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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:gshi1@uiuc.edu">Guochun Shi</a>, <a
href="mailto:sabre@nondot.org">Chris Lattner</a> and <a
href="http://www.cs.uiuc.edu/%7Evadve">Vikram Adve</a> </font></h1>
</center>
<!--=====================================================================-->
<h2><a name="Contents">Contents</a></h2>
<!--=====================================================================-->
<ul>
<li><a href="#overview">Overview</a> </li>
<li><a href="#starting">Getting started with LLVM</a>
<ol>
<li><a href="#quickstart">Getting started quickly (a summary)</a>
</li>
<li><a href="#checkout">Checkout LLVM from CVS</a> </li>
<li><a href="#terminology">Terminology and Notation</a> </li>
<li><a href="#objfiles">The location for object files</a> </li>
<li><a href="#config">Local Configuration Options</a> </li>
<li><a href="#environment">Setting up your environment</a>
</li>
<li><a href="#compile">Compiling the source code</a> </li>
</ol>
</li>
<li><a href="#layout">Program layout</a>
<ol>
<li><a href="#cvsdir">CVS directories</a> </li>
<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>
<li><a href="#lib"><tt>llvm/lib</tt></a> </li>
<li><a href="#test"><tt>llvm/test</tt></a> </li>
<li><a href="#tools"><tt>llvm/tools</tt></a> </li>
</ol>
</li>
<li><a href="#tutorial">An example using the LLVM tool chain</a>
</li>
<li><a href="#links">Links</a> </li>
</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>
<p>The later sections of this guide describe the <a href="" #layout="">general
layout</a> of 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. <!--=====================================================================-->
</p>
<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:
<ol>
<li>Find the path to the CVS repository containing LLVM (we'll call
this <i>CVSROOTDIR</i>). </li>
<li><tt>cd <i>where-you-want-llvm-to-live</i></tt> </li>
<li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt> </li>
<li><tt>cd llvm</tt> </li>
<li>Edit <tt>Makefile.config</tt> to set local paths. This includes
setting the install location of the C frontend and the various paths
to the C and C++ compilers used to build LLVM itself. </li>
<li>Set your LLVM_LIB_SEARCH_PATH environment variable. </li>
<li><tt>gmake -k |& tee gnumake.out # this is
csh or tcsh syntax</tt> </li>
</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. <!------------------------------------------------------------------------->
</p>
<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
the 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>
<p>To get a fresh copy of the entire source code, all you need to do
is check it out from CVS as follows: </p>
<ul>
<li><tt>cd <i>where-you-want-llvm-to-live</i></tt> </li>
<li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt>
<p></p>
</li>
</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):
</p>
<ul>
<p></p>
<li><i>CXX</i> = Path to C++ compiler to use.
<p></p>
</li>
<li><i>OBJ_ROOT</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></p>
</li>
<li><i>LLVMGCCDIR</i> = Path to the location of the LLVM front-end
binaries and associated libraries.
<p></p>
</li>
<li><i>PURIFY</i> = Path to the purify program. </li>
</ul>
In addition to settings in this file, you must set a <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,
<tt>/home/vadve/lattner/local/x86/llvm-gcc/bytecode-libs</tt> is used
for the X86 version of the C front-end on our research machines.
<p> <!------------------------------------------------------------------------->
</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>
<p>If you do not wish to use a different location for object files (i.e.
building into the source tree directly), just set this variable to ".".</p>
<p> <!------------------------------------------------------------------------->
</p>
<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).
</p>
<pre> # Make the C front end easy to use...<br> 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}<br> </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 are 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
GNU Make (<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></tt><tt>/llvm/tools/Debug</tt>.
If you want to look at the libraries that were compiled, look in <tt><i>OBJ_ROOT</i></tt><tt>/llvm/lib/Debug</tt>.</p>
If you get an error about the <tt>/localhome</tt> directory, chances
are good that something has been misconfigured. 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>OBJ_ROOT=.</tt>" option enabled in
the <tt>Makefile.config</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> <!------------------------------------------------------------------------->
</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> </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>
<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>
</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> </p>
<dl compact="compact">
<dt><tt>llvm/lib/VMCore/</tt></dt>
<dd> This directory holds the core LLVM source files that implement
core classes like Instruction and BasicBlock. </dd>
<dt><tt>llvm/lib/AsmParser/</tt></dt>
<dd> This directory holds the source code for the LLVM assembly language
parser library. </dd>
<dt><tt>llvm/lib/ByteCode/</tt></dt>
<dd> This directory holds code for reading and write LLVM bytecode.
