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="#unpack">Unpacking the LLVM Archives</a>
34 <li><a href="#checkout">Checkout LLVM from CVS</a>
35 <li><a href="#installcf">Install the C Front End</a>
36 <li><a href="#config">Local LLVM Configuration</tt></a>
37 <li><a href="#compile">Compiling the LLVM Suite Source Code</a>
38 <li><a href="#objfiles">The Location of LLVM Object Files</tt></a>
40 <li><a href="#layout">Program layout</a>
42 <li><a href="#cvsdir"><tt>CVS</tt> directories</a>
43 <li><a href="#include"><tt>llvm/include</tt></a>
44 <li><a href="#lib"><tt>llvm/lib</tt></a>
45 <li><a href="#test"><tt>llvm/test</tt></a>
46 <li><a href="#tools"><tt>llvm/tools</tt></a>
48 <li><a href="#cfront">Compiling the LLVM C Front End</a>
49 <li><a href="#tutorial">An Example Using the LLVM Tool Chain</a>
50 <li><a href="#problems">Common Problems</a>
51 <li><a href="#links">Links</a>
55 <!--=====================================================================-->
57 <h2><a name="overview"><b>Overview</b></a></h2>
59 <!--=====================================================================-->
61 Welcome to LLVM! In order to get started, you first need to know some
65 First, LLVM comes in two pieces. The first piece is the LLVM suite. This
66 contains all of the tools, libraries, and header files needed to use the
67 low level virtual machine. It also contains a test suite that can be used
68 to test the LLVM tools and the C front end.
70 The second piece is the C front end. This component provides a version
71 of GCC that compiles C code into LLVM bytecode. Currently, the C front end
72 is a modified version of GCC 3.4 (we track the GCC 3.4 development).
73 Once compiled into LLVM bytecode, a program can be manipulated with the
74 LLVM tools from the LLVM suite.
76 <!--=====================================================================-->
77 <h3><a name="requirements"><b>Requirements</b></a></h3>
78 <!--=====================================================================-->
80 Before you begin to use the LLVM system, review the requirements given
81 below. This may save you some trouble by knowing ahead of time what
82 hardware and software you will need.
84 <!--=====================================================================-->
85 <h4><a name="hardware"><b>Hardware</b></a></h4>
86 <!--=====================================================================-->
87 LLVM is known to work on the following platforms:
91 <li> Approximately 760 MB of Free Disk Space
93 <li>Source code: 30 MB
94 <li>Object code: 670 MB
95 <li>C front end: 60 MB
101 <li> Solaris on SparcV9 (Ultrasparc)
103 <li> Approximately 1.24 GB of Free Disk Space
105 <li>Source code: 30 MB
106 <li>Object code: 1000 MB
107 <li>C front end: 210 MB
113 If you want to compile your own version of the C front end, you will need
114 additional disk space:
120 <li> Approximately 249 MB of Free Disk Space
122 <li>Source code: 146 MB
123 <li>Object code: 82 MB
124 <li>Installed binaries: 21 MB
132 <li> Approximately 264 MB of Free Disk Space
134 <li>Source code: 146 MB
135 <li>Object code: 93 MB
136 <li>Installed binaries: 25 MB
142 LLVM <i>may</i> compile on other platforms. The LLVM utilities should work
143 on other platforms, so it should be possible to generate and produce LLVM
144 bytecode on unsupported platforms (although bytecode generated on one
145 platform may not work on another platform). However, the code generators
146 and Just-In-Time (JIT) compilers only generate SparcV9 or x86 machine code.
149 <!--=====================================================================-->
150 <h4><a name="software"><b>Software</b></a></h4>
151 <!--=====================================================================-->
154 Unpacking the distribution requires the following tools:
159 These tools are needed to uncompress and unarchive the software.
160 Regular Solaris <tt>tar</tt> may work for unpacking the TAR archive but
164 Compiling LLVM requires that you have several different software packages
170 The GNU Compiler Collection must be installed with C and C++ language
171 support. GCC 3.2.x works, and GCC 3.x is generally supported.
174 Note that we currently do not support any other C++ compiler.
179 The LLVM build system relies upon GNU Make extensions. Therefore, you
180 will need GNU Make (sometimes known as gmake) to build LLVM.
