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481 lines
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>Getting Started with LLVM System</title>
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</head>
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<body bgcolor=white>
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<center><h1>Getting Started with the LLVM System<br><font size=3>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> and
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<a href="http://www.cs.uiuc.edu/~vadve">Vikram Adve</a>
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</font></h1></center>
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<!--=====================================================================-->
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<h2><a name="Contents">Contents</a></h2>
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<!--=====================================================================-->
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<ul>
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<li><a href="#overview">Overview</a>
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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="#checkout">Checkout LLVM from CVS</a>
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<li><a href="#terminology">Terminology and Notation</tt></a>
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<li><a href="#objfiles">The location for object files</tt></a>
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<li><a href="#config">Local Configuration Options</tt></a>
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<li><a href="#environment">Setting up your environment</a>
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<li><a href="#compile">Compiling the source code</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="#dd"><tt>Depend</tt>, <tt>Debug</tt>, &
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<tt>Release</tt> directories</a></li>
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<li><a href="#include"><tt>llvm/include</tt></a>
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<li><a href="#lib"><tt>llvm/lib</tt></a>
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<li><a href="#test"><tt>llvm/test</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>
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</ul>
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<!--=====================================================================-->
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<center>
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<h2><a name="overview"><b>Overview</b></a></h2>
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</center>
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<!--=====================================================================-->
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<p>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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<p>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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<!--=====================================================================-->
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<center>
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<h2><a name="starting"><b>Getting Started</b></a></h2>
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</center>
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<!--=====================================================================-->
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<!--=====================================================================-->
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<h3><a name="quickstart"><b>Getting Started Quickly (A Summary)</b></a></h3>
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<!--=====================================================================-->
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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>Find the path to the CVS repository containing LLVM (we'll call this <i>CVSROOTDIR</i>).
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<li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
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<li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt>
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<li><tt>cd llvm</tt>
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<li>Edit <tt>Makefile.config</tt> to set local paths. This includes
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setting the install location of the C frontend and the various paths
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to the C and C++ compilers used to build LLVM itself.
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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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<p>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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<!------------------------------------------------------------------------->
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<h3><a name="terminology">Terminology and Notation</a></h3>
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<!------------------------------------------------------------------------->
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<p>Throughout this manual, the following names are used to denote paths
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specific to the local system and working environment. <i>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.</i>. 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:</p>
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<ul>
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</ul>
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<!------------------------------------------------------------------------->
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<h3><a name="checkout">Checkout LLVM from CVS</a></h3>
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<!------------------------------------------------------------------------->
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<p>Before checking out the source code, you will need to know the path to
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the CVS repository containing LLVM source code (we'll call this
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<i>CVSROOTDIR</i> below). Ask the person responsible for your local LLVM
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installation to give you this path.
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<p>To get a fresh copy of the entire source code, all you
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need to do is check it out from CVS as follows:
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<ul>
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<li><tt>cd <i>where-you-want-llvm-to-live</i></tt>
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<li><tt>cvs -d <i>CVSROOTDIR</i> checkout llvm</tt></p>
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</ul>
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<p>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.</p>
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<!------------------------------------------------------------------------->
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<h3><a name="config">Local Configuration Options</a></h3>
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<!------------------------------------------------------------------------->
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<p>The file <tt>llvm/Makefile.config</tt>
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defines the following path variables
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which are specific to a particular installation of LLVM.
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These need to be modified only once after checking out a copy
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of LLVM (if the default values do not already match your system):
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<ul>
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<p><li><i>CXX</i> = Path to C++ compiler to use.
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<p><li><i>OBJ_ROOT</i> = Path to the llvm directory where
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object files should be placed.
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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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<p><li><i>LLVMGCCDIR</i> = Path to the location of the LLVM front-end
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binaries and associated libraries.
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<p><li><i>PURIFY</i> = Path to the purify program.
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</ul>
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In addition to settings in this file, you must set a
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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. For example, one might use
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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.<p>
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<!------------------------------------------------------------------------->
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<h3><a name="objfiles">The location for LLVM object files</a></h3>
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<!------------------------------------------------------------------------->
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<p>The LLVM make system sends most output files generated during the build
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into the directory defined by the variable OBJ_ROOT in
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<tt>llvm/Makefile.config</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
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object files on a different filesystem either to keep them from being backed
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up or to speed up local builds.
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<p>If you do not wish to use a different location for object files (i.e.
