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<title>Getting Started with LLVM System</title>
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<center><h1>Getting Started with the LLVM System<br><font size=3>By: <a
href="mailto:gshi1@uiuc.edu">Guochun Shi</a>,
<a href="mailto:sabre@nondot.org">Chris Lattner,</a>
<a href="mailto:criswell@uiuc.edu">John Criswell,</a> and
<a href="http://www.cs.uiuc.edu/~vadve">Vikram Adve</a>
</font></h1></center>
<!--=====================================================================-->
<h2><a name="Contents">Contents</a></h2>
<!--=====================================================================-->
<ul>
<li><a href="#overview">Overview</a>
<li><a href="#starting">Getting started with LLVM</a>
<ol>
<li><a href="#requirements">Requirements</a>
<ol>
<li><a href="#hardware">Hardware</a>
<li><a href="#software">Software</a>
</ol>
<li><a href="#quickstart">Getting started quickly (a summary)</a>
<li><a href="#checkout">Checkout LLVM from CVS</a>
<li><a href="#terminology">Terminology and Notation</tt></a>
<li><a href="#objfiles">The location for object files</tt></a>
<li><a href="#config">Local Configuration Options</tt></a>
<li><a href="#environment">Setting up your environment</a>
<li><a href="#compile">Compiling the source code</a>
</ol>
<li><a href="#layout">Program layout</a>
<ol>
<li><a href="#cvsdir">CVS directories</a>
<li><a href="#dd"><tt>Depend</tt>, <tt>Debug</tt>, &amp;
<tt>Release</tt> directories</a></li>
<li><a href="#include"><tt>llvm/include</tt></a>
<li><a href="#lib"><tt>llvm/lib</tt></a>
<li><a href="#test"><tt>llvm/test</tt></a>
<li><a href="#tools"><tt>llvm/tools</tt></a>
</ol>
<li><a href="#tutorial">An example using the LLVM tool chain</a>
<li><a href="#links">Links</a>
</ul>
<!--=====================================================================-->
<center>
<h2><a name="overview"><b>Overview</b></a></h2>
</center>
<!--=====================================================================-->
<p>The <a href"starting">next section</a> of this guide is meant to get
you up and running with LLVM and to give you some basic information about
the LLVM environment. The <a href"#quickstart">first subsection</a> gives
a short summary for those who are already familiar with the system and
want to get started as quickly as possible.
<p>The later sections of this guide describe the <a
href"#layout">general layout</a> of the the LLVM source-tree, a <a
href="#tutorial">simple example</a> using the LLVM tool chain, and <a
href="#links">links</a> to find more information about LLVM or to get
help via e-mail.
<!--=====================================================================-->
<center>
<h2><a name="starting"><b>Getting Started</b></a></h2>
</center>
<!--=====================================================================-->
<!--=====================================================================-->
<h3><a name="requirements"><b>Requirements</b></a></h3>
<!--=====================================================================-->
<!--=====================================================================-->
<h4><a name="hardware"><b>Hardware</b></a></h4>
<!--=====================================================================-->
LLVM is known to work on the following platforms:
<ul>
<li> Linux on x86
<ul>
<li> Approximately 700 MB of Free Disk Space
<ul>
<li>Source code: 30 MB
<li>Object code: 670 MB
</ul>
</ul>
<li> Solaris on Sparc
<ul>
<li> Approximately 1.03 GB of Free Disk Space
<ul>
<li>Source code: 30 MB
<li>Object code: 1000 MB
</ul>
</ul>
</ul>
LLVM may compile on other platforms. While the LLVM utilities should work,
they will only generate Sparc or x86 machine code.
<!--=====================================================================-->
<h4><a name="software"><b>Software</b></a></h4>
<!--=====================================================================-->
<p>
Compiling LLVM requires that you have several different software packages
installed:
<ul>
<li> GCC
<p>
The GNU Compiler Collection must be installed with C and C++ language
support. GCC 3.x is supported, although some effort has been made to
support GCC 2.96.
</p>
<p>
Note that we currently do not support any other C++ compiler.
</p>
<li> GNU Make
<p>
The LLVM build system relies upon GNU Make extensions. Therefore, you
will need GNU Make (sometimes known as gmake) to build LLVM.
</p>
<li> Flex and Bison
<p>
The LLVM source code is built using flex and bison. You will not be
able to configure and compile LLVM without them.
