New Kaleidoscope chapter: Creating object files

This new chapter describes compiling LLVM IR to object files.

The new chaper is chapter 8, so later chapters have been renumbered.
Since this brings us to 10 chapters total, I've also needed to rename
the other chapters to use two digit numbering.

Differential Revision: http://reviews.llvm.org/D18070



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274441 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 1552 insertions, 328 deletions

diff --git a/examples/Kaleidoscope/Chapter8/CMakeLists.txt b/examples/Kaleidoscope/Chapter8/CMakeLists.txt
index d9b5cc421be..1bb1cd25af7 100644
--- a/examples/Kaleidoscope/Chapter8/CMakeLists.txt
+++ b/examples/Kaleidoscope/Chapter8/CMakeLists.txt
@@ -1,9 +1,5 @@
 set(LLVM_LINK_COMPONENTS
-  Core
-  ExecutionEngine
-  Object
-  Support
-  native
+  all
   )
 
 add_kaleidoscope_chapter(Kaleidoscope-Ch8
diff --git a/examples/Kaleidoscope/Chapter8/toy.cpp b/examples/Kaleidoscope/Chapter8/toy.cpp
index 99ff52bc1b4..f880bb8ea0f 100644
--- a/examples/Kaleidoscope/Chapter8/toy.cpp
+++ b/examples/Kaleidoscope/Chapter8/toy.cpp
@@ -1,28 +1,20 @@
 #include "llvm/ADT/APFloat.h"
-#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/Triple.h"
-#include "llvm/IR/BasicBlock.h"
-#include "llvm/IR/Constants.h"
-#include "llvm/IR/DebugInfoMetadata.h"
-#include "llvm/IR/DebugLoc.h"
-#include "llvm/IR/DerivedTypes.h"
-#include "llvm/IR/DIBuilder.h"
-#include "llvm/IR/Function.h"
-#include "llvm/IR/Instructions.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/Passes.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Verifier.h"
-#include "llvm/Support/Host.h"
-#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Target/TargetMachine.h"
-#include "../include/KaleidoscopeJIT.h"
-#include <cassert>
+#include "llvm/Target/TargetOptions.h"
+#include "llvm/Transforms/Scalar.h"
 #include <cctype>
 #include <cstdio>
 #include <cstdlib>
@@ -33,7 +25,7 @@
 #include <vector>
 
 using namespace llvm;
-using namespace llvm::orc;
+using namespace llvm::sys;
 
 //===----------------------------------------------------------------------===//
 // Lexer
@@ -67,71 +59,6 @@ enum Token {
   tok_var = -13
 };
 
-std::string getTokName(int Tok) {
-  switch (Tok) {
-  case tok_eof:
-    return "eof";
-  case tok_def:
-    return "def";
-  case tok_extern:
-    return "extern";
-  case tok_identifier:
-    return "identifier";
-  case tok_number:
-    return "number";
-  case tok_if:
-    return "if";
-  case tok_then:
-    return "then";
-  case tok_else:
-    return "else";
-  case tok_for:
-    return "for";
-  case tok_in:
-    return "in";
-  case tok_binary:
-    return "binary";
-  case tok_unary:
-    return "unary";
-  case tok_var:
-    return "var";
-  }
-  return std::string(1, (char)Tok);
-}
-
-namespace {
-class ExprAST;
-} // end anonymous namespace
-
-static LLVMContext TheContext;
-static IRBuilder<> Builder(TheContext);
-struct DebugInfo {
-  DICompileUnit *TheCU;
-  DIType *DblTy;
-  std::vector<DIScope *> LexicalBlocks;
-
-  void emitLocation(ExprAST *AST);
-  DIType *getDoubleTy();
-} KSDbgInfo;
-
-struct SourceLocation {
-  int Line;
-  int Col;
-};
-static SourceLocation CurLoc;
-static SourceLocation LexLoc = {1, 0};
-
-static int advance() {
-  int LastChar = getchar();
-
-  if (LastChar == '\n' || LastChar == '\r') {
-    LexLoc.Line++;
-    LexLoc.Col = 0;
-  } else
-    LexLoc.Col++;
-  return LastChar;
-}
-
 static std::string IdentifierStr; // Filled in if tok_identifier
 static double NumVal;             // Filled in if tok_number
 
@@ -141,13 +68,11 @@ static int gettok() {
 
   // Skip any whitespace.
   while (isspace(LastChar))
-    LastChar = advance();
-
-  CurLoc = LexLoc;
+    LastChar = getchar();
 
   if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
     IdentifierStr = LastChar;
-    while (isalnum((LastChar = advance())))
+    while (isalnum((LastChar = getchar())))
       IdentifierStr += LastChar;
 
     if (IdentifierStr == "def")
@@ -177,7 +102,7 @@ static int gettok() {
     std::string NumStr;
     do {
       NumStr += LastChar;
-      LastChar = advance();
+      LastChar = getchar();
     } while (isdigit(LastChar) || LastChar == '.');
 
     NumVal = strtod(NumStr.c_str(), nullptr);
@@ -187,7 +112,7 @@ static int gettok() {
   if (LastChar == '#') {
     // Comment until end of line.
     do
-      LastChar = advance();
+      LastChar = getchar();
     while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
 
     if (LastChar != EOF)
@@ -200,7 +125,7 @@ static int gettok() {
 
   // Otherwise, just return the character as its ascii value.
   int ThisChar = LastChar;
-  LastChar = advance();
+  LastChar = getchar();
   return ThisChar;
 }
 
@@ -208,25 +133,11 @@ static int gettok() {
 // Abstract Syntax Tree (aka Parse Tree)
 //===----------------------------------------------------------------------===//
 namespace {
-
-raw_ostream &indent(raw_ostream &O, int size) {
-  return O << std::string(size, ' ');
-}
-
 /// ExprAST - Base class for all expression nodes.
 class ExprAST {
-  SourceLocation Loc;
-
 public:
-  ExprAST(SourceLocation Loc = CurLoc) : Loc(Loc) {}
   virtual ~ExprAST() {}
   virtual Value *codegen() = 0;
-  int getLine() const { return Loc.Line; }
-  int getCol() const { return Loc.Col; }
-
-  virtual raw_ostream &dump(raw_ostream &out, int ind) {
-    return out << ':' << getLine() << ':' << getCol() << '\n';
-  }
 };
 
 /// NumberExprAST - Expression class for numeric literals like "1.0".
@@ -236,10 +147,6 @@ class NumberExprAST : public ExprAST {
 public:
   NumberExprAST(double Val) : Val(Val) {}
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    return ExprAST::dump(out << Val, ind);
-  }
 };
 
