVM.
271 We track certain versions of software that are *known* to fail when used as
272 part of the host toolchain. These even include linkers at times.
274 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
275 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
277 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
278 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
279 defined in a discarded section. You can safely ignore these messages as they are
280 erroneous and the linkage is correct. These messages disappear using ld 2.17.
282 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
283 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
284 times (minutes instead of seconds) when building LLVM. We recommend upgrading
285 to a newer version (2.17.50.0.4 or later).
287 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
288 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
289 intermittent failures when building LLVM with position independent code. The
290 symptom is an error about cyclic dependencies. We recommend upgrading to a
291 newer version of Gold.
293 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
294 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
295 3.0 does not implement a few builtins that are used in this library. We
296 recommend using the system GCC to compile LLVM and Clang in this case.
298 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
299 least some (``cxxabi.h``) libstdc++ headers.
301 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
302 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
303 causes Clang to refuse to compile condition_variable header file. At the time
304 of writing, this breaks LLD build.
306 Getting a Modern Host C++ Toolchain
307 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
309 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
310 have a sufficiently modern Xcode, or you will likely need to upgrade until you
311 do. On Windows, just use Visual Studio 2013 as the host compiler, it is
312 explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
313 Clang as the system compiler.
315 However, some Linux distributions and some other or older BSDs sometimes have
316 extremely old versions of GCC. These steps attempt to help you upgrade you
317 compiler even on such a system. However, if at all possible, we encourage you
318 to use a recent version of a distribution with a modern system compiler that
319 meets these requirements. Note that it is tempting to to install a prior
320 version of Clang and libc++ to be the host compiler, however libc++ was not
321 well tested or set up to build on Linux until relatively recently. As
322 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
323 initial host in a bootstrap, and then using Clang (and potentially libc++).
325 The first step is to get a recent GCC toolchain installed. The most common
326 distribution on which users have struggled with the version requirements is
327 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
328 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
329 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
330 not all users can use PPAs and there are many other distributions, so it may be
331 necessary (or just useful, if you're here you *are* doing compiler development
332 after all) to build and install GCC from source. It is also quite easy to do
335 .. _toolchain testing PPA:
336 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
337 .. _ask ubuntu stack exchange:
338 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
340 Easy steps for installing GCC 4.8.2:
342 .. code-block:: console
344 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
345 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2.sig
346 % wget https://ftp.gnu.org/gnu/gnu-keyring.gpg
347 % signature_invalid=`gpg --verify --no-default-keyring --keyring ./gnu-keyring.gpg gcc-4.8.2.tar.bz2.sig`
348 % if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
349 % tar -xvjf gcc-4.8.2.tar.bz2
351 % ./contrib/download_prerequisites
353 % mkdir gcc-4.8.2-build
355 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
359 For more details, check out the excellent `GCC wiki entry`_, where I got most
360 of this information from.
363 http://gcc.gnu.org/wiki/InstallingGCC
365 Once you have a GCC toolchain, configure your build of LLVM to use the new
366 toolchain for your host compiler and C++ standard library. Because the new
367 version of libstdc++ is not on the system library search path, you need to pass
368 extra linker flags so that it can be found at link time (``-L``) and at runtime
369 (``-rpath``). If you are using CMake, this invocation should produce working
372 .. code-block:: console
376 % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
377 cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
379 If you fail to set rpath, most LLVM binaries will fail on startup with a message
380 from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
381 found``. This means you need to tweak the -rpath linker flag.
383 When you build Clang, you will need to give *it* access to modern C++11
384 standard library in order to use it as your new host in part of a bootstrap.
385 There are two easy ways to do this, either build (and install) libc++ along
386 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
387 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
388 Clang will look within its own prefix for libstdc++ and use it if found. You
389 can also add an explicit prefix for Clang to look in for a GCC toolchain with
390 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
391 link commands when using your just-built-Clang to bootstrap.
393 .. _Getting Started with LLVM:
395 Getting Started with LLVM
396 =========================
398 The remainder of this guide is meant to get you up and running with LLVM and to
399 give you some basic information about the LLVM environment.
