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| <h1>Getting Started: Building and Running Clang</h1> |
| |
| <p>This page gives you the shortest path to checking out Clang and demos a few |
| options. This should get you up and running with the minimum of muss and fuss. |
| If you like what you see, please consider <a href="get_involved.html">getting |
| involved</a> with the Clang community. If you run into problems, please file |
| bugs on <a href="https://github.com/llvm/llvm-project/issues">the LLVM bug tracker</a>.</p> |
| |
| <h2 id="download">Release Clang Versions</h2> |
| |
| <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> |
| <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> |
| |
| <h2 id="build">Building Clang and Working with the Code</h2> |
| |
| <h3 id="buildNix">On Unix-like Systems</h3> |
| |
| <p>If you would like to check out and build Clang, the current procedure is as |
| follows:</p> |
| |
| <ol> |
| <li>Get the required tools. |
| <ul> |
| <li>See |
| <a href="https://llvm.org/docs/GettingStarted.html#requirements"> |
| Getting Started with the LLVM System - Requirements</a>.</li> |
| <li>Note also that Python is needed for running the test suite. |
| Get it at: <a href="https://www.python.org/downloads/"> |
| https://www.python.org/downloads/</a></li> |
| <li>Standard build process uses CMake. Get it at: |
| <a href="https://cmake.org/download/"> |
| https://cmake.org/download/</a></li> |
| </ul> |
| |
| <li>Check out the LLVM project: |
| <ul> |
| <li>Change directory to where you want the llvm directory placed.</li> |
| <li><tt>git clone https://github.com/llvm/llvm-project.git</tt></li> |
| <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: |
| <ul> |
| <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> |
| <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: |
| <ul> |
| <li><tt>cd llvm-project</tt></li> |
| <li><tt>git fetch --unshallow</tt></li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| <li>Build LLVM and Clang: |
| <ul> |
| <li><tt>cd llvm-project</tt></li> |
| <li><tt>mkdir build</tt> (in-tree build is not supported)</li> |
| <li><tt>cd build</tt></li> |
| <li>This builds both LLVM and Clang in release mode. Alternatively, if |
| you need a debug build, switch Release to Debug. See |
| <a href="https://llvm.org/docs/CMake.html#frequently-used-cmake-variables">frequently used cmake variables</a> |
| for more options. |
| </li> |
| <li><tt>cmake -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_BUILD_TYPE=Release -G "Unix Makefiles" ../llvm</tt></li> |
| <li><tt>make</tt></li> |
| <li>Note: For subsequent Clang development, you can just run |
| <tt>make clang</tt>.</li> |
| <li>CMake allows you to generate project files for several IDEs: Xcode, |
| Eclipse CDT4, CodeBlocks, Qt-Creator (use the CodeBlocks generator), |
| KDevelop3. For more details see |
| <a href="https://llvm.org/docs/CMake.html">Building LLVM with CMake</a> |
| page.</li> |
| </ul> |
| </li> |
| |
| <li>On Linux, you may need GCC runtime libraries (e.g. <tt>crtbeginS.o, |
| libstdc++.so</tt>) and libstdc++ headers. In general, Clang will detect |
| well-known GCC installation paths matching the target triple (configured at |
| build time (see <tt>clang --version</tt>); overriden by |
| <tt>--target=</tt>) and use the largest version. If your configuration fits |
| none of the standard scenarios, you can set <tt>--gcc-install-dir=</tt> to |
| the GCC installation directory (something like |
| <tt>/usr/lib/gcc/$triple/$major</tt>). If your GCC installation is under |
| <tt>/usr/lib/gcc</tt> but uses a different triple, you can set |
| <tt>--gcc-triple=$triple</tt>. |
| </li> |
| <li>Try it out (assuming you add llvm/build/bin to your path): |
| <ul> |
| <li><tt>clang --help</tt></li> |
| <li><tt>clang file.c -fsyntax-only</tt> (check for correctness)</li> |
| <li><tt>clang file.c -S -emit-llvm -o -</tt> (print out unoptimized llvm code)</li> |
| <li><tt>clang file.c -S -emit-llvm -o - -O3</tt></li> |
