1 ====================================
2 Getting Started with the LLVM System
3 ====================================
11 Welcome to LLVM! In order to get started, you first need to know some basic
14 First, LLVM comes in three pieces. The first piece is the LLVM suite. This
15 contains all of the tools, libraries, and header files needed to use LLVM. It
16 contains an assembler, disassembler, bitcode analyzer and bitcode optimizer. It
17 also contains basic regression tests that can be used to test the LLVM tools and
20 The second piece is the `Clang <http://clang.llvm.org/>`_ front end. This
21 component compiles C, C++, Objective C, and Objective C++ code into LLVM
22 bitcode. Once compiled into LLVM bitcode, a program can be manipulated with the
23 LLVM tools from the LLVM suite.
25 There is a third, optional piece called Test Suite. It is a suite of programs
26 with a testing harness that can be used to further test LLVM's functionality
29 Getting Started Quickly (A Summary)
30 ===================================
32 The LLVM Getting Started documentation may be out of date. So, the `Clang
33 Getting Started <http://clang.llvm.org/get_started.html>`_ page might also be a
36 Here's the short story for getting up and running quickly with LLVM:
38 #. Read the documentation.
39 #. Read the documentation.
40 #. Remember that you were warned twice about reading the documentation.
43 * ``cd where-you-want-llvm-to-live``
44 * ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
48 * ``cd where-you-want-llvm-to-live``
50 * ``svn co http://llvm.org/svn/llvm-project/cfe/trunk clang``
52 #. Checkout Compiler-RT:
54 * ``cd where-you-want-llvm-to-live``
55 * ``cd llvm/projects``
56 * ``svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt``
58 #. Get the Test Suite Source Code **[Optional]**
60 * ``cd where-you-want-llvm-to-live``
61 * ``cd llvm/projects``
62 * ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
64 #. Configure and build LLVM and Clang:
66 * ``cd where-you-want-to-build-llvm``
67 * ``mkdir build`` (for building without polluting the source dir)
69 * ``../llvm/configure [options]``
72 * ``--prefix=directory`` --- Specify for *directory* the full pathname of
73 where you want the LLVM tools and libraries to be installed (default
76 * ``--enable-optimized`` --- Compile with optimizations enabled (default
79 * ``--enable-assertions`` --- Compile with assertion checks enabled
82 * ``make [-j]`` --- The ``-j`` specifies the number of jobs (commands) to run
83 simultaneously. This builds both LLVM and Clang for Debug+Asserts mode.
84 The ``--enable-optimized`` configure option is used to specify a Release
87 * ``make check-all`` --- This run the regression tests to ensure everything
90 * It is also possible to use `CMake <CMake.html>`_ instead of the makefiles.
91 With CMake it is possible to generate project files for several IDEs:
92 Xcode, Eclipse CDT4, CodeBlocks, Qt-Creator (use the CodeBlocks
93 generator), KDevelop3.
95 * If you get an "internal compiler error (ICE)" or test failures, see
98 Consult the `Getting Started with LLVM`_ section for detailed information on
99 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
100 that simplify working with the Clang front end and LLVM tools. Go to `Program
101 Layout`_ to learn about the layout of the source code tree.
106 Before you begin to use the LLVM system, review the requirements given below.
107 This may save you some trouble by knowing ahead of time what hardware and
108 software you will need.
113 LLVM is known to work on the following host platforms:
115 ================== ===================== =============
117 ================== ===================== =============
118 AuroraUX x86\ :sup:`1` GCC
119 Linux x86\ :sup:`1` GCC, Clang
120 Linux amd64 GCC, Clang
121 Linux ARM\ :sup:`4` GCC, Clang
122 Linux PowerPC GCC, Clang
123 Solaris V9 (Ultrasparc) GCC
124 FreeBSD x86\ :sup:`1` GCC, Clang
125 FreeBSD amd64 GCC, Clang
126 MacOS X\ :sup:`2` PowerPC GCC
127 MacOS X x86 GCC, Clang
128 Cygwin/Win32 x86\ :sup:`1, 3` GCC
129 Windows x86\ :sup:`1` Visual Studio
130 Windows x64 x86-64 Visual Studio
131 ================== ===================== =============
135 #. Code generation supported for Pentium processors and up
136 #. Code generation supported for 32-bit ABI only
137 #. To use LLVM modules on Win32-based system, you may configure LLVM
138 with ``--enable-shared``.
