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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>Kaleidoscope: Implementing code generation to LLVM IR</title>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="author" content="Chris Lattner">
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<link rel="stylesheet" href="../llvm.css" type="text/css">
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</head>
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<body>
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<h1>Kaleidoscope: Code generation to LLVM IR</h1>
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<ul>
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<li><a href="index.html">Up to Tutorial Index</a></li>
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<li>Chapter 3
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<ol>
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<li><a href="#intro">Chapter 3 Introduction</a></li>
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<li><a href="#basics">Code Generation Setup</a></li>
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<li><a href="#exprs">Expression Code Generation</a></li>
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<li><a href="#funcs">Function Code Generation</a></li>
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<li><a href="#driver">Driver Changes and Closing Thoughts</a></li>
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<li><a href="#code">Full Code Listing</a></li>
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</ol>
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</li>
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<li><a href="LangImpl4.html">Chapter 4</a>: Adding JIT and Optimizer
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Support</li>
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</ul>
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<div class="doc_author">
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<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="intro">Chapter 3 Introduction</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language
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with LLVM</a>" tutorial. This chapter shows you how to transform the <a
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href="LangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into LLVM IR.
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This will teach you a little bit about how LLVM does things, as well as
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demonstrate how easy it is to use. It's much more work to build a lexer and
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parser than it is to generate LLVM IR code. :)
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</p>
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<p><b>Please note</b>: the code in this chapter and later require LLVM 2.2 or
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later. LLVM 2.1 and before will not work with it. Also note that you need
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to use a version of this tutorial that matches your LLVM release: If you are
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using an official LLVM release, use the version of the documentation included
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with your release or on the <a href="http://llvm.org/releases/">llvm.org
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releases page</a>.</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="basics">Code Generation Setup</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>
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In order to generate LLVM IR, we want some simple setup to get started. First
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we define virtual code generation (codegen) methods in each AST class:</p>
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<div class="doc_code">
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<pre>
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/// ExprAST - Base class for all expression nodes.
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class ExprAST {
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public:
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virtual ~ExprAST() {}
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<b>virtual Value *Codegen() = 0;</b>
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};
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/// NumberExprAST - Expression class for numeric literals like "1.0".
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class NumberExprAST : public ExprAST {
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double Val;
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public:
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NumberExprAST(double val) : Val(val) {}
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<b>virtual Value *Codegen();</b>
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};
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...
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</pre>
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</div>
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<p>The Codegen() method says to emit IR for that AST node along with all the things it
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depends on, and they all return an LLVM Value object.
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"Value" is the class used to represent a "<a
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href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
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Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect
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of SSA values is that their value is computed as the related instruction
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executes, and it does not get a new value until (and if) the instruction
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re-executes. In other words, there is no way to "change" an SSA value. For
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more information, please read up on <a
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href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single
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Assignment</a> - the concepts are really quite natural once you grok them.</p>
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<p>Note that instead of adding virtual methods to the ExprAST class hierarchy,
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it could also make sense to use a <a
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href="http://en.wikipedia.org/wiki/Visitor_pattern">visitor pattern</a> or some
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other way to model this. Again, this tutorial won't dwell on good software
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engineering practices: for our purposes, adding a virtual method is
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simplest.</p>
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<p>The
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second thing we want is an "Error" method like we used for the parser, which will
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be used to report errors found during code generation (for example, use of an
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undeclared parameter):</p>
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<div class="doc_code">
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<pre>
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Value *ErrorV(const char *Str) { Error(Str); return 0; }
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static Module *TheModule;
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static IRBuilder<> Builder(getGlobalContext());
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static std::map<std::string, Value*> NamedValues;
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</pre>
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</div>
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<p>The static variables will be used during code generation. <tt>TheModule</tt>
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is the LLVM construct that contains all of the functions and global variables in
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a chunk of code. In many ways, it is the top-level structure that the LLVM IR
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uses to contain code.</p>
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<p>The <tt>Builder</tt> object is a helper object that makes it easy to generate
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LLVM instructions. Instances of the <a
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href="http://llvm.org/doxygen/IRBuilder_8h-source.html"><tt>IRBuilder</tt></a>
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class template keep track of the current place to insert instructions and has
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methods to create new instructions.</p>
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<p>The <tt>NamedValues</tt> map keeps track of which values are defined in the
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current scope and what their LLVM representation is. (In other words, it is a
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symbol table for the code). In this form of Kaleidoscope, the only things that
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can be referenced are function parameters. As such, function parameters will
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be in this map when generating code for their function body.</p>
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<p>
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With these basics in place, we can start talking about how to generate code for
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each expression. Note that this assumes that the <tt>Builder</tt> has been set
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up to generate code <em>into</em> something. For now, we'll assume that this
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has already been done, and we'll just use it to emit code.
