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<title>Building the LLVM GCC Front-End</title>
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<h1>
Building the LLVM GCC Front-End
</h1>
<ol>
<li><a href="#instructions">Building llvm-gcc from Source</a></li>
<li><a href="#ada">Building the Ada front-end</a></li>
<li><a href="#fortran">Building the Fortran front-end</a></li>
<li><a href="#license">License Information</a></li>
</ol>
<div class="doc_author">
<p>Written by the LLVM Team</p>
</div>
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<h2><a name="instructions">Building llvm-gcc from Source</a></h2>
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<div>
<p>This section describes how to acquire and build llvm-gcc 4.2, which is based
on the GCC 4.2.1 front-end. Supported languages are Ada, C, C++, Fortran,
Objective-C and Objective-C++. Note that the instructions for building these
front-ends are completely different (and much easier!) than those for building
llvm-gcc3 in the past.</p>
<ol>
<li><p>Retrieve the appropriate llvm-gcc-4.2-<i>version</i>.source.tar.gz
archive from the <a href="http://llvm.org/releases/">LLVM web
site</a>.</p>
<p>It is also possible to download the sources of the llvm-gcc front end
from a read-only mirror using subversion. To check out the 4.2 code
for first time use:</p>
<div class="doc_code">
<pre>
svn co http://llvm.org/svn/llvm-project/llvm-gcc-4.2/trunk <i>dst-directory</i>
</pre>
</div>
<p>After that, the code can be be updated in the destination directory
using:</p>
<div class="doc_code">
<pre>svn update</pre>
</div>
<p>The mirror is brought up to date every evening.</p></li>
<li>Follow the directions in the top-level <tt>README.LLVM</tt> file for
up-to-date instructions on how to build llvm-gcc. See below for building
with support for Ada or Fortran.
</ol>
</div>
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<h2><a name="ada">Building the Ada front-end</a></h2>
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<div>
<p>Building with support for Ada amounts to following the directions in the
top-level <tt>README.LLVM</tt> file, adding ",ada" to EXTRALANGS, for example:
<tt>EXTRALANGS=,ada</tt></p>
<p>There are some complications however:</p>
<ol>
<li><p>The only platform for which the Ada front-end is known to build is
32 bit intel x86 running linux. It is unlikely to build for other
systems without some work.</p></li>
<li><p>The build requires having a compiler that supports Ada, C and C++.
The Ada front-end is written in Ada so an Ada compiler is needed to
build it. Compilers known to work with the
<a href="http://llvm.org/releases/download.html">LLVM 2.7 release</a>
are <a href="http://gcc.gnu.org/releases.html">gcc-4.2</a> and the
2005, 2006 and 2007 versions of the
<a href="http://libre.adacore.com/">GNAT GPL Edition</a>.
<b>GNAT GPL 2008, gcc-4.3 and later will not work</b>.
The LLVM parts of llvm-gcc are written in C++ so a C++ compiler is
needed to build them. The rest of gcc is written in C.
Some linux distributions provide a version of gcc that supports all
three languages (the Ada part often comes as an add-on package to
the rest of gcc). Otherwise it is possible to combine two versions
of gcc, one that supports Ada and C (such as the
<a href="http://libre.adacore.com/">2007 GNAT GPL Edition</a>)
and another which supports C++, see below.</p></li>
<li><p>Because the Ada front-end is experimental, it is wise to build the
compiler with checking enabled. This causes it to run much slower, but
helps catch mistakes in the compiler (please report any problems using
<a href="http://llvm.org/bugs/">LLVM bugzilla</a>).</p></li>
<li><p>The Ada front-end <a href="http://llvm.org/PR2007">fails to
bootstrap</a>, due to lack of LLVM support for
<tt>setjmp</tt>/<tt>longjmp</tt> style exception handling (used
internally by the compiler), so you must specify
<tt>--disable-bootstrap</tt>.</p></li>
</ol>
<p>Supposing appropriate compilers are available, llvm-gcc with Ada support can
