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32 The LLVM Getting Started documentation may be out of date.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:
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 #. Get the Test Suite Source Code **[Optional]**
60 * ``cd where-you-want-llvm-to-live``
61 * ``cd llvm/projects``
62 * ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
64 #. Configure and build LLVM and Clang:
66 The usual build uses `CMake <CMake.html>`_. If you would rather use
67 autotools, see `Building LLVM with autotools <BuildingLLVMWithAutotools.html>`_.
69 * ``cd where you want to build llvm``
72 * ``cmake -G <generator> [options] <path to llvm sources>``
74 Some common generators are:
76 * ``Unix Makefiles`` --- for generating make-compatible parallel makefiles.
77 * ``Ninja`` --- for generating `Ninja <http://martine.github.io/ninja/>`
79 * ``Visual Studio`` --- for generating Visual Studio projects and
81 * ``Xcode`` --- for generating Xcode projects.
85 * ``-DCMAKE_INSTALL_PREFIX=directory`` --- Specify for *directory* the full
86 pathname of where you want the LLVM tools and libraries to be installed
87 (default ``/usr/local``).
89 * ``-DCMAKE_BUILD_TYPE=type`` --- Valid options for *type* are Debug,
90 Release, RelWithDebInfo, and MinSizeRel. Default is Debug.
92 * ``-DLLVM_ENABLE_ASSERTIONS=On`` --- Compile with assertion checks enabled
93 (default is Yes for Debug builds, No for all other build types).
95 * Run your build tool of choice!
97 * The default target (i.e. ``make``) will build all of LLVM
99 * The ``check-all`` target (i.e. ``make check-all``) will run the
100 regression tests to ensure everything is in working order.
102 * CMake will generate build targets for each tool and library, and most
103 LLVM sub-projects generate their own ``check-<project>`` target.
105 * For more information see `CMake <CMake.html>`_
107 * If you get an "internal compiler error (ICE)" or test failures, see
110 Consult the `Getting Started with LLVM`_ section for detailed information on
111 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
112 that simplify working with the Clang front end and LLVM tools. Go to `Program
113 Layout`_ to learn about the layout of the source code tree.
118 Before you begin to use the LLVM system, review the requirements given below.
119 This may save you some trouble by knowing ahead of time what hardware and
120 software you will need.
125 LLVM is known to work on the following host platforms:
127 ================== ===================== =============
129 ================== ===================== =============
130 Linux x86\ :sup:`1` GCC, Clang
131 Linux amd64 GCC, Clang
132 Linux ARM\ :sup:`4` GCC, Clang
133 Linux PowerPC GCC, Clang
134 Solaris V9 (Ultrasparc) GCC
135 FreeBSD x86\ :sup:`1` GCC, Clang
136 FreeBSD amd64 GCC, Clang
137 MacOS X\ :sup:`2` PowerPC GCC
138 MacOS X x86 GCC, Clang
139 Cygwin/Win32 x86\ :sup:`1, 3` GCC
140 Windows x86\ :sup:`1` Visual Studio
141 Windows x64 x86-64 Visual Studio
142 ================== ===================== =============
146 #. Code generation supported for Pentium processors and up
147 #. Code generation supported for 32-bit ABI only
148 #. To use LLVM modules on Win32-based system, you may configure LLVM
149 with ``-DBUILD_SHARED_LIBS=On`` for CMake builds or ``--enable-shared``
150 for configure builds.
151 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
153 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
154 mode, depending on the system (it is so large because of all the debugging
155 information and the fact that the libraries are statically linked into multiple
156 tools). If you do not need many of the tools and you are space-conscious, you
157 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
158 considerably less space.
160 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
161 so. If compilation is successful, the LLVM utilities should be able to
162 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
163 should work as well, although the generated native code may not work on your
169 Compiling LLVM requires that you have several software packages installed. The
170 table below lists those required packages. The Package column is the usual name
171 for the software package that LLVM depends on. The Version column provides
172 "known to work" versions of the package. The Notes column describes how LLVM
173 uses the package and provides other details.
175 =========================================================== ============ ==========================================
176 Package Version Notes
177 =========================================================== ============ ==========================================
178 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
179 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
180 `python <http://www.python.org/>`_ >=2.7 Automated test suite\ :sup:`2`
181 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
182 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
183 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
184 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
185 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
186 =========================================================== ============ ==========================================
190 #. Only the C and C++ languages are needed so there's no need to build the
191 other languages for LLVM's purposes. See `below` for specific version
193 #. Only needed if you want to run the automated test suite in the
194 ``llvm/test`` directory.