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</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="exprs">Expression Code Generation</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Generating LLVM code for expression nodes is very straightforward: less
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than 45 lines of commented code for all four of our expression nodes. First
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we'll do numeric literals:</p>
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<div class="doc_code">
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<pre>
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Value *NumberExprAST::Codegen() {
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return ConstantFP::get(getGlobalContext(), APFloat(Val));
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}
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</pre>
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</div>
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<p>In the LLVM IR, numeric constants are represented with the
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<tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt>
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internally (<tt>APFloat</tt> has the capability of holding floating point
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constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just
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creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR
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that constants are all uniqued together and shared. For this reason, the API
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uses the "foo::get(...)" idiom instead of "new foo(..)" or "foo::Create(..)".</p>
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<div class="doc_code">
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<pre>
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Value *VariableExprAST::Codegen() {
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// Look this variable up in the function.
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Value *V = NamedValues[Name];
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return V ? V : ErrorV("Unknown variable name");
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}
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</pre>
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</div>
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<p>References to variables are also quite simple using LLVM. In the simple version
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of Kaleidoscope, we assume that the variable has already been emitted somewhere
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and its value is available. In practice, the only values that can be in the
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<tt>NamedValues</tt> map are function arguments. This
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code simply checks to see that the specified name is in the map (if not, an
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unknown variable is being referenced) and returns the value for it. In future
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chapters, we'll add support for <a href="LangImpl5.html#for">loop induction
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variables</a> in the symbol table, and for <a
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href="LangImpl7.html#localvars">local variables</a>.</p>
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<div class="doc_code">
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<pre>
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Value *BinaryExprAST::Codegen() {
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Value *L = LHS->Codegen();
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Value *R = RHS->Codegen();
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if (L == 0 || R == 0) return 0;
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switch (Op) {
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case '+': return Builder.CreateFAdd(L, R, "addtmp");
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case '-': return Builder.CreateFSub(L, R, "subtmp");
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case '*': return Builder.CreateFMul(L, R, "multmp");
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case '<':
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L = Builder.CreateFCmpULT(L, R, "cmptmp");
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// Convert bool 0/1 to double 0.0 or 1.0
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return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
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"booltmp");
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default: return ErrorV("invalid binary operator");
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}
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}
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</pre>
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</div>
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<p>Binary operators start to get more interesting. The basic idea here is that
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we recursively emit code for the left-hand side of the expression, then the
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right-hand side, then we compute the result of the binary expression. In this
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code, we do a simple switch on the opcode to create the right LLVM instruction.
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</p>
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<p>In the example above, the LLVM builder class is starting to show its value.
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IRBuilder knows where to insert the newly created instruction, all you have to
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do is specify what instruction to create (e.g. with <tt>CreateFAdd</tt>), which
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operands to use (<tt>L</tt> and <tt>R</tt> here) and optionally provide a name
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for the generated instruction.</p>
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<p>One nice thing about LLVM is that the name is just a hint. For instance, if
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the code above emits multiple "addtmp" variables, LLVM will automatically
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provide each one with an increasing, unique numeric suffix. Local value names
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for instructions are purely optional, but it makes it much easier to read the
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IR dumps.</p>
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<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by
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strict rules: for example, the Left and Right operators of
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an <a href="../LangRef.html#i_add">add instruction</a> must have the same
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type, and the result type of the add must match the operand types. Because
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all values in Kaleidoscope are doubles, this makes for very simple code for add,
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sub and mul.</p>
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<p>On the other hand, LLVM specifies that the <a
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href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value
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(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
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a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction
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converts its input integer into a floating point value by treating the input
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as an unsigned value. In contrast, if we used the <a
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href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<'
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operator would return 0.0 and -1.0, depending on the input value.</p>
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<div class="doc_code">
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<pre>
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Value *CallExprAST::Codegen() {
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// Look up the name in the global module table.
