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32 The LLVM Getting Started documentation may be out of date.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 * ``make update`` --- This command is used to update all the svn repositories
91 at once, rather then having to ``cd`` into the individual repositories and
92 running ``svn update``.
94 * It is also possible to use CMake instead of the makefiles. With CMake it is
95 possible to generate project files for several IDEs: Xcode, Eclipse CDT4,
96 CodeBlocks, Qt-Creator (use the CodeBlocks generator), KDevelop3.
98 * If you get an "internal compiler error (ICE)" or test failures, see
101 Consult the `Getting Started with LLVM`_ section for detailed information on
102 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
103 that simplify working with the Clang front end and LLVM tools. Go to `Program
104 Layout`_ to learn about the layout of the source code tree.
109 Before you begin to use the LLVM system, review the requirements given below.
110 This may save you some trouble by knowing ahead of time what hardware and
111 software you will need.
116 LLVM is known to work on the following host platforms:
118 +-----------------+----------------------+-------------------------+
119 |OS | Arch | Compilers |
120 +=================+======================+=========================+
121 |AuroraUX | x86\ :sup:`1` | GCC |
122 +-----------------+----------------------+-------------------------+
123 |Linux | x86\ :sup:`1` | GCC, Clang |
124 +-----------------+----------------------+-------------------------+
125 |Linux | amd64 | GCC, Clang |
126 +-----------------+----------------------+-------------------------+
127 |Linux | ARM\ :sup:`4` | GCC, Clang |
128 +-----------------+----------------------+-------------------------+
129 |Linux | PowerPC | GCC, Clang |
130 +-----------------+----------------------+-------------------------+
131 |Solaris | V9 (Ultrasparc) | GCC |
132 +-----------------+----------------------+-------------------------+
133 |FreeBSD | x86\ :sup:`1` | GCC, Clang |
134 +-----------------+----------------------+-------------------------+
135 |FreeBSD | amd64 | GCC, Clang |
136 +-----------------+----------------------+-------------------------+
137 |MacOS X\ :sup:`2`| PowerPC | GCC |
138 +-----------------+----------------------+-------------------------+
139 |MacOS X | x86 | GCC, Clang |
140 +-----------------+----------------------+-------------------------+
141 |Cygwin/Win32 | x86\ :sup:`1, 3` | GCC |
142 +-----------------+----------------------+-------------------------+
143 |Windows | x86\ :sup:`1` | Visual Studio |
144 +-----------------+----------------------+-------------------------+
145 |Windows x64 | x86-64 | Visual Studio |
146 +-----------------+----------------------+-------------------------+
150 #. Code generation supported for Pentium processors and up
151 #. Code generation supported for 32-bit ABI only
152 #. To use LLVM modules on Win32-based system, you may configure LLVM
153 with ``--enable-shared``.
154 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
156 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
157 mode, depending on the system (it is so large because of all the debugging
158 information and the fact that the libraries are statically linked into multiple
159 tools). If you do not need many of the tools and you are space-conscious, you
160 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
161 considerably less space.
163 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
164 so. If compilation is successful, the LLVM utilities should be able to
165 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
166 should work as well, although the generated native code may not work on your
172 Compiling LLVM requires that you have several software packages installed. The
173 table below lists those required packages. The Package column is the usual name
174 for the software package that LLVM depends on. The Version column provides
175 "known to work" versions of the package. The Notes column describes how LLVM
176 uses the package and provides other details.
178 +--------------------------------------------------------------+-----------------+---------------------------------------------+
179 | Package | Version | Notes |
180 +==============================================================+=================+=============================================+
181 | `GNU Make <http://savannah.gnu.org/projects/make>`_ | 3.79, 3.79.1 | Makefile/build processor |
182 +--------------------------------------------------------------+-----------------+---------------------------------------------+
183 | `GCC <http://gcc.gnu.org/>`_ | 3.4.2 | C/C++ compiler\ :sup:`1` |
184 +--------------------------------------------------------------+-----------------+---------------------------------------------+
185 | `TeXinfo <http://www.gnu.org/software/texinfo/>`_ | 4.5 | For building the CFE |
186 +--------------------------------------------------------------+-----------------+---------------------------------------------+
187 | `SVN <http://subversion.tigris.org/project_packages.html>`_ | >=1.3 | Subversion access to LLVM\ :sup:`2` |
188 +--------------------------------------------------------------+-----------------+---------------------------------------------+
189 | `python <http://www.python.org/>`_ | >=2.5 | Automated test suite\ :sup:`3` |
190 +--------------------------------------------------------------+-----------------+---------------------------------------------+
191 | `GNU M4 <http://savannah.gnu.org/projects/m4>`_ | 1.4 | Macro processor for configuration\ :sup:`4` |
192 +--------------------------------------------------------------+-----------------+---------------------------------------------+
193 | `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ | 2.60 | Configuration script builder\ :sup:`4` |
194 +--------------------------------------------------------------+-----------------+---------------------------------------------+
195 | `GNU Automake <http://www.gnu.org/software/automake/>`_ | 1.9.6 | aclocal macro generator\ :sup:`4` |
196 +--------------------------------------------------------------+-----------------+---------------------------------------------+
197 | `libtool <http://savannah.gnu.org/projects/libtool>`_ | 1.5.22 | Shared library manager\ :sup:`4` |
198 +--------------------------------------------------------------+-----------------+---------------------------------------------+
199 | `zlib <http://zlib.net>`_ | >=1.2.3.4 | Compression library\ :sup:`5` |
200 +--------------------------------------------------------------+-----------------+---------------------------------------------+
204 #. Only the C and C++ languages are needed so there's no need to build the
205 other languages for LLVM's purposes. See `below` for specific version
207 #. You only need Subversion if you intend to build from the latest LLVM
208 sources. If you're working from a release distribution, you don't need
210 #. Only needed if you want to run the automated test suite in the
211 ``llvm/test`` directory.
