1 ====================================
2 Getting Started with the LLVM System
3 ====================================
11 Welcome to LLVM! In order to get started, you first need to know some basic
14 First, LLVM comes in three pieces. The first piece is the LLVM suite. This
15 contains all of the tools, libraries, and header files needed to use LLVM. It
16 contains an assembler, disassembler, bitcode analyzer and bitcode optimizer. It
17 also contains basic regression tests that can be used to test the LLVM tools and
20 The second piece is the `Clang <http://clang.llvm.org/>`_ front end. This
21 component compiles C, C++, Objective C, and Objective C++ code into LLVM
22 bitcode. Once compiled into LLVM bitcode, a program can be manipulated with the
23 LLVM tools from the LLVM suite.
25 There is a third, optional piece called Test Suite. It is a suite of programs
26 with a testing harness that can be used to further test LLVM's functionality
29 Getting Started Quickly (A Summary)
30 ===================================
32 The LLVM Getting Started documentation may be out of date. So, the `Clang
33 Getting Started <http://clang.llvm.org/get_started.html>`_ page might also be a
36 Here's the short story for getting up and running quickly with LLVM:
38 #. Read the documentation.
39 #. Read the documentation.
40 #. Remember that you were warned twice about reading the documentation.
43 * ``cd where-you-want-llvm-to-live``
44 * ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
48 * ``cd where-you-want-llvm-to-live``
50 * ``svn co http://llvm.org/svn/llvm-project/cfe/trunk clang``
52 #. Checkout Compiler-RT:
54 * ``cd where-you-want-llvm-to-live``
55 * ``cd llvm/projects``
56 * ``svn co http://llvm.org/svn/llvm-project/compiler-rt/trunk compiler-rt``
58 #. Get the Test Suite Source Code **[Optional]**
60 * ``cd where-you-want-llvm-to-live``
61 * ``cd llvm/projects``
62 * ``svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite``
64 #. Configure and build LLVM and Clang:
66 * ``cd where-you-want-to-build-llvm``
67 * ``mkdir build`` (for building without polluting the source dir)
69 * ``../llvm/configure [options]``
72 * ``--prefix=directory`` --- Specify for *directory* the full pathname of
73 where you want the LLVM tools and libraries to be installed (default
76 * ``--enable-optimized`` --- Compile with optimizations enabled (default
79 * ``--enable-assertions`` --- Compile with assertion checks enabled
82 * ``make [-j]`` --- The ``-j`` specifies the number of jobs (commands) to run
83 simultaneously. This builds both LLVM and Clang for Debug+Asserts mode.
84 The ``--enable-optimized`` configure option is used to specify a Release
87 * ``make check-all`` --- This run the regression tests to ensure everything
90 * It is also possible to use CMake instead of the makefiles. With CMake it is
91 possible to generate project files for several IDEs: Xcode, Eclipse CDT4,
92 CodeBlocks, Qt-Creator (use the CodeBlocks generator), KDevelop3.
94 * If you get an "internal compiler error (ICE)" or test failures, see
97 Consult the `Getting Started with LLVM`_ section for detailed information on
98 configuring and compiling LLVM. See `Setting Up Your Environment`_ for tips
99 that simplify working with the Clang front end and LLVM tools. Go to `Program
100 Layout`_ to learn about the layout of the source code tree.
105 Before you begin to use the LLVM system, review the requirements given below.
106 This may save you some trouble by knowing ahead of time what hardware and
107 software you will need.
112 LLVM is known to work on the following host platforms:
114 ================== ===================== =============
116 ================== ===================== =============
117 AuroraUX x86\ :sup:`1` GCC
118 Linux x86\ :sup:`1` GCC, Clang
119 Linux amd64 GCC, Clang
120 Linux ARM\ :sup:`4` GCC, Clang
121 Linux PowerPC GCC, Clang
122 Solaris V9 (Ultrasparc) GCC
123 FreeBSD x86\ :sup:`1` GCC, Clang
124 FreeBSD amd64 GCC, Clang
125 MacOS X\ :sup:`2` PowerPC GCC
126 MacOS X x86 GCC, Clang
127 Cygwin/Win32 x86\ :sup:`1, 3` GCC
128 Windows x86\ :sup:`1` Visual Studio
129 Windows x64 x86-64 Visual Studio
130 ================== ===================== =============
134 #. Code generation supported for Pentium processors and up
135 #. Code generation supported for 32-bit ABI only
136 #. To use LLVM modules on Win32-based system, you may configure LLVM
137 with ``--enable-shared``.
138 #. MCJIT not working well pre-v7, old JIT engine not supported any more.
140 Note that you will need about 1-3 GB of space for a full LLVM build in Debug
141 mode, depending on the system (it is so large because of all the debugging
142 information and the fact that the libraries are statically linked into multiple
143 tools). If you do not need many of the tools and you are space-conscious, you
144 can pass ``ONLY_TOOLS="tools you need"`` to make. The Release build requires
145 considerably less space.
