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> and
11 <a href="http://www.cs.uiuc.edu/~vadve">Vikram Adve</a>
14 <!--=====================================================================-->
15 <h2><a name="Contents">Contents</a></h2>
16 <!--=====================================================================-->
19 <li><a href="#overview">Overview</a>
20 <li><a href="#starting">Getting started with LLVM</a>
22 <li><a href="#quickstart">Getting started quickly (a summary)</a>
23 <li><a href="#checkout">Checkout LLVM from CVS</a>
24 <li><a href="#terminology">Terminology and Notation</tt></a>
25 <li><a href="#objfiles">The location for object files</tt></a>
26 <li><a href="#config">Local Configuration Options</tt></a>
27 <li><a href="#environment">Setting up your environment</a>
28 <li><a href="#compile">Compiling the source code</a>
30 <li><a href="#layout">Program layout</a>
32 <li><a href="#cvsdir">CVS directories</a>
33 <li><a href="#dd"><tt>Depend</tt>, <tt>Debug</tt>, &
34 <tt>Release</tt> directories</a></li>
35 <li><a href="#include"><tt>llvm/include</tt></a>
36 <li><a href="#lib"><tt>llvm/lib</tt></a>
37 <li><a href="#test"><tt>llvm/test</tt></a>
38 <li><a href="#tools"><tt>llvm/tools</tt></a>
40 <li><a href="#tutorial">An example using the LLVM tool chain</a>
41 <li><a href="#links">Links</a>
45 <!--=====================================================================-->
47 <h2><a name="overview"><b>Overview</b></a></h2>
49 <!--=====================================================================-->
51 <p>The <a href"starting">next section</a> of this guide is meant to get
52 you up and running with LLVM, and to give you some basic information about
53 the LLVM environment. The <a href"#quickstart">first subsection</a> gives
54 a short summary for those who are already familiar with the system and
55 want to get started as quickly as possible.
57 <p>The later sections of this guide describe the <a
58 href"#layout">general layout</a> of the the LLVM source-tree, a <a
59 href="#tutorial">simple example</a> using the LLVM tool chain, and <a
60 href="#links">links</a> to find more information about LLVM or to get
63 <!--=====================================================================-->
65 <h2><a name="starting"><b>Getting Started</b></a></h2>
67 <!--=====================================================================-->
70 <!--=====================================================================-->
71 <h3><a name="quickstart"><b>Getting Started Quickly (A Summary)</b></a></h3>
72 <!--=====================================================================-->
74 Here's the short story for getting up and running quickly with LLVM:
76 <li>Find the path to the CVS repository containing LLVM (we'll call this <i>CVSROOTDIR</i>).
77 <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
78 <li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt>
79 <li>Edit <tt>llvm/Makefile.config</tt> to set local paths if necessary.
81 <li><tt>gmake -k |& tee gnumake.out
82 # this is csh or tcsh syntax</tt>
85 <p>See <a href="#environment">Setting up your environment</a> on tips to
86 simplify working with the LLVM front-end and compiled tools. See the
87 other sub-sections below for other useful details in working with LLVM,
88 or go straight to <a href="#layout">Program Layout</a> to learn about the
89 layout of the source code tree.
91 <!------------------------------------------------------------------------->
92 <h3><a name="terminology">Terminology and Notation</a></h3>
93 <!------------------------------------------------------------------------->
95 <p>Through this manual, the following names are used to denote paths
96 specific to the local system and working environment. <i>These are not
97 environment variables you need to set, but just strings used in the rest
98 of this document below.</i>. In any of the examples below, simply replace
99 each of these names with the appropriate pathname on your local system.
100 All these paths are absolute:</p>
104 <!------------------------------------------------------------------------->
105 <h3><a name="checkout">Checkout LLVM from CVS</a></h3>
106 <!------------------------------------------------------------------------->
108 <p>Before checking out the source code, you will need to know the path to
109 CVS repository containing LLVM source code (we'll call this
110 <i>CVSROOTDIR</i> below). Ask the person responsible for your local LLVM
111 installation to give you this path.
113 <p>To get a fresh copy of the entire source code, all you
114 need to do is check it out from CVS as follows:
116 <li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
117 <li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt></p>
120 <p>This will create an '<tt>llvm</tt>' directory in the current
121 directory and fully populate it with the LLVM source code, Makefiles,
122 test directories, and local copies of documentation files.</p>
124 <!------------------------------------------------------------------------->
125 <h3><a name="config">Local Configuration Options</a></h3>
126 <!------------------------------------------------------------------------->
128 <p>The file <tt>llvm/Makefile.config</tt>
129 defines the following path variables,
130 which are specific to a particular installation of LLVM.
