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32 The LLVM Getting Started documentation may be out of date.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 Host C++ Toolchain, both Compiler and Standard Library
224 ------------------------------------------------------
226 LLVM is very demanding of the host C++ compiler, and as such tends to expose
227 bugs in the compiler. We are also planning to follow improvements and
228 developments in the C++ language and library reasonably closely. As such, we
229 require a modern host C++ toolchain, both compiler and standard library, in
232 For the most popular host toolchains we check for specific minimum versions in
239 Anything older than these toolchains *may* work, but will require forcing the
240 build system with a special option and is not really a supported host platform.
241 Also note that older versions of these compilers have often crashed or
244 For less widely used host toolchains such as ICC or xlC, be aware that a very
245 recent version may be required to support all of the C++ features used in LLVM.
247 We track certain versions of software that are *known* to fail when used as
248 part of the host toolchain. These even include linkers at times.
250 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
251 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
253 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
254 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
255 defined in a discarded section. You can safely ignore these messages as they are
256 erroneous and the linkage is correct. These messages disappear using ld 2.17.
258 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
259 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
260 times (minutes instead of seconds) when building LLVM. We recommend upgrading
261 to a newer version (2.17.50.0.4 or later).
263 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
264 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
265 intermittent failures when building LLVM with position independent code. The
266 symptom is an error about cyclic dependencies. We recommend upgrading to a
267 newer version of Gold.
269 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
270 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
271 3.0 does not implement a few builtins that are used in this library. We
272 recommend using the system GCC to compile LLVM and Clang in this case.
274 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
275 least some (``cxxabi.h``) libstdc++ headers.
277 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
278 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
279 causes Clang to refuse to compile condition_variable header file. At the time
280 of writing, this breaks LLD build.
282 .. _Getting Started with LLVM:
284 Getting Started with LLVM
285 =========================
287 The remainder of this guide is meant to get you up and running with LLVM and to
288 give you some basic information about the LLVM environment.
290 The later sections of this guide describe the `general layout`_ of the LLVM
291 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
292 more information about LLVM or to get help via e-mail.
294 Terminology and Notation
295 ------------------------
297 Throughout this manual, the following names are used to denote paths specific to
298 the local system and working environment. *These are not environment variables
299 you need to set but just strings used in the rest of this document below*. In
300 any of the examples below, simply replace each of these names with the
301 appropriate pathname on your local system. All these paths are absolute:
305 This is the top level directory of the LLVM source tree.
309 This is the top level directory of the LLVM object tree (i.e. the tree where
310 object files and compiled programs will be placed. It can be the same as
313 .. _Setting Up Your Environment:
315 Setting Up Your Environment
316 ---------------------------
318 In order to compile and use LLVM, you may need to set some environment
321 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
323 [Optional] This environment variable helps LLVM linking tools find the
324 locations of your bitcode libraries. It is provided only as a convenience
325 since you can specify the paths using the -L options of the tools and the
326 C/C++ front-end will automatically use the bitcode files installed in its
329 Unpacking the LLVM Archives
330 ---------------------------
332 If you have the LLVM distribution, you will need to unpack it before you can
333 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
334 and the LLVM GCC front end compiled for your platform. There is an additional
335 test suite that is optional. Each file is a TAR archive that is compressed with
338 The files are as follows, with *x.y* marking the version number:
342 Source release for the LLVM libraries and tools.
344 ``llvm-test-x.y.tar.gz``
346 Source release for the LLVM test-suite.
350 Checkout LLVM from Subversion
351 -----------------------------
353 If you have access to our Subversion repository, you can get a fresh copy of the
354 entire source code. All you need to do is check it out from Subversion as
357 * ``cd where-you-want-llvm-to-live``
358 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
359 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
361 This will create an '``llvm``' directory in the current directory and fully
362 populate it with the LLVM source code, Makefiles, test directories, and local
363 copies of documentation files.
