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<head>

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<title>Getting Started with LLVM System</title>

</head>

<center><h1>Getting Started with the LLVM System By: <a

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href="mailto:gshi1@uiuc.edu">Guochun Shi</a>,

John Criswell

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<a href="mailto:sabre@nondot.org">Chris Lattner</a>,

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<a href="mailto:criswell@uiuc.edu">John Criswell</a>, and

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<a href="http://www.cs.uiuc.edu/~vadve">Vikram Adve</a>

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</h1></center>

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<h2><a name="Contents">Contents</a></h2>

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<ul>

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<li><a href="#overview">Overview</a>

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<ol>

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<li><a href="#requirements">Requirements</a>

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<ol>

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<li><a href="#hardware">Hardware</a>

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<li><a href="#software">Software</a>

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</ol>

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</ol>

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<li><a href="#starting">Getting started with LLVM</a>

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<ol>

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<li><a href="#quickstart">Getting Started Quickly (A Summary)</a>

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<li><a href="#terminology">Terminology and Notation</tt></a>

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<li><a href="#environment">Setting Up Your Environment</a>

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<li><a href="#unpack">Unpacking the LLVM Archives</a>

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<li><a href="#checkout">Checkout LLVM from CVS</a>

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<li><a href="#installcf">Install the C Front End</a>

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<li><a href="#config">Local LLVM Configuration</tt></a>

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<li><a href="#compile">Compiling the LLVM Suite Source Code</a>

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<li><a href="#objfiles">The Location of LLVM Object Files</tt></a>

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</ol>

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<li><a href="#layout">Program layout</a>

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<ol>

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<li><a href="#cvsdir"><tt>CVS</tt> directories</a>

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<li><a href="#include"><tt>llvm/include</tt></a>

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<li><a href="#tools"><tt>llvm/tools</tt></a>

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</ol>

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<li><a href="#cfront">Compiling the LLVM C Front End</a>

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<li><a href="#tutorial">An Example Using the LLVM Tool Chain</a>

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<li><a href="#problems">Common Problems</a>

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<li><a href="#links">Links</a>

</ul>

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<h2><a name="overview">Overview</a></h2>

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</center>

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Welcome to LLVM! In order to get started, you first need to know some

basic information.

First, LLVM comes in two pieces. The first piece is the LLVM suite. This

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contains all of the tools, libraries, and header files needed to use the

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low level virtual machine. It also contains a test suite that can be used

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to test the LLVM tools and the C front end.

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The second piece is the C front end. This component provides a version

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of GCC that compiles C code into LLVM bytecode. Currently, the C front end

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is a modified version of GCC 3.4 (we track the GCC 3.4 development).

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Once compiled into LLVM bytecode, a program can be manipulated with the

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LLVM tools from the LLVM suite.

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<h3><a name="requirements">Requirements</a></h3>

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Before you begin to use the LLVM system, review the requirements given

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below. This may save you some trouble by knowing ahead of time what

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hardware and software you will need.

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<h4><a name="hardware">Hardware</a></h4>

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LLVM is known to work on the following platforms:

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<ul>

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<li> Linux on x86

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<ul>

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<li> Approximately 760 MB of Free Disk Space

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<ul>

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<li>Source code: 30 MB

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<li>Object code: 670 MB

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<li>C front end: 60 MB

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</ul>

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</ul>

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<li> Solaris on SparcV9 (Ultrasparc)

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<ul>

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<li> Approximately 1.24 GB of Free Disk Space

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<ul>

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<li>Source code: 30 MB

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<li>Object code: 1000 MB

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<li>C front end: 210 MB

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</ul>

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</ul>

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If you want to compile your own version of the C front end, you will need

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additional disk space:

<ul>

<li>Linux on x86

<ul>

<li> Approximately 249 MB of Free Disk Space

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<ul>

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<li>Source code: 146 MB

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<li>Object code: 82 MB

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<li>Installed binaries: 21 MB

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<li>Solaris on Sparc

<ul>

<li> Approximately 264 MB of Free Disk Space

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<ul>

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<li>Source code: 146 MB

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<li>Object code: 93 MB

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<li>Installed binaries: 25 MB

</ul>

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</ul>

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LLVM may compile on other platforms. The LLVM utilities should work

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on other platforms, so it should be possible to generate and produce LLVM

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bytecode on unsupported platforms (although bytecode generated on one

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platform may not work on another platform). However, the code generators

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and Just-In-Time (JIT) compilers only generate SparcV9 or x86 machine code.

