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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.5: http://docutils.sourceforge.net/" />
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<title>Tutorial - Using LLVMC</title>
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<link rel="stylesheet" href="llvm.css" type="text/css" />
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</head>
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<div class="document" id="tutorial-using-llvmc">
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<h1 class="title">Tutorial - Using LLVMC</h1>
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<!-- This file was automatically generated by rst2html.
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Please do not edit directly!
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The ReST source lives in the directory 'tools/llvmc/doc'. -->
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<div class="contents topic" id="contents">
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<p class="topic-title first">Contents</p>
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<ul class="simple">
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<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
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<li><a class="reference internal" href="#compiling-with-llvmc" id="id2">Compiling with LLVMC</a></li>
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<li><a class="reference internal" href="#using-llvmc-to-generate-toolchain-drivers" id="id3">Using LLVMC to generate toolchain drivers</a></li>
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</ul>
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</div>
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<div class="doc_author">
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<p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
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</div><div class="section" id="introduction">
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<h1><a class="toc-backref" href="#id1">Introduction</a></h1>
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<p>LLVMC is a generic compiler driver, which plays the same role for LLVM
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as the <tt class="docutils literal"><span class="pre">gcc</span></tt> program does for GCC - the difference being that LLVMC
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is designed to be more adaptable and easier to customize. Most of
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LLVMC functionality is implemented via plugins, which can be loaded
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dynamically or compiled in. This tutorial describes the basic usage
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and configuration of LLVMC.</p>
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</div>
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<div class="section" id="compiling-with-llvmc">
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<h1><a class="toc-backref" href="#id2">Compiling with LLVMC</a></h1>
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<p>In general, LLVMC tries to be command-line compatible with <tt class="docutils literal"><span class="pre">gcc</span></tt> as
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much as possible, so most of the familiar options work:</p>
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<pre class="literal-block">
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$ llvmc -O3 -Wall hello.cpp
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$ ./a.out
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hello
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</pre>
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<p>This will invoke <tt class="docutils literal"><span class="pre">llvm-g++</span></tt> under the hood (you can see which
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commands are executed by using the <tt class="docutils literal"><span class="pre">-v</span></tt> option). For further help on
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command-line LLVMC usage, refer to the <tt class="docutils literal"><span class="pre">llvmc</span> <span class="pre">--help</span></tt> output.</p>
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</div>
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<div class="section" id="using-llvmc-to-generate-toolchain-drivers">
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<h1><a class="toc-backref" href="#id3">Using LLVMC to generate toolchain drivers</a></h1>
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<p>LLVMC plugins are written mostly using <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a>, so you need to
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be familiar with it to get anything done.</p>
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<p>Start by compiling <tt class="docutils literal"><span class="pre">example/Simple</span></tt>, which is a primitive wrapper for
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<tt class="docutils literal"><span class="pre">gcc</span></tt>:</p>
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<pre class="literal-block">
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$ cd $LLVM_DIR/tools/llvmc
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$ cp -r example/Simple plugins/Simple
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# NB: A less verbose way to compile standalone LLVMC-based drivers is
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# described in the reference manual.
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$ make LLVMC_BASED_DRIVER_NAME=mygcc LLVMC_BUILTIN_PLUGINS=Simple
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$ cat > hello.c
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[...]
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$ mygcc hello.c
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$ ./hello.out
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Hello
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</pre>
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<p>Here we link our plugin with the LLVMC core statically to form an executable
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file called <tt class="docutils literal"><span class="pre">mygcc</span></tt>. It is also possible to build our plugin as a dynamic
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library to be loaded by the <tt class="docutils literal"><span class="pre">llvmc</span></tt> executable (or any other LLVMC-based
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standalone driver); this is described in the reference manual.</p>
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<p>Contents of the file <tt class="docutils literal"><span class="pre">Simple.td</span></tt> look like this:</p>
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<pre class="literal-block">
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// Include common definitions
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include "llvm/CompilerDriver/Common.td"
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// Tool descriptions
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def gcc : Tool<
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[(in_language "c"),
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(out_language "executable"),
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(output_suffix "out"),
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(cmd_line "gcc $INFILE -o $OUTFILE"),
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(sink)
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]>;
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// Language map
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def LanguageMap : LanguageMap<[LangToSuffixes<"c", ["c"]>]>;
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// Compilation graph
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def CompilationGraph : CompilationGraph<[Edge<"root", "gcc">]>;
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</pre>
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<p>As you can see, this file consists of three parts: tool descriptions,
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language map, and the compilation graph definition.</p>
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<p>At the heart of LLVMC is the idea of a compilation graph: vertices in
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this graph are tools, and edges represent a transformation path
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between two tools (for example, assembly source produced by the
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compiler can be transformed into executable code by an assembler). The
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compilation graph is basically a list of edges; a special node named
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<tt class="docutils literal"><span class="pre">root</span></tt> is used to mark graph entry points.</p>
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<p>Tool descriptions are represented as property lists: most properties
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in the example above should be self-explanatory; the <tt class="docutils literal"><span class="pre">sink</span></tt> property
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means that all options lacking an explicit description should be
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forwarded to this tool.</p>
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<p>The <tt class="docutils literal"><span class="pre">LanguageMap</span></tt> associates a language name with a list of suffixes
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and is used for deciding which toolchain corresponds to a given input
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file.</p>
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<p>To learn more about LLVMC customization, refer to the reference
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manual and plugin source code in the <tt class="docutils literal"><span class="pre">plugins</span></tt> directory.</p>
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<hr />
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<address>
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<a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
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<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
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Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
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</address></div>
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