195 #. If you want to make changes to the configure scripts, you will need GNU
196 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
197 will also need automake (1.9.6). We only use aclocal from that package.
198 #. Optional, adds compression / uncompression capabilities to selected LLVM
201 Additionally, your compilation host is expected to have the usual plethora of
202 Unix utilities. Specifically:
204 * **ar** --- archive library builder
205 * **bzip2** --- bzip2 command for distribution generation
206 * **bunzip2** --- bunzip2 command for distribution checking
207 * **chmod** --- change permissions on a file
208 * **cat** --- output concatenation utility
209 * **cp** --- copy files
210 * **date** --- print the current date/time
211 * **echo** --- print to standard output
212 * **egrep** --- extended regular expression search utility
213 * **find** --- find files/dirs in a file system
214 * **grep** --- regular expression search utility
215 * **gzip** --- gzip command for distribution generation
216 * **gunzip** --- gunzip command for distribution checking
217 * **install** --- install directories/files
218 * **mkdir** --- create a directory
219 * **mv** --- move (rename) files
220 * **ranlib** --- symbol table builder for archive libraries
221 * **rm** --- remove (delete) files and directories
222 * **sed** --- stream editor for transforming output
223 * **sh** --- Bourne shell for make build scripts
224 * **tar** --- tape archive for distribution generation
225 * **test** --- test things in file system
226 * **unzip** --- unzip command for distribution checking
227 * **zip** --- zip command for distribution generation
232 Host C++ Toolchain, both Compiler and Standard Library
233 ------------------------------------------------------
235 LLVM is very demanding of the host C++ compiler, and as such tends to expose
236 bugs in the compiler. We are also planning to follow improvements and
237 developments in the C++ language and library reasonably closely. As such, we
238 require a modern host C++ toolchain, both compiler and standard library, in
241 For the most popular host toolchains we check for specific minimum versions in
248 Anything older than these toolchains *may* work, but will require forcing the
249 build system with a special option and is not really a supported host platform.
250 Also note that older versions of these compilers have often crashed or
253 For less widely used host toolchains such as ICC or xlC, be aware that a very
254 recent version may be required to support all of the C++ features used in LLVM.
256 We track certain versions of software that are *known* to fail when used as
257 part of the host toolchain. These even include linkers at times.
259 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
260 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
262 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
263 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
264 defined in a discarded section. You can safely ignore these messages as they are
265 erroneous and the linkage is correct. These messages disappear using ld 2.17.
267 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
268 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
269 times (minutes instead of seconds) when building LLVM. We recommend upgrading
270 to a newer version (2.17.50.0.4 or later).
272 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
273 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
274 intermittent failures when building LLVM with position independent code. The
275 symptom is an error about cyclic dependencies. We recommend upgrading to a
276 newer version of Gold.
278 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
279 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
280 3.0 does not implement a few builtins that are used in this library. We
281 recommend using the system GCC to compile LLVM and Clang in this case.
283 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
284 least some (``cxxabi.h``) libstdc++ headers.
286 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
287 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
288 causes Clang to refuse to compile condition_variable header file. At the time
289 of writing, this breaks LLD build.
291 Getting a Modern Host C++ Toolchain
292 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
294 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
295 have a sufficiently modern Xcode, or you will likely need to upgrade until you
296 do. On Windows, just use Visual Studio 2013 as the host compiler, it is
297 explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
298 Clang as the system compiler.
300 However, some Linux distributions and some other or older BSDs sometimes have
301 extremely old versions of GCC. These steps attempt to help you upgrade you
302 compiler even on such a system. However, if at all possible, we encourage you
303 to use a recent version of a distribution with a modern system compiler that
304 meets these requirements. Note that it is tempting to to install a prior
305 version of Clang and libc++ to be the host compiler, however libc++ was not
306 well tested or set up to build on Linux until relatively recently. As
307 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
308 initial host in a bootstrap, and then using Clang (and potentially libc++).