| <li><tt>clang file.c -S -O3 -o -</tt> (output native machine code)</li> |
| </ul> |
| </li> |
| <li>Run the testsuite: |
| <ul> |
| <li><tt>make check-clang</tt></li> |
| </ul> |
| </li> |
| </ol> |
| |
| <h3 id="buildWindows">Using Visual Studio</h3> |
| |
| <p>The following details setting up for and building Clang on Windows using |
| Visual Studio:</p> |
| |
| <ol> |
| <li>Get the required tools: |
| <ul> |
| <li><b>Git</b>. Source code control program. Get it from: |
| <a href="https://git-scm.com/download"> |
| https://git-scm.com/download</a></li> |
| <li><b>CMake</b>. This is used for generating Visual Studio solution and |
| project files. Get it from: |
| <a href="https://cmake.org/download/"> |
| https://cmake.org/download/</a></li> |
| <li><b>Visual Studio 2019 16.7 or later</b></li> |
| <li><b>Python</b>. It is used to run the clang test suite. Get it from: |
| <a href="https://www.python.org/download/"> |
| https://www.python.org/download/</a></li> |
| <li><b>GnuWin32 tools</b> |
| The Clang and LLVM test suite use various GNU core utilities, such as |
| <tt>grep</tt>, <tt>sed</tt>, and <tt>find</tt>. The gnuwin32 packages |
| are the oldest and most well-tested way to get these tools. However, the |
| MSys utilities provided by git for Windows have been known to work. |
| Cygwin has worked in the past, but is not well tested. |
| If you don't already have the core utilies from some other source, get |
| gnuwin32 from <a href="http://getgnuwin32.sourceforge.net/"> |
| http://getgnuwin32.sourceforge.net/</a>.</li> |
| </ul> |
| </li> |
| |
| <li>Check out LLVM and Clang: |
| <ul> |
| <li><tt>git clone https://github.com/llvm/llvm-project.git</tt></li> |
| </ul> |
| <p><em>Note</em>: Some Clang tests are sensitive to the line endings. Ensure |
| that checking out the files does not convert LF line endings to CR+LF. If |
| you're using git on Windows, make sure your <tt>core.autocrlf</tt> setting |
| is false.</p> |
| </li> |
| <li>Run CMake to generate the Visual Studio solution and project files: |
| <ul> |
| <li><tt>cd llvm-project</tt></li> |
| <li><tt>mkdir build</tt> (for building without polluting the source dir)</li> |
| <li><tt>cd build</tt></li> |
| <li> |
| If you are using Visual Studio 2019: |
| <tt>cmake -DLLVM_ENABLE_PROJECTS=clang -G "Visual Studio 16 2019" -A x64 -Thost=x64 ..\llvm</tt><br/> |
| <tt>-Thost=x64</tt> is required, since the 32-bit linker will run out of memory. |
| </li> |
| <li>To generate x86 binaries instead of x64, pass <tt>-A Win32</tt>.</li> |
| <li>See the <a href="https://www.llvm.org/docs/CMake.html">LLVM CMake guide</a> for |
| more information on other configuration options for CMake.</li> |
| <li>The above, if successful, will have created an LLVM.sln file in the |
| <tt>build</tt> directory. |
| </ul> |
| </li> |
| <li>Build Clang: |
| <ul> |
| <li>Open LLVM.sln in Visual Studio.</li> |
| <li>Build the "clang" project for just the compiler driver and front end, or |
| the "ALL_BUILD" project to build everything, including tools.</li> |
| </ul> |
| </li> |
| <li>Try it out (assuming you added llvm/debug/bin to your path). (See the |
| running examples from above.)</li> |
| <li>See <a href="hacking.html#testingWindows"> |
| Hacking on clang - Testing using Visual Studio on Windows</a> for information |
| on running regression tests on Windows.</li> |
| </ol> |
| |
| <h3 id="buildWindowsNinja">Using Ninja alongside Visual Studio</h3> |
| |
| <p>We recommend that developers who want the fastest incremental builds use the |
| <a href="https://ninja-build.org/">Ninja build system</a>. You can use the |
| generated Visual Studio project files to edit Clang source code and generate a |
| second build directory next to it for running the tests with these steps:</p> |
| |
| <ol> |
| <li>Check out clang and LLVM as described above</li> |
| <li>Open a developer command prompt with the appropriate environment. |
| <ul> |
| <li>If you open the start menu and search for "Command Prompt", you should |
