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32 The LLVM Getting Started documentation may be out of date.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 * ``cd where-you-want-to-build-llvm``
67 * ``mkdir build`` (for building without polluting the source dir)
69 * ``../llvm/configure [options]``
72 * ``--prefix=directory`` --- Specify for *directory* the full pathname of
73 where you want the LLVM tools and libraries to be installed (default
76 * ``--enable-optimized`` --- Compile with optimizations enabled (default
79 * ``--enable-assertions`` --- Compile with assertion checks enabled
82 * ``make [-j]`` --- The ``-j`` specifies the number of jobs (commands) to run
83 simultaneously. This builds both LLVM and Clang for Debug+Asserts mode.
84 The ``--enable-optimized`` configure option is used to specify a Release
87 * ``make check-all`` --- This run the regression tests to ensure everything
90 * It is also possible to use `CMake <CMake.html>`_ instead of the makefiles.
91 With CMake it is possible to generate project files for several IDEs:
92 Xcode, Eclipse CDT4, CodeBlocks, Qt-Creator (use the CodeBlocks
93 generator), KDevelop3.
95 * If you get an "internal compiler error (ICE)" or test failures, see
98 Consult the `Getting Started with LLVM`_ section for detailed information on
99 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
100 that simplify working with the Clang front end and LLVM tools. Go to `Program
101 Layout`_ to learn about the layout of the source code tree.
106 Before you begin to use the LLVM system, review the requirements given below.
107 This may save you some trouble by knowing ahead of time what hardware and
108 software you will need.
113 LLVM is known to work on the following host platforms:
115 ================== ===================== =============
117 ================== ===================== =============
118 AuroraUX x86\ :sup:`1` GCC
119 Linux x86\ :sup:`1` GCC, Clang
120 Linux amd64 GCC, Clang
121 Linux ARM\ :sup:`4` GCC, Clang
122 Linux PowerPC GCC, Clang
123 Solaris V9 (Ultrasparc) GCC
124 FreeBSD x86\ :sup:`1` GCC, Clang
125 FreeBSD amd64 GCC, Clang
126 MacOS X\ :sup:`2` PowerPC GCC
127 MacOS X x86 GCC, Clang
128 Cygwin/Win32 x86\ :sup:`1, 3` GCC
129 Windows x86\ :sup:`1` Visual Studio
130 Windows x64 x86-64 Visual Studio
131 ================== ===================== =============
135 #. Code generation supported for Pentium processors and up
136 #. Code generation supported for 32-bit ABI only
137 #. To use LLVM modules on Win32-based system, you may configure LLVM
138 with ``--enable-shared``.
139 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
141 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
142 mode, depending on the system (it is so large because of all the debugging
143 information and the fact that the libraries are statically linked into multiple
144 tools). If you do not need many of the tools and you are space-conscious, you
145 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
146 considerably less space.
148 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
149 so. If compilation is successful, the LLVM utilities should be able to
150 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
151 should work as well, although the generated native code may not work on your
157 Compiling LLVM requires that you have several software packages installed. The
158 table below lists those required packages. The Package column is the usual name
159 for the software package that LLVM depends on. The Version column provides
160 "known to work" versions of the package. The Notes column describes how LLVM
161 uses the package and provides other details.
163 =========================================================== ============ ==========================================
164 Package Version Notes
165 =========================================================== ============ ==========================================
166 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
167 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
168 `python <http://www.python.org/>`_ >=2.5 Automated test suite\ :sup:`2`
169 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
170 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
171 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
172 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
173 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
174 =========================================================== ============ ==========================================
178 #. Only the C and C++ languages are needed so there's no need to build the
179 other languages for LLVM's purposes. See `below` for specific version
181 #. Only needed if you want to run the automated test suite in the
182 ``llvm/test`` directory.
183 #. If you want to make changes to the configure scripts, you will need GNU
184 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
185 will also need automake (1.9.6). We only use aclocal from that package.
