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32 The LLVM Getting Started documentation may be out of date.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 libcxx and libcxxabi **[Optional]**:
60 * ``cd where-you-want-llvm-to-live``
61 * ``cd llvm/projects``
62 * ``svn co http://llvm.org/svn/llvm-project/libcxx/trunk libcxx``
63 * ``svn co http://llvm.org/svn/llvm-project/libcxxabi/trunk libcxxabi``
65 #. Get the Test Suite Source Code **[Optional]**
67 * ``cd where-you-want-llvm-to-live``
68 * ``cd llvm/projects``
69 * ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
71 #. Configure and build LLVM and Clang:
73 The usual build uses `CMake <CMake.html>`_. If you would rather use
74 autotools, see `Building LLVM with autotools <BuildingLLVMWithAutotools.html>`_.
76 * ``cd where you want to build llvm``
79 * ``cmake -G <generator> [options] <path to llvm sources>``
81 Some common generators are:
83 * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
84 * ``Ninja`` --- for generating `Ninja <http://martine.github.io/ninja/>`
86 * ``Visual Studio`` --- for generating Visual Studio projects and
88 * ``Xcode`` --- for generating Xcode projects.
92 * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
93 pathname of where you want the LLVM tools and libraries to be installed
94 (default ``/usr/local``).
96 * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
97 Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
99 * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
100 (default is Yes for Debug builds, No for all other build types).
102 * Run your build tool of choice!
104 * The default target (i.e. ``make``) will build all of LLVM
106 * The ``check-all`` target (i.e. ``make check-all``) will run the
107 regression tests to ensure everything is in working order.
109 * CMake will generate build targets for each tool and library, and most
110 LLVM sub-projects generate their own ``check-<project>`` target.
112 * For more information see `CMake <CMake.html>`_
114 * If you get an "internal compiler error (ICE)" or test failures, see
117 Consult the `Getting Started with LLVM`_ section for detailed information on
118 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
119 that simplify working with the Clang front end and LLVM tools. Go to `Program
120 Layout`_ to learn about the layout of the source code tree.
125 Before you begin to use the LLVM system, review the requirements given below.
126 This may save you some trouble by knowing ahead of time what hardware and
127 software you will need.
132 LLVM is known to work on the following host platforms:
134 ================== ===================== =============
136 ================== ===================== =============
137 Linux x86\ :sup:`1` GCC, Clang
138 Linux amd64 GCC, Clang
139 Linux ARM\ :sup:`4` GCC, Clang
140 Linux PowerPC GCC, Clang
141 Solaris V9 (Ultrasparc) GCC
142 FreeBSD x86\ :sup:`1` GCC, Clang
143 FreeBSD amd64 GCC, Clang
144 MacOS X\ :sup:`2` PowerPC GCC
145 MacOS X x86 GCC, Clang
146 Cygwin/Win32 x86\ :sup:`1, 3` GCC
147 Windows x86\ :sup:`1` Visual Studio
148 Windows x64 x86-64 Visual Studio
149 ================== ===================== =============
153 #. Code generation supported for Pentium processors and up
154 #. Code generation supported for 32-bit ABI only
155 #. To use LLVM modules on Win32-based system, you may configure LLVM
156 with ``-DBUILD_SHARED_LIBS=On`` for CMake builds or ``--enable-shared``
157 for configure builds.
158 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
160 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
161 mode, depending on the system (it is so large because of all the debugging
162 information and the fact that the libraries are statically linked into multiple
163 tools). If you do not need many of the tools and you are space-conscious, you
164 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
165 considerably less space.
167 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
168 so. If compilation is successful, the LLVM utilities should be able to
169 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
170 should work as well, although the generated native code may not work on your
176 Compiling LLVM requires that you have several software packages installed. The
177 table below lists those required packages. The Package column is the usual name
178 for the software package that LLVM depends on. The Version column provides
179 "known to work" versions of the package. The Notes column describes how LLVM
180 uses the package and provides other details.
182 =========================================================== ============ ==========================================
183 Package Version Notes
184 =========================================================== ============ ==========================================
185 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
186 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
187 `python <http://www.python.org/>`_ >=2.7 Automated test suite\ :sup:`2`
188 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
189 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
190 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
191 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
192 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
193 =========================================================== ============ ==========================================
197 #. Only the C and C++ languages are needed so there's no need to build the
198 other languages for LLVM's purposes. See `below` for specific version
200 #. Only needed if you want to run the automated test suite in the
201 ``llvm/test`` directory.