147 The LLVM suite *may* compile on other platforms, but it is not guaranteed to do
148 so. If compilation is successful, the LLVM utilities should be able to
149 assemble, disassemble, analyze, and optimize LLVM bitcode. Code generation
150 should work as well, although the generated native code may not work on your
156 Compiling LLVM requires that you have several software packages installed. The
157 table below lists those required packages. The Package column is the usual name
158 for the software package that LLVM depends on. The Version column provides
159 "known to work" versions of the package. The Notes column describes how LLVM
160 uses the package and provides other details.
162 =========================================================== ============ ==========================================
163 Package Version Notes
164 =========================================================== ============ ==========================================
165 `GNU Make <http://savannah.gnu.org/projects/make>`_ 3.79, 3.79.1 Makefile/build processor
166 `GCC <http://gcc.gnu.org/>`_ >=4.7.0 C/C++ compiler\ :sup:`1`
167 `python <http://www.python.org/>`_ >=2.5 Automated test suite\ :sup:`2`
168 `GNU M4 <http://savannah.gnu.org/projects/m4>`_ 1.4 Macro processor for configuration\ :sup:`3`
169 `GNU Autoconf <http://www.gnu.org/software/autoconf/>`_ 2.60 Configuration script builder\ :sup:`3`
170 `GNU Automake <http://www.gnu.org/software/automake/>`_ 1.9.6 aclocal macro generator\ :sup:`3`
171 `libtool <http://savannah.gnu.org/projects/libtool>`_ 1.5.22 Shared library manager\ :sup:`3`
172 `zlib <http://zlib.net>`_ >=1.2.3.4 Compression library\ :sup:`4`
173 =========================================================== ============ ==========================================
177 #. Only the C and C++ languages are needed so there's no need to build the
178 other languages for LLVM's purposes. See `below` for specific version
180 #. Only needed if you want to run the automated test suite in the
181 ``llvm/test`` directory.
182 #. If you want to make changes to the configure scripts, you will need GNU
183 autoconf (2.60), and consequently, GNU M4 (version 1.4 or higher). You
184 will also need automake (1.9.6). We only use aclocal from that package.
185 #. Optional, adds compression/uncompression capabilities to selected LLVM
188 Additionally, your compilation host is expected to have the usual plethora of
189 Unix utilities. Specifically:
191 * **ar** --- archive library builder
192 * **bzip2** --- bzip2 command for distribution generation
193 * **bunzip2** --- bunzip2 command for distribution checking
194 * **chmod** --- change permissions on a file
195 * **cat** --- output concatenation utility
196 * **cp** --- copy files
197 * **date** --- print the current date/time
198 * **echo** --- print to standard output
199 * **egrep** --- extended regular expression search utility
200 * **find** --- find files/dirs in a file system
201 * **grep** --- regular expression search utility
202 * **gzip** --- gzip command for distribution generation
203 * **gunzip** --- gunzip command for distribution checking
204 * **install** --- install directories/files
205 * **mkdir** --- create a directory
206 * **mv** --- move (rename) files
207 * **ranlib** --- symbol table builder for archive libraries
208 * **rm** --- remove (delete) files and directories
209 * **sed** --- stream editor for transforming output
210 * **sh** --- Bourne shell for make build scripts
211 * **tar** --- tape archive for distribution generation
212 * **test** --- test things in file system
213 * **unzip** --- unzip command for distribution checking
214 * **zip** --- zip command for distribution generation
219 Host C++ Toolchain, both Compiler and Standard Library
220 ------------------------------------------------------
222 LLVM is very demanding of the host C++ compiler, and as such tends to expose
223 bugs in the compiler. We are also planning to follow improvements and
224 developments in the C++ language and library reasonably closely. As such, we
225 require a modern host C++ toolchain, both compiler and standard library, in
228 For the most popular host toolchains we check for specific minimum versions in
235 Anything older than these toolchains *may* work, but will require forcing the
236 build system with a special option and is not really a supported host platform.
237 Also note that older versions of these compilers have often crashed or
240 For less widely used host toolchains such as ICC or xlC, be aware that a very
241 recent version may be required to support all of the C++ features used in LLVM.
243 We track certain versions of software that are *known* to fail when used as
244 part of the host toolchain. These even include linkers at times.
246 **GCC 4.6.3 on ARM**: Miscompiles ``llvm-readobj`` at ``-O3``. A test failure
247 in ``test/Object/readobj-shared-object.test`` is one symptom of the problem.
249 **GNU ld 2.16.X**. Some 2.16.X versions of the ld linker will produce very long
250 warning messages complaining that some "``.gnu.linkonce.t.*``" symbol was
251 defined in a discarded section. You can safely ignore these messages as they are
252 erroneous and the linkage is correct. These messages disappear using ld 2.17.
254 **GNU binutils 2.17**: Binutils 2.17 contains `a bug
255 <http://sourceware.org/bugzilla/show_bug.cgi?id=3111>`__ which causes huge link
256 times (minutes instead of seconds) when building LLVM. We recommend upgrading
257 to a newer version (2.17.50.0.4 or later).
259 **GNU Binutils 2.19.1 Gold**: This version of Gold contained `a bug
260 <http://sourceware.org/bugzilla/show_bug.cgi?id=9836>`__ which causes
261 intermittent failures when building LLVM with position independent code. The
262 symptom is an error about cyclic dependencies. We recommend upgrading to a
263 newer version of Gold.