365 If you want to get a specific release (as opposed to the most recent revision),
366 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
367 following releases are located in the following subdirectories of the '``tags``'
370 * Release 3.3: **RELEASE_33/final**
371 * Release 3.2: **RELEASE_32/final**
372 * Release 3.1: **RELEASE_31/final**
373 * Release 3.0: **RELEASE_30/final**
374 * Release 2.9: **RELEASE_29/final**
375 * Release 2.8: **RELEASE_28**
376 * Release 2.7: **RELEASE_27**
377 * Release 2.6: **RELEASE_26**
378 * Release 2.5: **RELEASE_25**
379 * Release 2.4: **RELEASE_24**
380 * Release 2.3: **RELEASE_23**
381 * Release 2.2: **RELEASE_22**
382 * Release 2.1: **RELEASE_21**
383 * Release 2.0: **RELEASE_20**
384 * Release 1.9: **RELEASE_19**
385 * Release 1.8: **RELEASE_18**
386 * Release 1.7: **RELEASE_17**
387 * Release 1.6: **RELEASE_16**
388 * Release 1.5: **RELEASE_15**
389 * Release 1.4: **RELEASE_14**
390 * Release 1.3: **RELEASE_13**
391 * Release 1.2: **RELEASE_12**
392 * Release 1.1: **RELEASE_11**
393 * Release 1.0: **RELEASE_1**
395 If you would like to get the LLVM test suite (a separate package as of 1.4), you
396 get it from the Subversion repository:
398 .. code-block:: console
401 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
403 By placing it in the ``llvm/projects``, it will be automatically configured by
404 the LLVM configure script as well as automatically updated when you run ``svn
410 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
411 automatically with each Subversion commit and contain all necessary git-svn
412 marks (so, you can recreate git-svn metadata locally). Note that right now
413 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
416 .. code-block:: console
418 % git clone http://llvm.org/git/llvm.git
420 If you want to check out clang too, run:
422 .. code-block:: console
425 % git clone http://llvm.org/git/clang.git
427 If you want to check out compiler-rt too, run:
429 .. code-block:: console
432 % git clone http://llvm.org/git/compiler-rt.git
434 If you want to check out the Test Suite Source Code (optional), run:
436 .. code-block:: console
439 % git clone http://llvm.org/git/test-suite.git
441 Since the upstream repository is in Subversion, you should use ``git
442 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
443 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
444 master branch, run the following command:
446 .. code-block:: console
448 % git config branch.master.rebase true
450 Sending patches with Git
451 ^^^^^^^^^^^^^^^^^^^^^^^^
453 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
455 Assume ``master`` points the upstream and ``mybranch`` points your working
456 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
457 sanity of whitespaces:
459 .. code-block:: console
461 % git diff --check master..mybranch
463 The easiest way to generate a patch is as below:
465 .. code-block:: console
467 % git diff master..mybranch > /path/to/mybranch.diff
469 It is a little different from svn-generated diff. git-diff-generated diff has
470 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
471 could be accepted with ``patch -p1 -N``.
473 But you may generate patchset with git-format-patch. It generates by-each-commit
474 patchset. To generate patch files to attach to your article:
476 .. code-block:: console
478 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
480 If you would like to send patches directly, you may use git-send-email or
481 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
483 .. code-block:: console
485 % git format-patch --attach master..mybranch --stdout | git imap-send
487 Then, your .git/config should have [imap] sections.
492 host = imaps://imap.gmail.com
493 user = your.gmail.account@gmail.com
498 folder = "[Gmail]/Drafts"
499 ; example for Japanese, "Modified UTF-7" encoded.
500 folder = "[Gmail]/&Tgtm+DBN-"
501 ; example for Traditional Chinese
502 folder = "[Gmail]/&g0l6Pw-"
504 For developers to work with git-svn
505 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
507 To set up clone from which you can submit code using ``git-svn``, run:
509 .. code-block:: console
511 % git clone http://llvm.org/git/llvm.git
513 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
514 % git config svn-remote.svn.fetch :refs/remotes/origin/master
515 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
517 # If you have clang too:
519 % git clone http://llvm.org/git/clang.git
521 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
522 % git config svn-remote.svn.fetch :refs/remotes/origin/master
525 Likewise for compiler-rt and test-suite.
527 To update this clone without generating git-svn tags that conflict with the
528 upstream Git repo, run:
530 .. code-block:: console
532 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
533 % git checkout master
536 git checkout master &&
539 Likewise for compiler-rt and test-suite.
541 This leaves your working directories on their master branches, so you'll need to
542 ``checkout`` each working branch individually and ``rebase`` it on top of its
545 For those who wish to be able to update an llvm repo/revert patches easily using
546 git-svn, please look in the directory for the scripts ``git-svnup`` and
549 To perform the aforementioned update steps go into your source directory and
550 just type ``git-svnup`` or ``git svnup`` and everything will just work.