 /// VariableExprAST - Expression class for referencing a variable, like "a".
@@ -247,14 +154,9 @@ class VariableExprAST : public ExprAST {
   std::string Name;
 
 public:
-  VariableExprAST(SourceLocation Loc, const std::string &Name)
-      : ExprAST(Loc), Name(Name) {}
+  VariableExprAST(const std::string &Name) : Name(Name) {}
   const std::string &getName() const { return Name; }
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    return ExprAST::dump(out << Name, ind);
-  }
 };
 
 /// UnaryExprAST - Expression class for a unary operator.
@@ -266,12 +168,6 @@ public:
   UnaryExprAST(char Opcode, std::unique_ptr<ExprAST> Operand)
       : Opcode(Opcode), Operand(std::move(Operand)) {}
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    ExprAST::dump(out << "unary" << Opcode, ind);
-    Operand->dump(out, ind + 1);
-    return out;
-  }
 };
 
 /// BinaryExprAST - Expression class for a binary operator.
@@ -280,17 +176,10 @@ class BinaryExprAST : public ExprAST {
   std::unique_ptr<ExprAST> LHS, RHS;
 
 public:
-  BinaryExprAST(SourceLocation Loc, char Op, std::unique_ptr<ExprAST> LHS,
+  BinaryExprAST(char Op, std::unique_ptr<ExprAST> LHS,
                 std::unique_ptr<ExprAST> RHS)
-      : ExprAST(Loc), Op(Op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
+      : Op(Op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    ExprAST::dump(out << "binary" << Op, ind);
-    LHS->dump(indent(out, ind) << "LHS:", ind + 1);
-    RHS->dump(indent(out, ind) << "RHS:", ind + 1);
-    return out;
-  }
 };
 
 /// CallExprAST - Expression class for function calls.
@@ -299,17 +188,10 @@ class CallExprAST : public ExprAST {
   std::vector<std::unique_ptr<ExprAST>> Args;
 
 public:
-  CallExprAST(SourceLocation Loc, const std::string &Callee,
+  CallExprAST(const std::string &Callee,
               std::vector<std::unique_ptr<ExprAST>> Args)
-      : ExprAST(Loc), Callee(Callee), Args(std::move(Args)) {}
+      : Callee(Callee), Args(std::move(Args)) {}
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    ExprAST::dump(out << "call " << Callee, ind);
-    for (const auto &Arg : Args)
-      Arg->dump(indent(out, ind + 1), ind + 1);
-    return out;
-  }
 };
 
 /// IfExprAST - Expression class for if/then/else.
@@ -317,19 +199,10 @@ class IfExprAST : public ExprAST {
   std::unique_ptr<ExprAST> Cond, Then, Else;
 
 public:
-  IfExprAST(SourceLocation Loc, std::unique_ptr<ExprAST> Cond,
-            std::unique_ptr<ExprAST> Then, std::unique_ptr<ExprAST> Else)
-      : ExprAST(Loc), Cond(std::move(Cond)), Then(std::move(Then)),
-        Else(std::move(Else)) {}
+  IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
+            std::unique_ptr<ExprAST> Else)
+      : Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    ExprAST::dump(out << "if", ind);
-    Cond->dump(indent(out, ind) << "Cond:", ind + 1);
-    Then->dump(indent(out, ind) << "Then:", ind + 1);
-    Else->dump(indent(out, ind) << "Else:", ind + 1);
-    return out;
-  }
 };
 
 /// ForExprAST - Expression class for for/in.
@@ -344,15 +217,6 @@ public:
       : VarName(VarName), Start(std::move(Start)), End(std::move(End)),
         Step(std::move(Step)), Body(std::move(Body)) {}
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    ExprAST::dump(out << "for", ind);
-    Start->dump(indent(out, ind) << "Cond:", ind + 1);
-    End->dump(indent(out, ind) << "End:", ind + 1);
-    Step->dump(indent(out, ind) << "Step:", ind + 1);
-    Body->dump(indent(out, ind) << "Body:", ind + 1);
-    return out;
-  }
 };
 
 /// VarExprAST - Expression class for var/in
@@ -366,14 +230,6 @@ public:
       std::unique_ptr<ExprAST> Body)
       : VarNames(std::move(VarNames)), Body(std::move(Body)) {}
   Value *codegen() override;
-
-  raw_ostream &dump(raw_ostream &out, int ind) override {
-    ExprAST::dump(out << "var", ind);
-    for (const auto &NamedVar : VarNames)
-      NamedVar.second->dump(indent(out, ind) << NamedVar.first << ':', ind + 1);
-    Body->dump(indent(out, ind) << "Body:", ind + 1);
-    return out;
-  }
 };
 
 /// PrototypeAST - This class represents the "prototype" for a function,
@@ -384,14 +240,12 @@ class PrototypeAST {
   std::vector<std::string> Args;
   bool IsOperator;
   unsigned Precedence; // Precedence if a binary op.
-  int Line;
 
 public:
-  PrototypeAST(SourceLocation Loc, const std::string &Name,
-               std::vector<std::string> Args, bool IsOperator = false,
-               unsigned Prec = 0)
+  PrototypeAST(const std::string &Name, std::vector<std::string> Args,
+               bool IsOperator = false, unsigned Prec = 0)
       : Name(Name), Args(std::move(Args)), IsOperator(IsOperator),
-        Precedence(Prec), Line(Loc.Line) {}
+        Precedence(Prec) {}
   Function *codegen();
   const std::string &getName() const { return Name; }
 
@@ -404,7 +258,6 @@ public:
   }
 
   unsigned getBinaryPrecedence() const { return Precedence; }
-  int getLine() const { return Line; }
 };
 
 /// FunctionAST - This class represents a function definition itself.
@@ -417,13 +270,6 @@ public:
               std::unique_ptr<ExprAST> Body)
       : Proto(std::move(Proto)), Body(std::move(Body)) {}
   Function *codegen();
-
-  raw_ostream &dump(raw_ostream &out, int ind) {
-    indent(out, ind) << "FunctionAST\n";
-    ++ind;
-    indent(out, ind) << "Body:";
-    return Body ? Body->dump(out, ind) : out << "null\n";
-  }
 };
 } // end anonymous namespace
 
@@ -492,12 +338,10 @@ static std::unique_ptr<ExprAST> ParseParenExpr() {
 static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
   std::string IdName = IdentifierStr;
 
-  SourceLocation LitLoc = CurLoc;
-
   getNextToken(); // eat identifier.
 
   if (CurTok != '(') // Simple variable ref.
-    return llvm::make_unique<VariableExprAST>(LitLoc, IdName);
+    return llvm::make_unique<VariableExprAST>(IdName);
 
   // Call.
   getNextToken(); // eat (
@@ -521,13 +365,11 @@ static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
   // Eat the ')'.
   getNextToken();
 
-  return llvm::make_unique<CallExprAST>(LitLoc, IdName, std::move(Args));
+  return llvm::make_unique<CallExprAST>(IdName, std::move(Args));
 }
 
 /// ifexpr ::= 'if' expression 'then' expression 'else' expression
 static std::unique_ptr<ExprAST> ParseIfExpr() {
-  SourceLocation IfLoc = CurLoc;
-
   getNextToken(); // eat the if.
 