265 **Clang 3.0 with libstdc++ 4.7.x**: a few Linux distributions (Ubuntu 12.10,
266 Fedora 17) have both Clang 3.0 and libstdc++ 4.7 in their repositories. Clang
267 3.0 does not implement a few builtins that are used in this library. We
268 recommend using the system GCC to compile LLVM and Clang in this case.
270 **Clang 3.0 on Mageia 2**. There's a packaging issue: Clang can not find at
271 least some (``cxxabi.h``) libstdc++ headers.
273 **Clang in C++11 mode and libstdc++ 4.7.2**. This version of libstdc++
274 contained `a bug <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53841>`__ which
275 causes Clang to refuse to compile condition_variable header file. At the time
276 of writing, this breaks LLD build.
278 .. _Getting Started with LLVM:
280 Getting Started with LLVM
281 =========================
283 The remainder of this guide is meant to get you up and running with LLVM and to
284 give you some basic information about the LLVM environment.
286 The later sections of this guide describe the `general layout`_ of the LLVM
287 source tree, a `simple example`_ using the LLVM tool chain, and `links`_ to find
288 more information about LLVM or to get help via e-mail.
290 Terminology and Notation
291 ------------------------
293 Throughout this manual, the following names are used to denote paths specific to
294 the local system and working environment. *These are not environment variables
295 you need to set but just strings used in the rest of this document below*. In
296 any of the examples below, simply replace each of these names with the
297 appropriate pathname on your local system. All these paths are absolute:
301 This is the top level directory of the LLVM source tree.
305 This is the top level directory of the LLVM object tree (i.e. the tree where
306 object files and compiled programs will be placed. It can be the same as
309 .. _Setting Up Your Environment:
311 Setting Up Your Environment
312 ---------------------------
314 In order to compile and use LLVM, you may need to set some environment
317 ``LLVM_LIB_SEARCH_PATH=/path/to/your/bitcode/libs``
319 [Optional] This environment variable helps LLVM linking tools find the
320 locations of your bitcode libraries. It is provided only as a convenience
321 since you can specify the paths using the -L options of the tools and the
322 C/C++ front-end will automatically use the bitcode files installed in its
325 Unpacking the LLVM Archives
326 ---------------------------
328 If you have the LLVM distribution, you will need to unpack it before you can
329 begin to compile it. LLVM is distributed as a set of two files: the LLVM suite
330 and the LLVM GCC front end compiled for your platform. There is an additional
331 test suite that is optional. Each file is a TAR archive that is compressed with
334 The files are as follows, with *x.y* marking the version number:
338 Source release for the LLVM libraries and tools.
340 ``llvm-test-x.y.tar.gz``
342 Source release for the LLVM test-suite.
346 Checkout LLVM from Subversion
347 -----------------------------
349 If you have access to our Subversion repository, you can get a fresh copy of the
350 entire source code. All you need to do is check it out from Subversion as
353 * ``cd where-you-want-llvm-to-live``
354 * Read-Only: ``svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm``
355 * Read-Write:``svn co https://user@llvm.org/svn/llvm-project/llvm/trunk llvm``
357 This will create an '``llvm``' directory in the current directory and fully
358 populate it with the LLVM source code, Makefiles, test directories, and local
359 copies of documentation files.
361 If you want to get a specific release (as opposed to the most recent revision),
362 you can checkout it from the '``tags``' directory (instead of '``trunk``'). The
363 following releases are located in the following subdirectories of the '``tags``'
366 * Release 3.3: **RELEASE_33/final**
367 * Release 3.2: **RELEASE_32/final**
368 * Release 3.1: **RELEASE_31/final**
369 * Release 3.0: **RELEASE_30/final**
370 * Release 2.9: **RELEASE_29/final**
371 * Release 2.8: **RELEASE_28**
372 * Release 2.7: **RELEASE_27**
373 * Release 2.6: **RELEASE_26**
374 * Release 2.5: **RELEASE_25**
375 * Release 2.4: **RELEASE_24**
376 * Release 2.3: **RELEASE_23**
377 * Release 2.2: **RELEASE_22**
378 * Release 2.1: **RELEASE_21**
379 * Release 2.0: **RELEASE_20**
380 * Release 1.9: **RELEASE_19**
381 * Release 1.8: **RELEASE_18**
382 * Release 1.7: **RELEASE_17**
383 * Release 1.6: **RELEASE_16**
384 * Release 1.5: **RELEASE_15**
385 * Release 1.4: **RELEASE_14**
386 * Release 1.3: **RELEASE_13**
387 * Release 1.2: **RELEASE_12**
388 * Release 1.1: **RELEASE_11**
389 * Release 1.0: **RELEASE_1**
391 If you would like to get the LLVM test suite (a separate package as of 1.4), you
392 get it from the Subversion repository:
394 .. code-block:: console
397 % svn co http://llvm.org/svn/llvm-project/test-suite/trunk test-suite
399 By placing it in the ``llvm/projects``, it will be automatically configured by
400 the LLVM configure script as well as automatically updated when you run ``svn
406 Git mirrors are available for a number of LLVM subprojects. These mirrors sync
407 automatically with each Subversion commit and contain all necessary git-svn
408 marks (so, you can recreate git-svn metadata locally). Note that right now
409 mirrors reflect only ``trunk`` for each project. You can do the read-only Git
412 .. code-block:: console
414 % git clone http://llvm.org/git/llvm.git
416 If you want to check out clang too, run:
418 .. code-block:: console
421 % git clone http://llvm.org/git/clang.git
423 If you want to check out compiler-rt too, run:
425 .. code-block:: console
428 % git clone http://llvm.org/git/compiler-rt.git
430 If you want to check out the Test Suite Source Code (optional), run:
432 .. code-block:: console
435 % git clone http://llvm.org/git/test-suite.git
437 Since the upstream repository is in Subversion, you should use ``git
438 pull --rebase`` instead of ``git pull`` to avoid generating a non-linear history
439 in your clone. To configure ``git pull`` to pass ``--rebase`` by default on the
440 master branch, run the following command:
442 .. code-block:: console
444 % git config branch.master.rebase true
446 Sending patches with Git
447 ^^^^^^^^^^^^^^^^^^^^^^^^
449 Please read `Developer Policy <DeveloperPolicy.html#one-off-patches>`_, too.
451 Assume ``master`` points the upstream and ``mybranch`` points your working
452 branch, and ``mybranch`` is rebased onto ``master``. At first you may check
453 sanity of whitespaces:
455 .. code-block:: console
457 % git diff --check master..mybranch
459 The easiest way to generate a patch is as below:
461 .. code-block:: console
463 % git diff master..mybranch > /path/to/mybranch.diff
465 It is a little different from svn-generated diff. git-diff-generated diff has
466 prefixes like ``a/`` and ``b/``. Don't worry, most developers might know it
467 could be accepted with ``patch -p1 -N``.
469 But you may generate patchset with git-format-patch. It generates by-each-commit
470 patchset. To generate patch files to attach to your article:
472 .. code-block:: console
474 % git format-patch --no-attach master..mybranch -o /path/to/your/patchset
476 If you would like to send patches directly, you may use git-send-email or
477 git-imap-send. Here is an example to generate the patchset in Gmail's [Drafts].
479 .. code-block:: console
481 % git format-patch --attach master..mybranch --stdout | git imap-send
483 Then, your .git/config should have [imap] sections.
488 host = imaps://imap.gmail.com
489 user = your.gmail.account@gmail.com
494 folder = "[Gmail]/Drafts"
495 ; example for Japanese, "Modified UTF-7" encoded.
496 folder = "[Gmail]/&Tgtm+DBN-"
497 ; example for Traditional Chinese
498 folder = "[Gmail]/&g0l6Pw-"
500 For developers to work with git-svn
501 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
503 To set up clone from which you can submit code using ``git-svn``, run:
505 .. code-block:: console
507 % git clone http://llvm.org/git/llvm.git
509 % git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
510 % git config svn-remote.svn.fetch :refs/remotes/origin/master
511 % git svn rebase -l # -l avoids fetching ahead of the git mirror.
513 # If you have clang too:
515 % git clone http://llvm.org/git/clang.git
517 % git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
518 % git config svn-remote.svn.fetch :refs/remotes/origin/master
521 Likewise for compiler-rt and test-suite.
523 To update this clone without generating git-svn tags that conflict with the
524 upstream Git repo, run:
526 .. code-block:: console
528 % git fetch && (cd tools/clang && git fetch) # Get matching revisions of both trees.
529 % git checkout master
532 git checkout master &&
535 Likewise for compiler-rt and test-suite.
537 This leaves your working directories on their master branches, so you'll need to
538 ``checkout`` each working branch individually and ``rebase`` it on top of its
541 For those who wish to be able to update an llvm repo/revert patches easily using
542 git-svn, please look in the directory for the scripts ``git-svnup`` and
545 To perform the aforementioned update steps go into your source directory and
546 just type ``git-svnup`` or ``git svnup`` and everything will just work.
548 If one wishes to revert a commit with git-svn, but do not want the git hash to
549 escape into the commit message, one can use the script ``git-svnrevert`` or
550 ``git svnrevert`` which will take in the git hash for the commit you want to
551 revert, look up the appropriate svn revision, and output a message where all
552 references to the git hash have been replaced with the svn revision.
554 To commit back changes via git-svn, use ``git svn dcommit``:
556 .. code-block:: console
560 Note that git-svn will create one SVN commit for each Git commit you have pending,
561 so squash and edit each commit before executing ``dcommit`` to make sure they all
562 conform to the coding standards and the developers' policy.