552 If one wishes to revert a commit with git-svn, but do not want the git hash to
553 escape into the commit message, one can use the script ``git-svnrevert`` or
554 ``git svnrevert`` which will take in the git hash for the commit you want to
555 revert, look up the appropriate svn revision, and output a message where all
556 references to the git hash have been replaced with the svn revision.
558 To commit back changes via git-svn, use ``git svn dcommit``:
560 .. code-block:: console
564 Note that git-svn will create one SVN commit for each Git commit you have pending,
565 so squash and edit each commit before executing ``dcommit`` to make sure they all
566 conform to the coding standards and the developers' policy.
568 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
569 please make sure your current branch is up-to-date (via fetch/rebase) before
572 The git-svn metadata can get out of sync after you mess around with branches and
573 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
574 about files with uncommitted changes. The fix is to rebuild the metadata:
576 .. code-block:: console
581 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
583 Local LLVM Configuration
584 ------------------------
586 Once checked out from the Subversion repository, the LLVM suite source code must
587 be configured via the ``configure`` script. This script sets variables in the
588 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
589 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
590 Makefiles needed to begin building LLVM.
592 The following environment variables are used by the ``configure`` script to
593 configure the build system:
595 +------------+-----------------------------------------------------------+
596 | Variable | Purpose |
597 +============+===========================================================+
598 | CC | Tells ``configure`` which C compiler to use. By default, |
599 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
600 | | compilers (in this order). Use this variable to override |
601 | | ``configure``\'s default behavior. |
602 +------------+-----------------------------------------------------------+
603 | CXX | Tells ``configure`` which C++ compiler to use. By |
604 | | default, ``configure`` will check ``PATH`` for |
605 | | ``clang++`` and GCC C++ compilers (in this order). Use |
606 | | this variable to override ``configure``'s default |
608 +------------+-----------------------------------------------------------+
610 The following options can be used to set or enable LLVM specific options:
612 ``--enable-optimized``
614 Enables optimized compilation (debugging symbols are removed and GCC
615 optimization flags are enabled). Note that this is the default setting if you
616 are using the LLVM distribution. The default behavior of an Subversion
617 checkout is to use an unoptimized build (also known as a debug build).
619 ``--enable-debug-runtime``
621 Enables debug symbols in the runtime libraries. The default is to strip debug
622 symbols from the runtime libraries.
626 Compile the Just In Time (JIT) compiler functionality. This is not available
627 on all platforms. The default is dependent on platform, so it is best to
628 explicitly enable it if you want it.
630 ``--enable-targets=target-option``
632 Controls which targets will be built and linked into llc. The default value
633 for ``target_options`` is "all" which builds and links all available targets.
634 The value "host-only" can be specified to build only a native compiler (no
635 cross-compiler targets available). The "native" target is selected as the
636 target of the build host. You can also specify a comma separated list of
637 target names that you want available in llc. The target names use all lower
638 case. The current set of targets is:
640 ``arm, cpp, hexagon, mips, mipsel, msp430, powerpc, ptx, sparc, spu,
641 systemz, x86, x86_64, xcore``.
645 Look for the doxygen program and enable construction of doxygen based
646 documentation from the source code. This is disabled by default because
647 generating the documentation can take a long time and producess 100s of
652 LLVM can use external disassembler library for various purposes (now it's used
653 only for examining code produced by JIT). This option will enable usage of
654 `udis86 <http://udis86.sourceforge.net/>`_ x86 (both 32 and 64 bits)
655 disassembler library.
657 To configure LLVM, follow these steps:
659 #. Change directory into the object root directory:
661 .. code-block:: console
665 #. Run the ``configure`` script located in the LLVM source tree:
667 .. code-block:: console
669 % SRC_ROOT/configure --prefix=/install/path [other options]
671 Compiling the LLVM Suite Source Code
672 ------------------------------------
674 Once you have configured LLVM, you can build it. There are three types of
679 These builds are the default when one is using an Subversion checkout and
680 types ``gmake`` (unless the ``--enable-optimized`` option was used during
681 configuration). The build system will compile the tools and libraries with
682 debugging information. To get a Debug Build using the LLVM distribution the
683 ``--disable-optimized`` option must be passed to ``configure``.
