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32 The LLVM Getting Started documentation may be out of date.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 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
171 `python <http://www.python.org/>`_ >=2.5 Automated test suite\ :sup:`2`
172 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
173 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
174 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
175 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
176 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
177 =========================================================== ============ ==========================================
181 #. Only the C and C++ languages are needed so there's no need to build the
182 other languages for LLVM's purposes. See `below` for specific version
184 #. Only needed if you want to run the automated test suite in the
185 ``llvm/test`` directory.
186 #. If you want to make changes to the configure scripts, you will need GNU
187 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
188 will also need automake (1.9.6). We only use aclocal from that package.
189 #. Optional, adds compression/uncompression capabilities to selected LLVM
192 Additionally, your compilation host is expected to have the usual plethora of
193 Unix utilities. Specifically:
195 * **ar** --- archive library builder
196 * **bzip2** --- bzip2 command for distribution generation
197 * **bunzip2** --- bunzip2 command for distribution checking
198 * **chmod** --- change permissions on a file
199 * **cat** --- output concatenation utility
200 * **cp** --- copy files
201 * **date** --- print the current date/time
202 * **echo** --- print to standard output
203 * **egrep** --- extended regular expression search utility
204 * **find** --- find files/dirs in a file system
205 * **grep** --- regular expression search utility
206 * **gzip** --- gzip command for distribution generation
207 * **gunzip** --- gunzip command for distribution checking
208 * **install** --- install directories/files
209 * **mkdir** --- create a directory
210 * **mv** --- move (rename) files
211 * **ranlib** --- symbol table builder for archive libraries
212 * **rm** --- remove (delete) files and directories
213 * **sed** --- stream editor for transforming output
214 * **sh** --- Bourne shell for make build scripts
215 * **tar** --- tape archive for distribution generation
216 * **test** --- test things in file system
217 * **unzip** --- unzip command for distribution checking
218 * **zip** --- zip command for distribution generation
223 Broken versions of GCC and other tools
224 --------------------------------------
226 LLVM is very demanding of the host C++ compiler, and as such tends to expose
227 bugs in the compiler. In particular, several versions of GCC crash when trying
228 to compile LLVM. We routinely use GCC 4.2 (and higher) or Clang. Other
229 versions of GCC will probably work as well. GCC versions listed here are known
230 to not work. If you are using one of these versions, please try to upgrade your
231 GCC to something more recent. If you run into a problem with a version of GCC
232 not listed here, please `let us know <mailto:llvmdev@cs.uiuc.edu>`_. Please use
233 the "``gcc -v``" command to find out which version of GCC you are using.
235 **GCC versions prior to 3.0**: GCC 2.96.x and before had several problems in the
236 STL that effectively prevent it from compiling LLVM.
238 **GCC 3.2.2 and 3.2.3**: These versions of GCC fails to compile LLVM with a
239 bogus template error. This was fixed in later GCCs.
241 **GCC 3.3.2**: This version of GCC suffered from a `serious bug
242 <http://gcc.gnu.org/PR13392>`_ which causes it to crash in the
243 "``convert_from_eh_region_ranges_1``" GCC function.
245 **Cygwin GCC 3.3.3**: The version of GCC 3.3.3 commonly shipped with Cygwin does
248 **SuSE GCC 3.3.3**: The version of GCC 3.3.3 shipped with SuSE 9.1 (and possibly
249 others) does not compile LLVM correctly (it appears that exception handling is
250 broken in some cases). Please download the FSF 3.3.3 or upgrade to a newer
253 **GCC 3.4.0 on linux/x86 (32-bit)**: GCC miscompiles portions of the code
254 generator, causing an infinite loop in the llvm-gcc build when built with
255 optimizations enabled (i.e. a release build).
257 **GCC 3.4.2 on linux/x86 (32-bit)**: GCC miscompiles portions of the code
258 generator at -O3, as with 3.4.0. However gcc 3.4.2 (unlike 3.4.0) correctly
259 compiles LLVM at -O2. A work around is to build release LLVM builds with
260 "``make ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O2 ...``"
262 **GCC 3.4.x on X86-64/amd64**: GCC `miscompiles portions of LLVM
263 <http://llvm.org/PR1056>`__.