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<h4><a name="software">Software</a></h4>

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Unpacking the distribution requires the following tools:

<dt>GNU Zip (gzip)

<dt>GNU Tar

<dd>

These tools are needed to uncompress and unarchive the software.

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Regular Solaris <tt>tar</tt> may work for unpacking the TAR archive but

is untested.

</dl>

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Compiling LLVM requires that you have several different software packages

installed:

<dt> GCC

<dd>

The GNU Compiler Collection must be installed with C and C++ language

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support. GCC 3.2.x works, and GCC 3.x is generally supported.

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Note that we currently do not support any other C++ compiler.

<dt> GNU Make

<dd>

The LLVM build system relies upon GNU Make extensions. Therefore, you

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will need GNU Make (sometimes known as gmake) to build LLVM.

<dt> Flex and Bison

<dd>

The LLVM source code is built using flex and bison. You will not be

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able to configure and compile LLVM without them.

<dt> GNU M4

<dd>

If you are installing Bison on your machine for the first time, you

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will need GNU M4 (version 1.4 or higher).

</dl>

There are some additional tools that you may want to have when working with

LLVM:

<ul>

<li>GNU Autoconf

<li>GNU M4

If you want to make changes to the configure scripts, you will need

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GNU autoconf (2.53 or higher), and consequently, GNU M4 (version 1.4

or higher).

</ul>

The <a href="starting">next section</a> of this guide is meant to get

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you up and running with LLVM and to give you some basic information about

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the LLVM environment. The <a href"#quickstart">first subsection</a> gives

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a short summary for those who are already familiar with the system and

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want to get started as quickly as possible.

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The later sections of this guide describe the <a

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href="#layout">general layout</a> of the the LLVM source-tree, a <a

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href="#tutorial">simple example</a> using the LLVM tool chain, and <a

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href="#links">links</a> to find more information about LLVM or to get

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help via e-mail.

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<h2><a name="starting">Getting Started with LLVM</a></h2>

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</center>

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<h3><a name="quickstart">Getting Started Quickly (A Summary)</a></h3>

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Here's the short story for getting up and running quickly with LLVM:

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<ol>

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<li>Install the C front end:

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<ol>

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<li><tt>cd where-you-want-the-C-front-end-to-live</tt>

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<li><tt>gunzip --stdout cfrontend.platform.tar.gz | tar -xvf

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-</tt>

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</ol>

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<li>Get the Source Code

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<ul>

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<li>With the distributed files:

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<ol>

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<li><tt>cd where-you-want-llvm-to-live</tt>

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<li><tt>gunzip --stdout llvm.tar.gz | tar -xvf -</tt>

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<li><tt>gunzip --stdout cfrontend.platform.tar.gz | tar -xvf -</tt>

</ol>

<li>With anonymous CVS access:

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<ol>

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<li>Find the path to the CVS repository containing LLVM (we'll call this CVSROOTDIR).

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<li><tt>cd where-you-want-llvm-to-live</tt>

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<li><tt>cvs -d CVSROOTDIR checkout llvm</tt>

</ol>

</ul>

</ul>

<li>Configure the LLVM Build Environment

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<li>Run <tt>configure</tt> to configure the Makefiles and header

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files for the default platform.

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Useful options include:

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<ul>

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<li><tt>--with-objroot=directory</tt>

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Specify where object files should be placed during the build.

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<li><tt>--with-llvmgccdir=directory</tt>

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Specify where the LLVM C frontend is going to be installed.

</ul>

</ol>

<li>Build the LLVM Suite

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<ol>

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<li>Set your LLVM_LIB_SEARCH_PATH environment variable.

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<li><tt>gmake -k |& tee gnumake.out

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# this is csh or tcsh syntax</tt>

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</ol>

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</ol>

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See <a href="#environment">Setting Up Your Environment</a> on tips to

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simplify working with the LLVM front-end and compiled tools. See the

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other sub-sections below for other useful details in working with LLVM,

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or go straight to <a href="#layout">Program Layout</a> to learn about the

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layout of the source code tree. For information on building the C front

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end yourself, see <a href="#cfront">Compiling the LLVM C Front End</a> for

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information.

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<h3><a name="terminology">Terminology and Notation</a></h3>

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Throughout this manual, the following names are used to denote paths

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specific to the local system and working environment. These are not

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environment variables you need to set but just strings used in the rest

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of this document below. In any of the examples below, simply replace

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each of these names with the appropriate pathname on your local system.