212 #. If you want to make changes to the configure scripts, you will need GNU
213 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
214 will also need automake (1.9.6). We only use aclocal from that package.
215 #. Optional, adds compression/uncompression capabilities to selected LLVM
218 Additionally, your compilation host is expected to have the usual plethora of
219 Unix utilities. Specifically:
221 * **ar** --- archive library builder
222 * **bzip2** --- bzip2 command for distribution generation
223 * **bunzip2** --- bunzip2 command for distribution checking
224 * **chmod** --- change permissions on a file
225 * **cat** --- output concatenation utility
226 * **cp** --- copy files
227 * **date** --- print the current date/time
228 * **echo** --- print to standard output
229 * **egrep** --- extended regular expression search utility
230 * **find** --- find files/dirs in a file system
231 * **grep** --- regular expression search utility
232 * **gzip** --- gzip command for distribution generation
233 * **gunzip** --- gunzip command for distribution checking
234 * **install** --- install directories/files
235 * **mkdir** --- create a directory
236 * **mv** --- move (rename) files
237 * **ranlib** --- symbol table builder for archive libraries
238 * **rm** --- remove (delete) files and directories
239 * **sed** --- stream editor for transforming output
240 * **sh** --- Bourne shell for make build scripts
241 * **tar** --- tape archive for distribution generation
242 * **test** --- test things in file system
243 * **unzip** --- unzip command for distribution checking
244 * **zip** --- zip command for distribution generation
249 Broken versions of GCC and other tools
250 --------------------------------------
252 LLVM is very demanding of the host C++ compiler, and as such tends to expose
253 bugs in the compiler. In particular, several versions of GCC crash when trying
254 to compile LLVM. We routinely use GCC 4.2 (and higher) or Clang. Other
255 versions of GCC will probably work as well. GCC versions listed here are known
256 to not work. If you are using one of these versions, please try to upgrade your
257 GCC to something more recent. If you run into a problem with a version of GCC
258 not listed here, please `let us know <mailto:llvmdev@cs.uiuc.edu>`_. Please use
259 the "``gcc -v``" command to find out which version of GCC you are using.
261 **GCC versions prior to 3.0**: GCC 2.96.x and before had several problems in the
262 STL that effectively prevent it from compiling LLVM.
264 **GCC 3.2.2 and 3.2.3**: These versions of GCC fails to compile LLVM with a
265 bogus template error. This was fixed in later GCCs.
267 **GCC 3.3.2**: This version of GCC suffered from a `serious bug
268 <http://gcc.gnu.org/PR13392>`_ which causes it to crash in the
269 "``convert_from_eh_region_ranges_1``" GCC function.
271 **Cygwin GCC 3.3.3**: The version of GCC 3.3.3 commonly shipped with Cygwin does
274 **SuSE GCC 3.3.3**: The version of GCC 3.3.3 shipped with SuSE 9.1 (and possibly
275 others) does not compile LLVM correctly (it appears that exception handling is
276 broken in some cases). Please download the FSF 3.3.3 or upgrade to a newer
279 **GCC 3.4.0 on linux/x86 (32-bit)**: GCC miscompiles portions of the code
280 generator, causing an infinite loop in the llvm-gcc build when built with
281 optimizations enabled (i.e. a release build).