| see shortcuts created by Visual Studio to do this. To use native x64 |
| tools, choose the one titled "x64 Native Tools Command Prompt for VS |
| 2017".</li> |
| <li> Alternatively, launch a regular <tt>cmd</tt> prompt and run the |
| appropriate vcvarsall.bat incantation. To get the 2017 x64 tools, this |
| would be:<br/> |
| <tt>"C:\Program Files (x86)\Microsoft Visual |
| Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" x64</tt> |
| </li> |
| </ul> |
| </li> |
| <li><tt>mkdir build_ninja</tt> (or <tt>build</tt>, or use your own |
| organization)</li> |
| <li><tt>cd build_ninja</tt></li> |
| <li><tt>set CC=cl</tt> (necessary to force CMake to choose MSVC over mingw GCC |
| if you have it installed)</li> |
| <li><tt>set CXX=cl</tt></li> |
| <li><tt>cmake -GNinja -DLLVM_ENABLE_PROJECTS=clang ..\llvm</tt></li> |
| <li><tt>ninja clang</tt> This will build just clang.</li> |
| <li><tt>ninja check-clang</tt> This will run the clang tests.</li> |
| </ol> |
| |
| <h2 id="driver">Clang Compiler Driver (Drop-in Substitute for GCC)</h2> |
| |
| <p>The <tt>clang</tt> tool is the compiler driver and front-end, which is |
| designed to be a drop-in replacement for the <tt>gcc</tt> command. Here are |
| some examples of how to use the high-level driver: |
| </p> |
| |
| <pre class="code"> |
| $ <b>cat t.c</b> |
| #include <stdio.h> |
| int main(int argc, char **argv) { printf("hello world\n"); } |
| $ <b>clang t.c</b> |
| $ <b>./a.out</b> |
| hello world |
| </pre> |
| |
| <p>The 'clang' driver is designed to work as closely to GCC as possible to |
| maximize portability. The only major difference between the two is that |
| Clang defaults to gnu99 mode while GCC defaults to gnu89 mode. If you see |
| weird link-time errors relating to inline functions, try passing -std=gnu89 |
| to clang.</p> |
| |
| <h2>Examples of using Clang</h2> |
| |
| <!-- Thanks to |
| http://shiflett.org/blog/2006/oct/formatting-and-highlighting-php-code-listings |
| Site suggested using pre in CSS, but doesn't work in IE, so went for the <pre> |
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| |
| <pre class="code"> |
| $ <b>cat ~/t.c</b> |
| typedef float V __attribute__((vector_size(16))); |
| V foo(V a, V b) { return a+b*a; } |
| </pre> |
| |
| |
| <h3>Preprocessing:</h3> |
| |
| <pre class="code"> |
| $ <b>clang ~/t.c -E</b> |
| # 1 "/Users/sabre/t.c" 1 |
| |
| typedef float V __attribute__((vector_size(16))); |
| |
| V foo(V a, V b) { return a+b*a; } |
| </pre> |
| |
| |
| <h3>Type checking:</h3> |
| |
| <pre class="code"> |
| $ <b>clang -fsyntax-only ~/t.c</b> |
| </pre> |
| |
| |
| <h3>GCC options:</h3> |
| |
| <pre class="code"> |
| $ <b>clang -fsyntax-only ~/t.c -pedantic</b> |
| /Users/sabre/t.c:2:17: <span style="color:magenta">warning:</span> extension used |
| <span style="color:darkgreen">typedef float V __attribute__((vector_size(16)));</span> |
| <span style="color:blue"> ^</span> |
| 1 diagnostic generated. |
| </pre> |
| |
| |
| <h3>Pretty printing from the AST:</h3> |
| |
| <p>Note, the <tt>-cc1</tt> argument indicates the compiler front-end, and |
| not the driver, should be run. The compiler front-end has several additional |
| Clang specific features which are not exposed through the GCC compatible driver |
| interface.</p> |
| |
| <pre class="code"> |
| $ <b>clang -cc1 ~/t.c -ast-print</b> |
| typedef float V __attribute__(( vector_size(16) )); |
| V foo(V a, V b) { |
| return a + b * a; |
| } |
| </pre> |
| |
| |
| <h3>Code generation with LLVM:</h3> |
| |
| <pre class="code"> |
| $ <b>clang ~/t.c -S -emit-llvm -o -</b> |
| define <4 x float> @foo(<4 x float> %a, <4 x float> %b) { |
| entry: |
| %mul = mul <4 x float> %b, %a |
| %add = add <4 x float> %mul, %a |
| ret <4 x float> %add |
| } |
| $ <b>clang -fomit-frame-pointer -O3 -S -o - t.c</b> <i># On x86_64</i> |
| ... |
| _foo: |
| Leh_func_begin1: |
| mulps %xmm0, %xmm1 |
| addps %xmm1, %xmm0 |
| ret |
| Leh_func_end1: |
| </pre> |
| |
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