202 #. If you want to make changes to the configure scripts, you will need GNU
203 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
204 will also need automake (1.9.6). We only use aclocal from that package.
205 #. Optional, adds compression / uncompression capabilities to selected LLVM
208 Additionally, your compilation host is expected to have the usual plethora of
209 Unix utilities. Specifically:
211 * **ar** --- archive library builder
212 * **bzip2** --- bzip2 command for distribution generation
213 * **bunzip2** --- bunzip2 command for distribution checking
214 * **chmod** --- change permissions on a file
215 * **cat** --- output concatenation utility
216 * **cp** --- copy files
217 * **date** --- print the current date/time
218 * **echo** --- print to standard output
219 * **egrep** --- extended regular expression search utility
220 * **find** --- find files/dirs in a file system
221 * **grep** --- regular expression search utility
222 * **gzip** --- gzip command for distribution generation
223 * **gunzip** --- gunzip command for distribution checking
224 * **install** --- install directories/files
225 * **mkdir** --- create a directory
226 * **mv** --- move (rename) files
227 * **ranlib** --- symbol table builder for archive libraries
228 * **rm** --- remove (delete) files and directories
229 * **sed** --- stream editor for transforming output
230 * **sh** --- Bourne shell for make build scripts
231 * **tar** --- tape archive for distribution generation
232 * **test** --- test things in file system
233 * **unzip** --- unzip command for distribution checking
234 * **zip** --- zip command for distribution generation
239 Host C++ Toolchain, both Compiler and Standard Library
240 ------------------------------------------------------
242 LLVM is very demanding of the host C++ compiler, and as such tends to expose
243 bugs in the compiler. We are also planning to follow improvements and
244 developments in the C++ language and library reasonably closely. As such, we
245 require a modern host C++ toolchain, both compiler and standard library, in
248 For the most popular host toolchains we check for specific minimum versions in
255 Anything older than these toolchains *may* work, but will require forcing the
256 build system with a special option and is not really a supported host platform.
257 Also note that older versions of these compilers have often crashed or
260 For less widely used host toolchains such as ICC or xlC, be aware that a very
261 recent version may be required to support all of the C++ features used in LLVM.
263 We track certain versions of software that are *known* to fail when used as
264 part of the host toolchain. These even include linkers at times.
266 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
267 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
269 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
270 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
271 defined in a discarded section. You can safely ignore these messages as they are
272 erroneous and the linkage is correct. These messages disappear using ld 2.17.
274 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
275 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
276 times (minutes instead of seconds) when building LLVM. We recommend upgrading
277 to a newer version (2.17.50.0.4 or later).
279 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
280 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
281 intermittent failures when building LLVM with position independent code. The
282 symptom is an error about cyclic dependencies. We recommend upgrading to a
283 newer version of Gold.
285 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
286 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
287 3.0 does not implement a few builtins that are used in this library. We
288 recommend using the system GCC to compile LLVM and Clang in this case.
290 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
291 least some (``cxxabi.h``) libstdc++ headers.
293 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
294 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
295 causes Clang to refuse to compile condition_variable header file. At the time
296 of writing, this breaks LLD build.
298 Getting a Modern Host C++ Toolchain
299 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
301 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
302 have a sufficiently modern Xcode, or you will likely need to upgrade until you
303 do. On Windows, just use Visual Studio 2013 as the host compiler, it is
304 explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
305 Clang as the system compiler.
307 However, some Linux distributions and some other or older BSDs sometimes have
308 extremely old versions of GCC. These steps attempt to help you upgrade you
309 compiler even on such a system. However, if at all possible, we encourage you
310 to use a recent version of a distribution with a modern system compiler that
311 meets these requirements. Note that it is tempting to to install a prior
312 version of Clang and libc++ to be the host compiler, however libc++ was not
313 well tested or set up to build on Linux until relatively recently. As
314 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
315 initial host in a bootstrap, and then using Clang (and potentially libc++).