</p>
</ul>
<p>
There are some additional tools that you may want to have when working with
LLVM:
</p>
<ul>
<li> GNU Autoconf and GNU M4
<p>
If you want to make changes to the autoconf scripts which configure LLVM
for compilation, you will need GNU autoconf, and consequently, GNU M4.
LLVM was built with autoconf 2.53, so that release and any later
release should work.
</p>
</ul>
<!--=====================================================================-->
<h3><a name="quickstart"><b>Getting Started Quickly (A Summary)</b></a></h3>
<!--=====================================================================-->
Here's the short story for getting up and running quickly with LLVM:
<ol>
<li>Find the path to the CVS repository containing LLVM (we'll call this <i>CVSROOTDIR</i>).
<li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
<li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt>
<li><tt>cd llvm</tt>
<li>Run <tt>configure</tt> to configure the Makefiles and header files.
Useful options include:
<ul>
<li><tt>--with-objroot=<i>directory</i></tt>
<br>
Specifiy where object files should be placed during the build.
<li><tt>--with-llvmgccdir=<i>directory</i></tt>
<br>
Specifiy where the LLVM C frontend has been installed.
</ul>
<li>Set your LLVM_LIB_SEARCH_PATH environment variable.
<li><tt>gmake -k |& tee gnumake.out
&nbsp;&nbsp;&nbsp;# this is csh or tcsh syntax</tt>
</ol>
<p>See <a href="#environment">Setting up your environment</a> on tips to
simplify working with the LLVM front-end and compiled tools. See the
other sub-sections below for other useful details in working with LLVM,
or go straight to <a href="#layout">Program Layout</a> to learn about the
layout of the source code tree.
<!------------------------------------------------------------------------->
<h3><a name="terminology">Terminology and Notation</a></h3>
<!------------------------------------------------------------------------->
<p>Throughout this manual, the following names are used to denote paths
specific to the local system and working environment. <i>These are not
environment variables you need to set but just strings used in the rest
of this document below</i>. In any of the examples below, simply replace
each of these names with the appropriate pathname on your local system.
All these paths are absolute:</p>
<ul>
</ul>
<!------------------------------------------------------------------------->
<h3><a name="checkout">Checkout LLVM from CVS</a></h3>
<!------------------------------------------------------------------------->
<p>Before checking out the source code, you will need to know the path to
the CVS repository containing the LLVM source code (we'll call this
<i>CVSROOTDIR</i> below). Ask the person responsible for your local LLVM
installation to give you this path.
<p>To get a fresh copy of the entire source code, all you
need to do is check it out from CVS as follows:
<ul>
<li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
<li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt></p>
</ul>
<p>This will create an '<tt>llvm</tt>' directory in the current
directory and fully populate it with the LLVM source code, Makefiles,
test directories, and local copies of documentation files.</p>
<!------------------------------------------------------------------------->
<h3><a name="config">Local Configuration Options</a></h3>
<!------------------------------------------------------------------------->
<p>Once checked out from the CVS repository, options and pathnames specific
to an installation of LLVM can be set via the <tt>configure</tt> script.
This script sets variables in <tt>llvm/Makefile.config</tt> and
<tt>llvm/include/Config/config.h</tt>.
<p>
The following environment variables are used by <tt>configure</tt> to
configure Makefile.config:
</p>
<ul>
<p><li><i>CXX</i> = Pathname of the C++ compiler to use.
<p><li><i>CC</i> = Pathname of the C compiler to use.
</ul>
The following options can be used to set or enable LLVM specific options:
<ul>
<p><li><i>--with-objroot=LLVM_OBJ_ROOT</i> =
Path to the directory where
object files, libraries, and executables should be placed.
(See the Section on <a href=#objfiles>
The location for LLVM object files</a>
for more information.)
<p><li><i>--with-llvmgccdir=LLVMGCCDIR</i> =
Path to the location of the LLVM front-end
binaries and associated libraries.
<p><li><i>--enable-optimized</i> =
Enables optimized compilation (debugging symbols are removed and GCC
optimization flags are enabled).
<p><li><i>--enable-jit</i> =
Compile the Just In Time (JIT) functionality. This is not available
on all platforms.
</ul>
In addition to running <tt>configure</tt>, you must set the
<tt>LLVM_LIB_SEARCH_PATH</tt> environment variable in your startup scripts.