   // condition.
@@ -552,7 +394,7 @@ static std::unique_ptr<ExprAST> ParseIfExpr() {
   if (!Else)
     return nullptr;
 
-  return llvm::make_unique<IfExprAST>(IfLoc, std::move(Cond), std::move(Then),
+  return llvm::make_unique<IfExprAST>(std::move(Cond), std::move(Then),
                                       std::move(Else));
 }
 
@@ -707,7 +549,6 @@ static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
 
     // Okay, we know this is a binop.
     int BinOp = CurTok;
-    SourceLocation BinLoc = CurLoc;
     getNextToken(); // eat binop
 
     // Parse the unary expression after the binary operator.
@@ -725,8 +566,8 @@ static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
     }
 
     // Merge LHS/RHS.
-    LHS = llvm::make_unique<BinaryExprAST>(BinLoc, BinOp, std::move(LHS),
-                                           std::move(RHS));
+    LHS =
+        llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS), std::move(RHS));
   }
 }
 
@@ -748,8 +589,6 @@ static std::unique_ptr<ExprAST> ParseExpression() {
 static std::unique_ptr<PrototypeAST> ParsePrototype() {
   std::string FnName;
 
-  SourceLocation FnLoc = CurLoc;
-
   unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
   unsigned BinaryPrecedence = 30;
 
@@ -805,7 +644,7 @@ static std::unique_ptr<PrototypeAST> ParsePrototype() {
   if (Kind && ArgNames.size() != Kind)
     return LogErrorP("Invalid number of operands for operator");
 
-  return llvm::make_unique<PrototypeAST>(FnLoc, FnName, ArgNames, Kind != 0,
+  return llvm::make_unique<PrototypeAST>(FnName, ArgNames, Kind != 0,
                                          BinaryPrecedence);
 }
 
@@ -823,10 +662,9 @@ static std::unique_ptr<FunctionAST> ParseDefinition() {
 
 /// toplevelexpr ::= expression
 static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
-  SourceLocation FnLoc = CurLoc;
   if (auto E = ParseExpression()) {
     // Make an anonymous proto.
-    auto Proto = llvm::make_unique<PrototypeAST>(FnLoc, "__anon_expr",
+    auto Proto = llvm::make_unique<PrototypeAST>("__anon_expr",
                                                  std::vector<std::string>());
     return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
   }
@@ -840,51 +678,13 @@ static std::unique_ptr<PrototypeAST> ParseExtern() {
 }
 
 //===----------------------------------------------------------------------===//
-// Debug Info Support
-//===----------------------------------------------------------------------===//
-
-static std::unique_ptr<DIBuilder> DBuilder;
-
-DIType *DebugInfo::getDoubleTy() {
-  if (DblTy)
-    return DblTy;
-
-  DblTy = DBuilder->createBasicType("double", 64, 64, dwarf::DW_ATE_float);
-  return DblTy;
-}
-
-void DebugInfo::emitLocation(ExprAST *AST) {
-  if (!AST)
-    return Builder.SetCurrentDebugLocation(DebugLoc());
-  DIScope *Scope;
-  if (LexicalBlocks.empty())
-    Scope = TheCU;
-  else
-    Scope = LexicalBlocks.back();
-  Builder.SetCurrentDebugLocation(
-      DebugLoc::get(AST->getLine(), AST->getCol(), Scope));
-}
-
-static DISubroutineType *CreateFunctionType(unsigned NumArgs, DIFile *Unit) {
-  SmallVector<Metadata *, 8> EltTys;
-  DIType *DblTy = KSDbgInfo.getDoubleTy();
-
-  // Add the result type.
-  EltTys.push_back(DblTy);
-
-  for (unsigned i = 0, e = NumArgs; i != e; ++i)
-    EltTys.push_back(DblTy);
-
-  return DBuilder->createSubroutineType(DBuilder->getOrCreateTypeArray(EltTys));
-}
-
-//===----------------------------------------------------------------------===//
 // Code Generation
 //===----------------------------------------------------------------------===//
 
+static LLVMContext TheContext;
+static IRBuilder<> Builder(TheContext);
 static std::unique_ptr<Module> TheModule;
 static std::map<std::string, AllocaInst *> NamedValues;
-static std::unique_ptr<KaleidoscopeJIT> TheJIT;
 static std::map<std::string, std::unique_ptr<PrototypeAST>> FunctionProtos;
 
 Value *LogErrorV(const char *Str) {
@@ -917,7 +717,6 @@ static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
 }
 
 Value *NumberExprAST::codegen() {
-  KSDbgInfo.emitLocation(this);
   return ConstantFP::get(TheContext, APFloat(Val));
 }
 
@@ -927,7 +726,6 @@ Value *VariableExprAST::codegen() {
   if (!V)
     return LogErrorV("Unknown variable name");
 
-  KSDbgInfo.emitLocation(this);
   // Load the value.
   return Builder.CreateLoad(V, Name.c_str());
 }
@@ -941,13 +739,10 @@ Value *UnaryExprAST::codegen() {
   if (!F)
     return LogErrorV("Unknown unary operator");
 
-  KSDbgInfo.emitLocation(this);
   return Builder.CreateCall(F, OperandV, "unop");
 }
 
 Value *BinaryExprAST::codegen() {
-  KSDbgInfo.emitLocation(this);
-
   // Special case '=' because we don't want to emit the LHS as an expression.
   if (Op == '=') {
     // Assignment requires the LHS to be an identifier.
@@ -1001,8 +796,6 @@ Value *BinaryExprAST::codegen() {
 }
 
 Value *CallExprAST::codegen() {
-  KSDbgInfo.emitLocation(this);
-
   // Look up the name in the global module table.
   Function *CalleeF = getFunction(Callee);
   if (!CalleeF)
@@ -1023,8 +816,6 @@ Value *CallExprAST::codegen() {
 }
 
 Value *IfExprAST::codegen() {
-  KSDbgInfo.emitLocation(this);
-
   Value *CondV = Cond->codegen();
   if (!CondV)
     return nullptr;
@@ -1101,8 +892,6 @@ Value *ForExprAST::codegen() {
   // Create an alloca for the variable in the entry block.
   AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
 