139 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
141 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
142 mode, depending on the system (it is so large because of all the debugging
143 information and the fact that the libraries are statically linked into multiple
144 tools). If you do not need many of the tools and you are space-conscious, you
145 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
146 considerably less space.
148 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
149 so. If compilation is successful, the LLVM utilities should be able to
150 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
151 should work as well, although the generated native code may not work on your
157 Compiling LLVM requires that you have several software packages installed. The
158 table below lists those required packages. The Package column is the usual name
159 for the software package that LLVM depends on. The Version column provides
160 "known to work" versions of the package. The Notes column describes how LLVM
161 uses the package and provides other details.
163 =========================================================== ============ ==========================================
164 Package Version Notes
165 =========================================================== ============ ==========================================
166 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
167 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
168 `python <http://www.python.org/>`_ >=2.5 Automated test suite\ :sup:`2`
169 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
170 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
171 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
172 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
173 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
174 =========================================================== ============ ==========================================
178 #. Only the C and C++ languages are needed so there's no need to build the
179 other languages for LLVM's purposes. See `below` for specific version
181 #. Only needed if you want to run the automated test suite in the
182 ``llvm/test`` directory.
183 #. If you want to make changes to the configure scripts, you will need GNU
184 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
185 will also need automake (1.9.6). We only use aclocal from that package.
186 #. Optional, adds compression / uncompression capabilities to selected LLVM
189 Additionally, your compilation host is expected to have the usual plethora of
190 Unix utilities. Specifically:
192 * **ar** --- archive library builder
193 * **bzip2** --- bzip2 command for distribution generation
194 * **bunzip2** --- bunzip2 command for distribution checking
195 * **chmod** --- change permissions on a file
196 * **cat** --- output concatenation utility
197 * **cp** --- copy files
198 * **date** --- print the current date/time
199 * **echo** --- print to standard output
200 * **egrep** --- extended regular expression search utility
201 * **find** --- find files/dirs in a file system
202 * **grep** --- regular expression search utility
203 * **gzip** --- gzip command for distribution generation
204 * **gunzip** --- gunzip command for distribution checking
205 * **install** --- install directories/files
206 * **mkdir** --- create a directory
207 * **mv** --- move (rename) files
208 * **ranlib** --- symbol table builder for archive libraries
209 * **rm** --- remove (delete) files and directories
210 * **sed** --- stream editor for transforming output
211 * **sh** --- Bourne shell for make build scripts
212 * **tar** --- tape archive for distribution generation
213 * **test** --- test things in file system
214 * **unzip** --- unzip command for distribution checking
215 * **zip** --- zip command for distribution generation
220 Host C++ Toolchain, both Compiler and Standard Library
221 ------------------------------------------------------
223 LLVM is very demanding of the host C++ compiler, and as such tends to expose
224 bugs in the compiler. We are also planning to follow improvements and
225 developments in the C++ language and library reasonably closely. As such, we
226 require a modern host C++ toolchain, both compiler and standard library, in
229 For the most popular host toolchains we check for specific minimum versions in
236 Anything older than these toolchains *may* work, but will require forcing the
237 build system with a special option and is not really a supported host platform.
238 Also note that older versions of these compilers have often crashed or
241 For less widely used host toolchains such as ICC or xlC, be aware that a very
242 recent version may be required to support all of the C++ features used in LLVM.
244 We track certain versions of software that are *known* to fail when used as
245 part of the host toolchain. These even include linkers at times.
247 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
248 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
250 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
251 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
252 defined in a discarded section. You can safely ignore these messages as they are
253 erroneous and the linkage is correct. These messages disappear using ld 2.17.
255 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
256 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
257 times (minutes instead of seconds) when building LLVM. We recommend upgrading
258 to a newer version (2.17.50.0.4 or later).
260 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
261 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
262 intermittent failures when building LLVM with position independent code. The
263 symptom is an error about cyclic dependencies. We recommend upgrading to a
264 newer version of Gold.
266 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
267 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
268 3.0 does not implement a few builtins that are used in this library. We
269 recommend using the system GCC to compile LLVM and Clang in this case.
271 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
272 least some (``cxxabi.h``) libstdc++ headers.
274 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
275 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
276 causes Clang to refuse to compile condition_variable header file. At the time
277 of writing, this breaks LLD build.
