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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>,
<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>
<ol>
<li><a href="#requirements">Requirements</a>
<ol>
<li><a href="#hardware">Hardware</a>
<li><a href="#software">Software</a>
</ol>
</ol>
<li><a href="#starting">Getting started with LLVM</a>
<ol>
<li><a href="#quickstart">Getting started quickly (a summary)</a>
<li><a href="#terminology">Terminology and Notation</tt></a>
<li><a href="#environment">Setting up your environment</a>
<li><a href="#checkout">Checkout LLVM from CVS</a>
<li><a href="#config">Local LLVM Configuration</tt></a>
<li><a href="#compile">Compiling the LLVM Suite Source Code</a>
<li><a href="#build">Building the LLVM C Front End</a>
<li><a href="#objfiles">The location for object files</tt></a>
</ol>
<li><a href="#layout">Program layout</a>
<ol>
<li><a href="#cvsdir">CVS directories</a>
<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>
<!--=====================================================================-->
Welcome to LLVM! In order to get started, you first need to know some
basic information.
<p>
First, LLVM comes in two pieces. The first piece is the LLVM suite. This
contains all of the tools, libraries, and header files needed to use the
low level virtual machine. It also contains a test suite that can be used
to test the LLVM tools and the GCC front end.
<p>
The second piece is the GCC front end. This component provides a version
of GCC that compiles C code into LLVM bytecode. Currently, the C front end
is a modified version of GCC 3.4 (we track the GCC 3.4 development).
Once compiled into LLVM bytecode, a program can be manipulated with the
LLVM tools.
<!--=====================================================================-->
<h3><a name="requirements"><b>Requirements</b></a></h3>
<!--=====================================================================-->
Before you begin to use the LLVM system, review the requirements given
below. This may save you some trouble by knowing ahead of time what
hardware and software you will need.
<!--=====================================================================-->
<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 SparcV9 (Ultrasparc)
<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 <i>may</i> compile on other platforms. The LLVM utilities should work
on other platforms, so it should be possible to generate and produce LLVM
bytecode on unsupported platforms (although bytecode generated on one
platform may not work on another platform). However, the code generators
and Just-In-Time (JIT) compilers only generate SparcV9 or x86 machine code.
<!--=====================================================================-->
<h4><a name="software"><b>Software</b></a></h4>
<!--=====================================================================-->
<p>
Unpacking the distribution requires the following tools:
<dl compact>
<dt>GNU Zip (gzip)
<dt>GNU Tar
<dd>
These tools are needed to uncompress and unarchive the software.
Regular Solaris <tt>tar</tt> may work for unpacking the TAR archive but
is untested.
</dl>
Compiling LLVM requires that you have several different software packages
installed:
<dl compact>
<dt> GCC
<dd>
The GNU Compiler Collection must be installed with C and C++ language
support. GCC 3.2.x works, and GCC 3.x is generally supported.
<p>
Note that we currently do not support any other C++ compiler.
</p>
<dt> GNU Make
<dd>
The LLVM build system relies upon GNU Make extensions. Therefore, you
will need GNU Make (sometimes known as gmake) to build LLVM.
<p>
<dt> Flex and Bison
<dd>
The LLVM source code is built using flex and bison. You will not be
able to configure and compile LLVM without them.
<p>
<dt> GNU M4
<dd>
If you are installing Bison on your machine for the first time, you
will need GNU M4 (version 1.4 or higher).
</dl>
<p>
There are some additional tools that you may want to have when working with
LLVM:
</p>
<ul>
<li>GNU Autoconf
<li>GNU M4
<p>
If you want to make changes to the configure scripts, you will need
GNU autoconf (2.53 or higher), and consequently, GNU M4 (version 1.4
or higher).
</p>
</ul>
<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:
<ol>
<li>Build the LLVM suite
<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>
Specify where object files should be placed during the build.
<li><tt>--with-llvmgccdir=<i>directory</i></tt>
<br>
Specify where the LLVM C frontend is going to be 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>
<li>Build the LLVM C Front End <b>(optional)</b>
<ol>
<li>Create a directory for the object files to live.
<li><tt>cd <i>object file directory</i></tt>
<li>Run <tt><i>Pathname-to-where-the-source-code-lives</i>/configure --prefix=<i>LLVMGCCDIR</i></tt> to configure GCC.