564 On success, ``dcommit`` will rebase against the HEAD of SVN, so to avoid conflict,
565 please make sure your current branch is up-to-date (via fetch/rebase) before
568 The git-svn metadata can get out of sync after you mess around with branches and
569 ``dcommit``. When that happens, ``git svn dcommit`` stops working, complaining
570 about files with uncommitted changes. The fix is to rebuild the metadata:
572 .. code-block:: console
577 Please, refer to the Git-SVN manual (``man git-svn``) for more information.
579 Local LLVM Configuration
580 ------------------------
582 Once checked out from the Subversion repository, the LLVM suite source code must
583 be configured via the ``configure`` script. This script sets variables in the
584 various ``*.in`` files, most notably ``llvm/Makefile.config`` and
585 ``llvm/include/Config/config.h``. It also populates *OBJ_ROOT* with the
586 Makefiles needed to begin building LLVM.
588 The following environment variables are used by the ``configure`` script to
589 configure the build system:
591 +------------+-----------------------------------------------------------+
592 | Variable | Purpose |
593 +============+===========================================================+
594 | CC | Tells ``configure`` which C compiler to use. By default, |
595 | | ``configure`` will check ``PATH`` for ``clang`` and GCC C |
596 | | compilers (in this order). Use this variable to override |
597 | | ``configure``\'s default behavior. |
598 +------------+-----------------------------------------------------------+
599 | CXX | Tells ``configure`` which C++ compiler to use. By |
600 | | default, ``configure`` will check ``PATH`` for |
601 | | ``clang++`` and GCC C++ compilers (in this order). Use |
602 | | this variable to override ``configure``'s default |
604 +------------+-----------------------------------------------------------+
606 The following options can be used to set or enable LLVM specific options:
608 ``--enable-optimized``
610 Enables optimized compilation (debugging symbols are removed and GCC
611 optimization flags are enabled). Note that this is the default setting if you
612 are using the LLVM distribution. The default behavior of an Subversion
613 checkout is to use an unoptimized build (also known as a debug build).
615 ``--enable-debug-runtime``
617 Enables debug symbols in the runtime libraries. The default is to strip debug
618 symbols from the runtime libraries.
622 Compile the Just In Time (JIT) compiler functionality. This is not available
623 on all platforms. The default is dependent on platform, so it is best to
624 explicitly enable it if you want it.
626 ``--enable-targets=target-option``
628 Controls which targets will be built and linked into llc. The default value
629 for ``target_options`` is "all" which builds and links all available targets.
630 The value "host-only" can be specified to build only a native compiler (no
631 cross-compiler targets available). The "native" target is selected as the
632 target of the build host. You can also specify a comma separated list of
633 target names that you want available in llc. The target names use all lower
634 case. The current set of targets is:
636 ``arm, cpp, hexagon, mips, mipsel, msp430, powerpc, ptx, sparc, spu,
637 systemz, x86, x86_64, xcore``.
641 Look for the doxygen program and enable construction of doxygen based
642 documentation from the source code. This is disabled by default because
643 generating the documentation can take a long time and producess 100s of
648 LLVM can use external disassembler library for various purposes (now it's used
649 only for examining code produced by JIT). This option will enable usage of
650 `udis86 <http://udis86.sourceforge.net/>`_ x86 (both 32 and 64 bits)
651 disassembler library.
653 To configure LLVM, follow these steps:
655 #. Change directory into the object root directory:
657 .. code-block:: console
661 #. Run the ``configure`` script located in the LLVM source tree:
663 .. code-block:: console
665 % SRC_ROOT/configure --prefix=/install/path [other options]
667 Compiling the LLVM Suite Source Code
668 ------------------------------------
670 Once you have configured LLVM, you can build it. There are three types of
675 These builds are the default when one is using an Subversion checkout and
676 types ``gmake`` (unless the ``--enable-optimized`` option was used during
677 configuration). The build system will compile the tools and libraries with
678 debugging information. To get a Debug Build using the LLVM distribution the
679 ``--disable-optimized`` option must be passed to ``configure``.
681 Release (Optimized) Builds
683 These builds are enabled with the ``--enable-optimized`` option to
684 ``configure`` or by specifying ``ENABLE_OPTIMIZED=1`` on the ``gmake`` command
685 line. For these builds, the build system will compile the tools and libraries
686 with GCC optimizations enabled and strip debugging information from the
687 libraries and executables it generates. Note that Release Builds are default
688 when using an LLVM distribution.
692 These builds are for use with profiling. They compile profiling information
693 into the code for use with programs like ``gprof``. Profile builds must be
694 started by specifying ``ENABLE_PROFILING=1`` on the ``gmake`` command line.
696 Once you have LLVM configured, you can build it by entering the *OBJ_ROOT*
697 directory and issuing the following command:
699 .. code-block:: console
703 If the build fails, please `check here`_ to see if you are using a version of
704 GCC that is known not to compile LLVM.
706 If you have multiple processors in your machine, you may wish to use some of the
707 parallel build options provided by GNU Make. For example, you could use the
710 .. code-block:: console
714 There are several special targets which are useful when working with the LLVM
719 Removes all files generated by the build. This includes object files,
720 generated C/C++ files, libraries, and executables.
724 Removes everything that ``gmake clean`` does, but also removes files generated
725 by ``configure``. It attempts to return the source tree to the original state
726 in which it was shipped.
730 Installs LLVM header files, libraries, tools, and documentation in a hierarchy
731 under ``$PREFIX``, specified with ``./configure --prefix=[dir]``, which
732 defaults to ``/usr/local``.
734 ``gmake -C runtime install-bytecode``
736 Assuming you built LLVM into $OBJDIR, when this command is run, it will
737 install bitcode libraries into the GCC front end's bitcode library directory.
