LLVM教程（三）LLVM IR代码生成

/// 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();
};
...

Value *ErrorV(const char *Str) { Error(Str); return 0; }

// TheModule是LLVM中用于存放代码段中所有函数和全局变量的结构。从某种意义上讲，可以把它当作LLVM IR代码的顶层容器。
static Module *TheModule; 
// Builder是用于简化LLVM指令生成的辅助对象，IRBuilder类模板的实例可用于跟踪当前插入指令的位置，同时还带有用于生成新指令的方法。
static IRBuilder<> Builder(getGlobalContext());
// NamedValues映射表用于记录定义于当前作用域内的变量及与之相对应的LLVM表示（换言之，也就是代码的符号表）。
static std::map<std::string, Value*> NamedValues;

    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;

      // opcode的取值用了一个简单的switch语句，从而为各种二元运算符创建出相应的LLVM指令。
      switch (Op) {
      // 只需想清楚该用哪些操作数（即此处的L和R）生成哪条指令（通过调用CreateFAdd等方法）即可，至于新指令该插入到什么位置，交给IRBuilder就可以了
      // 此处的指令名只是一个提示。假设代码生成了多条“addtmp”指令，LLVM会自动给每条指令的名字追加一个自增的唯一数字后缀。
      case '+': return Builder.CreateFAdd(L, R, "addtmp");
      case '-': return Builder.CreateFSub(L, R, "subtmp");
      case '*': return Builder.CreateFMul(L, R, "multmp");
      case '<':
      // add指令的Left、Right操作数必须同属一个类型，结果的类型则必须与操作数的类型相容。
      // fcmp指令的返回值类型必须是‘i1’（单比特整数），而Kaleidoscope只能接受0.0或1.0。为了弥合语义上的差异，给fcmp指令配上一条uitofp指令。
      // 这条指令会将输入的整数视作无符号数，并将之转换成浮点数。
      // 如果用的是sitofp指令，Kaleidoscope的‘<’运算符将视输入的不同而返回0.0或-1.0。
        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.
    // 创建了double的vector
    std::vector<Type*> Doubles(Args.size(),
    Type::getDoubleTy(getGlobalContext()));
    // FunctionType::get调用用于为给定的函数原型创建对应的FunctionType对象，创建出一个参数不可变的函数类型（false）。
    FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
    Doubles, false);

    // 创建与该函数原型相对应的函数，包含了类型、链接方式和函数名等，并指定该函数待插入的模块。
    // “ExternalLinkage”表示该函数可能定义于当前模块之外，且/或可以被当前模块之外的函数调用。
    // Name是用户指定的函数名.
    // 函数定义在“TheModule”内，函数名自然也注册在“TheModule”的符号表内。
    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.
    // 如果有函数名冲突，（调用eraseFunctionParent）将刚刚创建的函数对象删除
    if (F->getName() != Name) {
    // Delete the one we just made and get the existing one.
    F->eraseFromParent();
    // 然后调用getFunction获取与函数名相对应的函数对象。
    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;
}

    Function *FunctionAST::Codegen() {
    NamedValues.clear();

    Function *TheFunction = Proto->Codegen();
    if (TheFunction == 0)
    return 0;

// To build this:
// See example below.

#include "llvm/DerivedTypes.h"
#include "llvm/IRBuilder.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/Analysis/Verifier.h"
#include <cstdio>
#include <string>
#include <map>
#include <vector>
using namespace llvm;

//===----------------------------------------------------------------------===//
// Lexer
//===----------------------------------------------------------------------===//

// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
// of these for known things.
enum Token {
tok_eof = -1,

// commands
tok_def = -2, tok_extern = -3,

// primary
tok_identifier = -4, tok_number = -5
};

static std::string IdentifierStr;  // Filled in if tok_identifier
static double NumVal;              // Filled in if tok_number

/// gettok - Return the next token from standard input.
static int gettok() {
static int LastChar = ' ';

// Skip any whitespace.
while (isspace(LastChar))
LastChar = getchar();

if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
IdentifierStr = LastChar;
while (isalnum((LastChar = getchar())))
IdentifierStr += LastChar;

if (IdentifierStr == "def") return tok_def;
if (IdentifierStr == "extern") return tok_extern;
return tok_identifier;
}

if (isdigit(LastChar) || LastChar == '.') {   // Number: [0-9.]+
std::string NumStr;
do {
NumStr += LastChar;
LastChar = getchar();
} while (isdigit(LastChar) || LastChar == '.');