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All these paths are absolute:

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<dt>CVSROOTDIR

<dd>

This is the path for the CVS repository containing the LLVM source

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code. Ask the person responsible for your local LLVM installation to

give you this path.

<dt>OBJ_ROOT

<dd>

This is the top level directory for where the LLVM suite object files

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will be placed during the build.

<dt>LLVMGCCDIR

<dd>

This is the pathname to the location where the LLVM C Front End will

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be installed. Note that the C front end does not need to be installed

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during the LLVM suite build; you will just need to know where it will

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go for configuring the build system and running the test suite later.

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For the pre-built C front end binaries, the LLVMGCCDIR is

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<tt>cfrontend/platform/llvm-gcc</tt>.

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<dt>GCCSRC

<dd>

This is the pathname of the directory where the LLVM C front end source

code can be found.

<dt>GCCOBJ

<dd>

This is the pathname of the directory where the LLVM C front end object

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code will be placed during the build. It can be safely removed once

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the build is complete.

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</dl>

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<h3><a name="environment">Setting Up Your Environment</a></h3>

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In order to compile and use LLVM, you will need to set some environment

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variables. There are also some shell aliases which you may find useful.

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You can set these on the command line, or better yet, set them in your

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<tt>.cshrc</tt> or <tt>.profile</tt>.

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<dt><tt>LLVM_LIB_SEARCH_PATH</tt>=<tt>LLVMGCCDIR/llvm-gcc/bytecode-libs</tt>

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<dd>

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This environment variable helps the LLVM C front end find bytecode

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libraries that it will need for compilation.

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<dt>alias llvmgcc LLVMGCCDIR<tt>/bin/llvm-gcc</tt>

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<dd>

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This alias allows you to use the LLVM C front end without putting it in

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your <tt>PATH</tt> or typing in its complete pathname.

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</dl>

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<h3><a name="unpack">Unpacking the LLVM Archives</a></h3>

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If you have the LLVM distribution, you will need to unpack it before you

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can begin to compile it. LLVM is distributed as a set of four files. Each

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file is a TAR archive that is compressed with the gzip program.

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The four files are as follows:

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<dt>llvm.tar.gz

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<dd>This is the source code to the LLVM suite.

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<dt>cfrontend.sparc.tar.gz

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<dd>This is the binary release of the C front end for Solaris/Sparc.

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<dt>cfrontend.x86.tar.gz

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<dd>This is the binary release of the C front end for Linux/x86.

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<dt>cfrontend-src.tar.gz

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<dd>This is the source code release of the C front end.

</dl>

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<h3><a name="checkout">Checkout LLVM from CVS</a></h3>

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If you have access to our CVS repository, you can get a fresh copy of

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the entire source code. All you need to do is check it out from CVS as

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follows:

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<ul>

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<li><tt>cd where-you-want-llvm-to-live</tt>

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<li><tt>cvs -d CVSROOTDIR checkout llvm</tt>

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</ul>

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This will create an '<tt>llvm</tt>' directory in the current

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directory and fully populate it with the LLVM source code, Makefiles,

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test directories, and local copies of documentation files.

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Note that the C front end is not included in the CVS repository. You

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should have either downloaded the source, or better yet, downloaded the

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binary distribution for your platform.

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<h3><a name="installcf">Install the C Front End</a></h3>

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Before configuring and compiling the LLVM suite, it is best to extract the

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LLVM C front end. While not used in building, the C front end is used by

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the LLVM test suite, and its location must be given to the

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<tt>configure</tt> script before the LLVM suite can be built.

To install the C front end, do the following:

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<ol>

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<li><tt>cd where-you-want-the-front-end-to-live</tt>

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<li><tt>gunzip --stdout cfrontend.platform.tar.gz | tar -xvf

-</tt>

</ol>

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<h3><a name="config">Local LLVM Configuration</a></h3>

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Once checked out from the CVS repository, the LLVM suite source code

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must be configured via the <tt>configure</tt> script. This script sets

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variables in <tt>llvm/Makefile.config</tt> and

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<tt>llvm/include/Config/config.h</tt>.

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The following environment variables are used by the <tt>configure</tt>

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script to configure the build system:

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<tr>

<th>Variable</th>

<th>

Purpose

</th>

</tr>

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<tr>

<td>

Tells <tt>configure</tt> which C compiler to use. By default,

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<tt>configure</tt> will look for the first GCC compiler in

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<tt>PATH</tt>. Use this variable to override

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<tt>configure</tt>'s default behavior.

