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32 The LLVM Getting Started documentation may be out of date.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 ================== ===================== =============
120 ================== ===================== =============
121 AuroraUX x86\ :sup:`1` GCC
122 Linux x86\ :sup:`1` GCC, Clang
123 Linux amd64 GCC, Clang
124 Linux ARM\ :sup:`4` GCC, Clang
125 Linux PowerPC GCC, Clang
126 Solaris V9 (Ultrasparc) GCC
127 FreeBSD x86\ :sup:`1` GCC, Clang
128 FreeBSD amd64 GCC, Clang
129 MacOS X\ :sup:`2` PowerPC GCC
130 MacOS X x86 GCC, Clang
131 Cygwin/Win32 x86\ :sup:`1, 3` GCC
132 Windows x86\ :sup:`1` Visual Studio
133 Windows x64 x86-64 Visual Studio
134 ================== ===================== =============
138 #. Code generation supported for Pentium processors and up
139 #. Code generation supported for 32-bit ABI only
140 #. To use LLVM modules on Win32-based system, you may configure LLVM
141 with ``--enable-shared``.
142 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
144 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
145 mode, depending on the system (it is so large because of all the debugging
146 information and the fact that the libraries are statically linked into multiple
147 tools). If you do not need many of the tools and you are space-conscious, you
148 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
149 considerably less space.
151 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
152 so. If compilation is successful, the LLVM utilities should be able to
153 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
154 should work as well, although the generated native code may not work on your
160 Compiling LLVM requires that you have several software packages installed. The
161 table below lists those required packages. The Package column is the usual name
162 for the software package that LLVM depends on. The Version column provides
163 "known to work" versions of the package. The Notes column describes how LLVM
164 uses the package and provides other details.
166 +--------------------------------------------------------------+-----------------+---------------------------------------------+
167 | Package | Version | Notes |
168 +==============================================================+=================+=============================================+
169 | `GNU Make <http://savannah.gnu.org/projects/make>`_ | 3.79, 3.79.1 | Makefile/build processor |
170 +--------------------------------------------------------------+-----------------+---------------------------------------------+
171 | `GCC <http://gcc.gnu.org/>`_ | 3.4.2 | C/C++ compiler\ :sup:`1` |
172 +--------------------------------------------------------------+-----------------+---------------------------------------------+
173 | `TeXinfo <http://www.gnu.org/software/texinfo/>`_ | 4.5 | For building the CFE |
174 +--------------------------------------------------------------+-----------------+---------------------------------------------+
175 | `SVN <http://subversion.tigris.org/project_packages.html>`_ | >=1.3 | Subversion access to LLVM\ :sup:`2` |
176 +--------------------------------------------------------------+-----------------+---------------------------------------------+
177 | `python <http://www.python.org/>`_ | >=2.5 | Automated test suite\ :sup:`3` |
178 +--------------------------------------------------------------+-----------------+---------------------------------------------+
179 | `GNU M4 <http://savannah.gnu.org/projects/m4>`_ | 1.4 | Macro processor for configuration\ :sup:`4` |
180 +--------------------------------------------------------------+-----------------+---------------------------------------------+
181 | `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ | 2.60 | Configuration script builder\ :sup:`4` |
182 +--------------------------------------------------------------+-----------------+---------------------------------------------+
183 | `GNU Automake <http://www.gnu.org/software/automake/>`_ | 1.9.6 | aclocal macro generator\ :sup:`4` |
184 +--------------------------------------------------------------+-----------------+---------------------------------------------+
185 | `libtool <http://savannah.gnu.org/projects/libtool>`_ | 1.5.22 | Shared library manager\ :sup:`4` |
186 +--------------------------------------------------------------+-----------------+---------------------------------------------+
187 | `zlib <http://zlib.net>`_ | >=1.2.3.4 | Compression library\ :sup:`5` |
188 +--------------------------------------------------------------+-----------------+---------------------------------------------+
192 #. Only the C and C++ languages are needed so there's no need to build the
193 other languages for LLVM's purposes. See `below` for specific version
195 #. You only need Subversion if you intend to build from the latest LLVM
196 sources. If you're working from a release distribution, you don't need
198 #. Only needed if you want to run the automated test suite in the
199 ``llvm/test`` directory.
200 #. If you want to make changes to the configure scripts, you will need GNU
201 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
202 will also need automake (1.9.6). We only use aclocal from that package.
