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 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 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 <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>This builds both LLVM and Clang in release mode. Alternatively, if 73 you need a debug build, switch Release to Debug. See 74 <a href="https://llvm.org/docs/CMake.html#frequently-used-cmake-variables">frequently used cmake variables</a> 75 for more options. 76 </li> 77 <li><tt>cmake -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_BUILD_TYPE=Release -G "Unix Makefiles" ../llvm</tt></li> 78 <li><tt>make</tt></li> 79 <li>Note: For subsequent Clang development, you can just run 80 <tt>make clang</tt>.</li> 81 <li>CMake allows you to generate project files for several IDEs: Xcode, 82 Eclipse CDT4, CodeBlocks, Qt-Creator (use the CodeBlocks generator), 83 KDevelop3. For more details see 84 <a href="https://llvm.org/docs/CMake.html">Building LLVM with CMake</a> 85 page.</li> 86 </ul> 87 </li> 88 89 <li>If you intend to use Clang's C++ support, you may need to tell it how 90 to find your C++ standard library headers. In general, Clang will detect 91 the best version of libstdc++ headers available and use them - it will 92 look both for system installations of libstdc++ as well as installations 93 adjacent to Clang itself. If your configuration fits neither of these 94 scenarios, you can use the <tt>-DGCC_INSTALL_PREFIX</tt> cmake option 95 to tell Clang where the gcc containing the desired libstdc++ is installed. 96 </li> 97 <li>Try it out (assuming you add llvm/build/bin to your path): 98 <ul> 99 <li><tt>clang --help</tt></li> 100 <li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li> 101 <li><tt>clang file.c -S -emit-llvm -o -</tt> (print out unoptimized llvm code)</li> 102 <li><tt>clang file.c -S -emit-llvm -o - -O3</tt></li> 103 <li><tt>clang file.c -S -O3 -o -</tt> (output native machine code)</li> 104 </ul> 105 </li> 106 <li>Run the testsuite: 107 <ul> 108 <li><tt>make check-clang</tt></li> 109 </ul> 110 </li> 111</ol> 112 113<h3 id="buildWindows">Using Visual Studio</h3> 114 115<p>The following details setting up for and building Clang on Windows using 116Visual Studio:</p> 117 118<ol> 119 <li>Get the required tools: 120 <ul> 121 <li><b>Git</b>. Source code control program. Get it from: 122 <a href="https://git-scm.com/download"> 123 https://git-scm.com/download</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="https://cmake.org/download/"> 127 https://cmake.org/download/</a></li> 128 <li><b>Visual Studio 2017 or later</b></li> 129 <li><b>Python</b>. It is used to run the clang test suite. Get it from: 130 <a href="https://www.python.org/download/"> 131 https://www.python.org/download/</a></li> 132 <li><b>GnuWin32 tools</b> 133 The Clang and LLVM test suite use various GNU core utilities, such as 134 <tt>grep</tt>, <tt>sed</tt>, and <tt>find</tt>. The gnuwin32 packages 135 are the oldest and most well-tested way to get these tools. However, the 136 MSys utilities provided by git for Windows have been known to work. 137 Cygwin has worked in the past, but is not well tested. 138 If you don't already have the core utilies from some other source, get 139 gnuwin32 from <a href="http://getgnuwin32.sourceforge.net/"> 140 http://getgnuwin32.sourceforge.net/</a>.</li> 141 </ul> 142 </li> 143 144 <li>Check out LLVM and Clang: 145 <ul> 146 <li><tt>git clone https://github.com/llvm/llvm-project.git</tt></li> 147 </ul> 148 <p><em>Note</em>: Some Clang tests are sensitive to the line endings. Ensure 149 that checking out the files does not convert LF line endings to CR+LF. If 150 you're using git on Windows, make sure your <tt>core.autocrlf</tt> setting 151 is false.</p> 152 </li> 153 <li>Run CMake to generate the Visual Studio solution and project files: 154 <ul> 155 <li><tt>cd llvm-project</tt></li> 156 <li><tt>mkdir build</tt> (for building without polluting the source dir)</li> 157 <li><tt>cd build</tt></li> 158 <li> 159 If you are using Visual Studio 2017: 160 <tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Visual Studio 15 2017" -A x64 -Thost=x64 ..\llvm</tt><br/> 161 <tt>-Thost=x64</tt> is required, since the 32-bit linker will run out of memory. 162 </li> 163 <li>To generate x86 binaries instead of x64, pass <tt>-A Win32</tt>.</li> 164 <li>See the <a href="https://www.llvm.org/docs/CMake.html">LLVM CMake guide</a> for 165 more information on other configuration options for CMake.</li> 166 <li>The above, if successful, will have created an LLVM.sln file in the 167 <tt>build</tt> directory. 168 </ul> 169 </li> 170 <li>Build Clang: 171 <ul> 172 <li>Open LLVM.sln in Visual Studio.</li> 173 <li>Build the "clang" project for just the compiler driver and front end, or 174 the "ALL_BUILD" project to build everything, including tools.