-  KSDbgInfo.emitLocation(this);
-
   // Emit the start code first, without 'variable' in scope.
   Value *StartVal = Start->codegen();
   if (!StartVal)
@@ -1213,8 +1002,6 @@ Value *VarExprAST::codegen() {
     NamedValues[VarName] = Alloca;
   }
 
-  KSDbgInfo.emitLocation(this);
-
   // Codegen the body, now that all vars are in scope.
   Value *BodyVal = Body->codegen();
   if (!BodyVal)
@@ -1262,43 +1049,12 @@ Function *FunctionAST::codegen() {
   BasicBlock *BB = BasicBlock::Create(TheContext, "entry", TheFunction);
   Builder.SetInsertPoint(BB);
 
-  // Create a subprogram DIE for this function.
-  DIFile *Unit = DBuilder->createFile(KSDbgInfo.TheCU->getFilename(),
-                                      KSDbgInfo.TheCU->getDirectory());
-  DIScope *FContext = Unit;
-  unsigned LineNo = P.getLine();
-  unsigned ScopeLine = LineNo;
-  DISubprogram *SP = DBuilder->createFunction(
-      FContext, P.getName(), StringRef(), Unit, LineNo,
-      CreateFunctionType(TheFunction->arg_size(), Unit),
-      false /* internal linkage */, true /* definition */, ScopeLine,
-      DINode::FlagPrototyped, false);
-  TheFunction->setSubprogram(SP);
-
-  // Push the current scope.
-  KSDbgInfo.LexicalBlocks.push_back(SP);
-
-  // Unset the location for the prologue emission (leading instructions with no
-  // location in a function are considered part of the prologue and the debugger
-  // will run past them when breaking on a function)
-  KSDbgInfo.emitLocation(nullptr);
-
   // Record the function arguments in the NamedValues map.
   NamedValues.clear();
-  unsigned ArgIdx = 0;
   for (auto &Arg : TheFunction->args()) {
     // Create an alloca for this variable.
     AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, Arg.getName());
 
-    // Create a debug descriptor for the variable.
-    DILocalVariable *D = DBuilder->createParameterVariable(
-        SP, Arg.getName(), ++ArgIdx, Unit, LineNo, KSDbgInfo.getDoubleTy(),
-        true);
-
-    DBuilder->insertDeclare(Alloca, D, DBuilder->createExpression(),
-                            DebugLoc::get(LineNo, 0, SP),
-                            Builder.GetInsertBlock());
-
     // Store the initial value into the alloca.
     Builder.CreateStore(&Arg, Alloca);
 
@@ -1306,15 +1062,10 @@ Function *FunctionAST::codegen() {
     NamedValues[Arg.getName()] = Alloca;
   }
 
-  KSDbgInfo.emitLocation(Body.get());
-
   if (Value *RetVal = Body->codegen()) {
     // Finish off the function.
     Builder.CreateRet(RetVal);
 
-    // Pop off the lexical block for the function.
-    KSDbgInfo.LexicalBlocks.pop_back();
-
     // Validate the generated code, checking for consistency.
     verifyFunction(*TheFunction);
 
@@ -1326,11 +1077,6 @@ Function *FunctionAST::codegen() {
 
   if (P.isBinaryOp())
     BinopPrecedence.erase(Proto->getOperatorName());
-
-  // Pop off the lexical block for the function since we added it
-  // unconditionally.
-  KSDbgInfo.LexicalBlocks.pop_back();
-
   return nullptr;
 }
 
@@ -1338,16 +1084,17 @@ Function *FunctionAST::codegen() {
 // Top-Level parsing and JIT Driver
 //===----------------------------------------------------------------------===//
 
-static void InitializeModule() {
+static void InitializeModuleAndPassManager() {
   // Open a new module.
   TheModule = llvm::make_unique<Module>("my cool jit", TheContext);
-  TheModule->setDataLayout(TheJIT->getTargetMachine().createDataLayout());
 }
 
 static void HandleDefinition() {
   if (auto FnAST = ParseDefinition()) {
-    if (!FnAST->codegen())
-      fprintf(stderr, "Error reading function definition:");
+    if (auto *FnIR = FnAST->codegen()) {
+      fprintf(stderr, "Read function definition:");
+      FnIR->dump();
+    }
   } else {
     // Skip token for error recovery.
     getNextToken();
@@ -1356,10 +1103,11 @@ static void HandleDefinition() {
 
 static void HandleExtern() {
   if (auto ProtoAST = ParseExtern()) {
-    if (!ProtoAST->codegen())
-      fprintf(stderr, "Error reading extern");
-    else
+    if (auto *FnIR = ProtoAST->codegen()) {
+      fprintf(stderr, "Read extern: ");
+      FnIR->dump();
       FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
+    }
   } else {
     // Skip token for error recovery.
     getNextToken();
@@ -1369,9 +1117,7 @@ static void HandleExtern() {
 static void HandleTopLevelExpression() {
   // Evaluate a top-level expression into an anonymous function.
   if (auto FnAST = ParseTopLevelExpr()) {
-    if (!FnAST->codegen()) {
-      fprintf(stderr, "Error generating code for top level expr");
-    }
+    FnAST->codegen();
   } else {
     // Skip token for error recovery.
     getNextToken();
@@ -1421,50 +1167,74 @@ extern "C" double printd(double X) {
 //===----------------------------------------------------------------------===//
 
 int main() {
-  InitializeNativeTarget();
-  InitializeNativeTargetAsmPrinter();
-  InitializeNativeTargetAsmParser();
-
   // Install standard binary operators.
   // 1 is lowest precedence.
-  BinopPrecedence['='] = 2;
   BinopPrecedence['<'] = 10;
   BinopPrecedence['+'] = 20;
   BinopPrecedence['-'] = 20;
   BinopPrecedence['*'] = 40; // highest.
 