This environment variable is used to locate "system" libraries like
"<tt>-lc</tt>" and "<tt>-lm</tt>" when linking. This variable should be set
to the absolute path for the bytecode-libs subdirectory of the C front-end
install. For example, one might set <tt>LLVM_LIB_SEARCH_PATH</tt> to
<tt>/home/vadve/lattner/local/x86/llvm-gcc/bytecode-libs</tt> for the X86
version of the C front-end on our research machines.<p>
<!------------------------------------------------------------------------->
<h3><a name="objfiles">The location for LLVM object files</a></h3>
<!------------------------------------------------------------------------->
<p>The LLVM make system sends most output files generated during the build
into the directory defined by the variable OBJ_ROOT in
<tt>llvm/Makefile.config</tt>. This can be either just your normal LLVM
source tree or some other directory writable by you. You may wish to put
object files on a different filesystem either to keep them from being backed
up or to speed up local builds.
<p>If you wish to place output files into a separate directory, use the
<tt>--with-objroot=<i>directory</i></tt> option of <tt>configure</tt> to
set the top level directory of where the object files will go. Otherwise,
leave this option unspecified, and <tt>configure</tt> will place files
within the LLVM source tree.
<!------------------------------------------------------------------------->
<h3><a name="environment">Setting up your environment</a></h3>
<!------------------------------------------------------------------------->
<i>NOTE: This step is optional but will set up your environment so you
can use the compiled LLVM tools with as little hassle as
possible.</i>)
<p>Add the following lines to your <tt>.cshrc</tt> (or the corresponding
lines to your <tt>.profile</tt> if you use a bourne shell derivative).
<pre>
# Make the C front end easy to use...
alias llvmgcc <i>LLVMGCCDIR</i><tt>/bin/llvm-gcc</tt>
# Make the LLVM tools easy to use...
setenv PATH <i>OBJ_ROOT</i>/llvm/tools/Debug:${PATH}
</pre>
The <tt>llvmgcc</tt> alias is useful because the C compiler is not
included in the CVS tree you just checked out.
<p>The other <a href="#tools">LLVM tools</a> are part of the LLVM
source base and built when compiling LLVM. They will be built into the
<tt><i>OBJ_ROOT</i>/tools/Debug</tt> directory.</p>
<!------------------------------------------------------------------------->
<h3><a name="compile">Compiling the source code</a></h3>
<!------------------------------------------------------------------------->
<p>Every directory in the LLVM source tree includes a <tt>Makefile</tt> to
build it and any subdirectories that it contains. These makefiles require
that you use GNU Make (sometimes called <tt>gmake</tt>) instead of
<tt>make</tt> to
build them, but can
otherwise be used freely. To build the entire LLVM system, just enter the
top level <tt>llvm</tt> directory and type <tt>gmake</tt>. A few minutes
later you will hopefully have a freshly compiled toolchain waiting for you
in <tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt>. If you want to look at the
libraries that
were compiled, look in <tt><i>OBJ_ROOT</i>/llvm/lib/Debug</tt>.</p>
If you get an error about a <tt>/localhome</tt> directory, follow the
instructions in the section about <a href="#environment">Setting Up Your
Environment.</a>
<!--=====================================================================-->
<center>
<h2><a name="layout"><b>Program Layout</b></a></h2>
</center>
<!--=====================================================================-->
<p>One useful source of infomation about the LLVM sourcebase is the LLVM <a
href="http://www.doxygen.org">doxygen</a> documentation, available at <tt><a
href="http://llvm.cs.uiuc.edu/doxygen/">http://llvm.cs.uiuc.edu/doxygen/</a></tt>. The
following is a brief introduction to code layout:</p>
<!------------------------------------------------------------------------->
<h3><a name="cvsdir"><tt>CVS</tt> directories</a></h3>
<!------------------------------------------------------------------------->
Every directory checked out of CVS will contain a <tt>CVS</tt> directory;
for the most part these can just be ignored.
<!------------------------------------------------------------------------->
<h3><a name="ddr"><tt>Depend</tt>, <tt>Debug</tt>, &amp; <tt>Release</tt>
directories</a></h3>
<!------------------------------------------------------------------------->
If you are building with the "<tt>OBJ_ROOT=.</tt>" option enabled in the
<tt>Makefile.config</tt> file (i.e. you did not specify
<tt>--with-objroot</tt> when you ran <tt>configure</tt>), most source
directories will contain two
directories, <tt>Depend</tt> and <tt>Debug</tt>. The <tt>Depend</tt>
directory contains automatically generated dependance files which are used
during compilation to make sure that source files get rebuilt if a header
file they use is modified. The <tt>Debug</tt> directory holds the object
files, library files, and executables that are used for building a debug
enabled build. The <tt>Release</tt> directory is created to hold the same
files when the <tt>ENABLE_OPTIMIZED=1</tt> flag is passed to <tt>gmake</tt>,
causing an optimized build to be performed.<p>
<!------------------------------------------------------------------------->
<h3><a name="include"><tt>llvm/include</tt></a></h3>
<!------------------------------------------------------------------------->
This directory contains public header files exported from the LLVM
library. The three main subdirectories of this directory are:<p>
<ol>
<li><tt>llvm/include/llvm</tt> - This directory contains all of the LLVM
specific header files. This directory also has subdirectories for
different portions of LLVM: <tt>Analysis</tt>, <tt>CodeGen</tt>,
<tt>Reoptimizer</tt>, <tt>Target</tt>, <tt>Transforms</tt>, etc...