</li> 175 </ul> 176 </li> 177 <li>Try it out (assuming you added llvm/debug/bin to your path). (See the 178 running examples from above.)</li> 179 <li>See <a href="hacking.html#testingWindows"> 180 Hacking on clang - Testing using Visual Studio on Windows</a> for information 181 on running regression tests on Windows.</li> 182</ol> 183 184<h3 id="buildWindowsNinja">Using Ninja alongside Visual Studio</h3> 185 186<p>We recommend that developers who want the fastest incremental builds use the 187<a href="https://ninja-build.org/">Ninja build system</a>. You can use the 188generated Visual Studio project files to edit Clang source code and generate a 189second build directory next to it for running the tests with these steps:</p> 190 191<ol> 192 <li>Check out clang and LLVM as described above</li> 193 <li>Open a developer command prompt with the appropriate environment. 194 <ul> 195 <li>If you open the start menu and search for "Command Prompt", you should 196 see shortcuts created by Visual Studio to do this. To use native x64 197 tools, choose the one titled "x64 Native Tools Command Prompt for VS 198 2017".</li> 199 <li> Alternatively, launch a regular <tt>cmd</tt> prompt and run the 200 appropriate vcvarsall.bat incantation. To get the 2017 x64 tools, this 201 would be:<br/> 202 <tt>"C:\Program Files (x86)\Microsoft Visual 203 Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" x64</tt> 204 </li> 205 </ul> 206 </li> 207 <li><tt>mkdir build_ninja</tt> (or <tt>build</tt>, or use your own 208 organization)</li> 209 <li><tt>cd build_ninja</tt></li> 210 <li><tt>set CC=cl</tt> (necessary to force CMake to choose MSVC over mingw GCC 211 if you have it installed)</li> 212 <li><tt>set CXX=cl</tt></li> 213 <li><tt>cmake -GNinja -DLLVM_ENABLE_PROJECTS=clang ..\llvm</tt></li> 214 <li><tt>ninja clang</tt> This will build just clang.</li> 215 <li><tt>ninja check-clang</tt> This will run the clang tests.</li> 216</ol> 217 218<h2 id="driver">Clang Compiler Driver (Drop-in Substitute for GCC)</h2> 219 220<p>The <tt>clang</tt> tool is the compiler driver and front-end, which is 221designed to be a drop-in replacement for the <tt>gcc</tt> command. Here are 222some examples of how to use the high-level driver: 223</p> 224 225<pre class="code"> 226$ <b>cat t.c</b> 227#include <stdio.h> 228int main(int argc, char **argv) { printf("hello world\n"); } 229$ <b>clang t.c</b> 230$ <b>./a.out</b> 231hello world 232</pre> 233 234<p>The 'clang' driver is designed to work as closely to GCC as possible to 235 maximize portability. The only major difference between the two is that 236 Clang defaults to gnu99 mode while GCC defaults to gnu89 mode. If you see 237 weird link-time errors relating to inline functions, try passing -std=gnu89 238 to clang.</p> 239 240<h2>Examples of using Clang</h2> 241 242<!-- Thanks to 243 http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings 244Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre> 245tag. --> 246 247<pre class="code"> 248$ <b>cat ~/t.c</b> 249typedef float V __attribute__((vector_size(16))); 250V foo(V a, V b) { return a+b*a; } 251</pre> 252 253 254<h3>Preprocessing:</h3> 255 256<pre class="code"> 257$ <b>clang ~/t.c -E</b> 258# 1 "/Users/sabre/t.c" 1 259 260typedef float V __attribute__((vector_size(16))); 261 262V foo(V a, V b) { return a+b*a; } 263</pre> 264 265 266<h3>Type checking:</h3> 267 268<pre class="code"> 269$ <b>clang -fsyntax-only ~/t.c</b> 270</pre> 271 272 273<h3>GCC options:</h3> 274 275<pre class="code"> 276$ <b>clang -fsyntax-only ~/t.c -pedantic</b> 277/Users/sabre/t.c:2:17: <span style="color:magenta">warning:</span> extension used 278<span style="color:darkgreen">typedef float V __attribute__((vector_size(16)));</span> 279<span style="color:blue"> ^</span> 2801 diagnostic generated. 281</pre> 282 283 284<h3>Pretty printing from the AST:</h3> 285 286<p>Note, the <tt>-cc1</tt> argument indicates the compiler front-end, and 287not the driver, should be run. The compiler front-end has several additional 288Clang specific features which are not exposed through the GCC compatible driver 289interface.</p> 290 291<pre class="code"> 292$ <b>clang -cc1 ~/t.c -ast-print</b> 293typedef float V __attribute__(( vector_size(16) )); 294V foo(V a, V b) { 295 return a + b * a; 296} 297</pre> 298 299 300<h3>Code generation with LLVM:</h3> 301 302<pre class="code"> 303$ <b>clang ~/t.c -S -emit-llvm -o -</b> 304define <4 x float> @foo(<4 x float> %a, <4 x float> %b) { 305entry: 306 %mul = mul <4 x float> %b, %a 307 %add = add <4 x float> %mul, %a 308 ret <4 x float> %add 309} 310$ <b>clang -fomit-frame-pointer -O3 -S -o - t.c</b> <i># On x86_64</i> 311... 312_foo: 313Leh_func_begin1: 314 mulps %xmm0, %xmm1 315 addps %xmm1, %xmm0 316 ret 317Leh_func_end1: 318</pre> 319 320</div> 321</body> 322</html> 323