Date: Wed, 5 Dec 2012 00:26:32 +0000 Subject: docs: Sphinxify `docs/tutorial/` Sorry for the massive commit, but I just wanted to knock this one down and it is really straightforward. There are still a couple trivial (i.e. not related to the content) things left to fix: - Use of raw HTML links where :doc:`...` and :ref:`...` could be used instead. If you are a newbie and want to help fix this it would make for some good bite-sized patches; more experienced developers should be focusing on adding new content (to this tutorial or elsewhere, but please _do not_ waste your time on formatting when there is such dire need for documentation (see docs/SphinxQuickstartTemplate.rst to get started writing)). - Highlighting of the kaleidoscope code blocks (currently left as bare `::`). I will be working on writing a custom Pygments highlighter for this, mostly as training for maintaining the `llvm` code-block's lexer in-tree. I want to do this because I am extremely unhappy with how it just "gives up" on the slightest deviation from the expected syntax and leaves the whole code-block un-highlighted. More generally I am looking at writing some Sphinx extensions and keeping them in-tree as well, to support common use cases that currently have no good solution (like "monospace text inside a link"). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169343 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/tutorial/LangImpl4.html | 1152 ------------------------------------------ 1 file changed, 1152 deletions(-) delete mode 100644 docs/tutorial/LangImpl4.html (limited to 'docs/tutorial/LangImpl4.html') diff --git a/docs/tutorial/LangImpl4.html b/docs/tutorial/LangImpl4.html deleted file mode 100644 index 53695924b2..0000000000 --- a/docs/tutorial/LangImpl4.html +++ /dev/null @@ -1,1152 +0,0 @@ - - - - - Kaleidoscope: Adding JIT and Optimizer Support - - - - - - - -

Kaleidoscope: Adding JIT and Optimizer Support

- -

Up to Tutorial Index
Chapter 4 -
-
Chapter 5: Extending the Language: Control -Flow

- -

Written by Chris Lattner

- - -

Chapter 4 Introduction

- - -

- -

Welcome to Chapter 4 of the "Implementing a language -with LLVM" tutorial. Chapters 1-3 described the implementation of a simple -language and added support for generating LLVM IR. This chapter describes -two new techniques: adding optimizer support to your language, and adding JIT -compiler support. These additions will demonstrate how to get nice, efficient code -for the Kaleidoscope language.

- -

- - -

Trivial Constant Folding

- - -

- -

-Our demonstration for Chapter 3 is elegant and easy to extend. Unfortunately, -it does not produce wonderful code. The IRBuilder, however, does give us -obvious optimizations when compiling simple code:

- -

-ready> def test(x) 1+2+x;
-Read function definition:
-define double @test(double %x) {
-entry:
-        %addtmp = fadd double 3.000000e+00, %x
-        ret double %addtmp
-}
-

- -

This code is not a literal transcription of the AST built by parsing the -input. That would be: - -

-ready> def test(x) 1+2+x;
-Read function definition:
-define double @test(double %x) {
-entry:
-        %addtmp = fadd double 2.000000e+00, 1.000000e+00
-        %addtmp1 = fadd double %addtmp, %x
-        ret double %addtmp1
-}
-

- -

Constant folding, as seen above, in particular, is a very common and very -important optimization: so much so that many language implementors implement -constant folding support in their AST representation.

- -

With LLVM, you don't need this support in the AST. Since all calls to build -LLVM IR go through the LLVM IR builder, the builder itself checked to see if -there was a constant folding opportunity when you call it. If so, it just does -the constant fold and return the constant instead of creating an instruction. - -

Well, that was easy :). In practice, we recommend always using -IRBuilder when generating code like this. It has no -"syntactic overhead" for its use (you don't have to uglify your compiler with -constant checks everywhere) and it can dramatically reduce the amount of -LLVM IR that is generated in some cases (particular for languages with a macro -preprocessor or that use a lot of constants).

- -

On the other hand, the IRBuilder is limited by the fact -that it does all of its analysis inline with the code as it is built. If you -take a slightly more complex example:

- -

-ready> def test(x) (1+2+x)*(x+(1+2));
-ready> Read function definition:
-define double @test(double %x) {
-entry:
-        %addtmp = fadd double 3.000000e+00, %x
-        %addtmp1 = fadd double %x, 3.000000e+00
-        %multmp = fmul double %addtmp, %addtmp1
-        ret double %multmp
-}
-

- -

In this case, the LHS and RHS of the multiplication are the same value. We'd -really like to see this generate "tmp = x+3; result = tmp*tmp;" instead -of computing "x+3" twice.