265 **GCC 3.4.4 (CodeSourcery ARM 2005q3-2)**: this compiler miscompiles LLVM when
266 building with optimizations enabled. It appears to work with "``make
267 ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O1``" or build a debug build.
269 **IA-64 GCC 4.0.0**: The IA-64 version of GCC 4.0.0 is known to miscompile LLVM.
271 **Apple Xcode 2.3**: GCC crashes when compiling LLVM at -O3 (which is the
272 default with ENABLE_OPTIMIZED=1. To work around this, build with
273 "``ENABLE_OPTIMIZED=1 OPTIMIZE_OPTION=-O2``".
275 **GCC 4.1.1**: GCC fails to build LLVM with template concept check errors
276 compiling some files. At the time of this writing, GCC mainline (4.2) did not
279 **GCC 4.1.1 on X86-64/amd64**: GCC `miscompiles portions of LLVM
280 <http://llvm.org/PR1063>`__ when compiling llvm itself into 64-bit code. LLVM
281 will appear to mostly work but will be buggy, e.g. failing portions of its
284 **GCC 4.1.2 on OpenSUSE**: Seg faults during libstdc++ build and on x86_64
285 platforms compiling md5.c gets a mangled constant.
287 **GCC 4.1.2 (20061115 (prerelease) (Debian 4.1.1-21)) on Debian**: Appears to
288 miscompile parts of LLVM 2.4. One symptom is ValueSymbolTable complaining about
289 symbols remaining in the table on destruction.
291 **GCC 4.1.2 20071124 (Red Hat 4.1.2-42)**: Suffers from the same symptoms as the
292 previous one. It appears to work with ENABLE_OPTIMIZED=0 (the default).
294 **Cygwin GCC 4.3.2 20080827 (beta) 2**: Users `reported
295 <http://llvm.org/PR4145>`_ various problems related with link errors when using
298 **Debian GCC 4.3.2 on X86**: Crashes building some files in LLVM 2.6.
300 **GCC 4.3.3 (Debian 4.3.3-10) on ARM**: Miscompiles parts of LLVM 2.6 when
301 optimizations are turned on. The symptom is an infinite loop in
302 ``FoldingSetImpl::RemoveNode`` while running the code generator.
304 **SUSE 11 GCC 4.3.4**: Miscompiles LLVM, causing crashes in ValueHandle logic.
306 **GCC 4.3.5 and GCC 4.4.5 on ARM**: These can miscompile ``value >> 1`` even at
307 ``-O0``. A test failure in ``test/Assembler/alignstack.ll`` is one symptom of
310 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
311 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
313 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
314 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
315 defined in a discarded section. You can safely ignore these messages as they are
316 erroneous and the linkage is correct. These messages disappear using ld 2.17.
318 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
319 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
320 times (minutes instead of seconds) when building LLVM. We recommend upgrading
321 to a newer version (2.17.50.0.4 or later).
323 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
324 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
325 intermittent failures when building LLVM with position independent code. The
326 symptom is an error about cyclic dependencies. We recommend upgrading to a
327 newer version of Gold.
329 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
330 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
331 3.0 does not implement a few builtins that are used in this library. We
332 recommend using the system GCC to compile LLVM and Clang in this case.
334 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
335 least some (``cxxabi.h``) libstdc++ headers.
337 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
338 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
339 causes Clang to refuse to compile condition_variable header file. At the time
340 of writing, this breaks LLD build.
342 .. _Getting Started with LLVM:
344 Getting Started with LLVM
345 =========================
347 The remainder of this guide is meant to get you up and running with LLVM and to
348 give you some basic information about the LLVM environment.
350 The later sections of this guide describe the `general layout`_ of the LLVM
351 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
352 more information about LLVM or to get help via e-mail.