</td>

</tr>

<tr>

<td>

Tells <tt>configure</tt> which C++ compiler to use. By default,

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<tt>configure</tt> will look for the first GCC compiler in

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<tt>PATH</tt>. Use this variable to override

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<tt>configure</tt>'s default behavior.

</td>

</tr>

</table>

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The following options can be used to set or enable LLVM specific options:

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<dt>--with-objroot=OBJ_ROOT

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<dd>

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Path to the directory where

496

object files, libraries, and executables should be placed.

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If this is set to <tt>.</tt>, then the object files will be placed

498

within the source code tree. If left unspecified, the default value is

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the following:

<ul>

<li>

If the USER environment variable is specified and the directory

503

<tt>/localhome/$USER</tt> exists, then the default value is

504

<tt>/localhome/$USER</tt>.

505

506

<li>

507

Otherwise, the default value is <tt>.</tt>.

508

</ul>

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(See the Section on <a href=#objfiles>

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The Location of LLVM Object Files</a>

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[diff] [blame]

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for more information.)

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512

513

<dt>--with-llvmgccdir=LLVMGCCDIR

514

<dd>

515

Path to the location where the LLVM C front end binaries and

516

associated libraries will be installed.

517

518

<dt>--enable-optimized

519

<dd>

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520

Enables optimized compilation (debugging symbols are removed and GCC

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[diff] [blame]

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optimization flags are enabled). The default is to use an unoptimized

522

build (also known as a debug build).

523

524

<dt>--enable-jit

525

<dd>

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[diff] [blame]

526

Compile the Just In Time (JIT) functionality. This is not available

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[diff] [blame]

527

on all platforms. The default is dependent on platform, so it is best

528

to explicitly enable it if you want it.

529

</dl>

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531

In addition to running <tt>configure</tt>, you must set the

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[diff] [blame]

532

<tt>LLVM_LIB_SEARCH_PATH</tt> environment variable in your startup scripts.

533

This environment variable is used to locate "system" libraries like

534

"<tt>-lc</tt>" and "<tt>-lm</tt>" when linking. This variable should be set

535

to the absolute path for the bytecode-libs subdirectory of the C front-end

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install, or LLVMGCCDIR/llvm-gcc/bytecode-libs. For example, one might

537

set <tt>LLVM_LIB_SEARCH_PATH</tt> to

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538

<tt>/home/vadve/lattner/local/x86/llvm-gcc/bytecode-libs</tt> for the X86

539

version of the C front-end on our research machines.

540

541

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542

<h3><a name="compile">Compiling the LLVM Suite Source Code</a></h3>

543

544

545

Once you have configured LLVM, you can build it. There are three types of

builds:

<dt>Debug Builds

<dd>

These builds are the default. They compile the tools and libraries

552

with debugging information.

553

554

555

<dt>Release (Optimized) Builds

556

<dd>

557

These builds are enabled with the <tt>--enable-optimized</tt> option to

558

<tt>configure</tt>. They compile the tools and libraries with GCC

559

optimizer flags on and strip debugging information from the libraries

560

and executables it generates.

<dt>Profile Builds

<dd>

These builds are for use with profiling. They compile profiling

566

information into the code for use with programs like <tt>gprof</tt>.

567

Profile builds must be started by setting variables on the

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<tt>gmake</tt> command line.

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569

</dl>

570

571

Once you have LLVM configured, you can build it by entering the top level

572

<tt>llvm</tt> directory and issuing the following command:

573

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574

<tt>gmake</tt>

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576

577

If you have multiple processors in your machine, you may wish to use some

578

of the parallel build options provided by GNU Make. For example, you could

use the command:

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583

<tt>gmake -j2</tt>

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584

585

586

There are several other targets which are useful when working with the LLVM

source code:

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<dt><tt>gmake clean</tt>

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<dd>

592

Removes all files generated by the build. This includes object files,

593

generated C/C++ files, libraries, and executables.

594

595

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<dt><tt>gmake distclean</tt>

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[diff] [blame]

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<dd>

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[diff] [blame]

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Removes everything that <tt>gmake clean</tt> does, but also removes

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[diff] [blame]

599

files generated by <tt>configure</tt>. It attempts to return the

600

source tree to the original state in which it was shipped.

</dl>

It is also possible to override default values from <tt>configure</tt> by

605

declaring variables on the command line. The following are some examples:

606

607

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[diff] [blame]

608

<dt><tt>gmake ENABLE_OPTIMIZED=1</tt>

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609

<dd>

610

Perform a Release (Optimized) build.