186 #. Optional, adds compression / uncompression capabilities to selected LLVM
189 Additionally, your compilation host is expected to have the usual plethora of
190 Unix utilities. Specifically:
192 * **ar** --- archive library builder
193 * **bzip2** --- bzip2 command for distribution generation
194 * **bunzip2** --- bunzip2 command for distribution checking
195 * **chmod** --- change permissions on a file
196 * **cat** --- output concatenation utility
197 * **cp** --- copy files
198 * **date** --- print the current date/time
199 * **echo** --- print to standard output
200 * **egrep** --- extended regular expression search utility
201 * **find** --- find files/dirs in a file system
202 * **grep** --- regular expression search utility
203 * **gzip** --- gzip command for distribution generation
204 * **gunzip** --- gunzip command for distribution checking
205 * **install** --- install directories/files
206 * **mkdir** --- create a directory
207 * **mv** --- move (rename) files
208 * **ranlib** --- symbol table builder for archive libraries
209 * **rm** --- remove (delete) files and directories
210 * **sed** --- stream editor for transforming output
211 * **sh** --- Bourne shell for make build scripts
212 * **tar** --- tape archive for distribution generation
213 * **test** --- test things in file system
214 * **unzip** --- unzip command for distribution checking
215 * **zip** --- zip command for distribution generation
220 Host C++ Toolchain, both Compiler and Standard Library
221 ------------------------------------------------------
223 LLVM is very demanding of the host C++ compiler, and as such tends to expose
224 bugs in the compiler. We are also planning to follow improvements and
225 developments in the C++ language and library reasonably closely. As such, we
226 require a modern host C++ toolchain, both compiler and standard library, in
229 For the most popular host toolchains we check for specific minimum versions in
236 Anything older than these toolchains *may* work, but will require forcing the
237 build system with a special option and is not really a supported host platform.
238 Also note that older versions of these compilers have often crashed or
241 For less widely used host toolchains such as ICC or xlC, be aware that a very
242 recent version may be required to support all of the C++ features used in LLVM.
244 We track certain versions of software that are *known* to fail when used as
245 part of the host toolchain. These even include linkers at times.
247 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
248 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
250 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
251 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
252 defined in a discarded section. You can safely ignore these messages as they are
253 erroneous and the linkage is correct. These messages disappear using ld 2.17.
255 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
256 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
257 times (minutes instead of seconds) when building LLVM. We recommend upgrading
258 to a newer version (2.17.50.0.4 or later).
260 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
261 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
262 intermittent failures when building LLVM with position independent code. The
263 symptom is an error about cyclic dependencies. We recommend upgrading to a
264 newer version of Gold.
266 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
267 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
268 3.0 does not implement a few builtins that are used in this library. We
269 recommend using the system GCC to compile LLVM and Clang in this case.
271 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
272 least some (``cxxabi.h``) libstdc++ headers.
274 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
275 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
276 causes Clang to refuse to compile condition_variable header file. At the time
277 of writing, this breaks LLD build.
279 Getting a Modern Host C++ Toolchain
280 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
282 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
283 have a sufficiently modern Xcode, or you will likely need to upgrade until you
284 do. On Windows, just use Visual Studio 2012 as the host compiler, it is
285 explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
286 Clang as the system compiler.
288 However, some Linux distributions and some other or older BSDs sometimes have
289 extremely old versions of GCC. These steps attempt to help you upgrade you
290 compiler even on such a system. However, if at all possible, we encourage you
291 to use a recent version of a distribution with a modern system compiler that
292 meets these requirements. Note that it is tempting to to install a prior
293 version of Clang and libc++ to be the host compiler, however libc++ was not
294 well tested or set up to build on Linux until relatively recently. As
295 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
296 initial host in a bootstrap, and then using Clang (and potentially libc++).
298 The first step is to get a recent GCC toolchain installed. The most common
299 distribution on which users have struggled with the version requirements is
300 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
301 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
302 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
303 not all users can use PPAs and there are many other distributions, so it may be
304 necessary (or just useful, if you're here you *are* doing compiler development
305 after all) to build and install GCC from source. It is also quite easy to do
308 .. _toolchain testing PPA:
309 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
310 .. _ask ubuntu stack exchange:
311 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
313 Easy steps for installing GCC 4.8.2:
315 .. code-block:: console
317 % wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
318 % tar -xvjf gcc-4.8.2.tar.bz2
320 % ./contrib/download_prerequisites
322 % mkdir gcc-4.8.2-build
324 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
328 For more details, check out the excellent `GCC wiki entry`_, where I got most
329 of this information from.
