[llvm-commits] [llvm] r169343 [1/2] - in /llvm/trunk/docs: ./ tutorial/
Sean Silva
silvas at purdue.edu
Tue Dec 4 16:26:33 PST 2012
Author: silvas
Date: Tue Dec 4 18:26:32 2012
New Revision: 169343
URL: http://llvm.org/viewvc/llvm-project?rev=169343&view=rev
Log:
docs: Sphinxify `docs/tutorial/`
Sorry for the massive commit, but I just wanted to knock this one down
and it is really straightforward.
There are still a couple trivial (i.e. not related to the content)
things left to fix:
- Use of raw HTML links where :doc:`...` and :ref:`...` could be used
instead. If you are a newbie and want to help fix this it would make
for some good bite-sized patches; more experienced developers should
be focusing on adding new content (to this tutorial or elsewhere, but
please _do not_ waste your time on formatting when there is such dire
need for documentation (see docs/SphinxQuickstartTemplate.rst to get
started writing)).
- Highlighting of the kaleidoscope code blocks (currently left as bare
`::`). I will be working on writing a custom Pygments highlighter for
this, mostly as training for maintaining the `llvm` code-block's lexer
in-tree. I want to do this because I am extremely unhappy with how it
just "gives up" on the slightest deviation from the expected syntax
and leaves the whole code-block un-highlighted.
More generally I am looking at writing some Sphinx extensions and
keeping them in-tree as well, to support common use cases that
currently have no good solution (like "monospace text inside a link").
Added:
llvm/trunk/docs/tutorial/LangImpl1.rst
llvm/trunk/docs/tutorial/LangImpl2.rst
llvm/trunk/docs/tutorial/LangImpl3.rst
llvm/trunk/docs/tutorial/LangImpl4.rst
llvm/trunk/docs/tutorial/LangImpl5.rst
llvm/trunk/docs/tutorial/LangImpl6.rst
llvm/trunk/docs/tutorial/LangImpl7.rst
llvm/trunk/docs/tutorial/LangImpl8.rst
llvm/trunk/docs/tutorial/OCamlLangImpl1.rst
llvm/trunk/docs/tutorial/OCamlLangImpl2.rst
llvm/trunk/docs/tutorial/OCamlLangImpl3.rst
llvm/trunk/docs/tutorial/OCamlLangImpl4.rst
llvm/trunk/docs/tutorial/OCamlLangImpl5.rst
llvm/trunk/docs/tutorial/OCamlLangImpl6.rst
llvm/trunk/docs/tutorial/OCamlLangImpl7.rst
llvm/trunk/docs/tutorial/OCamlLangImpl8.rst
Removed:
llvm/trunk/docs/tutorial/LangImpl1.html
llvm/trunk/docs/tutorial/LangImpl2.html
llvm/trunk/docs/tutorial/LangImpl3.html
llvm/trunk/docs/tutorial/LangImpl4.html
llvm/trunk/docs/tutorial/LangImpl5.html
llvm/trunk/docs/tutorial/LangImpl6.html
llvm/trunk/docs/tutorial/LangImpl7.html
llvm/trunk/docs/tutorial/LangImpl8.html
llvm/trunk/docs/tutorial/OCamlLangImpl1.html
llvm/trunk/docs/tutorial/OCamlLangImpl2.html
llvm/trunk/docs/tutorial/OCamlLangImpl3.html
llvm/trunk/docs/tutorial/OCamlLangImpl4.html
llvm/trunk/docs/tutorial/OCamlLangImpl5.html
llvm/trunk/docs/tutorial/OCamlLangImpl6.html
llvm/trunk/docs/tutorial/OCamlLangImpl7.html
llvm/trunk/docs/tutorial/OCamlLangImpl8.html
Modified:
llvm/trunk/docs/Makefile.sphinx
llvm/trunk/docs/tutorial/index.rst
Modified: llvm/trunk/docs/Makefile.sphinx
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/Makefile.sphinx?rev=169343&r1=169342&r2=169343&view=diff
==============================================================================
--- llvm/trunk/docs/Makefile.sphinx (original)
+++ llvm/trunk/docs/Makefile.sphinx Tue Dec 4 18:26:32 2012
@@ -50,8 +50,6 @@
@# Kind of a hack, but HTML-formatted docs are on the way out anyway.
@echo "Copying legacy HTML-formatted docs into $(BUILDDIR)/html"
@cp -a *.html $(BUILDDIR)/html
- @mkdir -p $(BUILDDIR)/html/tutorial
- @cp tutorial/*.html tutorial/*.png $(BUILDDIR)/html/tutorial
@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."
dirhtml:
Removed: llvm/trunk/docs/tutorial/LangImpl1.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl1.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl1.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl1.html (removed)
@@ -1,348 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Tutorial Introduction and the Lexer</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Tutorial Introduction and the Lexer</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 1
- <ol>
- <li><a href="#intro">Tutorial Introduction</a></li>
- <li><a href="#language">The Basic Language</a></li>
- <li><a href="#lexer">The Lexer</a></li>
- </ol>
-</li>
-<li><a href="LangImpl2.html">Chapter 2</a>: Implementing a Parser and AST</li>
-</ul>
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Tutorial Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to the "Implementing a language with LLVM" tutorial. This tutorial
-runs through the implementation of a simple language, showing how fun and
-easy it can be. This tutorial will get you up and started as well as help to
-build a framework you can extend to other languages. The code in this tutorial
-can also be used as a playground to hack on other LLVM specific things.
-</p>
-
-<p>
-The goal of this tutorial is to progressively unveil our language, describing
-how it is built up over time. This will let us cover a fairly broad range of
-language design and LLVM-specific usage issues, showing and explaining the code
-for it all along the way, without overwhelming you with tons of details up
-front.</p>
-
-<p>It is useful to point out ahead of time that this tutorial is really about
-teaching compiler techniques and LLVM specifically, <em>not</em> about teaching
-modern and sane software engineering principles. In practice, this means that
-we'll take a number of shortcuts to simplify the exposition. For example, the
-code leaks memory, uses global variables all over the place, doesn't use nice
-design patterns like <a
-href="http://en.wikipedia.org/wiki/Visitor_pattern">visitors</a>, etc... but it
-is very simple. If you dig in and use the code as a basis for future projects,
-fixing these deficiencies shouldn't be hard.</p>
-
-<p>I've tried to put this tutorial together in a way that makes chapters easy to
-skip over if you are already familiar with or are uninterested in the various
-pieces. The structure of the tutorial is:
-</p>
-
-<ul>
-<li><b><a href="#language">Chapter #1</a>: Introduction to the Kaleidoscope
-language, and the definition of its Lexer</b> - This shows where we are going
-and the basic functionality that we want it to do. In order to make this
-tutorial maximally understandable and hackable, we choose to implement
-everything in C++ instead of using lexer and parser generators. LLVM obviously
-works just fine with such tools, feel free to use one if you prefer.</li>
-<li><b><a href="LangImpl2.html">Chapter #2</a>: Implementing a Parser and
-AST</b> - With the lexer in place, we can talk about parsing techniques and
-basic AST construction. This tutorial describes recursive descent parsing and
-operator precedence parsing. Nothing in Chapters 1 or 2 is LLVM-specific,
-the code doesn't even link in LLVM at this point. :)</li>
-<li><b><a href="LangImpl3.html">Chapter #3</a>: Code generation to LLVM IR</b> -
-With the AST ready, we can show off how easy generation of LLVM IR really
-is.</li>
-<li><b><a href="LangImpl4.html">Chapter #4</a>: Adding JIT and Optimizer
-Support</b> - Because a lot of people are interested in using LLVM as a JIT,
-we'll dive right into it and show you the 3 lines it takes to add JIT support.
-LLVM is also useful in many other ways, but this is one simple and "sexy" way
-to shows off its power. :)</li>
-<li><b><a href="LangImpl5.html">Chapter #5</a>: Extending the Language: Control
-Flow</b> - With the language up and running, we show how to extend it with
-control flow operations (if/then/else and a 'for' loop). This gives us a chance
-to talk about simple SSA construction and control flow.</li>
-<li><b><a href="LangImpl6.html">Chapter #6</a>: Extending the Language:
-User-defined Operators</b> - This is a silly but fun chapter that talks about
-extending the language to let the user program define their own arbitrary
-unary and binary operators (with assignable precedence!). This lets us build a
-significant piece of the "language" as library routines.</li>
-<li><b><a href="LangImpl7.html">Chapter #7</a>: Extending the Language: Mutable
-Variables</b> - This chapter talks about adding user-defined local variables
-along with an assignment operator. The interesting part about this is how
-easy and trivial it is to construct SSA form in LLVM: no, LLVM does <em>not</em>
-require your front-end to construct SSA form!</li>
-<li><b><a href="LangImpl8.html">Chapter #8</a>: Conclusion and other useful LLVM
-tidbits</b> - This chapter wraps up the series by talking about potential
-ways to extend the language, but also includes a bunch of pointers to info about
-"special topics" like adding garbage collection support, exceptions, debugging,
-support for "spaghetti stacks", and a bunch of other tips and tricks.</li>
-
-</ul>
-
-<p>By the end of the tutorial, we'll have written a bit less than 700 lines of
-non-comment, non-blank, lines of code. With this small amount of code, we'll
-have built up a very reasonable compiler for a non-trivial language including
-a hand-written lexer, parser, AST, as well as code generation support with a JIT
-compiler. While other systems may have interesting "hello world" tutorials,
-I think the breadth of this tutorial is a great testament to the strengths of
-LLVM and why you should consider it if you're interested in language or compiler
-design.</p>
-
-<p>A note about this tutorial: we expect you to extend the language and play
-with it on your own. Take the code and go crazy hacking away at it, compilers
-don't need to be scary creatures - it can be a lot of fun to play with
-languages!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="language">The Basic Language</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>This tutorial will be illustrated with a toy language that we'll call
-"<a href="http://en.wikipedia.org/wiki/Kaleidoscope">Kaleidoscope</a>" (derived
-from "meaning beautiful, form, and view").
-Kaleidoscope is a procedural language that allows you to define functions, use
-conditionals, math, etc. Over the course of the tutorial, we'll extend
-Kaleidoscope to support the if/then/else construct, a for loop, user defined
-operators, JIT compilation with a simple command line interface, etc.</p>
-
-<p>Because we want to keep things simple, the only datatype in Kaleidoscope is a
-64-bit floating point type (aka 'double' in C parlance). As such, all values
-are implicitly double precision and the language doesn't require type
-declarations. This gives the language a very nice and simple syntax. For
-example, the following simple example computes <a
-href="http://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci numbers:</a></p>
-
-<div class="doc_code">
-<pre>
-# Compute the x'th fibonacci number.
-def fib(x)
- if x < 3 then
- 1
- else
- fib(x-1)+fib(x-2)
-
-# This expression will compute the 40th number.
-fib(40)
-</pre>
-</div>
-
-<p>We also allow Kaleidoscope to call into standard library functions (the LLVM
-JIT makes this completely trivial). This means that you can use the 'extern'
-keyword to define a function before you use it (this is also useful for mutually
-recursive functions). For example:</p>
-
-<div class="doc_code">
-<pre>
-extern sin(arg);
-extern cos(arg);
-extern atan2(arg1 arg2);
-
-atan2(sin(.4), cos(42))
-</pre>
-</div>
-
-<p>A more interesting example is included in Chapter 6 where we write a little
-Kaleidoscope application that <a href="LangImpl6.html#example">displays
-a Mandelbrot Set</a> at various levels of magnification.</p>
-
-<p>Lets dive into the implementation of this language!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="lexer">The Lexer</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>When it comes to implementing a language, the first thing needed is
-the ability to process a text file and recognize what it says. The traditional
-way to do this is to use a "<a
-href="http://en.wikipedia.org/wiki/Lexical_analysis">lexer</a>" (aka 'scanner')
-to break the input up into "tokens". Each token returned by the lexer includes
-a token code and potentially some metadata (e.g. the numeric value of a number).
-First, we define the possibilities:
-</p>
-
-<div class="doc_code">
-<pre>
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
- tok_eof = -1,
-
- // commands
- tok_def = -2, tok_extern = -3,
-
- // primary
- tok_identifier = -4, tok_number = -5,
-};
-
-static std::string IdentifierStr; // Filled in if tok_identifier
-static double NumVal; // Filled in if tok_number
-</pre>
-</div>
-
-<p>Each token returned by our lexer will either be one of the Token enum values
-or it will be an 'unknown' character like '+', which is returned as its ASCII
-value. If the current token is an identifier, the <tt>IdentifierStr</tt>
-global variable holds the name of the identifier. If the current token is a
-numeric literal (like 1.0), <tt>NumVal</tt> holds its value. Note that we use
-global variables for simplicity, this is not the best choice for a real language
-implementation :).
-</p>
-
-<p>The actual implementation of the lexer is a single function named
-<tt>gettok</tt>. The <tt>gettok</tt> function is called to return the next token
-from standard input. Its definition starts as:</p>
-
-<div class="doc_code">
-<pre>
-/// gettok - Return the next token from standard input.
-static int gettok() {
- static int LastChar = ' ';
-
- // Skip any whitespace.
- while (isspace(LastChar))
- LastChar = getchar();
-</pre>
-</div>
-
-<p>
-<tt>gettok</tt> works by calling the C <tt>getchar()</tt> function to read
-characters one at a time from standard input. It eats them as it recognizes
-them and stores the last character read, but not processed, in LastChar. The
-first thing that it has to do is ignore whitespace between tokens. This is
-accomplished with the loop above.</p>
-
-<p>The next thing <tt>gettok</tt> needs to do is recognize identifiers and
-specific keywords like "def". Kaleidoscope does this with this simple loop:</p>
-
-<div class="doc_code">
-<pre>
- if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
- IdentifierStr = LastChar;
- while (isalnum((LastChar = getchar())))
- IdentifierStr += LastChar;
-
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- return tok_identifier;
- }
-</pre>
-</div>
-
-<p>Note that this code sets the '<tt>IdentifierStr</tt>' global whenever it
-lexes an identifier. Also, since language keywords are matched by the same
-loop, we handle them here inline. Numeric values are similar:</p>
-
-<div class="doc_code">
-<pre>
- if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
- std::string NumStr;
- do {
- NumStr += LastChar;
- LastChar = getchar();
- } while (isdigit(LastChar) || LastChar == '.');
-
- NumVal = strtod(NumStr.c_str(), 0);
- return tok_number;
- }
-</pre>
-</div>
-
-<p>This is all pretty straight-forward code for processing input. When reading
-a numeric value from input, we use the C <tt>strtod</tt> function to convert it
-to a numeric value that we store in <tt>NumVal</tt>. Note that this isn't doing
-sufficient error checking: it will incorrectly read "1.23.45.67" and handle it as
-if you typed in "1.23". Feel free to extend it :). Next we handle comments:
-</p>
-
-<div class="doc_code">
-<pre>
- if (LastChar == '#') {
- // Comment until end of line.
- do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-
- if (LastChar != EOF)
- return gettok();
- }
-</pre>
-</div>
-
-<p>We handle comments by skipping to the end of the line and then return the
-next token. Finally, if the input doesn't match one of the above cases, it is
-either an operator character like '+' or the end of the file. These are handled
-with this code:</p>
-
-<div class="doc_code">
-<pre>
- // Check for end of file. Don't eat the EOF.
- if (LastChar == EOF)
- return tok_eof;
-
- // Otherwise, just return the character as its ascii value.
- int ThisChar = LastChar;
- LastChar = getchar();
- return ThisChar;
-}
-</pre>
-</div>
-
-<p>With this, we have the complete lexer for the basic Kaleidoscope language
-(the <a href="LangImpl2.html#code">full code listing</a> for the Lexer is
-available in the <a href="LangImpl2.html">next chapter</a> of the tutorial).
-Next we'll <a href="LangImpl2.html">build a simple parser that uses this to
-build an Abstract Syntax Tree</a>. When we have that, we'll include a driver
-so that you can use the lexer and parser together.
-</p>
-
-<a href="LangImpl2.html">Next: Implementing a Parser and AST</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/LangImpl1.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl1.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl1.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl1.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,280 @@
+=================================================
+Kaleidoscope: Tutorial Introduction and the Lexer
+=================================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Tutorial Introduction
+=====================
+
+Welcome to the "Implementing a language with LLVM" tutorial. This
+tutorial runs through the implementation of a simple language, showing
+how fun and easy it can be. This tutorial will get you up and started as
+well as help to build a framework you can extend to other languages. The
+code in this tutorial can also be used as a playground to hack on other
+LLVM specific things.
+
+The goal of this tutorial is to progressively unveil our language,
+describing how it is built up over time. This will let us cover a fairly
+broad range of language design and LLVM-specific usage issues, showing
+and explaining the code for it all along the way, without overwhelming
+you with tons of details up front.
+
+It is useful to point out ahead of time that this tutorial is really
+about teaching compiler techniques and LLVM specifically, *not* about
+teaching modern and sane software engineering principles. In practice,
+this means that we'll take a number of shortcuts to simplify the
+exposition. For example, the code leaks memory, uses global variables
+all over the place, doesn't use nice design patterns like
+`visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but
+it is very simple. If you dig in and use the code as a basis for future
+projects, fixing these deficiencies shouldn't be hard.
+
+I've tried to put this tutorial together in a way that makes chapters
+easy to skip over if you are already familiar with or are uninterested
+in the various pieces. The structure of the tutorial is:
+
+- `Chapter #1 <#language>`_: Introduction to the Kaleidoscope
+ language, and the definition of its Lexer - This shows where we are
+ going and the basic functionality that we want it to do. In order to
+ make this tutorial maximally understandable and hackable, we choose
+ to implement everything in C++ instead of using lexer and parser
+ generators. LLVM obviously works just fine with such tools, feel free
+ to use one if you prefer.
+- `Chapter #2 <LangImpl2.html>`_: Implementing a Parser and AST -
+ With the lexer in place, we can talk about parsing techniques and
+ basic AST construction. This tutorial describes recursive descent
+ parsing and operator precedence parsing. Nothing in Chapters 1 or 2
+ is LLVM-specific, the code doesn't even link in LLVM at this point.
+ :)
+- `Chapter #3 <LangImpl3.html>`_: Code generation to LLVM IR - With
+ the AST ready, we can show off how easy generation of LLVM IR really
+ is.
+- `Chapter #4 <LangImpl4.html>`_: Adding JIT and Optimizer Support
+ - Because a lot of people are interested in using LLVM as a JIT,
+ we'll dive right into it and show you the 3 lines it takes to add JIT
+ support. LLVM is also useful in many other ways, but this is one
+ simple and "sexy" way to shows off its power. :)
+- `Chapter #5 <LangImpl5.html>`_: Extending the Language: Control
+ Flow - With the language up and running, we show how to extend it
+ with control flow operations (if/then/else and a 'for' loop). This
+ gives us a chance to talk about simple SSA construction and control
+ flow.
+- `Chapter #6 <LangImpl6.html>`_: Extending the Language:
+ User-defined Operators - This is a silly but fun chapter that talks
+ about extending the language to let the user program define their own
+ arbitrary unary and binary operators (with assignable precedence!).
+ This lets us build a significant piece of the "language" as library
+ routines.
+- `Chapter #7 <LangImpl7.html>`_: Extending the Language: Mutable
+ Variables - This chapter talks about adding user-defined local
+ variables along with an assignment operator. The interesting part
+ about this is how easy and trivial it is to construct SSA form in
+ LLVM: no, LLVM does *not* require your front-end to construct SSA
+ form!
+- `Chapter #8 <LangImpl8.html>`_: Conclusion and other useful LLVM
+ tidbits - This chapter wraps up the series by talking about
+ potential ways to extend the language, but also includes a bunch of
+ pointers to info about "special topics" like adding garbage
+ collection support, exceptions, debugging, support for "spaghetti
+ stacks", and a bunch of other tips and tricks.
+
+By the end of the tutorial, we'll have written a bit less than 700 lines
+of non-comment, non-blank, lines of code. With this small amount of
+code, we'll have built up a very reasonable compiler for a non-trivial
+language including a hand-written lexer, parser, AST, as well as code
+generation support with a JIT compiler. While other systems may have
+interesting "hello world" tutorials, I think the breadth of this
+tutorial is a great testament to the strengths of LLVM and why you
+should consider it if you're interested in language or compiler design.
+
+A note about this tutorial: we expect you to extend the language and
+play with it on your own. Take the code and go crazy hacking away at it,
+compilers don't need to be scary creatures - it can be a lot of fun to
+play with languages!
+
+The Basic Language
+==================
+
+This tutorial will be illustrated with a toy language that we'll call
+"`Kaleidoscope <http://en.wikipedia.org/wiki/Kaleidoscope>`_" (derived
+from "meaning beautiful, form, and view"). Kaleidoscope is a procedural
+language that allows you to define functions, use conditionals, math,
+etc. Over the course of the tutorial, we'll extend Kaleidoscope to
+support the if/then/else construct, a for loop, user defined operators,
+JIT compilation with a simple command line interface, etc.
+
+Because we want to keep things simple, the only datatype in Kaleidoscope
+is a 64-bit floating point type (aka 'double' in C parlance). As such,
+all values are implicitly double precision and the language doesn't
+require type declarations. This gives the language a very nice and
+simple syntax. For example, the following simple example computes
+`Fibonacci numbers: <http://en.wikipedia.org/wiki/Fibonacci_number>`_
+
+::
+
+ # Compute the x'th fibonacci number.
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2)
+
+ # This expression will compute the 40th number.
+ fib(40)
+
+We also allow Kaleidoscope to call into standard library functions (the
+LLVM JIT makes this completely trivial). This means that you can use the
+'extern' keyword to define a function before you use it (this is also
+useful for mutually recursive functions). For example:
+
+::
+
+ extern sin(arg);
+ extern cos(arg);
+ extern atan2(arg1 arg2);
+
+ atan2(sin(.4), cos(42))
+
+A more interesting example is included in Chapter 6 where we write a
+little Kaleidoscope application that `displays a Mandelbrot
+Set <LangImpl6.html#example>`_ at various levels of magnification.
+
+Lets dive into the implementation of this language!
+
+The Lexer
+=========
+
+When it comes to implementing a language, the first thing needed is the
+ability to process a text file and recognize what it says. The
+traditional way to do this is to use a
+"`lexer <http://en.wikipedia.org/wiki/Lexical_analysis>`_" (aka
+'scanner') to break the input up into "tokens". Each token returned by
+the lexer includes a token code and potentially some metadata (e.g. the
+numeric value of a number). First, we define the possibilities:
+
+.. code-block:: c++
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5,
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+Each token returned by our lexer will either be one of the Token enum
+values or it will be an 'unknown' character like '+', which is returned
+as its ASCII value. If the current token is an identifier, the
+``IdentifierStr`` global variable holds the name of the identifier. If
+the current token is a numeric literal (like 1.0), ``NumVal`` holds its
+value. Note that we use global variables for simplicity, this is not the
+best choice for a real language implementation :).
+
+The actual implementation of the lexer is a single function named
+``gettok``. The ``gettok`` function is called to return the next token
+from standard input. Its definition starts as:
+
+.. code-block:: c++
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+``gettok`` works by calling the C ``getchar()`` function to read
+characters one at a time from standard input. It eats them as it
+recognizes them and stores the last character read, but not processed,
+in LastChar. The first thing that it has to do is ignore whitespace
+between tokens. This is accomplished with the loop above.
+
+The next thing ``gettok`` needs to do is recognize identifiers and
+specific keywords like "def". Kaleidoscope does this with this simple
+loop:
+
+.. code-block:: c++
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ return tok_identifier;
+ }
+
+Note that this code sets the '``IdentifierStr``' global whenever it
+lexes an identifier. Also, since language keywords are matched by the
+same loop, we handle them here inline. Numeric values are similar:
+
+.. code-block:: c++
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+This is all pretty straight-forward code for processing input. When
+reading a numeric value from input, we use the C ``strtod`` function to
+convert it to a numeric value that we store in ``NumVal``. Note that
+this isn't doing sufficient error checking: it will incorrectly read
+"1.23.45.67" and handle it as if you typed in "1.23". Feel free to
+extend it :). Next we handle comments:
+
+.. code-block:: c++
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+We handle comments by skipping to the end of the line and then return
+the next token. Finally, if the input doesn't match one of the above
+cases, it is either an operator character like '+' or the end of the
+file. These are handled with this code:
+
+.. code-block:: c++
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+With this, we have the complete lexer for the basic Kaleidoscope
+language (the `full code listing <LangImpl2.html#code>`_ for the Lexer
+is available in the `next chapter <LangImpl2.html>`_ of the tutorial).
+Next we'll `build a simple parser that uses this to build an Abstract
+Syntax Tree <LangImpl2.html>`_. When we have that, we'll include a
+driver so that you can use the lexer and parser together.
+
+`Next: Implementing a Parser and AST <LangImpl2.html>`_
+
Removed: llvm/trunk/docs/tutorial/LangImpl2.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl2.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl2.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl2.html (removed)
@@ -1,1231 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Implementing a Parser and AST</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Implementing a Parser and AST</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 2
- <ol>
- <li><a href="#intro">Chapter 2 Introduction</a></li>
- <li><a href="#ast">The Abstract Syntax Tree (AST)</a></li>
- <li><a href="#parserbasics">Parser Basics</a></li>
- <li><a href="#parserprimexprs">Basic Expression Parsing</a></li>
- <li><a href="#parserbinops">Binary Expression Parsing</a></li>
- <li><a href="#parsertop">Parsing the Rest</a></li>
- <li><a href="#driver">The Driver</a></li>
- <li><a href="#conclusions">Conclusions</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="LangImpl3.html">Chapter 3</a>: Code generation to LLVM IR</li>
-</ul>
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 2 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 2 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. This chapter shows you how to use the lexer, built in
-<a href="LangImpl1.html">Chapter 1</a>, to build a full <a
-href="http://en.wikipedia.org/wiki/Parsing">parser</a> for
-our Kaleidoscope language. Once we have a parser, we'll define and build an <a
-href="http://en.wikipedia.org/wiki/Abstract_syntax_tree">Abstract Syntax
-Tree</a> (AST).</p>
-
-<p>The parser we will build uses a combination of <a
-href="http://en.wikipedia.org/wiki/Recursive_descent_parser">Recursive Descent
-Parsing</a> and <a href=
-"http://en.wikipedia.org/wiki/Operator-precedence_parser">Operator-Precedence
-Parsing</a> to parse the Kaleidoscope language (the latter for
-binary expressions and the former for everything else). Before we get to
-parsing though, lets talk about the output of the parser: the Abstract Syntax
-Tree.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="ast">The Abstract Syntax Tree (AST)</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>The AST for a program captures its behavior in such a way that it is easy for
-later stages of the compiler (e.g. code generation) to interpret. We basically
-want one object for each construct in the language, and the AST should closely
-model the language. In Kaleidoscope, we have expressions, a prototype, and a
-function object. We'll start with expressions first:</p>
-
-<div class="doc_code">
-<pre>
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
-};
-</pre>
-</div>
-
-<p>The code above shows the definition of the base ExprAST class and one
-subclass which we use for numeric literals. The important thing to note about
-this code is that the NumberExprAST class captures the numeric value of the
-literal as an instance variable. This allows later phases of the compiler to
-know what the stored numeric value is.</p>
-
-<p>Right now we only create the AST, so there are no useful accessor methods on
-them. It would be very easy to add a virtual method to pretty print the code,
-for example. Here are the other expression AST node definitions that we'll use
-in the basic form of the Kaleidoscope language:
-</p>
-
-<div class="doc_code">
-<pre>
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
- std::string Name;
-public:
- VariableExprAST(const std::string &name) : Name(name) {}
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
- char Op;
- ExprAST *LHS, *RHS;
-public:
- BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
- : Op(op), LHS(lhs), RHS(rhs) {}
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
- std::string Callee;
- std::vector<ExprAST*> Args;
-public:
- CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
- : Callee(callee), Args(args) {}
-};
-</pre>
-</div>
-
-<p>This is all (intentionally) rather straight-forward: variables capture the
-variable name, binary operators capture their opcode (e.g. '+'), and calls
-capture a function name as well as a list of any argument expressions. One thing
-that is nice about our AST is that it captures the language features without
-talking about the syntax of the language. Note that there is no discussion about
-precedence of binary operators, lexical structure, etc.</p>
-
-<p>For our basic language, these are all of the expression nodes we'll define.
-Because it doesn't have conditional control flow, it isn't Turing-complete;
-we'll fix that in a later installment. The two things we need next are a way
-to talk about the interface to a function, and a way to talk about functions
-themselves:</p>
-
-<div class="doc_code">
-<pre>
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes).
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args)
- : Name(name), Args(args) {}
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
- PrototypeAST *Proto;
- ExprAST *Body;
-public:
- FunctionAST(PrototypeAST *proto, ExprAST *body)
- : Proto(proto), Body(body) {}
-};
-</pre>
-</div>
-
-<p>In Kaleidoscope, functions are typed with just a count of their arguments.
-Since all values are double precision floating point, the type of each argument
-doesn't need to be stored anywhere. In a more aggressive and realistic
-language, the "ExprAST" class would probably have a type field.</p>
-
-<p>With this scaffolding, we can now talk about parsing expressions and function
-bodies in Kaleidoscope.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parserbasics">Parser Basics</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Now that we have an AST to build, we need to define the parser code to build
-it. The idea here is that we want to parse something like "x+y" (which is
-returned as three tokens by the lexer) into an AST that could be generated with
-calls like this:</p>
-
-<div class="doc_code">
-<pre>
- ExprAST *X = new VariableExprAST("x");
- ExprAST *Y = new VariableExprAST("y");
- ExprAST *Result = new BinaryExprAST('+', X, Y);
-</pre>
-</div>
-
-<p>In order to do this, we'll start by defining some basic helper routines:</p>
-
-<div class="doc_code">
-<pre>
-/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
-/// token the parser is looking at. getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
- return CurTok = gettok();
-}
-</pre>
-</div>
-
-<p>
-This implements a simple token buffer around the lexer. This allows
-us to look one token ahead at what the lexer is returning. Every function in
-our parser will assume that CurTok is the current token that needs to be
-parsed.</p>
-
-<div class="doc_code">
-<pre>
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-</pre>
-</div>
-
-<p>
-The <tt>Error</tt> routines are simple helper routines that our parser will use
-to handle errors. The error recovery in our parser will not be the best and
-is not particular user-friendly, but it will be enough for our tutorial. These
-routines make it easier to handle errors in routines that have various return
-types: they always return null.</p>
-
-<p>With these basic helper functions, we can implement the first
-piece of our grammar: numeric literals.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parserprimexprs">Basic Expression Parsing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>We start with numeric literals, because they are the simplest to process.
-For each production in our grammar, we'll define a function which parses that
-production. For numeric literals, we have:
-</p>
-
-<div class="doc_code">
-<pre>
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
- ExprAST *Result = new NumberExprAST(NumVal);
- getNextToken(); // consume the number
- return Result;
-}
-</pre>
-</div>
-
-<p>This routine is very simple: it expects to be called when the current token
-is a <tt>tok_number</tt> token. It takes the current number value, creates
-a <tt>NumberExprAST</tt> node, advances the lexer to the next token, and finally
-returns.</p>
-
-<p>There are some interesting aspects to this. The most important one is that
-this routine eats all of the tokens that correspond to the production and
-returns the lexer buffer with the next token (which is not part of the grammar
-production) ready to go. This is a fairly standard way to go for recursive
-descent parsers. For a better example, the parenthesis operator is defined like
-this:</p>
-
-<div class="doc_code">
-<pre>
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
- getNextToken(); // eat (.
- ExprAST *V = ParseExpression();
- if (!V) return 0;
-
- if (CurTok != ')')
- return Error("expected ')'");
- getNextToken(); // eat ).
- return V;
-}
-</pre>
-</div>
-
-<p>This function illustrates a number of interesting things about the
-parser:</p>
-
-<p>
-1) It shows how we use the Error routines. When called, this function expects
-that the current token is a '(' token, but after parsing the subexpression, it
-is possible that there is no ')' waiting. For example, if the user types in
-"(4 x" instead of "(4)", the parser should emit an error. Because errors can
-occur, the parser needs a way to indicate that they happened: in our parser, we
-return null on an error.</p>
-
-<p>2) Another interesting aspect of this function is that it uses recursion by
-calling <tt>ParseExpression</tt> (we will soon see that <tt>ParseExpression</tt> can call
-<tt>ParseParenExpr</tt>). This is powerful because it allows us to handle
-recursive grammars, and keeps each production very simple. Note that
-parentheses do not cause construction of AST nodes themselves. While we could
-do it this way, the most important role of parentheses are to guide the parser
-and provide grouping. Once the parser constructs the AST, parentheses are not
-needed.</p>
-
-<p>The next simple production is for handling variable references and function
-calls:</p>
-
-<div class="doc_code">
-<pre>
-/// identifierexpr
-/// ::= identifier
-/// ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
- std::string IdName = IdentifierStr;
-
- getNextToken(); // eat identifier.
-
- if (CurTok != '(') // Simple variable ref.
- return new VariableExprAST(IdName);
-
- // Call.
- getNextToken(); // eat (
- std::vector<ExprAST*> Args;
- if (CurTok != ')') {
- while (1) {
- ExprAST *Arg = ParseExpression();
- if (!Arg) return 0;
- Args.push_back(Arg);
-
- if (CurTok == ')') break;
-
- if (CurTok != ',')
- return Error("Expected ')' or ',' in argument list");
- getNextToken();
- }
- }
-
- // Eat the ')'.
- getNextToken();
-
- return new CallExprAST(IdName, Args);
-}
-</pre>
-</div>
-
-<p>This routine follows the same style as the other routines. (It expects to be
-called if the current token is a <tt>tok_identifier</tt> token). It also has
-recursion and error handling. One interesting aspect of this is that it uses
-<em>look-ahead</em> to determine if the current identifier is a stand alone
-variable reference or if it is a function call expression. It handles this by
-checking to see if the token after the identifier is a '(' token, constructing
-either a <tt>VariableExprAST</tt> or <tt>CallExprAST</tt> node as appropriate.
-</p>
-
-<p>Now that we have all of our simple expression-parsing logic in place, we can
-define a helper function to wrap it together into one entry point. We call this
-class of expressions "primary" expressions, for reasons that will become more
-clear <a href="LangImpl6.html#unary">later in the tutorial</a>. In order to
-parse an arbitrary primary expression, we need to determine what sort of
-expression it is:</p>
-
-<div class="doc_code">
-<pre>
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- }
-}
-</pre>
-</div>
-
-<p>Now that you see the definition of this function, it is more obvious why we
-can assume the state of CurTok in the various functions. This uses look-ahead
-to determine which sort of expression is being inspected, and then parses it
-with a function call.</p>
-
-<p>Now that basic expressions are handled, we need to handle binary expressions.
-They are a bit more complex.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parserbinops">Binary Expression Parsing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Binary expressions are significantly harder to parse because they are often
-ambiguous. For example, when given the string "x+y*z", the parser can choose
-to parse it as either "(x+y)*z" or "x+(y*z)". With common definitions from
-mathematics, we expect the later parse, because "*" (multiplication) has
-higher <em>precedence</em> than "+" (addition).</p>
-
-<p>There are many ways to handle this, but an elegant and efficient way is to
-use <a href=
-"http://en.wikipedia.org/wiki/Operator-precedence_parser">Operator-Precedence
-Parsing</a>. This parsing technique uses the precedence of binary operators to
-guide recursion. To start with, we need a table of precedences:</p>
-
-<div class="doc_code">
-<pre>
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
- if (!isascii(CurTok))
- return -1;
-
- // Make sure it's a declared binop.
- int TokPrec = BinopPrecedence[CurTok];
- if (TokPrec <= 0) return -1;
- return TokPrec;
-}
-
-int main() {
- // Install standard binary operators.
- // 1 is lowest precedence.
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
- BinopPrecedence['*'] = 40; // highest.
- ...
-}
-</pre>
-</div>
-
-<p>For the basic form of Kaleidoscope, we will only support 4 binary operators
-(this can obviously be extended by you, our brave and intrepid reader). The
-<tt>GetTokPrecedence</tt> function returns the precedence for the current token,
-or -1 if the token is not a binary operator. Having a map makes it easy to add
-new operators and makes it clear that the algorithm doesn't depend on the
-specific operators involved, but it would be easy enough to eliminate the map
-and do the comparisons in the <tt>GetTokPrecedence</tt> function. (Or just use
-a fixed-size array).</p>
-
-<p>With the helper above defined, we can now start parsing binary expressions.
-The basic idea of operator precedence parsing is to break down an expression
-with potentially ambiguous binary operators into pieces. Consider ,for example,
-the expression "a+b+(c+d)*e*f+g". Operator precedence parsing considers this
-as a stream of primary expressions separated by binary operators. As such,
-it will first parse the leading primary expression "a", then it will see the
-pairs [+, b] [+, (c+d)] [*, e] [*, f] and [+, g]. Note that because parentheses
-are primary expressions, the binary expression parser doesn't need to worry
-about nested subexpressions like (c+d) at all.
-</p>
-
-<p>
-To start, an expression is a primary expression potentially followed by a
-sequence of [binop,primaryexpr] pairs:</p>
-
-<div class="doc_code">
-<pre>
-/// expression
-/// ::= primary binoprhs
-///
-static ExprAST *ParseExpression() {
- ExprAST *LHS = ParsePrimary();
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-</pre>
-</div>
-
-<p><tt>ParseBinOpRHS</tt> is the function that parses the sequence of pairs for
-us. It takes a precedence and a pointer to an expression for the part that has been
-parsed so far. Note that "x" is a perfectly valid expression: As such, "binoprhs" is
-allowed to be empty, in which case it returns the expression that is passed into
-it. In our example above, the code passes the expression for "a" into
-<tt>ParseBinOpRHS</tt> and the current token is "+".</p>
-
-<p>The precedence value passed into <tt>ParseBinOpRHS</tt> indicates the <em>
-minimal operator precedence</em> that the function is allowed to eat. For
-example, if the current pair stream is [+, x] and <tt>ParseBinOpRHS</tt> is
-passed in a precedence of 40, it will not consume any tokens (because the
-precedence of '+' is only 20). With this in mind, <tt>ParseBinOpRHS</tt> starts
-with:</p>
-
-<div class="doc_code">
-<pre>
-/// binoprhs
-/// ::= ('+' primary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- // If this is a binop, find its precedence.
- while (1) {
- int TokPrec = GetTokPrecedence();
-
- // If this is a binop that binds at least as tightly as the current binop,
- // consume it, otherwise we are done.
- if (TokPrec < ExprPrec)
- return LHS;
-</pre>
-</div>
-
-<p>This code gets the precedence of the current token and checks to see if if is
-too low. Because we defined invalid tokens to have a precedence of -1, this
-check implicitly knows that the pair-stream ends when the token stream runs out
-of binary operators. If this check succeeds, we know that the token is a binary
-operator and that it will be included in this expression:</p>
-
-<div class="doc_code">
-<pre>
- // Okay, we know this is a binop.
- int BinOp = CurTok;
- getNextToken(); // eat binop
-
- // Parse the primary expression after the binary operator.
- ExprAST *RHS = ParsePrimary();
- if (!RHS) return 0;
-</pre>
-</div>
-
-<p>As such, this code eats (and remembers) the binary operator and then parses
-the primary expression that follows. This builds up the whole pair, the first of
-which is [+, b] for the running example.</p>
-
-<p>Now that we parsed the left-hand side of an expression and one pair of the
-RHS sequence, we have to decide which way the expression associates. In
-particular, we could have "(a+b) binop unparsed" or "a + (b binop unparsed)".
-To determine this, we look ahead at "binop" to determine its precedence and
-compare it to BinOp's precedence (which is '+' in this case):</p>
-
-<div class="doc_code">
-<pre>
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
-</pre>
-</div>
-
-<p>If the precedence of the binop to the right of "RHS" is lower or equal to the
-precedence of our current operator, then we know that the parentheses associate
-as "(a+b) binop ...". In our example, the current operator is "+" and the next
-operator is "+", we know that they have the same precedence. In this case we'll
-create the AST node for "a+b", and then continue parsing:</p>
-
-<div class="doc_code">
-<pre>
- ... if body omitted ...
- }
-
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- } // loop around to the top of the while loop.
-}
-</pre>
-</div>
-
-<p>In our example above, this will turn "a+b+" into "(a+b)" and execute the next
-iteration of the loop, with "+" as the current token. The code above will eat,
-remember, and parse "(c+d)" as the primary expression, which makes the
-current pair equal to [+, (c+d)]. It will then evaluate the 'if' conditional above with
-"*" as the binop to the right of the primary. In this case, the precedence of "*" is
-higher than the precedence of "+" so the if condition will be entered.</p>
-
-<p>The critical question left here is "how can the if condition parse the right
-hand side in full"? In particular, to build the AST correctly for our example,
-it needs to get all of "(c+d)*e*f" as the RHS expression variable. The code to
-do this is surprisingly simple (code from the above two blocks duplicated for
-context):</p>
-
-<div class="doc_code">
-<pre>
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
- <b>RHS = ParseBinOpRHS(TokPrec+1, RHS);
- if (RHS == 0) return 0;</b>
- }
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- } // loop around to the top of the while loop.
-}
-</pre>
-</div>
-
-<p>At this point, we know that the binary operator to the RHS of our primary
-has higher precedence than the binop we are currently parsing. As such, we know
-that any sequence of pairs whose operators are all higher precedence than "+"
-should be parsed together and returned as "RHS". To do this, we recursively
-invoke the <tt>ParseBinOpRHS</tt> function specifying "TokPrec+1" as the minimum
-precedence required for it to continue. In our example above, this will cause
-it to return the AST node for "(c+d)*e*f" as RHS, which is then set as the RHS
-of the '+' expression.</p>
-
-<p>Finally, on the next iteration of the while loop, the "+g" piece is parsed
-and added to the AST. With this little bit of code (14 non-trivial lines), we
-correctly handle fully general binary expression parsing in a very elegant way.
-This was a whirlwind tour of this code, and it is somewhat subtle. I recommend
-running through it with a few tough examples to see how it works.
-</p>
-
-<p>This wraps up handling of expressions. At this point, we can point the
-parser at an arbitrary token stream and build an expression from it, stopping
-at the first token that is not part of the expression. Next up we need to
-handle function definitions, etc.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parsertop">Parsing the Rest</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-The next thing missing is handling of function prototypes. In Kaleidoscope,
-these are used both for 'extern' function declarations as well as function body
-definitions. The code to do this is straight-forward and not very interesting
-(once you've survived expressions):
-</p>
-
-<div class="doc_code">
-<pre>
-/// prototype
-/// ::= id '(' id* ')'
-static PrototypeAST *ParsePrototype() {
- if (CurTok != tok_identifier)
- return ErrorP("Expected function name in prototype");
-
- std::string FnName = IdentifierStr;
- getNextToken();
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- // Read the list of argument names.
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- return new PrototypeAST(FnName, ArgNames);
-}
-</pre>
-</div>
-
-<p>Given this, a function definition is very simple, just a prototype plus
-an expression to implement the body:</p>
-
-<div class="doc_code">
-<pre>
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
- getNextToken(); // eat def.
- PrototypeAST *Proto = ParsePrototype();
- if (Proto == 0) return 0;
-
- if (ExprAST *E = ParseExpression())
- return new FunctionAST(Proto, E);
- return 0;
-}
-</pre>
-</div>
-
-<p>In addition, we support 'extern' to declare functions like 'sin' and 'cos' as
-well as to support forward declaration of user functions. These 'extern's are just
-prototypes with no body:</p>
-
-<div class="doc_code">
-<pre>
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
- getNextToken(); // eat extern.
- return ParsePrototype();
-}
-</pre>
-</div>
-
-<p>Finally, we'll also let the user type in arbitrary top-level expressions and
-evaluate them on the fly. We will handle this by defining anonymous nullary
-(zero argument) functions for them:</p>
-
-<div class="doc_code">
-<pre>
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
- if (ExprAST *E = ParseExpression()) {
- // Make an anonymous proto.
- PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
- return new FunctionAST(Proto, E);
- }
- return 0;
-}
-</pre>
-</div>
-
-<p>Now that we have all the pieces, let's build a little driver that will let us
-actually <em>execute</em> this code we've built!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="driver">The Driver</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>The driver for this simply invokes all of the parsing pieces with a top-level
-dispatch loop. There isn't much interesting here, so I'll just include the
-top-level loop. See <a href="#code">below</a> for full code in the "Top-Level
-Parsing" section.</p>
-
-<div class="doc_code">
-<pre>
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
- while (1) {
- fprintf(stderr, "ready> ");
- switch (CurTok) {
- case tok_eof: return;
- case ';': getNextToken(); break; // ignore top-level semicolons.
- case tok_def: HandleDefinition(); break;
- case tok_extern: HandleExtern(); break;
- default: HandleTopLevelExpression(); break;
- }
- }
-}
-</pre>
-</div>
-
-<p>The most interesting part of this is that we ignore top-level semicolons.
-Why is this, you ask? The basic reason is that if you type "4 + 5" at the
-command line, the parser doesn't know whether that is the end of what you will type
-or not. For example, on the next line you could type "def foo..." in which case
-4+5 is the end of a top-level expression. Alternatively you could type "* 6",
-which would continue the expression. Having top-level semicolons allows you to
-type "4+5;", and the parser will know you are done.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="conclusions">Conclusions</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>With just under 400 lines of commented code (240 lines of non-comment,
-non-blank code), we fully defined our minimal language, including a lexer,
-parser, and AST builder. With this done, the executable will validate
-Kaleidoscope code and tell us if it is grammatically invalid. For
-example, here is a sample interaction:</p>
-
-<div class="doc_code">
-<pre>
-$ <b>./a.out</b>
-ready> <b>def foo(x y) x+foo(y, 4.0);</b>
-Parsed a function definition.
-ready> <b>def foo(x y) x+y y;</b>
-Parsed a function definition.
-Parsed a top-level expr
-ready> <b>def foo(x y) x+y );</b>
-Parsed a function definition.
-Error: unknown token when expecting an expression
-ready> <b>extern sin(a);</b>
-ready> Parsed an extern
-ready> <b>^D</b>
-$
-</pre>
-</div>
-
-<p>There is a lot of room for extension here. You can define new AST nodes,
-extend the language in many ways, etc. In the <a href="LangImpl3.html">next
-installment</a>, we will describe how to generate LLVM Intermediate
-Representation (IR) from the AST.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for this and the previous chapter.
-Note that it is fully self-contained: you don't need LLVM or any external
-libraries at all for this. (Besides the C and C++ standard libraries, of
-course.) To build this, just compile with:</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-clang++ -g -O3 toy.cpp
-# Run
-./a.out
-</pre>
-</div>
-
-<p>Here is the code:</p>
-
-<div class="doc_code">
-<pre>
-#include <cstdio>
-#include <cstdlib>
-#include <string>
-#include <map>
-#include <vector>
-
-//===----------------------------------------------------------------------===//
-// Lexer
-//===----------------------------------------------------------------------===//
-
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
- tok_eof = -1,
-
- // commands
- tok_def = -2, tok_extern = -3,
-
- // primary
- tok_identifier = -4, tok_number = -5
-};
-
-static std::string IdentifierStr; // Filled in if tok_identifier
-static double NumVal; // Filled in if tok_number
-
-/// gettok - Return the next token from standard input.
-static int gettok() {
- static int LastChar = ' ';
-
- // Skip any whitespace.
- while (isspace(LastChar))
- LastChar = getchar();
-
- if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
- IdentifierStr = LastChar;
- while (isalnum((LastChar = getchar())))
- IdentifierStr += LastChar;
-
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- return tok_identifier;
- }
-
- if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
- std::string NumStr;
- do {
- NumStr += LastChar;
- LastChar = getchar();
- } while (isdigit(LastChar) || LastChar == '.');
-
- NumVal = strtod(NumStr.c_str(), 0);
- return tok_number;
- }
-
- if (LastChar == '#') {
- // Comment until end of line.
- do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-
- if (LastChar != EOF)
- return gettok();
- }
-
- // Check for end of file. Don't eat the EOF.
- if (LastChar == EOF)
- return tok_eof;
-
- // Otherwise, just return the character as its ascii value.
- int ThisChar = LastChar;
- LastChar = getchar();
- return ThisChar;
-}
-
-//===----------------------------------------------------------------------===//
-// Abstract Syntax Tree (aka Parse Tree)
-//===----------------------------------------------------------------------===//
-
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
-};
-
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
- std::string Name;
-public:
- VariableExprAST(const std::string &name) : Name(name) {}
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
- char Op;
- ExprAST *LHS, *RHS;
-public:
- BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
- : Op(op), LHS(lhs), RHS(rhs) {}
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
- std::string Callee;
- std::vector<ExprAST*> Args;
-public:
- CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
- : Callee(callee), Args(args) {}
-};
-
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes).
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args)
- : Name(name), Args(args) {}
-
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
- PrototypeAST *Proto;
- ExprAST *Body;
-public:
- FunctionAST(PrototypeAST *proto, ExprAST *body)
- : Proto(proto), Body(body) {}
-
-};
-
-//===----------------------------------------------------------------------===//
-// Parser
-//===----------------------------------------------------------------------===//
-
-/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
-/// token the parser is looking at. getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
- return CurTok = gettok();
-}
-
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
- if (!isascii(CurTok))
- return -1;
-
- // Make sure it's a declared binop.
- int TokPrec = BinopPrecedence[CurTok];
- if (TokPrec <= 0) return -1;
- return TokPrec;
-}
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-
-static ExprAST *ParseExpression();
-
-/// identifierexpr
-/// ::= identifier
-/// ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
- std::string IdName = IdentifierStr;
-
- getNextToken(); // eat identifier.
-
- if (CurTok != '(') // Simple variable ref.
- return new VariableExprAST(IdName);
-
- // Call.
- getNextToken(); // eat (
- std::vector<ExprAST*> Args;
- if (CurTok != ')') {
- while (1) {
- ExprAST *Arg = ParseExpression();
- if (!Arg) return 0;
- Args.push_back(Arg);
-
- if (CurTok == ')') break;
-
- if (CurTok != ',')
- return Error("Expected ')' or ',' in argument list");
- getNextToken();
- }
- }
-
- // Eat the ')'.
- getNextToken();
-
- return new CallExprAST(IdName, Args);
-}
-
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
- ExprAST *Result = new NumberExprAST(NumVal);
- getNextToken(); // consume the number
- return Result;
-}
-
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
- getNextToken(); // eat (.
- ExprAST *V = ParseExpression();
- if (!V) return 0;
-
- if (CurTok != ')')
- return Error("expected ')'");
- getNextToken(); // eat ).
- return V;
-}
-
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- }
-}
-
-/// binoprhs
-/// ::= ('+' primary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- // If this is a binop, find its precedence.
- while (1) {
- int TokPrec = GetTokPrecedence();
-
- // If this is a binop that binds at least as tightly as the current binop,
- // consume it, otherwise we are done.
- if (TokPrec < ExprPrec)
- return LHS;
-
- // Okay, we know this is a binop.
- int BinOp = CurTok;
- getNextToken(); // eat binop
-
- // Parse the primary expression after the binary operator.
- ExprAST *RHS = ParsePrimary();
- if (!RHS) return 0;
-
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
- RHS = ParseBinOpRHS(TokPrec+1, RHS);
- if (RHS == 0) return 0;
- }
-
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- }
-}
-
-/// expression
-/// ::= primary binoprhs
-///
-static ExprAST *ParseExpression() {
- ExprAST *LHS = ParsePrimary();
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-
-/// prototype
-/// ::= id '(' id* ')'
-static PrototypeAST *ParsePrototype() {
- if (CurTok != tok_identifier)
- return ErrorP("Expected function name in prototype");
-
- std::string FnName = IdentifierStr;
- getNextToken();
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- return new PrototypeAST(FnName, ArgNames);
-}
-
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
- getNextToken(); // eat def.
- PrototypeAST *Proto = ParsePrototype();
- if (Proto == 0) return 0;
-
- if (ExprAST *E = ParseExpression())
- return new FunctionAST(Proto, E);
- return 0;
-}
-
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
- if (ExprAST *E = ParseExpression()) {
- // Make an anonymous proto.
- PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
- return new FunctionAST(Proto, E);
- }
- return 0;
-}
-
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
- getNextToken(); // eat extern.
- return ParsePrototype();
-}
-
-//===----------------------------------------------------------------------===//
-// Top-Level parsing
-//===----------------------------------------------------------------------===//
-
-static void HandleDefinition() {
- if (ParseDefinition()) {
- fprintf(stderr, "Parsed a function definition.\n");
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleExtern() {
- if (ParseExtern()) {
- fprintf(stderr, "Parsed an extern\n");
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleTopLevelExpression() {
- // Evaluate a top-level expression into an anonymous function.
- if (ParseTopLevelExpr()) {
- fprintf(stderr, "Parsed a top-level expr\n");
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
- while (1) {
- fprintf(stderr, "ready> ");
- switch (CurTok) {
- case tok_eof: return;
- case ';': getNextToken(); break; // ignore top-level semicolons.
- case tok_def: HandleDefinition(); break;
- case tok_extern: HandleExtern(); break;
- default: HandleTopLevelExpression(); break;
- }
- }
-}
-
-//===----------------------------------------------------------------------===//
-// Main driver code.
-//===----------------------------------------------------------------------===//
-
-int main() {
- // Install standard binary operators.
- // 1 is lowest precedence.
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
- BinopPrecedence['*'] = 40; // highest.
-
- // Prime the first token.
- fprintf(stderr, "ready> ");
- getNextToken();
-
- // Run the main "interpreter loop" now.
- MainLoop();
-
- return 0;
-}
-</pre>
-</div>
-<a href="LangImpl3.html">Next: Implementing Code Generation to LLVM IR</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/LangImpl2.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl2.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl2.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl2.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,1098 @@
+===========================================
+Kaleidoscope: Implementing a Parser and AST
+===========================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Chapter 2 Introduction
+======================
+
+Welcome to Chapter 2 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to use the
+lexer, built in `Chapter 1 <LangImpl1.html>`_, to build a full
+`parser <http://en.wikipedia.org/wiki/Parsing>`_ for our Kaleidoscope
+language. Once we have a parser, we'll define and build an `Abstract
+Syntax Tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_ (AST).
+
+The parser we will build uses a combination of `Recursive Descent
+Parsing <http://en.wikipedia.org/wiki/Recursive_descent_parser>`_ and
+`Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_ to
+parse the Kaleidoscope language (the latter for binary expressions and
+the former for everything else). Before we get to parsing though, lets
+talk about the output of the parser: the Abstract Syntax Tree.
+
+The Abstract Syntax Tree (AST)
+==============================
+
+The AST for a program captures its behavior in such a way that it is
+easy for later stages of the compiler (e.g. code generation) to
+interpret. We basically want one object for each construct in the
+language, and the AST should closely model the language. In
+Kaleidoscope, we have expressions, a prototype, and a function object.
+We'll start with expressions first:
+
+.. code-block:: c++
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ };
+
+The code above shows the definition of the base ExprAST class and one
+subclass which we use for numeric literals. The important thing to note
+about this code is that the NumberExprAST class captures the numeric
+value of the literal as an instance variable. This allows later phases
+of the compiler to know what the stored numeric value is.
+
+Right now we only create the AST, so there are no useful accessor
+methods on them. It would be very easy to add a virtual method to pretty
+print the code, for example. Here are the other expression AST node
+definitions that we'll use in the basic form of the Kaleidoscope
+language:
+
+.. code-block:: c++
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ };
+
+This is all (intentionally) rather straight-forward: variables capture
+the variable name, binary operators capture their opcode (e.g. '+'), and
+calls capture a function name as well as a list of any argument
+expressions. One thing that is nice about our AST is that it captures
+the language features without talking about the syntax of the language.
+Note that there is no discussion about precedence of binary operators,
+lexical structure, etc.
+
+For our basic language, these are all of the expression nodes we'll
+define. Because it doesn't have conditional control flow, it isn't
+Turing-complete; we'll fix that in a later installment. The two things
+we need next are a way to talk about the interface to a function, and a
+way to talk about functions themselves:
+
+.. code-block:: c++
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes).
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args)
+ : Name(name), Args(args) {}
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+ };
+
+In Kaleidoscope, functions are typed with just a count of their
+arguments. Since all values are double precision floating point, the
+type of each argument doesn't need to be stored anywhere. In a more
+aggressive and realistic language, the "ExprAST" class would probably
+have a type field.
+
+With this scaffolding, we can now talk about parsing expressions and
+function bodies in Kaleidoscope.
+
+Parser Basics
+=============
+
+Now that we have an AST to build, we need to define the parser code to
+build it. The idea here is that we want to parse something like "x+y"
+(which is returned as three tokens by the lexer) into an AST that could
+be generated with calls like this:
+
+.. code-block:: c++
+
+ ExprAST *X = new VariableExprAST("x");
+ ExprAST *Y = new VariableExprAST("y");
+ ExprAST *Result = new BinaryExprAST('+', X, Y);
+
+In order to do this, we'll start by defining some basic helper routines:
+
+.. code-block:: c++
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+This implements a simple token buffer around the lexer. This allows us
+to look one token ahead at what the lexer is returning. Every function
+in our parser will assume that CurTok is the current token that needs to
+be parsed.
+
+.. code-block:: c++
+
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+The ``Error`` routines are simple helper routines that our parser will
+use to handle errors. The error recovery in our parser will not be the
+best and is not particular user-friendly, but it will be enough for our
+tutorial. These routines make it easier to handle errors in routines
+that have various return types: they always return null.
+
+With these basic helper functions, we can implement the first piece of
+our grammar: numeric literals.
+
+Basic Expression Parsing
+========================
+
+We start with numeric literals, because they are the simplest to
+process. For each production in our grammar, we'll define a function
+which parses that production. For numeric literals, we have:
+
+.. code-block:: c++
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+This routine is very simple: it expects to be called when the current
+token is a ``tok_number`` token. It takes the current number value,
+creates a ``NumberExprAST`` node, advances the lexer to the next token,
+and finally returns.
+
+There are some interesting aspects to this. The most important one is
+that this routine eats all of the tokens that correspond to the
+production and returns the lexer buffer with the next token (which is
+not part of the grammar production) ready to go. This is a fairly
+standard way to go for recursive descent parsers. For a better example,
+the parenthesis operator is defined like this:
+
+.. code-block:: c++
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+This function illustrates a number of interesting things about the
+parser:
+
+1) It shows how we use the Error routines. When called, this function
+expects that the current token is a '(' token, but after parsing the
+subexpression, it is possible that there is no ')' waiting. For example,
+if the user types in "(4 x" instead of "(4)", the parser should emit an
+error. Because errors can occur, the parser needs a way to indicate that
+they happened: in our parser, we return null on an error.
+
+2) Another interesting aspect of this function is that it uses recursion
+by calling ``ParseExpression`` (we will soon see that
+``ParseExpression`` can call ``ParseParenExpr``). This is powerful
+because it allows us to handle recursive grammars, and keeps each
+production very simple. Note that parentheses do not cause construction
+of AST nodes themselves. While we could do it this way, the most
+important role of parentheses are to guide the parser and provide
+grouping. Once the parser constructs the AST, parentheses are not
+needed.
+
+The next simple production is for handling variable references and
+function calls:
+
+.. code-block:: c++
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+This routine follows the same style as the other routines. (It expects
+to be called if the current token is a ``tok_identifier`` token). It
+also has recursion and error handling. One interesting aspect of this is
+that it uses *look-ahead* to determine if the current identifier is a
+stand alone variable reference or if it is a function call expression.
+It handles this by checking to see if the token after the identifier is
+a '(' token, constructing either a ``VariableExprAST`` or
+``CallExprAST`` node as appropriate.
+
+Now that we have all of our simple expression-parsing logic in place, we
+can define a helper function to wrap it together into one entry point.
+We call this class of expressions "primary" expressions, for reasons
+that will become more clear `later in the
+tutorial <LangImpl6.html#unary>`_. In order to parse an arbitrary
+primary expression, we need to determine what sort of expression it is:
+
+.. code-block:: c++
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ }
+ }
+
+Now that you see the definition of this function, it is more obvious why
+we can assume the state of CurTok in the various functions. This uses
+look-ahead to determine which sort of expression is being inspected, and
+then parses it with a function call.
+
+Now that basic expressions are handled, we need to handle binary
+expressions. They are a bit more complex.
+
+Binary Expression Parsing
+=========================
+
+Binary expressions are significantly harder to parse because they are
+often ambiguous. For example, when given the string "x+y\*z", the parser
+can choose to parse it as either "(x+y)\*z" or "x+(y\*z)". With common
+definitions from mathematics, we expect the later parse, because "\*"
+(multiplication) has higher *precedence* than "+" (addition).
+
+There are many ways to handle this, but an elegant and efficient way is
+to use `Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_.
+This parsing technique uses the precedence of binary operators to guide
+recursion. To start with, we need a table of precedences:
+
+.. code-block:: c++
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+ ...
+ }
+
+For the basic form of Kaleidoscope, we will only support 4 binary
+operators (this can obviously be extended by you, our brave and intrepid
+reader). The ``GetTokPrecedence`` function returns the precedence for
+the current token, or -1 if the token is not a binary operator. Having a
+map makes it easy to add new operators and makes it clear that the
+algorithm doesn't depend on the specific operators involved, but it
+would be easy enough to eliminate the map and do the comparisons in the
+``GetTokPrecedence`` function. (Or just use a fixed-size array).
+
+With the helper above defined, we can now start parsing binary
+expressions. The basic idea of operator precedence parsing is to break
+down an expression with potentially ambiguous binary operators into
+pieces. Consider ,for example, the expression "a+b+(c+d)\*e\*f+g".
+Operator precedence parsing considers this as a stream of primary
+expressions separated by binary operators. As such, it will first parse
+the leading primary expression "a", then it will see the pairs [+, b]
+[+, (c+d)] [\*, e] [\*, f] and [+, g]. Note that because parentheses are
+primary expressions, the binary expression parser doesn't need to worry
+about nested subexpressions like (c+d) at all.
+
+To start, an expression is a primary expression potentially followed by
+a sequence of [binop,primaryexpr] pairs:
+
+.. code-block:: c++
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParsePrimary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+``ParseBinOpRHS`` is the function that parses the sequence of pairs for
+us. It takes a precedence and a pointer to an expression for the part
+that has been parsed so far. Note that "x" is a perfectly valid
+expression: As such, "binoprhs" is allowed to be empty, in which case it
+returns the expression that is passed into it. In our example above, the
+code passes the expression for "a" into ``ParseBinOpRHS`` and the
+current token is "+".
+
+The precedence value passed into ``ParseBinOpRHS`` indicates the
+*minimal operator precedence* that the function is allowed to eat. For
+example, if the current pair stream is [+, x] and ``ParseBinOpRHS`` is
+passed in a precedence of 40, it will not consume any tokens (because
+the precedence of '+' is only 20). With this in mind, ``ParseBinOpRHS``
+starts with:
+
+.. code-block:: c++
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+This code gets the precedence of the current token and checks to see if
+if is too low. Because we defined invalid tokens to have a precedence of
+-1, this check implicitly knows that the pair-stream ends when the token
+stream runs out of binary operators. If this check succeeds, we know
+that the token is a binary operator and that it will be included in this
+expression:
+
+.. code-block:: c++
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ ExprAST *RHS = ParsePrimary();
+ if (!RHS) return 0;
+
+As such, this code eats (and remembers) the binary operator and then
+parses the primary expression that follows. This builds up the whole
+pair, the first of which is [+, b] for the running example.
+
+Now that we parsed the left-hand side of an expression and one pair of
+the RHS sequence, we have to decide which way the expression associates.
+In particular, we could have "(a+b) binop unparsed" or "a + (b binop
+unparsed)". To determine this, we look ahead at "binop" to determine its
+precedence and compare it to BinOp's precedence (which is '+' in this
+case):
+
+.. code-block:: c++
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+
+If the precedence of the binop to the right of "RHS" is lower or equal
+to the precedence of our current operator, then we know that the
+parentheses associate as "(a+b) binop ...". In our example, the current
+operator is "+" and the next operator is "+", we know that they have the
+same precedence. In this case we'll create the AST node for "a+b", and
+then continue parsing:
+
+.. code-block:: c++
+
+ ... if body omitted ...
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ } // loop around to the top of the while loop.
+ }
+
+In our example above, this will turn "a+b+" into "(a+b)" and execute the
+next iteration of the loop, with "+" as the current token. The code
+above will eat, remember, and parse "(c+d)" as the primary expression,
+which makes the current pair equal to [+, (c+d)]. It will then evaluate
+the 'if' conditional above with "\*" as the binop to the right of the
+primary. In this case, the precedence of "\*" is higher than the
+precedence of "+" so the if condition will be entered.
+
+The critical question left here is "how can the if condition parse the
+right hand side in full"? In particular, to build the AST correctly for
+our example, it needs to get all of "(c+d)\*e\*f" as the RHS expression
+variable. The code to do this is surprisingly simple (code from the
+above two blocks duplicated for context):
+
+.. code-block:: c++
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ } // loop around to the top of the while loop.
+ }
+
+At this point, we know that the binary operator to the RHS of our
+primary has higher precedence than the binop we are currently parsing.
+As such, we know that any sequence of pairs whose operators are all
+higher precedence than "+" should be parsed together and returned as
+"RHS". To do this, we recursively invoke the ``ParseBinOpRHS`` function
+specifying "TokPrec+1" as the minimum precedence required for it to
+continue. In our example above, this will cause it to return the AST
+node for "(c+d)\*e\*f" as RHS, which is then set as the RHS of the '+'
+expression.
+
+Finally, on the next iteration of the while loop, the "+g" piece is
+parsed and added to the AST. With this little bit of code (14
+non-trivial lines), we correctly handle fully general binary expression
+parsing in a very elegant way. This was a whirlwind tour of this code,
+and it is somewhat subtle. I recommend running through it with a few
+tough examples to see how it works.
+
+This wraps up handling of expressions. At this point, we can point the
+parser at an arbitrary token stream and build an expression from it,
+stopping at the first token that is not part of the expression. Next up
+we need to handle function definitions, etc.
+
+Parsing the Rest
+================
+
+The next thing missing is handling of function prototypes. In
+Kaleidoscope, these are used both for 'extern' function declarations as
+well as function body definitions. The code to do this is
+straight-forward and not very interesting (once you've survived
+expressions):
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static PrototypeAST *ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ // Read the list of argument names.
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return new PrototypeAST(FnName, ArgNames);
+ }
+
+Given this, a function definition is very simple, just a prototype plus
+an expression to implement the body:
+
+.. code-block:: c++
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+In addition, we support 'extern' to declare functions like 'sin' and
+'cos' as well as to support forward declaration of user functions. These
+'extern's are just prototypes with no body:
+
+.. code-block:: c++
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+Finally, we'll also let the user type in arbitrary top-level expressions
+and evaluate them on the fly. We will handle this by defining anonymous
+nullary (zero argument) functions for them:
+
+.. code-block:: c++
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+Now that we have all the pieces, let's build a little driver that will
+let us actually *execute* this code we've built!
+
+The Driver
+==========
+
+The driver for this simply invokes all of the parsing pieces with a
+top-level dispatch loop. There isn't much interesting here, so I'll just
+include the top-level loop. See `below <#code>`_ for full code in the
+"Top-Level Parsing" section.
+
+.. code-block:: c++
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+The most interesting part of this is that we ignore top-level
+semicolons. Why is this, you ask? The basic reason is that if you type
+"4 + 5" at the command line, the parser doesn't know whether that is the
+end of what you will type or not. For example, on the next line you
+could type "def foo..." in which case 4+5 is the end of a top-level
+expression. Alternatively you could type "\* 6", which would continue
+the expression. Having top-level semicolons allows you to type "4+5;",
+and the parser will know you are done.
+
+Conclusions
+===========
+
+With just under 400 lines of commented code (240 lines of non-comment,
+non-blank code), we fully defined our minimal language, including a
+lexer, parser, and AST builder. With this done, the executable will
+validate Kaleidoscope code and tell us if it is grammatically invalid.
+For example, here is a sample interaction:
+
+.. code-block:: bash
+
+ $ ./a.out
+ ready> def foo(x y) x+foo(y, 4.0);
+ Parsed a function definition.
+ ready> def foo(x y) x+y y;
+ Parsed a function definition.
+ Parsed a top-level expr
+ ready> def foo(x y) x+y );
+ Parsed a function definition.
+ Error: unknown token when expecting an expression
+ ready> extern sin(a);
+ ready> Parsed an extern
+ ready> ^D
+ $
+
+There is a lot of room for extension here. You can define new AST nodes,
+extend the language in many ways, etc. In the `next
+installment <LangImpl3.html>`_, we will describe how to generate LLVM
+Intermediate Representation (IR) from the AST.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for this and the previous chapter.
+Note that it is fully self-contained: you don't need LLVM or any
+external libraries at all for this. (Besides the C and C++ standard
+libraries, of course.) To build this, just compile with:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g -O3 toy.cpp
+ # Run
+ ./a.out
+
+Here is the code:
+
+.. code-block:: c++
+
+ #include <cstdio>
+ #include <cstdlib>
+ #include <string>
+ #include <map>
+ #include <vector>
+
+ //===----------------------------------------------------------------------===//
+ // Lexer
+ //===----------------------------------------------------------------------===//
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ return tok_identifier;
+ }
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Abstract Syntax Tree (aka Parse Tree)
+ //===----------------------------------------------------------------------===//
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ };
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ };
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes).
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args)
+ : Name(name), Args(args) {}
+
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ };
+
+ //===----------------------------------------------------------------------===//
+ // Parser
+ //===----------------------------------------------------------------------===//
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+ static ExprAST *ParseExpression();
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ }
+ }
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ ExprAST *RHS = ParsePrimary();
+ if (!RHS) return 0;
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+ }
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParsePrimary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static PrototypeAST *ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return new PrototypeAST(FnName, ArgNames);
+ }
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Top-Level parsing
+ //===----------------------------------------------------------------------===//
+
+ static void HandleDefinition() {
+ if (ParseDefinition()) {
+ fprintf(stderr, "Parsed a function definition.\n");
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (ParseExtern()) {
+ fprintf(stderr, "Parsed an extern\n");
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (ParseTopLevelExpr()) {
+ fprintf(stderr, "Parsed a top-level expr\n");
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Main driver code.
+ //===----------------------------------------------------------------------===//
+
+ int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ fprintf(stderr, "ready> ");
+ getNextToken();
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ return 0;
+ }
+
+`Next: Implementing Code Generation to LLVM IR <LangImpl3.html>`_
+
Removed: llvm/trunk/docs/tutorial/LangImpl3.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl3.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl3.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl3.html (removed)
@@ -1,1268 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Implementing code generation to LLVM IR</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Code generation to LLVM IR</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 3
- <ol>
- <li><a href="#intro">Chapter 3 Introduction</a></li>
- <li><a href="#basics">Code Generation Setup</a></li>
- <li><a href="#exprs">Expression Code Generation</a></li>
- <li><a href="#funcs">Function Code Generation</a></li>
- <li><a href="#driver">Driver Changes and Closing Thoughts</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="LangImpl4.html">Chapter 4</a>: Adding JIT and Optimizer
-Support</li>
-</ul>
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 3 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. This chapter shows you how to transform the <a
-href="LangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into LLVM IR.
-This will teach you a little bit about how LLVM does things, as well as
-demonstrate how easy it is to use. It's much more work to build a lexer and
-parser than it is to generate LLVM IR code. :)
-</p>
-
-<p><b>Please note</b>: the code in this chapter and later require LLVM 2.2 or
-later. LLVM 2.1 and before will not work with it. Also note that you need
-to use a version of this tutorial that matches your LLVM release: If you are
-using an official LLVM release, use the version of the documentation included
-with your release or on the <a href="http://llvm.org/releases/">llvm.org
-releases page</a>.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="basics">Code Generation Setup</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-In order to generate LLVM IR, we want some simple setup to get started. First
-we define virtual code generation (codegen) methods in each AST class:</p>
-
-<div class="doc_code">
-<pre>
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
- <b>virtual Value *Codegen() = 0;</b>
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
- <b>virtual Value *Codegen();</b>
-};
-...
-</pre>
-</div>
-
-<p>The Codegen() method says to emit IR for that AST node along with all the things it
-depends on, and they all return an LLVM Value object.
-"Value" is the class used to represent a "<a
-href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
-Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect
-of SSA values is that their value is computed as the related instruction
-executes, and it does not get a new value until (and if) the instruction
-re-executes. In other words, there is no way to "change" an SSA value. For
-more information, please read up on <a
-href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
-Assignment</a> - the concepts are really quite natural once you grok them.</p>
-
-<p>Note that instead of adding virtual methods to the ExprAST class hierarchy,
-it could also make sense to use a <a
-href="http://en.wikipedia.org/wiki/Visitor_pattern">visitor pattern</a> or some
-other way to model this. Again, this tutorial won't dwell on good software
-engineering practices: for our purposes, adding a virtual method is
-simplest.</p>
-
-<p>The
-second thing we want is an "Error" method like we used for the parser, which will
-be used to report errors found during code generation (for example, use of an
-undeclared parameter):</p>
-
-<div class="doc_code">
-<pre>
-Value *ErrorV(const char *Str) { Error(Str); return 0; }
-
-static Module *TheModule;
-static IRBuilder<> Builder(getGlobalContext());
-static std::map<std::string, Value*> NamedValues;
-</pre>
-</div>
-
-<p>The static variables will be used during code generation. <tt>TheModule</tt>
-is the LLVM construct that contains all of the functions and global variables in
-a chunk of code. In many ways, it is the top-level structure that the LLVM IR
-uses to contain code.</p>
-
-<p>The <tt>Builder</tt> object is a helper object that makes it easy to generate
-LLVM instructions. Instances of the <a
-href="http://llvm.org/doxygen/IRBuilder_8h-source.html"><tt>IRBuilder</tt></a>
-class template keep track of the current place to insert instructions and has
-methods to create new instructions.</p>
-
-<p>The <tt>NamedValues</tt> map keeps track of which values are defined in the
-current scope and what their LLVM representation is. (In other words, it is a
-symbol table for the code). In this form of Kaleidoscope, the only things that
-can be referenced are function parameters. As such, function parameters will
-be in this map when generating code for their function body.</p>
-
-<p>
-With these basics in place, we can start talking about how to generate code for
-each expression. Note that this assumes that the <tt>Builder</tt> has been set
-up to generate code <em>into</em> something. For now, we'll assume that this
-has already been done, and we'll just use it to emit code.
-</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="exprs">Expression Code Generation</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Generating LLVM code for expression nodes is very straightforward: less
-than 45 lines of commented code for all four of our expression nodes. First
-we'll do numeric literals:</p>
-
-<div class="doc_code">
-<pre>
-Value *NumberExprAST::Codegen() {
- return ConstantFP::get(getGlobalContext(), APFloat(Val));
-}
-</pre>
-</div>
-
-<p>In the LLVM IR, numeric constants are represented with the
-<tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt>
-internally (<tt>APFloat</tt> has the capability of holding floating point
-constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just
-creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR
-that constants are all uniqued together and shared. For this reason, the API
-uses the "foo::get(...)" idiom instead of "new foo(..)" or "foo::Create(..)".</p>
-
-<div class="doc_code">
-<pre>
-Value *VariableExprAST::Codegen() {
- // Look this variable up in the function.
- Value *V = NamedValues[Name];
- return V ? V : ErrorV("Unknown variable name");
-}
-</pre>
-</div>
-
-<p>References to variables are also quite simple using LLVM. In the simple version
-of Kaleidoscope, we assume that the variable has already been emitted somewhere
-and its value is available. In practice, the only values that can be in the
-<tt>NamedValues</tt> map are function arguments. This
-code simply checks to see that the specified name is in the map (if not, an
-unknown variable is being referenced) and returns the value for it. In future
-chapters, we'll add support for <a href="LangImpl5.html#for">loop induction
-variables</a> in the symbol table, and for <a
-href="LangImpl7.html#localvars">local variables</a>.</p>
-
-<div class="doc_code">
-<pre>
-Value *BinaryExprAST::Codegen() {
- Value *L = LHS->Codegen();
- Value *R = RHS->Codegen();
- if (L == 0 || R == 0) return 0;
-
- switch (Op) {
- case '+': return Builder.CreateFAdd(L, R, "addtmp");
- case '-': return Builder.CreateFSub(L, R, "subtmp");
- case '*': return Builder.CreateFMul(L, R, "multmp");
- case '<':
- L = Builder.CreateFCmpULT(L, R, "cmptmp");
- // Convert bool 0/1 to double 0.0 or 1.0
- return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
- "booltmp");
- default: return ErrorV("invalid binary operator");
- }
-}
-</pre>
-</div>
-
-<p>Binary operators start to get more interesting. The basic idea here is that
-we recursively emit code for the left-hand side of the expression, then the
-right-hand side, then we compute the result of the binary expression. In this
-code, we do a simple switch on the opcode to create the right LLVM instruction.
-</p>
-
-<p>In the example above, the LLVM builder class is starting to show its value.
-IRBuilder knows where to insert the newly created instruction, all you have to
-do is specify what instruction to create (e.g. with <tt>CreateFAdd</tt>), which
-operands to use (<tt>L</tt> and <tt>R</tt> here) and optionally provide a name
-for the generated instruction.</p>
-
-<p>One nice thing about LLVM is that the name is just a hint. For instance, if
-the code above emits multiple "addtmp" variables, LLVM will automatically
-provide each one with an increasing, unique numeric suffix. Local value names
-for instructions are purely optional, but it makes it much easier to read the
-IR dumps.</p>
-
-<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by
-strict rules: for example, the Left and Right operators of
-an <a href="../LangRef.html#i_add">add instruction</a> must have the same
-type, and the result type of the add must match the operand types. Because
-all values in Kaleidoscope are doubles, this makes for very simple code for add,
-sub and mul.</p>
-
-<p>On the other hand, LLVM specifies that the <a
-href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value
-(a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with
-a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction
-converts its input integer into a floating point value by treating the input
-as an unsigned value. In contrast, if we used the <a
-href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<'
-operator would return 0.0 and -1.0, depending on the input value.</p>
-
-<div class="doc_code">
-<pre>
-Value *CallExprAST::Codegen() {
- // Look up the name in the global module table.
- Function *CalleeF = TheModule->getFunction(Callee);
- if (CalleeF == 0)
- return ErrorV("Unknown function referenced");
-
- // If argument mismatch error.
- if (CalleeF->arg_size() != Args.size())
- return ErrorV("Incorrect # arguments passed");
-
- std::vector<Value*> ArgsV;
- for (unsigned i = 0, e = Args.size(); i != e; ++i) {
- ArgsV.push_back(Args[i]->Codegen());
- if (ArgsV.back() == 0) return 0;
- }
-
- return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
-}
-</pre>
-</div>
-
-<p>Code generation for function calls is quite straightforward with LLVM. The
-code above initially does a function name lookup in the LLVM Module's symbol
-table. Recall that the LLVM Module is the container that holds all of the
-functions we are JIT'ing. By giving each function the same name as what the
-user specifies, we can use the LLVM symbol table to resolve function names for
-us.</p>
-
-<p>Once we have the function to call, we recursively codegen each argument that
-is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call
-instruction</a>. Note that LLVM uses the native C calling conventions by
-default, allowing these calls to also call into standard library functions like
-"sin" and "cos", with no additional effort.</p>
-
-<p>This wraps up our handling of the four basic expressions that we have so far
-in Kaleidoscope. Feel free to go in and add some more. For example, by
-browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find
-several other interesting instructions that are really easy to plug into our
-basic framework.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="funcs">Function Code Generation</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Code generation for prototypes and functions must handle a number of
-details, which make their code less beautiful than expression code
-generation, but allows us to illustrate some important points. First, lets
-talk about code generation for prototypes: they are used both for function
-bodies and external function declarations. The code starts with:</p>
-
-<div class="doc_code">
-<pre>
-Function *PrototypeAST::Codegen() {
- // Make the function type: double(double,double) etc.
- std::vector<Type*> Doubles(Args.size(),
- Type::getDoubleTy(getGlobalContext()));
- FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
- Doubles, false);
-
- Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
-</pre>
-</div>
-
-<p>This code packs a lot of power into a few lines. Note first that this
-function returns a "Function*" instead of a "Value*". Because a "prototype"
-really talks about the external interface for a function (not the value computed
-by an expression), it makes sense for it to return the LLVM Function it
-corresponds to when codegen'd.</p>
-
-<p>The call to <tt>FunctionType::get</tt> creates
-the <tt>FunctionType</tt> that should be used for a given Prototype. Since all
-function arguments in Kaleidoscope are of type double, the first line creates
-a vector of "N" LLVM double types. It then uses the <tt>Functiontype::get</tt>
-method to create a function type that takes "N" doubles as arguments, returns
-one double as a result, and that is not vararg (the false parameter indicates
-this). Note that Types in LLVM are uniqued just like Constants are, so you
-don't "new" a type, you "get" it.</p>
-
-<p>The final line above actually creates the function that the prototype will
-correspond to. This indicates the type, linkage and name to use, as well as which
-module to insert into. "<a href="../LangRef.html#linkage">external linkage</a>"
-means that the function may be defined outside the current module and/or that it
-is callable by functions outside the module. The Name passed in is the name the
-user specified: since "<tt>TheModule</tt>" is specified, this name is registered
-in "<tt>TheModule</tt>"s symbol table, which is used by the function call code
-above.</p>
-
-<div class="doc_code">
-<pre>
- // If F conflicted, there was already something named 'Name'. If it has a
- // body, don't allow redefinition or reextern.