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you are building into the source tree directly), just set this variable to
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".".<p>
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<!------------------------------------------------------------------------->
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<h3><a name="environment">Setting up your environment</a></h3>
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<!------------------------------------------------------------------------->
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<i>NOTE: This step is optional but will set up your environment so you
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can use the compiled LLVM tools with as little hassle as
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possible.</i>)
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<p>Add the following lines to your <tt>.cshrc</tt> (or the corresponding
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lines to your <tt>.profile</tt> if you use a bourne shell derivative).
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<pre>
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# Make the C front end easy to use...
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alias llvmgcc <i>LLVMGCCDIR</i><tt>/bin/llvm-gcc</tt>
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# Make the LLVM tools easy to use...
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setenv PATH <i>OBJ_ROOT</i>/llvm/tools/Debug:${PATH}
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</pre>
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The <tt>llvmgcc</tt> alias is useful because the C compiler is not
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included in the CVS tree you just checked out.
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<p>The other <a href="#tools">LLVM tools</a> are part of the LLVM
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source base and built when compiling LLVM. They will be built into the
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<tt><i>OBJ_ROOT</i>/tools/Debug</tt> directory.</p>
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<!------------------------------------------------------------------------->
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<h3><a name="compile">Compiling the source code</a></h3>
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<!------------------------------------------------------------------------->
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<p>Every directory in the LLVM source tree includes a <tt>Makefile</tt> to
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build it and any subdirectories that it contains. These makefiles require
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that you use GNU Make (aka <tt>gmake</tt>) instead of <tt>make</tt> to
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build them, but can
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otherwise be used freely. To build the entire LLVM system, just enter the
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top level <tt>llvm</tt> directory and type <tt>gmake</tt>. A few minutes
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later you will hopefully have a freshly compiled toolchain waiting for you
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in <tt><i>OBJ_ROOT</i>/llvm/tools/Debug</tt>. If you want to look at the
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libraries that were compiled, look in
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<tt><i>OBJ_ROOT</i>/llvm/lib/Debug</tt>.</p>
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If you get an error about a <tt>/localhome</tt> directory, follow the
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instructions in the section about <a href="#environment">Setting Up Your
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Environment.</a>
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<!--=====================================================================-->
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<center>
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<h2><a name="layout"><b>Program Layout</b></a></h2>
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</center>
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<!--=====================================================================-->
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<p>One useful source of infomation about the LLVM sourcebase is the LLVM <a
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href="http://www.doxygen.org">doxygen</a> documentation, available at <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/">http://llvm.cs.uiuc.edu/doxygen/</a></tt>. The
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following is a brief introduction to code layout:</p>
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<!------------------------------------------------------------------------->
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<h3><a name="cvsdir"><tt>CVS</tt> directories</a></h3>
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<!------------------------------------------------------------------------->
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Every directory checked out of CVS will contain a <tt>CVS</tt> directory;
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for the most part these can just be ignored.
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<!------------------------------------------------------------------------->
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<h3><a name="ddr"><tt>Depend</tt>, <tt>Debug</tt>, & <tt>Release</tt>
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directories</a></h3>
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<!------------------------------------------------------------------------->
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If you are building with the "<tt>OBJ_ROOT=.</tt>" option enabled in the
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<tt>Makefile.config</tt> file, most source directories will contain two
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directories, <tt>Depend</tt> and <tt>Debug</tt>. The <tt>Depend</tt>
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directory contains automatically generated dependance files which are used
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during compilation to make sure that source files get rebuilt if a header
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file they use is modified. The <tt>Debug</tt> directory holds the object
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files, library files, and executables that are used for building a debug
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enabled build. The <tt>Release</tt> directory is created to hold the same
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files when the <tt>ENABLE_OPTIMIZED=1</tt> flag is passed to <tt>gmake</tt>,
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causing an optimized built to be performed.<p>
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<!------------------------------------------------------------------------->
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<h3><a name="include"><tt>llvm/include</tt></a></h3>
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<!------------------------------------------------------------------------->
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This directory contains public header files exported from the LLVM
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library. The two main subdirectories of this directory are:<p>
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<ol>
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<li><tt>llvm/include/llvm</tt> - This directory contains all of the LLVM
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specific header files. This directory also has subdirectories for
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different portions of LLVM: <tt>Analysis</tt>, <tt>CodeGen</tt>,
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<tt>Reoptimizer</tt>, <tt>Target</tt>, <tt>Transforms</tt>, etc...
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<li><tt>llvm/include/Support</tt> - This directory contains generic
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support libraries that are independant of LLVM, but are used by LLVM.
