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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>,

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<a href="http://misha.brukman.net">Misha Brukman</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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<li><a href="#utils"><tt>llvm/utils</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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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

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<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>

</ul>

</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

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-xvf -</tt>

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</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

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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

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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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<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,

486

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

487

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

488

<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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498

<dt>--with-objroot=OBJ_ROOT

499

<dd>

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Path to the directory where

501

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

503

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

508

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

509

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

510

511

<li>

512

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

513

</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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for more information.)

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518

<dt>--with-llvmgccdir=LLVMGCCDIR

519

<dd>

520

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

521

associated libraries will be installed.

522

523

<dt>--enable-optimized

524

<dd>

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Enables optimized compilation (debugging symbols are removed and GCC

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

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build (also known as a debug build).

528

529

<dt>--enable-jit

530

<dd>

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531

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

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

533

to explicitly enable it if you want it.

534

</dl>

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536

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

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537

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

538

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

539

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

540

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

542

set <tt>LLVM_LIB_SEARCH_PATH</tt> to

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

544

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

545

546

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

548

549

550

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

557

with debugging information.

558

559

560

<dt>Release (Optimized) Builds

561

<dd>

562

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

563

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

564

optimizer flags on and strip debugging information from the libraries

565

and executables it generates.

<dt>Profile Builds

<dd>

These builds are for use with profiling. They compile profiling

571

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

572

Profile builds must be started by setting variables on the

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573

<tt>gmake</tt> command line.

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</dl>

575

576

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

577

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

578

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579

<tt>gmake</tt>

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580

581

582

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

583

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

use the command:

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588

<tt>gmake -j2</tt>

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589

590

591

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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596

<dd>

597

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

598

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

599

600

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

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[diff] [blame]

602

<dd>

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[diff] [blame]

603

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

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604

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

605

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

610

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

611

612

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

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614

<dd>

615

Perform a Release (Optimized) build.

616

617

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[diff] [blame]

618

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

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619

<dd>

620

Perform a Profiling build.

621

622

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[diff] [blame]

623

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

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[diff] [blame]

624

<dd>

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625

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

630

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

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631

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

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[diff] [blame]

632

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

633

634

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

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[diff] [blame]

636

637

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

639

into the directory defined by the variable OBJ_ROOT in

640

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

641

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

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642

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

643

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

644

up or to speed up local builds.

645

John Criswell

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646

647

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

648

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

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649

relative to your home directory (unless OBJ_ROOT is set to

650

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

tree).

Note that

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

657

and

658

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

659

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

660

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

661

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

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[diff] [blame]

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[diff] [blame]

663

John Criswell

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664

665

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

666

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

667

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

668

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

669

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[diff] [blame]

670

John Criswell

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[diff] [blame]

671

672

The LLVM build will place files underneath OBJ_ROOT in directories

673

named after the build type:

674

John Criswell

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[diff] [blame]

675

John Criswell

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<dt>Debug Builds

<dd>

<dt>Tools

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

682

<dt>Libraries

683

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

684

</dl>

685

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[diff] [blame]

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John Criswell

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[diff] [blame]

<dt>Release Builds

<dd>

<dt>Tools

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

692

<dt>Libraries

693

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

694

</dl>

695

Chris Lattner

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[diff] [blame]

696

John Criswell

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<dt>Profile Builds

<dd>

<dt>Tools

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

702

<dt>Libraries

703

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

704

</dl>

705

</dl>

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706

707

708

709

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

710

</center>

711

712

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713

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

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[diff] [blame]

714

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

715

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

716

following is a brief introduction to code layout:

717

718

719

720

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

721

722

723

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

724

for the most part these can just be ignored.

725

726

727

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728

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

729

730

731

This directory contains public header files exported from the LLVM

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732

library. The three main subdirectories of this directory are:

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[diff] [blame]

733

John Criswell

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734

<ol>

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735

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

736

specific header files. This directory also has subdirectories for

737

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

738

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

739

740

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

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[diff] [blame]

741

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

John Criswell

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[diff] [blame]

742

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

743

library.

744

745

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

746

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

747

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

748

automatically take care of the conditional #includes that the configure

749

script generates.

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750

</ol>

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[diff] [blame]

751

752

753

754

755

John Criswell

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

757

LLVM almost all

758

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

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759

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

760

761

762

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

763

source files that implement core classes like Instruction and BasicBlock.