279 Getting a Modern Host C++ Toolchain
280 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
282 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
283 have a sufficiently modern Xcode, or you will likely need to upgrade until you
284 do. On Windows, just use Visual Studio 2012 as the host compiler, it is
285 explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
286 Clang as the system compiler.
288 However, some Linux distributions and some other or older BSDs sometimes have
289 extremely old versions of GCC. These steps attempt to help you upgrade you
290 compiler even on such a system. However, if at all possible, we encourage you
291 to use a recent version of a distribution with a modern system compiler that
292 meets these requirements. Note that it is tempting to to install a prior
293 version of Clang and libc++ to be the host compiler, however libc++ was not
294 well tested or set up to build on Linux until relatively recently. As
295 a consequence, this guide suggests just using libstdc++ and a modern GCC as the
296 initial host in a bootstrap, and then using Clang (and potentially libc++).
298 The first step is to get a recent GCC toolchain installed. The most common
299 distribution on which users have struggled with the version requirements is
300 Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is to install
301 the `toolchain testing PPA`_ and use it to install a modern GCC. There is
302 a really nice discussions of this on the `ask ubuntu stack exchange`_. However,
303 not all users can use PPAs and there are many other distributions, so it may be
304 necessary (or just useful, if you're here you *are* doing compiler development
305 after all) to build and install GCC from source. It is also quite easy to do
308 .. _toolchain testing PPA:
309 https://launchpad.net/~ubuntu-toolchain-r/+archive/test
310 .. _ask ubuntu stack exchange:
311 http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal
313 Easy steps for installing GCC 4.8.2:
315 .. code-block:: console
317 % wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
318 % tar -xvjf gcc-4.8.2.tar.bz2
320 % ./contrib/download_prerequisites
322 % mkdir gcc-4.8.2-build
324 % $PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains --enable-languages=c,c++
328 For more details, check out the excellent `GCC wiki entry`_, where I got most
329 of this information from.
332 http://gcc.gnu.org/wiki/InstallingGCC
334 Once you have a GCC toolchain, use it as your host compiler. Things should
335 generally "just work". You may need to pass a special linker flag,
336 ``-Wl,-rpath,$HOME/toolchains/lib`` or some variant thereof to get things to
337 find the libstdc++ DSO in this toolchain.
339 When you build Clang, you will need to give *it* access to modern C++11
340 standard library in order to use it as your new host in part of a bootstrap.
341 There are two easy ways to do this, either build (and install) libc++ along
342 with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,
343 or install Clang into the same prefix (``$HOME/toolchains`` above) as GCC.
344 Clang will look within its own prefix for libstdc++ and use it if found. You
345 can also add an explicit prefix for Clang to look in for a GCC toolchain with
346 the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both compile and
347 link commands when using your just-built-Clang to bootstrap.
349 .. _Getting Started with LLVM:
351 Getting Started with LLVM
352 =========================
354 The remainder of this guide is meant to get you up and running with LLVM and to
355 give you some basic information about the LLVM environment.
357 The later sections of this guide describe the `general layout`_ of the LLVM
358 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
359 more information about LLVM or to get help via e-mail.
361 Terminology and Notation
362 ------------------------
364 Throughout this manual, the following names are used to denote paths specific to
365 the local system and working environment. *These are not environment variables
366 you need to set but just strings used in the rest of this document below*. In
367 any of the examples below, simply replace each of these names with the
368 appropriate pathname on your local system. All these paths are absolute:
372 This is the top level directory of the LLVM source tree.
376 This is the top level directory of the LLVM object tree (i.e. the tree where
377 object files and compiled programs will be placed. It can be the same as
380 .. _Setting Up Your Environment:
382 Setting Up Your Environment
383 ---------------------------
385 In order to compile and use LLVM, you may need to set some environment
388 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
390 [Optional] This environment variable helps LLVM linking tools find the
391 locations of your bitcode libraries. It is provided only as a convenience
392 since you can specify the paths using the -L options of the tools and the
393 C/C++ front-end will automatically use the bitcode files installed in its
396 Unpacking the LLVM Archives
397 ---------------------------
399 If you have the LLVM distribution, you will need to unpack it before you can
400 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
401 and the LLVM GCC front end compiled for your platform. There is an additional
402 test suite that is optional. Each file is a TAR archive that is compressed with
405 The files are as follows, with *x.y* marking the version number:
409 Source release for the LLVM libraries and tools.
411 ``llvm-test-x.y.tar.gz``
413 Source release for the LLVM test-suite.
417 Checkout LLVM from Subversion
418 -----------------------------
420 If you have access to our Subversion repository, you can get a fresh copy of the
421 entire source code. All you need to do is check it out from Subversion as
424 * ``cd where-you-want-llvm-to-live``
425 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
426 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
428 This will create an '``llvm``' directory in the current directory and fully
429 populate it with the LLVM source code, Makefiles, test directories, and local
430 copies of documentation files.
