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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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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="generator" content="Docutils 0.6: 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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<body>
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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="#using-the-llvmc-program" id="id2">Using the <tt class="docutils literal">llvmc</tt> program</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 as the
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<tt class="docutils literal">gcc</tt> program does for GCC - the difference being that LLVMC is designed to be
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more adaptable and easier to customize. Most of LLVMC functionality is
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implemented via high-level TableGen code, from which a corresponding C++ source
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file is automatically generated. This tutorial describes the basic usage and
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configuration of LLVMC.</p>
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</div>
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<div class="section" id="using-the-llvmc-program">
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<h1><a class="toc-backref" href="#id2">Using the <tt class="docutils literal">llvmc</tt> program</a></h1>
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<p>In general, <tt class="docutils literal">llvmc</tt> tries to be command-line compatible with <tt class="docutils literal">gcc</tt> as much
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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 commands are
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executed by using the <tt class="docutils literal"><span class="pre">-v</span></tt> option). For further help on command-line LLVMC
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usage, refer to the <tt class="docutils literal">llvmc <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-based drivers are written mostly using <a class="reference external" href="http://llvm.org/docs/TableGenFundamentals.html">TableGen</a>, so you need to be
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familiar with it to get anything done.</p>
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<p>Start by compiling <tt class="docutils literal">example/Simple</tt>, which is a primitive wrapper for
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<tt class="docutils literal">gcc</tt>:</p>
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<pre class="literal-block">
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$ cd $LLVM_OBJ_DIR/tools/examples/Simple
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$ make
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$ cat > hello.c
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#include <stdio.h>
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int main() { printf("Hello\n"); }
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$ $LLVM_BIN_DIR/Simple -v hello.c
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gcc hello.c -o hello.out
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$ ./hello.out
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Hello
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</pre>
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<p>We have thus produced a simple driver called, appropriately, <tt class="docutils literal">Simple</tt>, from
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the input TableGen file <tt class="docutils literal">Simple.td</tt>. The <tt class="docutils literal">llvmc</tt> program itself is generated
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using a similar process (see <tt class="docutils literal">llvmc/src</tt>). Contents of the file <tt class="docutils literal">Simple.td</tt>
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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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(command "gcc"),
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(sink),
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// -o is what is used by default, out_file_option here is included for
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// instructive purposes.
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(out_file_option "-o")
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]>;
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// Language map
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def LanguageMap : LanguageMap<[(lang_to_suffixes "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, language
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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 this graph
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are tools, and edges represent a transformation path between two tools (for
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example, assembly source produced by the compiler can be transformed into
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executable code by an assembler). The compilation graph is basically a list of
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edges; a special node named <tt class="docutils literal">root</tt> is used to mark graph entry points.</p>
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<p>Tool descriptions are represented as property lists: most properties in the
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example above should be self-explanatory; the <tt class="docutils literal">sink</tt> property means that all
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options lacking an explicit description should be forwarded to this tool.</p>
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<p>The <tt class="docutils literal">LanguageMap</tt> associates a language name with a list of suffixes and is
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used for deciding which toolchain corresponds to a given input file.</p>
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<p>To learn more about writing your own drivers with LLVMC, refer to the reference
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manual and examples in the <tt class="docutils literal">examples</tt> directory. Of a particular interest is
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the <tt class="docutils literal">Skeleton</tt> example, which can serve as a template for your LLVMC-based
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drivers.</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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</div>
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</body>
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</html>
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