NumVal = strtod(NumStr.c_str(), 0);
return tok_number;
}

if (LastChar == '#') {
// Comment until end of line.
do LastChar = getchar();
while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');

if (LastChar != EOF)
return gettok();
}

// Check for end of file.  Don't eat the EOF.
if (LastChar == EOF)
return tok_eof;

// Otherwise, just return the character as its ascii value.
int ThisChar = LastChar;
LastChar = getchar();
return ThisChar;
}

//===----------------------------------------------------------------------===//
// Abstract Syntax Tree (aka Parse Tree)
//===----------------------------------------------------------------------===//

/// ExprAST - Base class for all expression nodes.
class ExprAST {
public:
virtual ~ExprAST() {}
virtual Value *Codegen() = 0;
};

/// NumberExprAST - Expression class for numeric literals like "1.0".
class NumberExprAST : public ExprAST {
double Val;
public:
NumberExprAST(double val) : Val(val) {}
virtual Value *Codegen();
};

/// VariableExprAST - Expression class for referencing a variable, like "a".
class VariableExprAST : public ExprAST {
std::string Name;
public:
VariableExprAST(const std::string &name) : Name(name) {}
virtual Value *Codegen();
};

/// BinaryExprAST - Expression class for a binary operator.
class BinaryExprAST : public ExprAST {
char Op;
ExprAST *LHS, *RHS;
public:
BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs)
: Op(op), LHS(lhs), RHS(rhs) {}
virtual Value *Codegen();
};

/// CallExprAST - Expression class for function calls.
class CallExprAST : public ExprAST {
std::string Callee;
std::vector<ExprAST*> Args;
public:
CallExprAST(const std::string &callee, std::vector<ExprAST*> &args)
: Callee(callee), Args(args) {}
virtual Value *Codegen();
};

/// PrototypeAST - This class represents the "prototype" for a function,
/// which captures its name, and its argument names (thus implicitly the number
/// of arguments the function takes).
class PrototypeAST {
std::string Name;
std::vector<std::string> Args;
public:
PrototypeAST(const std::string &name, const std::vector<std::string> &args)
: Name(name), Args(args) {}

Function *Codegen();
};

/// FunctionAST - This class represents a function definition itself.
class FunctionAST {
PrototypeAST *Proto;
ExprAST *Body;
public:
FunctionAST(PrototypeAST *proto, ExprAST *body)
: Proto(proto), Body(body) {}

Function *Codegen();
};

//===----------------------------------------------------------------------===//
// Parser
//===----------------------------------------------------------------------===//

/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current
/// token the parser is looking at.  getNextToken reads another token from the
/// lexer and updates CurTok with its results.
static int CurTok;
static int getNextToken() {
return CurTok = gettok();
}

/// BinopPrecedence - This holds the precedence for each binary operator that is
/// defined.
static std::map<char, int> BinopPrecedence;

/// GetTokPrecedence - Get the precedence of the pending binary operator token.
static int GetTokPrecedence() {
if (!isascii(CurTok))
return -1;

// Make sure it's a declared binop.
int TokPrec = BinopPrecedence[CurTok];
if (TokPrec <= 0) return -1;
return TokPrec;
}

/// Error* - These are little helper functions for error handling.
ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;}
PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; }
FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; }

static ExprAST *ParseExpression();

/// identifierexpr
///   ::= identifier
///   ::= identifier '(' expression* ')'
static ExprAST *ParseIdentifierExpr() {
std::string IdName = IdentifierStr;

getNextToken();  // eat identifier.

if (CurTok != '(') // Simple variable ref.
return new VariableExprAST(IdName);

// Call.
getNextToken();  // eat (
std::vector<ExprAST*> Args;
if (CurTok != ')') {
while (1) {
ExprAST *Arg = ParseExpression();
if (!Arg) return 0;
Args.push_back(Arg);

if (CurTok == ')') break;

if (CurTok != ',')
return Error("Expected ')' or ',' in argument list");
getNextToken();
}
}

// Eat the ')'.
getNextToken();

return new CallExprAST(IdName, Args);
}

/// numberexpr ::= number
static ExprAST *ParseNumberExpr() {
ExprAST *Result = new NumberExprAST(NumVal);
getNextToken(); // consume the number
return Result;
}