<li><tt>make bootstrap</tt>
<li><tt>make install</tt>
</ol>
</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>
<dl compact>
<dt>CVSROOTDIR
<dd>
This is the path for the CVS repository containing the LLVM source
code. Ask the person responsible for your local LLVM installation to
give you this path.
<p>
<dt>OBJ_ROOT
<dd>
This is the top level directory for where the LLVM suite object files
will be placed during the build.
<p>
<dt>LLVMGCCDIR
<dd>
This is the pathname to the location where the LLVM C Front End will
be installed. Note that the C front end does not need to be installed
during the LLVM suite build; you will just need to know where it will
go for configuring the build system and running the test suite later.
<p>
For the pre-built C front end binaries, the LLVMGCCDIR is
<tt>cfrontend/<i>platform</i>/llvm-gcc</tt>.
<dt>GCCSRC
<dd>
This is the pathname of the directory where the LLVM C front end source
code can be found.
<p>
<dt>GCCOBJ
<dd>
This is the pathname of the directory where the LLVM C front end object
code will be placed during the build. It can be safely removed once
the build is complete.
</dl>
<!------------------------------------------------------------------------->
<h3><a name="environment">Setting up your environment</a></h3>
<!------------------------------------------------------------------------->
<p>
In order to compile and use LLVM, you will need to set some environment
variables. There are also some shell aliases which you may find useful.
You can set these on the command line, or better yet, set them in your
<tt>.cshrc</tt> or <tt>.profile</tt>.
<dl compact>
<dt><tt>LLVM_LIB_SEARCH_PATH</tt>=<tt><i>LLVMGCCDIR</i>/llvm-gcc/bytecode-libs</tt>
<dd>
This environment variable helps the LLVM C front end find bytecode
libraries that it will need for compilation.
<p>
<dt><tt>PATH</tt>=<tt>${PATH}:<i>OBJ_ROOT</i>/llvm/tools/Debug</tt>
<dd>
Adding this directory to the end of your path will allow the
compilation of the C front end to find the LLVM tools. The LLVM tools
are needed for the C front end compile.
<p>
<dt><tt>CC</tt>=<i>Pathname to your GCC compiler</i>
<dd>
The GCC compiler that you want to use must be the first C compiler in
your <tt>PATH</tt>. Otherwise, set this variable so that
<tt>configure</tt> will use the GCC compiler that you want to use.
<p>
<dt><tt>CXX</tt>=<i>Pathname to your GCC C++ compiler</i>
<dd>
The GCC compiler that you want to use must be the first C++ compiler in
your <tt>PATH</tt>. Otherwise, set this variable so that
<tt>configure</tt> will use the GCC compiler that you want to use.
<p>
<dt><tt>CVSROOT</tt>=<i>CVSROOT</i>
<dd>
This environment variable tells CVS where to find the CVS repository.
<p>
<dt>alias llvmgcc <i>LLVMGCCDIR</i><tt>/bin/llvm-gcc</tt>
<dd>
This alias allows you to use the LLVM C front end without putting it in
your <tt>PATH</tt> or typing in its complete pathname.
</dl>
<!------------------------------------------------------------------------->
<h3><a name="checkout">Checkout LLVM from CVS</a></h3>
<!------------------------------------------------------------------------->
<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>
<p>
Note that the C front end is not included in the CVS repository. You
should have either downloaded the source, or better yet, downloaded the
binary distribution for your platform.
</p>
<!------------------------------------------------------------------------->
<h3><a name="config">Local LLVM Configuration</a></h3>
<!------------------------------------------------------------------------->
<p>Once checked out from the CVS repository, the LLVM suite source code
must be configured 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:
<dl compact>
<dt><i>--with-objroot=OBJ_ROOT</i>
<dd>
Path to the directory where
object files, libraries, and executables should be placed.
If this is set to <tt>.</tt>, then the object files will be placed
within the source code tree. If left unspecified, the default value is
<tt>.</tt>.
(See the Section on <a href=#objfiles>
The location for LLVM object files</a>
for more information.)
<p>
<dt><i>--with-llvmgccdir=LLVMGCCDIR</i>
<dd>
Path to the location where the LLVM C front end binaries and
associated libraries will be installed.
<p>
<dt><i>--enable-optimized</i>
<dd>
Enables optimized compilation (debugging symbols are removed and GCC
optimization flags are enabled). The default is to use an unoptimized
build (also known as a debug build).
