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<h1>Getting Started: Building and Running Clang</h1>
<p>This page gives you the shortest path to checking out Clang and demos a few
options. This should get you up and running with the minimum of muss and fuss.
If you like what you see, please consider <a href="get_involved.html">getting
involved</a> with the Clang community.</p>
<h2>A Word of Warning</h2>
<p>While this work aims to provide a fully functional C/C++/ObjC front-end, it
is still relatively new and under heavy development. Currently we believe clang
to be very usable as a C and Objective-C compiler, however there is no real C++
support yet (this is obviously a big project). Additionally, for C and
Objective-C:</p>
<ol>
<li>The semantic analyzer does not produce all of the warnings it should.</li>
<li>We don't consider the API to be stable yet, and reserve the right to
change fundamental things.</li>
<li>Only the X86-32 and X86-64 targets have been well tested.</li>
</ol>
<p>If you run into problems, please file
bugs in <a href="http://llvm.org/bugs/">LLVM Bugzilla</a> or bring up the issue
on the
<a href="http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev">Clang development
mailing list</a>.</p>
<h2 id="build">Building Clang and Working with the Code</h2>
<p>If you would like to check out and build Clang, the current procedure is as
follows:</p>
<ol>
<li><a href="http://www.llvm.org/docs/GettingStarted.html#checkout">Checkout
and build LLVM</a> from SVN head:</li>
<ul>
<li><tt>svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm</tt></li>
<li><tt>cd llvm</tt></li>
<li><tt>./configure; make</tt></li>
</ul>
<li>Checkout Clang:</li>
<ul>
<li>From within the <tt>llvm</tt> directory (where you
built llvm):</li>
<li><tt>cd tools</tt>
<li><tt>svn co http://llvm.org/svn/llvm-project/cfe/trunk clang</tt></li>
</ul>
<li>If you intend to work on Clang C++ support, you may need to tell it how
to find your C++ standard library headers. If Clang cannot find your
system libstdc++ headers, please follow these instructions:</li>
<ul>
<li>'<tt>touch empty.cpp; gcc -v empty.cpp -fsyntax-only</tt>' to get the
path.</li>
<li>Look for the comment "FIXME: temporary hack:
hard-coded paths" in <tt>clang/lib/Frontend/InitHeaderSearch.cpp</tt> and
change the lines below to include that path.</li>
</ul>
<li>Build Clang:</li>
<ul>
<li><tt>cd clang</tt> (assuming that you are in <tt>llvm/tools</tt>)</li>
<li><tt>make</tt> (this will give you a debug build)</li>
</ul>
<li>Try it out (assuming you add llvm/Debug/bin to your path):</li>
<ul>
<li><tt>clang-cc --help</tt></li>
<li><tt>clang-cc file.c -fsyntax-only</tt> (check for correctness)</li>
<li><tt>clang-cc file.c -ast-dump</tt> (internal debug dump of ast)</li>
<li><tt>clang-cc file.c -ast-view</tt> (<a
href="http://llvm.org/docs/ProgrammersManual.html#ViewGraph">set up graphviz
and rebuild llvm first</a>)</li>
<li><tt>clang-cc file.c -emit-llvm</tt> (print out unoptimized llvm code)</li>
<li><tt>clang-cc file.c -emit-llvm -o - | llvm-as | opt -std-compile-opts |
llvm-dis</tt> (print out optimized llvm code)</li>
<li><tt>clang-cc file.c -emit-llvm -o - | llvm-as | opt -std-compile-opts | llc
> file.s</tt> (output native machine code)</li>
</ul>
<p><em>Note</em>: Here <tt>clang-cc</tt> is the "low-level" frontend
executable that is similar in purpose to <tt>cc1</tt>. Clang also has a <a
href="#driver">high-level compiler driver</a> that acts as a drop-in
replacement for <tt>gcc</tt>.