685 Release (Optimized) Builds
687 These builds are enabled with the ``--enable-optimized`` option to
688 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
689 line. For these builds, the build system will compile the tools and libraries
690 with GCC optimizations enabled and strip debugging information from the
691 libraries and executables it generates. Note that Release Builds are default
692 when using an LLVM distribution.
696 These builds are for use with profiling. They compile profiling information
697 into the code for use with programs like ``gprof``. Profile builds must be
698 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
700 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
701 directory and issuing the following command:
703 .. code-block:: console
707 If the build fails, please `check here`_ to see if you are using a version of
708 GCC that is known not to compile LLVM.
710 If you have multiple processors in your machine, you may wish to use some of the
711 parallel build options provided by GNU Make. For example, you could use the
714 .. code-block:: console
718 There are several special targets which are useful when working with the LLVM
723 Removes all files generated by the build. This includes object files,
724 generated C/C++ files, libraries, and executables.
728 Removes everything that ``gmake clean`` does, but also removes files generated
729 by ``configure``. It attempts to return the source tree to the original state
730 in which it was shipped.
734 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
735 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
736 defaults to ``/usr/local``.
738 ``gmake -C runtime install-bytecode``
740 Assuming you built LLVM into $OBJDIR, when this command is run, it will
741 install bitcode libraries into the GCC front end's bitcode library directory.
742 If you need to update your bitcode libraries, this is the target to use once
745 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
746 these ``make`` targets and descriptions of other targets available.
748 It is also possible to override default values from ``configure`` by declaring
749 variables on the command line. The following are some examples:
751 ``gmake ENABLE_OPTIMIZED=1``
753 Perform a Release (Optimized) build.
755 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
757 Perform a Release (Optimized) build without assertions enabled.
759 ``gmake ENABLE_OPTIMIZED=0``
761 Perform a Debug build.
763 ``gmake ENABLE_PROFILING=1``
765 Perform a Profiling build.
769 Print what ``gmake`` is doing on standard output.
771 ``gmake TOOL_VERBOSE=1``
773 Ask each tool invoked by the makefiles to print out what it is doing on
774 the standard output. This also implies ``VERBOSE=1``.
776 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
777 any subdirectories that it contains. Entering any directory inside the LLVM
778 object tree and typing ``gmake`` should rebuild anything in or below that
779 directory that is out of date.
781 This does not apply to building the documentation.
782 LLVM's (non-Doxygen) documentation is produced with the
783 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
784 There are some HTML documents that have not yet been converted to the new
785 system (which uses the easy-to-read and easy-to-write
786 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
788 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
790 For instructions on how to install Sphinx, see
791 `Sphinx Introduction for LLVM Developers
792 <http://lld.llvm.org/sphinx_intro.html>`_.
793 After following the instructions there for installing Sphinx, build the LLVM
794 HTML documentation by doing the following:
796 .. code-block:: console
799 $ make -f Makefile.sphinx
801 This creates a ``_build/html`` sub-directory with all of the HTML files, not
802 just the generated ones.
803 This directory corresponds to ``llvm.org/docs``.
804 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
805 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
806 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
811 It is possible to cross-compile LLVM itself. That is, you can create LLVM
812 executables and libraries to be hosted on a platform different from the platform
813 where they are built (a Canadian Cross build). To configure a cross-compile,
814 supply the configure script with ``--build`` and ``--host`` options that are
815 different. The values of these options must be legal target triples that your
816 GCC compiler supports.
818 The result of such a build is executables that are not runnable on on the build
819 host (--build option) but can be executed on the compile host (--host option).
821 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
822 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
823 about cross-compiling.
825 The Location of LLVM Object Files
826 ---------------------------------
828 The LLVM build system is capable of sharing a single LLVM source tree among
829 several LLVM builds. Hence, it is possible to build LLVM for several different
830 platforms or configurations using the same source tree.