- if (F->getName() != Name) {
- // Delete the one we just made and get the existing one.
- F->eraseFromParent();
- F = TheModule->getFunction(Name);
-</pre>
-</div>
-
-<p>The Module symbol table works just like the Function symbol table when it
-comes to name conflicts: if a new function is created with a name that was previously
-added to the symbol table, the new function will get implicitly renamed when added to the
-Module. The code above exploits this fact to determine if there was a previous
-definition of this function.</p>
-
-<p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
-first, we want to allow 'extern'ing a function more than once, as long as the
-prototypes for the externs match (since all arguments have the same type, we
-just have to check that the number of arguments match). Second, we want to
-allow 'extern'ing a function and then defining a body for it. This is useful
-when defining mutually recursive functions.</p>
-
-<p>In order to implement this, the code above first checks to see if there is
-a collision on the name of the function. If so, it deletes the function we just
-created (by calling <tt>eraseFromParent</tt>) and then calling
-<tt>getFunction</tt> to get the existing function with the specified name. Note
-that many APIs in LLVM have "erase" forms and "remove" forms. The "remove" form
-unlinks the object from its parent (e.g. a Function from a Module) and returns
-it. The "erase" form unlinks the object and then deletes it.</p>
-
-<div class="doc_code">
-<pre>
- // If F already has a body, reject this.
- if (!F->empty()) {
- ErrorF("redefinition of function");
- return 0;
- }
-
- // If F took a different number of args, reject.
- if (F->arg_size() != Args.size()) {
- ErrorF("redefinition of function with different # args");
- return 0;
- }
- }
-</pre>
-</div>
-
-<p>In order to verify the logic above, we first check to see if the pre-existing
-function is "empty". In this case, empty means that it has no basic blocks in
-it, which means it has no body. If it has no body, it is a forward
-declaration. Since we don't allow anything after a full definition of the
-function, the code rejects this case. If the previous reference to a function
-was an 'extern', we simply verify that the number of arguments for that
-definition and this one match up. If not, we emit an error.</p>
-
-<div class="doc_code">
-<pre>
- // Set names for all arguments.
- unsigned Idx = 0;
- for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
- ++AI, ++Idx) {
- AI->setName(Args[Idx]);
-
- // Add arguments to variable symbol table.
- NamedValues[Args[Idx]] = AI;
- }
- return F;
-}
-</pre>
-</div>
-
-<p>The last bit of code for prototypes loops over all of the arguments in the
-function, setting the name of the LLVM Argument objects to match, and registering
-the arguments in the <tt>NamedValues</tt> map for future use by the
-<tt>VariableExprAST</tt> AST node. Once this is set up, it returns the Function
-object to the caller. Note that we don't check for conflicting
-argument names here (e.g. "extern foo(a b a)"). Doing so would be very
-straight-forward with the mechanics we have already used above.</p>
-
-<div class="doc_code">
-<pre>
-Function *FunctionAST::Codegen() {
- NamedValues.clear();
-
- Function *TheFunction = Proto->Codegen();
- if (TheFunction == 0)
- return 0;
-</pre>
-</div>
-
-<p>Code generation for function definitions starts out simply enough: we just
-codegen the prototype (Proto) and verify that it is ok. We then clear out the
-<tt>NamedValues</tt> map to make sure that there isn't anything in it from the
-last function we compiled. Code generation of the prototype ensures that there
-is an LLVM Function object that is ready to go for us.</p>
-
-<div class="doc_code">
-<pre>
- // Create a new basic block to start insertion into.
- BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
- Builder.SetInsertPoint(BB);
-
- if (Value *RetVal = Body->Codegen()) {
-</pre>
-</div>
-
-<p>Now we get to the point where the <tt>Builder</tt> is set up. The first
-line creates a new <a href="http://en.wikipedia.org/wiki/Basic_block">basic
-block</a> (named "entry"), which is inserted into <tt>TheFunction</tt>. The
-second line then tells the builder that new instructions should be inserted into
-the end of the new basic block. Basic blocks in LLVM are an important part
-of functions that define the <a
-href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>.
-Since we don't have any control flow, our functions will only contain one
-block at this point. We'll fix this in <a href="LangImpl5.html">Chapter 5</a> :).</p>
-
-<div class="doc_code">
-<pre>
- if (Value *RetVal = Body->Codegen()) {
- // Finish off the function.
- Builder.CreateRet(RetVal);
-
- // Validate the generated code, checking for consistency.
- verifyFunction(*TheFunction);
-
- return TheFunction;
- }
-</pre>
-</div>
-
-<p>Once the insertion point is set up, we call the <tt>CodeGen()</tt> method for
-the root expression of the function. If no error happens, this emits code to
-compute the expression into the entry block and returns the value that was
-computed. Assuming no error, we then create an LLVM <a
-href="../LangRef.html#i_ret">ret instruction</a>, which completes the function.
-Once the function is built, we call <tt>verifyFunction</tt>, which
-is provided by LLVM. This function does a variety of consistency checks on the
-generated code, to determine if our compiler is doing everything right. Using
-this is important: it can catch a lot of bugs. Once the function is finished
-and validated, we return it.</p>
-
-<div class="doc_code">
-<pre>
- // Error reading body, remove function.
- TheFunction->eraseFromParent();
- return 0;
-}
-</pre>
-</div>
-
-<p>The only piece left here is handling of the error case. For simplicity, we
-handle this by merely deleting the function we produced with the
-<tt>eraseFromParent</tt> method. This allows the user to redefine a function
-that they incorrectly typed in before: if we didn't delete it, it would live in
-the symbol table, with a body, preventing future redefinition.</p>
-
-<p>This code does have a bug, though. Since the <tt>PrototypeAST::Codegen</tt>
-can return a previously defined forward declaration, our code can actually delete
-a forward declaration. There are a number of ways to fix this bug, see what you
-can come up with! Here is a testcase:</p>
-
-<div class="doc_code">
-<pre>
-extern foo(a b); # ok, defines foo.
-def foo(a b) c; # error, 'c' is invalid.
-def bar() foo(1, 2); # error, unknown function "foo"
-</pre>
-</div>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="driver">Driver Changes and Closing Thoughts</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-For now, code generation to LLVM doesn't really get us much, except that we can
-look at the pretty IR calls. The sample code inserts calls to Codegen into the
-"<tt>HandleDefinition</tt>", "<tt>HandleExtern</tt>" etc functions, and then
-dumps out the LLVM IR. This gives a nice way to look at the LLVM IR for simple
-functions. For example:
-</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>4+5</b>;
-Read top-level expression:
-define double @0() {
-entry:
- ret double 9.000000e+00
-}
-</pre>
-</div>
-
-<p>Note how the parser turns the top-level expression into anonymous functions
-for us. This will be handy when we add <a href="LangImpl4.html#jit">JIT
-support</a> in the next chapter. Also note that the code is very literally
-transcribed, no optimizations are being performed except simple constant
-folding done by IRBuilder. We will
-<a href="LangImpl4.html#trivialconstfold">add optimizations</a> explicitly in
-the next chapter.</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def foo(a b) a*a + 2*a*b + b*b;</b>
-Read function definition:
-define double @foo(double %a, double %b) {
-entry:
- %multmp = fmul double %a, %a
- %multmp1 = fmul double 2.000000e+00, %a
- %multmp2 = fmul double %multmp1, %b
- %addtmp = fadd double %multmp, %multmp2
- %multmp3 = fmul double %b, %b
- %addtmp4 = fadd double %addtmp, %multmp3
- ret double %addtmp4
-}
-</pre>
-</div>
-
-<p>This shows some simple arithmetic. Notice the striking similarity to the
-LLVM builder calls that we use to create the instructions.</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def bar(a) foo(a, 4.0) + bar(31337);</b>
-Read function definition:
-define double @bar(double %a) {
-entry:
- %calltmp = call double @foo(double %a, double 4.000000e+00)
- %calltmp1 = call double @bar(double 3.133700e+04)
- %addtmp = fadd double %calltmp, %calltmp1
- ret double %addtmp
-}
-</pre>
-</div>
-
-<p>This shows some function calls. Note that this function will take a long
-time to execute if you call it. In the future we'll add conditional control
-flow to actually make recursion useful :).</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>extern cos(x);</b>
-Read extern:
-declare double @cos(double)
-
-ready> <b>cos(1.234);</b>
-Read top-level expression:
-define double @1() {
-entry:
- %calltmp = call double @cos(double 1.234000e+00)
- ret double %calltmp
-}
-</pre>
-</div>
-
-<p>This shows an extern for the libm "cos" function, and a call to it.</p>
-
-
-<div class="doc_code">
-<pre>
-ready> <b>^D</b>
-; ModuleID = 'my cool jit'
-
-define double @0() {
-entry:
- %addtmp = fadd double 4.000000e+00, 5.000000e+00
- ret double %addtmp
-}
-
-define double @foo(double %a, double %b) {
-entry:
- %multmp = fmul double %a, %a
- %multmp1 = fmul double 2.000000e+00, %a
- %multmp2 = fmul double %multmp1, %b
- %addtmp = fadd double %multmp, %multmp2
- %multmp3 = fmul double %b, %b
- %addtmp4 = fadd double %addtmp, %multmp3
- ret double %addtmp4
-}
-
-define double @bar(double %a) {
-entry:
- %calltmp = call double @foo(double %a, double 4.000000e+00)
- %calltmp1 = call double @bar(double 3.133700e+04)
- %addtmp = fadd double %calltmp, %calltmp1
- ret double %addtmp
-}
-
-declare double @cos(double)
-
-define double @1() {
-entry:
- %calltmp = call double @cos(double 1.234000e+00)
- ret double %calltmp
-}
-</pre>
-</div>
-
-<p>When you quit the current demo, it dumps out the IR for the entire module
-generated. Here you can see the big picture with all the functions referencing
-each other.</p>
-
-<p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll
-describe how to <a href="LangImpl4.html">add JIT codegen and optimizer
-support</a> to this so we can actually start running code!</p>
-
-</div>
-
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for our running example, enhanced with the
-LLVM code generator. Because this uses the LLVM libraries, we need to link
-them in. To do this, we use the <a
-href="http://llvm.org/cmds/llvm-config.html">llvm-config</a> tool to inform
-our makefile/command line about which options to use:</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-clang++ -g -O3 toy.cpp `llvm-config --cppflags --ldflags --libs core` -o toy
-# Run
-./toy
-</pre>
-</div>
-
-<p>Here is the code:</p>
-
-<div class="doc_code">
-<pre>
-// To build this:
-// See example below.
-
-#include "llvm/DerivedTypes.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/Analysis/Verifier.h"
-#include <cstdio>
-#include <string>
-#include <map>
-#include <vector>
-using namespace llvm;
-
-//===----------------------------------------------------------------------===//
-// Lexer
-//===----------------------------------------------------------------------===//
-
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
- tok_eof = -1,
-
- // commands
- tok_def = -2, tok_extern = -3,
-
- // primary
- tok_identifier = -4, tok_number = -5
-};
-
-static std::string IdentifierStr; // Filled in if tok_identifier
-static double NumVal; // Filled in if tok_number
-
-/// gettok - Return the next token from standard input.
-static int gettok() {
- static int LastChar = ' ';
-
- // Skip any whitespace.
- while (isspace(LastChar))
- LastChar = getchar();
-
- if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
- IdentifierStr = LastChar;
- while (isalnum((LastChar = getchar())))
- IdentifierStr += LastChar;
-
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- return tok_identifier;
- }
-
- if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
- std::string NumStr;
- do {
- NumStr += LastChar;
- LastChar = getchar();
- } while (isdigit(LastChar) || LastChar == '.');
-
- NumVal = strtod(NumStr.c_str(), 0);
- return tok_number;
- }
-
- if (LastChar == '#') {
- // Comment until end of line.
- do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-
- if (LastChar != EOF)
- return gettok();
- }
-
- // Check for end of file. Don't eat the EOF.
- if (LastChar == EOF)
- return tok_eof;
-
- // Otherwise, just return the character as its ascii value.
- int ThisChar = LastChar;
- LastChar = getchar();
- return ThisChar;
-}
-
-//===----------------------------------------------------------------------===//
-// Abstract Syntax Tree (aka Parse Tree)
-//===----------------------------------------------------------------------===//
-
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
- virtual Value *Codegen() = 0;
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
- virtual Value *Codegen();
-};
-
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
- std::string Name;
-public:
- VariableExprAST(const std::string &name) : Name(name) {}
- virtual Value *Codegen();
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
- char Op;
- ExprAST *LHS, *RHS;
-public:
- BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
- : Op(op), LHS(lhs), RHS(rhs) {}
- virtual Value *Codegen();
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
- std::string Callee;
- std::vector<ExprAST*> Args;
-public:
- CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
- : Callee(callee), Args(args) {}
- virtual Value *Codegen();
-};
-
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes).
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args)
- : Name(name), Args(args) {}
-
- Function *Codegen();
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
- PrototypeAST *Proto;
- ExprAST *Body;
-public:
- FunctionAST(PrototypeAST *proto, ExprAST *body)
- : Proto(proto), Body(body) {}
-
- Function *Codegen();
-};
-
-//===----------------------------------------------------------------------===//
-// Parser
-//===----------------------------------------------------------------------===//
-
-/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
-/// token the parser is looking at. getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
- return CurTok = gettok();
-}
-
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
- if (!isascii(CurTok))
- return -1;
-
- // Make sure it's a declared binop.
- int TokPrec = BinopPrecedence[CurTok];
- if (TokPrec <= 0) return -1;
- return TokPrec;
-}
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-
-static ExprAST *ParseExpression();
-
-/// identifierexpr
-/// ::= identifier
-/// ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
- std::string IdName = IdentifierStr;
-
- getNextToken(); // eat identifier.
-
- if (CurTok != '(') // Simple variable ref.
- return new VariableExprAST(IdName);
-
- // Call.
- getNextToken(); // eat (
- std::vector<ExprAST*> Args;
- if (CurTok != ')') {
- while (1) {
- ExprAST *Arg = ParseExpression();
- if (!Arg) return 0;
- Args.push_back(Arg);
-
- if (CurTok == ')') break;
-
- if (CurTok != ',')
- return Error("Expected ')' or ',' in argument list");
- getNextToken();
- }
- }
-
- // Eat the ')'.
- getNextToken();
-
- return new CallExprAST(IdName, Args);
-}
-
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
- ExprAST *Result = new NumberExprAST(NumVal);
- getNextToken(); // consume the number
- return Result;
-}
-
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
- getNextToken(); // eat (.
- ExprAST *V = ParseExpression();
- if (!V) return 0;
-
- if (CurTok != ')')
- return Error("expected ')'");
- getNextToken(); // eat ).
- return V;
-}
-
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- }
-}
-
-/// binoprhs
-/// ::= ('+' primary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- // If this is a binop, find its precedence.
- while (1) {
- int TokPrec = GetTokPrecedence();
-
- // If this is a binop that binds at least as tightly as the current binop,
- // consume it, otherwise we are done.
- if (TokPrec < ExprPrec)
- return LHS;
-
- // Okay, we know this is a binop.
- int BinOp = CurTok;
- getNextToken(); // eat binop
-
- // Parse the primary expression after the binary operator.
- ExprAST *RHS = ParsePrimary();
- if (!RHS) return 0;
-
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
- RHS = ParseBinOpRHS(TokPrec+1, RHS);
- if (RHS == 0) return 0;
- }
-
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- }
-}
-
-/// expression
-/// ::= primary binoprhs
-///
-static ExprAST *ParseExpression() {
- ExprAST *LHS = ParsePrimary();
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-
-/// prototype
-/// ::= id '(' id* ')'
-static PrototypeAST *ParsePrototype() {
- if (CurTok != tok_identifier)
- return ErrorP("Expected function name in prototype");
-
- std::string FnName = IdentifierStr;
- getNextToken();
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- return new PrototypeAST(FnName, ArgNames);
-}
-
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
- getNextToken(); // eat def.
- PrototypeAST *Proto = ParsePrototype();
- if (Proto == 0) return 0;
-
- if (ExprAST *E = ParseExpression())
- return new FunctionAST(Proto, E);
- return 0;
-}
-
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
- if (ExprAST *E = ParseExpression()) {
- // Make an anonymous proto.
- PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
- return new FunctionAST(Proto, E);
- }
- return 0;
-}
-
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
- getNextToken(); // eat extern.
- return ParsePrototype();
-}
-
-//===----------------------------------------------------------------------===//
-// Code Generation
-//===----------------------------------------------------------------------===//
-
-static Module *TheModule;
-static IRBuilder<> Builder(getGlobalContext());
-static std::map<std::string, Value*> NamedValues;
-
-Value *ErrorV(const char *Str) { Error(Str); return 0; }
-
-Value *NumberExprAST::Codegen() {
- return ConstantFP::get(getGlobalContext(), APFloat(Val));
-}
-
-Value *VariableExprAST::Codegen() {
- // Look this variable up in the function.
- Value *V = NamedValues[Name];
- return V ? V : ErrorV("Unknown variable name");
-}
-
-Value *BinaryExprAST::Codegen() {
- Value *L = LHS->Codegen();
- Value *R = RHS->Codegen();
- if (L == 0 || R == 0) return 0;
-
- switch (Op) {
- case '+': return Builder.CreateFAdd(L, R, "addtmp");
- case '-': return Builder.CreateFSub(L, R, "subtmp");
- case '*': return Builder.CreateFMul(L, R, "multmp");
- case '<':
- L = Builder.CreateFCmpULT(L, R, "cmptmp");
- // Convert bool 0/1 to double 0.0 or 1.0
- return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
- "booltmp");
- default: return ErrorV("invalid binary operator");
- }
-}
-
-Value *CallExprAST::Codegen() {
- // Look up the name in the global module table.
- Function *CalleeF = TheModule->getFunction(Callee);
- if (CalleeF == 0)
- return ErrorV("Unknown function referenced");
-
- // If argument mismatch error.
- if (CalleeF->arg_size() != Args.size())
- return ErrorV("Incorrect # arguments passed");
-
- std::vector<Value*> ArgsV;
- for (unsigned i = 0, e = Args.size(); i != e; ++i) {
- ArgsV.push_back(Args[i]->Codegen());
- if (ArgsV.back() == 0) return 0;
- }
-
- return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
-}
-
-Function *PrototypeAST::Codegen() {
- // Make the function type: double(double,double) etc.
- std::vector<Type*> Doubles(Args.size(),
- Type::getDoubleTy(getGlobalContext()));
- FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
- Doubles, false);
-
- Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
-
- // If F conflicted, there was already something named 'Name'. If it has a
- // body, don't allow redefinition or reextern.
- if (F->getName() != Name) {
- // Delete the one we just made and get the existing one.
- F->eraseFromParent();
- F = TheModule->getFunction(Name);
-
- // If F already has a body, reject this.
- if (!F->empty()) {
- ErrorF("redefinition of function");
- return 0;
- }
-
- // If F took a different number of args, reject.
- if (F->arg_size() != Args.size()) {
- ErrorF("redefinition of function with different # args");
- return 0;
- }
- }
-
- // Set names for all arguments.
- unsigned Idx = 0;
- for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
- ++AI, ++Idx) {
- AI->setName(Args[Idx]);
-
- // Add arguments to variable symbol table.
- NamedValues[Args[Idx]] = AI;
- }
-
- return F;
-}
-
-Function *FunctionAST::Codegen() {
- NamedValues.clear();
-
- Function *TheFunction = Proto->Codegen();
- if (TheFunction == 0)
- return 0;
-
- // Create a new basic block to start insertion into.
- BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
- Builder.SetInsertPoint(BB);
-
- if (Value *RetVal = Body->Codegen()) {
- // Finish off the function.
- Builder.CreateRet(RetVal);
-
- // Validate the generated code, checking for consistency.
- verifyFunction(*TheFunction);
-
- return TheFunction;
- }
-
- // Error reading body, remove function.
- TheFunction->eraseFromParent();
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Top-Level parsing and JIT Driver
-//===----------------------------------------------------------------------===//
-
-static void HandleDefinition() {
- if (FunctionAST *F = ParseDefinition()) {
- if (Function *LF = F->Codegen()) {
- fprintf(stderr, "Read function definition:");
- LF->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleExtern() {
- if (PrototypeAST *P = ParseExtern()) {
- if (Function *F = P->Codegen()) {
- fprintf(stderr, "Read extern: ");
- F->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleTopLevelExpression() {
- // Evaluate a top-level expression into an anonymous function.
- if (FunctionAST *F = ParseTopLevelExpr()) {
- if (Function *LF = F->Codegen()) {
- fprintf(stderr, "Read top-level expression:");
- LF->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
- while (1) {
- fprintf(stderr, "ready> ");
- switch (CurTok) {
- case tok_eof: return;
- case ';': getNextToken(); break; // ignore top-level semicolons.
- case tok_def: HandleDefinition(); break;
- case tok_extern: HandleExtern(); break;
- default: HandleTopLevelExpression(); break;
- }
- }
-}
-
-//===----------------------------------------------------------------------===//
-// "Library" functions that can be "extern'd" from user code.
-//===----------------------------------------------------------------------===//
-
-/// putchard - putchar that takes a double and returns 0.
-extern "C"
-double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Main driver code.
-//===----------------------------------------------------------------------===//
-
-int main() {
- LLVMContext &Context = getGlobalContext();
-
- // Install standard binary operators.
- // 1 is lowest precedence.
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
- BinopPrecedence['*'] = 40; // highest.
-
- // Prime the first token.
- fprintf(stderr, "ready> ");
- getNextToken();
-
- // Make the module, which holds all the code.
- TheModule = new Module("my cool jit", Context);
-
- // Run the main "interpreter loop" now.
- MainLoop();
-
- // Print out all of the generated code.
- TheModule->dump();
-
- return 0;
-}
-</pre>
-</div>
-<a href="LangImpl4.html">Next: Adding JIT and Optimizer Support</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
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Added: llvm/trunk/docs/tutorial/LangImpl3.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl3.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl3.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl3.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,1162 @@
+========================================
+Kaleidoscope: Code generation to LLVM IR
+========================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Chapter 3 Introduction
+======================
+
+Welcome to Chapter 3 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to transform
+the `Abstract Syntax Tree <LangImpl2.html>`_, built in Chapter 2, into
+LLVM IR. This will teach you a little bit about how LLVM does things, as
+well as demonstrate how easy it is to use. It's much more work to build
+a lexer and parser than it is to generate LLVM IR code. :)
+
+**Please note**: the code in this chapter and later require LLVM 2.2 or
+later. LLVM 2.1 and before will not work with it. Also note that you
+need to use a version of this tutorial that matches your LLVM release:
+If you are using an official LLVM release, use the version of the
+documentation included with your release or on the `llvm.org releases
+page <http://llvm.org/releases/>`_.
+
+Code Generation Setup
+=====================
+
+In order to generate LLVM IR, we want some simple setup to get started.
+First we define virtual code generation (codegen) methods in each AST
+class:
+
+.. code-block:: c++
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *Codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ virtual Value *Codegen();
+ };
+ ...
+
+The Codegen() method says to emit IR for that AST node along with all
+the things it depends on, and they all return an LLVM Value object.
+"Value" is the class used to represent a "`Static Single Assignment
+(SSA) <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+register" or "SSA value" in LLVM. The most distinct aspect of SSA values
+is that their value is computed as the related instruction executes, and
+it does not get a new value until (and if) the instruction re-executes.
+In other words, there is no way to "change" an SSA value. For more
+information, please read up on `Static Single
+Assignment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+- the concepts are really quite natural once you grok them.
+
+Note that instead of adding virtual methods to the ExprAST class
+hierarchy, it could also make sense to use a `visitor
+pattern <http://en.wikipedia.org/wiki/Visitor_pattern>`_ or some other
+way to model this. Again, this tutorial won't dwell on good software
+engineering practices: for our purposes, adding a virtual method is
+simplest.
+
+The second thing we want is an "Error" method like we used for the
+parser, which will be used to report errors found during code generation
+(for example, use of an undeclared parameter):
+
+.. code-block:: c++
+
+ Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+ static Module *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, Value*> NamedValues;
+
+The static variables will be used during code generation. ``TheModule``
+is the LLVM construct that contains all of the functions and global
+variables in a chunk of code. In many ways, it is the top-level
+structure that the LLVM IR uses to contain code.
+
+The ``Builder`` object is a helper object that makes it easy to generate
+LLVM instructions. Instances of the
+```IRBuilder`` <http://llvm.org/doxygen/IRBuilder_8h-source.html>`_
+class template keep track of the current place to insert instructions
+and has methods to create new instructions.
+
+The ``NamedValues`` map keeps track of which values are defined in the
+current scope and what their LLVM representation is. (In other words, it
+is a symbol table for the code). In this form of Kaleidoscope, the only
+things that can be referenced are function parameters. As such, function
+parameters will be in this map when generating code for their function
+body.
+
+With these basics in place, we can start talking about how to generate
+code for each expression. Note that this assumes that the ``Builder``
+has been set up to generate code *into* something. For now, we'll assume
+that this has already been done, and we'll just use it to emit code.
+
+Expression Code Generation
+==========================
+
+Generating LLVM code for expression nodes is very straightforward: less
+than 45 lines of commented code for all four of our expression nodes.
+First we'll do numeric literals:
+
+.. code-block:: c++
+
+ Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+In the LLVM IR, numeric constants are represented with the
+``ConstantFP`` class, which holds the numeric value in an ``APFloat``
+internally (``APFloat`` has the capability of holding floating point
+constants of Arbitrary Precision). This code basically just creates
+and returns a ``ConstantFP``. Note that in the LLVM IR that constants
+are all uniqued together and shared. For this reason, the API uses the
+"foo::get(...)" idiom instead of "new foo(..)" or "foo::Create(..)".
+
+.. code-block:: c++
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ return V ? V : ErrorV("Unknown variable name");
+ }
+
+References to variables are also quite simple using LLVM. In the simple
+version of Kaleidoscope, we assume that the variable has already been
+emitted somewhere and its value is available. In practice, the only
+values that can be in the ``NamedValues`` map are function arguments.
+This code simply checks to see that the specified name is in the map (if
+not, an unknown variable is being referenced) and returns the value for
+it. In future chapters, we'll add support for `loop induction
+variables <LangImpl5.html#for>`_ in the symbol table, and for `local
+variables <LangImpl7.html#localvars>`_.
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateFAdd(L, R, "addtmp");
+ case '-': return Builder.CreateFSub(L, R, "subtmp");
+ case '*': return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default: return ErrorV("invalid binary operator");
+ }
+ }
+
+Binary operators start to get more interesting. The basic idea here is
+that we recursively emit code for the left-hand side of the expression,
+then the right-hand side, then we compute the result of the binary
+expression. In this code, we do a simple switch on the opcode to create
+the right LLVM instruction.
+
+In the example above, the LLVM builder class is starting to show its
+value. IRBuilder knows where to insert the newly created instruction,
+all you have to do is specify what instruction to create (e.g. with
+``CreateFAdd``), which operands to use (``L`` and ``R`` here) and
+optionally provide a name for the generated instruction.
+
+One nice thing about LLVM is that the name is just a hint. For instance,
+if the code above emits multiple "addtmp" variables, LLVM will
+automatically provide each one with an increasing, unique numeric
+suffix. Local value names for instructions are purely optional, but it
+makes it much easier to read the IR dumps.
+
+`LLVM instructions <../LangRef.html#instref>`_ are constrained by strict
+rules: for example, the Left and Right operators of an `add
+instruction <../LangRef.html#i_add>`_ must have the same type, and the
+result type of the add must match the operand types. Because all values
+in Kaleidoscope are doubles, this makes for very simple code for add,
+sub and mul.
+
+On the other hand, LLVM specifies that the `fcmp
+instruction <../LangRef.html#i_fcmp>`_ always returns an 'i1' value (a
+one bit integer). The problem with this is that Kaleidoscope wants the
+value to be a 0.0 or 1.0 value. In order to get these semantics, we
+combine the fcmp instruction with a `uitofp
+instruction <../LangRef.html#i_uitofp>`_. This instruction converts its
+input integer into a floating point value by treating the input as an
+unsigned value. In contrast, if we used the `sitofp
+instruction <../LangRef.html#i_sitofp>`_, the Kaleidoscope '<' operator
+would return 0.0 and -1.0, depending on the input value.
+
+.. code-block:: c++
+
+ Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value*> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->Codegen());
+ if (ArgsV.back() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+Code generation for function calls is quite straightforward with LLVM.
+The code above initially does a function name lookup in the LLVM
+Module's symbol table. Recall that the LLVM Module is the container that
+holds all of the functions we are JIT'ing. By giving each function the
+same name as what the user specifies, we can use the LLVM symbol table
+to resolve function names for us.
+
+Once we have the function to call, we recursively codegen each argument
+that is to be passed in, and create an LLVM `call
+instruction <../LangRef.html#i_call>`_. Note that LLVM uses the native C
+calling conventions by default, allowing these calls to also call into
+standard library functions like "sin" and "cos", with no additional
+effort.
+
+This wraps up our handling of the four basic expressions that we have so
+far in Kaleidoscope. Feel free to go in and add some more. For example,
+by browsing the `LLVM language reference <../LangRef.html>`_ you'll find
+several other interesting instructions that are really easy to plug into
+our basic framework.
+
+Function Code Generation
+========================
+
+Code generation for prototypes and functions must handle a number of
+details, which make their code less beautiful than expression code
+generation, but allows us to illustrate some important points. First,
+lets talk about code generation for prototypes: they are used both for
+function bodies and external function declarations. The code starts
+with:
+
+.. code-block:: c++
+
+ Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
+ Doubles, false);
+
+ Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+This code packs a lot of power into a few lines. Note first that this
+function returns a "Function\*" instead of a "Value\*". Because a
+"prototype" really talks about the external interface for a function
+(not the value computed by an expression), it makes sense for it to
+return the LLVM Function it corresponds to when codegen'd.
+
+The call to ``FunctionType::get`` creates the ``FunctionType`` that
+should be used for a given Prototype. Since all function arguments in
+Kaleidoscope are of type double, the first line creates a vector of "N"
+LLVM double types. It then uses the ``Functiontype::get`` method to
+create a function type that takes "N" doubles as arguments, returns one
+double as a result, and that is not vararg (the false parameter
+indicates this). Note that Types in LLVM are uniqued just like Constants
+are, so you don't "new" a type, you "get" it.
+
+The final line above actually creates the function that the prototype
+will correspond to. This indicates the type, linkage and name to use, as
+well as which module to insert into. "`external
+linkage <../LangRef.html#linkage>`_" means that the function may be
+defined outside the current module and/or that it is callable by
+functions outside the module. The Name passed in is the name the user
+specified: since "``TheModule``" is specified, this name is registered
+in "``TheModule``"s symbol table, which is used by the function call
+code above.
+
+.. code-block:: c++
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+The Module symbol table works just like the Function symbol table when
+it comes to name conflicts: if a new function is created with a name
+that was previously added to the symbol table, the new function will get
+implicitly renamed when added to the Module. The code above exploits
+this fact to determine if there was a previous definition of this
+function.
+
+In Kaleidoscope, I choose to allow redefinitions of functions in two
+cases: first, we want to allow 'extern'ing a function more than once, as
+long as the prototypes for the externs match (since all arguments have
+the same type, we just have to check that the number of arguments
+match). Second, we want to allow 'extern'ing a function and then
+defining a body for it. This is useful when defining mutually recursive
+functions.
+
+In order to implement this, the code above first checks to see if there
+is a collision on the name of the function. If so, it deletes the
+function we just created (by calling ``eraseFromParent``) and then
+calling ``getFunction`` to get the existing function with the specified
+name. Note that many APIs in LLVM have "erase" forms and "remove" forms.
+The "remove" form unlinks the object from its parent (e.g. a Function
+from a Module) and returns it. The "erase" form unlinks the object and
+then deletes it.
+
+.. code-block:: c++
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+In order to verify the logic above, we first check to see if the
+pre-existing function is "empty". In this case, empty means that it has
+no basic blocks in it, which means it has no body. If it has no body, it
+is a forward declaration. Since we don't allow anything after a full
+definition of the function, the code rejects this case. If the previous
+reference to a function was an 'extern', we simply verify that the
+number of arguments for that definition and this one match up. If not,
+we emit an error.
+
+.. code-block:: c++
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx) {
+ AI->setName(Args[Idx]);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = AI;
+ }
+ return F;
+ }
+
+The last bit of code for prototypes loops over all of the arguments in
+the function, setting the name of the LLVM Argument objects to match,
+and registering the arguments in the ``NamedValues`` map for future use
+by the ``VariableExprAST`` AST node. Once this is set up, it returns the
+Function object to the caller. Note that we don't check for conflicting
+argument names here (e.g. "extern foo(a b a)"). Doing so would be very
+straight-forward with the mechanics we have already used above.
+
+.. code-block:: c++
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+Code generation for function definitions starts out simply enough: we
+just codegen the prototype (Proto) and verify that it is ok. We then
+clear out the ``NamedValues`` map to make sure that there isn't anything
+in it from the last function we compiled. Code generation of the
+prototype ensures that there is an LLVM Function object that is ready to
+go for us.
+
+.. code-block:: c++
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->Codegen()) {
+
+Now we get to the point where the ``Builder`` is set up. The first line
+creates a new `basic block <http://en.wikipedia.org/wiki/Basic_block>`_
+(named "entry"), which is inserted into ``TheFunction``. The second line
+then tells the builder that new instructions should be inserted into the
+end of the new basic block. Basic blocks in LLVM are an important part
+of functions that define the `Control Flow
+Graph <http://en.wikipedia.org/wiki/Control_flow_graph>`_. Since we
+don't have any control flow, our functions will only contain one block
+at this point. We'll fix this in `Chapter 5 <LangImpl5.html>`_ :).
+
+.. code-block:: c++
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ return TheFunction;
+ }
+
+Once the insertion point is set up, we call the ``CodeGen()`` method for
+the root expression of the function. If no error happens, this emits
+code to compute the expression into the entry block and returns the
+value that was computed. Assuming no error, we then create an LLVM `ret
+instruction <../LangRef.html#i_ret>`_, which completes the function.
+Once the function is built, we call ``verifyFunction``, which is
+provided by LLVM. This function does a variety of consistency checks on
+the generated code, to determine if our compiler is doing everything
+right. Using this is important: it can catch a lot of bugs. Once the
+function is finished and validated, we return it.
+
+.. code-block:: c++
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return 0;
+ }
+
+The only piece left here is handling of the error case. For simplicity,
+we handle this by merely deleting the function we produced with the
+``eraseFromParent`` method. This allows the user to redefine a function
+that they incorrectly typed in before: if we didn't delete it, it would
+live in the symbol table, with a body, preventing future redefinition.
+
+This code does have a bug, though. Since the ``PrototypeAST::Codegen``
+can return a previously defined forward declaration, our code can
+actually delete a forward declaration. There are a number of ways to fix
+this bug, see what you can come up with! Here is a testcase:
+
+::
+
+ extern foo(a b); # ok, defines foo.
+ def foo(a b) c; # error, 'c' is invalid.
+ def bar() foo(1, 2); # error, unknown function "foo"
+
+Driver Changes and Closing Thoughts
+===================================
+
+For now, code generation to LLVM doesn't really get us much, except that
+we can look at the pretty IR calls. The sample code inserts calls to
+Codegen into the "``HandleDefinition``", "``HandleExtern``" etc
+functions, and then dumps out the LLVM IR. This gives a nice way to look
+at the LLVM IR for simple functions. For example:
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @0() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+Note how the parser turns the top-level expression into anonymous
+functions for us. This will be handy when we add `JIT
+support <LangImpl4.html#jit>`_ in the next chapter. Also note that the
+code is very literally transcribed, no optimizations are being performed
+except simple constant folding done by IRBuilder. We will `add
+optimizations <LangImpl4.html#trivialconstfold>`_ explicitly in the next
+chapter.
+
+::
+
+ ready> def foo(a b) a*a + 2*a*b + b*b;
+ Read function definition:
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+This shows some simple arithmetic. Notice the striking similarity to the
+LLVM builder calls that we use to create the instructions.
+
+::
+
+ ready> def bar(a) foo(a, 4.0) + bar(31337);
+ Read function definition:
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+This shows some function calls. Note that this function will take a long
+time to execute if you call it. In the future we'll add conditional
+control flow to actually make recursion useful :).
+
+::
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> cos(1.234);
+ Read top-level expression:
+ define double @1() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+This shows an extern for the libm "cos" function, and a call to it.
+
+.. TODO:: Abandon Pygments' horrible `llvm` lexer. It just totally gives up
+ on highlighting this due to the first line.
+
+::
+
+ ready> ^D
+ ; ModuleID = 'my cool jit'
+
+ define double @0() {
+ entry:
+ %addtmp = fadd double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+ }
+
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+ declare double @cos(double)
+
+ define double @1() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+When you quit the current demo, it dumps out the IR for the entire
+module generated. Here you can see the big picture with all the
+functions referencing each other.
+
+This wraps up the third chapter of the Kaleidoscope tutorial. Up next,
+we'll describe how to `add JIT codegen and optimizer
+support <LangImpl4.html>`_ to this so we can actually start running
+code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM code generator. Because this uses the LLVM libraries, we need
+to link them in. To do this, we use the
+`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
+our makefile/command line about which options to use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g -O3 toy.cpp `llvm-config --cppflags --ldflags --libs core` -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. code-block:: c++
+
+ // To build this:
+ // See example below.
+
+ #include "llvm/DerivedTypes.h"
+ #include "llvm/IRBuilder.h"
+ #include "llvm/LLVMContext.h"
+ #include "llvm/Module.h"
+ #include "llvm/Analysis/Verifier.h"
+ #include <cstdio>
+ #include <string>
+ #include <map>
+ #include <vector>
+ using namespace llvm;
+
+ //===----------------------------------------------------------------------===//
+ // Lexer
+ //===----------------------------------------------------------------------===//
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ return tok_identifier;
+ }
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Abstract Syntax Tree (aka Parse Tree)
+ //===----------------------------------------------------------------------===//
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *Codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ virtual Value *Codegen();
+ };
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ virtual Value *Codegen();
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ virtual Value *Codegen();
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ virtual Value *Codegen();
+ };
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes).
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args)
+ : Name(name), Args(args) {}
+
+ Function *Codegen();
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ Function *Codegen();
+ };
+
+ //===----------------------------------------------------------------------===//
+ // Parser
+ //===----------------------------------------------------------------------===//
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+ static ExprAST *ParseExpression();
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ }
+ }
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ ExprAST *RHS = ParsePrimary();
+ if (!RHS) return 0;
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+ }
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParsePrimary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static PrototypeAST *ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return new PrototypeAST(FnName, ArgNames);
+ }
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Code Generation
+ //===----------------------------------------------------------------------===//
+
+ static Module *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, Value*> NamedValues;
+
+ Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+ Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ return V ? V : ErrorV("Unknown variable name");
+ }
+
+ Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateFAdd(L, R, "addtmp");
+ case '-': return Builder.CreateFSub(L, R, "subtmp");
+ case '*': return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default: return ErrorV("invalid binary operator");
+ }
+ }
+
+ Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value*> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->Codegen());
+ if (ArgsV.back() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+ Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
+ Doubles, false);
+
+ Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx) {
+ AI->setName(Args[Idx]);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = AI;
+ }
+
+ return F;
+ }
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ return TheFunction;
+ }
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Top-Level parsing and JIT Driver
+ //===----------------------------------------------------------------------===//
+
+ static void HandleDefinition() {
+ if (FunctionAST *F = ParseDefinition()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read function definition:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (PrototypeAST *P = ParseExtern()) {
+ if (Function *F = P->Codegen()) {
+ fprintf(stderr, "Read extern: ");
+ F->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read top-level expression:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+ //===----------------------------------------------------------------------===//
+ // "Library" functions that can be "extern'd" from user code.
+ //===----------------------------------------------------------------------===//
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Main driver code.
+ //===----------------------------------------------------------------------===//
+
+ int main() {
+ LLVMContext &Context = getGlobalContext();
+
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ fprintf(stderr, "ready> ");
+ getNextToken();
+
+ // Make the module, which holds all the code.
+ TheModule = new Module("my cool jit", Context);
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ // Print out all of the generated code.
+ TheModule->dump();
+
+ return 0;
+ }
+
+`Next: Adding JIT and Optimizer Support <LangImpl4.html>`_
+
Removed: llvm/trunk/docs/tutorial/LangImpl4.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl4.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl4.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl4.html (removed)
@@ -1,1152 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Adding JIT and Optimizer Support</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Adding JIT and Optimizer Support</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 4
- <ol>
- <li><a href="#intro">Chapter 4 Introduction</a></li>
- <li><a href="#trivialconstfold">Trivial Constant Folding</a></li>
- <li><a href="#optimizerpasses">LLVM Optimization Passes</a></li>
- <li><a href="#jit">Adding a JIT Compiler</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="LangImpl5.html">Chapter 5</a>: Extending the Language: Control
-Flow</li>
-</ul>
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 4 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 4 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. Chapters 1-3 described the implementation of a simple
-language and added support for generating LLVM IR. This chapter describes
-two new techniques: adding optimizer support to your language, and adding JIT
-compiler support. These additions will demonstrate how to get nice, efficient code
-for the Kaleidoscope language.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="trivialconstfold">Trivial Constant Folding</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Our demonstration for Chapter 3 is elegant and easy to extend. Unfortunately,
-it does not produce wonderful code. The IRBuilder, however, does give us
-obvious optimizations when compiling simple code:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) 1+2+x;</b>
-Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double 3.000000e+00, %x
- ret double %addtmp
-}
-</pre>
-</div>
-
-<p>This code is not a literal transcription of the AST built by parsing the
-input. That would be:
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) 1+2+x;</b>
-Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double 2.000000e+00, 1.000000e+00
- %addtmp1 = fadd double %addtmp, %x
- ret double %addtmp1
-}
-</pre>
-</div>
-
-<p>Constant folding, as seen above, in particular, is a very common and very
-important optimization: so much so that many language implementors implement
-constant folding support in their AST representation.</p>
-
-<p>With LLVM, you don't need this support in the AST. Since all calls to build
-LLVM IR go through the LLVM IR builder, the builder itself checked to see if
-there was a constant folding opportunity when you call it. If so, it just does
-the constant fold and return the constant instead of creating an instruction.
-
-<p>Well, that was easy :). In practice, we recommend always using
-<tt>IRBuilder</tt> when generating code like this. It has no
-"syntactic overhead" for its use (you don't have to uglify your compiler with
-constant checks everywhere) and it can dramatically reduce the amount of
-LLVM IR that is generated in some cases (particular for languages with a macro
-preprocessor or that use a lot of constants).</p>
-
-<p>On the other hand, the <tt>IRBuilder</tt> is limited by the fact
-that it does all of its analysis inline with the code as it is built. If you
-take a slightly more complex example:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
-ready> Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double 3.000000e+00, %x
- %addtmp1 = fadd double %x, 3.000000e+00
- %multmp = fmul double %addtmp, %addtmp1
- ret double %multmp
-}
-</pre>
-</div>
-
-<p>In this case, the LHS and RHS of the multiplication are the same value. We'd
-really like to see this generate "<tt>tmp = x+3; result = tmp*tmp;</tt>" instead
-of computing "<tt>x+3</tt>" twice.</p>
-
-<p>Unfortunately, no amount of local analysis will be able to detect and correct
-this. This requires two transformations: reassociation of expressions (to
-make the add's lexically identical) and Common Subexpression Elimination (CSE)
-to delete the redundant add instruction. Fortunately, LLVM provides a broad
-range of optimizations that you can use, in the form of "passes".</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="optimizerpasses">LLVM Optimization Passes</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>LLVM provides many optimization passes, which do many different sorts of
-things and have different tradeoffs. Unlike other systems, LLVM doesn't hold
-to the mistaken notion that one set of optimizations is right for all languages
-and for all situations. LLVM allows a compiler implementor to make complete
-decisions about what optimizations to use, in which order, and in what
-situation.</p>
-
-<p>As a concrete example, LLVM supports both "whole module" passes, which look
-across as large of body of code as they can (often a whole file, but if run
-at link time, this can be a substantial portion of the whole program). It also
-supports and includes "per-function" passes which just operate on a single
-function at a time, without looking at other functions. For more information
-on passes and how they are run, see the <a href="../WritingAnLLVMPass.html">How
-to Write a Pass</a> document and the <a href="../Passes.html">List of LLVM
-Passes</a>.</p>
-
-<p>For Kaleidoscope, we are currently generating functions on the fly, one at
-a time, as the user types them in. We aren't shooting for the ultimate
-optimization experience in this setting, but we also want to catch the easy and
-quick stuff where possible. As such, we will choose to run a few per-function
-optimizations as the user types the function in. If we wanted to make a "static
-Kaleidoscope compiler", we would use exactly the code we have now, except that
-we would defer running the optimizer until the entire file has been parsed.</p>
-
-<p>In order to get per-function optimizations going, we need to set up a
-<a href="../WritingAnLLVMPass.html#passmanager">FunctionPassManager</a> to hold and
-organize the LLVM optimizations that we want to run. Once we have that, we can
-add a set of optimizations to run. The code looks like this:</p>
-
-<div class="doc_code">
-<pre>
- FunctionPassManager OurFPM(TheModule);
-
- // Set up the optimizer pipeline. Start with registering info about how the
- // target lays out data structures.
- OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
- // Provide basic AliasAnalysis support for GVN.
- OurFPM.add(createBasicAliasAnalysisPass());
- // Do simple "peephole" optimizations and bit-twiddling optzns.
- OurFPM.add(createInstructionCombiningPass());
- // Reassociate expressions.
- OurFPM.add(createReassociatePass());
- // Eliminate Common SubExpressions.
- OurFPM.add(createGVNPass());
- // Simplify the control flow graph (deleting unreachable blocks, etc).
- OurFPM.add(createCFGSimplificationPass());
-
- OurFPM.doInitialization();
-
- // Set the global so the code gen can use this.
- TheFPM = &OurFPM;
-
- // Run the main "interpreter loop" now.
- MainLoop();
-</pre>
-</div>
-
-<p>This code defines a <tt>FunctionPassManager</tt>, "<tt>OurFPM</tt>". It
-requires a pointer to the <tt>Module</tt> to construct itself. Once it is set
-up, we use a series of "add" calls to add a bunch of LLVM passes. The first
-pass is basically boilerplate, it adds a pass so that later optimizations know
-how the data structures in the program are laid out. The
-"<tt>TheExecutionEngine</tt>" variable is related to the JIT, which we will get
-to in the next section.</p>
-
-<p>In this case, we choose to add 4 optimization passes. The passes we chose
-here are a pretty standard set of "cleanup" optimizations that are useful for
-a wide variety of code. I won't delve into what they do but, believe me,
-they are a good starting place :).</p>
-
-<p>Once the PassManager is set up, we need to make use of it. We do this by
-running it after our newly created function is constructed (in
-<tt>FunctionAST::Codegen</tt>), but before it is returned to the client:</p>
-
-<div class="doc_code">
-<pre>
- if (Value *RetVal = Body->Codegen()) {
- // Finish off the function.
- Builder.CreateRet(RetVal);
-
- // Validate the generated code, checking for consistency.
- verifyFunction(*TheFunction);
-
- <b>// Optimize the function.
- TheFPM->run(*TheFunction);</b>
-
- return TheFunction;
- }
-</pre>
-</div>
-
-<p>As you can see, this is pretty straightforward. The
-<tt>FunctionPassManager</tt> optimizes and updates the LLVM Function* in place,
-improving (hopefully) its body. With this in place, we can try our test above
-again:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
-ready> Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double %x, 3.000000e+00
- %multmp = fmul double %addtmp, %addtmp
- ret double %multmp
-}
-</pre>
-</div>
-
-<p>As expected, we now get our nicely optimized code, saving a floating point
-add instruction from every execution of this function.</p>
-
-<p>LLVM provides a wide variety of optimizations that can be used in certain
-circumstances. Some <a href="../Passes.html">documentation about the various
-passes</a> is available, but it isn't very complete. Another good source of
-ideas can come from looking at the passes that <tt>Clang</tt> runs to get
-started. The "<tt>opt</tt>" tool allows you to experiment with passes from the
-command line, so you can see if they do anything.</p>
-
-<p>Now that we have reasonable code coming out of our front-end, lets talk about
-executing it!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="jit">Adding a JIT Compiler</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Code that is available in LLVM IR can have a wide variety of tools
-applied to it. For example, you can run optimizations on it (as we did above),
-you can dump it out in textual or binary forms, you can compile the code to an
-assembly file (.s) for some target, or you can JIT compile it. The nice thing
-about the LLVM IR representation is that it is the "common currency" between
-many different parts of the compiler.
-</p>
-
-<p>In this section, we'll add JIT compiler support to our interpreter. The
-basic idea that we want for Kaleidoscope is to have the user enter function
-bodies as they do now, but immediately evaluate the top-level expressions they
-type in. For example, if they type in "1 + 2;", we should evaluate and print
-out 3. If they define a function, they should be able to call it from the
-command line.</p>
-
-<p>In order to do this, we first declare and initialize the JIT. This is done
-by adding a global variable and a call in <tt>main</tt>:</p>
-
-<div class="doc_code">
-<pre>
-<b>static ExecutionEngine *TheExecutionEngine;</b>
-...
-int main() {
- ..
- <b>// Create the JIT. This takes ownership of the module.
- TheExecutionEngine = EngineBuilder(TheModule).create();</b>
- ..
-}
-</pre>
-</div>
-
-<p>This creates an abstract "Execution Engine" which can be either a JIT
-compiler or the LLVM interpreter. LLVM will automatically pick a JIT compiler
-for you if one is available for your platform, otherwise it will fall back to
-the interpreter.</p>
-
-<p>Once the <tt>ExecutionEngine</tt> is created, the JIT is ready to be used.
-There are a variety of APIs that are useful, but the simplest one is the
-"<tt>getPointerToFunction(F)</tt>" method. This method JIT compiles the
-specified LLVM Function and returns a function pointer to the generated machine
-code. In our case, this means that we can change the code that parses a
-top-level expression to look like this:</p>
-
-<div class="doc_code">
-<pre>
-static void HandleTopLevelExpression() {
- // Evaluate a top-level expression into an anonymous function.
- if (FunctionAST *F = ParseTopLevelExpr()) {
- if (Function *LF = F->Codegen()) {
- LF->dump(); // Dump the function for exposition purposes.
-
- <b>// JIT the function, returning a function pointer.
- void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
-
- // Cast it to the right type (takes no arguments, returns a double) so we
- // can call it as a native function.
- double (*FP)() = (double (*)())(intptr_t)FPtr;
- fprintf(stderr, "Evaluated to %f\n", FP());</b>
- }
-</pre>
-</div>
-
-<p>Recall that we compile top-level expressions into a self-contained LLVM
-function that takes no arguments and returns the computed double. Because the
-LLVM JIT compiler matches the native platform ABI, this means that you can just
-cast the result pointer to a function pointer of that type and call it directly.
-This means, there is no difference between JIT compiled code and native machine
-code that is statically linked into your application.</p>
-
-<p>With just these two changes, lets see how Kaleidoscope works now!</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>4+5;</b>
-Read top-level expression:
-define double @0() {
-entry:
- ret double 9.000000e+00
-}
-
-<em>Evaluated to 9.000000</em>
-</pre>
-</div>
-
-<p>Well this looks like it is basically working. The dump of the function
-shows the "no argument function that always returns double" that we synthesize
-for each top-level expression that is typed in. This demonstrates very basic
-functionality, but can we do more?</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def testfunc(x y) x + y*2; </b>
-Read function definition:
-define double @testfunc(double %x, double %y) {
-entry:
- %multmp = fmul double %y, 2.000000e+00
- %addtmp = fadd double %multmp, %x
- ret double %addtmp
-}
-
-ready> <b>testfunc(4, 10);</b>
-Read top-level expression:
-define double @1() {
-entry:
- %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
- ret double %calltmp
-}
-
-<em>Evaluated to 24.000000</em>
-</pre>
-</div>
-
-<p>This illustrates that we can now call user code, but there is something a bit
-subtle going on here. Note that we only invoke the JIT on the anonymous
-functions that <em>call testfunc</em>, but we never invoked it
-on <em>testfunc</em> itself. What actually happened here is that the JIT
-scanned for all non-JIT'd functions transitively called from the anonymous
-function and compiled all of them before returning
-from <tt>getPointerToFunction()</tt>.</p>
-
-<p>The JIT provides a number of other more advanced interfaces for things like
-freeing allocated machine code, rejit'ing functions to update them, etc.
-However, even with this simple code, we get some surprisingly powerful
-capabilities - check this out (I removed the dump of the anonymous functions,
-you should get the idea by now :) :</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>extern sin(x);</b>
-Read extern:
-declare double @sin(double)
-
-ready> <b>extern cos(x);</b>
-Read extern:
-declare double @cos(double)
-
-ready> <b>sin(1.0);</b>
-Read top-level expression:
-define double @2() {
-entry:
- ret double 0x3FEAED548F090CEE
-}
-
-<em>Evaluated to 0.841471</em>
-
-ready> <b>def foo(x) sin(x)*sin(x) + cos(x)*cos(x);</b>
-Read function definition:
-define double @foo(double %x) {
-entry:
- %calltmp = call double @sin(double %x)
- %multmp = fmul double %calltmp, %calltmp
- %calltmp2 = call double @cos(double %x)
- %multmp4 = fmul double %calltmp2, %calltmp2
- %addtmp = fadd double %multmp, %multmp4
- ret double %addtmp
-}
-
-ready> <b>foo(4.0);</b>
-Read top-level expression:
-define double @3() {
-entry:
- %calltmp = call double @foo(double 4.000000e+00)
- ret double %calltmp
-}
-
-<em>Evaluated to 1.000000</em>
-</pre>
-</div>
-
-<p>Whoa, how does the JIT know about sin and cos? The answer is surprisingly
-simple: in this
-example, the JIT started execution of a function and got to a function call. It
-realized that the function was not yet JIT compiled and invoked the standard set
-of routines to resolve the function. In this case, there is no body defined
-for the function, so the JIT ended up calling "<tt>dlsym("sin")</tt>" on the
-Kaleidoscope process itself.
-Since "<tt>sin</tt>" is defined within the JIT's address space, it simply
-patches up calls in the module to call the libm version of <tt>sin</tt>
-directly.</p>
-
-<p>The LLVM JIT provides a number of interfaces (look in the
-<tt>ExecutionEngine.h</tt> file) for controlling how unknown functions get
-resolved. It allows you to establish explicit mappings between IR objects and
-addresses (useful for LLVM global variables that you want to map to static
-tables, for example), allows you to dynamically decide on the fly based on the
-function name, and even allows you to have the JIT compile functions lazily the
-first time they're called.</p>
-
-<p>One interesting application of this is that we can now extend the language
-by writing arbitrary C++ code to implement operations. For example, if we add:
-</p>
-
-<div class="doc_code">
-<pre>
-/// putchard - putchar that takes a double and returns 0.
-extern "C"
-double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-</pre>
-</div>
-
-<p>Now we can produce simple output to the console by using things like:
-"<tt>extern putchard(x); putchard(120);</tt>", which prints a lowercase 'x' on
-the console (120 is the ASCII code for 'x'). Similar code could be used to
-implement file I/O, console input, and many other capabilities in
-Kaleidoscope.</p>
-
-<p>This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At
-this point, we can compile a non-Turing-complete programming language, optimize
-and JIT compile it in a user-driven way. Next up we'll look into <a
-href="LangImpl5.html">extending the language with control flow constructs</a>,
-tackling some interesting LLVM IR issues along the way.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for our running example, enhanced with the
-LLVM JIT and optimizer. To build this example, use:
-</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
-# Run
-./toy
-</pre>
-</div>
-
-<p>
-If you are compiling this on Linux, make sure to add the "-rdynamic" option
-as well. This makes sure that the external functions are resolved properly
-at runtime.</p>
-
-<p>Here is the code:</p>
-
-<div class="doc_code">
-<pre>
-#include "llvm/DerivedTypes.h"
-#include "llvm/ExecutionEngine/ExecutionEngine.h"
-#include "llvm/ExecutionEngine/JIT.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/PassManager.h"
-#include "llvm/Analysis/Verifier.h"
-#include "llvm/Analysis/Passes.h"
-#include "llvm/DataLayout.h"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Support/TargetSelect.h"
-#include <cstdio>
-#include <string>
-#include <map>
-#include <vector>
-using namespace llvm;
-
-//===----------------------------------------------------------------------===//
-// Lexer
-//===----------------------------------------------------------------------===//
-
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
- tok_eof = -1,
-
- // commands
- tok_def = -2, tok_extern = -3,
-
- // primary
- tok_identifier = -4, tok_number = -5
-};
-
-static std::string IdentifierStr; // Filled in if tok_identifier
-static double NumVal; // Filled in if tok_number
-
-/// gettok - Return the next token from standard input.
-static int gettok() {
- static int LastChar = ' ';
-
- // Skip any whitespace.
- while (isspace(LastChar))
- LastChar = getchar();
-
- if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
- IdentifierStr = LastChar;
- while (isalnum((LastChar = getchar())))
- IdentifierStr += LastChar;
-
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- return tok_identifier;
- }
-
- if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
- std::string NumStr;
- do {
- NumStr += LastChar;
- LastChar = getchar();
- } while (isdigit(LastChar) || LastChar == '.');
-
- NumVal = strtod(NumStr.c_str(), 0);
- return tok_number;
- }
-
- if (LastChar == '#') {
- // Comment until end of line.
- do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-
- if (LastChar != EOF)
- return gettok();
- }
-
- // Check for end of file. Don't eat the EOF.
- if (LastChar == EOF)
- return tok_eof;
-
- // Otherwise, just return the character as its ascii value.
- int ThisChar = LastChar;
- LastChar = getchar();
- return ThisChar;
-}
-
-//===----------------------------------------------------------------------===//
-// Abstract Syntax Tree (aka Parse Tree)
-//===----------------------------------------------------------------------===//
-
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
- virtual Value *Codegen() = 0;
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
- virtual Value *Codegen();
-};
-
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
- std::string Name;
-public:
- VariableExprAST(const std::string &name) : Name(name) {}
- virtual Value *Codegen();
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
- char Op;
- ExprAST *LHS, *RHS;
-public:
- BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
- : Op(op), LHS(lhs), RHS(rhs) {}
- virtual Value *Codegen();
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
- std::string Callee;
- std::vector<ExprAST*> Args;
-public:
- CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
- : Callee(callee), Args(args) {}
- virtual Value *Codegen();
-};
-
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes).
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args)
- : Name(name), Args(args) {}
-
- Function *Codegen();
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
- PrototypeAST *Proto;
- ExprAST *Body;
-public:
- FunctionAST(PrototypeAST *proto, ExprAST *body)
- : Proto(proto), Body(body) {}
-
- Function *Codegen();
-};
-
-//===----------------------------------------------------------------------===//
-// Parser
-//===----------------------------------------------------------------------===//
-
-/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
-/// token the parser is looking at. getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
- return CurTok = gettok();
-}
-
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
- if (!isascii(CurTok))
- return -1;
-
- // Make sure it's a declared binop.
- int TokPrec = BinopPrecedence[CurTok];
- if (TokPrec <= 0) return -1;
- return TokPrec;
-}
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-
-static ExprAST *ParseExpression();
-
-/// identifierexpr
-/// ::= identifier
-/// ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
- std::string IdName = IdentifierStr;
-
- getNextToken(); // eat identifier.
-
- if (CurTok != '(') // Simple variable ref.
- return new VariableExprAST(IdName);
-
- // Call.
- getNextToken(); // eat (
- std::vector<ExprAST*> Args;
- if (CurTok != ')') {
- while (1) {
- ExprAST *Arg = ParseExpression();
- if (!Arg) return 0;
- Args.push_back(Arg);
-
- if (CurTok == ')') break;
-
- if (CurTok != ',')
- return Error("Expected ')' or ',' in argument list");
- getNextToken();
- }
- }
-
- // Eat the ')'.
- getNextToken();
-
- return new CallExprAST(IdName, Args);
-}
-
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
- ExprAST *Result = new NumberExprAST(NumVal);
- getNextToken(); // consume the number
- return Result;
-}
-
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
- getNextToken(); // eat (.
- ExprAST *V = ParseExpression();
- if (!V) return 0;
-
- if (CurTok != ')')
- return Error("expected ')'");
- getNextToken(); // eat ).
- return V;
-}
-
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- }
-}
-
-/// binoprhs
-/// ::= ('+' primary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- // If this is a binop, find its precedence.
- while (1) {
- int TokPrec = GetTokPrecedence();
-
- // If this is a binop that binds at least as tightly as the current binop,
- // consume it, otherwise we are done.
- if (TokPrec < ExprPrec)
- return LHS;
-
- // Okay, we know this is a binop.
- int BinOp = CurTok;
- getNextToken(); // eat binop
-
- // Parse the primary expression after the binary operator.
- ExprAST *RHS = ParsePrimary();
- if (!RHS) return 0;
-
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
- RHS = ParseBinOpRHS(TokPrec+1, RHS);
- if (RHS == 0) return 0;
- }
-
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- }
-}
-
-/// expression
-/// ::= primary binoprhs
-///
-static ExprAST *ParseExpression() {
- ExprAST *LHS = ParsePrimary();
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-
-/// prototype
-/// ::= id '(' id* ')'
-static PrototypeAST *ParsePrototype() {
- if (CurTok != tok_identifier)
- return ErrorP("Expected function name in prototype");
-
- std::string FnName = IdentifierStr;
- getNextToken();
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- return new PrototypeAST(FnName, ArgNames);
-}
-
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
- getNextToken(); // eat def.
- PrototypeAST *Proto = ParsePrototype();
- if (Proto == 0) return 0;
-
- if (ExprAST *E = ParseExpression())
- return new FunctionAST(Proto, E);
- return 0;
-}
-
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
- if (ExprAST *E = ParseExpression()) {
- // Make an anonymous proto.
- PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
- return new FunctionAST(Proto, E);
- }
- return 0;
-}
-
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
- getNextToken(); // eat extern.
- return ParsePrototype();
-}
-
-//===----------------------------------------------------------------------===//
-// Code Generation
-//===----------------------------------------------------------------------===//
-
-static Module *TheModule;
-static IRBuilder<> Builder(getGlobalContext());
-static std::map<std::string, Value*> NamedValues;
-static FunctionPassManager *TheFPM;
-
-Value *ErrorV(const char *Str) { Error(Str); return 0; }
-
-Value *NumberExprAST::Codegen() {
- return ConstantFP::get(getGlobalContext(), APFloat(Val));
-}
-
-Value *VariableExprAST::Codegen() {
- // Look this variable up in the function.
- Value *V = NamedValues[Name];
- return V ? V : ErrorV("Unknown variable name");
-}
-
-Value *BinaryExprAST::Codegen() {
- Value *L = LHS->Codegen();
- Value *R = RHS->Codegen();
- if (L == 0 || R == 0) return 0;
-
- switch (Op) {
- case '+': return Builder.CreateFAdd(L, R, "addtmp");
- case '-': return Builder.CreateFSub(L, R, "subtmp");
- case '*': return Builder.CreateFMul(L, R, "multmp");
- case '<':
- L = Builder.CreateFCmpULT(L, R, "cmptmp");
- // Convert bool 0/1 to double 0.0 or 1.0
- return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
- "booltmp");
- default: return ErrorV("invalid binary operator");
- }
-}
-
-Value *CallExprAST::Codegen() {
- // Look up the name in the global module table.
- Function *CalleeF = TheModule->getFunction(Callee);
- if (CalleeF == 0)
- return ErrorV("Unknown function referenced");
-
- // If argument mismatch error.
- if (CalleeF->arg_size() != Args.size())
- return ErrorV("Incorrect # arguments passed");
-
- std::vector<Value*> ArgsV;
- for (unsigned i = 0, e = Args.size(); i != e; ++i) {
- ArgsV.push_back(Args[i]->Codegen());
- if (ArgsV.back() == 0) return 0;
- }
-
- return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
-}
-
-Function *PrototypeAST::Codegen() {
- // Make the function type: double(double,double) etc.
- std::vector<Type*> Doubles(Args.size(),
- Type::getDoubleTy(getGlobalContext()));
- FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
- Doubles, false);
-
- Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
-
- // If F conflicted, there was already something named 'Name'. If it has a
- // body, don't allow redefinition or reextern.
- if (F->getName() != Name) {
- // Delete the one we just made and get the existing one.
- F->eraseFromParent();
- F = TheModule->getFunction(Name);
-
- // If F already has a body, reject this.
- if (!F->empty()) {
- ErrorF("redefinition of function");
- return 0;
- }
-
- // If F took a different number of args, reject.
- if (F->arg_size() != Args.size()) {
- ErrorF("redefinition of function with different # args");
- return 0;
- }
- }
-
- // Set names for all arguments.
- unsigned Idx = 0;
- for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
- ++AI, ++Idx) {
- AI->setName(Args[Idx]);
-
- // Add arguments to variable symbol table.
- NamedValues[Args[Idx]] = AI;
- }
-
- return F;
-}
-
-Function *FunctionAST::Codegen() {
- NamedValues.clear();
-
- Function *TheFunction = Proto->Codegen();
- if (TheFunction == 0)
- return 0;
-
- // Create a new basic block to start insertion into.
- BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
- Builder.SetInsertPoint(BB);
-
- if (Value *RetVal = Body->Codegen()) {
- // Finish off the function.
- Builder.CreateRet(RetVal);
-
- // Validate the generated code, checking for consistency.
- verifyFunction(*TheFunction);
-
- // Optimize the function.
- TheFPM->run(*TheFunction);
-
- return TheFunction;
- }
-
- // Error reading body, remove function.
- TheFunction->eraseFromParent();
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Top-Level parsing and JIT Driver
-//===----------------------------------------------------------------------===//
-
-static ExecutionEngine *TheExecutionEngine;
-
-static void HandleDefinition() {
- if (FunctionAST *F = ParseDefinition()) {
- if (Function *LF = F->Codegen()) {
- fprintf(stderr, "Read function definition:");
- LF->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleExtern() {
- if (PrototypeAST *P = ParseExtern()) {
- if (Function *F = P->Codegen()) {
- fprintf(stderr, "Read extern: ");
- F->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleTopLevelExpression() {
- // Evaluate a top-level expression into an anonymous function.
- if (FunctionAST *F = ParseTopLevelExpr()) {
- if (Function *LF = F->Codegen()) {
- fprintf(stderr, "Read top-level expression:");
- LF->dump();
-
- // JIT the function, returning a function pointer.
- void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
-
- // Cast it to the right type (takes no arguments, returns a double) so we
- // can call it as a native function.
- double (*FP)() = (double (*)())(intptr_t)FPtr;
- fprintf(stderr, "Evaluated to %f\n", FP());
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
- while (1) {
- fprintf(stderr, "ready> ");
- switch (CurTok) {
- case tok_eof: return;
- case ';': getNextToken(); break; // ignore top-level semicolons.
- case tok_def: HandleDefinition(); break;
- case tok_extern: HandleExtern(); break;
- default: HandleTopLevelExpression(); break;
- }
- }
-}
-
-//===----------------------------------------------------------------------===//
-// "Library" functions that can be "extern'd" from user code.
-//===----------------------------------------------------------------------===//
-
-/// putchard - putchar that takes a double and returns 0.
-extern "C"
-double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Main driver code.
-//===----------------------------------------------------------------------===//
-
-int main() {
- InitializeNativeTarget();
- LLVMContext &Context = getGlobalContext();
-
- // Install standard binary operators.
- // 1 is lowest precedence.
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
- BinopPrecedence['*'] = 40; // highest.
-
- // Prime the first token.
- fprintf(stderr, "ready> ");
- getNextToken();
-
- // Make the module, which holds all the code.
- TheModule = new Module("my cool jit", Context);
-
- // Create the JIT. This takes ownership of the module.
- std::string ErrStr;
- TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
- if (!TheExecutionEngine) {
- fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
- exit(1);
- }
-
- FunctionPassManager OurFPM(TheModule);
-
- // Set up the optimizer pipeline. Start with registering info about how the
- // target lays out data structures.
- OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
- // Provide basic AliasAnalysis support for GVN.
- OurFPM.add(createBasicAliasAnalysisPass());
- // Do simple "peephole" optimizations and bit-twiddling optzns.
- OurFPM.add(createInstructionCombiningPass());
- // Reassociate expressions.
- OurFPM.add(createReassociatePass());
- // Eliminate Common SubExpressions.
- OurFPM.add(createGVNPass());
- // Simplify the control flow graph (deleting unreachable blocks, etc).
- OurFPM.add(createCFGSimplificationPass());
-
- OurFPM.doInitialization();
-
- // Set the global so the code gen can use this.
- TheFPM = &OurFPM;
-
- // Run the main "interpreter loop" now.
- MainLoop();
-
- TheFPM = 0;
-
- // Print out all of the generated code.
- TheModule->dump();
-
- return 0;
-}
-</pre>
-</div>
-
-<a href="LangImpl5.html">Next: Extending the language: control flow</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
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Added: llvm/trunk/docs/tutorial/LangImpl4.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl4.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl4.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl4.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,1063 @@
+==============================================
+Kaleidoscope: Adding JIT and Optimizer Support
+==============================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Chapter 4 Introduction
+======================
+
+Welcome to Chapter 4 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Chapters 1-3 described the implementation
+of a simple language and added support for generating LLVM IR. This
+chapter describes two new techniques: adding optimizer support to your
+language, and adding JIT compiler support. These additions will
+demonstrate how to get nice, efficient code for the Kaleidoscope
+language.
+
+Trivial Constant Folding
+========================
+
+Our demonstration for Chapter 3 is elegant and easy to extend.
+Unfortunately, it does not produce wonderful code. The IRBuilder,
+however, does give us obvious optimizations when compiling simple code:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ ret double %addtmp
+ }
+
+This code is not a literal transcription of the AST built by parsing the
+input. That would be:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 2.000000e+00, 1.000000e+00
+ %addtmp1 = fadd double %addtmp, %x
+ ret double %addtmp1
+ }
+
+Constant folding, as seen above, in particular, is a very common and
+very important optimization: so much so that many language implementors
+implement constant folding support in their AST representation.
+
+With LLVM, you don't need this support in the AST. Since all calls to
+build LLVM IR go through the LLVM IR builder, the builder itself checked
+to see if there was a constant folding opportunity when you call it. If
+so, it just does the constant fold and return the constant instead of
+creating an instruction.
+
+Well, that was easy :). In practice, we recommend always using
+``IRBuilder`` when generating code like this. It has no "syntactic
+overhead" for its use (you don't have to uglify your compiler with
+constant checks everywhere) and it can dramatically reduce the amount of
+LLVM IR that is generated in some cases (particular for languages with a
+macro preprocessor or that use a lot of constants).
+
+On the other hand, the ``IRBuilder`` is limited by the fact that it does
+all of its analysis inline with the code as it is built. If you take a
+slightly more complex example:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ %addtmp1 = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp1
+ ret double %multmp
+ }
+
+In this case, the LHS and RHS of the multiplication are the same value.
+We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``"
+instead of computing "``x+3``" twice.
+
+Unfortunately, no amount of local analysis will be able to detect and
+correct this. This requires two transformations: reassociation of
+expressions (to make the add's lexically identical) and Common
+Subexpression Elimination (CSE) to delete the redundant add instruction.
+Fortunately, LLVM provides a broad range of optimizations that you can
+use, in the form of "passes".
+
+LLVM Optimization Passes
+========================
+
+LLVM provides many optimization passes, which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn't
+hold to the mistaken notion that one set of optimizations is right for
+all languages and for all situations. LLVM allows a compiler implementor
+to make complete decisions about what optimizations to use, in which
+order, and in what situation.
+
+As a concrete example, LLVM supports both "whole module" passes, which
+look across as large of body of code as they can (often a whole file,
+but if run at link time, this can be a substantial portion of the whole
+program). It also supports and includes "per-function" passes which just
+operate on a single function at a time, without looking at other
+functions. For more information on passes and how they are run, see the
+`How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the
+`List of LLVM Passes <../Passes.html>`_.
+
+For Kaleidoscope, we are currently generating functions on the fly, one
+at a time, as the user types them in. We aren't shooting for the
+ultimate optimization experience in this setting, but we also want to
+catch the easy and quick stuff where possible. As such, we will choose
+to run a few per-function optimizations as the user types the function
+in. If we wanted to make a "static Kaleidoscope compiler", we would use
+exactly the code we have now, except that we would defer running the
+optimizer until the entire file has been parsed.
+
+In order to get per-function optimizations going, we need to set up a
+`FunctionPassManager <../WritingAnLLVMPass.html#passmanager>`_ to hold
+and organize the LLVM optimizations that we want to run. Once we have
+that, we can add a set of optimizations to run. The code looks like
+this:
+
+.. code-block:: c++
+
+ FunctionPassManager OurFPM(TheModule);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Provide basic AliasAnalysis support for GVN.
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+This code defines a ``FunctionPassManager``, "``OurFPM``". It requires a
+pointer to the ``Module`` to construct itself. Once it is set up, we use
+a series of "add" calls to add a bunch of LLVM passes. The first pass is
+basically boilerplate, it adds a pass so that later optimizations know
+how the data structures in the program are laid out. The
+"``TheExecutionEngine``" variable is related to the JIT, which we will
+get to in the next section.
+
+In this case, we choose to add 4 optimization passes. The passes we
+chose here are a pretty standard set of "cleanup" optimizations that are
+useful for a wide variety of code. I won't delve into what they do but,
+believe me, they are a good starting place :).
+
+Once the PassManager is set up, we need to make use of it. We do this by
+running it after our newly created function is constructed (in
+``FunctionAST::Codegen``), but before it is returned to the client:
+
+.. code-block:: c++
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+As you can see, this is pretty straightforward. The
+``FunctionPassManager`` optimizes and updates the LLVM Function\* in
+place, improving (hopefully) its body. With this in place, we can try
+our test above again:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp
+ ret double %multmp
+ }
+
+As expected, we now get our nicely optimized code, saving a floating
+point add instruction from every execution of this function.
+
+LLVM provides a wide variety of optimizations that can be used in
+certain circumstances. Some `documentation about the various
+passes <../Passes.html>`_ is available, but it isn't very complete.
+Another good source of ideas can come from looking at the passes that
+``Clang`` runs to get started. The "``opt``" tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.
+
+Now that we have reasonable code coming out of our front-end, lets talk
+about executing it!
+
+Adding a JIT Compiler
+=====================
+
+Code that is available in LLVM IR can have a wide variety of tools
+applied to it. For example, you can run optimizations on it (as we did
+above), you can dump it out in textual or binary forms, you can compile
+the code to an assembly file (.s) for some target, or you can JIT
+compile it. The nice thing about the LLVM IR representation is that it
+is the "common currency" between many different parts of the compiler.
+
+In this section, we'll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter
+function bodies as they do now, but immediately evaluate the top-level
+expressions they type in. For example, if they type in "1 + 2;", we
+should evaluate and print out 3. If they define a function, they should
+be able to call it from the command line.
+
+In order to do this, we first declare and initialize the JIT. This is
+done by adding a global variable and a call in ``main``:
+
+.. code-block:: c++
+
+ static ExecutionEngine *TheExecutionEngine;
+ ...
+ int main() {
+ ..
+ // Create the JIT. This takes ownership of the module.
+ TheExecutionEngine = EngineBuilder(TheModule).create();
+ ..
+ }
+
+This creates an abstract "Execution Engine" which can be either a JIT
+compiler or the LLVM interpreter. LLVM will automatically pick a JIT
+compiler for you if one is available for your platform, otherwise it
+will fall back to the interpreter.
+
+Once the ``ExecutionEngine`` is created, the JIT is ready to be used.
+There are a variety of APIs that are useful, but the simplest one is the
+"``getPointerToFunction(F)``" method. This method JIT compiles the
+specified LLVM Function and returns a function pointer to the generated
+machine code. In our case, this means that we can change the code that
+parses a top-level expression to look like this:
+
+.. code-block:: c++
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ LF->dump(); // Dump the function for exposition purposes.
+
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // Cast it to the right type (takes no arguments, returns a double) so we
+ // can call it as a native function.
+ double (*FP)() = (double (*)())(intptr_t)FPtr;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+
+Recall that we compile top-level expressions into a self-contained LLVM
+function that takes no arguments and returns the computed double.
+Because the LLVM JIT compiler matches the native platform ABI, this
+means that you can just cast the result pointer to a function pointer of
+that type and call it directly. This means, there is no difference
+between JIT compiled code and native machine code that is statically
+linked into your application.
+
+With just these two changes, lets see how Kaleidoscope works now!
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @0() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+ Evaluated to 9.000000
+
+Well this looks like it is basically working. The dump of the function
+shows the "no argument function that always returns double" that we
+synthesize for each top-level expression that is typed in. This
+demonstrates very basic functionality, but can we do more?
+
+::
+
+ ready> def testfunc(x y) x + y*2;
+ Read function definition:
+ define double @testfunc(double %x, double %y) {
+ entry:
+ %multmp = fmul double %y, 2.000000e+00
+ %addtmp = fadd double %multmp, %x
+ ret double %addtmp
+ }
+
+ ready> testfunc(4, 10);
+ Read top-level expression:
+ define double @1() {
+ entry:
+ %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
+ ret double %calltmp
+ }
+
+ Evaluated to 24.000000
+
+This illustrates that we can now call user code, but there is something
+a bit subtle going on here. Note that we only invoke the JIT on the
+anonymous functions that *call testfunc*, but we never invoked it on
+*testfunc* itself. What actually happened here is that the JIT scanned
+for all non-JIT'd functions transitively called from the anonymous
+function and compiled all of them before returning from
+``getPointerToFunction()``.
+
+The JIT provides a number of other more advanced interfaces for things
+like freeing allocated machine code, rejit'ing functions to update them,
+etc. However, even with this simple code, we get some surprisingly
+powerful capabilities - check this out (I removed the dump of the
+anonymous functions, you should get the idea by now :) :
+
+::
+
+ ready> extern sin(x);
+ Read extern:
+ declare double @sin(double)
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> sin(1.0);
+ Read top-level expression:
+ define double @2() {
+ entry:
+ ret double 0x3FEAED548F090CEE
+ }
+
+ Evaluated to 0.841471
+
+ ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
+ Read function definition:
+ define double @foo(double %x) {
+ entry:
+ %calltmp = call double @sin(double %x)
+ %multmp = fmul double %calltmp, %calltmp
+ %calltmp2 = call double @cos(double %x)
+ %multmp4 = fmul double %calltmp2, %calltmp2
+ %addtmp = fadd double %multmp, %multmp4
+ ret double %addtmp
+ }
+
+ ready> foo(4.0);
+ Read top-level expression:
+ define double @3() {
+ entry:
+ %calltmp = call double @foo(double 4.000000e+00)
+ ret double %calltmp
+ }
+
+ Evaluated to 1.000000
+
+Whoa, how does the JIT know about sin and cos? The answer is
+surprisingly simple: in this example, the JIT started execution of a
+function and got to a function call. It realized that the function was
+not yet JIT compiled and invoked the standard set of routines to resolve
+the function. In this case, there is no body defined for the function,
+so the JIT ended up calling "``dlsym("sin")``" on the Kaleidoscope
+process itself. Since "``sin``" is defined within the JIT's address
+space, it simply patches up calls in the module to call the libm version
+of ``sin`` directly.
+
+The LLVM JIT provides a number of interfaces (look in the
+``ExecutionEngine.h`` file) for controlling how unknown functions get
+resolved. It allows you to establish explicit mappings between IR
+objects and addresses (useful for LLVM global variables that you want to
+map to static tables, for example), allows you to dynamically decide on
+the fly based on the function name, and even allows you to have the JIT
+compile functions lazily the first time they're called.
+
+One interesting application of this is that we can now extend the
+language by writing arbitrary C++ code to implement operations. For
+example, if we add:
+
+.. code-block:: c++
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+Now we can produce simple output to the console by using things like:
+"``extern putchard(x); putchard(120);``", which prints a lowercase 'x'
+on the console (120 is the ASCII code for 'x'). Similar code could be
+used to implement file I/O, console input, and many other capabilities
+in Kaleidoscope.
+
+This completes the JIT and optimizer chapter of the Kaleidoscope
+tutorial. At this point, we can compile a non-Turing-complete
+programming language, optimize and JIT compile it in a user-driven way.
+Next up we'll look into `extending the language with control flow
+constructs <LangImpl5.html>`_, tackling some interesting LLVM IR issues
+along the way.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM JIT and optimizer. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
+ # Run
+ ./toy
+
+If you are compiling this on Linux, make sure to add the "-rdynamic"
+option as well. This makes sure that the external functions are resolved
+properly at runtime.
