1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
4 <title>Getting Started with LLVM System</title>
8 <center><h1>Getting Started with the LLVM System<br><font size=3>By: <a
9 href="mailto:gshi1@uiuc.edu">Guochun Shi</a>,
10 <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
11 <a href="mailto:criswell@uiuc.edu">John Criswell</a>, and
12 <a href="http://www.cs.uiuc.edu/~vadve">Vikram Adve</a>
15 <!--=====================================================================-->
16 <h2><a name="Contents">Contents</a></h2>
17 <!--=====================================================================-->
20 <li><a href="#overview">Overview</a>
22 <li><a href="#requirements">Requirements</a>
24 <li><a href="#hardware">Hardware</a>
25 <li><a href="#software">Software</a>
28 <li><a href="#starting">Getting started with LLVM</a>
30 <li><a href="#quickstart">Getting started quickly (a summary)</a>
31 <li><a href="#terminology">Terminology and Notation</tt></a>
32 <li><a href="#environment">Setting up your environment</a>
33 <li><a href="#checkout">Checkout LLVM from CVS</a>
34 <li><a href="#config">Local LLVM Configuration</tt></a>
35 <li><a href="#compile">Compiling the LLVM Suite Source Code</a>
36 <li><a href="#build">Building the LLVM C Front End</a>
37 <li><a href="#objfiles">The location for object files</tt></a>
39 <li><a href="#layout">Program layout</a>
41 <li><a href="#cvsdir">CVS directories</a>
42 <li><a href="#include"><tt>llvm/include</tt></a>
43 <li><a href="#lib"><tt>llvm/lib</tt></a>
44 <li><a href="#test"><tt>llvm/test</tt></a>
45 <li><a href="#tools"><tt>llvm/tools</tt></a>
47 <li><a href="#tutorial">An example using the LLVM tool chain</a>
48 <li><a href="#links">Links</a>
52 <!--=====================================================================-->
54 <h2><a name="overview"><b>Overview</b></a></h2>
56 <!--=====================================================================-->
58 Welcome to LLVM! In order to get started, you first need to know some
62 First, LLVM comes in two pieces. The first piece is the LLVM suite. This
63 contains all of the tools, libraries, and header files needed to use the
64 low level virtual machine. It also contains a test suite that can be used
65 to test the LLVM tools and the GCC front end.
67 The second piece is the GCC front end. This component provides a version
68 of GCC that compiles C code into LLVM bytecode. Currently, the C front end
69 is a modified version of GCC 3.4 (we track the GCC 3.4 development).
70 Once compiled into LLVM bytecode, a program can be manipulated with the
73 <!--=====================================================================-->
74 <h3><a name="requirements"><b>Requirements</b></a></h3>
75 <!--=====================================================================-->
77 Before you begin to use the LLVM system, review the requirements given
78 below. This may save you some trouble by knowing ahead of time what
79 hardware and software you will need.
81 <!--=====================================================================-->
82 <h4><a name="hardware"><b>Hardware</b></a></h4>
83 <!--=====================================================================-->
84 LLVM is known to work on the following platforms:
88 <li> Approximately 700 MB of Free Disk Space
90 <li>Source code: 30 MB
91 <li>Object code: 670 MB
94 <li> Solaris on SparcV9 (Ultrasparc)
96 <li> Approximately 1.03 GB of Free Disk Space
98 <li>Source code: 30 MB
99 <li>Object code: 1000 MB
104 LLVM <i>may</i> compile on other platforms. The LLVM utilities should work
105 on other platforms, so it should be possible to generate and produce LLVM
106 bytecode on unsupported platforms (although bytecode generated on one
107 platform may not work on another platform). However, the code generators
108 and Just-In-Time (JIT) compilers only generate SparcV9 or x86 machine code.
110 <!--=====================================================================-->
111 <h4><a name="software"><b>Software</b></a></h4>
112 <!--=====================================================================-->
115 Unpacking the distribution requires the following tools:
120 These tools are needed to uncompress and unarchive the software.
121 Regular Solaris <tt>tar</tt> may work for unpacking the TAR archive but
125 Compiling LLVM requires that you have several different software packages
131 The GNU Compiler Collection must be installed with C and C++ language
132 support. GCC 3.2.x works, and GCC 3.x is generally supported.
135 Note that we currently do not support any other C++ compiler.
140 The LLVM build system relies upon GNU Make extensions. Therefore, you
141 will need GNU Make (sometimes known as gmake) to build LLVM.