203 #. Optional, adds compression/uncompression capabilities to selected LLVM
206 Additionally, your compilation host is expected to have the usual plethora of
207 Unix utilities. Specifically:
209 * **ar** --- archive library builder
210 * **bzip2** --- bzip2 command for distribution generation
211 * **bunzip2** --- bunzip2 command for distribution checking
212 * **chmod** --- change permissions on a file
213 * **cat** --- output concatenation utility
214 * **cp** --- copy files
215 * **date** --- print the current date/time
216 * **echo** --- print to standard output
217 * **egrep** --- extended regular expression search utility
218 * **find** --- find files/dirs in a file system
219 * **grep** --- regular expression search utility
220 * **gzip** --- gzip command for distribution generation
221 * **gunzip** --- gunzip command for distribution checking
222 * **install** --- install directories/files
223 * **mkdir** --- create a directory
224 * **mv** --- move (rename) files
225 * **ranlib** --- symbol table builder for archive libraries
226 * **rm** --- remove (delete) files and directories
227 * **sed** --- stream editor for transforming output
228 * **sh** --- Bourne shell for make build scripts
229 * **tar** --- tape archive for distribution generation
230 * **test** --- test things in file system
231 * **unzip** --- unzip command for distribution checking
232 * **zip** --- zip command for distribution generation
237 Broken versions of GCC and other tools
238 --------------------------------------
240 LLVM is very demanding of the host C++ compiler, and as such tends to expose
241 bugs in the compiler. In particular, several versions of GCC crash when trying
242 to compile LLVM. We routinely use GCC 4.2 (and higher) or Clang. Other
243 versions of GCC will probably work as well. GCC versions listed here are known
244 to not work. If you are using one of these versions, please try to upgrade your
245 GCC to something more recent. If you run into a problem with a version of GCC
246 not listed here, please `let us know <mailto:llvmdev@cs.uiuc.edu>`_. Please use
247 the "``gcc -v``" command to find out which version of GCC you are using.
249 **GCC versions prior to 3.0**: GCC 2.96.x and before had several problems in the
250 STL that effectively prevent it from compiling LLVM.
252 **GCC 3.2.2 and 3.2.3**: These versions of GCC fails to compile LLVM with a
253 bogus template error. This was fixed in later GCCs.
255 **GCC 3.3.2**: This version of GCC suffered from a `serious bug
256 <http://gcc.gnu.org/PR13392>`_ which causes it to crash in the
257 "``convert_from_eh_region_ranges_1``" GCC function.
259 **Cygwin GCC 3.3.3**: The version of GCC 3.3.3 commonly shipped with Cygwin does
262 **SuSE GCC 3.3.3**: The version of GCC 3.3.3 shipped with SuSE 9.1 (and possibly
263 others) does not compile LLVM correctly (it appears that exception handling is
264 broken in some cases). Please download the FSF 3.3.3 or upgrade to a newer
267 **GCC 3.4.0 on linux/x86 (32-bit)**: GCC miscompiles portions of the code
268 generator, causing an infinite loop in the llvm-gcc build when built with
269 optimizations enabled (i.e. a release build).
271 **GCC 3.4.2 on linux/x86 (32-bit)**: GCC miscompiles portions of the code
272 generator at -O3, as with 3.4.0. However gcc 3.4.2 (unlike 3.4.0) correctly
273 compiles LLVM at -O2. A work around is to build release LLVM builds with
274 "``make ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O2 ...``"
276 **GCC 3.4.x on X86-64/amd64**: GCC `miscompiles portions of LLVM
277 <http://llvm.org/PR1056>`__.
279 **GCC 3.4.4 (CodeSourcery ARM 2005q3-2)**: this compiler miscompiles LLVM when
280 building with optimizations enabled. It appears to work with "``make
281 ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O1``" or build a debug build.
283 **IA-64 GCC 4.0.0**: The IA-64 version of GCC 4.0.0 is known to miscompile LLVM.
285 **Apple Xcode 2.3**: GCC crashes when compiling LLVM at -O3 (which is the
286 default with ENABLE_OPTIMIZED=1. To work around this, build with
287 "``ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O2``".
289 **GCC 4.1.1**: GCC fails to build LLVM with template concept check errors
290 compiling some files. At the time of this writing, GCC mainline (4.2) did not
293 **GCC 4.1.1 on X86-64/amd64**: GCC `miscompiles portions of LLVM
294 <http://llvm.org/PR1063>`__ when compiling llvm itself into 64-bit code. LLVM
295 will appear to mostly work but will be buggy, e.g. failing portions of its
298 **GCC 4.1.2 on OpenSUSE**: Seg faults during libstdc++ build and on x86_64
299 platforms compiling md5.c gets a mangled constant.