/// parenexpr ::= '(' expression ')'
static ExprAST *ParseParenExpr() {
getNextToken();  // eat (.
ExprAST *V = ParseExpression();
if (!V) return 0;

if (CurTok != ')')
return Error("expected ')'");
getNextToken();  // eat ).
return V;
}

/// primary
///   ::= identifierexpr
///   ::= numberexpr
///   ::= parenexpr
static ExprAST *ParsePrimary() {
switch (CurTok) {
default: return Error("unknown token when expecting an expression");
case tok_identifier: return ParseIdentifierExpr();
case tok_number:     return ParseNumberExpr();
case '(':            return ParseParenExpr();
}
}

/// binoprhs
///   ::= ('+' primary)*
static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) {
// If this is a binop, find its precedence.
while (1) {
int TokPrec = GetTokPrecedence();

// If this is a binop that binds at least as tightly as the current binop,
// consume it, otherwise we are done.
if (TokPrec < ExprPrec)
return LHS;

// Okay, we know this is a binop.
int BinOp = CurTok;
getNextToken();  // eat binop

// Parse the primary expression after the binary operator.
ExprAST *RHS = ParsePrimary();
if (!RHS) return 0;

// If BinOp binds less tightly with RHS than the operator after RHS, let
// the pending operator take RHS as its LHS.
int NextPrec = GetTokPrecedence();
if (TokPrec < NextPrec) {
RHS = ParseBinOpRHS(TokPrec+1, RHS);
if (RHS == 0) return 0;
}

// Merge LHS/RHS.
LHS = new BinaryExprAST(BinOp, LHS, RHS);
}
}

/// expression
///   ::= primary binoprhs
///
static ExprAST *ParseExpression() {
ExprAST *LHS = ParsePrimary();
if (!LHS) return 0;

return ParseBinOpRHS(0, LHS);
}

/// prototype
///   ::= id '(' id* ')'
static PrototypeAST *ParsePrototype() {
if (CurTok != tok_identifier)
return ErrorP("Expected function name in prototype");

std::string FnName = IdentifierStr;
getNextToken();

if (CurTok != '(')
return ErrorP("Expected '(' in prototype");

std::vector<std::string> ArgNames;
while (getNextToken() == tok_identifier)
ArgNames.push_back(IdentifierStr);
if (CurTok != ')')
return ErrorP("Expected ')' in prototype");

// success.
getNextToken();  // eat ')'.

return new PrototypeAST(FnName, ArgNames);
}

/// definition ::= 'def' prototype expression
static FunctionAST *ParseDefinition() {
getNextToken();  // eat def.
PrototypeAST *Proto = ParsePrototype();
if (Proto == 0) return 0;

if (ExprAST *E = ParseExpression())
return new FunctionAST(Proto, E);
return 0;
}

/// toplevelexpr ::= expression
static FunctionAST *ParseTopLevelExpr() {
if (ExprAST *E = ParseExpression()) {
// Make an anonymous proto.
PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>());
return new FunctionAST(Proto, E);
}
return 0;
}

/// external ::= 'extern' prototype
static PrototypeAST *ParseExtern() {
getNextToken();  // eat extern.
return ParsePrototype();
}

//===----------------------------------------------------------------------===//
// Code Generation
//===----------------------------------------------------------------------===//

static Module *TheModule;
static IRBuilder<> Builder(getGlobalContext());
static std::map<std::string, Value*> NamedValues;

Value *ErrorV(const char *Str) { Error(Str); return 0; }

Value *NumberExprAST::Codegen() {
return ConstantFP::get(getGlobalContext(), APFloat(Val));
}

Value *VariableExprAST::Codegen() {
// Look this variable up in the function.
Value *V = NamedValues[Name];
return V ? V : ErrorV("Unknown variable name");
}

Value *BinaryExprAST::Codegen() {
Value *L = LHS->Codegen();
Value *R = RHS->Codegen();
if (L == 0 || R == 0) return 0;

switch (Op) {
case '+': return Builder.CreateFAdd(L, R, "addtmp");
case '-': return Builder.CreateFSub(L, R, "subtmp");
case '*': return Builder.CreateFMul(L, R, "multmp");
case '<':
L = Builder.CreateFCmpULT(L, R, "cmptmp");
// Convert bool 0/1 to double 0.0 or 1.0
return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()),
"booltmp");
default: return ErrorV("invalid binary operator");
}
}