146 The LLVM source code is built using flex and bison. You will not be
147 able to configure and compile LLVM without them.
152 If you are installing Bison on your machine for the first time, you
153 will need GNU M4 (version 1.4 or higher).
157 There are some additional tools that you may want to have when working with
165 If you want to make changes to the configure scripts, you will need
166 GNU autoconf (2.53 or higher), and consequently, GNU M4 (version 1.4
172 <p>The <a href="starting">next section</a> of this guide is meant to get
173 you up and running with LLVM and to give you some basic information about
174 the LLVM environment. The <a href"#quickstart">first subsection</a> gives
175 a short summary for those who are already familiar with the system and
176 want to get started as quickly as possible.
178 <p>The later sections of this guide describe the <a
179 href="#layout">general layout</a> of the the LLVM source-tree, a <a
180 href="#tutorial">simple example</a> using the LLVM tool chain, and <a
181 href="#links">links</a> to find more information about LLVM or to get
184 <!--=====================================================================-->
186 <h2><a name="starting"><b>Getting Started</b></a></h2>
188 <!--=====================================================================-->
190 <!--=====================================================================-->
191 <h3><a name="quickstart"><b>Getting Started Quickly (A Summary)</b></a></h3>
192 <!--=====================================================================-->
194 Here's the short story for getting up and running quickly with LLVM:
196 <li>Build the LLVM suite
198 <li>Find the path to the CVS repository containing LLVM (we'll call this <i>CVSROOTDIR</i>).
199 <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
200 <li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt>
202 <li>Run <tt>configure</tt> to configure the Makefiles and header files.
203 Useful options include:
205 <li><tt>--with-objroot=<i>directory</i></tt>
207 Specify where object files should be placed during the build.
209 <li><tt>--with-llvmgccdir=<i>directory</i></tt>
211 Specify where the LLVM C frontend is going to be installed.
213 <li>Set your LLVM_LIB_SEARCH_PATH environment variable.
214 <li><tt>gmake -k |& tee gnumake.out
215 # this is csh or tcsh syntax</tt>
218 <li>Build the LLVM C Front End <b>(optional)</b>
220 <li>Create a directory for the object files to live.
221 <li><tt>cd <i>object file directory</i></tt>
222 <li>Run <tt><i>Pathname-to-where-the-source-code-lives</i>/configure --prefix=<i>LLVMGCCDIR</i></tt> to configure GCC.
223 <li><tt>make bootstrap</tt>
224 <li><tt>make install</tt>
228 <p>See <a href="#environment">Setting up your environment</a> on tips to
229 simplify working with the LLVM front-end and compiled tools. See the
230 other sub-sections below for other useful details in working with LLVM,
231 or go straight to <a href="#layout">Program Layout</a> to learn about the
232 layout of the source code tree.
234 <!------------------------------------------------------------------------->
235 <h3><a name="terminology">Terminology and Notation</a></h3>
236 <!------------------------------------------------------------------------->
238 <p>Throughout this manual, the following names are used to denote paths
239 specific to the local system and working environment. <i>These are not
240 environment variables you need to set but just strings used in the rest
241 of this document below</i>. In any of the examples below, simply replace
242 each of these names with the appropriate pathname on your local system.
243 All these paths are absolute:</p>
247 This is the path for the CVS repository containing the LLVM source
248 code. Ask the person responsible for your local LLVM installation to
254 This is the top level directory for where the LLVM suite object files
255 will be placed during the build.
260 This is the pathname to the location where the LLVM C Front End will
261 be installed. Note that the C front end does not need to be installed
262 during the LLVM suite build; you will just need to know where it will
263 go for configuring the build system and running the test suite later.
265 For the pre-built binaries, the LLVMGCCDIR is
266 <tt>cfrontend/<platform>/llvm-gcc</tt>.
270 This is the pathname of the directory where the LLVM C front end source
276 This is the pathname of the directory where the LLVM C front end object
277 code will be placed during the build. It can be safely removed once
278 the build is complete.
281 <!------------------------------------------------------------------------->
282 <h3><a name="environment">Setting up your environment</a></h3>
283 <!------------------------------------------------------------------------->
286 In order to compile and use LLVM, you will need to set some environment
287 variables. There are also some shell aliases which you may find useful.
288 You can set these on the command line, or better yet, set them in your
289 <tt>.cshrc</tt> or <tt>.profile</tt>.
