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32 The LLVM Getting Started documentation may be out of date.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 Linux x86\ :sup:`1` GCC, Clang
119 Linux amd64 GCC, Clang
120 Linux ARM\ :sup:`4` GCC, Clang
121 Linux PowerPC GCC, Clang
122 Solaris V9 (Ultrasparc) GCC
123 FreeBSD x86\ :sup:`1` GCC, Clang
124 FreeBSD amd64 GCC, Clang
125 MacOS X\ :sup:`2` PowerPC GCC
126 MacOS X x86 GCC, Clang
127 Cygwin/Win32 x86\ :sup:`1, 3` GCC
128 Windows x86\ :sup:`1` Visual Studio
129 Windows x64 x86-64 Visual Studio
130 ================== ===================== =============
134 #. Code generation supported for Pentium processors and up
135 #. Code generation supported for 32-bit ABI only
136 #. To use LLVM modules on Win32-based system, you may configure LLVM
137 with ``--enable-shared``.
138 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
140 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
141 mode, depending on the system (it is so large because of all the debugging
142 information and the fact that the libraries are statically linked into multiple
143 tools). If you do not need many of the tools and you are space-conscious, you
144 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
145 considerably less space.
147 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
148 so. If compilation is successful, the LLVM utilities should be able to
149 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
150 should work as well, although the generated native code may not work on your
156 Compiling LLVM requires that you have several software packages installed. The
157 table below lists those required packages. The Package column is the usual name
158 for the software package that LLVM depends on. The Version column provides
159 "known to work" versions of the package. The Notes column describes how LLVM
160 uses the package and provides other details.
162 =========================================================== ============ ==========================================
163 Package Version Notes
164 =========================================================== ============ ==========================================
165 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
166 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
167 `python <http://www.python.org/>`_ >=2.5 Automated test suite\ :sup:`2`
168 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
169 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
170 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
171 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
172 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
173 =========================================================== ============ ==========================================
177 #. Only the C and C++ languages are needed so there's no need to build the
178 other languages for LLVM's purposes. See `below` for specific version
180 #. Only needed if you want to run the automated test suite in the
181 ``llvm/test`` directory.
182 #. If you want to make changes to the configure scripts, you will need GNU
183 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
184 will also need automake (1.9.6). We only use aclocal from that package.
185 #. Optional, adds compression / uncompression capabilities to selected LLVM
188 Additionally, your compilation host is expected to have the usual plethora of
189 Unix utilities. Specifically:
191 * **ar** --- archive library builder
192 * **bzip2** --- bzip2 command for distribution generation
193 * **bunzip2** --- bunzip2 command for distribution checking
194 * **chmod** --- change permissions on a file
195 * **cat** --- output concatenation utility
196 * **cp** --- copy files
197 * **date** --- print the current date/time
198 * **echo** --- print to standard output
199 * **egrep** --- extended regular expression search utility
200 * **find** --- find files/dirs in a file system
201 * **grep** --- regular expression search utility
202 * **gzip** --- gzip command for distribution generation
203 * **gunzip** --- gunzip command for distribution checking
204 * **install** --- install directories/files
205 * **mkdir** --- create a directory
206 * **mv** --- move (rename) files
207 * **ranlib** --- symbol table builder for archive libraries
208 * **rm** --- remove (delete) files and directories
209 * **sed** --- stream editor for transforming output
210 * **sh** --- Bourne shell for make build scripts
211 * **tar** --- tape archive for distribution generation
212 * **test** --- test things in file system
213 * **unzip** --- unzip command for distribution checking
214 * **zip** --- zip command for distribution generation
219 Host C++ Toolchain, both Compiler and Standard Library
220 ------------------------------------------------------
222 LLVM is very demanding of the host C++ compiler, and as such tends to expose
223 bugs in the compiler. We are also planning to follow improvements and
224 developments in the C++ language and library reasonably closely. As such, we
225 require a modern host C++ toolchain, both compiler and standard library, in
228 For the most popular host toolchains we check for specific minimum versions in
235 Anything older than these toolchains *may* work, but will require forcing the
236 build system with a special option and is not really a supported host platform.
