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| <div class="document" id="tutorial-using-llvmc"> |
| <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> |
| </div> |
| <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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