185 The LLVM source code is built using flex and bison. You will not be
186 able to configure and compile LLVM without them.
191 If you are installing Bison on your machine for the first time, you
192 will need GNU M4 (version 1.4 or higher).
196 There are some additional tools that you may want to have when working with
204 If you want to make changes to the configure scripts, you will need
205 GNU autoconf (2.53 or higher), and consequently, GNU M4 (version 1.4
211 <p>The <a href="starting">next section</a> of this guide is meant to get
212 you up and running with LLVM and to give you some basic information about
213 the LLVM environment. The <a href"#quickstart">first subsection</a> gives
214 a short summary for those who are already familiar with the system and
215 want to get started as quickly as possible.
217 <p>The later sections of this guide describe the <a
218 href="#layout">general layout</a> of the the LLVM source-tree, a <a
219 href="#tutorial">simple example</a> using the LLVM tool chain, and <a
220 href="#links">links</a> to find more information about LLVM or to get
223 <!--=====================================================================-->
225 <h2><a name="starting"><b>Getting Started with LLVM</b></a></h2>
227 <!--=====================================================================-->
229 <!--=====================================================================-->
230 <h3><a name="quickstart"><b>Getting Started Quickly (A Summary)</b></a></h3>
231 <!--=====================================================================-->
233 Here's the short story for getting up and running quickly with LLVM:
235 <li>Install the C front end:
237 <li><tt>cd <i>where-you-want-the-C-front-end-to-live</i></tt>
238 <li><tt>gunzip --stdout cfrontend.<i>platform</i>.tar.gz | tar -xvf
244 <li>Get the Source Code
246 <li>With the distributed files:
248 <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
249 <li><tt>gunzip --stdout llvm.tar.gz | tar -xvf -</tt>
250 <li><tt>gunzip --stdout cfrontend.<i>platform</i>.tar.gz | tar -xvf -</tt>
256 <li>With anonymous CVS access:
258 <li>Find the path to the CVS repository containing LLVM (we'll call this <i>CVSROOTDIR</i>).
259 <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
260 <li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt>
268 <li>Configure the LLVM Build Environment
270 <li>Run <tt>configure</tt> to configure the Makefiles and header
271 files for the default platform.
272 Useful options include:
274 <li><tt>--with-objroot=<i>directory</i></tt>
276 Specify where object files should be placed during the build.
278 <li><tt>--with-llvmgccdir=<i>directory</i></tt>
280 Specify where the LLVM C frontend is going to be installed.
286 <li>Build the LLVM Suite
288 <li>Set your LLVM_LIB_SEARCH_PATH environment variable.
289 <li><tt>gmake -k |& tee gnumake.out
290 # this is csh or tcsh syntax</tt>
297 <p>See <a href="#environment">Setting Up Your Environment</a> on tips to
298 simplify working with the LLVM front-end and compiled tools. See the
299 other sub-sections below for other useful details in working with LLVM,
300 or go straight to <a href="#layout">Program Layout</a> to learn about the
301 layout of the source code tree. For information on building the C front
302 end yourself, see <a href="#cfront">Compiling the LLVM C Front End</a> for
305 <!------------------------------------------------------------------------->
306 <h3><a name="terminology">Terminology and Notation</a></h3>
307 <!------------------------------------------------------------------------->
309 <p>Throughout this manual, the following names are used to denote paths
310 specific to the local system and working environment. <i>These are not
311 environment variables you need to set but just strings used in the rest
312 of this document below</i>. In any of the examples below, simply replace
313 each of these names with the appropriate pathname on your local system.
314 All these paths are absolute:</p>
318 This is the path for the CVS repository containing the LLVM source
319 code. Ask the person responsible for your local LLVM installation to
325 This is the top level directory for where the LLVM suite object files
326 will be placed during the build.
331 This is the pathname to the location where the LLVM C Front End will
332 be installed. Note that the C front end does not need to be installed
333 during the LLVM suite build; you will just need to know where it will
334 go for configuring the build system and running the test suite later.