<p>
<dt><i>--enable-jit</i>
<dd>
Compile the Just In Time (JIT) functionality. This is not available
on all platforms. The default is dependent on platform, so it is best
to explicitly enable it if you want it.
</dl>
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, or LLVMGCCDIR/llvm-gcc/bytecode-libs. 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="compile">Compiling the LLVM Suite Source Code</a></h3>
<!------------------------------------------------------------------------->
Once you have configured LLVM, you can build it. There are three types of
builds:
<dl compact>
<dt>Debug Builds
<dd>
These builds are the default. They compile the tools and libraries
with debugging information.
<p>
<dt>Release (Optimized) Builds
<dd>
These builds are enabled with the <tt>--enable-optimized</tt> option to
<tt>configure</tt>. They compile the tools and libraries with GCC
optimizer flags on and strip debugging information from the libraries
and executables it generates.
<p>
<dt>Profile Builds
<dd>
These builds are for use with profiling. They compile profiling
information into the code for use with programs like <tt>gprof</tt>.
Profile builds must be started by setting variables on the
<tt>make</tt> command line.
</dl>
Once you have LLVM configured, you can build it by entering the top level
<tt>llvm</tt> directory and issuing the following command:
<p>
<tt>make</tt>
<p>
If you have multiple processors in your machine, you may wish to use some
of the parallel build options provided by GNU Make. For example, you could
use the command:
</p>
<p>
<tt>make -j2</tt>
<p>
There are several other targets which are useful when working with the LLVM
source code:
<dl compact>
<dt><tt>make clean</tt>
<dd>
Removes all files generated by the build. This includes object files,
generated C/C++ files, libraries, and executables.
<p>
<dt><tt>make distclean</tt>
<dd>
Removes everything that <tt>make clean</tt> does, but also removes
files generated by <tt>configure</tt>. It attempts to return the
source tree to the original state in which it was shipped.
<p>
</dl>
It is also possible to override default values from <tt>configure</tt> by
declaring variables on the command line. The following are some examples:
<dl compact>
<dt><tt>make ENABLE_OPTIMIZED=1</tt>
<dd>
Perform a Release (Optimized) build.
<p>
<dt><tt>make ENABLE_PROFILING=1</tt>
<dd>
Perform a Profiling build.
<p>
<dt><tt>make VERBOSE=1</tt>
<dd>
Print what <tt>make</tt> is doing on standard output.
<p>
</dl>
Every directory in the LLVM source tree includes a <tt>Makefile</tt> to
build it and any subdirectories that it contains. Entering any directory
inside the LLVM source tree and typing <tt>make</tt> should rebuild
anything in or below that directory that is out of date.
<!------------------------------------------------------------------------->
<h3><a name="build">Building the LLVM C Front End</a></h3>
<!------------------------------------------------------------------------->
<b>
<p>
This step is optional if you have the C front end binary distrubtion for
your platform.
</p>
</b>
Now that you have the LLVM Suite built, you can build the C front end. For
those of you that have built GCC before, the process is very similar.
<p>
Be forewarned, though: the build system for the C front end is not as
polished as the rest of the LLVM code, so there will be many warnings and
errors that you will need to ignore for now:
<ol>
<li>Ensure that <tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt> is at the
<i>end</i> of your <tt>PATH</tt> environment variable.
<li><tt>cd <i>GCCOBJ</i></tt>
<li>Configure the source code:
<ul>
<li>On Linux/x86, use
<ul>
<li><tt><i>GCCSRC</i>/configure --prefix=<i>LLVMGCCDIR</i>
--enable-languages=c</tt>
</ul>
<li>On Solaris/Sparc, use
<ul>
<li><tt><i>GCCSRC</i>/configure --prefix=<i>LLVMGCCDIR</i>
--enable-languages=c --target=sparcv9-sun-solaris2</tt>
</ul>
</ul>
<li><tt>make bootstrap</tt>
<li>The build will eventually fail. Don't worry; chances are good that
everything that needed to build is built.
<li><tt>make install</tt>
</ol>
At this point, you should have a working copy of the LLVM C front end
installed in <i>LLVMGCCDIR</i>.