832 This is accomplished in the typical autoconf manner:
834 * Change directory to where the LLVM object files should live:
836 .. code-block:: console
840 * Run the ``configure`` script found in the LLVM source directory:
842 .. code-block:: console
846 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
849 Debug Builds with assertions enabled (the default)
853 ``OBJ_ROOT/Debug+Asserts/bin``
857 ``OBJ_ROOT/Debug+Asserts/lib``
863 ``OBJ_ROOT/Release/bin``
867 ``OBJ_ROOT/Release/lib``
873 ``OBJ_ROOT/Profile/bin``
877 ``OBJ_ROOT/Profile/lib``
879 Optional Configuration Items
880 ----------------------------
882 If you're running on a Linux system that supports the `binfmt_misc
883 <http://en.wikipedia.org/wiki/binfmt_misc>`_
884 module, and you have root access on the system, you can set your system up to
885 execute LLVM bitcode files directly. To do this, use commands like this (the
886 first command may not be required if you are already using the module):
888 .. code-block:: console
890 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
891 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
892 % chmod u+x hello.bc (if needed)
895 This allows you to execute LLVM bitcode files directly. On Debian, you can also
896 use this command instead of the 'echo' command above:
898 .. code-block:: console
900 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
908 One useful source of information about the LLVM source base is the LLVM `doxygen
909 <http://www.doxygen.org/>`_ documentation available at
910 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
916 This directory contains some simple examples of how to use the LLVM IR and JIT.
921 This directory contains public header files exported from the LLVM library. The
922 three main subdirectories of this directory are:
924 ``llvm/include/llvm``
926 This directory contains all of the LLVM specific header files. This directory
927 also has subdirectories for different portions of LLVM: ``Analysis``,
928 ``CodeGen``, ``Target``, ``Transforms``, etc...
930 ``llvm/include/llvm/Support``
932 This directory contains generic support libraries that are provided with LLVM
933 but not necessarily specific to LLVM. For example, some C++ STL utilities and
934 a Command Line option processing library store their header files here.
936 ``llvm/include/llvm/Config``
938 This directory contains header files configured by the ``configure`` script.
939 They wrap "standard" UNIX and C header files. Source code can include these
940 header files which automatically take care of the conditional #includes that
941 the ``configure`` script generates.
946 This directory contains most of the source files of the LLVM system. In LLVM,
947 almost all code exists in libraries, making it very easy to share code among the
952 This directory holds the core LLVM source files that implement core classes
953 like Instruction and BasicBlock.
955 ``llvm/lib/AsmParser/``
957 This directory holds the source code for the LLVM assembly language parser
960 ``llvm/lib/Bitcode/``
962 This directory holds code for reading and write LLVM bitcode.
964 ``llvm/lib/Analysis/``
966 This directory contains a variety of different program analyses, such as
967 Dominator Information, Call Graphs, Induction Variables, Interval
968 Identification, Natural Loop Identification, etc.
970 ``llvm/lib/Transforms/``
972 This directory contains the source code for the LLVM to LLVM program
973 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
974 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
975 Elimination, and many others.
979 This directory contains files that describe various target architectures for
980 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
981 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
984 ``llvm/lib/CodeGen/``
986 This directory contains the major parts of the code generator: Instruction
987 Selector, Instruction Scheduling, and Register Allocation.
993 ``llvm/lib/Debugger/``
995 This directory contains the source level debugger library that makes it
996 possible to instrument LLVM programs so that a debugger could identify source
997 code locations at which the program is executing.
999 ``llvm/lib/ExecutionEngine/``
1001 This directory contains libraries for executing LLVM bitcode directly at
1002 runtime in both interpreted and JIT compiled fashions.
1004 ``llvm/lib/Support/``
1006 This directory contains the source code that corresponds to the header files
1007 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1012 This directory contains projects that are not strictly part of LLVM but are
1013 shipped with LLVM. This is also the directory where you should create your own
1014 LLVM-based projects. See ``llvm/projects/sample`` for an example of how to set
1015 up your own project.
1020 This directory contains libraries which are compiled into LLVM bitcode and used
1021 when linking programs with the Clang front end. Most of these libraries are
1022 skeleton versions of real libraries; for example, libc is a stripped down
1025 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1031 This directory contains feature and regression tests and other basic sanity
1032 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1033 lot of territory without being exhaustive.
1038 This is not a directory in the normal llvm module; it is a separate Subversion
1039 module that must be checked out (usually to ``projects/test-suite``). This
1040 module contains a comprehensive correctness, performance, and benchmarking test
1041 suite for LLVM. It is a separate Subversion module because not every LLVM user
1042 is interested in downloading or building such a comprehensive test suite. For
1043 further details on this test suite, please see the :doc:`Testing Guide
1044 <TestingGuide>` document.
1051 The **tools** directory contains the executables built out of the libraries
1052 above, which form the main part of the user interface. You can always get help
1053 for a tool by typing ``tool_name -help``. The following is a brief introduction
1054 to the most important tools. More detailed information is in
1055 the `Command Guide <CommandGuide/index.html>`_.