283 **GCC 3.4.2 on linux/x86 (32-bit)**: GCC miscompiles portions of the code
284 generator at -O3, as with 3.4.0. However gcc 3.4.2 (unlike 3.4.0) correctly
285 compiles LLVM at -O2. A work around is to build release LLVM builds with
286 "``make ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O2 ...``"
288 **GCC 3.4.x on X86-64/amd64**: GCC `miscompiles portions of LLVM
289 <http://llvm.org/PR1056>`__.
291 **GCC 3.4.4 (CodeSourcery ARM 2005q3-2)**: this compiler miscompiles LLVM when
292 building with optimizations enabled. It appears to work with "``make
293 ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O1``" or build a debug build.
295 **IA-64 GCC 4.0.0**: The IA-64 version of GCC 4.0.0 is known to miscompile LLVM.
297 **Apple Xcode 2.3**: GCC crashes when compiling LLVM at -O3 (which is the
298 default with ENABLE_OPTIMIZED=1. To work around this, build with
299 "``ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O2``".
301 **GCC 4.1.1**: GCC fails to build LLVM with template concept check errors
302 compiling some files. At the time of this writing, GCC mainline (4.2) did not
305 **GCC 4.1.1 on X86-64/amd64**: GCC `miscompiles portions of LLVM
306 <http://llvm.org/PR1063>`__ when compiling llvm itself into 64-bit code. LLVM
307 will appear to mostly work but will be buggy, e.g. failing portions of its
310 **GCC 4.1.2 on OpenSUSE**: Seg faults during libstdc++ build and on x86_64
311 platforms compiling md5.c gets a mangled constant.
313 **GCC 4.1.2 (20061115 (prerelease) (Debian 4.1.1-21)) on Debian**: Appears to
314 miscompile parts of LLVM 2.4. One symptom is ValueSymbolTable complaining about
315 symbols remaining in the table on destruction.
317 **GCC 4.1.2 20071124 (Red Hat 4.1.2-42)**: Suffers from the same symptoms as the
318 previous one. It appears to work with ENABLE_OPTIMIZED=0 (the default).
320 **Cygwin GCC 4.3.2 20080827 (beta) 2**: Users `reported
321 <http://llvm.org/PR4145>`_ various problems related with link errors when using
324 **Debian GCC 4.3.2 on X86**: Crashes building some files in LLVM 2.6.
326 **GCC 4.3.3 (Debian 4.3.3-10) on ARM**: Miscompiles parts of LLVM 2.6 when
327 optimizations are turned on. The symptom is an infinite loop in
328 ``FoldingSetImpl::RemoveNode`` while running the code generator.
330 **SUSE 11 GCC 4.3.4**: Miscompiles LLVM, causing crashes in ValueHandle logic.
332 **GCC 4.3.5 and GCC 4.4.5 on ARM**: These can miscompile ``value >> 1`` even at
333 ``-O0``. A test failure in ``test/Assembler/alignstack.ll`` is one symptom of
336 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
337 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
339 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
340 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
341 defined in a discarded section. You can safely ignore these messages as they are
342 erroneous and the linkage is correct. These messages disappear using ld 2.17.
344 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
345 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
346 times (minutes instead of seconds) when building LLVM. We recommend upgrading
347 to a newer version (2.17.50.0.4 or later).
349 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
350 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
351 intermittent failures when building LLVM with position independent code. The
352 symptom is an error about cyclic dependencies. We recommend upgrading to a
353 newer version of Gold.
355 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
356 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
357 3.0 does not implement a few builtins that are used in this library. We
358 recommend using the system GCC to compile LLVM and Clang in this case.
360 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
361 least some (``cxxabi.h``) libstdc++ headers.
363 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
364 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
365 causes Clang to refuse to compile condition_variable header file. At the time
366 of writing, this breaks LLD build.
368 .. _Getting Started with LLVM:
370 Getting Started with LLVM
371 =========================
373 The remainder of this guide is meant to get you up and running with LLVM and to
374 give you some basic information about the LLVM environment.
376 The later sections of this guide describe the `general layout`_ of the LLVM
377 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
378 more information about LLVM or to get help via e-mail.
380 Terminology and Notation
381 ------------------------
383 Throughout this manual, the following names are used to denote paths specific to
384 the local system and working environment. *These are not environment variables
385 you need to set but just strings used in the rest of this document below*. In
386 any of the examples below, simply replace each of these names with the
387 appropriate pathname on your local system. All these paths are absolute:
391 This is the top level directory of the LLVM source tree.
395 This is the top level directory of the LLVM object tree (i.e. the tree where
396 object files and compiled programs will be placed. It can be the same as
399 .. _Setting Up Your Environment:
401 Setting Up Your Environment
402 ---------------------------
404 In order to compile and use LLVM, you may need to set some environment
407 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
409 [Optional] This environment variable helps LLVM linking tools find the
410 locations of your bitcode libraries. It is provided only as a convenience
411 since you can specify the paths using the -L options of the tools and the
412 C/C++ front-end will automatically use the bitcode files installed in its
415 Unpacking the LLVM Archives
416 ---------------------------
418 If you have the LLVM distribution, you will need to unpack it before you can
419 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
420 and the LLVM GCC front end compiled for your platform. There is an additional
421 test suite that is optional. Each file is a TAR archive that is compressed with
424 The files are as follows, with *x.y* marking the version number:
428 Source release for the LLVM libraries and tools.
430 ``llvm-test-x.y.tar.gz``
432 Source release for the LLVM test-suite.
436 Checkout LLVM from Subversion
437 -----------------------------
439 If you have access to our Subversion repository, you can get a fresh copy of the
440 entire source code. All you need to do is check it out from Subversion as
443 * ``cd where-you-want-llvm-to-live``
444 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
445 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
447 This will create an '``llvm``' directory in the current directory and fully
448 populate it with the LLVM source code, Makefiles, test directories, and local
449 copies of documentation files.
451 If you want to get a specific release (as opposed to the most recent revision),
452 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
453 following releases are located in the following subdirectories of the '``tags``'
456 * Release 3.3: **RELEASE_33/final**
457 * Release 3.2: **RELEASE_32/final**
458 * Release 3.1: **RELEASE_31/final**
459 * Release 3.0: **RELEASE_30/final**
460 * Release 2.9: **RELEASE_29/final**
461 * Release 2.8: **RELEASE_28**
462 * Release 2.7: **RELEASE_27**
463 * Release 2.6: **RELEASE_26**
464 * Release 2.5: **RELEASE_25**
465 * Release 2.4: **RELEASE_24**
466 * Release 2.3: **RELEASE_23**
467 * Release 2.2: **RELEASE_22**
468 * Release 2.1: **RELEASE_21**
469 * Release 2.0: **RELEASE_20**
470 * Release 1.9: **RELEASE_19**
471 * Release 1.8: **RELEASE_18**
472 * Release 1.7: **RELEASE_17**
473 * Release 1.6: **RELEASE_16**
474 * Release 1.5: **RELEASE_15**
475 * Release 1.4: **RELEASE_14**
476 * Release 1.3: **RELEASE_13**
477 * Release 1.2: **RELEASE_12**
478 * Release 1.1: **RELEASE_11**
479 * Release 1.0: **RELEASE_1**
481 If you would like to get the LLVM test suite (a separate package as of 1.4), you
482 get it from the Subversion repository:
484 .. code-block:: console
487 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
489 By placing it in the ``llvm/projects``, it will be automatically configured by
490 the LLVM configure script as well as automatically updated when you run ``svn
496 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
497 automatically with each Subversion commit and contain all necessary git-svn
498 marks (so, you can recreate git-svn metadata locally). Note that right now
499 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
502 .. code-block:: console
504 % git clone http://llvm.org/git/llvm.git
506 If you want to check out clang too, run:
508 .. code-block:: console
511 % git clone http://llvm.org/git/clang.git
513 If you want to check out compiler-rt too, run:
515 .. code-block:: console
518 % git clone http://llvm.org/git/compiler-rt.git
520 If you want to check out the Test Suite Source Code (optional), run:
522 .. code-block:: console
525 % git clone http://llvm.org/git/test-suite.git
527 Since the upstream repository is in Subversion, you should use ``git
528 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
529 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
530 master branch, run the following command:
532 .. code-block:: console
534 % git config branch.master.rebase true
536 Sending patches with Git
537 ^^^^^^^^^^^^^^^^^^^^^^^^
539 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
541 Assume ``master`` points the upstream and ``mybranch`` points your working
542 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
543 sanity of whitespaces:
545 .. code-block:: console
547 % git diff --check master..mybranch
549 The easiest way to generate a patch is as below:
551 .. code-block:: console
553 % git diff master..mybranch > /path/to/mybranch.diff
555 It is a little different from svn-generated diff. git-diff-generated diff has
556 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
557 could be accepted with ``patch -p1 -N``.
559 But you may generate patchset with git-format-patch. It generates by-each-commit
560 patchset. To generate patch files to attach to your article:
562 .. code-block:: console
564 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
566 If you would like to send patches directly, you may use git-send-email or
567 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
569 .. code-block:: console
571 % git format-patch --attach master..mybranch --stdout | git imap-send
573 Then, your .git/config should have [imap] sections.
578 host = imaps://imap.gmail.com
579 user = your.gmail.account@gmail.com
584 folder = "[Gmail]/Drafts"
585 ; example for Japanese, "Modified UTF-7" encoded.