</dd>
<dt><tt>llvm/lib/CWriter/</tt></dt>
<dd> This directory implements the LLVM to C converter. </dd>
<dt><tt>llvm/lib/Analysis/</tt></dt>
<dd> This directory contains a variety of different program analyses,
such as Dominator Information, Call Graphs, Induction Variables, Interval
Identification, Natural Loop Identification, etc... </dd>
<dt><tt>llvm/lib/Transforms/</tt></dt>
<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...
</dd>
<dt><tt>llvm/lib/Target/</tt></dt>
<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>
</dd>
<dt><tt>llvm/lib/CodeGen/</tt></dt>
<dd> This directory contains the major parts of the code generator:
Instruction Selector, Instruction Scheduling, and Register Allocation.
</dd>
<dt><tt>llvm/lib/Reoptimizer/</tt></dt>
<dd> This directory holds code related to the runtime reoptimizer
framework that is currently under development. </dd>
<dt><tt>llvm/lib/Support/</tt></dt>
<dd> This directory contains the source code that corresponds to
the header files located in <tt>llvm/include/Support/</tt>. </dd>
</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="compact">
<dt><tt><b>as</b></tt></dt>
<dd>The assembler transforms the human readable LLVM assembly to
LLVM bytecode.
<p> </p>
</dd>
<dt><tt><b>dis</b></tt></dt>
<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> </p>
</dd>
<dt><tt><b>lli</b></tt></dt>
<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> </p>
</dd>
<dt><tt><b>llc</b></tt></dt>
<dd> <tt>llc</tt> is the LLVM backend compiler, which translates
LLVM bytecode to a SPARC assembly file.
<p> </p>
</dd>
<dt><tt><b>llvmgcc</b></tt></dt>
<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> </p>
<ol>
<dt><tt><b>gccas</b></tt></dt>
<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> </p>
</dd>
<dt><tt><b>gccld</b></tt></dt>
<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> </p>
</dd>
</ol>
</dd>
<dt><tt><b>opt</b></tt></dt>
<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> </p>
</dd>
<dt><tt><b>analyze</b></tt></dt>
<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> </p>
</dd>
</dl>
<!--=====================================================================-->
<h2><a name="tutorial">An example using the LLVM tool chain</a></h2>
<a name="tutorial"> <!--=====================================================================-->
</a>
<ol>
<a name="tutorial"> <li>First, create a simple C file, name it 'hello.c':
<pre> #include <stdio.h><br> int main() {<br> printf("hello world\n");<br> return 0;<br> }<br> </pre>
</li>
<li>Next, compile the C file into a LLVM bytecode file:
<p> <tt>% llvmgcc hello.c -o hello</tt></p>
<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>
<p> </p>
</li>
<li>Run the program. To make sure the program ran, execute one of the
following commands:
<p> <tt>% ./hello</tt></p>
<p> or</p>
<p> <tt>% lli hello.bc</tt></p>
<p> </p>
</li>
<li>Use the <tt>dis</tt> utility to take a look at the LLVM assembly
code:
<p> <tt>% dis < hello.bc | less</tt></p>
<p> </p>
</li>
<li>Compile the program to native Sparc assembly using the code generator:
<p> <tt>% llc hello.bc -o hello.s</tt></p>
<p> </p>
</li>
<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>
<p> </p>
</li>
<li>Execute the native sparc program:
<p> <tt>% ./hello.sparc</tt></p>
<p> </p>
</li>
</a>
</ol>
<a name="tutorial"> <!--=====================================================================-->
</a>
<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></p>
<!-- Created: Mon Jul 1 02:29:02 CDT 2002 --> <!-- hhmts start -->
Last modified: Tue Jun 3 22:06:43 CDT 2003 <!-- hhmts end --> <br>
</body>
</html>
|