336 For the pre-built C front end binaries, the LLVMGCCDIR is
337 <tt>cfrontend/<i>platform</i>/llvm-gcc</tt>.
341 This is the pathname of the directory where the LLVM C front end source
347 This is the pathname of the directory where the LLVM C front end object
348 code will be placed during the build. It can be safely removed once
349 the build is complete.
352 <!------------------------------------------------------------------------->
353 <h3><a name="environment">Setting Up Your Environment</a></h3>
354 <!------------------------------------------------------------------------->
357 In order to compile and use LLVM, you will need to set some environment
358 variables. There are also some shell aliases which you may find useful.
359 You can set these on the command line, or better yet, set them in your
360 <tt>.cshrc</tt> or <tt>.profile</tt>.
363 <dt><tt>LLVM_LIB_SEARCH_PATH</tt>=<tt><i>LLVMGCCDIR</i>/llvm-gcc/bytecode-libs</tt>
365 This environment variable helps the LLVM C front end find bytecode
366 libraries that it will need for compilation.
369 <dt>alias llvmgcc <i>LLVMGCCDIR</i><tt>/bin/llvm-gcc</tt>
371 This alias allows you to use the LLVM C front end without putting it in
372 your <tt>PATH</tt> or typing in its complete pathname.
375 <!------------------------------------------------------------------------->
376 <h3><a name="unpack">Unpacking the LLVM Archives</a></h3>
377 <!------------------------------------------------------------------------->
380 If you have the LLVM distribution, you will need to unpack it before you
381 can begin to compile it. LLVM is distributed as a set of four files. Each
382 file is a TAR archive that is compressed with the gzip program.
385 <p> The four files are as follows:
388 <dd>This is the source code to the LLVM suite.
391 <dt>cfrontend.sparc.tar.gz
392 <dd>This is the binary release of the C front end for Solaris/Sparc.
395 <dt>cfrontend.x86.tar.gz
396 <dd>This is the binary release of the C front end for Linux/x86.
399 <dt>cfrontend-src.tar.gz
400 <dd>This is the source code release of the C front end.
404 <!------------------------------------------------------------------------->
405 <h3><a name="checkout">Checkout LLVM from CVS</a></h3>
406 <!------------------------------------------------------------------------->
408 <p>If you have access to our CVS repository, you can get a fresh copy of
409 the entire source code. All you need to do is check it out from CVS as
412 <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
413 <li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt></p>
416 <p>This will create an '<tt>llvm</tt>' directory in the current
417 directory and fully populate it with the LLVM source code, Makefiles,
418 test directories, and local copies of documentation files.</p>
421 Note that the C front end is not included in the CVS repository. You
422 should have either downloaded the source, or better yet, downloaded the
423 binary distribution for your platform.
426 <!------------------------------------------------------------------------->
427 <h3><a name="installcf">Install the C Front End</a></h3>
428 <!------------------------------------------------------------------------->
431 Before configuring and compiling the LLVM suite, it is best to extract the
432 LLVM C front end. While not used in building, the C front end is used by
433 the LLVM test suite, and its location must be given to the
434 <tt>configure</tt> script before the LLVM suite can be built.
438 To install the C front end, do the following:
440 <li><tt>cd <i>where-you-want-the-front-end-to-live</i></tt>
441 <li><tt>gunzip --stdout cfrontend.<i>platform</i>.tar.gz | tar -xvf
445 <!------------------------------------------------------------------------->
446 <h3><a name="config">Local LLVM Configuration</a></h3>
447 <!------------------------------------------------------------------------->
449 <p>Once checked out from the CVS repository, the LLVM suite source code
450 must be configured via the <tt>configure</tt> script. This script sets
451 variables in <tt>llvm/Makefile.config</tt> and
452 <tt>llvm/include/Config/config.h</tt>.
455 The following environment variables are used by the <tt>configure</tt>
456 script to configure the build system:
470 Tells <tt>configure</tt> which C compiler to use. By default,
471 <tt>configure</tt> will look for the first GCC compiler in
472 <tt>PATH</tt>. Use this variable to override
473 <tt>configure</tt>'s default behavior.