   // Prime the first token.
+  fprintf(stderr, "ready> ");
   getNextToken();
 
-  TheJIT = llvm::make_unique<KaleidoscopeJIT>();
+  InitializeModuleAndPassManager();
 
-  InitializeModule();
+  // Run the main "interpreter loop" now.
+  MainLoop();
 
-  // Add the current debug info version into the module.
-  TheModule->addModuleFlag(Module::Warning, "Debug Info Version",
-                           DEBUG_METADATA_VERSION);
+  // Initialize the target registry etc.
+  InitializeAllTargetInfos();
+  InitializeAllTargets();
+  InitializeAllTargetMCs();
+  InitializeAllAsmParsers();
+  InitializeAllAsmPrinters();
+
+  auto TargetTriple = sys::getDefaultTargetTriple();
+  TheModule->setTargetTriple(TargetTriple);
+
+  std::string Error;
+  auto Target = TargetRegistry::lookupTarget(TargetTriple, Error);
+
+  // Print an error and exit if we couldn't find the requested target.
+  // This generally occurs if we've forgotten to initialise the
+  // TargetRegistry or we have a bogus target triple.
+  if (!Target) {
+    errs() << Error;
+    return 1;
+  }
 
-  // Darwin only supports dwarf2.
-  if (Triple(sys::getProcessTriple()).isOSDarwin())
-    TheModule->addModuleFlag(llvm::Module::Warning, "Dwarf Version", 2);
+  auto CPU = "generic";
+  auto Features = "";
 
-  // Construct the DIBuilder, we do this here because we need the module.
-  DBuilder = llvm::make_unique<DIBuilder>(*TheModule);
+  TargetOptions opt;
+  auto RM = Optional<Reloc::Model>();
+  auto TheTargetMachine =
+      Target->createTargetMachine(TargetTriple, CPU, Features, opt, RM);
 
-  // Create the compile unit for the module.
-  // Currently down as "fib.ks" as a filename since we're redirecting stdin
-  // but we'd like actual source locations.
-  KSDbgInfo.TheCU = DBuilder->createCompileUnit(
-      dwarf::DW_LANG_C, "fib.ks", ".", "Kaleidoscope Compiler", false, "", 0);
+  TheModule->setDataLayout(TheTargetMachine->createDataLayout());
 
-  // Run the main "interpreter loop" now.
-  MainLoop();
+  auto Filename = "output.o";
+  std::error_code EC;
+  raw_fd_ostream dest(Filename, EC, sys::fs::F_None);
+
+  if (EC) {
+    errs() << "Could not open file: " << EC.message();
+    return 1;
+  }
+
+  legacy::PassManager pass;
+  auto FileType = TargetMachine::CGFT_ObjectFile;
+
+  if (TheTargetMachine->addPassesToEmitFile(pass, dest, FileType)) {
+    errs() << "TheTargetMachine can't emit a file of this type";
+    return 1;
+  }
 
-  // Finalize the debug info.
-  DBuilder->finalize();
+  pass.run(*TheModule);
+  dest.flush();
 
-  // Print out all of the generated code.
-  TheModule->dump();
+  outs() << "Wrote " << Filename << "\n";
 
