1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2 "http://www.w3.org/TR/html4/strict.dtd"> 3<html> 4<head> 5 <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 6 <title>Clang - Getting Started</title> 7 <link type="text/css" rel="stylesheet" href="menu.css"> 8 <link type="text/css" rel="stylesheet" href="content.css"> 9</head> 10<body> 11 12<!--#include virtual="menu.html.incl"--> 13 14<div id="content"> 15 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 19options. This should get you up and running with the minimum of muss and fuss. 20If you like what you see, please consider <a href="get_involved.html">getting 21involved</a> with the Clang community. If you run into problems, please file 22bugs 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 34follows:</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 101Visual 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 173generated Visual Studio project files to edit Clang source code and generate a 174second 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 206designed to be a drop-in replacement for the <tt>gcc</tt> command. Here are 207some examples of how to use the high-level driver: 208</p> 209 210<pre class="code"> 211$ <b>cat t.c</b> 212#include <stdio.h> 213int main(int argc, char **argv) { printf("hello world\n"); } 214$ <b>clang t.c</b> 215$ <b>./a.out</b> 216hello 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 229Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre> 230tag. --> 231 232<pre class="code"> 233$ <b>cat ~/t.c</b> 234typedef float V __attribute__((vector_size(16))); 235V 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 245typedef float V __attribute__((vector_size(16))); 246 247V 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> 2651 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 272not the driver, should be run. The compiler front-end has several additional 273Clang specific features which are not exposed through the GCC compatible driver 274interface.</p> 275 276<pre class="code"> 277$ <b>clang -cc1 ~/t.c -ast-print</b> 278typedef float V __attribute__(( vector_size(16) )); 279V 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> 289define <4 x float> @foo(<4 x float> %a, <4 x float> %b) { 290entry: 291 %mul = mul <4 x float> %b, %a 292 %add = add <4 x float> %mul, %a 293 ret <4 x float> %add 294} 295$ <b>clang -fomit-frame-pointer -O3 -S -o - t.c</b> <i># On x86_64</i> 296... 297_foo: 298Leh_func_begin1: 299 mulps %xmm0, %xmm1 300 addps %xmm1, %xmm0 301 ret 302Leh_func_end1: 303</pre> 304 305</div> 306</body> 307</html> 308