432 If you want to get a specific release (as opposed to the most recent revision),
433 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
434 following releases are located in the following subdirectories of the '``tags``'
437 * Release 3.4: **RELEASE_34/final**
438 * Release 3.3: **RELEASE_33/final**
439 * Release 3.2: **RELEASE_32/final**
440 * Release 3.1: **RELEASE_31/final**
441 * Release 3.0: **RELEASE_30/final**
442 * Release 2.9: **RELEASE_29/final**
443 * Release 2.8: **RELEASE_28**
444 * Release 2.7: **RELEASE_27**
445 * Release 2.6: **RELEASE_26**
446 * Release 2.5: **RELEASE_25**
447 * Release 2.4: **RELEASE_24**
448 * Release 2.3: **RELEASE_23**
449 * Release 2.2: **RELEASE_22**
450 * Release 2.1: **RELEASE_21**
451 * Release 2.0: **RELEASE_20**
452 * Release 1.9: **RELEASE_19**
453 * Release 1.8: **RELEASE_18**
454 * Release 1.7: **RELEASE_17**
455 * Release 1.6: **RELEASE_16**
456 * Release 1.5: **RELEASE_15**
457 * Release 1.4: **RELEASE_14**
458 * Release 1.3: **RELEASE_13**
459 * Release 1.2: **RELEASE_12**
460 * Release 1.1: **RELEASE_11**
461 * Release 1.0: **RELEASE_1**
463 If you would like to get the LLVM test suite (a separate package as of 1.4), you
464 get it from the Subversion repository:
466 .. code-block:: console
469 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
471 By placing it in the ``llvm/projects``, it will be automatically configured by
472 the LLVM configure script as well as automatically updated when you run ``svn
478 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
479 automatically with each Subversion commit and contain all necessary git-svn
480 marks (so, you can recreate git-svn metadata locally). Note that right now
481 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
484 .. code-block:: console
486 % git clone http://llvm.org/git/llvm.git
488 If you want to check out clang too, run:
490 .. code-block:: console
493 % git clone http://llvm.org/git/clang.git
495 If you want to check out compiler-rt too, run:
497 .. code-block:: console
500 % git clone http://llvm.org/git/compiler-rt.git
502 If you want to check out the Test Suite Source Code (optional), run:
504 .. code-block:: console
507 % git clone http://llvm.org/git/test-suite.git
509 Since the upstream repository is in Subversion, you should use ``git
510 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
511 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
512 master branch, run the following command:
514 .. code-block:: console
516 % git config branch.master.rebase true
518 Sending patches with Git
519 ^^^^^^^^^^^^^^^^^^^^^^^^
521 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
523 Assume ``master`` points the upstream and ``mybranch`` points your working
524 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
525 sanity of whitespaces:
527 .. code-block:: console
529 % git diff --check master..mybranch
531 The easiest way to generate a patch is as below:
533 .. code-block:: console
535 % git diff master..mybranch > /path/to/mybranch.diff
537 It is a little different from svn-generated diff. git-diff-generated diff has
538 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
539 could be accepted with ``patch -p1 -N``.
541 But you may generate patchset with git-format-patch. It generates by-each-commit
542 patchset. To generate patch files to attach to your article:
544 .. code-block:: console
546 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
548 If you would like to send patches directly, you may use git-send-email or
549 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
551 .. code-block:: console
553 % git format-patch --attach master..mybranch --stdout | git imap-send
555 Then, your .git/config should have [imap] sections.
560 host = imaps://imap.gmail.com
561 user = your.gmail.account@gmail.com
566 folder = "[Gmail]/Drafts"
567 ; example for Japanese, "Modified UTF-7" encoded.
