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  16 <h1>Getting Started: Building and Running Clang</h1>
  17
  18 <p>This page gives you the shortest path to checking out Clang and demos a few
  19 options.  This should get you up and running with the minimum of muss and fuss.
  20 If you like what you see, please consider <a href="get_involved.html">getting
  21 involved</a> with the Clang community.  If you run into problems, please file
  22 bugs in <a href="http://llvm.org/bugs/">LLVM Bugzilla</a>.</p>
  23
  24 <h2 id="download">Release Clang Versions</h2>
  25
  26 <p>Clang has been released as part of regular LLVM releases since LLVM 2.6. You
  27 can download the release versions
  28 from <a href="http://llvm.org/releases/">http://llvm.org/releases/</a>.</p>
  29
  30 <h2 id="build">Building Clang and Working with the Code</h2>
  31
  32 <h3 id="buildNix">On Unix-like Systems</h3>
  33
  34 <p>If you would like to check out and build Clang, the current procedure is as
  35 follows:</p>
  36
  37 <ol>
  38   <li>Get the required tools.
  39   <ul>
  40     <li>See
  41       <a href="http://llvm.org/docs/GettingStarted.html#requirements">
  42       Getting Started with the LLVM System - Requirements</a>.</li>
  43     <li>Note also that Python is needed for running the test suite.
  44       Get it at: <a href="http://www.python.org/download">
  45       http://www.python.org/download</a></li>
  46   </ul>
  47
  48   <li>Checkout LLVM:</li>
  49   <ul>
  50     <li>Change directory to where you want the llvm directory placed.</li>
  51     <li><tt>svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm</tt></li>
  52   </ul>
  53   <li>Checkout Clang:</li>
  54   <ul>
  55     <li><tt>cd llvm/tools</tt>
  56     <li><tt>svn co http://llvm.org/svn/llvm-project/cfe/trunk clang</tt></li>
  57   </ul>
  58   <li>Build LLVM and Clang:</li>
  59   <ul>
  60     <li><tt>cd ../..</tt>  (back to where you started)</li>
  61     <li><tt>mkdir build</tt> (for building without polluting the source dir)
  62     </li>
  63     <li><tt>cd build</tt></li>
  64     <li><tt>../llvm/configure</tt></li>
  65     <li><tt>make</tt></li>
  66     <li>This builds both LLVM and Clang for debug mode.</li>
  67     <li>Note: For subsequent Clang development, you can just do make at the
  68     clang directory level.</li>
  69   </ul>
  70
  71   <p>It is also possible to use CMake instead of the makefiles. With CMake it
  72      is also possible to generate project files for several IDEs: Eclipse CDT4,
  73      CodeBlocks, Qt-Creator (use the CodeBlocks generator), KDevelop3.</p>
  74
  75   <li>If you intend to work on Clang C++ support, you may need to tell it how
  76       to find your C++ standard library headers.  If Clang cannot find your
  77       system libstdc++ headers, please follow these instructions:</li>
  78   <ul>
  79     <li>'<tt>gcc -v -x c++ /dev/null -fsyntax-only</tt>' to get the
  80     path.</li>
  81     <li>Look for the comment "FIXME: temporary hack:
  82     hard-coded paths" in <tt>clang/lib/Frontend/InitHeaderSearch.cpp</tt> and
  83     change the lines below to include that path.</li>
  84   </ul>
  85   <li>Try it out (assuming you add llvm/Debug+Asserts/bin to your path):</li>
  86   <ul>
  87     <li><tt>clang --help</tt></li>
  88     <li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li>
  89     <li><tt>clang file.c -S -emit-llvm -o -</tt> (print out unoptimized llvm code)</li>
  90     <li><tt>clang file.c -S -emit-llvm -o - -O3</tt></li>
  91     <li><tt>clang file.c -S -O3 -o -</tt> (output native machine code)</li>