354 Terminology and Notation
355 ------------------------
357 Throughout this manual, the following names are used to denote paths specific to
358 the local system and working environment. *These are not environment variables
359 you need to set but just strings used in the rest of this document below*. In
360 any of the examples below, simply replace each of these names with the
361 appropriate pathname on your local system. All these paths are absolute:
365 This is the top level directory of the LLVM source tree.
369 This is the top level directory of the LLVM object tree (i.e. the tree where
370 object files and compiled programs will be placed. It can be the same as
373 .. _Setting Up Your Environment:
375 Setting Up Your Environment
376 ---------------------------
378 In order to compile and use LLVM, you may need to set some environment
381 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
383 [Optional] This environment variable helps LLVM linking tools find the
384 locations of your bitcode libraries. It is provided only as a convenience
385 since you can specify the paths using the -L options of the tools and the
386 C/C++ front-end will automatically use the bitcode files installed in its
389 Unpacking the LLVM Archives
390 ---------------------------
392 If you have the LLVM distribution, you will need to unpack it before you can
393 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
394 and the LLVM GCC front end compiled for your platform. There is an additional
395 test suite that is optional. Each file is a TAR archive that is compressed with
398 The files are as follows, with *x.y* marking the version number:
402 Source release for the LLVM libraries and tools.
404 ``llvm-test-x.y.tar.gz``
406 Source release for the LLVM test-suite.
410 Checkout LLVM from Subversion
411 -----------------------------
413 If you have access to our Subversion repository, you can get a fresh copy of the
414 entire source code. All you need to do is check it out from Subversion as
417 * ``cd where-you-want-llvm-to-live``
418 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
419 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
421 This will create an '``llvm``' directory in the current directory and fully
422 populate it with the LLVM source code, Makefiles, test directories, and local
423 copies of documentation files.
425 If you want to get a specific release (as opposed to the most recent revision),
426 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
427 following releases are located in the following subdirectories of the '``tags``'
430 * Release 3.3: **RELEASE_33/final**
431 * Release 3.2: **RELEASE_32/final**
432 * Release 3.1: **RELEASE_31/final**
433 * Release 3.0: **RELEASE_30/final**
434 * Release 2.9: **RELEASE_29/final**
435 * Release 2.8: **RELEASE_28**
436 * Release 2.7: **RELEASE_27**
437 * Release 2.6: **RELEASE_26**
438 * Release 2.5: **RELEASE_25**
439 * Release 2.4: **RELEASE_24**
440 * Release 2.3: **RELEASE_23**
441 * Release 2.2: **RELEASE_22**
442 * Release 2.1: **RELEASE_21**
443 * Release 2.0: **RELEASE_20**
444 * Release 1.9: **RELEASE_19**
445 * Release 1.8: **RELEASE_18**
446 * Release 1.7: **RELEASE_17**
447 * Release 1.6: **RELEASE_16**
448 * Release 1.5: **RELEASE_15**
449 * Release 1.4: **RELEASE_14**
450 * Release 1.3: **RELEASE_13**
451 * Release 1.2: **RELEASE_12**
452 * Release 1.1: **RELEASE_11**
453 * Release 1.0: **RELEASE_1**
455 If you would like to get the LLVM test suite (a separate package as of 1.4), you
456 get it from the Subversion repository:
458 .. code-block:: console
461 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
463 By placing it in the ``llvm/projects``, it will be automatically configured by
464 the LLVM configure script as well as automatically updated when you run ``svn
470 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
471 automatically with each Subversion commit and contain all necessary git-svn
472 marks (so, you can recreate git-svn metadata locally). Note that right now
473 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
476 .. code-block:: console
478 % git clone http://llvm.org/git/llvm.git
480 If you want to check out clang too, run:
482 .. code-block:: console
485 % git clone http://llvm.org/git/clang.git
487 If you want to check out compiler-rt too, run:
489 .. code-block:: console
492 % git clone http://llvm.org/git/compiler-rt.git
494 If you want to check out the Test Suite Source Code (optional), run:
496 .. code-block:: console
499 % git clone http://llvm.org/git/test-suite.git
501 Since the upstream repository is in Subversion, you should use ``git
502 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
503 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
504 master branch, run the following command:
506 .. code-block:: console
508 % git config branch.master.rebase true
510 Sending patches with Git
511 ^^^^^^^^^^^^^^^^^^^^^^^^
513 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
515 Assume ``master`` points the upstream and ``mybranch`` points your working
516 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
517 sanity of whitespaces:
519 .. code-block:: console
521 % git diff --check master..mybranch
523 The easiest way to generate a patch is as below:
525 .. code-block:: console
527 % git diff master..mybranch > /path/to/mybranch.diff
529 It is a little different from svn-generated diff. git-diff-generated diff has
530 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
531 could be accepted with ``patch -p1 -N``.
