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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>,

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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="#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="#build">Compiling the LLVM C Front End</a>

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<li><a href="#objfiles">The location for 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">CVS 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="#tutorial">An example using the LLVM tool chain</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 GCC front end.

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The second piece is the GCC 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.

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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:

<ul>

<li> Linux on x86

<ul>

<li> Approximately 700 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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</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 1.03 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

</ul>

</ul>

</ul>

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</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>Build the LLVM suite

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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>

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

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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.

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</ul>

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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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<li>Build the LLVM C Front End (optional)

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<ol>

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<li>Create a directory for the object files to live.

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<li><tt>cd object file directory</tt>

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<li>Run <tt>Pathname-to-where-the-source-code-lives/configure --prefix=LLVMGCCDIR</tt> to configure GCC.

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<li><tt>make bootstrap</tt>

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<li><tt>make install</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.

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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><tt>PATH</tt>=<tt>${PATH}:OBJ_ROOT/llvm/tools/Debug</tt>

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<dd>

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Adding this directory to the end of your path will allow the

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compilation of the C front end to find the LLVM tools. The LLVM tools

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are needed for the C front end compile.

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<dt><tt>CC</tt>=Pathname to your GCC compiler

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<dd>

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The GCC compiler that you want to use must be the first C compiler in

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your <tt>PATH</tt>. Otherwise, set this variable so that

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<tt>configure</tt> will use the GCC compiler that you want to use.

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<dt><tt>CXX</tt>=Pathname to your GCC C++ compiler

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<dd>

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The GCC compiler that you want to use must be the first C++ compiler in

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your <tt>PATH</tt>. Otherwise, set this variable so that

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<tt>configure</tt> will use the GCC compiler that you want to use.

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<dt><tt>CVSROOT</tt>=CVSROOT

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<dd>

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This environment variable tells CVS where to find the CVS repository.

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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 the following:

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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>

To unpack the files, take each one, unzip it, and then untar it. A fast

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way to do that is with the following:

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<tt>gunzip --stdout name of file | tar -xvf -</tt>

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For example, to extract the LLVM source code, use the following command:

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

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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="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 <tt>configure</tt> to

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configure Makefile.config:

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<ul>

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<li>CXX = Pathname of the C++ compiler to use.

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<li>CC = Pathname of the C compiler to use.

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</ul>

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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

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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

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

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<tt>.</tt>.

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

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The location for LLVM object files</a>

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for more information.)

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<dt>--with-llvmgccdir=LLVMGCCDIR

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<dd>

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

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associated libraries will be installed.

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<dt>--enable-optimized

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<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).

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<dt>--enable-jit

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<dd>

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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

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to explicitly enable it if you want it.

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</dl>

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

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

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

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

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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

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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

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

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

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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

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with debugging information.

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<dt>Release (Optimized) Builds

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<dd>

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

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

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optimizer flags on and strip debugging information from the libraries

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and executables it generates.

<dt>Profile Builds

<dd>

These builds are for use with profiling. They compile profiling

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

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Profile builds must be started by setting variables on the

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<tt>make</tt> command line.

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</dl>

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

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

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

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

use the command:

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

source code:

<dt><tt>make clean</tt>

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<dd>

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

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

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<dt><tt>make distclean</tt>

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<dd>

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

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

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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

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

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

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<dd>

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Perform a Release (Optimized) build.

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

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<dd>

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Perform a Profiling build.

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

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<dd>

535

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

</dl>

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

540

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

541

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

542

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

543

544

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<h3><a name="build">Compiling the LLVM C Front End</a></h3>

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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

556

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

557

558

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

559

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

560

errors that you will need to ignore for now:

561

562

<ol>

563

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

564

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

565

566

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

567

568

<li>Configure the source code:

569

<ul>

570

<li>On Linux/x86, use

571

<ul>

572

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

573

--enable-languages=c</tt>

574

</ul>

575

576

<li>On Solaris/Sparc, use

577

<ul>

578

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

579

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

</ul>

</ul>

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585

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

586

everything that needed to build is built.

587

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

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</ol>

590

591

At this point, you should have a working copy of the LLVM C front end

592

installed in LLVMGCCDIR.

593

594

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<h3><a name="objfiles">The location for LLVM object files</a></h3>

596

597

John Criswell

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

599

into the directory defined by the variable OBJ_ROOT in

600

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

601

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

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

603

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

604

up or to speed up local builds.

605

John Criswell

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607

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

608

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

609

relative to your home directory.