  92   </ul>
  93 </ol>
  94
  95 <p>Note that the C front-end uses LLVM, but does not depend on llvm-gcc. If you
  96 encounter problems with building Clang, make sure you have the latest SVN
  97 version of LLVM. LLVM contains support libraries for Clang that will be updated
  98 as well as development on Clang progresses.</p>
  99
 100 <h3>Simultaneously Building Clang and LLVM:</h3>
 101
 102 <p>Once you have checked out Clang into the llvm source tree it will build along
 103 with the rest of <tt>llvm</tt>. To build all of LLVM and Clang together all at
 104 once simply run <tt>make</tt> from the root LLVM directory.</p>
 105
 106 <p><em>Note:</em> Observe that Clang is technically part of a separate
 107 Subversion repository. As mentioned above, the latest Clang sources are tied to
 108 the latest sources in the LLVM tree. You can update your toplevel LLVM project
 109 and all (possibly unrelated) projects inside it with <tt><b>make
 110 update</b></tt>. This will run <tt>svn update</tt> on all subdirectories related
 111 to subversion. </p>
 112
 113 <h3 id="buildWindows">Using Visual Studio</h3>
 114
 115 <p>The following details setting up for and building Clang on Windows using
 116 Visual Studio:</p>
 117
 118 <ol>
 119   <li>Get the required tools:</li>
 120   <ul>
 121     <li><b>Subversion</b>.  Source code control program.  Get it from:
 122         <a href="http://subversion.tigris.org/getting.html">
 123         http://subversion.tigris.org/getting.html</a></li>
 124     <li><b>cmake</b>.  This is used for generating Visual Studio solution and
 125         project files.  Get it from:
 126         <a href="http://www.cmake.org/cmake/resources/software.html">
 127         http://www.cmake.org/cmake/resources/software.html</a></li>
 128     <li><b>Visual Studio 2005, 2008, or 2010</b></li>
 129     <li><b>Python</b>.  This is needed only if you will be running the tests
 130         (which is essential, if you will be developing for clang).
 131         Get it from:
 132         <a href="http://www.python.org/download">
 133         http://www.python.org/download</a></li>
 134     <li><b>GnuWin32 tools</b>
 135         These are also necessary for running the tests.
 136         (Note that the grep from MSYS or Cygwin doesn't work with the tests
 137         because of embedded double-quotes in the search strings.  The GNU
 138         grep does work in this case.)
 139         Get them from <a href="http://getgnuwin32.sourceforge.net">
 140         http://getgnuwin32.sourceforge.net</a>.</li>
 141   </ul>
 142
 143   <li>Checkout LLVM:</li>
 144   <ul>
 145     <li><tt>svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm</tt></li>
 146   </ul>
 147   <li>Checkout Clang:</li>
 148   <ul>
 149      <li><tt>cd llvm\tools</tt>
 150      <li><tt>svn co http://llvm.org/svn/llvm-project/cfe/trunk clang</tt></li>
 151   </ul>
 152   <li>Run cmake to generate the Visual Studio solution and project files:</li>
 153   <ul>
 154     <li><tt>cd ..\..</tt>  (back to where you started)</li>
 155     <li><tt>mkdir build</tt> (for building without polluting the source dir)</li>
 156     <li><tt>cd build</tt></li>
 157     <li>If you are using Visual Studio 2005:  <tt>cmake -G "Visual Studio 8 2005" ..\llvm</tt></li>
 158     <li>Or if you are using Visual Studio 2008:  <tt>cmake -G "Visual Studio 9 2008" ..\llvm</tt></li>
 159     <li>Or if you are using Visual Studio 2010:  <tt>cmake -G "Visual Studio 10" ..\llvm</tt></li>
 160     <li>The above, if successful, will have created an LLVM.sln file in the
 161        llvm directory.