317 The first step is to get a recent GCC toolchain installed. The most common
318 distribution on which users have struggled with the version requirements is
319 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
320 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
321 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
322 not all users can use PPAs and there are many other distributions, so it may be
323 necessary (or just useful, if you're here you *are* doing compiler development
324 after all) to build and install GCC from source. It is also quite easy to do
327 .. _toolchain testing PPA:
328 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
329 .. _ask ubuntu stack exchange:
330 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
332 Easy steps for installing GCC 4.8.2:
334 .. code-block:: console
336 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
337 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2.sig
338 % wget https://ftp.gnu.org/gnu/gnu-keyring.gpg
339 % signature_invalid=`gpg --verify --no-default-keyring --keyring ./gnu-keyring.gpg gcc-4.8.2.tar.bz2.sig`
340 % if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
341 % tar -xvjf gcc-4.8.2.tar.bz2
343 % ./contrib/download_prerequisites
345 % mkdir gcc-4.8.2-build
347 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
351 For more details, check out the excellent `GCC wiki entry`_, where I got most
352 of this information from.
355 http://gcc.gnu.org/wiki/InstallingGCC
357 Once you have a GCC toolchain, configure your build of LLVM to use the new
358 toolchain for your host compiler and C++ standard library. Because the new
359 version of libstdc++ is not on the system library search path, you need to pass
360 extra linker flags so that it can be found at link time (``-L``) and at runtime
361 (``-rpath``). If you are using CMake, this invocation should produce working
364 .. code-block:: console
368 % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
369 cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
371 If you fail to set rpath, most LLVM binaries will fail on startup with a message
372 from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
373 found``. This means you need to tweak the -rpath linker flag.
375 When you build Clang, you will need to give *it* access to modern C++11
376 standard library in order to use it as your new host in part of a bootstrap.
377 There are two easy ways to do this, either build (and install) libc++ along
378 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
379 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
380 Clang will look within its own prefix for libstdc++ and use it if found. You
381 can also add an explicit prefix for Clang to look in for a GCC toolchain with
382 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
383 link commands when using your just-built-Clang to bootstrap.
385 .. _Getting Started with LLVM:
387 Getting Started with LLVM
388 =========================
390 The remainder of this guide is meant to get you up and running with LLVM and to
391 give you some basic information about the LLVM environment.
393 The later sections of this guide describe the `general layout`_ of the LLVM
394 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
395 more information about LLVM or to get help via e-mail.
397 Terminology and Notation
398 ------------------------
400 Throughout this manual, the following names are used to denote paths specific to
401 the local system and working environment. *These are not environment variables
402 you need to set but just strings used in the rest of this document below*. In
403 any of the examples below, simply replace each of these names with the
404 appropriate pathname on your local system. All these paths are absolute:
408 This is the top level directory of the LLVM source tree.
412 This is the top level directory of the LLVM object tree (i.e. the tree where
413 object files and compiled programs will be placed. It can be the same as
416 .. _Setting Up Your Environment:
418 Setting Up Your Environment
419 ---------------------------
421 In order to compile and use LLVM, you may need to set some environment
424 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
426 [Optional] This environment variable helps LLVM linking tools find the
427 locations of your bitcode libraries. It is provided only as a convenience
428 since you can specify the paths using the -L options of the tools and the
429 C/C++ front-end will automatically use the bitcode files installed in its
432 Unpacking the LLVM Archives
433 ---------------------------
435 If you have the LLVM distribution, you will need to unpack it before you can
436 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
437 and the LLVM GCC front end compiled for your platform. There is an additional
438 test suite that is optional. Each file is a TAR archive that is compressed with
441 The files are as follows, with *x.y* marking the version number:
445 Source release for the LLVM libraries and tools.
447 ``llvm-test-x.y.tar.gz``
449 Source release for the LLVM test-suite.
453 Checkout LLVM from Subversion
454 -----------------------------
456 If you have access to our Subversion repository, you can get a fresh copy of the
457 entire source code. All you need to do is check it out from Subversion as
460 * ``cd where-you-want-llvm-to-live``
461 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
462 * Read-Write: ``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
464 This will create an '``llvm``' directory in the current directory and fully
465 populate it with the LLVM source code, Makefiles, test directories, and local
466 copies of documentation files.