   return 0;
 }
diff --git a/examples/Kaleidoscope/Chapter9/CMakeLists.txt b/examples/Kaleidoscope/Chapter9/CMakeLists.txt
new file mode 100644
index 00000000000..a85b2c5e8b3
--- /dev/null
+++ b/examples/Kaleidoscope/Chapter9/CMakeLists.txt
@@ -0,0 +1,13 @@
+set(LLVM_LINK_COMPONENTS
+  Core
+  ExecutionEngine
+  Object
+  Support
+  native
+  )
+
+add_kaleidoscope_chapter(Kaleidoscope-Ch9
+  toy.cpp
+  )
+
+export_executable_symbols(Kaleidoscope-Ch9)
diff --git a/examples/Kaleidoscope/Chapter9/toy.cpp b/examples/Kaleidoscope/Chapter9/toy.cpp
new file mode 100644
index 00000000000..a482ccd7352
--- /dev/null
+++ b/examples/Kaleidoscope/Chapter9/toy.cpp
@@ -0,0 +1,1445 @@
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/Passes.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Verifier.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Transforms/Scalar.h"
+#include <cctype>
+#include <cstdio>
+#include <map>
+#include <string>
+#include <vector>
+#include "../include/KaleidoscopeJIT.h"
+
+using namespace llvm;
+using namespace llvm::orc;
+
+//===----------------------------------------------------------------------===//
+// Lexer
+//===----------------------------------------------------------------------===//
+
+// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+// of these for known things.
+enum Token {
+  tok_eof = -1,
+
+  // commands
+  tok_def = -2,
+  tok_extern = -3,
+
+  // primary
+  tok_identifier = -4,
+  tok_number = -5,
+
+  // control
+  tok_if = -6,
+  tok_then = -7,
+  tok_else = -8,
+  tok_for = -9,
+  tok_in = -10,
+
+  // operators
+  tok_binary = -11,
+  tok_unary = -12,
+
+  // var definition
+  tok_var = -13
+};
+
+std::string getTokName(int Tok) {
+  switch (Tok) {
+  case tok_eof:
+    return "eof";
+  case tok_def:
+    return "def";
+  case tok_extern:
+    return "extern";
+  case tok_identifier:
+    return "identifier";
+  case tok_number:
+    return "number";
+  case tok_if:
+    return "if";
+  case tok_then:
+    return "then";
+  case tok_else:
+    return "else";
+  case tok_for:
+    return "for";
+  case tok_in:
+    return "in";
+  case tok_binary:
+    return "binary";
+  case tok_unary:
+    return "unary";
+  case tok_var:
+    return "var";
+  }
+  return std::string(1, (char)Tok);
+}
+
+namespace {
+class PrototypeAST;
+class ExprAST;
+}
+static LLVMContext TheContext;
+static IRBuilder<> Builder(TheContext);
+struct DebugInfo {
+  DICompileUnit *TheCU;
+  DIType *DblTy;
+  std::vector<DIScope *> LexicalBlocks;
+
+  void emitLocation(ExprAST *AST);
+  DIType *getDoubleTy();
+} KSDbgInfo;
+
+struct SourceLocation {
+  int Line;
+  int Col;
+};
+static SourceLocation CurLoc;
+static SourceLocation LexLoc = {1, 0};
+
+static int advance() {
+  int LastChar = getchar();
+
+  if (LastChar == '\n' || LastChar == '\r') {
+    LexLoc.Line++;
+    LexLoc.Col = 0;
+  } else
+    LexLoc.Col++;
+  return LastChar;
+}
+
+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 = advance();
+
+  CurLoc = LexLoc;
+
+  if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+    IdentifierStr = LastChar;
+    while (isalnum((LastChar = advance())))
+      IdentifierStr += LastChar;
+
+    if (IdentifierStr == "def")
+      return tok_def;
+    if (IdentifierStr == "extern")
+      return tok_extern;
+    if (IdentifierStr == "if")
+      return tok_if;
+    if (IdentifierStr == "then")
+      return tok_then;
+    if (IdentifierStr == "else")
+      return tok_else;
+    if (IdentifierStr == "for")
+      return tok_for;
+    if (IdentifierStr == "in")
+      return tok_in;
+    if (IdentifierStr == "binary")
+      return tok_binary;
+    if (IdentifierStr == "unary")
+      return tok_unary;
+    if (IdentifierStr == "var")
+      return tok_var;
+    return tok_identifier;
+  }
+
+  if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+    std::string NumStr;
+    do {
+      NumStr += LastChar;
+      LastChar = advance();
+    } while (isdigit(LastChar) || LastChar == '.');
+
+    NumVal = strtod(NumStr.c_str(), nullptr);
+    return tok_number;
+  }
+
+  if (LastChar == '#') {
+    // Comment until end of line.
+    do
+      LastChar = advance();
+    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 = advance();
+  return ThisChar;
+}
+
+//===----------------------------------------------------------------------===//
+// Abstract Syntax Tree (aka Parse Tree)
+//===----------------------------------------------------------------------===//
+namespace {
+
+raw_ostream &indent(raw_ostream &O, int size) {
+  return O << std::string(size, ' ');
+}
+
+/// ExprAST - Base class for all expression nodes.
+class ExprAST {
+  SourceLocation Loc;
+
+public:
+  ExprAST(SourceLocation Loc = CurLoc) : Loc(Loc) {}
+  virtual ~ExprAST() {}
+  virtual Value *codegen() = 0;
+  int getLine() const { return Loc.Line; }
+  int getCol() const { return Loc.Col; }
+  virtual raw_ostream &dump(raw_ostream &out, int ind) {
+    return out << ':' << getLine() << ':' << getCol() << '\n';
+  }
+};
+
+/// NumberExprAST - Expression class for numeric literals like "1.0".
+class NumberExprAST : public ExprAST {
+  double Val;
+
+public:
+  NumberExprAST(double Val) : Val(Val) {}
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    return ExprAST::dump(out << Val, ind);
+  }
+  Value *codegen() override;
+};
+
+/// VariableExprAST - Expression class for referencing a variable, like "a".
+class VariableExprAST : public ExprAST {
+  std::string Name;
+
+public:
+  VariableExprAST(SourceLocation Loc, const std::string &Name)
+      : ExprAST(Loc), Name(Name) {}
+  const std::string &getName() const { return Name; }
+  Value *codegen() override;
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    return ExprAST::dump(out << Name, ind);
+  }
+};
+
+/// UnaryExprAST - Expression class for a unary operator.
+class UnaryExprAST : public ExprAST {
+  char Opcode;
+  std::unique_ptr<ExprAST> Operand;
+
+public:
+  UnaryExprAST(char Opcode, std::unique_ptr<ExprAST> Operand)
+      : Opcode(Opcode), Operand(std::move(Operand)) {}
+  Value *codegen() override;
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    ExprAST::dump(out << "unary" << Opcode, ind);
+    Operand->dump(out, ind + 1);
+    return out;
+  }
+};
+
+/// BinaryExprAST - Expression class for a binary operator.
+class BinaryExprAST : public ExprAST {
+  char Op;
+  std::unique_ptr<ExprAST> LHS, RHS;
+
+public:
+  BinaryExprAST(SourceLocation Loc, char Op, std::unique_ptr<ExprAST> LHS,
+                std::unique_ptr<ExprAST> RHS)
+      : ExprAST(Loc), Op(Op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
+  Value *codegen() override;
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    ExprAST::dump(out << "binary" << Op, ind);
+    LHS->dump(indent(out, ind) << "LHS:", ind + 1);
+    RHS->dump(indent(out, ind) << "RHS:", ind + 1);
+    return out;
+  }
+};
+
+/// CallExprAST - Expression class for function calls.
+class CallExprAST : public ExprAST {
+  std::string Callee;
+  std::vector<std::unique_ptr<ExprAST>> Args;
+
+public:
+  CallExprAST(SourceLocation Loc, const std::string &Callee,
+              std::vector<std::unique_ptr<ExprAST>> Args)
+      : ExprAST(Loc), Callee(Callee), Args(std::move(Args)) {}
+  Value *codegen() override;