+
+Here is the code:
+
+.. code-block:: c++
+
+ #include "llvm/DerivedTypes.h"
+ #include "llvm/ExecutionEngine/ExecutionEngine.h"
+ #include "llvm/ExecutionEngine/JIT.h"
+ #include "llvm/IRBuilder.h"
+ #include "llvm/LLVMContext.h"
+ #include "llvm/Module.h"
+ #include "llvm/PassManager.h"
+ #include "llvm/Analysis/Verifier.h"
+ #include "llvm/Analysis/Passes.h"
+ #include "llvm/DataLayout.h"
+ #include "llvm/Transforms/Scalar.h"
+ #include "llvm/Support/TargetSelect.h"
+ #include <cstdio>
+ #include <string>
+ #include <map>
+ #include <vector>
+ using namespace llvm;
+
+ //===----------------------------------------------------------------------===//
+ // Lexer
+ //===----------------------------------------------------------------------===//
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ return tok_identifier;
+ }
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Abstract Syntax Tree (aka Parse Tree)
+ //===----------------------------------------------------------------------===//
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *Codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ virtual Value *Codegen();
+ };
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ virtual Value *Codegen();
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ virtual Value *Codegen();
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ virtual Value *Codegen();
+ };
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes).
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args)
+ : Name(name), Args(args) {}
+
+ Function *Codegen();
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ Function *Codegen();
+ };
+
+ //===----------------------------------------------------------------------===//
+ // Parser
+ //===----------------------------------------------------------------------===//
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+ static ExprAST *ParseExpression();
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ }
+ }
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ ExprAST *RHS = ParsePrimary();
+ if (!RHS) return 0;
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+ }
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParsePrimary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static PrototypeAST *ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return new PrototypeAST(FnName, ArgNames);
+ }
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Code Generation
+ //===----------------------------------------------------------------------===//
+
+ static Module *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, Value*> NamedValues;
+ static FunctionPassManager *TheFPM;
+
+ Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+ Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ return V ? V : ErrorV("Unknown variable name");
+ }
+
+ Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateFAdd(L, R, "addtmp");
+ case '-': return Builder.CreateFSub(L, R, "subtmp");
+ case '*': return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default: return ErrorV("invalid binary operator");
+ }
+ }
+
+ Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value*> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->Codegen());
+ if (ArgsV.back() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+ Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
+ Doubles, false);
+
+ Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx) {
+ AI->setName(Args[Idx]);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = AI;
+ }
+
+ return F;
+ }
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Top-Level parsing and JIT Driver
+ //===----------------------------------------------------------------------===//
+
+ static ExecutionEngine *TheExecutionEngine;
+
+ static void HandleDefinition() {
+ if (FunctionAST *F = ParseDefinition()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read function definition:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (PrototypeAST *P = ParseExtern()) {
+ if (Function *F = P->Codegen()) {
+ fprintf(stderr, "Read extern: ");
+ F->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read top-level expression:");
+ LF->dump();
+
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // Cast it to the right type (takes no arguments, returns a double) so we
+ // can call it as a native function.
+ double (*FP)() = (double (*)())(intptr_t)FPtr;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+ //===----------------------------------------------------------------------===//
+ // "Library" functions that can be "extern'd" from user code.
+ //===----------------------------------------------------------------------===//
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Main driver code.
+ //===----------------------------------------------------------------------===//
+
+ int main() {
+ InitializeNativeTarget();
+ LLVMContext &Context = getGlobalContext();
+
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ fprintf(stderr, "ready> ");
+ getNextToken();
+
+ // Make the module, which holds all the code.
+ TheModule = new Module("my cool jit", Context);
+
+ // Create the JIT. This takes ownership of the module.
+ std::string ErrStr;
+ TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
+ if (!TheExecutionEngine) {
+ fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
+ exit(1);
+ }
+
+ FunctionPassManager OurFPM(TheModule);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Provide basic AliasAnalysis support for GVN.
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ TheFPM = 0;
+
+ // Print out all of the generated code.
+ TheModule->dump();
+
+ return 0;
+ }
+
+`Next: Extending the language: control flow <LangImpl5.html>`_
+
Removed: llvm/trunk/docs/tutorial/LangImpl5.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl5.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl5.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl5.html (removed)
@@ -1,1772 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Extending the Language: Control Flow</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Extending the Language: Control Flow</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 5
- <ol>
- <li><a href="#intro">Chapter 5 Introduction</a></li>
- <li><a href="#ifthen">If/Then/Else</a>
- <ol>
- <li><a href="#iflexer">Lexer Extensions</a></li>
- <li><a href="#ifast">AST Extensions</a></li>
- <li><a href="#ifparser">Parser Extensions</a></li>
- <li><a href="#ifir">LLVM IR</a></li>
- <li><a href="#ifcodegen">Code Generation</a></li>
- </ol>
- </li>
- <li><a href="#for">'for' Loop Expression</a>
- <ol>
- <li><a href="#forlexer">Lexer Extensions</a></li>
- <li><a href="#forast">AST Extensions</a></li>
- <li><a href="#forparser">Parser Extensions</a></li>
- <li><a href="#forir">LLVM IR</a></li>
- <li><a href="#forcodegen">Code Generation</a></li>
- </ol>
- </li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="LangImpl6.html">Chapter 6</a>: Extending the Language:
-User-defined Operators</li>
-</ul>
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 5 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 5 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. Parts 1-4 described the implementation of the simple
-Kaleidoscope language and included support for generating LLVM IR, followed by
-optimizations and a JIT compiler. Unfortunately, as presented, Kaleidoscope is
-mostly useless: it has no control flow other than call and return. This means
-that you can't have conditional branches in the code, significantly limiting its
-power. In this episode of "build that compiler", we'll extend Kaleidoscope to
-have an if/then/else expression plus a simple 'for' loop.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="ifthen">If/Then/Else</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Extending Kaleidoscope to support if/then/else is quite straightforward. It
-basically requires adding support for this "new" concept to the lexer,
-parser, AST, and LLVM code emitter. This example is nice, because it shows how
-easy it is to "grow" a language over time, incrementally extending it as new
-ideas are discovered.</p>
-
-<p>Before we get going on "how" we add this extension, lets talk about "what" we
-want. The basic idea is that we want to be able to write this sort of thing:
-</p>
-
-<div class="doc_code">
-<pre>
-def fib(x)
- if x < 3 then
- 1
- else
- fib(x-1)+fib(x-2);
-</pre>
-</div>
-
-<p>In Kaleidoscope, every construct is an expression: there are no statements.
-As such, the if/then/else expression needs to return a value like any other.
-Since we're using a mostly functional form, we'll have it evaluate its
-conditional, then return the 'then' or 'else' value based on how the condition
-was resolved. This is very similar to the C "?:" expression.</p>
-
-<p>The semantics of the if/then/else expression is that it evaluates the
-condition to a boolean equality value: 0.0 is considered to be false and
-everything else is considered to be true.
-If the condition is true, the first subexpression is evaluated and returned, if
-the condition is false, the second subexpression is evaluated and returned.
-Since Kaleidoscope allows side-effects, this behavior is important to nail down.
-</p>
-
-<p>Now that we know what we "want", lets break this down into its constituent
-pieces.</p>
-
-<!-- ======================================================================= -->
-<h4><a name="iflexer">Lexer Extensions for If/Then/Else</a></h4>
-<!-- ======================================================================= -->
-
-
-<div>
-
-<p>The lexer extensions are straightforward. First we add new enum values
-for the relevant tokens:</p>
-
-<div class="doc_code">
-<pre>
- // control
- tok_if = -6, tok_then = -7, tok_else = -8,
-</pre>
-</div>
-
-<p>Once we have that, we recognize the new keywords in the lexer. This is pretty simple
-stuff:</p>
-
-<div class="doc_code">
-<pre>
- ...
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- <b>if (IdentifierStr == "if") return tok_if;
- if (IdentifierStr == "then") return tok_then;
- if (IdentifierStr == "else") return tok_else;</b>
- return tok_identifier;
-</pre>
-</div>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="ifast">AST Extensions for If/Then/Else</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>To represent the new expression we add a new AST node for it:</p>
-
-<div class="doc_code">
-<pre>
-/// IfExprAST - Expression class for if/then/else.
-class IfExprAST : public ExprAST {
- ExprAST *Cond, *Then, *Else;
-public:
- IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
- : Cond(cond), Then(then), Else(_else) {}
- virtual Value *Codegen();
-};
-</pre>
-</div>
-
-<p>The AST node just has pointers to the various subexpressions.</p>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="ifparser">Parser Extensions for If/Then/Else</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>Now that we have the relevant tokens coming from the lexer and we have the
-AST node to build, our parsing logic is relatively straightforward. First we
-define a new parsing function:</p>
-
-<div class="doc_code">
-<pre>
-/// ifexpr ::= 'if' expression 'then' expression 'else' expression
-static ExprAST *ParseIfExpr() {
- getNextToken(); // eat the if.
-
- // condition.
- ExprAST *Cond = ParseExpression();
- if (!Cond) return 0;
-
- if (CurTok != tok_then)
- return Error("expected then");
- getNextToken(); // eat the then
-
- ExprAST *Then = ParseExpression();
- if (Then == 0) return 0;
-
- if (CurTok != tok_else)
- return Error("expected else");
-
- getNextToken();
-
- ExprAST *Else = ParseExpression();
- if (!Else) return 0;
-
- return new IfExprAST(Cond, Then, Else);
-}
-</pre>
-</div>
-
-<p>Next we hook it up as a primary expression:</p>
-
-<div class="doc_code">
-<pre>
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- <b>case tok_if: return ParseIfExpr();</b>
- }
-}
-</pre>
-</div>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="ifir">LLVM IR for If/Then/Else</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>Now that we have it parsing and building the AST, the final piece is adding
-LLVM code generation support. This is the most interesting part of the
-if/then/else example, because this is where it starts to introduce new concepts.
-All of the code above has been thoroughly described in previous chapters.
-</p>
-
-<p>To motivate the code we want to produce, lets take a look at a simple
-example. Consider:</p>
-
-<div class="doc_code">
-<pre>
-extern foo();
-extern bar();
-def baz(x) if x then foo() else bar();
-</pre>
-</div>
-
-<p>If you disable optimizations, the code you'll (soon) get from Kaleidoscope
-looks like this:</p>
-
-<div class="doc_code">
-<pre>
-declare double @foo()
-
-declare double @bar()
-
-define double @baz(double %x) {
-entry:
- %ifcond = fcmp one double %x, 0.000000e+00
- br i1 %ifcond, label %then, label %else
-
-then: ; preds = %entry
- %calltmp = call double @foo()
- br label %ifcont
-
-else: ; preds = %entry
- %calltmp1 = call double @bar()
- br label %ifcont
-
-ifcont: ; preds = %else, %then
- %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
- ret double %iftmp
-}
-</pre>
-</div>
-
-<p>To visualize the control flow graph, you can use a nifty feature of the LLVM
-'<a href="http://llvm.org/cmds/opt.html">opt</a>' tool. If you put this LLVM IR
-into "t.ll" and run "<tt>llvm-as < t.ll | opt -analyze -view-cfg</tt>", <a
-href="../ProgrammersManual.html#ViewGraph">a window will pop up</a> and you'll
-see this graph:</p>
-
-<div style="text-align: center"><img src="LangImpl5-cfg.png" alt="Example CFG" width="423"
-height="315"></div>
-
-<p>Another way to get this is to call "<tt>F->viewCFG()</tt>" or
-"<tt>F->viewCFGOnly()</tt>" (where F is a "<tt>Function*</tt>") either by
-inserting actual calls into the code and recompiling or by calling these in the
-debugger. LLVM has many nice features for visualizing various graphs.</p>
-
-<p>Getting back to the generated code, it is fairly simple: the entry block
-evaluates the conditional expression ("x" in our case here) and compares the
-result to 0.0 with the "<tt><a href="../LangRef.html#i_fcmp">fcmp</a> one</tt>"
-instruction ('one' is "Ordered and Not Equal"). Based on the result of this
-expression, the code jumps to either the "then" or "else" blocks, which contain
-the expressions for the true/false cases.</p>
-
-<p>Once the then/else blocks are finished executing, they both branch back to the
-'ifcont' block to execute the code that happens after the if/then/else. In this
-case the only thing left to do is to return to the caller of the function. The
-question then becomes: how does the code know which expression to return?</p>
-
-<p>The answer to this question involves an important SSA operation: the
-<a href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Phi
-operation</a>. If you're not familiar with SSA, <a
-href="http://en.wikipedia.org/wiki/Static_single_assignment_form">the wikipedia
-article</a> is a good introduction and there are various other introductions to
-it available on your favorite search engine. The short version is that
-"execution" of the Phi operation requires "remembering" which block control came
-from. The Phi operation takes on the value corresponding to the input control
-block. In this case, if control comes in from the "then" block, it gets the
-value of "calltmp". If control comes from the "else" block, it gets the value
-of "calltmp1".</p>
-
-<p>At this point, you are probably starting to think "Oh no! This means my
-simple and elegant front-end will have to start generating SSA form in order to
-use LLVM!". Fortunately, this is not the case, and we strongly advise
-<em>not</em> implementing an SSA construction algorithm in your front-end
-unless there is an amazingly good reason to do so. In practice, there are two
-sorts of values that float around in code written for your average imperative
-programming language that might need Phi nodes:</p>
-
-<ol>
-<li>Code that involves user variables: <tt>x = 1; x = x + 1; </tt></li>
-<li>Values that are implicit in the structure of your AST, such as the Phi node
-in this case.</li>
-</ol>
-
-<p>In <a href="LangImpl7.html">Chapter 7</a> of this tutorial ("mutable
-variables"), we'll talk about #1
-in depth. For now, just believe me that you don't need SSA construction to
-handle this case. For #2, you have the choice of using the techniques that we will
-describe for #1, or you can insert Phi nodes directly, if convenient. In this
-case, it is really really easy to generate the Phi node, so we choose to do it
-directly.</p>
-
-<p>Okay, enough of the motivation and overview, lets generate code!</p>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="ifcodegen">Code Generation for If/Then/Else</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>In order to generate code for this, we implement the <tt>Codegen</tt> method
-for <tt>IfExprAST</tt>:</p>
-
-<div class="doc_code">
-<pre>
-Value *IfExprAST::Codegen() {
- Value *CondV = Cond->Codegen();
- if (CondV == 0) return 0;
-
- // Convert condition to a bool by comparing equal to 0.0.
- CondV = Builder.CreateFCmpONE(CondV,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "ifcond");
-</pre>
-</div>
-
-<p>This code is straightforward and similar to what we saw before. We emit the
-expression for the condition, then compare that value to zero to get a truth
-value as a 1-bit (bool) value.</p>
-
-<div class="doc_code">
-<pre>
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- // Create blocks for the then and else cases. Insert the 'then' block at the
- // end of the function.
- BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
- BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
- BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
-
- Builder.CreateCondBr(CondV, ThenBB, ElseBB);
-</pre>
-</div>
-
-<p>This code creates the basic blocks that are related to the if/then/else
-statement, and correspond directly to the blocks in the example above. The
-first line gets the current Function object that is being built. It
-gets this by asking the builder for the current BasicBlock, and asking that
-block for its "parent" (the function it is currently embedded into).</p>
-
-<p>Once it has that, it creates three blocks. Note that it passes "TheFunction"
-into the constructor for the "then" block. This causes the constructor to
-automatically insert the new block into the end of the specified function. The
-other two blocks are created, but aren't yet inserted into the function.</p>
-
-<p>Once the blocks are created, we can emit the conditional branch that chooses
-between them. Note that creating new blocks does not implicitly affect the
-IRBuilder, so it is still inserting into the block that the condition
-went into. Also note that it is creating a branch to the "then" block and the
-"else" block, even though the "else" block isn't inserted into the function yet.
-This is all ok: it is the standard way that LLVM supports forward
-references.</p>
-
-<div class="doc_code">
-<pre>
- // Emit then value.
- Builder.SetInsertPoint(ThenBB);
-
- Value *ThenV = Then->Codegen();
- if (ThenV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
- ThenBB = Builder.GetInsertBlock();
-</pre>
-</div>
-
-<p>After the conditional branch is inserted, we move the builder to start
-inserting into the "then" block. Strictly speaking, this call moves the
-insertion point to be at the end of the specified block. However, since the
-"then" block is empty, it also starts out by inserting at the beginning of the
-block. :)</p>
-
-<p>Once the insertion point is set, we recursively codegen the "then" expression
-from the AST. To finish off the "then" block, we create an unconditional branch
-to the merge block. One interesting (and very important) aspect of the LLVM IR
-is that it <a href="../LangRef.html#functionstructure">requires all basic blocks
-to be "terminated"</a> with a <a href="../LangRef.html#terminators">control flow
-instruction</a> such as return or branch. This means that all control flow,
-<em>including fall throughs</em> must be made explicit in the LLVM IR. If you
-violate this rule, the verifier will emit an error.</p>
-
-<p>The final line here is quite subtle, but is very important. The basic issue
-is that when we create the Phi node in the merge block, we need to set up the
-block/value pairs that indicate how the Phi will work. Importantly, the Phi
-node expects to have an entry for each predecessor of the block in the CFG. Why
-then, are we getting the current block when we just set it to ThenBB 5 lines
-above? The problem is that the "Then" expression may actually itself change the
-block that the Builder is emitting into if, for example, it contains a nested
-"if/then/else" expression. Because calling Codegen recursively could
-arbitrarily change the notion of the current block, we are required to get an
-up-to-date value for code that will set up the Phi node.</p>
-
-<div class="doc_code">
-<pre>
- // Emit else block.
- TheFunction->getBasicBlockList().push_back(ElseBB);
- Builder.SetInsertPoint(ElseBB);
-
- Value *ElseV = Else->Codegen();
- if (ElseV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
- ElseBB = Builder.GetInsertBlock();
-</pre>
-</div>
-
-<p>Code generation for the 'else' block is basically identical to codegen for
-the 'then' block. The only significant difference is the first line, which adds
-the 'else' block to the function. Recall previously that the 'else' block was
-created, but not added to the function. Now that the 'then' and 'else' blocks
-are emitted, we can finish up with the merge code:</p>
-
-<div class="doc_code">
-<pre>
- // Emit merge block.
- TheFunction->getBasicBlockList().push_back(MergeBB);
- Builder.SetInsertPoint(MergeBB);
- PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
- "iftmp");
-
- PN->addIncoming(ThenV, ThenBB);
- PN->addIncoming(ElseV, ElseBB);
- return PN;
-}
-</pre>
-</div>
-
-<p>The first two lines here are now familiar: the first adds the "merge" block
-to the Function object (it was previously floating, like the else block above).
-The second block changes the insertion point so that newly created code will go
-into the "merge" block. Once that is done, we need to create the PHI node and
-set up the block/value pairs for the PHI.</p>
-
-<p>Finally, the CodeGen function returns the phi node as the value computed by
-the if/then/else expression. In our example above, this returned value will
-feed into the code for the top-level function, which will create the return
-instruction.</p>
-
-<p>Overall, we now have the ability to execute conditional code in
-Kaleidoscope. With this extension, Kaleidoscope is a fairly complete language
-that can calculate a wide variety of numeric functions. Next up we'll add
-another useful expression that is familiar from non-functional languages...</p>
-
-</div>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="for">'for' Loop Expression</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Now that we know how to add basic control flow constructs to the language,
-we have the tools to add more powerful things. Lets add something more
-aggressive, a 'for' expression:</p>
-
-<div class="doc_code">
-<pre>
- extern putchard(char)
- def printstar(n)
- for i = 1, i < n, 1.0 in
- putchard(42); # ascii 42 = '*'
-
- # print 100 '*' characters
- printstar(100);
-</pre>
-</div>
-
-<p>This expression defines a new variable ("i" in this case) which iterates from
-a starting value, while the condition ("i < n" in this case) is true,
-incrementing by an optional step value ("1.0" in this case). If the step value
-is omitted, it defaults to 1.0. While the loop is true, it executes its
-body expression. Because we don't have anything better to return, we'll just
-define the loop as always returning 0.0. In the future when we have mutable
-variables, it will get more useful.</p>
-
-<p>As before, lets talk about the changes that we need to Kaleidoscope to
-support this.</p>
-
-<!-- ======================================================================= -->
-<h4><a name="forlexer">Lexer Extensions for the 'for' Loop</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>The lexer extensions are the same sort of thing as for if/then/else:</p>
-
-<div class="doc_code">
-<pre>
- ... in enum Token ...
- // control
- tok_if = -6, tok_then = -7, tok_else = -8,
-<b> tok_for = -9, tok_in = -10</b>
-
- ... in gettok ...
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- if (IdentifierStr == "if") return tok_if;
- if (IdentifierStr == "then") return tok_then;
- if (IdentifierStr == "else") return tok_else;
- <b>if (IdentifierStr == "for") return tok_for;
- if (IdentifierStr == "in") return tok_in;</b>
- return tok_identifier;
-</pre>
-</div>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="forast">AST Extensions for the 'for' Loop</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>The AST node is just as simple. It basically boils down to capturing
-the variable name and the constituent expressions in the node.</p>
-
-<div class="doc_code">
-<pre>
-/// ForExprAST - Expression class for for/in.
-class ForExprAST : public ExprAST {
- std::string VarName;
- ExprAST *Start, *End, *Step, *Body;
-public:
- ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
- ExprAST *step, ExprAST *body)
- : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
- virtual Value *Codegen();
-};
-</pre>
-</div>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="forparser">Parser Extensions for the 'for' Loop</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>The parser code is also fairly standard. The only interesting thing here is
-handling of the optional step value. The parser code handles it by checking to
-see if the second comma is present. If not, it sets the step value to null in
-the AST node:</p>
-
-<div class="doc_code">
-<pre>
-/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
-static ExprAST *ParseForExpr() {
- getNextToken(); // eat the for.
-
- if (CurTok != tok_identifier)
- return Error("expected identifier after for");
-
- std::string IdName = IdentifierStr;
- getNextToken(); // eat identifier.
-
- if (CurTok != '=')
- return Error("expected '=' after for");
- getNextToken(); // eat '='.
-
-
- ExprAST *Start = ParseExpression();
- if (Start == 0) return 0;
- if (CurTok != ',')
- return Error("expected ',' after for start value");
- getNextToken();
-
- ExprAST *End = ParseExpression();
- if (End == 0) return 0;
-
- // The step value is optional.
- ExprAST *Step = 0;
- if (CurTok == ',') {
- getNextToken();
- Step = ParseExpression();
- if (Step == 0) return 0;
- }
-
- if (CurTok != tok_in)
- return Error("expected 'in' after for");
- getNextToken(); // eat 'in'.
-
- ExprAST *Body = ParseExpression();
- if (Body == 0) return 0;
-
- return new ForExprAST(IdName, Start, End, Step, Body);
-}
-</pre>
-</div>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="forir">LLVM IR for the 'for' Loop</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>Now we get to the good part: the LLVM IR we want to generate for this thing.
-With the simple example above, we get this LLVM IR (note that this dump is
-generated with optimizations disabled for clarity):
-</p>
-
-<div class="doc_code">
-<pre>
-declare double @putchard(double)
-
-define double @printstar(double %n) {
-entry:
- ; initial value = 1.0 (inlined into phi)
- br label %loop
-
-loop: ; preds = %loop, %entry
- %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
- ; body
- %calltmp = call double @putchard(double 4.200000e+01)
- ; increment
- %nextvar = fadd double %i, 1.000000e+00
-
- ; termination test
- %cmptmp = fcmp ult double %i, %n
- %booltmp = uitofp i1 %cmptmp to double
- %loopcond = fcmp one double %booltmp, 0.000000e+00
- br i1 %loopcond, label %loop, label %afterloop
-
-afterloop: ; preds = %loop
- ; loop always returns 0.0
- ret double 0.000000e+00
-}
-</pre>
-</div>
-
-<p>This loop contains all the same constructs we saw before: a phi node, several
-expressions, and some basic blocks. Lets see how this fits together.</p>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="forcodegen">Code Generation for the 'for' Loop</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>The first part of Codegen is very simple: we just output the start expression
-for the loop value:</p>
-
-<div class="doc_code">
-<pre>
-Value *ForExprAST::Codegen() {
- // Emit the start code first, without 'variable' in scope.
- Value *StartVal = Start->Codegen();
- if (StartVal == 0) return 0;
-</pre>
-</div>
-
-<p>With this out of the way, the next step is to set up the LLVM basic block
-for the start of the loop body. In the case above, the whole loop body is one
-block, but remember that the body code itself could consist of multiple blocks
-(e.g. if it contains an if/then/else or a for/in expression).</p>
-
-<div class="doc_code">
-<pre>
- // Make the new basic block for the loop header, inserting after current
- // block.
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
- BasicBlock *PreheaderBB = Builder.GetInsertBlock();
- BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
-
- // Insert an explicit fall through from the current block to the LoopBB.
- Builder.CreateBr(LoopBB);
-</pre>
-</div>
-
-<p>This code is similar to what we saw for if/then/else. Because we will need
-it to create the Phi node, we remember the block that falls through into the
-loop. Once we have that, we create the actual block that starts the loop and
-create an unconditional branch for the fall-through between the two blocks.</p>
-
-<div class="doc_code">
-<pre>
- // Start insertion in LoopBB.
- Builder.SetInsertPoint(LoopBB);
-
- // Start the PHI node with an entry for Start.
- PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str());
- Variable->addIncoming(StartVal, PreheaderBB);
-</pre>
-</div>
-
-<p>Now that the "preheader" for the loop is set up, we switch to emitting code
-for the loop body. To begin with, we move the insertion point and create the
-PHI node for the loop induction variable. Since we already know the incoming
-value for the starting value, we add it to the Phi node. Note that the Phi will
-eventually get a second value for the backedge, but we can't set it up yet
-(because it doesn't exist!).</p>
-
-<div class="doc_code">
-<pre>
- // Within the loop, the variable is defined equal to the PHI node. If it
- // shadows an existing variable, we have to restore it, so save it now.
- Value *OldVal = NamedValues[VarName];
- NamedValues[VarName] = Variable;
-
- // Emit the body of the loop. This, like any other expr, can change the
- // current BB. Note that we ignore the value computed by the body, but don't
- // allow an error.
- if (Body->Codegen() == 0)
- return 0;
-</pre>
-</div>
-
-<p>Now the code starts to get more interesting. Our 'for' loop introduces a new
-variable to the symbol table. This means that our symbol table can now contain
-either function arguments or loop variables. To handle this, before we codegen
-the body of the loop, we add the loop variable as the current value for its
-name. Note that it is possible that there is a variable of the same name in the
-outer scope. It would be easy to make this an error (emit an error and return
-null if there is already an entry for VarName) but we choose to allow shadowing
-of variables. In order to handle this correctly, we remember the Value that
-we are potentially shadowing in <tt>OldVal</tt> (which will be null if there is
-no shadowed variable).</p>
-
-<p>Once the loop variable is set into the symbol table, the code recursively
-codegen's the body. This allows the body to use the loop variable: any
-references to it will naturally find it in the symbol table.</p>
-
-<div class="doc_code">
-<pre>
- // Emit the step value.
- Value *StepVal;
- if (Step) {
- StepVal = Step->Codegen();
- if (StepVal == 0) return 0;
- } else {
- // If not specified, use 1.0.
- StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
- }
-
- Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
-</pre>
-</div>
-
-<p>Now that the body is emitted, we compute the next value of the iteration
-variable by adding the step value, or 1.0 if it isn't present. '<tt>NextVar</tt>'
-will be the value of the loop variable on the next iteration of the loop.</p>
-
-<div class="doc_code">
-<pre>
- // Compute the end condition.
- Value *EndCond = End->Codegen();
- if (EndCond == 0) return EndCond;
-
- // Convert condition to a bool by comparing equal to 0.0.
- EndCond = Builder.CreateFCmpONE(EndCond,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "loopcond");
-</pre>
-</div>
-
-<p>Finally, we evaluate the exit value of the loop, to determine whether the
-loop should exit. This mirrors the condition evaluation for the if/then/else
-statement.</p>
-
-<div class="doc_code">
-<pre>
- // Create the "after loop" block and insert it.
- BasicBlock *LoopEndBB = Builder.GetInsertBlock();
- BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
-
- // Insert the conditional branch into the end of LoopEndBB.
- Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
-
- // Any new code will be inserted in AfterBB.
- Builder.SetInsertPoint(AfterBB);
-</pre>
-</div>
-
-<p>With the code for the body of the loop complete, we just need to finish up
-the control flow for it. This code remembers the end block (for the phi node),
-then creates the block for the loop exit ("afterloop"). Based on the value of
-the exit condition, it creates a conditional branch that chooses between
-executing the loop again and exiting the loop. Any future code is emitted in
-the "afterloop" block, so it sets the insertion position to it.</p>
-
-<div class="doc_code">
-<pre>
- // Add a new entry to the PHI node for the backedge.
- Variable->addIncoming(NextVar, LoopEndBB);
-
- // Restore the unshadowed variable.
- if (OldVal)
- NamedValues[VarName] = OldVal;
- else
- NamedValues.erase(VarName);
-
- // for expr always returns 0.0.
- return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
-}
-</pre>
-</div>
-
-<p>The final code handles various cleanups: now that we have the "NextVar"
-value, we can add the incoming value to the loop PHI node. After that, we
-remove the loop variable from the symbol table, so that it isn't in scope after
-the for loop. Finally, code generation of the for loop always returns 0.0, so
-that is what we return from <tt>ForExprAST::Codegen</tt>.</p>
-
-<p>With this, we conclude the "adding control flow to Kaleidoscope" chapter of
-the tutorial. In this chapter we added two control flow constructs, and used them to motivate a couple of aspects of the LLVM IR that are important for front-end implementors
-to know. In the next chapter of our saga, we will get a bit crazier and add
-<a href="LangImpl6.html">user-defined operators</a> to our poor innocent
-language.</p>
-
-</div>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for our running example, enhanced with the
-if/then/else and for expressions.. To build this example, use:
-</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
-# Run
-./toy
-</pre>
-</div>
-
-<p>Here is the code:</p>
-
-<div class="doc_code">
-<pre>
-#include "llvm/DerivedTypes.h"
-#include "llvm/ExecutionEngine/ExecutionEngine.h"
-#include "llvm/ExecutionEngine/JIT.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/PassManager.h"
-#include "llvm/Analysis/Verifier.h"
-#include "llvm/Analysis/Passes.h"
-#include "llvm/DataLayout.h"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Support/TargetSelect.h"
-#include <cstdio>
-#include <string>
-#include <map>
-#include <vector>
-using namespace llvm;
-
-//===----------------------------------------------------------------------===//
-// Lexer
-//===----------------------------------------------------------------------===//
-
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
- tok_eof = -1,
-
- // commands
- tok_def = -2, tok_extern = -3,
-
- // primary
- tok_identifier = -4, tok_number = -5,
-
- // control
- tok_if = -6, tok_then = -7, tok_else = -8,
- tok_for = -9, tok_in = -10
-};
-
-static std::string IdentifierStr; // Filled in if tok_identifier
-static double NumVal; // Filled in if tok_number
-
-/// gettok - Return the next token from standard input.
-static int gettok() {
- static int LastChar = ' ';
-
- // Skip any whitespace.
- while (isspace(LastChar))
- LastChar = getchar();
-
- if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
- IdentifierStr = LastChar;
- while (isalnum((LastChar = getchar())))
- IdentifierStr += LastChar;
-
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- if (IdentifierStr == "if") return tok_if;
- if (IdentifierStr == "then") return tok_then;
- if (IdentifierStr == "else") return tok_else;
- if (IdentifierStr == "for") return tok_for;
- if (IdentifierStr == "in") return tok_in;
- return tok_identifier;
- }
-
- if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
- std::string NumStr;
- do {
- NumStr += LastChar;
- LastChar = getchar();
- } while (isdigit(LastChar) || LastChar == '.');
-
- NumVal = strtod(NumStr.c_str(), 0);
- return tok_number;
- }
-
- if (LastChar == '#') {
- // Comment until end of line.
- do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-
- if (LastChar != EOF)
- return gettok();
- }
-
- // Check for end of file. Don't eat the EOF.
- if (LastChar == EOF)
- return tok_eof;
-
- // Otherwise, just return the character as its ascii value.
- int ThisChar = LastChar;
- LastChar = getchar();
- return ThisChar;
-}
-
-//===----------------------------------------------------------------------===//
-// Abstract Syntax Tree (aka Parse Tree)
-//===----------------------------------------------------------------------===//
-
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
- virtual Value *Codegen() = 0;
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
- virtual Value *Codegen();
-};
-
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
- std::string Name;
-public:
- VariableExprAST(const std::string &name) : Name(name) {}
- virtual Value *Codegen();
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
- char Op;
- ExprAST *LHS, *RHS;
-public:
- BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
- : Op(op), LHS(lhs), RHS(rhs) {}
- virtual Value *Codegen();
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
- std::string Callee;
- std::vector<ExprAST*> Args;
-public:
- CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
- : Callee(callee), Args(args) {}
- virtual Value *Codegen();
-};
-
-/// IfExprAST - Expression class for if/then/else.
-class IfExprAST : public ExprAST {
- ExprAST *Cond, *Then, *Else;
-public:
- IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
- : Cond(cond), Then(then), Else(_else) {}
- virtual Value *Codegen();
-};
-
-/// ForExprAST - Expression class for for/in.
-class ForExprAST : public ExprAST {
- std::string VarName;
- ExprAST *Start, *End, *Step, *Body;
-public:
- ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
- ExprAST *step, ExprAST *body)
- : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
- virtual Value *Codegen();
-};
-
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes).
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args)
- : Name(name), Args(args) {}
-
- Function *Codegen();
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
- PrototypeAST *Proto;
- ExprAST *Body;
-public:
- FunctionAST(PrototypeAST *proto, ExprAST *body)
- : Proto(proto), Body(body) {}
-
- Function *Codegen();
-};
-
-//===----------------------------------------------------------------------===//
-// Parser
-//===----------------------------------------------------------------------===//
-
-/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
-/// token the parser is looking at. getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
- return CurTok = gettok();
-}
-
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
- if (!isascii(CurTok))
- return -1;
-
- // Make sure it's a declared binop.
- int TokPrec = BinopPrecedence[CurTok];
- if (TokPrec <= 0) return -1;
- return TokPrec;
-}
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-
-static ExprAST *ParseExpression();
-
-/// identifierexpr
-/// ::= identifier
-/// ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
- std::string IdName = IdentifierStr;
-
- getNextToken(); // eat identifier.
-
- if (CurTok != '(') // Simple variable ref.
- return new VariableExprAST(IdName);
-
- // Call.
- getNextToken(); // eat (
- std::vector<ExprAST*> Args;
- if (CurTok != ')') {
- while (1) {
- ExprAST *Arg = ParseExpression();
- if (!Arg) return 0;
- Args.push_back(Arg);
-
- if (CurTok == ')') break;
-
- if (CurTok != ',')
- return Error("Expected ')' or ',' in argument list");
- getNextToken();
- }
- }
-
- // Eat the ')'.
- getNextToken();
-
- return new CallExprAST(IdName, Args);
-}
-
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
- ExprAST *Result = new NumberExprAST(NumVal);
- getNextToken(); // consume the number
- return Result;
-}
-
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
- getNextToken(); // eat (.
- ExprAST *V = ParseExpression();
- if (!V) return 0;
-
- if (CurTok != ')')
- return Error("expected ')'");
- getNextToken(); // eat ).
- return V;
-}
-
-/// ifexpr ::= 'if' expression 'then' expression 'else' expression
-static ExprAST *ParseIfExpr() {
- getNextToken(); // eat the if.
-
- // condition.
- ExprAST *Cond = ParseExpression();
- if (!Cond) return 0;
-
- if (CurTok != tok_then)
- return Error("expected then");
- getNextToken(); // eat the then
-
- ExprAST *Then = ParseExpression();
- if (Then == 0) return 0;
-
- if (CurTok != tok_else)
- return Error("expected else");
-
- getNextToken();
-
- ExprAST *Else = ParseExpression();
- if (!Else) return 0;
-
- return new IfExprAST(Cond, Then, Else);
-}
-
-/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
-static ExprAST *ParseForExpr() {
- getNextToken(); // eat the for.
-
- if (CurTok != tok_identifier)
- return Error("expected identifier after for");
-
- std::string IdName = IdentifierStr;
- getNextToken(); // eat identifier.
-
- if (CurTok != '=')
- return Error("expected '=' after for");
- getNextToken(); // eat '='.
-
-
- ExprAST *Start = ParseExpression();
- if (Start == 0) return 0;
- if (CurTok != ',')
- return Error("expected ',' after for start value");
- getNextToken();
-
- ExprAST *End = ParseExpression();
- if (End == 0) return 0;
-
- // The step value is optional.
- ExprAST *Step = 0;
- if (CurTok == ',') {
- getNextToken();
- Step = ParseExpression();
- if (Step == 0) return 0;
- }
-
- if (CurTok != tok_in)
- return Error("expected 'in' after for");
- getNextToken(); // eat 'in'.
-
- ExprAST *Body = ParseExpression();
- if (Body == 0) return 0;
-
- return new ForExprAST(IdName, Start, End, Step, Body);
-}
-
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-/// ::= ifexpr
-/// ::= forexpr
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- case tok_if: return ParseIfExpr();
- case tok_for: return ParseForExpr();
- }
-}
-
-/// binoprhs
-/// ::= ('+' primary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- // If this is a binop, find its precedence.
- while (1) {
- int TokPrec = GetTokPrecedence();
-
- // If this is a binop that binds at least as tightly as the current binop,
- // consume it, otherwise we are done.
- if (TokPrec < ExprPrec)
- return LHS;
-
- // Okay, we know this is a binop.
- int BinOp = CurTok;
- getNextToken(); // eat binop
-
- // Parse the primary expression after the binary operator.
- ExprAST *RHS = ParsePrimary();
- if (!RHS) return 0;
-
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
- RHS = ParseBinOpRHS(TokPrec+1, RHS);
- if (RHS == 0) return 0;
- }
-
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- }
-}
-
-/// expression
-/// ::= primary binoprhs
-///
-static ExprAST *ParseExpression() {
- ExprAST *LHS = ParsePrimary();
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-
-/// prototype
-/// ::= id '(' id* ')'
-static PrototypeAST *ParsePrototype() {
- if (CurTok != tok_identifier)
- return ErrorP("Expected function name in prototype");
-
- std::string FnName = IdentifierStr;
- getNextToken();
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- return new PrototypeAST(FnName, ArgNames);
-}
-
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
- getNextToken(); // eat def.
- PrototypeAST *Proto = ParsePrototype();
- if (Proto == 0) return 0;
-
- if (ExprAST *E = ParseExpression())
- return new FunctionAST(Proto, E);
- return 0;
-}
-
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
- if (ExprAST *E = ParseExpression()) {
- // Make an anonymous proto.
- PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
- return new FunctionAST(Proto, E);
- }
- return 0;
-}
-
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
- getNextToken(); // eat extern.
- return ParsePrototype();
-}
-
-//===----------------------------------------------------------------------===//
-// Code Generation
-//===----------------------------------------------------------------------===//
-
-static Module *TheModule;
-static IRBuilder<> Builder(getGlobalContext());
-static std::map<std::string, Value*> NamedValues;
-static FunctionPassManager *TheFPM;
-
-Value *ErrorV(const char *Str) { Error(Str); return 0; }
-
-Value *NumberExprAST::Codegen() {
- return ConstantFP::get(getGlobalContext(), APFloat(Val));
-}
-
-Value *VariableExprAST::Codegen() {
- // Look this variable up in the function.
- Value *V = NamedValues[Name];
- return V ? V : ErrorV("Unknown variable name");
-}
-
-Value *BinaryExprAST::Codegen() {
- Value *L = LHS->Codegen();
- Value *R = RHS->Codegen();
- if (L == 0 || R == 0) return 0;
-
- switch (Op) {
- case '+': return Builder.CreateFAdd(L, R, "addtmp");
- case '-': return Builder.CreateFSub(L, R, "subtmp");
- case '*': return Builder.CreateFMul(L, R, "multmp");
- case '<':
- L = Builder.CreateFCmpULT(L, R, "cmptmp");
- // Convert bool 0/1 to double 0.0 or 1.0
- return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
- "booltmp");
- default: return ErrorV("invalid binary operator");
- }
-}
-
-Value *CallExprAST::Codegen() {
- // Look up the name in the global module table.
- Function *CalleeF = TheModule->getFunction(Callee);
- if (CalleeF == 0)
- return ErrorV("Unknown function referenced");
-
- // If argument mismatch error.
- if (CalleeF->arg_size() != Args.size())
- return ErrorV("Incorrect # arguments passed");
-
- std::vector<Value*> ArgsV;
- for (unsigned i = 0, e = Args.size(); i != e; ++i) {
- ArgsV.push_back(Args[i]->Codegen());
- if (ArgsV.back() == 0) return 0;
- }
-
- return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
-}
-
-Value *IfExprAST::Codegen() {
- Value *CondV = Cond->Codegen();
- if (CondV == 0) return 0;
-
- // Convert condition to a bool by comparing equal to 0.0.
- CondV = Builder.CreateFCmpONE(CondV,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "ifcond");
-
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- // Create blocks for the then and else cases. Insert the 'then' block at the
- // end of the function.
- BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
- BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
- BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
-
- Builder.CreateCondBr(CondV, ThenBB, ElseBB);
-
- // Emit then value.
- Builder.SetInsertPoint(ThenBB);
-
- Value *ThenV = Then->Codegen();
- if (ThenV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
- ThenBB = Builder.GetInsertBlock();
-
- // Emit else block.
- TheFunction->getBasicBlockList().push_back(ElseBB);
- Builder.SetInsertPoint(ElseBB);
-
- Value *ElseV = Else->Codegen();
- if (ElseV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
- ElseBB = Builder.GetInsertBlock();
-
- // Emit merge block.
- TheFunction->getBasicBlockList().push_back(MergeBB);
- Builder.SetInsertPoint(MergeBB);
- PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
- "iftmp");
-
- PN->addIncoming(ThenV, ThenBB);
- PN->addIncoming(ElseV, ElseBB);
- return PN;
-}
-
-Value *ForExprAST::Codegen() {
- // Output this as:
- // ...
- // start = startexpr
- // goto loop
- // loop:
- // variable = phi [start, loopheader], [nextvariable, loopend]
- // ...
- // bodyexpr
- // ...
- // loopend:
- // step = stepexpr
- // nextvariable = variable + step
- // endcond = endexpr
- // br endcond, loop, endloop
- // outloop:
-
- // Emit the start code first, without 'variable' in scope.
- Value *StartVal = Start->Codegen();
- if (StartVal == 0) return 0;
-
- // Make the new basic block for the loop header, inserting after current
- // block.
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
- BasicBlock *PreheaderBB = Builder.GetInsertBlock();
- BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
-
- // Insert an explicit fall through from the current block to the LoopBB.
- Builder.CreateBr(LoopBB);
-
- // Start insertion in LoopBB.
- Builder.SetInsertPoint(LoopBB);
-
- // Start the PHI node with an entry for Start.
- PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str());
- Variable->addIncoming(StartVal, PreheaderBB);
-
- // Within the loop, the variable is defined equal to the PHI node. If it
- // shadows an existing variable, we have to restore it, so save it now.
- Value *OldVal = NamedValues[VarName];
- NamedValues[VarName] = Variable;
-
- // Emit the body of the loop. This, like any other expr, can change the
- // current BB. Note that we ignore the value computed by the body, but don't
- // allow an error.
- if (Body->Codegen() == 0)
- return 0;
-
- // Emit the step value.
- Value *StepVal;
- if (Step) {
- StepVal = Step->Codegen();
- if (StepVal == 0) return 0;
- } else {
- // If not specified, use 1.0.
- StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
- }
-
- Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
-
- // Compute the end condition.
- Value *EndCond = End->Codegen();
- if (EndCond == 0) return EndCond;
-
- // Convert condition to a bool by comparing equal to 0.0.
- EndCond = Builder.CreateFCmpONE(EndCond,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "loopcond");
-
- // Create the "after loop" block and insert it.
- BasicBlock *LoopEndBB = Builder.GetInsertBlock();
- BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
-
- // Insert the conditional branch into the end of LoopEndBB.
- Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
-
- // Any new code will be inserted in AfterBB.
- Builder.SetInsertPoint(AfterBB);
-
- // Add a new entry to the PHI node for the backedge.
- Variable->addIncoming(NextVar, LoopEndBB);
-
- // Restore the unshadowed variable.
- if (OldVal)
- NamedValues[VarName] = OldVal;
- else
- NamedValues.erase(VarName);
-
-
- // for expr always returns 0.0.
- return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
-}
-
-Function *PrototypeAST::Codegen() {
- // Make the function type: double(double,double) etc.
- std::vector<Type*> Doubles(Args.size(),
- Type::getDoubleTy(getGlobalContext()));
- FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
- Doubles, false);
-
- Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
-
- // If F conflicted, there was already something named 'Name'. If it has a
- // body, don't allow redefinition or reextern.
- if (F->getName() != Name) {
- // Delete the one we just made and get the existing one.
- F->eraseFromParent();
- F = TheModule->getFunction(Name);
-
- // If F already has a body, reject this.
- if (!F->empty()) {
- ErrorF("redefinition of function");
- return 0;
- }
-
- // If F took a different number of args, reject.
- if (F->arg_size() != Args.size()) {
- ErrorF("redefinition of function with different # args");
- return 0;
- }
- }
-
- // Set names for all arguments.
- unsigned Idx = 0;
- for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
- ++AI, ++Idx) {
- AI->setName(Args[Idx]);
-
- // Add arguments to variable symbol table.
- NamedValues[Args[Idx]] = AI;
- }
-
- return F;
-}
-
-Function *FunctionAST::Codegen() {
- NamedValues.clear();
-
- Function *TheFunction = Proto->Codegen();
- if (TheFunction == 0)
- return 0;
-
- // Create a new basic block to start insertion into.
- BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
- Builder.SetInsertPoint(BB);
-
- if (Value *RetVal = Body->Codegen()) {
- // Finish off the function.
- Builder.CreateRet(RetVal);
-
- // Validate the generated code, checking for consistency.
- verifyFunction(*TheFunction);
-
- // Optimize the function.
- TheFPM->run(*TheFunction);
-
- return TheFunction;
- }
-
- // Error reading body, remove function.
- TheFunction->eraseFromParent();
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Top-Level parsing and JIT Driver
-//===----------------------------------------------------------------------===//
-
-static ExecutionEngine *TheExecutionEngine;
-
-static void HandleDefinition() {
- if (FunctionAST *F = ParseDefinition()) {
- if (Function *LF = F->Codegen()) {
- fprintf(stderr, "Read function definition:");
- LF->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleExtern() {
- if (PrototypeAST *P = ParseExtern()) {
- if (Function *F = P->Codegen()) {
- fprintf(stderr, "Read extern: ");
- F->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleTopLevelExpression() {
- // Evaluate a top-level expression into an anonymous function.
- if (FunctionAST *F = ParseTopLevelExpr()) {
- if (Function *LF = F->Codegen()) {
- // JIT the function, returning a function pointer.
- void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
-
- // Cast it to the right type (takes no arguments, returns a double) so we
- // can call it as a native function.
- double (*FP)() = (double (*)())(intptr_t)FPtr;
- fprintf(stderr, "Evaluated to %f\n", FP());
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
- while (1) {
- fprintf(stderr, "ready> ");
- switch (CurTok) {
- case tok_eof: return;
- case ';': getNextToken(); break; // ignore top-level semicolons.
- case tok_def: HandleDefinition(); break;
- case tok_extern: HandleExtern(); break;
- default: HandleTopLevelExpression(); break;
- }
- }
-}
-
-//===----------------------------------------------------------------------===//
-// "Library" functions that can be "extern'd" from user code.
-//===----------------------------------------------------------------------===//
-
-/// putchard - putchar that takes a double and returns 0.
-extern "C"
-double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Main driver code.
-//===----------------------------------------------------------------------===//
-
-int main() {
- InitializeNativeTarget();
- LLVMContext &Context = getGlobalContext();
-
- // Install standard binary operators.
- // 1 is lowest precedence.
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
- BinopPrecedence['*'] = 40; // highest.
-
- // Prime the first token.
- fprintf(stderr, "ready> ");
- getNextToken();
-
- // Make the module, which holds all the code.
- TheModule = new Module("my cool jit", Context);
-
- // Create the JIT. This takes ownership of the module.
- std::string ErrStr;
- TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
- if (!TheExecutionEngine) {
- fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
- exit(1);
- }
-
- FunctionPassManager OurFPM(TheModule);
-
- // Set up the optimizer pipeline. Start with registering info about how the
- // target lays out data structures.
- OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
- // Provide basic AliasAnalysis support for GVN.
- OurFPM.add(createBasicAliasAnalysisPass());
- // Do simple "peephole" optimizations and bit-twiddling optzns.
- OurFPM.add(createInstructionCombiningPass());
- // Reassociate expressions.
- OurFPM.add(createReassociatePass());
- // Eliminate Common SubExpressions.
- OurFPM.add(createGVNPass());
- // Simplify the control flow graph (deleting unreachable blocks, etc).
- OurFPM.add(createCFGSimplificationPass());
-
- OurFPM.doInitialization();
-
- // Set the global so the code gen can use this.
- TheFPM = &OurFPM;
-
- // Run the main "interpreter loop" now.
- MainLoop();
-
- TheFPM = 0;
-
- // Print out all of the generated code.
- TheModule->dump();
-
- return 0;
-}
-</pre>
-</div>
-
-<a href="LangImpl6.html">Next: Extending the language: user-defined operators</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
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Added: llvm/trunk/docs/tutorial/LangImpl5.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl5.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl5.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl5.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,1609 @@
+==================================================
+Kaleidoscope: Extending the Language: Control Flow
+==================================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Chapter 5 Introduction
+======================
+
+Welcome to Chapter 5 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Parts 1-4 described the implementation of
+the simple Kaleidoscope language and included support for generating
+LLVM IR, followed by optimizations and a JIT compiler. Unfortunately, as
+presented, Kaleidoscope is mostly useless: it has no control flow other
+than call and return. This means that you can't have conditional
+branches in the code, significantly limiting its power. In this episode
+of "build that compiler", we'll extend Kaleidoscope to have an
+if/then/else expression plus a simple 'for' loop.
+
+If/Then/Else
+============
+
+Extending Kaleidoscope to support if/then/else is quite straightforward.
+It basically requires adding support for this "new" concept to the
+lexer, parser, AST, and LLVM code emitter. This example is nice, because
+it shows how easy it is to "grow" a language over time, incrementally
+extending it as new ideas are discovered.
+
+Before we get going on "how" we add this extension, lets talk about
+"what" we want. The basic idea is that we want to be able to write this
+sort of thing:
+
+::
+
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+In Kaleidoscope, every construct is an expression: there are no
+statements. As such, the if/then/else expression needs to return a value
+like any other. Since we're using a mostly functional form, we'll have
+it evaluate its conditional, then return the 'then' or 'else' value
+based on how the condition was resolved. This is very similar to the C
+"?:" expression.
+
+The semantics of the if/then/else expression is that it evaluates the
+condition to a boolean equality value: 0.0 is considered to be false and
+everything else is considered to be true. If the condition is true, the
+first subexpression is evaluated and returned, if the condition is
+false, the second subexpression is evaluated and returned. Since
+Kaleidoscope allows side-effects, this behavior is important to nail
+down.
+
+Now that we know what we "want", lets break this down into its
+constituent pieces.
+
+Lexer Extensions for If/Then/Else
+---------------------------------
+
+The lexer extensions are straightforward. First we add new enum values
+for the relevant tokens:
+
+.. code-block:: c++
+
+ // control
+ tok_if = -6, tok_then = -7, tok_else = -8,
+
+Once we have that, we recognize the new keywords in the lexer. This is
+pretty simple stuff:
+
+.. code-block:: c++
+
+ ...
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ if (IdentifierStr == "if") return tok_if;
+ if (IdentifierStr == "then") return tok_then;
+ if (IdentifierStr == "else") return tok_else;
+ return tok_identifier;
+
+AST Extensions for If/Then/Else
+-------------------------------
+
+To represent the new expression we add a new AST node for it:
+
+.. code-block:: c++
+
+ /// IfExprAST - Expression class for if/then/else.
+ class IfExprAST : public ExprAST {
+ ExprAST *Cond, *Then, *Else;
+ public:
+ IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
+ : Cond(cond), Then(then), Else(_else) {}
+ virtual Value *Codegen();
+ };
+
+The AST node just has pointers to the various subexpressions.
+
+Parser Extensions for If/Then/Else
+----------------------------------
+
+Now that we have the relevant tokens coming from the lexer and we have
+the AST node to build, our parsing logic is relatively straightforward.
+First we define a new parsing function:
+
+.. code-block:: c++
+
+ /// ifexpr ::= 'if' expression 'then' expression 'else' expression
+ static ExprAST *ParseIfExpr() {
+ getNextToken(); // eat the if.
+
+ // condition.
+ ExprAST *Cond = ParseExpression();
+ if (!Cond) return 0;
+
+ if (CurTok != tok_then)
+ return Error("expected then");
+ getNextToken(); // eat the then
+
+ ExprAST *Then = ParseExpression();
+ if (Then == 0) return 0;
+
+ if (CurTok != tok_else)
+ return Error("expected else");
+
+ getNextToken();
+
+ ExprAST *Else = ParseExpression();
+ if (!Else) return 0;
+
+ return new IfExprAST(Cond, Then, Else);
+ }
+
+Next we hook it up as a primary expression:
+
+.. code-block:: c++
+
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ case tok_if: return ParseIfExpr();
+ }
+ }
+
+LLVM IR for If/Then/Else
+------------------------
+
+Now that we have it parsing and building the AST, the final piece is
+adding LLVM code generation support. This is the most interesting part
+of the if/then/else example, because this is where it starts to
+introduce new concepts. All of the code above has been thoroughly
+described in previous chapters.
+
+To motivate the code we want to produce, lets take a look at a simple
+example. Consider:
+
+::
+
+ extern foo();
+ extern bar();
+ def baz(x) if x then foo() else bar();
+
+If you disable optimizations, the code you'll (soon) get from
+Kaleidoscope looks like this:
+
+.. code-block:: llvm
+
+ declare double @foo()
+
+ declare double @bar()
+
+ define double @baz(double %x) {
+ entry:
+ %ifcond = fcmp one double %x, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then: ; preds = %entry
+ %calltmp = call double @foo()
+ br label %ifcont
+
+ else: ; preds = %entry
+ %calltmp1 = call double @bar()
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
+ ret double %iftmp
+ }
+
+To visualize the control flow graph, you can use a nifty feature of the
+LLVM '`opt <http://llvm.org/cmds/opt.html>`_' tool. If you put this LLVM
+IR into "t.ll" and run "``llvm-as < t.ll | opt -analyze -view-cfg``", `a
+window will pop up <../ProgrammersManual.html#ViewGraph>`_ and you'll
+see this graph:
+
+.. figure:: LangImpl5-cfg.png
+ :align: center
+ :alt: Example CFG
+
+ Example CFG
+
+Another way to get this is to call "``F->viewCFG()``" or
+"``F->viewCFGOnly()``" (where F is a "``Function*``") either by
+inserting actual calls into the code and recompiling or by calling these
+in the debugger. LLVM has many nice features for visualizing various
+graphs.
+
+Getting back to the generated code, it is fairly simple: the entry block
+evaluates the conditional expression ("x" in our case here) and compares
+the result to 0.0 with the "``fcmp one``" instruction ('one' is "Ordered
+and Not Equal"). Based on the result of this expression, the code jumps
+to either the "then" or "else" blocks, which contain the expressions for
+the true/false cases.
+
+Once the then/else blocks are finished executing, they both branch back
+to the 'ifcont' block to execute the code that happens after the
+if/then/else. In this case the only thing left to do is to return to the
+caller of the function. The question then becomes: how does the code
+know which expression to return?
+
+The answer to this question involves an important SSA operation: the
+`Phi
+operation <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+If you're not familiar with SSA, `the wikipedia
+article <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+is a good introduction and there are various other introductions to it
+available on your favorite search engine. The short version is that
+"execution" of the Phi operation requires "remembering" which block
+control came from. The Phi operation takes on the value corresponding to
+the input control block. In this case, if control comes in from the
+"then" block, it gets the value of "calltmp". If control comes from the
+"else" block, it gets the value of "calltmp1".
+
+At this point, you are probably starting to think "Oh no! This means my
+simple and elegant front-end will have to start generating SSA form in
+order to use LLVM!". Fortunately, this is not the case, and we strongly
+advise *not* implementing an SSA construction algorithm in your
+front-end unless there is an amazingly good reason to do so. In
+practice, there are two sorts of values that float around in code
+written for your average imperative programming language that might need
+Phi nodes:
+
+#. Code that involves user variables: ``x = 1; x = x + 1;``
+#. Values that are implicit in the structure of your AST, such as the
+ Phi node in this case.
+
+In `Chapter 7 <LangImpl7.html>`_ of this tutorial ("mutable variables"),
+we'll talk about #1 in depth. For now, just believe me that you don't
+need SSA construction to handle this case. For #2, you have the choice
+of using the techniques that we will describe for #1, or you can insert
+Phi nodes directly, if convenient. In this case, it is really really
+easy to generate the Phi node, so we choose to do it directly.
+
+Okay, enough of the motivation and overview, lets generate code!
+
+Code Generation for If/Then/Else
+--------------------------------
+
+In order to generate code for this, we implement the ``Codegen`` method
+for ``IfExprAST``:
+
+.. code-block:: c++
+
+ Value *IfExprAST::Codegen() {
+ Value *CondV = Cond->Codegen();
+ if (CondV == 0) return 0;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ CondV = Builder.CreateFCmpONE(CondV,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "ifcond");
+
+This code is straightforward and similar to what we saw before. We emit
+the expression for the condition, then compare that value to zero to get
+a truth value as a 1-bit (bool) value.
+
+.. code-block:: c++
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create blocks for the then and else cases. Insert the 'then' block at the
+ // end of the function.
+ BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
+ BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
+ BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
+
+ Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+This code creates the basic blocks that are related to the if/then/else
+statement, and correspond directly to the blocks in the example above.
+The first line gets the current Function object that is being built. It
+gets this by asking the builder for the current BasicBlock, and asking
+that block for its "parent" (the function it is currently embedded
+into).
+
+Once it has that, it creates three blocks. Note that it passes
+"TheFunction" into the constructor for the "then" block. This causes the
+constructor to automatically insert the new block into the end of the
+specified function. The other two blocks are created, but aren't yet
+inserted into the function.
+
+Once the blocks are created, we can emit the conditional branch that
+chooses between them. Note that creating new blocks does not implicitly
+affect the IRBuilder, so it is still inserting into the block that the
+condition went into. Also note that it is creating a branch to the
+"then" block and the "else" block, even though the "else" block isn't
+inserted into the function yet. This is all ok: it is the standard way
+that LLVM supports forward references.
+
+.. code-block:: c++
+
+ // Emit then value.
+ Builder.SetInsertPoint(ThenBB);
+
+ Value *ThenV = Then->Codegen();
+ if (ThenV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+ ThenBB = Builder.GetInsertBlock();
+
+After the conditional branch is inserted, we move the builder to start
+inserting into the "then" block. Strictly speaking, this call moves the
+insertion point to be at the end of the specified block. However, since
+the "then" block is empty, it also starts out by inserting at the
+beginning of the block. :)
+
+Once the insertion point is set, we recursively codegen the "then"
+expression from the AST. To finish off the "then" block, we create an
+unconditional branch to the merge block. One interesting (and very
+important) aspect of the LLVM IR is that it `requires all basic blocks
+to be "terminated" <../LangRef.html#functionstructure>`_ with a `control
+flow instruction <../LangRef.html#terminators>`_ such as return or
+branch. This means that all control flow, *including fall throughs* must
+be made explicit in the LLVM IR. If you violate this rule, the verifier
+will emit an error.
+
+The final line here is quite subtle, but is very important. The basic
+issue is that when we create the Phi node in the merge block, we need to
+set up the block/value pairs that indicate how the Phi will work.
+Importantly, the Phi node expects to have an entry for each predecessor
+of the block in the CFG. Why then, are we getting the current block when
+we just set it to ThenBB 5 lines above? The problem is that the "Then"
+expression may actually itself change the block that the Builder is
+emitting into if, for example, it contains a nested "if/then/else"
+expression. Because calling Codegen recursively could arbitrarily change
+the notion of the current block, we are required to get an up-to-date
+value for code that will set up the Phi node.
+
+.. code-block:: c++
+
+ // Emit else block.
+ TheFunction->getBasicBlockList().push_back(ElseBB);
+ Builder.SetInsertPoint(ElseBB);
+
+ Value *ElseV = Else->Codegen();
+ if (ElseV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
+ ElseBB = Builder.GetInsertBlock();
+
+Code generation for the 'else' block is basically identical to codegen
+for the 'then' block. The only significant difference is the first line,
+which adds the 'else' block to the function. Recall previously that the
+'else' block was created, but not added to the function. Now that the
+'then' and 'else' blocks are emitted, we can finish up with the merge
+code:
+
+.. code-block:: c++
+
+ // Emit merge block.
+ TheFunction->getBasicBlockList().push_back(MergeBB);
+ Builder.SetInsertPoint(MergeBB);
+ PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
+ "iftmp");
+
+ PN->addIncoming(ThenV, ThenBB);
+ PN->addIncoming(ElseV, ElseBB);
+ return PN;
+ }
+
+The first two lines here are now familiar: the first adds the "merge"
+block to the Function object (it was previously floating, like the else
+block above). The second block changes the insertion point so that newly
+created code will go into the "merge" block. Once that is done, we need
+to create the PHI node and set up the block/value pairs for the PHI.
+
+Finally, the CodeGen function returns the phi node as the value computed
+by the if/then/else expression. In our example above, this returned
+value will feed into the code for the top-level function, which will
+create the return instruction.
+
+Overall, we now have the ability to execute conditional code in
+Kaleidoscope. With this extension, Kaleidoscope is a fairly complete
+language that can calculate a wide variety of numeric functions. Next up
+we'll add another useful expression that is familiar from non-functional
+languages...
+
+'for' Loop Expression
+=====================
+
+Now that we know how to add basic control flow constructs to the
+language, we have the tools to add more powerful things. Lets add
+something more aggressive, a 'for' expression:
+
+::
+
+ extern putchard(char)
+ def printstar(n)
+ for i = 1, i < n, 1.0 in
+ putchard(42); # ascii 42 = '*'
+
+ # print 100 '*' characters
+ printstar(100);
+
+This expression defines a new variable ("i" in this case) which iterates
+from a starting value, while the condition ("i < n" in this case) is
+true, incrementing by an optional step value ("1.0" in this case). If
+the step value is omitted, it defaults to 1.0. While the loop is true,
+it executes its body expression. Because we don't have anything better
+to return, we'll just define the loop as always returning 0.0. In the
+future when we have mutable variables, it will get more useful.
+
+As before, lets talk about the changes that we need to Kaleidoscope to
+support this.
+
+Lexer Extensions for the 'for' Loop
+-----------------------------------
+
+The lexer extensions are the same sort of thing as for if/then/else:
+
+.. code-block:: c++
+
+ ... in enum Token ...
+ // control
+ tok_if = -6, tok_then = -7, tok_else = -8,
+ tok_for = -9, tok_in = -10
+
+ ... in gettok ...
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ if (IdentifierStr == "if") return tok_if;
+ if (IdentifierStr == "then") return tok_then;
+ if (IdentifierStr == "else") return tok_else;
+ if (IdentifierStr == "for") return tok_for;
+ if (IdentifierStr == "in") return tok_in;
+ return tok_identifier;
+
+AST Extensions for the 'for' Loop
+---------------------------------
+
+The AST node is just as simple. It basically boils down to capturing the
+variable name and the constituent expressions in the node.
+
+.. code-block:: c++
+
+ /// ForExprAST - Expression class for for/in.
+ class ForExprAST : public ExprAST {
+ std::string VarName;
+ ExprAST *Start, *End, *Step, *Body;
+ public:
+ ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
+ ExprAST *step, ExprAST *body)
+ : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
+ virtual Value *Codegen();
+ };
+
+Parser Extensions for the 'for' Loop
+------------------------------------
+
+The parser code is also fairly standard. The only interesting thing here
+is handling of the optional step value. The parser code handles it by
+checking to see if the second comma is present. If not, it sets the step
+value to null in the AST node:
+
+.. code-block:: c++
+
+ /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+ static ExprAST *ParseForExpr() {
+ getNextToken(); // eat the for.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after for");
+
+ std::string IdName = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '=')
+ return Error("expected '=' after for");
+ getNextToken(); // eat '='.
+
+
+ ExprAST *Start = ParseExpression();
+ if (Start == 0) return 0;
+ if (CurTok != ',')
+ return Error("expected ',' after for start value");
+ getNextToken();
+
+ ExprAST *End = ParseExpression();
+ if (End == 0) return 0;
+
+ // The step value is optional.
+ ExprAST *Step = 0;
+ if (CurTok == ',') {
+ getNextToken();
+ Step = ParseExpression();
+ if (Step == 0) return 0;
+ }
+
+ if (CurTok != tok_in)
+ return Error("expected 'in' after for");
+ getNextToken(); // eat 'in'.
+
+ ExprAST *Body = ParseExpression();
+ if (Body == 0) return 0;
+
+ return new ForExprAST(IdName, Start, End, Step, Body);
+ }
+
+LLVM IR for the 'for' Loop
+--------------------------
+
+Now we get to the good part: the LLVM IR we want to generate for this
+thing. With the simple example above, we get this LLVM IR (note that
+this dump is generated with optimizations disabled for clarity):
+
+.. code-block:: llvm
+
+ declare double @putchard(double)
+
+ define double @printstar(double %n) {
+ entry:
+ ; initial value = 1.0 (inlined into phi)
+ br label %loop
+
+ loop: ; preds = %loop, %entry
+ %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
+ ; body
+ %calltmp = call double @putchard(double 4.200000e+01)
+ ; increment
+ %nextvar = fadd double %i, 1.000000e+00
+
+ ; termination test
+ %cmptmp = fcmp ult double %i, %n
+ %booltmp = uitofp i1 %cmptmp to double
+ %loopcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %loopcond, label %loop, label %afterloop
+
+ afterloop: ; preds = %loop
+ ; loop always returns 0.0
+ ret double 0.000000e+00
+ }
+
+This loop contains all the same constructs we saw before: a phi node,
+several expressions, and some basic blocks. Lets see how this fits
+together.
+
+Code Generation for the 'for' Loop
+----------------------------------
+
+The first part of Codegen is very simple: we just output the start
+expression for the loop value:
+
+.. code-block:: c++
+
+ Value *ForExprAST::Codegen() {
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->Codegen();
+ if (StartVal == 0) return 0;
+
+With this out of the way, the next step is to set up the LLVM basic
+block for the start of the loop body. In the case above, the whole loop
+body is one block, but remember that the body code itself could consist
+of multiple blocks (e.g. if it contains an if/then/else or a for/in
+expression).
+
+.. code-block:: c++
+
+ // Make the new basic block for the loop header, inserting after current
+ // block.
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+ BasicBlock *PreheaderBB = Builder.GetInsertBlock();
+ BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
+
+ // Insert an explicit fall through from the current block to the LoopBB.
+ Builder.CreateBr(LoopBB);
+
+This code is similar to what we saw for if/then/else. Because we will
+need it to create the Phi node, we remember the block that falls through
+into the loop. Once we have that, we create the actual block that starts
+the loop and create an unconditional branch for the fall-through between
+the two blocks.
+
+.. code-block:: c++
+
+ // Start insertion in LoopBB.
+ Builder.SetInsertPoint(LoopBB);
+
+ // Start the PHI node with an entry for Start.
+ PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str());
+ Variable->addIncoming(StartVal, PreheaderBB);
+
+Now that the "preheader" for the loop is set up, we switch to emitting
+code for the loop body. To begin with, we move the insertion point and
+create the PHI node for the loop induction variable. Since we already
+know the incoming value for the starting value, we add it to the Phi
+node. Note that the Phi will eventually get a second value for the
+backedge, but we can't set it up yet (because it doesn't exist!).
+
+.. code-block:: c++
+
+ // Within the loop, the variable is defined equal to the PHI node. If it
+ // shadows an existing variable, we have to restore it, so save it now.
+ Value *OldVal = NamedValues[VarName];
+ NamedValues[VarName] = Variable;
+
+ // Emit the body of the loop. This, like any other expr, can change the
+ // current BB. Note that we ignore the value computed by the body, but don't
+ // allow an error.
+ if (Body->Codegen() == 0)
+ return 0;
+
+Now the code starts to get more interesting. Our 'for' loop introduces a
+new variable to the symbol table. This means that our symbol table can
+now contain either function arguments or loop variables. To handle this,
+before we codegen the body of the loop, we add the loop variable as the
+current value for its name. Note that it is possible that there is a
+variable of the same name in the outer scope. It would be easy to make
+this an error (emit an error and return null if there is already an
+entry for VarName) but we choose to allow shadowing of variables. In
+order to handle this correctly, we remember the Value that we are
+potentially shadowing in ``OldVal`` (which will be null if there is no
+shadowed variable).
+
+Once the loop variable is set into the symbol table, the code
+recursively codegen's the body. This allows the body to use the loop
+variable: any references to it will naturally find it in the symbol
+table.
+
+.. code-block:: c++
+
+ // Emit the step value.
+ Value *StepVal;
+ if (Step) {
+ StepVal = Step->Codegen();
+ if (StepVal == 0) return 0;
+ } else {
+ // If not specified, use 1.0.
+ StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
+ }
+
+ Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
+
+Now that the body is emitted, we compute the next value of the iteration
+variable by adding the step value, or 1.0 if it isn't present.
+'``NextVar``' will be the value of the loop variable on the next
+iteration of the loop.
+
+.. code-block:: c++
+
+ // Compute the end condition.
+ Value *EndCond = End->Codegen();
+ if (EndCond == 0) return EndCond;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ EndCond = Builder.CreateFCmpONE(EndCond,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "loopcond");
+
+Finally, we evaluate the exit value of the loop, to determine whether
+the loop should exit. This mirrors the condition evaluation for the
+if/then/else statement.
+
+.. code-block:: c++
+
+ // Create the "after loop" block and insert it.
+ BasicBlock *LoopEndBB = Builder.GetInsertBlock();
+ BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
+
+ // Insert the conditional branch into the end of LoopEndBB.
+ Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+ // Any new code will be inserted in AfterBB.
+ Builder.SetInsertPoint(AfterBB);
+
+With the code for the body of the loop complete, we just need to finish
+up the control flow for it. This code remembers the end block (for the
+phi node), then creates the block for the loop exit ("afterloop"). Based
+on the value of the exit condition, it creates a conditional branch that
+chooses between executing the loop again and exiting the loop. Any
+future code is emitted in the "afterloop" block, so it sets the
+insertion position to it.
+
+.. code-block:: c++
+
+ // Add a new entry to the PHI node for the backedge.
+ Variable->addIncoming(NextVar, LoopEndBB);
+
+ // Restore the unshadowed variable.
+ if (OldVal)
+ NamedValues[VarName] = OldVal;
+ else
+ NamedValues.erase(VarName);
+
+ // for expr always returns 0.0.
+ return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
+ }
+
+The final code handles various cleanups: now that we have the "NextVar"
+value, we can add the incoming value to the loop PHI node. After that,
+we remove the loop variable from the symbol table, so that it isn't in
+scope after the for loop. Finally, code generation of the for loop
+always returns 0.0, so that is what we return from
+``ForExprAST::Codegen``.
+
+With this, we conclude the "adding control flow to Kaleidoscope" chapter
+of the tutorial. In this chapter we added two control flow constructs,
+and used them to motivate a couple of aspects of the LLVM IR that are
+important for front-end implementors to know. In the next chapter of our
+saga, we will get a bit crazier and add `user-defined
+operators <LangImpl6.html>`_ to our poor innocent language.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. code-block:: c++
+
+ #include "llvm/DerivedTypes.h"
+ #include "llvm/ExecutionEngine/ExecutionEngine.h"
+ #include "llvm/ExecutionEngine/JIT.h"
+ #include "llvm/IRBuilder.h"
+ #include "llvm/LLVMContext.h"
+ #include "llvm/Module.h"
+ #include "llvm/PassManager.h"
+ #include "llvm/Analysis/Verifier.h"
+ #include "llvm/Analysis/Passes.h"
+ #include "llvm/DataLayout.h"
+ #include "llvm/Transforms/Scalar.h"
+ #include "llvm/Support/TargetSelect.h"
+ #include <cstdio>
+ #include <string>
+ #include <map>
+ #include <vector>
+ using namespace llvm;
+
+ //===----------------------------------------------------------------------===//
+ // Lexer
+ //===----------------------------------------------------------------------===//
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5,
+
+ // control
+ tok_if = -6, tok_then = -7, tok_else = -8,
+ tok_for = -9, tok_in = -10
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ if (IdentifierStr == "if") return tok_if;
+ if (IdentifierStr == "then") return tok_then;
+ if (IdentifierStr == "else") return tok_else;
+ if (IdentifierStr == "for") return tok_for;
+ if (IdentifierStr == "in") return tok_in;
+ return tok_identifier;
+ }
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Abstract Syntax Tree (aka Parse Tree)
+ //===----------------------------------------------------------------------===//
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *Codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ virtual Value *Codegen();
+ };
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ virtual Value *Codegen();
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ virtual Value *Codegen();
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ virtual Value *Codegen();
+ };
+
+ /// IfExprAST - Expression class for if/then/else.
+ class IfExprAST : public ExprAST {
+ ExprAST *Cond, *Then, *Else;
+ public:
+ IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
+ : Cond(cond), Then(then), Else(_else) {}
+ virtual Value *Codegen();
+ };
+
+ /// ForExprAST - Expression class for for/in.
+ class ForExprAST : public ExprAST {
+ std::string VarName;
+ ExprAST *Start, *End, *Step, *Body;
+ public:
+ ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
+ ExprAST *step, ExprAST *body)
+ : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
+ virtual Value *Codegen();
+ };
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes).
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args)
+ : Name(name), Args(args) {}
+
+ Function *Codegen();
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ Function *Codegen();
+ };
+
+ //===----------------------------------------------------------------------===//
+ // Parser
+ //===----------------------------------------------------------------------===//
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+ static ExprAST *ParseExpression();
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+ /// ifexpr ::= 'if' expression 'then' expression 'else' expression
+ static ExprAST *ParseIfExpr() {
+ getNextToken(); // eat the if.
+
+ // condition.
+ ExprAST *Cond = ParseExpression();
+ if (!Cond) return 0;
+
+ if (CurTok != tok_then)
+ return Error("expected then");
+ getNextToken(); // eat the then
+
+ ExprAST *Then = ParseExpression();
+ if (Then == 0) return 0;
+
+ if (CurTok != tok_else)
+ return Error("expected else");
+
+ getNextToken();
+
+ ExprAST *Else = ParseExpression();
+ if (!Else) return 0;
+
+ return new IfExprAST(Cond, Then, Else);
+ }
+
+ /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+ static ExprAST *ParseForExpr() {
+ getNextToken(); // eat the for.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after for");
+
+ std::string IdName = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '=')
+ return Error("expected '=' after for");
+ getNextToken(); // eat '='.
+
+
+ ExprAST *Start = ParseExpression();
+ if (Start == 0) return 0;
+ if (CurTok != ',')
+ return Error("expected ',' after for start value");
+ getNextToken();
+
+ ExprAST *End = ParseExpression();
+ if (End == 0) return 0;
+
+ // The step value is optional.
+ ExprAST *Step = 0;
+ if (CurTok == ',') {
+ getNextToken();
+ Step = ParseExpression();
+ if (Step == 0) return 0;
+ }
+
+ if (CurTok != tok_in)
+ return Error("expected 'in' after for");
+ getNextToken(); // eat 'in'.
+
+ ExprAST *Body = ParseExpression();
+ if (Body == 0) return 0;
+
+ return new ForExprAST(IdName, Start, End, Step, Body);
+ }
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ /// ::= ifexpr
+ /// ::= forexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ case tok_if: return ParseIfExpr();
+ case tok_for: return ParseForExpr();
+ }
+ }
+
+ /// binoprhs
+ /// ::= ('+' primary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the primary expression after the binary operator.
+ ExprAST *RHS = ParsePrimary();
+ if (!RHS) return 0;
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+ }
+
+ /// expression
+ /// ::= primary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParsePrimary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ static PrototypeAST *ParsePrototype() {
+ if (CurTok != tok_identifier)
+ return ErrorP("Expected function name in prototype");
+
+ std::string FnName = IdentifierStr;
+ getNextToken();
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ return new PrototypeAST(FnName, ArgNames);
+ }
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Code Generation
+ //===----------------------------------------------------------------------===//
+
+ static Module *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, Value*> NamedValues;
+ static FunctionPassManager *TheFPM;
+
+ Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+ Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ return V ? V : ErrorV("Unknown variable name");
+ }
+
+ Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateFAdd(L, R, "addtmp");
+ case '-': return Builder.CreateFSub(L, R, "subtmp");
+ case '*': return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default: return ErrorV("invalid binary operator");
+ }
+ }
+
+ Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value*> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->Codegen());
+ if (ArgsV.back() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+ Value *IfExprAST::Codegen() {
+ Value *CondV = Cond->Codegen();
+ if (CondV == 0) return 0;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ CondV = Builder.CreateFCmpONE(CondV,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "ifcond");
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create blocks for the then and else cases. Insert the 'then' block at the
+ // end of the function.
+ BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
+ BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
+ BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
+
+ Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+ // Emit then value.
+ Builder.SetInsertPoint(ThenBB);
+
+ Value *ThenV = Then->Codegen();
+ if (ThenV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+ ThenBB = Builder.GetInsertBlock();
+
+ // Emit else block.
+ TheFunction->getBasicBlockList().push_back(ElseBB);
+ Builder.SetInsertPoint(ElseBB);
+
+ Value *ElseV = Else->Codegen();
+ if (ElseV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
+ ElseBB = Builder.GetInsertBlock();
+
+ // Emit merge block.
+ TheFunction->getBasicBlockList().push_back(MergeBB);
+ Builder.SetInsertPoint(MergeBB);
+ PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
+ "iftmp");
+
+ PN->addIncoming(ThenV, ThenBB);
+ PN->addIncoming(ElseV, ElseBB);
+ return PN;
+ }
+
+ Value *ForExprAST::Codegen() {
+ // Output this as:
+ // ...
+ // start = startexpr
+ // goto loop
+ // loop:
+ // variable = phi [start, loopheader], [nextvariable, loopend]
+ // ...
+ // bodyexpr
+ // ...
+ // loopend:
+ // step = stepexpr
+ // nextvariable = variable + step
+ // endcond = endexpr
+ // br endcond, loop, endloop
+ // outloop:
+
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->Codegen();
+ if (StartVal == 0) return 0;
+
+ // Make the new basic block for the loop header, inserting after current
+ // block.
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+ BasicBlock *PreheaderBB = Builder.GetInsertBlock();
+ BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
+
+ // Insert an explicit fall through from the current block to the LoopBB.
+ Builder.CreateBr(LoopBB);
+
+ // Start insertion in LoopBB.
+ Builder.SetInsertPoint(LoopBB);
+
+ // Start the PHI node with an entry for Start.
+ PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str());
+ Variable->addIncoming(StartVal, PreheaderBB);
+
+ // Within the loop, the variable is defined equal to the PHI node. If it
+ // shadows an existing variable, we have to restore it, so save it now.
+ Value *OldVal = NamedValues[VarName];
+ NamedValues[VarName] = Variable;
+
+ // Emit the body of the loop. This, like any other expr, can change the
+ // current BB. Note that we ignore the value computed by the body, but don't
+ // allow an error.
+ if (Body->Codegen() == 0)
+ return 0;
+
+ // Emit the step value.
+ Value *StepVal;
+ if (Step) {
+ StepVal = Step->Codegen();
+ if (StepVal == 0) return 0;
+ } else {
+ // If not specified, use 1.0.
+ StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
+ }
+
+ Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
+
+ // Compute the end condition.
+ Value *EndCond = End->Codegen();
+ if (EndCond == 0) return EndCond;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ EndCond = Builder.CreateFCmpONE(EndCond,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "loopcond");
+
+ // Create the "after loop" block and insert it.
+ BasicBlock *LoopEndBB = Builder.GetInsertBlock();
+ BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
+
+ // Insert the conditional branch into the end of LoopEndBB.
+ Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+ // Any new code will be inserted in AfterBB.
+ Builder.SetInsertPoint(AfterBB);
+
+ // Add a new entry to the PHI node for the backedge.
+ Variable->addIncoming(NextVar, LoopEndBB);
+
+ // Restore the unshadowed variable.
+ if (OldVal)
+ NamedValues[VarName] = OldVal;
+ else
+ NamedValues.erase(VarName);
+
+
+ // for expr always returns 0.0.