237 Also note that older versions of these compilers have often crashed or
240 For less widely used host toolchains such as ICC or xlC, be aware that a very
241 recent version may be required to support all of the C++ features used in LLVM.
243 We track certain versions of software that are *known* to fail when used as
244 part of the host toolchain. These even include linkers at times.
246 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
247 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
249 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
250 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
251 defined in a discarded section. You can safely ignore these messages as they are
252 erroneous and the linkage is correct. These messages disappear using ld 2.17.
254 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
255 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
256 times (minutes instead of seconds) when building LLVM. We recommend upgrading
257 to a newer version (2.17.50.0.4 or later).
259 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
260 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
261 intermittent failures when building LLVM with position independent code. The
262 symptom is an error about cyclic dependencies. We recommend upgrading to a
263 newer version of Gold.
265 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
266 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
267 3.0 does not implement a few builtins that are used in this library. We
268 recommend using the system GCC to compile LLVM and Clang in this case.
270 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
271 least some (``cxxabi.h``) libstdc++ headers.
273 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
274 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
275 causes Clang to refuse to compile condition_variable header file. At the time
276 of writing, this breaks LLD build.
278 Getting a Modern Host C++ Toolchain
279 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
281 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
282 have a sufficiently modern Xcode, or you will likely need to upgrade until you
283 do. On Windows, just use Visual Studio 2012 as the host compiler, it is
284 explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
285 Clang as the system compiler.
287 However, some Linux distributions and some other or older BSDs sometimes have
288 extremely old versions of GCC. These steps attempt to help you upgrade you
289 compiler even on such a system. However, if at all possible, we encourage you
290 to use a recent version of a distribution with a modern system compiler that
291 meets these requirements. Note that it is tempting to to install a prior
292 version of Clang and libc++ to be the host compiler, however libc++ was not
293 well tested or set up to build on Linux until relatively recently. As
294 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
295 initial host in a bootstrap, and then using Clang (and potentially libc++).
297 The first step is to get a recent GCC toolchain installed. The most common
298 distribution on which users have struggled with the version requirements is
299 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
300 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
301 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
302 not all users can use PPAs and there are many other distributions, so it may be
303 necessary (or just useful, if you're here you *are* doing compiler development
304 after all) to build and install GCC from source. It is also quite easy to do
307 .. _toolchain testing PPA:
308 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
309 .. _ask ubuntu stack exchange:
310 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
312 Easy steps for installing GCC 4.8.2:
314 .. code-block:: console
316 % wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
317 % tar -xvjf gcc-4.8.2.tar.bz2
319 % ./contrib/download_prerequisites
321 % mkdir gcc-4.8.2-build
323 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
327 For more details, check out the excellent `GCC wiki entry`_, where I got most
328 of this information from.
331 http://gcc.gnu.org/wiki/InstallingGCC
333 Once you have a GCC toolchain, configure your build of LLVM to use the new
334 toolchain for your host compiler and C++ standard library. Because the new
335 version of libstdc++ is not on the system library search path, you need to pass
336 extra linker flags so that it can be found at link time (``-L``) and at runtime
337 (``-rpath``). If you are using CMake, this invocation should produce working
340 .. code-block:: console
344 % CC=$HOME/toolchains/bin/gcc CXX=$HOME/toolchains/bin/g++ \
345 cmake .. -DCMAKE_CXX_LINK_FLAGS="-Wl,-rpath,$HOME/toolchains/lib64 -L$HOME/toolchains/lib64"
347 If you fail to set rpath, most LLVM binaries will fail on startup with a message
348 from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not
349 found``. This means you need to tweak the -rpath linker flag.
351 When you build Clang, you will need to give *it* access to modern C++11
352 standard library in order to use it as your new host in part of a bootstrap.
353 There are two easy ways to do this, either build (and install) libc++ along
354 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
355 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
356 Clang will look within its own prefix for libstdc++ and use it if found. You
357 can also add an explicit prefix for Clang to look in for a GCC toolchain with
358 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
359 link commands when using your just-built-Clang to bootstrap.