301 **GCC 4.1.2 (20061115 (prerelease) (Debian 4.1.1-21)) on Debian**: Appears to
302 miscompile parts of LLVM 2.4. One symptom is ValueSymbolTable complaining about
303 symbols remaining in the table on destruction.
305 **GCC 4.1.2 20071124 (Red Hat 4.1.2-42)**: Suffers from the same symptoms as the
306 previous one. It appears to work with ENABLE_OPTIMIZED=0 (the default).
308 **Cygwin GCC 4.3.2 20080827 (beta) 2**: Users `reported
309 <http://llvm.org/PR4145>`_ various problems related with link errors when using
312 **Debian GCC 4.3.2 on X86**: Crashes building some files in LLVM 2.6.
314 **GCC 4.3.3 (Debian 4.3.3-10) on ARM**: Miscompiles parts of LLVM 2.6 when
315 optimizations are turned on. The symptom is an infinite loop in
316 ``FoldingSetImpl::RemoveNode`` while running the code generator.
318 **SUSE 11 GCC 4.3.4**: Miscompiles LLVM, causing crashes in ValueHandle logic.
320 **GCC 4.3.5 and GCC 4.4.5 on ARM**: These can miscompile ``value >> 1`` even at
321 ``-O0``. A test failure in ``test/Assembler/alignstack.ll`` is one symptom of
324 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
325 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
327 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
328 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
329 defined in a discarded section. You can safely ignore these messages as they are
330 erroneous and the linkage is correct. These messages disappear using ld 2.17.
332 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
333 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
334 times (minutes instead of seconds) when building LLVM. We recommend upgrading
335 to a newer version (2.17.50.0.4 or later).
337 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
338 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
339 intermittent failures when building LLVM with position independent code. The
340 symptom is an error about cyclic dependencies. We recommend upgrading to a
341 newer version of Gold.
343 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
344 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
345 3.0 does not implement a few builtins that are used in this library. We
346 recommend using the system GCC to compile LLVM and Clang in this case.
348 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
349 least some (``cxxabi.h``) libstdc++ headers.
351 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
352 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
353 causes Clang to refuse to compile condition_variable header file. At the time
354 of writing, this breaks LLD build.
356 .. _Getting Started with LLVM:
358 Getting Started with LLVM
359 =========================
361 The remainder of this guide is meant to get you up and running with LLVM and to
362 give you some basic information about the LLVM environment.
364 The later sections of this guide describe the `general layout`_ of the LLVM
365 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
366 more information about LLVM or to get help via e-mail.
368 Terminology and Notation
369 ------------------------
371 Throughout this manual, the following names are used to denote paths specific to
372 the local system and working environment. *These are not environment variables
373 you need to set but just strings used in the rest of this document below*. In
374 any of the examples below, simply replace each of these names with the
375 appropriate pathname on your local system. All these paths are absolute:
379 This is the top level directory of the LLVM source tree.
383 This is the top level directory of the LLVM object tree (i.e. the tree where
384 object files and compiled programs will be placed. It can be the same as
387 .. _Setting Up Your Environment:
389 Setting Up Your Environment
390 ---------------------------
392 In order to compile and use LLVM, you may need to set some environment
395 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
397 [Optional] This environment variable helps LLVM linking tools find the
398 locations of your bitcode libraries. It is provided only as a convenience
399 since you can specify the paths using the -L options of the tools and the
400 C/C++ front-end will automatically use the bitcode files installed in its
403 Unpacking the LLVM Archives
404 ---------------------------
406 If you have the LLVM distribution, you will need to unpack it before you can
407 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
408 and the LLVM GCC front end compiled for your platform. There is an additional
409 test suite that is optional. Each file is a TAR archive that is compressed with
412 The files are as follows, with *x.y* marking the version number:
416 Source release for the LLVM libraries and tools.
418 ``llvm-test-x.y.tar.gz``
420 Source release for the LLVM test-suite.
424 Checkout LLVM from Subversion
425 -----------------------------
427 If you have access to our Subversion repository, you can get a fresh copy of the
428 entire source code. All you need to do is check it out from Subversion as
431 * ``cd where-you-want-llvm-to-live``
432 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
433 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
435 This will create an '``llvm``' directory in the current directory and fully
436 populate it with the LLVM source code, Makefiles, test directories, and local
437 copies of documentation files.