 162   </ul>
 163   <li>Build Clang:</li>
 164   <ul>
 165     <li>Open LLVM.sln in Visual Studio.</li>
 166     <li>Build the "clang" project for just the compiler driver and front end, or
 167       the "ALL_BUILD" project to build everything, including tools.</li>
 168   </ul>
 169   <li>Try it out (assuming you added llvm/debug/bin to your path).  (See the
 170     running examples from above.)</li>
 171   <li>See <a href="hacking.html#testingWindows">
 172      Hacking on clang - Testing using Visual Studio on Windows</a> for information
 173      on running regression tests on Windows.</li>
 174 </ol>
 175
 176 <p>Note that once you have checked out both llvm and clang, to synchronize
 177 to the latest code base, use the <tt>svn update</tt> command in both the
 178 llvm and llvm\tools\clang directories, as they are separate repositories.</p>
 179
 180 <a name="driver"><h2>Clang Compiler Driver (Drop-in Substitute for GCC)</h2></a>
 181
 182 <p>The <tt>clang</tt> tool is the compiler driver and front-end, which is
 183 designed to be a drop-in replacement for the <tt>gcc</tt> command.  Here are
 184 some examples of how to use the high-level driver:
 185 </p>
 186
 187 <pre class="code">
 188 $ <b>cat t.c</b>
 189 #include &lt;stdio.h&gt;
 190 int main(int argc, char **argv) { printf("hello world\n"); }
 191 $ <b>clang t.c</b>
 192 $ <b>./a.out</b>
 193 hello world
 194 </pre>
 195
 196 <p>The 'clang' driver is designed to work as closely to GCC as possible to
 197   maximize portability.  The only major difference between the two is that
 198   Clang defaults to gnu99 mode while GCC defaults to gnu89 mode.  If you see
 199   weird link-time errors relating to inline functions, try passing -std=gnu89
 200   to clang.</p>
 201
 202 <h2>Examples of using Clang</h2>
 203
 204 <!-- Thanks to
 205  http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings
 206 Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre>
 207 tag. -->
 208
 209 <pre class="code">
 210 $ <b>cat ~/t.c</b>
 211 typedef float V __attribute__((vector_size(16)));
 212 V foo(V a, V b) { return a+b*a; }
 213 </pre>
 214
 215
 216 <h3>Preprocessing:</h3>
 217
 218 <pre class="code">
 219 $ <b>clang ~/t.c -E</b>
 220 # 1 "/Users/sabre/t.c" 1
 221
 222 typedef float V __attribute__((vector_size(16)));
 223
 224 V foo(V a, V b) { return a+b*a; }
 225 </pre>
 226
 227
 228 <h3>Type checking:</h3>
 229
 230 <pre class="code">
 231 $ <b>clang -fsyntax-only ~/t.c</b>
 232 </pre>
 233
 234
 235 <h3>GCC options:</h3>
 236
 237 <pre class="code">
 238 $ <b>clang -fsyntax-only ~/t.c -pedantic</b>
 239 /Users/sabre/t.c:2:17: warning: extension used
 240 typedef float V __attribute__((vector_size(16)));
 241                 ^
 242 1 diagnostic generated.
 243 </pre>
 244
 245
 246 <h3>Pretty printing from the AST:</h3>
 247
 248 <p>Note, the <tt>-cc1</tt> argument indicates the the compiler front-end, and
 249 not the driver, should be run. The compiler front-end has several additional
 250 Clang specific features which are not exposed through the GCC compatible driver
 251 interface.</p>
 252
 253 <pre class="code">
 254 $ <b>clang -cc1 ~/t.c -ast-print</b>
 255 typedef float V __attribute__(( vector_size(16) ));
 256 V foo(V a, V b) {
 257    return a + b * a;
 258 }
 259 </pre>
 260
 261
 262 <h3>Code generation with LLVM:</h3>
 263
 264 <pre class="code">
 265 $ <b>clang ~/t.c -S -emit-llvm -o -</b>
 266 define &lt;4 x float&gt; @foo(&lt;4 x float&gt; %a, &lt;4 x float&gt; %b) {
 267 entry:
 268          %mul = mul &lt;4 x float&gt; %b, %a
 269          %add = add &lt;4 x float&gt; %mul, %a
 270          ret &lt;4 x float&gt; %add
 271 }
 272 $ <b>clang -fomit-frame-pointer -O3 -S -o - t.c</b> <i># On x86_64</i>
 273 ...
 274 _foo:
 275 Leh_func_begin1:
 276         mulps   %xmm0, %xmm1
 277         addps   %xmm1, %xmm0
 278         ret
 279 Leh_func_end1:
 280 </pre>
 281
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