361 .. _Getting Started with LLVM:
363 Getting Started with LLVM
364 =========================
366 The remainder of this guide is meant to get you up and running with LLVM and to
367 give you some basic information about the LLVM environment.
369 The later sections of this guide describe the `general layout`_ of the LLVM
370 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
371 more information about LLVM or to get help via e-mail.
373 Terminology and Notation
374 ------------------------
376 Throughout this manual, the following names are used to denote paths specific to
377 the local system and working environment. *These are not environment variables
378 you need to set but just strings used in the rest of this document below*. In
379 any of the examples below, simply replace each of these names with the
380 appropriate pathname on your local system. All these paths are absolute:
384 This is the top level directory of the LLVM source tree.
388 This is the top level directory of the LLVM object tree (i.e. the tree where
389 object files and compiled programs will be placed. It can be the same as
392 .. _Setting Up Your Environment:
394 Setting Up Your Environment
395 ---------------------------
397 In order to compile and use LLVM, you may need to set some environment
400 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
402 [Optional] This environment variable helps LLVM linking tools find the
403 locations of your bitcode libraries. It is provided only as a convenience
404 since you can specify the paths using the -L options of the tools and the
405 C/C++ front-end will automatically use the bitcode files installed in its
408 Unpacking the LLVM Archives
409 ---------------------------
411 If you have the LLVM distribution, you will need to unpack it before you can
412 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
413 and the LLVM GCC front end compiled for your platform. There is an additional
414 test suite that is optional. Each file is a TAR archive that is compressed with
417 The files are as follows, with *x.y* marking the version number:
421 Source release for the LLVM libraries and tools.
423 ``llvm-test-x.y.tar.gz``
425 Source release for the LLVM test-suite.
429 Checkout LLVM from Subversion
430 -----------------------------
432 If you have access to our Subversion repository, you can get a fresh copy of the
433 entire source code. All you need to do is check it out from Subversion as
436 * ``cd where-you-want-llvm-to-live``
437 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
438 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
440 This will create an '``llvm``' directory in the current directory and fully
441 populate it with the LLVM source code, Makefiles, test directories, and local
442 copies of documentation files.
444 If you want to get a specific release (as opposed to the most recent revision),
445 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
446 following releases are located in the following subdirectories of the '``tags``'
449 * Release 3.4: **RELEASE_34/final**
450 * Release 3.3: **RELEASE_33/final**
451 * Release 3.2: **RELEASE_32/final**
452 * Release 3.1: **RELEASE_31/final**
453 * Release 3.0: **RELEASE_30/final**
454 * Release 2.9: **RELEASE_29/final**
455 * Release 2.8: **RELEASE_28**
456 * Release 2.7: **RELEASE_27**
457 * Release 2.6: **RELEASE_26**
458 * Release 2.5: **RELEASE_25**
459 * Release 2.4: **RELEASE_24**
460 * Release 2.3: **RELEASE_23**
461 * Release 2.2: **RELEASE_22**
462 * Release 2.1: **RELEASE_21**
463 * Release 2.0: **RELEASE_20**
464 * Release 1.9: **RELEASE_19**
465 * Release 1.8: **RELEASE_18**
466 * Release 1.7: **RELEASE_17**
467 * Release 1.6: **RELEASE_16**
468 * Release 1.5: **RELEASE_15**
469 * Release 1.4: **RELEASE_14**
470 * Release 1.3: **RELEASE_13**
471 * Release 1.2: **RELEASE_12**
472 * Release 1.1: **RELEASE_11**
473 * Release 1.0: **RELEASE_1**
475 If you would like to get the LLVM test suite (a separate package as of 1.4), you
476 get it from the Subversion repository:
478 .. code-block:: console
481 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
483 By placing it in the ``llvm/projects``, it will be automatically configured by
484 the LLVM configure script as well as automatically updated when you run ``svn
490 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
491 automatically with each Subversion commit and contain all necessary git-svn
492 marks (so, you can recreate git-svn metadata locally). Note that right now
493 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
496 .. code-block:: console
498 % git clone http://llvm.org/git/llvm.git
500 If you want to check out clang too, run:
502 .. code-block:: console
505 % git clone http://llvm.org/git/clang.git
507 If you want to check out compiler-rt too, run:
509 .. code-block:: console
512 % git clone http://llvm.org/git/compiler-rt.git
514 If you want to check out the Test Suite Source Code (optional), run:
516 .. code-block:: console
519 % git clone http://llvm.org/git/test-suite.git
521 Since the upstream repository is in Subversion, you should use ``git
522 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
523 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
524 master branch, run the following command:
526 .. code-block:: console
528 % git config branch.master.rebase true
530 Sending patches with Git
531 ^^^^^^^^^^^^^^^^^^^^^^^^
533 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
535 Assume ``master`` points the upstream and ``mybranch`` points your working
536 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
537 sanity of whitespaces:
539 .. code-block:: console
541 % git diff --check master..mybranch
543 The easiest way to generate a patch is as below:
545 .. code-block:: console
547 % git diff master..mybranch > /path/to/mybranch.diff
549 It is a little different from svn-generated diff. git-diff-generated diff has
550 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
551 could be accepted with ``patch -p1 -N``.