+ return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
+ }
+
+ Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
+ Doubles, false);
+
+ Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx) {
+ AI->setName(Args[Idx]);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = AI;
+ }
+
+ return F;
+ }
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Top-Level parsing and JIT Driver
+ //===----------------------------------------------------------------------===//
+
+ static ExecutionEngine *TheExecutionEngine;
+
+ static void HandleDefinition() {
+ if (FunctionAST *F = ParseDefinition()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read function definition:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (PrototypeAST *P = ParseExtern()) {
+ if (Function *F = P->Codegen()) {
+ fprintf(stderr, "Read extern: ");
+ F->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // Cast it to the right type (takes no arguments, returns a double) so we
+ // can call it as a native function.
+ double (*FP)() = (double (*)())(intptr_t)FPtr;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+ //===----------------------------------------------------------------------===//
+ // "Library" functions that can be "extern'd" from user code.
+ //===----------------------------------------------------------------------===//
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Main driver code.
+ //===----------------------------------------------------------------------===//
+
+ int main() {
+ InitializeNativeTarget();
+ LLVMContext &Context = getGlobalContext();
+
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ fprintf(stderr, "ready> ");
+ getNextToken();
+
+ // Make the module, which holds all the code.
+ TheModule = new Module("my cool jit", Context);
+
+ // Create the JIT. This takes ownership of the module.
+ std::string ErrStr;
+ TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
+ if (!TheExecutionEngine) {
+ fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
+ exit(1);
+ }
+
+ FunctionPassManager OurFPM(TheModule);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Provide basic AliasAnalysis support for GVN.
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ TheFPM = 0;
+
+ // Print out all of the generated code.
+ TheModule->dump();
+
+ return 0;
+ }
+
+`Next: Extending the language: user-defined operators <LangImpl6.html>`_
+
Removed: llvm/trunk/docs/tutorial/LangImpl6.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl6.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl6.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl6.html (removed)
@@ -1,1829 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Extending the Language: User-defined Operators</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Extending the Language: User-defined Operators</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 6
- <ol>
- <li><a href="#intro">Chapter 6 Introduction</a></li>
- <li><a href="#idea">User-defined Operators: the Idea</a></li>
- <li><a href="#binary">User-defined Binary Operators</a></li>
- <li><a href="#unary">User-defined Unary Operators</a></li>
- <li><a href="#example">Kicking the Tires</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="LangImpl7.html">Chapter 7</a>: Extending the Language: Mutable
-Variables / SSA Construction</li>
-</ul>
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 6 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 6 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. At this point in our tutorial, we now have a fully
-functional language that is fairly minimal, but also useful. There
-is still one big problem with it, however. Our language doesn't have many
-useful operators (like division, logical negation, or even any comparisons
-besides less-than).</p>
-
-<p>This chapter of the tutorial takes a wild digression into adding user-defined
-operators to the simple and beautiful Kaleidoscope language. This digression now gives
-us a simple and ugly language in some ways, but also a powerful one at the same time.
-One of the great things about creating your own language is that you get to
-decide what is good or bad. In this tutorial we'll assume that it is okay to
-use this as a way to show some interesting parsing techniques.</p>
-
-<p>At the end of this tutorial, we'll run through an example Kaleidoscope
-application that <a href="#example">renders the Mandelbrot set</a>. This gives
-an example of what you can build with Kaleidoscope and its feature set.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="idea">User-defined Operators: the Idea</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-The "operator overloading" that we will add to Kaleidoscope is more general than
-languages like C++. In C++, you are only allowed to redefine existing
-operators: you can't programatically change the grammar, introduce new
-operators, change precedence levels, etc. In this chapter, we will add this
-capability to Kaleidoscope, which will let the user round out the set of
-operators that are supported.</p>
-
-<p>The point of going into user-defined operators in a tutorial like this is to
-show the power and flexibility of using a hand-written parser. Thus far, the parser
-we have been implementing uses recursive descent for most parts of the grammar and
-operator precedence parsing for the expressions. See <a
-href="LangImpl2.html">Chapter 2</a> for details. Without using operator
-precedence parsing, it would be very difficult to allow the programmer to
-introduce new operators into the grammar: the grammar is dynamically extensible
-as the JIT runs.</p>
-
-<p>The two specific features we'll add are programmable unary operators (right
-now, Kaleidoscope has no unary operators at all) as well as binary operators.
-An example of this is:</p>
-
-<div class="doc_code">
-<pre>
-# Logical unary not.
-def unary!(v)
- if v then
- 0
- else
- 1;
-
-# Define > with the same precedence as <.
-def binary> 10 (LHS RHS)
- RHS < LHS;
-
-# Binary "logical or", (note that it does not "short circuit")
-def binary| 5 (LHS RHS)
- if LHS then
- 1
- else if RHS then
- 1
- else
- 0;
-
-# Define = with slightly lower precedence than relationals.
-def binary= 9 (LHS RHS)
- !(LHS < RHS | LHS > RHS);
-</pre>
-</div>
-
-<p>Many languages aspire to being able to implement their standard runtime
-library in the language itself. In Kaleidoscope, we can implement significant
-parts of the language in the library!</p>
-
-<p>We will break down implementation of these features into two parts:
-implementing support for user-defined binary operators and adding unary
-operators.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="binary">User-defined Binary Operators</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Adding support for user-defined binary operators is pretty simple with our
-current framework. We'll first add support for the unary/binary keywords:</p>
-
-<div class="doc_code">
-<pre>
-enum Token {
- ...
- <b>// operators
- tok_binary = -11, tok_unary = -12</b>
-};
-...
-static int gettok() {
-...
- if (IdentifierStr == "for") return tok_for;
- if (IdentifierStr == "in") return tok_in;
- <b>if (IdentifierStr == "binary") return tok_binary;
- if (IdentifierStr == "unary") return tok_unary;</b>
- return tok_identifier;
-</pre>
-</div>
-
-<p>This just adds lexer support for the unary and binary keywords, like we
-did in <a href="LangImpl5.html#iflexer">previous chapters</a>. One nice thing
-about our current AST, is that we represent binary operators with full generalisation
-by using their ASCII code as the opcode. For our extended operators, we'll use this
-same representation, so we don't need any new AST or parser support.</p>
-
-<p>On the other hand, we have to be able to represent the definitions of these
-new operators, in the "def binary| 5" part of the function definition. In our
-grammar so far, the "name" for the function definition is parsed as the
-"prototype" production and into the <tt>PrototypeAST</tt> AST node. To
-represent our new user-defined operators as prototypes, we have to extend
-the <tt>PrototypeAST</tt> AST node like this:</p>
-
-<div class="doc_code">
-<pre>
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its argument names as well as if it is an operator.
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
- <b>bool isOperator;
- unsigned Precedence; // Precedence if a binary op.</b>
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args,
- <b>bool isoperator = false, unsigned prec = 0</b>)
- : Name(name), Args(args), <b>isOperator(isoperator), Precedence(prec)</b> {}
-
- <b>bool isUnaryOp() const { return isOperator && Args.size() == 1; }
- bool isBinaryOp() const { return isOperator && Args.size() == 2; }
-
- char getOperatorName() const {
- assert(isUnaryOp() || isBinaryOp());
- return Name[Name.size()-1];
- }
-
- unsigned getBinaryPrecedence() const { return Precedence; }</b>
-
- Function *Codegen();
-};
-</pre>
-</div>
-
-<p>Basically, in addition to knowing a name for the prototype, we now keep track
-of whether it was an operator, and if it was, what precedence level the operator
-is at. The precedence is only used for binary operators (as you'll see below,
-it just doesn't apply for unary operators). Now that we have a way to represent
-the prototype for a user-defined operator, we need to parse it:</p>
-
-<div class="doc_code">
-<pre>
-/// prototype
-/// ::= id '(' id* ')'
-<b>/// ::= binary LETTER number? (id, id)</b>
-static PrototypeAST *ParsePrototype() {
- std::string FnName;
-
- <b>unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
- unsigned BinaryPrecedence = 30;</b>
-
- switch (CurTok) {
- default:
- return ErrorP("Expected function name in prototype");
- case tok_identifier:
- FnName = IdentifierStr;
- Kind = 0;
- getNextToken();
- break;
- <b>case tok_binary:
- getNextToken();
- if (!isascii(CurTok))
- return ErrorP("Expected binary operator");
- FnName = "binary";
- FnName += (char)CurTok;
- Kind = 2;
- getNextToken();
-
- // Read the precedence if present.
- if (CurTok == tok_number) {
- if (NumVal < 1 || NumVal > 100)
- return ErrorP("Invalid precedecnce: must be 1..100");
- BinaryPrecedence = (unsigned)NumVal;
- getNextToken();
- }
- break;</b>
- }
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- <b>// Verify right number of names for operator.
- if (Kind && ArgNames.size() != Kind)
- return ErrorP("Invalid number of operands for operator");
-
- return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence);</b>
-}
-</pre>
-</div>
-
-<p>This is all fairly straightforward parsing code, and we have already seen
-a lot of similar code in the past. One interesting part about the code above is
-the couple lines that set up <tt>FnName</tt> for binary operators. This builds names
-like "binary@" for a newly defined "@" operator. This then takes advantage of the
-fact that symbol names in the LLVM symbol table are allowed to have any character in
-them, including embedded nul characters.</p>
-
-<p>The next interesting thing to add, is codegen support for these binary operators.
-Given our current structure, this is a simple addition of a default case for our
-existing binary operator node:</p>
-
-<div class="doc_code">
-<pre>
-Value *BinaryExprAST::Codegen() {
- Value *L = LHS->Codegen();
- Value *R = RHS->Codegen();
- if (L == 0 || R == 0) return 0;
-
- switch (Op) {
- case '+': return Builder.CreateFAdd(L, R, "addtmp");
- case '-': return Builder.CreateFSub(L, R, "subtmp");
- case '*': return Builder.CreateFMul(L, R, "multmp");
- case '<':
- L = Builder.CreateFCmpULT(L, R, "cmptmp");
- // Convert bool 0/1 to double 0.0 or 1.0
- return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
- "booltmp");
- <b>default: break;</b>
- }
-
- <b>// If it wasn't a builtin binary operator, it must be a user defined one. Emit
- // a call to it.
- Function *F = TheModule->getFunction(std::string("binary")+Op);
- assert(F && "binary operator not found!");
-
- Value *Ops[2] = { L, R };
- return Builder.CreateCall(F, Ops, "binop");</b>
-}
-
-</pre>
-</div>
-
-<p>As you can see above, the new code is actually really simple. It just does
-a lookup for the appropriate operator in the symbol table and generates a
-function call to it. Since user-defined operators are just built as normal
-functions (because the "prototype" boils down to a function with the right
-name) everything falls into place.</p>
-
-<p>The final piece of code we are missing, is a bit of top-level magic:</p>
-
-<div class="doc_code">
-<pre>
-Function *FunctionAST::Codegen() {
- NamedValues.clear();
-
- Function *TheFunction = Proto->Codegen();
- if (TheFunction == 0)
- return 0;
-
- <b>// If this is an operator, install it.
- if (Proto->isBinaryOp())
- BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();</b>
-
- // Create a new basic block to start insertion into.
- BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
- Builder.SetInsertPoint(BB);
-
- if (Value *RetVal = Body->Codegen()) {
- ...
-</pre>
-</div>
-
-<p>Basically, before codegening a function, if it is a user-defined operator, we
-register it in the precedence table. This allows the binary operator parsing
-logic we already have in place to handle it. Since we are working on a fully-general operator precedence parser, this is all we need to do to "extend the grammar".</p>
-
-<p>Now we have useful user-defined binary operators. This builds a lot
-on the previous framework we built for other operators. Adding unary operators
-is a bit more challenging, because we don't have any framework for it yet - lets
-see what it takes.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="unary">User-defined Unary Operators</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Since we don't currently support unary operators in the Kaleidoscope
-language, we'll need to add everything to support them. Above, we added simple
-support for the 'unary' keyword to the lexer. In addition to that, we need an
-AST node:</p>
-
-<div class="doc_code">
-<pre>
-/// UnaryExprAST - Expression class for a unary operator.
-class UnaryExprAST : public ExprAST {
- char Opcode;
- ExprAST *Operand;
-public:
- UnaryExprAST(char opcode, ExprAST *operand)
- : Opcode(opcode), Operand(operand) {}
- virtual Value *Codegen();
-};
-</pre>
-</div>
-
-<p>This AST node is very simple and obvious by now. It directly mirrors the
-binary operator AST node, except that it only has one child. With this, we
-need to add the parsing logic. Parsing a unary operator is pretty simple: we'll
-add a new function to do it:</p>
-
-<div class="doc_code">
-<pre>
-/// unary
-/// ::= primary
-/// ::= '!' unary
-static ExprAST *ParseUnary() {
- // If the current token is not an operator, it must be a primary expr.
- if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
- return ParsePrimary();
-
- // If this is a unary operator, read it.
- int Opc = CurTok;
- getNextToken();
- if (ExprAST *Operand = ParseUnary())
- return new UnaryExprAST(Opc, Operand);
- return 0;
-}
-</pre>
-</div>
-
-<p>The grammar we add is pretty straightforward here. If we see a unary
-operator when parsing a primary operator, we eat the operator as a prefix and
-parse the remaining piece as another unary operator. This allows us to handle
-multiple unary operators (e.g. "!!x"). Note that unary operators can't have
-ambiguous parses like binary operators can, so there is no need for precedence
-information.</p>
-
-<p>The problem with this function, is that we need to call ParseUnary from somewhere.
-To do this, we change previous callers of ParsePrimary to call ParseUnary
-instead:</p>
-
-<div class="doc_code">
-<pre>
-/// binoprhs
-/// ::= ('+' unary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- ...
- <b>// Parse the unary expression after the binary operator.
- ExprAST *RHS = ParseUnary();
- if (!RHS) return 0;</b>
- ...
-}
-/// expression
-/// ::= unary binoprhs
-///
-static ExprAST *ParseExpression() {
- <b>ExprAST *LHS = ParseUnary();</b>
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-</pre>
-</div>
-
-<p>With these two simple changes, we are now able to parse unary operators and build the
-AST for them. Next up, we need to add parser support for prototypes, to parse
-the unary operator prototype. We extend the binary operator code above
-with:</p>
-
-<div class="doc_code">
-<pre>
-/// prototype
-/// ::= id '(' id* ')'
-/// ::= binary LETTER number? (id, id)
-<b>/// ::= unary LETTER (id)</b>
-static PrototypeAST *ParsePrototype() {
- std::string FnName;
-
- unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
- unsigned BinaryPrecedence = 30;
-
- switch (CurTok) {
- default:
- return ErrorP("Expected function name in prototype");
- case tok_identifier:
- FnName = IdentifierStr;
- Kind = 0;
- getNextToken();
- break;
- <b>case tok_unary:
- getNextToken();
- if (!isascii(CurTok))
- return ErrorP("Expected unary operator");
- FnName = "unary";
- FnName += (char)CurTok;
- Kind = 1;
- getNextToken();
- break;</b>
- case tok_binary:
- ...
-</pre>
-</div>
-
-<p>As with binary operators, we name unary operators with a name that includes
-the operator character. This assists us at code generation time. Speaking of,
-the final piece we need to add is codegen support for unary operators. It looks
-like this:</p>
-
-<div class="doc_code">
-<pre>
-Value *UnaryExprAST::Codegen() {
- Value *OperandV = Operand->Codegen();
- if (OperandV == 0) return 0;
-
- Function *F = TheModule->getFunction(std::string("unary")+Opcode);
- if (F == 0)
- return ErrorV("Unknown unary operator");
-
- return Builder.CreateCall(F, OperandV, "unop");
-}
-</pre>
-</div>
-
-<p>This code is similar to, but simpler than, the code for binary operators. It
-is simpler primarily because it doesn't need to handle any predefined operators.
-</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="example">Kicking the Tires</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>It is somewhat hard to believe, but with a few simple extensions we've
-covered in the last chapters, we have grown a real-ish language. With this, we
-can do a lot of interesting things, including I/O, math, and a bunch of other
-things. For example, we can now add a nice sequencing operator (printd is
-defined to print out the specified value and a newline):</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>extern printd(x);</b>
-Read extern:
-declare double @printd(double)
-
-ready> <b>def binary : 1 (x y) 0; # Low-precedence operator that ignores operands.</b>
-..
-ready> <b>printd(123) : printd(456) : printd(789);</b>
-123.000000
-456.000000
-789.000000
-Evaluated to 0.000000
-</pre>
-</div>
-
-<p>We can also define a bunch of other "primitive" operations, such as:</p>
-
-<div class="doc_code">
-<pre>
-# Logical unary not.
-def unary!(v)
- if v then
- 0
- else
- 1;
-
-# Unary negate.
-def unary-(v)
- 0-v;
-
-# Define > with the same precedence as <.
-def binary> 10 (LHS RHS)
- RHS < LHS;
-
-# Binary logical or, which does not short circuit.
-def binary| 5 (LHS RHS)
- if LHS then
- 1
- else if RHS then
- 1
- else
- 0;
-
-# Binary logical and, which does not short circuit.
-def binary& 6 (LHS RHS)
- if !LHS then
- 0
- else
- !!RHS;
-
-# Define = with slightly lower precedence than relationals.
-def binary = 9 (LHS RHS)
- !(LHS < RHS | LHS > RHS);
-
-# Define ':' for sequencing: as a low-precedence operator that ignores operands
-# and just returns the RHS.
-def binary : 1 (x y) y;
-</pre>
-</div>
-
-
-<p>Given the previous if/then/else support, we can also define interesting
-functions for I/O. For example, the following prints out a character whose
-"density" reflects the value passed in: the lower the value, the denser the
-character:</p>
-
-<div class="doc_code">
-<pre>
-ready>
-<b>
-extern putchard(char)
-def printdensity(d)
- if d > 8 then
- putchard(32) # ' '
- else if d > 4 then
- putchard(46) # '.'
- else if d > 2 then
- putchard(43) # '+'
- else
- putchard(42); # '*'</b>
-...
-ready> <b>printdensity(1): printdensity(2): printdensity(3):
- printdensity(4): printdensity(5): printdensity(9):
- putchard(10);</b>
-**++.
-Evaluated to 0.000000
-</pre>
-</div>
-
-<p>Based on these simple primitive operations, we can start to define more
-interesting things. For example, here's a little function that solves for the
-number of iterations it takes a function in the complex plane to
-converge:</p>
-
-<div class="doc_code">
-<pre>
-# Determine whether the specific location diverges.
-# Solve for z = z^2 + c in the complex plane.
-def mandleconverger(real imag iters creal cimag)
- if iters > 255 | (real*real + imag*imag > 4) then
- iters
- else
- mandleconverger(real*real - imag*imag + creal,
- 2*real*imag + cimag,
- iters+1, creal, cimag);
-
-# Return the number of iterations required for the iteration to escape
-def mandleconverge(real imag)
- mandleconverger(real, imag, 0, real, imag);
-</pre>
-</div>
-
-<p>This "<code>z = z<sup>2</sup> + c</code>" function is a beautiful little
-creature that is the basis for computation of
-the <a href="http://en.wikipedia.org/wiki/Mandelbrot_set">Mandelbrot Set</a>.
-Our <tt>mandelconverge</tt> function returns the number of iterations that it
-takes for a complex orbit to escape, saturating to 255. This is not a very
-useful function by itself, but if you plot its value over a two-dimensional
-plane, you can see the Mandelbrot set. Given that we are limited to using
-putchard here, our amazing graphical output is limited, but we can whip together
-something using the density plotter above:</p>
-
-<div class="doc_code">
-<pre>
-# Compute and plot the mandlebrot set with the specified 2 dimensional range
-# info.
-def mandelhelp(xmin xmax xstep ymin ymax ystep)
- for y = ymin, y < ymax, ystep in (
- (for x = xmin, x < xmax, xstep in
- printdensity(mandleconverge(x,y)))
- : putchard(10)
- )
-
-# mandel - This is a convenient helper function for plotting the mandelbrot set
-# from the specified position with the specified Magnification.
-def mandel(realstart imagstart realmag imagmag)
- mandelhelp(realstart, realstart+realmag*78, realmag,
- imagstart, imagstart+imagmag*40, imagmag);
-</pre>
-</div>
-
-<p>Given this, we can try plotting out the mandlebrot set! Lets try it out:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>mandel(-2.3, -1.3, 0.05, 0.07);</b>
-*******************************+++++++++++*************************************
-*************************+++++++++++++++++++++++*******************************
-**********************+++++++++++++++++++++++++++++****************************
-*******************+++++++++++++++++++++.. ...++++++++*************************
-*****************++++++++++++++++++++++.... ...+++++++++***********************
-***************+++++++++++++++++++++++..... ...+++++++++*********************
-**************+++++++++++++++++++++++.... ....+++++++++********************
-*************++++++++++++++++++++++...... .....++++++++*******************
-************+++++++++++++++++++++....... .......+++++++******************
-***********+++++++++++++++++++.... ... .+++++++*****************
-**********+++++++++++++++++....... .+++++++****************
-*********++++++++++++++........... ...+++++++***************
-********++++++++++++............ ...++++++++**************
-********++++++++++... .......... .++++++++**************
-*******+++++++++..... .+++++++++*************
-*******++++++++...... ..+++++++++*************
-*******++++++....... ..+++++++++*************
-*******+++++...... ..+++++++++*************
-*******.... .... ...+++++++++*************
-*******.... . ...+++++++++*************
-*******+++++...... ...+++++++++*************
-*******++++++....... ..+++++++++*************
-*******++++++++...... .+++++++++*************
-*******+++++++++..... ..+++++++++*************
-********++++++++++... .......... .++++++++**************
-********++++++++++++............ ...++++++++**************
-*********++++++++++++++.......... ...+++++++***************
-**********++++++++++++++++........ .+++++++****************
-**********++++++++++++++++++++.... ... ..+++++++****************
-***********++++++++++++++++++++++....... .......++++++++*****************
-************+++++++++++++++++++++++...... ......++++++++******************
-**************+++++++++++++++++++++++.... ....++++++++********************
-***************+++++++++++++++++++++++..... ...+++++++++*********************
-*****************++++++++++++++++++++++.... ...++++++++***********************
-*******************+++++++++++++++++++++......++++++++*************************
-*********************++++++++++++++++++++++.++++++++***************************
-*************************+++++++++++++++++++++++*******************************
-******************************+++++++++++++************************************
-*******************************************************************************
-*******************************************************************************
-*******************************************************************************
-Evaluated to 0.000000
-ready> <b>mandel(-2, -1, 0.02, 0.04);</b>
-**************************+++++++++++++++++++++++++++++++++++++++++++++++++++++
-***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++
-*********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
-*******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++...
-*****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.....
-***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........
-**************++++++++++++++++++++++++++++++++++++++++++++++++++++++...........
-************+++++++++++++++++++++++++++++++++++++++++++++++++++++..............
-***********++++++++++++++++++++++++++++++++++++++++++++++++++........ .
-**********++++++++++++++++++++++++++++++++++++++++++++++.............
-********+++++++++++++++++++++++++++++++++++++++++++..................
-*******+++++++++++++++++++++++++++++++++++++++.......................
-******+++++++++++++++++++++++++++++++++++...........................
-*****++++++++++++++++++++++++++++++++............................
-*****++++++++++++++++++++++++++++...............................
-****++++++++++++++++++++++++++...... .........................
-***++++++++++++++++++++++++......... ...... ...........
-***++++++++++++++++++++++............
-**+++++++++++++++++++++..............
-**+++++++++++++++++++................
-*++++++++++++++++++.................
-*++++++++++++++++............ ...
-*++++++++++++++..............
-*+++....++++................
-*.......... ...........
-*
-*.......... ...........
-*+++....++++................
-*++++++++++++++..............
-*++++++++++++++++............ ...
-*++++++++++++++++++.................
-**+++++++++++++++++++................
-**+++++++++++++++++++++..............
-***++++++++++++++++++++++............
-***++++++++++++++++++++++++......... ...... ...........
-****++++++++++++++++++++++++++...... .........................
-*****++++++++++++++++++++++++++++...............................
-*****++++++++++++++++++++++++++++++++............................
-******+++++++++++++++++++++++++++++++++++...........................
-*******+++++++++++++++++++++++++++++++++++++++.......................
-********+++++++++++++++++++++++++++++++++++++++++++..................
-Evaluated to 0.000000
-ready> <b>mandel(-0.9, -1.4, 0.02, 0.03);</b>
-*******************************************************************************
-*******************************************************************************
-*******************************************************************************
-**********+++++++++++++++++++++************************************************
-*+++++++++++++++++++++++++++++++++++++++***************************************
-+++++++++++++++++++++++++++++++++++++++++++++**********************************
-++++++++++++++++++++++++++++++++++++++++++++++++++*****************************
-++++++++++++++++++++++++++++++++++++++++++++++++++++++*************************
-+++++++++++++++++++++++++++++++++++++++++++++++++++++++++**********************
-+++++++++++++++++++++++++++++++++.........++++++++++++++++++*******************
-+++++++++++++++++++++++++++++++.... ......+++++++++++++++++++****************
-+++++++++++++++++++++++++++++....... ........+++++++++++++++++++**************
-++++++++++++++++++++++++++++........ ........++++++++++++++++++++************
-+++++++++++++++++++++++++++......... .. ...+++++++++++++++++++++**********
-++++++++++++++++++++++++++........... ....++++++++++++++++++++++********
-++++++++++++++++++++++++............. .......++++++++++++++++++++++******
-+++++++++++++++++++++++............. ........+++++++++++++++++++++++****
-++++++++++++++++++++++........... ..........++++++++++++++++++++++***
-++++++++++++++++++++........... .........++++++++++++++++++++++*
-++++++++++++++++++............ ...........++++++++++++++++++++
-++++++++++++++++............... .............++++++++++++++++++
-++++++++++++++................. ...............++++++++++++++++
-++++++++++++.................. .................++++++++++++++
-+++++++++.................. .................+++++++++++++
-++++++........ . ......... ..++++++++++++
-++............ ...... ....++++++++++
-.............. ...++++++++++
-.............. ....+++++++++
-.............. .....++++++++
-............. ......++++++++
-........... .......++++++++
-......... ........+++++++
-......... ........+++++++
-......... ....+++++++
-........ ...+++++++
-....... ...+++++++
- ....+++++++
- .....+++++++
- ....+++++++
- ....+++++++
- ....+++++++
-Evaluated to 0.000000
-ready> <b>^D</b>
-</pre>
-</div>
-
-<p>At this point, you may be starting to realize that Kaleidoscope is a real
-and powerful language. It may not be self-similar :), but it can be used to
-plot things that are!</p>
-
-<p>With this, we conclude the "adding user-defined operators" chapter of the
-tutorial. We have successfully augmented our language, adding the ability to extend the
-language in the library, and we have shown how this can be used to build a simple but
-interesting end-user application in Kaleidoscope. At this point, Kaleidoscope
-can build a variety of applications that are functional and can call functions
-with side-effects, but it can't actually define and mutate a variable itself.
-</p>
-
-<p>Strikingly, variable mutation is an important feature of some
-languages, and it is not at all obvious how to <a href="LangImpl7.html">add
-support for mutable variables</a> without having to add an "SSA construction"
-phase to your front-end. In the next chapter, we will describe how you can
-add variable mutation without building SSA in your front-end.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for our running example, enhanced with the
-if/then/else and for expressions.. To build this example, use:
-</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
-# Run
-./toy
-</pre>
-</div>
-
-<p>On some platforms, you will need to specify -rdynamic or -Wl,--export-dynamic
-when linking. This ensures that symbols defined in the main executable are
-exported to the dynamic linker and so are available for symbol resolution at
-run time. This is not needed if you compile your support code into a shared
-library, although doing that will cause problems on Windows.</p>
-
-<p>Here is the code:</p>
-
-<div class="doc_code">
-<pre>
-#include "llvm/DerivedTypes.h"
-#include "llvm/ExecutionEngine/ExecutionEngine.h"
-#include "llvm/ExecutionEngine/JIT.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/PassManager.h"
-#include "llvm/Analysis/Verifier.h"
-#include "llvm/Analysis/Passes.h"
-#include "llvm/DataLayout.h"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Support/TargetSelect.h"
-#include <cstdio>
-#include <string>
-#include <map>
-#include <vector>
-using namespace llvm;
-
-//===----------------------------------------------------------------------===//
-// Lexer
-//===----------------------------------------------------------------------===//
-
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
- tok_eof = -1,
-
- // commands
- tok_def = -2, tok_extern = -3,
-
- // primary
- tok_identifier = -4, tok_number = -5,
-
- // control
- tok_if = -6, tok_then = -7, tok_else = -8,
- tok_for = -9, tok_in = -10,
-
- // operators
- tok_binary = -11, tok_unary = -12
-};
-
-static std::string IdentifierStr; // Filled in if tok_identifier
-static double NumVal; // Filled in if tok_number
-
-/// gettok - Return the next token from standard input.
-static int gettok() {
- static int LastChar = ' ';
-
- // Skip any whitespace.
- while (isspace(LastChar))
- LastChar = getchar();
-
- if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
- IdentifierStr = LastChar;
- while (isalnum((LastChar = getchar())))
- IdentifierStr += LastChar;
-
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- if (IdentifierStr == "if") return tok_if;
- if (IdentifierStr == "then") return tok_then;
- if (IdentifierStr == "else") return tok_else;
- if (IdentifierStr == "for") return tok_for;
- if (IdentifierStr == "in") return tok_in;
- if (IdentifierStr == "binary") return tok_binary;
- if (IdentifierStr == "unary") return tok_unary;
- return tok_identifier;
- }
-
- if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
- std::string NumStr;
- do {
- NumStr += LastChar;
- LastChar = getchar();
- } while (isdigit(LastChar) || LastChar == '.');
-
- NumVal = strtod(NumStr.c_str(), 0);
- return tok_number;
- }
-
- if (LastChar == '#') {
- // Comment until end of line.
- do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-
- if (LastChar != EOF)
- return gettok();
- }
-
- // Check for end of file. Don't eat the EOF.
- if (LastChar == EOF)
- return tok_eof;
-
- // Otherwise, just return the character as its ascii value.
- int ThisChar = LastChar;
- LastChar = getchar();
- return ThisChar;
-}
-
-//===----------------------------------------------------------------------===//
-// Abstract Syntax Tree (aka Parse Tree)
-//===----------------------------------------------------------------------===//
-
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
- virtual Value *Codegen() = 0;
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
- virtual Value *Codegen();
-};
-
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
- std::string Name;
-public:
- VariableExprAST(const std::string &name) : Name(name) {}
- virtual Value *Codegen();
-};
-
-/// UnaryExprAST - Expression class for a unary operator.
-class UnaryExprAST : public ExprAST {
- char Opcode;
- ExprAST *Operand;
-public:
- UnaryExprAST(char opcode, ExprAST *operand)
- : Opcode(opcode), Operand(operand) {}
- virtual Value *Codegen();
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
- char Op;
- ExprAST *LHS, *RHS;
-public:
- BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
- : Op(op), LHS(lhs), RHS(rhs) {}
- virtual Value *Codegen();
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
- std::string Callee;
- std::vector<ExprAST*> Args;
-public:
- CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
- : Callee(callee), Args(args) {}
- virtual Value *Codegen();
-};
-
-/// IfExprAST - Expression class for if/then/else.
-class IfExprAST : public ExprAST {
- ExprAST *Cond, *Then, *Else;
-public:
- IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
- : Cond(cond), Then(then), Else(_else) {}
- virtual Value *Codegen();
-};
-
-/// ForExprAST - Expression class for for/in.
-class ForExprAST : public ExprAST {
- std::string VarName;
- ExprAST *Start, *End, *Step, *Body;
-public:
- ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
- ExprAST *step, ExprAST *body)
- : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
- virtual Value *Codegen();
-};
-
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes), as well as if it is an operator.
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
- bool isOperator;
- unsigned Precedence; // Precedence if a binary op.
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args,
- bool isoperator = false, unsigned prec = 0)
- : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {}
-
- bool isUnaryOp() const { return isOperator && Args.size() == 1; }
- bool isBinaryOp() const { return isOperator && Args.size() == 2; }
-
- char getOperatorName() const {
- assert(isUnaryOp() || isBinaryOp());
- return Name[Name.size()-1];
- }
-
- unsigned getBinaryPrecedence() const { return Precedence; }
-
- Function *Codegen();
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
- PrototypeAST *Proto;
- ExprAST *Body;
-public:
- FunctionAST(PrototypeAST *proto, ExprAST *body)
- : Proto(proto), Body(body) {}
-
- Function *Codegen();
-};
-
-//===----------------------------------------------------------------------===//
-// Parser
-//===----------------------------------------------------------------------===//
-
-/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
-/// token the parser is looking at. getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
- return CurTok = gettok();
-}
-
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
- if (!isascii(CurTok))
- return -1;
-
- // Make sure it's a declared binop.
- int TokPrec = BinopPrecedence[CurTok];
- if (TokPrec <= 0) return -1;
- return TokPrec;
-}
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-
-static ExprAST *ParseExpression();
-
-/// identifierexpr
-/// ::= identifier
-/// ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
- std::string IdName = IdentifierStr;
-
- getNextToken(); // eat identifier.
-
- if (CurTok != '(') // Simple variable ref.
- return new VariableExprAST(IdName);
-
- // Call.
- getNextToken(); // eat (
- std::vector<ExprAST*> Args;
- if (CurTok != ')') {
- while (1) {
- ExprAST *Arg = ParseExpression();
- if (!Arg) return 0;
- Args.push_back(Arg);
-
- if (CurTok == ')') break;
-
- if (CurTok != ',')
- return Error("Expected ')' or ',' in argument list");
- getNextToken();
- }
- }
-
- // Eat the ')'.
- getNextToken();
-
- return new CallExprAST(IdName, Args);
-}
-
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
- ExprAST *Result = new NumberExprAST(NumVal);
- getNextToken(); // consume the number
- return Result;
-}
-
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
- getNextToken(); // eat (.
- ExprAST *V = ParseExpression();
- if (!V) return 0;
-
- if (CurTok != ')')
- return Error("expected ')'");
- getNextToken(); // eat ).
- return V;
-}
-
-/// ifexpr ::= 'if' expression 'then' expression 'else' expression
-static ExprAST *ParseIfExpr() {
- getNextToken(); // eat the if.
-
- // condition.
- ExprAST *Cond = ParseExpression();
- if (!Cond) return 0;
-
- if (CurTok != tok_then)
- return Error("expected then");
- getNextToken(); // eat the then
-
- ExprAST *Then = ParseExpression();
- if (Then == 0) return 0;
-
- if (CurTok != tok_else)
- return Error("expected else");
-
- getNextToken();
-
- ExprAST *Else = ParseExpression();
- if (!Else) return 0;
-
- return new IfExprAST(Cond, Then, Else);
-}
-
-/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
-static ExprAST *ParseForExpr() {
- getNextToken(); // eat the for.
-
- if (CurTok != tok_identifier)
- return Error("expected identifier after for");
-
- std::string IdName = IdentifierStr;
- getNextToken(); // eat identifier.
-
- if (CurTok != '=')
- return Error("expected '=' after for");
- getNextToken(); // eat '='.
-
-
- ExprAST *Start = ParseExpression();
- if (Start == 0) return 0;
- if (CurTok != ',')
- return Error("expected ',' after for start value");
- getNextToken();
-
- ExprAST *End = ParseExpression();
- if (End == 0) return 0;
-
- // The step value is optional.
- ExprAST *Step = 0;
- if (CurTok == ',') {
- getNextToken();
- Step = ParseExpression();
- if (Step == 0) return 0;
- }
-
- if (CurTok != tok_in)
- return Error("expected 'in' after for");
- getNextToken(); // eat 'in'.
-
- ExprAST *Body = ParseExpression();
- if (Body == 0) return 0;
-
- return new ForExprAST(IdName, Start, End, Step, Body);
-}
-
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-/// ::= ifexpr
-/// ::= forexpr
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- case tok_if: return ParseIfExpr();
- case tok_for: return ParseForExpr();
- }
-}
-
-/// unary
-/// ::= primary
-/// ::= '!' unary
-static ExprAST *ParseUnary() {
- // If the current token is not an operator, it must be a primary expr.
- if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
- return ParsePrimary();
-
- // If this is a unary operator, read it.
- int Opc = CurTok;
- getNextToken();
- if (ExprAST *Operand = ParseUnary())
- return new UnaryExprAST(Opc, Operand);
- return 0;
-}
-
-/// binoprhs
-/// ::= ('+' unary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- // If this is a binop, find its precedence.
- while (1) {
- int TokPrec = GetTokPrecedence();
-
- // If this is a binop that binds at least as tightly as the current binop,
- // consume it, otherwise we are done.
- if (TokPrec < ExprPrec)
- return LHS;
-
- // Okay, we know this is a binop.
- int BinOp = CurTok;
- getNextToken(); // eat binop
-
- // Parse the unary expression after the binary operator.
- ExprAST *RHS = ParseUnary();
- if (!RHS) return 0;
-
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
- RHS = ParseBinOpRHS(TokPrec+1, RHS);
- if (RHS == 0) return 0;
- }
-
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- }
-}
-
-/// expression
-/// ::= unary binoprhs
-///
-static ExprAST *ParseExpression() {
- ExprAST *LHS = ParseUnary();
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-
-/// prototype
-/// ::= id '(' id* ')'
-/// ::= binary LETTER number? (id, id)
-/// ::= unary LETTER (id)
-static PrototypeAST *ParsePrototype() {
- std::string FnName;
-
- unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
- unsigned BinaryPrecedence = 30;
-
- switch (CurTok) {
- default:
- return ErrorP("Expected function name in prototype");
- case tok_identifier:
- FnName = IdentifierStr;
- Kind = 0;
- getNextToken();
- break;
- case tok_unary:
- getNextToken();
- if (!isascii(CurTok))
- return ErrorP("Expected unary operator");
- FnName = "unary";
- FnName += (char)CurTok;
- Kind = 1;
- getNextToken();
- break;
- case tok_binary:
- getNextToken();
- if (!isascii(CurTok))
- return ErrorP("Expected binary operator");
- FnName = "binary";
- FnName += (char)CurTok;
- Kind = 2;
- getNextToken();
-
- // Read the precedence if present.
- if (CurTok == tok_number) {
- if (NumVal < 1 || NumVal > 100)
- return ErrorP("Invalid precedecnce: must be 1..100");
- BinaryPrecedence = (unsigned)NumVal;
- getNextToken();
- }
- break;
- }
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- // Verify right number of names for operator.
- if (Kind && ArgNames.size() != Kind)
- return ErrorP("Invalid number of operands for operator");
-
- return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence);
-}
-
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
- getNextToken(); // eat def.
- PrototypeAST *Proto = ParsePrototype();
- if (Proto == 0) return 0;
-
- if (ExprAST *E = ParseExpression())
- return new FunctionAST(Proto, E);
- return 0;
-}
-
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
- if (ExprAST *E = ParseExpression()) {
- // Make an anonymous proto.
- PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
- return new FunctionAST(Proto, E);
- }
- return 0;
-}
-
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
- getNextToken(); // eat extern.
- return ParsePrototype();
-}
-
-//===----------------------------------------------------------------------===//
-// Code Generation
-//===----------------------------------------------------------------------===//
-
-static Module *TheModule;
-static IRBuilder<> Builder(getGlobalContext());
-static std::map<std::string, Value*> NamedValues;
-static FunctionPassManager *TheFPM;
-
-Value *ErrorV(const char *Str) { Error(Str); return 0; }
-
-Value *NumberExprAST::Codegen() {
- return ConstantFP::get(getGlobalContext(), APFloat(Val));
-}
-
-Value *VariableExprAST::Codegen() {
- // Look this variable up in the function.
- Value *V = NamedValues[Name];
- return V ? V : ErrorV("Unknown variable name");
-}
-
-Value *UnaryExprAST::Codegen() {
- Value *OperandV = Operand->Codegen();
- if (OperandV == 0) return 0;
-
- Function *F = TheModule->getFunction(std::string("unary")+Opcode);
- if (F == 0)
- return ErrorV("Unknown unary operator");
-
- return Builder.CreateCall(F, OperandV, "unop");
-}
-
-Value *BinaryExprAST::Codegen() {
- Value *L = LHS->Codegen();
- Value *R = RHS->Codegen();
- if (L == 0 || R == 0) return 0;
-
- switch (Op) {
- case '+': return Builder.CreateFAdd(L, R, "addtmp");
- case '-': return Builder.CreateFSub(L, R, "subtmp");
- case '*': return Builder.CreateFMul(L, R, "multmp");
- case '<':
- L = Builder.CreateFCmpULT(L, R, "cmptmp");
- // Convert bool 0/1 to double 0.0 or 1.0
- return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
- "booltmp");
- default: break;
- }
-
- // If it wasn't a builtin binary operator, it must be a user defined one. Emit
- // a call to it.
- Function *F = TheModule->getFunction(std::string("binary")+Op);
- assert(F && "binary operator not found!");
-
- Value *Ops[2] = { L, R };
- return Builder.CreateCall(F, Ops, "binop");
-}
-
-Value *CallExprAST::Codegen() {
- // Look up the name in the global module table.
- Function *CalleeF = TheModule->getFunction(Callee);
- if (CalleeF == 0)
- return ErrorV("Unknown function referenced");
-
- // If argument mismatch error.
- if (CalleeF->arg_size() != Args.size())
- return ErrorV("Incorrect # arguments passed");
-
- std::vector<Value*> ArgsV;
- for (unsigned i = 0, e = Args.size(); i != e; ++i) {
- ArgsV.push_back(Args[i]->Codegen());
- if (ArgsV.back() == 0) return 0;
- }
-
- return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
-}
-
-Value *IfExprAST::Codegen() {
- Value *CondV = Cond->Codegen();
- if (CondV == 0) return 0;
-
- // Convert condition to a bool by comparing equal to 0.0.
- CondV = Builder.CreateFCmpONE(CondV,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "ifcond");
-
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- // Create blocks for the then and else cases. Insert the 'then' block at the
- // end of the function.
- BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
- BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
- BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
-
- Builder.CreateCondBr(CondV, ThenBB, ElseBB);
-
- // Emit then value.
- Builder.SetInsertPoint(ThenBB);
-
- Value *ThenV = Then->Codegen();
- if (ThenV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
- ThenBB = Builder.GetInsertBlock();
-
- // Emit else block.
- TheFunction->getBasicBlockList().push_back(ElseBB);
- Builder.SetInsertPoint(ElseBB);
-
- Value *ElseV = Else->Codegen();
- if (ElseV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
- ElseBB = Builder.GetInsertBlock();
-
- // Emit merge block.
- TheFunction->getBasicBlockList().push_back(MergeBB);
- Builder.SetInsertPoint(MergeBB);
- PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
- "iftmp");
-
- PN->addIncoming(ThenV, ThenBB);
- PN->addIncoming(ElseV, ElseBB);
- return PN;
-}
-
-Value *ForExprAST::Codegen() {
- // Output this as:
- // ...
- // start = startexpr
- // goto loop
- // loop:
- // variable = phi [start, loopheader], [nextvariable, loopend]
- // ...
- // bodyexpr
- // ...
- // loopend:
- // step = stepexpr
- // nextvariable = variable + step
- // endcond = endexpr
- // br endcond, loop, endloop
- // outloop:
-
- // Emit the start code first, without 'variable' in scope.
- Value *StartVal = Start->Codegen();
- if (StartVal == 0) return 0;
-
- // Make the new basic block for the loop header, inserting after current
- // block.
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
- BasicBlock *PreheaderBB = Builder.GetInsertBlock();
- BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
-
- // Insert an explicit fall through from the current block to the LoopBB.
- Builder.CreateBr(LoopBB);
-
- // Start insertion in LoopBB.
- Builder.SetInsertPoint(LoopBB);
-
- // Start the PHI node with an entry for Start.
- PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str());
- Variable->addIncoming(StartVal, PreheaderBB);
-
- // Within the loop, the variable is defined equal to the PHI node. If it
- // shadows an existing variable, we have to restore it, so save it now.
- Value *OldVal = NamedValues[VarName];
- NamedValues[VarName] = Variable;
-
- // Emit the body of the loop. This, like any other expr, can change the
- // current BB. Note that we ignore the value computed by the body, but don't
- // allow an error.
- if (Body->Codegen() == 0)
- return 0;
-
- // Emit the step value.
- Value *StepVal;
- if (Step) {
- StepVal = Step->Codegen();
- if (StepVal == 0) return 0;
- } else {
- // If not specified, use 1.0.
- StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
- }
-
- Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
-
- // Compute the end condition.
- Value *EndCond = End->Codegen();
- if (EndCond == 0) return EndCond;
-
- // Convert condition to a bool by comparing equal to 0.0.
- EndCond = Builder.CreateFCmpONE(EndCond,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "loopcond");
-
- // Create the "after loop" block and insert it.
- BasicBlock *LoopEndBB = Builder.GetInsertBlock();
- BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
-
- // Insert the conditional branch into the end of LoopEndBB.
- Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
-
- // Any new code will be inserted in AfterBB.
- Builder.SetInsertPoint(AfterBB);
-
- // Add a new entry to the PHI node for the backedge.
- Variable->addIncoming(NextVar, LoopEndBB);
-
- // Restore the unshadowed variable.
- if (OldVal)
- NamedValues[VarName] = OldVal;
- else
- NamedValues.erase(VarName);
-
-
- // for expr always returns 0.0.
- return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
-}
-
-Function *PrototypeAST::Codegen() {
- // Make the function type: double(double,double) etc.
- std::vector<Type*> Doubles(Args.size(),
- Type::getDoubleTy(getGlobalContext()));
- FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
- Doubles, false);
-
- Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
-
- // If F conflicted, there was already something named 'Name'. If it has a
- // body, don't allow redefinition or reextern.
- if (F->getName() != Name) {
- // Delete the one we just made and get the existing one.
- F->eraseFromParent();
- F = TheModule->getFunction(Name);
-
- // If F already has a body, reject this.
- if (!F->empty()) {
- ErrorF("redefinition of function");
- return 0;
- }
-
- // If F took a different number of args, reject.
- if (F->arg_size() != Args.size()) {
- ErrorF("redefinition of function with different # args");
- return 0;
- }
- }
-
- // Set names for all arguments.
- unsigned Idx = 0;
- for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
- ++AI, ++Idx) {
- AI->setName(Args[Idx]);
-
- // Add arguments to variable symbol table.
- NamedValues[Args[Idx]] = AI;
- }
-
- return F;
-}
-
-Function *FunctionAST::Codegen() {
- NamedValues.clear();
-
- Function *TheFunction = Proto->Codegen();
- if (TheFunction == 0)
- return 0;
-
- // If this is an operator, install it.
- if (Proto->isBinaryOp())
- BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();
-
- // Create a new basic block to start insertion into.
- BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
- Builder.SetInsertPoint(BB);
-
- if (Value *RetVal = Body->Codegen()) {
- // Finish off the function.
- Builder.CreateRet(RetVal);
-
- // Validate the generated code, checking for consistency.
- verifyFunction(*TheFunction);
-
- // Optimize the function.
- TheFPM->run(*TheFunction);
-
- return TheFunction;
- }
-
- // Error reading body, remove function.
- TheFunction->eraseFromParent();
-
- if (Proto->isBinaryOp())
- BinopPrecedence.erase(Proto->getOperatorName());
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Top-Level parsing and JIT Driver
-//===----------------------------------------------------------------------===//
-
-static ExecutionEngine *TheExecutionEngine;
-
-static void HandleDefinition() {
- if (FunctionAST *F = ParseDefinition()) {
- if (Function *LF = F->Codegen()) {
- fprintf(stderr, "Read function definition:");
- LF->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleExtern() {
- if (PrototypeAST *P = ParseExtern()) {
- if (Function *F = P->Codegen()) {
- fprintf(stderr, "Read extern: ");
- F->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleTopLevelExpression() {
- // Evaluate a top-level expression into an anonymous function.
- if (FunctionAST *F = ParseTopLevelExpr()) {
- if (Function *LF = F->Codegen()) {
- // JIT the function, returning a function pointer.
- void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
-
- // Cast it to the right type (takes no arguments, returns a double) so we
- // can call it as a native function.
- double (*FP)() = (double (*)())(intptr_t)FPtr;
- fprintf(stderr, "Evaluated to %f\n", FP());
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
- while (1) {
- fprintf(stderr, "ready> ");
- switch (CurTok) {
- case tok_eof: return;
- case ';': getNextToken(); break; // ignore top-level semicolons.
- case tok_def: HandleDefinition(); break;
- case tok_extern: HandleExtern(); break;
- default: HandleTopLevelExpression(); break;
- }
- }
-}
-
-//===----------------------------------------------------------------------===//
-// "Library" functions that can be "extern'd" from user code.
-//===----------------------------------------------------------------------===//
-
-/// putchard - putchar that takes a double and returns 0.
-extern "C"
-double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-
-/// printd - printf that takes a double prints it as "%f\n", returning 0.
-extern "C"
-double printd(double X) {
- printf("%f\n", X);
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Main driver code.
-//===----------------------------------------------------------------------===//
-
-int main() {
- InitializeNativeTarget();
- LLVMContext &Context = getGlobalContext();
-
- // Install standard binary operators.
- // 1 is lowest precedence.
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
- BinopPrecedence['*'] = 40; // highest.
-
- // Prime the first token.
- fprintf(stderr, "ready> ");
- getNextToken();
-
- // Make the module, which holds all the code.
- TheModule = new Module("my cool jit", Context);
-
- // Create the JIT. This takes ownership of the module.
- std::string ErrStr;
- TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
- if (!TheExecutionEngine) {
- fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
- exit(1);
- }
-
- FunctionPassManager OurFPM(TheModule);
-
- // Set up the optimizer pipeline. Start with registering info about how the
- // target lays out data structures.
- OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
- // Provide basic AliasAnalysis support for GVN.
- OurFPM.add(createBasicAliasAnalysisPass());
- // Do simple "peephole" optimizations and bit-twiddling optzns.
- OurFPM.add(createInstructionCombiningPass());
- // Reassociate expressions.
- OurFPM.add(createReassociatePass());
- // Eliminate Common SubExpressions.
- OurFPM.add(createGVNPass());
- // Simplify the control flow graph (deleting unreachable blocks, etc).
- OurFPM.add(createCFGSimplificationPass());
-
- OurFPM.doInitialization();
-
- // Set the global so the code gen can use this.
- TheFPM = &OurFPM;
-
- // Run the main "interpreter loop" now.
- MainLoop();
-
- TheFPM = 0;
-
- // Print out all of the generated code.
- TheModule->dump();
-
- return 0;
-}
-</pre>
-</div>
-
-<a href="LangImpl7.html">Next: Extending the language: mutable variables / SSA construction</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/LangImpl6.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl6.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl6.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl6.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,1728 @@
+============================================================
+Kaleidoscope: Extending the Language: User-defined Operators
+============================================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Chapter 6 Introduction
+======================
+
+Welcome to Chapter 6 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. At this point in our tutorial, we now
+have a fully functional language that is fairly minimal, but also
+useful. There is still one big problem with it, however. Our language
+doesn't have many useful operators (like division, logical negation, or
+even any comparisons besides less-than).
+
+This chapter of the tutorial takes a wild digression into adding
+user-defined operators to the simple and beautiful Kaleidoscope
+language. This digression now gives us a simple and ugly language in
+some ways, but also a powerful one at the same time. One of the great
+things about creating your own language is that you get to decide what
+is good or bad. In this tutorial we'll assume that it is okay to use
+this as a way to show some interesting parsing techniques.
+
+At the end of this tutorial, we'll run through an example Kaleidoscope
+application that `renders the Mandelbrot set <#example>`_. This gives an
+example of what you can build with Kaleidoscope and its feature set.
+
+User-defined Operators: the Idea
+================================
+
+The "operator overloading" that we will add to Kaleidoscope is more
+general than languages like C++. In C++, you are only allowed to
+redefine existing operators: you can't programatically change the
+grammar, introduce new operators, change precedence levels, etc. In this
+chapter, we will add this capability to Kaleidoscope, which will let the
+user round out the set of operators that are supported.
+
+The point of going into user-defined operators in a tutorial like this
+is to show the power and flexibility of using a hand-written parser.
+Thus far, the parser we have been implementing uses recursive descent
+for most parts of the grammar and operator precedence parsing for the
+expressions. See `Chapter 2 <LangImpl2.html>`_ for details. Without
+using operator precedence parsing, it would be very difficult to allow
+the programmer to introduce new operators into the grammar: the grammar
+is dynamically extensible as the JIT runs.
+
+The two specific features we'll add are programmable unary operators
+(right now, Kaleidoscope has no unary operators at all) as well as
+binary operators. An example of this is:
+
+::
+
+ # Logical unary not.
+ def unary!(v)
+ if v then
+ 0
+ else
+ 1;
+
+ # Define > with the same precedence as <.
+ def binary> 10 (LHS RHS)
+ RHS < LHS;
+
+ # Binary "logical or", (note that it does not "short circuit")
+ def binary| 5 (LHS RHS)
+ if LHS then
+ 1
+ else if RHS then
+ 1
+ else
+ 0;
+
+ # Define = with slightly lower precedence than relationals.
+ def binary= 9 (LHS RHS)
+ !(LHS < RHS | LHS > RHS);
+
+Many languages aspire to being able to implement their standard runtime
+library in the language itself. In Kaleidoscope, we can implement
+significant parts of the language in the library!
+
+We will break down implementation of these features into two parts:
+implementing support for user-defined binary operators and adding unary
+operators.
+
+User-defined Binary Operators
+=============================
+
+Adding support for user-defined binary operators is pretty simple with
+our current framework. We'll first add support for the unary/binary
+keywords:
+
+.. code-block:: c++
+
+ enum Token {
+ ...
+ // operators
+ tok_binary = -11, tok_unary = -12
+ };
+ ...
+ static int gettok() {
+ ...
+ if (IdentifierStr == "for") return tok_for;
+ if (IdentifierStr == "in") return tok_in;
+ if (IdentifierStr == "binary") return tok_binary;
+ if (IdentifierStr == "unary") return tok_unary;
+ return tok_identifier;
+
+This just adds lexer support for the unary and binary keywords, like we
+did in `previous chapters <LangImpl5.html#iflexer>`_. One nice thing
+about our current AST, is that we represent binary operators with full
+generalisation by using their ASCII code as the opcode. For our extended
+operators, we'll use this same representation, so we don't need any new
+AST or parser support.
+
+On the other hand, we have to be able to represent the definitions of
+these new operators, in the "def binary\| 5" part of the function
+definition. In our grammar so far, the "name" for the function
+definition is parsed as the "prototype" production and into the
+``PrototypeAST`` AST node. To represent our new user-defined operators
+as prototypes, we have to extend the ``PrototypeAST`` AST node like
+this:
+
+.. code-block:: c++
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its argument names as well as if it is an operator.
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ bool isOperator;
+ unsigned Precedence; // Precedence if a binary op.
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args,
+ bool isoperator = false, unsigned prec = 0)
+ : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {}
+
+ bool isUnaryOp() const { return isOperator && Args.size() == 1; }
+ bool isBinaryOp() const { return isOperator && Args.size() == 2; }
+
+ char getOperatorName() const {
+ assert(isUnaryOp() || isBinaryOp());
+ return Name[Name.size()-1];
+ }
+
+ unsigned getBinaryPrecedence() const { return Precedence; }
+
+ Function *Codegen();
+ };
+
+Basically, in addition to knowing a name for the prototype, we now keep
+track of whether it was an operator, and if it was, what precedence
+level the operator is at. The precedence is only used for binary
+operators (as you'll see below, it just doesn't apply for unary
+operators). Now that we have a way to represent the prototype for a
+user-defined operator, we need to parse it:
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ static PrototypeAST *ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return ErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_binary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected binary operator");
+ FnName = "binary";
+ FnName += (char)CurTok;
+ Kind = 2;
+ getNextToken();
+
+ // Read the precedence if present.
+ if (CurTok == tok_number) {
+ if (NumVal < 1 || NumVal > 100)
+ return ErrorP("Invalid precedecnce: must be 1..100");
+ BinaryPrecedence = (unsigned)NumVal;
+ getNextToken();
+ }
+ break;
+ }
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ // Verify right number of names for operator.
+ if (Kind && ArgNames.size() != Kind)
+ return ErrorP("Invalid number of operands for operator");
+
+ return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence);
+ }
+
+This is all fairly straightforward parsing code, and we have already
+seen a lot of similar code in the past. One interesting part about the
+code above is the couple lines that set up ``FnName`` for binary
+operators. This builds names like "binary@" for a newly defined "@"
+operator. This then takes advantage of the fact that symbol names in the
+LLVM symbol table are allowed to have any character in them, including
+embedded nul characters.
+
+The next interesting thing to add, is codegen support for these binary
+operators. Given our current structure, this is a simple addition of a
+default case for our existing binary operator node:
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateFAdd(L, R, "addtmp");
+ case '-': return Builder.CreateFSub(L, R, "subtmp");
+ case '*': return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default: break;
+ }
+
+ // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+ // a call to it.
+ Function *F = TheModule->getFunction(std::string("binary")+Op);
+ assert(F && "binary operator not found!");
+
+ Value *Ops[2] = { L, R };
+ return Builder.CreateCall(F, Ops, "binop");
+ }
+
+As you can see above, the new code is actually really simple. It just
+does a lookup for the appropriate operator in the symbol table and
+generates a function call to it. Since user-defined operators are just
+built as normal functions (because the "prototype" boils down to a
+function with the right name) everything falls into place.
+
+The final piece of code we are missing, is a bit of top-level magic:
+
+.. code-block:: c++
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // If this is an operator, install it.
+ if (Proto->isBinaryOp())
+ BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->Codegen()) {
+ ...
+
+Basically, before codegening a function, if it is a user-defined
+operator, we register it in the precedence table. This allows the binary
+operator parsing logic we already have in place to handle it. Since we
+are working on a fully-general operator precedence parser, this is all
+we need to do to "extend the grammar".
+
+Now we have useful user-defined binary operators. This builds a lot on
+the previous framework we built for other operators. Adding unary
+operators is a bit more challenging, because we don't have any framework
+for it yet - lets see what it takes.
+
+User-defined Unary Operators
+============================
+
+Since we don't currently support unary operators in the Kaleidoscope
+language, we'll need to add everything to support them. Above, we added
+simple support for the 'unary' keyword to the lexer. In addition to
+that, we need an AST node:
+
+.. code-block:: c++
+
+ /// UnaryExprAST - Expression class for a unary operator.
+ class UnaryExprAST : public ExprAST {
+ char Opcode;
+ ExprAST *Operand;
+ public:
+ UnaryExprAST(char opcode, ExprAST *operand)
+ : Opcode(opcode), Operand(operand) {}
+ virtual Value *Codegen();
+ };
+
+This AST node is very simple and obvious by now. It directly mirrors the
+binary operator AST node, except that it only has one child. With this,
+we need to add the parsing logic. Parsing a unary operator is pretty
+simple: we'll add a new function to do it:
+
+.. code-block:: c++
+
+ /// unary
+ /// ::= primary
+ /// ::= '!' unary
+ static ExprAST *ParseUnary() {
+ // If the current token is not an operator, it must be a primary expr.
+ if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+ return ParsePrimary();
+
+ // If this is a unary operator, read it.
+ int Opc = CurTok;
+ getNextToken();
+ if (ExprAST *Operand = ParseUnary())
+ return new UnaryExprAST(Opc, Operand);
+ return 0;
+ }
+
+The grammar we add is pretty straightforward here. If we see a unary
+operator when parsing a primary operator, we eat the operator as a
+prefix and parse the remaining piece as another unary operator. This
+allows us to handle multiple unary operators (e.g. "!!x"). Note that
+unary operators can't have ambiguous parses like binary operators can,
+so there is no need for precedence information.
+
+The problem with this function, is that we need to call ParseUnary from
+somewhere. To do this, we change previous callers of ParsePrimary to
+call ParseUnary instead:
+
+.. code-block:: c++
+
+ /// binoprhs
+ /// ::= ('+' unary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ ...
+ // Parse the unary expression after the binary operator.
+ ExprAST *RHS = ParseUnary();
+ if (!RHS) return 0;
+ ...
+ }
+ /// expression
+ /// ::= unary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParseUnary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+With these two simple changes, we are now able to parse unary operators
+and build the AST for them. Next up, we need to add parser support for
+prototypes, to parse the unary operator prototype. We extend the binary
+operator code above with:
+
+.. code-block:: c++
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ /// ::= unary LETTER (id)
+ static PrototypeAST *ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return ErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_unary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected unary operator");
+ FnName = "unary";
+ FnName += (char)CurTok;
+ Kind = 1;
+ getNextToken();
+ break;
+ case tok_binary:
+ ...
+
+As with binary operators, we name unary operators with a name that
+includes the operator character. This assists us at code generation
+time. Speaking of, the final piece we need to add is codegen support for
+unary operators. It looks like this:
+
+.. code-block:: c++
+
+ Value *UnaryExprAST::Codegen() {
+ Value *OperandV = Operand->Codegen();
+ if (OperandV == 0) return 0;
+
+ Function *F = TheModule->getFunction(std::string("unary")+Opcode);
+ if (F == 0)
+ return ErrorV("Unknown unary operator");
+
+ return Builder.CreateCall(F, OperandV, "unop");
+ }
+
+This code is similar to, but simpler than, the code for binary
+operators. It is simpler primarily because it doesn't need to handle any
+predefined operators.
+
+Kicking the Tires
+=================
+
+It is somewhat hard to believe, but with a few simple extensions we've
+covered in the last chapters, we have grown a real-ish language. With
+this, we can do a lot of interesting things, including I/O, math, and a
+bunch of other things. For example, we can now add a nice sequencing
+operator (printd is defined to print out the specified value and a
+newline):
+
+::
+
+ ready> extern printd(x);
+ Read extern:
+ declare double @printd(double)
+
+ ready> def binary : 1 (x y) 0; # Low-precedence operator that ignores operands.
+ ..
+ ready> printd(123) : printd(456) : printd(789);
+ 123.000000
+ 456.000000
+ 789.000000
+ Evaluated to 0.000000
+
+We can also define a bunch of other "primitive" operations, such as:
+
+::
+
+ # Logical unary not.
+ def unary!(v)
+ if v then
+ 0
+ else
+ 1;
+
+ # Unary negate.
+ def unary-(v)
+ 0-v;
+
+ # Define > with the same precedence as <.
+ def binary> 10 (LHS RHS)
+ RHS < LHS;
+
+ # Binary logical or, which does not short circuit.
+ def binary| 5 (LHS RHS)
+ if LHS then
+ 1
+ else if RHS then
+ 1
+ else
+ 0;
+
+ # Binary logical and, which does not short circuit.
+ def binary& 6 (LHS RHS)
+ if !LHS then
+ 0
+ else
+ !!RHS;
+
+ # Define = with slightly lower precedence than relationals.
+ def binary = 9 (LHS RHS)
+ !(LHS < RHS | LHS > RHS);
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+Given the previous if/then/else support, we can also define interesting
+functions for I/O. For example, the following prints out a character
+whose "density" reflects the value passed in: the lower the value, the
+denser the character:
+
+::
+
+ ready>
+
+ extern putchard(char)
+ def printdensity(d)
+ if d > 8 then
+ putchard(32) # ' '
+ else if d > 4 then
+ putchard(46) # '.'
+ else if d > 2 then
+ putchard(43) # '+'
+ else
+ putchard(42); # '*'
+ ...
+ ready> printdensity(1): printdensity(2): printdensity(3):
+ printdensity(4): printdensity(5): printdensity(9):
+ putchard(10);
+ **++.
+ Evaluated to 0.000000
+
+Based on these simple primitive operations, we can start to define more
+interesting things. For example, here's a little function that solves
+for the number of iterations it takes a function in the complex plane to
+converge:
+
+::
+
+ # Determine whether the specific location diverges.
+ # Solve for z = z^2 + c in the complex plane.
+ def mandleconverger(real imag iters creal cimag)
+ if iters > 255 | (real*real + imag*imag > 4) then
+ iters
+ else
+ mandleconverger(real*real - imag*imag + creal,
+ 2*real*imag + cimag,
+ iters+1, creal, cimag);
+
+ # Return the number of iterations required for the iteration to escape
+ def mandleconverge(real imag)
+ mandleconverger(real, imag, 0, real, imag);
+
+This "``z = z2 + c``" function is a beautiful little creature that is
+the basis for computation of the `Mandelbrot
+Set <http://en.wikipedia.org/wiki/Mandelbrot_set>`_. Our
+``mandelconverge`` function returns the number of iterations that it
+takes for a complex orbit to escape, saturating to 255. This is not a
+very useful function by itself, but if you plot its value over a
+two-dimensional plane, you can see the Mandelbrot set. Given that we are
+limited to using putchard here, our amazing graphical output is limited,
+but we can whip together something using the density plotter above:
+
+::
+
+ # Compute and plot the mandlebrot set with the specified 2 dimensional range
+ # info.
+ def mandelhelp(xmin xmax xstep ymin ymax ystep)
+ for y = ymin, y < ymax, ystep in (
+ (for x = xmin, x < xmax, xstep in
+ printdensity(mandleconverge(x,y)))
+ : putchard(10)
+ )
+
+ # mandel - This is a convenient helper function for plotting the mandelbrot set
+ # from the specified position with the specified Magnification.
+ def mandel(realstart imagstart realmag imagmag)
+ mandelhelp(realstart, realstart+realmag*78, realmag,
+ imagstart, imagstart+imagmag*40, imagmag);
+
+Given this, we can try plotting out the mandlebrot set! Lets try it out:
+
+::
+
+ ready> mandel(-2.3, -1.3, 0.05, 0.07);
+ *******************************+++++++++++*************************************
+ *************************+++++++++++++++++++++++*******************************
+ **********************+++++++++++++++++++++++++++++****************************
+ *******************+++++++++++++++++++++.. ...++++++++*************************
+ *****************++++++++++++++++++++++.... ...+++++++++***********************
+ ***************+++++++++++++++++++++++..... ...+++++++++*********************
+ **************+++++++++++++++++++++++.... ....+++++++++********************
+ *************++++++++++++++++++++++...... .....++++++++*******************
+ ************+++++++++++++++++++++....... .......+++++++******************
+ ***********+++++++++++++++++++.... ... .+++++++*****************
+ **********+++++++++++++++++....... .+++++++****************
+ *********++++++++++++++........... ...+++++++***************
+ ********++++++++++++............ ...++++++++**************
+ ********++++++++++... .......... .++++++++**************
+ *******+++++++++..... .+++++++++*************
+ *******++++++++...... ..+++++++++*************
+ *******++++++....... ..+++++++++*************
+ *******+++++...... ..+++++++++*************
+ *******.... .... ...+++++++++*************
+ *******.... . ...+++++++++*************
+ *******+++++...... ...+++++++++*************
+ *******++++++....... ..+++++++++*************
+ *******++++++++...... .+++++++++*************
+ *******+++++++++..... ..+++++++++*************
+ ********++++++++++... .......... .++++++++**************
+ ********++++++++++++............ ...++++++++**************
+ *********++++++++++++++.......... ...+++++++***************
+ **********++++++++++++++++........ .+++++++****************
+ **********++++++++++++++++++++.... ... ..+++++++****************
+ ***********++++++++++++++++++++++....... .......++++++++*****************
+ ************+++++++++++++++++++++++...... ......++++++++******************
+ **************+++++++++++++++++++++++.... ....++++++++********************
+ ***************+++++++++++++++++++++++..... ...+++++++++*********************
+ *****************++++++++++++++++++++++.... ...++++++++***********************
+ *******************+++++++++++++++++++++......++++++++*************************
+ *********************++++++++++++++++++++++.++++++++***************************
+ *************************+++++++++++++++++++++++*******************************
+ ******************************+++++++++++++************************************
+ *******************************************************************************
+ *******************************************************************************
+ *******************************************************************************
+ Evaluated to 0.000000
+ ready> mandel(-2, -1, 0.02, 0.04);
+ **************************+++++++++++++++++++++++++++++++++++++++++++++++++++++
+ ***********************++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ *********************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.
+ *******************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++...
+ *****************+++++++++++++++++++++++++++++++++++++++++++++++++++++++++.....
+ ***************++++++++++++++++++++++++++++++++++++++++++++++++++++++++........
+ **************++++++++++++++++++++++++++++++++++++++++++++++++++++++...........
+ ************+++++++++++++++++++++++++++++++++++++++++++++++++++++..............
+ ***********++++++++++++++++++++++++++++++++++++++++++++++++++........ .
+ **********++++++++++++++++++++++++++++++++++++++++++++++.............
+ ********+++++++++++++++++++++++++++++++++++++++++++..................
+ *******+++++++++++++++++++++++++++++++++++++++.......................
+ ******+++++++++++++++++++++++++++++++++++...........................
+ *****++++++++++++++++++++++++++++++++............................
+ *****++++++++++++++++++++++++++++...............................
+ ****++++++++++++++++++++++++++...... .........................
+ ***++++++++++++++++++++++++......... ...... ...........
+ ***++++++++++++++++++++++............
+ **+++++++++++++++++++++..............
+ **+++++++++++++++++++................
+ *++++++++++++++++++.................
+ *++++++++++++++++............ ...
+ *++++++++++++++..............
+ *+++....++++................
+ *.......... ...........
+ *
+ *.......... ...........
+ *+++....++++................
+ *++++++++++++++..............
+ *++++++++++++++++............ ...
+ *++++++++++++++++++.................
+ **+++++++++++++++++++................
+ **+++++++++++++++++++++..............
+ ***++++++++++++++++++++++............
+ ***++++++++++++++++++++++++......... ...... ...........
+ ****++++++++++++++++++++++++++...... .........................
+ *****++++++++++++++++++++++++++++...............................
+ *****++++++++++++++++++++++++++++++++............................
+ ******+++++++++++++++++++++++++++++++++++...........................
+ *******+++++++++++++++++++++++++++++++++++++++.......................
+ ********+++++++++++++++++++++++++++++++++++++++++++..................
+ Evaluated to 0.000000
+ ready> mandel(-0.9, -1.4, 0.02, 0.03);
+ *******************************************************************************
+ *******************************************************************************
+ *******************************************************************************
+ **********+++++++++++++++++++++************************************************
+ *+++++++++++++++++++++++++++++++++++++++***************************************
+ +++++++++++++++++++++++++++++++++++++++++++++**********************************
+ ++++++++++++++++++++++++++++++++++++++++++++++++++*****************************
+ ++++++++++++++++++++++++++++++++++++++++++++++++++++++*************************
+ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++**********************
+ +++++++++++++++++++++++++++++++++.........++++++++++++++++++*******************
+ +++++++++++++++++++++++++++++++.... ......+++++++++++++++++++****************
+ +++++++++++++++++++++++++++++....... ........+++++++++++++++++++**************
+ ++++++++++++++++++++++++++++........ ........++++++++++++++++++++************
+ +++++++++++++++++++++++++++......... .. ...+++++++++++++++++++++**********
+ ++++++++++++++++++++++++++........... ....++++++++++++++++++++++********
+ ++++++++++++++++++++++++............. .......++++++++++++++++++++++******
+ +++++++++++++++++++++++............. ........+++++++++++++++++++++++****
+ ++++++++++++++++++++++........... ..........++++++++++++++++++++++***
+ ++++++++++++++++++++........... .........++++++++++++++++++++++*
+ ++++++++++++++++++............ ...........++++++++++++++++++++
+ ++++++++++++++++............... .............++++++++++++++++++
+ ++++++++++++++................. ...............++++++++++++++++
+ ++++++++++++.................. .................++++++++++++++
+ +++++++++.................. .................+++++++++++++
+ ++++++........ . ......... ..++++++++++++
+ ++............ ...... ....++++++++++
+ .............. ...++++++++++
+ .............. ....+++++++++
+ .............. .....++++++++
+ ............. ......++++++++
+ ........... .......++++++++
+ ......... ........+++++++
+ ......... ........+++++++
+ ......... ....+++++++
+ ........ ...+++++++
+ ....... ...+++++++
+ ....+++++++
+ .....+++++++
+ ....+++++++
+ ....+++++++
+ ....+++++++
+ Evaluated to 0.000000
+ ready> ^D
+
+At this point, you may be starting to realize that Kaleidoscope is a
+real and powerful language. It may not be self-similar :), but it can be
+used to plot things that are!
+
+With this, we conclude the "adding user-defined operators" chapter of
+the tutorial. We have successfully augmented our language, adding the
+ability to extend the language in the library, and we have shown how
+this can be used to build a simple but interesting end-user application
+in Kaleidoscope. At this point, Kaleidoscope can build a variety of
+applications that are functional and can call functions with
+side-effects, but it can't actually define and mutate a variable itself.
+
+Strikingly, variable mutation is an important feature of some languages,
+and it is not at all obvious how to `add support for mutable
+variables <LangImpl7.html>`_ without having to add an "SSA construction"
+phase to your front-end. In the next chapter, we will describe how you
+can add variable mutation without building SSA in your front-end.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the if/then/else and for expressions.. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
+ # Run
+ ./toy
+
+On some platforms, you will need to specify -rdynamic or
+-Wl,--export-dynamic when linking. This ensures that symbols defined in
+the main executable are exported to the dynamic linker and so are
+available for symbol resolution at run time. This is not needed if you
+compile your support code into a shared library, although doing that
+will cause problems on Windows.
+
+Here is the code:
+
+.. code-block:: c++
+
+ #include "llvm/DerivedTypes.h"
+ #include "llvm/ExecutionEngine/ExecutionEngine.h"
+ #include "llvm/ExecutionEngine/JIT.h"
+ #include "llvm/IRBuilder.h"
+ #include "llvm/LLVMContext.h"
+ #include "llvm/Module.h"
+ #include "llvm/PassManager.h"
+ #include "llvm/Analysis/Verifier.h"
+ #include "llvm/Analysis/Passes.h"
+ #include "llvm/DataLayout.h"
+ #include "llvm/Transforms/Scalar.h"
+ #include "llvm/Support/TargetSelect.h"
+ #include <cstdio>
+ #include <string>
+ #include <map>
+ #include <vector>
+ using namespace llvm;
+
+ //===----------------------------------------------------------------------===//
+ // Lexer
+ //===----------------------------------------------------------------------===//
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5,
+
+ // control
+ tok_if = -6, tok_then = -7, tok_else = -8,
+ tok_for = -9, tok_in = -10,
+
+ // operators
+ tok_binary = -11, tok_unary = -12
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ if (IdentifierStr == "if") return tok_if;
+ if (IdentifierStr == "then") return tok_then;
+ if (IdentifierStr == "else") return tok_else;
+ if (IdentifierStr == "for") return tok_for;
+ if (IdentifierStr == "in") return tok_in;
+ if (IdentifierStr == "binary") return tok_binary;
+ if (IdentifierStr == "unary") return tok_unary;
+ return tok_identifier;
+ }
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Abstract Syntax Tree (aka Parse Tree)
+ //===----------------------------------------------------------------------===//
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *Codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ virtual Value *Codegen();
+ };
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ virtual Value *Codegen();
+ };
+
+ /// UnaryExprAST - Expression class for a unary operator.
+ class UnaryExprAST : public ExprAST {
+ char Opcode;
+ ExprAST *Operand;
+ public:
+ UnaryExprAST(char opcode, ExprAST *operand)
+ : Opcode(opcode), Operand(operand) {}
+ virtual Value *Codegen();
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ virtual Value *Codegen();
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ virtual Value *Codegen();
+ };
+
+ /// IfExprAST - Expression class for if/then/else.
+ class IfExprAST : public ExprAST {
+ ExprAST *Cond, *Then, *Else;
+ public:
+ IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
+ : Cond(cond), Then(then), Else(_else) {}
+ virtual Value *Codegen();
+ };
+
+ /// ForExprAST - Expression class for for/in.
+ class ForExprAST : public ExprAST {
+ std::string VarName;
+ ExprAST *Start, *End, *Step, *Body;
+ public:
+ ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
+ ExprAST *step, ExprAST *body)
+ : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
+ virtual Value *Codegen();
+ };
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes), as well as if it is an operator.
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ bool isOperator;
+ unsigned Precedence; // Precedence if a binary op.
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args,
+ bool isoperator = false, unsigned prec = 0)
+ : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {}
+
+ bool isUnaryOp() const { return isOperator && Args.size() == 1; }
+ bool isBinaryOp() const { return isOperator && Args.size() == 2; }
+
+ char getOperatorName() const {
+ assert(isUnaryOp() || isBinaryOp());
+ return Name[Name.size()-1];
+ }
+
+ unsigned getBinaryPrecedence() const { return Precedence; }
+
+ Function *Codegen();
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ Function *Codegen();
+ };
+
+ //===----------------------------------------------------------------------===//
+ // Parser
+ //===----------------------------------------------------------------------===//
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+ static ExprAST *ParseExpression();
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+ /// ifexpr ::= 'if' expression 'then' expression 'else' expression
+ static ExprAST *ParseIfExpr() {
+ getNextToken(); // eat the if.
+
+ // condition.
+ ExprAST *Cond = ParseExpression();
+ if (!Cond) return 0;
+
+ if (CurTok != tok_then)
+ return Error("expected then");
+ getNextToken(); // eat the then
+
+ ExprAST *Then = ParseExpression();
+ if (Then == 0) return 0;
+
+ if (CurTok != tok_else)
+ return Error("expected else");
+
+ getNextToken();
+
+ ExprAST *Else = ParseExpression();
+ if (!Else) return 0;
+
+ return new IfExprAST(Cond, Then, Else);
+ }
+
+ /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+ static ExprAST *ParseForExpr() {
+ getNextToken(); // eat the for.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after for");
+
+ std::string IdName = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '=')
+ return Error("expected '=' after for");
+ getNextToken(); // eat '='.
+
+
+ ExprAST *Start = ParseExpression();
+ if (Start == 0) return 0;
+ if (CurTok != ',')
+ return Error("expected ',' after for start value");
+ getNextToken();
+
+ ExprAST *End = ParseExpression();
+ if (End == 0) return 0;
+
+ // The step value is optional.
+ ExprAST *Step = 0;
+ if (CurTok == ',') {
+ getNextToken();
+ Step = ParseExpression();
+ if (Step == 0) return 0;
+ }
+
+ if (CurTok != tok_in)
+ return Error("expected 'in' after for");
+ getNextToken(); // eat 'in'.
+
+ ExprAST *Body = ParseExpression();
+ if (Body == 0) return 0;
+
+ return new ForExprAST(IdName, Start, End, Step, Body);
+ }
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ /// ::= ifexpr
+ /// ::= forexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ case tok_if: return ParseIfExpr();
+ case tok_for: return ParseForExpr();
+ }
+ }
+
+ /// unary
+ /// ::= primary
+ /// ::= '!' unary
+ static ExprAST *ParseUnary() {
+ // If the current token is not an operator, it must be a primary expr.
+ if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+ return ParsePrimary();
+
+ // If this is a unary operator, read it.
+ int Opc = CurTok;
+ getNextToken();
+ if (ExprAST *Operand = ParseUnary())
+ return new UnaryExprAST(Opc, Operand);
+ return 0;
+ }
+
+ /// binoprhs
+ /// ::= ('+' unary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the unary expression after the binary operator.
+ ExprAST *RHS = ParseUnary();
+ if (!RHS) return 0;
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+ }
+
+ /// expression
+ /// ::= unary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParseUnary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ /// ::= unary LETTER (id)
+ static PrototypeAST *ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return ErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_unary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected unary operator");
+ FnName = "unary";
+ FnName += (char)CurTok;
+ Kind = 1;
+ getNextToken();
+ break;
+ case tok_binary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected binary operator");
+ FnName = "binary";
+ FnName += (char)CurTok;
+ Kind = 2;
+ getNextToken();
+
+ // Read the precedence if present.
+ if (CurTok == tok_number) {
+ if (NumVal < 1 || NumVal > 100)
+ return ErrorP("Invalid precedecnce: must be 1..100");
+ BinaryPrecedence = (unsigned)NumVal;
+ getNextToken();
+ }
+ break;
+ }
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ // Verify right number of names for operator.
+ if (Kind && ArgNames.size() != Kind)
+ return ErrorP("Invalid number of operands for operator");
+
+ return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence);
+ }
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Code Generation
+ //===----------------------------------------------------------------------===//
+
+ static Module *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, Value*> NamedValues;
+ static FunctionPassManager *TheFPM;
+
+ Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+ Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ return V ? V : ErrorV("Unknown variable name");
+ }
+
+ Value *UnaryExprAST::Codegen() {
+ Value *OperandV = Operand->Codegen();
+ if (OperandV == 0) return 0;
+
+ Function *F = TheModule->getFunction(std::string("unary")+Opcode);
+ if (F == 0)
+ return ErrorV("Unknown unary operator");
+
+ return Builder.CreateCall(F, OperandV, "unop");
+ }
+
+ Value *BinaryExprAST::Codegen() {
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateFAdd(L, R, "addtmp");
+ case '-': return Builder.CreateFSub(L, R, "subtmp");
+ case '*': return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default: break;
+ }
+
+ // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+ // a call to it.
+ Function *F = TheModule->getFunction(std::string("binary")+Op);
+ assert(F && "binary operator not found!");
+
+ Value *Ops[2] = { L, R };
+ return Builder.CreateCall(F, Ops, "binop");
+ }
+
+ Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value*> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->Codegen());
+ if (ArgsV.back() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+ Value *IfExprAST::Codegen() {
+ Value *CondV = Cond->Codegen();
+ if (CondV == 0) return 0;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ CondV = Builder.CreateFCmpONE(CondV,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "ifcond");
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create blocks for the then and else cases. Insert the 'then' block at the
+ // end of the function.
+ BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
+ BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
+ BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
+
+ Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+ // Emit then value.
+ Builder.SetInsertPoint(ThenBB);
+
+ Value *ThenV = Then->Codegen();
+ if (ThenV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+ ThenBB = Builder.GetInsertBlock();
+
+ // Emit else block.
+ TheFunction->getBasicBlockList().push_back(ElseBB);
+ Builder.SetInsertPoint(ElseBB);
+
+ Value *ElseV = Else->Codegen();
+ if (ElseV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
+ ElseBB = Builder.GetInsertBlock();
+
+ // Emit merge block.
+ TheFunction->getBasicBlockList().push_back(MergeBB);
+ Builder.SetInsertPoint(MergeBB);
+ PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
+ "iftmp");
+
+ PN->addIncoming(ThenV, ThenBB);
+ PN->addIncoming(ElseV, ElseBB);
+ return PN;
+ }
+
+ Value *ForExprAST::Codegen() {
+ // Output this as:
+ // ...
+ // start = startexpr
+ // goto loop
+ // loop:
+ // variable = phi [start, loopheader], [nextvariable, loopend]
+ // ...
+ // bodyexpr
+ // ...
+ // loopend:
+ // step = stepexpr
+ // nextvariable = variable + step
+ // endcond = endexpr
+ // br endcond, loop, endloop
+ // outloop:
+
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->Codegen();
+ if (StartVal == 0) return 0;
+
+ // Make the new basic block for the loop header, inserting after current
+ // block.
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+ BasicBlock *PreheaderBB = Builder.GetInsertBlock();
+ BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
+
+ // Insert an explicit fall through from the current block to the LoopBB.
+ Builder.CreateBr(LoopBB);
+
+ // Start insertion in LoopBB.
+ Builder.SetInsertPoint(LoopBB);
+
+ // Start the PHI node with an entry for Start.
+ PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str());
+ Variable->addIncoming(StartVal, PreheaderBB);
+
+ // Within the loop, the variable is defined equal to the PHI node. If it
+ // shadows an existing variable, we have to restore it, so save it now.
+ Value *OldVal = NamedValues[VarName];
+ NamedValues[VarName] = Variable;
+
+ // Emit the body of the loop. This, like any other expr, can change the
+ // current BB. Note that we ignore the value computed by the body, but don't
+ // allow an error.
+ if (Body->Codegen() == 0)
+ return 0;
+
+ // Emit the step value.
+ Value *StepVal;
+ if (Step) {
+ StepVal = Step->Codegen();
+ if (StepVal == 0) return 0;
+ } else {
+ // If not specified, use 1.0.
+ StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
+ }
+
+ Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");
+
+ // Compute the end condition.
+ Value *EndCond = End->Codegen();
+ if (EndCond == 0) return EndCond;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ EndCond = Builder.CreateFCmpONE(EndCond,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "loopcond");
+
+ // Create the "after loop" block and insert it.
+ BasicBlock *LoopEndBB = Builder.GetInsertBlock();
+ BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
+
+ // Insert the conditional branch into the end of LoopEndBB.
+ Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+ // Any new code will be inserted in AfterBB.
+ Builder.SetInsertPoint(AfterBB);
+
+ // Add a new entry to the PHI node for the backedge.
+ Variable->addIncoming(NextVar, LoopEndBB);
+
+ // Restore the unshadowed variable.
+ if (OldVal)
+ NamedValues[VarName] = OldVal;
+ else
+ NamedValues.erase(VarName);
+
+
+ // for expr always returns 0.0.
+ return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
+ }
+
+ Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
+ Doubles, false);
+
+ Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx) {
+ AI->setName(Args[Idx]);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = AI;
+ }
+
+ return F;
+ }
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // If this is an operator, install it.
+ if (Proto->isBinaryOp())
+ BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+
+ if (Proto->isBinaryOp())
+ BinopPrecedence.erase(Proto->getOperatorName());
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Top-Level parsing and JIT Driver
+ //===----------------------------------------------------------------------===//
+
+ static ExecutionEngine *TheExecutionEngine;
+
+ static void HandleDefinition() {
+ if (FunctionAST *F = ParseDefinition()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read function definition:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (PrototypeAST *P = ParseExtern()) {
+ if (Function *F = P->Codegen()) {
+ fprintf(stderr, "Read extern: ");
+ F->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // Cast it to the right type (takes no arguments, returns a double) so we
+ // can call it as a native function.
+ double (*FP)() = (double (*)())(intptr_t)FPtr;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+ //===----------------------------------------------------------------------===//
+ // "Library" functions that can be "extern'd" from user code.
+ //===----------------------------------------------------------------------===//
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+ /// printd - printf that takes a double prints it as "%f\n", returning 0.
+ extern "C"
+ double printd(double X) {
+ printf("%f\n", X);
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Main driver code.
+ //===----------------------------------------------------------------------===//
+
+ int main() {
+ InitializeNativeTarget();
+ LLVMContext &Context = getGlobalContext();
+
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ fprintf(stderr, "ready> ");
+ getNextToken();
+
+ // Make the module, which holds all the code.
+ TheModule = new Module("my cool jit", Context);
+
+ // Create the JIT. This takes ownership of the module.
+ std::string ErrStr;
+ TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
+ if (!TheExecutionEngine) {
+ fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
+ exit(1);
+ }
+
+ FunctionPassManager OurFPM(TheModule);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Provide basic AliasAnalysis support for GVN.
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ TheFPM = 0;
+
+ // Print out all of the generated code.
+ TheModule->dump();
+
+ return 0;
+ }
+
+`Next: Extending the language: mutable variables / SSA
+construction <LangImpl7.html>`_
+
Removed: llvm/trunk/docs/tutorial/LangImpl7.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl7.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl7.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl7.html (removed)
@@ -1,2164 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Extending the Language: Mutable Variables / SSA
- construction</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Extending the Language: Mutable Variables</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 7
- <ol>
- <li><a href="#intro">Chapter 7 Introduction</a></li>
- <li><a href="#why">Why is this a hard problem?</a></li>
- <li><a href="#memory">Memory in LLVM</a></li>
- <li><a href="#kalvars">Mutable Variables in Kaleidoscope</a></li>
- <li><a href="#adjustments">Adjusting Existing Variables for
- Mutation</a></li>
- <li><a href="#assignment">New Assignment Operator</a></li>
- <li><a href="#localvars">User-defined Local Variables</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="LangImpl8.html">Chapter 8</a>: Conclusion and other useful LLVM
- tidbits</li>
-</ul>
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 7 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 7 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. In chapters 1 through 6, we've built a very
-respectable, albeit simple, <a
-href="http://en.wikipedia.org/wiki/Functional_programming">functional
-programming language</a>. In our journey, we learned some parsing techniques,
-how to build and represent an AST, how to build LLVM IR, and how to optimize
-the resultant code as well as JIT compile it.</p>
-
-<p>While Kaleidoscope is interesting as a functional language, the fact that it
-is functional makes it "too easy" to generate LLVM IR for it. In particular, a
-functional language makes it very easy to build LLVM IR directly in <a
-href="http://en.wikipedia.org/wiki/Static_single_assignment_form">SSA form</a>.
-Since LLVM requires that the input code be in SSA form, this is a very nice
-property and it is often unclear to newcomers how to generate code for an
-imperative language with mutable variables.</p>
-
-<p>The short (and happy) summary of this chapter is that there is no need for
-your front-end to build SSA form: LLVM provides highly tuned and well tested
-support for this, though the way it works is a bit unexpected for some.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="why">Why is this a hard problem?</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-To understand why mutable variables cause complexities in SSA construction,
-consider this extremely simple C example:
-</p>
-
-<div class="doc_code">
-<pre>
-int G, H;
-int test(_Bool Condition) {
- int X;
- if (Condition)
- X = G;
- else
- X = H;
- return X;
-}
-</pre>
-</div>
-
-<p>In this case, we have the variable "X", whose value depends on the path
-executed in the program. Because there are two different possible values for X
-before the return instruction, a PHI node is inserted to merge the two values.
-The LLVM IR that we want for this example looks like this:</p>
-
-<div class="doc_code">
-<pre>
- at G = weak global i32 0 ; type of @G is i32*
- at H = weak global i32 0 ; type of @H is i32*
-
-define i32 @test(i1 %Condition) {
-entry:
- br i1 %Condition, label %cond_true, label %cond_false
-
-cond_true:
- %X.0 = load i32* @G
- br label %cond_next
-
-cond_false:
- %X.1 = load i32* @H
- br label %cond_next
-
-cond_next:
- %X.2 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
- ret i32 %X.2
-}
-</pre>
-</div>
-
-<p>In this example, the loads from the G and H global variables are explicit in
-the LLVM IR, and they live in the then/else branches of the if statement
-(cond_true/cond_false). In order to merge the incoming values, the X.2 phi node
-in the cond_next block selects the right value to use based on where control
-flow is coming from: if control flow comes from the cond_false block, X.2 gets
-the value of X.1. Alternatively, if control flow comes from cond_true, it gets
-the value of X.0. The intent of this chapter is not to explain the details of
-SSA form. For more information, see one of the many <a
-href="http://en.wikipedia.org/wiki/Static_single_assignment_form">online
-references</a>.</p>
-
-<p>The question for this article is "who places the phi nodes when lowering
-assignments to mutable variables?". The issue here is that LLVM
-<em>requires</em> that its IR be in SSA form: there is no "non-ssa" mode for it.
-However, SSA construction requires non-trivial algorithms and data structures,
-so it is inconvenient and wasteful for every front-end to have to reproduce this
-logic.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="memory">Memory in LLVM</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>The 'trick' here is that while LLVM does require all register values to be
-in SSA form, it does not require (or permit) memory objects to be in SSA form.
-In the example above, note that the loads from G and H are direct accesses to
-G and H: they are not renamed or versioned. This differs from some other
-compiler systems, which do try to version memory objects. In LLVM, instead of
-encoding dataflow analysis of memory into the LLVM IR, it is handled with <a
-href="../WritingAnLLVMPass.html">Analysis Passes</a> which are computed on
-demand.</p>
-
-<p>
-With this in mind, the high-level idea is that we want to make a stack variable
-(which lives in memory, because it is on the stack) for each mutable object in
-a function. To take advantage of this trick, we need to talk about how LLVM
-represents stack variables.
-</p>
-
-<p>In LLVM, all memory accesses are explicit with load/store instructions, and
-it is carefully designed not to have (or need) an "address-of" operator. Notice
-how the type of the @G/@H global variables is actually "i32*" even though the
-variable is defined as "i32". What this means is that @G defines <em>space</em>
-for an i32 in the global data area, but its <em>name</em> actually refers to the
-address for that space. Stack variables work the same way, except that instead of
-being declared with global variable definitions, they are declared with the
-<a href="../LangRef.html#i_alloca">LLVM alloca instruction</a>:</p>
-
-<div class="doc_code">
-<pre>
-define i32 @example() {
-entry:
- %X = alloca i32 ; type of %X is i32*.
- ...
- %tmp = load i32* %X ; load the stack value %X from the stack.
- %tmp2 = add i32 %tmp, 1 ; increment it
- store i32 %tmp2, i32* %X ; store it back
- ...
-</pre>
-</div>
-
-<p>This code shows an example of how you can declare and manipulate a stack
-variable in the LLVM IR. Stack memory allocated with the alloca instruction is
-fully general: you can pass the address of the stack slot to functions, you can
-store it in other variables, etc. In our example above, we could rewrite the
-example to use the alloca technique to avoid using a PHI node:</p>
-
-<div class="doc_code">
-<pre>
- at G = weak global i32 0 ; type of @G is i32*
- at H = weak global i32 0 ; type of @H is i32*
-
-define i32 @test(i1 %Condition) {
-entry:
- %X = alloca i32 ; type of %X is i32*.
- br i1 %Condition, label %cond_true, label %cond_false
-
-cond_true:
- %X.0 = load i32* @G
- store i32 %X.0, i32* %X ; Update X
- br label %cond_next
-
-cond_false:
- %X.1 = load i32* @H
- store i32 %X.1, i32* %X ; Update X
- br label %cond_next
-
-cond_next:
- %X.2 = load i32* %X ; Read X
- ret i32 %X.2
-}
-</pre>
-</div>
-
-<p>With this, we have discovered a way to handle arbitrary mutable variables
-without the need to create Phi nodes at all:</p>
-
-<ol>
-<li>Each mutable variable becomes a stack allocation.</li>
-<li>Each read of the variable becomes a load from the stack.</li>
-<li>Each update of the variable becomes a store to the stack.</li>
-<li>Taking the address of a variable just uses the stack address directly.</li>
-</ol>
-
-<p>While this solution has solved our immediate problem, it introduced another
-one: we have now apparently introduced a lot of stack traffic for very simple
-and common operations, a major performance problem. Fortunately for us, the
-LLVM optimizer has a highly-tuned optimization pass named "mem2reg" that handles
-this case, promoting allocas like this into SSA registers, inserting Phi nodes
-as appropriate. If you run this example through the pass, for example, you'll
-get:</p>
-
-<div class="doc_code">
-<pre>
-$ <b>llvm-as < example.ll | opt -mem2reg | llvm-dis</b>
- at G = weak global i32 0
- at H = weak global i32 0
-
-define i32 @test(i1 %Condition) {
-entry:
- br i1 %Condition, label %cond_true, label %cond_false
-
-cond_true:
- %X.0 = load i32* @G
- br label %cond_next
-
-cond_false:
- %X.1 = load i32* @H
- br label %cond_next
-
-cond_next:
- %X.01 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
- ret i32 %X.01
-}
-</pre>
-</div>
-
-<p>The mem2reg pass implements the standard "iterated dominance frontier"
-algorithm for constructing SSA form and has a number of optimizations that speed
-up (very common) degenerate cases. The mem2reg optimization pass is the answer to dealing
-with mutable variables, and we highly recommend that you depend on it. Note that
-mem2reg only works on variables in certain circumstances:</p>
-
-<ol>
-<li>mem2reg is alloca-driven: it looks for allocas and if it can handle them, it
-promotes them. It does not apply to global variables or heap allocations.</li>
-
-<li>mem2reg only looks for alloca instructions in the entry block of the
-function. Being in the entry block guarantees that the alloca is only executed
-once, which makes analysis simpler.</li>
-
-<li>mem2reg only promotes allocas whose uses are direct loads and stores. If
-the address of the stack object is passed to a function, or if any funny pointer
-arithmetic is involved, the alloca will not be promoted.</li>
-
-<li>mem2reg only works on allocas of <a
-href="../LangRef.html#t_classifications">first class</a>
-values (such as pointers, scalars and vectors), and only if the array size
-of the allocation is 1 (or missing in the .ll file). mem2reg is not capable of
-promoting structs or arrays to registers. Note that the "scalarrepl" pass is
-more powerful and can promote structs, "unions", and arrays in many cases.</li>
-
-</ol>
-
-<p>
-All of these properties are easy to satisfy for most imperative languages, and
-we'll illustrate it below with Kaleidoscope. The final question you may be
-asking is: should I bother with this nonsense for my front-end? Wouldn't it be
-better if I just did SSA construction directly, avoiding use of the mem2reg
-optimization pass? In short, we strongly recommend that you use this technique
-for building SSA form, unless there is an extremely good reason not to. Using
-this technique is:</p>
-
-<ul>
-<li>Proven and well tested: llvm-gcc and clang both use this technique for local
-mutable variables. As such, the most common clients of LLVM are using this to
-handle a bulk of their variables. You can be sure that bugs are found fast and
-fixed early.</li>
-
-<li>Extremely Fast: mem2reg has a number of special cases that make it fast in
-common cases as well as fully general. For example, it has fast-paths for
-variables that are only used in a single block, variables that only have one
-assignment point, good heuristics to avoid insertion of unneeded phi nodes, etc.
-</li>
-
-<li>Needed for debug info generation: <a href="../SourceLevelDebugging.html">
-Debug information in LLVM</a> relies on having the address of the variable
-exposed so that debug info can be attached to it. This technique dovetails
-very naturally with this style of debug info.</li>
-</ul>
-
-<p>If nothing else, this makes it much easier to get your front-end up and
-running, and is very simple to implement. Lets extend Kaleidoscope with mutable
-variables now!
-</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="kalvars">Mutable Variables in Kaleidoscope</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Now that we know the sort of problem we want to tackle, lets see what this
-looks like in the context of our little Kaleidoscope language. We're going to
-add two features:</p>
-
-<ol>
-<li>The ability to mutate variables with the '=' operator.</li>
-<li>The ability to define new variables.</li>
-</ol>
-
-<p>While the first item is really what this is about, we only have variables
-for incoming arguments as well as for induction variables, and redefining those only
-goes so far :). Also, the ability to define new variables is a
-useful thing regardless of whether you will be mutating them. Here's a
-motivating example that shows how we could use these:</p>
-
-<div class="doc_code">
-<pre>
-# Define ':' for sequencing: as a low-precedence operator that ignores operands
-# and just returns the RHS.
-def binary : 1 (x y) y;
-
-# Recursive fib, we could do this before.
-def fib(x)
- if (x < 3) then
- 1
- else
- fib(x-1)+fib(x-2);
-
-# Iterative fib.
-def fibi(x)
- <b>var a = 1, b = 1, c in</b>
- (for i = 3, i < x in
- <b>c = a + b</b> :
- <b>a = b</b> :
- <b>b = c</b>) :
- b;
-
-# Call it.
-fibi(10);
-</pre>
-</div>
-
-<p>
-In order to mutate variables, we have to change our existing variables to use
-the "alloca trick". Once we have that, we'll add our new operator, then extend
-Kaleidoscope to support new variable definitions.
-</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="adjustments">Adjusting Existing Variables for Mutation</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-The symbol table in Kaleidoscope is managed at code generation time by the
-'<tt>NamedValues</tt>' map. This map currently keeps track of the LLVM "Value*"
-that holds the double value for the named variable. In order to support
-mutation, we need to change this slightly, so that it <tt>NamedValues</tt> holds
-the <em>memory location</em> of the variable in question. Note that this
-change is a refactoring: it changes the structure of the code, but does not
-(by itself) change the behavior of the compiler. All of these changes are
-isolated in the Kaleidoscope code generator.</p>
-
-<p>
-At this point in Kaleidoscope's development, it only supports variables for two
-things: incoming arguments to functions and the induction variable of 'for'
-loops. For consistency, we'll allow mutation of these variables in addition to
-other user-defined variables. This means that these will both need memory
-locations.
-</p>
-
-<p>To start our transformation of Kaleidoscope, we'll change the NamedValues
-map so that it maps to AllocaInst* instead of Value*. Once we do this, the C++
-compiler will tell us what parts of the code we need to update:</p>
-
-<div class="doc_code">
-<pre>
-static std::map<std::string, AllocaInst*> NamedValues;
-</pre>
-</div>
-
-<p>Also, since we will need to create these alloca's, we'll use a helper
-function that ensures that the allocas are created in the entry block of the
-function:</p>
-
-<div class="doc_code">
-<pre>
-/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
-/// the function. This is used for mutable variables etc.
-static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
- const std::string &VarName) {
- IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
- TheFunction->getEntryBlock().begin());
- return TmpB.CreateAlloca(Type::getDoubleTy(getGlobalContext()), 0,
- VarName.c_str());
-}
-</pre>
-</div>
-
-<p>This funny looking code creates an IRBuilder object that is pointing at
-the first instruction (.begin()) of the entry block. It then creates an alloca
-with the expected name and returns it. Because all values in Kaleidoscope are
-doubles, there is no need to pass in a type to use.</p>
-
-<p>With this in place, the first functionality change we want to make is to
-variable references. In our new scheme, variables live on the stack, so code
-generating a reference to them actually needs to produce a load from the stack
-slot:</p>
-
-<div class="doc_code">
-<pre>
-Value *VariableExprAST::Codegen() {
- // Look this variable up in the function.
- Value *V = NamedValues[Name];
- if (V == 0) return ErrorV("Unknown variable name");
-
- <b>// Load the value.
- return Builder.CreateLoad(V, Name.c_str());</b>
-}
-</pre>
-</div>
-
-<p>As you can see, this is pretty straightforward. Now we need to update the
-things that define the variables to set up the alloca. We'll start with
-<tt>ForExprAST::Codegen</tt> (see the <a href="#code">full code listing</a> for
-the unabridged code):</p>
-
-<div class="doc_code">
-<pre>
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- <b>// Create an alloca for the variable in the entry block.
- AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);</b>
-
- // Emit the start code first, without 'variable' in scope.
- Value *StartVal = Start->Codegen();
- if (StartVal == 0) return 0;
-
- <b>// Store the value into the alloca.
- Builder.CreateStore(StartVal, Alloca);</b>
- ...
-
- // Compute the end condition.
- Value *EndCond = End->Codegen();
- if (EndCond == 0) return EndCond;
-
- <b>// Reload, increment, and restore the alloca. This handles the case where
- // the body of the loop mutates the variable.
- Value *CurVar = Builder.CreateLoad(Alloca);
- Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
- Builder.CreateStore(NextVar, Alloca);</b>
- ...
-</pre>
-</div>
-
-<p>This code is virtually identical to the code <a
-href="LangImpl5.html#forcodegen">before we allowed mutable variables</a>. The
-big difference is that we no longer have to construct a PHI node, and we use
-load/store to access the variable as needed.</p>
-
-<p>To support mutable argument variables, we need to also make allocas for them.
-The code for this is also pretty simple:</p>
-
-<div class="doc_code">
-<pre>
-/// CreateArgumentAllocas - Create an alloca for each argument and register the
-/// argument in the symbol table so that references to it will succeed.
-void PrototypeAST::CreateArgumentAllocas(Function *F) {
- Function::arg_iterator AI = F->arg_begin();
- for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) {
- // Create an alloca for this variable.
- AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]);
-
- // Store the initial value into the alloca.
- Builder.CreateStore(AI, Alloca);
-
- // Add arguments to variable symbol table.
- NamedValues[Args[Idx]] = Alloca;
- }
-}
-</pre>
-</div>
-
-<p>For each argument, we make an alloca, store the input value to the function
-into the alloca, and register the alloca as the memory location for the
-argument. This method gets invoked by <tt>FunctionAST::Codegen</tt> right after
-it sets up the entry block for the function.</p>
-
-<p>The final missing piece is adding the mem2reg pass, which allows us to get
-good codegen once again:</p>
-
-<div class="doc_code">
-<pre>
- // Set up the optimizer pipeline. Start with registering info about how the
- // target lays out data structures.
- OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
- <b>// Promote allocas to registers.
- OurFPM.add(createPromoteMemoryToRegisterPass());</b>
- // Do simple "peephole" optimizations and bit-twiddling optzns.
- OurFPM.add(createInstructionCombiningPass());
- // Reassociate expressions.
- OurFPM.add(createReassociatePass());
-</pre>
-</div>
-
-<p>It is interesting to see what the code looks like before and after the
-mem2reg optimization runs. For example, this is the before/after code for our
-recursive fib function. Before the optimization:</p>
-
-<div class="doc_code">
-<pre>
-define double @fib(double %x) {
-entry:
- <b>%x1 = alloca double
- store double %x, double* %x1
- %x2 = load double* %x1</b>
- %cmptmp = fcmp ult double %x2, 3.000000e+00
- %booltmp = uitofp i1 %cmptmp to double
- %ifcond = fcmp one double %booltmp, 0.000000e+00
- br i1 %ifcond, label %then, label %else
-
-then: ; preds = %entry
- br label %ifcont
-
-else: ; preds = %entry
- <b>%x3 = load double* %x1</b>
- %subtmp = fsub double %x3, 1.000000e+00
- %calltmp = call double @fib(double %subtmp)
- <b>%x4 = load double* %x1</b>
- %subtmp5 = fsub double %x4, 2.000000e+00
- %calltmp6 = call double @fib(double %subtmp5)
- %addtmp = fadd double %calltmp, %calltmp6
- br label %ifcont
-
-ifcont: ; preds = %else, %then
- %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
- ret double %iftmp
-}
-</pre>
-</div>
-
-<p>Here there is only one variable (x, the input argument) but you can still
-see the extremely simple-minded code generation strategy we are using. In the
-entry block, an alloca is created, and the initial input value is stored into
-it. Each reference to the variable does a reload from the stack. Also, note
-that we didn't modify the if/then/else expression, so it still inserts a PHI
-node. While we could make an alloca for it, it is actually easier to create a
-PHI node for it, so we still just make the PHI.</p>
-
-<p>Here is the code after the mem2reg pass runs:</p>
-
-<div class="doc_code">
-<pre>
-define double @fib(double %x) {
-entry:
- %cmptmp = fcmp ult double <b>%x</b>, 3.000000e+00
- %booltmp = uitofp i1 %cmptmp to double
- %ifcond = fcmp one double %booltmp, 0.000000e+00
- br i1 %ifcond, label %then, label %else
-
-then:
- br label %ifcont
-
-else:
- %subtmp = fsub double <b>%x</b>, 1.000000e+00
- %calltmp = call double @fib(double %subtmp)
- %subtmp5 = fsub double <b>%x</b>, 2.000000e+00
- %calltmp6 = call double @fib(double %subtmp5)
- %addtmp = fadd double %calltmp, %calltmp6
- br label %ifcont
-
-ifcont: ; preds = %else, %then
- %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
- ret double %iftmp
-}
-</pre>
-</div>
-
-<p>This is a trivial case for mem2reg, since there are no redefinitions of the
-variable. The point of showing this is to calm your tension about inserting
-such blatent inefficiencies :).</p>
-
-<p>After the rest of the optimizers run, we get:</p>
-
-<div class="doc_code">
-<pre>
-define double @fib(double %x) {
-entry:
- %cmptmp = fcmp ult double %x, 3.000000e+00
- %booltmp = uitofp i1 %cmptmp to double
- %ifcond = fcmp ueq double %booltmp, 0.000000e+00
- br i1 %ifcond, label %else, label %ifcont
-
-else:
- %subtmp = fsub double %x, 1.000000e+00
- %calltmp = call double @fib(double %subtmp)
- %subtmp5 = fsub double %x, 2.000000e+00
- %calltmp6 = call double @fib(double %subtmp5)
- %addtmp = fadd double %calltmp, %calltmp6
- ret double %addtmp
-
-ifcont:
- ret double 1.000000e+00
-}
-</pre>
-</div>
-
-<p>Here we see that the simplifycfg pass decided to clone the return instruction
-into the end of the 'else' block. This allowed it to eliminate some branches
-and the PHI node.</p>
-
-<p>Now that all symbol table references are updated to use stack variables,
-we'll add the assignment operator.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="assignment">New Assignment Operator</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>With our current framework, adding a new assignment operator is really
-simple. We will parse it just like any other binary operator, but handle it
-internally (instead of allowing the user to define it). The first step is to
-set a precedence:</p>
-
-<div class="doc_code">
-<pre>
- int main() {
- // Install standard binary operators.
- // 1 is lowest precedence.
- <b>BinopPrecedence['='] = 2;</b>
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
-</pre>
-</div>
-
-<p>Now that the parser knows the precedence of the binary operator, it takes
-care of all the parsing and AST generation. We just need to implement codegen
-for the assignment operator. This looks like:</p>
-
-<div class="doc_code">
-<pre>
-Value *BinaryExprAST::Codegen() {
- // Special case '=' because we don't want to emit the LHS as an expression.
- if (Op == '=') {
- // Assignment requires the LHS to be an identifier.
- VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS);
- if (!LHSE)
- return ErrorV("destination of '=' must be a variable");
-</pre>
-</div>
-
-<p>Unlike the rest of the binary operators, our assignment operator doesn't
-follow the "emit LHS, emit RHS, do computation" model. As such, it is handled
-as a special case before the other binary operators are handled. The other
-strange thing is that it requires the LHS to be a variable. It is invalid to
-have "(x+1) = expr" - only things like "x = expr" are allowed.
-</p>
-
-<div class="doc_code">
-<pre>
- // Codegen the RHS.
- Value *Val = RHS->Codegen();
- if (Val == 0) return 0;
-
- // Look up the name.
- Value *Variable = NamedValues[LHSE->getName()];
- if (Variable == 0) return ErrorV("Unknown variable name");
-
- Builder.CreateStore(Val, Variable);
- return Val;
- }
- ...
-</pre>
-</div>
-
-<p>Once we have the variable, codegen'ing the assignment is straightforward:
-we emit the RHS of the assignment, create a store, and return the computed
-value. Returning a value allows for chained assignments like "X = (Y = Z)".</p>
-
-<p>Now that we have an assignment operator, we can mutate loop variables and
-arguments. For example, we can now run code like this:</p>
-
-<div class="doc_code">
-<pre>
-# Function to print a double.
-extern printd(x);
-
-# Define ':' for sequencing: as a low-precedence operator that ignores operands
-# and just returns the RHS.
-def binary : 1 (x y) y;
-
-def test(x)
- printd(x) :
- x = 4 :
- printd(x);
-
-test(123);
-</pre>
-</div>
-
-<p>When run, this example prints "123" and then "4", showing that we did
-actually mutate the value! Okay, we have now officially implemented our goal:
-getting this to work requires SSA construction in the general case. However,
-to be really useful, we want the ability to define our own local variables, lets
-add this next!
-</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="localvars">User-defined Local Variables</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Adding var/in is just like any other other extensions we made to
-Kaleidoscope: we extend the lexer, the parser, the AST and the code generator.
-The first step for adding our new 'var/in' construct is to extend the lexer.
-As before, this is pretty trivial, the code looks like this:</p>
-
-<div class="doc_code">
-<pre>
-enum Token {
- ...
- <b>// var definition
- tok_var = -13</b>
-...
-}
-...
-static int gettok() {
-...
- if (IdentifierStr == "in") return tok_in;
- if (IdentifierStr == "binary") return tok_binary;
- if (IdentifierStr == "unary") return tok_unary;
- <b>if (IdentifierStr == "var") return tok_var;</b>
- return tok_identifier;
-...
-</pre>
-</div>
-
-<p>The next step is to define the AST node that we will construct. For var/in,
-it looks like this:</p>
-
-<div class="doc_code">
-<pre>
-/// VarExprAST - Expression class for var/in
-class VarExprAST : public ExprAST {
- std::vector<std::pair<std::string, ExprAST*> > VarNames;
- ExprAST *Body;
-public:
- VarExprAST(const std::vector<std::pair<std::string, ExprAST*> > &varnames,
- ExprAST *body)
- : VarNames(varnames), Body(body) {}
-
- virtual Value *Codegen();
-};
-</pre>
-</div>
-
-<p>var/in allows a list of names to be defined all at once, and each name can
-optionally have an initializer value. As such, we capture this information in
-the VarNames vector. Also, var/in has a body, this body is allowed to access
-the variables defined by the var/in.</p>
-
-<p>With this in place, we can define the parser pieces. The first thing we do is add
-it as a primary expression:</p>
-
-<div class="doc_code">
-<pre>
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-/// ::= ifexpr
-/// ::= forexpr
-<b>/// ::= varexpr</b>
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- case tok_if: return ParseIfExpr();
- case tok_for: return ParseForExpr();
- <b>case tok_var: return ParseVarExpr();</b>
- }
-}
-</pre>
-</div>
-
-<p>Next we define ParseVarExpr:</p>
-
-<div class="doc_code">
-<pre>
-/// varexpr ::= 'var' identifier ('=' expression)?
-// (',' identifier ('=' expression)?)* 'in' expression
-static ExprAST *ParseVarExpr() {
- getNextToken(); // eat the var.
-
- std::vector<std::pair<std::string, ExprAST*> > VarNames;
-
- // At least one variable name is required.
- if (CurTok != tok_identifier)
- return Error("expected identifier after var");
-</pre>
-</div>
-
-<p>The first part of this code parses the list of identifier/expr pairs into the
-local <tt>VarNames</tt> vector.
-
-<div class="doc_code">
-<pre>
- while (1) {
- std::string Name = IdentifierStr;
- getNextToken(); // eat identifier.
-
- // Read the optional initializer.
- ExprAST *Init = 0;
- if (CurTok == '=') {
- getNextToken(); // eat the '='.
-
- Init = ParseExpression();
- if (Init == 0) return 0;
- }
-
- VarNames.push_back(std::make_pair(Name, Init));
-
- // End of var list, exit loop.
- if (CurTok != ',') break;
- getNextToken(); // eat the ','.
-
- if (CurTok != tok_identifier)
- return Error("expected identifier list after var");
- }
-</pre>
-</div>
-
-<p>Once all the variables are parsed, we then parse the body and create the
-AST node:</p>
-
-<div class="doc_code">
-<pre>
- // At this point, we have to have 'in'.
- if (CurTok != tok_in)
- return Error("expected 'in' keyword after 'var'");
- getNextToken(); // eat 'in'.
-
- ExprAST *Body = ParseExpression();
- if (Body == 0) return 0;
-
- return new VarExprAST(VarNames, Body);
-}
-</pre>
-</div>
-
-<p>Now that we can parse and represent the code, we need to support emission of
-LLVM IR for it. This code starts out with:</p>
-
-<div class="doc_code">
-<pre>
-Value *VarExprAST::Codegen() {
- std::vector<AllocaInst *> OldBindings;
-
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- // Register all variables and emit their initializer.
- for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
- const std::string &VarName = VarNames[i].first;
- ExprAST *Init = VarNames[i].second;
-</pre>
-</div>
-
-<p>Basically it loops over all the variables, installing them one at a time.
-For each variable we put into the symbol table, we remember the previous value
-that we replace in OldBindings.</p>
-
-<div class="doc_code">
-<pre>
- // Emit the initializer before adding the variable to scope, this prevents
- // the initializer from referencing the variable itself, and permits stuff
- // like this:
- // var a = 1 in
- // var a = a in ... # refers to outer 'a'.
- Value *InitVal;
- if (Init) {
- InitVal = Init->Codegen();
- if (InitVal == 0) return 0;
- } else { // If not specified, use 0.0.
- InitVal = ConstantFP::get(getGlobalContext(), APFloat(0.0));
- }
-
- AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
- Builder.CreateStore(InitVal, Alloca);
-
- // Remember the old variable binding so that we can restore the binding when
- // we unrecurse.
- OldBindings.push_back(NamedValues[VarName]);
-
- // Remember this binding.
- NamedValues[VarName] = Alloca;
- }
-</pre>
-</div>
-
-<p>There are more comments here than code. The basic idea is that we emit the
-initializer, create the alloca, then update the symbol table to point to it.
-Once all the variables are installed in the symbol table, we evaluate the body
-of the var/in expression:</p>
-
-<div class="doc_code">
-<pre>
- // Codegen the body, now that all vars are in scope.
- Value *BodyVal = Body->Codegen();
- if (BodyVal == 0) return 0;
-</pre>
-</div>
-
-<p>Finally, before returning, we restore the previous variable bindings:</p>
-
-<div class="doc_code">
-<pre>
- // Pop all our variables from scope.
- for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
- NamedValues[VarNames[i].first] = OldBindings[i];
-
- // Return the body computation.
- return BodyVal;
-}
-</pre>
-</div>
-
-<p>The end result of all of this is that we get properly scoped variable
-definitions, and we even (trivially) allow mutation of them :).</p>
-
-<p>With this, we completed what we set out to do. Our nice iterative fib
-example from the intro compiles and runs just fine. The mem2reg pass optimizes
-all of our stack variables into SSA registers, inserting PHI nodes where needed,
-and our front-end remains simple: no "iterated dominance frontier" computation
-anywhere in sight.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for our running example, enhanced with mutable
-variables and var/in support. To build this example, use:
-</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
-# Run
-./toy
-</pre>
-</div>
-
-<p>Here is the code:</p>
-
-<div class="doc_code">
-<pre>
-#include "llvm/DerivedTypes.h"
-#include "llvm/ExecutionEngine/ExecutionEngine.h"
-#include "llvm/ExecutionEngine/JIT.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/PassManager.h"
-#include "llvm/Analysis/Verifier.h"
-#include "llvm/Analysis/Passes.h"
-#include "llvm/DataLayout.h"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Support/TargetSelect.h"
-#include <cstdio>
-#include <string>
-#include <map>
-#include <vector>
-using namespace llvm;
-
-//===----------------------------------------------------------------------===//
-// Lexer
-//===----------------------------------------------------------------------===//
-
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
- tok_eof = -1,
-
- // commands
- tok_def = -2, tok_extern = -3,
-
- // primary
- tok_identifier = -4, tok_number = -5,
-
- // control
- tok_if = -6, tok_then = -7, tok_else = -8,
- tok_for = -9, tok_in = -10,
-
- // operators
- tok_binary = -11, tok_unary = -12,
-
- // var definition
- tok_var = -13
-};
-
-static std::string IdentifierStr; // Filled in if tok_identifier
-static double NumVal; // Filled in if tok_number
-
-/// gettok - Return the next token from standard input.
-static int gettok() {
- static int LastChar = ' ';
-
- // Skip any whitespace.
- while (isspace(LastChar))
- LastChar = getchar();
-
- if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
- IdentifierStr = LastChar;
- while (isalnum((LastChar = getchar())))
- IdentifierStr += LastChar;
-
- if (IdentifierStr == "def") return tok_def;
- if (IdentifierStr == "extern") return tok_extern;
- if (IdentifierStr == "if") return tok_if;
- if (IdentifierStr == "then") return tok_then;
- if (IdentifierStr == "else") return tok_else;
- if (IdentifierStr == "for") return tok_for;
- if (IdentifierStr == "in") return tok_in;
- if (IdentifierStr == "binary") return tok_binary;
- if (IdentifierStr == "unary") return tok_unary;
- if (IdentifierStr == "var") return tok_var;
- return tok_identifier;
- }
-
- if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
- std::string NumStr;
- do {
- NumStr += LastChar;
- LastChar = getchar();
- } while (isdigit(LastChar) || LastChar == '.');
-
- NumVal = strtod(NumStr.c_str(), 0);
- return tok_number;
- }
-
- if (LastChar == '#') {
- // Comment until end of line.
- do LastChar = getchar();
- while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-
- if (LastChar != EOF)
- return gettok();
- }
-
- // Check for end of file. Don't eat the EOF.
- if (LastChar == EOF)
- return tok_eof;
-
- // Otherwise, just return the character as its ascii value.
- int ThisChar = LastChar;
- LastChar = getchar();
- return ThisChar;
-}
-
-//===----------------------------------------------------------------------===//
-// Abstract Syntax Tree (aka Parse Tree)
-//===----------------------------------------------------------------------===//
-
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
- virtual ~ExprAST() {}
- virtual Value *Codegen() = 0;
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
- double Val;
-public:
- NumberExprAST(double val) : Val(val) {}
- virtual Value *Codegen();
-};
-
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
- std::string Name;
-public:
- VariableExprAST(const std::string &name) : Name(name) {}
- const std::string &getName() const { return Name; }
- virtual Value *Codegen();
-};
-
-/// UnaryExprAST - Expression class for a unary operator.
-class UnaryExprAST : public ExprAST {
- char Opcode;
- ExprAST *Operand;
-public:
- UnaryExprAST(char opcode, ExprAST *operand)
- : Opcode(opcode), Operand(operand) {}
- virtual Value *Codegen();
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
- char Op;
- ExprAST *LHS, *RHS;
-public:
- BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
- : Op(op), LHS(lhs), RHS(rhs) {}
- virtual Value *Codegen();
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
- std::string Callee;
- std::vector<ExprAST*> Args;
-public:
- CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
- : Callee(callee), Args(args) {}
- virtual Value *Codegen();
-};
-
-/// IfExprAST - Expression class for if/then/else.
-class IfExprAST : public ExprAST {
- ExprAST *Cond, *Then, *Else;
-public:
- IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
- : Cond(cond), Then(then), Else(_else) {}
- virtual Value *Codegen();
-};
-
-/// ForExprAST - Expression class for for/in.
-class ForExprAST : public ExprAST {
- std::string VarName;
- ExprAST *Start, *End, *Step, *Body;
-public:
- ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
- ExprAST *step, ExprAST *body)
- : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
- virtual Value *Codegen();
-};
-
-/// VarExprAST - Expression class for var/in
-class VarExprAST : public ExprAST {
- std::vector<std::pair<std::string, ExprAST*> > VarNames;
- ExprAST *Body;
-public:
- VarExprAST(const std::vector<std::pair<std::string, ExprAST*> > &varnames,
- ExprAST *body)
- : VarNames(varnames), Body(body) {}
-
- virtual Value *Codegen();
-};
-
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes), as well as if it is an operator.
-class PrototypeAST {
- std::string Name;
- std::vector<std::string> Args;
- bool isOperator;
- unsigned Precedence; // Precedence if a binary op.
-public:
- PrototypeAST(const std::string &name, const std::vector<std::string> &args,
- bool isoperator = false, unsigned prec = 0)
- : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {}
-
- bool isUnaryOp() const { return isOperator && Args.size() == 1; }
- bool isBinaryOp() const { return isOperator && Args.size() == 2; }
-
- char getOperatorName() const {
- assert(isUnaryOp() || isBinaryOp());
- return Name[Name.size()-1];
- }
-
- unsigned getBinaryPrecedence() const { return Precedence; }
-
- Function *Codegen();
-
- void CreateArgumentAllocas(Function *F);
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
- PrototypeAST *Proto;
- ExprAST *Body;
-public:
- FunctionAST(PrototypeAST *proto, ExprAST *body)
- : Proto(proto), Body(body) {}
-
- Function *Codegen();
-};
-
-//===----------------------------------------------------------------------===//
-// Parser
-//===----------------------------------------------------------------------===//
-
-/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
-/// token the parser is looking at. getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
- return CurTok = gettok();
-}
-
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
- if (!isascii(CurTok))
- return -1;
-
- // Make sure it's a declared binop.
- int TokPrec = BinopPrecedence[CurTok];
- if (TokPrec <= 0) return -1;
- return TokPrec;
-}
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-
-static ExprAST *ParseExpression();
-
-/// identifierexpr
-/// ::= identifier
-/// ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
- std::string IdName = IdentifierStr;
-
- getNextToken(); // eat identifier.
-
- if (CurTok != '(') // Simple variable ref.
- return new VariableExprAST(IdName);
-
- // Call.
- getNextToken(); // eat (
- std::vector<ExprAST*> Args;
- if (CurTok != ')') {
- while (1) {
- ExprAST *Arg = ParseExpression();
- if (!Arg) return 0;
- Args.push_back(Arg);
-
- if (CurTok == ')') break;
-
- if (CurTok != ',')
- return Error("Expected ')' or ',' in argument list");
- getNextToken();
- }
- }
-
- // Eat the ')'.
- getNextToken();
-
- return new CallExprAST(IdName, Args);
-}
-
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
- ExprAST *Result = new NumberExprAST(NumVal);
- getNextToken(); // consume the number
- return Result;
-}
-
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
- getNextToken(); // eat (.
- ExprAST *V = ParseExpression();
- if (!V) return 0;
-
- if (CurTok != ')')
- return Error("expected ')'");
- getNextToken(); // eat ).
- return V;
-}
-
-/// ifexpr ::= 'if' expression 'then' expression 'else' expression
-static ExprAST *ParseIfExpr() {
- getNextToken(); // eat the if.
-
- // condition.
- ExprAST *Cond = ParseExpression();
- if (!Cond) return 0;
-
- if (CurTok != tok_then)
- return Error("expected then");
- getNextToken(); // eat the then
-
- ExprAST *Then = ParseExpression();
- if (Then == 0) return 0;
-
- if (CurTok != tok_else)
- return Error("expected else");
-
- getNextToken();
-
- ExprAST *Else = ParseExpression();
- if (!Else) return 0;
-
- return new IfExprAST(Cond, Then, Else);
-}
-
-/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
-static ExprAST *ParseForExpr() {
- getNextToken(); // eat the for.
-
- if (CurTok != tok_identifier)
- return Error("expected identifier after for");
-
- std::string IdName = IdentifierStr;
- getNextToken(); // eat identifier.
-
- if (CurTok != '=')
- return Error("expected '=' after for");
- getNextToken(); // eat '='.
-
-
- ExprAST *Start = ParseExpression();
- if (Start == 0) return 0;
- if (CurTok != ',')
- return Error("expected ',' after for start value");
- getNextToken();
-
- ExprAST *End = ParseExpression();
- if (End == 0) return 0;
-
- // The step value is optional.
- ExprAST *Step = 0;
- if (CurTok == ',') {
- getNextToken();
- Step = ParseExpression();
- if (Step == 0) return 0;
- }
-
- if (CurTok != tok_in)
- return Error("expected 'in' after for");
- getNextToken(); // eat 'in'.
-
- ExprAST *Body = ParseExpression();
- if (Body == 0) return 0;
-
- return new ForExprAST(IdName, Start, End, Step, Body);
-}
-
-/// varexpr ::= 'var' identifier ('=' expression)?
-// (',' identifier ('=' expression)?)* 'in' expression
-static ExprAST *ParseVarExpr() {
- getNextToken(); // eat the var.
-
- std::vector<std::pair<std::string, ExprAST*> > VarNames;
-
- // At least one variable name is required.
- if (CurTok != tok_identifier)
- return Error("expected identifier after var");
-
- while (1) {
- std::string Name = IdentifierStr;
- getNextToken(); // eat identifier.
-
- // Read the optional initializer.
- ExprAST *Init = 0;
- if (CurTok == '=') {
- getNextToken(); // eat the '='.
-
- Init = ParseExpression();
- if (Init == 0) return 0;
- }
-
- VarNames.push_back(std::make_pair(Name, Init));
-
- // End of var list, exit loop.
- if (CurTok != ',') break;
- getNextToken(); // eat the ','.
-
- if (CurTok != tok_identifier)
- return Error("expected identifier list after var");
- }
-
- // At this point, we have to have 'in'.
- if (CurTok != tok_in)
- return Error("expected 'in' keyword after 'var'");
- getNextToken(); // eat 'in'.
-
- ExprAST *Body = ParseExpression();
- if (Body == 0) return 0;
-
- return new VarExprAST(VarNames, Body);
-}
-
-/// primary
-/// ::= identifierexpr
-/// ::= numberexpr
-/// ::= parenexpr
-/// ::= ifexpr
-/// ::= forexpr
-/// ::= varexpr
-static ExprAST *ParsePrimary() {
- switch (CurTok) {
- default: return Error("unknown token when expecting an expression");
- case tok_identifier: return ParseIdentifierExpr();
- case tok_number: return ParseNumberExpr();
- case '(': return ParseParenExpr();
- case tok_if: return ParseIfExpr();
- case tok_for: return ParseForExpr();
- case tok_var: return ParseVarExpr();
- }
-}
-
-/// unary
-/// ::= primary
-/// ::= '!' unary
-static ExprAST *ParseUnary() {
- // If the current token is not an operator, it must be a primary expr.
- if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
- return ParsePrimary();
-
- // If this is a unary operator, read it.
- int Opc = CurTok;
- getNextToken();
- if (ExprAST *Operand = ParseUnary())
- return new UnaryExprAST(Opc, Operand);
- return 0;
-}
-
-/// binoprhs
-/// ::= ('+' unary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
- // If this is a binop, find its precedence.
- while (1) {
- int TokPrec = GetTokPrecedence();
-
- // If this is a binop that binds at least as tightly as the current binop,
- // consume it, otherwise we are done.
- if (TokPrec < ExprPrec)
- return LHS;
-
- // Okay, we know this is a binop.
- int BinOp = CurTok;
- getNextToken(); // eat binop
-
- // Parse the unary expression after the binary operator.
- ExprAST *RHS = ParseUnary();
- if (!RHS) return 0;
-
- // If BinOp binds less tightly with RHS than the operator after RHS, let
- // the pending operator take RHS as its LHS.
- int NextPrec = GetTokPrecedence();
- if (TokPrec < NextPrec) {
- RHS = ParseBinOpRHS(TokPrec+1, RHS);
- if (RHS == 0) return 0;
- }
-
- // Merge LHS/RHS.
- LHS = new BinaryExprAST(BinOp, LHS, RHS);
- }
-}
-
-/// expression
-/// ::= unary binoprhs
-///
-static ExprAST *ParseExpression() {
- ExprAST *LHS = ParseUnary();
- if (!LHS) return 0;
-
- return ParseBinOpRHS(0, LHS);
-}
-
-/// prototype
-/// ::= id '(' id* ')'
-/// ::= binary LETTER number? (id, id)
-/// ::= unary LETTER (id)
-static PrototypeAST *ParsePrototype() {
- std::string FnName;
-
- unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
- unsigned BinaryPrecedence = 30;
-
- switch (CurTok) {
- default:
- return ErrorP("Expected function name in prototype");
- case tok_identifier:
- FnName = IdentifierStr;
- Kind = 0;
- getNextToken();
- break;
- case tok_unary:
- getNextToken();
- if (!isascii(CurTok))
- return ErrorP("Expected unary operator");
- FnName = "unary";
- FnName += (char)CurTok;
- Kind = 1;
- getNextToken();
- break;
- case tok_binary:
- getNextToken();
- if (!isascii(CurTok))
- return ErrorP("Expected binary operator");
- FnName = "binary";
- FnName += (char)CurTok;
- Kind = 2;
- getNextToken();
-
- // Read the precedence if present.
- if (CurTok == tok_number) {
- if (NumVal < 1 || NumVal > 100)
- return ErrorP("Invalid precedecnce: must be 1..100");
- BinaryPrecedence = (unsigned)NumVal;
- getNextToken();
- }
- break;
- }
-
- if (CurTok != '(')
- return ErrorP("Expected '(' in prototype");
-
- std::vector<std::string> ArgNames;
- while (getNextToken() == tok_identifier)
- ArgNames.push_back(IdentifierStr);
- if (CurTok != ')')
- return ErrorP("Expected ')' in prototype");
-
- // success.
- getNextToken(); // eat ')'.
-
- // Verify right number of names for operator.
- if (Kind && ArgNames.size() != Kind)
- return ErrorP("Invalid number of operands for operator");
-
- return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence);
-}
-
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
- getNextToken(); // eat def.
- PrototypeAST *Proto = ParsePrototype();
- if (Proto == 0) return 0;
-
- if (ExprAST *E = ParseExpression())
- return new FunctionAST(Proto, E);
- return 0;
-}
-
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
- if (ExprAST *E = ParseExpression()) {
- // Make an anonymous proto.
- PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
- return new FunctionAST(Proto, E);
- }
- return 0;
-}
-
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
- getNextToken(); // eat extern.
- return ParsePrototype();
-}
-
-//===----------------------------------------------------------------------===//
-// Code Generation
-//===----------------------------------------------------------------------===//
-
-static Module *TheModule;
-static IRBuilder<> Builder(getGlobalContext());
-static std::map<std::string, AllocaInst*> NamedValues;
-static FunctionPassManager *TheFPM;
-
-Value *ErrorV(const char *Str) { Error(Str); return 0; }
-
-/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
-/// the function. This is used for mutable variables etc.
-static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
- const std::string &VarName) {
- IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
- TheFunction->getEntryBlock().begin());
- return TmpB.CreateAlloca(Type::getDoubleTy(getGlobalContext()), 0,
- VarName.c_str());
-}
-
-Value *NumberExprAST::Codegen() {
- return ConstantFP::get(getGlobalContext(), APFloat(Val));
-}
-
-Value *VariableExprAST::Codegen() {
- // Look this variable up in the function.
- Value *V = NamedValues[Name];
- if (V == 0) return ErrorV("Unknown variable name");
-
- // Load the value.
- return Builder.CreateLoad(V, Name.c_str());
-}
-
-Value *UnaryExprAST::Codegen() {
- Value *OperandV = Operand->Codegen();
- if (OperandV == 0) return 0;
-
- Function *F = TheModule->getFunction(std::string("unary")+Opcode);
- if (F == 0)
- return ErrorV("Unknown unary operator");
-
- return Builder.CreateCall(F, OperandV, "unop");
-}
-
-Value *BinaryExprAST::Codegen() {
- // Special case '=' because we don't want to emit the LHS as an expression.
- if (Op == '=') {
- // Assignment requires the LHS to be an identifier.
- VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS);
- if (!LHSE)
- return ErrorV("destination of '=' must be a variable");
- // Codegen the RHS.
- Value *Val = RHS->Codegen();
- if (Val == 0) return 0;
-
- // Look up the name.
- Value *Variable = NamedValues[LHSE->getName()];
- if (Variable == 0) return ErrorV("Unknown variable name");
-
- Builder.CreateStore(Val, Variable);
- return Val;
- }
-
- Value *L = LHS->Codegen();
- Value *R = RHS->Codegen();
- if (L == 0 || R == 0) return 0;
-
- switch (Op) {
- case '+': return Builder.CreateFAdd(L, R, "addtmp");
- case '-': return Builder.CreateFSub(L, R, "subtmp");
- case '*': return Builder.CreateFMul(L, R, "multmp");
- case '<':
- L = Builder.CreateFCmpULT(L, R, "cmptmp");
- // Convert bool 0/1 to double 0.0 or 1.0
- return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
- "booltmp");
- default: break;
- }
-
- // If it wasn't a builtin binary operator, it must be a user defined one. Emit
- // a call to it.
- Function *F = TheModule->getFunction(std::string("binary")+Op);
- assert(F && "binary operator not found!");
-
- Value *Ops[2] = { L, R };
- return Builder.CreateCall(F, Ops, "binop");
-}
-
-Value *CallExprAST::Codegen() {
- // Look up the name in the global module table.
- Function *CalleeF = TheModule->getFunction(Callee);
- if (CalleeF == 0)
- return ErrorV("Unknown function referenced");
-
- // If argument mismatch error.
- if (CalleeF->arg_size() != Args.size())
- return ErrorV("Incorrect # arguments passed");
-
- std::vector<Value*> ArgsV;
- for (unsigned i = 0, e = Args.size(); i != e; ++i) {
- ArgsV.push_back(Args[i]->Codegen());
- if (ArgsV.back() == 0) return 0;
- }
-
- return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
-}
-
-Value *IfExprAST::Codegen() {
- Value *CondV = Cond->Codegen();
- if (CondV == 0) return 0;
-
- // Convert condition to a bool by comparing equal to 0.0.
- CondV = Builder.CreateFCmpONE(CondV,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "ifcond");
-
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- // Create blocks for the then and else cases. Insert the 'then' block at the
- // end of the function.
- BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
- BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
- BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
-
- Builder.CreateCondBr(CondV, ThenBB, ElseBB);
-
- // Emit then value.
- Builder.SetInsertPoint(ThenBB);
-
- Value *ThenV = Then->Codegen();
- if (ThenV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
- ThenBB = Builder.GetInsertBlock();
-
- // Emit else block.
- TheFunction->getBasicBlockList().push_back(ElseBB);
- Builder.SetInsertPoint(ElseBB);
-
- Value *ElseV = Else->Codegen();
- if (ElseV == 0) return 0;
-
- Builder.CreateBr(MergeBB);
- // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
- ElseBB = Builder.GetInsertBlock();
-
- // Emit merge block.
- TheFunction->getBasicBlockList().push_back(MergeBB);
- Builder.SetInsertPoint(MergeBB);
- PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
- "iftmp");
-
- PN->addIncoming(ThenV, ThenBB);
- PN->addIncoming(ElseV, ElseBB);
- return PN;
-}
-
-Value *ForExprAST::Codegen() {
- // Output this as:
- // var = alloca double
- // ...
- // start = startexpr
- // store start -> var
- // goto loop
- // loop:
- // ...
- // bodyexpr
- // ...
- // loopend:
- // step = stepexpr
- // endcond = endexpr
- //
- // curvar = load var
- // nextvar = curvar + step
- // store nextvar -> var
- // br endcond, loop, endloop
- // outloop:
-
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- // Create an alloca for the variable in the entry block.
- AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
-
- // Emit the start code first, without 'variable' in scope.
- Value *StartVal = Start->Codegen();
- if (StartVal == 0) return 0;
-
- // Store the value into the alloca.
- Builder.CreateStore(StartVal, Alloca);
-
- // Make the new basic block for the loop header, inserting after current
- // block.
- BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
-
- // Insert an explicit fall through from the current block to the LoopBB.
- Builder.CreateBr(LoopBB);
-
- // Start insertion in LoopBB.
- Builder.SetInsertPoint(LoopBB);
-
- // Within the loop, the variable is defined equal to the PHI node. If it
- // shadows an existing variable, we have to restore it, so save it now.
- AllocaInst *OldVal = NamedValues[VarName];
- NamedValues[VarName] = Alloca;
-
- // Emit the body of the loop. This, like any other expr, can change the
- // current BB. Note that we ignore the value computed by the body, but don't
- // allow an error.
- if (Body->Codegen() == 0)
- return 0;
-
- // Emit the step value.
- Value *StepVal;
- if (Step) {
- StepVal = Step->Codegen();
- if (StepVal == 0) return 0;
- } else {
- // If not specified, use 1.0.
- StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
- }
-
- // Compute the end condition.
- Value *EndCond = End->Codegen();
- if (EndCond == 0) return EndCond;
-
- // Reload, increment, and restore the alloca. This handles the case where
- // the body of the loop mutates the variable.
- Value *CurVar = Builder.CreateLoad(Alloca, VarName.c_str());
- Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
- Builder.CreateStore(NextVar, Alloca);
-
- // Convert condition to a bool by comparing equal to 0.0.
- EndCond = Builder.CreateFCmpONE(EndCond,
- ConstantFP::get(getGlobalContext(), APFloat(0.0)),
- "loopcond");
-
- // Create the "after loop" block and insert it.
- BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
-
- // Insert the conditional branch into the end of LoopEndBB.
- Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
-
- // Any new code will be inserted in AfterBB.
- Builder.SetInsertPoint(AfterBB);
-
- // Restore the unshadowed variable.
- if (OldVal)
- NamedValues[VarName] = OldVal;
- else
- NamedValues.erase(VarName);
-
-
- // for expr always returns 0.0.
- return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
-}
-
-Value *VarExprAST::Codegen() {
- std::vector<AllocaInst *> OldBindings;
-
- Function *TheFunction = Builder.GetInsertBlock()->getParent();
-
- // Register all variables and emit their initializer.
- for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
- const std::string &VarName = VarNames[i].first;
- ExprAST *Init = VarNames[i].second;
-
- // Emit the initializer before adding the variable to scope, this prevents
- // the initializer from referencing the variable itself, and permits stuff
- // like this:
- // var a = 1 in
- // var a = a in ... # refers to outer 'a'.
- Value *InitVal;
- if (Init) {
- InitVal = Init->Codegen();
- if (InitVal == 0) return 0;
- } else { // If not specified, use 0.0.
- InitVal = ConstantFP::get(getGlobalContext(), APFloat(0.0));
- }
-
- AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
- Builder.CreateStore(InitVal, Alloca);
-
- // Remember the old variable binding so that we can restore the binding when
- // we unrecurse.
- OldBindings.push_back(NamedValues[VarName]);
-
- // Remember this binding.
- NamedValues[VarName] = Alloca;
- }
-
- // Codegen the body, now that all vars are in scope.
- Value *BodyVal = Body->Codegen();
- if (BodyVal == 0) return 0;
-
- // Pop all our variables from scope.
- for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
- NamedValues[VarNames[i].first] = OldBindings[i];
-
- // Return the body computation.
- return BodyVal;
-}
-
-Function *PrototypeAST::Codegen() {
- // Make the function type: double(double,double) etc.
- std::vector<Type*> Doubles(Args.size(),
- Type::getDoubleTy(getGlobalContext()));
- FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
- Doubles, false);
-
- Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
-
- // If F conflicted, there was already something named 'Name'. If it has a
- // body, don't allow redefinition or reextern.
- if (F->getName() != Name) {
- // Delete the one we just made and get the existing one.
- F->eraseFromParent();
- F = TheModule->getFunction(Name);
-
- // If F already has a body, reject this.
- if (!F->empty()) {
- ErrorF("redefinition of function");
- return 0;
- }
-
- // If F took a different number of args, reject.
- if (F->arg_size() != Args.size()) {
- ErrorF("redefinition of function with different # args");
- return 0;
- }
- }
-
- // Set names for all arguments.
- unsigned Idx = 0;
- for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
- ++AI, ++Idx)
- AI->setName(Args[Idx]);
-
- return F;
-}
-
-/// CreateArgumentAllocas - Create an alloca for each argument and register the
-/// argument in the symbol table so that references to it will succeed.
-void PrototypeAST::CreateArgumentAllocas(Function *F) {
- Function::arg_iterator AI = F->arg_begin();
- for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) {
- // Create an alloca for this variable.
- AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]);
-
- // Store the initial value into the alloca.
- Builder.CreateStore(AI, Alloca);
-
- // Add arguments to variable symbol table.
- NamedValues[Args[Idx]] = Alloca;
- }
-}
-
-Function *FunctionAST::Codegen() {
- NamedValues.clear();
-
- Function *TheFunction = Proto->Codegen();
- if (TheFunction == 0)
- return 0;
-
- // If this is an operator, install it.
- if (Proto->isBinaryOp())
- BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();
-
- // Create a new basic block to start insertion into.
- BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
- Builder.SetInsertPoint(BB);
-
- // Add all arguments to the symbol table and create their allocas.
- Proto->CreateArgumentAllocas(TheFunction);
-
- if (Value *RetVal = Body->Codegen()) {
- // Finish off the function.
- Builder.CreateRet(RetVal);
-
- // Validate the generated code, checking for consistency.
- verifyFunction(*TheFunction);
-
- // Optimize the function.
- TheFPM->run(*TheFunction);
-
- return TheFunction;
- }
-
- // Error reading body, remove function.
- TheFunction->eraseFromParent();
-
- if (Proto->isBinaryOp())
- BinopPrecedence.erase(Proto->getOperatorName());
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Top-Level parsing and JIT Driver
-//===----------------------------------------------------------------------===//
-
-static ExecutionEngine *TheExecutionEngine;
-
-static void HandleDefinition() {
- if (FunctionAST *F = ParseDefinition()) {
- if (Function *LF = F->Codegen()) {
- fprintf(stderr, "Read function definition:");
- LF->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleExtern() {
- if (PrototypeAST *P = ParseExtern()) {
- if (Function *F = P->Codegen()) {
- fprintf(stderr, "Read extern: ");
- F->dump();
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-static void HandleTopLevelExpression() {
- // Evaluate a top-level expression into an anonymous function.
- if (FunctionAST *F = ParseTopLevelExpr()) {
- if (Function *LF = F->Codegen()) {
- // JIT the function, returning a function pointer.
- void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
-
- // Cast it to the right type (takes no arguments, returns a double) so we
- // can call it as a native function.
- double (*FP)() = (double (*)())(intptr_t)FPtr;
- fprintf(stderr, "Evaluated to %f\n", FP());
- }
- } else {
- // Skip token for error recovery.
- getNextToken();
- }
-}
-
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
- while (1) {
- fprintf(stderr, "ready> ");
- switch (CurTok) {
- case tok_eof: return;
- case ';': getNextToken(); break; // ignore top-level semicolons.
- case tok_def: HandleDefinition(); break;
- case tok_extern: HandleExtern(); break;
- default: HandleTopLevelExpression(); break;
- }
- }
-}
-
-//===----------------------------------------------------------------------===//
-// "Library" functions that can be "extern'd" from user code.
-//===----------------------------------------------------------------------===//
-
-/// putchard - putchar that takes a double and returns 0.
-extern "C"
-double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-
-/// printd - printf that takes a double prints it as "%f\n", returning 0.
-extern "C"
-double printd(double X) {
- printf("%f\n", X);
- return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Main driver code.
-//===----------------------------------------------------------------------===//
-
-int main() {
- InitializeNativeTarget();
- LLVMContext &Context = getGlobalContext();
-
- // Install standard binary operators.
- // 1 is lowest precedence.
- BinopPrecedence['='] = 2;
- BinopPrecedence['<'] = 10;
- BinopPrecedence['+'] = 20;
- BinopPrecedence['-'] = 20;
- BinopPrecedence['*'] = 40; // highest.
-
- // Prime the first token.
- fprintf(stderr, "ready> ");
- getNextToken();
-
- // Make the module, which holds all the code.
- TheModule = new Module("my cool jit", Context);
-
- // Create the JIT. This takes ownership of the module.
- std::string ErrStr;
- TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
- if (!TheExecutionEngine) {
- fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
- exit(1);
- }
-
- FunctionPassManager OurFPM(TheModule);
-
- // Set up the optimizer pipeline. Start with registering info about how the
- // target lays out data structures.
- OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
- // Provide basic AliasAnalysis support for GVN.
- OurFPM.add(createBasicAliasAnalysisPass());
- // Promote allocas to registers.
- OurFPM.add(createPromoteMemoryToRegisterPass());
- // Do simple "peephole" optimizations and bit-twiddling optzns.
- OurFPM.add(createInstructionCombiningPass());
- // Reassociate expressions.
- OurFPM.add(createReassociatePass());
- // Eliminate Common SubExpressions.
- OurFPM.add(createGVNPass());
- // Simplify the control flow graph (deleting unreachable blocks, etc).
- OurFPM.add(createCFGSimplificationPass());
-
- OurFPM.doInitialization();
-
- // Set the global so the code gen can use this.
- TheFPM = &OurFPM;
-
- // Run the main "interpreter loop" now.
- MainLoop();
-
- TheFPM = 0;
-
- // Print out all of the generated code.
- TheModule->dump();
-
- return 0;
-}
-</pre>
-</div>
-
-<a href="LangImpl8.html">Next: Conclusion and other useful LLVM tidbits</a>
-</div>
-
-<!-- *********************************************************************** -->
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Added: llvm/trunk/docs/tutorial/LangImpl7.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl7.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl7.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl7.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,2005 @@
+=======================================================
+Kaleidoscope: Extending the Language: Mutable Variables
+=======================================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Chapter 7 Introduction
+======================
+
+Welcome to Chapter 7 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. In chapters 1 through 6, we've built a
+very respectable, albeit simple, `functional programming
+language <http://en.wikipedia.org/wiki/Functional_programming>`_. In our
+journey, we learned some parsing techniques, how to build and represent
+an AST, how to build LLVM IR, and how to optimize the resultant code as
+well as JIT compile it.
+
+While Kaleidoscope is interesting as a functional language, the fact
+that it is functional makes it "too easy" to generate LLVM IR for it. In
+particular, a functional language makes it very easy to build LLVM IR
+directly in `SSA
+form <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+Since LLVM requires that the input code be in SSA form, this is a very
+nice property and it is often unclear to newcomers how to generate code
+for an imperative language with mutable variables.
+
+The short (and happy) summary of this chapter is that there is no need
+for your front-end to build SSA form: LLVM provides highly tuned and
+well tested support for this, though the way it works is a bit
+unexpected for some.
+
+Why is this a hard problem?
+===========================
+
+To understand why mutable variables cause complexities in SSA
+construction, consider this extremely simple C example:
+
+.. code-block:: c
+
+ int G, H;
+ int test(_Bool Condition) {
+ int X;
+ if (Condition)
+ X = G;
+ else
+ X = H;
+ return X;
+ }
+
+In this case, we have the variable "X", whose value depends on the path
+executed in the program. Because there are two different possible values
+for X before the return instruction, a PHI node is inserted to merge the
+two values. The LLVM IR that we want for this example looks like this:
+
+.. code-block:: llvm
+
+ @G = weak global i32 0 ; type of @G is i32*
+ @H = weak global i32 0 ; type of @H is i32*
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ br label %cond_next
+
+ cond_next:
+ %X.2 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+ ret i32 %X.2
+ }
+
+In this example, the loads from the G and H global variables are
+explicit in the LLVM IR, and they live in the then/else branches of the
+if statement (cond\_true/cond\_false). In order to merge the incoming
+values, the X.2 phi node in the cond\_next block selects the right value
+to use based on where control flow is coming from: if control flow comes
+from the cond\_false block, X.2 gets the value of X.1. Alternatively, if
+control flow comes from cond\_true, it gets the value of X.0. The intent
+of this chapter is not to explain the details of SSA form. For more
+information, see one of the many `online
+references <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
+
+The question for this article is "who places the phi nodes when lowering
+assignments to mutable variables?". The issue here is that LLVM
+*requires* that its IR be in SSA form: there is no "non-ssa" mode for
+it. However, SSA construction requires non-trivial algorithms and data
+structures, so it is inconvenient and wasteful for every front-end to
+have to reproduce this logic.
+
+Memory in LLVM
+==============
+
+The 'trick' here is that while LLVM does require all register values to
+be in SSA form, it does not require (or permit) memory objects to be in
+SSA form. In the example above, note that the loads from G and H are
+direct accesses to G and H: they are not renamed or versioned. This
+differs from some other compiler systems, which do try to version memory
+objects. In LLVM, instead of encoding dataflow analysis of memory into
+the LLVM IR, it is handled with `Analysis
+Passes <../WritingAnLLVMPass.html>`_ which are computed on demand.
+
+With this in mind, the high-level idea is that we want to make a stack
+variable (which lives in memory, because it is on the stack) for each
+mutable object in a function. To take advantage of this trick, we need
+to talk about how LLVM represents stack variables.
+
+In LLVM, all memory accesses are explicit with load/store instructions,
+and it is carefully designed not to have (or need) an "address-of"
+operator. Notice how the type of the @G/@H global variables is actually
+"i32\*" even though the variable is defined as "i32". What this means is
+that @G defines *space* for an i32 in the global data area, but its
+*name* actually refers to the address for that space. Stack variables
+work the same way, except that instead of being declared with global
+variable definitions, they are declared with the `LLVM alloca
+instruction <../LangRef.html#i_alloca>`_:
+
+.. code-block:: llvm
+
+ define i32 @example() {
+ entry:
+ %X = alloca i32 ; type of %X is i32*.
+ ...
+ %tmp = load i32* %X ; load the stack value %X from the stack.
+ %tmp2 = add i32 %tmp, 1 ; increment it
+ store i32 %tmp2, i32* %X ; store it back
+ ...
+
+This code shows an example of how you can declare and manipulate a stack
+variable in the LLVM IR. Stack memory allocated with the alloca
+instruction is fully general: you can pass the address of the stack slot
+to functions, you can store it in other variables, etc. In our example
+above, we could rewrite the example to use the alloca technique to avoid
+using a PHI node:
+
+.. code-block:: llvm
+
+ @G = weak global i32 0 ; type of @G is i32*
+ @H = weak global i32 0 ; type of @H is i32*
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ %X = alloca i32 ; type of %X is i32*.
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ store i32 %X.0, i32* %X ; Update X
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ store i32 %X.1, i32* %X ; Update X
+ br label %cond_next
+
+ cond_next:
+ %X.2 = load i32* %X ; Read X
+ ret i32 %X.2
+ }
+
+With this, we have discovered a way to handle arbitrary mutable
+variables without the need to create Phi nodes at all:
+
+#. Each mutable variable becomes a stack allocation.
+#. Each read of the variable becomes a load from the stack.
+#. Each update of the variable becomes a store to the stack.
+#. Taking the address of a variable just uses the stack address
+ directly.
+
+While this solution has solved our immediate problem, it introduced
+another one: we have now apparently introduced a lot of stack traffic
+for very simple and common operations, a major performance problem.
+Fortunately for us, the LLVM optimizer has a highly-tuned optimization
+pass named "mem2reg" that handles this case, promoting allocas like this
+into SSA registers, inserting Phi nodes as appropriate. If you run this
+example through the pass, for example, you'll get:
+
+.. code-block:: bash
+
+ $ llvm-as < example.ll | opt -mem2reg | llvm-dis
+ @G = weak global i32 0
+ @H = weak global i32 0
+
+ define i32 @test(i1 %Condition) {
+ entry:
+ br i1 %Condition, label %cond_true, label %cond_false
+
+ cond_true:
+ %X.0 = load i32* @G
+ br label %cond_next
+
+ cond_false:
+ %X.1 = load i32* @H
+ br label %cond_next
+
+ cond_next:
+ %X.01 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
+ ret i32 %X.01
+ }
+
+The mem2reg pass implements the standard "iterated dominance frontier"
+algorithm for constructing SSA form and has a number of optimizations
+that speed up (very common) degenerate cases. The mem2reg optimization
+pass is the answer to dealing with mutable variables, and we highly
+recommend that you depend on it. Note that mem2reg only works on
+variables in certain circumstances:
+
+#. mem2reg is alloca-driven: it looks for allocas and if it can handle
+ them, it promotes them. It does not apply to global variables or heap
+ allocations.
+#. mem2reg only looks for alloca instructions in the entry block of the
+ function. Being in the entry block guarantees that the alloca is only
+ executed once, which makes analysis simpler.
+#. mem2reg only promotes allocas whose uses are direct loads and stores.
+ If the address of the stack object is passed to a function, or if any
+ funny pointer arithmetic is involved, the alloca will not be
+ promoted.
+#. mem2reg only works on allocas of `first
+ class <../LangRef.html#t_classifications>`_ values (such as pointers,
+ scalars and vectors), and only if the array size of the allocation is
+ 1 (or missing in the .ll file). mem2reg is not capable of promoting
+ structs or arrays to registers. Note that the "scalarrepl" pass is
+ more powerful and can promote structs, "unions", and arrays in many
+ cases.
+
+All of these properties are easy to satisfy for most imperative
+languages, and we'll illustrate it below with Kaleidoscope. The final
+question you may be asking is: should I bother with this nonsense for my
+front-end? Wouldn't it be better if I just did SSA construction
+directly, avoiding use of the mem2reg optimization pass? In short, we
+strongly recommend that you use this technique for building SSA form,
+unless there is an extremely good reason not to. Using this technique
+is:
+
+- Proven and well tested: llvm-gcc and clang both use this technique
+ for local mutable variables. As such, the most common clients of LLVM
+ are using this to handle a bulk of their variables. You can be sure
+ that bugs are found fast and fixed early.
+- Extremely Fast: mem2reg has a number of special cases that make it
+ fast in common cases as well as fully general. For example, it has
+ fast-paths for variables that are only used in a single block,
+ variables that only have one assignment point, good heuristics to
+ avoid insertion of unneeded phi nodes, etc.
+- Needed for debug info generation: `Debug information in
+ LLVM <../SourceLevelDebugging.html>`_ relies on having the address of
+ the variable exposed so that debug info can be attached to it. This
+ technique dovetails very naturally with this style of debug info.
+
+If nothing else, this makes it much easier to get your front-end up and
+running, and is very simple to implement. Lets extend Kaleidoscope with
+mutable variables now!
+
+Mutable Variables in Kaleidoscope
+=================================
+
+Now that we know the sort of problem we want to tackle, lets see what
+this looks like in the context of our little Kaleidoscope language.
+We're going to add two features:
+
+#. The ability to mutate variables with the '=' operator.
+#. The ability to define new variables.
+
+While the first item is really what this is about, we only have
+variables for incoming arguments as well as for induction variables, and
+redefining those only goes so far :). Also, the ability to define new
+variables is a useful thing regardless of whether you will be mutating
+them. Here's a motivating example that shows how we could use these:
+
+::
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+ # Recursive fib, we could do this before.
+ def fib(x)
+ if (x < 3) then
+ 1
+ else
+ fib(x-1)+fib(x-2);
+
+ # Iterative fib.
+ def fibi(x)
+ var a = 1, b = 1, c in
+ (for i = 3, i < x in
+ c = a + b :
+ a = b :
+ b = c) :
+ b;
+
+ # Call it.
+ fibi(10);
+
+In order to mutate variables, we have to change our existing variables
+to use the "alloca trick". Once we have that, we'll add our new
+operator, then extend Kaleidoscope to support new variable definitions.
+
+Adjusting Existing Variables for Mutation
+=========================================
+
+The symbol table in Kaleidoscope is managed at code generation time by
+the '``NamedValues``' map. This map currently keeps track of the LLVM
+"Value\*" that holds the double value for the named variable. In order
+to support mutation, we need to change this slightly, so that it
+``NamedValues`` holds the *memory location* of the variable in question.
+Note that this change is a refactoring: it changes the structure of the
+code, but does not (by itself) change the behavior of the compiler. All
+of these changes are isolated in the Kaleidoscope code generator.
+
+At this point in Kaleidoscope's development, it only supports variables
+for two things: incoming arguments to functions and the induction
+variable of 'for' loops. For consistency, we'll allow mutation of these
+variables in addition to other user-defined variables. This means that
+these will both need memory locations.
+
+To start our transformation of Kaleidoscope, we'll change the
+NamedValues map so that it maps to AllocaInst\* instead of Value\*. Once
+we do this, the C++ compiler will tell us what parts of the code we need
+to update:
+
+.. code-block:: c++
+
+ static std::map<std::string, AllocaInst*> NamedValues;
+
+Also, since we will need to create these alloca's, we'll use a helper
+function that ensures that the allocas are created in the entry block of
+the function:
+
+.. code-block:: c++
+
+ /// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
+ /// the function. This is used for mutable variables etc.
+ static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
+ const std::string &VarName) {
+ IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
+ TheFunction->getEntryBlock().begin());
+ return TmpB.CreateAlloca(Type::getDoubleTy(getGlobalContext()), 0,
+ VarName.c_str());
+ }
+
+This funny looking code creates an IRBuilder object that is pointing at
+the first instruction (.begin()) of the entry block. It then creates an
+alloca with the expected name and returns it. Because all values in
+Kaleidoscope are doubles, there is no need to pass in a type to use.
+
+With this in place, the first functionality change we want to make is to
+variable references. In our new scheme, variables live on the stack, so
+code generating a reference to them actually needs to produce a load
+from the stack slot:
+
+.. code-block:: c++
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ if (V == 0) return ErrorV("Unknown variable name");
+
+ // Load the value.
+ return Builder.CreateLoad(V, Name.c_str());
+ }
+
+As you can see, this is pretty straightforward. Now we need to update
+the things that define the variables to set up the alloca. We'll start
+with ``ForExprAST::Codegen`` (see the `full code listing <#code>`_ for
+the unabridged code):
+
+.. code-block:: c++
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create an alloca for the variable in the entry block.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->Codegen();
+ if (StartVal == 0) return 0;
+
+ // Store the value into the alloca.
+ Builder.CreateStore(StartVal, Alloca);
+ ...
+
+ // Compute the end condition.
+ Value *EndCond = End->Codegen();
+ if (EndCond == 0) return EndCond;
+
+ // Reload, increment, and restore the alloca. This handles the case where
+ // the body of the loop mutates the variable.
+ Value *CurVar = Builder.CreateLoad(Alloca);
+ Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
+ Builder.CreateStore(NextVar, Alloca);
+ ...
+
+This code is virtually identical to the code `before we allowed mutable
+variables <LangImpl5.html#forcodegen>`_. The big difference is that we
+no longer have to construct a PHI node, and we use load/store to access
+the variable as needed.
+
+To support mutable argument variables, we need to also make allocas for
+them. The code for this is also pretty simple:
+
+.. code-block:: c++
+
+ /// CreateArgumentAllocas - Create an alloca for each argument and register the
+ /// argument in the symbol table so that references to it will succeed.
+ void PrototypeAST::CreateArgumentAllocas(Function *F) {
+ Function::arg_iterator AI = F->arg_begin();
+ for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) {
+ // Create an alloca for this variable.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]);
+
+ // Store the initial value into the alloca.
+ Builder.CreateStore(AI, Alloca);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = Alloca;
+ }
+ }
+
+For each argument, we make an alloca, store the input value to the
+function into the alloca, and register the alloca as the memory location
+for the argument. This method gets invoked by ``FunctionAST::Codegen``
+right after it sets up the entry block for the function.
+
+The final missing piece is adding the mem2reg pass, which allows us to
+get good codegen once again:
+
+.. code-block:: c++
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Promote allocas to registers.
+ OurFPM.add(createPromoteMemoryToRegisterPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+
+It is interesting to see what the code looks like before and after the
+mem2reg optimization runs. For example, this is the before/after code
+for our recursive fib function. Before the optimization:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %x1 = alloca double
+ store double %x, double* %x1
+ %x2 = load double* %x1
+ %cmptmp = fcmp ult double %x2, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then: ; preds = %entry
+ br label %ifcont
+
+ else: ; preds = %entry
+ %x3 = load double* %x1
+ %subtmp = fsub double %x3, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %x4 = load double* %x1
+ %subtmp5 = fsub double %x4, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+ ret double %iftmp
+ }
+
+Here there is only one variable (x, the input argument) but you can
+still see the extremely simple-minded code generation strategy we are
+using. In the entry block, an alloca is created, and the initial input
+value is stored into it. Each reference to the variable does a reload
+from the stack. Also, note that we didn't modify the if/then/else
+expression, so it still inserts a PHI node. While we could make an
+alloca for it, it is actually easier to create a PHI node for it, so we
+still just make the PHI.
+
+Here is the code after the mem2reg pass runs:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %cmptmp = fcmp ult double %x, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp one double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %then, label %else
+
+ then:
+ br label %ifcont
+
+ else:
+ %subtmp = fsub double %x, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %subtmp5 = fsub double %x, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ br label %ifcont
+
+ ifcont: ; preds = %else, %then
+ %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
+ ret double %iftmp
+ }
+
+This is a trivial case for mem2reg, since there are no redefinitions of
+the variable. The point of showing this is to calm your tension about
+inserting such blatent inefficiencies :).