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For example, header files for some C++ STL utilities and a Command Line
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option processing library are located here.
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</ol>
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<!------------------------------------------------------------------------->
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<h3><a name="lib"><tt>llvm/lib</tt></a></h3>
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<!------------------------------------------------------------------------->
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This directory contains most source files of LLVM system. In LLVM, almost
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all code exists in libraries, making it very easy to share code among the
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different <a href="#tools">tools</a>.<p>
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<dl compact>
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<dt><tt>llvm/lib/VMCore/</tt><dd> This directory holds the core LLVM
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source files that implement core classes like Instruction and BasicBlock.
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<dt><tt>llvm/lib/AsmParser/</tt><dd> This directory holds the source code
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for the LLVM assembly language parser library.
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<dt><tt>llvm/lib/ByteCode/</tt><dd> This directory holds code for reading
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and write LLVM bytecode.
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<dt><tt>llvm/lib/CWriter/</tt><dd> This directory implements the LLVM to C
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converter.
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<dt><tt>llvm/lib/Analysis/</tt><dd> This directory contains a variety of
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different program analyses, such as Dominator Information, Call Graphs,
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Induction Variables, Interval Identification, Natural Loop Identification,
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etc...
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<dt><tt>llvm/lib/Transforms/</tt><dd> This directory contains the source
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code for the LLVM to LLVM program transformations, such as Aggressive Dead
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Code Elimination, Sparse Conditional Constant Propagation, Inlining, Loop
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Invarient Code Motion, Dead Global Elimination, Pool Allocation, and many
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others...
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<dt><tt>llvm/lib/Target/</tt><dd> This directory contains files that
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describe various target architectures for code generation. For example,
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the llvm/lib/Target/Sparc directory holds the Sparc machine
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description.<br>
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<dt><tt>llvm/lib/CodeGen/</tt><dd> This directory contains the major parts
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of the code generator: Instruction Selector, Instruction Scheduling, and
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Register Allocation.
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<dt><tt>llvm/lib/Reoptimizer/</tt><dd> This directory holds code related
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to the runtime reoptimizer framework that is currently under development.
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<dt><tt>llvm/lib/Support/</tt><dd> This directory contains the source code
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that corresponds to the header files located in
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<tt>llvm/include/Support/</tt>.
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</dl>
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<!------------------------------------------------------------------------->
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<h3><a name="test"><tt>llvm/test</tt></a></h3>
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<!------------------------------------------------------------------------->
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<p>This directory contains regression tests and source code that is used to
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test the LLVM infrastructure...</p>
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<!------------------------------------------------------------------------->
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<h3><a name="tools"><tt>llvm/tools</tt></a></h3>
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<!------------------------------------------------------------------------->
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<p>The <b>tools</b> directory contains the executables built out of the
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libraries above, which form the main part of the user interface. You can
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always get help for a tool by typing <tt>tool_name --help</tt>. The
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following is a brief introduction to the most important tools.</p>
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<dl compact>
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<dt><tt><b>as</b></tt><dd>The assembler transforms the human readable
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LLVM assembly to LLVM bytecode.<p>
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<dt><tt><b>dis</b></tt><dd>The disassembler transforms the LLVM bytecode
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to human readable LLVM assembly. Additionally it can convert LLVM
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bytecode to C, which is enabled with the <tt>-c</tt> option.<p>
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<dt><tt><b>lli</b></tt><dd> <tt>lli</tt> is the LLVM interpreter, which
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can directly execute LLVM bytecode (although very slowly...). In addition
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to a simple intepreter, <tt>lli</tt> is also has debugger and tracing
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modes (entered by specifying <tt>-debug</tt> or <tt>-trace</tt> on the
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command line, respectively).<p>
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<dt><tt><b>llc</b></tt><dd> <tt>llc</tt> is the LLVM backend compiler,
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which translates LLVM bytecode to a SPARC assembly file.<p>
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<dt><tt><b>llvmgcc</b></tt><dd> <tt>llvmgcc</tt> is a GCC based C frontend
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that has been retargeted to emit LLVM code as the machine code output. It
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works just like any other GCC compiler, taking the typical <tt>-c, -S, -E,
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-o</tt> options that are typically used. The source code for the
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<tt>llvmgcc</tt> tool is currently not included in the LLVM cvs tree