480 Tells <tt>configure</tt> which C++ compiler to use. By default,
481 <tt>configure</tt> will look for the first GCC compiler in
482 <tt>PATH</tt>. Use this variable to override
483 <tt>configure</tt>'s default behavior.
489 The following options can be used to set or enable LLVM specific options:
493 <dt><i>--with-objroot=OBJ_ROOT</i>
495 Path to the directory where
496 object files, libraries, and executables should be placed.
497 If this is set to <tt>.</tt>, then the object files will be placed
498 within the source code tree. If left unspecified, the default value is
502 If the USER environment variable is specified and the directory
503 <tt>/localhome/$USER</tt> exists, then the default value is
504 <tt>/localhome/$USER</tt>.
507 Otherwise, the default value is <tt>.</tt>.
509 (See the Section on <a href=#objfiles>
510 The Location of LLVM Object Files</a>
511 for more information.)
513 <dt><i>--with-llvmgccdir=LLVMGCCDIR</i>
515 Path to the location where the LLVM C front end binaries and
516 associated libraries will be installed.
518 <dt><i>--enable-optimized</i>
520 Enables optimized compilation (debugging symbols are removed and GCC
521 optimization flags are enabled). The default is to use an unoptimized
522 build (also known as a debug build).
524 <dt><i>--enable-jit</i>
526 Compile the Just In Time (JIT) functionality. This is not available
527 on all platforms. The default is dependent on platform, so it is best
528 to explicitly enable it if you want it.
531 In addition to running <tt>configure</tt>, you must set the
532 <tt>LLVM_LIB_SEARCH_PATH</tt> environment variable in your startup scripts.
533 This environment variable is used to locate "system" libraries like
534 "<tt>-lc</tt>" and "<tt>-lm</tt>" when linking. This variable should be set
535 to the absolute path for the bytecode-libs subdirectory of the C front-end
536 install, or LLVMGCCDIR/llvm-gcc/bytecode-libs. For example, one might
537 set <tt>LLVM_LIB_SEARCH_PATH</tt> to
538 <tt>/home/vadve/lattner/local/x86/llvm-gcc/bytecode-libs</tt> for the X86
539 version of the C front-end on our research machines.<p>
541 <!------------------------------------------------------------------------->
542 <h3><a name="compile">Compiling the LLVM Suite Source Code</a></h3>
543 <!------------------------------------------------------------------------->
545 Once you have configured LLVM, you can build it. There are three types of
551 These builds are the default. They compile the tools and libraries
552 with debugging information.
555 <dt>Release (Optimized) Builds
557 These builds are enabled with the <tt>--enable-optimized</tt> option to
558 <tt>configure</tt>. They compile the tools and libraries with GCC
559 optimizer flags on and strip debugging information from the libraries
560 and executables it generates.
565 These builds are for use with profiling. They compile profiling
566 information into the code for use with programs like <tt>gprof</tt>.
567 Profile builds must be started by setting variables on the
568 <tt>gmake</tt> command line.
571 Once you have LLVM configured, you can build it by entering the top level
572 <tt>llvm</tt> directory and issuing the following command:
577 If you have multiple processors in your machine, you may wish to use some
578 of the parallel build options provided by GNU Make. For example, you could
586 There are several other targets which are useful when working with the LLVM
590 <dt><tt>gmake clean</tt>
592 Removes all files generated by the build. This includes object files,
593 generated C/C++ files, libraries, and executables.
596 <dt><tt>gmake distclean</tt>
598 Removes everything that <tt>gmake clean</tt> does, but also removes
599 files generated by <tt>configure</tt>. It attempts to return the
600 source tree to the original state in which it was shipped.
604 It is also possible to override default values from <tt>configure</tt> by
605 declaring variables on the command line. The following are some examples:
608 <dt><tt>gmake ENABLE_OPTIMIZED=1</tt>
610 Perform a Release (Optimized) build.
613 <dt><tt>gmake ENABLE_PROFILING=1</tt>
615 Perform a Profiling build.
618 <dt><tt>gmake VERBOSE=1</tt>
620 Print what <tt>gmake</tt> is doing on standard output.
624 Every directory in the LLVM source tree includes a <tt>Makefile</tt> to
625 build it and any subdirectories that it contains. Entering any directory
626 inside the LLVM source tree and typing <tt>gmake</tt> should rebuild
627 anything in or below that directory that is out of date.