<li><tt>llvm/include/Support</tt> - This directory contains generic
support libraries that are independant of LLVM, but are used by LLVM.
For example, some C++ STL utilities and a Command Line option processing
library.
<li><tt>llvm/include/Config</tt> - This directory contains header files
configured by the <tt>configure</tt> script. They wrap "standard" UNIX
and C header files. Source code can include these header files which
automatically take care of the conditional #includes that the configure
script generates.
</ol>
<!------------------------------------------------------------------------->
<h3><a name="lib"><tt>llvm/lib</tt></a></h3>
<!------------------------------------------------------------------------->
This directory contains most of the source files of the LLVM system. In
LLVM almost all
code exists in libraries, making it very easy to share code among the
different <a href="#tools">tools</a>.<p>
<dl compact>
<dt><tt>llvm/lib/VMCore/</tt><dd> This directory holds the core LLVM
source files that implement core classes like Instruction and BasicBlock.
<dt><tt>llvm/lib/AsmParser/</tt><dd> This directory holds the source code
for the LLVM assembly language parser library.
<dt><tt>llvm/lib/ByteCode/</tt><dd> This directory holds code for reading
and write LLVM bytecode.
<dt><tt>llvm/lib/CWriter/</tt><dd> This directory implements the LLVM to C
converter.
<dt><tt>llvm/lib/Analysis/</tt><dd> This directory contains a variety of
different program analyses, such as Dominator Information, Call Graphs,
Induction Variables, Interval Identification, Natural Loop Identification,
etc...
<dt><tt>llvm/lib/Transforms/</tt><dd> This directory contains the source
code for the LLVM to LLVM program transformations, such as Aggressive Dead
Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop
Invarient Code Motion, Dead Global Elimination, Pool Allocation, and many
others...
<dt><tt>llvm/lib/Target/</tt><dd> This directory contains files that
describe various target architectures for code generation. For example,
the llvm/lib/Target/Sparc directory holds the Sparc machine
description.<br>
<dt><tt>llvm/lib/CodeGen/</tt><dd> This directory contains the major parts
of the code generator: Instruction Selector, Instruction Scheduling, and
Register Allocation.
<dt><tt>llvm/lib/Reoptimizer/</tt><dd> This directory holds code related
to the runtime reoptimizer framework that is currently under development.
<dt><tt>llvm/lib/Support/</tt><dd> This directory contains the source code
that corresponds to the header files located in
<tt>llvm/include/Support/</tt>.
</dl>
<!------------------------------------------------------------------------->
<h3><a name="test"><tt>llvm/test</tt></a></h3>
<!------------------------------------------------------------------------->
<p>This directory contains regression tests and source code that is used to
test the LLVM infrastructure...</p>
<!------------------------------------------------------------------------->
<h3><a name="tools"><tt>llvm/tools</tt></a></h3>
<!------------------------------------------------------------------------->
<p>The <b>tools</b> directory contains the executables built out of the
libraries above, which form the main part of the user interface. You can
always get help for a tool by typing <tt>tool_name --help</tt>. The
following is a brief introduction to the most important tools.</p>
<dl compact>
<dt><tt><b>as</b></tt><dd>The assembler transforms the human readable
LLVM assembly to LLVM bytecode.<p>
<dt><tt><b>dis</b></tt><dd>The disassembler transforms the LLVM bytecode
to human readable LLVM assembly. Additionally it can convert LLVM
bytecode to C, which is enabled with the <tt>-c</tt> option.<p>
<dt><tt><b>lli</b></tt><dd> <tt>lli</tt> is the LLVM interpreter, which
can directly execute LLVM bytecode (although very slowly...). In addition
to a simple intepreter, <tt>lli</tt> is also has debugger and tracing
modes (entered by specifying <tt>-debug</tt> or <tt>-trace</tt> on the
command line, respectively).<p>
<dt><tt><b>llc</b></tt><dd> <tt>llc</tt> is the LLVM backend compiler,
which translates LLVM bytecode to a SPARC assembly file.<p>
<dt><tt><b>llvmgcc</b></tt><dd> <tt>llvmgcc</tt> is a GCC based C frontend
that has been retargeted to emit LLVM code as the machine code output. It