401 The later sections of this guide describe the `general layout`_ of the LLVM
402 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
403 more information about LLVM or to get help via e-mail.
405 Terminology and Notation
406 ------------------------
408 Throughout this manual, the following names are used to denote paths specific to
409 the local system and working environment. *These are not environment variables
410 you need to set but just strings used in the rest of this document below*. In
411 any of the examples below, simply replace each of these names with the
412 appropriate pathname on your local system. All these paths are absolute:
416 This is the top level directory of the LLVM source tree.
420 This is the top level directory of the LLVM object tree (i.e. the tree where
421 object files and compiled programs will be placed. It can be the same as
424 .. _Setting Up Your Environment:
426 Setting Up Your Environment
427 ---------------------------
429 In order to compile and use LLVM, you may need to set some environment
432 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
434 [Optional] This environment variable helps LLVM linking tools find the
435 locations of your bitcode libraries. It is provided only as a convenience
436 since you can specify the paths using the -L options of the tools and the
437 C/C++ front-end will automatically use the bitcode files installed in its
440 Unpacking the LLVM Archives
441 ---------------------------
443 If you have the LLVM distribution, you will need to unpack it before you can
444 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
445 and the LLVM GCC front end compiled for your platform. There is an additional
446 test suite that is optional. Each file is a TAR archive that is compressed with
449 The files are as follows, with *x.y* marking the version number:
453 Source release for the LLVM libraries and tools.
455 ``llvm-test-x.y.tar.gz``
457 Source release for the LLVM test-suite.
461 Checkout LLVM from Subversion
462 -----------------------------
464 If you have access to our Subversion repository, you can get a fresh copy of the
465 entire source code. All you need to do is check it out from Subversion as
468 * ``cd where-you-want-llvm-to-live``
469 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
470 * Read-Write: ``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
472 This will create an '``llvm``' directory in the current directory and fully
473 populate it with the LLVM source code, Makefiles, test directories, and local
474 copies of documentation files.
476 If you want to get a specific release (as opposed to the most recent revision),
477 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
478 following releases are located in the following subdirectories of the '``tags``'
481 * Release 3.4: **RELEASE_34/final**
482 * Release 3.3: **RELEASE_33/final**
483 * Release 3.2: **RELEASE_32/final**
484 * Release 3.1: **RELEASE_31/final**
485 * Release 3.0: **RELEASE_30/final**
486 * Release 2.9: **RELEASE_29/final**
487 * Release 2.8: **RELEASE_28**
488 * Release 2.7: **RELEASE_27**
489 * Release 2.6: **RELEASE_26**
490 * Release 2.5: **RELEASE_25**
491 * Release 2.4: **RELEASE_24**
492 * Release 2.3: **RELEASE_23**
493 * Release 2.2: **RELEASE_22**
494 * Release 2.1: **RELEASE_21**
495 * Release 2.0: **RELEASE_20**
496 * Release 1.9: **RELEASE_19**
497 * Release 1.8: **RELEASE_18**
498 * Release 1.7: **RELEASE_17**
499 * Release 1.6: **RELEASE_16**
500 * Release 1.5: **RELEASE_15**
501 * Release 1.4: **RELEASE_14**
502 * Release 1.3: **RELEASE_13**
503 * Release 1.2: **RELEASE_12**
504 * Release 1.1: **RELEASE_11**
505 * Release 1.0: **RELEASE_1**
507 If you would like to get the LLVM test suite (a separate package as of 1.4), you
508 get it from the Subversion repository:
510 .. code-block:: console
513 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
515 By placing it in the ``llvm/projects``, it will be automatically configured by
516 the LLVM configure script as well as automatically updated when you run ``svn
522 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
523 automatically with each Subversion commit and contain all necessary git-svn
524 marks (so, you can recreate git-svn metadata locally). Note that right now
525 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
528 .. code-block:: console
530 % git clone http://llvm.org/git/llvm.git
532 If you want to check out clang too, run:
534 .. code-block:: console
537 % git clone http://llvm.org/git/clang.git