131 These should need to be modified only once after checking out a copy
132 of LLVM (if the default values do not already match your system):
135 <p><li><i>CXX</i> = Path to C++ compiler to use.
136 <p><li><i>LLVM_OBJ_DIR</i> = Path to the llvm directory where
137 object files should be placed.
138 (See the Section on <a href=#objfiles>
139 The location for LLVM object files</a>
140 for more information.)
141 <p><li><i>LLVMGCCDIR</i> = Path to the location of the LLVM front-end
142 binaries and associated libraries.
143 <p><li><i>PURIFY</i> = Path to the purify program.
146 <!------------------------------------------------------------------------->
147 <h3><a name="objfiles">The location for LLVM object files</a></h3>
148 <!------------------------------------------------------------------------->
150 <p>The LLVM make system sends most output files generated during the build
151 into the directory defined by the variable LLVM_OBJ_DIR in
152 <tt>llvm/Makefile.config</tt>. This can be either just your normal LLVM
153 source tree or some other directory writable by you. You may wish to put
154 object files on a different filesystem either to keep them from being backed
155 up or to speed up local builds.
157 <p>If you do not wish to use a different location for object files (building
158 into the source tree directly), just set this variable to ".".<p>
160 <!------------------------------------------------------------------------->
161 <h3><a name="environment">Setting up your environment</a></h3>
162 <!------------------------------------------------------------------------->
164 <i>NOTE: This step is optional but will set up your environment so you
165 can use the compiled LLVM tools with as little hassle as
168 <p>Add the following lines to your <tt>.cshrc</tt> (or the corresponding
169 lines to your <tt>.profile</tt> if you use a bourne shell derivative).
172 # Make the C front end easy to use...
173 alias llvmgcc <i>LLVMGCCDIR</i><tt>/bin/llvm-gcc</tt>
175 # Make the LLVM tools easy to use...
176 setenv PATH <i>LLVM_OBJ_DIR</i>/tools/Debug:${PATH}
178 The <tt>llvmgcc</tt> alias is useful because the C compiler is not
179 included in the CVS tree you just checked out.
181 <p>The other <a href="#tools">LLVM tools</a> are part of the LLVM
182 source base, and built when compiling LLVM. They will be built into the
183 <tt><i>LLVM_OBJ_DIR</i>/tools/Debug</tt> directory.</p>
185 <!------------------------------------------------------------------------->
186 <h3><a name="compile">Compiling the source code</a></h3>
187 <!------------------------------------------------------------------------->
189 <p>Every directory in the LLVM source tree includes a <tt>Makefile</tt> to
190 build it, and any subdirectories that it contains. These makefiles require
191 that you use <tt>gmake</tt>, instead of <tt>make</tt> to build them, but can
192 otherwise be used freely. To build the entire LLVM system, just enter the
193 top level <tt>llvm</tt> directory and type <tt>gmake</tt>. A few minutes
194 later you will hopefully have a freshly compiled toolchain waiting for you
195 in <tt>llvm/tools/Debug</tt>. If you want to look at the libraries that
196 were compiled, look in <tt>llvm/lib/Debug</tt>.</p>
198 If you get an error talking about a <tt>/localhome</tt> directory, follow
199 the instructions in the section about <a href="#environment">Setting Up Your
204 <!--=====================================================================-->
206 <h2><a name="layout"><b>Program Layout</b></a></h2>
208 <!--=====================================================================-->
210 <p>One useful source of infomation about the LLVM sourcebase is the LLVM <a
211 href="http://www.doxygen.org">doxygen</a> documentation, available at <tt><a
212 href="http://llvm.cs.uiuc.edu/doxygen/">http://llvm.cs.uiuc.edu/doxygen/</a></tt>. The
213 following is a brief introduction to code layout:</p>
216 <!------------------------------------------------------------------------->
217 <h3><a name="cvsdir"><tt>CVS</tt> directories</a></h3>
218 <!------------------------------------------------------------------------->
220 Every directory checked out of CVS will contain a <tt>CVS</tt> directory,
221 for the most part these can just be ignored.