568 folder = "[Gmail]/&Tgtm+DBN-"
569 ; example for Traditional Chinese
570 folder = "[Gmail]/&g0l6Pw-"
572 For developers to work with git-svn
573 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
575 To set up clone from which you can submit code using ``git-svn``, run:
577 .. code-block:: console
579 % git clone http://llvm.org/git/llvm.git
581 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
582 % git config svn-remote.svn.fetch :refs/remotes/origin/master
583 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
585 # If you have clang too:
587 % git clone http://llvm.org/git/clang.git
589 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
590 % git config svn-remote.svn.fetch :refs/remotes/origin/master
593 Likewise for compiler-rt and test-suite.
595 To update this clone without generating git-svn tags that conflict with the
596 upstream Git repo, run:
598 .. code-block:: console
600 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
601 % git checkout master
604 git checkout master &&
607 Likewise for compiler-rt and test-suite.
609 This leaves your working directories on their master branches, so you'll need to
610 ``checkout`` each working branch individually and ``rebase`` it on top of its
613 For those who wish to be able to update an llvm repo/revert patches easily using
614 git-svn, please look in the directory for the scripts ``git-svnup`` and
617 To perform the aforementioned update steps go into your source directory and
618 just type ``git-svnup`` or ``git svnup`` and everything will just work.
620 If one wishes to revert a commit with git-svn, but do not want the git hash to
621 escape into the commit message, one can use the script ``git-svnrevert`` or
622 ``git svnrevert`` which will take in the git hash for the commit you want to
623 revert, look up the appropriate svn revision, and output a message where all
624 references to the git hash have been replaced with the svn revision.
626 To commit back changes via git-svn, use ``git svn dcommit``:
628 .. code-block:: console
632 Note that git-svn will create one SVN commit for each Git commit you have pending,
633 so squash and edit each commit before executing ``dcommit`` to make sure they all
634 conform to the coding standards and the developers' policy.
636 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
637 please make sure your current branch is up-to-date (via fetch/rebase) before
640 The git-svn metadata can get out of sync after you mess around with branches and
641 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
642 about files with uncommitted changes. The fix is to rebuild the metadata:
644 .. code-block:: console
649 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
651 Local LLVM Configuration
652 ------------------------
654 Once checked out from the Subversion repository, the LLVM suite source code must
655 be configured via the ``configure`` script. This script sets variables in the
656 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
657 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
658 Makefiles needed to begin building LLVM.
660 The following environment variables are used by the ``configure`` script to
661 configure the build system:
663 +------------+-----------------------------------------------------------+
664 | Variable | Purpose |
665 +============+===========================================================+
666 | CC | Tells ``configure`` which C compiler to use. By default, |
667 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
668 | | compilers (in this order). Use this variable to override |
669 | | ``configure``\'s default behavior. |
670 +------------+-----------------------------------------------------------+
671 | CXX | Tells ``configure`` which C++ compiler to use. By |
672 | | default, ``configure`` will check ``PATH`` for |
673 | | ``clang++`` and GCC C++ compilers (in this order). Use |
674 | | this variable to override ``configure``'s default |
676 +------------+-----------------------------------------------------------+
678 The following options can be used to set or enable LLVM specific options:
680 ``--enable-optimized``
682 Enables optimized compilation (debugging symbols are removed and GCC
683 optimization flags are enabled). Note that this is the default setting if you
684 are using the LLVM distribution. The default behavior of a Subversion
685 checkout is to use an unoptimized build (also known as a debug build).
687 ``--enable-debug-runtime``
689 Enables debug symbols in the runtime libraries. The default is to strip debug
690 symbols from the runtime libraries.
694 Compile the Just In Time (JIT) compiler functionality. This is not available
695 on all platforms. The default is dependent on platform, so it is best to
696 explicitly enable it if you want it.
698 ``--enable-targets=target-option``
700 Controls which targets will be built and linked into llc. The default value
701 for ``target_options`` is "all" which builds and links all available targets.
702 The "host" target is selected as the target of the build host. You can also
703 specify a comma separated list of target names that you want available in llc.
704 The target names use all lower case. The current set of targets is:
706 ``aarch64, arm, arm64, cpp, hexagon, mips, mipsel, mips64, mips64el, msp430,
707 powerpc, nvptx, r600, sparc, systemz, x86, x86_64, xcore``.
711 Look for the doxygen program and enable construction of doxygen based
712 documentation from the source code. This is disabled by default because
713 generating the documentation can take a long time and producess 100s of
716 To configure LLVM, follow these steps:
718 #. Change directory into the object root directory:
720 .. code-block:: console
724 #. Run the ``configure`` script located in the LLVM source tree:
726 .. code-block:: console
728 % SRC_ROOT/configure --prefix=/install/path [other options]
730 Compiling the LLVM Suite Source Code
731 ------------------------------------
733 Once you have configured LLVM, you can build it. There are three types of
738 These builds are the default when one is using a Subversion checkout and
739 types ``gmake`` (unless the ``--enable-optimized`` option was used during
740 configuration). The build system will compile the tools and libraries with
741 debugging information. To get a Debug Build using the LLVM distribution the
742 ``--disable-optimized`` option must be passed to ``configure``.
