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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ -->
<html>
<head>
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Hacking on clang</title>
<link type="text/css" rel="stylesheet" href="menu.css" />
<link type="text/css" rel="stylesheet" href="content.css" />
</head>
<body>
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<div id="content">
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<h1>Hacking on Clang</h1>
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<p>This document provides some hints for how to get started hacking
on Clang for developers who are new to the Clang and/or LLVM
codebases.</p>
<ul>
<li><a href="#docs">Developer Documentation</a></li>
<li><a href="#debugging">Debugging</a></li>
<li><a href="#testing">Testing</a></li>
<li><a href="#irgen">LLVM IR Generation</a></li>
</ul>
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<h2 id="docs">Developer Documentation</h2>
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<p>Both Clang and LLVM use doxygen to provide API documentation. Their
respective web pages (generated nightly) are here:</p>
<ul>
<li><a href="http://clang.llvm.org/doxygen">Clang</a></li>
<li><a href="http://llvm.org/doxygen">LLVM</a></li>
</ul>
<p>For work on the LLVM IR generation, the LLVM assembly language
<a href="http://llvm.org/docs/LangRef.html">reference manual</a> is
also useful.</p>
<!--=====================================================================-->
<h2 id="debugging">Debugging</h2>
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<p>Inspecting data structures in a debugger:</p>
<ul>
<li>Many LLVM and Clang data structures provide
a <tt>dump()</tt> method which will print a description of the
data structure to <tt>stderr</tt>.</li>
<li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>
structure is used pervasively. This is a simple value class for
wrapping types with qualifiers; you can use
the <tt>isConstQualified()</tt>, for example, to get one of the
qualifiers, and the <tt>getTypePtr()</tt> method to get the
wrapped <tt>Type*</tt> which you can then dump.</li>
</ul>
<!--=====================================================================-->
<h2 id="testing">Testing</h2>
<!--=====================================================================-->
<p>Clang includes a basic regression suite in the tree which can be
run with <tt>make test</tt> from the top-level clang directory, or
just <tt>make</tt> in the <em>test</em> sub-directory. <tt>make
report</tt> can be used after running the tests to summarize the
results, and <tt>make VERBOSE=1</tt> can be used to show more detail
about what is being run.</p>
<p>For more intensive changes, running
the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM
Test Suite</a> with clang is recommended. Currently the best way to
override LLVMGCC, as in: <tt>make LLVMGCC="ccc -std=gnu89"
TEST=nightly report</tt> (make sure ccc is in your PATH or use the
full path).</p>
<!--=====================================================================-->
<h2 id="irgen">LLVM IR Generation</h2>
<!--=====================================================================-->
<p>The LLVM IR generation part of clang handles conversion of the
AST nodes output by the Sema module to the LLVM Intermediate
Representation (IR). Historically, this was referred to as
"codegen", and the Clang code for this lives
in <tt>lib/CodeGen</tt>.</p>
<p>The output is most easily inspected using the <tt>-emit-llvm</tt>
option to clang (possibly in conjunction with <tt>-o -</tt>). You
can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file
which can be processed by the suite of LLVM tools
like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM
<a href="http://llvm.org/docs/CommandGuide/">Command Guide</a>
for more information.</p>
</div>
</body>
</html>