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32 The LLVM Getting Started documentation may be out of date.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 instead of the makefiles. With CMake it is
91 possible to generate project files for several IDEs: Xcode, Eclipse CDT4,
92 CodeBlocks, Qt-Creator (use the CodeBlocks generator), KDevelop3.
94 * If you get an "internal compiler error (ICE)" or test failures, see
97 Consult the `Getting Started with LLVM`_ section for detailed information on
98 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
99 that simplify working with the Clang front end and LLVM tools. Go to `Program
100 Layout`_ to learn about the layout of the source code tree.
105 Before you begin to use the LLVM system, review the requirements given below.
106 This may save you some trouble by knowing ahead of time what hardware and
107 software you will need.
112 LLVM is known to work on the following host platforms:
114 ================== ===================== =============
116 ================== ===================== =============
117 AuroraUX x86\ :sup:`1` GCC
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
301 <https://launchpad.net/~ubuntu-toolchain-r/+archive/test>` and use it to
302 install a modern GCC. There is a really nice discussions of this on the `ask
303 ubuntu stack exchange
304 <http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal>`.
305 However, not all users can use PPAs and there are many other distros, so it may
306 be necessory (or just useful, if you're here you *are* doing compiler
307 development after all) to build and install GCC from source. It is also quite
308 easy to do these days.
310 Easy steps for installing GCC 4.8.2:
312 .. code-block:: console
314 wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
315 tar -xvjf gcc-4.8.2.tar.bz2
317 ./contrib/download_prerequisites
319 mkdir gcc-4.8.2-build
321 %PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
325 For more details, check out the `excellent GCC wiki entry
326 <http://gcc.gnu.org/wiki/InstallingGCC>`, where I got most of this information
329 Once you have a GCC toolchain, use it as your host compiler. Things should
330 generally "just work". You may need to pass a special linker flag,
331 ``-Wl,-rpath,$HOME/toolchains/lib`` or some variant thereof to get things to
332 find the libstdc++ DSO in this toolchain.
334 When you build Clang, you will need to give *it* access to modern C++11
335 standard library in order to use it as your new host in part of a bootstrap.
336 There are two easy ways to do this, either build (and install) libc++ along
337 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
338 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
339 Clang will look within its own prefix for libstdc++ and use it if found. You
340 can also add an explicit prefix for Clang to look in for a GCC toolchain with
341 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
342 link commands when using your just-built-Clang to bootstrap.
344 .. _Getting Started with LLVM:
346 Getting Started with LLVM
347 =========================
349 The remainder of this guide is meant to get you up and running with LLVM and to
350 give you some basic information about the LLVM environment.
352 The later sections of this guide describe the `general layout`_ of the LLVM
353 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
354 more information about LLVM or to get help via e-mail.
356 Terminology and Notation
357 ------------------------
359 Throughout this manual, the following names are used to denote paths specific to
360 the local system and working environment. *These are not environment variables
361 you need to set but just strings used in the rest of this document below*. In
362 any of the examples below, simply replace each of these names with the
363 appropriate pathname on your local system. All these paths are absolute:
367 This is the top level directory of the LLVM source tree.
371 This is the top level directory of the LLVM object tree (i.e. the tree where
372 object files and compiled programs will be placed. It can be the same as
375 .. _Setting Up Your Environment:
377 Setting Up Your Environment
378 ---------------------------
380 In order to compile and use LLVM, you may need to set some environment
383 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
385 [Optional] This environment variable helps LLVM linking tools find the
386 locations of your bitcode libraries. It is provided only as a convenience
387 since you can specify the paths using the -L options of the tools and the
388 C/C++ front-end will automatically use the bitcode files installed in its
391 Unpacking the LLVM Archives
392 ---------------------------
394 If you have the LLVM distribution, you will need to unpack it before you can
395 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
396 and the LLVM GCC front end compiled for your platform. There is an additional
397 test suite that is optional. Each file is a TAR archive that is compressed with
400 The files are as follows, with *x.y* marking the version number:
404 Source release for the LLVM libraries and tools.
406 ``llvm-test-x.y.tar.gz``
408 Source release for the LLVM test-suite.
412 Checkout LLVM from Subversion
413 -----------------------------
415 If you have access to our Subversion repository, you can get a fresh copy of the
416 entire source code. All you need to do is check it out from Subversion as
419 * ``cd where-you-want-llvm-to-live``
420 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
421 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
423 This will create an '``llvm``' directory in the current directory and fully
424 populate it with the LLVM source code, Makefiles, test directories, and local
425 copies of documentation files.