533 But you may generate patchset with git-format-patch. It generates by-each-commit
534 patchset. To generate patch files to attach to your article:
536 .. code-block:: console
538 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
540 If you would like to send patches directly, you may use git-send-email or
541 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
543 .. code-block:: console
545 % git format-patch --attach master..mybranch --stdout | git imap-send
547 Then, your .git/config should have [imap] sections.
552 host = imaps://imap.gmail.com
553 user = your.gmail.account@gmail.com
558 folder = "[Gmail]/Drafts"
559 ; example for Japanese, "Modified UTF-7" encoded.
560 folder = "[Gmail]/&Tgtm+DBN-"
561 ; example for Traditional Chinese
562 folder = "[Gmail]/&g0l6Pw-"
564 For developers to work with git-svn
565 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
567 To set up clone from which you can submit code using ``git-svn``, run:
569 .. code-block:: console
571 % git clone http://llvm.org/git/llvm.git
573 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
574 % git config svn-remote.svn.fetch :refs/remotes/origin/master
575 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
577 # If you have clang too:
579 % git clone http://llvm.org/git/clang.git
581 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
582 % git config svn-remote.svn.fetch :refs/remotes/origin/master
585 Likewise for compiler-rt and test-suite.
587 To update this clone without generating git-svn tags that conflict with the
588 upstream Git repo, run:
590 .. code-block:: console
592 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
593 % git checkout master
596 git checkout master &&
599 Likewise for compiler-rt and test-suite.
601 This leaves your working directories on their master branches, so you'll need to
602 ``checkout`` each working branch individually and ``rebase`` it on top of its
605 For those who wish to be able to update an llvm repo/revert patches easily using
606 git-svn, please look in the directory for the scripts ``git-svnup`` and
609 To perform the aforementioned update steps go into your source directory and
610 just type ``git-svnup`` or ``git svnup`` and everything will just work.
612 If one wishes to revert a commit with git-svn, but do not want the git hash to
613 escape into the commit message, one can use the script ``git-svnrevert`` or
614 ``git svnrevert`` which will take in the git hash for the commit you want to
615 revert, look up the appropriate svn revision, and output a message where all
616 references to the git hash have been replaced with the svn revision.
618 To commit back changes via git-svn, use ``git svn dcommit``:
620 .. code-block:: console
624 Note that git-svn will create one SVN commit for each Git commit you have pending,
625 so squash and edit each commit before executing ``dcommit`` to make sure they all
626 conform to the coding standards and the developers' policy.
628 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
629 please make sure your current branch is up-to-date (via fetch/rebase) before
632 The git-svn metadata can get out of sync after you mess around with branches and
633 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
634 about files with uncommitted changes. The fix is to rebuild the metadata:
636 .. code-block:: console
641 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
643 Local LLVM Configuration
644 ------------------------
646 Once checked out from the Subversion repository, the LLVM suite source code must
647 be configured via the ``configure`` script. This script sets variables in the