611

612

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[diff] [blame]

613

<dt><tt>gmake ENABLE_PROFILING=1</tt>

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[diff] [blame]

614

<dd>

615

Perform a Profiling build.

616

617

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[diff] [blame]

618

<dt><tt>gmake VERBOSE=1</tt>

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[diff] [blame]

619

<dd>

John Criswell

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[diff] [blame]

620

Print what <tt>gmake</tt> is doing on standard output.

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[diff] [blame]

</dl>

Every directory in the LLVM source tree includes a <tt>Makefile</tt> to

625

build it and any subdirectories that it contains. Entering any directory

John Criswell

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[diff] [blame]

626

inside the LLVM source tree and typing <tt>gmake</tt> should rebuild

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[diff] [blame]

627

anything in or below that directory that is out of date.

628

629

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[diff] [blame]

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<h3><a name="objfiles">The Location of LLVM Object Files</a></h3>

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[diff] [blame]

631

632

John Criswell

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The LLVM build system sends most output files generated during the build

634

into the directory defined by the variable OBJ_ROOT in

635

<tt>llvm/Makefile.config</tt>, which is set by the --with-objroot

636

option in <tt>configure</tt>. This can be either just your normal LLVM

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[diff] [blame]

637

source tree or some other directory writable by you. You may wish to put

638

object files on a different filesystem either to keep them from being backed

639

up or to speed up local builds.

640

John Criswell

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[diff] [blame]

641

642

If OBJ_ROOT is specified, then the build system will create a

643

directory tree underneath it that resembles the source code's pathname

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644

relative to your home directory (unless OBJ_ROOT is set to

645

<tt>.</tt>, in which case object files are placed within the LLVM source

tree).

Note that

--with-objroot=<tt>.</tt>

652

and

653

--with-objroot=<tt>`pwd`</tt>

654

are not the same thing. The former will simply place object files within

655

the source tree, while the latter will set the location of object files

656

using the source tree's relative path from the home directory.

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[diff] [blame]

657

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[diff] [blame]

658

John Criswell

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[diff] [blame]

659

660

For example, suppose that OBJ_ROOT is set to <tt>/tmp</tt> and the

661

LLVM suite source code is located in <tt>/usr/home/joe/src/llvm</tt>, where

662

<tt>/usr/home/joe</tt> is the home directory of a user named Joe. Then,

663

the object files will be placed in <tt>/tmp/src/llvm</tt>.

664

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[diff] [blame]

665

John Criswell

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[diff] [blame]

666

667

The LLVM build will place files underneath OBJ_ROOT in directories

668

named after the build type:

669

John Criswell

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[diff] [blame]

670

John Criswell

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[diff] [blame]

<dt>Debug Builds

<dd>

<dt>Tools

<dd><tt>OBJ_ROOT/llvm/tools/Debug</tt>

677

<dt>Libraries

678

<dd><tt>OBJ_ROOT/llvm/lib/Debug</tt>

679

</dl>

680

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[diff] [blame]

681

John Criswell

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[diff] [blame]

<dt>Release Builds

<dd>

<dt>Tools

<dd><tt>OBJ_ROOT/llvm/tools/Release</tt>

687

<dt>Libraries

688

<dd><tt>OBJ_ROOT/llvm/lib/Release</tt>

689

</dl>

690

Chris Lattner

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[diff] [blame]

691

John Criswell

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[diff] [blame]

<dt>Profile Builds

<dd>

<dt>Tools

<dd><tt>OBJ_ROOT/llvm/tools/Profile</tt>

697

<dt>Libraries

698

<dd><tt>OBJ_ROOT/llvm/lib/Profile</tt>

699

</dl>

700

</dl>

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[diff] [blame]

701

702

703

704

<h2><a name="layout">Program Layout</a></h2>

705

</center>

706

707

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[diff] [blame]

708

One useful source of information about the LLVM source base is the LLVM <a

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[diff] [blame]

709

href="http://www.doxygen.org">doxygen</a> documentation, available at <tt><a

710

href="http://llvm.cs.uiuc.edu/doxygen/">http://llvm.cs.uiuc.edu/doxygen/</a></tt>. The

711

following is a brief introduction to code layout:

712

713

714

715

<h3><a name="cvsdir"><tt>CVS</tt> directories</a></h3>

716

717

718

Every directory checked out of CVS will contain a <tt>CVS</tt> directory;

719

for the most part these can just be ignored.