539 If you want to check out compiler-rt (required to build the sanitizers), run:
541 .. code-block:: console
544 % git clone http://llvm.org/git/compiler-rt.git
546 If you want to check out libomp (required for OpenMP support), run:
548 .. code-block:: console
551 % git clone http://llvm.org/git/openmp.git
553 If you want to check out libcxx and libcxxabi (optional), run:
555 .. code-block:: console
558 % git clone http://llvm.org/git/libcxx.git
559 % git clone http://llvm.org/git/libcxxabi.git
561 If you want to check out the Test Suite Source Code (optional), run:
563 .. code-block:: console
566 % git clone http://llvm.org/git/test-suite.git
568 Since the upstream repository is in Subversion, you should use ``git
569 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
570 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
571 master branch, run the following command:
573 .. code-block:: console
575 % git config branch.master.rebase true
577 Sending patches with Git
578 ^^^^^^^^^^^^^^^^^^^^^^^^
580 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
582 Assume ``master`` points the upstream and ``mybranch`` points your working
583 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
584 sanity of whitespaces:
586 .. code-block:: console
588 % git diff --check master..mybranch
590 The easiest way to generate a patch is as below:
592 .. code-block:: console
594 % git diff master..mybranch > /path/to/mybranch.diff
596 It is a little different from svn-generated diff. git-diff-generated diff has
597 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
598 could be accepted with ``patch -p1 -N``.
600 But you may generate patchset with git-format-patch. It generates by-each-commit
601 patchset. To generate patch files to attach to your article:
603 .. code-block:: console
605 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
607 If you would like to send patches directly, you may use git-send-email or
608 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
610 .. code-block:: console
612 % git format-patch --attach master..mybranch --stdout | git imap-send
614 Then, your .git/config should have [imap] sections.
619 host = imaps://imap.gmail.com
620 user = your.gmail.account@gmail.com
625 folder = "[Gmail]/Drafts"
626 ; example for Japanese, "Modified UTF-7" encoded.
627 folder = "[Gmail]/&Tgtm+DBN-"
628 ; example for Traditional Chinese
629 folder = "[Gmail]/&g0l6Pw-"
631 For developers to work with git-svn
632 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
634 To set up clone from which you can submit code using ``git-svn``, run:
636 .. code-block:: console
638 % git clone http://llvm.org/git/llvm.git
640 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
641 % git config svn-remote.svn.fetch :refs/remotes/origin/master
642 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
644 # If you have clang too:
646 % git clone http://llvm.org/git/clang.git
648 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
649 % git config svn-remote.svn.fetch :refs/remotes/origin/master
652 Likewise for compiler-rt, libomp and test-suite.
654 To update this clone without generating git-svn tags that conflict with the
655 upstream Git repo, run:
657 .. code-block:: console
659 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
660 % git checkout master
663 git checkout master &&
666 Likewise for compiler-rt, libomp and test-suite.
668 This leaves your working directories on their master branches, so you'll need to
669 ``checkout`` each working branch individually and ``rebase`` it on top of its
672 For those who wish to be able to update an llvm repo/revert patches easily using
673 git-svn, please look in the directory for the scripts ``git-svnup`` and
676 To perform the aforementioned update steps go into your source directory and
677 just type ``git-svnup`` or ``git svnup`` and everything will just work.
679 If one wishes to revert a commit with git-svn, but do not want the git hash to
680 escape into the commit message, one can use the script ``git-svnrevert`` or
681 ``git svnrevert`` which will take in the git hash for the commit you want to
682 revert, look up the appropriate svn revision, and output a message where all
683 references to the git hash have been replaced with the svn revision.
685 To commit back changes via git-svn, use ``git svn dcommit``:
687 .. code-block:: console
691 Note that git-svn will create one SVN commit for each Git commit you have pending,
692 so squash and edit each commit before executing ``dcommit`` to make sure they all
693 conform to the coding standards and the developers' policy.