648 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
649 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
650 Makefiles needed to begin building LLVM.
652 The following environment variables are used by the ``configure`` script to
653 configure the build system:
655 +------------+-----------------------------------------------------------+
656 | Variable | Purpose |
657 +============+===========================================================+
658 | CC | Tells ``configure`` which C compiler to use. By default, |
659 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
660 | | compilers (in this order). Use this variable to override |
661 | | ``configure``\'s default behavior. |
662 +------------+-----------------------------------------------------------+
663 | CXX | Tells ``configure`` which C++ compiler to use. By |
664 | | default, ``configure`` will check ``PATH`` for |
665 | | ``clang++`` and GCC C++ compilers (in this order). Use |
666 | | this variable to override ``configure``'s default |
668 +------------+-----------------------------------------------------------+
670 The following options can be used to set or enable LLVM specific options:
672 ``--enable-optimized``
674 Enables optimized compilation (debugging symbols are removed and GCC
675 optimization flags are enabled). Note that this is the default setting if you
676 are using the LLVM distribution. The default behavior of an Subversion
677 checkout is to use an unoptimized build (also known as a debug build).
679 ``--enable-debug-runtime``
681 Enables debug symbols in the runtime libraries. The default is to strip debug
682 symbols from the runtime libraries.
686 Compile the Just In Time (JIT) compiler functionality. This is not available
687 on all platforms. The default is dependent on platform, so it is best to
688 explicitly enable it if you want it.
690 ``--enable-targets=target-option``
692 Controls which targets will be built and linked into llc. The default value
693 for ``target_options`` is "all" which builds and links all available targets.
694 The value "host-only" can be specified to build only a native compiler (no
695 cross-compiler targets available). The "native" target is selected as the
696 target of the build host. You can also specify a comma separated list of
697 target names that you want available in llc. The target names use all lower
698 case. The current set of targets is:
700 ``arm, cpp, hexagon, mips, mipsel, msp430, powerpc, ptx, sparc, spu,
701 systemz, x86, x86_64, xcore``.
705 Look for the doxygen program and enable construction of doxygen based
706 documentation from the source code. This is disabled by default because
707 generating the documentation can take a long time and producess 100s of
712 LLVM can use external disassembler library for various purposes (now it's used
713 only for examining code produced by JIT). This option will enable usage of
714 `udis86 <http://udis86.sourceforge.net/>`_ x86 (both 32 and 64 bits)
715 disassembler library.
717 To configure LLVM, follow these steps:
719 #. Change directory into the object root directory:
721 .. code-block:: console
725 #. Run the ``configure`` script located in the LLVM source tree:
727 .. code-block:: console
729 % SRC_ROOT/configure --prefix=/install/path [other options]
731 Compiling the LLVM Suite Source Code
732 ------------------------------------
734 Once you have configured LLVM, you can build it. There are three types of
739 These builds are the default when one is using an Subversion checkout and
740 types ``gmake`` (unless the ``--enable-optimized`` option was used during
741 configuration). The build system will compile the tools and libraries with
742 debugging information. To get a Debug Build using the LLVM distribution the
743 ``--disable-optimized`` option must be passed to ``configure``.
745 Release (Optimized) Builds
747 These builds are enabled with the ``--enable-optimized`` option to
748 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
749 line. For these builds, the build system will compile the tools and libraries
750 with GCC optimizations enabled and strip debugging information from the
751 libraries and executables it generates. Note that Release Builds are default
752 when using an LLVM distribution.
756 These builds are for use with profiling. They compile profiling information
757 into the code for use with programs like ``gprof``. Profile builds must be
758 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
760 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
761 directory and issuing the following command:
763 .. code-block:: console
767 If the build fails, please `check here`_ to see if you are using a version of
768 GCC that is known not to compile LLVM.
770 If you have multiple processors in your machine, you may wish to use some of the
771 parallel build options provided by GNU Make. For example, you could use the
774 .. code-block:: console
778 There are several special targets which are useful when working with the LLVM
783 Removes all files generated by the build. This includes object files,
784 generated C/C++ files, libraries, and executables.
788 Removes everything that ``gmake clean`` does, but also removes files generated
789 by ``configure``. It attempts to return the source tree to the original state
790 in which it was shipped.
794 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
795 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
796 defaults to ``/usr/local``.
798 ``gmake -C runtime install-bytecode``
800 Assuming you built LLVM into $OBJDIR, when this command is run, it will
801 install bitcode libraries into the GCC front end's bitcode library directory.