439 If you want to get a specific release (as opposed to the most recent revision),
440 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
441 following releases are located in the following subdirectories of the '``tags``'
444 * Release 3.3: **RELEASE_33/final**
445 * Release 3.2: **RELEASE_32/final**
446 * Release 3.1: **RELEASE_31/final**
447 * Release 3.0: **RELEASE_30/final**
448 * Release 2.9: **RELEASE_29/final**
449 * Release 2.8: **RELEASE_28**
450 * Release 2.7: **RELEASE_27**
451 * Release 2.6: **RELEASE_26**
452 * Release 2.5: **RELEASE_25**
453 * Release 2.4: **RELEASE_24**
454 * Release 2.3: **RELEASE_23**
455 * Release 2.2: **RELEASE_22**
456 * Release 2.1: **RELEASE_21**
457 * Release 2.0: **RELEASE_20**
458 * Release 1.9: **RELEASE_19**
459 * Release 1.8: **RELEASE_18**
460 * Release 1.7: **RELEASE_17**
461 * Release 1.6: **RELEASE_16**
462 * Release 1.5: **RELEASE_15**
463 * Release 1.4: **RELEASE_14**
464 * Release 1.3: **RELEASE_13**
465 * Release 1.2: **RELEASE_12**
466 * Release 1.1: **RELEASE_11**
467 * Release 1.0: **RELEASE_1**
469 If you would like to get the LLVM test suite (a separate package as of 1.4), you
470 get it from the Subversion repository:
472 .. code-block:: console
475 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
477 By placing it in the ``llvm/projects``, it will be automatically configured by
478 the LLVM configure script as well as automatically updated when you run ``svn
484 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
485 automatically with each Subversion commit and contain all necessary git-svn
486 marks (so, you can recreate git-svn metadata locally). Note that right now
487 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
490 .. code-block:: console
492 % git clone http://llvm.org/git/llvm.git
494 If you want to check out clang too, run:
496 .. code-block:: console
499 % git clone http://llvm.org/git/clang.git
501 If you want to check out compiler-rt too, run:
503 .. code-block:: console
506 % git clone http://llvm.org/git/compiler-rt.git
508 If you want to check out the Test Suite Source Code (optional), run:
510 .. code-block:: console
513 % git clone http://llvm.org/git/test-suite.git
515 Since the upstream repository is in Subversion, you should use ``git
516 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
517 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
518 master branch, run the following command:
520 .. code-block:: console
522 % git config branch.master.rebase true
524 Sending patches with Git
525 ^^^^^^^^^^^^^^^^^^^^^^^^
527 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
529 Assume ``master`` points the upstream and ``mybranch`` points your working
530 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
531 sanity of whitespaces:
533 .. code-block:: console
535 % git diff --check master..mybranch
537 The easiest way to generate a patch is as below:
539 .. code-block:: console
541 % git diff master..mybranch > /path/to/mybranch.diff
543 It is a little different from svn-generated diff. git-diff-generated diff has
544 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
545 could be accepted with ``patch -p1 -N``.
547 But you may generate patchset with git-format-patch. It generates by-each-commit
548 patchset. To generate patch files to attach to your article:
550 .. code-block:: console
552 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
554 If you would like to send patches directly, you may use git-send-email or
555 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
557 .. code-block:: console
559 % git format-patch --attach master..mybranch --stdout | git imap-send
561 Then, your .git/config should have [imap] sections.
566 host = imaps://imap.gmail.com
567 user = your.gmail.account@gmail.com
572 folder = "[Gmail]/Drafts"
573 ; example for Japanese, "Modified UTF-7" encoded.
574 folder = "[Gmail]/&Tgtm+DBN-"
575 ; example for Traditional Chinese
576 folder = "[Gmail]/&g0l6Pw-"
578 For developers to work with git-svn
579 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
581 To set up clone from which you can submit code using ``git-svn``, run:
583 .. code-block:: console
585 % git clone http://llvm.org/git/llvm.git
587 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
588 % git config svn-remote.svn.fetch :refs/remotes/origin/master
589 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
591 # If you have clang too:
593 % git clone http://llvm.org/git/clang.git
595 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
596 % git config svn-remote.svn.fetch :refs/remotes/origin/master
599 Likewise for compiler-rt and test-suite.
601 To update this clone without generating git-svn tags that conflict with the
602 upstream Git repo, run:
604 .. code-block:: console
606 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
607 % git checkout master
610 git checkout master &&
613 Likewise for compiler-rt and test-suite.
615 This leaves your working directories on their master branches, so you'll need to
616 ``checkout`` each working branch individually and ``rebase`` it on top of its
619 For those who wish to be able to update an llvm repo/revert patches easily using
620 git-svn, please look in the directory for the scripts ``git-svnup`` and
623 To perform the aforementioned update steps go into your source directory and
624 just type ``git-svnup`` or ``git svnup`` and everything will just work.