695 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
696 please make sure your current branch is up-to-date (via fetch/rebase) before
699 The git-svn metadata can get out of sync after you mess around with branches and
700 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
701 about files with uncommitted changes. The fix is to rebuild the metadata:
703 .. code-block:: console
708 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
710 Local LLVM Configuration
711 ------------------------
713 Once checked out from the Subversion repository, the LLVM suite source code must
714 be configured before being built. For instructions using autotools please see
715 `Building LLVM With Autotools <BuildingLLVMWithAutotools.html>`_. The
716 recommended process uses CMake. Unlinke the normal ``configure`` script, CMake
717 generates the build files in whatever format you request as well as various
718 ``*.inc`` files, and ``llvm/include/Config/config.h``.
720 Variables are passed to ``cmake`` on the command line using the format
721 ``-D<variable name>=<value>``. The following variables are some common options
722 used by people developing LLVM.
724 +-------------------------+----------------------------------------------------+
725 | Variable | Purpose |
726 +=========================+====================================================+
727 | CMAKE_C_COMPILER | Tells ``cmake`` which C compiler to use. By |
728 | | default, this will be /usr/bin/cc. |
729 +-------------------------+----------------------------------------------------+
730 | CMAKE_CXX_COMPILER | Tells ``cmake`` which C++ compiler to use. By |
731 | | default, this will be /usr/bin/c++. |
732 +-------------------------+----------------------------------------------------+
733 | CMAKE_BUILD_TYPE | Tells ``cmake`` what type of build you are trying |
734 | | to generate files for. Valid options are Debug, |
735 | | Release, RelWithDebInfo, and MinSizeRel. Default |
737 +-------------------------+----------------------------------------------------+
738 | CMAKE_INSTALL_PREFIX | Specifies the install directory to target when |
739 | | running the install action of the build files. |
740 +-------------------------+----------------------------------------------------+
741 | LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
742 | | targets will be built and linked into llc. This is |
743 | | equivalent to the ``--enable-targets`` option in |
744 | | the configure script. The default list is defined |
745 | | as ``LLVM_ALL_TARGETS``, and can be set to include |
746 | | out-of-tree targets. The default value includes: |
747 | | ``AArch64, AMDGPU, ARM, BPF, CppBackend, Hexagon, |
748 | | Mips, MSP430, NVPTX, PowerPC, Sparc, SystemZ |
750 +-------------------------+----------------------------------------------------+
751 | LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
752 | | code This is disabled by default because it is |
753 | | slow and generates a lot of output. |
754 +-------------------------+----------------------------------------------------+
755 | LLVM_ENABLE_SPHINX | Build sphinx-based documentation from the source |
756 | | code. This is disabled by default because it is |
757 | | slow and generates a lot of output. |
758 +-------------------------+----------------------------------------------------+
759 | LLVM_BUILD_LLVM_DYLIB | Generate libLLVM.so. This library contains a |
760 | | default set of LLVM components that can be |
761 | | overridden with ``LLVM_DYLIB_COMPONENTS``. The |
762 | | default contains most of LLVM and is defined in |
763 | | ``tools/llvm-shlib/CMakelists.txt``. |
764 +-------------------------+----------------------------------------------------+
765 | LLVM_OPTIMIZED_TABLEGEN | Builds a release tablegen that gets used during |
766 | | the LLVM build. This can dramatically speed up |
768 +-------------------------+----------------------------------------------------+
770 To configure LLVM, follow these steps:
772 #. Change directory into the object root directory:
774 .. code-block:: console
778 #. Run the ``cmake``:
780 .. code-block:: console
782 % cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=prefix=/install/path
783 [other options] SRC_ROOT
785 Compiling the LLVM Suite Source Code
786 ------------------------------------
788 Unlike with autotools, with CMake your build type is defined at configuration.
789 If you want to change your build type, you can re-run cmake with the following
792 .. code-block:: console
794 % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=type SRC_ROOT
796 Between runs, CMake preserves the values set for all options. CMake has the
797 following build types defined:
801 These builds are the default. The build system will compile the tools and
802 libraries unoptimized, with debugging information, and asserts enabled.