310 The first step is to get a recent GCC toolchain installed. The most common
311 distribution on which users have struggled with the version requirements is
312 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
313 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
314 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
315 not all users can use PPAs and there are many other distributions, so it may be
316 necessary (or just useful, if you're here you *are* doing compiler development
317 after all) to build and install GCC from source. It is also quite easy to do
320 .. _toolchain testing PPA:
321 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
322 .. _ask ubuntu stack exchange:
323 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
325 Easy steps for installing GCC 4.8.2:
327 .. code-block:: console
329 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
330 % wget https://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2.sig
331 % wget https://ftp.gnu.org/gnu/gnu-keyring.gpg
332 % signature_invalid=`gpg --verify --no-default-keyring --keyring ./gnu-keyring.gpg gcc-4.8.2.tar.bz2.sig`
333 % if [ $signature_invalid ]; then echo "Invalid signature" ; exit 1 ; fi
334 % tar -xvjf gcc-4.8.2.tar.bz2
336 % ./contrib/download_prerequisites
338 % mkdir gcc-4.8.2-build
340 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
344 For more details, check out the excellent `GCC wiki entry`_, where I got most
345 of this information from.
348 http://gcc.gnu.org/wiki/InstallingGCC
350 Once you have a GCC toolchain, configure your build of LLVM to use the new
351 toolchain for your host compiler and C++ standard library. Because the new
352 version of libstdc++ is not on the system library search path, you need to pass
353 extra linker flags so that it can be found at link time (``-L``) and at runtime
354 (``-rpath``). If you are using CMake, this invocation should produce working
357 .. code-block:: console
361 % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
362 cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
364 If you fail to set rpath, most LLVM binaries will fail on startup with a message
365 from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
366 found``. This means you need to tweak the -rpath linker flag.
368 When you build Clang, you will need to give *it* access to modern C++11
369 standard library in order to use it as your new host in part of a bootstrap.
370 There are two easy ways to do this, either build (and install) libc++ along
371 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
372 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
373 Clang will look within its own prefix for libstdc++ and use it if found. You
374 can also add an explicit prefix for Clang to look in for a GCC toolchain with
375 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
376 link commands when using your just-built-Clang to bootstrap.
378 .. _Getting Started with LLVM:
380 Getting Started with LLVM
381 =========================
383 The remainder of this guide is meant to get you up and running with LLVM and to
384 give you some basic information about the LLVM environment.
386 The later sections of this guide describe the `general layout`_ of the LLVM
387 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
388 more information about LLVM or to get help via e-mail.
390 Terminology and Notation
391 ------------------------
393 Throughout this manual, the following names are used to denote paths specific to
394 the local system and working environment. *These are not environment variables
395 you need to set but just strings used in the rest of this document below*. In
396 any of the examples below, simply replace each of these names with the
397 appropriate pathname on your local system. All these paths are absolute:
401 This is the top level directory of the LLVM source tree.
405 This is the top level directory of the LLVM object tree (i.e. the tree where
406 object files and compiled programs will be placed. It can be the same as
409 .. _Setting Up Your Environment:
411 Setting Up Your Environment
412 ---------------------------
414 In order to compile and use LLVM, you may need to set some environment
417 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
419 [Optional] This environment variable helps LLVM linking tools find the
420 locations of your bitcode libraries. It is provided only as a convenience
421 since you can specify the paths using the -L options of the tools and the
422 C/C++ front-end will automatically use the bitcode files installed in its
425 Unpacking the LLVM Archives
426 ---------------------------
428 If you have the LLVM distribution, you will need to unpack it before you can
429 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
430 and the LLVM GCC front end compiled for your platform. There is an additional
431 test suite that is optional. Each file is a TAR archive that is compressed with
434 The files are as follows, with *x.y* marking the version number:
438 Source release for the LLVM libraries and tools.
440 ``llvm-test-x.y.tar.gz``
442 Source release for the LLVM test-suite.
446 Checkout LLVM from Subversion
447 -----------------------------
449 If you have access to our Subversion repository, you can get a fresh copy of the
450 entire source code. All you need to do is check it out from Subversion as
453 * ``cd where-you-want-llvm-to-live``
454 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
455 * Read-Write: ``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
457 This will create an '``llvm``' directory in the current directory and fully
458 populate it with the LLVM source code, Makefiles, test directories, and local
459 copies of documentation files.