553 But you may generate patchset with git-format-patch. It generates by-each-commit
554 patchset. To generate patch files to attach to your article:
556 .. code-block:: console
558 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
560 If you would like to send patches directly, you may use git-send-email or
561 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
563 .. code-block:: console
565 % git format-patch --attach master..mybranch --stdout | git imap-send
567 Then, your .git/config should have [imap] sections.
572 host = imaps://imap.gmail.com
573 user = your.gmail.account@gmail.com
578 folder = "[Gmail]/Drafts"
579 ; example for Japanese, "Modified UTF-7" encoded.
580 folder = "[Gmail]/&Tgtm+DBN-"
581 ; example for Traditional Chinese
582 folder = "[Gmail]/&g0l6Pw-"
584 For developers to work with git-svn
585 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
587 To set up clone from which you can submit code using ``git-svn``, run:
589 .. code-block:: console
591 % git clone http://llvm.org/git/llvm.git
593 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
594 % git config svn-remote.svn.fetch :refs/remotes/origin/master
595 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
597 # If you have clang too:
599 % git clone http://llvm.org/git/clang.git
601 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
602 % git config svn-remote.svn.fetch :refs/remotes/origin/master
605 Likewise for compiler-rt and test-suite.
607 To update this clone without generating git-svn tags that conflict with the
608 upstream Git repo, run:
610 .. code-block:: console
612 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
613 % git checkout master
616 git checkout master &&
619 Likewise for compiler-rt and test-suite.
621 This leaves your working directories on their master branches, so you'll need to
622 ``checkout`` each working branch individually and ``rebase`` it on top of its
625 For those who wish to be able to update an llvm repo/revert patches easily using
626 git-svn, please look in the directory for the scripts ``git-svnup`` and
629 To perform the aforementioned update steps go into your source directory and
630 just type ``git-svnup`` or ``git svnup`` and everything will just work.
632 If one wishes to revert a commit with git-svn, but do not want the git hash to
633 escape into the commit message, one can use the script ``git-svnrevert`` or
634 ``git svnrevert`` which will take in the git hash for the commit you want to
635 revert, look up the appropriate svn revision, and output a message where all
636 references to the git hash have been replaced with the svn revision.
638 To commit back changes via git-svn, use ``git svn dcommit``:
640 .. code-block:: console
644 Note that git-svn will create one SVN commit for each Git commit you have pending,
645 so squash and edit each commit before executing ``dcommit`` to make sure they all
646 conform to the coding standards and the developers' policy.