629 <!------------------------------------------------------------------------->
630 <h3><a name="objfiles">The Location of LLVM Object Files</a></h3>
631 <!------------------------------------------------------------------------->
633 <p>The LLVM build system sends most output files generated during the build
634 into the directory defined by the variable <i>OBJ_ROOT</i> in
635 <tt>llvm/Makefile.config</tt>, which is set by the <i>--with-objroot</i>
636 option in <tt>configure</tt>. This can be either just your normal LLVM
637 source tree or some other directory writable by you. You may wish to put
638 object files on a different filesystem either to keep them from being backed
639 up or to speed up local builds.
642 If <i>OBJ_ROOT</i> is specified, then the build system will create a
643 directory tree underneath it that resembles the source code's pathname
644 relative to your home directory (unless <i>OBJ_ROOT</i> is set to
645 <tt>.</tt>, in which case object files are placed within the LLVM source
651 <i>--with-objroot</i>=<tt>.</tt>
653 <i>--with-objroot</i>=<tt>`pwd`</tt>
654 are not the same thing. The former will simply place object files within
655 the source tree, while the latter will set the location of object files
656 using the source tree's relative path from the home directory.
660 For example, suppose that <i>OBJ_ROOT</i> is set to <tt>/tmp</tt> and the
661 LLVM suite source code is located in <tt>/usr/home/joe/src/llvm</tt>, where
662 <tt>/usr/home/joe</tt> is the home directory of a user named Joe. Then,
663 the object files will be placed in <tt>/tmp/src/llvm</tt>.
667 The LLVM build will place files underneath <i>OBJ_ROOT</i> in directories
668 named after the build type:
676 <dd><tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt>
678 <dd><tt><i>OBJ_ROOT</i>/llvm/lib/Debug</tt>
686 <dd><tt><i>OBJ_ROOT</i>/llvm/tools/Release</tt>
688 <dd><tt><i>OBJ_ROOT</i>/llvm/lib/Release</tt>
696 <dd><tt><i>OBJ_ROOT</i>/llvm/tools/Profile</tt>
698 <dd><tt><i>OBJ_ROOT</i>/llvm/lib/Profile</tt>
702 <!--=====================================================================-->
704 <h2><a name="layout"><b>Program Layout</b></a></h2>
706 <!--=====================================================================-->
708 <p>One useful source of information about the LLVM source base is the LLVM <a
709 href="http://www.doxygen.org">doxygen</a> documentation, available at <tt><a
710 href="http://llvm.cs.uiuc.edu/doxygen/">http://llvm.cs.uiuc.edu/doxygen/</a></tt>. The
711 following is a brief introduction to code layout:</p>
714 <!------------------------------------------------------------------------->
715 <h3><a name="cvsdir"><tt>CVS</tt> directories</a></h3>
716 <!------------------------------------------------------------------------->
718 Every directory checked out of CVS will contain a <tt>CVS</tt> directory;
719 for the most part these can just be ignored.
722 <!------------------------------------------------------------------------->
723 <h3><a name="include"><tt>llvm/include</tt></a></h3>
724 <!------------------------------------------------------------------------->
726 This directory contains public header files exported from the LLVM
727 library. The three main subdirectories of this directory are:<p>
730 <li><tt>llvm/include/llvm</tt> - This directory contains all of the LLVM
731 specific header files. This directory also has subdirectories for
732 different portions of LLVM: <tt>Analysis</tt>, <tt>CodeGen</tt>,
733 <tt>Reoptimizer</tt>, <tt>Target</tt>, <tt>Transforms</tt>, etc...
735 <li><tt>llvm/include/Support</tt> - This directory contains generic
736 support libraries that are independent of LLVM, but are used by LLVM.
