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<h1 class="title">Tutorial - Using LLVMC</h1>
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<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
<li><a class="reference internal" href="#using-the-llvmc-program" id="id2">Using the <tt class="docutils literal">llvmc</tt> program</a></li>
<li><a class="reference internal" href="#using-llvmc-to-generate-toolchain-drivers" id="id3">Using LLVMC to generate toolchain drivers</a></li>
</ul>
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<div class="doc_author">
<p>Written by <a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a></p>
</div><div class="section" id="introduction">
<h1><a class="toc-backref" href="#id1">Introduction</a></h1>
<p>LLVMC is a generic compiler driver, which plays the same role for LLVM as the
<tt class="docutils literal">gcc</tt> program does for GCC - the difference being that LLVMC is designed to be
more adaptable and easier to customize. Most of LLVMC functionality is
implemented via high-level TableGen code, from which a corresponding C++ source
file is automatically generated. This tutorial describes the basic usage and
configuration of LLVMC.</p>
</div>
<div class="section" id="using-the-llvmc-program">
<h1><a class="toc-backref" href="#id2">Using the <tt class="docutils literal">llvmc</tt> program</a></h1>
<p>In general, <tt class="docutils literal">llvmc</tt> tries to be command-line compatible with <tt class="docutils literal">gcc</tt> as much
as possible, so most of the familiar options work:</p>
<pre class="literal-block">
$ llvmc -O3 -Wall hello.cpp
$ ./a.out
hello
</pre>
<p>This will invoke <tt class="docutils literal"><span class="pre">llvm-g++</span></tt> under the hood (you can see which commands are
executed by using the <tt class="docutils literal"><span class="pre">-v</span></tt> option). For further help on command-line LLVMC
usage, refer to the <tt class="docutils literal">llvmc <span class="pre">--help</span></tt> output.</p>
</div>
<div class="section" id="using-llvmc-to-generate-toolchain-drivers">
<h1><a class="toc-backref" href="#id3">Using LLVMC to generate toolchain drivers</a></h1>
<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
familiar with it to get anything done.</p>
<p>Start by compiling <tt class="docutils literal">example/Simple</tt>, which is a primitive wrapper for
<tt class="docutils literal">gcc</tt>:</p>
<pre class="literal-block">
$ cd $LLVM_OBJ_DIR/tools/examples/Simple
$ make
$ cat > hello.c
#include <stdio.h>
int main() { printf("Hello\n"); }
$ $LLVM_BIN_DIR/Simple -v hello.c
gcc hello.c -o hello.out
$ ./hello.out
Hello
</pre>
<p>We have thus produced a simple driver called, appropriately, <tt class="docutils literal">Simple</tt>, from
the input TableGen file <tt class="docutils literal">Simple.td</tt>. The <tt class="docutils literal">llvmc</tt> program itself is generated
using a similar process (see <tt class="docutils literal">llvmc/src</tt>). Contents of the file <tt class="docutils literal">Simple.td</tt>
look like this:</p>
<pre class="literal-block">
// Include common definitions
include "llvm/CompilerDriver/Common.td"
// Tool descriptions
def gcc : Tool<
[(in_language "c"),
(out_language "executable"),
(output_suffix "out"),
(command "gcc"),
(sink),
// -o is what is used by default, out_file_option here is included for
// instructive purposes.
(out_file_option "-o")
]>;
// Language map
def LanguageMap : LanguageMap<[(lang_to_suffixes "c", "c")]>;
// Compilation graph
def CompilationGraph : CompilationGraph<[(edge "root", "gcc")]>;
</pre>
<p>As you can see, this file consists of three parts: tool descriptions, language
map, and the compilation graph definition.</p>
<p>At the heart of LLVMC is the idea of a compilation graph: vertices in this graph
are tools, and edges represent a transformation path between two tools (for
example, assembly source produced by the compiler can be transformed into
executable code by an assembler). The compilation graph is basically a list of
edges; a special node named <tt class="docutils literal">root</tt> is used to mark graph entry points.</p>
<p>Tool descriptions are represented as property lists: most properties in the
example above should be self-explanatory; the <tt class="docutils literal">sink</tt> property means that all
options lacking an explicit description should be forwarded to this tool.</p>
<p>The <tt class="docutils literal">LanguageMap</tt> associates a language name with a list of suffixes and is
used for deciding which toolchain corresponds to a given input file.</p>
<p>To learn more about writing your own drivers with LLVMC, refer to the reference
manual and examples in the <tt class="docutils literal">examples</tt> directory. Of a particular interest is
the <tt class="docutils literal">Skeleton</tt> example, which can serve as a template for your LLVMC-based
drivers.</p>
<hr />
<address>
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<a href="mailto:foldr@codedgers.com">Mikhail Glushenkov</a><br />
<a href="http://llvm.org">LLVM Compiler Infrastructure</a><br />
Last modified: $Date: 2008-12-11 11:34:48 -0600 (Thu, 11 Dec 2008) $
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