- -

Unfortunately, no amount of local analysis will be able to detect and correct -this. This requires two transformations: reassociation of expressions (to -make the add's lexically identical) and Common Subexpression Elimination (CSE) -to delete the redundant add instruction. Fortunately, LLVM provides a broad -range of optimizations that you can use, in the form of "passes".

- -

- - -

LLVM Optimization Passes

- - -

- -

LLVM provides many optimization passes, which do many different sorts of -things and have different tradeoffs. Unlike other systems, LLVM doesn't hold -to the mistaken notion that one set of optimizations is right for all languages -and for all situations. LLVM allows a compiler implementor to make complete -decisions about what optimizations to use, in which order, and in what -situation.

- -

As a concrete example, LLVM supports both "whole module" passes, which look -across as large of body of code as they can (often a whole file, but if run -at link time, this can be a substantial portion of the whole program). It also -supports and includes "per-function" passes which just operate on a single -function at a time, without looking at other functions. For more information -on passes and how they are run, see the How -to Write a Pass document and the List of LLVM -Passes.

- -

For Kaleidoscope, we are currently generating functions on the fly, one at -a time, as the user types them in. We aren't shooting for the ultimate -optimization experience in this setting, but we also want to catch the easy and -quick stuff where possible. As such, we will choose to run a few per-function -optimizations as the user types the function in. If we wanted to make a "static -Kaleidoscope compiler", we would use exactly the code we have now, except that -we would defer running the optimizer until the entire file has been parsed.

- -

In order to get per-function optimizations going, we need to set up a -FunctionPassManager 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:

- -

-  FunctionPassManager OurFPM(TheModule);
-
-  // Set up the optimizer pipeline.  Start with registering info about how the
-  // target lays out data structures.
-  OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
-  // Provide basic AliasAnalysis support for GVN.
-  OurFPM.add(createBasicAliasAnalysisPass());
-  // Do simple "peephole" optimizations and bit-twiddling optzns.
-  OurFPM.add(createInstructionCombiningPass());
-  // Reassociate expressions.
-  OurFPM.add(createReassociatePass());
-  // Eliminate Common SubExpressions.
-  OurFPM.add(createGVNPass());
-  // Simplify the control flow graph (deleting unreachable blocks, etc).
-  OurFPM.add(createCFGSimplificationPass());
-
-  OurFPM.doInitialization();
-
-  // Set the global so the code gen can use this.
-  TheFPM = &OurFPM;
-
-  // Run the main "interpreter loop" now.
-  MainLoop();
-

- -

This code defines a FunctionPassManager, "OurFPM". It -requires a pointer to the Module to construct itself. Once it is set -up, we use a series of "add" calls to add a bunch of LLVM passes. The first -pass is basically boilerplate, it adds a pass so that later optimizations know -how the data structures in the program are laid out. The -"TheExecutionEngine" variable is related to the JIT, which we will get -to in the next section.

- -

In this case, we choose to add 4 optimization passes. The passes we chose -here are a pretty standard set of "cleanup" optimizations that are useful for -a wide variety of code. I won't delve into what they do but, believe me, -they are a good starting place :).

- -

Once the PassManager is set up, we need to make use of it. We do this by -running it after our newly created function is constructed (in -FunctionAST::Codegen), but before it is returned to the client:

- -

-  if (Value *RetVal = Body->Codegen()) {
-    // Finish off the function.
-    Builder.CreateRet(RetVal);
-
-    // Validate the generated code, checking for consistency.
-    verifyFunction(*TheFunction);
-
-    // Optimize the function.
-    TheFPM->run(*TheFunction);
-    
-    return TheFunction;
-  }
-

- -

As you can see, this is pretty straightforward. The -FunctionPassManager optimizes and updates the LLVM Function* in place, -improving (hopefully) its body. With this in place, we can try our test above -again:

- -

-ready> def test(x) (1+2+x)*(x+(1+2));
-ready> Read function definition:
-define double @test(double %x) {
-entry:
-        %addtmp = fadd double %x, 3.000000e+00
-        %multmp = fmul double %addtmp, %addtmp
-        ret double %multmp
-}
-

- -

As expected, we now get our nicely optimized code, saving a floating point -add instruction from every execution of this function.