586 folder = "[Gmail]/&Tgtm+DBN-"
587 ; example for Traditional Chinese
588 folder = "[Gmail]/&g0l6Pw-"
590 For developers to work with git-svn
591 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
593 To set up clone from which you can submit code using ``git-svn``, run:
595 .. code-block:: console
597 % git clone http://llvm.org/git/llvm.git
599 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
600 % git config svn-remote.svn.fetch :refs/remotes/origin/master
601 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
603 # If you have clang too:
605 % git clone http://llvm.org/git/clang.git
607 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
608 % git config svn-remote.svn.fetch :refs/remotes/origin/master
611 Likewise for compiler-rt and test-suite.
613 To update this clone without generating git-svn tags that conflict with the
614 upstream Git repo, run:
616 .. code-block:: console
618 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
619 % git checkout master
622 git checkout master &&
625 Likewise for compiler-rt and test-suite.
627 This leaves your working directories on their master branches, so you'll need to
628 ``checkout`` each working branch individually and ``rebase`` it on top of its
631 For those who wish to be able to update an llvm repo/revert patches easily using
632 git-svn, please look in the directory for the scripts ``git-svnup`` and
635 To perform the aforementioned update steps go into your source directory and
636 just type ``git-svnup`` or ``git svnup`` and everything will just work.
638 If one wishes to revert a commit with git-svn, but do not want the git hash to
639 escape into the commit message, one can use the script ``git-svnrevert`` or
640 ``git svnrevert`` which will take in the git hash for the commit you want to
641 revert, look up the appropriate svn revision, and output a message where all
642 references to the git hash have been replaced with the svn revision.
644 To commit back changes via git-svn, use ``git svn dcommit``:
646 .. code-block:: console
650 Note that git-svn will create one SVN commit for each Git commit you have pending,
651 so squash and edit each commit before executing ``dcommit`` to make sure they all
652 conform to the coding standards and the developers' policy.
654 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
655 please make sure your current branch is up-to-date (via fetch/rebase) before
658 The git-svn metadata can get out of sync after you mess around with branches and
659 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
660 about files with uncommitted changes. The fix is to rebuild the metadata:
662 .. code-block:: console
667 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
669 Local LLVM Configuration
670 ------------------------
672 Once checked out from the Subversion repository, the LLVM suite source code must
673 be configured via the ``configure`` script. This script sets variables in the
674 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
675 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
676 Makefiles needed to begin building LLVM.
678 The following environment variables are used by the ``configure`` script to
679 configure the build system:
681 +------------+-----------------------------------------------------------+
682 | Variable | Purpose |
683 +============+===========================================================+
684 | CC | Tells ``configure`` which C compiler to use. By default, |
685 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
686 | | compilers (in this order). Use this variable to override |
687 | | ``configure``\'s default behavior. |
688 +------------+-----------------------------------------------------------+
689 | CXX | Tells ``configure`` which C++ compiler to use. By |
690 | | default, ``configure`` will check ``PATH`` for |
691 | | ``clang++`` and GCC C++ compilers (in this order). Use |
692 | | this variable to override ``configure``'s default |
694 +------------+-----------------------------------------------------------+
696 The following options can be used to set or enable LLVM specific options:
698 ``--enable-optimized``
700 Enables optimized compilation (debugging symbols are removed and GCC
701 optimization flags are enabled). Note that this is the default setting if you
702 are using the LLVM distribution. The default behavior of an Subversion
703 checkout is to use an unoptimized build (also known as a debug build).
705 ``--enable-debug-runtime``
707 Enables debug symbols in the runtime libraries. The default is to strip debug
708 symbols from the runtime libraries.
712 Compile the Just In Time (JIT) compiler functionality. This is not available
713 on all platforms. The default is dependent on platform, so it is best to
714 explicitly enable it if you want it.
716 ``--enable-targets=target-option``
718 Controls which targets will be built and linked into llc. The default value
719 for ``target_options`` is "all" which builds and links all available targets.
720 The value "host-only" can be specified to build only a native compiler (no
721 cross-compiler targets available). The "native" target is selected as the
722 target of the build host. You can also specify a comma separated list of
723 target names that you want available in llc. The target names use all lower
724 case. The current set of targets is:
726 ``arm, cpp, hexagon, mips, mipsel, msp430, powerpc, ptx, sparc, spu,
727 systemz, x86, x86_64, xcore``.
731 Look for the doxygen program and enable construction of doxygen based
732 documentation from the source code. This is disabled by default because
733 generating the documentation can take a long time and producess 100s of
738 LLVM can use external disassembler library for various purposes (now it's used
739 only for examining code produced by JIT). This option will enable usage of
740 `udis86 <http://udis86.sourceforge.net/>`_ x86 (both 32 and 64 bits)
741 disassembler library.
