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 on <a href="https://github.com/llvm/llvm-project/issues">the LLVM bug tracker</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     <li>The above command is very slow. It can be made faster by creating a shallow clone. Shallow clone saves storage and speeds up the checkout time. This is done by using the command:
  55       <ul>
  56         <li><tt>git clone --depth=1 https://github.com/llvm/llvm-project.git (using this only the latest version of llvm can be built)</tt></li>
  57         <li>For normal users looking to just compile, this command works fine. But if someone later becomes a contributor, since they can't push code from a shallow clone, it needs to be converted into a full clone:
  58           <ul>
  59             <li><tt>cd llvm-project</tt></li>
  60             <li><tt>git fetch --unshallow</tt></li>
  61           </ul>
  62         </li>
  63       </ul>
  64     </li>
  65   </ul>
  66   </li>
  67   <li>Build LLVM and Clang:
  68   <ul>
  69     <li><tt>cd llvm-project</tt></li>
  70     <li><tt>mkdir build</tt> (in-tree build is not supported)</li>
  71     <li><tt>cd build</tt></li>
  72     <li><tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" ../llvm</tt></li>
  73     <li><tt>make</tt></li>
  74     <li>This builds both LLVM and Clang for debug mode.</li>
  75     <li>Note: For subsequent Clang development, you can just run
  76         <tt>make clang</tt>.</li>
  77     <li>CMake allows you to generate project files for several IDEs: Xcode,
  78         Eclipse CDT4, CodeBlocks, Qt-Creator (use the CodeBlocks generator),
  79         KDevelop3. For more details see
  80         <a href="https://llvm.org/docs/CMake.html">Building LLVM with CMake</a>
  81         page.</li>
  82   </ul>
  83   </li>
  84
  85   <li>If you intend to use Clang's C++ support, you may need to tell it how
  86       to find your C++ standard library headers. In general, Clang will detect
  87       the best version of libstdc++ headers available and use them - it will
  88       look both for system installations of libstdc++ as well as installations
  89       adjacent to Clang itself. If your configuration fits neither of these
  90       scenarios, you can use the <tt>-DGCC_INSTALL_PREFIX</tt> cmake option
  91       to tell Clang where the gcc containing the desired libstdc++ is installed.
  92   </li>
  93   <li>Try it out (assuming you add llvm/build/bin to your path):
  94   <ul>
  95     <li><tt>clang --help</tt></li>
  96     <li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li>
  97     <li><tt>clang file.c -S -emit-llvm -o -</tt> (print out unoptimized llvm code)</li>
  98     <li><tt>clang file.c -S -emit-llvm -o - -O3</tt></li>
  99     <li><tt>clang file.c -S -O3 -o -</tt> (output native machine code)</li>
 100   </ul>
 101   </li>
 102   <li>Run the testsuite:
 103   <ul>
 104     <li><tt>make check-clang</tt></li>
 105   </ul>
 106   </li>
 107 </ol>
 108
 109 <h3 id="buildWindows">Using Visual Studio</h3>
 110
 111 <p>The following details setting up for and building Clang on Windows using
 112 Visual Studio:</p>
 113
 114 <ol>
 115   <li>Get the required tools:
 116   <ul>
 117     <li><b>Git</b>.  Source code control program.  Get it from:
 118         <a href="https://git-scm.com/download">
 119         https://git-scm.com/download</a></li>
 120     <li><b>CMake</b>.  This is used for generating Visual Studio solution and
 121         project files.  Get it from:
 122         <a href="https://cmake.org/download/">
 123         https://cmake.org/download/</a></li>
 124     <li><b>Visual Studio 2017 or later</b></li>
 125     <li><b>Python</b>.  It is used to run the clang test suite. Get it from:
 126         <a href="https://www.python.org/download/">
 127         https://www.python.org/download/</a></li>
 128     <li><b>GnuWin32 tools</b>
 129         The Clang and LLVM test suite use various GNU core utilities, such as
 130         <tt>grep</tt>, <tt>sed</tt>, and <tt>find</tt>. The gnuwin32 packages
 131         are the oldest and most well-tested way to get these tools. However, the