- -

LLVM provides a wide variety of optimizations that can be used in certain -circumstances. Some documentation about the various -passes is available, but it isn't very complete. Another good source of -ideas can come from looking at the passes that Clang runs to get -started. The "opt" tool allows you to experiment with passes from the -command line, so you can see if they do anything.

- -

Now that we have reasonable code coming out of our front-end, lets talk about -executing it!

- -

- - -

Adding a JIT Compiler

- - -

- -

Code that is available in LLVM IR can have a wide variety of tools -applied to it. For example, you can run optimizations on it (as we did above), -you can dump it out in textual or binary forms, you can compile the code to an -assembly file (.s) for some target, or you can JIT compile it. The nice thing -about the LLVM IR representation is that it is the "common currency" between -many different parts of the compiler. -

- -

In this section, we'll add JIT compiler support to our interpreter. The -basic idea that we want for Kaleidoscope is to have the user enter function -bodies as they do now, but immediately evaluate the top-level expressions they -type in. For example, if they type in "1 + 2;", we should evaluate and print -out 3. If they define a function, they should be able to call it from the -command line.

- -

In order to do this, we first declare and initialize the JIT. This is done -by adding a global variable and a call in main:

- -

-static ExecutionEngine *TheExecutionEngine;
-...
-int main() {
-  ..
-  // Create the JIT.  This takes ownership of the module.
-  TheExecutionEngine = EngineBuilder(TheModule).create();
-  ..
-}
-

- -

This creates an abstract "Execution Engine" which can be either a JIT -compiler or the LLVM interpreter. LLVM will automatically pick a JIT compiler -for you if one is available for your platform, otherwise it will fall back to -the interpreter.

- -

Once the ExecutionEngine is created, the JIT is ready to be used. -There are a variety of APIs that are useful, but the simplest one is the -"getPointerToFunction(F)" method. This method JIT compiles the -specified LLVM Function and returns a function pointer to the generated machine -code. In our case, this means that we can change the code that parses a -top-level expression to look like this:

- -

-static void HandleTopLevelExpression() {
-  // Evaluate a top-level expression into an anonymous function.
-  if (FunctionAST *F = ParseTopLevelExpr()) {
-    if (Function *LF = F->Codegen()) {
-      LF->dump();  // Dump the function for exposition purposes.
-    
-      // JIT the function, returning a function pointer.
-      void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
-      
-      // Cast it to the right type (takes no arguments, returns a double) so we
-      // can call it as a native function.
-      double (*FP)() = (double (*)())(intptr_t)FPtr;
-      fprintf(stderr, "Evaluated to %f\n", FP());
-    }
-

- -

Recall that we compile top-level expressions into a self-contained LLVM -function that takes no arguments and returns the computed double. Because the -LLVM JIT compiler matches the native platform ABI, this means that you can just -cast the result pointer to a function pointer of that type and call it directly. -This means, there is no difference between JIT compiled code and native machine -code that is statically linked into your application.

- -

With just these two changes, lets see how Kaleidoscope works now!

- -

-ready> 4+5;
-Read top-level expression:
-define double @0() {
-entry:
-  ret double 9.000000e+00
-}
-
-Evaluated to 9.000000
-

- -

Well this looks like it is basically working. The dump of the function -shows the "no argument function that always returns double" that we synthesize -for each top-level expression that is typed in. This demonstrates very basic -functionality, but can we do more?

- -

-ready> def testfunc(x y) x + y*2;  
-Read function definition:
-define double @testfunc(double %x, double %y) {
-entry:
-  %multmp = fmul double %y, 2.000000e+00
-  %addtmp = fadd double %multmp, %x
-  ret double %addtmp
-}
-
-ready> testfunc(4, 10);
-Read top-level expression:
-define double @1() {
-entry:
-  %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01)
-  ret double %calltmp
-}
-
-Evaluated to 24.000000
-

- -

This illustrates that we can now call user code, but there is something a bit -subtle going on here. Note that we only invoke the JIT on the anonymous -functions that call testfunc, but we never invoked it -on testfunc itself. What actually happened here is that the JIT -scanned for all non-JIT'd functions transitively called from the anonymous -function and compiled all of them before returning -from getPointerToFunction().