468 If you want to get a specific release (as opposed to the most recent revision),
469 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
470 following releases are located in the following subdirectories of the '``tags``'
473 * Release 3.4: **RELEASE_34/final**
474 * Release 3.3: **RELEASE_33/final**
475 * Release 3.2: **RELEASE_32/final**
476 * Release 3.1: **RELEASE_31/final**
477 * Release 3.0: **RELEASE_30/final**
478 * Release 2.9: **RELEASE_29/final**
479 * Release 2.8: **RELEASE_28**
480 * Release 2.7: **RELEASE_27**
481 * Release 2.6: **RELEASE_26**
482 * Release 2.5: **RELEASE_25**
483 * Release 2.4: **RELEASE_24**
484 * Release 2.3: **RELEASE_23**
485 * Release 2.2: **RELEASE_22**
486 * Release 2.1: **RELEASE_21**
487 * Release 2.0: **RELEASE_20**
488 * Release 1.9: **RELEASE_19**
489 * Release 1.8: **RELEASE_18**
490 * Release 1.7: **RELEASE_17**
491 * Release 1.6: **RELEASE_16**
492 * Release 1.5: **RELEASE_15**
493 * Release 1.4: **RELEASE_14**
494 * Release 1.3: **RELEASE_13**
495 * Release 1.2: **RELEASE_12**
496 * Release 1.1: **RELEASE_11**
497 * Release 1.0: **RELEASE_1**
499 If you would like to get the LLVM test suite (a separate package as of 1.4), you
500 get it from the Subversion repository:
502 .. code-block:: console
505 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
507 By placing it in the ``llvm/projects``, it will be automatically configured by
508 the LLVM configure script as well as automatically updated when you run ``svn
514 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
515 automatically with each Subversion commit and contain all necessary git-svn
516 marks (so, you can recreate git-svn metadata locally). Note that right now
517 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
520 .. code-block:: console
522 % git clone http://llvm.org/git/llvm.git
524 If you want to check out clang too, run:
526 .. code-block:: console
529 % git clone http://llvm.org/git/clang.git
531 If you want to check out compiler-rt (required to build the sanitizers), run:
533 .. code-block:: console
536 % git clone http://llvm.org/git/compiler-rt.git
538 If you want to check out libcxx and libcxxabi (optional), run:
540 .. code-block:: console
543 % git clone http://llvm.org/git/libcxx.git
544 % git clone http://llvm.org/git/libcxxabi.git
546 If you want to check out the Test Suite Source Code (optional), run:
548 .. code-block:: console
551 % git clone http://llvm.org/git/test-suite.git
553 Since the upstream repository is in Subversion, you should use ``git
554 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
555 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
556 master branch, run the following command:
558 .. code-block:: console
560 % git config branch.master.rebase true
562 Sending patches with Git
563 ^^^^^^^^^^^^^^^^^^^^^^^^
565 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
567 Assume ``master`` points the upstream and ``mybranch`` points your working
568 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
569 sanity of whitespaces:
571 .. code-block:: console
573 % git diff --check master..mybranch
575 The easiest way to generate a patch is as below:
577 .. code-block:: console
579 % git diff master..mybranch > /path/to/mybranch.diff
581 It is a little different from svn-generated diff. git-diff-generated diff has
582 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
583 could be accepted with ``patch -p1 -N``.
585 But you may generate patchset with git-format-patch. It generates by-each-commit
586 patchset. To generate patch files to attach to your article:
588 .. code-block:: console
590 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
592 If you would like to send patches directly, you may use git-send-email or
593 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
595 .. code-block:: console
597 % git format-patch --attach master..mybranch --stdout | git imap-send
599 Then, your .git/config should have [imap] sections.
604 host = imaps://imap.gmail.com
605 user = your.gmail.account@gmail.com
610 folder = "[Gmail]/Drafts"
611 ; example for Japanese, "Modified UTF-7" encoded.
612 folder = "[Gmail]/&Tgtm+DBN-"
613 ; example for Traditional Chinese
614 folder = "[Gmail]/&g0l6Pw-"
616 For developers to work with git-svn
617 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
619 To set up clone from which you can submit code using ``git-svn``, run:
621 .. code-block:: console
623 % git clone http://llvm.org/git/llvm.git
625 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
626 % git config svn-remote.svn.fetch :refs/remotes/origin/master
627 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
629 # If you have clang too:
631 % git clone http://llvm.org/git/clang.git
633 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
634 % git config svn-remote.svn.fetch :refs/remotes/origin/master
637 Likewise for compiler-rt and test-suite.
639 To update this clone without generating git-svn tags that conflict with the
640 upstream Git repo, run:
642 .. code-block:: console
644 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
645 % git checkout master
648 git checkout master &&
651 Likewise for compiler-rt and test-suite.
653 This leaves your working directories on their master branches, so you'll need to
654 ``checkout`` each working branch individually and ``rebase`` it on top of its
657 For those who wish to be able to update an llvm repo/revert patches easily using
658 git-svn, please look in the directory for the scripts ``git-svnup`` and
661 To perform the aforementioned update steps go into your source directory and
662 just type ``git-svnup`` or ``git svnup`` and everything will just work.