332 http://gcc.gnu.org/wiki/InstallingGCC
334 Once you have a GCC toolchain, configure your build of LLVM to use the new
335 toolchain for your host compiler and C++ standard library. Because the new
336 version of libstdc++ is not on the system library search path, you need to pass
337 extra linker flags so that it can be found at link time (``-L``) and at runtime
338 (``-rpath``). If you are using CMake, this invocation should produce working
341 .. code-block:: console
345 % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
346 cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
348 If you fail to set rpath, most LLVM binaries will fail on startup with a message
349 from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
350 found``. This means you need to tweak the -rpath linker flag.
352 When you build Clang, you will need to give *it* access to modern C++11
353 standard library in order to use it as your new host in part of a bootstrap.
354 There are two easy ways to do this, either build (and install) libc++ along
355 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
356 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
357 Clang will look within its own prefix for libstdc++ and use it if found. You
358 can also add an explicit prefix for Clang to look in for a GCC toolchain with
359 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
360 link commands when using your just-built-Clang to bootstrap.
362 .. _Getting Started with LLVM:
364 Getting Started with LLVM
365 =========================
367 The remainder of this guide is meant to get you up and running with LLVM and to
368 give you some basic information about the LLVM environment.
370 The later sections of this guide describe the `general layout`_ of the LLVM
371 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
372 more information about LLVM or to get help via e-mail.
374 Terminology and Notation
375 ------------------------
377 Throughout this manual, the following names are used to denote paths specific to
378 the local system and working environment. *These are not environment variables
379 you need to set but just strings used in the rest of this document below*. In
380 any of the examples below, simply replace each of these names with the
381 appropriate pathname on your local system. All these paths are absolute:
385 This is the top level directory of the LLVM source tree.
389 This is the top level directory of the LLVM object tree (i.e. the tree where
390 object files and compiled programs will be placed. It can be the same as
393 .. _Setting Up Your Environment:
395 Setting Up Your Environment
396 ---------------------------
398 In order to compile and use LLVM, you may need to set some environment
401 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
403 [Optional] This environment variable helps LLVM linking tools find the
404 locations of your bitcode libraries. It is provided only as a convenience
405 since you can specify the paths using the -L options of the tools and the
406 C/C++ front-end will automatically use the bitcode files installed in its
409 Unpacking the LLVM Archives
410 ---------------------------
412 If you have the LLVM distribution, you will need to unpack it before you can
413 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
414 and the LLVM GCC front end compiled for your platform. There is an additional
415 test suite that is optional. Each file is a TAR archive that is compressed with
418 The files are as follows, with *x.y* marking the version number:
422 Source release for the LLVM libraries and tools.
424 ``llvm-test-x.y.tar.gz``
426 Source release for the LLVM test-suite.
430 Checkout LLVM from Subversion
431 -----------------------------
433 If you have access to our Subversion repository, you can get a fresh copy of the
434 entire source code. All you need to do is check it out from Subversion as
437 * ``cd where-you-want-llvm-to-live``
438 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
439 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
441 This will create an '``llvm``' directory in the current directory and fully
442 populate it with the LLVM source code, Makefiles, test directories, and local
443 copies of documentation files.
