2008-02-08 09:45:49 +03:00
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<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
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<title>Clang - Getting Started</title>
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<!--#include virtual="menu.html.incl"-->
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<div id="content">
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<h1>Getting Started: Building and Running Clang</h1>
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<p>This page gives you the shortest path to checking out clang and demos a few
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options. This should get you up and running with the minimum of muss and fuss.
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If you like what you see, please consider <a href="get_involved.html">getting
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involved</a> with the clang community.</p>
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<h2>A word of warning</h2>
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<p>While this work aims to provide a fully functional C/C++/ObjC front-end, it
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2008-02-28 17:59:26 +03:00
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is <em>still early work</em> and is under heavy development. In particular,
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2008-02-08 09:45:49 +03:00
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there is no real C++ support yet (this is obviously a big project), and C/ObjC
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support is still missing some features. Some of the more notable missing pieces
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of C support are:</p>
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<ol>
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<li>The semantic analyzer does not produce all of the warnings and errors it
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should.</li>
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<li>The LLVM code generator is still missing important features. clang is not
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ready to be used as a general purpose C code generator yet, but if you
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hit problems and report them to cfe-dev, we'll fix them :).</li>
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<li>We don't consider the API to be stable yet, and reserve the right to
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change fundamental things.</li>
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</ol>
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<p>Our plan is to continue chipping away at these issues until C works really
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well, but we'd love help from other interested contributors. We expect C to be
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in good shape by mid to late 2008.</p>
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<h3><a name="build">Building clang / working with the code</a></h3>
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<p>If you would like to check out and build the project, the current scheme
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is:</p>
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<ol>
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<li><a href="http://www.llvm.org/docs/GettingStarted.html#checkout">Checkout
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and build LLVM</a> from SVN head:</li>
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<ul>
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<li><tt>svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm</tt></li>
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<li><tt>cd llvm</tt></li>
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<li><tt>./configure; make</tt></li>
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</ul>
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<li>Checkout clang:</li>
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<ul>
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<li>From within the <tt>llvm</tt> directory (where you
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built llvm):</li>
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<li><tt>cd llvm/tools</tt>
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<li><tt>svn co http://llvm.org/svn/llvm-project/cfe/trunk clang</tt></li>
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</ul>
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<li>Non-mac users: Paths to system header files are currently hard coded
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into clang; as a result, if clang can't find your system headers,
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please follow these instructions:</li>
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<ul>
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<li>'<tt>touch empty.c; gcc -v empty.c -fsyntax-only</tt>' to get the
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path.</li>
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<li>Look for the comment "FIXME: temporary hack:
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hard-coded paths" in <tt>clang/Driver/clang.cpp</tt> and
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change the lines below to include that path.</li>
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</ul>
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<li>Build clang:</li>
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<ul>
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<li><tt>cd clang</tt> (assuming that you are in <tt>llvm/tools</tt>)</li>
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<li><tt>make</tt> (this will give you a debug build)</li>
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</ul>
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<li>Try it out (assuming you add llvm/Debug/bin to your path):</li>
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<ul>
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<li><tt>clang --help</tt></li>
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<li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li>
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<li><tt>clang file.c -ast-dump</tt> (internal debug dump of ast)</li>
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<li><tt>clang file.c -ast-view</tt> (<a
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href="http://llvm.org/docs/ProgrammersManual.html#ViewGraph">set up graphviz
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and rebuild llvm first</a>)</li>
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<li><tt>clang file.c -emit-llvm</tt> (print out unoptimized llvm code)</li>
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<li><tt>clang file.c -emit-llvm | llvm-as | opt -std-compile-opts |
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llvm-dis</tt> (print out optimized llvm code)</li>
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<li><tt>clang file.c -emit-llvm | llvm-as | opt -std-compile-opts | llc
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> file.s</tt> (output native machine code)</li>
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</ul>
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</ol>
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2008-02-08 10:32:26 +03:00
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<p>Note that the C front-end uses LLVM, but does not depend on
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llvm-gcc. If you encounter problems with building clang, make
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sure you have the latest SVN version of LLVM. LLVM contains
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support libraries for clang that will be updated as well as
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development on clang progresses.</p>
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2008-02-08 10:10:48 +03:00