648 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
649 please make sure your current branch is up-to-date (via fetch/rebase) before
652 The git-svn metadata can get out of sync after you mess around with branches and
653 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
654 about files with uncommitted changes. The fix is to rebuild the metadata:
656 .. code-block:: console
661 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
663 Local LLVM Configuration
664 ------------------------
666 Once checked out from the Subversion repository, the LLVM suite source code must
667 be configured via the ``configure`` script. This script sets variables in the
668 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
669 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
670 Makefiles needed to begin building LLVM.
672 The following environment variables are used by the ``configure`` script to
673 configure the build system:
675 +------------+-----------------------------------------------------------+
676 | Variable | Purpose |
677 +============+===========================================================+
678 | CC | Tells ``configure`` which C compiler to use. By default, |
679 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
680 | | compilers (in this order). Use this variable to override |
681 | | ``configure``\'s default behavior. |
682 +------------+-----------------------------------------------------------+
683 | CXX | Tells ``configure`` which C++ compiler to use. By |
684 | | default, ``configure`` will check ``PATH`` for |
685 | | ``clang++`` and GCC C++ compilers (in this order). Use |
686 | | this variable to override ``configure``'s default |
688 +------------+-----------------------------------------------------------+
690 The following options can be used to set or enable LLVM specific options:
692 ``--enable-optimized``
694 Enables optimized compilation (debugging symbols are removed and GCC
695 optimization flags are enabled). Note that this is the default setting if you
696 are using the LLVM distribution. The default behavior of a Subversion
697 checkout is to use an unoptimized build (also known as a debug build).
699 ``--enable-debug-runtime``
701 Enables debug symbols in the runtime libraries. The default is to strip debug
702 symbols from the runtime libraries.
706 Compile the Just In Time (JIT) compiler functionality. This is not available
707 on all platforms. The default is dependent on platform, so it is best to
708 explicitly enable it if you want it.
710 ``--enable-targets=target-option``
712 Controls which targets will be built and linked into llc. The default value
713 for ``target_options`` is "all" which builds and links all available targets.
714 The "host" target is selected as the target of the build host. You can also
715 specify a comma separated list of target names that you want available in llc.
716 The target names use all lower case. The current set of targets is:
718 ``aarch64, arm, arm64, cpp, hexagon, mips, mipsel, mips64, mips64el, msp430,
719 powerpc, nvptx, r600, sparc, systemz, x86, x86_64, xcore``.
723 Look for the doxygen program and enable construction of doxygen based
724 documentation from the source code. This is disabled by default because
725 generating the documentation can take a long time and producess 100s of
728 To configure LLVM, follow these steps:
730 #. Change directory into the object root directory:
732 .. code-block:: console
736 #. Run the ``configure`` script located in the LLVM source tree:
738 .. code-block:: console
740 % SRC_ROOT/configure --prefix=/install/path [other options]
742 Compiling the LLVM Suite Source Code
743 ------------------------------------
745 Once you have configured LLVM, you can build it. There are three types of
750 These builds are the default when one is using a Subversion checkout and
751 types ``gmake`` (unless the ``--enable-optimized`` option was used during
752 configuration). The build system will compile the tools and libraries with
753 debugging information. To get a Debug Build using the LLVM distribution the
754 ``--disable-optimized`` option must be passed to ``configure``.
756 Release (Optimized) Builds
758 These builds are enabled with the ``--enable-optimized`` option to
759 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
760 line. For these builds, the build system will compile the tools and libraries
761 with GCC optimizations enabled and strip debugging information from the
762 libraries and executables it generates. Note that Release Builds are default
763 when using an LLVM distribution.
767 These builds are for use with profiling. They compile profiling information
768 into the code for use with programs like ``gprof``. Profile builds must be
769 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
771 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
772 directory and issuing the following command:
774 .. code-block:: console
778 If the build fails, please `check here`_ to see if you are using a version of
779 GCC that is known not to compile LLVM.
781 If you have multiple processors in your machine, you may wish to use some of the
782 parallel build options provided by GNU Make. For example, you could use the
785 .. code-block:: console
789 There are several special targets which are useful when working with the LLVM
794 Removes all files generated by the build. This includes object files,
795 generated C/C++ files, libraries, and executables.
799 Removes everything that ``gmake clean`` does, but also removes files generated
800 by ``configure``. It attempts to return the source tree to the original state
801 in which it was shipped.
805 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
806 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
807 defaults to ``/usr/local``.