- -

The JIT provides a number of other more advanced interfaces for things like -freeing allocated machine code, rejit'ing functions to update them, etc. -However, even with this simple code, we get some surprisingly powerful -capabilities - check this out (I removed the dump of the anonymous functions, -you should get the idea by now :) :

- -

-ready> extern sin(x);
-Read extern: 
-declare double @sin(double)
-
-ready> extern cos(x);
-Read extern: 
-declare double @cos(double)
-
-ready> sin(1.0);
-Read top-level expression:
-define double @2() {
-entry:
-  ret double 0x3FEAED548F090CEE
-}
-
-Evaluated to 0.841471
-
-ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x);
-Read function definition:
-define double @foo(double %x) {
-entry:
-  %calltmp = call double @sin(double %x)
-  %multmp = fmul double %calltmp, %calltmp
-  %calltmp2 = call double @cos(double %x)
-  %multmp4 = fmul double %calltmp2, %calltmp2
-  %addtmp = fadd double %multmp, %multmp4
-  ret double %addtmp
-}
-
-ready> foo(4.0);
-Read top-level expression:
-define double @3() {
-entry:
-  %calltmp = call double @foo(double 4.000000e+00)
-  ret double %calltmp
-}
-
-Evaluated to 1.000000
-

- -

Whoa, how does the JIT know about sin and cos? The answer is surprisingly -simple: in this -example, the JIT started execution of a function and got to a function call. It -realized that the function was not yet JIT compiled and invoked the standard set -of routines to resolve the function. In this case, there is no body defined -for the function, so the JIT ended up calling "dlsym("sin")" on the -Kaleidoscope process itself. -Since "sin" is defined within the JIT's address space, it simply -patches up calls in the module to call the libm version of sin -directly.

- -

The LLVM JIT provides a number of interfaces (look in the -ExecutionEngine.h file) for controlling how unknown functions get -resolved. It allows you to establish explicit mappings between IR objects and -addresses (useful for LLVM global variables that you want to map to static -tables, for example), allows you to dynamically decide on the fly based on the -function name, and even allows you to have the JIT compile functions lazily the -first time they're called.

- -

One interesting application of this is that we can now extend the language -by writing arbitrary C++ code to implement operations. For example, if we add: -

- -

-/// putchard - putchar that takes a double and returns 0.
-extern "C" 
-double putchard(double X) {
-  putchar((char)X);
-  return 0;
-}
-

- -

Now we can produce simple output to the console by using things like: -"extern putchard(x); putchard(120);", which prints a lowercase 'x' on -the console (120 is the ASCII code for 'x'). Similar code could be used to -implement file I/O, console input, and many other capabilities in -Kaleidoscope.

- -

This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At -this point, we can compile a non-Turing-complete programming language, optimize -and JIT compile it in a user-driven way. Next up we'll look into extending the language with control flow constructs, -tackling some interesting LLVM IR issues along the way.

- -

- - -

Full Code Listing

- - -

- -

-Here is the complete code listing for our running example, enhanced with the -LLVM JIT and optimizer. To build this example, use: -

- -

-# Compile
-clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy
-# Run
-./toy
-

- -

-If you are compiling this on Linux, make sure to add the "-rdynamic" option -as well. This makes sure that the external functions are resolved properly -at runtime.

- -

Here is the code:

- -

-#include "llvm/DerivedTypes.h"
-#include "llvm/ExecutionEngine/ExecutionEngine.h"
-#include "llvm/ExecutionEngine/JIT.h"
-#include "llvm/IRBuilder.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/PassManager.h"
-#include "llvm/Analysis/Verifier.h"
-#include "llvm/Analysis/Passes.h"
-#include "llvm/DataLayout.h"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Support/TargetSelect.h"
-#include <cstdio>
-#include <string>
-#include <map>
-#include <vector>
-using namespace llvm;
-
-//===----------------------------------------------------------------------===//
-// Lexer
-//===----------------------------------------------------------------------===//
-
-// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
-// of these for known things.
-enum Token {
-  tok_eof = -1,
-
-  // commands
-  tok_def = -2, tok_extern = -3,
-
-  // primary
-  tok_identifier = -4, tok_number = -5
-};
-
-static std::string IdentifierStr;  // Filled in if tok_identifier
-static double NumVal;              // Filled in if tok_number
-
-/// gettok - Return the next token from standard input.
-static int gettok() {
-  static int LastChar = ' ';
-
-  // Skip any whitespace.
-  while (isspace(LastChar))
-    LastChar = getchar();
-
-  if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
-    IdentifierStr = LastChar;
-    while (isalnum((LastChar = getchar())))
-      IdentifierStr += LastChar;
-
-    if (IdentifierStr == "def") return tok_def;
-    if (IdentifierStr == "extern") return tok_extern;
-    return tok_identifier;
-  }
-
-  if (isdigit(LastChar) || LastChar == '.') {   // Number: [0-9.]+
-    std::string NumStr;
-    do {
-      NumStr += LastChar;
-      LastChar = getchar();
-    } while (isdigit(LastChar) || LastChar == '.');
-
-    NumVal = strtod(NumStr.c_str(), 0);
-    return tok_number;
-  }
-
-  if (LastChar == '#') {
-    // Comment until end of line.
-    do LastChar = getchar();
-    while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
-    
-    if (LastChar != EOF)
-      return gettok();
-  }
-  
-  // Check for end of file.  Don't eat the EOF.
-  if (LastChar == EOF)
-    return tok_eof;
-
-  // Otherwise, just return the character as its ascii value.
-  int ThisChar = LastChar;
-  LastChar = getchar();
-  return ThisChar;
-}
-
-//===----------------------------------------------------------------------===//
-// Abstract Syntax Tree (aka Parse Tree)
-//===----------------------------------------------------------------------===//
-
-/// ExprAST - Base class for all expression nodes.
-class ExprAST {
-public:
-  virtual ~ExprAST() {}
-  virtual Value *Codegen() = 0;
-};
-
-/// NumberExprAST - Expression class for numeric literals like "1.0".
-class NumberExprAST : public ExprAST {
-  double Val;
-public:
-  NumberExprAST(double val) : Val(val) {}
-  virtual Value *Codegen();
-};
-
-/// VariableExprAST - Expression class for referencing a variable, like "a".
-class VariableExprAST : public ExprAST {
-  std::string Name;
-public:
-  VariableExprAST(const std::string &name) : Name(name) {}
-  virtual Value *Codegen();
-};
-
-/// BinaryExprAST - Expression class for a binary operator.
-class BinaryExprAST : public ExprAST {
-  char Op;
-  ExprAST *LHS, *RHS;
-public:
-  BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs) 
-    : Op(op), LHS(lhs), RHS(rhs) {}
-  virtual Value *Codegen();
-};
-
-/// CallExprAST - Expression class for function calls.
-class CallExprAST : public ExprAST {
-  std::string Callee;
-  std::vector<ExprAST*> Args;
-public:
-  CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
-    : Callee(callee), Args(args) {}
-  virtual Value *Codegen();
-};
-
-/// PrototypeAST - This class represents the "prototype" for a function,
-/// which captures its name, and its argument names (thus implicitly the number
-/// of arguments the function takes).
-class PrototypeAST {
-  std::string Name;
-  std::vector<std::string> Args;
-public:
-  PrototypeAST(const std::string &name, const std::vector<std::string> &args)
-    : Name(name), Args(args) {}
-  
-  Function *Codegen();
-};
-
-/// FunctionAST - This class represents a function definition itself.
-class FunctionAST {
-  PrototypeAST *Proto;
-  ExprAST *Body;
-public:
-  FunctionAST(PrototypeAST *proto, ExprAST *body)
-    : Proto(proto), Body(body) {}
-  
-  Function *Codegen();
-};
-
-//===----------------------------------------------------------------------===//
-// Parser