</ol>
<p>Note that the C front-end uses LLVM, but does not depend on llvm-gcc. If you
encounter problems with building Clang, make sure you have the latest SVN
version of LLVM. LLVM contains support libraries for Clang that will be updated
as well as development on Clang progresses.</p>
<h3>Simultaneously Building Clang and LLVM:</h3>
<p>Once you have checked out Clang into the llvm source tree it will build along
with the rest of <tt>llvm</tt>. To build all of LLVM and Clang together all at
once simply run <tt>make</tt> from the root LLVM directory.</p>
<p><em>Note:</em> Observe that Clang is technically part of a separate
Subversion repository. As mentioned above, the latest Clang sources are tied to
the latest sources in the LLVM tree. You can update your toplevel LLVM project
and all (possibly unrelated) projects inside it with <tt><b>make
update</b></tt>. This will run <tt>svn update</tt> on all subdirectories related
to subversion. </p>
<a name="driver"><h2>High-Level Compiler Driver (Drop-in Substitute for GCC)</h2></a>
<p>While the <tt>clang-cc</tt> executable is a low-level frontend executable
that can perform code generation, program analysis, and other actions, it is not
designed to be a drop-in replacement for GCC's <tt>cc</tt>. For this purpose,
use the high-level driver, aptly named <tt>clang</tt>. Here are some
examples of how to use the high-level driver:
</p>
<pre class="code">
$ <b>cat t.c</b>
#include <stdio.h>
int main(int argc, char **argv) { printf("hello world\n"); }
$ <b>clang t.c</b>
$ <b>./a.out</b>
hello world
</pre>
<h2>Examples of using Clang</h2>
<p>The high-level driver <tt>clang</tt> is designed to understand most of GCC's
options, and the lower-level <tt>clang-cc</tt> executable also directly takes
many of GCC's options. You can see which options <tt>clang-cc</tt> accepts with
'<tt>clang-cc --help</tt>'. Here are a few examples of using <tt>clang</tt> and
<tt>clang-cc</tt>:</p>
<!-- Thanks to
http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings
Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre>
tag. -->
<pre class="code">
$ <b>cat ~/t.c</b>
typedef float V __attribute__((vector_size(16)));
V foo(V a, V b) { return a+b*a; }
</pre>
<h3>Preprocessing:</h3>
<pre class="code">
$ <b>clang ~/t.c -E</b>
# 1 "/Users/sabre/t.c" 1
typedef float V __attribute__((vector_size(16)));
V foo(V a, V b) { return a+b*a; }
</pre>
<h3>Type checking:</h3>
<pre class="code">
$ <b>clang -fsyntax-only ~/t.c</b>
</pre>
<h3>GCC options:</h3>
<pre class="code">
$ <b>clang -fsyntax-only ~/t.c -pedantic</b>
/Users/sabre/t.c:2:17: warning: extension used
typedef float V __attribute__((vector_size(16)));
^
1 diagnostic generated.
</pre>
<h3>Pretty printing from the AST:</h3>
<pre class="code">
$ <b>clang-cc ~/t.c -ast-print</b>
typedef float V __attribute__(( vector_size(16) ));
V foo(V a, V b) {
return a + b * a;
}
</pre>
<h3>Code generation with LLVM:</h3>
<pre class="code">
$ <b>clang-cc ~/t.c -emit-llvm -o - | llvm-as | opt -std-compile-opts | llvm-dis</b>
define <4 x float> @foo(<4 x float> %a, <4 x float> %b) {
entry:
%mul = mul <4 x float> %b, %a
%add = add <4 x float> %mul, %a
ret <4 x float> %add
}
$ <b>clang-cc ~/t.c -emit-llvm -o - | llvm-as | opt -std-compile-opts | llc -march=ppc32 -mcpu=g5</b>
..
_foo:
vmaddfp v2, v3, v2, v2
blr
$ <b>clang-cc ~/t.c -emit-llvm -o - | llvm-as | opt -std-compile-opts | llc -march=x86 -mcpu=yonah</b>
..
_foo:
mulps %xmm0, %xmm1
addps %xmm0, %xmm1
movaps %xmm1, %xmm0
ret
</pre>
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