<!------------------------------------------------------------------------->
<h3><a name="objfiles">The location for LLVM object files</a></h3>
<!------------------------------------------------------------------------->
<p>The LLVM build system sends most output files generated during the build
into the directory defined by the variable <i>OBJ_ROOT</i> in
<tt>llvm/Makefile.config</tt>, which is set by the <i>--with-objroot</i>
option in <tt>configure</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 <i>OBJ_ROOT</i> is specified, then the build system will create a
directory tree underneath it that resembles the source code's pathname
relative to your home directory.
</p>
<p>
For example, suppose that <i>OBJ_ROOT</i> is set to <tt>/tmp</tt> and the
LLVM suite source code is located in <tt>/usr/home/joe/src/llvm</tt>, where
<tt>/usr/home/joe</tt> is the home directory of a user named Joe. Then,
the object files will be placed in <tt>/tmp/src/llvm</tt>.
</p>
<p>
The LLVM build will place files underneath <i>OBJ_ROOT</i> in directories
named after the build type:
</p>
<dl compact>
<dt>Debug Builds
<dd>
<dl compact>
<dt>Tools
<dd><tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt>
<dt>Libraries
<dd><tt><i>OBJ_ROOT</i>/llvm/lib/Debug</tt>
</dl>
<p>
<dt>Release Builds
<dd>
<dl compact>
<dt>Tools
<dd><tt><i>OBJ_ROOT</i>/llvm/tools/Release</tt>
<dt>Libraries
<dd><tt><i>OBJ_ROOT</i>/llvm/lib/Release</tt>
</dl>
<p>
<dt>Profile Builds
<dd>
<dl compact>
<dt>Tools
<dd><tt><i>OBJ_ROOT</i>/llvm/tools/Profile</tt>
<dt>Libraries
<dd><tt><i>OBJ_ROOT</i>/llvm/lib/Profile</tt>
</dl>
</dl>
<!--=====================================================================-->
<center>
<h2><a name="layout"><b>Program Layout</b></a></h2>
</center>
<!--=====================================================================-->
<p>One useful source of information about the LLVM source base 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="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 independent 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 interpreter, <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). Finally, for architectures that support it
(currently only x86 and Sparc), by default, <tt>lli</tt> will function as
a Just-In-Time compiler (if the functionality was compiled in), and will
execute the code <i>much</i> faster than the interpreter.<p>
<dt><tt><b>llc</b></tt><dd> <tt>llc</tt> is the LLVM backend compiler,
which translates LLVM bytecode to a SPARC or x86 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 "weird"
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 (assuming you are currently on a Sparc system):<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="help">Common Problems</a></h2>
<!--=====================================================================-->
Below are common problems and their remedies:
<dl compact>
<dt><b>When I run configure, it finds the wrong C compiler.</b>
<dd>
The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and
then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and
<tt>CXX</tt> for the C and C++ compiler, respectively.
If <tt>configure</tt> finds the wrong compiler, either adjust your
<tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
explicitly.
<p>
<dt><b>I compile the code, and I get some error about /localhome</b>.
<dd>
There are several possible causes for this. The first is that you
didn't set a pathname properly when using <tt>configure</tt>, and it
defaulted to a pathname that we use on our research machines.
<p>
Another possibility is that we hardcoded a path in our Makefiles. If
you see this, please email the LLVM bug mailing list with the name of
the offending Makefile and a description of what is wrong with it.
<dt><b>The <tt>configure</tt> script finds the right C compiler, but it
uses the LLVM linker from a previous build. What do I do?</b>
<dd>
The <tt>configure</tt> script uses the <tt>PATH</tt> to find
executables, so if it's grabbing the wrong linker/assembler/etc, there
are two ways to fix it:
<ol>
<li>Adjust your <tt>PATH</tt> environment variable so that the
correct program appears first in the <tt>PATH</tt>. This may work,
but may not be convenient when you want them <i>first</i> in your
path for other work.
<p>
<li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that
is correct. In a Borne compatible shell, the syntax would be:
<p>
<tt>PATH=<the path without the bad program> ./configure ...</tt>
<p>
This is still somewhat inconvenient, but it allows
<tt>configure</tt> to do its work without having to adjust your
<tt>PATH</tt> permanently.
</ol>
</dl>
<!--=====================================================================-->
<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>
<li><a href="http://llvm.cs.uiuc.edu/docs/Projects.html">Starting a Project that Uses LLVM</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 -->
<!-- hhmts start -->
Last modified: Tue Jun 3 22:06:43 CDT 2003
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