-//===----------------------------------------------------------------------===//
-
-/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current
-/// token the parser is looking at.  getNextToken reads another token from the
-/// lexer and updates CurTok with its results.
-static int CurTok;
-static int getNextToken() {
-  return CurTok = gettok();
-}
-
-/// BinopPrecedence - This holds the precedence for each binary operator that is
-/// defined.
-static std::map<char, int> BinopPrecedence;
-
-/// GetTokPrecedence - Get the precedence of the pending binary operator token.
-static int GetTokPrecedence() {
-  if (!isascii(CurTok))
-    return -1;
-  
-  // Make sure it's a declared binop.
-  int TokPrec = BinopPrecedence[CurTok];
-  if (TokPrec <= 0) return -1;
-  return TokPrec;
-}
-
-/// Error* - These are little helper functions for error handling.
-ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
-PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
-FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }
-
-static ExprAST *ParseExpression();
-
-/// identifierexpr
-///   ::= identifier
-///   ::= identifier '(' expression* ')'
-static ExprAST *ParseIdentifierExpr() {
-  std::string IdName = IdentifierStr;
-  
-  getNextToken();  // eat identifier.
-  
-  if (CurTok != '(') // Simple variable ref.
-    return new VariableExprAST(IdName);
-  
-  // Call.
-  getNextToken();  // eat (
-  std::vector<ExprAST*> Args;
-  if (CurTok != ')') {
-    while (1) {
-      ExprAST *Arg = ParseExpression();
-      if (!Arg) return 0;
-      Args.push_back(Arg);
-
-      if (CurTok == ')') break;
-
-      if (CurTok != ',')
-        return Error("Expected ')' or ',' in argument list");
-      getNextToken();
-    }
-  }
-
-  // Eat the ')'.
-  getNextToken();
-  
-  return new CallExprAST(IdName, Args);
-}
-
-/// numberexpr ::= number
-static ExprAST *ParseNumberExpr() {
-  ExprAST *Result = new NumberExprAST(NumVal);
-  getNextToken(); // consume the number
-  return Result;
-}
-
-/// parenexpr ::= '(' expression ')'
-static ExprAST *ParseParenExpr() {
-  getNextToken();  // eat (.
-  ExprAST *V = ParseExpression();
-  if (!V) return 0;
-  
-  if (CurTok != ')')
-    return Error("expected ')'");
-  getNextToken();  // eat ).
-  return V;
-}
-
-/// primary
-///   ::= identifierexpr
-///   ::= numberexpr
-///   ::= parenexpr
-static ExprAST *ParsePrimary() {
-  switch (CurTok) {
-  default: return Error("unknown token when expecting an expression");
-  case tok_identifier: return ParseIdentifierExpr();
-  case tok_number:     return ParseNumberExpr();
-  case '(':            return ParseParenExpr();
-  }
-}
-
-/// binoprhs
-///   ::= ('+' primary)*
-static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
-  // If this is a binop, find its precedence.
-  while (1) {
-    int TokPrec = GetTokPrecedence();
-    
-    // If this is a binop that binds at least as tightly as the current binop,
-    // consume it, otherwise we are done.
-    if (TokPrec < ExprPrec)
-      return LHS;
-    
-    // Okay, we know this is a binop.
-    int BinOp = CurTok;
-    getNextToken();  // eat binop
-    
-    // Parse the primary expression after the binary operator.
-    ExprAST *RHS = ParsePrimary();
-    if (!RHS) return 0;
-    
-    // If BinOp binds less tightly with RHS than the operator after RHS, let
-    // the pending operator take RHS as its LHS.
-    int NextPrec = GetTokPrecedence();
-    if (TokPrec < NextPrec) {
-      RHS = ParseBinOpRHS(TokPrec+1, RHS);
-      if (RHS == 0) return 0;
-    }
-    
-    // Merge LHS/RHS.
-    LHS = new BinaryExprAST(BinOp, LHS, RHS);
-  }
-}
-
-/// expression
-///   ::= primary binoprhs
-///
-static ExprAST *ParseExpression() {
-  ExprAST *LHS = ParsePrimary();
-  if (!LHS) return 0;
-  
-  return ParseBinOpRHS(0, LHS);
-}
-
-/// prototype
-///   ::= id '(' id* ')'
-static PrototypeAST *ParsePrototype() {
-  if (CurTok != tok_identifier)
-    return ErrorP("Expected function name in prototype");
-
-  std::string FnName = IdentifierStr;
-  getNextToken();
-  
-  if (CurTok != '(')
-    return ErrorP("Expected '(' in prototype");
-  
-  std::vector<std::string> ArgNames;
-  while (getNextToken() == tok_identifier)
-    ArgNames.push_back(IdentifierStr);
-  if (CurTok != ')')
-    return ErrorP("Expected ')' in prototype");
-  
-  // success.
-  getNextToken();  // eat ')'.
-  
-  return new PrototypeAST(FnName, ArgNames);
-}
-
-/// definition ::= 'def' prototype expression
