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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. If you run into problems, please file
bugs in <a href="">LLVM Bugzilla</a> or bring up the issue
on the
<a href="">Clang development
mailing list</a>.</p>
<h2 id="build">Building Clang and Working with the Code</h2>
<h3 id="buildNix">On Unix-like Systems</h3>
<p>If you would like to check out and build Clang, the current procedure is as
<li>Get the required tools.
<a href="">
Getting Started with the LLVM System - Requirements</a>.</li>
<li>Note also that Python is needed for running the test suite.
Get it at: <a href=""></a></li>
<li>Checkout LLVM:</li>
<li>Change directory to where you want the llvm directory placed.</li>
<li><tt>svn co llvm</tt></li>
<li>Checkout Clang:</li>
<li><tt>cd llvm/tools</tt>
<li><tt>svn co clang</tt></li>
<li>Build LLVM and Clang:</li>
<li><tt>cd ..</tt> (back to llvm)</li>
<li>This builds both LLVM and Clang for debug mode.</li>
<li>Note: For subsequent Clang development, you can just do make at the
clang directory level.</li>
<p>It is also possible to use CMake instead of the makefiles. With CMake it
is also possible to generate project files for several IDEs: Eclipse CDT4,
CodeBlocks, Qt-Creator (use the CodeBlocks generator), KDevelop3.</p>
<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>
<li>'<tt>gcc -v -x c++ /dev/null -fsyntax-only</tt>' to get the
<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>
<li>Try it out (assuming you add llvm/Debug+Asserts/bin to your path):</li>
<li><tt>clang --help</tt></li>
<li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li>
<li><tt>clang file.c -S -emit-llvm -o -</tt> (print out unoptimized llvm code)</li>
<li><tt>clang file.c -S -emit-llvm -o - -O3</tt></li>
<li><tt>clang file.c -S -O3 -o -</tt> (output native machine code)</li>
<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>
<h3 id="buildWindows">Using Visual Studio</h3>
<p>The following details setting up for and building Clang on Windows using
Visual Studio:</p>
<li>Get the required tools:</li>
<li><b>Subversion</b>. Source code control program. Get it from:
<a href=""></a></li>
<li><b>cmake</b>. This is used for generating Visual Studio solution and
project files. Get it from:
<a href=""></a></li>
<li><b>Visual Studio 2005 or 2008</b></li>
<li><b>Python</b>. This is needed only if you will be running the tests
(which is essential, if you will be developing for clang).
Get it from:
<a href=""></a></li>
<li><b>GnuWin32 tools</b>
These are also necessary for running the tests.
(Note that the grep from MSYS or Cygwin doesn't work with the tests
because of embedded double-quotes in the search strings. The GNU
grep does work in this case.)
Get them from <a href=""></a>.</li>
<li>Checkout LLVM:</li>
<li><tt>svn co llvm</tt></li>
<li>Checkout Clang:</li>
<li><tt>cd llvm\tools</tt>
<li><tt>svn co clang</tt></li>
<li>Run cmake to generate the Visual Studio solution and project files:</li>
<li><tt>cd ..</tt> (Change directory back to the llvm top.)</li>
<li>If you are using Visual Studio 2005: <tt>cmake .</tt></li>
<li>Or if you are using Visual Studio 2008: <tt>cmake -G "Visual Studio 9 2008" .</tt></li>
<li>The above, if successful, will have created an LLVM.sln file in the
llvm directory.
<li>Build Clang:</li>
<li>Open LLVM.sln in Visual Studio.</li>
<li>Build the "clang" project for just the compiler driver and front end, or
the "ALL_BUILD" project to build everything, including tools.</li>
<li>Try it out (assuming you added llvm/debug/bin to your path). (See the
running examples from above.)</li>
<li>See <a href="hacking.html#testingWindows">
Hacking on clang - Testing using Visual Studio on Windows</a> for information
on running regression tests on Windows.</li>
<p>Note that once you have checked out both llvm and clang, to synchronize
to the latest code base, use the <tt>svn update</tt> command in both the
llvm and llvm\tools\clang directories, as they are separate repositories.</p>
<a name="driver"><h2>Clang Compiler Driver (Drop-in Substitute for GCC)</h2></a>
<p>The <tt>clang</tt> tool is the compiler driver and front-end, which is
designed to be a drop-in replacement for the <tt>gcc</tt> command. Here are
some examples of how to use the high-level driver:
<pre class="code">
$ <b>cat t.c</b>
#include &lt;stdio.h&gt;
int main(int argc, char **argv) { printf("hello world\n"); }
$ <b>clang t.c</b>
$ <b>./a.out</b>
hello world
<p>The 'clang' driver is designed to work as closely to GCC as possible to
maximize portability. The only major difference between the two is that
Clang defaults to gnu99 mode while GCC defaults to gnu89 mode. If you see
weird link-time errors relating to inline functions, try passing -std=gnu89
to clang.</p>
<h2>Examples of using Clang</h2>
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<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 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; }
<h3>Type checking:</h3>
<pre class="code">
$ <b>clang -fsyntax-only ~/t.c</b>
<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.
<h3>Pretty printing from the AST:</h3>
<p>Note, the <tt>-cc1</tt> argument indicates the the compiler front-end, and
not the driver, should be run. The compiler front-end has several additional
Clang specific features which are not exposed through the GCC compatible driver
<pre class="code">
$ <b>clang -cc1 ~/t.c -ast-print</b>
typedef float V __attribute__(( vector_size(16) ));
V foo(V a, V b) {
return a + b * a;
<h3>Code generation with LLVM:</h3>
<pre class="code">
$ <b>clang ~/t.c -S -emit-llvm -o -</b>
define &lt;4 x float&gt; @foo(&lt;4 x float&gt; %a, &lt;4 x float&gt; %b) {
%mul = mul &lt;4 x float&gt; %b, %a
%add = add &lt;4 x float&gt; %mul, %a
ret &lt;4 x float&gt; %add
$ <b>clang -fomit-frame-pointer -O3 -S -o - t.c</b> <i># On x86_64</i>
mulps %xmm0, %xmm1
addps %xmm1, %xmm0