764

765

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

766

for the LLVM assembly language parser library.

767

768

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

769

and write LLVM bytecode.

770

771

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

772

converter.

773

774

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

775

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

776

Induction Variables, Interval Identification, Natural Loop Identification,

777

etc...

778

779

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

780

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

781

Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop

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Invarient Code Motion, Dead Global Elimination, and many others...

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[diff] [blame]

783

784

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

785

describe various target architectures for code generation. For example,

786

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

787

description.

788

789

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

790

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

791

Register Allocation.

792

793

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

794

to the runtime reoptimizer framework that is currently under development.

795

796

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

797

that corresponds to the header files located in

798

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

799

</dl>

800

801

802

803

804

805

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

806

test the LLVM infrastructure...

807

808

809

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

810

811

812

The tools directory contains the executables built out of the

813

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

814

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

815

following is a brief introduction to the most important tools.

816

817

818

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

819

LLVM assembly to LLVM bytecode.

820

821

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

822

to human readable LLVM assembly. Additionally it can convert LLVM

823

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

824

825

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

826

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

John Criswell

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[diff] [blame]

827

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

John Criswell

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[diff] [blame]

828

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

Misha Brukman

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

[diff] [blame]

829

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

830

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

831

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

832

execute the code much faster than the interpreter.

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[diff] [blame]

833

834

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

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[diff] [blame]

835

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

John Criswell

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[diff] [blame]

836

837

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

838

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

839

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

840

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

841

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

842

because it is quite large and not very interesting.

843

844

<ol>

845

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

846

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

847

tool actually assembles LLVM assembly to LLVM bytecode,

John Criswell

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[diff] [blame]

848

performs a variety of optimizations,

John Criswell

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[diff] [blame]

849

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

850

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

851

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

852

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

853

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

854

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

John Criswell

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[diff] [blame]

855

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

John Criswell

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[diff] [blame]

856

assembler.

857

858

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

859

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

860

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

861

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

862

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

863

interfacing with the GCC frontend.

864

</ol>

865

866

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

867

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

868

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

869

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

874

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

875

primarily useful for debugging analyses, or familiarizing yourself with

876

what an analysis does.

877

878

</dl>

John Criswell

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[diff] [blame]

879

Misha Brukman

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[diff] [blame^]

880

881

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

882

883

884

This directory contains utilities for working with LLVM sourcecode, and some

885

of the utilities are actually required as part of the build process because

886

they are code generators for parts of LLVM infrastructure.

887

888

889

<td><tt>Burg</tt><dd> <tt>Burg</tt> is an instruction selector

890

generator -- it builds trees on which it then performs pattern-matching to

891

select instructions according to the patterns the user has specified. Burg

892

is currently used in the Sparc V9 backend.

893

894

<dt><tt>codegen-diff</tt><dd> <tt>codegen-diff</tt> is a script

895

that finds differences between code that LLC generates and code that LLI

896

generates. This is a useful tool if you are debugging one of them,

897

assuming that the other generates correct output. For the full user

898

manual, run <tt>`perldoc codegen-diff'</tt>.

899

900

<dt><tt>cvsupdate</tt><dd> <tt>cvsupdate</tt> is a script that will

901

update your CVS tree, but produce a much cleaner and more organized output

902

than simply running <tt>`cvs up -dP'</tt> will. For example, it will group

903

together all the new and updated files and modified files in separate

904

sections, so you can see at a glance what has changed. If you are at the

905

top of your LLVM CVS tree, running <tt>utils/cvsupdate</tt> is the

906

preferred way of updating the tree.

907

908

<dt><tt>emacs</tt><dd> The <tt>emacs</tt> directory contains

909

syntax-highlighting files which will work with Emacs and XEmacs editors,

910

providing syntax highlighting support for LLVM assembly files and TableGen

911

description files.

912

913

<dt><tt>getsrcs.sh</tt><dd> The <tt>getsrcs.sh</tt> script finds

914

and outputs all non-generated source files, which is useful if one wishes

915

to do a lot of development across directories and does not want to

916

individually find each file. One way to use it is to run, for example:

917

<tt>xemacs `utils/getsources.sh`</tt> from the top of your LLVM source

918

tree.