-static FunctionAST *ParseDefinition() {
-  getNextToken();  // eat def.
-  PrototypeAST *Proto = ParsePrototype();
-  if (Proto == 0) return 0;
-
-  if (ExprAST *E = ParseExpression())
-    return new FunctionAST(Proto, E);
-  return 0;
-}
-
-/// toplevelexpr ::= expression
-static FunctionAST *ParseTopLevelExpr() {
-  if (ExprAST *E = ParseExpression()) {
-    // Make an anonymous proto.
-    PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
-    return new FunctionAST(Proto, E);
-  }
-  return 0;
-}
-
-/// external ::= 'extern' prototype
-static PrototypeAST *ParseExtern() {
-  getNextToken();  // eat extern.
-  return ParsePrototype();
-}
-
-//===----------------------------------------------------------------------===//
-// Code Generation
-//===----------------------------------------------------------------------===//
-
-static Module *TheModule;
-static IRBuilder<> Builder(getGlobalContext());
-static std::map<std::string, Value*> NamedValues;
-static FunctionPassManager *TheFPM;
-
-Value *ErrorV(const char *Str) { Error(Str); return 0; }
-
-Value *NumberExprAST::Codegen() {
-  return ConstantFP::get(getGlobalContext(), APFloat(Val));
-}
-
-Value *VariableExprAST::Codegen() {
-  // Look this variable up in the function.
-  Value *V = NamedValues[Name];
-  return V ? V : ErrorV("Unknown variable name");
-}
-
-Value *BinaryExprAST::Codegen() {
-  Value *L = LHS->Codegen();
-  Value *R = RHS->Codegen();
-  if (L == 0 || R == 0) return 0;
-  
-  switch (Op) {
-  case '+': return Builder.CreateFAdd(L, R, "addtmp");
-  case '-': return Builder.CreateFSub(L, R, "subtmp");
-  case '*': return Builder.CreateFMul(L, R, "multmp");
-  case '<':
-    L = Builder.CreateFCmpULT(L, R, "cmptmp");
-    // Convert bool 0/1 to double 0.0 or 1.0
-    return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
-                                "booltmp");
-  default: return ErrorV("invalid binary operator");
-  }
-}
-
-Value *CallExprAST::Codegen() {
-  // Look up the name in the global module table.
-  Function *CalleeF = TheModule->getFunction(Callee);
-  if (CalleeF == 0)
-    return ErrorV("Unknown function referenced");
-  
-  // If argument mismatch error.
-  if (CalleeF->arg_size() != Args.size())
-    return ErrorV("Incorrect # arguments passed");
-
-  std::vector<Value*> ArgsV;
-  for (unsigned i = 0, e = Args.size(); i != e; ++i) {
-    ArgsV.push_back(Args[i]->Codegen());
-    if (ArgsV.back() == 0) return 0;
-  }
-  
-  return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
-}
-
-Function *PrototypeAST::Codegen() {
-  // Make the function type:  double(double,double) etc.
-  std::vector<Type*> Doubles(Args.size(),
-                             Type::getDoubleTy(getGlobalContext()));
-  FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
-                                       Doubles, false);
-  
-  Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);
-  
-  // If F conflicted, there was already something named 'Name'.  If it has a
-  // body, don't allow redefinition or reextern.
-  if (F->getName() != Name) {
-    // Delete the one we just made and get the existing one.
-    F->eraseFromParent();
-    F = TheModule->getFunction(Name);
-    
-    // If F already has a body, reject this.
-    if (!F->empty()) {
-      ErrorF("redefinition of function");
-      return 0;
-    }
-    
-    // If F took a different number of args, reject.
-    if (F->arg_size() != Args.size()) {
-      ErrorF("redefinition of function with different # args");
-      return 0;
-    }
-  }
-  
-  // Set names for all arguments.
-  unsigned Idx = 0;
-  for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
-       ++AI, ++Idx) {
-    AI->setName(Args[Idx]);
-    
-    // Add arguments to variable symbol table.
-    NamedValues[Args[Idx]] = AI;
-  }
-  
-  return F;
-}
-
-Function *FunctionAST::Codegen() {
-  NamedValues.clear();
-  
-  Function *TheFunction = Proto->Codegen();
-  if (TheFunction == 0)
-    return 0;
-  
-  // Create a new basic block to start insertion into.
-  BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
-  Builder.SetInsertPoint(BB);
-  
-  if (Value *RetVal = Body->Codegen()) {
-    // Finish off the function.
-    Builder.CreateRet(RetVal);
-
-    // Validate the generated code, checking for consistency.
-    verifyFunction(*TheFunction);
-
-    // Optimize the function.
-    TheFPM->run(*TheFunction);
-    
-    return TheFunction;
