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144 lines
6.7 KiB
HTML
144 lines
6.7 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>Kaleidoscope: Conclusion, ideas for extensions, and other useful tidbits</title>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="author" content="Chris Lattner">
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<link rel="stylesheet" href="../llvm.css" type="text/css">
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</head>
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<body>
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<div class="doc_title">Kaleidoscope: Conclusion</div>
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<div class="doc_author">
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<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section"><a name="intro">Tutorial Conclusion</a></div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>Welcome to the the final chapter of the "<a href="index.html">Implementing a
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language with LLVM</a>" tutorial. In the course of this tutorial, we have grown
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our little Kaleidoscope language from being a useless toy, to being a
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semi-interesting (but probably still useless) toy. :)</p>
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<p>It is interesting to see how far we've come, and how little code it has
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taken. We built the entire lexer, parser, AST, code generator, and an
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interactive run-loop (with a JIT!) by-hand in under 700 lines of
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(non-comment/non-blank) code.</p>
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<p>Our little language supports a couple of interesting features: it supports
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user defined binary and unary operators, it uses JIT compilation for immediate
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evaluation, and it supports a few control flow constructs with SSA construction.
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</p>
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<p>Part of the idea of this tutorial was to show you how easy and fun it can be
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to define, build, and play with languages. Building a compiler need not be a
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scary or mystical process! Now that you've seen some of the basics, I strongly
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encourage you to take the code and hack on it. For example, try adding:</p>
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<ul>
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<li><b>global variables</b> - While global variables have questional value in
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modern software engineering, they are often useful when putting together quick
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little hacks like the Kaleidoscope compiler itself. Fortunately, our current
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setup makes it very easy to add global variables: just have value lookup check
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to see if an unresolved variable is in the global variable symbol table before
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rejecting it. To create a new global variable, make an instance of the LLVM
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<tt>GlobalVariable</tt> class.</li>
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<li><b>typed variables</b> - Kaleidoscope currently only supports variables of
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type double. This gives the language a very nice elegance, because only
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supporting one type means that you never have to specify types. Different
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languages have different ways of handling this. The easiest way is to require
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the user to specify types for every variable definition, and record the type
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of the variable in the symbol table along with its Value*.</li>
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<li><b>arrays, structs, vectors, etc</b> - Once you add types, you can start
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extending the type system in all sorts of interesting ways. Simple arrays are
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very easy and are quite useful for many different applications. Adding them is
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mostly an exercise in learning how the LLVM <a
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href="../LangRef.html#i_getelementptr">getelementptr</a> instruction works.
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The getelementptr instruction is so nifty/unconventional, it <a
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href="../GetElementPtr.html">has its own FAQ</a>!).</li>
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<li><b>standard runtime</b> - Our current language allows the user to access
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arbitrary external functions, and we use it for things like "printd" and
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"putchard". As you extend the language to add higher-level constructs, often
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these constructs make the most amount of sense to be lowered into calls into a
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language-supplied runtime. For example, if you add hash tables to the language,
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it would probably make sense to add the routines to a runtime, instead of
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inlining them all the way.</li>
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<li><b>memory management</b> - Currently we can only access the stack in
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Kaleidoscope. It would also be useful to be able to allocate heap memory,
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either with calls to the standard libc malloc/free interface or with a garbage
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collector. If you choose to use garbage collection, note that LLVM fully
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supports <a href="../GarbageCollection.html">Accurate Garbage Collection</a>
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including algorithms that move objects and need to scan/update the stack.</li>
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<li><b>debugger support</b> - LLVM supports generation of <a
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href="../SourceLevelDebugging.html">DWARF Debug info</a> which is understood by
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common debuggers like GDB. Adding support for debug info is fairly
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straight-forward. The best way to understand it is to compile some C/C++ code
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with "<tt>llvm-gcc -g -O0</tt>" and taking a look at what it produces.</li>
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<li><b>exception handlingsupport</b> - LLVM supports generation of <a
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href="../ExceptionHandling.html">zero cost exceptions</a> which interoperate
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with code compiled in other languages. You could also generate code by
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implicitly making every function return an error value and checking it. You
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could also make explicit use of setjmp/longjmp. There are many different ways
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to go here.</li>
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<li><b>object orientation, generics, database access, complex numbers,
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geometric programming, ...</b> - Really, there is
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no end of crazy features that you can add to the language.</li>
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</ul>
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<p>
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Have fun - try doing something crazy and unusual. Building a language like
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everyone else always has is much less fun than trying something a little crazy
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and off the wall and seeing how it turns out. If you get stuck or want to talk
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about it, feel free to email the <a
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href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev mailing
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list</a>: it has lots of people who are interested in languages and are often
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willing to help out.
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</p>
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<p>Before we end, I want to talk about some "tips and tricks" for generating
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LLVM IR. These are some of the more subtle things that may not be obvious, but
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are very useful if you want to take advantage of LLVM's capabilities.</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section"><a name="tipsandtricks">Tips and Tricks</a></div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p></p>
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</div>
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<!-- *********************************************************************** -->
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<hr>
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<address>
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
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Last modified: $Date: 2007-10-17 11:05:13 -0700 (Wed, 17 Oct 2007) $
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</address>
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</body>
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</html>
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