802 If you need to update your bitcode libraries, this is the target to use once
805 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
806 these ``make`` targets and descriptions of other targets available.
808 It is also possible to override default values from ``configure`` by declaring
809 variables on the command line. The following are some examples:
811 ``gmake ENABLE_OPTIMIZED=1``
813 Perform a Release (Optimized) build.
815 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
817 Perform a Release (Optimized) build without assertions enabled.
819 ``gmake ENABLE_OPTIMIZED=0``
821 Perform a Debug build.
823 ``gmake ENABLE_PROFILING=1``
825 Perform a Profiling build.
829 Print what ``gmake`` is doing on standard output.
831 ``gmake TOOL_VERBOSE=1``
833 Ask each tool invoked by the makefiles to print out what it is doing on
834 the standard output. This also implies ``VERBOSE=1``.
836 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
837 any subdirectories that it contains. Entering any directory inside the LLVM
838 object tree and typing ``gmake`` should rebuild anything in or below that
839 directory that is out of date.
841 This does not apply to building the documentation.
842 LLVM's (non-Doxygen) documentation is produced with the
843 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
844 There are some HTML documents that have not yet been converted to the new
845 system (which uses the easy-to-read and easy-to-write
846 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
848 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
850 For instructions on how to install Sphinx, see
851 `Sphinx Introduction for LLVM Developers
852 <http://lld.llvm.org/sphinx_intro.html>`_.
853 After following the instructions there for installing Sphinx, build the LLVM
854 HTML documentation by doing the following:
856 .. code-block:: console
859 $ make -f Makefile.sphinx
861 This creates a ``_build/html`` sub-directory with all of the HTML files, not
862 just the generated ones.
863 This directory corresponds to ``llvm.org/docs``.
864 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
865 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
866 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
871 It is possible to cross-compile LLVM itself. That is, you can create LLVM
872 executables and libraries to be hosted on a platform different from the platform
873 where they are built (a Canadian Cross build). To configure a cross-compile,
874 supply the configure script with ``--build`` and ``--host`` options that are
875 different. The values of these options must be legal target triples that your
876 GCC compiler supports.
878 The result of such a build is executables that are not runnable on on the build
879 host (--build option) but can be executed on the compile host (--host option).
881 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
882 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
883 about cross-compiling.
885 The Location of LLVM Object Files
886 ---------------------------------
888 The LLVM build system is capable of sharing a single LLVM source tree among
889 several LLVM builds. Hence, it is possible to build LLVM for several different
890 platforms or configurations using the same source tree.
892 This is accomplished in the typical autoconf manner:
894 * Change directory to where the LLVM object files should live:
896 .. code-block:: console
900 * Run the ``configure`` script found in the LLVM source directory:
902 .. code-block:: console
906 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
909 Debug Builds with assertions enabled (the default)
913 ``OBJ_ROOT/Debug+Asserts/bin``
917 ``OBJ_ROOT/Debug+Asserts/lib``
923 ``OBJ_ROOT/Release/bin``
927 ``OBJ_ROOT/Release/lib``
933 ``OBJ_ROOT/Profile/bin``
937 ``OBJ_ROOT/Profile/lib``
939 Optional Configuration Items
940 ----------------------------
942 If you're running on a Linux system that supports the `binfmt_misc
943 <http://en.wikipedia.org/wiki/binfmt_misc>`_
944 module, and you have root access on the system, you can set your system up to
945 execute LLVM bitcode files directly. To do this, use commands like this (the
946 first command may not be required if you are already using the module):
948 .. code-block:: console
950 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
951 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
952 % chmod u+x hello.bc (if needed)
955 This allows you to execute LLVM bitcode files directly. On Debian, you can also
956 use this command instead of the 'echo' command above:
958 .. code-block:: console
960 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
968 One useful source of information about the LLVM source base is the LLVM `doxygen
969 <http://www.doxygen.org/>`_ documentation available at
970 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
976 This directory contains some simple examples of how to use the LLVM IR and JIT.
981 This directory contains public header files exported from the LLVM library. The
982 three main subdirectories of this directory are:
984 ``llvm/include/llvm``
986 This directory contains all of the LLVM specific header files. This directory
987 also has subdirectories for different portions of LLVM: ``Analysis``,
988 ``CodeGen``, ``Target``, ``Transforms``, etc...
