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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Getting Started with LLVM System</title>
</head>
<body bgcolor=white>
<center><h1>Getting Started with the LLVM System<br><font size=3>By: <a
href="mailto:[email protected]">Guochun Shi</a>,
<a href="mailto:[email protected]">Chris Lattner</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="#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>, &
<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="quickstart"><b>Getting Started Quickly (A Summary)</b></a></h3>
<!--=====================================================================-->
Here's the short story for getting up and running quickly with LLVM:
<ul>
<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>Edit <tt>llvm/Makefile.config</tt> to set local paths if necessary.
<li><tt>cd llvm</tt>
<li><tt>gmake -k |& tee gnumake.out
# this is csh or tcsh syntax</tt>
</ul>
<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>Through 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
CVS repository containing 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>The file <tt>llvm/Makefile.config</tt>
defines the following path variables,
which are specific to a particular installation of LLVM.
These should need to be modified only once after checking out a copy
of LLVM (if the default values do not already match your system):
<ul>
<p><li><i>LLVM_OBJ_DIR</i> = Path to the llvm directory where
object files should be placed.
(See the Section on <a href=#objfiles>
The location for LLVM object files</a>
for more information.)
<p><li><i>LLVMGCCDIR</i> = Path to the location of the LLVM front-end
binaries and associated libraries.
<p><li><i>BURG</i> = Path to the burg program used for instruction
selection.
<p><li><i>PURIFY</i> = Path to the purify program.
</ul>
<!------------------------------------------------------------------------->
<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 LLVM_OBJ_DIR in
<tt>llvm/Makefile.config</tt>.
This can be either just your normal </tt>llvm</tt> 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 do not wish to use a different location for object files,
just set this variable to ".".
<!------------------------------------------------------------------------->
<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/gcc</tt>
# Make the LLVM tools easy to use...
setenv PATH <i>LLVM_OBJ_DIR</i>/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 LLVM <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>LLVM_OBJ_DIR</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 Makefile to build it,
and any subdirectories that it contains. These makefiles require that you
use <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>llvm/tools/Debug</tt>. If you want to look at the libraries that
were compiled, look in <tt>llvm/lib/Debug</tt>.</p>
If you get an error talking about a <tt>/shared</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>, & <tt>Release</tt>
directories</a></h3>
<!------------------------------------------------------------------------->
If you are building with the "<tt>BUILD_ROOT=.</tt>" option enabled in the
<tt>Makefile.common</tt> file, 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 built 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 two 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.
</ol>
<!------------------------------------------------------------------------->
<h3><a name="lib"><tt>llvm/lib</tt></a></h3>
<!------------------------------------------------------------------------->
This directory contains most source files of 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/CWrite/</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 Propogation, 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 <stdio.h>
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://tank.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:[email protected]">Nicholas Hildenbrandt</a> or
<a href="mailto:[email protected]">Chris Lattner</a>.</p>
<!-- Created: Mon Jul 1 02:29:02 CDT 2002 -->
<!-- hhmts start -->
Last modified: Tue Aug 13 16:09:25 CDT 2002
<!-- hhmts end -->
</body>
</html>