224 <!------------------------------------------------------------------------->
225 <h3><a name="ddr"><tt>Depend</tt>, <tt>Debug</tt>, & <tt>Release</tt>
227 <!------------------------------------------------------------------------->
229 If you are building with the "<tt>BUILD_ROOT=.</tt>" option enabled in the
230 <tt>Makefile.common</tt> file, most source directories will contain two
231 directories, <tt>Depend</tt> and <tt>Debug</tt>. The <tt>Depend</tt>
232 directory contains automatically generated dependance files which are used
233 during compilation to make sure that source files get rebuilt if a header
234 file they use is modified. The <tt>Debug</tt> directory holds the object
235 files, library files and executables that are used for building a debug
236 enabled build. The <tt>Release</tt> directory is created to hold the same
237 files when the <tt>ENABLE_OPTIMIZED=1</tt> flag is passed to <tt>gmake</tt>,
238 causing an optimized built to be performed.<p>
241 <!------------------------------------------------------------------------->
242 <h3><a name="include"><tt>llvm/include</tt></a></h3>
243 <!------------------------------------------------------------------------->
245 This directory contains public header files exported from the LLVM
246 library. The two main subdirectories of this directory are:<p>
249 <li><tt>llvm/include/llvm</tt> - This directory contains all of the LLVM
250 specific header files. This directory also has subdirectories for
251 different portions of LLVM: <tt>Analysis</tt>, <tt>CodeGen</tt>,
252 <tt>Reoptimizer</tt>, <tt>Target</tt>, <tt>Transforms</tt>, etc...
254 <li><tt>llvm/include/Support</tt> - This directory contains generic
255 support libraries that are independant of LLVM, but are used by LLVM.
256 For example, some C++ STL utilities and a Command Line option processing
260 <!------------------------------------------------------------------------->
261 <h3><a name="lib"><tt>llvm/lib</tt></a></h3>
262 <!------------------------------------------------------------------------->
264 This directory contains most source files of LLVM system. In LLVM almost all
265 code exists in libraries, making it very easy to share code among the
266 different <a href="#tools">tools</a>.<p>
269 <dt><tt>llvm/lib/VMCore/</tt><dd> This directory holds the core LLVM
270 source files that implement core classes like Instruction and BasicBlock.
272 <dt><tt>llvm/lib/AsmParser/</tt><dd> This directory holds the source code
273 for the LLVM assembly language parser library.
275 <dt><tt>llvm/lib/ByteCode/</tt><dd> This directory holds code for reading
276 and write LLVM bytecode.
278 <dt><tt>llvm/lib/CWriter/</tt><dd> This directory implements the LLVM to C
281 <dt><tt>llvm/lib/Analysis/</tt><dd> This directory contains a variety of
282 different program analyses, such as Dominator Information, Call Graphs,
283 Induction Variables, Interval Identification, Natural Loop Identification,
286 <dt><tt>llvm/lib/Transforms/</tt><dd> This directory contains the source
287 code for the LLVM to LLVM program transformations, such as Aggressive Dead
288 Code Elimination, Sparse Conditional Constant Propogation, Inlining, Loop
289 Invarient Code Motion, Dead Global Elimination, Pool Allocation, and many
292 <dt><tt>llvm/lib/Target/</tt><dd> This directory contains files that
293 describe various target architectures for code generation. For example,
294 the llvm/lib/Target/Sparc directory holds the Sparc machine
297 <dt><tt>llvm/lib/CodeGen/</tt><dd> This directory contains the major parts
298 of the code generator: Instruction Selector, Instruction Scheduling, and
301 <dt><tt>llvm/lib/Reoptimizer/</tt><dd> This directory holds code related
302 to the runtime reoptimizer framework that is currently under development.
304 <dt><tt>llvm/lib/Support/</tt><dd> This directory contains the source code
305 that corresponds to the header files located in
306 <tt>llvm/include/Support/</tt>.
309 <!------------------------------------------------------------------------->
310 <h3><a name="test"><tt>llvm/test</tt></a></h3>
311 <!------------------------------------------------------------------------->
313 <p>This directory contains regression tests and source code that is used to
314 test the LLVM infrastructure...</p>
316 <!------------------------------------------------------------------------->
317 <h3><a name="tools"><tt>llvm/tools</tt></a></h3>
318 <!------------------------------------------------------------------------->
320 <p>The <b>tools</b> directory contains the executables built out of the
321 libraries above, which form the main part of the user interface. You can
322 always get help for a tool by typing <tt>tool_name --help</tt>. The
323 following is a brief introduction to the most important tools.</p>
326 <dt><tt><b>as</b></tt><dd>The assembler transforms the human readable
327 LLVM assembly to LLVM bytecode.<p>
329 <dt><tt><b>dis</b></tt><dd>The disassembler transforms the LLVM bytecode
330 to human readable LLVM assembly. Additionally it can convert LLVM
