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2My First Language Frontend with LLVM Tutorial
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4
5**Requirements:** This tutorial assumes you know C++, but no previous
6compiler experience is necessary.
7
8Welcome to the "My First Language Frontend with LLVM" tutorial. Here we
9run through the implementation of a simple language, showing
10how fun and easy it can be.  This tutorial will get you up and running
11fast and show a concrete example of something that uses LLVM to generate
12code.
13
14This tutorial introduces the simple "Kaleidoscope" language, building it
15iteratively over the course of several chapters, showing how it is built
16over time. This lets us cover a range of language design and LLVM-specific
17ideas, showing and explaining the code for it all along the way,
18and reduces the overwhelming amount of details up front.  We strongly
19encourage that you *work with this code* - make a copy and hack it up and
20experiment.
21
22**Warning**: In order to focus on teaching compiler techniques and LLVM
23specifically,
24this tutorial does *not* show best practices in software engineering
25principles.  For example, the code uses global variables
26pervasively, doesn't use
27`visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but
28instead keeps things simple and focuses on the topics at hand.
29
30This tutorial is structured into chapters covering individual topics,
31allowing you to skip ahead as you wish:
32
33-  `Chapter #1: Kaleidoscope language and Lexer <LangImpl01.html>`_ -
34   This shows where we are
35   going and the basic functionality that we want to build.  A lexer
36   is also the first part of building a parser for a language, and we
37   use a simple C++ lexer which is easy to understand.
38-  `Chapter #2: Implementing a Parser and AST <LangImpl02.html>`_ -
39   With the lexer in place, we can talk about parsing techniques and
40   basic AST construction. This tutorial describes recursive descent
41   parsing and operator precedence parsing.
42-  `Chapter #3: Code generation to LLVM IR <LangImpl03.html>`_ - with
43   the AST ready, we show how easy it is to generate LLVM IR, and show
44   a simple way to incorporate LLVM into your project.
45-  `Chapter #4: Adding JIT and Optimizer Support <LangImpl04.html>`_ -
46   One great thing about LLVM is its support for JIT compilation, so
47   we'll dive right into it and show you the 3 lines it takes to add JIT
48   support. Later chapters show how to generate .o files.
49-  `Chapter #5: Extending the Language: Control Flow <LangImpl05.html>`_ - With the basic language up and running, we show how to extend
50   it with control flow operations ('if' statement and a 'for' loop). This
51   gives us a chance to talk about SSA construction and control
52   flow.
53-  `Chapter #6: Extending the Language: User-defined Operators
54   <LangImpl06.html>`_ - This chapter extends the language to let
55   users define arbitrary unary and binary operators - with assignable
56   precedence!  This allows us to build a significant piece of the
57   "language" as library routines.
58-  `Chapter #7: Extending the Language: Mutable Variables
59   <LangImpl07.html>`_ - This chapter talks about adding user-defined local
60   variables along with an assignment operator. This shows how easy it is
61   to construct SSA form in LLVM: LLVM does *not* require your front-end
62   to construct SSA form in order to use it!
63-  `Chapter #8: Compiling to Object Files <LangImpl08.html>`_ - This
64   chapter explains how to take LLVM IR and compile it down to object
65   files, like a static compiler does.
66-  `Chapter #9: Debug Information <LangImpl09.html>`_ - A real language
67   needs to support debuggers, so we
68   add debug information that allows setting breakpoints in Kaleidoscope
69   functions, print out argument variables, and call functions!
70-  `Chapter #10: Conclusion and other tidbits <LangImpl10.html>`_ - This
71   chapter wraps up the series by discussing ways to extend the language
72   and includes pointers to info on "special topics" like adding garbage
73   collection support, exceptions, debugging, support for "spaghetti
74   stacks", etc.
75
76By the end of the tutorial, we'll have written a bit less than 1000 lines
77of (non-comment, non-blank) lines of code. With this small amount of
78code, we'll have built up a nice little compiler for a non-trivial
79language including a hand-written lexer, parser, AST, as well as code
80generation support - both static and JIT!  The breadth of this is a great
81testament to the strengths of LLVM and shows why it is such a popular
82target for language designers and others who need high performance code
83generation.
84