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

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<li><a href="LangImpl5.html">Extending the language: control flow</a></li>
<li><a href="LangImpl6.html">Extending the language: user-defined operators</a></li>
<li><a href="LangImpl7.html">Extending the language: mutable variables / SSA construction</a></li>
<li>Thoughts and ideas for extensions</li>
<li><a href="LangImpl8.html">Conclusion, ideas for extensions, and other useful tidbits</a></li>
</ol></li>
<li>Advanced Topics
<ol>