445 If you want to get a specific release (as opposed to the most recent revision),
446 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
447 following releases are located in the following subdirectories of the '``tags``'
450 * Release 3.4: **RELEASE_34/final**
451 * Release 3.3: **RELEASE_33/final**
452 * Release 3.2: **RELEASE_32/final**
453 * Release 3.1: **RELEASE_31/final**
454 * Release 3.0: **RELEASE_30/final**
455 * Release 2.9: **RELEASE_29/final**
456 * Release 2.8: **RELEASE_28**
457 * Release 2.7: **RELEASE_27**
458 * Release 2.6: **RELEASE_26**
459 * Release 2.5: **RELEASE_25**
460 * Release 2.4: **RELEASE_24**
461 * Release 2.3: **RELEASE_23**
462 * Release 2.2: **RELEASE_22**
463 * Release 2.1: **RELEASE_21**
464 * Release 2.0: **RELEASE_20**
465 * Release 1.9: **RELEASE_19**
466 * Release 1.8: **RELEASE_18**
467 * Release 1.7: **RELEASE_17**
468 * Release 1.6: **RELEASE_16**
469 * Release 1.5: **RELEASE_15**
470 * Release 1.4: **RELEASE_14**
471 * Release 1.3: **RELEASE_13**
472 * Release 1.2: **RELEASE_12**
473 * Release 1.1: **RELEASE_11**
474 * Release 1.0: **RELEASE_1**
476 If you would like to get the LLVM test suite (a separate package as of 1.4), you
477 get it from the Subversion repository:
479 .. code-block:: console
482 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
484 By placing it in the ``llvm/projects``, it will be automatically configured by
485 the LLVM configure script as well as automatically updated when you run ``svn
491 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
492 automatically with each Subversion commit and contain all necessary git-svn
493 marks (so, you can recreate git-svn metadata locally). Note that right now
494 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
497 .. code-block:: console
499 % git clone http://llvm.org/git/llvm.git
501 If you want to check out clang too, run:
503 .. code-block:: console
506 % git clone http://llvm.org/git/clang.git
508 If you want to check out compiler-rt too, run:
510 .. code-block:: console
513 % git clone http://llvm.org/git/compiler-rt.git
515 If you want to check out the Test Suite Source Code (optional), run:
517 .. code-block:: console
520 % git clone http://llvm.org/git/test-suite.git
522 Since the upstream repository is in Subversion, you should use ``git
523 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
524 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
525 master branch, run the following command:
527 .. code-block:: console
529 % git config branch.master.rebase true
531 Sending patches with Git
532 ^^^^^^^^^^^^^^^^^^^^^^^^
534 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
536 Assume ``master`` points the upstream and ``mybranch`` points your working
537 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
538 sanity of whitespaces:
540 .. code-block:: console
542 % git diff --check master..mybranch
544 The easiest way to generate a patch is as below:
546 .. code-block:: console
548 % git diff master..mybranch > /path/to/mybranch.diff
550 It is a little different from svn-generated diff. git-diff-generated diff has
551 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
552 could be accepted with ``patch -p1 -N``.
554 But you may generate patchset with git-format-patch. It generates by-each-commit
555 patchset. To generate patch files to attach to your article:
557 .. code-block:: console
559 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
561 If you would like to send patches directly, you may use git-send-email or
562 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
564 .. code-block:: console
566 % git format-patch --attach master..mybranch --stdout | git imap-send
568 Then, your .git/config should have [imap] sections.
573 host = imaps://imap.gmail.com
574 user = your.gmail.account@gmail.com
579 folder = "[Gmail]/Drafts"
580 ; example for Japanese, "Modified UTF-7" encoded.
581 folder = "[Gmail]/&Tgtm+DBN-"
582 ; example for Traditional Chinese
583 folder = "[Gmail]/&g0l6Pw-"
585 For developers to work with git-svn
586 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
588 To set up clone from which you can submit code using ``git-svn``, run:
590 .. code-block:: console
592 % git clone http://llvm.org/git/llvm.git
594 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
595 % git config svn-remote.svn.fetch :refs/remotes/origin/master
596 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
598 # If you have clang too:
600 % git clone http://llvm.org/git/clang.git
602 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
603 % git config svn-remote.svn.fetch :refs/remotes/origin/master
606 Likewise for compiler-rt and test-suite.
608 To update this clone without generating git-svn tags that conflict with the
609 upstream Git repo, run:
611 .. code-block:: console
613 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
614 % git checkout master
617 git checkout master &&
620 Likewise for compiler-rt and test-suite.
622 This leaves your working directories on their master branches, so you'll need to
623 ``checkout`` each working branch individually and ``rebase`` it on top of its
626 For those who wish to be able to update an llvm repo/revert patches easily using
627 git-svn, please look in the directory for the scripts ``git-svnup`` and
630 To perform the aforementioned update steps go into your source directory and
631 just type ``git-svnup`` or ``git svnup`` and everything will just work.
633 If one wishes to revert a commit with git-svn, but do not want the git hash to
634 escape into the commit message, one can use the script ``git-svnrevert`` or
635 ``git svnrevert`` which will take in the git hash for the commit you want to
636 revert, look up the appropriate svn revision, and output a message where all
637 references to the git hash have been replaced with the svn revision.