806 For these builds, the build system will compile the tools and libraries
807 with optimizations enabled and not generate debug info. CMakes default
808 optimization level is -O3. This can be configured by setting the
809 ``CMAKE_CXX_FLAGS_RELEASE`` variable on the CMake command line.
813 These builds are useful when debugging. They generate optimized binaries with
814 debug information. CMakes default optimization level is -O2. This can be
815 configured by setting the ``CMAKE_CXX_FLAGS_RELWITHDEBINFO`` variable on the
818 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
819 directory and issuing the following command:
821 .. code-block:: console
825 If the build fails, please `check here`_ to see if you are using a version of
826 GCC that is known not to compile LLVM.
828 If you have multiple processors in your machine, you may wish to use some of the
829 parallel build options provided by GNU Make. For example, you could use the
832 .. code-block:: console
836 There are several special targets which are useful when working with the LLVM
841 Removes all files generated by the build. This includes object files,
842 generated C/C++ files, libraries, and executables.
846 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
847 under ``$PREFIX``, specified with ``CMAKE_INSTALL_PREFIX``, which
848 defaults to ``/usr/local``.
850 ``make docs-llvm-html``
852 If configured with ``-DLLVM_ENABLE_SPHINX=On``, this will generate a directory
853 at ``OBJ_ROOT/docs/html`` which contains the HTML formatted documentation.
858 It is possible to cross-compile LLVM itself. That is, you can create LLVM
859 executables and libraries to be hosted on a platform different from the platform
860 where they are built (a Canadian Cross build). To generate build files for
861 cross-compiling CMake provides a variable ``CMAKE_TOOLCHAIN_FILE`` which can
862 define compiler flags and variables used during the CMake test operations.
864 The result of such a build is executables that are not runnable on on the build
865 host but can be executed on the target. As an example the following CMake
866 invocation can generate build files targeting iOS. This will work on Mac OS X
867 with the latest Xcode:
869 .. code-block:: console
871 % cmake -G "Ninja" -DCMAKE_OSX_ARCHITECTURES="armv7;armv7s;arm64"
872 -DCMAKE_TOOLCHAIN_FILE=<PATH_TO_LLVM>/cmake/platforms/iOS.cmake
873 -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_RUNTIME=Off -DLLVM_INCLUDE_TESTS=Off
874 -DLLVM_INCLUDE_EXAMPLES=Off -DLLVM_ENABLE_BACKTRACES=Off [options]
877 Note: There are some additional flags that need to be passed when building for
878 iOS due to limitations in the iOS SDK.
880 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
881 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
882 about cross-compiling.
884 The Location of LLVM Object Files
885 ---------------------------------
887 The LLVM build system is capable of sharing a single LLVM source tree among
888 several LLVM builds. Hence, it is possible to build LLVM for several different
889 platforms or configurations using the same source tree.
891 This is accomplished in the typical autoconf manner:
893 * Change directory to where the LLVM object files should live:
895 .. code-block:: console
901 .. code-block:: console
903 % cmake -G "Unix Makefiles" SRC_ROOT
905 The LLVM build will create a structure underneath *OBJ_ROOT* that matches the
906 LLVM source tree. At each level where source files are present in the source
907 tree there will be a corresponding ``CMakeFiles`` directory in the *OBJ_ROOT*.
908 Underneath that directory there is another directory with a name ending in
909 ``.dir`` under which you'll find object files for each source.
913 .. code-block:: console
916 % find lib/Support/ -name APFloat*
917 lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
919 Optional Configuration Items
920 ----------------------------
922 If you're running on a Linux system that supports the `binfmt_misc
923 <http://en.wikipedia.org/wiki/binfmt_misc>`_
924 module, and you have root access on the system, you can set your system up to
925 execute LLVM bitcode files directly. To do this, use commands like this (the
926 first command may not be required if you are already using the module):
928 .. code-block:: console
930 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
931 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
932 % chmod u+x hello.bc (if needed)
935 This allows you to execute LLVM bitcode files directly. On Debian, you can also
936 use this command instead of the 'echo' command above:
938 .. code-block:: console
940 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
948 One useful source of information about the LLVM source base is the LLVM `doxygen
949 <http://www.doxygen.org/>`_ documentation available at
950 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
956 This directory contains some simple examples of how to use the LLVM IR and JIT.
961 This directory contains public header files exported from the LLVM library. The
962 three main subdirectories of this directory are:
964 ``llvm/include/llvm``
966 This directory contains all of the LLVM specific header files. This directory
967 also has subdirectories for different portions of LLVM: ``Analysis``,
968 ``CodeGen``, ``Target``, ``Transforms``, etc...