461 If you want to get a specific release (as opposed to the most recent revision),
462 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
463 following releases are located in the following subdirectories of the '``tags``'
466 * Release 3.4: **RELEASE_34/final**
467 * Release 3.3: **RELEASE_33/final**
468 * Release 3.2: **RELEASE_32/final**
469 * Release 3.1: **RELEASE_31/final**
470 * Release 3.0: **RELEASE_30/final**
471 * Release 2.9: **RELEASE_29/final**
472 * Release 2.8: **RELEASE_28**
473 * Release 2.7: **RELEASE_27**
474 * Release 2.6: **RELEASE_26**
475 * Release 2.5: **RELEASE_25**
476 * Release 2.4: **RELEASE_24**
477 * Release 2.3: **RELEASE_23**
478 * Release 2.2: **RELEASE_22**
479 * Release 2.1: **RELEASE_21**
480 * Release 2.0: **RELEASE_20**
481 * Release 1.9: **RELEASE_19**
482 * Release 1.8: **RELEASE_18**
483 * Release 1.7: **RELEASE_17**
484 * Release 1.6: **RELEASE_16**
485 * Release 1.5: **RELEASE_15**
486 * Release 1.4: **RELEASE_14**
487 * Release 1.3: **RELEASE_13**
488 * Release 1.2: **RELEASE_12**
489 * Release 1.1: **RELEASE_11**
490 * Release 1.0: **RELEASE_1**
492 If you would like to get the LLVM test suite (a separate package as of 1.4), you
493 get it from the Subversion repository:
495 .. code-block:: console
498 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
500 By placing it in the ``llvm/projects``, it will be automatically configured by
501 the LLVM configure script as well as automatically updated when you run ``svn
507 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
508 automatically with each Subversion commit and contain all necessary git-svn
509 marks (so, you can recreate git-svn metadata locally). Note that right now
510 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
513 .. code-block:: console
515 % git clone http://llvm.org/git/llvm.git
517 If you want to check out clang too, run:
519 .. code-block:: console
522 % git clone http://llvm.org/git/clang.git
524 If you want to check out compiler-rt too, run:
526 .. code-block:: console
529 % git clone http://llvm.org/git/compiler-rt.git
531 If you want to check out the Test Suite Source Code (optional), run:
533 .. code-block:: console
536 % git clone http://llvm.org/git/test-suite.git
538 Since the upstream repository is in Subversion, you should use ``git
539 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
540 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
541 master branch, run the following command:
543 .. code-block:: console
545 % git config branch.master.rebase true
547 Sending patches with Git
548 ^^^^^^^^^^^^^^^^^^^^^^^^
550 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
552 Assume ``master`` points the upstream and ``mybranch`` points your working
553 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
554 sanity of whitespaces:
556 .. code-block:: console
558 % git diff --check master..mybranch
560 The easiest way to generate a patch is as below:
562 .. code-block:: console
564 % git diff master..mybranch > /path/to/mybranch.diff
566 It is a little different from svn-generated diff. git-diff-generated diff has
567 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
568 could be accepted with ``patch -p1 -N``.
570 But you may generate patchset with git-format-patch. It generates by-each-commit
571 patchset. To generate patch files to attach to your article:
573 .. code-block:: console
575 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
577 If you would like to send patches directly, you may use git-send-email or
578 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
580 .. code-block:: console
582 % git format-patch --attach master..mybranch --stdout | git imap-send
584 Then, your .git/config should have [imap] sections.
589 host = imaps://imap.gmail.com
590 user = your.gmail.account@gmail.com
595 folder = "[Gmail]/Drafts"
596 ; example for Japanese, "Modified UTF-7" encoded.
597 folder = "[Gmail]/&Tgtm+DBN-"
598 ; example for Traditional Chinese
599 folder = "[Gmail]/&g0l6Pw-"
601 For developers to work with git-svn
602 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
604 To set up clone from which you can submit code using ``git-svn``, run:
606 .. code-block:: console
608 % git clone http://llvm.org/git/llvm.git
610 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
611 % git config svn-remote.svn.fetch :refs/remotes/origin/master
612 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
614 # If you have clang too:
616 % git clone http://llvm.org/git/clang.git
618 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
619 % git config svn-remote.svn.fetch :refs/remotes/origin/master
622 Likewise for compiler-rt and test-suite.
624 To update this clone without generating git-svn tags that conflict with the
625 upstream Git repo, run:
627 .. code-block:: console
629 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
630 % git checkout master
633 git checkout master &&
636 Likewise for compiler-rt and test-suite.
638 This leaves your working directories on their master branches, so you'll need to
639 ``checkout`` each working branch individually and ``rebase`` it on top of its
642 For those who wish to be able to update an llvm repo/revert patches easily using
643 git-svn, please look in the directory for the scripts ``git-svnup`` and
646 To perform the aforementioned update steps go into your source directory and
647 just type ``git-svnup`` or ``git svnup`` and everything will just work.