737 For example, some C++ STL utilities and a Command Line option processing
740 <li><tt>llvm/include/Config</tt> - This directory contains header files
741 configured by the <tt>configure</tt> script. They wrap "standard" UNIX
742 and C header files. Source code can include these header files which
743 automatically take care of the conditional #includes that the configure
747 <!------------------------------------------------------------------------->
748 <h3><a name="lib"><tt>llvm/lib</tt></a></h3>
749 <!------------------------------------------------------------------------->
751 This directory contains most of the source files of the LLVM system. In
753 code exists in libraries, making it very easy to share code among the
754 different <a href="#tools">tools</a>.<p>
757 <dt><tt>llvm/lib/VMCore/</tt><dd> This directory holds the core LLVM
758 source files that implement core classes like Instruction and BasicBlock.
760 <dt><tt>llvm/lib/AsmParser/</tt><dd> This directory holds the source code
761 for the LLVM assembly language parser library.
763 <dt><tt>llvm/lib/ByteCode/</tt><dd> This directory holds code for reading
764 and write LLVM bytecode.
766 <dt><tt>llvm/lib/CWriter/</tt><dd> This directory implements the LLVM to C
769 <dt><tt>llvm/lib/Analysis/</tt><dd> This directory contains a variety of
770 different program analyses, such as Dominator Information, Call Graphs,
771 Induction Variables, Interval Identification, Natural Loop Identification,
774 <dt><tt>llvm/lib/Transforms/</tt><dd> This directory contains the source
775 code for the LLVM to LLVM program transformations, such as Aggressive Dead
776 Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop
777 Invarient Code Motion, Dead Global Elimination, and many others...
779 <dt><tt>llvm/lib/Target/</tt><dd> This directory contains files that
780 describe various target architectures for code generation. For example,
781 the llvm/lib/Target/Sparc directory holds the Sparc machine
784 <dt><tt>llvm/lib/CodeGen/</tt><dd> This directory contains the major parts
785 of the code generator: Instruction Selector, Instruction Scheduling, and
788 <dt><tt>llvm/lib/Reoptimizer/</tt><dd> This directory holds code related
789 to the runtime reoptimizer framework that is currently under development.
791 <dt><tt>llvm/lib/Support/</tt><dd> This directory contains the source code
792 that corresponds to the header files located in
793 <tt>llvm/include/Support/</tt>.
796 <!------------------------------------------------------------------------->
797 <h3><a name="test"><tt>llvm/test</tt></a></h3>
798 <!------------------------------------------------------------------------->
800 <p>This directory contains regression tests and source code that is used to
801 test the LLVM infrastructure...</p>
803 <!------------------------------------------------------------------------->
804 <h3><a name="tools"><tt>llvm/tools</tt></a></h3>
805 <!------------------------------------------------------------------------->
807 <p>The <b>tools</b> directory contains the executables built out of the
808 libraries above, which form the main part of the user interface. You can
809 always get help for a tool by typing <tt>tool_name --help</tt>. The
810 following is a brief introduction to the most important tools.</p>
813 <dt><tt><b>as</b></tt><dd>The assembler transforms the human readable
814 LLVM assembly to LLVM bytecode.<p>
816 <dt><tt><b>dis</b></tt><dd>The disassembler transforms the LLVM bytecode
817 to human readable LLVM assembly. Additionally it can convert LLVM
818 bytecode to C, which is enabled with the <tt>-c</tt> option.<p>
820 <dt><tt><b>lli</b></tt><dd> <tt>lli</tt> is the LLVM interpreter, which
821 can directly execute LLVM bytecode (although very slowly...). In addition
822 to a simple interpreter, <tt>lli</tt> is also has debugger and tracing
823 modes (entered by specifying <tt>-debug</tt> or <tt>-trace</tt> on the
824 command line, respectively). Finally, for architectures that support it
825 (currently only x86 and Sparc), by default, <tt>lli</tt> will function as