738 If you need to update your bitcode libraries, this is the target to use once
741 Please see the `Makefile Guide <MakefileGuide.html>`_ for further details on
742 these ``make`` targets and descriptions of other targets available.
744 It is also possible to override default values from ``configure`` by declaring
745 variables on the command line. The following are some examples:
747 ``gmake ENABLE_OPTIMIZED=1``
749 Perform a Release (Optimized) build.
751 ``gmake ENABLE_OPTIMIZED=1 DISABLE_ASSERTIONS=1``
753 Perform a Release (Optimized) build without assertions enabled.
755 ``gmake ENABLE_OPTIMIZED=0``
757 Perform a Debug build.
759 ``gmake ENABLE_PROFILING=1``
761 Perform a Profiling build.
765 Print what ``gmake`` is doing on standard output.
767 ``gmake TOOL_VERBOSE=1``
769 Ask each tool invoked by the makefiles to print out what it is doing on
770 the standard output. This also implies ``VERBOSE=1``.
772 Every directory in the LLVM object tree includes a ``Makefile`` to build it and
773 any subdirectories that it contains. Entering any directory inside the LLVM
774 object tree and typing ``gmake`` should rebuild anything in or below that
775 directory that is out of date.
777 This does not apply to building the documentation.
778 LLVM's (non-Doxygen) documentation is produced with the
779 `Sphinx <http://sphinx-doc.org/>`_ documentation generation system.
780 There are some HTML documents that have not yet been converted to the new
781 system (which uses the easy-to-read and easy-to-write
782 `reStructuredText <http://sphinx-doc.org/rest.html>`_ plaintext markup
784 The generated documentation is built in the ``SRC_ROOT/docs`` directory using
786 For instructions on how to install Sphinx, see
787 `Sphinx Introduction for LLVM Developers
788 <http://lld.llvm.org/sphinx_intro.html>`_.
789 After following the instructions there for installing Sphinx, build the LLVM
790 HTML documentation by doing the following:
792 .. code-block:: console
795 $ make -f Makefile.sphinx
797 This creates a ``_build/html`` sub-directory with all of the HTML files, not
798 just the generated ones.
799 This directory corresponds to ``llvm.org/docs``.
800 For example, ``_build/html/SphinxQuickstartTemplate.html`` corresponds to
801 ``llvm.org/docs/SphinxQuickstartTemplate.html``.
802 The :doc:`SphinxQuickstartTemplate` is useful when creating a new document.
807 It is possible to cross-compile LLVM itself. That is, you can create LLVM
808 executables and libraries to be hosted on a platform different from the platform
809 where they are built (a Canadian Cross build). To configure a cross-compile,
810 supply the configure script with ``--build`` and ``--host`` options that are
811 different. The values of these options must be legal target triples that your
812 GCC compiler supports.
814 The result of such a build is executables that are not runnable on on the build
815 host (--build option) but can be executed on the compile host (--host option).
817 Check :doc:`HowToCrossCompileLLVM` and `Clang docs on how to cross-compile in general
818 <http://clang.llvm.org/docs/CrossCompilation.html>`_ for more information
819 about cross-compiling.
821 The Location of LLVM Object Files
822 ---------------------------------
824 The LLVM build system is capable of sharing a single LLVM source tree among
825 several LLVM builds. Hence, it is possible to build LLVM for several different
826 platforms or configurations using the same source tree.
828 This is accomplished in the typical autoconf manner:
830 * Change directory to where the LLVM object files should live:
832 .. code-block:: console
836 * Run the ``configure`` script found in the LLVM source directory:
838 .. code-block:: console
842 The LLVM build will place files underneath *OBJ_ROOT* in directories named after
845 Debug Builds with assertions enabled (the default)
849 ``OBJ_ROOT/Debug+Asserts/bin``
853 ``OBJ_ROOT/Debug+Asserts/lib``
859 ``OBJ_ROOT/Release/bin``
863 ``OBJ_ROOT/Release/lib``
869 ``OBJ_ROOT/Profile/bin``
873 ``OBJ_ROOT/Profile/lib``
875 Optional Configuration Items
876 ----------------------------
878 If you're running on a Linux system that supports the `binfmt_misc
879 <http://en.wikipedia.org/wiki/binfmt_misc>`_
880 module, and you have root access on the system, you can set your system up to
881 execute LLVM bitcode files directly. To do this, use commands like this (the
882 first command may not be required if you are already using the module):
884 .. code-block:: console
886 % mount -t binfmt_misc none /proc/sys/fs/binfmt_misc
887 % echo ':llvm:M::BC::/path/to/lli:' > /proc/sys/fs/binfmt_misc/register
888 % chmod u+x hello.bc (if needed)
891 This allows you to execute LLVM bitcode files directly. On Debian, you can also
892 use this command instead of the 'echo' command above:
894 .. code-block:: console
896 % sudo update-binfmts --install llvm /path/to/lli --magic 'BC'
904 One useful source of information about the LLVM source base is the LLVM `doxygen
905 <http://www.doxygen.org/>`_ documentation available at
906 `<http://llvm.org/doxygen/>`_. The following is a brief introduction to code
912 This directory contains some simple examples of how to use the LLVM IR and JIT.
917 This directory contains public header files exported from the LLVM library. The
918 three main subdirectories of this directory are:
920 ``llvm/include/llvm``
922 This directory contains all of the LLVM specific header files. This directory
923 also has subdirectories for different portions of LLVM: ``Analysis``,
924 ``CodeGen``, ``Target``, ``Transforms``, etc...