743 To configure LLVM, follow these steps:
745 #. Change directory into the object root directory:
747 .. code-block:: console
751 #. Run the ``configure`` script located in the LLVM source tree:
753 .. code-block:: console
755 % SRC_ROOT/configure --prefix=/install/path [other options]
757 Compiling the LLVM Suite Source Code
758 ------------------------------------
760 Once you have configured LLVM, you can build it. There are three types of
765 These builds are the default when one is using an Subversion checkout and
766 types ``gmake`` (unless the ``--enable-optimized`` option was used during
767 configuration). The build system will compile the tools and libraries with
768 debugging information. To get a Debug Build using the LLVM distribution the
769 ``--disable-optimized`` option must be passed to ``configure``.
771 Release (Optimized) Builds
773 These builds are enabled with the ``--enable-optimized`` option to
774 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
775 line. For these builds, the build system will compile the tools and libraries
776 with GCC optimizations enabled and strip debugging information from the
777 libraries and executables it generates. Note that Release Builds are default
778 when using an LLVM distribution.
782 These builds are for use with profiling. They compile profiling information
783 into the code for use with programs like ``gprof``. Profile builds must be
784 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
786 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
787 directory and issuing the following command:
789 .. code-block:: console
793 If the build fails, please `check here`_ to see if you are using a version of
794 GCC that is known not to compile LLVM.
796 If you have multiple processors in your machine, you may wish to use some of the
797 parallel build options provided by GNU Make. For example, you could use the
800 .. code-block:: console
804 There are several special targets which are useful when working with the LLVM
809 Removes all files generated by the build. This includes object files,
810 generated C/C++ files, libraries, and executables.
814 Removes everything that ``gmake clean`` does, but also removes files generated
815 by ``configure``. It attempts to return the source tree to the original state
816 in which it was shipped.
820 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
821 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
822 defaults to ``/usr/local``.
824 ``gmake -C runtime install-bytecode``
826 Assuming you built LLVM into $OBJDIR, when this command is run, it will
827 install bitcode libraries into the GCC front end's bitcode library directory.
828 If you need to update your bitcode libraries, this is the target to use once
831 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
832 these ``make`` targets and descriptions of other targets available.
834 It is also possible to override default values from ``configure`` by declaring
835 variables on the command line. The following are some examples:
837 ``gmake ENABLE_OPTIMIZED=1``
839 Perform a Release (Optimized) build.
841 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
843 Perform a Release (Optimized) build without assertions enabled.
845 ``gmake ENABLE_OPTIMIZED=0``
847 Perform a Debug build.
849 ``gmake ENABLE_PROFILING=1``
851 Perform a Profiling build.
855 Print what ``gmake`` is doing on standard output.
857 ``gmake TOOL_VERBOSE=1``
859 Ask each tool invoked by the makefiles to print out what it is doing on
860 the standard output. This also implies ``VERBOSE=1``.
862 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
863 any subdirectories that it contains. Entering any directory inside the LLVM
864 object tree and typing ``gmake`` should rebuild anything in or below that
865 directory that is out of date.
867 This does not apply to building the documentation.
868 LLVM's (non-Doxygen) documentation is produced with the
869 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
870 There are some HTML documents that have not yet been converted to the new
871 system (which uses the easy-to-read and easy-to-write
872 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
874 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
876 For instructions on how to install Sphinx, see
877 `Sphinx Introduction for LLVM Developers
878 <http://lld.llvm.org/sphinx_intro.html>`_.
879 After following the instructions there for installing Sphinx, build the LLVM
880 HTML documentation by doing the following:
882 .. code-block:: console
885 $ make -f Makefile.sphinx
887 This creates a ``_build/html`` sub-directory with all of the HTML files, not
888 just the generated ones.
889 This directory corresponds to ``llvm.org/docs``.
890 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
891 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
892 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
897 It is possible to cross-compile LLVM itself. That is, you can create LLVM
898 executables and libraries to be hosted on a platform different from the platform
899 where they are built (a Canadian Cross build). To configure a cross-compile,
900 supply the configure script with ``--build`` and ``--host`` options that are
901 different. The values of these options must be legal target triples that your
902 GCC compiler supports.
904 The result of such a build is executables that are not runnable on on the build
905 host (--build option) but can be executed on the compile host (--host option).
907 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
908 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
909 about cross-compiling.
911 The Location of LLVM Object Files
912 ---------------------------------
914 The LLVM build system is capable of sharing a single LLVM source tree among
915 several LLVM builds. Hence, it is possible to build LLVM for several different
916 platforms or configurations using the same source tree.