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    ExprAST::dump(out << "call " << Callee, ind);
+    for (const auto &Arg : Args)
+      Arg->dump(indent(out, ind + 1), ind + 1);
+    return out;
+  }
+};
+
+/// IfExprAST - Expression class for if/then/else.
+class IfExprAST : public ExprAST {
+  std::unique_ptr<ExprAST> Cond, Then, Else;
+
+public:
+  IfExprAST(SourceLocation Loc, std::unique_ptr<ExprAST> Cond,
+            std::unique_ptr<ExprAST> Then, std::unique_ptr<ExprAST> Else)
+      : ExprAST(Loc), Cond(std::move(Cond)), Then(std::move(Then)),
+        Else(std::move(Else)) {}
+  Value *codegen() override;
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    ExprAST::dump(out << "if", ind);
+    Cond->dump(indent(out, ind) << "Cond:", ind + 1);
+    Then->dump(indent(out, ind) << "Then:", ind + 1);
+    Else->dump(indent(out, ind) << "Else:", ind + 1);
+    return out;
+  }
+};
+
+/// ForExprAST - Expression class for for/in.
+class ForExprAST : public ExprAST {
+  std::string VarName;
+  std::unique_ptr<ExprAST> Start, End, Step, Body;
+
+public:
+  ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
+             std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
+             std::unique_ptr<ExprAST> Body)
+      : VarName(VarName), Start(std::move(Start)), End(std::move(End)),
+        Step(std::move(Step)), Body(std::move(Body)) {}
+  Value *codegen() override;
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    ExprAST::dump(out << "for", ind);
+    Start->dump(indent(out, ind) << "Cond:", ind + 1);
+    End->dump(indent(out, ind) << "End:", ind + 1);
+    Step->dump(indent(out, ind) << "Step:", ind + 1);
+    Body->dump(indent(out, ind) << "Body:", ind + 1);
+    return out;
+  }
+};
+
+/// VarExprAST - Expression class for var/in
+class VarExprAST : public ExprAST {
+  std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+  std::unique_ptr<ExprAST> Body;
+
+public:
+  VarExprAST(
+      std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames,
+      std::unique_ptr<ExprAST> Body)
+      : VarNames(std::move(VarNames)), Body(std::move(Body)) {}
+  Value *codegen() override;
+  raw_ostream &dump(raw_ostream &out, int ind) override {
+    ExprAST::dump(out << "var", ind);
+    for (const auto &NamedVar : VarNames)
+      NamedVar.second->dump(indent(out, ind) << NamedVar.first << ':', ind + 1);
+    Body->dump(indent(out, ind) << "Body:", ind + 1);
+    return out;
+  }
+};
+
+/// PrototypeAST - This class represents the "prototype" for a function,
+/// which captures its name, and its argument names (thus implicitly the number
+/// of arguments the function takes), as well as if it is an operator.
+class PrototypeAST {
+  std::string Name;
+  std::vector<std::string> Args;
+  bool IsOperator;
+  unsigned Precedence; // Precedence if a binary op.
+  int Line;
+
+public:
+  PrototypeAST(SourceLocation Loc, const std::string &Name,
+               std::vector<std::string> Args, bool IsOperator = false,
+               unsigned Prec = 0)
+      : Name(Name), Args(std::move(Args)), IsOperator(IsOperator),
+        Precedence(Prec), Line(Loc.Line) {}
+  Function *codegen();
+  const std::string &getName() const { return Name; }
+
+  bool isUnaryOp() const { return IsOperator && Args.size() == 1; }
+  bool isBinaryOp() const { return IsOperator && Args.size() == 2; }
+
+  char getOperatorName() const {
+    assert(isUnaryOp() || isBinaryOp());
+    return Name[Name.size() - 1];
+  }
+
+  unsigned getBinaryPrecedence() const { return Precedence; }
+  int getLine() const { return Line; }
+};
+
+/// FunctionAST - This class represents a function definition itself.
+class FunctionAST {
+  std::unique_ptr<PrototypeAST> Proto;
+  std::unique_ptr<ExprAST> Body;
+
+public:
+  FunctionAST(std::unique_ptr<PrototypeAST> Proto,
+              std::unique_ptr<ExprAST> Body)
+      : Proto(std::move(Proto)), Body(std::move(Body)) {}
+  Function *codegen();
+  raw_ostream &dump(raw_ostream &out, int ind) {
+    indent(out, ind) << "FunctionAST\n";
+    ++ind;
+    indent(out, ind) << "Body:";
+    return Body ? Body->dump(out, ind) : out << "null\n";
+  }
+};
+} // end anonymous namespace
+
+//===----------------------------------------------------------------------===//
+// 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;
+}
+
+/// LogError* - These are little helper functions for error handling.
+std::unique_ptr<ExprAST> LogError(const char *Str) {
+  fprintf(stderr, "Error: %s\n", Str);
+  return nullptr;
+}
+
+std::unique_ptr<PrototypeAST> LogErrorP(const char *Str) {
+  LogError(Str);
+  return nullptr;
+}
+
+static std::unique_ptr<ExprAST> ParseExpression();
+
+/// numberexpr ::= number
+static std::unique_ptr<ExprAST> ParseNumberExpr() {
+  auto Result = llvm::make_unique<NumberExprAST>(NumVal);
+  getNextToken(); // consume the number
+  return std::move(Result);
+}
+
+/// parenexpr ::= '(' expression ')'
+static std::unique_ptr<ExprAST> ParseParenExpr() {
+  getNextToken(); // eat (.
+  auto V = ParseExpression();
+  if (!V)
+    return nullptr;
+
+  if (CurTok != ')')
+    return LogError("expected ')'");
+  getNextToken(); // eat ).
+  return V;
+}
+
+/// identifierexpr
+///   ::= identifier
+///   ::= identifier '(' expression* ')'
+static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
+  std::string IdName = IdentifierStr;
+
+  SourceLocation LitLoc = CurLoc;
+
+  getNextToken(); // eat identifier.
+
+  if (CurTok != '(') // Simple variable ref.
+    return llvm::make_unique<VariableExprAST>(LitLoc, IdName);
+
+  // Call.
+  getNextToken(); // eat (
+  std::vector<std::unique_ptr<ExprAST>> Args;
+  if (CurTok != ')') {
+    while (1) {
+      if (auto Arg = ParseExpression())
+        Args.push_back(std::move(Arg));
+      else
+        return nullptr;
+
+      if (CurTok == ')')
+        break;
+
+      if (CurTok != ',')
+        return LogError("Expected ')' or ',' in argument list");
+      getNextToken();
+    }
+  }
+
+  // Eat the ')'.
+  getNextToken();
+
+  return llvm::make_unique<CallExprAST>(LitLoc, IdName, std::move(Args));
+}
+
+/// ifexpr ::= 'if' expression 'then' expression 'else' expression
+static std::unique_ptr<ExprAST> ParseIfExpr() {
+  SourceLocation IfLoc = CurLoc;
+
+  getNextToken(); // eat the if.
+
+  // condition.
+  auto Cond = ParseExpression();
+  if (!Cond)
+    return nullptr;
+
+  if (CurTok != tok_then)
+    return LogError("expected then");
+  getNextToken(); // eat the then
+
+  auto Then = ParseExpression();
+  if (!Then)
+    return nullptr;
+
+  if (CurTok != tok_else)
+    return LogError("expected else");
+
+  getNextToken();
+
+  auto Else = ParseExpression();
+  if (!Else)
+    return nullptr;
+
+  return llvm::make_unique<IfExprAST>(IfLoc, std::move(Cond), std::move(Then),
+                                      std::move(Else));
+}
+
+/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+static std::unique_ptr<ExprAST> ParseForExpr() {
+  getNextToken(); // eat the for.
+
+  if (CurTok != tok_identifier)
+    return LogError("expected identifier after for");
+
+  std::string IdName = IdentifierStr;
+  getNextToken(); // eat identifier.
+
+  if (CurTok != '=')
+    return LogError("expected '=' after for");
+  getNextToken(); // eat '='.
+
+  auto Start = ParseExpression();
+  if (!Start)