Value *CallExprAST::Codegen() {
// Look up the name in the global module table.
Function *CalleeF = TheModule->getFunction(Callee);
if (CalleeF == 0)
return ErrorV("Unknown function referenced");

// If argument mismatch error.
if (CalleeF->arg_size() != Args.size())
return ErrorV("Incorrect # arguments passed");

std::vector<Value*> ArgsV;
for (unsigned i = 0, e = Args.size(); i != e; ++i) {
ArgsV.push_back(Args[i]->Codegen());
if (ArgsV.back() == 0) return 0;
}

return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
}

Function *PrototypeAST::Codegen() {
// Make the function type:  double(double,double) etc.
std::vector<Type*> Doubles(Args.size(),
Type::getDoubleTy(getGlobalContext()));
FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()),
Doubles, false);

Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule);

// If F conflicted, there was already something named 'Name'.  If it has a
// body, don't allow redefinition or reextern.
if (F->getName() != Name) {
// Delete the one we just made and get the existing one.
F->eraseFromParent();
F = TheModule->getFunction(Name);

// If F already has a body, reject this.
if (!F->empty()) {
ErrorF("redefinition of function");
return 0;
}

// If F took a different number of args, reject.
if (F->arg_size() != Args.size()) {
ErrorF("redefinition of function with different # args");
return 0;
}
}

// Set names for all arguments.
unsigned Idx = 0;
for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size();
++AI, ++Idx) {
AI->setName(Args[Idx]);

// Add arguments to variable symbol table.
NamedValues[Args[Idx]] = AI;
}

return F;
}

Function *FunctionAST::Codegen() {
NamedValues.clear();

Function *TheFunction = Proto->Codegen();
if (TheFunction == 0)
return 0;

// Create a new basic block to start insertion into.
BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction);
Builder.SetInsertPoint(BB);

if (Value *RetVal = Body->Codegen()) {
// Finish off the function.
Builder.CreateRet(RetVal);

// Validate the generated code, checking for consistency.
verifyFunction(*TheFunction);

return TheFunction;
}

// Error reading body, remove function.
TheFunction->eraseFromParent();
return 0;
}

//===----------------------------------------------------------------------===//
// Top-Level parsing and JIT Driver
//===----------------------------------------------------------------------===//

static void HandleDefinition() {
if (FunctionAST *F = ParseDefinition()) {
if (Function *LF = F->Codegen()) {
fprintf(stderr, "Read function definition:");
LF->dump();
}
} else {
// Skip token for error recovery.
getNextToken();
}
}

static void HandleExtern() {
if (PrototypeAST *P = ParseExtern()) {
if (Function *F = P->Codegen()) {
fprintf(stderr, "Read extern: ");
F->dump();
}
} else {
// Skip token for error recovery.
getNextToken();
}
}

static void HandleTopLevelExpression() {
// Evaluate a top-level expression into an anonymous function.
if (FunctionAST *F = ParseTopLevelExpr()) {
if (Function *LF = F->Codegen()) {
fprintf(stderr, "Read top-level expression:");
LF->dump();
}
} else {
// Skip token for error recovery.
getNextToken();
}
}

/// top ::= definition | external | expression | ';'
static void MainLoop() {
while (1) {
fprintf(stderr, "ready> ");
switch (CurTok) {
case tok_eof:    return;
case ';':        getNextToken(); break;  // ignore top-level semicolons.
case tok_def:    HandleDefinition(); break;
case tok_extern: HandleExtern(); break;
default:         HandleTopLevelExpression(); break;
}
}
}

//===----------------------------------------------------------------------===//
// "Library" functions that can be "extern'd" from user code.
//===----------------------------------------------------------------------===//

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

//===----------------------------------------------------------------------===//
// Main driver code.
//===----------------------------------------------------------------------===//

int main() {
LLVMContext &Context = getGlobalContext();

// Install standard binary operators.
// 1 is lowest precedence.
BinopPrecedence['<'] = 10;
BinopPrecedence['+'] = 20;
BinopPrecedence['-'] = 20;
BinopPrecedence['*'] = 40;  // highest.

// Prime the first token.
fprintf(stderr, "ready> ");
getNextToken();

// Make the module, which holds all the code.
TheModule = new Module("my cool jit", Context);

// Run the main "interpreter loop" now.
MainLoop();

// Print out all of the generated code.
TheModule->dump();

return 0;
}