649 If one wishes to revert a commit with git-svn, but do not want the git hash to
650 escape into the commit message, one can use the script ``git-svnrevert`` or
651 ``git svnrevert`` which will take in the git hash for the commit you want to
652 revert, look up the appropriate svn revision, and output a message where all
653 references to the git hash have been replaced with the svn revision.
655 To commit back changes via git-svn, use ``git svn dcommit``:
657 .. code-block:: console
661 Note that git-svn will create one SVN commit for each Git commit you have pending,
662 so squash and edit each commit before executing ``dcommit`` to make sure they all
663 conform to the coding standards and the developers' policy.
665 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
666 please make sure your current branch is up-to-date (via fetch/rebase) before
669 The git-svn metadata can get out of sync after you mess around with branches and
670 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
671 about files with uncommitted changes. The fix is to rebuild the metadata:
673 .. code-block:: console
678 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
680 Local LLVM Configuration
681 ------------------------
683 Once checked out from the Subversion repository, the LLVM suite source code must
684 be configured before being built. For instructions using autotools please see
685 `Building LLVM With Autotools <BuildingLLVMWithAutotools.html>`_. The
686 recommended process uses CMake. Unlinke the normal ``configure`` script, CMake
687 generates the build files in whatever format you request as well as various
688 ``*.inc`` files, and ``llvm/include/Config/config.h``.
690 Variables are passed to ``cmake`` on the command line using the format
691 ``-D<variable name>=<value>``. The following variables are some common options
692 used by people developing LLVM.
694 +-------------------------+----------------------------------------------------+
695 | Variable | Purpose |
696 +=========================+====================================================+
697 | CMAKE_C_COMPILER | Tells ``cmake`` which C compiler to use. By |
698 | | default, this will be /usr/bin/cc. |
699 +-------------------------+----------------------------------------------------+
700 | CMAKE_CXX_COMPILER | Tells ``cmake`` which C++ compiler to use. By |
701 | | default, this will be /usr/bin/c++. |
702 +-------------------------+----------------------------------------------------+
703 | CMAKE_BUILD_TYPE | Tells ``cmake`` what type of build you are trying |
704 | | to generate files for. Valid options are Debug, |
705 | | Release, RelWithDebInfo, and MinSizeRel. Default |
707 +-------------------------+----------------------------------------------------+
708 | CMAKE_INSTALL_PREFIX | Specifies the install directory to target when |
709 | | running the install action of the build files. |
710 +-------------------------+----------------------------------------------------+
711 | LLVM_TARGETS_TO_BUILD | A semicolon delimited list controlling which |
712 | | targets will be built and linked into llc. This is |
713 | | equivalent to the ``--enable-targets`` option in |
714 | | the configure script. The default list is defined |
715 | | as ``LLVM_ALL_TARGETS``, and can be set to include |
716 | | out-of-tree targets. The default value includes: |
717 | | ``AArch64, ARM, CppBackend, Hexagon, |
718 | | Mips, MSP430, NVPTX, PowerPC, AMDGPU, Sparc, |
719 | | SystemZ, X86, XCore``. |
720 +-------------------------+----------------------------------------------------+
721 | LLVM_ENABLE_DOXYGEN | Build doxygen-based documentation from the source |
722 | | code This is disabled by default because it is |
723 | | slow and generates a lot of output. |
724 +-------------------------+----------------------------------------------------+
725 | LLVM_ENABLE_SPHINX | Build sphinx-based documentation from the source |
726 | | code. This is disabled by default because it is |
727 | | slow and generates a lot of output. |
728 +-------------------------+----------------------------------------------------+
729 | LLVM_BUILD_LLVM_DYLIB | Generate libLLVM.so. This library contains a |
730 | | default set of LLVM components that can be |
731 | | overridden with ``LLVM_DYLIB_COMPONENTS``. The |
732 | | default contains most of LLVM and is defined in |
733 | | ``tools/llvm-shlib/CMakelists.txt``. |
734 +-------------------------+----------------------------------------------------+
735 | LLVM_OPTIMIZED_TABLEGEN | Builds a release tablegen that gets used during |
736 | | the LLVM build. This can dramatically speed up |
738 +-------------------------+----------------------------------------------------+
740 To configure LLVM, follow these steps:
742 #. Change directory into the object root directory:
744 .. code-block:: console
748 #. Run the ``cmake``:
750 .. code-block:: console
752 % cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=prefix=/install/path