664 If one wishes to revert a commit with git-svn, but do not want the git hash to
665 escape into the commit message, one can use the script ``git-svnrevert`` or
666 ``git svnrevert`` which will take in the git hash for the commit you want to
667 revert, look up the appropriate svn revision, and output a message where all
668 references to the git hash have been replaced with the svn revision.
670 To commit back changes via git-svn, use ``git svn dcommit``:
672 .. code-block:: console
676 Note that git-svn will create one SVN commit for each Git commit you have pending,
677 so squash and edit each commit before executing ``dcommit`` to make sure they all
678 conform to the coding standards and the developers' policy.
680 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
681 please make sure your current branch is up-to-date (via fetch/rebase) before
684 The git-svn metadata can get out of sync after you mess around with branches and
685 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
686 about files with uncommitted changes. The fix is to rebuild the metadata:
688 .. code-block:: console
693 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
695 Local LLVM Configuration
696 ------------------------
698 Once checked out from the Subversion repository, the LLVM suite source code must
699 be configured before being built. For instructions using autotools please see
700 `Building LLVM With Autotools <BuildingLLVMWithAutotools.html>`_. The
701 recommended process uses CMake. Unlinke the normal ``configure`` script, CMake
702 generates the build files in whatever format you request as well as various
703 ``*.inc`` files, and ``llvm/include/Config/config.h``.
705 Variables are passed to ``cmake`` on the command line using the format
706 ``-D<variable name>=<value>``. The following variables are some common options
707 used by people developing LLVM.
709 +-------------------------+----------------------------------------------------+
710 | Variable | Purpose |
711 +=========================+====================================================+
712 | CMAKE_C_COMPILER | Tells ``cmake`` which C compiler to use. By |
713 | | default, this will be /usr/bin/cc. |
714 +-------------------------+----------------------------------------------------+
715 | CMAKE_CXX_COMPILER | Tells ``cmake`` which C++ compiler to use. By |
716 | | default, this will be /usr/bin/c++. |
717 +-------------------------+----------------------------------------------------+
718 | CMAKE_BUILD_TYPE | Tells ``cmake`` what type of build you are trying |
719 | | to generate files for. Valid options are Debug, |
720 | | Release, RelWithDebInfo, and MinSizeRel. Default |
722 +-------------------------+----------------------------------------------------+
723 | CMAKE_INSTALL_PREFIX | Specifies the install directory to target when |
724 | | running the install action of the build files. |
725 +-------------------------+----------------------------------------------------+
726 | LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
727 | | targets will be built and linked into llc. This is |
728 | | equivalent to the ``--enable-targets`` option in |
729 | | the configure script. The default list is defined |
730 | | as ``LLVM_ALL_TARGETS``, and can be set to include |
731 | | out-of-tree targets. The default value includes: |
732 | | ``AArch64, AMDGPU, ARM, BPF, CppBackend, Hexagon, |
733 | | Mips, MSP430, NVPTX, PowerPC, Sparc, SystemZ |
735 +-------------------------+----------------------------------------------------+
736 | LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
737 | | code This is disabled by default because it is |
738 | | slow and generates a lot of output. |
739 +-------------------------+----------------------------------------------------+
740 | LLVM_ENABLE_SPHINX | Build sphinx-based documentation from the source |
741 | | code. This is disabled by default because it is |
742 | | slow and generates a lot of output. |
743 +-------------------------+----------------------------------------------------+
744 | LLVM_BUILD_LLVM_DYLIB | Generate libLLVM.so. This library contains a |
745 | | default set of LLVM components that can be |
746 | | overridden with ``LLVM_DYLIB_COMPONENTS``. The |
747 | | default contains most of LLVM and is defined in |
748 | | ``tools/llvm-shlib/CMakelists.txt``. |
749 +-------------------------+----------------------------------------------------+
750 | LLVM_OPTIMIZED_TABLEGEN | Builds a release tablegen that gets used during |
751 | | the LLVM build. This can dramatically speed up |
753 +-------------------------+----------------------------------------------------+
755 To configure LLVM, follow these steps:
757 #. Change directory into the object root directory:
759 .. code-block:: console
763 #. Run the ``cmake``:
765 .. code-block:: console
767 % cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=prefix=/install/path