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<h3>Building clang while building llvm:</h3>
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<p>Since you've checked out clang into the llvm source tree you can
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build them all at once with a simple Makefile change. This moves
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Step 1 above to Step 4.</p>
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<ul>
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<li><tt>cd llvm/tools</tt></li>
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<li>then edit <tt>Makefile</tt> to have a clang target in <tt>PARALLEL_DIRS</tt>
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just like <tt>llvm-config</tt></li>
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<li>then just build llvm normally as above and clang will build at
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the same time</li>
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<li><em>Note:</em> you can update your toplevel project and all (possibly unrelated)
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projects inside it with <tt><b>make update</b></tt>. This will run
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<tt>svn update</tt> on all subdirectories related to subversion.</li>
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</ul>
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2008-02-08 09:45:49 +03:00
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<h3>Examples of using clang</h3>
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<p>The clang driver takes a lot of GCC compatible options, which you can see
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with 'clang --help'. Here are a few examples:</p>
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<!-- Thanks to
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http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings
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Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre>
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tag. -->
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<pre class="code">
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$ <b>cat ~/t.c</b>
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typedef float V __attribute__((vector_size(16)));
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V foo(V a, V b) { return a+b*a; }
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</pre>
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<h4>Preprocessing:</h4>
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<pre class="code">
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$ <b>clang ~/t.c -E</b>
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# 1 "/Users/sabre/t.c" 1
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typedef float V __attribute__((vector_size(16)));
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V foo(V a, V b) { return a+b*a; }
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</pre>
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<h4>Type checking:</h4>
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<pre class="code">
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$ <b>clang -fsyntax-only ~/t.c</b>
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</pre>
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<h4>GCC options:</h4>
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<pre class="code">
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$ <b>clang -fsyntax-only ~/t.c -pedantic</b>
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/Users/sabre/t.c:2:17: warning: extension used
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typedef float V __attribute__((vector_size(16)));
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^
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1 diagnostic generated.
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</pre>
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<h4>Pretty printing from the AST:</h4>
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<pre class="code">
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$ <b>clang ~/t.c -ast-print</b>
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typedef float V __attribute__(( vector_size(16) ));
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V foo(V a, V b) {
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return a + b * a;
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}
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</pre>
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<h4>Code generation with LLVM:</h4>
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<pre class="code">
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$ <b>clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llvm-dis</b>
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define <4 x float> @foo(<4 x float> %a, <4 x float> %b) {
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entry:
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%mul = mul <4 x float> %b, %a
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%add = add <4 x float> %mul, %a
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ret <4 x float> %add
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}
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$ <b>clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llc -march=ppc32 -mcpu=g5</b>
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..
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_foo:
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vmaddfp v2, v3, v2, v2
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blr
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$ <b>clang ~/t.c -emit-llvm | llvm-as | opt -std-compile-opts | llc -march=x86 -mcpu=yonah</b>
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..
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_foo:
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mulps %xmm0, %xmm1
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addps %xmm0, %xmm1
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movaps %xmm1, %xmm0
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ret
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</pre>
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<h3>GCC "Emulation" Driver</h3>
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While the <tt>clang</tt> executable is a compiler driver that can perform code
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generation, program analysis, and other actions, it is not designed to be a
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drop-in replacement for GCC's <tt>cc</tt>. There is interest in developing such
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a driver for clang, but in the interim the clang source tree includes a Python
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script <tt>ccc</tt> in the <tt>utils</tt> subdirectory that provides some of
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this functionality (the script is intended to be used where GCC's <tt>cc</tt>
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could be used). It is currently a work in progress, and eventually will likely
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be replaced by a more complete driver.
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<p>Example use:</p>
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<pre class="code">
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$ <b>ccc t.c</b>
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clang -emit-llvm-bc -o t.o -U__GNUC__ t.c
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llvm-ld -native -o a.out t.o
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$ <b>ls</b>
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a.out a.out.bc t.c t.o
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</pre>
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</div>
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</body>
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</html>
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