1059 ``bugpoint`` is used to debug optimization passes or code generation backends
1060 by narrowing down the given test case to the minimum number of passes and/or
1061 instructions that still cause a problem, whether it is a crash or
1062 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1067 The archiver produces an archive containing the given LLVM bitcode files,
1068 optionally with an index for faster lookup.
1072 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1076 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1080 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1085 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1086 (although very slowly...). For architectures that support it (currently x86,
1087 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1088 compiler (if the functionality was compiled in), and will execute the code
1089 *much* faster than the interpreter.
1093 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1094 native code assembly file or to C code (with the ``-march=c`` option).
1098 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1099 (which are specified on the command line), and then outputs the resultant
1100 bitcode. The '``opt -help``' command is a good way to get a list of the
1101 program transformations available in LLVM.
1103 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1104 file and print out the results. It is primarily useful for debugging
1105 analyses, or familiarizing yourself with what an analysis does.
1110 This directory contains utilities for working with LLVM source code, and some of
1111 the utilities are actually required as part of the build process because they
1112 are code generators for parts of LLVM infrastructure.
1117 ``codegen-diff`` is a script that finds differences between code that LLC
1118 generates and code that LLI generates. This is a useful tool if you are
1119 debugging one of them, assuming that the other generates correct output. For
1120 the full user manual, run ```perldoc codegen-diff'``.
1124 The ``emacs`` directory contains syntax-highlighting files which will work
1125 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1126 assembly files and TableGen description files. For information on how to use
1127 the syntax files, consult the ``README`` file in that directory.
1131 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1132 which is useful if one wishes to do a lot of development across directories
1133 and does not want to individually find each file. One way to use it is to run,
1134 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1139 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1140 passes to it a regular expression provided on ``llvmgrep``'s command
1141 line. This is a very efficient way of searching the source base for a
1142 particular regular expression.
1146 The ``makellvm`` script compiles all files in the current directory and then
1147 compiles and links the tool that is the first argument. For example, assuming
1148 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1149 path, simply running ``makellvm llc`` will make a build of the current
1150 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1155 The ``TableGen`` directory contains the tool used to generate register
1156 descriptions, instruction set descriptions, and even assemblers from common
1157 TableGen description files.
1161 The ``vim`` directory contains syntax-highlighting files which will work with
1162 the VIM editor, providing syntax highlighting support for LLVM assembly files
1163 and TableGen description files. For information on how to use the syntax
1164 files, consult the ``README`` file in that directory.
1168 An Example Using the LLVM Tool Chain
1169 ====================================
1171 This section gives an example of using LLVM with the Clang front end.
1176 #. First, create a simple C file, name it 'hello.c':
1183 printf("hello world\n");
1187 #. Next, compile the C file into a native executable:
1189 .. code-block:: console
1191 % clang hello.c -o hello
1195 Clang works just like GCC by default. The standard -S and -c arguments
1196 work as usual (producing a native .s or .o file, respectively).
1198 #. Next, compile the C file into an LLVM bitcode file:
1200 .. code-block:: console
1202 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1204 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1205 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1206 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1208 #. Run the program in both forms. To run the program, use:
1210 .. code-block:: console
1216 .. code-block:: console
1220 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1221 <CommandGuide/lli>`.
1223 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1225 .. code-block:: console
1227 % llvm-dis < hello.bc | less
1229 #. Compile the program to native assembly using the LLC code generator:
1231 .. code-block:: console
1233 % llc hello.bc -o hello.s
1235 #. Assemble the native assembly language file into a program:
1237 .. code-block:: console
1239 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1241 % gcc hello.s -o hello.native # On others
1243 #. Execute the native code program:
1245 .. code-block:: console
1249 Note that using clang to compile directly to native code (i.e. when the
1250 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1255 If you are having problems building or using LLVM, or if you have any other
1256 general questions about LLVM, please consult the `Frequently Asked
1257 Questions <FAQ.html>`_ page.
1264 This document is just an **introduction** on how to use LLVM to do some simple
1265 things... there are many more interesting and complicated things that you can do
1266 that aren't documented here (but we'll gladly accept a patch if you want to
1267 write something up!). For more information about LLVM, check out:
1269 * `LLVM Homepage <http://llvm.org/>`_
1270 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1271 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_