427 If you want to get a specific release (as opposed to the most recent revision),
428 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
429 following releases are located in the following subdirectories of the '``tags``'
432 * Release 3.3: **RELEASE_33/final**
433 * Release 3.2: **RELEASE_32/final**
434 * Release 3.1: **RELEASE_31/final**
435 * Release 3.0: **RELEASE_30/final**
436 * Release 2.9: **RELEASE_29/final**
437 * Release 2.8: **RELEASE_28**
438 * Release 2.7: **RELEASE_27**
439 * Release 2.6: **RELEASE_26**
440 * Release 2.5: **RELEASE_25**
441 * Release 2.4: **RELEASE_24**
442 * Release 2.3: **RELEASE_23**
443 * Release 2.2: **RELEASE_22**
444 * Release 2.1: **RELEASE_21**
445 * Release 2.0: **RELEASE_20**
446 * Release 1.9: **RELEASE_19**
447 * Release 1.8: **RELEASE_18**
448 * Release 1.7: **RELEASE_17**
449 * Release 1.6: **RELEASE_16**
450 * Release 1.5: **RELEASE_15**
451 * Release 1.4: **RELEASE_14**
452 * Release 1.3: **RELEASE_13**
453 * Release 1.2: **RELEASE_12**
454 * Release 1.1: **RELEASE_11**
455 * Release 1.0: **RELEASE_1**
457 If you would like to get the LLVM test suite (a separate package as of 1.4), you
458 get it from the Subversion repository:
460 .. code-block:: console
463 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
465 By placing it in the ``llvm/projects``, it will be automatically configured by
466 the LLVM configure script as well as automatically updated when you run ``svn
472 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
473 automatically with each Subversion commit and contain all necessary git-svn
474 marks (so, you can recreate git-svn metadata locally). Note that right now
475 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
478 .. code-block:: console
480 % git clone http://llvm.org/git/llvm.git
482 If you want to check out clang too, run:
484 .. code-block:: console
487 % git clone http://llvm.org/git/clang.git
489 If you want to check out compiler-rt too, run:
491 .. code-block:: console
494 % git clone http://llvm.org/git/compiler-rt.git
496 If you want to check out the Test Suite Source Code (optional), run:
498 .. code-block:: console
501 % git clone http://llvm.org/git/test-suite.git
503 Since the upstream repository is in Subversion, you should use ``git
504 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
505 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
506 master branch, run the following command:
508 .. code-block:: console
510 % git config branch.master.rebase true
512 Sending patches with Git
513 ^^^^^^^^^^^^^^^^^^^^^^^^
515 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
517 Assume ``master`` points the upstream and ``mybranch`` points your working
518 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
519 sanity of whitespaces:
521 .. code-block:: console
523 % git diff --check master..mybranch
525 The easiest way to generate a patch is as below:
527 .. code-block:: console
529 % git diff master..mybranch > /path/to/mybranch.diff
531 It is a little different from svn-generated diff. git-diff-generated diff has
532 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
533 could be accepted with ``patch -p1 -N``.
535 But you may generate patchset with git-format-patch. It generates by-each-commit
536 patchset. To generate patch files to attach to your article:
538 .. code-block:: console
540 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
542 If you would like to send patches directly, you may use git-send-email or
543 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
545 .. code-block:: console
547 % git format-patch --attach master..mybranch --stdout | git imap-send
549 Then, your .git/config should have [imap] sections.
554 host = imaps://imap.gmail.com
555 user = your.gmail.account@gmail.com
560 folder = "[Gmail]/Drafts"
561 ; example for Japanese, "Modified UTF-7" encoded.
562 folder = "[Gmail]/&Tgtm+DBN-"
563 ; example for Traditional Chinese
564 folder = "[Gmail]/&g0l6Pw-"
566 For developers to work with git-svn
567 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
569 To set up clone from which you can submit code using ``git-svn``, run:
571 .. code-block:: console
573 % git clone http://llvm.org/git/llvm.git
575 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
576 % git config svn-remote.svn.fetch :refs/remotes/origin/master
577 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
579 # If you have clang too:
581 % git clone http://llvm.org/git/clang.git
583 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
584 % git config svn-remote.svn.fetch :refs/remotes/origin/master
587 Likewise for compiler-rt and test-suite.
589 To update this clone without generating git-svn tags that conflict with the
590 upstream Git repo, run:
592 .. code-block:: console
594 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
595 % git checkout master
598 git checkout master &&
601 Likewise for compiler-rt and test-suite.
603 This leaves your working directories on their master branches, so you'll need to
604 ``checkout`` each working branch individually and ``rebase`` it on top of its
607 For those who wish to be able to update an llvm repo/revert patches easily using
608 git-svn, please look in the directory for the scripts ``git-svnup`` and
611 To perform the aforementioned update steps go into your source directory and
612 just type ``git-svnup`` or ``git svnup`` and everything will just work.