990 ``llvm/include/llvm/Support``
992 This directory contains generic support libraries that are provided with LLVM
993 but not necessarily specific to LLVM. For example, some C++ STL utilities and
994 a Command Line option processing library store their header files here.
996 ``llvm/include/llvm/Config``
998 This directory contains header files configured by the ``configure`` script.
999 They wrap "standard" UNIX and C header files. Source code can include these
1000 header files which automatically take care of the conditional #includes that
1001 the ``configure`` script generates.
1006 This directory contains most of the source files of the LLVM system. In LLVM,
1007 almost all code exists in libraries, making it very easy to share code among the
1010 ``llvm/lib/VMCore/``
1012 This directory holds the core LLVM source files that implement core classes
1013 like Instruction and BasicBlock.
1015 ``llvm/lib/AsmParser/``
1017 This directory holds the source code for the LLVM assembly language parser
1020 ``llvm/lib/Bitcode/``
1022 This directory holds code for reading and write LLVM bitcode.
1024 ``llvm/lib/Analysis/``
1026 This directory contains a variety of different program analyses, such as
1027 Dominator Information, Call Graphs, Induction Variables, Interval
1028 Identification, Natural Loop Identification, etc.
1030 ``llvm/lib/Transforms/``
1032 This directory contains the source code for the LLVM to LLVM program
1033 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
1034 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
1035 Elimination, and many others.
1037 ``llvm/lib/Target/``
1039 This directory contains files that describe various target architectures for
1040 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
1041 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
1044 ``llvm/lib/CodeGen/``
1046 This directory contains the major parts of the code generator: Instruction
1047 Selector, Instruction Scheduling, and Register Allocation.
1053 ``llvm/lib/Debugger/``
1055 This directory contains the source level debugger library that makes it
1056 possible to instrument LLVM programs so that a debugger could identify source
1057 code locations at which the program is executing.
1059 ``llvm/lib/ExecutionEngine/``
1061 This directory contains libraries for executing LLVM bitcode directly at
1062 runtime in both interpreted and JIT compiled fashions.
1064 ``llvm/lib/Support/``
1066 This directory contains the source code that corresponds to the header files
1067 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1072 This directory contains projects that are not strictly part of LLVM but are
1073 shipped with LLVM. This is also the directory where you should create your own
1074 LLVM-based projects. See ``llvm/projects/sample`` for an example of how to set
1075 up your own project.
1080 This directory contains libraries which are compiled into LLVM bitcode and used
1081 when linking programs with the Clang front end. Most of these libraries are
1082 skeleton versions of real libraries; for example, libc is a stripped down
1085 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1091 This directory contains feature and regression tests and other basic sanity
1092 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1093 lot of territory without being exhaustive.
1098 This is not a directory in the normal llvm module; it is a separate Subversion
1099 module that must be checked out (usually to ``projects/test-suite``). This
1100 module contains a comprehensive correctness, performance, and benchmarking test
1101 suite for LLVM. It is a separate Subversion module because not every LLVM user
1102 is interested in downloading or building such a comprehensive test suite. For
1103 further details on this test suite, please see the :doc:`Testing Guide
1104 <TestingGuide>` document.
1111 The **tools** directory contains the executables built out of the libraries
1112 above, which form the main part of the user interface. You can always get help
1113 for a tool by typing ``tool_name -help``. The following is a brief introduction
1114 to the most important tools. More detailed information is in
1115 the `Command Guide <CommandGuide/index.html>`_.
1119 ``bugpoint`` is used to debug optimization passes or code generation backends
1120 by narrowing down the given test case to the minimum number of passes and/or
1121 instructions that still cause a problem, whether it is a crash or
1122 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1127 The archiver produces an archive containing the given LLVM bitcode files,
1128 optionally with an index for faster lookup.