744 Release (Optimized) Builds
746 These builds are enabled with the ``--enable-optimized`` option to
747 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
748 line. For these builds, the build system will compile the tools and libraries
749 with GCC optimizations enabled and strip debugging information from the
750 libraries and executables it generates. Note that Release Builds are default
751 when using an LLVM distribution.
755 These builds are for use with profiling. They compile profiling information
756 into the code for use with programs like ``gprof``. Profile builds must be
757 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
759 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
760 directory and issuing the following command:
762 .. code-block:: console
766 If the build fails, please `check here`_ to see if you are using a version of
767 GCC that is known not to compile LLVM.
769 If you have multiple processors in your machine, you may wish to use some of the
770 parallel build options provided by GNU Make. For example, you could use the
773 .. code-block:: console
777 There are several special targets which are useful when working with the LLVM
782 Removes all files generated by the build. This includes object files,
783 generated C/C++ files, libraries, and executables.
787 Removes everything that ``gmake clean`` does, but also removes files generated
788 by ``configure``. It attempts to return the source tree to the original state
789 in which it was shipped.
793 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
794 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
795 defaults to ``/usr/local``.
797 ``gmake -C runtime install-bytecode``
799 Assuming you built LLVM into $OBJDIR, when this command is run, it will
800 install bitcode libraries into the GCC front end's bitcode library directory.
801 If you need to update your bitcode libraries, this is the target to use once
804 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
805 these ``make`` targets and descriptions of other targets available.
807 It is also possible to override default values from ``configure`` by declaring
808 variables on the command line. The following are some examples:
810 ``gmake ENABLE_OPTIMIZED=1``
812 Perform a Release (Optimized) build.
814 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
816 Perform a Release (Optimized) build without assertions enabled.
818 ``gmake ENABLE_OPTIMIZED=0``
820 Perform a Debug build.
822 ``gmake ENABLE_PROFILING=1``
824 Perform a Profiling build.
828 Print what ``gmake`` is doing on standard output.
830 ``gmake TOOL_VERBOSE=1``
832 Ask each tool invoked by the makefiles to print out what it is doing on
833 the standard output. This also implies ``VERBOSE=1``.
835 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
836 any subdirectories that it contains. Entering any directory inside the LLVM
837 object tree and typing ``gmake`` should rebuild anything in or below that
838 directory that is out of date.
840 This does not apply to building the documentation.
841 LLVM's (non-Doxygen) documentation is produced with the
842 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
843 There are some HTML documents that have not yet been converted to the new
844 system (which uses the easy-to-read and easy-to-write
845 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
847 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
849 For instructions on how to install Sphinx, see
850 `Sphinx Introduction for LLVM Developers
851 <http://lld.llvm.org/sphinx_intro.html>`_.
852 After following the instructions there for installing Sphinx, build the LLVM
853 HTML documentation by doing the following:
855 .. code-block:: console
858 $ make -f Makefile.sphinx
860 This creates a ``_build/html`` sub-directory with all of the HTML files, not
861 just the generated ones.
862 This directory corresponds to ``llvm.org/docs``.
863 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
864 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
865 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
870 It is possible to cross-compile LLVM itself. That is, you can create LLVM
871 executables and libraries to be hosted on a platform different from the platform
872 where they are built (a Canadian Cross build). To configure a cross-compile,
873 supply the configure script with ``--build`` and ``--host`` options that are
874 different. The values of these options must be legal target triples that your
875 GCC compiler supports.
877 The result of such a build is executables that are not runnable on on the build
878 host (--build option) but can be executed on the compile host (--host option).
880 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
881 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
882 about cross-compiling.
884 The Location of LLVM Object Files
885 ---------------------------------
887 The LLVM build system is capable of sharing a single LLVM source tree among
888 several LLVM builds. Hence, it is possible to build LLVM for several different
889 platforms or configurations using the same source tree.