610

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613

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

614

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

615

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

616

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

617

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620

The LLVM build will place files underneath OBJ_ROOT in directories

621

named after the build type:

622

John Criswell

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John Criswell

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<dt>Debug Builds

<dd>

<dt>Tools

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

630

<dt>Libraries

631

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

632

</dl>

633

John Criswell

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John Criswell

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<dt>Release Builds

<dd>

<dt>Tools

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

640

<dt>Libraries

641

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

642

</dl>

643

Chris Lattner

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[diff] [blame]

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John Criswell

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<dt>Profile Builds

<dd>

<dt>Tools

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

650

<dt>Libraries

651

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

652

</dl>

653

</dl>

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655

656

657

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

658

</center>

659

660

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

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[diff] [blame]

662

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

663

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

664

following is a brief introduction to code layout:

665

666

667

668

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

669

670

671

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

672

for the most part these can just be ignored.

673

674

675

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

677

678

679

This directory contains public header files exported from the LLVM

John Criswell

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

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680

library. The three main subdirectories of this directory are:

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[diff] [blame]

681

John Criswell

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682

<ol>

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

684

specific header files. This directory also has subdirectories for

685

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

686

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

687

688

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

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

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690

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

691

library.

692

693

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

694

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

695

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

696

automatically take care of the conditional #includes that the configure

697

script generates.

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698

</ol>

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[diff] [blame]

699

700

701

702

703

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

705

LLVM almost all

706

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

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707

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

708

709

710

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

711

source files that implement core classes like Instruction and BasicBlock.

712

713

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

714

for the LLVM assembly language parser library.

715

716

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

717

and write LLVM bytecode.

718

719

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

720

converter.

721

722

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

723

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

724

Induction Variables, Interval Identification, Natural Loop Identification,

725

etc...

726

727

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

728

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

729

Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop

730

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

731

others...

732

733

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

734

describe various target architectures for code generation. For example,

735

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

736

description.

737

738

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

739

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

740

Register Allocation.

741

742

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

743

to the runtime reoptimizer framework that is currently under development.

744

745

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

746

that corresponds to the header files located in

747

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

748

</dl>

749

750

751

752

753

754

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

755

test the LLVM infrastructure...

756

757

758

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

759

760

761

The tools directory contains the executables built out of the

762

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

763

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

764

following is a brief introduction to the most important tools.

765

766

767

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

768

LLVM assembly to LLVM bytecode.

769

770

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

771

to human readable LLVM assembly. Additionally it can convert LLVM

772

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

773

774

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

775

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

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776

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

John Criswell

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777

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

Misha Brukman

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

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778

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

779

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

780

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

781

execute the code much faster than the interpreter.

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783

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

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784

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

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785

786

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

787

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

788

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

789

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

790

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

791

because it is quite large and not very interesting.

792

793

<ol>

794

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

795

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

796

tool actually assembles LLVM assembly to LLVM bytecode,

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[diff] [blame]

797

performs a variety of optimizations,

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798

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

799

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

800

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

801

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

802

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

803

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

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[diff] [blame]

804

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

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805

assembler.

806

807

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

808

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

809

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

810

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

811

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

812

interfacing with the GCC frontend.

813

</ol>

814

815

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

816

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

817

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

818

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

823

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

824

primarily useful for debugging analyses, or familiarizing yourself with

825

what an analysis does.

</dl>

830

<h2><a name="tutorial">An example using the LLVM tool chain</h2>

831

832

833

<ol>

834

<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:

844

845

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

846

847

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

848

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

849

corresponds the the compiled program and the library facilities that it

850

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

851

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

852

853

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

854

following commands:

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855

John Criswell

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<tt>% ./hello</tt>

or

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

861

862

<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

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[diff] [blame]

868

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

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[diff] [blame]

869

870

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

871

872

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

873

874

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

875

876

<li>Execute the native sparc program:

877

878

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

</ol>

John Criswell

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884

<h2><a name="help">Common Problems</a></h2>

885

886

887

Below are common problems and their remedies:

888

889

890

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

891

<dd>

892

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

893

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

894

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

895

896

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

897

<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.

902

<dd>

903

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

904

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

905

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

906

907

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

908

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

909

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

910

911

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

912

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

913

<dd>

914

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

915

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

916

are two ways to fix it:

917

<ol>

918

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

919

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

920

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

925

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

926

927

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

928

929

This is still somewhat inconvenient, but it allows

930

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

931

<tt>PATH</tt> permanently.

</ol>

</dl>

John Criswell

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[diff] [blame]

936

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

937

938

939

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

940

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

941

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

942

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>

947

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

John Criswell

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[diff] [blame]

948

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

John Criswell