2009-02-14 23:20:19 +03:00
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<title>Hacking on clang</title>
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<!--*********************************************************************-->
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<h1>Hacking on Clang</h1>
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<!--*********************************************************************-->
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<p>This document provides some hints for how to get started hacking
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on Clang for developers who are new to the Clang and/or LLVM
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codebases.</p>
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<ul>
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<li><a href="#docs">Developer Documentation</a></li>
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<li><a href="#debugging">Debugging</a></li>
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<li><a href="#testing">Testing</a></li>
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<li><a href="#irgen">LLVM IR Generation</a></li>
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</ul>
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<!--=====================================================================-->
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<h2 id="docs">Developer Documentation</h2>
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<!--=====================================================================-->
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<p>Both Clang and LLVM use doxygen to provide API documentation. Their
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respective web pages (generated nightly) are here:</p>
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<ul>
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<li><a href="http://clang.llvm.org/doxygen">Clang</a></li>
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<li><a href="http://llvm.org/doxygen">LLVM</a></li>
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</ul>
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<p>For work on the LLVM IR generation, the LLVM assembly language
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<a href="http://llvm.org/docs/LangRef.html">reference manual</a> is
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also useful.</p>
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<!--=====================================================================-->
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<h2 id="debugging">Debugging</h2>
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<!--=====================================================================-->
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<p>Inspecting data structures in a debugger:</p>
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<ul>
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<li>Many LLVM and Clang data structures provide
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a <tt>dump()</tt> method which will print a description of the
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data structure to <tt>stderr</tt>.</li>
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<li>The <a href="docs/InternalsManual.html#QualType"><tt>QualType</tt></a>
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structure is used pervasively. This is a simple value class for
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wrapping types with qualifiers; you can use
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the <tt>isConstQualified()</tt>, for example, to get one of the
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qualifiers, and the <tt>getTypePtr()</tt> method to get the
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wrapped <tt>Type*</tt> which you can then dump.</li>
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</ul>
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<!--=====================================================================-->
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<h2 id="testing">Testing</h2>
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<!--=====================================================================-->
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<p>Clang includes a basic regression suite in the tree which can be
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run with <tt>make test</tt> from the top-level clang directory, or
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just <tt>make</tt> in the <em>test</em> sub-directory. <tt>make
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report</tt> can be used after running the tests to summarize the
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results, and <tt>make VERBOSE=1</tt> can be used to show more detail
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about what is being run.</p>
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<p>The regression suite can also be run with Valgrind by running
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<tt>make test VG=1</tt> in the top-level clang directory.</p>
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<p>For more intensive changes, running
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the <a href="http://llvm.org/docs/TestingGuide.html#testsuiterun">LLVM
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Test Suite</a> with clang is recommended. Currently the best way to
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override LLVMGCC, as in: <tt>make LLVMGCC="ccc -std=gnu89"
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TEST=nightly report</tt> (make sure ccc is in your PATH or use the
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full path).</p>
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<!--=====================================================================-->
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<h2 id="irgen">LLVM IR Generation</h2>
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<!--=====================================================================-->
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<p>The LLVM IR generation part of clang handles conversion of the
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AST nodes output by the Sema module to the LLVM Intermediate
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Representation (IR). Historically, this was referred to as
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"codegen", and the Clang code for this lives
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in <tt>lib/CodeGen</tt>.</p>
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<p>The output is most easily inspected using the <tt>-emit-llvm</tt>
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option to clang (possibly in conjunction with <tt>-o -</tt>). You
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can also use <tt>-emit-llvm-bc</tt> to write an LLVM bitcode file
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which can be processed by the suite of LLVM tools
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like <tt>llvm-dis</tt>, <tt>llvm-nm</tt>, etc. See the LLVM
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<a href="http://llvm.org/docs/CommandGuide/">Command Guide</a>
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for more information.</p>
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</div>
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</body>
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