720

721

722

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[diff] [blame]

723

<h3><a name="include"><tt>llvm/include</tt></a></h3>

724

725

726

This directory contains public header files exported from the LLVM

John Criswell

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727

library. The three main subdirectories of this directory are:

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[diff] [blame]

728

John Criswell

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[diff] [blame]

729

<ol>

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730

<li><tt>llvm/include/llvm</tt> - This directory contains all of the LLVM

731

specific header files. This directory also has subdirectories for

732

different portions of LLVM: <tt>Analysis</tt>, <tt>CodeGen</tt>,

733

<tt>Reoptimizer</tt>, <tt>Target</tt>, <tt>Transforms</tt>, etc...

734

735

<li><tt>llvm/include/Support</tt> - This directory contains generic

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[diff] [blame]

736

support libraries that are independent of LLVM, but are used by LLVM.

John Criswell

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[diff] [blame]

737

For example, some C++ STL utilities and a Command Line option processing

738

library.

739

740

<li><tt>llvm/include/Config</tt> - This directory contains header files

741

configured by the <tt>configure</tt> script. They wrap "standard" UNIX

742

and C header files. Source code can include these header files which

743

automatically take care of the conditional #includes that the configure

744

script generates.

Chris Lattner

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[diff] [blame]

745

</ol>

John Criswell

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[diff] [blame]

746

747

748

749

750

John Criswell

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751

This directory contains most of the source files of the LLVM system. In

752

LLVM almost all

753

code exists in libraries, making it very easy to share code among the

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754

different <a href="#tools">tools</a>.

755

756

757

<dt><tt>llvm/lib/VMCore/</tt><dd> This directory holds the core LLVM

758

source files that implement core classes like Instruction and BasicBlock.

759

760

<dt><tt>llvm/lib/AsmParser/</tt><dd> This directory holds the source code

761

for the LLVM assembly language parser library.

762

763

<dt><tt>llvm/lib/ByteCode/</tt><dd> This directory holds code for reading

764

and write LLVM bytecode.

765

766

<dt><tt>llvm/lib/CWriter/</tt><dd> This directory implements the LLVM to C

767

converter.

768

769

<dt><tt>llvm/lib/Analysis/</tt><dd> This directory contains a variety of

770

different program analyses, such as Dominator Information, Call Graphs,

771

Induction Variables, Interval Identification, Natural Loop Identification,

772

etc...

773

774

<dt><tt>llvm/lib/Transforms/</tt><dd> This directory contains the source

775

code for the LLVM to LLVM program transformations, such as Aggressive Dead

776

Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop

777

Invarient Code Motion, Dead Global Elimination, Pool Allocation, and many

778

others...

779

780

<dt><tt>llvm/lib/Target/</tt><dd> This directory contains files that

781

describe various target architectures for code generation. For example,

782

the llvm/lib/Target/Sparc directory holds the Sparc machine

783

description.

784

785

<dt><tt>llvm/lib/CodeGen/</tt><dd> This directory contains the major parts

786

of the code generator: Instruction Selector, Instruction Scheduling, and

787

Register Allocation.

788

789

<dt><tt>llvm/lib/Reoptimizer/</tt><dd> This directory holds code related

790

to the runtime reoptimizer framework that is currently under development.

791

792

<dt><tt>llvm/lib/Support/</tt><dd> This directory contains the source code

793

that corresponds to the header files located in

794

<tt>llvm/include/Support/</tt>.

795

</dl>

796

797

798

799

800

801

This directory contains regression tests and source code that is used to

802

test the LLVM infrastructure...

803

804

805

<h3><a name="tools"><tt>llvm/tools</tt></a></h3>

806

807

808

The tools directory contains the executables built out of the

809

libraries above, which form the main part of the user interface. You can

810

always get help for a tool by typing <tt>tool_name --help</tt>. The

811

following is a brief introduction to the most important tools.

812

813

814

<dt><tt>as</tt><dd>The assembler transforms the human readable

815

LLVM assembly to LLVM bytecode.

816

817

<dt><tt>dis</tt><dd>The disassembler transforms the LLVM bytecode

818

to human readable LLVM assembly. Additionally it can convert LLVM

819

bytecode to C, which is enabled with the <tt>-c</tt> option.

820

821

<dt><tt>lli</tt><dd> <tt>lli</tt> is the LLVM interpreter, which

822

can directly execute LLVM bytecode (although very slowly...). In addition

John Criswell

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[diff] [blame]

823

to a simple interpreter, <tt>lli</tt> is also has debugger and tracing

John Criswell

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[diff] [blame]

824

modes (entered by specifying <tt>-debug</tt> or <tt>-trace</tt> on the

Misha Brukman

2003-07-03 16:29:36 +0000

[diff] [blame]

825

command line, respectively). Finally, for architectures that support it

826

(currently only x86 and Sparc), by default, <tt>lli</tt> will function as

827

a Just-In-Time compiler (if the functionality was compiled in), and will

828

execute the code much faster than the interpreter.