 132         MSys utilities provided by git for Windows have been known to work.
 133         Cygwin has worked in the past, but is not well tested.
 134         If you don't already have the core utilies from some other source, get
 135         gnuwin32 from <a href="http://getgnuwin32.sourceforge.net/">
 136         http://getgnuwin32.sourceforge.net/</a>.</li>
 137   </ul>
 138   </li>
 139
 140   <li>Check out LLVM and Clang:
 141   <ul>
 142     <li><tt>git clone https://github.com/llvm/llvm-project.git</tt></li>
 143   </ul>
 144   <p><em>Note</em>: Some Clang tests are sensitive to the line endings.  Ensure
 145      that checking out the files does not convert LF line endings to CR+LF.  If
 146      you're using git on Windows, make sure your <tt>core.autocrlf</tt> setting
 147      is false.</p>
 148   </li>
 149   <li>Run CMake to generate the Visual Studio solution and project files:
 150   <ul>
 151     <li><tt>cd llvm-project</tt></li>
 152     <li><tt>mkdir build</tt> (for building without polluting the source dir)</li>
 153     <li><tt>cd build</tt></li>
 154     <li>
 155       If you are using Visual Studio 2017:
 156       <tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Visual Studio 15 2017" -A x64 -Thost=x64 ..\llvm</tt><br/>
 157       <tt>-Thost=x64</tt> is required, since the 32-bit linker will run out of memory.
 158     </li>
 159     <li>To generate x86 binaries instead of x64, pass <tt>-A Win32</tt>.</li>
 160     <li>See the <a href="https://www.llvm.org/docs/CMake.html">LLVM CMake guide</a> for
 161         more information on other configuration options for CMake.</li>
 162     <li>The above, if successful, will have created an LLVM.sln file in the
 163        <tt>build</tt> directory.
 164   </ul>
 165   </li>
 166   <li>Build Clang:
 167   <ul>
 168     <li>Open LLVM.sln in Visual Studio.</li>
 169     <li>Build the "clang" project for just the compiler driver and front end, or
 170       the "ALL_BUILD" project to build everything, including tools.</li>
 171   </ul>
 172   </li>
 173   <li>Try it out (assuming you added llvm/debug/bin to your path).  (See the
 174     running examples from above.)</li>
 175   <li>See <a href="hacking.html#testingWindows">
 176      Hacking on clang - Testing using Visual Studio on Windows</a> for information
 177      on running regression tests on Windows.</li>
 178 </ol>
 179
 180 <h3 id="buildWindowsNinja">Using Ninja alongside Visual Studio</h3>
 181
 182 <p>We recommend that developers who want the fastest incremental builds use the
 183 <a href="https://ninja-build.org/">Ninja build system</a>. You can use the
 184 generated Visual Studio project files to edit Clang source code and generate a
 185 second build directory next to it for running the tests with these steps:</p>
 186
 187 <ol>
 188   <li>Check out clang and LLVM as described above</li>
 189   <li>Open a developer command prompt with the appropriate environment.