292 <dt><tt>LLVM_LIB_SEARCH_PATH</tt>=<tt><i>LLVMGCCDIR</i>/llvm-gcc/bytecode-libs</tt>
294 This environment variable helps the LLVM C front end find bytecode
295 libraries that it will need for compilation.
298 <dt><tt>PATH</tt>=<tt>${PATH}:<i>OBJ_ROOT</i>/llvm/tools/Debug</tt>
300 Adding this directory to the end of your path will allow the
301 compilation of the C front end to find the LLVM tools. The LLVM tools
302 are needed for the C front end compile.
305 <dt><tt>CC</tt>=<i>Pathname to your GCC compiler</i>
307 The GCC compiler that you want to use must be the first C compiler in
308 your <tt>PATH</tt>. Otherwise, set this variable so that
309 <tt>configure</tt> will use the GCC compiler that you want to use.
312 <dt><tt>CXX</tt>=<i>Pathname to your GCC C++ compiler</i>
314 The GCC compiler that you want to use must be the first C++ compiler in
315 your <tt>PATH</tt>. Otherwise, set this variable so that
316 <tt>configure</tt> will use the GCC compiler that you want to use.
319 <dt><tt>CVSROOT</tt>=<i>CVSROOT</i>
321 This environment variable tells CVS where to find the CVS repository.
324 <dt>alias llvmgcc <i>LLVMGCCDIR</i><tt>/bin/llvm-gcc</tt>
326 This alias allows you to use the LLVM C front end without putting it in
327 your <tt>PATH</tt> or typing in its complete pathname.
330 <!------------------------------------------------------------------------->
331 <h3><a name="checkout">Checkout LLVM from CVS</a></h3>
332 <!------------------------------------------------------------------------->
334 <p>To get a fresh copy of the entire source code, all you
335 need to do is check it out from CVS as follows:
337 <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
338 <li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt></p>
341 <p>This will create an '<tt>llvm</tt>' directory in the current
342 directory and fully populate it with the LLVM source code, Makefiles,
343 test directories, and local copies of documentation files.</p>
346 Note that the C front end is not included in the CVS repository. You
347 should have either downloaded the source, or better yet, downloaded the
348 binary distribution for your platform.
351 <!------------------------------------------------------------------------->
352 <h3><a name="config">Local LLVM Configuration</a></h3>
353 <!------------------------------------------------------------------------->
355 <p>Once checked out from the CVS repository, the LLVM suite source code
356 must be configured via the <tt>configure</tt> script. This script sets
357 variables in <tt>llvm/Makefile.config</tt> and
358 <tt>llvm/include/Config/config.h</tt>.
361 The following environment variables are used by <tt>configure</tt> to
362 configure Makefile.config:
366 <p><li><i>CXX</i> = Pathname of the C++ compiler to use.
367 <p><li><i>CC</i> = Pathname of the C compiler to use.
370 The following options can be used to set or enable LLVM specific options:
373 <dt><i>--with-objroot=OBJ_ROOT</i>
375 Path to the directory where
376 object files, libraries, and executables should be placed.
377 If this is set to <tt>.</tt>, then the object files will be placed
378 within the source code tree. If left unspecified, the default value is
380 (See the Section on <a href=#objfiles>
381 The location for LLVM object files</a>
382 for more information.)
384 <dt><i>--with-llvmgccdir=LLVMGCCDIR</i>
386 Path to the location where the LLVM C front end binaries and
387 associated libraries will be installed.
389 <dt><i>--enable-optimized</i>
391 Enables optimized compilation (debugging symbols are removed and GCC
392 optimization flags are enabled). The default is to use an unoptimized
393 build (also known as a debug build).
395 <dt><i>--enable-jit</i>
397 Compile the Just In Time (JIT) functionality. This is not available
398 on all platforms. The default is dependent on platform, so it is best
399 to explicitly enable it if you want it.
402 In addition to running <tt>configure</tt>, you must set the
403 <tt>LLVM_LIB_SEARCH_PATH</tt> environment variable in your startup scripts.