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[diff] [blame]

829

830

<dt><tt>llc</tt><dd> <tt>llc</tt> is the LLVM backend compiler,

Misha Brukman

2003-07-03 16:29:36 +0000

[diff] [blame]

831

which translates LLVM bytecode to a SPARC or x86 assembly file.

John Criswell

2003-06-12 19:34:44 +0000

[diff] [blame]

832

833

<dt><tt>llvmgcc</tt><dd> <tt>llvmgcc</tt> is a GCC based C frontend

834

that has been retargeted to emit LLVM code as the machine code output. It

835

works just like any other GCC compiler, taking the typical <tt>-c, -S, -E,

836

-o</tt> options that are typically used. The source code for the

837

<tt>llvmgcc</tt> tool is currently not included in the LLVM cvs tree

838

because it is quite large and not very interesting.

839

840

<ol>

841

<dt><tt>gccas</tt><dd> This tool is invoked by the

842

<tt>llvmgcc</tt> frontend as the "assembler" part of the compiler. This

843

tool actually assembles LLVM assembly to LLVM bytecode,

John Criswell

2003-06-30 21:59:07 +0000

[diff] [blame]

844

performs a variety of optimizations,

John Criswell

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[diff] [blame]

845

and outputs LLVM bytecode. Thus when you invoke <tt>llvmgcc -c x.c -o

846

x.o</tt>, you are causing <tt>gccas</tt> to be run, which writes the

847

<tt>x.o</tt> file (which is an LLVM bytecode file that can be

848

disassembled or manipulated just like any other bytecode file). The

849

command line interface to <tt>gccas</tt> is designed to be as close as

850

possible to the system '<tt>as</tt>' utility so that the gcc

John Criswell

2003-07-03 16:01:38 +0000

[diff] [blame]

851

frontend itself did not have to be modified to interface to a "weird"

John Criswell

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[diff] [blame]

852

assembler.

853

854

<dt><tt>gccld</tt><dd> <tt>gccld</tt> links together several LLVM

855

bytecode files into one bytecode file and does some optimization. It is

856

the linker invoked by the gcc frontend when multiple .o files need to be

857

linked together. Like <tt>gccas</tt> the command line interface of

858

<tt>gccld</tt> is designed to match the system linker, to aid

859

interfacing with the GCC frontend.

860

</ol>

861

862

<dt><tt>opt</tt><dd> <tt>opt</tt> reads LLVM bytecode, applies a

863

series of LLVM to LLVM transformations (which are specified on the command

864

line), and then outputs the resultant bytecode. The '<tt>opt --help</tt>'

865

command is a good way to get a list of the program transformations

available in LLVM.

<dt><tt>analyze</tt><dd> <tt>analyze</tt> is used to run a specific

870

analysis on an input LLVM bytecode file and print out the results. It is

871

primarily useful for debugging analyses, or familiarizing yourself with

872

what an analysis does.

873

874

</dl>

John Criswell

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[diff] [blame]

875

John Criswell

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[diff] [blame]

876

John Criswell

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[diff] [blame]

877

<h2><center><a name="cfront">Compiling the LLVM C Front End</center></h2>

878

This step is optional if you have the C front end binary distrubtion for

your platform.

Now that you have the LLVM suite built, you can build the C front end. For

888

those of you that have built GCC before, the process is very similar.

889

890

Be forewarned, though: the build system for the C front end is not as

891

polished as the rest of the LLVM code, so there will be many warnings and

892

errors that you will need to ignore for now:

893

894

<ol>

895

<li>Ensure that <tt>OBJ_ROOT/llvm/tools/Debug</tt> is at the

896

end of your <tt>PATH</tt> environment variable. The front end

897

build needs to know where to find the LLVM tools, but you want to

898

ensure that these tools are not found before the system assembler and

899

linker that you normally use for compilation.