768 [other options] SRC_ROOT
770 Compiling the LLVM Suite Source Code
771 ------------------------------------
773 Unlike with autotools, with CMake your build type is defined at configuration.
774 If you want to change your build type, you can re-run cmake with the following
777 .. code-block:: console
779 % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=type SRC_ROOT
781 Between runs, CMake preserves the values set for all options. CMake has the
782 following build types defined:
786 These builds are the default. The build system will compile the tools and
787 libraries unoptimized, with debugging information, and asserts enabled.
791 For these builds, the build system will compile the tools and libraries
792 with optimizations enabled and not generate debug info. CMakes default
793 optimization level is -O3. This can be configured by setting the
794 ``CMAKE_CXX_FLAGS_RELEASE`` variable on the CMake command line.
798 These builds are useful when debugging. They generate optimized binaries with
799 debug information. CMakes default optimization level is -O2. This can be
800 configured by setting the ``CMAKE_CXX_FLAGS_RELWITHDEBINFO`` variable on the
803 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
804 directory and issuing the following command:
806 .. code-block:: console
810 If the build fails, please `check here`_ to see if you are using a version of
811 GCC that is known not to compile LLVM.
813 If you have multiple processors in your machine, you may wish to use some of the
814 parallel build options provided by GNU Make. For example, you could use the
817 .. code-block:: console
821 There are several special targets which are useful when working with the LLVM
826 Removes all files generated by the build. This includes object files,
827 generated C/C++ files, libraries, and executables.
831 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
832 under ``$PREFIX``, specified with ``CMAKE_INSTALL_PREFIX``, which
833 defaults to ``/usr/local``.
835 ``make docs-llvm-html``
837 If configured with ``-DLLVM_ENABLE_SPHINX=On``, this will generate a directory
838 at ``OBJ_ROOT/docs/html`` which contains the HTML formatted documentation.
843 It is possible to cross-compile LLVM itself. That is, you can create LLVM
844 executables and libraries to be hosted on a platform different from the platform
845 where they are built (a Canadian Cross build). To generate build files for
846 cross-compiling CMake provides a variable ``CMAKE_TOOLCHAIN_FILE`` which can
847 define compiler flags and variables used during the CMake test operations.
849 The result of such a build is executables that are not runnable on on the build
850 host but can be executed on the target. As an example the following CMake
851 invocation can generate build files targeting iOS. This will work on Mac OS X
852 with the latest Xcode:
854 .. code-block:: console
856 % cmake -G "Ninja" -DCMAKE_OSX_ARCHITECTURES=“armv7;armv7s;arm64"
857 -DCMAKE_TOOLCHAIN_FILE=<PATH_TO_LLVM>/cmake/platforms/iOS.cmake
858 -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_RUNTIME=Off -DLLVM_INCLUDE_TESTS=Off
859 -DLLVM_INCLUDE_EXAMPLES=Off -DLLVM_ENABLE_BACKTRACES=Off [options]
862 Note: There are some additional flags that need to be passed when building for
863 iOS due to limitations in the iOS SDK.
865 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
866 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
867 about cross-compiling.
869 The Location of LLVM Object Files
870 ---------------------------------
872 The LLVM build system is capable of sharing a single LLVM source tree among
873 several LLVM builds. Hence, it is possible to build LLVM for several different
874 platforms or configurations using the same source tree.
876 This is accomplished in the typical autoconf manner:
878 * Change directory to where the LLVM object files should live:
880 .. code-block:: console
886 .. code-block:: console
888 % cmake -G "Unix Makefiles" SRC_ROOT
890 The LLVM build will create a structure underneath *OBJ_ROOT* that matches the
891 LLVM source tree. At each level where source files are present in the source
892 tree there will be a corresponding ``CMakeFiles`` directory in the *OBJ_ROOT*.
893 Underneath that directory there is another directory with a name ending in
894 ``.dir`` under which you'll find object files for each source.