826 a Just-In-Time compiler (if the functionality was compiled in), and will
827 execute the code <i>much</i> faster than the interpreter.<p>
829 <dt><tt><b>llc</b></tt><dd> <tt>llc</tt> is the LLVM backend compiler,
830 which translates LLVM bytecode to a SPARC or x86 assembly file.<p>
832 <dt><tt><b>llvmgcc</b></tt><dd> <tt>llvmgcc</tt> is a GCC based C frontend
833 that has been retargeted to emit LLVM code as the machine code output. It
834 works just like any other GCC compiler, taking the typical <tt>-c, -S, -E,
835 -o</tt> options that are typically used. The source code for the
836 <tt>llvmgcc</tt> tool is currently not included in the LLVM cvs tree
837 because it is quite large and not very interesting.<p>
840 <dt><tt><b>gccas</b></tt><dd> This tool is invoked by the
841 <tt>llvmgcc</tt> frontend as the "assembler" part of the compiler. This
842 tool actually assembles LLVM assembly to LLVM bytecode,
843 performs a variety of optimizations,
844 and outputs LLVM bytecode. Thus when you invoke <tt>llvmgcc -c x.c -o
845 x.o</tt>, you are causing <tt>gccas</tt> to be run, which writes the
846 <tt>x.o</tt> file (which is an LLVM bytecode file that can be
847 disassembled or manipulated just like any other bytecode file). The
848 command line interface to <tt>gccas</tt> is designed to be as close as
849 possible to the <b>system</b> '<tt>as</tt>' utility so that the gcc
850 frontend itself did not have to be modified to interface to a "weird"
853 <dt><tt><b>gccld</b></tt><dd> <tt>gccld</tt> links together several LLVM
854 bytecode files into one bytecode file and does some optimization. It is
855 the linker invoked by the gcc frontend when multiple .o files need to be
856 linked together. Like <tt>gccas</tt> the command line interface of
857 <tt>gccld</tt> is designed to match the system linker, to aid
858 interfacing with the GCC frontend.<p>
861 <dt><tt><b>opt</b></tt><dd> <tt>opt</tt> reads LLVM bytecode, applies a
862 series of LLVM to LLVM transformations (which are specified on the command
863 line), and then outputs the resultant bytecode. The '<tt>opt --help</tt>'
864 command is a good way to get a list of the program transformations
865 available in LLVM.<p>
868 <dt><tt><b>analyze</b></tt><dd> <tt>analyze</tt> is used to run a specific
869 analysis on an input LLVM bytecode file and print out the results. It is
870 primarily useful for debugging analyses, or familiarizing yourself with
871 what an analysis does.<p>
875 <!--=====================================================================-->
876 <h2><center><a name="cfront">Compiling the LLVM C Front End</center></h2>
877 <!--=====================================================================-->
881 This step is optional if you have the C front end binary distribution for
886 Now that you have the LLVM suite built, you can build the C front end. For
887 those of you that have built GCC before, the process is very similar.
889 Be forewarned, though: the build system for the C front end is not as
890 polished as the rest of the LLVM code, so there will be many warnings and
891 errors that you will need to ignore for now:
894 <li>Ensure that <tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt> is at the
895 <i>end</i> of your <tt>PATH</tt> environment variable. The front end
896 build needs to know where to find the LLVM tools, but you want to
897 ensure that these tools are not found before the system assembler and
898 linker that you normally use for compilation.
900 <li><tt>cd <i>GCCOBJ</i></tt>
902 <li>Configure the source code:
904 <li>On Linux/x86, use
906 <li><tt><i>GCCSRC</i>/configure --prefix=<i>LLVMGCCDIR</i>
907 --enable-languages=c</tt>
910 <li>On Solaris/Sparc, use
912 <li><tt><i>GCCSRC</i>/configure --prefix=<i>LLVMGCCDIR</i>
913 --enable-languages=c --target=sparcv9-sun-solaris2</tt>
919 <li>The build will eventually fail. Don't worry; chances are good that
920 everything that needed to build is built.
922 <li><tt>gmake -k install</tt>
926 Once this is done, you should have a built front end compiler in
927 <tt><i>LLVMGCCDIR</i></tt>.