+
+After the rest of the optimizers run, we get:
+
+.. code-block:: llvm
+
+ define double @fib(double %x) {
+ entry:
+ %cmptmp = fcmp ult double %x, 3.000000e+00
+ %booltmp = uitofp i1 %cmptmp to double
+ %ifcond = fcmp ueq double %booltmp, 0.000000e+00
+ br i1 %ifcond, label %else, label %ifcont
+
+ else:
+ %subtmp = fsub double %x, 1.000000e+00
+ %calltmp = call double @fib(double %subtmp)
+ %subtmp5 = fsub double %x, 2.000000e+00
+ %calltmp6 = call double @fib(double %subtmp5)
+ %addtmp = fadd double %calltmp, %calltmp6
+ ret double %addtmp
+
+ ifcont:
+ ret double 1.000000e+00
+ }
+
+Here we see that the simplifycfg pass decided to clone the return
+instruction into the end of the 'else' block. This allowed it to
+eliminate some branches and the PHI node.
+
+Now that all symbol table references are updated to use stack variables,
+we'll add the assignment operator.
+
+New Assignment Operator
+=======================
+
+With our current framework, adding a new assignment operator is really
+simple. We will parse it just like any other binary operator, but handle
+it internally (instead of allowing the user to define it). The first
+step is to set a precedence:
+
+.. code-block:: c++
+
+ int main() {
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['='] = 2;
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+
+Now that the parser knows the precedence of the binary operator, it
+takes care of all the parsing and AST generation. We just need to
+implement codegen for the assignment operator. This looks like:
+
+.. code-block:: c++
+
+ Value *BinaryExprAST::Codegen() {
+ // Special case '=' because we don't want to emit the LHS as an expression.
+ if (Op == '=') {
+ // Assignment requires the LHS to be an identifier.
+ VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS);
+ if (!LHSE)
+ return ErrorV("destination of '=' must be a variable");
+
+Unlike the rest of the binary operators, our assignment operator doesn't
+follow the "emit LHS, emit RHS, do computation" model. As such, it is
+handled as a special case before the other binary operators are handled.
+The other strange thing is that it requires the LHS to be a variable. It
+is invalid to have "(x+1) = expr" - only things like "x = expr" are
+allowed.
+
+.. code-block:: c++
+
+ // Codegen the RHS.
+ Value *Val = RHS->Codegen();
+ if (Val == 0) return 0;
+
+ // Look up the name.
+ Value *Variable = NamedValues[LHSE->getName()];
+ if (Variable == 0) return ErrorV("Unknown variable name");
+
+ Builder.CreateStore(Val, Variable);
+ return Val;
+ }
+ ...
+
+Once we have the variable, codegen'ing the assignment is
+straightforward: we emit the RHS of the assignment, create a store, and
+return the computed value. Returning a value allows for chained
+assignments like "X = (Y = Z)".
+
+Now that we have an assignment operator, we can mutate loop variables
+and arguments. For example, we can now run code like this:
+
+::
+
+ # Function to print a double.
+ extern printd(x);
+
+ # Define ':' for sequencing: as a low-precedence operator that ignores operands
+ # and just returns the RHS.
+ def binary : 1 (x y) y;
+
+ def test(x)
+ printd(x) :
+ x = 4 :
+ printd(x);
+
+ test(123);
+
+When run, this example prints "123" and then "4", showing that we did
+actually mutate the value! Okay, we have now officially implemented our
+goal: getting this to work requires SSA construction in the general
+case. However, to be really useful, we want the ability to define our
+own local variables, lets add this next!
+
+User-defined Local Variables
+============================
+
+Adding var/in is just like any other other extensions we made to
+Kaleidoscope: we extend the lexer, the parser, the AST and the code
+generator. The first step for adding our new 'var/in' construct is to
+extend the lexer. As before, this is pretty trivial, the code looks like
+this:
+
+.. code-block:: c++
+
+ enum Token {
+ ...
+ // var definition
+ tok_var = -13
+ ...
+ }
+ ...
+ static int gettok() {
+ ...
+ if (IdentifierStr == "in") return tok_in;
+ if (IdentifierStr == "binary") return tok_binary;
+ if (IdentifierStr == "unary") return tok_unary;
+ if (IdentifierStr == "var") return tok_var;
+ return tok_identifier;
+ ...
+
+The next step is to define the AST node that we will construct. For
+var/in, it looks like this:
+
+.. code-block:: c++
+
+ /// VarExprAST - Expression class for var/in
+ class VarExprAST : public ExprAST {
+ std::vector<std::pair<std::string, ExprAST*> > VarNames;
+ ExprAST *Body;
+ public:
+ VarExprAST(const std::vector<std::pair<std::string, ExprAST*> > &varnames,
+ ExprAST *body)
+ : VarNames(varnames), Body(body) {}
+
+ virtual Value *Codegen();
+ };
+
+var/in allows a list of names to be defined all at once, and each name
+can optionally have an initializer value. As such, we capture this
+information in the VarNames vector. Also, var/in has a body, this body
+is allowed to access the variables defined by the var/in.
+
+With this in place, we can define the parser pieces. The first thing we
+do is add it as a primary expression:
+
+.. code-block:: c++
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ /// ::= ifexpr
+ /// ::= forexpr
+ /// ::= varexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ case tok_if: return ParseIfExpr();
+ case tok_for: return ParseForExpr();
+ case tok_var: return ParseVarExpr();
+ }
+ }
+
+Next we define ParseVarExpr:
+
+.. code-block:: c++
+
+ /// varexpr ::= 'var' identifier ('=' expression)?
+ // (',' identifier ('=' expression)?)* 'in' expression
+ static ExprAST *ParseVarExpr() {
+ getNextToken(); // eat the var.
+
+ std::vector<std::pair<std::string, ExprAST*> > VarNames;
+
+ // At least one variable name is required.
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after var");
+
+The first part of this code parses the list of identifier/expr pairs
+into the local ``VarNames`` vector.
+
+.. code-block:: c++
+
+ while (1) {
+ std::string Name = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ // Read the optional initializer.
+ ExprAST *Init = 0;
+ if (CurTok == '=') {
+ getNextToken(); // eat the '='.
+
+ Init = ParseExpression();
+ if (Init == 0) return 0;
+ }
+
+ VarNames.push_back(std::make_pair(Name, Init));
+
+ // End of var list, exit loop.
+ if (CurTok != ',') break;
+ getNextToken(); // eat the ','.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier list after var");
+ }
+
+Once all the variables are parsed, we then parse the body and create the
+AST node:
+
+.. code-block:: c++
+
+ // At this point, we have to have 'in'.
+ if (CurTok != tok_in)
+ return Error("expected 'in' keyword after 'var'");
+ getNextToken(); // eat 'in'.
+
+ ExprAST *Body = ParseExpression();
+ if (Body == 0) return 0;
+
+ return new VarExprAST(VarNames, Body);
+ }
+
+Now that we can parse and represent the code, we need to support
+emission of LLVM IR for it. This code starts out with:
+
+.. code-block:: c++
+
+ Value *VarExprAST::Codegen() {
+ std::vector<AllocaInst *> OldBindings;
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Register all variables and emit their initializer.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
+ const std::string &VarName = VarNames[i].first;
+ ExprAST *Init = VarNames[i].second;
+
+Basically it loops over all the variables, installing them one at a
+time. For each variable we put into the symbol table, we remember the
+previous value that we replace in OldBindings.
+
+.. code-block:: c++
+
+ // Emit the initializer before adding the variable to scope, this prevents
+ // the initializer from referencing the variable itself, and permits stuff
+ // like this:
+ // var a = 1 in
+ // var a = a in ... # refers to outer 'a'.
+ Value *InitVal;
+ if (Init) {
+ InitVal = Init->Codegen();
+ if (InitVal == 0) return 0;
+ } else { // If not specified, use 0.0.
+ InitVal = ConstantFP::get(getGlobalContext(), APFloat(0.0));
+ }
+
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+ Builder.CreateStore(InitVal, Alloca);
+
+ // Remember the old variable binding so that we can restore the binding when
+ // we unrecurse.
+ OldBindings.push_back(NamedValues[VarName]);
+
+ // Remember this binding.
+ NamedValues[VarName] = Alloca;
+ }
+
+There are more comments here than code. The basic idea is that we emit
+the initializer, create the alloca, then update the symbol table to
+point to it. Once all the variables are installed in the symbol table,
+we evaluate the body of the var/in expression:
+
+.. code-block:: c++
+
+ // Codegen the body, now that all vars are in scope.
+ Value *BodyVal = Body->Codegen();
+ if (BodyVal == 0) return 0;
+
+Finally, before returning, we restore the previous variable bindings:
+
+.. code-block:: c++
+
+ // Pop all our variables from scope.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
+ NamedValues[VarNames[i].first] = OldBindings[i];
+
+ // Return the body computation.
+ return BodyVal;
+ }
+
+The end result of all of this is that we get properly scoped variable
+definitions, and we even (trivially) allow mutation of them :).
+
+With this, we completed what we set out to do. Our nice iterative fib
+example from the intro compiles and runs just fine. The mem2reg pass
+optimizes all of our stack variables into SSA registers, inserting PHI
+nodes where needed, and our front-end remains simple: no "iterated
+dominance frontier" computation anywhere in sight.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+mutable variables and var/in support. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
+ # Run
+ ./toy
+
+Here is the code:
+
+.. code-block:: c++
+
+ #include "llvm/DerivedTypes.h"
+ #include "llvm/ExecutionEngine/ExecutionEngine.h"
+ #include "llvm/ExecutionEngine/JIT.h"
+ #include "llvm/IRBuilder.h"
+ #include "llvm/LLVMContext.h"
+ #include "llvm/Module.h"
+ #include "llvm/PassManager.h"
+ #include "llvm/Analysis/Verifier.h"
+ #include "llvm/Analysis/Passes.h"
+ #include "llvm/DataLayout.h"
+ #include "llvm/Transforms/Scalar.h"
+ #include "llvm/Support/TargetSelect.h"
+ #include <cstdio>
+ #include <string>
+ #include <map>
+ #include <vector>
+ using namespace llvm;
+
+ //===----------------------------------------------------------------------===//
+ // Lexer
+ //===----------------------------------------------------------------------===//
+
+ // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+ // of these for known things.
+ enum Token {
+ tok_eof = -1,
+
+ // commands
+ tok_def = -2, tok_extern = -3,
+
+ // primary
+ tok_identifier = -4, tok_number = -5,
+
+ // control
+ tok_if = -6, tok_then = -7, tok_else = -8,
+ tok_for = -9, tok_in = -10,
+
+ // operators
+ tok_binary = -11, tok_unary = -12,
+
+ // var definition
+ tok_var = -13
+ };
+
+ static std::string IdentifierStr; // Filled in if tok_identifier
+ static double NumVal; // Filled in if tok_number
+
+ /// gettok - Return the next token from standard input.
+ static int gettok() {
+ static int LastChar = ' ';
+
+ // Skip any whitespace.
+ while (isspace(LastChar))
+ LastChar = getchar();
+
+ if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+ IdentifierStr = LastChar;
+ while (isalnum((LastChar = getchar())))
+ IdentifierStr += LastChar;
+
+ if (IdentifierStr == "def") return tok_def;
+ if (IdentifierStr == "extern") return tok_extern;
+ if (IdentifierStr == "if") return tok_if;
+ if (IdentifierStr == "then") return tok_then;
+ if (IdentifierStr == "else") return tok_else;
+ if (IdentifierStr == "for") return tok_for;
+ if (IdentifierStr == "in") return tok_in;
+ if (IdentifierStr == "binary") return tok_binary;
+ if (IdentifierStr == "unary") return tok_unary;
+ if (IdentifierStr == "var") return tok_var;
+ return tok_identifier;
+ }
+
+ if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+ std::string NumStr;
+ do {
+ NumStr += LastChar;
+ LastChar = getchar();
+ } while (isdigit(LastChar) || LastChar == '.');
+
+ NumVal = strtod(NumStr.c_str(), 0);
+ return tok_number;
+ }
+
+ if (LastChar == '#') {
+ // Comment until end of line.
+ do LastChar = getchar();
+ while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+ if (LastChar != EOF)
+ return gettok();
+ }
+
+ // Check for end of file. Don't eat the EOF.
+ if (LastChar == EOF)
+ return tok_eof;
+
+ // Otherwise, just return the character as its ascii value.
+ int ThisChar = LastChar;
+ LastChar = getchar();
+ return ThisChar;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Abstract Syntax Tree (aka Parse Tree)
+ //===----------------------------------------------------------------------===//
+
+ /// ExprAST - Base class for all expression nodes.
+ class ExprAST {
+ public:
+ virtual ~ExprAST() {}
+ virtual Value *Codegen() = 0;
+ };
+
+ /// NumberExprAST - Expression class for numeric literals like "1.0".
+ class NumberExprAST : public ExprAST {
+ double Val;
+ public:
+ NumberExprAST(double val) : Val(val) {}
+ virtual Value *Codegen();
+ };
+
+ /// VariableExprAST - Expression class for referencing a variable, like "a".
+ class VariableExprAST : public ExprAST {
+ std::string Name;
+ public:
+ VariableExprAST(const std::string &name) : Name(name) {}
+ const std::string &getName() const { return Name; }
+ virtual Value *Codegen();
+ };
+
+ /// UnaryExprAST - Expression class for a unary operator.
+ class UnaryExprAST : public ExprAST {
+ char Opcode;
+ ExprAST *Operand;
+ public:
+ UnaryExprAST(char opcode, ExprAST *operand)
+ : Opcode(opcode), Operand(operand) {}
+ virtual Value *Codegen();
+ };
+
+ /// BinaryExprAST - Expression class for a binary operator.
+ class BinaryExprAST : public ExprAST {
+ char Op;
+ ExprAST *LHS, *RHS;
+ public:
+ BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
+ : Op(op), LHS(lhs), RHS(rhs) {}
+ virtual Value *Codegen();
+ };
+
+ /// CallExprAST - Expression class for function calls.
+ class CallExprAST : public ExprAST {
+ std::string Callee;
+ std::vector<ExprAST*> Args;
+ public:
+ CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
+ : Callee(callee), Args(args) {}
+ virtual Value *Codegen();
+ };
+
+ /// IfExprAST - Expression class for if/then/else.
+ class IfExprAST : public ExprAST {
+ ExprAST *Cond, *Then, *Else;
+ public:
+ IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else)
+ : Cond(cond), Then(then), Else(_else) {}
+ virtual Value *Codegen();
+ };
+
+ /// ForExprAST - Expression class for for/in.
+ class ForExprAST : public ExprAST {
+ std::string VarName;
+ ExprAST *Start, *End, *Step, *Body;
+ public:
+ ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end,
+ ExprAST *step, ExprAST *body)
+ : VarName(varname), Start(start), End(end), Step(step), Body(body) {}
+ virtual Value *Codegen();
+ };
+
+ /// VarExprAST - Expression class for var/in
+ class VarExprAST : public ExprAST {
+ std::vector<std::pair<std::string, ExprAST*> > VarNames;
+ ExprAST *Body;
+ public:
+ VarExprAST(const std::vector<std::pair<std::string, ExprAST*> > &varnames,
+ ExprAST *body)
+ : VarNames(varnames), Body(body) {}
+
+ virtual Value *Codegen();
+ };
+
+ /// PrototypeAST - This class represents the "prototype" for a function,
+ /// which captures its name, and its argument names (thus implicitly the number
+ /// of arguments the function takes), as well as if it is an operator.
+ class PrototypeAST {
+ std::string Name;
+ std::vector<std::string> Args;
+ bool isOperator;
+ unsigned Precedence; // Precedence if a binary op.
+ public:
+ PrototypeAST(const std::string &name, const std::vector<std::string> &args,
+ bool isoperator = false, unsigned prec = 0)
+ : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {}
+
+ bool isUnaryOp() const { return isOperator && Args.size() == 1; }
+ bool isBinaryOp() const { return isOperator && Args.size() == 2; }
+
+ char getOperatorName() const {
+ assert(isUnaryOp() || isBinaryOp());
+ return Name[Name.size()-1];
+ }
+
+ unsigned getBinaryPrecedence() const { return Precedence; }
+
+ Function *Codegen();
+
+ void CreateArgumentAllocas(Function *F);
+ };
+
+ /// FunctionAST - This class represents a function definition itself.
+ class FunctionAST {
+ PrototypeAST *Proto;
+ ExprAST *Body;
+ public:
+ FunctionAST(PrototypeAST *proto, ExprAST *body)
+ : Proto(proto), Body(body) {}
+
+ Function *Codegen();
+ };
+
+ //===----------------------------------------------------------------------===//
+ // Parser
+ //===----------------------------------------------------------------------===//
+
+ /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
+ /// token the parser is looking at. getNextToken reads another token from the
+ /// lexer and updates CurTok with its results.
+ static int CurTok;
+ static int getNextToken() {
+ return CurTok = gettok();
+ }
+
+ /// BinopPrecedence - This holds the precedence for each binary operator that is
+ /// defined.
+ static std::map<char, int> BinopPrecedence;
+
+ /// GetTokPrecedence - Get the precedence of the pending binary operator token.
+ static int GetTokPrecedence() {
+ if (!isascii(CurTok))
+ return -1;
+
+ // Make sure it's a declared binop.
+ int TokPrec = BinopPrecedence[CurTok];
+ if (TokPrec <= 0) return -1;
+ return TokPrec;
+ }
+
+ /// Error* - These are little helper functions for error handling.
+ ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
+ PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
+ FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
+
+ static ExprAST *ParseExpression();
+
+ /// identifierexpr
+ /// ::= identifier
+ /// ::= identifier '(' expression* ')'
+ static ExprAST *ParseIdentifierExpr() {
+ std::string IdName = IdentifierStr;
+
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '(') // Simple variable ref.
+ return new VariableExprAST(IdName);
+
+ // Call.
+ getNextToken(); // eat (
+ std::vector<ExprAST*> Args;
+ if (CurTok != ')') {
+ while (1) {
+ ExprAST *Arg = ParseExpression();
+ if (!Arg) return 0;
+ Args.push_back(Arg);
+
+ if (CurTok == ')') break;
+
+ if (CurTok != ',')
+ return Error("Expected ')' or ',' in argument list");
+ getNextToken();
+ }
+ }
+
+ // Eat the ')'.
+ getNextToken();
+
+ return new CallExprAST(IdName, Args);
+ }
+
+ /// numberexpr ::= number
+ static ExprAST *ParseNumberExpr() {
+ ExprAST *Result = new NumberExprAST(NumVal);
+ getNextToken(); // consume the number
+ return Result;
+ }
+
+ /// parenexpr ::= '(' expression ')'
+ static ExprAST *ParseParenExpr() {
+ getNextToken(); // eat (.
+ ExprAST *V = ParseExpression();
+ if (!V) return 0;
+
+ if (CurTok != ')')
+ return Error("expected ')'");
+ getNextToken(); // eat ).
+ return V;
+ }
+
+ /// ifexpr ::= 'if' expression 'then' expression 'else' expression
+ static ExprAST *ParseIfExpr() {
+ getNextToken(); // eat the if.
+
+ // condition.
+ ExprAST *Cond = ParseExpression();
+ if (!Cond) return 0;
+
+ if (CurTok != tok_then)
+ return Error("expected then");
+ getNextToken(); // eat the then
+
+ ExprAST *Then = ParseExpression();
+ if (Then == 0) return 0;
+
+ if (CurTok != tok_else)
+ return Error("expected else");
+
+ getNextToken();
+
+ ExprAST *Else = ParseExpression();
+ if (!Else) return 0;
+
+ return new IfExprAST(Cond, Then, Else);
+ }
+
+ /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+ static ExprAST *ParseForExpr() {
+ getNextToken(); // eat the for.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after for");
+
+ std::string IdName = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ if (CurTok != '=')
+ return Error("expected '=' after for");
+ getNextToken(); // eat '='.
+
+
+ ExprAST *Start = ParseExpression();
+ if (Start == 0) return 0;
+ if (CurTok != ',')
+ return Error("expected ',' after for start value");
+ getNextToken();
+
+ ExprAST *End = ParseExpression();
+ if (End == 0) return 0;
+
+ // The step value is optional.
+ ExprAST *Step = 0;
+ if (CurTok == ',') {
+ getNextToken();
+ Step = ParseExpression();
+ if (Step == 0) return 0;
+ }
+
+ if (CurTok != tok_in)
+ return Error("expected 'in' after for");
+ getNextToken(); // eat 'in'.
+
+ ExprAST *Body = ParseExpression();
+ if (Body == 0) return 0;
+
+ return new ForExprAST(IdName, Start, End, Step, Body);
+ }
+
+ /// varexpr ::= 'var' identifier ('=' expression)?
+ // (',' identifier ('=' expression)?)* 'in' expression
+ static ExprAST *ParseVarExpr() {
+ getNextToken(); // eat the var.
+
+ std::vector<std::pair<std::string, ExprAST*> > VarNames;
+
+ // At least one variable name is required.
+ if (CurTok != tok_identifier)
+ return Error("expected identifier after var");
+
+ while (1) {
+ std::string Name = IdentifierStr;
+ getNextToken(); // eat identifier.
+
+ // Read the optional initializer.
+ ExprAST *Init = 0;
+ if (CurTok == '=') {
+ getNextToken(); // eat the '='.
+
+ Init = ParseExpression();
+ if (Init == 0) return 0;
+ }
+
+ VarNames.push_back(std::make_pair(Name, Init));
+
+ // End of var list, exit loop.
+ if (CurTok != ',') break;
+ getNextToken(); // eat the ','.
+
+ if (CurTok != tok_identifier)
+ return Error("expected identifier list after var");
+ }
+
+ // At this point, we have to have 'in'.
+ if (CurTok != tok_in)
+ return Error("expected 'in' keyword after 'var'");
+ getNextToken(); // eat 'in'.
+
+ ExprAST *Body = ParseExpression();
+ if (Body == 0) return 0;
+
+ return new VarExprAST(VarNames, Body);
+ }
+
+ /// primary
+ /// ::= identifierexpr
+ /// ::= numberexpr
+ /// ::= parenexpr
+ /// ::= ifexpr
+ /// ::= forexpr
+ /// ::= varexpr
+ static ExprAST *ParsePrimary() {
+ switch (CurTok) {
+ default: return Error("unknown token when expecting an expression");
+ case tok_identifier: return ParseIdentifierExpr();
+ case tok_number: return ParseNumberExpr();
+ case '(': return ParseParenExpr();
+ case tok_if: return ParseIfExpr();
+ case tok_for: return ParseForExpr();
+ case tok_var: return ParseVarExpr();
+ }
+ }
+
+ /// unary
+ /// ::= primary
+ /// ::= '!' unary
+ static ExprAST *ParseUnary() {
+ // If the current token is not an operator, it must be a primary expr.
+ if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+ return ParsePrimary();
+
+ // If this is a unary operator, read it.
+ int Opc = CurTok;
+ getNextToken();
+ if (ExprAST *Operand = ParseUnary())
+ return new UnaryExprAST(Opc, Operand);
+ return 0;
+ }
+
+ /// binoprhs
+ /// ::= ('+' unary)*
+ static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
+ // If this is a binop, find its precedence.
+ while (1) {
+ int TokPrec = GetTokPrecedence();
+
+ // If this is a binop that binds at least as tightly as the current binop,
+ // consume it, otherwise we are done.
+ if (TokPrec < ExprPrec)
+ return LHS;
+
+ // Okay, we know this is a binop.
+ int BinOp = CurTok;
+ getNextToken(); // eat binop
+
+ // Parse the unary expression after the binary operator.
+ ExprAST *RHS = ParseUnary();
+ if (!RHS) return 0;
+
+ // If BinOp binds less tightly with RHS than the operator after RHS, let
+ // the pending operator take RHS as its LHS.
+ int NextPrec = GetTokPrecedence();
+ if (TokPrec < NextPrec) {
+ RHS = ParseBinOpRHS(TokPrec+1, RHS);
+ if (RHS == 0) return 0;
+ }
+
+ // Merge LHS/RHS.
+ LHS = new BinaryExprAST(BinOp, LHS, RHS);
+ }
+ }
+
+ /// expression
+ /// ::= unary binoprhs
+ ///
+ static ExprAST *ParseExpression() {
+ ExprAST *LHS = ParseUnary();
+ if (!LHS) return 0;
+
+ return ParseBinOpRHS(0, LHS);
+ }
+
+ /// prototype
+ /// ::= id '(' id* ')'
+ /// ::= binary LETTER number? (id, id)
+ /// ::= unary LETTER (id)
+ static PrototypeAST *ParsePrototype() {
+ std::string FnName;
+
+ unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+ unsigned BinaryPrecedence = 30;
+
+ switch (CurTok) {
+ default:
+ return ErrorP("Expected function name in prototype");
+ case tok_identifier:
+ FnName = IdentifierStr;
+ Kind = 0;
+ getNextToken();
+ break;
+ case tok_unary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected unary operator");
+ FnName = "unary";
+ FnName += (char)CurTok;
+ Kind = 1;
+ getNextToken();
+ break;
+ case tok_binary:
+ getNextToken();
+ if (!isascii(CurTok))
+ return ErrorP("Expected binary operator");
+ FnName = "binary";
+ FnName += (char)CurTok;
+ Kind = 2;
+ getNextToken();
+
+ // Read the precedence if present.
+ if (CurTok == tok_number) {
+ if (NumVal < 1 || NumVal > 100)
+ return ErrorP("Invalid precedecnce: must be 1..100");
+ BinaryPrecedence = (unsigned)NumVal;
+ getNextToken();
+ }
+ break;
+ }
+
+ if (CurTok != '(')
+ return ErrorP("Expected '(' in prototype");
+
+ std::vector<std::string> ArgNames;
+ while (getNextToken() == tok_identifier)
+ ArgNames.push_back(IdentifierStr);
+ if (CurTok != ')')
+ return ErrorP("Expected ')' in prototype");
+
+ // success.
+ getNextToken(); // eat ')'.
+
+ // Verify right number of names for operator.
+ if (Kind && ArgNames.size() != Kind)
+ return ErrorP("Invalid number of operands for operator");
+
+ return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence);
+ }
+
+ /// definition ::= 'def' prototype expression
+ static FunctionAST *ParseDefinition() {
+ getNextToken(); // eat def.
+ PrototypeAST *Proto = ParsePrototype();
+ if (Proto == 0) return 0;
+
+ if (ExprAST *E = ParseExpression())
+ return new FunctionAST(Proto, E);
+ return 0;
+ }
+
+ /// toplevelexpr ::= expression
+ static FunctionAST *ParseTopLevelExpr() {
+ if (ExprAST *E = ParseExpression()) {
+ // Make an anonymous proto.
+ PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
+ return new FunctionAST(Proto, E);
+ }
+ return 0;
+ }
+
+ /// external ::= 'extern' prototype
+ static PrototypeAST *ParseExtern() {
+ getNextToken(); // eat extern.
+ return ParsePrototype();
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Code Generation
+ //===----------------------------------------------------------------------===//
+
+ static Module *TheModule;
+ static IRBuilder<> Builder(getGlobalContext());
+ static std::map<std::string, AllocaInst*> NamedValues;
+ static FunctionPassManager *TheFPM;
+
+ Value *ErrorV(const char *Str) { Error(Str); return 0; }
+
+ /// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
+ /// the function. This is used for mutable variables etc.
+ static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
+ const std::string &VarName) {
+ IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
+ TheFunction->getEntryBlock().begin());
+ return TmpB.CreateAlloca(Type::getDoubleTy(getGlobalContext()), 0,
+ VarName.c_str());
+ }
+
+ Value *NumberExprAST::Codegen() {
+ return ConstantFP::get(getGlobalContext(), APFloat(Val));
+ }
+
+ Value *VariableExprAST::Codegen() {
+ // Look this variable up in the function.
+ Value *V = NamedValues[Name];
+ if (V == 0) return ErrorV("Unknown variable name");
+
+ // Load the value.
+ return Builder.CreateLoad(V, Name.c_str());
+ }
+
+ Value *UnaryExprAST::Codegen() {
+ Value *OperandV = Operand->Codegen();
+ if (OperandV == 0) return 0;
+
+ Function *F = TheModule->getFunction(std::string("unary")+Opcode);
+ if (F == 0)
+ return ErrorV("Unknown unary operator");
+
+ return Builder.CreateCall(F, OperandV, "unop");
+ }
+
+ Value *BinaryExprAST::Codegen() {
+ // Special case '=' because we don't want to emit the LHS as an expression.
+ if (Op == '=') {
+ // Assignment requires the LHS to be an identifier.
+ VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS);
+ if (!LHSE)
+ return ErrorV("destination of '=' must be a variable");
+ // Codegen the RHS.
+ Value *Val = RHS->Codegen();
+ if (Val == 0) return 0;
+
+ // Look up the name.
+ Value *Variable = NamedValues[LHSE->getName()];
+ if (Variable == 0) return ErrorV("Unknown variable name");
+
+ Builder.CreateStore(Val, Variable);
+ return Val;
+ }
+
+ Value *L = LHS->Codegen();
+ Value *R = RHS->Codegen();
+ if (L == 0 || R == 0) return 0;
+
+ switch (Op) {
+ case '+': return Builder.CreateFAdd(L, R, "addtmp");
+ case '-': return Builder.CreateFSub(L, R, "subtmp");
+ case '*': return Builder.CreateFMul(L, R, "multmp");
+ case '<':
+ L = Builder.CreateFCmpULT(L, R, "cmptmp");
+ // Convert bool 0/1 to double 0.0 or 1.0
+ return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
+ "booltmp");
+ default: break;
+ }
+
+ // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+ // a call to it.
+ Function *F = TheModule->getFunction(std::string("binary")+Op);
+ assert(F && "binary operator not found!");
+
+ Value *Ops[2] = { L, R };
+ return Builder.CreateCall(F, Ops, "binop");
+ }
+
+ Value *CallExprAST::Codegen() {
+ // Look up the name in the global module table.
+ Function *CalleeF = TheModule->getFunction(Callee);
+ if (CalleeF == 0)
+ return ErrorV("Unknown function referenced");
+
+ // If argument mismatch error.
+ if (CalleeF->arg_size() != Args.size())
+ return ErrorV("Incorrect # arguments passed");
+
+ std::vector<Value*> ArgsV;
+ for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+ ArgsV.push_back(Args[i]->Codegen());
+ if (ArgsV.back() == 0) return 0;
+ }
+
+ return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+ }
+
+ Value *IfExprAST::Codegen() {
+ Value *CondV = Cond->Codegen();
+ if (CondV == 0) return 0;
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ CondV = Builder.CreateFCmpONE(CondV,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "ifcond");
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create blocks for the then and else cases. Insert the 'then' block at the
+ // end of the function.
+ BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction);
+ BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
+ BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");
+
+ Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+ // Emit then value.
+ Builder.SetInsertPoint(ThenBB);
+
+ Value *ThenV = Then->Codegen();
+ if (ThenV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+ ThenBB = Builder.GetInsertBlock();
+
+ // Emit else block.
+ TheFunction->getBasicBlockList().push_back(ElseBB);
+ Builder.SetInsertPoint(ElseBB);
+
+ Value *ElseV = Else->Codegen();
+ if (ElseV == 0) return 0;
+
+ Builder.CreateBr(MergeBB);
+ // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
+ ElseBB = Builder.GetInsertBlock();
+
+ // Emit merge block.
+ TheFunction->getBasicBlockList().push_back(MergeBB);
+ Builder.SetInsertPoint(MergeBB);
+ PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2,
+ "iftmp");
+
+ PN->addIncoming(ThenV, ThenBB);
+ PN->addIncoming(ElseV, ElseBB);
+ return PN;
+ }
+
+ Value *ForExprAST::Codegen() {
+ // Output this as:
+ // var = alloca double
+ // ...
+ // start = startexpr
+ // store start -> var
+ // goto loop
+ // loop:
+ // ...
+ // bodyexpr
+ // ...
+ // loopend:
+ // step = stepexpr
+ // endcond = endexpr
+ //
+ // curvar = load var
+ // nextvar = curvar + step
+ // store nextvar -> var
+ // br endcond, loop, endloop
+ // outloop:
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Create an alloca for the variable in the entry block.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+
+ // Emit the start code first, without 'variable' in scope.
+ Value *StartVal = Start->Codegen();
+ if (StartVal == 0) return 0;
+
+ // Store the value into the alloca.
+ Builder.CreateStore(StartVal, Alloca);
+
+ // Make the new basic block for the loop header, inserting after current
+ // block.
+ BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction);
+
+ // Insert an explicit fall through from the current block to the LoopBB.
+ Builder.CreateBr(LoopBB);
+
+ // Start insertion in LoopBB.
+ Builder.SetInsertPoint(LoopBB);
+
+ // Within the loop, the variable is defined equal to the PHI node. If it
+ // shadows an existing variable, we have to restore it, so save it now.
+ AllocaInst *OldVal = NamedValues[VarName];
+ NamedValues[VarName] = Alloca;
+
+ // Emit the body of the loop. This, like any other expr, can change the
+ // current BB. Note that we ignore the value computed by the body, but don't
+ // allow an error.
+ if (Body->Codegen() == 0)
+ return 0;
+
+ // Emit the step value.
+ Value *StepVal;
+ if (Step) {
+ StepVal = Step->Codegen();
+ if (StepVal == 0) return 0;
+ } else {
+ // If not specified, use 1.0.
+ StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
+ }
+
+ // Compute the end condition.
+ Value *EndCond = End->Codegen();
+ if (EndCond == 0) return EndCond;
+
+ // Reload, increment, and restore the alloca. This handles the case where
+ // the body of the loop mutates the variable.
+ Value *CurVar = Builder.CreateLoad(Alloca, VarName.c_str());
+ Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
+ Builder.CreateStore(NextVar, Alloca);
+
+ // Convert condition to a bool by comparing equal to 0.0.
+ EndCond = Builder.CreateFCmpONE(EndCond,
+ ConstantFP::get(getGlobalContext(), APFloat(0.0)),
+ "loopcond");
+
+ // Create the "after loop" block and insert it.
+ BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);
+
+ // Insert the conditional branch into the end of LoopEndBB.
+ Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+ // Any new code will be inserted in AfterBB.
+ Builder.SetInsertPoint(AfterBB);
+
+ // Restore the unshadowed variable.
+ if (OldVal)
+ NamedValues[VarName] = OldVal;
+ else
+ NamedValues.erase(VarName);
+
+
+ // for expr always returns 0.0.
+ return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
+ }
+
+ Value *VarExprAST::Codegen() {
+ std::vector<AllocaInst *> OldBindings;
+
+ Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+ // Register all variables and emit their initializer.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
+ const std::string &VarName = VarNames[i].first;
+ ExprAST *Init = VarNames[i].second;
+
+ // Emit the initializer before adding the variable to scope, this prevents
+ // the initializer from referencing the variable itself, and permits stuff
+ // like this:
+ // var a = 1 in
+ // var a = a in ... # refers to outer 'a'.
+ Value *InitVal;
+ if (Init) {
+ InitVal = Init->Codegen();
+ if (InitVal == 0) return 0;
+ } else { // If not specified, use 0.0.
+ InitVal = ConstantFP::get(getGlobalContext(), APFloat(0.0));
+ }
+
+ AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+ Builder.CreateStore(InitVal, Alloca);
+
+ // Remember the old variable binding so that we can restore the binding when
+ // we unrecurse.
+ OldBindings.push_back(NamedValues[VarName]);
+
+ // Remember this binding.
+ NamedValues[VarName] = Alloca;
+ }
+
+ // Codegen the body, now that all vars are in scope.
+ Value *BodyVal = Body->Codegen();
+ if (BodyVal == 0) return 0;
+
+ // Pop all our variables from scope.
+ for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
+ NamedValues[VarNames[i].first] = OldBindings[i];
+
+ // Return the body computation.
+ return BodyVal;
+ }
+
+ Function *PrototypeAST::Codegen() {
+ // Make the function type: double(double,double) etc.
+ std::vector<Type*> Doubles(Args.size(),
+ Type::getDoubleTy(getGlobalContext()));
+ FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
+ Doubles, false);
+
+ Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
+
+ // If F conflicted, there was already something named 'Name'. If it has a
+ // body, don't allow redefinition or reextern.
+ if (F->getName() != Name) {
+ // Delete the one we just made and get the existing one.
+ F->eraseFromParent();
+ F = TheModule->getFunction(Name);
+
+ // If F already has a body, reject this.
+ if (!F->empty()) {
+ ErrorF("redefinition of function");
+ return 0;
+ }
+
+ // If F took a different number of args, reject.
+ if (F->arg_size() != Args.size()) {
+ ErrorF("redefinition of function with different # args");
+ return 0;
+ }
+ }
+
+ // Set names for all arguments.
+ unsigned Idx = 0;
+ for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
+ ++AI, ++Idx)
+ AI->setName(Args[Idx]);
+
+ return F;
+ }
+
+ /// CreateArgumentAllocas - Create an alloca for each argument and register the
+ /// argument in the symbol table so that references to it will succeed.
+ void PrototypeAST::CreateArgumentAllocas(Function *F) {
+ Function::arg_iterator AI = F->arg_begin();
+ for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) {
+ // Create an alloca for this variable.
+ AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]);
+
+ // Store the initial value into the alloca.
+ Builder.CreateStore(AI, Alloca);
+
+ // Add arguments to variable symbol table.
+ NamedValues[Args[Idx]] = Alloca;
+ }
+ }
+
+ Function *FunctionAST::Codegen() {
+ NamedValues.clear();
+
+ Function *TheFunction = Proto->Codegen();
+ if (TheFunction == 0)
+ return 0;
+
+ // If this is an operator, install it.
+ if (Proto->isBinaryOp())
+ BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence();
+
+ // Create a new basic block to start insertion into.
+ BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
+ Builder.SetInsertPoint(BB);
+
+ // Add all arguments to the symbol table and create their allocas.
+ Proto->CreateArgumentAllocas(TheFunction);
+
+ if (Value *RetVal = Body->Codegen()) {
+ // Finish off the function.
+ Builder.CreateRet(RetVal);
+
+ // Validate the generated code, checking for consistency.
+ verifyFunction(*TheFunction);
+
+ // Optimize the function.
+ TheFPM->run(*TheFunction);
+
+ return TheFunction;
+ }
+
+ // Error reading body, remove function.
+ TheFunction->eraseFromParent();
+
+ if (Proto->isBinaryOp())
+ BinopPrecedence.erase(Proto->getOperatorName());
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Top-Level parsing and JIT Driver
+ //===----------------------------------------------------------------------===//
+
+ static ExecutionEngine *TheExecutionEngine;
+
+ static void HandleDefinition() {
+ if (FunctionAST *F = ParseDefinition()) {
+ if (Function *LF = F->Codegen()) {
+ fprintf(stderr, "Read function definition:");
+ LF->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleExtern() {
+ if (PrototypeAST *P = ParseExtern()) {
+ if (Function *F = P->Codegen()) {
+ fprintf(stderr, "Read extern: ");
+ F->dump();
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ static void HandleTopLevelExpression() {
+ // Evaluate a top-level expression into an anonymous function.
+ if (FunctionAST *F = ParseTopLevelExpr()) {
+ if (Function *LF = F->Codegen()) {
+ // JIT the function, returning a function pointer.
+ void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
+
+ // Cast it to the right type (takes no arguments, returns a double) so we
+ // can call it as a native function.
+ double (*FP)() = (double (*)())(intptr_t)FPtr;
+ fprintf(stderr, "Evaluated to %f\n", FP());
+ }
+ } else {
+ // Skip token for error recovery.
+ getNextToken();
+ }
+ }
+
+ /// top ::= definition | external | expression | ';'
+ static void MainLoop() {
+ while (1) {
+ fprintf(stderr, "ready> ");
+ switch (CurTok) {
+ case tok_eof: return;
+ case ';': getNextToken(); break; // ignore top-level semicolons.
+ case tok_def: HandleDefinition(); break;
+ case tok_extern: HandleExtern(); break;
+ default: HandleTopLevelExpression(); break;
+ }
+ }
+ }
+
+ //===----------------------------------------------------------------------===//
+ // "Library" functions that can be "extern'd" from user code.
+ //===----------------------------------------------------------------------===//
+
+ /// putchard - putchar that takes a double and returns 0.
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+ /// printd - printf that takes a double prints it as "%f\n", returning 0.
+ extern "C"
+ double printd(double X) {
+ printf("%f\n", X);
+ return 0;
+ }
+
+ //===----------------------------------------------------------------------===//
+ // Main driver code.
+ //===----------------------------------------------------------------------===//
+
+ int main() {
+ InitializeNativeTarget();
+ LLVMContext &Context = getGlobalContext();
+
+ // Install standard binary operators.
+ // 1 is lowest precedence.
+ BinopPrecedence['='] = 2;
+ BinopPrecedence['<'] = 10;
+ BinopPrecedence['+'] = 20;
+ BinopPrecedence['-'] = 20;
+ BinopPrecedence['*'] = 40; // highest.
+
+ // Prime the first token.
+ fprintf(stderr, "ready> ");
+ getNextToken();
+
+ // Make the module, which holds all the code.
+ TheModule = new Module("my cool jit", Context);
+
+ // Create the JIT. This takes ownership of the module.
+ std::string ErrStr;
+ TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
+ if (!TheExecutionEngine) {
+ fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
+ exit(1);
+ }
+
+ FunctionPassManager OurFPM(TheModule);
+
+ // Set up the optimizer pipeline. Start with registering info about how the
+ // target lays out data structures.
+ OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
+ // Provide basic AliasAnalysis support for GVN.
+ OurFPM.add(createBasicAliasAnalysisPass());
+ // Promote allocas to registers.
+ OurFPM.add(createPromoteMemoryToRegisterPass());
+ // Do simple "peephole" optimizations and bit-twiddling optzns.
+ OurFPM.add(createInstructionCombiningPass());
+ // Reassociate expressions.
+ OurFPM.add(createReassociatePass());
+ // Eliminate Common SubExpressions.
+ OurFPM.add(createGVNPass());
+ // Simplify the control flow graph (deleting unreachable blocks, etc).
+ OurFPM.add(createCFGSimplificationPass());
+
+ OurFPM.doInitialization();
+
+ // Set the global so the code gen can use this.
+ TheFPM = &OurFPM;
+
+ // Run the main "interpreter loop" now.
+ MainLoop();
+
+ TheFPM = 0;
+
+ // Print out all of the generated code.
+ TheModule->dump();
+
+ return 0;
+ }
+
+`Next: Conclusion and other useful LLVM tidbits <LangImpl8.html>`_
+
Removed: llvm/trunk/docs/tutorial/LangImpl8.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl8.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl8.html (original)
+++ llvm/trunk/docs/tutorial/LangImpl8.html (removed)
@@ -1,359 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Conclusion and other useful LLVM tidbits</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Conclusion and other useful LLVM tidbits</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 8
- <ol>
- <li><a href="#conclusion">Tutorial Conclusion</a></li>
- <li><a href="#llvmirproperties">Properties of LLVM IR</a>
- <ul>
- <li><a href="#targetindep">Target Independence</a></li>
- <li><a href="#safety">Safety Guarantees</a></li>
- <li><a href="#langspecific">Language-Specific Optimizations</a></li>
- </ul>
- </li>
- <li><a href="#tipsandtricks">Tips and Tricks</a>
- <ul>
- <li><a href="#offsetofsizeof">Implementing portable
- offsetof/sizeof</a></li>
- <li><a href="#gcstack">Garbage Collected Stack Frames</a></li>
- </ul>
- </li>
- </ol>
-</li>
-</ul>
-
-
-<div class="doc_author">
- <p>Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a></p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="conclusion">Tutorial Conclusion</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to 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: it
-is so nifty/unconventional, it <a
-href="../GetElementPtr.html">has its own FAQ</a>! If you add support
-for recursive types (e.g. linked lists), make sure to read the <a
-href="../ProgrammersManual.html#TypeResolve">section in the LLVM
-Programmer's Manual</a> that describes how to construct them.</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 sense if they are lowered to 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 would like 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
-straightforward. 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 handling support</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>
-
-<li><b>unusual domains</b> - We've been talking about applying LLVM to a domain
-that many people are interested in: building a compiler for a specific language.
-However, there are many other domains that can use compiler technology that are
-not typically considered. For example, LLVM has been used to implement OpenGL
-graphics acceleration, translate C++ code to ActionScript, and many other
-cute and clever things. Maybe you will be the first to JIT compile a regular
-expression interpreter into native code with LLVM?</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
-or 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 this tutorial, 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>
-
-<!-- *********************************************************************** -->
-<h2><a name="llvmirproperties">Properties of the LLVM IR</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>We have a couple common questions about code in the LLVM IR form - lets just
-get these out of the way right now, shall we?</p>
-
-<!-- ======================================================================= -->
-<h4><a name="targetindep">Target Independence</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>Kaleidoscope is an example of a "portable language": any program written in
-Kaleidoscope will work the same way on any target that it runs on. Many other
-languages have this property, e.g. lisp, java, haskell, javascript, python, etc
-(note that while these languages are portable, not all their libraries are).</p>
-
-<p>One nice aspect of LLVM is that it is often capable of preserving target
-independence in the IR: you can take the LLVM IR for a Kaleidoscope-compiled
-program and run it on any target that LLVM supports, even emitting C code and
-compiling that on targets that LLVM doesn't support natively. You can trivially
-tell that the Kaleidoscope compiler generates target-independent code because it
-never queries for any target-specific information when generating code.</p>
-
-<p>The fact that LLVM provides a compact, target-independent, representation for
-code gets a lot of people excited. Unfortunately, these people are usually
-thinking about C or a language from the C family when they are asking questions
-about language portability. I say "unfortunately", because there is really no
-way to make (fully general) C code portable, other than shipping the source code
-around (and of course, C source code is not actually portable in general
-either - ever port a really old application from 32- to 64-bits?).</p>
-
-<p>The problem with C (again, in its full generality) is that it is heavily
-laden with target specific assumptions. As one simple example, the preprocessor
-often destructively removes target-independence from the code when it processes
-the input text:</p>
-
-<div class="doc_code">
-<pre>
-#ifdef __i386__
- int X = 1;
-#else
- int X = 42;
-#endif
-</pre>
-</div>
-
-<p>While it is possible to engineer more and more complex solutions to problems
-like this, it cannot be solved in full generality in a way that is better than shipping
-the actual source code.</p>
-
-<p>That said, there are interesting subsets of C that can be made portable. If
-you are willing to fix primitive types to a fixed size (say int = 32-bits,
-and long = 64-bits), don't care about ABI compatibility with existing binaries,
-and are willing to give up some other minor features, you can have portable
-code. This can make sense for specialized domains such as an
-in-kernel language.</p>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="safety">Safety Guarantees</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>Many of the languages above are also "safe" languages: it is impossible for
-a program written in Java to corrupt its address space and crash the process
-(assuming the JVM has no bugs).
-Safety is an interesting property that requires a combination of language
-design, runtime support, and often operating system support.</p>
-
-<p>It is certainly possible to implement a safe language in LLVM, but LLVM IR
-does not itself guarantee safety. The LLVM IR allows unsafe pointer casts,
-use after free bugs, buffer over-runs, and a variety of other problems. Safety
-needs to be implemented as a layer on top of LLVM and, conveniently, several
-groups have investigated this. Ask on the <a
-href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">llvmdev mailing
-list</a> if you are interested in more details.</p>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="langspecific">Language-Specific Optimizations</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>One thing about LLVM that turns off many people is that it does not solve all
-the world's problems in one system (sorry 'world hunger', someone else will have
-to solve you some other day). One specific complaint is that people perceive
-LLVM as being incapable of performing high-level language-specific optimization:
-LLVM "loses too much information".</p>
-
-<p>Unfortunately, this is really not the place to give you a full and unified
-version of "Chris Lattner's theory of compiler design". Instead, I'll make a
-few observations:</p>
-
-<p>First, you're right that LLVM does lose information. For example, as of this
-writing, there is no way to distinguish in the LLVM IR whether an SSA-value came
-from a C "int" or a C "long" on an ILP32 machine (other than debug info). Both
-get compiled down to an 'i32' value and the information about what it came from
-is lost. The more general issue here, is that the LLVM type system uses
-"structural equivalence" instead of "name equivalence". Another place this
-surprises people is if you have two types in a high-level language that have the
-same structure (e.g. two different structs that have a single int field): these
-types will compile down into a single LLVM type and it will be impossible to
-tell what it came from.</p>
-
-<p>Second, while LLVM does lose information, LLVM is not a fixed target: we
-continue to enhance and improve it in many different ways. In addition to
-adding new features (LLVM did not always support exceptions or debug info), we
-also extend the IR to capture important information for optimization (e.g.
-whether an argument is sign or zero extended, information about pointers
-aliasing, etc). Many of the enhancements are user-driven: people want LLVM to
-include some specific feature, so they go ahead and extend it.</p>
-
-<p>Third, it is <em>possible and easy</em> to add language-specific
-optimizations, and you have a number of choices in how to do it. As one trivial
-example, it is easy to add language-specific optimization passes that
-"know" things about code compiled for a language. In the case of the C family,
-there is an optimization pass that "knows" about the standard C library
-functions. If you call "exit(0)" in main(), it knows that it is safe to
-optimize that into "return 0;" because C specifies what the 'exit'
-function does.</p>
-
-<p>In addition to simple library knowledge, it is possible to embed a variety of
-other language-specific information into the LLVM IR. If you have a specific
-need and run into a wall, please bring the topic up on the llvmdev list. At the
-very worst, you can always treat LLVM as if it were a "dumb code generator" and
-implement the high-level optimizations you desire in your front-end, on the
-language-specific AST.
-</p>
-
-</div>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="tipsandtricks">Tips and Tricks</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>There is a variety of useful tips and tricks that you come to know after
-working on/with LLVM that aren't obvious at first glance. Instead of letting
-everyone rediscover them, this section talks about some of these issues.</p>
-
-<!-- ======================================================================= -->
-<h4><a name="offsetofsizeof">Implementing portable offsetof/sizeof</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>One interesting thing that comes up, if you are trying to keep the code
-generated by your compiler "target independent", is that you often need to know
-the size of some LLVM type or the offset of some field in an llvm structure.
-For example, you might need to pass the size of a type into a function that
-allocates memory.</p>
-
-<p>Unfortunately, this can vary widely across targets: for example the width of
-a pointer is trivially target-specific. However, there is a <a
-href="http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt">clever
-way to use the getelementptr instruction</a> that allows you to compute this
-in a portable way.</p>
-
-</div>
-
-<!-- ======================================================================= -->
-<h4><a name="gcstack">Garbage Collected Stack Frames</a></h4>
-<!-- ======================================================================= -->
-
-<div>
-
-<p>Some languages want to explicitly manage their stack frames, often so that
-they are garbage collected or to allow easy implementation of closures. There
-are often better ways to implement these features than explicit stack frames,
-but <a
-href="http://nondot.org/sabre/LLVMNotes/ExplicitlyManagedStackFrames.txt">LLVM
-does support them,</a> if you want. It requires your front-end to convert the
-code into <a
-href="http://en.wikipedia.org/wiki/Continuation-passing_style">Continuation
-Passing Style</a> and the use of tail calls (which LLVM also supports).</p>
-
-</div>
-
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/LangImpl8.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/LangImpl8.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/LangImpl8.rst (added)
+++ llvm/trunk/docs/tutorial/LangImpl8.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,269 @@
+======================================================
+Kaleidoscope: Conclusion and other useful LLVM tidbits
+======================================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_
+
+Tutorial Conclusion
+===================
+
+Welcome to the final chapter of the "`Implementing a language with
+LLVM <index.html>`_" 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. :)
+
+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.
+
+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.
+
+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:
+
+- **global variables** - 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
+ ``GlobalVariable`` class.
+- **typed variables** - 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\*.
+- **arrays, structs, vectors, etc** - 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 `getelementptr <../LangRef.html#i_getelementptr>`_ instruction
+ works: it is so nifty/unconventional, it `has its own
+ FAQ <../GetElementPtr.html>`_! If you add support for recursive types
+ (e.g. linked lists), make sure to read the `section in the LLVM
+ Programmer's Manual <../ProgrammersManual.html#TypeResolve>`_ that
+ describes how to construct them.
+- **standard runtime** - 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 sense if they are
+ lowered to 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.
+- **memory management** - 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 would like to use garbage
+ collection, note that LLVM fully supports `Accurate Garbage
+ Collection <../GarbageCollection.html>`_ including algorithms that
+ move objects and need to scan/update the stack.
+- **debugger support** - LLVM supports generation of `DWARF Debug
+ info <../SourceLevelDebugging.html>`_ which is understood by common
+ debuggers like GDB. Adding support for debug info is fairly
+ straightforward. The best way to understand it is to compile some
+ C/C++ code with "``llvm-gcc -g -O0``" and taking a look at what it
+ produces.
+- **exception handling support** - LLVM supports generation of `zero
+ cost exceptions <../ExceptionHandling.html>`_ 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.
+- **object orientation, generics, database access, complex numbers,
+ geometric programming, ...** - Really, there is no end of crazy
+ features that you can add to the language.
+- **unusual domains** - We've been talking about applying LLVM to a
+ domain that many people are interested in: building a compiler for a
+ specific language. However, there are many other domains that can use
+ compiler technology that are not typically considered. For example,
+ LLVM has been used to implement OpenGL graphics acceleration,
+ translate C++ code to ActionScript, and many other cute and clever
+ things. Maybe you will be the first to JIT compile a regular
+ expression interpreter into native code with LLVM?
+
+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 or off the wall and seeing how it turns out. If you get
+stuck or want to talk about it, feel free to email the `llvmdev mailing
+list <http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_: it has lots
+of people who are interested in languages and are often willing to help
+out.
+
+Before we end this tutorial, 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.
+
+Properties of the LLVM IR
+=========================
+
+We have a couple common questions about code in the LLVM IR form - lets
+just get these out of the way right now, shall we?
+
+Target Independence
+-------------------
+
+Kaleidoscope is an example of a "portable language": any program written
+in Kaleidoscope will work the same way on any target that it runs on.
+Many other languages have this property, e.g. lisp, java, haskell,
+javascript, python, etc (note that while these languages are portable,
+not all their libraries are).
+
+One nice aspect of LLVM is that it is often capable of preserving target
+independence in the IR: you can take the LLVM IR for a
+Kaleidoscope-compiled program and run it on any target that LLVM
+supports, even emitting C code and compiling that on targets that LLVM
+doesn't support natively. You can trivially tell that the Kaleidoscope
+compiler generates target-independent code because it never queries for
+any target-specific information when generating code.
+
+The fact that LLVM provides a compact, target-independent,
+representation for code gets a lot of people excited. Unfortunately,
+these people are usually thinking about C or a language from the C
+family when they are asking questions about language portability. I say
+"unfortunately", because there is really no way to make (fully general)
+C code portable, other than shipping the source code around (and of
+course, C source code is not actually portable in general either - ever
+port a really old application from 32- to 64-bits?).
+
+The problem with C (again, in its full generality) is that it is heavily
+laden with target specific assumptions. As one simple example, the
+preprocessor often destructively removes target-independence from the
+code when it processes the input text:
+
+.. code-block:: c
+
+ #ifdef __i386__
+ int X = 1;
+ #else
+ int X = 42;
+ #endif
+
+While it is possible to engineer more and more complex solutions to
+problems like this, it cannot be solved in full generality in a way that
+is better than shipping the actual source code.
+
+That said, there are interesting subsets of C that can be made portable.
+If you are willing to fix primitive types to a fixed size (say int =
+32-bits, and long = 64-bits), don't care about ABI compatibility with
+existing binaries, and are willing to give up some other minor features,
+you can have portable code. This can make sense for specialized domains
+such as an in-kernel language.
+
+Safety Guarantees
+-----------------
+
+Many of the languages above are also "safe" languages: it is impossible
+for a program written in Java to corrupt its address space and crash the
+process (assuming the JVM has no bugs). Safety is an interesting
+property that requires a combination of language design, runtime
+support, and often operating system support.
+
+It is certainly possible to implement a safe language in LLVM, but LLVM
+IR does not itself guarantee safety. The LLVM IR allows unsafe pointer
+casts, use after free bugs, buffer over-runs, and a variety of other
+problems. Safety needs to be implemented as a layer on top of LLVM and,
+conveniently, several groups have investigated this. Ask on the `llvmdev
+mailing list <http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>`_ if
+you are interested in more details.
+
+Language-Specific Optimizations
+-------------------------------
+
+One thing about LLVM that turns off many people is that it does not
+solve all the world's problems in one system (sorry 'world hunger',
+someone else will have to solve you some other day). One specific
+complaint is that people perceive LLVM as being incapable of performing
+high-level language-specific optimization: LLVM "loses too much
+information".
+
+Unfortunately, this is really not the place to give you a full and
+unified version of "Chris Lattner's theory of compiler design". Instead,
+I'll make a few observations:
+
+First, you're right that LLVM does lose information. For example, as of
+this writing, there is no way to distinguish in the LLVM IR whether an
+SSA-value came from a C "int" or a C "long" on an ILP32 machine (other
+than debug info). Both get compiled down to an 'i32' value and the
+information about what it came from is lost. The more general issue
+here, is that the LLVM type system uses "structural equivalence" instead
+of "name equivalence". Another place this surprises people is if you
+have two types in a high-level language that have the same structure
+(e.g. two different structs that have a single int field): these types
+will compile down into a single LLVM type and it will be impossible to
+tell what it came from.
+
+Second, while LLVM does lose information, LLVM is not a fixed target: we
+continue to enhance and improve it in many different ways. In addition
+to adding new features (LLVM did not always support exceptions or debug
+info), we also extend the IR to capture important information for
+optimization (e.g. whether an argument is sign or zero extended,
+information about pointers aliasing, etc). Many of the enhancements are
+user-driven: people want LLVM to include some specific feature, so they
+go ahead and extend it.
+
+Third, it is *possible and easy* to add language-specific optimizations,
+and you have a number of choices in how to do it. As one trivial
+example, it is easy to add language-specific optimization passes that
+"know" things about code compiled for a language. In the case of the C
+family, there is an optimization pass that "knows" about the standard C
+library functions. If you call "exit(0)" in main(), it knows that it is
+safe to optimize that into "return 0;" because C specifies what the
+'exit' function does.
+
+In addition to simple library knowledge, it is possible to embed a
+variety of other language-specific information into the LLVM IR. If you
+have a specific need and run into a wall, please bring the topic up on
+the llvmdev list. At the very worst, you can always treat LLVM as if it
+were a "dumb code generator" and implement the high-level optimizations
+you desire in your front-end, on the language-specific AST.
+
+Tips and Tricks
+===============
+
+There is a variety of useful tips and tricks that you come to know after
+working on/with LLVM that aren't obvious at first glance. Instead of
+letting everyone rediscover them, this section talks about some of these
+issues.
+
+Implementing portable offsetof/sizeof
+-------------------------------------
+
+One interesting thing that comes up, if you are trying to keep the code
+generated by your compiler "target independent", is that you often need
+to know the size of some LLVM type or the offset of some field in an
+llvm structure. For example, you might need to pass the size of a type
+into a function that allocates memory.
+
+Unfortunately, this can vary widely across targets: for example the
+width of a pointer is trivially target-specific. However, there is a
+`clever way to use the getelementptr
+instruction <http://nondot.org/sabre/LLVMNotes/SizeOf-OffsetOf-VariableSizedStructs.txt>`_
+that allows you to compute this in a portable way.
+
+Garbage Collected Stack Frames
+------------------------------
+
+Some languages want to explicitly manage their stack frames, often so
+that they are garbage collected or to allow easy implementation of
+closures. There are often better ways to implement these features than
+explicit stack frames, but `LLVM does support
+them, <http://nondot.org/sabre/LLVMNotes/ExplicitlyManagedStackFrames.txt>`_
+if you want. It requires your front-end to convert the code into
+`Continuation Passing
+Style <http://en.wikipedia.org/wiki/Continuation-passing_style>`_ and
+the use of tail calls (which LLVM also supports).
+
Removed: llvm/trunk/docs/tutorial/OCamlLangImpl1.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl1.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl1.html (original)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl1.html (removed)
@@ -1,365 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Tutorial Introduction and the Lexer</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <meta name="author" content="Erick Tryzelaar">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Tutorial Introduction and the Lexer</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 1
- <ol>
- <li><a href="#intro">Tutorial Introduction</a></li>
- <li><a href="#language">The Basic Language</a></li>
- <li><a href="#lexer">The Lexer</a></li>
- </ol>
-</li>
-<li><a href="OCamlLangImpl2.html">Chapter 2</a>: Implementing a Parser and
-AST</li>
-</ul>
-
-<div class="doc_author">
- <p>
- Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>
- and <a href="mailto:idadesub at users.sourceforge.net">Erick Tryzelaar</a>
- </p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Tutorial Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to the "Implementing a language with LLVM" tutorial. This tutorial
-runs through the implementation of a simple language, showing how fun and
-easy it can be. This tutorial will get you up and started as well as help to
-build a framework you can extend to other languages. The code in this tutorial
-can also be used as a playground to hack on other LLVM specific things.
-</p>
-
-<p>
-The goal of this tutorial is to progressively unveil our language, describing
-how it is built up over time. This will let us cover a fairly broad range of
-language design and LLVM-specific usage issues, showing and explaining the code
-for it all along the way, without overwhelming you with tons of details up
-front.</p>
-
-<p>It is useful to point out ahead of time that this tutorial is really about
-teaching compiler techniques and LLVM specifically, <em>not</em> about teaching
-modern and sane software engineering principles. In practice, this means that
-we'll take a number of shortcuts to simplify the exposition. For example, the
-code leaks memory, uses global variables all over the place, doesn't use nice
-design patterns like <a
-href="http://en.wikipedia.org/wiki/Visitor_pattern">visitors</a>, etc... but it
-is very simple. If you dig in and use the code as a basis for future projects,
-fixing these deficiencies shouldn't be hard.</p>
-
-<p>I've tried to put this tutorial together in a way that makes chapters easy to
-skip over if you are already familiar with or are uninterested in the various
-pieces. The structure of the tutorial is:
-</p>
-
-<ul>
-<li><b><a href="#language">Chapter #1</a>: Introduction to the Kaleidoscope
-language, and the definition of its Lexer</b> - This shows where we are going
-and the basic functionality that we want it to do. In order to make this
-tutorial maximally understandable and hackable, we choose to implement
-everything in Objective Caml instead of using lexer and parser generators.
-LLVM obviously works just fine with such tools, feel free to use one if you
-prefer.</li>
-<li><b><a href="OCamlLangImpl2.html">Chapter #2</a>: Implementing a Parser and
-AST</b> - With the lexer in place, we can talk about parsing techniques and
-basic AST construction. This tutorial describes recursive descent parsing and
-operator precedence parsing. Nothing in Chapters 1 or 2 is LLVM-specific,
-the code doesn't even link in LLVM at this point. :)</li>
-<li><b><a href="OCamlLangImpl3.html">Chapter #3</a>: Code generation to LLVM
-IR</b> - With the AST ready, we can show off how easy generation of LLVM IR
-really is.</li>
-<li><b><a href="OCamlLangImpl4.html">Chapter #4</a>: Adding JIT and Optimizer
-Support</b> - Because a lot of people are interested in using LLVM as a JIT,
-we'll dive right into it and show you the 3 lines it takes to add JIT support.
-LLVM is also useful in many other ways, but this is one simple and "sexy" way
-to shows off its power. :)</li>
-<li><b><a href="OCamlLangImpl5.html">Chapter #5</a>: Extending the Language:
-Control Flow</b> - With the language up and running, we show how to extend it
-with control flow operations (if/then/else and a 'for' loop). This gives us a
-chance to talk about simple SSA construction and control flow.</li>
-<li><b><a href="OCamlLangImpl6.html">Chapter #6</a>: Extending the Language:
-User-defined Operators</b> - This is a silly but fun chapter that talks about
-extending the language to let the user program define their own arbitrary
-unary and binary operators (with assignable precedence!). This lets us build a
-significant piece of the "language" as library routines.</li>
-<li><b><a href="OCamlLangImpl7.html">Chapter #7</a>: Extending the Language:
-Mutable Variables</b> - This chapter talks about adding user-defined local
-variables along with an assignment operator. The interesting part about this
-is how easy and trivial it is to construct SSA form in LLVM: no, LLVM does
-<em>not</em> require your front-end to construct SSA form!</li>
-<li><b><a href="OCamlLangImpl8.html">Chapter #8</a>: Conclusion and other
-useful LLVM tidbits</b> - This chapter wraps up the series by talking about
-potential ways to extend the language, but also includes a bunch of pointers to
-info about "special topics" like adding garbage collection support, exceptions,
-debugging, support for "spaghetti stacks", and a bunch of other tips and
-tricks.</li>
-
-</ul>
-
-<p>By the end of the tutorial, we'll have written a bit less than 700 lines of
-non-comment, non-blank, lines of code. With this small amount of code, we'll
-have built up a very reasonable compiler for a non-trivial language including
-a hand-written lexer, parser, AST, as well as code generation support with a JIT
-compiler. While other systems may have interesting "hello world" tutorials,
-I think the breadth of this tutorial is a great testament to the strengths of
-LLVM and why you should consider it if you're interested in language or compiler
-design.</p>
-
-<p>A note about this tutorial: we expect you to extend the language and play
-with it on your own. Take the code and go crazy hacking away at it, compilers
-don't need to be scary creatures - it can be a lot of fun to play with
-languages!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="language">The Basic Language</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>This tutorial will be illustrated with a toy language that we'll call
-"<a href="http://en.wikipedia.org/wiki/Kaleidoscope">Kaleidoscope</a>" (derived
-from "meaning beautiful, form, and view").
-Kaleidoscope is a procedural language that allows you to define functions, use
-conditionals, math, etc. Over the course of the tutorial, we'll extend
-Kaleidoscope to support the if/then/else construct, a for loop, user defined
-operators, JIT compilation with a simple command line interface, etc.</p>
-
-<p>Because we want to keep things simple, the only datatype in Kaleidoscope is a
-64-bit floating point type (aka 'float' in O'Caml parlance). As such, all
-values are implicitly double precision and the language doesn't require type
-declarations. This gives the language a very nice and simple syntax. For
-example, the following simple example computes <a
-href="http://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci numbers:</a></p>
-
-<div class="doc_code">
-<pre>
-# Compute the x'th fibonacci number.
-def fib(x)
- if x < 3 then
- 1
- else
- fib(x-1)+fib(x-2)
-
-# This expression will compute the 40th number.
-fib(40)
-</pre>
-</div>
-
-<p>We also allow Kaleidoscope to call into standard library functions (the LLVM
-JIT makes this completely trivial). This means that you can use the 'extern'
-keyword to define a function before you use it (this is also useful for mutually
-recursive functions). For example:</p>
-
-<div class="doc_code">
-<pre>
-extern sin(arg);
-extern cos(arg);
-extern atan2(arg1 arg2);
-
-atan2(sin(.4), cos(42))
-</pre>
-</div>
-
-<p>A more interesting example is included in Chapter 6 where we write a little
-Kaleidoscope application that <a href="OCamlLangImpl6.html#example">displays
-a Mandelbrot Set</a> at various levels of magnification.</p>
-
-<p>Lets dive into the implementation of this language!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="lexer">The Lexer</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>When it comes to implementing a language, the first thing needed is
-the ability to process a text file and recognize what it says. The traditional
-way to do this is to use a "<a
-href="http://en.wikipedia.org/wiki/Lexical_analysis">lexer</a>" (aka 'scanner')
-to break the input up into "tokens". Each token returned by the lexer includes
-a token code and potentially some metadata (e.g. the numeric value of a number).
-First, we define the possibilities:
-</p>
-
-<div class="doc_code">
-<pre>
-(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
- * these others for known things. *)
-type token =
- (* commands *)
- | Def | Extern
-
- (* primary *)
- | Ident of string | Number of float
-
- (* unknown *)
- | Kwd of char
-</pre>
-</div>
-
-<p>Each token returned by our lexer will be one of the token variant values.
-An unknown character like '+' will be returned as <tt>Token.Kwd '+'</tt>. If
-the curr token is an identifier, the value will be <tt>Token.Ident s</tt>. If
-the current token is a numeric literal (like 1.0), the value will be
-<tt>Token.Number 1.0</tt>.
-</p>
-
-<p>The actual implementation of the lexer is a collection of functions driven
-by a function named <tt>Lexer.lex</tt>. The <tt>Lexer.lex</tt> function is
-called to return the next token from standard input. We will use
-<a href="http://caml.inria.fr/pub/docs/manual-camlp4/index.html">Camlp4</a>
-to simplify the tokenization of the standard input. Its definition starts
-as:</p>
-
-<div class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Lexer
- *===----------------------------------------------------------------------===*)
-
-let rec lex = parser
- (* Skip any whitespace. *)
- | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
-</pre>
-</div>
-
-<p>
-<tt>Lexer.lex</tt> works by recursing over a <tt>char Stream.t</tt> to read
-characters one at a time from the standard input. It eats them as it recognizes
-them and stores them in in a <tt>Token.token</tt> variant. The first thing that
-it has to do is ignore whitespace between tokens. This is accomplished with the
-recursive call above.</p>
-
-<p>The next thing <tt>Lexer.lex</tt> needs to do is recognize identifiers and
-specific keywords like "def". Kaleidoscope does this with a pattern match
-and a helper function.<p>
-
-<div class="doc_code">
-<pre>
- (* identifier: [a-zA-Z][a-zA-Z0-9] *)
- | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_ident buffer stream
-
-...
-
-and lex_ident buffer = parser
- | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_ident buffer stream
- | [< stream=lex >] ->
- match Buffer.contents buffer with
- | "def" -> [< 'Token.Def; stream >]
- | "extern" -> [< 'Token.Extern; stream >]
- | id -> [< 'Token.Ident id; stream >]
-</pre>
-</div>
-
-<p>Numeric values are similar:</p>
-
-<div class="doc_code">
-<pre>
- (* number: [0-9.]+ *)
- | [< ' ('0' .. '9' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_number buffer stream
-
-...
-
-and lex_number buffer = parser
- | [< ' ('0' .. '9' | '.' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_number buffer stream
- | [< stream=lex >] ->
- [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
-</pre>
-</div>
-
-<p>This is all pretty straight-forward code for processing input. When reading
-a numeric value from input, we use the ocaml <tt>float_of_string</tt> function
-to convert it to a numeric value that we store in <tt>Token.Number</tt>. Note
-that this isn't doing sufficient error checking: it will raise <tt>Failure</tt>
-if the string "1.23.45.67". Feel free to extend it :). Next we handle
-comments:
-</p>
-
-<div class="doc_code">
-<pre>
- (* Comment until end of line. *)
- | [< ' ('#'); stream >] ->
- lex_comment stream
-
-...
-
-and lex_comment = parser
- | [< ' ('\n'); stream=lex >] -> stream
- | [< 'c; e=lex_comment >] -> e
- | [< >] -> [< >]
-</pre>
-</div>
-
-<p>We handle comments by skipping to the end of the line and then return the
-next token. Finally, if the input doesn't match one of the above cases, it is
-either an operator character like '+' or the end of the file. These are handled
-with this code:</p>
-
-<div class="doc_code">
-<pre>
- (* Otherwise, just return the character as its ascii value. *)
- | [< 'c; stream >] ->
- [< 'Token.Kwd c; lex stream >]
-
- (* end of stream. *)
- | [< >] -> [< >]
-</pre>
-</div>
-
-<p>With this, we have the complete lexer for the basic Kaleidoscope language
-(the <a href="OCamlLangImpl2.html#code">full code listing</a> for the Lexer is
-available in the <a href="OCamlLangImpl2.html">next chapter</a> of the
-tutorial). Next we'll <a href="OCamlLangImpl2.html">build a simple parser that
-uses this to build an Abstract Syntax Tree</a>. When we have that, we'll
-include a driver so that you can use the lexer and parser together.
-</p>
-
-<a href="OCamlLangImpl2.html">Next: Implementing a Parser and AST</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="mailto:idadesub at users.sourceforge.net">Erick Tryzelaar</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/OCamlLangImpl1.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl1.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl1.rst (added)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl1.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,288 @@
+=================================================
+Kaleidoscope: Tutorial Introduction and the Lexer
+=================================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_ and `Erick
+Tryzelaar <mailto:idadesub at users.sourceforge.net>`_
+
+Tutorial Introduction
+=====================
+
+Welcome to the "Implementing a language with LLVM" tutorial. This
+tutorial runs through the implementation of a simple language, showing
+how fun and easy it can be. This tutorial will get you up and started as
+well as help to build a framework you can extend to other languages. The
+code in this tutorial can also be used as a playground to hack on other
+LLVM specific things.
+
+The goal of this tutorial is to progressively unveil our language,
+describing how it is built up over time. This will let us cover a fairly
+broad range of language design and LLVM-specific usage issues, showing
+and explaining the code for it all along the way, without overwhelming
+you with tons of details up front.
+
+It is useful to point out ahead of time that this tutorial is really
+about teaching compiler techniques and LLVM specifically, *not* about
+teaching modern and sane software engineering principles. In practice,
+this means that we'll take a number of shortcuts to simplify the
+exposition. For example, the code leaks memory, uses global variables
+all over the place, doesn't use nice design patterns like
+`visitors <http://en.wikipedia.org/wiki/Visitor_pattern>`_, etc... but
+it is very simple. If you dig in and use the code as a basis for future
+projects, fixing these deficiencies shouldn't be hard.
+
+I've tried to put this tutorial together in a way that makes chapters
+easy to skip over if you are already familiar with or are uninterested
+in the various pieces. The structure of the tutorial is:
+
+- `Chapter #1 <#language>`_: Introduction to the Kaleidoscope
+ language, and the definition of its Lexer - This shows where we are
+ going and the basic functionality that we want it to do. In order to
+ make this tutorial maximally understandable and hackable, we choose
+ to implement everything in Objective Caml instead of using lexer and
+ parser generators. LLVM obviously works just fine with such tools,
+ feel free to use one if you prefer.
+- `Chapter #2 <OCamlLangImpl2.html>`_: Implementing a Parser and
+ AST - With the lexer in place, we can talk about parsing techniques
+ and basic AST construction. This tutorial describes recursive descent
+ parsing and operator precedence parsing. Nothing in Chapters 1 or 2
+ is LLVM-specific, the code doesn't even link in LLVM at this point.
+ :)
+- `Chapter #3 <OCamlLangImpl3.html>`_: Code generation to LLVM IR -
+ With the AST ready, we can show off how easy generation of LLVM IR
+ really is.
+- `Chapter #4 <OCamlLangImpl4.html>`_: Adding JIT and Optimizer
+ Support - Because a lot of people are interested in using LLVM as a
+ JIT, we'll dive right into it and show you the 3 lines it takes to
+ add JIT support. LLVM is also useful in many other ways, but this is
+ one simple and "sexy" way to shows off its power. :)
+- `Chapter #5 <OCamlLangImpl5.html>`_: Extending the Language:
+ Control Flow - With the language up and running, we show how to
+ extend it with control flow operations (if/then/else and a 'for'
+ loop). This gives us a chance to talk about simple SSA construction
+ and control flow.
+- `Chapter #6 <OCamlLangImpl6.html>`_: Extending the Language:
+ User-defined Operators - This is a silly but fun chapter that talks
+ about extending the language to let the user program define their own
+ arbitrary unary and binary operators (with assignable precedence!).
+ This lets us build a significant piece of the "language" as library
+ routines.
+- `Chapter #7 <OCamlLangImpl7.html>`_: Extending the Language:
+ Mutable Variables - This chapter talks about adding user-defined
+ local variables along with an assignment operator. The interesting
+ part about this is how easy and trivial it is to construct SSA form
+ in LLVM: no, LLVM does *not* require your front-end to construct SSA
+ form!
+- `Chapter #8 <OCamlLangImpl8.html>`_: Conclusion and other useful
+ LLVM tidbits - This chapter wraps up the series by talking about
+ potential ways to extend the language, but also includes a bunch of
+ pointers to info about "special topics" like adding garbage
+ collection support, exceptions, debugging, support for "spaghetti
+ stacks", and a bunch of other tips and tricks.
+
+By the end of the tutorial, we'll have written a bit less than 700 lines
+of non-comment, non-blank, lines of code. With this small amount of
+code, we'll have built up a very reasonable compiler for a non-trivial
+language including a hand-written lexer, parser, AST, as well as code
+generation support with a JIT compiler. While other systems may have
+interesting "hello world" tutorials, I think the breadth of this
+tutorial is a great testament to the strengths of LLVM and why you
+should consider it if you're interested in language or compiler design.
+
+A note about this tutorial: we expect you to extend the language and
+play with it on your own. Take the code and go crazy hacking away at it,
+compilers don't need to be scary creatures - it can be a lot of fun to
+play with languages!
+
+The Basic Language
+==================
+
+This tutorial will be illustrated with a toy language that we'll call
+"`Kaleidoscope <http://en.wikipedia.org/wiki/Kaleidoscope>`_" (derived
+from "meaning beautiful, form, and view"). Kaleidoscope is a procedural
+language that allows you to define functions, use conditionals, math,
+etc. Over the course of the tutorial, we'll extend Kaleidoscope to
+support the if/then/else construct, a for loop, user defined operators,
+JIT compilation with a simple command line interface, etc.
+
+Because we want to keep things simple, the only datatype in Kaleidoscope
+is a 64-bit floating point type (aka 'float' in O'Caml parlance). As
+such, all values are implicitly double precision and the language
+doesn't require type declarations. This gives the language a very nice
+and simple syntax. For example, the following simple example computes
+`Fibonacci numbers: <http://en.wikipedia.org/wiki/Fibonacci_number>`_
+
+::
+
+ # Compute the x'th fibonacci number.
+ def fib(x)
+ if x < 3 then
+ 1
+ else
+ fib(x-1)+fib(x-2)
+
+ # This expression will compute the 40th number.
+ fib(40)
+
+We also allow Kaleidoscope to call into standard library functions (the
+LLVM JIT makes this completely trivial). This means that you can use the
+'extern' keyword to define a function before you use it (this is also
+useful for mutually recursive functions). For example:
+
+::
+
+ extern sin(arg);
+ extern cos(arg);
+ extern atan2(arg1 arg2);
+
+ atan2(sin(.4), cos(42))
+
+A more interesting example is included in Chapter 6 where we write a
+little Kaleidoscope application that `displays a Mandelbrot
+Set <OCamlLangImpl6.html#example>`_ at various levels of magnification.
+
+Lets dive into the implementation of this language!
+
+The Lexer
+=========
+
+When it comes to implementing a language, the first thing needed is the
+ability to process a text file and recognize what it says. The
+traditional way to do this is to use a
+"`lexer <http://en.wikipedia.org/wiki/Lexical_analysis>`_" (aka
+'scanner') to break the input up into "tokens". Each token returned by
+the lexer includes a token code and potentially some metadata (e.g. the
+numeric value of a number). First, we define the possibilities:
+
+.. code-block:: ocaml
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+Each token returned by our lexer will be one of the token variant
+values. An unknown character like '+' will be returned as
+``Token.Kwd '+'``. If the curr token is an identifier, the value will be
+``Token.Ident s``. If the current token is a numeric literal (like 1.0),
+the value will be ``Token.Number 1.0``.
+
+The actual implementation of the lexer is a collection of functions
+driven by a function named ``Lexer.lex``. The ``Lexer.lex`` function is
+called to return the next token from standard input. We will use
+`Camlp4 <http://caml.inria.fr/pub/docs/manual-camlp4/index.html>`_ to
+simplify the tokenization of the standard input. Its definition starts
+as:
+
+.. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+``Lexer.lex`` works by recursing over a ``char Stream.t`` to read
+characters one at a time from the standard input. It eats them as it
+recognizes them and stores them in in a ``Token.token`` variant. The
+first thing that it has to do is ignore whitespace between tokens. This
+is accomplished with the recursive call above.
+
+The next thing ``Lexer.lex`` needs to do is recognize identifiers and
+specific keywords like "def". Kaleidoscope does this with a pattern
+match and a helper function.
+
+.. code-block:: ocaml
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ ...
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+Numeric values are similar:
+
+.. code-block:: ocaml
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ ...
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+This is all pretty straight-forward code for processing input. When
+reading a numeric value from input, we use the ocaml ``float_of_string``
+function to convert it to a numeric value that we store in
+``Token.Number``. Note that this isn't doing sufficient error checking:
+it will raise ``Failure`` if the string "1.23.45.67". Feel free to
+extend it :). Next we handle comments:
+
+.. code-block:: ocaml
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ ...
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+We handle comments by skipping to the end of the line and then return
+the next token. Finally, if the input doesn't match one of the above
+cases, it is either an operator character like '+' or the end of the
+file. These are handled with this code:
+
+.. code-block:: ocaml
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+With this, we have the complete lexer for the basic Kaleidoscope
+language (the `full code listing <OCamlLangImpl2.html#code>`_ for the
+Lexer is available in the `next chapter <OCamlLangImpl2.html>`_ of the
+tutorial). Next we'll `build a simple parser that uses this to build an
+Abstract Syntax Tree <OCamlLangImpl2.html>`_. When we have that, we'll
+include a driver so that you can use the lexer and parser together.