891 This is accomplished in the typical autoconf manner:
893 * Change directory to where the LLVM object files should live:
895 .. code-block:: console
899 * Run the ``configure`` script found in the LLVM source directory:
901 .. code-block:: console
905 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
908 Debug Builds with assertions enabled (the default)
912 ``OBJ_ROOT/Debug+Asserts/bin``
916 ``OBJ_ROOT/Debug+Asserts/lib``
922 ``OBJ_ROOT/Release/bin``
926 ``OBJ_ROOT/Release/lib``
932 ``OBJ_ROOT/Profile/bin``
936 ``OBJ_ROOT/Profile/lib``
938 Optional Configuration Items
939 ----------------------------
941 If you're running on a Linux system that supports the `binfmt_misc
942 <http://en.wikipedia.org/wiki/binfmt_misc>`_
943 module, and you have root access on the system, you can set your system up to
944 execute LLVM bitcode files directly. To do this, use commands like this (the
945 first command may not be required if you are already using the module):
947 .. code-block:: console
949 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
950 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
951 % chmod u+x hello.bc (if needed)
954 This allows you to execute LLVM bitcode files directly. On Debian, you can also
955 use this command instead of the 'echo' command above:
957 .. code-block:: console
959 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
967 One useful source of information about the LLVM source base is the LLVM `doxygen
968 <http://www.doxygen.org/>`_ documentation available at
969 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
975 This directory contains some simple examples of how to use the LLVM IR and JIT.
980 This directory contains public header files exported from the LLVM library. The
981 three main subdirectories of this directory are:
983 ``llvm/include/llvm``
985 This directory contains all of the LLVM specific header files. This directory
986 also has subdirectories for different portions of LLVM: ``Analysis``,
987 ``CodeGen``, ``Target``, ``Transforms``, etc...
989 ``llvm/include/llvm/Support``
991 This directory contains generic support libraries that are provided with LLVM
992 but not necessarily specific to LLVM. For example, some C++ STL utilities and
993 a Command Line option processing library store their header files here.
995 ``llvm/include/llvm/Config``
997 This directory contains header files configured by the ``configure`` script.
998 They wrap "standard" UNIX and C header files. Source code can include these
999 header files which automatically take care of the conditional #includes that
1000 the ``configure`` script generates.
1005 This directory contains most of the source files of the LLVM system. In LLVM,
1006 almost all code exists in libraries, making it very easy to share code among the
1009 ``llvm/lib/VMCore/``
1011 This directory holds the core LLVM source files that implement core classes
1012 like Instruction and BasicBlock.
1014 ``llvm/lib/AsmParser/``
1016 This directory holds the source code for the LLVM assembly language parser
1019 ``llvm/lib/Bitcode/``
1021 This directory holds code for reading and write LLVM bitcode.
1023 ``llvm/lib/Analysis/``
1025 This directory contains a variety of different program analyses, such as
1026 Dominator Information, Call Graphs, Induction Variables, Interval
1027 Identification, Natural Loop Identification, etc.
1029 ``llvm/lib/Transforms/``
1031 This directory contains the source code for the LLVM to LLVM program
1032 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1033 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1034 Elimination, and many others.
1036 ``llvm/lib/Target/``
1038 This directory contains files that describe various target architectures for
1039 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1040 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1043 ``llvm/lib/CodeGen/``
1045 This directory contains the major parts of the code generator: Instruction
1046 Selector, Instruction Scheduling, and Register Allocation.
1052 ``llvm/lib/Debugger/``
1054 This directory contains the source level debugger library that makes it
1055 possible to instrument LLVM programs so that a debugger could identify source
1056 code locations at which the program is executing.
1058 ``llvm/lib/ExecutionEngine/``
1060 This directory contains libraries for executing LLVM bitcode directly at
1061 runtime in both interpreted and JIT compiled fashions.
1063 ``llvm/lib/Support/``
1065 This directory contains the source code that corresponds to the header files
1066 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1071 This directory contains projects that are not strictly part of LLVM but are
1072 shipped with LLVM. This is also the directory where you should create your own
1073 LLVM-based projects.
1078 This directory contains libraries which are compiled into LLVM bitcode and used
1079 when linking programs with the Clang front end. Most of these libraries are
1080 skeleton versions of real libraries; for example, libc is a stripped down
1083 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1089 This directory contains feature and regression tests and other basic sanity
1090 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1091 lot of territory without being exhaustive.
1096 This is not a directory in the normal llvm module; it is a separate Subversion
1097 module that must be checked out (usually to ``projects/test-suite``). This
1098 module contains a comprehensive correctness, performance, and benchmarking test
1099 suite for LLVM. It is a separate Subversion module because not every LLVM user
1100 is interested in downloading or building such a comprehensive test suite. For
1101 further details on this test suite, please see the :doc:`Testing Guide
1102 <TestingGuide>` document.