753 [other options] SRC_ROOT
755 Compiling the LLVM Suite Source Code
756 ------------------------------------
758 Unlike with autotools, with CMake your build type is defined at configuration.
759 If you want to change your build type, you can re-run cmake with the following
762 .. code-block:: console
764 % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=type SRC_ROOT
766 Between runs, CMake preserves the values set for all options. CMake has the
767 following build types defined:
771 These builds are the default. The build system will compile the tools and
772 libraries unoptimized, with debugging information, and asserts enabled.
776 For these builds, the build system will compile the tools and libraries
777 with optimizations enabled and not generate debug info. CMakes default
778 optimization level is -O3. This can be configured by setting the
779 ``CMAKE_CXX_FLAGS_RELEASE`` variable on the CMake command line.
783 These builds are useful when debugging. They generate optimized binaries with
784 debug information. CMakes default optimization level is -O2. This can be
785 configured by setting the ``CMAKE_CXX_FLAGS_RELWITHDEBINFO`` variable on the
788 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
789 directory and issuing the following command:
791 .. code-block:: console
795 If the build fails, please `check here`_ to see if you are using a version of
796 GCC that is known not to compile LLVM.
798 If you have multiple processors in your machine, you may wish to use some of the
799 parallel build options provided by GNU Make. For example, you could use the
802 .. code-block:: console
806 There are several special targets which are useful when working with the LLVM
811 Removes all files generated by the build. This includes object files,
812 generated C/C++ files, libraries, and executables.
816 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
817 under ``$PREFIX``, specified with ``CMAKE_INSTALL_PREFIX``, which
818 defaults to ``/usr/local``.
820 ``make docs-llvm-html``
822 If configured with ``-DLLVM_ENABLE_SPHINX=On``, this will generate a directory
823 at ``OBJ_ROOT/docs/html`` which contains the HTML formatted documentation.
828 It is possible to cross-compile LLVM itself. That is, you can create LLVM
829 executables and libraries to be hosted on a platform different from the platform
830 where they are built (a Canadian Cross build). To generate build files for
831 cross-compiling CMake provides a variable ``CMAKE_TOOLCHAIN_FILE`` which can
832 define compiler flags and variables used during the CMake test operations.
834 The result of such a build is executables that are not runnable on on the build
835 host but can be executed on the target. As an example the following CMake
836 invocation can generate build files targeting iOS. This will work on Mac OS X
837 with the latest Xcode:
839 .. code-block:: console
841 % cmake -G "Ninja" -DCMAKE_OSX_ARCHITECTURES=“armv7;armv7s;arm64"
842 -DCMAKE_TOOLCHAIN_FILE=<PATH_TO_LLVM>/cmake/platforms/iOS.cmake
843 -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_RUNTIME=Off -DLLVM_INCLUDE_TESTS=Off
844 -DLLVM_INCLUDE_EXAMPLES=Off -DLLVM_ENABLE_BACKTRACES=Off [options]
847 Note: There are some additional flags that need to be passed when building for
848 iOS due to limitations in the iOS SDK.
850 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
851 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
852 about cross-compiling.
854 The Location of LLVM Object Files
855 ---------------------------------
857 The LLVM build system is capable of sharing a single LLVM source tree among
858 several LLVM builds. Hence, it is possible to build LLVM for several different
859 platforms or configurations using the same source tree.
861 This is accomplished in the typical autoconf manner:
863 * Change directory to where the LLVM object files should live:
865 .. code-block:: console
871 .. code-block:: console
873 % cmake -G "Unix Makefiles" SRC_ROOT
875 The LLVM build will create a structure underneath *OBJ_ROOT* that matches the
876 LLVM source tree. At each level where source files are present in the source
877 tree there will be a corresponding ``CMakeFiles`` directory in the *OBJ_ROOT*.
878 Underneath that directory there is another directory with a name ending in
879 ``.dir`` under which you'll find object files for each source.
