clang/www/get_started.html

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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="https://bugs.llvm.org/">LLVM Bugzilla</a>.</p>
  23
  24 <h2 id="download">Release Clang Versions</h2>
  25
  26 <p>Clang is released as part of regular LLVM releases. You can download the release versions from <a href="https://llvm.org/releases/">https://llvm.org/releases/</a>.</p>
  27 <p>Clang is also provided in all major BSD or GNU/Linux distributions as part of their respective packaging systems. From Xcode 4.2, Clang is the default compiler for Mac OS X.</p>
  28
  29 <h2 id="build">Building Clang and Working with the Code</h2>
  30
  31 <h3 id="buildNix">On Unix-like Systems</h3>
  32
  33 <p>If you would like to check out and build Clang, the current procedure is as
  34 follows:</p>
  35
  36 <ol>
  37   <li>Get the required tools.
  38   <ul>
  39     <li>See
  40       <a href="https://llvm.org/docs/GettingStarted.html#requirements">
  41       Getting Started with the LLVM System - Requirements</a>.</li>
  42     <li>Note also that Python is needed for running the test suite.
  43       Get it at: <a href="https://www.python.org/downloads/">
  44       https://www.python.org/downloads/</a></li>
  45     <li>Standard build process uses CMake. Get it at:
  46       <a href="https://cmake.org/download/">
  47       https://cmake.org/download/</a></li>
  48   </ul>
  49
  50   <li>Check out the LLVM project:
  51   <ul>
  52     <li>Change directory to where you want the llvm directory placed.</li>
  53     <li><tt>git clone https://github.com/llvm/llvm-project.git</tt></li>
  54   </ul>
  55   </li>
  56   <li>Build LLVM and Clang:
  57   <ul>
  58     <li><tt>cd llvm-project</tt></li>
  59     <li><tt>mkdir build</tt> (in-tree build is not supported)</li>
  60     <li><tt>cd build</tt></li>
  61     <li><tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" ../llvm</tt></li>
  62     <li><tt>make</tt></li>
  63     <li>This builds both LLVM and Clang for debug mode.</li>
  64     <li>Note: For subsequent Clang development, you can just run
  65         <tt>make clang</tt>.</li>
  66     <li>CMake allows you to generate project files for several IDEs: Xcode,
  67         Eclipse CDT4, CodeBlocks, Qt-Creator (use the CodeBlocks generator),
  68         KDevelop3. For more details see
  69         <a href="https://llvm.org/docs/CMake.html">Building LLVM with CMake</a>
  70         page.</li>
  71   </ul>
  72   </li>
  73
  74   <li>If you intend to use Clang's C++ support, you may need to tell it how
  75       to find your C++ standard library headers. In general, Clang will detect
  76       the best version of libstdc++ headers available and use them - it will
  77       look both for system installations of libstdc++ as well as installations
  78       adjacent to Clang itself. If your configuration fits neither of these
  79       scenarios, you can use the <tt>-DGCC_INSTALL_PREFIX</tt> cmake option
  80       to tell Clang where the gcc containing the desired libstdc++ is installed.
  81   </li>
  82   <li>Try it out (assuming you add llvm/build/bin to your path):
  83   <ul>
  84     <li><tt>clang --help</tt></li>
  85     <li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li>
  86     <li><tt>clang file.c -S -emit-llvm -o -</tt> (print out unoptimized llvm code)</li>
  87     <li><tt>clang file.c -S -emit-llvm -o - -O3</tt></li>
  88     <li><tt>clang file.c -S -O3 -o -</tt> (output native machine code)</li>
  89   </ul>
  90   </li>
  91   <li>Run the testsuite:
  92   <ul>
  93     <li><tt>make check-clang</tt></li>
  94   </ul>
  95   </li>
  96 </ol>
  97
  98 <h3 id="buildWindows">Using Visual Studio</h3>
  99
 100 <p>The following details setting up for and building Clang on Windows using
 101 Visual Studio:</p>
 102
 103 <ol>
 104   <li>Get the required tools:
 105   <ul>
 106     <li><b>Git</b>.  Source code control program.  Get it from:
 107         <a href="https://git-scm.com/download">
 108         https://git-scm.com/download</a></li>
 109     <li><b>CMake</b>.  This is used for generating Visual Studio solution and
 110         project files.  Get it from:
 111         <a href="https://cmake.org/download/">
 112         https://cmake.org/download/</a></li>
 113     <li><b>Visual Studio 2017 or later</b></li>
 114     <li><b>Python</b>.  It is used to run the clang test suite. Get it from:
 115         <a href="https://www.python.org/download/">
 116         https://www.python.org/download/</a></li>
 117     <li><b>GnuWin32 tools</b>
 118         The Clang and LLVM test suite use various GNU core utilities, such as
 119         <tt>grep</tt>, <tt>sed</tt>, and <tt>find</tt>. The gnuwin32 packages
 120         are the oldest and most well-tested way to get these tools. However, the