809 ``gmake -C runtime install-bytecode``
811 Assuming you built LLVM into $OBJDIR, when this command is run, it will
812 install bitcode libraries into the GCC front end's bitcode library directory.
813 If you need to update your bitcode libraries, this is the target to use once
816 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
817 these ``make`` targets and descriptions of other targets available.
819 It is also possible to override default values from ``configure`` by declaring
820 variables on the command line. The following are some examples:
822 ``gmake ENABLE_OPTIMIZED=1``
824 Perform a Release (Optimized) build.
826 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
828 Perform a Release (Optimized) build without assertions enabled.
830 ``gmake ENABLE_OPTIMIZED=0``
832 Perform a Debug build.
834 ``gmake ENABLE_PROFILING=1``
836 Perform a Profiling build.
840 Print what ``gmake`` is doing on standard output.
842 ``gmake TOOL_VERBOSE=1``
844 Ask each tool invoked by the makefiles to print out what it is doing on
845 the standard output. This also implies ``VERBOSE=1``.
847 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
848 any subdirectories that it contains. Entering any directory inside the LLVM
849 object tree and typing ``gmake`` should rebuild anything in or below that
850 directory that is out of date.
852 This does not apply to building the documentation.
853 LLVM's (non-Doxygen) documentation is produced with the
854 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
855 There are some HTML documents that have not yet been converted to the new
856 system (which uses the easy-to-read and easy-to-write
857 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
859 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
861 For instructions on how to install Sphinx, see
862 `Sphinx Introduction for LLVM Developers
863 <http://lld.llvm.org/sphinx_intro.html>`_.
864 After following the instructions there for installing Sphinx, build the LLVM
865 HTML documentation by doing the following:
867 .. code-block:: console
870 $ make -f Makefile.sphinx
872 This creates a ``_build/html`` sub-directory with all of the HTML files, not
873 just the generated ones.
874 This directory corresponds to ``llvm.org/docs``.
875 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
876 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
877 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
882 It is possible to cross-compile LLVM itself. That is, you can create LLVM
883 executables and libraries to be hosted on a platform different from the platform
884 where they are built (a Canadian Cross build). To configure a cross-compile,
885 supply the configure script with ``--build`` and ``--host`` options that are
886 different. The values of these options must be legal target triples that your
887 GCC compiler supports.
889 The result of such a build is executables that are not runnable on on the build
890 host (--build option) but can be executed on the compile host (--host option).
892 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
893 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
894 about cross-compiling.
896 The Location of LLVM Object Files
897 ---------------------------------
899 The LLVM build system is capable of sharing a single LLVM source tree among
900 several LLVM builds. Hence, it is possible to build LLVM for several different
901 platforms or configurations using the same source tree.
903 This is accomplished in the typical autoconf manner:
905 * Change directory to where the LLVM object files should live:
907 .. code-block:: console
911 * Run the ``configure`` script found in the LLVM source directory:
913 .. code-block:: console
917 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
920 Debug Builds with assertions enabled (the default)
924 ``OBJ_ROOT/Debug+Asserts/bin``
928 ``OBJ_ROOT/Debug+Asserts/lib``
934 ``OBJ_ROOT/Release/bin``
938 ``OBJ_ROOT/Release/lib``
944 ``OBJ_ROOT/Profile/bin``
948 ``OBJ_ROOT/Profile/lib``
950 Optional Configuration Items
951 ----------------------------
953 If you're running on a Linux system that supports the `binfmt_misc
954 <http://en.wikipedia.org/wiki/binfmt_misc>`_
955 module, and you have root access on the system, you can set your system up to
956 execute LLVM bitcode files directly. To do this, use commands like this (the
957 first command may not be required if you are already using the module):
959 .. code-block:: console
961 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
962 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
963 % chmod u+x hello.bc (if needed)
966 This allows you to execute LLVM bitcode files directly. On Debian, you can also
967 use this command instead of the 'echo' command above:
969 .. code-block:: console
971 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
979 One useful source of information about the LLVM source base is the LLVM `doxygen
980 <http://www.doxygen.org/>`_ documentation available at
981 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
987 This directory contains some simple examples of how to use the LLVM IR and JIT.
992 This directory contains public header files exported from the LLVM library. The
993 three main subdirectories of this directory are:
995 ``llvm/include/llvm``
997 This directory contains all of the LLVM specific header files. This directory
998 also has subdirectories for different portions of LLVM: ``Analysis``,
999 ``CodeGen``, ``Target``, ``Transforms``, etc...