626 If one wishes to revert a commit with git-svn, but do not want the git hash to
627 escape into the commit message, one can use the script ``git-svnrevert`` or
628 ``git svnrevert`` which will take in the git hash for the commit you want to
629 revert, look up the appropriate svn revision, and output a message where all
630 references to the git hash have been replaced with the svn revision.
632 To commit back changes via git-svn, use ``git svn dcommit``:
634 .. code-block:: console
638 Note that git-svn will create one SVN commit for each Git commit you have pending,
639 so squash and edit each commit before executing ``dcommit`` to make sure they all
640 conform to the coding standards and the developers' policy.
642 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
643 please make sure your current branch is up-to-date (via fetch/rebase) before
646 The git-svn metadata can get out of sync after you mess around with branches and
647 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
648 about files with uncommitted changes. The fix is to rebuild the metadata:
650 .. code-block:: console
655 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
657 Local LLVM Configuration
658 ------------------------
660 Once checked out from the Subversion repository, the LLVM suite source code must
661 be configured via the ``configure`` script. This script sets variables in the
662 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
663 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
664 Makefiles needed to begin building LLVM.
666 The following environment variables are used by the ``configure`` script to
667 configure the build system:
669 +------------+-----------------------------------------------------------+
670 | Variable | Purpose |
671 +============+===========================================================+
672 | CC | Tells ``configure`` which C compiler to use. By default, |
673 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
674 | | compilers (in this order). Use this variable to override |
675 | | ``configure``\'s default behavior. |
676 +------------+-----------------------------------------------------------+
677 | CXX | Tells ``configure`` which C++ compiler to use. By |
678 | | default, ``configure`` will check ``PATH`` for |
679 | | ``clang++`` and GCC C++ compilers (in this order). Use |
680 | | this variable to override ``configure``'s default |
682 +------------+-----------------------------------------------------------+
684 The following options can be used to set or enable LLVM specific options:
686 ``--enable-optimized``
688 Enables optimized compilation (debugging symbols are removed and GCC
689 optimization flags are enabled). Note that this is the default setting if you
690 are using the LLVM distribution. The default behavior of an Subversion
691 checkout is to use an unoptimized build (also known as a debug build).
693 ``--enable-debug-runtime``
695 Enables debug symbols in the runtime libraries. The default is to strip debug
696 symbols from the runtime libraries.
700 Compile the Just In Time (JIT) compiler functionality. This is not available
701 on all platforms. The default is dependent on platform, so it is best to
702 explicitly enable it if you want it.
704 ``--enable-targets=target-option``
706 Controls which targets will be built and linked into llc. The default value
707 for ``target_options`` is "all" which builds and links all available targets.
708 The value "host-only" can be specified to build only a native compiler (no
709 cross-compiler targets available). The "native" target is selected as the
710 target of the build host. You can also specify a comma separated list of
711 target names that you want available in llc. The target names use all lower
712 case. The current set of targets is:
714 ``arm, cpp, hexagon, mips, mipsel, msp430, powerpc, ptx, sparc, spu,
715 systemz, x86, x86_64, xcore``.
719 Look for the doxygen program and enable construction of doxygen based
720 documentation from the source code. This is disabled by default because
721 generating the documentation can take a long time and producess 100s of
726 LLVM can use external disassembler library for various purposes (now it's used
727 only for examining code produced by JIT). This option will enable usage of
728 `udis86 <http://udis86.sourceforge.net/>`_ x86 (both 32 and 64 bits)
729 disassembler library.
731 To configure LLVM, follow these steps:
733 #. Change directory into the object root directory:
735 .. code-block:: console
739 #. Run the ``configure`` script located in the LLVM source tree:
741 .. code-block:: console
743 % SRC_ROOT/configure --prefix=/install/path [other options]
745 Compiling the LLVM Suite Source Code
746 ------------------------------------
748 Once you have configured LLVM, you can build it. There are three types of
753 These builds are the default when one is using an Subversion checkout and
754 types ``gmake`` (unless the ``--enable-optimized`` option was used during
755 configuration). The build system will compile the tools and libraries with
756 debugging information. To get a Debug Build using the LLVM distribution the
757 ``--disable-optimized`` option must be passed to ``configure``.