919

920

<dt><tt>makellvm</tt><dd> The <tt>makellvm</tt> script compiles all

921

files in the current directory and then compiles and links the tool that

922

is the first argument. For example, assuming you are in the directory

923

<tt>llvm/lib/Target/Sparc</tt>, if <tt>makellvm</tt> is in your path,

924

simply running <tt>makellvm llc</tt> will make a build of the current

925

directory, switch to directory <tt>llvm/tools/llc</tt> and build it,

926

causing a re-linking of LLC.

927

928

<dt><tt>NightlyTest.pl</tt> and

929

<tt>NightlyTestTemplate.html</tt><dd> These files are used in a

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cron script to generate nightly status reports of the functionality of

931

tools, and the results can be seen by following the appropriate link on

932

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

933

934

<dt><tt>TableGen</tt><dd> The <tt>TableGen</tt> directory contains

935

the tool used to generate register descriptions, instruction set

936

descriptins, and even assemblers from common TableGen description

937

files.

938

939

<dt><tt>vim</tt><dd> The <tt>vim</tt> directory contains

940

syntax-highlighting files which will work with the VIM editor, providing

941

syntax highlighting support for LLVM assembly files and TableGen

description files.

</dl>

John Criswell

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

[diff] [blame]

946

John Criswell

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

[diff] [blame]

947

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

948

John Criswell

2003-08-08 22:46:30 +0000

[diff] [blame]

952

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

John Criswell

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

[diff] [blame]

your platform.

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

958

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

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960

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

961

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

962

errors that you will need to ignore for now:

963

964

<ol>

965

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

966

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

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

968

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

969

linker that you normally use for compilation.

970

971

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

972

973

<li>Configure the source code:

974

<ul>

975

<li>On Linux/x86, use

976

<ul>

977

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

978

--enable-languages=c</tt>

979

</ul>

980

981

<li>On Solaris/Sparc, use

982

<ul>

983

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

984

--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

991

everything that needed to build is built.

992

993

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

</ol>

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

<tt>LLVMGCCDIR</tt>.

1002

<h2>

1003

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

1004

</h2>

John Criswell

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

[diff] [blame]

1005

1006

1007

<ol>

1008

<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:

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1019

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

1020

1021

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

1022

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

1023

corresponds the the compiled program and the library facilities that it

1024

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

1025

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

1026

1027

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

1028

following commands:

John Criswell

8df90e0

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

[diff] [blame]

1029

John Criswell

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

[diff] [blame]

<tt>% ./hello</tt>

or

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

1035

1036

<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]

1042

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

John Criswell

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

[diff] [blame]

1043

1044

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

1045

1046

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

1047

1048

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

1049

1050

<li>Execute the native sparc program:

1051

1052

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

</ol>

John Criswell

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

[diff] [blame]

1058

<h2>

1059

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

1060

</h2>

John Criswell

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

[diff] [blame]

1061

1062

1063

Below are common problems and their remedies:

1064

1065

1066

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

1067

<dd>

1068

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

1069

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

1070

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

1071

1072

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

1073

<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.

1078

<dd>

1079

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

1080

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

1081

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

1082

1083

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

1084

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

1085

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

1086

1087

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

1088

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

1089

<dd>

1090

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

1091

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

1092

are two ways to fix it:

1093

<ol>

1094

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

1095

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

1096

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

1101

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

1102

1103

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

1104

1105

This is still somewhat inconvenient, but it allows

1106

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

1107

<tt>PATH</tt> permanently.

1108

</ol>

John Criswell

3c852b6

2003-08-08 22:43:39 +0000

[diff] [blame]

1109

1110

<dt>I've upgraded to a new version of LLVM, and I get strange build

1111

errors.

1112

<dd>

1113

Sometimes changes to the LLVM source code alters how the build system

1114

works. Changes in libtool, autoconf, or header file dependencies are

1115

especially prone to this sort of problem.

1116

1117

The best thing to try is to remove the old files and re-build. In most

1118

cases, this takes care of the problem. To do this, just type <tt>make

1119

clean</tt> and then <tt>make</tt> in the directory that fails to build.

1120

1121

John Criswell

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

[diff] [blame]

1122

</dl>

1123

1124

John Criswell

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

[diff] [blame]

1125

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

John Criswell

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

[diff] [blame]

1126

1127

1128

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

1129

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

1130

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

1131

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>

1136

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

John Criswell

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

[diff] [blame]

1137

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

John Criswell