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Function *CalleeF = TheModule->getFunction(Callee);
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if (CalleeF == 0)
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return ErrorV("Unknown function referenced");
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// If argument mismatch error.
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if (CalleeF->arg_size() != Args.size())
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return ErrorV("Incorrect # arguments passed");
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std::vector<Value*> ArgsV;
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for (unsigned i = 0, e = Args.size(); i != e; ++i) {
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ArgsV.push_back(Args[i]->Codegen());
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if (ArgsV.back() == 0) return 0;
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}
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return Builder.CreateCall(CalleeF, ArgsV.begin(), ArgsV.end(), "calltmp");
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}
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</pre>
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</div>
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<p>Code generation for function calls is quite straightforward with LLVM. The
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code above initially does a function name lookup in the LLVM Module's symbol
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table. Recall that the LLVM Module is the container that holds all of the
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functions we are JIT'ing. By giving each function the same name as what the
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user specifies, we can use the LLVM symbol table to resolve function names for
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us.</p>
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<p>Once we have the function to call, we recursively codegen each argument that
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is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call
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instruction</a>. Note that LLVM uses the native C calling conventions by
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default, allowing these calls to also call into standard library functions like
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"sin" and "cos", with no additional effort.</p>
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<p>This wraps up our handling of the four basic expressions that we have so far
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in Kaleidoscope. Feel free to go in and add some more. For example, by
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browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find
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several other interesting instructions that are really easy to plug into our
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basic framework.</p>
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</div>
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<!-- *********************************************************************** -->
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<h2><a name="funcs">Function Code Generation</a></h2>
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<!-- *********************************************************************** -->
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<div>
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<p>Code generation for prototypes and functions must handle a number of
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details, which make their code less beautiful than expression code
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generation, but allows us to illustrate some important points. First, lets
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talk about code generation for prototypes: they are used both for function
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bodies and external function declarations. The code starts with:</p>
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<div class="doc_code">
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<pre>
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Function *PrototypeAST::Codegen() {
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// Make the function type: double(double,double) etc.
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std::vector<const Type*> Doubles(Args.size(),
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Type::getDoubleTy(getGlobalContext()));
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FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
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Doubles, false);
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Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
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</pre>
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</div>
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<p>This code packs a lot of power into a few lines. Note first that this
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function returns a "Function*" instead of a "Value*". Because a "prototype"
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really talks about the external interface for a function (not the value computed
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by an expression), it makes sense for it to return the LLVM Function it
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corresponds to when codegen'd.</p>
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<p>The call to <tt>FunctionType::get</tt> creates
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the <tt>FunctionType</tt> that should be used for a given Prototype. Since all
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function arguments in Kaleidoscope are of type double, the first line creates
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a vector of "N" LLVM double types. It then uses the <tt>Functiontype::get</tt>
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method to create a function type that takes "N" doubles as arguments, returns
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one double as a result, and that is not vararg (the false parameter indicates
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this). Note that Types in LLVM are uniqued just like Constants are, so you
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don't "new" a type, you "get" it.</p>
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<p>The final line above actually creates the function that the prototype will
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correspond to. This indicates the type, linkage and name to use, as well as which
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module to insert into. "<a href="../LangRef.html#linkage">external linkage</a>"
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means that the function may be defined outside the current module and/or that it
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is callable by functions outside the module. The Name passed in is the name the
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user specified: since "<tt>TheModule</tt>" is specified, this name is registered
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in "<tt>TheModule</tt>"s symbol table, which is used by the function call code
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above.</p>
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<div class="doc_code">
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<pre>
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// If F conflicted, there was already something named 'Name'. If it has a
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// body, don't allow redefinition or reextern.