926 ``llvm/include/llvm/Support``
928 This directory contains generic support libraries that are provided with LLVM
929 but not necessarily specific to LLVM. For example, some C++ STL utilities and
930 a Command Line option processing library store their header files here.
932 ``llvm/include/llvm/Config``
934 This directory contains header files configured by the ``configure`` script.
935 They wrap "standard" UNIX and C header files. Source code can include these
936 header files which automatically take care of the conditional #includes that
937 the ``configure`` script generates.
942 This directory contains most of the source files of the LLVM system. In LLVM,
943 almost all code exists in libraries, making it very easy to share code among the
948 This directory holds the core LLVM source files that implement core classes
949 like Instruction and BasicBlock.
951 ``llvm/lib/AsmParser/``
953 This directory holds the source code for the LLVM assembly language parser
956 ``llvm/lib/Bitcode/``
958 This directory holds code for reading and write LLVM bitcode.
960 ``llvm/lib/Analysis/``
962 This directory contains a variety of different program analyses, such as
963 Dominator Information, Call Graphs, Induction Variables, Interval
964 Identification, Natural Loop Identification, etc.
966 ``llvm/lib/Transforms/``
968 This directory contains the source code for the LLVM to LLVM program
969 transformations, such as Aggressive Dead Code Elimination, Sparse Conditional
970 Constant Propagation, Inlining, Loop Invariant Code Motion, Dead Global
971 Elimination, and many others.
975 This directory contains files that describe various target architectures for
976 code generation. For example, the ``llvm/lib/Target/X86`` directory holds the
977 X86 machine description while ``llvm/lib/Target/ARM`` implements the ARM
980 ``llvm/lib/CodeGen/``
982 This directory contains the major parts of the code generator: Instruction
983 Selector, Instruction Scheduling, and Register Allocation.
989 ``llvm/lib/Debugger/``
991 This directory contains the source level debugger library that makes it
992 possible to instrument LLVM programs so that a debugger could identify source
993 code locations at which the program is executing.
995 ``llvm/lib/ExecutionEngine/``
997 This directory contains libraries for executing LLVM bitcode directly at
998 runtime in both interpreted and JIT compiled fashions.
1000 ``llvm/lib/Support/``
1002 This directory contains the source code that corresponds to the header files
1003 located in ``llvm/include/ADT/`` and ``llvm/include/Support/``.
1008 This directory contains projects that are not strictly part of LLVM but are
1009 shipped with LLVM. This is also the directory where you should create your own
1010 LLVM-based projects. See ``llvm/projects/sample`` for an example of how to set
1011 up your own project.
1016 This directory contains libraries which are compiled into LLVM bitcode and used
1017 when linking programs with the Clang front end. Most of these libraries are
1018 skeleton versions of real libraries; for example, libc is a stripped down
1021 Unlike the rest of the LLVM suite, this directory needs the LLVM GCC front end
1027 This directory contains feature and regression tests and other basic sanity
1028 checks on the LLVM infrastructure. These are intended to run quickly and cover a
1029 lot of territory without being exhaustive.
1034 This is not a directory in the normal llvm module; it is a separate Subversion
1035 module that must be checked out (usually to ``projects/test-suite``). This
1036 module contains a comprehensive correctness, performance, and benchmarking test
1037 suite for LLVM. It is a separate Subversion module because not every LLVM user
1038 is interested in downloading or building such a comprehensive test suite. For
1039 further details on this test suite, please see the :doc:`Testing Guide
1040 <TestingGuide>` document.
1047 The **tools** directory contains the executables built out of the libraries
1048 above, which form the main part of the user interface. You can always get help
1049 for a tool by typing ``tool_name -help``. The following is a brief introduction
1050 to the most important tools. More detailed information is in
1051 the `Command Guide <CommandGuide/index.html>`_.
1055 ``bugpoint`` is used to debug optimization passes or code generation backends
1056 by narrowing down the given test case to the minimum number of passes and/or
1057 instructions that still cause a problem, whether it is a crash or
1058 miscompilation. See `<HowToSubmitABug.html>`_ for more information on using
1063 The archiver produces an archive containing the given LLVM bitcode files,
1064 optionally with an index for faster lookup.
1068 The assembler transforms the human readable LLVM assembly to LLVM bitcode.
1072 The disassembler transforms the LLVM bitcode to human readable LLVM assembly.
1076 ``llvm-link``, not surprisingly, links multiple LLVM modules into a single
1081 ``lli`` is the LLVM interpreter, which can directly execute LLVM bitcode
1082 (although very slowly...). For architectures that support it (currently x86,
1083 Sparc, and PowerPC), by default, ``lli`` will function as a Just-In-Time
1084 compiler (if the functionality was compiled in), and will execute the code
1085 *much* faster than the interpreter.