759 Release (Optimized) Builds
761 These builds are enabled with the ``--enable-optimized`` option to
762 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
763 line. For these builds, the build system will compile the tools and libraries
764 with GCC optimizations enabled and strip debugging information from the
765 libraries and executables it generates. Note that Release Builds are default
766 when using an LLVM distribution.
770 These builds are for use with profiling. They compile profiling information
771 into the code for use with programs like ``gprof``. Profile builds must be
772 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
774 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
775 directory and issuing the following command:
777 .. code-block:: console
781 If the build fails, please `check here`_ to see if you are using a version of
782 GCC that is known not to compile LLVM.
784 If you have multiple processors in your machine, you may wish to use some of the
785 parallel build options provided by GNU Make. For example, you could use the
788 .. code-block:: console
792 There are several special targets which are useful when working with the LLVM
797 Removes all files generated by the build. This includes object files,
798 generated C/C++ files, libraries, and executables.
802 Removes everything that ``gmake clean`` does, but also removes files generated
803 by ``configure``. It attempts to return the source tree to the original state
804 in which it was shipped.
808 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
809 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
810 defaults to ``/usr/local``.
812 ``gmake -C runtime install-bytecode``
814 Assuming you built LLVM into $OBJDIR, when this command is run, it will
815 install bitcode libraries into the GCC front end's bitcode library directory.
816 If you need to update your bitcode libraries, this is the target to use once
819 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
820 these ``make`` targets and descriptions of other targets available.
822 It is also possible to override default values from ``configure`` by declaring
823 variables on the command line. The following are some examples:
825 ``gmake ENABLE_OPTIMIZED=1``
827 Perform a Release (Optimized) build.
829 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
831 Perform a Release (Optimized) build without assertions enabled.
833 ``gmake ENABLE_OPTIMIZED=0``
835 Perform a Debug build.
837 ``gmake ENABLE_PROFILING=1``
839 Perform a Profiling build.
843 Print what ``gmake`` is doing on standard output.
845 ``gmake TOOL_VERBOSE=1``
847 Ask each tool invoked by the makefiles to print out what it is doing on
848 the standard output. This also implies ``VERBOSE=1``.
850 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
851 any subdirectories that it contains. Entering any directory inside the LLVM
852 object tree and typing ``gmake`` should rebuild anything in or below that
853 directory that is out of date.
855 This does not apply to building the documentation.
856 LLVM's (non-Doxygen) documentation is produced with the
857 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
858 There are some HTML documents that have not yet been converted to the new
859 system (which uses the easy-to-read and easy-to-write
860 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
862 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
864 For instructions on how to install Sphinx, see
865 `Sphinx Introduction for LLVM Developers
866 <http://lld.llvm.org/sphinx_intro.html>`_.
867 After following the instructions there for installing Sphinx, build the LLVM
868 HTML documentation by doing the following:
870 .. code-block:: console
873 $ make -f Makefile.sphinx
875 This creates a ``_build/html`` sub-directory with all of the HTML files, not
876 just the generated ones.
877 This directory corresponds to ``llvm.org/docs``.
878 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
879 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
880 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
885 It is possible to cross-compile LLVM itself. That is, you can create LLVM
886 executables and libraries to be hosted on a platform different from the platform
887 where they are built (a Canadian Cross build). To configure a cross-compile,
888 supply the configure script with ``--build`` and ``--host`` options that are
889 different. The values of these options must be legal target triples that your
890 GCC compiler supports.
892 The result of such a build is executables that are not runnable on on the build
893 host (--build option) but can be executed on the compile host (--host option).
895 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
896 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
897 about cross-compiling.
899 The Location of LLVM Object Files
900 ---------------------------------
902 The LLVM build system is capable of sharing a single LLVM source tree among
903 several LLVM builds. Hence, it is possible to build LLVM for several different
904 platforms or configurations using the same source tree.