614 If one wishes to revert a commit with git-svn, but do not want the git hash to
615 escape into the commit message, one can use the script ``git-svnrevert`` or
616 ``git svnrevert`` which will take in the git hash for the commit you want to
617 revert, look up the appropriate svn revision, and output a message where all
618 references to the git hash have been replaced with the svn revision.
620 To commit back changes via git-svn, use ``git svn dcommit``:
622 .. code-block:: console
626 Note that git-svn will create one SVN commit for each Git commit you have pending,
627 so squash and edit each commit before executing ``dcommit`` to make sure they all
628 conform to the coding standards and the developers' policy.
630 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
631 please make sure your current branch is up-to-date (via fetch/rebase) before
634 The git-svn metadata can get out of sync after you mess around with branches and
635 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
636 about files with uncommitted changes. The fix is to rebuild the metadata:
638 .. code-block:: console
643 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
645 Local LLVM Configuration
646 ------------------------
648 Once checked out from the Subversion repository, the LLVM suite source code must
649 be configured via the ``configure`` script. This script sets variables in the
650 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
651 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
652 Makefiles needed to begin building LLVM.
654 The following environment variables are used by the ``configure`` script to
655 configure the build system:
657 +------------+-----------------------------------------------------------+
658 | Variable | Purpose |
659 +============+===========================================================+
660 | CC | Tells ``configure`` which C compiler to use. By default, |
661 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
662 | | compilers (in this order). Use this variable to override |
663 | | ``configure``\'s default behavior. |
664 +------------+-----------------------------------------------------------+
665 | CXX | Tells ``configure`` which C++ compiler to use. By |
666 | | default, ``configure`` will check ``PATH`` for |
667 | | ``clang++`` and GCC C++ compilers (in this order). Use |
668 | | this variable to override ``configure``'s default |
670 +------------+-----------------------------------------------------------+
672 The following options can be used to set or enable LLVM specific options:
674 ``--enable-optimized``
676 Enables optimized compilation (debugging symbols are removed and GCC
677 optimization flags are enabled). Note that this is the default setting if you
678 are using the LLVM distribution. The default behavior of an Subversion
679 checkout is to use an unoptimized build (also known as a debug build).
681 ``--enable-debug-runtime``
683 Enables debug symbols in the runtime libraries. The default is to strip debug
684 symbols from the runtime libraries.
688 Compile the Just In Time (JIT) compiler functionality. This is not available
689 on all platforms. The default is dependent on platform, so it is best to
690 explicitly enable it if you want it.
692 ``--enable-targets=target-option``
694 Controls which targets will be built and linked into llc. The default value
695 for ``target_options`` is "all" which builds and links all available targets.
696 The value "host-only" can be specified to build only a native compiler (no
697 cross-compiler targets available). The "native" target is selected as the
698 target of the build host. You can also specify a comma separated list of
699 target names that you want available in llc. The target names use all lower
700 case. The current set of targets is:
702 ``arm, cpp, hexagon, mips, mipsel, msp430, powerpc, ptx, sparc, spu,
703 systemz, x86, x86_64, xcore``.
707 Look for the doxygen program and enable construction of doxygen based
708 documentation from the source code. This is disabled by default because
709 generating the documentation can take a long time and producess 100s of
714 LLVM can use external disassembler library for various purposes (now it's used
715 only for examining code produced by JIT). This option will enable usage of
716 `udis86 <http://udis86.sourceforge.net/>`_ x86 (both 32 and 64 bits)
717 disassembler library.
719 To configure LLVM, follow these steps:
721 #. Change directory into the object root directory:
723 .. code-block:: console
727 #. Run the ``configure`` script located in the LLVM source tree:
729 .. code-block:: console
731 % SRC_ROOT/configure --prefix=/install/path [other options]
733 Compiling the LLVM Suite Source Code
734 ------------------------------------
736 Once you have configured LLVM, you can build it. There are three types of
741 These builds are the default when one is using an Subversion checkout and
742 types ``gmake`` (unless the ``--enable-optimized`` option was used during
743 configuration). The build system will compile the tools and libraries with
744 debugging information. To get a Debug Build using the LLVM distribution the
745 ``--disable-optimized`` option must be passed to ``configure``.