1001 ``llvm/include/llvm/Support``
1003 This directory contains generic support libraries that are provided with LLVM
1004 but not necessarily specific to LLVM. For example, some C++ STL utilities and
1005 a Command Line option processing library store their header files here.
1007 ``llvm/include/llvm/Config``
1009 This directory contains header files configured by the ``configure`` script.
1010 They wrap "standard" UNIX and C header files. Source code can include these
1011 header files which automatically take care of the conditional #includes that
1012 the ``configure`` script generates.
1017 This directory contains most of the source files of the LLVM system. In LLVM,
1018 almost all code exists in libraries, making it very easy to share code among the
1021 ``llvm/lib/VMCore/``
1023 This directory holds the core LLVM source files that implement core classes
1024 like Instruction and BasicBlock.
1026 ``llvm/lib/AsmParser/``
1028 This directory holds the source code for the LLVM assembly language parser
1031 ``llvm/lib/Bitcode/``
1033 This directory holds code for reading and write LLVM bitcode.
1035 ``llvm/lib/Analysis/``
1037 This directory contains a variety of different program analyses, such as
1038 Dominator Information, Call Graphs, Induction Variables, Interval
1039 Identification, Natural Loop Identification, etc.
1041 ``llvm/lib/Transforms/``
1043 This directory contains the source code for the LLVM to LLVM program
1044 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1045 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1046 Elimination, and many others.
1048 ``llvm/lib/Target/``
1050 This directory contains files that describe various target architectures for
1051 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1052 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1055 ``llvm/lib/CodeGen/``
1057 This directory contains the major parts of the code generator: Instruction
1058 Selector, Instruction Scheduling, and Register Allocation.
1064 ``llvm/lib/Debugger/``
1066 This directory contains the source level debugger library that makes it
1067 possible to instrument LLVM programs so that a debugger could identify source
1068 code locations at which the program is executing.
1070 ``llvm/lib/ExecutionEngine/``
1072 This directory contains libraries for executing LLVM bitcode directly at
1073 runtime in both interpreted and JIT compiled fashions.
1075 ``llvm/lib/Support/``
1077 This directory contains the source code that corresponds to the header files
1078 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1083 This directory contains projects that are not strictly part of LLVM but are
1084 shipped with LLVM. This is also the directory where you should create your own
1085 LLVM-based projects.
1090 This directory contains libraries which are compiled into LLVM bitcode and used
1091 when linking programs with the Clang front end. Most of these libraries are
1092 skeleton versions of real libraries; for example, libc is a stripped down
1095 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1101 This directory contains feature and regression tests and other basic sanity
1102 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1103 lot of territory without being exhaustive.
1108 This is not a directory in the normal llvm module; it is a separate Subversion
1109 module that must be checked out (usually to ``projects/test-suite``). This
1110 module contains a comprehensive correctness, performance, and benchmarking test
1111 suite for LLVM. It is a separate Subversion module because not every LLVM user
1112 is interested in downloading or building such a comprehensive test suite. For
1113 further details on this test suite, please see the :doc:`Testing Guide
1114 <TestingGuide>` document.
1121 The **tools** directory contains the executables built out of the libraries
1122 above, which form the main part of the user interface. You can always get help
1123 for a tool by typing ``tool_name -help``. The following is a brief introduction
1124 to the most important tools. More detailed information is in
1125 the `Command Guide <CommandGuide/index.html>`_.
1129 ``bugpoint`` is used to debug optimization passes or code generation backends
1130 by narrowing down the given test case to the minimum number of passes and/or
1131 instructions that still cause a problem, whether it is a crash or
1132 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1137 The archiver produces an archive containing the given LLVM bitcode files,
1138 optionally with an index for faster lookup.