930 <!--=====================================================================-->
932 <center><a name="tutorial">An Example Using the LLVM Tool Chain</center>
934 <!--=====================================================================-->
937 <li>First, create a simple C file, name it 'hello.c':
939 #include <stdio.h>
941 printf("hello world\n");
946 <li>Next, compile the C file into a LLVM bytecode file:<p>
948 <tt>% llvmgcc hello.c -o hello</tt><p>
950 This will create two result files: <tt>hello</tt> and
951 <tt>hello.bc</tt>. The <tt>hello.bc</tt> is the LLVM bytecode that
952 corresponds the the compiled program and the library facilities that it
953 required. <tt>hello</tt> is a simple shell script that runs the bytecode
954 file with <tt>lli</tt>, making the result directly executable.<p>
956 <li>Run the program. To make sure the program ran, execute one of the
957 following commands:<p>
959 <tt>% ./hello</tt><p>
963 <tt>% lli hello.bc</tt><p>
965 <li>Use the <tt>dis</tt> utility to take a look at the LLVM assembly
968 <tt>% dis < hello.bc | less</tt><p>
970 <li>Compile the program to native Sparc assembly using the code
971 generator (assuming you are currently on a Sparc system):<p>
973 <tt>% llc hello.bc -o hello.s</tt><p>
975 <li>Assemble the native sparc assemble file into a program:<p>
977 <tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.sparc</tt><p>
979 <li>Execute the native sparc program:<p>
981 <tt>% ./hello.sparc</tt><p>
986 <!--=====================================================================-->
988 <center><a name="problems">Common Problems</a></center>
990 <!--=====================================================================-->
992 Below are common problems and their remedies:
995 <dt><b>When I run configure, it finds the wrong C compiler.</b>
997 The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and
998 then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and
999 <tt>CXX</tt> for the C and C++ compiler, respectively.
1001 If <tt>configure</tt> finds the wrong compiler, either adjust your
1002 <tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
1006 <dt><b>I compile the code, and I get some error about /localhome</b>.
1008 There are several possible causes for this. The first is that you
1009 didn't set a pathname properly when using <tt>configure</tt>, and it
1010 defaulted to a pathname that we use on our research machines.
1012 Another possibility is that we hardcoded a path in our Makefiles. If
1013 you see this, please email the LLVM bug mailing list with the name of
1014 the offending Makefile and a description of what is wrong with it.
1016 <dt><b>The <tt>configure</tt> script finds the right C compiler, but it
1017 uses the LLVM linker from a previous build. What do I do?</b>
1019 The <tt>configure</tt> script uses the <tt>PATH</tt> to find
1020 executables, so if it's grabbing the wrong linker/assembler/etc, there
1021 are two ways to fix it:
1023 <li>Adjust your <tt>PATH</tt> environment variable so that the
1024 correct program appears first in the <tt>PATH</tt>. This may work,
1025 but may not be convenient when you want them <i>first</i> in your
1026 path for other work.
1029 <li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that
1030 is correct. In a Borne compatible shell, the syntax would be:
1032 <tt>PATH=<the path without the bad program> ./configure ...</tt>
1034 This is still somewhat inconvenient, but it allows
1035 <tt>configure</tt> to do its work without having to adjust your
1036 <tt>PATH</tt> permanently.
1039 <dt><b>I've upgraded to a new version of LLVM, and I get strange build
1042 Sometimes changes to the LLVM source code alters how the build system
1043 works. Changes in libtool, autoconf, or header file dependencies are
1044 especially prone to this sort of problem.
1046 The best thing to try is to remove the old files and re-build. In most
1047 cases, this takes care of the problem. To do this, just type <tt>make
1048 clean</tt> and then <tt>make</tt> in the directory that fails to build.
1053 <!--=====================================================================-->
1054 <h2><center><a name="links">Links</a></center></h2>
1055 <!--=====================================================================-->
1057 <p>This document is just an <b>introduction</b> to how to use LLVM to do
1058 some simple things... there are many more interesting and complicated things
1059 that you can do that aren't documented here (but we'll gladly accept a patch
1060 if you want to write something up!). For more information about LLVM, check
1064 <li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>
1065 <li><a href="http://llvm.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>
1066 <li><a href="http://llvm.cs.uiuc.edu/docs/Projects.html">Starting a Project that Uses LLVM</a></li>
1071 If you have any questions or run into any snags (or you have any
1072 additions...), please send an email to
1073 <a href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
1075 <!-- Created: Mon Jul 1 02:29:02 CDT 2002 -->
1076 <!-- hhmts start -->
1077 Last modified: Tue Jun 3 22:06:43 CDT 2003