+
+`Next: Implementing a Parser and AST <OCamlLangImpl2.html>`_
+
Removed: llvm/trunk/docs/tutorial/OCamlLangImpl2.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl2.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl2.html (original)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl2.html (removed)
@@ -1,1043 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Implementing a Parser and AST</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <meta name="author" content="Erick Tryzelaar">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Implementing a Parser and AST</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 2
- <ol>
- <li><a href="#intro">Chapter 2 Introduction</a></li>
- <li><a href="#ast">The Abstract Syntax Tree (AST)</a></li>
- <li><a href="#parserbasics">Parser Basics</a></li>
- <li><a href="#parserprimexprs">Basic Expression Parsing</a></li>
- <li><a href="#parserbinops">Binary Expression Parsing</a></li>
- <li><a href="#parsertop">Parsing the Rest</a></li>
- <li><a href="#driver">The Driver</a></li>
- <li><a href="#conclusions">Conclusions</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="OCamlLangImpl3.html">Chapter 3</a>: Code generation to LLVM IR</li>
-</ul>
-
-<div class="doc_author">
- <p>
- Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>
- and <a href="mailto:idadesub at users.sourceforge.net">Erick Tryzelaar</a>
- </p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 2 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 2 of the "<a href="index.html">Implementing a language
-with LLVM in Objective Caml</a>" tutorial. This chapter shows you how to use
-the lexer, built in <a href="OCamlLangImpl1.html">Chapter 1</a>, to build a
-full <a href="http://en.wikipedia.org/wiki/Parsing">parser</a> for our
-Kaleidoscope language. Once we have a parser, we'll define and build an <a
-href="http://en.wikipedia.org/wiki/Abstract_syntax_tree">Abstract Syntax
-Tree</a> (AST).</p>
-
-<p>The parser we will build uses a combination of <a
-href="http://en.wikipedia.org/wiki/Recursive_descent_parser">Recursive Descent
-Parsing</a> and <a href=
-"http://en.wikipedia.org/wiki/Operator-precedence_parser">Operator-Precedence
-Parsing</a> to parse the Kaleidoscope language (the latter for
-binary expressions and the former for everything else). Before we get to
-parsing though, lets talk about the output of the parser: the Abstract Syntax
-Tree.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="ast">The Abstract Syntax Tree (AST)</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>The AST for a program captures its behavior in such a way that it is easy for
-later stages of the compiler (e.g. code generation) to interpret. We basically
-want one object for each construct in the language, and the AST should closely
-model the language. In Kaleidoscope, we have expressions, a prototype, and a
-function object. We'll start with expressions first:</p>
-
-<div class="doc_code">
-<pre>
-(* expr - Base type for all expression nodes. *)
-type expr =
- (* variant for numeric literals like "1.0". *)
- | Number of float
-</pre>
-</div>
-
-<p>The code above shows the definition of the base ExprAST class and one
-subclass which we use for numeric literals. The important thing to note about
-this code is that the Number variant captures the numeric value of the
-literal as an instance variable. This allows later phases of the compiler to
-know what the stored numeric value is.</p>
-
-<p>Right now we only create the AST, so there are no useful functions on
-them. It would be very easy to add a function to pretty print the code,
-for example. Here are the other expression AST node definitions that we'll use
-in the basic form of the Kaleidoscope language:
-</p>
-
-<div class="doc_code">
-<pre>
- (* variant for referencing a variable, like "a". *)
- | Variable of string
-
- (* variant for a binary operator. *)
- | Binary of char * expr * expr
-
- (* variant for function calls. *)
- | Call of string * expr array
-</pre>
-</div>
-
-<p>This is all (intentionally) rather straight-forward: variables capture the
-variable name, binary operators capture their opcode (e.g. '+'), and calls
-capture a function name as well as a list of any argument expressions. One thing
-that is nice about our AST is that it captures the language features without
-talking about the syntax of the language. Note that there is no discussion about
-precedence of binary operators, lexical structure, etc.</p>
-
-<p>For our basic language, these are all of the expression nodes we'll define.
-Because it doesn't have conditional control flow, it isn't Turing-complete;
-we'll fix that in a later installment. The two things we need next are a way
-to talk about the interface to a function, and a way to talk about functions
-themselves:</p>
-
-<div class="doc_code">
-<pre>
-(* proto - This type represents the "prototype" for a function, which captures
- * its name, and its argument names (thus implicitly the number of arguments the
- * function takes). *)
-type proto = Prototype of string * string array
-
-(* func - This type represents a function definition itself. *)
-type func = Function of proto * expr
-</pre>
-</div>
-
-<p>In Kaleidoscope, functions are typed with just a count of their arguments.
-Since all values are double precision floating point, the type of each argument
-doesn't need to be stored anywhere. In a more aggressive and realistic
-language, the "expr" variants would probably have a type field.</p>
-
-<p>With this scaffolding, we can now talk about parsing expressions and function
-bodies in Kaleidoscope.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parserbasics">Parser Basics</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Now that we have an AST to build, we need to define the parser code to build
-it. The idea here is that we want to parse something like "x+y" (which is
-returned as three tokens by the lexer) into an AST that could be generated with
-calls like this:</p>
-
-<div class="doc_code">
-<pre>
- let x = Variable "x" in
- let y = Variable "y" in
- let result = Binary ('+', x, y) in
- ...
-</pre>
-</div>
-
-<p>
-The error handling routines make use of the builtin <tt>Stream.Failure</tt> and
-<tt>Stream.Error</tt>s. <tt>Stream.Failure</tt> is raised when the parser is
-unable to find any matching token in the first position of a pattern.
-<tt>Stream.Error</tt> is raised when the first token matches, but the rest do
-not. The error recovery in our parser will not be the best and is not
-particular user-friendly, but it will be enough for our tutorial. These
-exceptions make it easier to handle errors in routines that have various return
-types.</p>
-
-<p>With these basic types and exceptions, we can implement the first
-piece of our grammar: numeric literals.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parserprimexprs">Basic Expression Parsing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>We start with numeric literals, because they are the simplest to process.
-For each production in our grammar, we'll define a function which parses that
-production. We call this class of expressions "primary" expressions, for
-reasons that will become more clear <a href="OCamlLangImpl6.html#unary">
-later in the tutorial</a>. In order to parse an arbitrary primary expression,
-we need to determine what sort of expression it is. For numeric literals, we
-have:</p>
-
-<div class="doc_code">
-<pre>
-(* primary
- * ::= identifier
- * ::= numberexpr
- * ::= parenexpr *)
-parse_primary = parser
- (* numberexpr ::= number *)
- | [< 'Token.Number n >] -> Ast.Number n
-</pre>
-</div>
-
-<p>This routine is very simple: it expects to be called when the current token
-is a <tt>Token.Number</tt> token. It takes the current number value, creates
-a <tt>Ast.Number</tt> node, advances the lexer to the next token, and finally
-returns.</p>
-
-<p>There are some interesting aspects to this. The most important one is that
-this routine eats all of the tokens that correspond to the production and
-returns the lexer buffer with the next token (which is not part of the grammar
-production) ready to go. This is a fairly standard way to go for recursive
-descent parsers. For a better example, the parenthesis operator is defined like
-this:</p>
-
-<div class="doc_code">
-<pre>
- (* parenexpr ::= '(' expression ')' *)
- | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
-</pre>
-</div>
-
-<p>This function illustrates a number of interesting things about the
-parser:</p>
-
-<p>
-1) It shows how we use the <tt>Stream.Error</tt> exception. When called, this
-function expects that the current token is a '(' token, but after parsing the
-subexpression, it is possible that there is no ')' waiting. For example, if
-the user types in "(4 x" instead of "(4)", the parser should emit an error.
-Because errors can occur, the parser needs a way to indicate that they
-happened. In our parser, we use the camlp4 shortcut syntax <tt>token ?? "parse
-error"</tt>, where if the token before the <tt>??</tt> does not match, then
-<tt>Stream.Error "parse error"</tt> will be raised.</p>
-
-<p>2) Another interesting aspect of this function is that it uses recursion by
-calling <tt>Parser.parse_primary</tt> (we will soon see that
-<tt>Parser.parse_primary</tt> can call <tt>Parser.parse_primary</tt>). This is
-powerful because it allows us to handle recursive grammars, and keeps each
-production very simple. Note that parentheses do not cause construction of AST
-nodes themselves. While we could do it this way, the most important role of
-parentheses are to guide the parser and provide grouping. Once the parser
-constructs the AST, parentheses are not needed.</p>
-
-<p>The next simple production is for handling variable references and function
-calls:</p>
-
-<div class="doc_code">
-<pre>
- (* identifierexpr
- * ::= identifier
- * ::= identifier '(' argumentexpr ')' *)
- | [< 'Token.Ident id; stream >] ->
- let rec parse_args accumulator = parser
- | [< e=parse_expr; stream >] ->
- begin parser
- | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
- | [< >] -> e :: accumulator
- end stream
- | [< >] -> accumulator
- in
- let rec parse_ident id = parser
- (* Call. *)
- | [< 'Token.Kwd '(';
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')'">] ->
- Ast.Call (id, Array.of_list (List.rev args))
-
- (* Simple variable ref. *)
- | [< >] -> Ast.Variable id
- in
- parse_ident id stream
-</pre>
-</div>
-
-<p>This routine follows the same style as the other routines. (It expects to be
-called if the current token is a <tt>Token.Ident</tt> token). It also has
-recursion and error handling. One interesting aspect of this is that it uses
-<em>look-ahead</em> to determine if the current identifier is a stand alone
-variable reference or if it is a function call expression. It handles this by
-checking to see if the token after the identifier is a '(' token, constructing
-either a <tt>Ast.Variable</tt> or <tt>Ast.Call</tt> node as appropriate.
-</p>
-
-<p>We finish up by raising an exception if we received a token we didn't
-expect:</p>
-
-<div class="doc_code">
-<pre>
- | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
-</pre>
-</div>
-
-<p>Now that basic expressions are handled, we need to handle binary expressions.
-They are a bit more complex.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parserbinops">Binary Expression Parsing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Binary expressions are significantly harder to parse because they are often
-ambiguous. For example, when given the string "x+y*z", the parser can choose
-to parse it as either "(x+y)*z" or "x+(y*z)". With common definitions from
-mathematics, we expect the later parse, because "*" (multiplication) has
-higher <em>precedence</em> than "+" (addition).</p>
-
-<p>There are many ways to handle this, but an elegant and efficient way is to
-use <a href=
-"http://en.wikipedia.org/wiki/Operator-precedence_parser">Operator-Precedence
-Parsing</a>. This parsing technique uses the precedence of binary operators to
-guide recursion. To start with, we need a table of precedences:</p>
-
-<div class="doc_code">
-<pre>
-(* binop_precedence - This holds the precedence for each binary operator that is
- * defined *)
-let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
-
-(* precedence - Get the precedence of the pending binary operator token. *)
-let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
-
-...
-
-let main () =
- (* Install standard binary operators.
- * 1 is the lowest precedence. *)
- Hashtbl.add Parser.binop_precedence '<' 10;
- Hashtbl.add Parser.binop_precedence '+' 20;
- Hashtbl.add Parser.binop_precedence '-' 20;
- Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
- ...
-</pre>
-</div>
-
-<p>For the basic form of Kaleidoscope, we will only support 4 binary operators
-(this can obviously be extended by you, our brave and intrepid reader). The
-<tt>Parser.precedence</tt> function returns the precedence for the current
-token, or -1 if the token is not a binary operator. Having a <tt>Hashtbl.t</tt>
-makes it easy to add new operators and makes it clear that the algorithm doesn't
-depend on the specific operators involved, but it would be easy enough to
-eliminate the <tt>Hashtbl.t</tt> and do the comparisons in the
-<tt>Parser.precedence</tt> function. (Or just use a fixed-size array).</p>
-
-<p>With the helper above defined, we can now start parsing binary expressions.
-The basic idea of operator precedence parsing is to break down an expression
-with potentially ambiguous binary operators into pieces. Consider ,for example,
-the expression "a+b+(c+d)*e*f+g". Operator precedence parsing considers this
-as a stream of primary expressions separated by binary operators. As such,
-it will first parse the leading primary expression "a", then it will see the
-pairs [+, b] [+, (c+d)] [*, e] [*, f] and [+, g]. Note that because parentheses
-are primary expressions, the binary expression parser doesn't need to worry
-about nested subexpressions like (c+d) at all.
-</p>
-
-<p>
-To start, an expression is a primary expression potentially followed by a
-sequence of [binop,primaryexpr] pairs:</p>
-
-<div class="doc_code">
-<pre>
-(* expression
- * ::= primary binoprhs *)
-and parse_expr = parser
- | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
-</pre>
-</div>
-
-<p><tt>Parser.parse_bin_rhs</tt> is the function that parses the sequence of
-pairs for us. It takes a precedence and a pointer to an expression for the part
-that has been parsed so far. Note that "x" is a perfectly valid expression: As
-such, "binoprhs" is allowed to be empty, in which case it returns the expression
-that is passed into it. In our example above, the code passes the expression for
-"a" into <tt>Parser.parse_bin_rhs</tt> and the current token is "+".</p>
-
-<p>The precedence value passed into <tt>Parser.parse_bin_rhs</tt> indicates the
-<em>minimal operator precedence</em> that the function is allowed to eat. For
-example, if the current pair stream is [+, x] and <tt>Parser.parse_bin_rhs</tt>
-is passed in a precedence of 40, it will not consume any tokens (because the
-precedence of '+' is only 20). With this in mind, <tt>Parser.parse_bin_rhs</tt>
-starts with:</p>
-
-<div class="doc_code">
-<pre>
-(* binoprhs
- * ::= ('+' primary)* *)
-and parse_bin_rhs expr_prec lhs stream =
- match Stream.peek stream with
- (* If this is a binop, find its precedence. *)
- | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
- let token_prec = precedence c in
-
- (* If this is a binop that binds at least as tightly as the current binop,
- * consume it, otherwise we are done. *)
- if token_prec < expr_prec then lhs else begin
-</pre>
-</div>
-
-<p>This code gets the precedence of the current token and checks to see if if is
-too low. Because we defined invalid tokens to have a precedence of -1, this
-check implicitly knows that the pair-stream ends when the token stream runs out
-of binary operators. If this check succeeds, we know that the token is a binary
-operator and that it will be included in this expression:</p>
-
-<div class="doc_code">
-<pre>
- (* Eat the binop. *)
- Stream.junk stream;
-
- (* Okay, we know this is a binop. *)
- let rhs =
- match Stream.peek stream with
- | Some (Token.Kwd c2) ->
-</pre>
-</div>
-
-<p>As such, this code eats (and remembers) the binary operator and then parses
-the primary expression that follows. This builds up the whole pair, the first of
-which is [+, b] for the running example.</p>
-
-<p>Now that we parsed the left-hand side of an expression and one pair of the
-RHS sequence, we have to decide which way the expression associates. In
-particular, we could have "(a+b) binop unparsed" or "a + (b binop unparsed)".
-To determine this, we look ahead at "binop" to determine its precedence and
-compare it to BinOp's precedence (which is '+' in this case):</p>
-
-<div class="doc_code">
-<pre>
- (* If BinOp binds less tightly with rhs than the operator after
- * rhs, let the pending operator take rhs as its lhs. *)
- let next_prec = precedence c2 in
- if token_prec < next_prec
-</pre>
-</div>
-
-<p>If the precedence of the binop to the right of "RHS" is lower or equal to the
-precedence of our current operator, then we know that the parentheses associate
-as "(a+b) binop ...". In our example, the current operator is "+" and the next
-operator is "+", we know that they have the same precedence. In this case we'll
-create the AST node for "a+b", and then continue parsing:</p>
-
-<div class="doc_code">
-<pre>
- ... if body omitted ...
- in
-
- (* Merge lhs/rhs. *)
- let lhs = Ast.Binary (c, lhs, rhs) in
- parse_bin_rhs expr_prec lhs stream
- end
-</pre>
-</div>
-
-<p>In our example above, this will turn "a+b+" into "(a+b)" and execute the next
-iteration of the loop, with "+" as the current token. The code above will eat,
-remember, and parse "(c+d)" as the primary expression, which makes the
-current pair equal to [+, (c+d)]. It will then evaluate the 'if' conditional above with
-"*" as the binop to the right of the primary. In this case, the precedence of "*" is
-higher than the precedence of "+" so the if condition will be entered.</p>
-
-<p>The critical question left here is "how can the if condition parse the right
-hand side in full"? In particular, to build the AST correctly for our example,
-it needs to get all of "(c+d)*e*f" as the RHS expression variable. The code to
-do this is surprisingly simple (code from the above two blocks duplicated for
-context):</p>
-
-<div class="doc_code">
-<pre>
- match Stream.peek stream with
- | Some (Token.Kwd c2) ->
- (* If BinOp binds less tightly with rhs than the operator after
- * rhs, let the pending operator take rhs as its lhs. *)
- if token_prec < precedence c2
- then <b>parse_bin_rhs (token_prec + 1) rhs stream</b>
- else rhs
- | _ -> rhs
- in
-
- (* Merge lhs/rhs. *)
- let lhs = Ast.Binary (c, lhs, rhs) in
- parse_bin_rhs expr_prec lhs stream
- end
-</pre>
-</div>
-
-<p>At this point, we know that the binary operator to the RHS of our primary
-has higher precedence than the binop we are currently parsing. As such, we know
-that any sequence of pairs whose operators are all higher precedence than "+"
-should be parsed together and returned as "RHS". To do this, we recursively
-invoke the <tt>Parser.parse_bin_rhs</tt> function specifying "token_prec+1" as
-the minimum precedence required for it to continue. In our example above, this
-will cause it to return the AST node for "(c+d)*e*f" as RHS, which is then set
-as the RHS of the '+' expression.</p>
-
-<p>Finally, on the next iteration of the while loop, the "+g" piece is parsed
-and added to the AST. With this little bit of code (14 non-trivial lines), we
-correctly handle fully general binary expression parsing in a very elegant way.
-This was a whirlwind tour of this code, and it is somewhat subtle. I recommend
-running through it with a few tough examples to see how it works.
-</p>
-
-<p>This wraps up handling of expressions. At this point, we can point the
-parser at an arbitrary token stream and build an expression from it, stopping
-at the first token that is not part of the expression. Next up we need to
-handle function definitions, etc.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="parsertop">Parsing the Rest</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-The next thing missing is handling of function prototypes. In Kaleidoscope,
-these are used both for 'extern' function declarations as well as function body
-definitions. The code to do this is straight-forward and not very interesting
-(once you've survived expressions):
-</p>
-
-<div class="doc_code">
-<pre>
-(* prototype
- * ::= id '(' id* ')' *)
-let parse_prototype =
- let rec parse_args accumulator = parser
- | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
- | [< >] -> accumulator
- in
-
- parser
- | [< 'Token.Ident id;
- 'Token.Kwd '(' ?? "expected '(' in prototype";
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
- (* success. *)
- Ast.Prototype (id, Array.of_list (List.rev args))
-
- | [< >] ->
- raise (Stream.Error "expected function name in prototype")
-</pre>
-</div>
-
-<p>Given this, a function definition is very simple, just a prototype plus
-an expression to implement the body:</p>
-
-<div class="doc_code">
-<pre>
-(* definition ::= 'def' prototype expression *)
-let parse_definition = parser
- | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
- Ast.Function (p, e)
-</pre>
-</div>
-
-<p>In addition, we support 'extern' to declare functions like 'sin' and 'cos' as
-well as to support forward declaration of user functions. These 'extern's are just
-prototypes with no body:</p>
-
-<div class="doc_code">
-<pre>
-(* external ::= 'extern' prototype *)
-let parse_extern = parser
- | [< 'Token.Extern; e=parse_prototype >] -> e
-</pre>
-</div>
-
-<p>Finally, we'll also let the user type in arbitrary top-level expressions and
-evaluate them on the fly. We will handle this by defining anonymous nullary
-(zero argument) functions for them:</p>
-
-<div class="doc_code">
-<pre>
-(* toplevelexpr ::= expression *)
-let parse_toplevel = parser
- | [< e=parse_expr >] ->
- (* Make an anonymous proto. *)
- Ast.Function (Ast.Prototype ("", [||]), e)
-</pre>
-</div>
-
-<p>Now that we have all the pieces, let's build a little driver that will let us
-actually <em>execute</em> this code we've built!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="driver">The Driver</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>The driver for this simply invokes all of the parsing pieces with a top-level
-dispatch loop. There isn't much interesting here, so I'll just include the
-top-level loop. See <a href="#code">below</a> for full code in the "Top-Level
-Parsing" section.</p>
-
-<div class="doc_code">
-<pre>
-(* top ::= definition | external | expression | ';' *)
-let rec main_loop stream =
- match Stream.peek stream with
- | None -> ()
-
- (* ignore top-level semicolons. *)
- | Some (Token.Kwd ';') ->
- Stream.junk stream;
- main_loop stream
-
- | Some token ->
- begin
- try match token with
- | Token.Def ->
- ignore(Parser.parse_definition stream);
- print_endline "parsed a function definition.";
- | Token.Extern ->
- ignore(Parser.parse_extern stream);
- print_endline "parsed an extern.";
- | _ ->
- (* Evaluate a top-level expression into an anonymous function. *)
- ignore(Parser.parse_toplevel stream);
- print_endline "parsed a top-level expr";
- with Stream.Error s ->
- (* Skip token for error recovery. *)
- Stream.junk stream;
- print_endline s;
- end;
- print_string "ready> "; flush stdout;
- main_loop stream
-</pre>
-</div>
-
-<p>The most interesting part of this is that we ignore top-level semicolons.
-Why is this, you ask? The basic reason is that if you type "4 + 5" at the
-command line, the parser doesn't know whether that is the end of what you will type
-or not. For example, on the next line you could type "def foo..." in which case
-4+5 is the end of a top-level expression. Alternatively you could type "* 6",
-which would continue the expression. Having top-level semicolons allows you to
-type "4+5;", and the parser will know you are done.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="conclusions">Conclusions</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>With just under 300 lines of commented code (240 lines of non-comment,
-non-blank code), we fully defined our minimal language, including a lexer,
-parser, and AST builder. With this done, the executable will validate
-Kaleidoscope code and tell us if it is grammatically invalid. For
-example, here is a sample interaction:</p>
-
-<div class="doc_code">
-<pre>
-$ <b>./toy.byte</b>
-ready> <b>def foo(x y) x+foo(y, 4.0);</b>
-Parsed a function definition.
-ready> <b>def foo(x y) x+y y;</b>
-Parsed a function definition.
-Parsed a top-level expr
-ready> <b>def foo(x y) x+y );</b>
-Parsed a function definition.
-Error: unknown token when expecting an expression
-ready> <b>extern sin(a);</b>
-ready> Parsed an extern
-ready> <b>^D</b>
-$
-</pre>
-</div>
-
-<p>There is a lot of room for extension here. You can define new AST nodes,
-extend the language in many ways, etc. In the <a href="OCamlLangImpl3.html">
-next installment</a>, we will describe how to generate LLVM Intermediate
-Representation (IR) from the AST.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for this and the previous chapter.
-Note that it is fully self-contained: you don't need LLVM or any external
-libraries at all for this. (Besides the ocaml standard libraries, of
-course.) To build this, just compile with:</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-ocamlbuild toy.byte
-# Run
-./toy.byte
-</pre>
-</div>
-
-<p>Here is the code:</p>
-
-<dl>
-<dt>_tags:</dt>
-<dd class="doc_code">
-<pre>
-<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
-</pre>
-</dd>
-
-<dt>token.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Lexer Tokens
- *===----------------------------------------------------------------------===*)
-
-(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
- * these others for known things. *)
-type token =
- (* commands *)
- | Def | Extern
-
- (* primary *)
- | Ident of string | Number of float
-
- (* unknown *)
- | Kwd of char
-</pre>
-</dd>
-
-<dt>lexer.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Lexer
- *===----------------------------------------------------------------------===*)
-
-let rec lex = parser
- (* Skip any whitespace. *)
- | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
-
- (* identifier: [a-zA-Z][a-zA-Z0-9] *)
- | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_ident buffer stream
-
- (* number: [0-9.]+ *)
- | [< ' ('0' .. '9' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_number buffer stream
-
- (* Comment until end of line. *)
- | [< ' ('#'); stream >] ->
- lex_comment stream
-
- (* Otherwise, just return the character as its ascii value. *)
- | [< 'c; stream >] ->
- [< 'Token.Kwd c; lex stream >]
-
- (* end of stream. *)
- | [< >] -> [< >]
-
-and lex_number buffer = parser
- | [< ' ('0' .. '9' | '.' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_number buffer stream
- | [< stream=lex >] ->
- [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
-
-and lex_ident buffer = parser
- | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_ident buffer stream
- | [< stream=lex >] ->
- match Buffer.contents buffer with
- | "def" -> [< 'Token.Def; stream >]
- | "extern" -> [< 'Token.Extern; stream >]
- | id -> [< 'Token.Ident id; stream >]
-
-and lex_comment = parser
- | [< ' ('\n'); stream=lex >] -> stream
- | [< 'c; e=lex_comment >] -> e
- | [< >] -> [< >]
-</pre>
-</dd>
-
-<dt>ast.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Abstract Syntax Tree (aka Parse Tree)
- *===----------------------------------------------------------------------===*)
-
-(* expr - Base type for all expression nodes. *)
-type expr =
- (* variant for numeric literals like "1.0". *)
- | Number of float
-
- (* variant for referencing a variable, like "a". *)
- | Variable of string
-
- (* variant for a binary operator. *)
- | Binary of char * expr * expr
-
- (* variant for function calls. *)
- | Call of string * expr array
-
-(* proto - This type represents the "prototype" for a function, which captures
- * its name, and its argument names (thus implicitly the number of arguments the
- * function takes). *)
-type proto = Prototype of string * string array
-
-(* func - This type represents a function definition itself. *)
-type func = Function of proto * expr
-</pre>
-</dd>
-
-<dt>parser.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===---------------------------------------------------------------------===
- * Parser
- *===---------------------------------------------------------------------===*)
-
-(* binop_precedence - This holds the precedence for each binary operator that is
- * defined *)
-let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
-
-(* precedence - Get the precedence of the pending binary operator token. *)
-let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
-
-(* primary
- * ::= identifier
- * ::= numberexpr
- * ::= parenexpr *)
-let rec parse_primary = parser
- (* numberexpr ::= number *)
- | [< 'Token.Number n >] -> Ast.Number n
-
- (* parenexpr ::= '(' expression ')' *)
- | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
-
- (* identifierexpr
- * ::= identifier
- * ::= identifier '(' argumentexpr ')' *)
- | [< 'Token.Ident id; stream >] ->
- let rec parse_args accumulator = parser
- | [< e=parse_expr; stream >] ->
- begin parser
- | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
- | [< >] -> e :: accumulator
- end stream
- | [< >] -> accumulator
- in
- let rec parse_ident id = parser
- (* Call. *)
- | [< 'Token.Kwd '(';
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')'">] ->
- Ast.Call (id, Array.of_list (List.rev args))
-
- (* Simple variable ref. *)
- | [< >] -> Ast.Variable id
- in
- parse_ident id stream
-
- | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
-
-(* binoprhs
- * ::= ('+' primary)* *)
-and parse_bin_rhs expr_prec lhs stream =
- match Stream.peek stream with
- (* If this is a binop, find its precedence. *)
- | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
- let token_prec = precedence c in
-
- (* If this is a binop that binds at least as tightly as the current binop,
- * consume it, otherwise we are done. *)
- if token_prec < expr_prec then lhs else begin
- (* Eat the binop. *)
- Stream.junk stream;
-
- (* Parse the primary expression after the binary operator. *)
- let rhs = parse_primary stream in
-
- (* Okay, we know this is a binop. *)
- let rhs =
- match Stream.peek stream with
- | Some (Token.Kwd c2) ->
- (* If BinOp binds less tightly with rhs than the operator after
- * rhs, let the pending operator take rhs as its lhs. *)
- let next_prec = precedence c2 in
- if token_prec < next_prec
- then parse_bin_rhs (token_prec + 1) rhs stream
- else rhs
- | _ -> rhs
- in
-
- (* Merge lhs/rhs. *)
- let lhs = Ast.Binary (c, lhs, rhs) in
- parse_bin_rhs expr_prec lhs stream
- end
- | _ -> lhs
-
-(* expression
- * ::= primary binoprhs *)
-and parse_expr = parser
- | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
-
-(* prototype
- * ::= id '(' id* ')' *)
-let parse_prototype =
- let rec parse_args accumulator = parser
- | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
- | [< >] -> accumulator
- in
-
- parser
- | [< 'Token.Ident id;
- 'Token.Kwd '(' ?? "expected '(' in prototype";
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
- (* success. *)
- Ast.Prototype (id, Array.of_list (List.rev args))
-
- | [< >] ->
- raise (Stream.Error "expected function name in prototype")
-
-(* definition ::= 'def' prototype expression *)
-let parse_definition = parser
- | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
- Ast.Function (p, e)
-
-(* toplevelexpr ::= expression *)
-let parse_toplevel = parser
- | [< e=parse_expr >] ->
- (* Make an anonymous proto. *)
- Ast.Function (Ast.Prototype ("", [||]), e)
-
-(* external ::= 'extern' prototype *)
-let parse_extern = parser
- | [< 'Token.Extern; e=parse_prototype >] -> e
-</pre>
-</dd>
-
-<dt>toplevel.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Top-Level parsing and JIT Driver
- *===----------------------------------------------------------------------===*)
-
-(* top ::= definition | external | expression | ';' *)
-let rec main_loop stream =
- match Stream.peek stream with
- | None -> ()
-
- (* ignore top-level semicolons. *)
- | Some (Token.Kwd ';') ->
- Stream.junk stream;
- main_loop stream
-
- | Some token ->
- begin
- try match token with
- | Token.Def ->
- ignore(Parser.parse_definition stream);
- print_endline "parsed a function definition.";
- | Token.Extern ->
- ignore(Parser.parse_extern stream);
- print_endline "parsed an extern.";
- | _ ->
- (* Evaluate a top-level expression into an anonymous function. *)
- ignore(Parser.parse_toplevel stream);
- print_endline "parsed a top-level expr";
- with Stream.Error s ->
- (* Skip token for error recovery. *)
- Stream.junk stream;
- print_endline s;
- end;
- print_string "ready> "; flush stdout;
- main_loop stream
-</pre>
-</dd>
-
-<dt>toy.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Main driver code.
- *===----------------------------------------------------------------------===*)
-
-let main () =
- (* Install standard binary operators.
- * 1 is the lowest precedence. *)
- Hashtbl.add Parser.binop_precedence '<' 10;
- Hashtbl.add Parser.binop_precedence '+' 20;
- Hashtbl.add Parser.binop_precedence '-' 20;
- Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
-
- (* Prime the first token. *)
- print_string "ready> "; flush stdout;
- let stream = Lexer.lex (Stream.of_channel stdin) in
-
- (* Run the main "interpreter loop" now. *)
- Toplevel.main_loop stream;
-;;
-
-main ()
-</pre>
-</dd>
-</dl>
-
-<a href="OCamlLangImpl3.html">Next: Implementing Code Generation to LLVM IR</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a>
- <a href="mailto:erickt at users.sourceforge.net">Erick Tryzelaar</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/OCamlLangImpl2.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl2.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl2.rst (added)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl2.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,899 @@
+===========================================
+Kaleidoscope: Implementing a Parser and AST
+===========================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_ and `Erick
+Tryzelaar <mailto:idadesub at users.sourceforge.net>`_
+
+Chapter 2 Introduction
+======================
+
+Welcome to Chapter 2 of the "`Implementing a language with LLVM in
+Objective Caml <index.html>`_" tutorial. This chapter shows you how to
+use the lexer, built in `Chapter 1 <OCamlLangImpl1.html>`_, to build a
+full `parser <http://en.wikipedia.org/wiki/Parsing>`_ for our
+Kaleidoscope language. Once we have a parser, we'll define and build an
+`Abstract Syntax
+Tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_ (AST).
+
+The parser we will build uses a combination of `Recursive Descent
+Parsing <http://en.wikipedia.org/wiki/Recursive_descent_parser>`_ and
+`Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_ to
+parse the Kaleidoscope language (the latter for binary expressions and
+the former for everything else). Before we get to parsing though, lets
+talk about the output of the parser: the Abstract Syntax Tree.
+
+The Abstract Syntax Tree (AST)
+==============================
+
+The AST for a program captures its behavior in such a way that it is
+easy for later stages of the compiler (e.g. code generation) to
+interpret. We basically want one object for each construct in the
+language, and the AST should closely model the language. In
+Kaleidoscope, we have expressions, a prototype, and a function object.
+We'll start with expressions first:
+
+.. code-block:: ocaml
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+The code above shows the definition of the base ExprAST class and one
+subclass which we use for numeric literals. The important thing to note
+about this code is that the Number variant captures the numeric value of
+the literal as an instance variable. This allows later phases of the
+compiler to know what the stored numeric value is.
+
+Right now we only create the AST, so there are no useful functions on
+them. It would be very easy to add a function to pretty print the code,
+for example. Here are the other expression AST node definitions that
+we'll use in the basic form of the Kaleidoscope language:
+
+.. code-block:: ocaml
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+This is all (intentionally) rather straight-forward: variables capture
+the variable name, binary operators capture their opcode (e.g. '+'), and
+calls capture a function name as well as a list of any argument
+expressions. One thing that is nice about our AST is that it captures
+the language features without talking about the syntax of the language.
+Note that there is no discussion about precedence of binary operators,
+lexical structure, etc.
+
+For our basic language, these are all of the expression nodes we'll
+define. Because it doesn't have conditional control flow, it isn't
+Turing-complete; we'll fix that in a later installment. The two things
+we need next are a way to talk about the interface to a function, and a
+way to talk about functions themselves:
+
+.. code-block:: ocaml
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+In Kaleidoscope, functions are typed with just a count of their
+arguments. Since all values are double precision floating point, the
+type of each argument doesn't need to be stored anywhere. In a more
+aggressive and realistic language, the "expr" variants would probably
+have a type field.
+
+With this scaffolding, we can now talk about parsing expressions and
+function bodies in Kaleidoscope.
+
+Parser Basics
+=============
+
+Now that we have an AST to build, we need to define the parser code to
+build it. The idea here is that we want to parse something like "x+y"
+(which is returned as three tokens by the lexer) into an AST that could
+be generated with calls like this:
+
+.. code-block:: ocaml
+
+ let x = Variable "x" in
+ let y = Variable "y" in
+ let result = Binary ('+', x, y) in
+ ...
+
+The error handling routines make use of the builtin ``Stream.Failure``
+and ``Stream.Error``s. ``Stream.Failure`` is raised when the parser is
+unable to find any matching token in the first position of a pattern.
+``Stream.Error`` is raised when the first token matches, but the rest do
+not. The error recovery in our parser will not be the best and is not
+particular user-friendly, but it will be enough for our tutorial. These
+exceptions make it easier to handle errors in routines that have various
+return types.
+
+With these basic types and exceptions, we can implement the first piece
+of our grammar: numeric literals.
+
+Basic Expression Parsing
+========================
+
+We start with numeric literals, because they are the simplest to
+process. For each production in our grammar, we'll define a function
+which parses that production. We call this class of expressions
+"primary" expressions, for reasons that will become more clear `later in
+the tutorial <OCamlLangImpl6.html#unary>`_. In order to parse an
+arbitrary primary expression, we need to determine what sort of
+expression it is. For numeric literals, we have:
+
+.. code-block:: ocaml
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+This routine is very simple: it expects to be called when the current
+token is a ``Token.Number`` token. It takes the current number value,
+creates a ``Ast.Number`` node, advances the lexer to the next token, and
+finally returns.
+
+There are some interesting aspects to this. The most important one is
+that this routine eats all of the tokens that correspond to the
+production and returns the lexer buffer with the next token (which is
+not part of the grammar production) ready to go. This is a fairly
+standard way to go for recursive descent parsers. For a better example,
+the parenthesis operator is defined like this:
+
+.. code-block:: ocaml
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+This function illustrates a number of interesting things about the
+parser:
+
+1) It shows how we use the ``Stream.Error`` exception. When called, this
+function expects that the current token is a '(' token, but after
+parsing the subexpression, it is possible that there is no ')' waiting.
+For example, if the user types in "(4 x" instead of "(4)", the parser
+should emit an error. Because errors can occur, the parser needs a way
+to indicate that they happened. In our parser, we use the camlp4
+shortcut syntax ``token ?? "parse error"``, where if the token before
+the ``??`` does not match, then ``Stream.Error "parse error"`` will be
+raised.
+
+2) Another interesting aspect of this function is that it uses recursion
+by calling ``Parser.parse_primary`` (we will soon see that
+``Parser.parse_primary`` can call ``Parser.parse_primary``). This is
+powerful because it allows us to handle recursive grammars, and keeps
+each production very simple. Note that parentheses do not cause
+construction of AST nodes themselves. While we could do it this way, the
+most important role of parentheses are to guide the parser and provide
+grouping. Once the parser constructs the AST, parentheses are not
+needed.
+
+The next simple production is for handling variable references and
+function calls:
+
+.. code-block:: ocaml
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+This routine follows the same style as the other routines. (It expects
+to be called if the current token is a ``Token.Ident`` token). It also
+has recursion and error handling. One interesting aspect of this is that
+it uses *look-ahead* to determine if the current identifier is a stand
+alone variable reference or if it is a function call expression. It
+handles this by checking to see if the token after the identifier is a
+'(' token, constructing either a ``Ast.Variable`` or ``Ast.Call`` node
+as appropriate.
+
+We finish up by raising an exception if we received a token we didn't
+expect:
+
+.. code-block:: ocaml
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+Now that basic expressions are handled, we need to handle binary
+expressions. They are a bit more complex.
+
+Binary Expression Parsing
+=========================
+
+Binary expressions are significantly harder to parse because they are
+often ambiguous. For example, when given the string "x+y\*z", the parser
+can choose to parse it as either "(x+y)\*z" or "x+(y\*z)". With common
+definitions from mathematics, we expect the later parse, because "\*"
+(multiplication) has higher *precedence* than "+" (addition).
+
+There are many ways to handle this, but an elegant and efficient way is
+to use `Operator-Precedence
+Parsing <http://en.wikipedia.org/wiki/Operator-precedence_parser>`_.
+This parsing technique uses the precedence of binary operators to guide
+recursion. To start with, we need a table of precedences:
+
+.. code-block:: ocaml
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ ...
+
+ let main () =
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+ ...
+
+For the basic form of Kaleidoscope, we will only support 4 binary
+operators (this can obviously be extended by you, our brave and intrepid
+reader). The ``Parser.precedence`` function returns the precedence for
+the current token, or -1 if the token is not a binary operator. Having a
+``Hashtbl.t`` makes it easy to add new operators and makes it clear that
+the algorithm doesn't depend on the specific operators involved, but it
+would be easy enough to eliminate the ``Hashtbl.t`` and do the
+comparisons in the ``Parser.precedence`` function. (Or just use a
+fixed-size array).
+
+With the helper above defined, we can now start parsing binary
+expressions. The basic idea of operator precedence parsing is to break
+down an expression with potentially ambiguous binary operators into
+pieces. Consider ,for example, the expression "a+b+(c+d)\*e\*f+g".
+Operator precedence parsing considers this as a stream of primary
+expressions separated by binary operators. As such, it will first parse
+the leading primary expression "a", then it will see the pairs [+, b]
+[+, (c+d)] [\*, e] [\*, f] and [+, g]. Note that because parentheses are
+primary expressions, the binary expression parser doesn't need to worry
+about nested subexpressions like (c+d) at all.
+
+To start, an expression is a primary expression potentially followed by
+a sequence of [binop,primaryexpr] pairs:
+
+.. code-block:: ocaml
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+``Parser.parse_bin_rhs`` is the function that parses the sequence of
+pairs for us. It takes a precedence and a pointer to an expression for
+the part that has been parsed so far. Note that "x" is a perfectly valid
+expression: As such, "binoprhs" is allowed to be empty, in which case it
+returns the expression that is passed into it. In our example above, the
+code passes the expression for "a" into ``Parser.parse_bin_rhs`` and the
+current token is "+".
+
+The precedence value passed into ``Parser.parse_bin_rhs`` indicates the
+*minimal operator precedence* that the function is allowed to eat. For
+example, if the current pair stream is [+, x] and
+``Parser.parse_bin_rhs`` is passed in a precedence of 40, it will not
+consume any tokens (because the precedence of '+' is only 20). With this
+in mind, ``Parser.parse_bin_rhs`` starts with:
+
+.. code-block:: ocaml
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+
+This code gets the precedence of the current token and checks to see if
+if is too low. Because we defined invalid tokens to have a precedence of
+-1, this check implicitly knows that the pair-stream ends when the token
+stream runs out of binary operators. If this check succeeds, we know
+that the token is a binary operator and that it will be included in this
+expression:
+
+.. code-block:: ocaml
+
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+
+As such, this code eats (and remembers) the binary operator and then
+parses the primary expression that follows. This builds up the whole
+pair, the first of which is [+, b] for the running example.
+
+Now that we parsed the left-hand side of an expression and one pair of
+the RHS sequence, we have to decide which way the expression associates.
+In particular, we could have "(a+b) binop unparsed" or "a + (b binop
+unparsed)". To determine this, we look ahead at "binop" to determine its
+precedence and compare it to BinOp's precedence (which is '+' in this
+case):
+
+.. code-block:: ocaml
+
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+
+If the precedence of the binop to the right of "RHS" is lower or equal
+to the precedence of our current operator, then we know that the
+parentheses associate as "(a+b) binop ...". In our example, the current
+operator is "+" and the next operator is "+", we know that they have the
+same precedence. In this case we'll create the AST node for "a+b", and
+then continue parsing:
+
+.. code-block:: ocaml
+
+ ... if body omitted ...
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+
+In our example above, this will turn "a+b+" into "(a+b)" and execute the
+next iteration of the loop, with "+" as the current token. The code
+above will eat, remember, and parse "(c+d)" as the primary expression,
+which makes the current pair equal to [+, (c+d)]. It will then evaluate
+the 'if' conditional above with "\*" as the binop to the right of the
+primary. In this case, the precedence of "\*" is higher than the
+precedence of "+" so the if condition will be entered.
+
+The critical question left here is "how can the if condition parse the
+right hand side in full"? In particular, to build the AST correctly for
+our example, it needs to get all of "(c+d)\*e\*f" as the RHS expression
+variable. The code to do this is surprisingly simple (code from the
+above two blocks duplicated for context):
+
+.. code-block:: ocaml
+
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ if token_prec < precedence c2
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+
+At this point, we know that the binary operator to the RHS of our
+primary has higher precedence than the binop we are currently parsing.
+As such, we know that any sequence of pairs whose operators are all
+higher precedence than "+" should be parsed together and returned as
+"RHS". To do this, we recursively invoke the ``Parser.parse_bin_rhs``
+function specifying "token\_prec+1" as the minimum precedence required
+for it to continue. In our example above, this will cause it to return
+the AST node for "(c+d)\*e\*f" as RHS, which is then set as the RHS of
+the '+' expression.
+
+Finally, on the next iteration of the while loop, the "+g" piece is
+parsed and added to the AST. With this little bit of code (14
+non-trivial lines), we correctly handle fully general binary expression
+parsing in a very elegant way. This was a whirlwind tour of this code,
+and it is somewhat subtle. I recommend running through it with a few
+tough examples to see how it works.
+
+This wraps up handling of expressions. At this point, we can point the
+parser at an arbitrary token stream and build an expression from it,
+stopping at the first token that is not part of the expression. Next up
+we need to handle function definitions, etc.
+
+Parsing the Rest
+================
+
+The next thing missing is handling of function prototypes. In
+Kaleidoscope, these are used both for 'extern' function declarations as
+well as function body definitions. The code to do this is
+straight-forward and not very interesting (once you've survived
+expressions):
+
+.. code-block:: ocaml
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+Given this, a function definition is very simple, just a prototype plus
+an expression to implement the body:
+
+.. code-block:: ocaml
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+In addition, we support 'extern' to declare functions like 'sin' and
+'cos' as well as to support forward declaration of user functions. These
+'extern's are just prototypes with no body:
+
+.. code-block:: ocaml
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+Finally, we'll also let the user type in arbitrary top-level expressions
+and evaluate them on the fly. We will handle this by defining anonymous
+nullary (zero argument) functions for them:
+
+.. code-block:: ocaml
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+Now that we have all the pieces, let's build a little driver that will
+let us actually *execute* this code we've built!
+
+The Driver
+==========
+
+The driver for this simply invokes all of the parsing pieces with a
+top-level dispatch loop. There isn't much interesting here, so I'll just
+include the top-level loop. See `below <#code>`_ for full code in the
+"Top-Level Parsing" section.
+
+.. code-block:: ocaml
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ ignore(Parser.parse_definition stream);
+ print_endline "parsed a function definition.";
+ | Token.Extern ->
+ ignore(Parser.parse_extern stream);
+ print_endline "parsed an extern.";
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ ignore(Parser.parse_toplevel stream);
+ print_endline "parsed a top-level expr";
+ with Stream.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop stream
+
+The most interesting part of this is that we ignore top-level
+semicolons. Why is this, you ask? The basic reason is that if you type
+"4 + 5" at the command line, the parser doesn't know whether that is the
+end of what you will type or not. For example, on the next line you
+could type "def foo..." in which case 4+5 is the end of a top-level
+expression. Alternatively you could type "\* 6", which would continue
+the expression. Having top-level semicolons allows you to type "4+5;",
+and the parser will know you are done.
+
+Conclusions
+===========
+
+With just under 300 lines of commented code (240 lines of non-comment,
+non-blank code), we fully defined our minimal language, including a
+lexer, parser, and AST builder. With this done, the executable will
+validate Kaleidoscope code and tell us if it is grammatically invalid.
+For example, here is a sample interaction:
+
+.. code-block:: bash
+
+ $ ./toy.byte
+ ready> def foo(x y) x+foo(y, 4.0);
+ Parsed a function definition.
+ ready> def foo(x y) x+y y;
+ Parsed a function definition.
+ Parsed a top-level expr
+ ready> def foo(x y) x+y );
+ Parsed a function definition.
+ Error: unknown token when expecting an expression
+ ready> extern sin(a);
+ ready> Parsed an extern
+ ready> ^D
+ $
+
+There is a lot of room for extension here. You can define new AST nodes,
+extend the language in many ways, etc. In the `next
+installment <OCamlLangImpl3.html>`_, we will describe how to generate
+LLVM Intermediate Representation (IR) from the AST.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for this and the previous chapter.
+Note that it is fully self-contained: you don't need LLVM or any
+external libraries at all for this. (Besides the ocaml standard
+libraries, of course.) To build this, just compile with:
+
+.. code-block:: bash
+
+ # Compile
+ ocamlbuild toy.byte
+ # Run
+ ./toy.byte
+
+Here is the code:
+
+\_tags:
+ ::
+
+ <{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
+
+token.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer Tokens
+ *===----------------------------------------------------------------------===*)
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+lexer.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+ast.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Abstract Syntax Tree (aka Parse Tree)
+ *===----------------------------------------------------------------------===*)
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+parser.ml:
+ .. code-block:: ocaml
+
+ (*===---------------------------------------------------------------------===
+ * Parser
+ *===---------------------------------------------------------------------===*)
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ let rec parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Parse the primary expression after the binary operator. *)
+ let rhs = parse_primary stream in
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+ | _ -> lhs
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+toplevel.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Top-Level parsing and JIT Driver
+ *===----------------------------------------------------------------------===*)
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ ignore(Parser.parse_definition stream);
+ print_endline "parsed a function definition.";
+ | Token.Extern ->
+ ignore(Parser.parse_extern stream);
+ print_endline "parsed an extern.";
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ ignore(Parser.parse_toplevel stream);
+ print_endline "parsed a top-level expr";
+ with Stream.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop stream
+
+toy.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Main driver code.
+ *===----------------------------------------------------------------------===*)
+
+ let main () =
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+
+ (* Prime the first token. *)
+ print_string "ready> "; flush stdout;
+ let stream = Lexer.lex (Stream.of_channel stdin) in
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop stream;
+ ;;
+
+ main ()
+
+`Next: Implementing Code Generation to LLVM IR <OCamlLangImpl3.html>`_
+
Removed: llvm/trunk/docs/tutorial/OCamlLangImpl3.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl3.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl3.html (original)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl3.html (removed)
@@ -1,1093 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Implementing code generation to LLVM IR</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <meta name="author" content="Erick Tryzelaar">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Code generation to LLVM IR</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 3
- <ol>
- <li><a href="#intro">Chapter 3 Introduction</a></li>
- <li><a href="#basics">Code Generation Setup</a></li>
- <li><a href="#exprs">Expression Code Generation</a></li>
- <li><a href="#funcs">Function Code Generation</a></li>
- <li><a href="#driver">Driver Changes and Closing Thoughts</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="OCamlLangImpl4.html">Chapter 4</a>: Adding JIT and Optimizer
-Support</li>
-</ul>
-
-<div class="doc_author">
- <p>
- Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>
- and <a href="mailto:idadesub at users.sourceforge.net">Erick Tryzelaar</a>
- </p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 3 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. This chapter shows you how to transform the <a
-href="OCamlLangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into
-LLVM IR. This will teach you a little bit about how LLVM does things, as well
-as demonstrate how easy it is to use. It's much more work to build a lexer and
-parser than it is to generate LLVM IR code. :)
-</p>
-
-<p><b>Please note</b>: the code in this chapter and later require LLVM 2.3 or
-LLVM SVN to work. LLVM 2.2 and before will not work with it.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="basics">Code Generation Setup</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-In order to generate LLVM IR, we want some simple setup to get started. First
-we define virtual code generation (codegen) methods in each AST class:</p>
-
-<div class="doc_code">
-<pre>
-let rec codegen_expr = function
- | Ast.Number n -> ...
- | Ast.Variable name -> ...
-</pre>
-</div>
-
-<p>The <tt>Codegen.codegen_expr</tt> function says to emit IR for that AST node
-along with all the things it depends on, and they all return an LLVM Value
-object. "Value" is the class used to represent a "<a
-href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
-Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect
-of SSA values is that their value is computed as the related instruction
-executes, and it does not get a new value until (and if) the instruction
-re-executes. In other words, there is no way to "change" an SSA value. For
-more information, please read up on <a
-href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
-Assignment</a> - the concepts are really quite natural once you grok them.</p>
-
-<p>The
-second thing we want is an "Error" exception like we used for the parser, which
-will be used to report errors found during code generation (for example, use of
-an undeclared parameter):</p>
-
-<div class="doc_code">
-<pre>
-exception Error of string
-
-let context = global_context ()
-let the_module = create_module context "my cool jit"
-let builder = builder context
-let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
-let double_type = double_type context
-</pre>
-</div>
-
-<p>The static variables will be used during code generation.
-<tt>Codgen.the_module</tt> is the LLVM construct that contains all of the
-functions and global variables in a chunk of code. In many ways, it is the
-top-level structure that the LLVM IR uses to contain code.</p>
-
-<p>The <tt>Codegen.builder</tt> object is a helper object that makes it easy to
-generate LLVM instructions. Instances of the <a
-href="http://llvm.org/doxygen/IRBuilder_8h-source.html"><tt>IRBuilder</tt></a>
-class keep track of the current place to insert instructions and has methods to
-create new instructions.</p>
-
-<p>The <tt>Codegen.named_values</tt> map keeps track of which values are defined
-in the current scope and what their LLVM representation is. (In other words, it
-is a symbol table for the code). In this form of Kaleidoscope, the only things
-that can be referenced are function parameters. As such, function parameters
-will be in this map when generating code for their function body.</p>
-
-<p>
-With these basics in place, we can start talking about how to generate code for
-each expression. Note that this assumes that the <tt>Codgen.builder</tt> has
-been set up to generate code <em>into</em> something. For now, we'll assume
-that this has already been done, and we'll just use it to emit code.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="exprs">Expression Code Generation</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Generating LLVM code for expression nodes is very straightforward: less
-than 30 lines of commented code for all four of our expression nodes. First
-we'll do numeric literals:</p>
-
-<div class="doc_code">
-<pre>
- | Ast.Number n -> const_float double_type n
-</pre>
-</div>
-
-<p>In the LLVM IR, numeric constants are represented with the
-<tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt>
-internally (<tt>APFloat</tt> has the capability of holding floating point
-constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just
-creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR
-that constants are all uniqued together and shared. For this reason, the API
-uses "the foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)".</p>
-
-<div class="doc_code">
-<pre>
- | Ast.Variable name ->
- (try Hashtbl.find named_values name with
- | Not_found -> raise (Error "unknown variable name"))
-</pre>
-</div>
-
-<p>References to variables are also quite simple using LLVM. In the simple
-version of Kaleidoscope, we assume that the variable has already been emitted
-somewhere and its value is available. In practice, the only values that can be
-in the <tt>Codegen.named_values</tt> map are function arguments. This code
-simply checks to see that the specified name is in the map (if not, an unknown
-variable is being referenced) and returns the value for it. In future chapters,
-we'll add support for <a href="LangImpl5.html#for">loop induction variables</a>
-in the symbol table, and for <a href="LangImpl7.html#localvars">local
-variables</a>.</p>
-
-<div class="doc_code">
-<pre>
- | Ast.Binary (op, lhs, rhs) ->
- let lhs_val = codegen_expr lhs in
- let rhs_val = codegen_expr rhs in
- begin
- match op with
- | '+' -> build_fadd lhs_val rhs_val "addtmp" builder
- | '-' -> build_fsub lhs_val rhs_val "subtmp" builder
- | '*' -> build_fmul lhs_val rhs_val "multmp" builder
- | '<' ->
- (* Convert bool 0/1 to double 0.0 or 1.0 *)
- let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
- build_uitofp i double_type "booltmp" builder
- | _ -> raise (Error "invalid binary operator")
- end
-</pre>
-</div>
-
-<p>Binary operators start to get more interesting. The basic idea here is that
-we recursively emit code for the left-hand side of the expression, then the
-right-hand side, then we compute the result of the binary expression. In this
-code, we do a simple switch on the opcode to create the right LLVM instruction.
-</p>
-
-<p>In the example above, the LLVM builder class is starting to show its value.
-IRBuilder knows where to insert the newly created instruction, all you have to
-do is specify what instruction to create (e.g. with <tt>Llvm.create_add</tt>),
-which operands to use (<tt>lhs</tt> and <tt>rhs</tt> here) and optionally
-provide a name for the generated instruction.</p>
-
-<p>One nice thing about LLVM is that the name is just a hint. For instance, if
-the code above emits multiple "addtmp" variables, LLVM will automatically
-provide each one with an increasing, unique numeric suffix. Local value names
-for instructions are purely optional, but it makes it much easier to read the
-IR dumps.</p>
-
-<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by
-strict rules: for example, the Left and Right operators of
-an <a href="../LangRef.html#i_add">add instruction</a> must have the same
-type, and the result type of the add must match the operand types. Because
-all values in Kaleidoscope are doubles, this makes for very simple code for add,
-sub and mul.</p>
-
-<p>On the other hand, LLVM specifies that the <a
-href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value
-(a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with
-a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction
-converts its input integer into a floating point value by treating the input
-as an unsigned value. In contrast, if we used the <a
-href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<'
-operator would return 0.0 and -1.0, depending on the input value.</p>
-
-<div class="doc_code">
-<pre>
- | Ast.Call (callee, args) ->
- (* Look up the name in the module table. *)
- let callee =
- match lookup_function callee the_module with
- | Some callee -> callee
- | None -> raise (Error "unknown function referenced")
- in
- let params = params callee in
-
- (* If argument mismatch error. *)
- if Array.length params == Array.length args then () else
- raise (Error "incorrect # arguments passed");
- let args = Array.map codegen_expr args in
- build_call callee args "calltmp" builder
-</pre>
-</div>
-
-<p>Code generation for function calls is quite straightforward with LLVM. The
-code above initially does a function name lookup in the LLVM Module's symbol
-table. Recall that the LLVM Module is the container that holds all of the
-functions we are JIT'ing. By giving each function the same name as what the
-user specifies, we can use the LLVM symbol table to resolve function names for
-us.</p>
-
-<p>Once we have the function to call, we recursively codegen each argument that
-is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call
-instruction</a>. Note that LLVM uses the native C calling conventions by
-default, allowing these calls to also call into standard library functions like
-"sin" and "cos", with no additional effort.</p>
-
-<p>This wraps up our handling of the four basic expressions that we have so far
-in Kaleidoscope. Feel free to go in and add some more. For example, by
-browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find
-several other interesting instructions that are really easy to plug into our
-basic framework.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="funcs">Function Code Generation</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Code generation for prototypes and functions must handle a number of
-details, which make their code less beautiful than expression code
-generation, but allows us to illustrate some important points. First, lets
-talk about code generation for prototypes: they are used both for function
-bodies and external function declarations. The code starts with:</p>
-
-<div class="doc_code">
-<pre>
-let codegen_proto = function
- | Ast.Prototype (name, args) ->
- (* Make the function type: double(double,double) etc. *)
- let doubles = Array.make (Array.length args) double_type in
- let ft = function_type double_type doubles in
- let f =
- match lookup_function name the_module with
-</pre>
-</div>
-
-<p>This code packs a lot of power into a few lines. Note first that this
-function returns a "Function*" instead of a "Value*" (although at the moment
-they both are modeled by <tt>llvalue</tt> in ocaml). Because a "prototype"
-really talks about the external interface for a function (not the value computed
-by an expression), it makes sense for it to return the LLVM Function it
-corresponds to when codegen'd.</p>
-
-<p>The call to <tt>Llvm.function_type</tt> creates the <tt>Llvm.llvalue</tt>
-that should be used for a given Prototype. Since all function arguments in
-Kaleidoscope are of type double, the first line creates a vector of "N" LLVM
-double types. It then uses the <tt>Llvm.function_type</tt> method to create a
-function type that takes "N" doubles as arguments, returns one double as a
-result, and that is not vararg (that uses the function
-<tt>Llvm.var_arg_function_type</tt>). Note that Types in LLVM are uniqued just
-like <tt>Constant</tt>s are, so you don't "new" a type, you "get" it.</p>
-
-<p>The final line above checks if the function has already been defined in
-<tt>Codegen.the_module</tt>. If not, we will create it.</p>
-
-<div class="doc_code">
-<pre>
- | None -> declare_function name ft the_module
-</pre>
-</div>
-
-<p>This indicates the type and name to use, as well as which module to insert
-into. By default we assume a function has
-<tt>Llvm.Linkage.ExternalLinkage</tt>. "<a href="LangRef.html#linkage">external
-linkage</a>" means that the function may be defined outside the current module
-and/or that it is callable by functions outside the module. The "<tt>name</tt>"
-passed in is the name the user specified: this name is registered in
-"<tt>Codegen.the_module</tt>"s symbol table, which is used by the function call
-code above.</p>
-
-<p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
-first, we want to allow 'extern'ing a function more than once, as long as the
-prototypes for the externs match (since all arguments have the same type, we
-just have to check that the number of arguments match). Second, we want to
-allow 'extern'ing a function and then defining a body for it. This is useful
-when defining mutually recursive functions.</p>
-
-<div class="doc_code">
-<pre>
- (* If 'f' conflicted, there was already something named 'name'. If it
- * has a body, don't allow redefinition or reextern. *)
- | Some f ->
- (* If 'f' already has a body, reject this. *)
- if Array.length (basic_blocks f) == 0 then () else
- raise (Error "redefinition of function");
-
- (* If 'f' took a different number of arguments, reject. *)
- if Array.length (params f) == Array.length args then () else
- raise (Error "redefinition of function with different # args");
- f
- in
-</pre>
-</div>
-
-<p>In order to verify the logic above, we first check to see if the pre-existing
-function is "empty". In this case, empty means that it has no basic blocks in
-it, which means it has no body. If it has no body, it is a forward
-declaration. Since we don't allow anything after a full definition of the
-function, the code rejects this case. If the previous reference to a function
-was an 'extern', we simply verify that the number of arguments for that
-definition and this one match up. If not, we emit an error.</p>
-
-<div class="doc_code">
-<pre>
- (* Set names for all arguments. *)
- Array.iteri (fun i a ->
- let n = args.(i) in
- set_value_name n a;
- Hashtbl.add named_values n a;
- ) (params f);
- f
-</pre>
-</div>
-
-<p>The last bit of code for prototypes loops over all of the arguments in the
-function, setting the name of the LLVM Argument objects to match, and registering
-the arguments in the <tt>Codegen.named_values</tt> map for future use by the
-<tt>Ast.Variable</tt> variant. Once this is set up, it returns the Function
-object to the caller. Note that we don't check for conflicting
-argument names here (e.g. "extern foo(a b a)"). Doing so would be very
-straight-forward with the mechanics we have already used above.</p>
-
-<div class="doc_code">
-<pre>
-let codegen_func = function
- | Ast.Function (proto, body) ->
- Hashtbl.clear named_values;
- let the_function = codegen_proto proto in
-</pre>
-</div>
-
-<p>Code generation for function definitions starts out simply enough: we just
-codegen the prototype (Proto) and verify that it is ok. We then clear out the
-<tt>Codegen.named_values</tt> map to make sure that there isn't anything in it
-from the last function we compiled. Code generation of the prototype ensures
-that there is an LLVM Function object that is ready to go for us.</p>
-
-<div class="doc_code">
-<pre>
- (* Create a new basic block to start insertion into. *)
- let bb = append_block context "entry" the_function in
- position_at_end bb builder;
-
- try
- let ret_val = codegen_expr body in
-</pre>
-</div>
-
-<p>Now we get to the point where the <tt>Codegen.builder</tt> is set up. The
-first line creates a new
-<a href="http://en.wikipedia.org/wiki/Basic_block">basic block</a> (named
-"entry"), which is inserted into <tt>the_function</tt>. The second line then
-tells the builder that new instructions should be inserted into the end of the
-new basic block. Basic blocks in LLVM are an important part of functions that
-define the <a
-href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>.
-Since we don't have any control flow, our functions will only contain one
-block at this point. We'll fix this in <a href="OCamlLangImpl5.html">Chapter
-5</a> :).</p>
-
-<div class="doc_code">
-<pre>
- let ret_val = codegen_expr body in
-
- (* Finish off the function. *)
- let _ = build_ret ret_val builder in
-
- (* Validate the generated code, checking for consistency. *)
- Llvm_analysis.assert_valid_function the_function;
-
- the_function
-</pre>
-</div>
-
-<p>Once the insertion point is set up, we call the <tt>Codegen.codegen_func</tt>
-method for the root expression of the function. If no error happens, this emits
-code to compute the expression into the entry block and returns the value that
-was computed. Assuming no error, we then create an LLVM <a
-href="../LangRef.html#i_ret">ret instruction</a>, which completes the function.
-Once the function is built, we call
-<tt>Llvm_analysis.assert_valid_function</tt>, which is provided by LLVM. This
-function does a variety of consistency checks on the generated code, to
-determine if our compiler is doing everything right. Using this is important:
-it can catch a lot of bugs. Once the function is finished and validated, we
-return it.</p>
-
-<div class="doc_code">
-<pre>
- with e ->
- delete_function the_function;
- raise e
-</pre>
-</div>
-
-<p>The only piece left here is handling of the error case. For simplicity, we
-handle this by merely deleting the function we produced with the
-<tt>Llvm.delete_function</tt> method. This allows the user to redefine a
-function that they incorrectly typed in before: if we didn't delete it, it
-would live in the symbol table, with a body, preventing future redefinition.</p>
-
-<p>This code does have a bug, though. Since the <tt>Codegen.codegen_proto</tt>
-can return a previously defined forward declaration, our code can actually delete
-a forward declaration. There are a number of ways to fix this bug, see what you
-can come up with! Here is a testcase:</p>
-
-<div class="doc_code">
-<pre>
-extern foo(a b); # ok, defines foo.
-def foo(a b) c; # error, 'c' is invalid.
-def bar() foo(1, 2); # error, unknown function "foo"
-</pre>
-</div>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="driver">Driver Changes and Closing Thoughts</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-For now, code generation to LLVM doesn't really get us much, except that we can
-look at the pretty IR calls. The sample code inserts calls to Codegen into the
-"<tt>Toplevel.main_loop</tt>", and then dumps out the LLVM IR. This gives a
-nice way to look at the LLVM IR for simple functions. For example:
-</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>4+5</b>;
-Read top-level expression:
-define double @""() {
-entry:
- %addtmp = fadd double 4.000000e+00, 5.000000e+00
- ret double %addtmp
-}
-</pre>
-</div>
-
-<p>Note how the parser turns the top-level expression into anonymous functions
-for us. This will be handy when we add <a href="OCamlLangImpl4.html#jit">JIT
-support</a> in the next chapter. Also note that the code is very literally
-transcribed, no optimizations are being performed. We will
-<a href="OCamlLangImpl4.html#trivialconstfold">add optimizations</a> explicitly
-in the next chapter.</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def foo(a b) a*a + 2*a*b + b*b;</b>
-Read function definition:
-define double @foo(double %a, double %b) {
-entry:
- %multmp = fmul double %a, %a
- %multmp1 = fmul double 2.000000e+00, %a
- %multmp2 = fmul double %multmp1, %b
- %addtmp = fadd double %multmp, %multmp2
- %multmp3 = fmul double %b, %b
- %addtmp4 = fadd double %addtmp, %multmp3
- ret double %addtmp4
-}
-</pre>
-</div>
-
-<p>This shows some simple arithmetic. Notice the striking similarity to the
-LLVM builder calls that we use to create the instructions.</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def bar(a) foo(a, 4.0) + bar(31337);</b>
-Read function definition:
-define double @bar(double %a) {
-entry:
- %calltmp = call double @foo(double %a, double 4.000000e+00)
- %calltmp1 = call double @bar(double 3.133700e+04)
- %addtmp = fadd double %calltmp, %calltmp1
- ret double %addtmp
-}
-</pre>
-</div>
-
-<p>This shows some function calls. Note that this function will take a long
-time to execute if you call it. In the future we'll add conditional control
-flow to actually make recursion useful :).</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>extern cos(x);</b>
-Read extern:
-declare double @cos(double)
-
-ready> <b>cos(1.234);</b>
-Read top-level expression:
-define double @""() {
-entry:
- %calltmp = call double @cos(double 1.234000e+00)
- ret double %calltmp
-}
-</pre>
-</div>
-
-<p>This shows an extern for the libm "cos" function, and a call to it.</p>
-
-
-<div class="doc_code">
-<pre>
-ready> <b>^D</b>
-; ModuleID = 'my cool jit'
-
-define double @""() {
-entry:
- %addtmp = fadd double 4.000000e+00, 5.000000e+00
- ret double %addtmp
-}
-
-define double @foo(double %a, double %b) {
-entry:
- %multmp = fmul double %a, %a
- %multmp1 = fmul double 2.000000e+00, %a
- %multmp2 = fmul double %multmp1, %b
- %addtmp = fadd double %multmp, %multmp2
- %multmp3 = fmul double %b, %b
- %addtmp4 = fadd double %addtmp, %multmp3
- ret double %addtmp4
-}
-
-define double @bar(double %a) {
-entry:
- %calltmp = call double @foo(double %a, double 4.000000e+00)
- %calltmp1 = call double @bar(double 3.133700e+04)
- %addtmp = fadd double %calltmp, %calltmp1
- ret double %addtmp
-}
-
-declare double @cos(double)
-
-define double @""() {
-entry:
- %calltmp = call double @cos(double 1.234000e+00)
- ret double %calltmp
-}
-</pre>
-</div>
-
-<p>When you quit the current demo, it dumps out the IR for the entire module
-generated. Here you can see the big picture with all the functions referencing
-each other.</p>
-
-<p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll
-describe how to <a href="OCamlLangImpl4.html">add JIT codegen and optimizer
-support</a> to this so we can actually start running code!</p>
-
-</div>
-
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for our running example, enhanced with the
-LLVM code generator. Because this uses the LLVM libraries, we need to link
-them in. To do this, we use the <a
-href="http://llvm.org/cmds/llvm-config.html">llvm-config</a> tool to inform
-our makefile/command line about which options to use:</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-ocamlbuild toy.byte
-# Run
-./toy.byte
-</pre>
-</div>
-
-<p>Here is the code:</p>
-
-<dl>
-<dt>_tags:</dt>
-<dd class="doc_code">
-<pre>
-<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
-<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
-</pre>
-</dd>
-
-<dt>myocamlbuild.ml:</dt>
-<dd class="doc_code">
-<pre>
-open Ocamlbuild_plugin;;
-
-ocaml_lib ~extern:true "llvm";;
-ocaml_lib ~extern:true "llvm_analysis";;
-
-flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
-</pre>
-</dd>
-
-<dt>token.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Lexer Tokens
- *===----------------------------------------------------------------------===*)
-
-(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
- * these others for known things. *)
-type token =
- (* commands *)
- | Def | Extern
-
- (* primary *)
- | Ident of string | Number of float
-
- (* unknown *)
- | Kwd of char
-</pre>
-</dd>
-
-<dt>lexer.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Lexer
- *===----------------------------------------------------------------------===*)
-
-let rec lex = parser
- (* Skip any whitespace. *)
- | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
-
- (* identifier: [a-zA-Z][a-zA-Z0-9] *)
- | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_ident buffer stream
-
- (* number: [0-9.]+ *)
- | [< ' ('0' .. '9' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_number buffer stream
-
- (* Comment until end of line. *)
- | [< ' ('#'); stream >] ->
- lex_comment stream
-
- (* Otherwise, just return the character as its ascii value. *)
- | [< 'c; stream >] ->
- [< 'Token.Kwd c; lex stream >]
-
- (* end of stream. *)
- | [< >] -> [< >]
-
-and lex_number buffer = parser
- | [< ' ('0' .. '9' | '.' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_number buffer stream
- | [< stream=lex >] ->
- [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
-
-and lex_ident buffer = parser
- | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_ident buffer stream
- | [< stream=lex >] ->
- match Buffer.contents buffer with
- | "def" -> [< 'Token.Def; stream >]
- | "extern" -> [< 'Token.Extern; stream >]
- | id -> [< 'Token.Ident id; stream >]
-
-and lex_comment = parser
- | [< ' ('\n'); stream=lex >] -> stream
- | [< 'c; e=lex_comment >] -> e
- | [< >] -> [< >]
-</pre>
-</dd>
-
-<dt>ast.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Abstract Syntax Tree (aka Parse Tree)
- *===----------------------------------------------------------------------===*)
-
-(* expr - Base type for all expression nodes. *)
-type expr =
- (* variant for numeric literals like "1.0". *)
- | Number of float
-
- (* variant for referencing a variable, like "a". *)
- | Variable of string
-
- (* variant for a binary operator. *)
- | Binary of char * expr * expr
-
- (* variant for function calls. *)
- | Call of string * expr array
-
-(* proto - This type represents the "prototype" for a function, which captures
- * its name, and its argument names (thus implicitly the number of arguments the
- * function takes). *)
-type proto = Prototype of string * string array
-
-(* func - This type represents a function definition itself. *)
-type func = Function of proto * expr
-</pre>
-</dd>
-
-<dt>parser.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===---------------------------------------------------------------------===
- * Parser
- *===---------------------------------------------------------------------===*)
-
-(* binop_precedence - This holds the precedence for each binary operator that is
- * defined *)
-let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
-
-(* precedence - Get the precedence of the pending binary operator token. *)
-let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
-
-(* primary
- * ::= identifier
- * ::= numberexpr
- * ::= parenexpr *)
-let rec parse_primary = parser
- (* numberexpr ::= number *)
- | [< 'Token.Number n >] -> Ast.Number n
-
- (* parenexpr ::= '(' expression ')' *)
- | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
-
- (* identifierexpr
- * ::= identifier
- * ::= identifier '(' argumentexpr ')' *)
- | [< 'Token.Ident id; stream >] ->
- let rec parse_args accumulator = parser
- | [< e=parse_expr; stream >] ->
- begin parser
- | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
- | [< >] -> e :: accumulator
- end stream
- | [< >] -> accumulator
- in
- let rec parse_ident id = parser
- (* Call. *)
- | [< 'Token.Kwd '(';
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')'">] ->
- Ast.Call (id, Array.of_list (List.rev args))
-
- (* Simple variable ref. *)
- | [< >] -> Ast.Variable id
- in
- parse_ident id stream
-
- | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
-
-(* binoprhs
- * ::= ('+' primary)* *)
-and parse_bin_rhs expr_prec lhs stream =
- match Stream.peek stream with
- (* If this is a binop, find its precedence. *)
- | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
- let token_prec = precedence c in
-
- (* If this is a binop that binds at least as tightly as the current binop,
- * consume it, otherwise we are done. *)
- if token_prec < expr_prec then lhs else begin
- (* Eat the binop. *)
- Stream.junk stream;
-
- (* Parse the primary expression after the binary operator. *)
- let rhs = parse_primary stream in
-
- (* Okay, we know this is a binop. *)
- let rhs =
- match Stream.peek stream with
- | Some (Token.Kwd c2) ->
- (* If BinOp binds less tightly with rhs than the operator after
- * rhs, let the pending operator take rhs as its lhs. *)
- let next_prec = precedence c2 in
- if token_prec < next_prec
- then parse_bin_rhs (token_prec + 1) rhs stream
- else rhs
- | _ -> rhs
- in
-
- (* Merge lhs/rhs. *)
- let lhs = Ast.Binary (c, lhs, rhs) in
- parse_bin_rhs expr_prec lhs stream
- end
- | _ -> lhs
-
-(* expression
- * ::= primary binoprhs *)
-and parse_expr = parser
- | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
-
-(* prototype
- * ::= id '(' id* ')' *)
-let parse_prototype =
- let rec parse_args accumulator = parser
- | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
- | [< >] -> accumulator
- in
-
- parser
- | [< 'Token.Ident id;
- 'Token.Kwd '(' ?? "expected '(' in prototype";
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
- (* success. *)
- Ast.Prototype (id, Array.of_list (List.rev args))
-
- | [< >] ->
- raise (Stream.Error "expected function name in prototype")
-
-(* definition ::= 'def' prototype expression *)
-let parse_definition = parser
- | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
- Ast.Function (p, e)
-
-(* toplevelexpr ::= expression *)
-let parse_toplevel = parser
- | [< e=parse_expr >] ->
- (* Make an anonymous proto. *)
- Ast.Function (Ast.Prototype ("", [||]), e)
-
-(* external ::= 'extern' prototype *)
-let parse_extern = parser
- | [< 'Token.Extern; e=parse_prototype >] -> e
-</pre>
-</dd>
-
-<dt>codegen.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Code Generation
- *===----------------------------------------------------------------------===*)
-
-open Llvm
-
-exception Error of string
-
-let context = global_context ()
-let the_module = create_module context "my cool jit"
-let builder = builder context
-let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
-let double_type = double_type context
-
-let rec codegen_expr = function
- | Ast.Number n -> const_float double_type n
- | Ast.Variable name ->
- (try Hashtbl.find named_values name with
- | Not_found -> raise (Error "unknown variable name"))
- | Ast.Binary (op, lhs, rhs) ->
- let lhs_val = codegen_expr lhs in
- let rhs_val = codegen_expr rhs in
- begin
- match op with
- | '+' -> build_add lhs_val rhs_val "addtmp" builder
- | '-' -> build_sub lhs_val rhs_val "subtmp" builder
- | '*' -> build_mul lhs_val rhs_val "multmp" builder
- | '<' ->
- (* Convert bool 0/1 to double 0.0 or 1.0 *)
- let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
- build_uitofp i double_type "booltmp" builder
- | _ -> raise (Error "invalid binary operator")
- end
- | Ast.Call (callee, args) ->
- (* Look up the name in the module table. *)
- let callee =
- match lookup_function callee the_module with
- | Some callee -> callee
- | None -> raise (Error "unknown function referenced")
- in
- let params = params callee in
-
- (* If argument mismatch error. *)
- if Array.length params == Array.length args then () else
- raise (Error "incorrect # arguments passed");
- let args = Array.map codegen_expr args in
- build_call callee args "calltmp" builder
-
-let codegen_proto = function
- | Ast.Prototype (name, args) ->
- (* Make the function type: double(double,double) etc. *)
- let doubles = Array.make (Array.length args) double_type in
- let ft = function_type double_type doubles in
- let f =
- match lookup_function name the_module with
- | None -> declare_function name ft the_module
-
- (* If 'f' conflicted, there was already something named 'name'. If it
- * has a body, don't allow redefinition or reextern. *)
- | Some f ->
- (* If 'f' already has a body, reject this. *)
- if block_begin f <> At_end f then
- raise (Error "redefinition of function");
-
- (* If 'f' took a different number of arguments, reject. *)
- if element_type (type_of f) <> ft then
- raise (Error "redefinition of function with different # args");
- f
- in
-
- (* Set names for all arguments. *)
- Array.iteri (fun i a ->
- let n = args.(i) in
- set_value_name n a;
- Hashtbl.add named_values n a;
- ) (params f);
- f
-
-let codegen_func = function
- | Ast.Function (proto, body) ->
- Hashtbl.clear named_values;
- let the_function = codegen_proto proto in
-
- (* Create a new basic block to start insertion into. *)
- let bb = append_block context "entry" the_function in
- position_at_end bb builder;
-
- try
- let ret_val = codegen_expr body in
-
- (* Finish off the function. *)
- let _ = build_ret ret_val builder in
-
- (* Validate the generated code, checking for consistency. *)
- Llvm_analysis.assert_valid_function the_function;
-
- the_function
- with e ->
- delete_function the_function;
- raise e
-</pre>
-</dd>
-
-<dt>toplevel.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Top-Level parsing and JIT Driver
- *===----------------------------------------------------------------------===*)
-
-open Llvm
-
-(* top ::= definition | external | expression | ';' *)
-let rec main_loop stream =
- match Stream.peek stream with
- | None -> ()
-
- (* ignore top-level semicolons. *)
- | Some (Token.Kwd ';') ->
- Stream.junk stream;
- main_loop stream
-
- | Some token ->
- begin
- try match token with
- | Token.Def ->
- let e = Parser.parse_definition stream in
- print_endline "parsed a function definition.";
- dump_value (Codegen.codegen_func e);
- | Token.Extern ->
- let e = Parser.parse_extern stream in
- print_endline "parsed an extern.";
- dump_value (Codegen.codegen_proto e);
- | _ ->
- (* Evaluate a top-level expression into an anonymous function. *)
- let e = Parser.parse_toplevel stream in
- print_endline "parsed a top-level expr";
- dump_value (Codegen.codegen_func e);
- with Stream.Error s | Codegen.Error s ->
- (* Skip token for error recovery. *)
- Stream.junk stream;
- print_endline s;
- end;
- print_string "ready> "; flush stdout;
- main_loop stream
-</pre>
-</dd>
-
-<dt>toy.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Main driver code.
- *===----------------------------------------------------------------------===*)
-
-open Llvm
-
-let main () =
- (* Install standard binary operators.
- * 1 is the lowest precedence. *)
- Hashtbl.add Parser.binop_precedence '<' 10;
- Hashtbl.add Parser.binop_precedence '+' 20;
- Hashtbl.add Parser.binop_precedence '-' 20;
- Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
-
- (* Prime the first token. *)
- print_string "ready> "; flush stdout;
- let stream = Lexer.lex (Stream.of_channel stdin) in
-
- (* Run the main "interpreter loop" now. *)
- Toplevel.main_loop stream;
-
- (* Print out all the generated code. *)
- dump_module Codegen.the_module
-;;
-
-main ()
-</pre>
-</dd>
-</dl>
-
-<a href="OCamlLangImpl4.html">Next: Adding JIT and Optimizer Support</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="mailto:idadesub at users.sourceforge.net">Erick Tryzelaar</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/OCamlLangImpl3.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl3.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl3.rst (added)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl3.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,964 @@
+========================================
+Kaleidoscope: Code generation to LLVM IR
+========================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_ and `Erick
+Tryzelaar <mailto:idadesub at users.sourceforge.net>`_
+
+Chapter 3 Introduction
+======================
+
+Welcome to Chapter 3 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. This chapter shows you how to transform
+the `Abstract Syntax Tree <OCamlLangImpl2.html>`_, built in Chapter 2,
+into LLVM IR. This will teach you a little bit about how LLVM does
+things, as well as demonstrate how easy it is to use. It's much more
+work to build a lexer and parser than it is to generate LLVM IR code. :)
+
+**Please note**: the code in this chapter and later require LLVM 2.3 or
+LLVM SVN to work. LLVM 2.2 and before will not work with it.
+
+Code Generation Setup
+=====================
+
+In order to generate LLVM IR, we want some simple setup to get started.
+First we define virtual code generation (codegen) methods in each AST
+class:
+
+.. code-block:: ocaml
+
+ let rec codegen_expr = function
+ | Ast.Number n -> ...
+ | Ast.Variable name -> ...
+
+The ``Codegen.codegen_expr`` function says to emit IR for that AST node
+along with all the things it depends on, and they all return an LLVM
+Value object. "Value" is the class used to represent a "`Static Single
+Assignment
+(SSA) <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+register" or "SSA value" in LLVM. The most distinct aspect of SSA values
+is that their value is computed as the related instruction executes, and
+it does not get a new value until (and if) the instruction re-executes.