1142 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1146 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1150 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1155 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1156 (although very slowly...). For architectures that support it (currently x86,
1157 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1158 compiler (if the functionality was compiled in), and will execute the code
1159 *much* faster than the interpreter.
1163 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1164 native code assembly file or to C code (with the ``-march=c`` option).
1168 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1169 (which are specified on the command line), and then outputs the resultant
1170 bitcode. The '``opt -help``' command is a good way to get a list of the
1171 program transformations available in LLVM.
1173 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1174 file and print out the results. It is primarily useful for debugging
1175 analyses, or familiarizing yourself with what an analysis does.
1180 This directory contains utilities for working with LLVM source code, and some of
1181 the utilities are actually required as part of the build process because they
1182 are code generators for parts of LLVM infrastructure.
1187 ``codegen-diff`` is a script that finds differences between code that LLC
1188 generates and code that LLI generates. This is a useful tool if you are
1189 debugging one of them, assuming that the other generates correct output. For
1190 the full user manual, run ```perldoc codegen-diff'``.
1194 The ``emacs`` directory contains syntax-highlighting files which will work
1195 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1196 assembly files and TableGen description files. For information on how to use
1197 the syntax files, consult the ``README`` file in that directory.
1201 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1202 which is useful if one wishes to do a lot of development across directories
1203 and does not want to individually find each file. One way to use it is to run,
1204 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1209 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1210 passes to it a regular expression provided on ``llvmgrep``'s command
1211 line. This is a very efficient way of searching the source base for a
1212 particular regular expression.
1216 The ``makellvm`` script compiles all files in the current directory and then
1217 compiles and links the tool that is the first argument. For example, assuming
1218 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1219 path, simply running ``makellvm llc`` will make a build of the current
1220 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1225 The ``TableGen`` directory contains the tool used to generate register
1226 descriptions, instruction set descriptions, and even assemblers from common
1227 TableGen description files.
1231 The ``vim`` directory contains syntax-highlighting files which will work with
1232 the VIM editor, providing syntax highlighting support for LLVM assembly files
1233 and TableGen description files. For information on how to use the syntax
1234 files, consult the ``README`` file in that directory.
1238 An Example Using the LLVM Tool Chain
1239 ====================================
1241 This section gives an example of using LLVM with the Clang front end.
1246 #. First, create a simple C file, name it 'hello.c':
1253 printf("hello world\n");
1257 #. Next, compile the C file into a native executable:
1259 .. code-block:: console
1261 % clang hello.c -o hello
1265 Clang works just like GCC by default. The standard -S and -c arguments
1266 work as usual (producing a native .s or .o file, respectively).
1268 #. Next, compile the C file into an LLVM bitcode file:
1270 .. code-block:: console
1272 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1274 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1275 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1276 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1278 #. Run the program in both forms. To run the program, use:
1280 .. code-block:: console
1286 .. code-block:: console
1290 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1291 <CommandGuide/lli>`.
1293 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1295 .. code-block:: console
1297 % llvm-dis < hello.bc | less
1299 #. Compile the program to native assembly using the LLC code generator:
1301 .. code-block:: console
1303 % llc hello.bc -o hello.s
1305 #. Assemble the native assembly language file into a program:
1307 .. code-block:: console
1309 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1311 % gcc hello.s -o hello.native # On others
1313 #. Execute the native code program:
1315 .. code-block:: console
1319 Note that using clang to compile directly to native code (i.e. when the
1320 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1325 If you are having problems building or using LLVM, or if you have any other
1326 general questions about LLVM, please consult the `Frequently Asked
1327 Questions <FAQ.html>`_ page.
1334 This document is just an **introduction** on how to use LLVM to do some simple
1335 things... there are many more interesting and complicated things that you can do
1336 that aren't documented here (but we'll gladly accept a patch if you want to
1337 write something up!). For more information about LLVM, check out:
1339 * `LLVM Homepage <http://llvm.org/>`_
1340 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1341 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_