900

901

<li><tt>cd GCCOBJ</tt>

902

903

<li>Configure the source code:

904

<ul>

905

<li>On Linux/x86, use

906

<ul>

907

<li><tt>GCCSRC/configure --prefix=LLVMGCCDIR

908

--enable-languages=c</tt>

909

</ul>

910

911

<li>On Solaris/Sparc, use

912

<ul>

913

<li><tt>GCCSRC/configure --prefix=LLVMGCCDIR

914

--enable-languages=c --target=sparcv9-sun-solaris2</tt>

</ul>

</ul>

<li><tt>gmake</tt>

<li>The build will eventually fail. Don't worry; chances are good that

921

everything that needed to build is built.

922

923

<li><tt>gmake -k install</tt>

</ol>

Once this is done, you should have a built front end compiler in

<tt>LLVMGCCDIR</tt>.

932

<h2>

933

<center><a name="tutorial">An Example Using the LLVM Tool Chain</center>

934

</h2>

John Criswell

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[diff] [blame]

935

936

937

<ol>

938

<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:

948

949

<tt>% llvmgcc hello.c -o hello</tt>

950

951

This will create two result files: <tt>hello</tt> and

952

<tt>hello.bc</tt>. The <tt>hello.bc</tt> is the LLVM bytecode that

953

corresponds the the compiled program and the library facilities that it

954

required. <tt>hello</tt> is a simple shell script that runs the bytecode

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file with <tt>lli</tt>, making the result directly executable.

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<li>Run the program. To make sure the program ran, execute one of the

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following commands:

John Criswell

8df90e0

2003-06-11 20:46:40 +0000

[diff] [blame]

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John Criswell

2003-06-12 19:34:44 +0000

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<tt>% ./hello</tt>

or

<tt>% lli hello.bc</tt>

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<li>Use the <tt>dis</tt> utility to take a look at the LLVM assembly

code:

<li>Compile the program to native Sparc assembly using the code

Misha Brukman

2003-07-03 16:29:36 +0000

[diff] [blame]

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generator (assuming you are currently on a Sparc system):

John Criswell

2003-06-12 19:34:44 +0000

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<tt>% llc hello.bc -o hello.s</tt>

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<li>Assemble the native sparc assemble file into a program:

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<tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.sparc</tt>

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<li>Execute the native sparc program:

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<tt>% ./hello.sparc</tt>

</ol>

John Criswell

2003-07-08 20:35:59 +0000

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<h2>

989

<center><a name="problems">Common Problems</a></center>

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</h2>

John Criswell

2003-07-03 16:01:38 +0000

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992

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Below are common problems and their remedies:

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<dt>When I run configure, it finds the wrong C compiler.

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<dd>

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The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and

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then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and

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<tt>CXX</tt> for the C and C++ compiler, respectively.

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If <tt>configure</tt> finds the wrong compiler, either adjust your

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<tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>

explicitly.

<dt>I compile the code, and I get some error about /localhome.

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<dd>

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There are several possible causes for this. The first is that you

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didn't set a pathname properly when using <tt>configure</tt>, and it

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defaulted to a pathname that we use on our research machines.

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Another possibility is that we hardcoded a path in our Makefiles. If

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you see this, please email the LLVM bug mailing list with the name of

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the offending Makefile and a description of what is wrong with it.

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<dt>The <tt>configure</tt> script finds the right C compiler, but it

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uses the LLVM linker from a previous build. What do I do?

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<dd>

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The <tt>configure</tt> script uses the <tt>PATH</tt> to find

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executables, so if it's grabbing the wrong linker/assembler/etc, there

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are two ways to fix it:

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<ol>

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<li>Adjust your <tt>PATH</tt> environment variable so that the

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correct program appears first in the <tt>PATH</tt>. This may work,

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but may not be convenient when you want them first in your

path for other work.

<li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that

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is correct. In a Borne compatible shell, the syntax would be:

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<tt>PATH=<the path without the bad program> ./configure ...</tt>

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This is still somewhat inconvenient, but it allows

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<tt>configure</tt> to do its work without having to adjust your

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<tt>PATH</tt> permanently.

</ol>

</dl>

John Criswell

2003-07-08 20:35:59 +0000

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<h2><center><a name="links">Links</a></center></h2>

John Criswell

2003-06-12 19:34:44 +0000

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This document is just an introduction to how to use LLVM to do

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some simple things... there are many more interesting and complicated things

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that you can do that aren't documented here (but we'll gladly accept a patch

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if you want to write something up!). For more information about LLVM, check

out:

<ul>

<li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>

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<li><a href="http://llvm.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>

John Criswell

2003-07-03 16:01:38 +0000

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<li><a href="http://llvm.cs.uiuc.edu/docs/Projects.html">Starting a Project that Uses LLVM</a></li>

John Criswell