+In other words, there is no way to "change" an SSA value. For more
+information, please read up on `Static Single
+Assignment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
+- the concepts are really quite natural once you grok them.
+
+The second thing we want is an "Error" exception like we used for the
+parser, which will be used to report errors found during code generation
+(for example, use of an undeclared parameter):
+
+.. code-block:: ocaml
+
+ exception Error of string
+
+ let context = global_context ()
+ let the_module = create_module context "my cool jit"
+ let builder = builder context
+ let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+ let double_type = double_type context
+
+The static variables will be used during code generation.
+``Codgen.the_module`` is the LLVM construct that contains all of the
+functions and global variables in a chunk of code. In many ways, it is
+the top-level structure that the LLVM IR uses to contain code.
+
+The ``Codegen.builder`` object is a helper object that makes it easy to
+generate LLVM instructions. Instances of the
+```IRBuilder`` <http://llvm.org/doxygen/IRBuilder_8h-source.html>`_
+class keep track of the current place to insert instructions and has
+methods to create new instructions.
+
+The ``Codegen.named_values`` map keeps track of which values are defined
+in the current scope and what their LLVM representation is. (In other
+words, it is a symbol table for the code). In this form of Kaleidoscope,
+the only things that can be referenced are function parameters. As such,
+function parameters will be in this map when generating code for their
+function body.
+
+With these basics in place, we can start talking about how to generate
+code for each expression. Note that this assumes that the
+``Codgen.builder`` has been set up to generate code *into* something.
+For now, we'll assume that this has already been done, and we'll just
+use it to emit code.
+
+Expression Code Generation
+==========================
+
+Generating LLVM code for expression nodes is very straightforward: less
+than 30 lines of commented code for all four of our expression nodes.
+First we'll do numeric literals:
+
+.. code-block:: ocaml
+
+ | Ast.Number n -> const_float double_type n
+
+In the LLVM IR, numeric constants are represented with the
+``ConstantFP`` class, which holds the numeric value in an ``APFloat``
+internally (``APFloat`` has the capability of holding floating point
+constants of Arbitrary Precision). This code basically just creates
+and returns a ``ConstantFP``. Note that in the LLVM IR that constants
+are all uniqued together and shared. For this reason, the API uses "the
+foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)".
+
+.. code-block:: ocaml
+
+ | Ast.Variable name ->
+ (try Hashtbl.find named_values name with
+ | Not_found -> raise (Error "unknown variable name"))
+
+References to variables are also quite simple using LLVM. In the simple
+version of Kaleidoscope, we assume that the variable has already been
+emitted somewhere and its value is available. In practice, the only
+values that can be in the ``Codegen.named_values`` map are function
+arguments. This code simply checks to see that the specified name is in
+the map (if not, an unknown variable is being referenced) and returns
+the value for it. In future chapters, we'll add support for `loop
+induction variables <LangImpl5.html#for>`_ in the symbol table, and for
+`local variables <LangImpl7.html#localvars>`_.
+
+.. code-block:: ocaml
+
+ | Ast.Binary (op, lhs, rhs) ->
+ let lhs_val = codegen_expr lhs in
+ let rhs_val = codegen_expr rhs in
+ begin
+ match op with
+ | '+' -> build_fadd lhs_val rhs_val "addtmp" builder
+ | '-' -> build_fsub lhs_val rhs_val "subtmp" builder
+ | '*' -> build_fmul lhs_val rhs_val "multmp" builder
+ | '<' ->
+ (* Convert bool 0/1 to double 0.0 or 1.0 *)
+ let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
+ build_uitofp i double_type "booltmp" builder
+ | _ -> raise (Error "invalid binary operator")
+ end
+
+Binary operators start to get more interesting. The basic idea here is
+that we recursively emit code for the left-hand side of the expression,
+then the right-hand side, then we compute the result of the binary
+expression. In this code, we do a simple switch on the opcode to create
+the right LLVM instruction.
+
+In the example above, the LLVM builder class is starting to show its
+value. IRBuilder knows where to insert the newly created instruction,
+all you have to do is specify what instruction to create (e.g. with
+``Llvm.create_add``), which operands to use (``lhs`` and ``rhs`` here)
+and optionally provide a name for the generated instruction.
+
+One nice thing about LLVM is that the name is just a hint. For instance,
+if the code above emits multiple "addtmp" variables, LLVM will
+automatically provide each one with an increasing, unique numeric
+suffix. Local value names for instructions are purely optional, but it
+makes it much easier to read the IR dumps.
+
+`LLVM instructions <../LangRef.html#instref>`_ are constrained by strict
+rules: for example, the Left and Right operators of an `add
+instruction <../LangRef.html#i_add>`_ must have the same type, and the
+result type of the add must match the operand types. Because all values
+in Kaleidoscope are doubles, this makes for very simple code for add,
+sub and mul.
+
+On the other hand, LLVM specifies that the `fcmp
+instruction <../LangRef.html#i_fcmp>`_ always returns an 'i1' value (a
+one bit integer). The problem with this is that Kaleidoscope wants the
+value to be a 0.0 or 1.0 value. In order to get these semantics, we
+combine the fcmp instruction with a `uitofp
+instruction <../LangRef.html#i_uitofp>`_. This instruction converts its
+input integer into a floating point value by treating the input as an
+unsigned value. In contrast, if we used the `sitofp
+instruction <../LangRef.html#i_sitofp>`_, the Kaleidoscope '<' operator
+would return 0.0 and -1.0, depending on the input value.
+
+.. code-block:: ocaml
+
+ | Ast.Call (callee, args) ->
+ (* Look up the name in the module table. *)
+ let callee =
+ match lookup_function callee the_module with
+ | Some callee -> callee
+ | None -> raise (Error "unknown function referenced")
+ in
+ let params = params callee in
+
+ (* If argument mismatch error. *)
+ if Array.length params == Array.length args then () else
+ raise (Error "incorrect # arguments passed");
+ let args = Array.map codegen_expr args in
+ build_call callee args "calltmp" builder
+
+Code generation for function calls is quite straightforward with LLVM.
+The code above initially does a function name lookup in the LLVM
+Module's symbol table. Recall that the LLVM Module is the container that
+holds all of the functions we are JIT'ing. By giving each function the
+same name as what the user specifies, we can use the LLVM symbol table
+to resolve function names for us.
+
+Once we have the function to call, we recursively codegen each argument
+that is to be passed in, and create an LLVM `call
+instruction <../LangRef.html#i_call>`_. Note that LLVM uses the native C
+calling conventions by default, allowing these calls to also call into
+standard library functions like "sin" and "cos", with no additional
+effort.
+
+This wraps up our handling of the four basic expressions that we have so
+far in Kaleidoscope. Feel free to go in and add some more. For example,
+by browsing the `LLVM language reference <../LangRef.html>`_ you'll find
+several other interesting instructions that are really easy to plug into
+our basic framework.
+
+Function Code Generation
+========================
+
+Code generation for prototypes and functions must handle a number of
+details, which make their code less beautiful than expression code
+generation, but allows us to illustrate some important points. First,
+lets talk about code generation for prototypes: they are used both for
+function bodies and external function declarations. The code starts
+with:
+
+.. code-block:: ocaml
+
+ let codegen_proto = function
+ | Ast.Prototype (name, args) ->
+ (* Make the function type: double(double,double) etc. *)
+ let doubles = Array.make (Array.length args) double_type in
+ let ft = function_type double_type doubles in
+ let f =
+ match lookup_function name the_module with
+
+This code packs a lot of power into a few lines. Note first that this
+function returns a "Function\*" instead of a "Value\*" (although at the
+moment they both are modeled by ``llvalue`` in ocaml). Because a
+"prototype" really talks about the external interface for a function
+(not the value computed by an expression), it makes sense for it to
+return the LLVM Function it corresponds to when codegen'd.
+
+The call to ``Llvm.function_type`` creates the ``Llvm.llvalue`` that
+should be used for a given Prototype. Since all function arguments in
+Kaleidoscope are of type double, the first line creates a vector of "N"
+LLVM double types. It then uses the ``Llvm.function_type`` method to
+create a function type that takes "N" doubles as arguments, returns one
+double as a result, and that is not vararg (that uses the function
+``Llvm.var_arg_function_type``). Note that Types in LLVM are uniqued
+just like ``Constant``'s are, so you don't "new" a type, you "get" it.
+
+The final line above checks if the function has already been defined in
+``Codegen.the_module``. If not, we will create it.
+
+.. code-block:: ocaml
+
+ | None -> declare_function name ft the_module
+
+This indicates the type and name to use, as well as which module to
+insert into. By default we assume a function has
+``Llvm.Linkage.ExternalLinkage``. "`external
+linkage <LangRef.html#linkage>`_" means that the function may be defined
+outside the current module and/or that it is callable by functions
+outside the module. The "``name``" passed in is the name the user
+specified: this name is registered in "``Codegen.the_module``"s symbol
+table, which is used by the function call code above.
+
+In Kaleidoscope, I choose to allow redefinitions of functions in two
+cases: first, we want to allow 'extern'ing a function more than once, as
+long as the prototypes for the externs match (since all arguments have
+the same type, we just have to check that the number of arguments
+match). Second, we want to allow 'extern'ing a function and then
+defining a body for it. This is useful when defining mutually recursive
+functions.
+
+.. code-block:: ocaml
+
+ (* If 'f' conflicted, there was already something named 'name'. If it
+ * has a body, don't allow redefinition or reextern. *)
+ | Some f ->
+ (* If 'f' already has a body, reject this. *)
+ if Array.length (basic_blocks f) == 0 then () else
+ raise (Error "redefinition of function");
+
+ (* If 'f' took a different number of arguments, reject. *)
+ if Array.length (params f) == Array.length args then () else
+ raise (Error "redefinition of function with different # args");
+ f
+ in
+
+In order to verify the logic above, we first check to see if the
+pre-existing function is "empty". In this case, empty means that it has
+no basic blocks in it, which means it has no body. If it has no body, it
+is a forward declaration. Since we don't allow anything after a full
+definition of the function, the code rejects this case. If the previous
+reference to a function was an 'extern', we simply verify that the
+number of arguments for that definition and this one match up. If not,
+we emit an error.
+
+.. code-block:: ocaml
+
+ (* Set names for all arguments. *)
+ Array.iteri (fun i a ->
+ let n = args.(i) in
+ set_value_name n a;
+ Hashtbl.add named_values n a;
+ ) (params f);
+ f
+
+The last bit of code for prototypes loops over all of the arguments in
+the function, setting the name of the LLVM Argument objects to match,
+and registering the arguments in the ``Codegen.named_values`` map for
+future use by the ``Ast.Variable`` variant. Once this is set up, it
+returns the Function object to the caller. Note that we don't check for
+conflicting argument names here (e.g. "extern foo(a b a)"). Doing so
+would be very straight-forward with the mechanics we have already used
+above.
+
+.. code-block:: ocaml
+
+ let codegen_func = function
+ | Ast.Function (proto, body) ->
+ Hashtbl.clear named_values;
+ let the_function = codegen_proto proto in
+
+Code generation for function definitions starts out simply enough: we
+just codegen the prototype (Proto) and verify that it is ok. We then
+clear out the ``Codegen.named_values`` map to make sure that there isn't
+anything in it from the last function we compiled. Code generation of
+the prototype ensures that there is an LLVM Function object that is
+ready to go for us.
+
+.. code-block:: ocaml
+
+ (* Create a new basic block to start insertion into. *)
+ let bb = append_block context "entry" the_function in
+ position_at_end bb builder;
+
+ try
+ let ret_val = codegen_expr body in
+
+Now we get to the point where the ``Codegen.builder`` is set up. The
+first line creates a new `basic
+block <http://en.wikipedia.org/wiki/Basic_block>`_ (named "entry"),
+which is inserted into ``the_function``. The second line then tells the
+builder that new instructions should be inserted into the end of the new
+basic block. Basic blocks in LLVM are an important part of functions
+that define the `Control Flow
+Graph <http://en.wikipedia.org/wiki/Control_flow_graph>`_. Since we
+don't have any control flow, our functions will only contain one block
+at this point. We'll fix this in `Chapter 5 <OCamlLangImpl5.html>`_ :).
+
+.. code-block:: ocaml
+
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ the_function
+
+Once the insertion point is set up, we call the ``Codegen.codegen_func``
+method for the root expression of the function. If no error happens,
+this emits code to compute the expression into the entry block and
+returns the value that was computed. Assuming no error, we then create
+an LLVM `ret instruction <../LangRef.html#i_ret>`_, which completes the
+function. Once the function is built, we call
+``Llvm_analysis.assert_valid_function``, which is provided by LLVM. This
+function does a variety of consistency checks on the generated code, to
+determine if our compiler is doing everything right. Using this is
+important: it can catch a lot of bugs. Once the function is finished and
+validated, we return it.
+
+.. code-block:: ocaml
+
+ with e ->
+ delete_function the_function;
+ raise e
+
+The only piece left here is handling of the error case. For simplicity,
+we handle this by merely deleting the function we produced with the
+``Llvm.delete_function`` method. This allows the user to redefine a
+function that they incorrectly typed in before: if we didn't delete it,
+it would live in the symbol table, with a body, preventing future
+redefinition.
+
+This code does have a bug, though. Since the ``Codegen.codegen_proto``
+can return a previously defined forward declaration, our code can
+actually delete a forward declaration. There are a number of ways to fix
+this bug, see what you can come up with! Here is a testcase:
+
+::
+
+ extern foo(a b); # ok, defines foo.
+ def foo(a b) c; # error, 'c' is invalid.
+ def bar() foo(1, 2); # error, unknown function "foo"
+
+Driver Changes and Closing Thoughts
+===================================
+
+For now, code generation to LLVM doesn't really get us much, except that
+we can look at the pretty IR calls. The sample code inserts calls to
+Codegen into the "``Toplevel.main_loop``", and then dumps out the LLVM
+IR. This gives a nice way to look at the LLVM IR for simple functions.
+For example:
+
+::
+
+ ready> 4+5;
+ Read top-level expression:
+ define double @""() {
+ entry:
+ %addtmp = fadd double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+ }
+
+Note how the parser turns the top-level expression into anonymous
+functions for us. This will be handy when we add `JIT
+support <OCamlLangImpl4.html#jit>`_ in the next chapter. Also note that
+the code is very literally transcribed, no optimizations are being
+performed. We will `add
+optimizations <OCamlLangImpl4.html#trivialconstfold>`_ explicitly in the
+next chapter.
+
+::
+
+ ready> def foo(a b) a*a + 2*a*b + b*b;
+ Read function definition:
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+This shows some simple arithmetic. Notice the striking similarity to the
+LLVM builder calls that we use to create the instructions.
+
+::
+
+ ready> def bar(a) foo(a, 4.0) + bar(31337);
+ Read function definition:
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+This shows some function calls. Note that this function will take a long
+time to execute if you call it. In the future we'll add conditional
+control flow to actually make recursion useful :).
+
+::
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> cos(1.234);
+ Read top-level expression:
+ define double @""() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+This shows an extern for the libm "cos" function, and a call to it.
+
+::
+
+ ready> ^D
+ ; ModuleID = 'my cool jit'
+
+ define double @""() {
+ entry:
+ %addtmp = fadd double 4.000000e+00, 5.000000e+00
+ ret double %addtmp
+ }
+
+ define double @foo(double %a, double %b) {
+ entry:
+ %multmp = fmul double %a, %a
+ %multmp1 = fmul double 2.000000e+00, %a
+ %multmp2 = fmul double %multmp1, %b
+ %addtmp = fadd double %multmp, %multmp2
+ %multmp3 = fmul double %b, %b
+ %addtmp4 = fadd double %addtmp, %multmp3
+ ret double %addtmp4
+ }
+
+ define double @bar(double %a) {
+ entry:
+ %calltmp = call double @foo(double %a, double 4.000000e+00)
+ %calltmp1 = call double @bar(double 3.133700e+04)
+ %addtmp = fadd double %calltmp, %calltmp1
+ ret double %addtmp
+ }
+
+ declare double @cos(double)
+
+ define double @""() {
+ entry:
+ %calltmp = call double @cos(double 1.234000e+00)
+ ret double %calltmp
+ }
+
+When you quit the current demo, it dumps out the IR for the entire
+module generated. Here you can see the big picture with all the
+functions referencing each other.
+
+This wraps up the third chapter of the Kaleidoscope tutorial. Up next,
+we'll describe how to `add JIT codegen and optimizer
+support <OCamlLangImpl4.html>`_ to this so we can actually start running
+code!
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM code generator. Because this uses the LLVM libraries, we need
+to link them in. To do this, we use the
+`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
+our makefile/command line about which options to use:
+
+.. code-block:: bash
+
+ # Compile
+ ocamlbuild toy.byte
+ # Run
+ ./toy.byte
+
+Here is the code:
+
+\_tags:
+ ::
+
+ <{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
+ <*.{byte,native}>: g++, use_llvm, use_llvm_analysis
+
+myocamlbuild.ml:
+ .. code-block:: ocaml
+
+ open Ocamlbuild_plugin;;
+
+ ocaml_lib ~extern:true "llvm";;
+ ocaml_lib ~extern:true "llvm_analysis";;
+
+ flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
+
+token.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer Tokens
+ *===----------------------------------------------------------------------===*)
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+lexer.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+ast.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Abstract Syntax Tree (aka Parse Tree)
+ *===----------------------------------------------------------------------===*)
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+parser.ml:
+ .. code-block:: ocaml
+
+ (*===---------------------------------------------------------------------===
+ * Parser
+ *===---------------------------------------------------------------------===*)
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ let rec parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Parse the primary expression after the binary operator. *)
+ let rhs = parse_primary stream in
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+ | _ -> lhs
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+codegen.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Code Generation
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ exception Error of string
+
+ let context = global_context ()
+ let the_module = create_module context "my cool jit"
+ let builder = builder context
+ let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+ let double_type = double_type context
+
+ let rec codegen_expr = function
+ | Ast.Number n -> const_float double_type n
+ | Ast.Variable name ->
+ (try Hashtbl.find named_values name with
+ | Not_found -> raise (Error "unknown variable name"))
+ | Ast.Binary (op, lhs, rhs) ->
+ let lhs_val = codegen_expr lhs in
+ let rhs_val = codegen_expr rhs in
+ begin
+ match op with
+ | '+' -> build_add lhs_val rhs_val "addtmp" builder
+ | '-' -> build_sub lhs_val rhs_val "subtmp" builder
+ | '*' -> build_mul lhs_val rhs_val "multmp" builder
+ | '<' ->
+ (* Convert bool 0/1 to double 0.0 or 1.0 *)
+ let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
+ build_uitofp i double_type "booltmp" builder
+ | _ -> raise (Error "invalid binary operator")
+ end
+ | Ast.Call (callee, args) ->
+ (* Look up the name in the module table. *)
+ let callee =
+ match lookup_function callee the_module with
+ | Some callee -> callee
+ | None -> raise (Error "unknown function referenced")
+ in
+ let params = params callee in
+
+ (* If argument mismatch error. *)
+ if Array.length params == Array.length args then () else
+ raise (Error "incorrect # arguments passed");
+ let args = Array.map codegen_expr args in
+ build_call callee args "calltmp" builder
+
+ let codegen_proto = function
+ | Ast.Prototype (name, args) ->
+ (* Make the function type: double(double,double) etc. *)
+ let doubles = Array.make (Array.length args) double_type in
+ let ft = function_type double_type doubles in
+ let f =
+ match lookup_function name the_module with
+ | None -> declare_function name ft the_module
+
+ (* If 'f' conflicted, there was already something named 'name'. If it
+ * has a body, don't allow redefinition or reextern. *)
+ | Some f ->
+ (* If 'f' already has a body, reject this. *)
+ if block_begin f <> At_end f then
+ raise (Error "redefinition of function");
+
+ (* If 'f' took a different number of arguments, reject. *)
+ if element_type (type_of f) <> ft then
+ raise (Error "redefinition of function with different # args");
+ f
+ in
+
+ (* Set names for all arguments. *)
+ Array.iteri (fun i a ->
+ let n = args.(i) in
+ set_value_name n a;
+ Hashtbl.add named_values n a;
+ ) (params f);
+ f
+
+ let codegen_func = function
+ | Ast.Function (proto, body) ->
+ Hashtbl.clear named_values;
+ let the_function = codegen_proto proto in
+
+ (* Create a new basic block to start insertion into. *)
+ let bb = append_block context "entry" the_function in
+ position_at_end bb builder;
+
+ try
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ the_function
+ with e ->
+ delete_function the_function;
+ raise e
+
+toplevel.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Top-Level parsing and JIT Driver
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ let e = Parser.parse_definition stream in
+ print_endline "parsed a function definition.";
+ dump_value (Codegen.codegen_func e);
+ | Token.Extern ->
+ let e = Parser.parse_extern stream in
+ print_endline "parsed an extern.";
+ dump_value (Codegen.codegen_proto e);
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ let e = Parser.parse_toplevel stream in
+ print_endline "parsed a top-level expr";
+ dump_value (Codegen.codegen_func e);
+ with Stream.Error s | Codegen.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop stream
+
+toy.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Main driver code.
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ let main () =
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+
+ (* Prime the first token. *)
+ print_string "ready> "; flush stdout;
+ let stream = Lexer.lex (Stream.of_channel stdin) in
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop stream;
+
+ (* Print out all the generated code. *)
+ dump_module Codegen.the_module
+ ;;
+
+ main ()
+
+`Next: Adding JIT and Optimizer Support <OCamlLangImpl4.html>`_
+
Removed: llvm/trunk/docs/tutorial/OCamlLangImpl4.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl4.html?rev=169342&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl4.html (original)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl4.html (removed)
@@ -1,1026 +0,0 @@
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
- "http://www.w3.org/TR/html4/strict.dtd">
-
-<html>
-<head>
- <title>Kaleidoscope: Adding JIT and Optimizer Support</title>
- <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
- <meta name="author" content="Chris Lattner">
- <meta name="author" content="Erick Tryzelaar">
- <link rel="stylesheet" href="../_static/llvm.css" type="text/css">
-</head>
-
-<body>
-
-<h1>Kaleidoscope: Adding JIT and Optimizer Support</h1>
-
-<ul>
-<li><a href="index.html">Up to Tutorial Index</a></li>
-<li>Chapter 4
- <ol>
- <li><a href="#intro">Chapter 4 Introduction</a></li>
- <li><a href="#trivialconstfold">Trivial Constant Folding</a></li>
- <li><a href="#optimizerpasses">LLVM Optimization Passes</a></li>
- <li><a href="#jit">Adding a JIT Compiler</a></li>
- <li><a href="#code">Full Code Listing</a></li>
- </ol>
-</li>
-<li><a href="OCamlLangImpl5.html">Chapter 5</a>: Extending the Language: Control
-Flow</li>
-</ul>
-
-<div class="doc_author">
- <p>
- Written by <a href="mailto:sabre at nondot.org">Chris Lattner</a>
- and <a href="mailto:idadesub at users.sourceforge.net">Erick Tryzelaar</a>
- </p>
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="intro">Chapter 4 Introduction</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Welcome to Chapter 4 of the "<a href="index.html">Implementing a language
-with LLVM</a>" tutorial. Chapters 1-3 described the implementation of a simple
-language and added support for generating LLVM IR. This chapter describes
-two new techniques: adding optimizer support to your language, and adding JIT
-compiler support. These additions will demonstrate how to get nice, efficient code
-for the Kaleidoscope language.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="trivialconstfold">Trivial Constant Folding</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p><b>Note:</b> the default <tt>IRBuilder</tt> now always includes the constant
-folding optimisations below.<p>
-
-<p>
-Our demonstration for Chapter 3 is elegant and easy to extend. Unfortunately,
-it does not produce wonderful code. For example, when compiling simple code,
-we don't get obvious optimizations:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) 1+2+x;</b>
-Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double 1.000000e+00, 2.000000e+00
- %addtmp1 = fadd double %addtmp, %x
- ret double %addtmp1
-}
-</pre>
-</div>
-
-<p>This code is a very, very literal transcription of the AST built by parsing
-the input. As such, this transcription lacks optimizations like constant folding
-(we'd like to get "<tt>add x, 3.0</tt>" in the example above) as well as other
-more important optimizations. Constant folding, in particular, is a very common
-and very important optimization: so much so that many language implementors
-implement constant folding support in their AST representation.</p>
-
-<p>With LLVM, you don't need this support in the AST. Since all calls to build
-LLVM IR go through the LLVM builder, it would be nice if the builder itself
-checked to see if there was a constant folding opportunity when you call it.
-If so, it could just do the constant fold and return the constant instead of
-creating an instruction. This is exactly what the <tt>LLVMFoldingBuilder</tt>
-class does.
-
-<p>All we did was switch from <tt>LLVMBuilder</tt> to
-<tt>LLVMFoldingBuilder</tt>. Though we change no other code, we now have all of our
-instructions implicitly constant folded without us having to do anything
-about it. For example, the input above now compiles to:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) 1+2+x;</b>
-Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double 3.000000e+00, %x
- ret double %addtmp
-}
-</pre>
-</div>
-
-<p>Well, that was easy :). In practice, we recommend always using
-<tt>LLVMFoldingBuilder</tt> when generating code like this. It has no
-"syntactic overhead" for its use (you don't have to uglify your compiler with
-constant checks everywhere) and it can dramatically reduce the amount of
-LLVM IR that is generated in some cases (particular for languages with a macro
-preprocessor or that use a lot of constants).</p>
-
-<p>On the other hand, the <tt>LLVMFoldingBuilder</tt> is limited by the fact
-that it does all of its analysis inline with the code as it is built. If you
-take a slightly more complex example:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
-ready> Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double 3.000000e+00, %x
- %addtmp1 = fadd double %x, 3.000000e+00
- %multmp = fmul double %addtmp, %addtmp1
- ret double %multmp
-}
-</pre>
-</div>
-
-<p>In this case, the LHS and RHS of the multiplication are the same value. We'd
-really like to see this generate "<tt>tmp = x+3; result = tmp*tmp;</tt>" instead
-of computing "<tt>x*3</tt>" twice.</p>
-
-<p>Unfortunately, no amount of local analysis will be able to detect and correct
-this. This requires two transformations: reassociation of expressions (to
-make the add's lexically identical) and Common Subexpression Elimination (CSE)
-to delete the redundant add instruction. Fortunately, LLVM provides a broad
-range of optimizations that you can use, in the form of "passes".</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="optimizerpasses">LLVM Optimization Passes</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>LLVM provides many optimization passes, which do many different sorts of
-things and have different tradeoffs. Unlike other systems, LLVM doesn't hold
-to the mistaken notion that one set of optimizations is right for all languages
-and for all situations. LLVM allows a compiler implementor to make complete
-decisions about what optimizations to use, in which order, and in what
-situation.</p>
-
-<p>As a concrete example, LLVM supports both "whole module" passes, which look
-across as large of body of code as they can (often a whole file, but if run
-at link time, this can be a substantial portion of the whole program). It also
-supports and includes "per-function" passes which just operate on a single
-function at a time, without looking at other functions. For more information
-on passes and how they are run, see the <a href="../WritingAnLLVMPass.html">How
-to Write a Pass</a> document and the <a href="../Passes.html">List of LLVM
-Passes</a>.</p>
-
-<p>For Kaleidoscope, we are currently generating functions on the fly, one at
-a time, as the user types them in. We aren't shooting for the ultimate
-optimization experience in this setting, but we also want to catch the easy and
-quick stuff where possible. As such, we will choose to run a few per-function
-optimizations as the user types the function in. If we wanted to make a "static
-Kaleidoscope compiler", we would use exactly the code we have now, except that
-we would defer running the optimizer until the entire file has been parsed.</p>
-
-<p>In order to get per-function optimizations going, we need to set up a
-<a href="../WritingAnLLVMPass.html#passmanager">Llvm.PassManager</a> to hold and
-organize the LLVM optimizations that we want to run. Once we have that, we can
-add a set of optimizations to run. The code looks like this:</p>
-
-<div class="doc_code">
-<pre>
- (* Create the JIT. *)
- let the_execution_engine = ExecutionEngine.create Codegen.the_module in
- let the_fpm = PassManager.create_function Codegen.the_module in
-
- (* Set up the optimizer pipeline. Start with registering info about how the
- * target lays out data structures. *)
- DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
-
- (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
- add_instruction_combining the_fpm;
-
- (* reassociate expressions. *)
- add_reassociation the_fpm;
-
- (* Eliminate Common SubExpressions. *)
- add_gvn the_fpm;
-
- (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
- add_cfg_simplification the_fpm;
-
- ignore (PassManager.initialize the_fpm);
-
- (* Run the main "interpreter loop" now. *)
- Toplevel.main_loop the_fpm the_execution_engine stream;
-</pre>
-</div>
-
-<p>The meat of the matter here, is the definition of "<tt>the_fpm</tt>". It
-requires a pointer to the <tt>the_module</tt> to construct itself. Once it is
-set up, we use a series of "add" calls to add a bunch of LLVM passes. The
-first pass is basically boilerplate, it adds a pass so that later optimizations
-know how the data structures in the program are laid out. The
-"<tt>the_execution_engine</tt>" variable is related to the JIT, which we will
-get to in the next section.</p>
-
-<p>In this case, we choose to add 4 optimization passes. The passes we chose
-here are a pretty standard set of "cleanup" optimizations that are useful for
-a wide variety of code. I won't delve into what they do but, believe me,
-they are a good starting place :).</p>
-
-<p>Once the <tt>Llvm.PassManager.</tt> is set up, we need to make use of it.
-We do this by running it after our newly created function is constructed (in
-<tt>Codegen.codegen_func</tt>), but before it is returned to the client:</p>
-
-<div class="doc_code">
-<pre>
-let codegen_func the_fpm = function
- ...
- try
- let ret_val = codegen_expr body in
-
- (* Finish off the function. *)
- let _ = build_ret ret_val builder in
-
- (* Validate the generated code, checking for consistency. *)
- Llvm_analysis.assert_valid_function the_function;
-
- (* Optimize the function. *)
- let _ = PassManager.run_function the_function the_fpm in
-
- the_function
-</pre>
-</div>
-
-<p>As you can see, this is pretty straightforward. The <tt>the_fpm</tt>
-optimizes and updates the LLVM Function* in place, improving (hopefully) its
-body. With this in place, we can try our test above again:</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def test(x) (1+2+x)*(x+(1+2));</b>
-ready> Read function definition:
-define double @test(double %x) {
-entry:
- %addtmp = fadd double %x, 3.000000e+00
- %multmp = fmul double %addtmp, %addtmp
- ret double %multmp
-}
-</pre>
-</div>
-
-<p>As expected, we now get our nicely optimized code, saving a floating point
-add instruction from every execution of this function.</p>
-
-<p>LLVM provides a wide variety of optimizations that can be used in certain
-circumstances. Some <a href="../Passes.html">documentation about the various
-passes</a> is available, but it isn't very complete. Another good source of
-ideas can come from looking at the passes that <tt>Clang</tt> runs to get
-started. The "<tt>opt</tt>" tool allows you to experiment with passes from the
-command line, so you can see if they do anything.</p>
-
-<p>Now that we have reasonable code coming out of our front-end, lets talk about
-executing it!</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="jit">Adding a JIT Compiler</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>Code that is available in LLVM IR can have a wide variety of tools
-applied to it. For example, you can run optimizations on it (as we did above),
-you can dump it out in textual or binary forms, you can compile the code to an
-assembly file (.s) for some target, or you can JIT compile it. The nice thing
-about the LLVM IR representation is that it is the "common currency" between
-many different parts of the compiler.
-</p>
-
-<p>In this section, we'll add JIT compiler support to our interpreter. The
-basic idea that we want for Kaleidoscope is to have the user enter function
-bodies as they do now, but immediately evaluate the top-level expressions they
-type in. For example, if they type in "1 + 2;", we should evaluate and print
-out 3. If they define a function, they should be able to call it from the
-command line.</p>
-
-<p>In order to do this, we first declare and initialize the JIT. This is done
-by adding a global variable and a call in <tt>main</tt>:</p>
-
-<div class="doc_code">
-<pre>
-...
-let main () =
- ...
- <b>(* Create the JIT. *)
- let the_execution_engine = ExecutionEngine.create Codegen.the_module in</b>
- ...
-</pre>
-</div>
-
-<p>This creates an abstract "Execution Engine" which can be either a JIT
-compiler or the LLVM interpreter. LLVM will automatically pick a JIT compiler
-for you if one is available for your platform, otherwise it will fall back to
-the interpreter.</p>
-
-<p>Once the <tt>Llvm_executionengine.ExecutionEngine.t</tt> is created, the JIT
-is ready to be used. There are a variety of APIs that are useful, but the
-simplest one is the "<tt>Llvm_executionengine.ExecutionEngine.run_function</tt>"
-function. This method JIT compiles the specified LLVM Function and returns a
-function pointer to the generated machine code. In our case, this means that we
-can change the code that parses a top-level expression to look like this:</p>
-
-<div class="doc_code">
-<pre>
- (* Evaluate a top-level expression into an anonymous function. *)
- let e = Parser.parse_toplevel stream in
- print_endline "parsed a top-level expr";
- let the_function = Codegen.codegen_func the_fpm e in
- dump_value the_function;
-
- (* JIT the function, returning a function pointer. *)
- let result = ExecutionEngine.run_function the_function [||]
- the_execution_engine in
-
- print_string "Evaluated to ";
- print_float (GenericValue.as_float Codegen.double_type result);
- print_newline ();
-</pre>
-</div>
-
-<p>Recall that we compile top-level expressions into a self-contained LLVM
-function that takes no arguments and returns the computed double. Because the
-LLVM JIT compiler matches the native platform ABI, this means that you can just
-cast the result pointer to a function pointer of that type and call it directly.
-This means, there is no difference between JIT compiled code and native machine
-code that is statically linked into your application.</p>
-
-<p>With just these two changes, lets see how Kaleidoscope works now!</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>4+5;</b>
-define double @""() {
-entry:
- ret double 9.000000e+00
-}
-
-<em>Evaluated to 9.000000</em>
-</pre>
-</div>
-
-<p>Well this looks like it is basically working. The dump of the function
-shows the "no argument function that always returns double" that we synthesize
-for each top level expression that is typed in. This demonstrates very basic
-functionality, but can we do more?</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>def testfunc(x y) x + y*2; </b>
-Read function definition:
-define double @testfunc(double %x, double %y) {
-entry:
- %multmp = fmul double %y, 2.000000e+00
- %addtmp = fadd double %multmp, %x
- ret double %addtmp
-}
-
-ready> <b>testfunc(4, 10);</b>
-define double @""() {
-entry:
- %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
- ret double %calltmp
-}
-
-<em>Evaluated to 24.000000</em>
-</pre>
-</div>
-
-<p>This illustrates that we can now call user code, but there is something a bit
-subtle going on here. Note that we only invoke the JIT on the anonymous
-functions that <em>call testfunc</em>, but we never invoked it
-on <em>testfunc</em> itself. What actually happened here is that the JIT
-scanned for all non-JIT'd functions transitively called from the anonymous
-function and compiled all of them before returning
-from <tt>run_function</tt>.</p>
-
-<p>The JIT provides a number of other more advanced interfaces for things like
-freeing allocated machine code, rejit'ing functions to update them, etc.
-However, even with this simple code, we get some surprisingly powerful
-capabilities - check this out (I removed the dump of the anonymous functions,
-you should get the idea by now :) :</p>
-
-<div class="doc_code">
-<pre>
-ready> <b>extern sin(x);</b>
-Read extern:
-declare double @sin(double)
-
-ready> <b>extern cos(x);</b>
-Read extern:
-declare double @cos(double)
-
-ready> <b>sin(1.0);</b>
-<em>Evaluated to 0.841471</em>
-
-ready> <b>def foo(x) sin(x)*sin(x) + cos(x)*cos(x);</b>
-Read function definition:
-define double @foo(double %x) {
-entry:
- %calltmp = call double @sin(double %x)
- %multmp = fmul double %calltmp, %calltmp
- %calltmp2 = call double @cos(double %x)
- %multmp4 = fmul double %calltmp2, %calltmp2
- %addtmp = fadd double %multmp, %multmp4
- ret double %addtmp
-}
-
-ready> <b>foo(4.0);</b>
-<em>Evaluated to 1.000000</em>
-</pre>
-</div>
-
-<p>Whoa, how does the JIT know about sin and cos? The answer is surprisingly
-simple: in this example, the JIT started execution of a function and got to a
-function call. It realized that the function was not yet JIT compiled and
-invoked the standard set of routines to resolve the function. In this case,
-there is no body defined for the function, so the JIT ended up calling
-"<tt>dlsym("sin")</tt>" on the Kaleidoscope process itself. Since
-"<tt>sin</tt>" is defined within the JIT's address space, it simply patches up
-calls in the module to call the libm version of <tt>sin</tt> directly.</p>
-
-<p>The LLVM JIT provides a number of interfaces (look in the
-<tt>llvm_executionengine.mli</tt> file) for controlling how unknown functions
-get resolved. It allows you to establish explicit mappings between IR objects
-and addresses (useful for LLVM global variables that you want to map to static
-tables, for example), allows you to dynamically decide on the fly based on the
-function name, and even allows you to have the JIT compile functions lazily the
-first time they're called.</p>
-
-<p>One interesting application of this is that we can now extend the language
-by writing arbitrary C code to implement operations. For example, if we add:
-</p>
-
-<div class="doc_code">
-<pre>
-/* putchard - putchar that takes a double and returns 0. */
-extern "C"
-double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-</pre>
-</div>
-
-<p>Now we can produce simple output to the console by using things like:
-"<tt>extern putchard(x); putchard(120);</tt>", which prints a lowercase 'x' on
-the console (120 is the ASCII code for 'x'). Similar code could be used to
-implement file I/O, console input, and many other capabilities in
-Kaleidoscope.</p>
-
-<p>This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At
-this point, we can compile a non-Turing-complete programming language, optimize
-and JIT compile it in a user-driven way. Next up we'll look into <a
-href="OCamlLangImpl5.html">extending the language with control flow
-constructs</a>, tackling some interesting LLVM IR issues along the way.</p>
-
-</div>
-
-<!-- *********************************************************************** -->
-<h2><a name="code">Full Code Listing</a></h2>
-<!-- *********************************************************************** -->
-
-<div>
-
-<p>
-Here is the complete code listing for our running example, enhanced with the
-LLVM JIT and optimizer. To build this example, use:
-</p>
-
-<div class="doc_code">
-<pre>
-# Compile
-ocamlbuild toy.byte
-# Run
-./toy.byte
-</pre>
-</div>
-
-<p>Here is the code:</p>
-
-<dl>
-<dt>_tags:</dt>
-<dd class="doc_code">
-<pre>
-<{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
-<*.{byte,native}>: g++, use_llvm, use_llvm_analysis
-<*.{byte,native}>: use_llvm_executionengine, use_llvm_target
-<*.{byte,native}>: use_llvm_scalar_opts, use_bindings
-</pre>
-</dd>
-
-<dt>myocamlbuild.ml:</dt>
-<dd class="doc_code">
-<pre>
-open Ocamlbuild_plugin;;
-
-ocaml_lib ~extern:true "llvm";;
-ocaml_lib ~extern:true "llvm_analysis";;
-ocaml_lib ~extern:true "llvm_executionengine";;
-ocaml_lib ~extern:true "llvm_target";;
-ocaml_lib ~extern:true "llvm_scalar_opts";;
-
-flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
-dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];;
-</pre>
-</dd>
-
-<dt>token.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Lexer Tokens
- *===----------------------------------------------------------------------===*)
-
-(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
- * these others for known things. *)
-type token =
- (* commands *)
- | Def | Extern
-
- (* primary *)
- | Ident of string | Number of float
-
- (* unknown *)
- | Kwd of char
-</pre>
-</dd>
-
-<dt>lexer.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Lexer
- *===----------------------------------------------------------------------===*)
-
-let rec lex = parser
- (* Skip any whitespace. *)
- | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
-
- (* identifier: [a-zA-Z][a-zA-Z0-9] *)
- | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_ident buffer stream
-
- (* number: [0-9.]+ *)
- | [< ' ('0' .. '9' as c); stream >] ->
- let buffer = Buffer.create 1 in
- Buffer.add_char buffer c;
- lex_number buffer stream
-
- (* Comment until end of line. *)
- | [< ' ('#'); stream >] ->
- lex_comment stream
-
- (* Otherwise, just return the character as its ascii value. *)
- | [< 'c; stream >] ->
- [< 'Token.Kwd c; lex stream >]
-
- (* end of stream. *)
- | [< >] -> [< >]
-
-and lex_number buffer = parser
- | [< ' ('0' .. '9' | '.' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_number buffer stream
- | [< stream=lex >] ->
- [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
-
-and lex_ident buffer = parser
- | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
- Buffer.add_char buffer c;
- lex_ident buffer stream
- | [< stream=lex >] ->
- match Buffer.contents buffer with
- | "def" -> [< 'Token.Def; stream >]
- | "extern" -> [< 'Token.Extern; stream >]
- | id -> [< 'Token.Ident id; stream >]
-
-and lex_comment = parser
- | [< ' ('\n'); stream=lex >] -> stream
- | [< 'c; e=lex_comment >] -> e
- | [< >] -> [< >]
-</pre>
-</dd>
-
-<dt>ast.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Abstract Syntax Tree (aka Parse Tree)
- *===----------------------------------------------------------------------===*)
-
-(* expr - Base type for all expression nodes. *)
-type expr =
- (* variant for numeric literals like "1.0". *)
- | Number of float
-
- (* variant for referencing a variable, like "a". *)
- | Variable of string
-
- (* variant for a binary operator. *)
- | Binary of char * expr * expr
-
- (* variant for function calls. *)
- | Call of string * expr array
-
-(* proto - This type represents the "prototype" for a function, which captures
- * its name, and its argument names (thus implicitly the number of arguments the
- * function takes). *)
-type proto = Prototype of string * string array
-
-(* func - This type represents a function definition itself. *)
-type func = Function of proto * expr
-</pre>
-</dd>
-
-<dt>parser.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===---------------------------------------------------------------------===
- * Parser
- *===---------------------------------------------------------------------===*)
-
-(* binop_precedence - This holds the precedence for each binary operator that is
- * defined *)
-let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
-
-(* precedence - Get the precedence of the pending binary operator token. *)
-let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
-
-(* primary
- * ::= identifier
- * ::= numberexpr
- * ::= parenexpr *)
-let rec parse_primary = parser
- (* numberexpr ::= number *)
- | [< 'Token.Number n >] -> Ast.Number n
-
- (* parenexpr ::= '(' expression ')' *)
- | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
-
- (* identifierexpr
- * ::= identifier
- * ::= identifier '(' argumentexpr ')' *)
- | [< 'Token.Ident id; stream >] ->
- let rec parse_args accumulator = parser
- | [< e=parse_expr; stream >] ->
- begin parser
- | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
- | [< >] -> e :: accumulator
- end stream
- | [< >] -> accumulator
- in
- let rec parse_ident id = parser
- (* Call. *)
- | [< 'Token.Kwd '(';
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')'">] ->
- Ast.Call (id, Array.of_list (List.rev args))
-
- (* Simple variable ref. *)
- | [< >] -> Ast.Variable id
- in
- parse_ident id stream
-
- | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
-
-(* binoprhs
- * ::= ('+' primary)* *)
-and parse_bin_rhs expr_prec lhs stream =
- match Stream.peek stream with
- (* If this is a binop, find its precedence. *)
- | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
- let token_prec = precedence c in
-
- (* If this is a binop that binds at least as tightly as the current binop,
- * consume it, otherwise we are done. *)
- if token_prec < expr_prec then lhs else begin
- (* Eat the binop. *)
- Stream.junk stream;
-
- (* Parse the primary expression after the binary operator. *)
- let rhs = parse_primary stream in
-
- (* Okay, we know this is a binop. *)
- let rhs =
- match Stream.peek stream with
- | Some (Token.Kwd c2) ->
- (* If BinOp binds less tightly with rhs than the operator after
- * rhs, let the pending operator take rhs as its lhs. *)
- let next_prec = precedence c2 in
- if token_prec < next_prec
- then parse_bin_rhs (token_prec + 1) rhs stream
- else rhs
- | _ -> rhs
- in
-
- (* Merge lhs/rhs. *)
- let lhs = Ast.Binary (c, lhs, rhs) in
- parse_bin_rhs expr_prec lhs stream
- end
- | _ -> lhs
-
-(* expression
- * ::= primary binoprhs *)
-and parse_expr = parser
- | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
-
-(* prototype
- * ::= id '(' id* ')' *)
-let parse_prototype =
- let rec parse_args accumulator = parser
- | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
- | [< >] -> accumulator
- in
-
- parser
- | [< 'Token.Ident id;
- 'Token.Kwd '(' ?? "expected '(' in prototype";
- args=parse_args [];
- 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
- (* success. *)
- Ast.Prototype (id, Array.of_list (List.rev args))
-
- | [< >] ->
- raise (Stream.Error "expected function name in prototype")
-
-(* definition ::= 'def' prototype expression *)
-let parse_definition = parser
- | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
- Ast.Function (p, e)
-
-(* toplevelexpr ::= expression *)
-let parse_toplevel = parser
- | [< e=parse_expr >] ->
- (* Make an anonymous proto. *)
- Ast.Function (Ast.Prototype ("", [||]), e)
-
-(* external ::= 'extern' prototype *)
-let parse_extern = parser
- | [< 'Token.Extern; e=parse_prototype >] -> e
-</pre>
-</dd>
-
-<dt>codegen.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Code Generation
- *===----------------------------------------------------------------------===*)
-
-open Llvm
-
-exception Error of string
-
-let context = global_context ()
-let the_module = create_module context "my cool jit"
-let builder = builder context
-let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
-let double_type = double_type context
-
-let rec codegen_expr = function
- | Ast.Number n -> const_float double_type n
- | Ast.Variable name ->
- (try Hashtbl.find named_values name with
- | Not_found -> raise (Error "unknown variable name"))
- | Ast.Binary (op, lhs, rhs) ->
- let lhs_val = codegen_expr lhs in
- let rhs_val = codegen_expr rhs in
- begin
- match op with
- | '+' -> build_add lhs_val rhs_val "addtmp" builder
- | '-' -> build_sub lhs_val rhs_val "subtmp" builder
- | '*' -> build_mul lhs_val rhs_val "multmp" builder
- | '<' ->
- (* Convert bool 0/1 to double 0.0 or 1.0 *)
- let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
- build_uitofp i double_type "booltmp" builder
- | _ -> raise (Error "invalid binary operator")
- end
- | Ast.Call (callee, args) ->
- (* Look up the name in the module table. *)
- let callee =
- match lookup_function callee the_module with
- | Some callee -> callee
- | None -> raise (Error "unknown function referenced")
- in
- let params = params callee in
-
- (* If argument mismatch error. *)
- if Array.length params == Array.length args then () else
- raise (Error "incorrect # arguments passed");
- let args = Array.map codegen_expr args in
- build_call callee args "calltmp" builder
-
-let codegen_proto = function
- | Ast.Prototype (name, args) ->
- (* Make the function type: double(double,double) etc. *)
- let doubles = Array.make (Array.length args) double_type in
- let ft = function_type double_type doubles in
- let f =
- match lookup_function name the_module with
- | None -> declare_function name ft the_module
-
- (* If 'f' conflicted, there was already something named 'name'. If it
- * has a body, don't allow redefinition or reextern. *)
- | Some f ->
- (* If 'f' already has a body, reject this. *)
- if block_begin f <> At_end f then
- raise (Error "redefinition of function");
-
- (* If 'f' took a different number of arguments, reject. *)
- if element_type (type_of f) <> ft then
- raise (Error "redefinition of function with different # args");
- f
- in
-
- (* Set names for all arguments. *)
- Array.iteri (fun i a ->
- let n = args.(i) in
- set_value_name n a;
- Hashtbl.add named_values n a;
- ) (params f);
- f
-
-let codegen_func the_fpm = function
- | Ast.Function (proto, body) ->
- Hashtbl.clear named_values;
- let the_function = codegen_proto proto in
-
- (* Create a new basic block to start insertion into. *)
- let bb = append_block context "entry" the_function in
- position_at_end bb builder;
-
- try
- let ret_val = codegen_expr body in
-
- (* Finish off the function. *)
- let _ = build_ret ret_val builder in
-
- (* Validate the generated code, checking for consistency. *)
- Llvm_analysis.assert_valid_function the_function;
-
- (* Optimize the function. *)
- let _ = PassManager.run_function the_function the_fpm in
-
- the_function
- with e ->
- delete_function the_function;
- raise e
-</pre>
-</dd>
-
-<dt>toplevel.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Top-Level parsing and JIT Driver
- *===----------------------------------------------------------------------===*)
-
-open Llvm
-open Llvm_executionengine
-
-(* top ::= definition | external | expression | ';' *)
-let rec main_loop the_fpm the_execution_engine stream =
- match Stream.peek stream with
- | None -> ()
-
- (* ignore top-level semicolons. *)
- | Some (Token.Kwd ';') ->
- Stream.junk stream;
- main_loop the_fpm the_execution_engine stream
-
- | Some token ->
- begin
- try match token with
- | Token.Def ->
- let e = Parser.parse_definition stream in
- print_endline "parsed a function definition.";
- dump_value (Codegen.codegen_func the_fpm e);
- | Token.Extern ->
- let e = Parser.parse_extern stream in
- print_endline "parsed an extern.";
- dump_value (Codegen.codegen_proto e);
- | _ ->
- (* Evaluate a top-level expression into an anonymous function. *)
- let e = Parser.parse_toplevel stream in
- print_endline "parsed a top-level expr";
- let the_function = Codegen.codegen_func the_fpm e in
- dump_value the_function;
-
- (* JIT the function, returning a function pointer. *)
- let result = ExecutionEngine.run_function the_function [||]
- the_execution_engine in
-
- print_string "Evaluated to ";
- print_float (GenericValue.as_float Codegen.double_type result);
- print_newline ();
- with Stream.Error s | Codegen.Error s ->
- (* Skip token for error recovery. *)
- Stream.junk stream;
- print_endline s;
- end;
- print_string "ready> "; flush stdout;
- main_loop the_fpm the_execution_engine stream
-</pre>
-</dd>
-
-<dt>toy.ml:</dt>
-<dd class="doc_code">
-<pre>
-(*===----------------------------------------------------------------------===
- * Main driver code.
- *===----------------------------------------------------------------------===*)
-
-open Llvm
-open Llvm_executionengine
-open Llvm_target
-open Llvm_scalar_opts
-
-let main () =
- ignore (initialize_native_target ());
-
- (* Install standard binary operators.
- * 1 is the lowest precedence. *)
- Hashtbl.add Parser.binop_precedence '<' 10;
- Hashtbl.add Parser.binop_precedence '+' 20;
- Hashtbl.add Parser.binop_precedence '-' 20;
- Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
-
- (* Prime the first token. *)
- print_string "ready> "; flush stdout;
- let stream = Lexer.lex (Stream.of_channel stdin) in
-
- (* Create the JIT. *)
- let the_execution_engine = ExecutionEngine.create Codegen.the_module in
- let the_fpm = PassManager.create_function Codegen.the_module in
-
- (* Set up the optimizer pipeline. Start with registering info about how the
- * target lays out data structures. *)
- DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
-
- (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
- add_instruction_combination the_fpm;
-
- (* reassociate expressions. *)
- add_reassociation the_fpm;
-
- (* Eliminate Common SubExpressions. *)
- add_gvn the_fpm;
-
- (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
- add_cfg_simplification the_fpm;
-
- ignore (PassManager.initialize the_fpm);
-
- (* Run the main "interpreter loop" now. *)
- Toplevel.main_loop the_fpm the_execution_engine stream;
-
- (* Print out all the generated code. *)
- dump_module Codegen.the_module
-;;
-
-main ()
-</pre>
-</dd>
-
-<dt>bindings.c</dt>
-<dd class="doc_code">
-<pre>
-#include <stdio.h>
-
-/* putchard - putchar that takes a double and returns 0. */
-extern double putchard(double X) {
- putchar((char)X);
- return 0;
-}
-</pre>
-</dd>
-</dl>
-
-<a href="OCamlLangImpl5.html">Next: Extending the language: control flow</a>
-</div>
-
-<!-- *********************************************************************** -->
-<hr>
-<address>
- <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
- src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
- <a href="http://validator.w3.org/check/referer"><img
- src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
-
- <a href="mailto:sabre at nondot.org">Chris Lattner</a><br>
- <a href="mailto:idadesub at users.sourceforge.net">Erick Tryzelaar</a><br>
- <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
- Last modified: $Date$
-</address>
-</body>
-</html>
Added: llvm/trunk/docs/tutorial/OCamlLangImpl4.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/tutorial/OCamlLangImpl4.rst?rev=169343&view=auto
==============================================================================
--- llvm/trunk/docs/tutorial/OCamlLangImpl4.rst (added)
+++ llvm/trunk/docs/tutorial/OCamlLangImpl4.rst Tue Dec 4 18:26:32 2012
@@ -0,0 +1,918 @@
+==============================================
+Kaleidoscope: Adding JIT and Optimizer Support
+==============================================
+
+.. contents::
+ :local:
+
+Written by `Chris Lattner <mailto:sabre at nondot.org>`_ and `Erick
+Tryzelaar <mailto:idadesub at users.sourceforge.net>`_
+
+Chapter 4 Introduction
+======================
+
+Welcome to Chapter 4 of the "`Implementing a language with
+LLVM <index.html>`_" tutorial. Chapters 1-3 described the implementation
+of a simple language and added support for generating LLVM IR. This
+chapter describes two new techniques: adding optimizer support to your
+language, and adding JIT compiler support. These additions will
+demonstrate how to get nice, efficient code for the Kaleidoscope
+language.
+
+Trivial Constant Folding
+========================
+
+**Note:** the default ``IRBuilder`` now always includes the constant
+folding optimisations below.
+
+Our demonstration for Chapter 3 is elegant and easy to extend.
+Unfortunately, it does not produce wonderful code. For example, when
+compiling simple code, we don't get obvious optimizations:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 1.000000e+00, 2.000000e+00
+ %addtmp1 = fadd double %addtmp, %x
+ ret double %addtmp1
+ }
+
+This code is a very, very literal transcription of the AST built by
+parsing the input. As such, this transcription lacks optimizations like
+constant folding (we'd like to get "``add x, 3.0``" in the example
+above) as well as other more important optimizations. Constant folding,
+in particular, is a very common and very important optimization: so much
+so that many language implementors implement constant folding support in
+their AST representation.
+
+With LLVM, you don't need this support in the AST. Since all calls to
+build LLVM IR go through the LLVM builder, it would be nice if the
+builder itself checked to see if there was a constant folding
+opportunity when you call it. If so, it could just do the constant fold
+and return the constant instead of creating an instruction. This is
+exactly what the ``LLVMFoldingBuilder`` class does.
+
+All we did was switch from ``LLVMBuilder`` to ``LLVMFoldingBuilder``.
+Though we change no other code, we now have all of our instructions
+implicitly constant folded without us having to do anything about it.
+For example, the input above now compiles to:
+
+::
+
+ ready> def test(x) 1+2+x;
+ Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ ret double %addtmp
+ }
+
+Well, that was easy :). In practice, we recommend always using
+``LLVMFoldingBuilder`` when generating code like this. It has no
+"syntactic overhead" for its use (you don't have to uglify your compiler
+with constant checks everywhere) and it can dramatically reduce the
+amount of LLVM IR that is generated in some cases (particular for
+languages with a macro preprocessor or that use a lot of constants).
+
+On the other hand, the ``LLVMFoldingBuilder`` is limited by the fact
+that it does all of its analysis inline with the code as it is built. If
+you take a slightly more complex example:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double 3.000000e+00, %x
+ %addtmp1 = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp1
+ ret double %multmp
+ }
+
+In this case, the LHS and RHS of the multiplication are the same value.
+We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``"
+instead of computing "``x*3``" twice.
+
+Unfortunately, no amount of local analysis will be able to detect and
+correct this. This requires two transformations: reassociation of
+expressions (to make the add's lexically identical) and Common
+Subexpression Elimination (CSE) to delete the redundant add instruction.
+Fortunately, LLVM provides a broad range of optimizations that you can
+use, in the form of "passes".
+
+LLVM Optimization Passes
+========================
+
+LLVM provides many optimization passes, which do many different sorts of
+things and have different tradeoffs. Unlike other systems, LLVM doesn't
+hold to the mistaken notion that one set of optimizations is right for
+all languages and for all situations. LLVM allows a compiler implementor
+to make complete decisions about what optimizations to use, in which
+order, and in what situation.
+
+As a concrete example, LLVM supports both "whole module" passes, which
+look across as large of body of code as they can (often a whole file,
+but if run at link time, this can be a substantial portion of the whole
+program). It also supports and includes "per-function" passes which just
+operate on a single function at a time, without looking at other
+functions. For more information on passes and how they are run, see the
+`How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the
+`List of LLVM Passes <../Passes.html>`_.
+
+For Kaleidoscope, we are currently generating functions on the fly, one
+at a time, as the user types them in. We aren't shooting for the
+ultimate optimization experience in this setting, but we also want to
+catch the easy and quick stuff where possible. As such, we will choose
+to run a few per-function optimizations as the user types the function
+in. If we wanted to make a "static Kaleidoscope compiler", we would use
+exactly the code we have now, except that we would defer running the
+optimizer until the entire file has been parsed.
+
+In order to get per-function optimizations going, we need to set up a
+`Llvm.PassManager <../WritingAnLLVMPass.html#passmanager>`_ to hold and
+organize the LLVM optimizations that we want to run. Once we have that,
+we can add a set of optimizations to run. The code looks like this:
+
+.. code-block:: ocaml
+
+ (* Create the JIT. *)
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ let the_fpm = PassManager.create_function Codegen.the_module in
+
+ (* Set up the optimizer pipeline. Start with registering info about how the
+ * target lays out data structures. *)
+ DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
+
+ (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
+ add_instruction_combining the_fpm;
+
+ (* reassociate expressions. *)
+ add_reassociation the_fpm;
+
+ (* Eliminate Common SubExpressions. *)
+ add_gvn the_fpm;
+
+ (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
+ add_cfg_simplification the_fpm;
+
+ ignore (PassManager.initialize the_fpm);
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop the_fpm the_execution_engine stream;
+
+The meat of the matter here, is the definition of "``the_fpm``". It
+requires a pointer to the ``the_module`` to construct itself. Once it is
+set up, we use a series of "add" calls to add a bunch of LLVM passes.
+The first pass is basically boilerplate, it adds a pass so that later
+optimizations know how the data structures in the program are laid out.
+The "``the_execution_engine``" variable is related to the JIT, which we
+will get to in the next section.
+
+In this case, we choose to add 4 optimization passes. The passes we
+chose here are a pretty standard set of "cleanup" optimizations that are
+useful for a wide variety of code. I won't delve into what they do but,
+believe me, they are a good starting place :).
+
+Once the ``Llvm.PassManager.`` is set up, we need to make use of it. We
+do this by running it after our newly created function is constructed
+(in ``Codegen.codegen_func``), but before it is returned to the client:
+
+.. code-block:: ocaml
+
+ let codegen_func the_fpm = function
+ ...
+ try
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ (* Optimize the function. *)
+ let _ = PassManager.run_function the_function the_fpm in
+
+ the_function
+
+As you can see, this is pretty straightforward. The ``the_fpm``
+optimizes and updates the LLVM Function\* in place, improving
+(hopefully) its body. With this in place, we can try our test above
+again:
+
+::
+
+ ready> def test(x) (1+2+x)*(x+(1+2));
+ ready> Read function definition:
+ define double @test(double %x) {
+ entry:
+ %addtmp = fadd double %x, 3.000000e+00
+ %multmp = fmul double %addtmp, %addtmp
+ ret double %multmp
+ }
+
+As expected, we now get our nicely optimized code, saving a floating
+point add instruction from every execution of this function.
+
+LLVM provides a wide variety of optimizations that can be used in
+certain circumstances. Some `documentation about the various
+passes <../Passes.html>`_ is available, but it isn't very complete.
+Another good source of ideas can come from looking at the passes that
+``Clang`` runs to get started. The "``opt``" tool allows you to
+experiment with passes from the command line, so you can see if they do
+anything.
+
+Now that we have reasonable code coming out of our front-end, lets talk
+about executing it!
+
+Adding a JIT Compiler
+=====================
+
+Code that is available in LLVM IR can have a wide variety of tools
+applied to it. For example, you can run optimizations on it (as we did
+above), you can dump it out in textual or binary forms, you can compile
+the code to an assembly file (.s) for some target, or you can JIT
+compile it. The nice thing about the LLVM IR representation is that it
+is the "common currency" between many different parts of the compiler.
+
+In this section, we'll add JIT compiler support to our interpreter. The
+basic idea that we want for Kaleidoscope is to have the user enter
+function bodies as they do now, but immediately evaluate the top-level
+expressions they type in. For example, if they type in "1 + 2;", we
+should evaluate and print out 3. If they define a function, they should
+be able to call it from the command line.
+
+In order to do this, we first declare and initialize the JIT. This is
+done by adding a global variable and a call in ``main``:
+
+.. code-block:: ocaml
+
+ ...
+ let main () =
+ ...
+ (* Create the JIT. *)
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ ...
+
+This creates an abstract "Execution Engine" which can be either a JIT
+compiler or the LLVM interpreter. LLVM will automatically pick a JIT
+compiler for you if one is available for your platform, otherwise it
+will fall back to the interpreter.
+
+Once the ``Llvm_executionengine.ExecutionEngine.t`` is created, the JIT
+is ready to be used. There are a variety of APIs that are useful, but
+the simplest one is the
+"``Llvm_executionengine.ExecutionEngine.run_function``" function. This
+method JIT compiles the specified LLVM Function and returns a function
+pointer to the generated machine code. In our case, this means that we
+can change the code that parses a top-level expression to look like
+this:
+
+.. code-block:: ocaml
+
+ (* Evaluate a top-level expression into an anonymous function. *)
+ let e = Parser.parse_toplevel stream in
+ print_endline "parsed a top-level expr";
+ let the_function = Codegen.codegen_func the_fpm e in
+ dump_value the_function;
+
+ (* JIT the function, returning a function pointer. *)
+ let result = ExecutionEngine.run_function the_function [||]
+ the_execution_engine in
+
+ print_string "Evaluated to ";
+ print_float (GenericValue.as_float Codegen.double_type result);
+ print_newline ();
+
+Recall that we compile top-level expressions into a self-contained LLVM
+function that takes no arguments and returns the computed double.
+Because the LLVM JIT compiler matches the native platform ABI, this
+means that you can just cast the result pointer to a function pointer of
+that type and call it directly. This means, there is no difference
+between JIT compiled code and native machine code that is statically
+linked into your application.
+
+With just these two changes, lets see how Kaleidoscope works now!
+
+::
+
+ ready> 4+5;
+ define double @""() {
+ entry:
+ ret double 9.000000e+00
+ }
+
+ Evaluated to 9.000000
+
+Well this looks like it is basically working. The dump of the function
+shows the "no argument function that always returns double" that we
+synthesize for each top level expression that is typed in. This
+demonstrates very basic functionality, but can we do more?
+
+::
+
+ ready> def testfunc(x y) x + y*2;
+ Read function definition:
+ define double @testfunc(double %x, double %y) {
+ entry:
+ %multmp = fmul double %y, 2.000000e+00
+ %addtmp = fadd double %multmp, %x
+ ret double %addtmp
+ }
+
+ ready> testfunc(4, 10);
+ define double @""() {
+ entry:
+ %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
+ ret double %calltmp
+ }
+
+ Evaluated to 24.000000
+
+This illustrates that we can now call user code, but there is something
+a bit subtle going on here. Note that we only invoke the JIT on the
+anonymous functions that *call testfunc*, but we never invoked it on
+*testfunc* itself. What actually happened here is that the JIT scanned
+for all non-JIT'd functions transitively called from the anonymous
+function and compiled all of them before returning from
+``run_function``.
+
+The JIT provides a number of other more advanced interfaces for things
+like freeing allocated machine code, rejit'ing functions to update them,
+etc. However, even with this simple code, we get some surprisingly
+powerful capabilities - check this out (I removed the dump of the
+anonymous functions, you should get the idea by now :) :
+
+::
+
+ ready> extern sin(x);
+ Read extern:
+ declare double @sin(double)
+
+ ready> extern cos(x);
+ Read extern:
+ declare double @cos(double)
+
+ ready> sin(1.0);
+ Evaluated to 0.841471
+
+ ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
+ Read function definition:
+ define double @foo(double %x) {
+ entry:
+ %calltmp = call double @sin(double %x)
+ %multmp = fmul double %calltmp, %calltmp
+ %calltmp2 = call double @cos(double %x)
+ %multmp4 = fmul double %calltmp2, %calltmp2
+ %addtmp = fadd double %multmp, %multmp4
+ ret double %addtmp
+ }
+
+ ready> foo(4.0);
+ Evaluated to 1.000000
+
+Whoa, how does the JIT know about sin and cos? The answer is
+surprisingly simple: in this example, the JIT started execution of a
+function and got to a function call. It realized that the function was
+not yet JIT compiled and invoked the standard set of routines to resolve
+the function. In this case, there is no body defined for the function,
+so the JIT ended up calling "``dlsym("sin")``" on the Kaleidoscope
+process itself. Since "``sin``" is defined within the JIT's address
+space, it simply patches up calls in the module to call the libm version
+of ``sin`` directly.
+
+The LLVM JIT provides a number of interfaces (look in the
+``llvm_executionengine.mli`` file) for controlling how unknown functions
+get resolved. It allows you to establish explicit mappings between IR
+objects and addresses (useful for LLVM global variables that you want to
+map to static tables, for example), allows you to dynamically decide on
+the fly based on the function name, and even allows you to have the JIT
+compile functions lazily the first time they're called.
+
+One interesting application of this is that we can now extend the
+language by writing arbitrary C code to implement operations. For
+example, if we add:
+
+.. code-block:: c++
+
+ /* putchard - putchar that takes a double and returns 0. */
+ extern "C"
+ double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+Now we can produce simple output to the console by using things like:
+"``extern putchard(x); putchard(120);``", which prints a lowercase 'x'
+on the console (120 is the ASCII code for 'x'). Similar code could be
+used to implement file I/O, console input, and many other capabilities
+in Kaleidoscope.
+
+This completes the JIT and optimizer chapter of the Kaleidoscope
+tutorial. At this point, we can compile a non-Turing-complete
+programming language, optimize and JIT compile it in a user-driven way.
+Next up we'll look into `extending the language with control flow
+constructs <OCamlLangImpl5.html>`_, tackling some interesting LLVM IR
+issues along the way.
+
+Full Code Listing
+=================
+
+Here is the complete code listing for our running example, enhanced with
+the LLVM JIT and optimizer. To build this example, use:
+
+.. code-block:: bash
+
+ # Compile
+ ocamlbuild toy.byte
+ # Run
+ ./toy.byte
+
+Here is the code:
+
+\_tags:
+ ::
+
+ <{lexer,parser}.ml>: use_camlp4, pp(camlp4of)
+ <*.{byte,native}>: g++, use_llvm, use_llvm_analysis
+ <*.{byte,native}>: use_llvm_executionengine, use_llvm_target
+ <*.{byte,native}>: use_llvm_scalar_opts, use_bindings
+
+myocamlbuild.ml:
+ .. code-block:: ocaml
+
+ open Ocamlbuild_plugin;;
+
+ ocaml_lib ~extern:true "llvm";;
+ ocaml_lib ~extern:true "llvm_analysis";;
+ ocaml_lib ~extern:true "llvm_executionengine";;
+ ocaml_lib ~extern:true "llvm_target";;
+ ocaml_lib ~extern:true "llvm_scalar_opts";;
+
+ flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);;
+ dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];;
+
+token.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer Tokens
+ *===----------------------------------------------------------------------===*)
+
+ (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
+ * these others for known things. *)
+ type token =
+ (* commands *)
+ | Def | Extern
+
+ (* primary *)
+ | Ident of string | Number of float
+
+ (* unknown *)
+ | Kwd of char
+
+lexer.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Lexer
+ *===----------------------------------------------------------------------===*)
+
+ let rec lex = parser
+ (* Skip any whitespace. *)
+ | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
+
+ (* identifier: [a-zA-Z][a-zA-Z0-9] *)
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+
+ (* number: [0-9.]+ *)
+ | [< ' ('0' .. '9' as c); stream >] ->
+ let buffer = Buffer.create 1 in
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+
+ (* Comment until end of line. *)
+ | [< ' ('#'); stream >] ->
+ lex_comment stream
+
+ (* Otherwise, just return the character as its ascii value. *)
+ | [< 'c; stream >] ->
+ [< 'Token.Kwd c; lex stream >]
+
+ (* end of stream. *)
+ | [< >] -> [< >]
+
+ and lex_number buffer = parser
+ | [< ' ('0' .. '9' | '.' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_number buffer stream
+ | [< stream=lex >] ->
+ [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
+
+ and lex_ident buffer = parser
+ | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
+ Buffer.add_char buffer c;
+ lex_ident buffer stream
+ | [< stream=lex >] ->
+ match Buffer.contents buffer with
+ | "def" -> [< 'Token.Def; stream >]
+ | "extern" -> [< 'Token.Extern; stream >]
+ | id -> [< 'Token.Ident id; stream >]
+
+ and lex_comment = parser
+ | [< ' ('\n'); stream=lex >] -> stream
+ | [< 'c; e=lex_comment >] -> e
+ | [< >] -> [< >]
+
+ast.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Abstract Syntax Tree (aka Parse Tree)
+ *===----------------------------------------------------------------------===*)
+
+ (* expr - Base type for all expression nodes. *)
+ type expr =
+ (* variant for numeric literals like "1.0". *)
+ | Number of float
+
+ (* variant for referencing a variable, like "a". *)
+ | Variable of string
+
+ (* variant for a binary operator. *)
+ | Binary of char * expr * expr
+
+ (* variant for function calls. *)
+ | Call of string * expr array
+
+ (* proto - This type represents the "prototype" for a function, which captures
+ * its name, and its argument names (thus implicitly the number of arguments the
+ * function takes). *)
+ type proto = Prototype of string * string array
+
+ (* func - This type represents a function definition itself. *)
+ type func = Function of proto * expr
+
+parser.ml:
+ .. code-block:: ocaml
+
+ (*===---------------------------------------------------------------------===
+ * Parser
+ *===---------------------------------------------------------------------===*)
+
+ (* binop_precedence - This holds the precedence for each binary operator that is
+ * defined *)
+ let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
+
+ (* precedence - Get the precedence of the pending binary operator token. *)
+ let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1
+
+ (* primary
+ * ::= identifier
+ * ::= numberexpr
+ * ::= parenexpr *)
+ let rec parse_primary = parser
+ (* numberexpr ::= number *)
+ | [< 'Token.Number n >] -> Ast.Number n
+
+ (* parenexpr ::= '(' expression ')' *)
+ | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e
+
+ (* identifierexpr
+ * ::= identifier
+ * ::= identifier '(' argumentexpr ')' *)
+ | [< 'Token.Ident id; stream >] ->
+ let rec parse_args accumulator = parser
+ | [< e=parse_expr; stream >] ->
+ begin parser
+ | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e
+ | [< >] -> e :: accumulator
+ end stream
+ | [< >] -> accumulator
+ in
+ let rec parse_ident id = parser
+ (* Call. *)
+ | [< 'Token.Kwd '(';
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')'">] ->
+ Ast.Call (id, Array.of_list (List.rev args))
+
+ (* Simple variable ref. *)
+ | [< >] -> Ast.Variable id
+ in
+ parse_ident id stream
+
+ | [< >] -> raise (Stream.Error "unknown token when expecting an expression.")
+
+ (* binoprhs
+ * ::= ('+' primary)* *)
+ and parse_bin_rhs expr_prec lhs stream =
+ match Stream.peek stream with
+ (* If this is a binop, find its precedence. *)
+ | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
+ let token_prec = precedence c in
+
+ (* If this is a binop that binds at least as tightly as the current binop,
+ * consume it, otherwise we are done. *)
+ if token_prec < expr_prec then lhs else begin
+ (* Eat the binop. *)
+ Stream.junk stream;
+
+ (* Parse the primary expression after the binary operator. *)
+ let rhs = parse_primary stream in
+
+ (* Okay, we know this is a binop. *)
+ let rhs =
+ match Stream.peek stream with
+ | Some (Token.Kwd c2) ->
+ (* If BinOp binds less tightly with rhs than the operator after
+ * rhs, let the pending operator take rhs as its lhs. *)
+ let next_prec = precedence c2 in
+ if token_prec < next_prec
+ then parse_bin_rhs (token_prec + 1) rhs stream
+ else rhs
+ | _ -> rhs
+ in
+
+ (* Merge lhs/rhs. *)
+ let lhs = Ast.Binary (c, lhs, rhs) in
+ parse_bin_rhs expr_prec lhs stream
+ end
+ | _ -> lhs
+
+ (* expression
+ * ::= primary binoprhs *)
+ and parse_expr = parser
+ | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream
+
+ (* prototype
+ * ::= id '(' id* ')' *)
+ let parse_prototype =
+ let rec parse_args accumulator = parser
+ | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e
+ | [< >] -> accumulator
+ in
+
+ parser
+ | [< 'Token.Ident id;
+ 'Token.Kwd '(' ?? "expected '(' in prototype";
+ args=parse_args [];
+ 'Token.Kwd ')' ?? "expected ')' in prototype" >] ->
+ (* success. *)
+ Ast.Prototype (id, Array.of_list (List.rev args))
+
+ | [< >] ->
+ raise (Stream.Error "expected function name in prototype")
+
+ (* definition ::= 'def' prototype expression *)
+ let parse_definition = parser
+ | [< 'Token.Def; p=parse_prototype; e=parse_expr >] ->
+ Ast.Function (p, e)
+
+ (* toplevelexpr ::= expression *)
+ let parse_toplevel = parser
+ | [< e=parse_expr >] ->
+ (* Make an anonymous proto. *)
+ Ast.Function (Ast.Prototype ("", [||]), e)
+
+ (* external ::= 'extern' prototype *)
+ let parse_extern = parser
+ | [< 'Token.Extern; e=parse_prototype >] -> e
+
+codegen.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Code Generation
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+
+ exception Error of string
+
+ let context = global_context ()
+ let the_module = create_module context "my cool jit"
+ let builder = builder context
+ let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
+ let double_type = double_type context
+
+ let rec codegen_expr = function
+ | Ast.Number n -> const_float double_type n
+ | Ast.Variable name ->
+ (try Hashtbl.find named_values name with
+ | Not_found -> raise (Error "unknown variable name"))
+ | Ast.Binary (op, lhs, rhs) ->
+ let lhs_val = codegen_expr lhs in
+ let rhs_val = codegen_expr rhs in
+ begin
+ match op with
+ | '+' -> build_add lhs_val rhs_val "addtmp" builder
+ | '-' -> build_sub lhs_val rhs_val "subtmp" builder
+ | '*' -> build_mul lhs_val rhs_val "multmp" builder
+ | '<' ->
+ (* Convert bool 0/1 to double 0.0 or 1.0 *)
+ let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
+ build_uitofp i double_type "booltmp" builder
+ | _ -> raise (Error "invalid binary operator")
+ end
+ | Ast.Call (callee, args) ->
+ (* Look up the name in the module table. *)
+ let callee =
+ match lookup_function callee the_module with
+ | Some callee -> callee
+ | None -> raise (Error "unknown function referenced")
+ in
+ let params = params callee in
+
+ (* If argument mismatch error. *)
+ if Array.length params == Array.length args then () else
+ raise (Error "incorrect # arguments passed");
+ let args = Array.map codegen_expr args in
+ build_call callee args "calltmp" builder
+
+ let codegen_proto = function
+ | Ast.Prototype (name, args) ->
+ (* Make the function type: double(double,double) etc. *)
+ let doubles = Array.make (Array.length args) double_type in
+ let ft = function_type double_type doubles in
+ let f =
+ match lookup_function name the_module with
+ | None -> declare_function name ft the_module
+
+ (* If 'f' conflicted, there was already something named 'name'. If it
+ * has a body, don't allow redefinition or reextern. *)
+ | Some f ->
+ (* If 'f' already has a body, reject this. *)
+ if block_begin f <> At_end f then
+ raise (Error "redefinition of function");
+
+ (* If 'f' took a different number of arguments, reject. *)
+ if element_type (type_of f) <> ft then
+ raise (Error "redefinition of function with different # args");
+ f
+ in
+
+ (* Set names for all arguments. *)
+ Array.iteri (fun i a ->
+ let n = args.(i) in
+ set_value_name n a;
+ Hashtbl.add named_values n a;
+ ) (params f);
+ f
+
+ let codegen_func the_fpm = function
+ | Ast.Function (proto, body) ->
+ Hashtbl.clear named_values;
+ let the_function = codegen_proto proto in
+
+ (* Create a new basic block to start insertion into. *)
+ let bb = append_block context "entry" the_function in
+ position_at_end bb builder;
+
+ try
+ let ret_val = codegen_expr body in
+
+ (* Finish off the function. *)
+ let _ = build_ret ret_val builder in
+
+ (* Validate the generated code, checking for consistency. *)
+ Llvm_analysis.assert_valid_function the_function;
+
+ (* Optimize the function. *)
+ let _ = PassManager.run_function the_function the_fpm in
+
+ the_function
+ with e ->
+ delete_function the_function;
+ raise e
+
+toplevel.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Top-Level parsing and JIT Driver
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+ open Llvm_executionengine
+
+ (* top ::= definition | external | expression | ';' *)
+ let rec main_loop the_fpm the_execution_engine stream =
+ match Stream.peek stream with
+ | None -> ()
+
+ (* ignore top-level semicolons. *)
+ | Some (Token.Kwd ';') ->
+ Stream.junk stream;
+ main_loop the_fpm the_execution_engine stream
+
+ | Some token ->
+ begin
+ try match token with
+ | Token.Def ->
+ let e = Parser.parse_definition stream in
+ print_endline "parsed a function definition.";
+ dump_value (Codegen.codegen_func the_fpm e);
+ | Token.Extern ->
+ let e = Parser.parse_extern stream in
+ print_endline "parsed an extern.";
+ dump_value (Codegen.codegen_proto e);
+ | _ ->
+ (* Evaluate a top-level expression into an anonymous function. *)
+ let e = Parser.parse_toplevel stream in
+ print_endline "parsed a top-level expr";
+ let the_function = Codegen.codegen_func the_fpm e in
+ dump_value the_function;
+
+ (* JIT the function, returning a function pointer. *)
+ let result = ExecutionEngine.run_function the_function [||]
+ the_execution_engine in
+
+ print_string "Evaluated to ";
+ print_float (GenericValue.as_float Codegen.double_type result);
+ print_newline ();
+ with Stream.Error s | Codegen.Error s ->
+ (* Skip token for error recovery. *)
+ Stream.junk stream;
+ print_endline s;
+ end;
+ print_string "ready> "; flush stdout;
+ main_loop the_fpm the_execution_engine stream
+
+toy.ml:
+ .. code-block:: ocaml
+
+ (*===----------------------------------------------------------------------===
+ * Main driver code.
+ *===----------------------------------------------------------------------===*)
+
+ open Llvm
+ open Llvm_executionengine
+ open Llvm_target
+ open Llvm_scalar_opts
+
+ let main () =
+ ignore (initialize_native_target ());
+
+ (* Install standard binary operators.
+ * 1 is the lowest precedence. *)
+ Hashtbl.add Parser.binop_precedence '<' 10;
+ Hashtbl.add Parser.binop_precedence '+' 20;
+ Hashtbl.add Parser.binop_precedence '-' 20;
+ Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
+
+ (* Prime the first token. *)
+ print_string "ready> "; flush stdout;
+ let stream = Lexer.lex (Stream.of_channel stdin) in
+
+ (* Create the JIT. *)
+ let the_execution_engine = ExecutionEngine.create Codegen.the_module in
+ let the_fpm = PassManager.create_function Codegen.the_module in
+
+ (* Set up the optimizer pipeline. Start with registering info about how the
+ * target lays out data structures. *)
+ DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
+
+ (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
+ add_instruction_combination the_fpm;
+
+ (* reassociate expressions. *)
+ add_reassociation the_fpm;
+
+ (* Eliminate Common SubExpressions. *)
+ add_gvn the_fpm;
+
+ (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
+ add_cfg_simplification the_fpm;
+
+ ignore (PassManager.initialize the_fpm);
+
+ (* Run the main "interpreter loop" now. *)
+ Toplevel.main_loop the_fpm the_execution_engine stream;
+
+ (* Print out all the generated code. *)
+ dump_module Codegen.the_module
+ ;;
+
+ main ()
+
+bindings.c
+ .. code-block:: c
+
+ #include <stdio.h>
+
+ /* putchard - putchar that takes a double and returns 0. */
+ extern double putchard(double X) {
+ putchar((char)X);
+ return 0;
+ }
+
+`Next: Extending the language: control flow <OCamlLangImpl5.html>`_
+
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