-  }
-  
-  // Error reading body, remove function.
-  TheFunction->eraseFromParent();
-  return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Top-Level parsing and JIT Driver
-//===----------------------------------------------------------------------===//
-
-static ExecutionEngine *TheExecutionEngine;
-
-static void HandleDefinition() {
-  if (FunctionAST *F = ParseDefinition()) {
-    if (Function *LF = F->Codegen()) {
-      fprintf(stderr, "Read function definition:");
-      LF->dump();
-    }
-  } else {
-    // Skip token for error recovery.
-    getNextToken();
-  }
-}
-
-static void HandleExtern() {
-  if (PrototypeAST *P = ParseExtern()) {
-    if (Function *F = P->Codegen()) {
-      fprintf(stderr, "Read extern: ");
-      F->dump();
-    }
-  } else {
-    // Skip token for error recovery.
-    getNextToken();
-  }
-}
-
-static void HandleTopLevelExpression() {
-  // Evaluate a top-level expression into an anonymous function.
-  if (FunctionAST *F = ParseTopLevelExpr()) {
-    if (Function *LF = F->Codegen()) {
-      fprintf(stderr, "Read top-level expression:");
-      LF->dump();
-
-      // JIT the function, returning a function pointer.
-      void *FPtr = TheExecutionEngine->getPointerToFunction(LF);
-      
-      // Cast it to the right type (takes no arguments, returns a double) so we
-      // can call it as a native function.
-      double (*FP)() = (double (*)())(intptr_t)FPtr;
-      fprintf(stderr, "Evaluated to %f\n", FP());
-    }
-  } else {
-    // Skip token for error recovery.
-    getNextToken();
-  }
-}
-
-/// top ::= definition | external | expression | ';'
-static void MainLoop() {
-  while (1) {
-    fprintf(stderr, "ready> ");
-    switch (CurTok) {
-    case tok_eof:    return;
-    case ';':        getNextToken(); break;  // ignore top-level semicolons.
-    case tok_def:    HandleDefinition(); break;
-    case tok_extern: HandleExtern(); break;
-    default:         HandleTopLevelExpression(); break;
-    }
-  }
-}
-
-//===----------------------------------------------------------------------===//
-// "Library" functions that can be "extern'd" from user code.
-//===----------------------------------------------------------------------===//
-
-/// putchard - putchar that takes a double and returns 0.
-extern "C" 
-double putchard(double X) {
-  putchar((char)X);
-  return 0;
-}
-
-//===----------------------------------------------------------------------===//
-// Main driver code.
-//===----------------------------------------------------------------------===//
-
-int main() {
-  InitializeNativeTarget();
-  LLVMContext &Context = getGlobalContext();
-
-  // Install standard binary operators.
-  // 1 is lowest precedence.
-  BinopPrecedence['<'] = 10;
-  BinopPrecedence['+'] = 20;
-  BinopPrecedence['-'] = 20;
-  BinopPrecedence['*'] = 40;  // highest.
-
-  // Prime the first token.
-  fprintf(stderr, "ready> ");
-  getNextToken();
-
-  // Make the module, which holds all the code.
-  TheModule = new Module("my cool jit", Context);
-
-  // Create the JIT.  This takes ownership of the module.
-  std::string ErrStr;
-  TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create();
-  if (!TheExecutionEngine) {
-    fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str());
-    exit(1);
-  }
-
-  FunctionPassManager OurFPM(TheModule);
-
-  // Set up the optimizer pipeline.  Start with registering info about how the
-  // target lays out data structures.
-  OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout()));
-  // Provide basic AliasAnalysis support for GVN.
-  OurFPM.add(createBasicAliasAnalysisPass());
-  // Do simple "peephole" optimizations and bit-twiddling optzns.
-  OurFPM.add(createInstructionCombiningPass());
-  // Reassociate expressions.
-  OurFPM.add(createReassociatePass());
-  // Eliminate Common SubExpressions.
-  OurFPM.add(createGVNPass());
-  // Simplify the control flow graph (deleting unreachable blocks, etc).
-  OurFPM.add(createCFGSimplificationPass());
-
-  OurFPM.doInitialization();
-
-  // Set the global so the code gen can use this.
-  TheFPM = &OurFPM;
-
-  // Run the main "interpreter loop" now.
-  MainLoop();
-
-  TheFPM = 0;
-
-  // Print out all of the generated code.
-  TheModule->dump();
-
-  return 0;
-}
-

- -Next: Extending the language: control flow -

- - -

- - Chris Lattner
- The LLVM Compiler Infrastructure
- Last modified: $Date$ -

- - -- cgit v1.2.3-18-g5258