 121         MSys utilities provided by git for Windows have been known to work.
 122         Cygwin has worked in the past, but is not well tested.
 123         If you don't already have the core utilies from some other source, get
 124         gnuwin32 from <a href="http://getgnuwin32.sourceforge.net/">
 125         http://getgnuwin32.sourceforge.net/</a>.</li>
 126   </ul>
 127   </li>
 128
 129   <li>Check out LLVM and Clang:
 130   <ul>
 131     <li><tt>git clone https://github.com/llvm/llvm-project.git</tt></li>
 132   </ul>
 133   <p><em>Note</em>: Some Clang tests are sensitive to the line endings.  Ensure
 134      that checking out the files does not convert LF line endings to CR+LF.  If
 135      you're using git on Windows, make sure your <tt>core.autocrlf</tt> setting
 136      is false.</p>
 137   </li>
 138   <li>Run CMake to generate the Visual Studio solution and project files:
 139   <ul>
 140     <li><tt>cd ..\..</tt>  (back to where you started)</li>
 141     <li><tt>mkdir build</tt> (for building without polluting the source dir)</li>
 142     <li><tt>cd build</tt></li>
 143     <li>
 144       If you are using Visual Studio 2017:
 145       <tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Visual Studio 15 2017" -A x64 -Thost=x64 ..\llvm</tt><br/>
 146       <tt>-Thost=x64</tt> is required, since the 32-bit linker will run out of memory.
 147     </li>
 148     <li>To generate x86 binaries instead of x64, pass <tt>-A Win32</tt>.</li>
 149     <li>See the <a href="https://www.llvm.org/docs/CMake.html">LLVM CMake guide</a> for
 150         more information on other configuration options for CMake.</li>
 151     <li>The above, if successful, will have created an LLVM.sln file in the
 152        <tt>build</tt> directory.
 153   </ul>
 154   </li>
 155   <li>Build Clang:
 156   <ul>
 157     <li>Open LLVM.sln in Visual Studio.</li>
 158     <li>Build the "clang" project for just the compiler driver and front end, or
 159       the "ALL_BUILD" project to build everything, including tools.</li>
 160   </ul>
 161   </li>
 162   <li>Try it out (assuming you added llvm/debug/bin to your path).  (See the
 163     running examples from above.)</li>
 164   <li>See <a href="hacking.html#testingWindows">
 165      Hacking on clang - Testing using Visual Studio on Windows</a> for information
 166      on running regression tests on Windows.</li>
 167 </ol>
 168
 169 <h3 id="buildWindowsNinja">Using Ninja alongside Visual Studio</h3>
 170
 171 <p>We recommend that developers who want the fastest incremental builds use the
 172 <a href="https://ninja-build.org/">Ninja build system</a>. You can use the
 173 generated Visual Studio project files to edit Clang source code and generate a
 174 second build directory next to it for running the tests with these steps:</p>
 175
 176 <ol>
 177   <li>Check out clang and LLVM as described above</li>
 178   <li>Open a developer command prompt with the appropriate environment.