747 Release (Optimized) Builds
749 These builds are enabled with the ``--enable-optimized`` option to
750 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
751 line. For these builds, the build system will compile the tools and libraries
752 with GCC optimizations enabled and strip debugging information from the
753 libraries and executables it generates. Note that Release Builds are default
754 when using an LLVM distribution.
758 These builds are for use with profiling. They compile profiling information
759 into the code for use with programs like ``gprof``. Profile builds must be
760 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
762 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
763 directory and issuing the following command:
765 .. code-block:: console
769 If the build fails, please `check here`_ to see if you are using a version of
770 GCC that is known not to compile LLVM.
772 If you have multiple processors in your machine, you may wish to use some of the
773 parallel build options provided by GNU Make. For example, you could use the
776 .. code-block:: console
780 There are several special targets which are useful when working with the LLVM
785 Removes all files generated by the build. This includes object files,
786 generated C/C++ files, libraries, and executables.
790 Removes everything that ``gmake clean`` does, but also removes files generated
791 by ``configure``. It attempts to return the source tree to the original state
792 in which it was shipped.
796 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
797 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
798 defaults to ``/usr/local``.
800 ``gmake -C runtime install-bytecode``
802 Assuming you built LLVM into $OBJDIR, when this command is run, it will
803 install bitcode libraries into the GCC front end's bitcode library directory.
804 If you need to update your bitcode libraries, this is the target to use once
807 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
808 these ``make`` targets and descriptions of other targets available.
810 It is also possible to override default values from ``configure`` by declaring
811 variables on the command line. The following are some examples:
813 ``gmake ENABLE_OPTIMIZED=1``
815 Perform a Release (Optimized) build.
817 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
819 Perform a Release (Optimized) build without assertions enabled.
821 ``gmake ENABLE_OPTIMIZED=0``
823 Perform a Debug build.
825 ``gmake ENABLE_PROFILING=1``
827 Perform a Profiling build.
831 Print what ``gmake`` is doing on standard output.
833 ``gmake TOOL_VERBOSE=1``
835 Ask each tool invoked by the makefiles to print out what it is doing on
836 the standard output. This also implies ``VERBOSE=1``.
838 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
839 any subdirectories that it contains. Entering any directory inside the LLVM
840 object tree and typing ``gmake`` should rebuild anything in or below that
841 directory that is out of date.
843 This does not apply to building the documentation.
844 LLVM's (non-Doxygen) documentation is produced with the
845 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
846 There are some HTML documents that have not yet been converted to the new
847 system (which uses the easy-to-read and easy-to-write
848 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
850 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
852 For instructions on how to install Sphinx, see
853 `Sphinx Introduction for LLVM Developers
854 <http://lld.llvm.org/sphinx_intro.html>`_.
855 After following the instructions there for installing Sphinx, build the LLVM
856 HTML documentation by doing the following:
858 .. code-block:: console
861 $ make -f Makefile.sphinx
863 This creates a ``_build/html`` sub-directory with all of the HTML files, not
864 just the generated ones.
865 This directory corresponds to ``llvm.org/docs``.
866 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
867 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
868 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
873 It is possible to cross-compile LLVM itself. That is, you can create LLVM
874 executables and libraries to be hosted on a platform different from the platform
875 where they are built (a Canadian Cross build). To configure a cross-compile,
876 supply the configure script with ``--build`` and ``--host`` options that are
877 different. The values of these options must be legal target triples that your
878 GCC compiler supports.
880 The result of such a build is executables that are not runnable on on the build
881 host (--build option) but can be executed on the compile host (--host option).
883 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
884 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
885 about cross-compiling.
887 The Location of LLVM Object Files
888 ---------------------------------
890 The LLVM build system is capable of sharing a single LLVM source tree among
891 several LLVM builds. Hence, it is possible to build LLVM for several different
892 platforms or configurations using the same source tree.