331 bytecode to C, which is enabled with the <tt>-c</tt> option.<p>
333 <dt><tt><b>lli</b></tt><dd> <tt>lli</tt> is the LLVM interpreter, which
334 can directly execute LLVM bytecode (although very slowly...). In addition
335 to a simple intepreter, <tt>lli</tt> is also has debugger and tracing
336 modes (entered by specifying <tt>-debug</tt> or <tt>-trace</tt> on the
337 command line, respectively).<p>
339 <dt><tt><b>llc</b></tt><dd> <tt>llc</tt> is the LLVM backend compiler,
340 which translates LLVM bytecode to a SPARC assembly file.<p>
342 <dt><tt><b>llvmgcc</b></tt><dd> <tt>llvmgcc</tt> is a GCC based C frontend
343 that has been retargeted to emit LLVM code as the machine code output. It
344 works just like any other GCC compiler, taking the typical <tt>-c, -S, -E,
345 -o</tt> options that are typically used. The source code for the
346 <tt>llvmgcc</tt> tool is currently not included in the LLVM cvs tree
347 because it is quite large and not very interesting.<p>
350 <dt><tt><b>gccas</b></tt><dd> This tool is invoked by the
351 <tt>llvmgcc</tt> frontend as the "assembler" part of the compiler. This
352 tool actually assembles LLVM assembly to LLVM bytecode,
353 performs a variety of optimizations,
354 and outputs LLVM bytecode. Thus when you invoke <tt>llvmgcc -c x.c -o
355 x.o</tt>, you are causing <tt>gccas</tt> to be run, which writes the
356 <tt>x.o</tt> file (which is an LLVM bytecode file that can be
357 disassembled or manipulated just like any other bytecode file). The
358 command line interface to <tt>gccas</tt> is designed to be as close as
359 possible to the <b>system</b> <tt>as</tt> utility so that the gcc
360 frontend itself did not have to be modified to interface to a "wierd"
363 <dt><tt><b>gccld</b></tt><dd> <tt>gccld</tt> links together several LLVM
364 bytecode files into one bytecode file and does some optimization. It is
365 the linker invoked by the gcc frontend when multiple .o files need to be
366 linked together. Like <tt>gccas</tt> the command line interface of
367 <tt>gccld</tt> is designed to match the system linker, to aid
368 interfacing with the GCC frontend.<p>
371 <dt><tt><b>opt</b></tt><dd> <tt>opt</tt> reads LLVM bytecode, applies a
372 series of LLVM to LLVM transformations (which are specified on the command
373 line), and then outputs the resultant bytecode. The '<tt>opt --help</tt>'
374 command is a good way to get a list of the program transformations
375 available in LLVM.<p>
378 <dt><tt><b>analyze</b></tt><dd> <tt>analyze</tt> is used to run a specific
379 analysis on an input LLVM bytecode file and print out the results. It is
380 primarily useful for debugging analyses, or familiarizing yourself with
381 what an analysis does.<p>
385 <!--=====================================================================-->
386 <h2><a name="tutorial">An example using the LLVM tool chain</h2>
387 <!--=====================================================================-->
390 <li>First, create a simple C file, name it 'hello.c':
392 #include <stdio.h>
394 printf("hello world\n");
399 <li>Next, compile the C file into a LLVM bytecode file:<p>
401 <tt>% llvmgcc hello.c -o hello</tt><p>
403 This will create two result files: <tt>hello</tt> and
404 <tt>hello.bc</tt>. The <tt>hello.bc</tt> is the LLVM bytecode that
405 corresponds the the compiled program and the library facilities that it
406 required. <tt>hello</tt> is a simple shell script that runs the bytecode
407 file with <tt>lli</tt>, making the result directly executable.<p>
409 <li>Run the program. To make sure the program ran, execute one of the
410 following commands:<p>
412 <tt>% ./hello</tt><p>
416 <tt>% lli hello.bc</tt><p>
418 <li>Use the <tt>dis</tt> utility to take a look at the LLVM assembly
421 <tt>% dis < hello.bc | less</tt><p>
423 <li>Compile the program to native Sparc assembly using the code
426 <tt>% llc hello.bc -o hello.s</tt><p>
428 <li>Assemble the native sparc assemble file into a program:<p>
430 <tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.sparc</tt><p>
432 <li>Execute the native sparc program:<p>
434 <tt>% ./hello.sparc</tt><p>
439 <!--=====================================================================-->
440 <h2><a name="links">Links</a></h2>
441 <!--=====================================================================-->
443 <p>This document is just an <b>introduction</b> to how to use LLVM to do
444 some simple things... there are many more interesting and complicated things
445 that you can do that aren't documented here (but we'll gladly accept a patch
446 if you want to write something up!). For more information about LLVM, check
450 <li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>
451 <li><a href="http://tank.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>
456 If you have any questions or run into any snags (or you have any
457 additions...), please send an email to
458 <a href="mailto:hldnbrnd@uiuc.edu">Nicholas Hildenbrandt</a> or
459 <a href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
461 <!-- Created: Mon Jul 1 02:29:02 CDT 2002 -->
463 Last modified: Thu Sep 19 14:55:19 CDT 2002