918 This is accomplished in the typical autoconf manner:
920 * Change directory to where the LLVM object files should live:
922 .. code-block:: console
926 * Run the ``configure`` script found in the LLVM source directory:
928 .. code-block:: console
932 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
935 Debug Builds with assertions enabled (the default)
939 ``OBJ_ROOT/Debug+Asserts/bin``
943 ``OBJ_ROOT/Debug+Asserts/lib``
949 ``OBJ_ROOT/Release/bin``
953 ``OBJ_ROOT/Release/lib``
959 ``OBJ_ROOT/Profile/bin``
963 ``OBJ_ROOT/Profile/lib``
965 Optional Configuration Items
966 ----------------------------
968 If you're running on a Linux system that supports the `binfmt_misc
969 <http://en.wikipedia.org/wiki/binfmt_misc>`_
970 module, and you have root access on the system, you can set your system up to
971 execute LLVM bitcode files directly. To do this, use commands like this (the
972 first command may not be required if you are already using the module):
974 .. code-block:: console
976 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
977 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
978 % chmod u+x hello.bc (if needed)
981 This allows you to execute LLVM bitcode files directly. On Debian, you can also
982 use this command instead of the 'echo' command above:
984 .. code-block:: console
986 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
994 One useful source of information about the LLVM source base is the LLVM `doxygen
995 <http://www.doxygen.org/>`_ documentation available at
996 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
1002 This directory contains some simple examples of how to use the LLVM IR and JIT.
1007 This directory contains public header files exported from the LLVM library. The
1008 three main subdirectories of this directory are:
1010 ``llvm/include/llvm``
1012 This directory contains all of the LLVM specific header files. This directory
1013 also has subdirectories for different portions of LLVM: ``Analysis``,
1014 ``CodeGen``, ``Target``, ``Transforms``, etc...
1016 ``llvm/include/llvm/Support``
1018 This directory contains generic support libraries that are provided with LLVM
1019 but not necessarily specific to LLVM. For example, some C++ STL utilities and
1020 a Command Line option processing library store their header files here.
1022 ``llvm/include/llvm/Config``
1024 This directory contains header files configured by the ``configure`` script.
1025 They wrap "standard" UNIX and C header files. Source code can include these
1026 header files which automatically take care of the conditional #includes that
1027 the ``configure`` script generates.
1032 This directory contains most of the source files of the LLVM system. In LLVM,
1033 almost all code exists in libraries, making it very easy to share code among the
1036 ``llvm/lib/VMCore/``
1038 This directory holds the core LLVM source files that implement core classes
1039 like Instruction and BasicBlock.
1041 ``llvm/lib/AsmParser/``
1043 This directory holds the source code for the LLVM assembly language parser
1046 ``llvm/lib/Bitcode/``
1048 This directory holds code for reading and write LLVM bitcode.
1050 ``llvm/lib/Analysis/``
1052 This directory contains a variety of different program analyses, such as
1053 Dominator Information, Call Graphs, Induction Variables, Interval
1054 Identification, Natural Loop Identification, etc.
1056 ``llvm/lib/Transforms/``
1058 This directory contains the source code for the LLVM to LLVM program
1059 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1060 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1061 Elimination, and many others.
1063 ``llvm/lib/Target/``
1065 This directory contains files that describe various target architectures for
1066 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1067 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1070 ``llvm/lib/CodeGen/``
1072 This directory contains the major parts of the code generator: Instruction
1073 Selector, Instruction Scheduling, and Register Allocation.
1079 ``llvm/lib/Debugger/``
1081 This directory contains the source level debugger library that makes it
1082 possible to instrument LLVM programs so that a debugger could identify source
1083 code locations at which the program is executing.
1085 ``llvm/lib/ExecutionEngine/``
1087 This directory contains libraries for executing LLVM bitcode directly at
1088 runtime in both interpreted and JIT compiled fashions.
1090 ``llvm/lib/Support/``
1092 This directory contains the source code that corresponds to the header files
1093 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1098 This directory contains projects that are not strictly part of LLVM but are
1099 shipped with LLVM. This is also the directory where you should create your own
1100 LLVM-based projects. See ``llvm/projects/sample`` for an example of how to set
1101 up your own project.
1106 This directory contains libraries which are compiled into LLVM bitcode and used
1107 when linking programs with the Clang front end. Most of these libraries are
1108 skeleton versions of real libraries; for example, libc is a stripped down
1111 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1117 This directory contains feature and regression tests and other basic sanity
1118 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1119 lot of territory without being exhaustive.
1124 This is not a directory in the normal llvm module; it is a separate Subversion
1125 module that must be checked out (usually to ``projects/test-suite``). This
1126 module contains a comprehensive correctness, performance, and benchmarking test
1127 suite for LLVM. It is a separate Subversion module because not every LLVM user
1128 is interested in downloading or building such a comprehensive test suite. For
1129 further details on this test suite, please see the :doc:`Testing Guide
1130 <TestingGuide>` document.