894 This is accomplished in the typical autoconf manner:
896 * Change directory to where the LLVM object files should live:
898 .. code-block:: console
902 * Run the ``configure`` script found in the LLVM source directory:
904 .. code-block:: console
908 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
911 Debug Builds with assertions enabled (the default)
915 ``OBJ_ROOT/Debug+Asserts/bin``
919 ``OBJ_ROOT/Debug+Asserts/lib``
925 ``OBJ_ROOT/Release/bin``
929 ``OBJ_ROOT/Release/lib``
935 ``OBJ_ROOT/Profile/bin``
939 ``OBJ_ROOT/Profile/lib``
941 Optional Configuration Items
942 ----------------------------
944 If you're running on a Linux system that supports the `binfmt_misc
945 <http://en.wikipedia.org/wiki/binfmt_misc>`_
946 module, and you have root access on the system, you can set your system up to
947 execute LLVM bitcode files directly. To do this, use commands like this (the
948 first command may not be required if you are already using the module):
950 .. code-block:: console
952 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
953 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
954 % chmod u+x hello.bc (if needed)
957 This allows you to execute LLVM bitcode files directly. On Debian, you can also
958 use this command instead of the 'echo' command above:
960 .. code-block:: console
962 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
970 One useful source of information about the LLVM source base is the LLVM `doxygen
971 <http://www.doxygen.org/>`_ documentation available at
972 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
978 This directory contains some simple examples of how to use the LLVM IR and JIT.
983 This directory contains public header files exported from the LLVM library. The
984 three main subdirectories of this directory are:
986 ``llvm/include/llvm``
988 This directory contains all of the LLVM specific header files. This directory
989 also has subdirectories for different portions of LLVM: ``Analysis``,
990 ``CodeGen``, ``Target``, ``Transforms``, etc...
992 ``llvm/include/llvm/Support``
994 This directory contains generic support libraries that are provided with LLVM
995 but not necessarily specific to LLVM. For example, some C++ STL utilities and
996 a Command Line option processing library store their header files here.
998 ``llvm/include/llvm/Config``
1000 This directory contains header files configured by the ``configure`` script.
1001 They wrap "standard" UNIX and C header files. Source code can include these
1002 header files which automatically take care of the conditional #includes that
1003 the ``configure`` script generates.
1008 This directory contains most of the source files of the LLVM system. In LLVM,
1009 almost all code exists in libraries, making it very easy to share code among the
1012 ``llvm/lib/VMCore/``
1014 This directory holds the core LLVM source files that implement core classes
1015 like Instruction and BasicBlock.
1017 ``llvm/lib/AsmParser/``
1019 This directory holds the source code for the LLVM assembly language parser
1022 ``llvm/lib/Bitcode/``
1024 This directory holds code for reading and write LLVM bitcode.
1026 ``llvm/lib/Analysis/``
1028 This directory contains a variety of different program analyses, such as
1029 Dominator Information, Call Graphs, Induction Variables, Interval
1030 Identification, Natural Loop Identification, etc.
1032 ``llvm/lib/Transforms/``
1034 This directory contains the source code for the LLVM to LLVM program
1035 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1036 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1037 Elimination, and many others.
1039 ``llvm/lib/Target/``
1041 This directory contains files that describe various target architectures for
1042 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1043 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1046 ``llvm/lib/CodeGen/``
1048 This directory contains the major parts of the code generator: Instruction
1049 Selector, Instruction Scheduling, and Register Allocation.
1055 ``llvm/lib/Debugger/``
1057 This directory contains the source level debugger library that makes it
1058 possible to instrument LLVM programs so that a debugger could identify source
1059 code locations at which the program is executing.
1061 ``llvm/lib/ExecutionEngine/``
1063 This directory contains libraries for executing LLVM bitcode directly at
1064 runtime in both interpreted and JIT compiled fashions.
1066 ``llvm/lib/Support/``
1068 This directory contains the source code that corresponds to the header files
1069 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1074 This directory contains projects that are not strictly part of LLVM but are
1075 shipped with LLVM. This is also the directory where you should create your own
1076 LLVM-based projects. See ``llvm/projects/sample`` for an example of how to set
1077 up your own project.
1082 This directory contains libraries which are compiled into LLVM bitcode and used
1083 when linking programs with the Clang front end. Most of these libraries are
1084 skeleton versions of real libraries; for example, libc is a stripped down
1087 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1093 This directory contains feature and regression tests and other basic sanity
1094 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1095 lot of territory without being exhaustive.
1100 This is not a directory in the normal llvm module; it is a separate Subversion
1101 module that must be checked out (usually to ``projects/test-suite``). This
1102 module contains a comprehensive correctness, performance, and benchmarking test
1103 suite for LLVM. It is a separate Subversion module because not every LLVM user
1104 is interested in downloading or building such a comprehensive test suite. For
1105 further details on this test suite, please see the :doc:`Testing Guide
1106 <TestingGuide>` document.