970 ``llvm/include/llvm/Support``
972 This directory contains generic support libraries that are provided with LLVM
973 but not necessarily specific to LLVM. For example, some C++ STL utilities and
974 a Command Line option processing library store their header files here.
976 ``llvm/include/llvm/Config``
978 This directory contains header files configured by the ``configure`` script.
979 They wrap "standard" UNIX and C header files. Source code can include these
980 header files which automatically take care of the conditional #includes that
981 the ``configure`` script generates.
986 This directory contains most of the source files of the LLVM system. In LLVM,
987 almost all code exists in libraries, making it very easy to share code among the
992 This directory holds the core LLVM source files that implement core classes
993 like Instruction and BasicBlock.
995 ``llvm/lib/AsmParser/``
997 This directory holds the source code for the LLVM assembly language parser
1000 ``llvm/lib/Bitcode/``
1002 This directory holds code for reading and write LLVM bitcode.
1004 ``llvm/lib/Analysis/``
1006 This directory contains a variety of different program analyses, such as
1007 Dominator Information, Call Graphs, Induction Variables, Interval
1008 Identification, Natural Loop Identification, etc.
1010 ``llvm/lib/Transforms/``
1012 This directory contains the source code for the LLVM to LLVM program
1013 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1014 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1015 Elimination, and many others.
1017 ``llvm/lib/Target/``
1019 This directory contains files that describe various target architectures for
1020 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1021 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1024 ``llvm/lib/CodeGen/``
1026 This directory contains the major parts of the code generator: Instruction
1027 Selector, Instruction Scheduling, and Register Allocation.
1033 ``llvm/lib/Debugger/``
1035 This directory contains the source level debugger library that makes it
1036 possible to instrument LLVM programs so that a debugger could identify source
1037 code locations at which the program is executing.
1039 ``llvm/lib/ExecutionEngine/``
1041 This directory contains libraries for executing LLVM bitcode directly at
1042 runtime in both interpreted and JIT compiled fashions.
1044 ``llvm/lib/Support/``
1046 This directory contains the source code that corresponds to the header files
1047 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1052 This directory contains projects that are not strictly part of LLVM but are
1053 shipped with LLVM. This is also the directory where you should create your own
1054 LLVM-based projects.
1059 This directory contains libraries which are compiled into LLVM bitcode and used
1060 when linking programs with the Clang front end. Most of these libraries are
1061 skeleton versions of real libraries; for example, libc is a stripped down
1064 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1070 This directory contains feature and regression tests and other basic sanity
1071 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1072 lot of territory without being exhaustive.
1077 This is not a directory in the normal llvm module; it is a separate Subversion
1078 module that must be checked out (usually to ``projects/test-suite``). This
1079 module contains a comprehensive correctness, performance, and benchmarking test
1080 suite for LLVM. It is a separate Subversion module because not every LLVM user
1081 is interested in downloading or building such a comprehensive test suite. For
1082 further details on this test suite, please see the :doc:`Testing Guide
1083 <TestingGuide>` document.
1090 The **tools** directory contains the executables built out of the libraries
1091 above, which form the main part of the user interface. You can always get help
1092 for a tool by typing ``tool_name -help``. The following is a brief introduction
1093 to the most important tools. More detailed information is in
1094 the `Command Guide <CommandGuide/index.html>`_.
1098 ``bugpoint`` is used to debug optimization passes or code generation backends
1099 by narrowing down the given test case to the minimum number of passes and/or
1100 instructions that still cause a problem, whether it is a crash or
1101 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1106 The archiver produces an archive containing the given LLVM bitcode files,
1107 optionally with an index for faster lookup.