906 This is accomplished in the typical autoconf manner:
908 * Change directory to where the LLVM object files should live:
910 .. code-block:: console
914 * Run the ``configure`` script found in the LLVM source directory:
916 .. code-block:: console
920 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
923 Debug Builds with assertions enabled (the default)
927 ``OBJ_ROOT/Debug+Asserts/bin``
931 ``OBJ_ROOT/Debug+Asserts/lib``
937 ``OBJ_ROOT/Release/bin``
941 ``OBJ_ROOT/Release/lib``
947 ``OBJ_ROOT/Profile/bin``
951 ``OBJ_ROOT/Profile/lib``
953 Optional Configuration Items
954 ----------------------------
956 If you're running on a Linux system that supports the `binfmt_misc
957 <http://en.wikipedia.org/wiki/binfmt_misc>`_
958 module, and you have root access on the system, you can set your system up to
959 execute LLVM bitcode files directly. To do this, use commands like this (the
960 first command may not be required if you are already using the module):
962 .. code-block:: console
964 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
965 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
966 % chmod u+x hello.bc (if needed)
969 This allows you to execute LLVM bitcode files directly. On Debian, you can also
970 use this command instead of the 'echo' command above:
972 .. code-block:: console
974 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
982 One useful source of information about the LLVM source base is the LLVM `doxygen
983 <http://www.doxygen.org/>`_ documentation available at
984 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
990 This directory contains some simple examples of how to use the LLVM IR and JIT.
995 This directory contains public header files exported from the LLVM library. The
996 three main subdirectories of this directory are:
998 ``llvm/include/llvm``
1000 This directory contains all of the LLVM specific header files. This directory
1001 also has subdirectories for different portions of LLVM: ``Analysis``,
1002 ``CodeGen``, ``Target``, ``Transforms``, etc...
1004 ``llvm/include/llvm/Support``
1006 This directory contains generic support libraries that are provided with LLVM
1007 but not necessarily specific to LLVM. For example, some C++ STL utilities and
1008 a Command Line option processing library store their header files here.
1010 ``llvm/include/llvm/Config``
1012 This directory contains header files configured by the ``configure`` script.
1013 They wrap "standard" UNIX and C header files. Source code can include these
1014 header files which automatically take care of the conditional #includes that
1015 the ``configure`` script generates.
1020 This directory contains most of the source files of the LLVM system. In LLVM,
1021 almost all code exists in libraries, making it very easy to share code among the
1024 ``llvm/lib/VMCore/``
1026 This directory holds the core LLVM source files that implement core classes
1027 like Instruction and BasicBlock.
1029 ``llvm/lib/AsmParser/``
1031 This directory holds the source code for the LLVM assembly language parser
1034 ``llvm/lib/Bitcode/``
1036 This directory holds code for reading and write LLVM bitcode.
1038 ``llvm/lib/Analysis/``
1040 This directory contains a variety of different program analyses, such as
1041 Dominator Information, Call Graphs, Induction Variables, Interval
1042 Identification, Natural Loop Identification, etc.
1044 ``llvm/lib/Transforms/``
1046 This directory contains the source code for the LLVM to LLVM program
1047 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1048 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1049 Elimination, and many others.
1051 ``llvm/lib/Target/``
1053 This directory contains files that describe various target architectures for
1054 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1055 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1058 ``llvm/lib/CodeGen/``
1060 This directory contains the major parts of the code generator: Instruction
1061 Selector, Instruction Scheduling, and Register Allocation.
1067 ``llvm/lib/Debugger/``
1069 This directory contains the source level debugger library that makes it
1070 possible to instrument LLVM programs so that a debugger could identify source
1071 code locations at which the program is executing.
1073 ``llvm/lib/ExecutionEngine/``
1075 This directory contains libraries for executing LLVM bitcode directly at
1076 runtime in both interpreted and JIT compiled fashions.
1078 ``llvm/lib/Support/``
1080 This directory contains the source code that corresponds to the header files
1081 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1086 This directory contains projects that are not strictly part of LLVM but are
1087 shipped with LLVM. This is also the directory where you should create your own
1088 LLVM-based projects. See ``llvm/projects/sample`` for an example of how to set
1089 up your own project.
1094 This directory contains libraries which are compiled into LLVM bitcode and used
1095 when linking programs with the Clang front end. Most of these libraries are
1096 skeleton versions of real libraries; for example, libc is a stripped down
1099 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1105 This directory contains feature and regression tests and other basic sanity
1106 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1107 lot of territory without being exhaustive.
1112 This is not a directory in the normal llvm module; it is a separate Subversion
1113 module that must be checked out (usually to ``projects/test-suite``). This
1114 module contains a comprehensive correctness, performance, and benchmarking test
1115 suite for LLVM. It is a separate Subversion module because not every LLVM user
1116 is interested in downloading or building such a comprehensive test suite. For
1117 further details on this test suite, please see the :doc:`Testing Guide
1118 <TestingGuide>` document.