1113 The **tools** directory contains the executables built out of the libraries
1114 above, which form the main part of the user interface. You can always get help
1115 for a tool by typing ``tool_name -help``. The following is a brief introduction
1116 to the most important tools. More detailed information is in
1117 the `Command Guide <CommandGuide/index.html>`_.
1121 ``bugpoint`` is used to debug optimization passes or code generation backends
1122 by narrowing down the given test case to the minimum number of passes and/or
1123 instructions that still cause a problem, whether it is a crash or
1124 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1129 The archiver produces an archive containing the given LLVM bitcode files,
1130 optionally with an index for faster lookup.
1134 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1138 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1142 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1147 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1148 (although very slowly...). For architectures that support it (currently x86,
1149 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1150 compiler (if the functionality was compiled in), and will execute the code
1151 *much* faster than the interpreter.
1155 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1156 native code assembly file or to C code (with the ``-march=c`` option).
1160 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1161 (which are specified on the command line), and then outputs the resultant
1162 bitcode. The '``opt -help``' command is a good way to get a list of the
1163 program transformations available in LLVM.
1165 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1166 file and print out the results. It is primarily useful for debugging
1167 analyses, or familiarizing yourself with what an analysis does.
1172 This directory contains utilities for working with LLVM source code, and some of
1173 the utilities are actually required as part of the build process because they
1174 are code generators for parts of LLVM infrastructure.
1179 ``codegen-diff`` is a script that finds differences between code that LLC
1180 generates and code that LLI generates. This is a useful tool if you are
1181 debugging one of them, assuming that the other generates correct output. For
1182 the full user manual, run ```perldoc codegen-diff'``.
1186 The ``emacs`` directory contains syntax-highlighting files which will work
1187 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1188 assembly files and TableGen description files. For information on how to use
1189 the syntax files, consult the ``README`` file in that directory.
1193 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1194 which is useful if one wishes to do a lot of development across directories
1195 and does not want to individually find each file. One way to use it is to run,
1196 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1201 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1202 passes to it a regular expression provided on ``llvmgrep``'s command
1203 line. This is a very efficient way of searching the source base for a
1204 particular regular expression.
1208 The ``makellvm`` script compiles all files in the current directory and then
1209 compiles and links the tool that is the first argument. For example, assuming
1210 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1211 path, simply running ``makellvm llc`` will make a build of the current
1212 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1217 The ``TableGen`` directory contains the tool used to generate register
1218 descriptions, instruction set descriptions, and even assemblers from common
1219 TableGen description files.
1223 The ``vim`` directory contains syntax-highlighting files which will work with
1224 the VIM editor, providing syntax highlighting support for LLVM assembly files
1225 and TableGen description files. For information on how to use the syntax
1226 files, consult the ``README`` file in that directory.
1230 An Example Using the LLVM Tool Chain
1231 ====================================
1233 This section gives an example of using LLVM with the Clang front end.
1238 #. First, create a simple C file, name it 'hello.c':
1245 printf("hello world\n");
1249 #. Next, compile the C file into a native executable:
1251 .. code-block:: console
1253 % clang hello.c -o hello
1257 Clang works just like GCC by default. The standard -S and -c arguments
1258 work as usual (producing a native .s or .o file, respectively).
1260 #. Next, compile the C file into an LLVM bitcode file:
1262 .. code-block:: console
1264 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1266 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1267 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1268 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1270 #. Run the program in both forms. To run the program, use:
1272 .. code-block:: console
1278 .. code-block:: console
1282 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1283 <CommandGuide/lli>`.
1285 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1287 .. code-block:: console
1289 % llvm-dis < hello.bc | less
1291 #. Compile the program to native assembly using the LLC code generator:
1293 .. code-block:: console
1295 % llc hello.bc -o hello.s
1297 #. Assemble the native assembly language file into a program:
1299 .. code-block:: console
1301 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1303 % gcc hello.s -o hello.native # On others
1305 #. Execute the native code program:
1307 .. code-block:: console
1311 Note that using clang to compile directly to native code (i.e. when the
1312 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1317 If you are having problems building or using LLVM, or if you have any other
1318 general questions about LLVM, please consult the `Frequently Asked
1319 Questions <FAQ.html>`_ page.
1326 This document is just an **introduction** on how to use LLVM to do some simple
1327 things... there are many more interesting and complicated things that you can do
1328 that aren't documented here (but we'll gladly accept a patch if you want to
1329 write something up!). For more information about LLVM, check out:
1331 * `LLVM Homepage <http://llvm.org/>`_
1332 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1333 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_