898 .. code-block:: console
901 % find lib/Support/ -name APFloat*
902 lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
904 Optional Configuration Items
905 ----------------------------
907 If you're running on a Linux system that supports the `binfmt_misc
908 <http://en.wikipedia.org/wiki/binfmt_misc>`_
909 module, and you have root access on the system, you can set your system up to
910 execute LLVM bitcode files directly. To do this, use commands like this (the
911 first command may not be required if you are already using the module):
913 .. code-block:: console
915 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
916 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
917 % chmod u+x hello.bc (if needed)
920 This allows you to execute LLVM bitcode files directly. On Debian, you can also
921 use this command instead of the 'echo' command above:
923 .. code-block:: console
925 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
933 One useful source of information about the LLVM source base is the LLVM `doxygen
934 <http://www.doxygen.org/>`_ documentation available at
935 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
941 This directory contains some simple examples of how to use the LLVM IR and JIT.
946 This directory contains public header files exported from the LLVM library. The
947 three main subdirectories of this directory are:
949 ``llvm/include/llvm``
951 This directory contains all of the LLVM specific header files. This directory
952 also has subdirectories for different portions of LLVM: ``Analysis``,
953 ``CodeGen``, ``Target``, ``Transforms``, etc...
955 ``llvm/include/llvm/Support``
957 This directory contains generic support libraries that are provided with LLVM
958 but not necessarily specific to LLVM. For example, some C++ STL utilities and
959 a Command Line option processing library store their header files here.
961 ``llvm/include/llvm/Config``
963 This directory contains header files configured by the ``configure`` script.
964 They wrap "standard" UNIX and C header files. Source code can include these
965 header files which automatically take care of the conditional #includes that
966 the ``configure`` script generates.
971 This directory contains most of the source files of the LLVM system. In LLVM,
972 almost all code exists in libraries, making it very easy to share code among the
977 This directory holds the core LLVM source files that implement core classes
978 like Instruction and BasicBlock.
980 ``llvm/lib/AsmParser/``
982 This directory holds the source code for the LLVM assembly language parser
985 ``llvm/lib/Bitcode/``
987 This directory holds code for reading and write LLVM bitcode.
989 ``llvm/lib/Analysis/``
991 This directory contains a variety of different program analyses, such as
992 Dominator Information, Call Graphs, Induction Variables, Interval
993 Identification, Natural Loop Identification, etc.
995 ``llvm/lib/Transforms/``
997 This directory contains the source code for the LLVM to LLVM program
998 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
999 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1000 Elimination, and many others.
1002 ``llvm/lib/Target/``
1004 This directory contains files that describe various target architectures for
1005 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1006 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1009 ``llvm/lib/CodeGen/``
1011 This directory contains the major parts of the code generator: Instruction
1012 Selector, Instruction Scheduling, and Register Allocation.
1018 ``llvm/lib/Debugger/``
1020 This directory contains the source level debugger library that makes it
1021 possible to instrument LLVM programs so that a debugger could identify source
1022 code locations at which the program is executing.
1024 ``llvm/lib/ExecutionEngine/``
1026 This directory contains libraries for executing LLVM bitcode directly at
1027 runtime in both interpreted and JIT compiled fashions.
1029 ``llvm/lib/Support/``
1031 This directory contains the source code that corresponds to the header files
1032 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1037 This directory contains projects that are not strictly part of LLVM but are
1038 shipped with LLVM. This is also the directory where you should create your own
1039 LLVM-based projects.
1044 This directory contains libraries which are compiled into LLVM bitcode and used
1045 when linking programs with the Clang front end. Most of these libraries are
1046 skeleton versions of real libraries; for example, libc is a stripped down
1049 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1055 This directory contains feature and regression tests and other basic sanity
1056 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1057 lot of territory without being exhaustive.
1062 This is not a directory in the normal llvm module; it is a separate Subversion
1063 module that must be checked out (usually to ``projects/test-suite``). This
1064 module contains a comprehensive correctness, performance, and benchmarking test
1065 suite for LLVM. It is a separate Subversion module because not every LLVM user
1066 is interested in downloading or building such a comprehensive test suite. For
1067 further details on this test suite, please see the :doc:`Testing Guide
1068 <TestingGuide>` document.
1075 The **tools** directory contains the executables built out of the libraries
1076 above, which form the main part of the user interface. You can always get help
1077 for a tool by typing ``tool_name -help``. The following is a brief introduction
1078 to the most important tools. More detailed information is in
1079 the `Command Guide <CommandGuide/index.html>`_.
