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diff --git a/docs/tutorial/LangImpl4.html b/docs/tutorial/LangImpl4.html new file mode 100644 index 0000000000..230e6e5dc5 --- /dev/null +++ b/docs/tutorial/LangImpl4.html @@ -0,0 +1,1132 @@ +<!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="../llvm.css" type="text/css"> +</head> + +<body> + +<div class="doc_title">Kaleidoscope: Adding JIT and Optimizer Support</div> + +<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@nondot.org">Chris Lattner</a></p> +</div> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="intro">Chapter 4 Introduction</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<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> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="trivialconstfold">Trivial Constant +Folding</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<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> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="optimizerpasses">LLVM Optimization + Passes</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<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 TargetData(*TheExecutionEngine->getTargetData())); + // 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>llvm-gcc</tt> or +<tt>llvm-ld</tt> run 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> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="jit">Adding a JIT Compiler</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<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> +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>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> +<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>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> + +<!-- *********************************************************************** --> +<div class="doc_section"><a name="code">Full Code Listing</a></div> +<!-- *********************************************************************** --> + +<div class="doc_text"> + +<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 + g++ -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/LLVMContext.h" +#include "llvm/Module.h" +#include "llvm/PassManager.h" +#include "llvm/Analysis/Verifier.h" +#include "llvm/Target/TargetData.h" +#include "llvm/Target/TargetSelect.h" +#include "llvm/Transforms/Scalar.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; +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.CreateAdd(L, R, "addtmp"); + case '-': return Builder.CreateSub(L, R, "subtmp"); + case '*': return Builder.CreateMul(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); + + // 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 TargetData(*TheExecutionEngine->getTargetData())); + // 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> + <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@nondot.org">Chris Lattner</a><br> + <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> + Last modified: $Date$ +</address> +</body> +</html> |