639 To commit back changes via git-svn, use ``git svn dcommit``:
641 .. code-block:: console
645 Note that git-svn will create one SVN commit for each Git commit you have pending,
646 so squash and edit each commit before executing ``dcommit`` to make sure they all
647 conform to the coding standards and the developers' policy.
649 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
650 please make sure your current branch is up-to-date (via fetch/rebase) before
653 The git-svn metadata can get out of sync after you mess around with branches and
654 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
655 about files with uncommitted changes. The fix is to rebuild the metadata:
657 .. code-block:: console
662 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
664 Local LLVM Configuration
665 ------------------------
667 Once checked out from the Subversion repository, the LLVM suite source code must
668 be configured via the ``configure`` script. This script sets variables in the
669 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
670 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
671 Makefiles needed to begin building LLVM.
673 The following environment variables are used by the ``configure`` script to
674 configure the build system:
676 +------------+-----------------------------------------------------------+
677 | Variable | Purpose |
678 +============+===========================================================+
679 | CC | Tells ``configure`` which C compiler to use. By default, |
680 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
681 | | compilers (in this order). Use this variable to override |
682 | | ``configure``\'s default behavior. |
683 +------------+-----------------------------------------------------------+
684 | CXX | Tells ``configure`` which C++ compiler to use. By |
685 | | default, ``configure`` will check ``PATH`` for |
686 | | ``clang++`` and GCC C++ compilers (in this order). Use |
687 | | this variable to override ``configure``'s default |
689 +------------+-----------------------------------------------------------+
691 The following options can be used to set or enable LLVM specific options:
693 ``--enable-optimized``
695 Enables optimized compilation (debugging symbols are removed and GCC
696 optimization flags are enabled). Note that this is the default setting if you
697 are using the LLVM distribution. The default behavior of a Subversion
698 checkout is to use an unoptimized build (also known as a debug build).
700 ``--enable-debug-runtime``
702 Enables debug symbols in the runtime libraries. The default is to strip debug
703 symbols from the runtime libraries.
707 Compile the Just In Time (JIT) compiler functionality. This is not available
708 on all platforms. The default is dependent on platform, so it is best to
709 explicitly enable it if you want it.
711 ``--enable-targets=target-option``
713 Controls which targets will be built and linked into llc. The default value
714 for ``target_options`` is "all" which builds and links all available targets.
715 The "host" target is selected as the target of the build host. You can also
716 specify a comma separated list of target names that you want available in llc.
717 The target names use all lower case. The current set of targets is:
719 ``aarch64, arm, arm64, cpp, hexagon, mips, mipsel, mips64, mips64el, msp430,
720 powerpc, nvptx, r600, sparc, systemz, x86, x86_64, xcore``.
724 Look for the doxygen program and enable construction of doxygen based
725 documentation from the source code. This is disabled by default because
726 generating the documentation can take a long time and producess 100s of
729 To configure LLVM, follow these steps:
731 #. Change directory into the object root directory:
733 .. code-block:: console
737 #. Run the ``configure`` script located in the LLVM source tree:
739 .. code-block:: console
741 % SRC_ROOT/configure --prefix=/install/path [other options]
743 Compiling the LLVM Suite Source Code
744 ------------------------------------
746 Once you have configured LLVM, you can build it. There are three types of
751 These builds are the default when one is using a Subversion checkout and
752 types ``gmake`` (unless the ``--enable-optimized`` option was used during
753 configuration). The build system will compile the tools and libraries with
754 debugging information. To get a Debug Build using the LLVM distribution the
755 ``--disable-optimized`` option must be passed to ``configure``.
757 Release (Optimized) Builds
759 These builds are enabled with the ``--enable-optimized`` option to
760 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
761 line. For these builds, the build system will compile the tools and libraries
762 with GCC optimizations enabled and strip debugging information from the
763 libraries and executables it generates. Note that Release Builds are default
764 when using an LLVM distribution.