404 This environment variable is used to locate "system" libraries like
405 "<tt>-lc</tt>" and "<tt>-lm</tt>" when linking. This variable should be set
406 to the absolute path for the bytecode-libs subdirectory of the C front-end
407 install, or LLVMGCCDIR/llvm-gcc/bytecode-libs. For example, one might
408 set <tt>LLVM_LIB_SEARCH_PATH</tt> to
409 <tt>/home/vadve/lattner/local/x86/llvm-gcc/bytecode-libs</tt> for the X86
410 version of the C front-end on our research machines.<p>
412 <!------------------------------------------------------------------------->
413 <h3><a name="compile">Compiling the LLVM Suite Source Code</a></h3>
414 <!------------------------------------------------------------------------->
416 Once you have configured LLVM, you can build it. There are three types of
422 These builds are the default. They compile the tools and libraries
423 with debugging information.
426 <dt>Release (Optimized) Builds
428 These builds are enabled with the <tt>--enable-optimized</tt> option to
429 <tt>configure</tt>. They compile the tools and libraries with GCC
430 optimizer flags on and strip debugging information from the libraries
431 and executables it generates.
436 These builds are for use with profiling. They compile profiling
437 information into the code for use with programs like <tt>gprof</tt>.
438 Profile builds must be started by setting variables on the
439 <tt>make</tt> command line.
442 Once you have LLVM configured, you can build it by entering the top level
443 <tt>llvm</tt> directory and issuing the following command:
448 If you have multiple processors in your machine, you may wish to use some
449 of the parallel build options provided by GNU Make. For example, you could
457 There are several other targets which are useful when working with the LLVM
461 <dt><tt>make clean</tt>
463 Removes all files generated by the build. This includes object files,
464 generated C/C++ files, libraries, and executables.
467 <dt><tt>make distclean</tt>
469 Removes everything that <tt>make clean</tt> does, but also removes
470 files generated by <tt>configure</tt>. It attempts to return the
471 source tree to the original state in which it was shipped.
475 It is also possible to override default values from <tt>configure</tt> by
476 declaring variables on the command line. The following are some examples:
479 <dt><tt>make ENABLE_OPTIMIZED=1</tt>
481 Perform a Release (Optimized) build.
484 <dt><tt>make ENABLE_PROFILING=1</tt>
486 Perform a Profiling build.
489 <dt><tt>make VERBOSE=1</tt>
491 Print what <tt>make</tt> is doing on standard output.
495 Every directory in the LLVM source tree includes a <tt>Makefile</tt> to
496 build it and any subdirectories that it contains. Entering any directory
497 inside the LLVM source tree and typing <tt>make</tt> should rebuild
498 anything in or below that directory that is out of date.
500 <!------------------------------------------------------------------------->
501 <h3><a name="build">Building the LLVM C Front End</a></h3>
502 <!------------------------------------------------------------------------->
506 This step is optional if you have the C front end binary distrubtion for
511 Now that you have the LLVM Suite built, you can build the C front end. For
512 those of you that have built GCC before, the process is very similar.
514 Be forewarned, though: the build system for the C front end is not as
515 polished as the rest of the LLVM code, so there will be many warnings and
516 errors that you will need to ignore for now:
519 <li>Ensure that <tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt> is at the
520 <i>end</i> of your <tt>PATH</tt> environment variable.
522 <li><tt>cd <i>GCCOBJ</i></tt>
524 <li>Configure the source code:
526 <li>On Linux/x86, use
528 <li><tt><i>GCCSRC</i>/configure --prefix=<i>LLVMGCCDIR</i>
529 --enable-languages=c</tt>
532 <li>On Solaris/Sparc, use
534 <li><tt><i>GCCSRC</i>/configure --prefix=<i>LLVMGCCDIR</i>
535 --enable-languages=c --target=sparcv9-sun-solaris2</tt>
539 <li><tt>make bootstrap</tt>
541 <li>The build will eventually fail. Don't worry; chances are good that
542 everything that needed to build is built.
544 <li><tt>make install</tt>
547 At this point, you should have a working copy of the LLVM C front end
548 installed in <i>LLVMGCCDIR</i>.
550 <!------------------------------------------------------------------------->
551 <h3><a name="objfiles">The location for LLVM object files</a></h3>
552 <!------------------------------------------------------------------------->
554 <p>The LLVM build system sends most output files generated during the build
555 into the directory defined by the variable <i>OBJ_ROOT</i> in
556 <tt>llvm/Makefile.config</tt>, which is set by the <i>--with-objroot</i>
557 option in <tt>configure</tt>. This can be either just your normal LLVM
558 source tree or some other directory writable by you. You may wish to put
559 object files on a different filesystem either to keep them from being backed
560 up or to speed up local builds.