1083 ``bugpoint`` is used to debug optimization passes or code generation backends
1084 by narrowing down the given test case to the minimum number of passes and/or
1085 instructions that still cause a problem, whether it is a crash or
1086 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1091 The archiver produces an archive containing the given LLVM bitcode files,
1092 optionally with an index for faster lookup.
1096 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1100 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1104 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1109 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1110 (although very slowly...). For architectures that support it (currently x86,
1111 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1112 compiler (if the functionality was compiled in), and will execute the code
1113 *much* faster than the interpreter.
1117 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1118 native code assembly file or to C code (with the ``-march=c`` option).
1122 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1123 (which are specified on the command line), and then outputs the resultant
1124 bitcode. The '``opt -help``' command is a good way to get a list of the
1125 program transformations available in LLVM.
1127 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1128 file and print out the results. It is primarily useful for debugging
1129 analyses, or familiarizing yourself with what an analysis does.
1134 This directory contains utilities for working with LLVM source code, and some of
1135 the utilities are actually required as part of the build process because they
1136 are code generators for parts of LLVM infrastructure.
1141 ``codegen-diff`` is a script that finds differences between code that LLC
1142 generates and code that LLI generates. This is a useful tool if you are
1143 debugging one of them, assuming that the other generates correct output. For
1144 the full user manual, run ```perldoc codegen-diff'``.
1148 The ``emacs`` directory contains syntax-highlighting files which will work
1149 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1150 assembly files and TableGen description files. For information on how to use
1151 the syntax files, consult the ``README`` file in that directory.
1155 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1156 which is useful if one wishes to do a lot of development across directories
1157 and does not want to individually find each file. One way to use it is to run,
1158 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1163 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1164 passes to it a regular expression provided on ``llvmgrep``'s command
1165 line. This is a very efficient way of searching the source base for a
1166 particular regular expression.
1170 The ``makellvm`` script compiles all files in the current directory and then
1171 compiles and links the tool that is the first argument. For example, assuming
1172 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1173 path, simply running ``makellvm llc`` will make a build of the current
1174 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1179 The ``TableGen`` directory contains the tool used to generate register
1180 descriptions, instruction set descriptions, and even assemblers from common
1181 TableGen description files.
1185 The ``vim`` directory contains syntax-highlighting files which will work with
1186 the VIM editor, providing syntax highlighting support for LLVM assembly files
1187 and TableGen description files. For information on how to use the syntax
1188 files, consult the ``README`` file in that directory.
1192 An Example Using the LLVM Tool Chain
1193 ====================================
1195 This section gives an example of using LLVM with the Clang front end.
1200 #. First, create a simple C file, name it 'hello.c':
1207 printf("hello world\n");
1211 #. Next, compile the C file into a native executable:
1213 .. code-block:: console
1215 % clang hello.c -o hello
1219 Clang works just like GCC by default. The standard -S and -c arguments
1220 work as usual (producing a native .s or .o file, respectively).
1222 #. Next, compile the C file into an LLVM bitcode file:
1224 .. code-block:: console
1226 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1228 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1229 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1230 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1232 #. Run the program in both forms. To run the program, use:
1234 .. code-block:: console
1240 .. code-block:: console
1244 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1245 <CommandGuide/lli>`.
1247 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1249 .. code-block:: console
1251 % llvm-dis < hello.bc | less
1253 #. Compile the program to native assembly using the LLC code generator:
1255 .. code-block:: console
1257 % llc hello.bc -o hello.s
1259 #. Assemble the native assembly language file into a program:
1261 .. code-block:: console
1263 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1265 % gcc hello.s -o hello.native # On others
1267 #. Execute the native code program:
1269 .. code-block:: console
1273 Note that using clang to compile directly to native code (i.e. when the
1274 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1279 If you are having problems building or using LLVM, or if you have any other
1280 general questions about LLVM, please consult the `Frequently Asked
1281 Questions <FAQ.html>`_ page.
1288 This document is just an **introduction** on how to use LLVM to do some simple
1289 things... there are many more interesting and complicated things that you can do
1290 that aren't documented here (but we'll gladly accept a patch if you want to
1291 write something up!). For more information about LLVM, check out:
1293 * `LLVM Homepage <http://llvm.org/>`_
1294 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1295 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_