1132 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1136 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1140 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1145 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1146 (although very slowly...). For architectures that support it (currently x86,
1147 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1148 compiler (if the functionality was compiled in), and will execute the code
1149 *much* faster than the interpreter.
1153 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1154 native code assembly file or to C code (with the ``-march=c`` option).
1158 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1159 (which are specified on the command line), and then outputs the resultant
1160 bitcode. The '``opt -help``' command is a good way to get a list of the
1161 program transformations available in LLVM.
1163 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1164 file and print out the results. It is primarily useful for debugging
1165 analyses, or familiarizing yourself with what an analysis does.
1170 This directory contains utilities for working with LLVM source code, and some of
1171 the utilities are actually required as part of the build process because they
1172 are code generators for parts of LLVM infrastructure.
1177 ``codegen-diff`` is a script that finds differences between code that LLC
1178 generates and code that LLI generates. This is a useful tool if you are
1179 debugging one of them, assuming that the other generates correct output. For
1180 the full user manual, run ```perldoc codegen-diff'``.
1184 The ``emacs`` directory contains syntax-highlighting files which will work
1185 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1186 assembly files and TableGen description files. For information on how to use
1187 the syntax files, consult the ``README`` file in that directory.
1191 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1192 which is useful if one wishes to do a lot of development across directories
1193 and does not want to individually find each file. One way to use it is to run,
1194 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1199 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1200 passes to it a regular expression provided on ``llvmgrep``'s command
1201 line. This is a very efficient way of searching the source base for a
1202 particular regular expression.
1206 The ``makellvm`` script compiles all files in the current directory and then
1207 compiles and links the tool that is the first argument. For example, assuming
1208 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1209 path, simply running ``makellvm llc`` will make a build of the current
1210 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1215 The ``TableGen`` directory contains the tool used to generate register
1216 descriptions, instruction set descriptions, and even assemblers from common
1217 TableGen description files.
1221 The ``vim`` directory contains syntax-highlighting files which will work with
1222 the VIM editor, providing syntax highlighting support for LLVM assembly files
1223 and TableGen description files. For information on how to use the syntax
1224 files, consult the ``README`` file in that directory.
1228 An Example Using the LLVM Tool Chain
1229 ====================================
1231 This section gives an example of using LLVM with the Clang front end.
1236 #. First, create a simple C file, name it 'hello.c':
1243 printf("hello world\n");
1247 #. Next, compile the C file into a native executable:
1249 .. code-block:: console
1251 % clang hello.c -o hello
1255 Clang works just like GCC by default. The standard -S and -c arguments
1256 work as usual (producing a native .s or .o file, respectively).
1258 #. Next, compile the C file into an LLVM bitcode file:
1260 .. code-block:: console
1262 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1264 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1265 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1266 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1268 #. Run the program in both forms. To run the program, use:
1270 .. code-block:: console
1276 .. code-block:: console
1280 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1281 <CommandGuide/lli>`.
1283 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1285 .. code-block:: console
1287 % llvm-dis < hello.bc | less
1289 #. Compile the program to native assembly using the LLC code generator:
1291 .. code-block:: console
1293 % llc hello.bc -o hello.s
1295 #. Assemble the native assembly language file into a program:
1297 .. code-block:: console
1299 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1301 % gcc hello.s -o hello.native # On others
1303 #. Execute the native code program:
1305 .. code-block:: console
1309 Note that using clang to compile directly to native code (i.e. when the
1310 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1315 If you are having problems building or using LLVM, or if you have any other
1316 general questions about LLVM, please consult the `Frequently Asked
1317 Questions <FAQ.html>`_ page.
1324 This document is just an **introduction** on how to use LLVM to do some simple
1325 things... there are many more interesting and complicated things that you can do
1326 that aren't documented here (but we'll gladly accept a patch if you want to
1327 write something up!). For more information about LLVM, check out:
1329 * `LLVM Homepage <http://llvm.org/>`_
1330 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1331 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_