1137 The **tools** directory contains the executables built out of the libraries
1138 above, which form the main part of the user interface. You can always get help
1139 for a tool by typing ``tool_name -help``. The following is a brief introduction
1140 to the most important tools. More detailed information is in
1141 the `Command Guide <CommandGuide/index.html>`_.
1145 ``bugpoint`` is used to debug optimization passes or code generation backends
1146 by narrowing down the given test case to the minimum number of passes and/or
1147 instructions that still cause a problem, whether it is a crash or
1148 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1153 The archiver produces an archive containing the given LLVM bitcode files,
1154 optionally with an index for faster lookup.
1158 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1162 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1166 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1171 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1172 (although very slowly...). For architectures that support it (currently x86,
1173 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1174 compiler (if the functionality was compiled in), and will execute the code
1175 *much* faster than the interpreter.
1179 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1180 native code assembly file or to C code (with the ``-march=c`` option).
1184 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1185 (which are specified on the command line), and then outputs the resultant
1186 bitcode. The '``opt -help``' command is a good way to get a list of the
1187 program transformations available in LLVM.
1189 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1190 file and print out the results. It is primarily useful for debugging
1191 analyses, or familiarizing yourself with what an analysis does.
1196 This directory contains utilities for working with LLVM source code, and some of
1197 the utilities are actually required as part of the build process because they
1198 are code generators for parts of LLVM infrastructure.
1203 ``codegen-diff`` is a script that finds differences between code that LLC
1204 generates and code that LLI generates. This is a useful tool if you are
1205 debugging one of them, assuming that the other generates correct output. For
1206 the full user manual, run ```perldoc codegen-diff'``.
1210 The ``emacs`` directory contains syntax-highlighting files which will work
1211 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1212 assembly files and TableGen description files. For information on how to use
1213 the syntax files, consult the ``README`` file in that directory.
1217 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1218 which is useful if one wishes to do a lot of development across directories
1219 and does not want to individually find each file. One way to use it is to run,
1220 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1225 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1226 passes to it a regular expression provided on ``llvmgrep``'s command
1227 line. This is a very efficient way of searching the source base for a
1228 particular regular expression.
1232 The ``makellvm`` script compiles all files in the current directory and then
1233 compiles and links the tool that is the first argument. For example, assuming
1234 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1235 path, simply running ``makellvm llc`` will make a build of the current
1236 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1241 The ``TableGen`` directory contains the tool used to generate register
1242 descriptions, instruction set descriptions, and even assemblers from common
1243 TableGen description files.
1247 The ``vim`` directory contains syntax-highlighting files which will work with
1248 the VIM editor, providing syntax highlighting support for LLVM assembly files
1249 and TableGen description files. For information on how to use the syntax
1250 files, consult the ``README`` file in that directory.
1254 An Example Using the LLVM Tool Chain
1255 ====================================
1257 This section gives an example of using LLVM with the Clang front end.
1262 #. First, create a simple C file, name it 'hello.c':
1269 printf("hello world\n");
1273 #. Next, compile the C file into a native executable:
1275 .. code-block:: console
1277 % clang hello.c -o hello
1281 Clang works just like GCC by default. The standard -S and -c arguments
1282 work as usual (producing a native .s or .o file, respectively).
1284 #. Next, compile the C file into an LLVM bitcode file:
1286 .. code-block:: console
1288 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1290 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1291 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1292 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1294 #. Run the program in both forms. To run the program, use:
1296 .. code-block:: console
1302 .. code-block:: console
1306 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1307 <CommandGuide/lli>`.
1309 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1311 .. code-block:: console
1313 % llvm-dis < hello.bc | less
1315 #. Compile the program to native assembly using the LLC code generator:
1317 .. code-block:: console
1319 % llc hello.bc -o hello.s
1321 #. Assemble the native assembly language file into a program:
1323 .. code-block:: console
1325 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1327 % gcc hello.s -o hello.native # On others
1329 #. Execute the native code program:
1331 .. code-block:: console
1335 Note that using clang to compile directly to native code (i.e. when the
1336 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1341 If you are having problems building or using LLVM, or if you have any other
1342 general questions about LLVM, please consult the `Frequently Asked
1343 Questions <FAQ.html>`_ page.
1350 This document is just an **introduction** on how to use LLVM to do some simple
1351 things... there are many more interesting and complicated things that you can do
1352 that aren't documented here (but we'll gladly accept a patch if you want to
1353 write something up!). For more information about LLVM, check out:
1355 * `LLVM Homepage <http://llvm.org/>`_
1356 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1357 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_