 190     <ul>
 191       <li>If you open the start menu and search for "Command Prompt", you should
 192         see shortcuts created by Visual Studio to do this. To use native x64
 193         tools, choose the one titled "x64 Native Tools Command Prompt for VS
 194         2017".</li>
 195       <li> Alternatively, launch a regular <tt>cmd</tt> prompt and run the
 196         appropriate vcvarsall.bat incantation. To get the 2017 x64 tools, this
 197         would be:<br/>
 198         <tt>"C:\Program Files (x86)\Microsoft Visual
 199           Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" x64</tt>
 200       </li>
 201     </ul>
 202   </li>
 203   <li><tt>mkdir build_ninja</tt> (or <tt>build</tt>, or use your own
 204     organization)</li>
 205   <li><tt>cd build_ninja</tt></li>
 206   <li><tt>set CC=cl</tt> (necessary to force CMake to choose MSVC over mingw GCC
 207     if you have it installed)</li>
 208   <li><tt>set CXX=cl</tt></li>
 209   <li><tt>cmake -GNinja -DLLVM_ENABLE_PROJECTS=clang ..\llvm</tt></li>
 210   <li><tt>ninja clang</tt> This will build just clang.</li>
 211   <li><tt>ninja check-clang</tt> This will run the clang tests.</li>
 212 </ol>
 213
 214 <h2 id="driver">Clang Compiler Driver (Drop-in Substitute for GCC)</h2>
 215
 216 <p>The <tt>clang</tt> tool is the compiler driver and front-end, which is
 217 designed to be a drop-in replacement for the <tt>gcc</tt> command.  Here are
 218 some examples of how to use the high-level driver:
 219 </p>
 220
 221 <pre class="code">
 222 $ <b>cat t.c</b>
 223 #include &lt;stdio.h&gt;
 224 int main(int argc, char **argv) { printf("hello world\n"); }
 225 $ <b>clang t.c</b>
 226 $ <b>./a.out</b>
 227 hello world
 228 </pre>
 229
 230 <p>The 'clang' driver is designed to work as closely to GCC as possible to
 231   maximize portability.  The only major difference between the two is that
 232   Clang defaults to gnu99 mode while GCC defaults to gnu89 mode.  If you see
 233   weird link-time errors relating to inline functions, try passing -std=gnu89
 234   to clang.</p>
 235
 236 <h2>Examples of using Clang</h2>
 237
 238 <!-- Thanks to
 239  http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings
 240 Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre>
 241 tag. -->
 242
 243 <pre class="code">
 244 $ <b>cat ~/t.c</b>
 245 typedef float V __attribute__((vector_size(16)));
 246 V foo(V a, V b) { return a+b*a; }
 247 </pre>
 248
 249
 250 <h3>Preprocessing:</h3>
 251
 252 <pre class="code">
 253 $ <b>clang ~/t.c -E</b>
 254 # 1 "/Users/sabre/t.c" 1
 255
 256 typedef float V __attribute__((vector_size(16)));
 257
 258 V foo(V a, V b) { return a+b*a; }
 259 </pre>
 260
 261
 262 <h3>Type checking:</h3>
 263
 264 <pre class="code">
 265 $ <b>clang -fsyntax-only ~/t.c</b>
 266 </pre>
 267
 268
 269 <h3>GCC options:</h3>
 270
 271 <pre class="code">
 272 $ <b>clang -fsyntax-only ~/t.c -pedantic</b>
 273 /Users/sabre/t.c:2:17: <span style="color:magenta">warning:</span> extension used
 274 <span style="color:darkgreen">typedef float V __attribute__((vector_size(16)));</span>
 275 <span style="color:blue">                ^</span>
 276 1 diagnostic generated.
 277 </pre>
 278
 279
 280 <h3>Pretty printing from the AST:</h3>
 281
 282 <p>Note, the <tt>-cc1</tt> argument indicates the compiler front-end, and
 283 not the driver, should be run. The compiler front-end has several additional
 284 Clang specific features which are not exposed through the GCC compatible driver
 285 interface.</p>
 286
 287 <pre class="code">
 288 $ <b>clang -cc1 ~/t.c -ast-print</b>
 289 typedef float V __attribute__(( vector_size(16) ));
 290 V foo(V a, V b) {
 291    return a + b * a;
 292 }
 293 </pre>
 294
 295
 296 <h3>Code generation with LLVM:</h3>
 297
 298 <pre class="code">
 299 $ <b>clang ~/t.c -S -emit-llvm -o -</b>
 300 define &lt;4 x float&gt; @foo(&lt;4 x float&gt; %a, &lt;4 x float&gt; %b) {
 301 entry:
 302          %mul = mul &lt;4 x float&gt; %b, %a
 303          %add = add &lt;4 x float&gt; %mul, %a
 304          ret &lt;4 x float&gt; %add
 305 }
 306 $ <b>clang -fomit-frame-pointer -O3 -S -o - t.c</b> <i># On x86_64</i>
 307 ...
 308 _foo:
 309 Leh_func_begin1:
 310         mulps   %xmm0, %xmm1
 311         addps   %xmm1, %xmm0
 312         ret
 313 Leh_func_end1:
 314 </pre>
 315
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