works just like any other GCC compiler, taking the typical <tt>-c, -S, -E,
-o</tt> options that are typically used. The source code for the
<tt>llvmgcc</tt> tool is currently not included in the LLVM cvs tree
because it is quite large and not very interesting.<p>
<ol>
<dt><tt><b>gccas</b></tt><dd> This tool is invoked by the
<tt>llvmgcc</tt> frontend as the "assembler" part of the compiler. This
tool actually assembles LLVM assembly to LLVM bytecode,
performs a variety of optimizations,
and outputs LLVM bytecode. Thus when you invoke <tt>llvmgcc -c x.c -o
x.o</tt>, you are causing <tt>gccas</tt> to be run, which writes the
<tt>x.o</tt> file (which is an LLVM bytecode file that can be
disassembled or manipulated just like any other bytecode file). The
command line interface to <tt>gccas</tt> is designed to be as close as
possible to the <b>system</b> '<tt>as</tt>' utility so that the gcc
frontend itself did not have to be modified to interface to a "wierd"
assembler.<p>
<dt><tt><b>gccld</b></tt><dd> <tt>gccld</tt> links together several LLVM
bytecode files into one bytecode file and does some optimization. It is
the linker invoked by the gcc frontend when multiple .o files need to be
linked together. Like <tt>gccas</tt> the command line interface of
<tt>gccld</tt> is designed to match the system linker, to aid
interfacing with the GCC frontend.<p>
</ol>
<dt><tt><b>opt</b></tt><dd> <tt>opt</tt> reads LLVM bytecode, applies a
series of LLVM to LLVM transformations (which are specified on the command
line), and then outputs the resultant bytecode. The '<tt>opt --help</tt>'
command is a good way to get a list of the program transformations
available in LLVM.<p>
<dt><tt><b>analyze</b></tt><dd> <tt>analyze</tt> is used to run a specific
analysis on an input LLVM bytecode file and print out the results. It is
primarily useful for debugging analyses, or familiarizing yourself with
what an analysis does.<p>
</dl>
<!--=====================================================================-->
<h2><a name="tutorial">An example using the LLVM tool chain</h2>
<!--=====================================================================-->
<ol>
<li>First, create a simple C file, name it 'hello.c':
<pre>
#include &lt;stdio.h&gt;
int main() {
printf("hello world\n");
return 0;
}
</pre>
<li>Next, compile the C file into a LLVM bytecode file:<p>
<tt>% llvmgcc hello.c -o hello</tt><p>
This will create two result files: <tt>hello</tt> and
<tt>hello.bc</tt>. The <tt>hello.bc</tt> is the LLVM bytecode that
corresponds the the compiled program and the library facilities that it
required. <tt>hello</tt> is a simple shell script that runs the bytecode
file with <tt>lli</tt>, making the result directly executable.<p>
<li>Run the program. To make sure the program ran, execute one of the
following commands:<p>
<tt>% ./hello</tt><p>
or<p>
<tt>% lli hello.bc</tt><p>
<li>Use the <tt>dis</tt> utility to take a look at the LLVM assembly
code:<p>
<tt>% dis < hello.bc | less</tt><p>
<li>Compile the program to native Sparc assembly using the code
generator:<p>
<tt>% llc hello.bc -o hello.s</tt><p>
<li>Assemble the native sparc assemble file into a program:<p>
<tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.sparc</tt><p>
<li>Execute the native sparc program:<p>
<tt>% ./hello.sparc</tt><p>
</ol>
<!--=====================================================================-->
<h2><a name="links">Links</a></h2>
<!--=====================================================================-->
<p>This document is just an <b>introduction</b> to how to use LLVM to do
some simple things... there are many more interesting and complicated things
that you can do that aren't documented here (but we'll gladly accept a patch
if you want to write something up!). For more information about LLVM, check
out:</p>
<ul>
<li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>
<li><a href="http://llvm.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>
</ul>
<hr>
If you have any questions or run into any snags (or you have any
additions...), please send an email to
<a href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
<!-- Created: Mon Jul 1 02:29:02 CDT 2002 -->
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Last modified: Tue Jun 3 22:06:43 CDT 2003
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