 179     <ul>
 180       <li>If you open the start menu and search for "Command Prompt", you should
 181         see shortcuts created by Visual Studio to do this. To use native x64
 182         tools, choose the one titled "x64 Native Tools Command Prompt for VS
 183         2017".</li>
 184       <li> Alternatively, launch a regular <tt>cmd</tt> prompt and run the
 185         appropriate vcvarsall.bat incantation. To get the 2017 x64 tools, this
 186         would be:<br/>
 187         <tt>"C:\Program Files (x86)\Microsoft Visual
 188           Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" x64</tt>
 189       </li>
 190     </ul>
 191   </li>
 192   <li><tt>mkdir build_ninja</tt> (or <tt>build</tt>, or use your own
 193     organization)</li>
 194   <li><tt>cd build_ninja</tt></li>
 195   <li><tt>set CC=cl</tt> (necessary to force CMake to choose MSVC over mingw GCC
 196     if you have it installed)</li>
 197   <li><tt>set CXX=cl</tt></li>
 198   <li><tt>cmake -GNinja ..\llvm</tt></li>
 199   <li><tt>ninja clang</tt> This will build just clang.</li>
 200   <li><tt>ninja check-clang</tt> This will run the clang tests.</li>
 201 </ol>
 202
 203 <h2 id="driver">Clang Compiler Driver (Drop-in Substitute for GCC)</h2>
 204
 205 <p>The <tt>clang</tt> tool is the compiler driver and front-end, which is
 206 designed to be a drop-in replacement for the <tt>gcc</tt> command.  Here are
 207 some examples of how to use the high-level driver:
 208 </p>
 209
 210 <pre class="code">
 211 $ <b>cat t.c</b>
 212 #include &lt;stdio.h&gt;
 213 int main(int argc, char **argv) { printf("hello world\n"); }
 214 $ <b>clang t.c</b>
 215 $ <b>./a.out</b>
 216 hello world
 217 </pre>
 218
 219 <p>The 'clang' driver is designed to work as closely to GCC as possible to
 220   maximize portability.  The only major difference between the two is that
 221   Clang defaults to gnu99 mode while GCC defaults to gnu89 mode.  If you see
 222   weird link-time errors relating to inline functions, try passing -std=gnu89
 223   to clang.</p>
 224
 225 <h2>Examples of using Clang</h2>
 226
 227 <!-- Thanks to
 228  http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings
 229 Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre>
 230 tag. -->
 231
 232 <pre class="code">
 233 $ <b>cat ~/t.c</b>
 234 typedef float V __attribute__((vector_size(16)));
 235 V foo(V a, V b) { return a+b*a; }
 236 </pre>
 237
 238
 239 <h3>Preprocessing:</h3>
 240
 241 <pre class="code">
 242 $ <b>clang ~/t.c -E</b>
 243 # 1 "/Users/sabre/t.c" 1
 244
 245 typedef float V __attribute__((vector_size(16)));
 246
 247 V foo(V a, V b) { return a+b*a; }
 248 </pre>
 249
 250
 251 <h3>Type checking:</h3>
 252
 253 <pre class="code">
 254 $ <b>clang -fsyntax-only ~/t.c</b>
 255 </pre>
 256
 257
 258 <h3>GCC options:</h3>
 259
 260 <pre class="code">
 261 $ <b>clang -fsyntax-only ~/t.c -pedantic</b>
 262 /Users/sabre/t.c:2:17: <span style="color:magenta">warning:</span> extension used
 263 <span style="color:darkgreen">typedef float V __attribute__((vector_size(16)));</span>
 264 <span style="color:blue">                ^</span>
 265 1 diagnostic generated.
 266 </pre>
 267
 268
 269 <h3>Pretty printing from the AST:</h3>
 270
 271 <p>Note, the <tt>-cc1</tt> argument indicates the compiler front-end, and
 272 not the driver, should be run. The compiler front-end has several additional
 273 Clang specific features which are not exposed through the GCC compatible driver
 274 interface.</p>
 275
 276 <pre class="code">
 277 $ <b>clang -cc1 ~/t.c -ast-print</b>
 278 typedef float V __attribute__(( vector_size(16) ));
 279 V foo(V a, V b) {
 280    return a + b * a;
 281 }
 282 </pre>
 283
 284
 285 <h3>Code generation with LLVM:</h3>
 286
 287 <pre class="code">
 288 $ <b>clang ~/t.c -S -emit-llvm -o -</b>
 289 define &lt;4 x float&gt; @foo(&lt;4 x float&gt; %a, &lt;4 x float&gt; %b) {
 290 entry:
 291          %mul = mul &lt;4 x float&gt; %b, %a
 292          %add = add &lt;4 x float&gt; %mul, %a
 293          ret &lt;4 x float&gt; %add
 294 }
 295 $ <b>clang -fomit-frame-pointer -O3 -S -o - t.c</b> <i># On x86_64</i>
 296 ...
 297 _foo:
 298 Leh_func_begin1:
 299         mulps   %xmm0, %xmm1
 300         addps   %xmm1, %xmm0
 301         ret
 302 Leh_func_end1:
 303 </pre>
 304
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