883 .. code-block:: console
886 % find lib/Support/ -name APFloat*
887 lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
889 Optional Configuration Items
890 ----------------------------
892 If you're running on a Linux system that supports the `binfmt_misc
893 <http://en.wikipedia.org/wiki/binfmt_misc>`_
894 module, and you have root access on the system, you can set your system up to
895 execute LLVM bitcode files directly. To do this, use commands like this (the
896 first command may not be required if you are already using the module):
898 .. code-block:: console
900 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
901 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
902 % chmod u+x hello.bc (if needed)
905 This allows you to execute LLVM bitcode files directly. On Debian, you can also
906 use this command instead of the 'echo' command above:
908 .. code-block:: console
910 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
918 One useful source of information about the LLVM source base is the LLVM `doxygen
919 <http://www.doxygen.org/>`_ documentation available at
920 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
926 This directory contains some simple examples of how to use the LLVM IR and JIT.
931 This directory contains public header files exported from the LLVM library. The
932 three main subdirectories of this directory are:
934 ``llvm/include/llvm``
936 This directory contains all of the LLVM specific header files. This directory
937 also has subdirectories for different portions of LLVM: ``Analysis``,
938 ``CodeGen``, ``Target``, ``Transforms``, etc...
940 ``llvm/include/llvm/Support``
942 This directory contains generic support libraries that are provided with LLVM
943 but not necessarily specific to LLVM. For example, some C++ STL utilities and
944 a Command Line option processing library store their header files here.
946 ``llvm/include/llvm/Config``
948 This directory contains header files configured by the ``configure`` script.
949 They wrap "standard" UNIX and C header files. Source code can include these
950 header files which automatically take care of the conditional #includes that
951 the ``configure`` script generates.
956 This directory contains most of the source files of the LLVM system. In LLVM,
957 almost all code exists in libraries, making it very easy to share code among the
962 This directory holds the core LLVM source files that implement core classes
963 like Instruction and BasicBlock.
965 ``llvm/lib/AsmParser/``
967 This directory holds the source code for the LLVM assembly language parser
970 ``llvm/lib/Bitcode/``
972 This directory holds code for reading and write LLVM bitcode.
974 ``llvm/lib/Analysis/``
976 This directory contains a variety of different program analyses, such as
977 Dominator Information, Call Graphs, Induction Variables, Interval
978 Identification, Natural Loop Identification, etc.
980 ``llvm/lib/Transforms/``
982 This directory contains the source code for the LLVM to LLVM program
983 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
984 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
985 Elimination, and many others.
989 This directory contains files that describe various target architectures for
990 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
991 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
994 ``llvm/lib/CodeGen/``
996 This directory contains the major parts of the code generator: Instruction
997 Selector, Instruction Scheduling, and Register Allocation.
1003 ``llvm/lib/Debugger/``
1005 This directory contains the source level debugger library that makes it
1006 possible to instrument LLVM programs so that a debugger could identify source
1007 code locations at which the program is executing.
1009 ``llvm/lib/ExecutionEngine/``
1011 This directory contains libraries for executing LLVM bitcode directly at
1012 runtime in both interpreted and JIT compiled fashions.
1014 ``llvm/lib/Support/``
1016 This directory contains the source code that corresponds to the header files
1017 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1022 This directory contains projects that are not strictly part of LLVM but are
1023 shipped with LLVM. This is also the directory where you should create your own
1024 LLVM-based projects.
1029 This directory contains libraries which are compiled into LLVM bitcode and used
1030 when linking programs with the Clang front end. Most of these libraries are
1031 skeleton versions of real libraries; for example, libc is a stripped down
1034 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1040 This directory contains feature and regression tests and other basic sanity
1041 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1042 lot of territory without being exhaustive.
1047 This is not a directory in the normal llvm module; it is a separate Subversion
1048 module that must be checked out (usually to ``projects/test-suite``). This
1049 module contains a comprehensive correctness, performance, and benchmarking test
1050 suite for LLVM. It is a separate Subversion module because not every LLVM user
1051 is interested in downloading or building such a comprehensive test suite. For
1052 further details on this test suite, please see the :doc:`Testing Guide
1053 <TestingGuide>` document.
1060 The **tools** directory contains the executables built out of the libraries
1061 above, which form the main part of the user interface. You can always get help
1062 for a tool by typing ``tool_name -help``. The following is a brief introduction
1063 to the most important tools. More detailed information is in
1064 the `Command Guide <CommandGuide/index.html>`_.