1109 The **tools** directory contains the executables built out of the libraries
1110 above, which form the main part of the user interface. You can always get help
1111 for a tool by typing ``tool_name -help``. The following is a brief introduction
1112 to the most important tools. More detailed information is in
1113 the `Command Guide <CommandGuide/index.html>`_.
1117 ``bugpoint`` is used to debug optimization passes or code generation backends
1118 by narrowing down the given test case to the minimum number of passes and/or
1119 instructions that still cause a problem, whether it is a crash or
1120 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1125 The archiver produces an archive containing the given LLVM bitcode files,
1126 optionally with an index for faster lookup.
1130 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1134 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1138 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1143 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1144 (although very slowly...). For architectures that support it (currently x86,
1145 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1146 compiler (if the functionality was compiled in), and will execute the code
1147 *much* faster than the interpreter.
1151 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1152 native code assembly file or to C code (with the ``-march=c`` option).
1156 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1157 (which are specified on the command line), and then outputs the resultant
1158 bitcode. The '``opt -help``' command is a good way to get a list of the
1159 program transformations available in LLVM.
1161 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1162 file and print out the results. It is primarily useful for debugging
1163 analyses, or familiarizing yourself with what an analysis does.
1168 This directory contains utilities for working with LLVM source code, and some of
1169 the utilities are actually required as part of the build process because they
1170 are code generators for parts of LLVM infrastructure.
1175 ``codegen-diff`` is a script that finds differences between code that LLC
1176 generates and code that LLI generates. This is a useful tool if you are
1177 debugging one of them, assuming that the other generates correct output. For
1178 the full user manual, run ```perldoc codegen-diff'``.
1182 The ``emacs`` directory contains syntax-highlighting files which will work
1183 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1184 assembly files and TableGen description files. For information on how to use
1185 the syntax files, consult the ``README`` file in that directory.
1189 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1190 which is useful if one wishes to do a lot of development across directories
1191 and does not want to individually find each file. One way to use it is to run,
1192 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1197 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1198 passes to it a regular expression provided on ``llvmgrep``'s command
1199 line. This is a very efficient way of searching the source base for a
1200 particular regular expression.
1204 The ``makellvm`` script compiles all files in the current directory and then
1205 compiles and links the tool that is the first argument. For example, assuming
1206 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1207 path, simply running ``makellvm llc`` will make a build of the current
1208 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1213 The ``TableGen`` directory contains the tool used to generate register
1214 descriptions, instruction set descriptions, and even assemblers from common
1215 TableGen description files.
1219 The ``vim`` directory contains syntax-highlighting files which will work with
1220 the VIM editor, providing syntax highlighting support for LLVM assembly files
1221 and TableGen description files. For information on how to use the syntax
1222 files, consult the ``README`` file in that directory.
1226 An Example Using the LLVM Tool Chain
1227 ====================================
1229 This section gives an example of using LLVM with the Clang front end.
1234 #. First, create a simple C file, name it 'hello.c':
1241 printf("hello world\n");
1245 #. Next, compile the C file into a native executable:
1247 .. code-block:: console
1249 % clang hello.c -o hello
1253 Clang works just like GCC by default. The standard -S and -c arguments
1254 work as usual (producing a native .s or .o file, respectively).
1256 #. Next, compile the C file into an LLVM bitcode file:
1258 .. code-block:: console
1260 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1262 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1263 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1264 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1266 #. Run the program in both forms. To run the program, use:
1268 .. code-block:: console
1274 .. code-block:: console
1278 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1279 <CommandGuide/lli>`.
1281 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1283 .. code-block:: console
1285 % llvm-dis < hello.bc | less
1287 #. Compile the program to native assembly using the LLC code generator:
1289 .. code-block:: console
1291 % llc hello.bc -o hello.s
1293 #. Assemble the native assembly language file into a program:
1295 .. code-block:: console
1297 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1299 % gcc hello.s -o hello.native # On others
1301 #. Execute the native code program:
1303 .. code-block:: console
1307 Note that using clang to compile directly to native code (i.e. when the
1308 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1313 If you are having problems building or using LLVM, or if you have any other
1314 general questions about LLVM, please consult the `Frequently Asked
1315 Questions <FAQ.html>`_ page.
1322 This document is just an **introduction** on how to use LLVM to do some simple
1323 things... there are many more interesting and complicated things that you can do
1324 that aren't documented here (but we'll gladly accept a patch if you want to
1325 write something up!). For more information about LLVM, check out:
1327 * `LLVM Homepage <http://llvm.org/>`_
1328 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1329 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_