Daniel Duan's Articles About swift

Daniel Duan's Articles About swift https://duan.ca/tag/swift/ Let's Play LLVM in Swift: Setup The prospect of Swift being open-source excites me. In preparation for it, I decided to learn a little bit about LLVM. In the offical <a href="http://llvm.org/docs/tutorial/index.html">tutorial</a>, C++ and OCaml are used to create a programming language. So I asked myself: why not Swift? As you'll see in this post, Swift is as good as any language when it comes to leveraging LLVM. LLVM is an "compiler infrastructure". As a user, that translates to "a set of libraries to help us create programming language and tools". Since this is not an introduction to the LLVM project, it suffices to say that LLVM makes creating programming language easy: give your language in <a href="http://llvm.org/docs/LangRef.html">LLVM IR</a> form and you get the rest of a native/JIT language for free, optimization included! LLVM's default API is in C++. In addition, it officially offers a C wrapper. Lucky for us, Swift is C-interoperable – no bridging necessary :) Now we arrive at our goal for this post: create an Xcode project that can make calls into LLVM's C API, aka to compile this single line of code: <pre><code>let module = LLVMModuleCreateWithName("my_module") </code></pre> I assume you have Xcode 7.1 installed on OS X 10.11, but no more. <h2>1. Getting LLVM</h2> There are a lot of materials on the internet dedicated to setting up an LLVM environment. As we are not working on LLVM itself, and we are not on some crazy custom Linux environment (to be fair, it's trivial to set LLVM up on most major Linux distributions), the <a href="http://llvm.org/releases/download.html">pre-built Clang binaries</a> is good enough. Download and unpack the .tar file somewhere handy in on your hard drive. For example, I put it at <code>$(HOME)/usr/local/clang-3.4</code>. Aaaand we're done. We have LLVM. Sidenote: Xcode installs clang the compiler, but a lot of LLVM tools are missing. That's why we need a separate LLVM/Clang setup. <h2>2. Create an Xcode Project</h2> Create a new OS X - Command Line Tool Xcode project, choose Swift as it's language. <img src="/assets/2015/10/llvm-swift-01-create-cmd-project.png" alt="Create A Command Line Xcode Project For LLVM" /> Accessing C stuff in Swift is the same as using your Objective-C classes. So we need to <a href="https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/MixandMatch.html">create a bridging header</a>. (I usually create a Objective-C class so that Xcode prompts me for creating the header, then I delete the .h and .m files). The project layout is now: <img src="/assets/2015/10/llvm-swift-02-bridging-header.png" alt="Create a bridging header to import LLVM C libraries" /> Import the LLVM headers for its C interface. For our example, this is the entire bridging header: <pre><code>#import <llvm-c/Core.h> </code></pre> It's probably a good time to replace content of <code>main.swift</code> with our awesome LLVM IR-generating code: <pre><code>let module = LLVMModuleCreateWithName("my_module") </code></pre> <h2>3. Teach Xcode About LLVM</h2> Our code would not compile at this point. Xcode complains that the LLVM header can not be found. Before you jump to the target build settings, allow me introduce <code>llvm-config</code>. It turns out that the compliler flags for building a compiler can get complex pretty quickly. So LLVM comes with a command that generates them. For me it lives under <code>$(HOME)/usr/local/clang-3.4/bin</code>. We can ask it for flags that compiles standard C++, links standard and core libraries like so: <pre><code>llvm-config --cxxflags --ldflags --system-libs --libs core </code></pre> (As we use more and more LLVM libraries in the future, the list following <code>--libs</code> will grow. <code>core</code> is all we need to compile our example). To anyone who's used GCC/Clang in command line, the output should be pretty self-explanatory: <pre><code>-I/Users/drchrono/local/clang-3.4/include -DNDEBUG -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -O3 -std=c++11 -fvisibility-inlines-hidden -fno-exceptions -fno-rtti -fno-common -Wcast-qual -L/Users/drchrono/local/clang-3.4/lib -lLLVMCore -lLLVMSupport -lz -lpthread -ledit -lcurses -lm </code></pre> I'll walk through how to ask Xcode to respect these. First, go to build settings and set search paths for header files and libraries according to output from <code>llvm-config</code>. For me that means: <img src="/assets/2015/10/llvm-swift-03-header-search-path.png" alt="Set LLVM header search path in Xcode" /> <img src="/assets/2015/10/llvm-swift-04-library-search-path.png" alt="Set LLVM library search path in Xcode" /> If you try to compile, now Xcode tells you some #define is missing. Again, we can find them in <code>llvm-config</code>'s result. Navigate to "Preprocessing" in build setting and add those values starting with <code>-D</code>, with out the <code>-D</code>: <img src="/assets/2015/10/llvm-swift-05-macros.png" alt="Set preprocessor macros" /> Remember to add these for both "Debug" and "Release". The last step is asking Xcode to link againt the LLVM libraries. Paste in the <code>-l</code> flags from <code>llvm-config</code> at "Other Linker Flags": <img src="/assets/2015/10/llvm-swift-06-link-libraries.png" alt="Ask Xcode to link against LLVM libraries" /> <h2>4. Conclusion</h2> Now our Swift LLVM code compiles! Looking back, setting LLVM up with Xcode is no more special than setting up with any C libraries. Hopefully this post will cut down research time for some. Now go create awesome natively languages in Swift! Sun, 25 Oct 2015 11:53:15 -0700 https://duan.ca/2015/10/25/lets-play-llvm-in-swift-setup/ https://duan.ca/2015/10/25/lets-play-llvm-in-swift-setup/