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if (F->getName() != Name) {
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// Delete the one we just made and get the existing one.
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F->eraseFromParent();
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F = TheModule->getFunction(Name);
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</pre>
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</div>
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<p>The Module symbol table works just like the Function symbol table when it
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comes to name conflicts: if a new function is created with a name that was previously
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added to the symbol table, the new function will get implicitly renamed when added to the
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Module. The code above exploits this fact to determine if there was a previous
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definition of this function.</p>
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<p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases:
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first, we want to allow 'extern'ing a function more than once, as long as the
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prototypes for the externs match (since all arguments have the same type, we
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just have to check that the number of arguments match). Second, we want to
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allow 'extern'ing a function and then defining a body for it. This is useful
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when defining mutually recursive functions.</p>
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<p>In order to implement this, the code above first checks to see if there is
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a collision on the name of the function. If so, it deletes the function we just
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created (by calling <tt>eraseFromParent</tt>) and then calling
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<tt>getFunction</tt> to get the existing function with the specified name. Note
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that many APIs in LLVM have "erase" forms and "remove" forms. The "remove" form
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unlinks the object from its parent (e.g. a Function from a Module) and returns
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it. The "erase" form unlinks the object and then deletes it.</p>
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<div class="doc_code">
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<pre>
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// If F already has a body, reject this.
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if (!F->empty()) {
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ErrorF("redefinition of function");
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return 0;
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}
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// If F took a different number of args, reject.
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if (F->arg_size() != Args.size()) {
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ErrorF("redefinition of function with different # args");
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return 0;
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}
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}
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</pre>
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</div>
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<p>In order to verify the logic above, we first check to see if the pre-existing
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function is "empty". In this case, empty means that it has no basic blocks in
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it, which means it has no body. If it has no body, it is a forward
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declaration. Since we don't allow anything after a full definition of the
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function, the code rejects this case. If the previous reference to a function
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was an 'extern', we simply verify that the number of arguments for that
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definition and this one match up. If not, we emit an error.</p>
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<div class="doc_code">
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<pre>
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// Set names for all arguments.
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unsigned Idx = 0;
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for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
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++AI, ++Idx) {
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AI->setName(Args[Idx]);
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// Add arguments to variable symbol table.
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NamedValues[Args[Idx]] = AI;
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}
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return F;
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}
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</pre>
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</div>
|
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<p>The last bit of code for prototypes loops over all of the arguments in the
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function, setting the name of the LLVM Argument objects to match, and registering
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the arguments in the <tt>NamedValues</tt> map for future use by the
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<tt>VariableExprAST</tt> AST node. Once this is set up, it returns the Function
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object to the caller. Note that we don't check for conflicting
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argument names here (e.g. "extern foo(a b a)"). Doing so would be very
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straight-forward with the mechanics we have already used above.</p>
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<div class="doc_code">
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<pre>
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Function *FunctionAST::Codegen() {
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NamedValues.clear();
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Function *TheFunction = Proto->Codegen();
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if (TheFunction == 0)
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return 0;
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</pre>
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</div>
|
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<p>Code generation for function definitions starts out simply enough: we just
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codegen the prototype (Proto) and verify that it is ok. We then clear out the
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<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 @""() {
|
|
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 @""() {
|
|
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="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
|
|
g++ -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/LLVMContext.h"
|
|
#include "llvm/Module.h"
|
|
#include "llvm/Analysis/Verifier.h"
|
|
#include "llvm/Support/IRBuilder.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.begin(), ArgsV.end(), "calltmp");
|
|
}
|
|
|
|
Function *PrototypeAST::Codegen() {
|
|
// Make the function type: double(double,double) etc.
|
|
std::vector<const 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>
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|
|
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
|
|
<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
|
|
Last modified: $Date$
|
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</address>
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