1089 ``llc`` is the LLVM backend compiler, which translates LLVM bitcode to a
1090 native code assembly file or to C code (with the ``-march=c`` option).
1094 ``opt`` reads LLVM bitcode, applies a series of LLVM to LLVM transformations
1095 (which are specified on the command line), and then outputs the resultant
1096 bitcode. The '``opt -help``' command is a good way to get a list of the
1097 program transformations available in LLVM.
1099 ``opt`` can also be used to run a specific analysis on an input LLVM bitcode
1100 file and print out the results. It is primarily useful for debugging
1101 analyses, or familiarizing yourself with what an analysis does.
1106 This directory contains utilities for working with LLVM source code, and some of
1107 the utilities are actually required as part of the build process because they
1108 are code generators for parts of LLVM infrastructure.
1113 ``codegen-diff`` is a script that finds differences between code that LLC
1114 generates and code that LLI generates. This is a useful tool if you are
1115 debugging one of them, assuming that the other generates correct output. For
1116 the full user manual, run ```perldoc codegen-diff'``.
1120 The ``emacs`` directory contains syntax-highlighting files which will work
1121 with Emacs and XEmacs editors, providing syntax highlighting support for LLVM
1122 assembly files and TableGen description files. For information on how to use
1123 the syntax files, consult the ``README`` file in that directory.
1127 The ``getsrcs.sh`` script finds and outputs all non-generated source files,
1128 which is useful if one wishes to do a lot of development across directories
1129 and does not want to individually find each file. One way to use it is to run,
1130 for example: ``xemacs `utils/getsources.sh``` from the top of your LLVM source
1135 This little tool performs an ``egrep -H -n`` on each source file in LLVM and
1136 passes to it a regular expression provided on ``llvmgrep``'s command
1137 line. This is a very efficient way of searching the source base for a
1138 particular regular expression.
1142 The ``makellvm`` script compiles all files in the current directory and then
1143 compiles and links the tool that is the first argument. For example, assuming
1144 you are in the directory ``llvm/lib/Target/Sparc``, if ``makellvm`` is in your
1145 path, simply running ``makellvm llc`` will make a build of the current
1146 directory, switch to directory ``llvm/tools/llc`` and build it, causing a
1151 The ``TableGen`` directory contains the tool used to generate register
1152 descriptions, instruction set descriptions, and even assemblers from common
1153 TableGen description files.
1157 The ``vim`` directory contains syntax-highlighting files which will work with
1158 the VIM editor, providing syntax highlighting support for LLVM assembly files
1159 and TableGen description files. For information on how to use the syntax
1160 files, consult the ``README`` file in that directory.
1164 An Example Using the LLVM Tool Chain
1165 ====================================
1167 This section gives an example of using LLVM with the Clang front end.
1172 #. First, create a simple C file, name it 'hello.c':
1179 printf("hello world\n");
1183 #. Next, compile the C file into a native executable:
1185 .. code-block:: console
1187 % clang hello.c -o hello
1191 Clang works just like GCC by default. The standard -S and -c arguments
1192 work as usual (producing a native .s or .o file, respectively).
1194 #. Next, compile the C file into an LLVM bitcode file:
1196 .. code-block:: console
1198 % clang -O3 -emit-llvm hello.c -c -o hello.bc
1200 The -emit-llvm option can be used with the -S or -c options to emit an LLVM
1201 ``.ll`` or ``.bc`` file (respectively) for the code. This allows you to use
1202 the `standard LLVM tools <CommandGuide/index.html>`_ on the bitcode file.
1204 #. Run the program in both forms. To run the program, use:
1206 .. code-block:: console
1212 .. code-block:: console
1216 The second examples shows how to invoke the LLVM JIT, :doc:`lli
1217 <CommandGuide/lli>`.
1219 #. Use the ``llvm-dis`` utility to take a look at the LLVM assembly code:
1221 .. code-block:: console
1223 % llvm-dis < hello.bc | less
1225 #. Compile the program to native assembly using the LLC code generator:
1227 .. code-block:: console
1229 % llc hello.bc -o hello.s
1231 #. Assemble the native assembly language file into a program:
1233 .. code-block:: console
1235 % /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.native # On Solaris
1237 % gcc hello.s -o hello.native # On others
1239 #. Execute the native code program:
1241 .. code-block:: console
1245 Note that using clang to compile directly to native code (i.e. when the
1246 ``-emit-llvm`` option is not present) does steps 6/7/8 for you.
1251 If you are having problems building or using LLVM, or if you have any other
1252 general questions about LLVM, please consult the `Frequently Asked
1253 Questions <FAQ.html>`_ page.
1260 This document is just an **introduction** on how to use LLVM to do some simple
1261 things... there are many more interesting and complicated things that you can do
1262 that aren't documented here (but we'll gladly accept a patch if you want to
1263 write something up!). For more information about LLVM, check out:
1265 * `LLVM Homepage <http://llvm.org/>`_
1266 * `LLVM Doxygen Tree <http://llvm.org/doxygen/>`_
1267 * `Starting a Project that Uses LLVM <http://llvm.org/docs/Projects.html>`_