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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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<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> and <a
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href="mailto:sabre@nondot.org">Chris Lattner</a></font></h1>
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<ul>
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<li><a href="#quickstart">Getting started with LLVM</a>
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<ol>
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<li><a href="#cvs">Checkout LLVM from CVS</a>
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<li><a href="#shared">Access to <tt>/shared</tt></a>
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<li><a href="#environment">Set 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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<h2><a name="quickstart">Getting Started with LLVM</a></h2>
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<!--=====================================================================-->
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<p>This guide is meant to get you up and running with LLVM as quickly as
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possible. Once you get the basic system running you can choose an area to
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dive into and learn more about. If you get stuck or something is missing
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from this document, please email <a
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href="mailto:sabre@nondot.org">Chris</a>.</p>
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<!------------------------------------------------------------------------->
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<h3><a name="tools">Checkout LLVM from CVS</a></h3>
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<!------------------------------------------------------------------------->
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<p>First step is to get the actual source code. To do this, all you need to
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do is check it out from CVS. From your home directory, just enter:</p>
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<p><tt>cvs -d /home/vadve/vadve/Research/DynOpt/CVSRepository checkout
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llvm</tt></p>
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<p>This will create an '<tt>llvm</tt>' directory in your home directory and
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fully populate it with the source code for LLVM.</p>
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<!------------------------------------------------------------------------->
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<h3><a name="shared">Access to <tt>/shared</tt></a></h3>
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<!------------------------------------------------------------------------->
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By default, LLVM is configured to send all compiled files into the
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<tt>/shared/[yourloginname]/</tt> directory. The idea is that this
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directory is local to the machine you're working on, so the huge libraries
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and <tt>.o</tt> files you will be compiling will not have to be sent over
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NFS. If you are in a situation where this setup is correct, you don't have
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to do anything. If you don't have a <tt>/shared</tt> directory, you will
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have to make a couple of modifications to your setup.<p>
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The first modification is that you need to enable the "<tt>BUILD_ROOT =
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.</tt> line in the top level <tt>Makefile.common</tt>. This will instruct
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LLVM to build into the current directory tree instead of
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<tt>/shared</tt>.<p>
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<!------------------------------------------------------------------------->
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<h3><a name="tools">Set up your environment</a></h3>
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<!------------------------------------------------------------------------->
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<p>Now that you have the source code available, you should set up your
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environment to be able to use the LLVM tools (once compiled) with as little
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hassle as possible. To do this, we recommend that you add the following
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lines to your <tt>.cshrc</tt> (or the corresponding lines to your
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<tt>.profile</tt> if you use a bourne shell derivative):
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<pre>
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# Make the C frontend easy to use...
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alias llvmgcc /home/vadve/lattner/cvs/gcc_install/bin/gcc
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# Make the LLVM tools easy to use...
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setenv PATH /shared/[yourloginname]/llvm/tools/Debug:${PATH}
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</pre>
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<p>The C compiler is not included in the CVS tree you just checked out, so
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we just point to the cannonical location, and access it with the
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<tt>llvmgcc</tt> command. The rest of the <a href="#tools">LLVM tools</a>
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will be built into the <tt>llvm/tools/Debug</tt> directory. If you do not
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have access to <tt>/shared</tt>, use this line instead:</p>
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<pre>
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setenv PATH ~/llvm/tools/Debug:${PATH}
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</pre>
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Adding these two lines to your path will make it much easier to use the LLVM
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tools.</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 Makefile to build it,
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and any subdirectories that it contains. These makefiles require that you
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use <tt>gmake</tt>, instead of <tt>make</tt> to 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>llvm/tools/Debug</tt>. If you want to look at the libraries that
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were compiled, look in <tt>llvm/lib/Debug</tt>.</p>
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<p>By default, the LLVM build process sends all temporary (<tt>.o</tt>,
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<tt>.so</tt>, <tt>.a</tt>) files into a <tt>/shared/[your login
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name]/...</tt> directory, which is supposed to be on a disk local to the
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current machine. If you get an error talking about a <tt>/shared</tt>
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directory, follow the instructions in the <a href="#shared">section about
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<tt>/shared</tt></a>.<p>
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<!--=====================================================================-->
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<h2><a name="layout">Program Layout</a></h2>
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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>BUILD_ROOT=.</tt>" option enabled in the
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<tt>Makefile.common</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, some C++ STL utilities and a Command Line option processing
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library.
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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 all
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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/CWrite/</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 Propogation, 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 took 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 its input, 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>
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<tt>% dis < hello.bc | less</tt><p>
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<li>Compile the program to native Sparc assembly using the code
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generator:<p>
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<tt>% llc hello.bc -o hello.s</tt><p>
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<li>Assemble the native sparc assemble file into a program:<p>
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<tt>% /opt/SUNWspro/bin/cc -xarch=v9 hello.s -o hello.sparc</tt><p>
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<li>Execute the native sparc program:<p>
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<tt>% ./hello.sparc</tt><p>
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</ol>
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<!--=====================================================================-->
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<h2><a name="links">Links</a></h2>
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<!--=====================================================================-->
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<p>This document is just an <b>introduction</b> to how to use LLVM to do
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some simple things... there are many more interesting and complicated things
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that you can do that aren't documented here (but we'll gladly accept a patch
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if you want to write something up!). For more information about LLVM, check
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out:</p>
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<ul>
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<li><a href="http://llvm.cs.uiuc.edu/">LLVM homepage</a></li>
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<li><a href="http://tank.cs.uiuc.edu/doxygen/">LLVM doxygen tree</a></li>
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</ul>
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<hr>
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If you have any questions or run into any snags (or you have any
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additions...), please send an email to <a
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href="mailto:sabre@nondot.org">Chris Lattner</a> or <a
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href="mailto:gshi1@uiuc.edu">Guochun Shi</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 Aug 13 16:09:25 CDT 2002
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<!-- hhmts end -->
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</body>
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</html>
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