563 If <i>OBJ_ROOT</i> is specified, then the build system will create a
564 directory tree underneath it that resembles the source code's pathname
565 relative to your home directory.
569 For example, suppose that <i>OBJ_ROOT</i> is set to <tt>/tmp</tt> and the
570 LLVM suite source code is located in <tt>/usr/home/joe/src/llvm</tt>, where
571 <tt>/usr/home/joe</tt> is the home directory of a user named Joe. Then,
572 the object files will be placed in <tt>/tmp/src/llvm</tt>.
576 The LLVM build will place files underneath <i>OBJ_ROOT</i> in directories
577 named after the build type:
585 <dd><tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt>
587 <dd><tt><i>OBJ_ROOT</i>/llvm/lib/Debug</tt>
595 <dd><tt><i>OBJ_ROOT</i>/llvm/tools/Release</tt>
597 <dd><tt><i>OBJ_ROOT</i>/llvm/lib/Release</tt>
605 <dd><tt><i>OBJ_ROOT</i>/llvm/tools/Profile</tt>
607 <dd><tt><i>OBJ_ROOT</i>/llvm/lib/Profile</tt>
611 <!--=====================================================================-->
613 <h2><a name="layout"><b>Program Layout</b></a></h2>
615 <!--=====================================================================-->
617 <p>One useful source of information about the LLVM source base is the LLVM <a
618 href="http://www.doxygen.org">doxygen</a> documentation, available at <tt><a
619 href="http://llvm.cs.uiuc.edu/doxygen/">http://llvm.cs.uiuc.edu/doxygen/</a></tt>. The
620 following is a brief introduction to code layout:</p>
623 <!------------------------------------------------------------------------->
624 <h3><a name="cvsdir"><tt>CVS</tt> directories</a></h3>
625 <!------------------------------------------------------------------------->
627 Every directory checked out of CVS will contain a <tt>CVS</tt> directory;
628 for the most part these can just be ignored.
631 <!------------------------------------------------------------------------->
632 <h3><a name="include"><tt>llvm/include</tt></a></h3>
633 <!------------------------------------------------------------------------->
635 This directory contains public header files exported from the LLVM
636 library. The three main subdirectories of this directory are:<p>
639 <li><tt>llvm/include/llvm</tt> - This directory contains all of the LLVM
640 specific header files. This directory also has subdirectories for
641 different portions of LLVM: <tt>Analysis</tt>, <tt>CodeGen</tt>,
642 <tt>Reoptimizer</tt>, <tt>Target</tt>, <tt>Transforms</tt>, etc...
644 <li><tt>llvm/include/Support</tt> - This directory contains generic
645 support libraries that are independent of LLVM, but are used by LLVM.
646 For example, some C++ STL utilities and a Command Line option processing
649 <li><tt>llvm/include/Config</tt> - This directory contains header files
650 configured by the <tt>configure</tt> script. They wrap "standard" UNIX
651 and C header files. Source code can include these header files which
652 automatically take care of the conditional #includes that the configure
656 <!------------------------------------------------------------------------->
657 <h3><a name="lib"><tt>llvm/lib</tt></a></h3>
658 <!------------------------------------------------------------------------->
660 This directory contains most of the source files of the LLVM system. In
662 code exists in libraries, making it very easy to share code among the
663 different <a href="#tools">tools</a>.<p>
666 <dt><tt>llvm/lib/VMCore/</tt><dd> This directory holds the core LLVM
667 source files that implement core classes like Instruction and BasicBlock.
669 <dt><tt>llvm/lib/AsmParser/</tt><dd> This directory holds the source code
670 for the LLVM assembly language parser library.
672 <dt><tt>llvm/lib/ByteCode/</tt><dd> This directory holds code for reading
673 and write LLVM bytecode.
675 <dt><tt>llvm/lib/CWriter/</tt><dd> This directory implements the LLVM to C
678 <dt><tt>llvm/lib/Analysis/</tt><dd> This directory contains a variety of
679 different program analyses, such as Dominator Information, Call Graphs,
680 Induction Variables, Interval Identification, Natural Loop Identification,
683 <dt><tt>llvm/lib/Transforms/</tt><dd> This directory contains the source
684 code for the LLVM to LLVM program transformations, such as Aggressive Dead
685 Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop
686 Invarient Code Motion, Dead Global Elimination, Pool Allocation, and many
689 <dt><tt>llvm/lib/Target/</tt><dd> This directory contains files that
690 describe various target architectures for code generation. For example,
691 the llvm/lib/Target/Sparc directory holds the Sparc machine
694 <dt><tt>llvm/lib/CodeGen/</tt><dd> This directory contains the major parts
695 of the code generator: Instruction Selector, Instruction Scheduling, and
698 <dt><tt>llvm/lib/Reoptimizer/</tt><dd> This directory holds code related
699 to the runtime reoptimizer framework that is currently under development.