1125 The **tools** directory contains the executables built out of the libraries
1126 above, which form the main part of the user interface. You can always get help
1127 for a tool by typing ``tool_name -help``. The following is a brief introduction
1128 to the most important tools. More detailed information is in
1129 the `Command Guide <CommandGuide/index.html>`_.
1133 ``bugpoint`` is used to debug optimization passes or code generation backends
1134 by narrowing down the given test case to the minimum number of passes and/or
1135 instructions that still cause a problem, whether it is a crash or
1136 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1141 The archiver produces an archive containing the given LLVM bitcode files,
1142 optionally with an index for faster lookup.
1146 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1150 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1154 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1159 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1160 (although very slowly...). For architectures that support it (currently x86,
1161 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1162 compiler (if the functionality was compiled in), and will execute the code
1163 *much* faster than the interpreter.
1167 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1168 native code assembly file or to C code (with the ``-march=c`` option).
1172 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1173 (which are specified on the command line), and then outputs the resultant
1174 bitcode. The '``opt -help``' command is a good way to get a list of the
1175 program transformations available in LLVM.
1177 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1178 file and print out the results. It is primarily useful for debugging
1179 analyses, or familiarizing yourself with what an analysis does.
1184 This directory contains utilities for working with LLVM source code, and some of
1185 the utilities are actually required as part of the build process because they
1186 are code generators for parts of LLVM infrastructure.
1191 ``codegen-diff`` is a script that finds differences between code that LLC
1192 generates and code that LLI generates. This is a useful tool if you are
1193 debugging one of them, assuming that the other generates correct output. For
1194 the full user manual, run ```perldoc codegen-diff'``.
1198 The ``emacs`` directory contains syntax-highlighting files which will work
1199 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1200 assembly files and TableGen description files. For information on how to use
1201 the syntax files, consult the ``README`` file in that directory.
1205 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1206 which is useful if one wishes to do a lot of development across directories
1207 and does not want to individually find each file. One way to use it is to run,
1208 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1213 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1214 passes to it a regular expression provided on ``llvmgrep``'s command
1215 line. This is a very efficient way of searching the source base for a
1216 particular regular expression.
1220 The ``makellvm`` script compiles all files in the current directory and then
1221 compiles and links the tool that is the first argument. For example, assuming
1222 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1223 path, simply running ``makellvm llc`` will make a build of the current
1224 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1229 The ``TableGen`` directory contains the tool used to generate register
1230 descriptions, instruction set descriptions, and even assemblers from common
1231 TableGen description files.
1235 The ``vim`` directory contains syntax-highlighting files which will work with
1236 the VIM editor, providing syntax highlighting support for LLVM assembly files
1237 and TableGen description files. For information on how to use the syntax
1238 files, consult the ``README`` file in that directory.
1242 An Example Using the LLVM Tool Chain
1243 ====================================
1245 This section gives an example of using LLVM with the Clang front end.
1250 #. First, create a simple C file, name it 'hello.c':
1257 printf("hello world\n");
1261 #. Next, compile the C file into a native executable:
1263 .. code-block:: console
1265 % clang hello.c -o hello
1269 Clang works just like GCC by default. The standard -S and -c arguments
1270 work as usual (producing a native .s or .o file, respectively).
1272 #. Next, compile the C file into an LLVM bitcode file:
1274 .. code-block:: console
1276 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1278 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1279 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1280 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1282 #. Run the program in both forms. To run the program, use:
1284 .. code-block:: console
1290 .. code-block:: console
1294 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1295 <CommandGuide/lli>`.
1297 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1299 .. code-block:: console
1301 % llvm-dis < hello.bc | less
1303 #. Compile the program to native assembly using the LLC code generator:
1305 .. code-block:: console
1307 % llc hello.bc -o hello.s
1309 #. Assemble the native assembly language file into a program:
1311 .. code-block:: console
1313 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1315 % gcc hello.s -o hello.native # On others
1317 #. Execute the native code program:
1319 .. code-block:: console
1323 Note that using clang to compile directly to native code (i.e. when the
1324 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1329 If you are having problems building or using LLVM, or if you have any other
1330 general questions about LLVM, please consult the `Frequently Asked
1331 Questions <FAQ.html>`_ page.
1338 This document is just an **introduction** on how to use LLVM to do some simple
1339 things... there are many more interesting and complicated things that you can do
1340 that aren't documented here (but we'll gladly accept a patch if you want to
1341 write something up!). For more information about LLVM, check out:
1343 * `LLVM Homepage <http://llvm.org/>`_
1344 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1345 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_