1111 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1115 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1119 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1124 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1125 (although very slowly...). For architectures that support it (currently x86,
1126 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1127 compiler (if the functionality was compiled in), and will execute the code
1128 *much* faster than the interpreter.
1132 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1133 native code assembly file or to C code (with the ``-march=c`` option).
1137 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1138 (which are specified on the command line), and then outputs the resultant
1139 bitcode. The '``opt -help``' command is a good way to get a list of the
1140 program transformations available in LLVM.
1142 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1143 file and print out the results. It is primarily useful for debugging
1144 analyses, or familiarizing yourself with what an analysis does.
1149 This directory contains utilities for working with LLVM source code, and some of
1150 the utilities are actually required as part of the build process because they
1151 are code generators for parts of LLVM infrastructure.
1156 ``codegen-diff`` is a script that finds differences between code that LLC
1157 generates and code that LLI generates. This is a useful tool if you are
1158 debugging one of them, assuming that the other generates correct output. For
1159 the full user manual, run ```perldoc codegen-diff'``.
1163 The ``emacs`` directory contains syntax-highlighting files which will work
1164 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1165 assembly files and TableGen description files. For information on how to use
1166 the syntax files, consult the ``README`` file in that directory.
1170 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1171 which is useful if one wishes to do a lot of development across directories
1172 and does not want to individually find each file. One way to use it is to run,
1173 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1178 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1179 passes to it a regular expression provided on ``llvmgrep``'s command
1180 line. This is a very efficient way of searching the source base for a
1181 particular regular expression.
1185 The ``makellvm`` script compiles all files in the current directory and then
1186 compiles and links the tool that is the first argument. For example, assuming
1187 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1188 path, simply running ``makellvm llc`` will make a build of the current
1189 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1194 The ``TableGen`` directory contains the tool used to generate register
1195 descriptions, instruction set descriptions, and even assemblers from common
1196 TableGen description files.
1200 The ``vim`` directory contains syntax-highlighting files which will work with
1201 the VIM editor, providing syntax highlighting support for LLVM assembly files
1202 and TableGen description files. For information on how to use the syntax
1203 files, consult the ``README`` file in that directory.
1207 An Example Using the LLVM Tool Chain
1208 ====================================
1210 This section gives an example of using LLVM with the Clang front end.
1215 #. First, create a simple C file, name it 'hello.c':
1222 printf("hello world\n");
1226 #. Next, compile the C file into a native executable:
1228 .. code-block:: console
1230 % clang hello.c -o hello
1234 Clang works just like GCC by default. The standard -S and -c arguments
1235 work as usual (producing a native .s or .o file, respectively).
1237 #. Next, compile the C file into an LLVM bitcode file:
1239 .. code-block:: console
1241 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1243 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1244 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1245 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1247 #. Run the program in both forms. To run the program, use:
1249 .. code-block:: console
1255 .. code-block:: console
1259 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1260 <CommandGuide/lli>`.
1262 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1264 .. code-block:: console
1266 % llvm-dis < hello.bc | less
1268 #. Compile the program to native assembly using the LLC code generator:
1270 .. code-block:: console
1272 % llc hello.bc -o hello.s
1274 #. Assemble the native assembly language file into a program:
1276 .. code-block:: console
1278 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1280 % gcc hello.s -o hello.native # On others
1282 #. Execute the native code program:
1284 .. code-block:: console
1288 Note that using clang to compile directly to native code (i.e. when the
1289 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1294 If you are having problems building or using LLVM, or if you have any other
1295 general questions about LLVM, please consult the `Frequently Asked
1296 Questions <FAQ.html>`_ page.
1303 This document is just an **introduction** on how to use LLVM to do some simple
1304 things... there are many more interesting and complicated things that you can do
1305 that aren't documented here (but we'll gladly accept a patch if you want to
1306 write something up!). For more information about LLVM, check out:
1308 * `LLVM Homepage <http://llvm.org/>`_
1309 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1310 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_