701 <dt><tt>llvm/lib/Support/</tt><dd> This directory contains the source code
702 that corresponds to the header files located in
703 <tt>llvm/include/Support/</tt>.
706 <!------------------------------------------------------------------------->
707 <h3><a name="test"><tt>llvm/test</tt></a></h3>
708 <!------------------------------------------------------------------------->
710 <p>This directory contains regression tests and source code that is used to
711 test the LLVM infrastructure...</p>
713 <!------------------------------------------------------------------------->
714 <h3><a name="tools"><tt>llvm/tools</tt></a></h3>
715 <!------------------------------------------------------------------------->
717 <p>The <b>tools</b> directory contains the executables built out of the
718 libraries above, which form the main part of the user interface. You can
719 always get help for a tool by typing <tt>tool_name --help</tt>. The
720 following is a brief introduction to the most important tools.</p>
723 <dt><tt><b>as</b></tt><dd>The assembler transforms the human readable
724 LLVM assembly to LLVM bytecode.<p>
726 <dt><tt><b>dis</b></tt><dd>The disassembler transforms the LLVM bytecode
727 to human readable LLVM assembly. Additionally it can convert LLVM
728 bytecode to C, which is enabled with the <tt>-c</tt> option.<p>
730 <dt><tt><b>lli</b></tt><dd> <tt>lli</tt> is the LLVM interpreter, which
731 can directly execute LLVM bytecode (although very slowly...). In addition
732 to a simple interpreter, <tt>lli</tt> is also has debugger and tracing
733 modes (entered by specifying <tt>-debug</tt> or <tt>-trace</tt> on the
734 command line, respectively). Finally, for architectures that support it
735 (currently only x86 and Sparc), by default, <tt>lli</tt> will function as
736 a Just-In-Time compiler (if the functionality was compiled in), and will
737 execute the code <i>much</i> faster than the interpreter.<p>
739 <dt><tt><b>llc</b></tt><dd> <tt>llc</tt> is the LLVM backend compiler,
740 which translates LLVM bytecode to a SPARC or x86 assembly file.<p>
742 <dt><tt><b>llvmgcc</b></tt><dd> <tt>llvmgcc</tt> is a GCC based C frontend
743 that has been retargeted to emit LLVM code as the machine code output. It
744 works just like any other GCC compiler, taking the typical <tt>-c, -S, -E,
745 -o</tt> options that are typically used. The source code for the
746 <tt>llvmgcc</tt> tool is currently not included in the LLVM cvs tree
747 because it is quite large and not very interesting.<p>
750 <dt><tt><b>gccas</b></tt><dd> This tool is invoked by the
751 <tt>llvmgcc</tt> frontend as the "assembler" part of the compiler. This
752 tool actually assembles LLVM assembly to LLVM bytecode,
753 performs a variety of optimizations,
754 and outputs LLVM bytecode. Thus when you invoke <tt>llvmgcc -c x.c -o
755 x.o</tt>, you are causing <tt>gccas</tt> to be run, which writes the
756 <tt>x.o</tt> file (which is an LLVM bytecode file that can be
757 disassembled or manipulated just like any other bytecode file). The
758 command line interface to <tt>gccas</tt> is designed to be as close as
759 possible to the <b>system</b> '<tt>as</tt>' utility so that the gcc
760 frontend itself did not have to be modified to interface to a "weird"
763 <dt><tt><b>gccld</b></tt><dd> <tt>gccld</tt> links together several LLVM
764 bytecode files into one bytecode file and does some optimization. It is
765 the linker invoked by the gcc frontend when multiple .o files need to be
766 linked together. Like <tt>gccas</tt> the command line interface of
767 <tt>gccld</tt> is designed to match the system linker, to aid
768 interfacing with the GCC frontend.<p>
771 <dt><tt><b>opt</b></tt><dd> <tt>opt</tt> reads LLVM bytecode, applies a
772 series of LLVM to LLVM transformations (which are specified on the command
773 line), and then outputs the resultant bytecode. The '<tt>opt --help</tt>'
774 command is a good way to get a list of the program transformations
775 available in LLVM.<p>
778 <dt><tt><b>analyze</b></tt><dd> <tt>analyze</tt> is used to run a specific
779 analysis on an input LLVM bytecode file and print out the results. It is
780 primarily useful for debugging analyses, or familiarizing yourself with
781 what an analysis does.<p>
785 <!--=====================================================================-->
786 <h2><a name="tutorial">An example using the LLVM tool chain</h2>