768 These builds are for use with profiling. They compile profiling information
769 into the code for use with programs like ``gprof``. Profile builds must be
770 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
772 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
773 directory and issuing the following command:
775 .. code-block:: console
779 If the build fails, please `check here`_ to see if you are using a version of
780 GCC that is known not to compile LLVM.
782 If you have multiple processors in your machine, you may wish to use some of the
783 parallel build options provided by GNU Make. For example, you could use the
786 .. code-block:: console
790 There are several special targets which are useful when working with the LLVM
795 Removes all files generated by the build. This includes object files,
796 generated C/C++ files, libraries, and executables.
800 Removes everything that ``gmake clean`` does, but also removes files generated
801 by ``configure``. It attempts to return the source tree to the original state
802 in which it was shipped.
806 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
807 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
808 defaults to ``/usr/local``.
810 ``gmake -C runtime install-bytecode``
812 Assuming you built LLVM into $OBJDIR, when this command is run, it will
813 install bitcode libraries into the GCC front end's bitcode library directory.
814 If you need to update your bitcode libraries, this is the target to use once
817 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
818 these ``make`` targets and descriptions of other targets available.
820 It is also possible to override default values from ``configure`` by declaring
821 variables on the command line. The following are some examples:
823 ``gmake ENABLE_OPTIMIZED=1``
825 Perform a Release (Optimized) build.
827 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
829 Perform a Release (Optimized) build without assertions enabled.
831 ``gmake ENABLE_OPTIMIZED=0``
833 Perform a Debug build.
835 ``gmake ENABLE_PROFILING=1``
837 Perform a Profiling build.
841 Print what ``gmake`` is doing on standard output.
843 ``gmake TOOL_VERBOSE=1``
845 Ask each tool invoked by the makefiles to print out what it is doing on
846 the standard output. This also implies ``VERBOSE=1``.
848 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
849 any subdirectories that it contains. Entering any directory inside the LLVM
850 object tree and typing ``gmake`` should rebuild anything in or below that
851 directory that is out of date.
853 This does not apply to building the documentation.
854 LLVM's (non-Doxygen) documentation is produced with the
855 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
856 There are some HTML documents that have not yet been converted to the new
857 system (which uses the easy-to-read and easy-to-write
858 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
860 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
862 For instructions on how to install Sphinx, see
863 `Sphinx Introduction for LLVM Developers
864 <http://lld.llvm.org/sphinx_intro.html>`_.
865 After following the instructions there for installing Sphinx, build the LLVM
866 HTML documentation by doing the following:
868 .. code-block:: console
871 $ make -f Makefile.sphinx
873 This creates a ``_build/html`` sub-directory with all of the HTML files, not
874 just the generated ones.
875 This directory corresponds to ``llvm.org/docs``.
876 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
877 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
878 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
883 It is possible to cross-compile LLVM itself. That is, you can create LLVM
884 executables and libraries to be hosted on a platform different from the platform
885 where they are built (a Canadian Cross build). To configure a cross-compile,
886 supply the configure script with ``--build`` and ``--host`` options that are
887 different. The values of these options must be legal target triples that your
888 GCC compiler supports.
890 The result of such a build is executables that are not runnable on on the build
891 host (--build option) but can be executed on the compile host (--host option).
893 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
894 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
895 about cross-compiling.
897 The Location of LLVM Object Files
898 ---------------------------------
900 The LLVM build system is capable of sharing a single LLVM source tree among
901 several LLVM builds. Hence, it is possible to build LLVM for several different
902 platforms or configurations using the same source tree.
904 This is accomplished in the typical autoconf manner:
906 * Change directory to where the LLVM object files should live:
908 .. code-block:: console
912 * Run the ``configure`` script found in the LLVM source directory:
914 .. code-block:: console
918 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
921 Debug Builds with assertions enabled (the default)
925 ``OBJ_ROOT/Debug+Asserts/bin``
929 ``OBJ_ROOT/Debug+Asserts/lib``
935 ``OBJ_ROOT/Release/bin``
939 ``OBJ_ROOT/Release/lib``
945 ``OBJ_ROOT/Profile/bin``
949 ``OBJ_ROOT/Profile/lib``
951 Optional Configuration Items
952 ----------------------------
954 If you're running on a Linux system that supports the `binfmt_misc
955 <http://en.wikipedia.org/wiki/binfmt_misc>`_
956 module, and you have root access on the system, you can set your system up to
957 execute LLVM bitcode files directly. To do this, use commands like this (the
958 first command may not be required if you are already using the module):
960 .. code-block:: console
962 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
963 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
964 % chmod u+x hello.bc (if needed)
967 This allows you to execute LLVM bitcode files directly. On Debian, you can also
968 use this command instead of the 'echo' command above:
970 .. code-block:: console
972 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
980 One useful source of information about the LLVM source base is the LLVM `doxygen
981 <http://www.doxygen.org/>`_ documentation available at
982 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
988 This directory contains some simple examples of how to use the LLVM IR and JIT.
993 This directory contains public header files exported from the LLVM library. The
994 three main subdirectories of this directory are:
996 ``llvm/include/llvm``
998 This directory contains all of the LLVM specific header files. This directory
999 also has subdirectories for different portions of LLVM: ``Analysis``,
1000 ``CodeGen``, ``Target``, ``Transforms``, etc...
1002 ``llvm/include/llvm/Support``
1004 This directory contains generic support libraries that are provided with LLVM
1005 but not necessarily specific to LLVM. For example, some C++ STL utilities and
1006 a Command Line option processing library store their header files here.
1008 ``llvm/include/llvm/Config``
1010 This directory contains header files configured by the ``configure`` script.
1011 They wrap "standard" UNIX and C header files. Source code can include these
1012 header files which automatically take care of the conditional #includes that
1013 the ``configure`` script generates.
1018 This directory contains most of the source files of the LLVM system. In LLVM,
1019 almost all code exists in libraries, making it very easy to share code among the
1022 ``llvm/lib/VMCore/``
1024 This directory holds the core LLVM source files that implement core classes
1025 like Instruction and BasicBlock.
1027 ``llvm/lib/AsmParser/``
1029 This directory holds the source code for the LLVM assembly language parser
1032 ``llvm/lib/Bitcode/``
1034 This directory holds code for reading and write LLVM bitcode.
1036 ``llvm/lib/Analysis/``
1038 This directory contains a variety of different program analyses, such as
1039 Dominator Information, Call Graphs, Induction Variables, Interval
1040 Identification, Natural Loop Identification, etc.
1042 ``llvm/lib/Transforms/``
1044 This directory contains the source code for the LLVM to LLVM program
1045 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1046 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1047 Elimination, and many others.
1049 ``llvm/lib/Target/``
1051 This directory contains files that describe various target architectures for
1052 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1053 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1056 ``llvm/lib/CodeGen/``
1058 This directory contains the major parts of the code generator: Instruction
1059 Selector, Instruction Scheduling, and Register Allocation.
1065 ``llvm/lib/Debugger/``
1067 This directory contains the source level debugger library that makes it
1068 possible to instrument LLVM programs so that a debugger could identify source
1069 code locations at which the program is executing.
1071 ``llvm/lib/ExecutionEngine/``
1073 This directory contains libraries for executing LLVM bitcode directly at
1074 runtime in both interpreted and JIT compiled fashions.
1076 ``llvm/lib/Support/``
1078 This directory contains the source code that corresponds to the header files
1079 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1084 This directory contains projects that are not strictly part of LLVM but are
1085 shipped with LLVM. This is also the directory where you should create your own
1086 LLVM-based projects.
1091 This directory contains libraries which are compiled into LLVM bitcode and used
1092 when linking programs with the Clang front end. Most of these libraries are
1093 skeleton versions of real libraries; for example, libc is a stripped down
1096 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1102 This directory contains feature and regression tests and other basic sanity
1103 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1104 lot of territory without being exhaustive.
1109 This is not a directory in the normal llvm module; it is a separate Subversion
1110 module that must be checked out (usually to ``projects/test-suite``). This
1111 module contains a comprehensive correctness, performance, and benchmarking test
1112 suite for LLVM. It is a separate Subversion module because not every LLVM user
1113 is interested in downloading or building such a comprehensive test suite. For
1114 further details on this test suite, please see the :doc:`Testing Guide
1115 <TestingGuide>` document.
1122 The **tools** directory contains the executables built out of the libraries
1123 above, which form the main part of the user interface. You can always get help
1124 for a tool by typing ``tool_name -help``. The following is a brief introduction
1125 to the most important tools. More detailed information is in
1126 the `Command Guide <CommandGuide/index.html>`_.