1068 ``bugpoint`` is used to debug optimization passes or code generation backends
1069 by narrowing down the given test case to the minimum number of passes and/or
1070 instructions that still cause a problem, whether it is a crash or
1071 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1076 The archiver produces an archive containing the given LLVM bitcode files,
1077 optionally with an index for faster lookup.
1081 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1085 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1089 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1094 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1095 (although very slowly...). For architectures that support it (currently x86,
1096 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1097 compiler (if the functionality was compiled in), and will execute the code
1098 *much* faster than the interpreter.
1102 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1103 native code assembly file or to C code (with the ``-march=c`` option).
1107 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1108 (which are specified on the command line), and then outputs the resultant
1109 bitcode. The '``opt -help``' command is a good way to get a list of the
1110 program transformations available in LLVM.
1112 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1113 file and print out the results. It is primarily useful for debugging
1114 analyses, or familiarizing yourself with what an analysis does.
1119 This directory contains utilities for working with LLVM source code, and some of
1120 the utilities are actually required as part of the build process because they
1121 are code generators for parts of LLVM infrastructure.
1126 ``codegen-diff`` is a script that finds differences between code that LLC
1127 generates and code that LLI generates. This is a useful tool if you are
1128 debugging one of them, assuming that the other generates correct output. For
1129 the full user manual, run ```perldoc codegen-diff'``.
1133 The ``emacs`` directory contains syntax-highlighting files which will work
1134 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1135 assembly files and TableGen description files. For information on how to use
1136 the syntax files, consult the ``README`` file in that directory.
1140 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1141 which is useful if one wishes to do a lot of development across directories
1142 and does not want to individually find each file. One way to use it is to run,
1143 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1148 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1149 passes to it a regular expression provided on ``llvmgrep``'s command
1150 line. This is a very efficient way of searching the source base for a
1151 particular regular expression.
1155 The ``makellvm`` script compiles all files in the current directory and then
1156 compiles and links the tool that is the first argument. For example, assuming
1157 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1158 path, simply running ``makellvm llc`` will make a build of the current
1159 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1164 The ``TableGen`` directory contains the tool used to generate register
1165 descriptions, instruction set descriptions, and even assemblers from common
1166 TableGen description files.
1170 The ``vim`` directory contains syntax-highlighting files which will work with
1171 the VIM editor, providing syntax highlighting support for LLVM assembly files
1172 and TableGen description files. For information on how to use the syntax
1173 files, consult the ``README`` file in that directory.
1177 An Example Using the LLVM Tool Chain
1178 ====================================
1180 This section gives an example of using LLVM with the Clang front end.
1185 #. First, create a simple C file, name it 'hello.c':
1192 printf("hello world\n");
1196 #. Next, compile the C file into a native executable:
1198 .. code-block:: console
1200 % clang hello.c -o hello
1204 Clang works just like GCC by default. The standard -S and -c arguments
1205 work as usual (producing a native .s or .o file, respectively).
1207 #. Next, compile the C file into an LLVM bitcode file:
1209 .. code-block:: console
1211 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1213 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1214 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1215 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1217 #. Run the program in both forms. To run the program, use:
1219 .. code-block:: console
1225 .. code-block:: console
1229 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1230 <CommandGuide/lli>`.
1232 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1234 .. code-block:: console
1236 % llvm-dis < hello.bc | less
1238 #. Compile the program to native assembly using the LLC code generator:
1240 .. code-block:: console
1242 % llc hello.bc -o hello.s
1244 #. Assemble the native assembly language file into a program:
1246 .. code-block:: console
1248 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1250 % gcc hello.s -o hello.native # On others
1252 #. Execute the native code program:
1254 .. code-block:: console
1258 Note that using clang to compile directly to native code (i.e. when the
1259 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1264 If you are having problems building or using LLVM, or if you have any other
1265 general questions about LLVM, please consult the `Frequently Asked
1266 Questions <FAQ.html>`_ page.
1273 This document is just an **introduction** on how to use LLVM to do some simple
1274 things... there are many more interesting and complicated things that you can do
1275 that aren't documented here (but we'll gladly accept a patch if you want to
1276 write something up!). For more information about LLVM, check out:
1278 * `LLVM Homepage <http://llvm.org/>`_
1279 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1280 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_