787 <!--=====================================================================-->
790 <li>First, create a simple C file, name it 'hello.c':
792 #include <stdio.h>
794 printf("hello world\n");
799 <li>Next, compile the C file into a LLVM bytecode file:<p>
801 <tt>% llvmgcc hello.c -o hello</tt><p>
803 This will create two result files: <tt>hello</tt> and
804 <tt>hello.bc</tt>. The <tt>hello.bc</tt> is the LLVM bytecode that
805 corresponds the the compiled program and the library facilities that it
806 required. <tt>hello</tt> is a simple shell script that runs the bytecode
807 file with <tt>lli</tt>, making the result directly executable.<p>
809 <li>Run the program. To make sure the program ran, execute one of the
810 following commands:<p>
812 <tt>% ./hello</tt><p>
816 <tt>% lli hello.bc</tt><p>
818 <li>Use the <tt>dis</tt> utility to take a look at the LLVM assembly
821 <tt>% dis < hello.bc | less</tt><p>
823 <li>Compile the program to native Sparc assembly using the code
824 generator (assuming you are currently on a Sparc system):<p>
826 <tt>% llc hello.bc -o hello.s</tt><p>
828 <li>Assemble the native sparc assemble file into a program:<p>
830 <tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.sparc</tt><p>
832 <li>Execute the native sparc program:<p>
834 <tt>% ./hello.sparc</tt><p>
839 <!--=====================================================================-->
840 <h2><a name="help">Common Problems</a></h2>
841 <!--=====================================================================-->
843 Below are common problems and their remedies:
846 <dt><b>When I run configure, it finds the wrong C compiler.</b>
848 The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and
849 then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and
850 <tt>CXX</tt> for the C and C++ compiler, respectively.
852 If <tt>configure</tt> finds the wrong compiler, either adjust your
853 <tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
857 <dt><b>I compile the code, and I get some error about /localhome</b>.
859 There are several possible causes for this. The first is that you
860 didn't set a pathname properly when using <tt>configure</tt>, and it
861 defaulted to a pathname that we use on our research machines.
863 Another possibility is that we hardcoded a path in our Makefiles. If
864 you see this, please email the LLVM bug mailing list with the name of
865 the offending Makefile and a description of what is wrong with it.
867 <dt><b>The <tt>configure</tt> script finds the right C compiler, but it
868 uses the LLVM linker from a previous build. What do I do?</b>
870 The <tt>configure</tt> script uses the <tt>PATH</tt> to find
871 executables, so if it's grabbing the wrong linker/assembler/etc, there
872 are two ways to fix it:
874 <li>Adjust your <tt>PATH</tt> environment variable so that the
875 correct program appears first in the <tt>PATH</tt>. This may work,
876 but may not be convenient when you want them <i>first</i> in your
880 <li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that
881 is correct. In a Borne compatible shell, the syntax would be:
883 <tt>PATH=<the path without the bad program> ./configure ...</tt>
885 This is still somewhat inconvenient, but it allows
886 <tt>configure</tt> to do its work without having to adjust your
887 <tt>PATH</tt> permanently.
891 <!--=====================================================================-->
892 <h2><a name="links">Links</a></h2>
893 <!--=====================================================================-->
895 <p>This document is just an <b>introduction</b> to how to use LLVM to do
896 some simple things... there are many more interesting and complicated things
897 that you can do that aren't documented here (but we'll gladly accept a patch
898 if you want to write something up!). For more information about LLVM, check
902 <li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>
903 <li><a href="http://llvm.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>
904 <li><a href="http://llvm.cs.uiuc.edu/docs/Projects.html">Starting a Project that Uses LLVM</a></li>
909 If you have any questions or run into any snags (or you have any
910 additions...), please send an email to
911 <a href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
913 <!-- Created: Mon Jul 1 02:29:02 CDT 2002 -->
915 Last modified: Tue Jun 3 22:06:43 CDT 2003