1130 ``bugpoint`` is used to debug optimization passes or code generation backends
1131 by narrowing down the given test case to the minimum number of passes and/or
1132 instructions that still cause a problem, whether it is a crash or
1133 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1138 The archiver produces an archive containing the given LLVM bitcode files,
1139 optionally with an index for faster lookup.
1143 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1147 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1151 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1156 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1157 (although very slowly...). For architectures that support it (currently x86,
1158 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1159 compiler (if the functionality was compiled in), and will execute the code
1160 *much* faster than the interpreter.
1164 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1165 native code assembly file or to C code (with the ``-march=c`` option).
1169 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1170 (which are specified on the command line), and then outputs the resultant
1171 bitcode. The '``opt -help``' command is a good way to get a list of the
1172 program transformations available in LLVM.
1174 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1175 file and print out the results. It is primarily useful for debugging
1176 analyses, or familiarizing yourself with what an analysis does.
1181 This directory contains utilities for working with LLVM source code, and some of
1182 the utilities are actually required as part of the build process because they
1183 are code generators for parts of LLVM infrastructure.
1188 ``codegen-diff`` is a script that finds differences between code that LLC
1189 generates and code that LLI generates. This is a useful tool if you are
1190 debugging one of them, assuming that the other generates correct output. For
1191 the full user manual, run ```perldoc codegen-diff'``.
1195 The ``emacs`` directory contains syntax-highlighting files which will work
1196 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1197 assembly files and TableGen description files. For information on how to use
1198 the syntax files, consult the ``README`` file in that directory.
1202 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1203 which is useful if one wishes to do a lot of development across directories
1204 and does not want to individually find each file. One way to use it is to run,
1205 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1210 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1211 passes to it a regular expression provided on ``llvmgrep``'s command
1212 line. This is a very efficient way of searching the source base for a
1213 particular regular expression.
1217 The ``makellvm`` script compiles all files in the current directory and then
1218 compiles and links the tool that is the first argument. For example, assuming
1219 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1220 path, simply running ``makellvm llc`` will make a build of the current
1221 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1226 The ``TableGen`` directory contains the tool used to generate register
1227 descriptions, instruction set descriptions, and even assemblers from common
1228 TableGen description files.
1232 The ``vim`` directory contains syntax-highlighting files which will work with
1233 the VIM editor, providing syntax highlighting support for LLVM assembly files
1234 and TableGen description files. For information on how to use the syntax
1235 files, consult the ``README`` file in that directory.
1239 An Example Using the LLVM Tool Chain
1240 ====================================
1242 This section gives an example of using LLVM with the Clang front end.
1247 #. First, create a simple C file, name it 'hello.c':
1254 printf("hello world\n");
1258 #. Next, compile the C file into a native executable:
1260 .. code-block:: console
1262 % clang hello.c -o hello
1266 Clang works just like GCC by default. The standard -S and -c arguments
1267 work as usual (producing a native .s or .o file, respectively).
1269 #. Next, compile the C file into an LLVM bitcode file:
1271 .. code-block:: console
1273 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1275 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1276 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1277 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1279 #. Run the program in both forms. To run the program, use:
1281 .. code-block:: console
1287 .. code-block:: console
1291 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1292 <CommandGuide/lli>`.
1294 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1296 .. code-block:: console
1298 % llvm-dis < hello.bc | less
1300 #. Compile the program to native assembly using the LLC code generator:
1302 .. code-block:: console
1304 % llc hello.bc -o hello.s
1306 #. Assemble the native assembly language file into a program:
1308 .. code-block:: console
1310 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1312 % gcc hello.s -o hello.native # On others
1314 #. Execute the native code program:
1316 .. code-block:: console
1320 Note that using clang to compile directly to native code (i.e. when the
1321 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1326 If you are having problems building or using LLVM, or if you have any other
1327 general questions about LLVM, please consult the `Frequently Asked
1328 Questions <FAQ.html>`_ page.
1335 This document is just an **introduction** on how to use LLVM to do some simple
1336 things... there are many more interesting and complicated things that you can do
1337 that aren't documented here (but we'll gladly accept a patch if you want to
1338 write something up!). For more information about LLVM, check out:
1340 * `LLVM Homepage <http://llvm.org/>`_
1341 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1342 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_