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because it is quite large and not very interesting.<p>
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<ol>
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<dt><tt><b>gccas</b></tt><dd> This tool is invoked by the
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<tt>llvmgcc</tt> frontend as the "assembler" part of the compiler. This
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tool actually assembles LLVM assembly to LLVM bytecode,
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performs a variety of optimizations,
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and outputs LLVM bytecode. Thus when you invoke <tt>llvmgcc -c x.c -o
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x.o</tt>, you are causing <tt>gccas</tt> to be run, which writes the
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<tt>x.o</tt> file (which is an LLVM bytecode file that can be
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disassembled or manipulated just like any other bytecode file). The
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command line interface to <tt>gccas</tt> is designed to be as close as
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possible to the <b>system</b> '<tt>as</tt>' utility so that the gcc
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frontend itself did not have to be modified to interface to a "wierd"
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assembler.<p>
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<dt><tt><b>gccld</b></tt><dd> <tt>gccld</tt> links together several LLVM
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bytecode files into one bytecode file and does some optimization. It is
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the linker invoked by the gcc frontend when multiple .o files need to be
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linked together. Like <tt>gccas</tt> the command line interface of
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<tt>gccld</tt> is designed to match the system linker, to aid
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interfacing with the GCC frontend.<p>
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</ol>
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<dt><tt><b>opt</b></tt><dd> <tt>opt</tt> reads LLVM bytecode, applies a
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series of LLVM to LLVM transformations (which are specified on the command
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line), and then outputs the resultant bytecode. The '<tt>opt --help</tt>'
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command is a good way to get a list of the program transformations
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available in LLVM.<p>
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<dt><tt><b>analyze</b></tt><dd> <tt>analyze</tt> is used to run a specific
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analysis on an input LLVM bytecode file and print out the results. It is
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primarily useful for debugging analyses, or familiarizing yourself with
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what an analysis does.<p>
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</dl>
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<!--=====================================================================-->
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<h2><a name="tutorial">An example using the LLVM tool chain</h2>
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<!--=====================================================================-->
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<ol>
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<li>First, create a simple C file, name it 'hello.c':
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<pre>
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#include <stdio.h>
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int main() {
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printf("hello world\n");
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return 0;
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}
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</pre>
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<li>Next, compile the C file into a LLVM bytecode file:<p>
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<tt>% llvmgcc hello.c -o hello</tt><p>
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This will create two result files: <tt>hello</tt> and
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<tt>hello.bc</tt>. The <tt>hello.bc</tt> is the LLVM bytecode that
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corresponds the the compiled program and the library facilities that it
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required. <tt>hello</tt> is a simple shell script that runs the bytecode
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file with <tt>lli</tt>, making the result directly executable.<p>
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<li>Run the program. To make sure the program ran, execute one of the
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following commands:<p>
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<tt>% ./hello</tt><p>
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or<p>
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<tt>% lli hello.bc</tt><p>
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<li>Use the <tt>dis</tt> utility to take a look at the LLVM assembly
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|
code:<p>
|
|
|
|
<tt>% dis < hello.bc | less</tt><p>
|
|
|
|
<li>Compile the program to native Sparc assembly using the code
|
|
generator:<p>
|
|
|
|
<tt>% llc hello.bc -o hello.s</tt><p>
|
|
|
|
<li>Assemble the native sparc assemble file into a program:<p>
|
|
|
|
<tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.sparc</tt><p>
|
|
|
|
<li>Execute the native sparc program:<p>
|
|
|
|
<tt>% ./hello.sparc</tt><p>
|
|
|
|
</ol>
|
|
|
|
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|
<!--=====================================================================-->
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|
<h2><a name="links">Links</a></h2>
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|
<!--=====================================================================-->
|
|
|
|
<p>This document is just an <b>introduction</b> to how to use LLVM to do
|
|
some simple things... there are many more interesting and complicated things
|
|
that you can do that aren't documented here (but we'll gladly accept a patch
|
|
if you want to write something up!). For more information about LLVM, check
|
|
out:</p>
|
|
|
|
<ul>
|
|
<li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>
|
|
<li><a href="http://llvm.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>
|
|
</ul>
|
|
|
|
<hr>
|
|
|
|
If you have any questions or run into any snags (or you have any
|
|
additions...), please send an email to
|
|
<a href="mailto:sabre@nondot.org">Chris Lattner</a>.</p>
|
|
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|
<!-- Created: Mon Jul 1 02:29:02 CDT 2002 -->
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<!-- hhmts start -->
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|
Last modified: Tue Jun 3 22:06:43 CDT 2003
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|
<!-- hhmts end -->
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</body>
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</html>
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