be built on an x86-32 linux box using the following recipe:</p>
<ol>
<li><p>Download the <a href="http://llvm.org/releases/download.html">LLVM source</a>
and unpack it:</p>
<pre class="doc_code">
wget http://llvm.org/releases/2.7/llvm-2.7.tgz
tar xzf llvm-2.7.tgz
mv llvm-2.7 llvm
</pre>
<p>or <a href="GettingStarted.html#checkout">check out the
latest version from subversion</a>:</p>
<pre class="doc_code">svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm</pre>
</li>
<li><p>Download the
<a href="http://llvm.org/releases/download.html">llvm-gcc-4.2 source</a>
and unpack it:</p>
<pre class="doc_code">
wget http://llvm.org/releases/2.7/llvm-gcc-4.2-2.7.source.tgz
tar xzf llvm-gcc-4.2-2.7.source.tgz
mv llvm-gcc-4.2-2.7.source llvm-gcc-4.2
</pre>
<p>or <a href="GettingStarted.html#checkout">check out the
latest version from subversion</a>:</p>
<pre class="doc_code">
svn co http://llvm.org/svn/llvm-project/llvm-gcc-4.2/trunk llvm-gcc-4.2
</pre>
</li>
<li><p>Make a build directory <tt>llvm-objects</tt> for llvm and make it the
current directory:</p>
<pre class="doc_code">
mkdir llvm-objects
cd llvm-objects
</pre>
</li>
<li><p>Configure LLVM (here it is configured to install into <tt>/usr/local</tt>):</p>
<pre class="doc_code">
../llvm/configure --prefix=<b>/usr/local</b> --enable-optimized --enable-assertions
</pre>
<p>If you have a multi-compiler setup and the C++ compiler is not the
default, then you can configure like this:</p>
<pre class="doc_code">
CXX=<b>PATH_TO_C++_COMPILER</b> ../llvm/configure --prefix=<b>/usr/local</b> --enable-optimized --enable-assertions
</pre>
<p>To compile without checking (not recommended), replace
<tt>--enable-assertions</tt> with <tt>--disable-assertions</tt>.</p>
</li>
<li><p>Build LLVM:</p>
<pre class="doc_code">
make
</pre>
</li>
<li><p>Install LLVM (optional):</p>
<pre class="doc_code">
make install
</pre>
</li>
<li><p>Make a build directory <tt>llvm-gcc-4.2-objects</tt> for llvm-gcc and make it the
current directory:</p>
<pre class="doc_code">
cd ..
mkdir llvm-gcc-4.2-objects
cd llvm-gcc-4.2-objects
</pre>
</li>
<li><p>Configure llvm-gcc (here it is configured to install into <tt>/usr/local</tt>).
The <tt>--enable-checking</tt> flag turns on sanity checks inside the compiler.
To turn off these checks (not recommended), replace <tt>--enable-checking</tt>
with <tt>--disable-checking</tt>.
Additional languages can be appended to the <tt>--enable-languages</tt> switch,
for example <tt>--enable-languages=ada,c,c++</tt>.</p>
<pre class="doc_code">
../llvm-gcc-4.2/configure --prefix=<b>/usr/local</b> --enable-languages=ada,c \
--enable-checking --enable-llvm=$PWD/../llvm-objects \
--disable-bootstrap --disable-multilib
</pre>
<p>If you have a multi-compiler setup, then you can configure like this:</p>
<pre class="doc_code">
export CC=<b>PATH_TO_C_AND_ADA_COMPILER</b>
export CXX=<b>PATH_TO_C++_COMPILER</b>
../llvm-gcc-4.2/configure --prefix=<b>/usr/local</b> --enable-languages=ada,c \
--enable-checking --enable-llvm=$PWD/../llvm-objects \
--disable-bootstrap --disable-multilib
</pre>
</li>
<li><p>Build and install the compiler:</p>
<pre class="doc_code">
make
make install
</pre>
</li>
</ol>
</div>
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<h2><a name="fortran">Building the Fortran front-end</a></h2>
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<div>
<p>To build with support for Fortran, follow the directions in the top-level
<tt>README.LLVM</tt> file, adding ",fortran" to EXTRALANGS, for example:</p>
<pre class="doc_code">
EXTRALANGS=,fortran
</pre>
</div>
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<h2><a name="license">License Information</a></h2>
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<div>
<p>
The LLVM GCC frontend is licensed to you under the GNU General Public License
and the GNU Lesser General Public License. Please see the files COPYING and
COPYING.LIB for more details.
</p>
<p>
More information is <a href="FAQ.html#license">available in the FAQ</a>.
</p>
</div>
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