docs/CompilerDriverTutorial.html

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  11 <div class="document" id="tutorial-using-llvmc">
  12 <h1 class="title">Tutorial - Using LLVMC</h1>
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  17 <div class="contents topic" id="contents">
  18 <p class="topic-title first">Contents</p>
  19 <ul class="simple">
  20 <li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
  21 <li><a class="reference internal" href="#using-the-llvmc-program" id="id2">Using the <tt class="docutils literal">llvmc</tt> program</a></li>
  22 <li><a class="reference internal" href="#using-llvmc-to-generate-toolchain-drivers" id="id3">Using LLVMC to generate toolchain drivers</a></li>
  23 </ul>
  24 </div>
  25 <div class="doc_author">
  26 <p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
  27 </div><div class="section" id="introduction">
  28 <h1><a class="toc-backref" href="#id1">Introduction</a></h1>
  29 <p>LLVMC is a generic compiler driver, which plays the same role for LLVM as the
  30 <tt class="docutils literal">gcc</tt> program does for GCC - the difference being that LLVMC is designed to be
  31 more adaptable and easier to customize. Most of LLVMC functionality is
  32 implemented via high-level TableGen code, from which a corresponding C++ source
  33 file is automatically generated. This tutorial describes the basic usage and
  34 configuration of LLVMC.</p>
  35 </div>
  36 <div class="section" id="using-the-llvmc-program">
  37 <h1><a class="toc-backref" href="#id2">Using the <tt class="docutils literal">llvmc</tt> program</a></h1>
  38 <p>In general, <tt class="docutils literal">llvmc</tt> tries to be command-line compatible with <tt class="docutils literal">gcc</tt> as much
  39 as possible, so most of the familiar options work:</p>
  40 <pre class="literal-block">
  41 $ llvmc -O3 -Wall hello.cpp
  42 $ ./a.out
  43 hello
  44 </pre>
  45 <p>This will invoke <tt class="docutils literal"><span class="pre">llvm-g++</span></tt> under the hood (you can see which commands are
  46 executed by using the <tt class="docutils literal"><span class="pre">-v</span></tt> option). For further help on command-line LLVMC
  47 usage, refer to the <tt class="docutils literal">llvmc <span class="pre">--help</span></tt> output.</p>
  48 </div>
  49 <div class="section" id="using-llvmc-to-generate-toolchain-drivers">
  50 <h1><a class="toc-backref" href="#id3">Using LLVMC to generate toolchain drivers</a></h1>
  51 <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
  52 familiar with it to get anything done.</p>
  53 <p>Start by compiling <tt class="docutils literal">example/Simple</tt>, which is a primitive wrapper for
  54 <tt class="docutils literal">gcc</tt>:</p>
  55 <pre class="literal-block">
  56 $ cd $LLVM_OBJ_DIR/tools/examples/Simple
  57 $ make
  58 $ cat &gt; hello.c
  59 #include &lt;stdio.h&gt;
  60 int main() { printf(&quot;Hello\n&quot;); }
  61 $ $LLVM_BIN_DIR/Simple -v hello.c
  62 gcc hello.c -o hello.out
  63 $ ./hello.out
  64 Hello
  65 </pre>
  66 <p>We have thus produced a simple driver called, appropriately, <tt class="docutils literal">Simple</tt>, from
  67 the input TableGen file <tt class="docutils literal">Simple.td</tt>. The <tt class="docutils literal">llvmc</tt> program itself is generated
  68 using a similar process (see <tt class="docutils literal">llvmc/src</tt>). Contents of the file <tt class="docutils literal">Simple.td</tt>
  69 look like this:</p>
  70 <pre class="literal-block">
  71 // Include common definitions
  72 include &quot;llvm/CompilerDriver/Common.td&quot;
  73
  74 // Tool descriptions
  75 def gcc : Tool&lt;
  76 [(in_language &quot;c&quot;),
  77  (out_language &quot;executable&quot;),
  78  (output_suffix &quot;out&quot;),
  79  (command &quot;gcc&quot;),
  80  (sink),
  81
  82  // -o is what is used by default, out_file_option here is included for
  83  // instructive purposes.
  84  (out_file_option &quot;-o&quot;)
  85 ]&gt;;
  86
  87 // Language map
  88 def LanguageMap : LanguageMap&lt;[(lang_to_suffixes &quot;c&quot;, &quot;c&quot;)]&gt;;
  89
  90 // Compilation graph
  91 def CompilationGraph : CompilationGraph&lt;[(edge &quot;root&quot;, &quot;gcc&quot;)]&gt;;
  92 </pre>
  93 <p>As you can see, this file consists of three parts: tool descriptions, language
  94 map, and the compilation graph definition.</p>
  95 <p>At the heart of LLVMC is the idea of a compilation graph: vertices in this graph
  96 are tools, and edges represent a transformation path between two tools (for
  97 example, assembly source produced by the compiler can be transformed into
  98 executable code by an assembler). The compilation graph is basically a list of
  99 edges; a special node named <tt class="docutils literal">root</tt> is used to mark graph entry points.</p>
 100 <p>Tool descriptions are represented as property lists: most properties in the
 101 example above should be self-explanatory; the <tt class="docutils literal">sink</tt> property means that all
 102 options lacking an explicit description should be forwarded to this tool.</p>
 103 <p>The <tt class="docutils literal">LanguageMap</tt> associates a language name with a list of suffixes and is
 104 used for deciding which toolchain corresponds to a given input file.</p>
 105 <p>To learn more about writing your own drivers with LLVMC, refer to the reference
 106 manual and examples in the <tt class="docutils literal">examples</tt> directory. Of a particular interest is
 107 the <tt class="docutils literal">Skeleton</tt> example, which can serve as a template for your LLVMC-based
 108 drivers.</p>
 109 <hr />
 110 <address>
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 118 <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
 119 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
 120
 121 Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
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