+    return nullptr;
+  if (CurTok != ',')
+    return LogError("expected ',' after for start value");
+  getNextToken();
+
+  auto End = ParseExpression();
+  if (!End)
+    return nullptr;
+
+  // The step value is optional.
+  std::unique_ptr<ExprAST> Step;
+  if (CurTok == ',') {
+    getNextToken();
+    Step = ParseExpression();
+    if (!Step)
+      return nullptr;
+  }
+
+  if (CurTok != tok_in)
+    return LogError("expected 'in' after for");
+  getNextToken(); // eat 'in'.
+
+  auto Body = ParseExpression();
+  if (!Body)
+    return nullptr;
+
+  return llvm::make_unique<ForExprAST>(IdName, std::move(Start), std::move(End),
+                                       std::move(Step), std::move(Body));
+}
+
+/// varexpr ::= 'var' identifier ('=' expression)?
+//                    (',' identifier ('=' expression)?)* 'in' expression
+static std::unique_ptr<ExprAST> ParseVarExpr() {
+  getNextToken(); // eat the var.
+
+  std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+
+  // At least one variable name is required.
+  if (CurTok != tok_identifier)
+    return LogError("expected identifier after var");
+
+  while (1) {
+    std::string Name = IdentifierStr;
+    getNextToken(); // eat identifier.
+
+    // Read the optional initializer.
+    std::unique_ptr<ExprAST> Init = nullptr;
+    if (CurTok == '=') {
+      getNextToken(); // eat the '='.
+
+      Init = ParseExpression();
+      if (!Init)
+        return nullptr;
+    }
+
+    VarNames.push_back(std::make_pair(Name, std::move(Init)));
+
+    // End of var list, exit loop.
+    if (CurTok != ',')
+      break;
+    getNextToken(); // eat the ','.
+
+    if (CurTok != tok_identifier)
+      return LogError("expected identifier list after var");
+  }
+
+  // At this point, we have to have 'in'.
+  if (CurTok != tok_in)
+    return LogError("expected 'in' keyword after 'var'");
+  getNextToken(); // eat 'in'.
+
+  auto Body = ParseExpression();
+  if (!Body)
+    return nullptr;
+
+  return llvm::make_unique<VarExprAST>(std::move(VarNames), std::move(Body));
+}
+
+/// primary
+///   ::= identifierexpr
+///   ::= numberexpr
+///   ::= parenexpr
+///   ::= ifexpr
+///   ::= forexpr
+///   ::= varexpr
+static std::unique_ptr<ExprAST> ParsePrimary() {
+  switch (CurTok) {
+  default:
+    return LogError("unknown token when expecting an expression");
+  case tok_identifier:
+    return ParseIdentifierExpr();
+  case tok_number:
+    return ParseNumberExpr();
+  case '(':
+    return ParseParenExpr();
+  case tok_if:
+    return ParseIfExpr();
+  case tok_for:
+    return ParseForExpr();
+  case tok_var:
+    return ParseVarExpr();
+  }
+}
+
+/// unary
+///   ::= primary
+///   ::= '!' unary
+static std::unique_ptr<ExprAST> ParseUnary() {
+  // If the current token is not an operator, it must be a primary expr.
+  if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+    return ParsePrimary();
+
+  // If this is a unary operator, read it.
+  int Opc = CurTok;
+  getNextToken();
+  if (auto Operand = ParseUnary())
+    return llvm::make_unique<UnaryExprAST>(Opc, std::move(Operand));
+  return nullptr;
+}
+
+/// binoprhs
+///   ::= ('+' unary)*
+static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+                                              std::unique_ptr<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;
+    SourceLocation BinLoc = CurLoc;
+    getNextToken(); // eat binop
+
+    // Parse the unary expression after the binary operator.
+    auto RHS = ParseUnary();
+    if (!RHS)
+      return nullptr;
+
+    // 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, std::move(RHS));
+      if (!RHS)
+        return nullptr;
+    }
+
+    // Merge LHS/RHS.
+    LHS = llvm::make_unique<BinaryExprAST>(BinLoc, BinOp, std::move(LHS),
+                                           std::move(RHS));
+  }
+}
+
+/// expression
+///   ::= unary binoprhs
+///
+static std::unique_ptr<ExprAST> ParseExpression() {
+  auto LHS = ParseUnary();
+  if (!LHS)
+    return nullptr;
+
+  return ParseBinOpRHS(0, std::move(LHS));
+}
+
+/// prototype
+///   ::= id '(' id* ')'
+///   ::= binary LETTER number? (id, id)
+///   ::= unary LETTER (id)
+static std::unique_ptr<PrototypeAST> ParsePrototype() {
+  std::string FnName;
+
+  SourceLocation FnLoc = CurLoc;
+
+  unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+  unsigned BinaryPrecedence = 30;
+
+  switch (CurTok) {
+  default:
+    return LogErrorP("Expected function name in prototype");
+  case tok_identifier:
+    FnName = IdentifierStr;
+    Kind = 0;
+    getNextToken();
+    break;
+  case tok_unary:
+    getNextToken();
+    if (!isascii(CurTok))
+      return LogErrorP("Expected unary operator");
+    FnName = "unary";
+    FnName += (char)CurTok;
+    Kind = 1;
+    getNextToken();
+    break;
+  case tok_binary:
+    getNextToken();
+    if (!isascii(CurTok))
+      return LogErrorP("Expected binary operator");
+    FnName = "binary";
+    FnName += (char)CurTok;
+    Kind = 2;
+    getNextToken();
+
+    // Read the precedence if present.
+    if (CurTok == tok_number) {
+      if (NumVal < 1 || NumVal > 100)
+        return LogErrorP("Invalid precedecnce: must be 1..100");
+      BinaryPrecedence = (unsigned)NumVal;
+      getNextToken();
+    }
+    break;
+  }
+
+  if (CurTok != '(')
+    return LogErrorP("Expected '(' in prototype");
+
+  std::vector<std::string> ArgNames;
+  while (getNextToken() == tok_identifier)
+    ArgNames.push_back(IdentifierStr);
+  if (CurTok != ')')
+    return LogErrorP("Expected ')' in prototype");
+
+  // success.
+  getNextToken(); // eat ')'.
+
+  // Verify right number of names for operator.
+  if (Kind && ArgNames.size() != Kind)
+    return LogErrorP("Invalid number of operands for operator");
+
+  return llvm::make_unique<PrototypeAST>(FnLoc, FnName, ArgNames, Kind != 0,
+                                         BinaryPrecedence);
+}
+
+/// definition ::= 'def' prototype expression
+static std::unique_ptr<FunctionAST> ParseDefinition() {
+  getNextToken(); // eat def.
+  auto Proto = ParsePrototype();
+  if (!Proto)
+    return nullptr;
+
+  if (auto E = ParseExpression())
+    return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+  return nullptr;
+}
+
+/// toplevelexpr ::= expression
+static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
+  SourceLocation FnLoc = CurLoc;
+  if (auto E = ParseExpression()) {
+    // Make an anonymous proto.
+    auto Proto = llvm::make_unique<PrototypeAST>(FnLoc, "__anon_expr",
+                                                 std::vector<std::string>());
+    return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+  }
+  return nullptr;
+}
+
+/// external ::= 'extern' prototype
+static std::unique_ptr<PrototypeAST> ParseExtern() {
+  getNextToken(); // eat extern.
+  return ParsePrototype();
+}
+
+//===----------------------------------------------------------------------===//
+// Debug Info Support
+//===----------------------------------------------------------------------===//
+
+static std::unique_ptr<DIBuilder> DBuilder;
+
+DIType *DebugInfo::getDoubleTy() {
+  if (DblTy)
+    return DblTy;
+
+  DblTy = DBuilder->createBasicType("double", 64, 64, dwarf::DW_ATE_float);
+  return DblTy;
+}
+
+void DebugInfo::emitLocation(ExprAST *AST) {
+  if (!AST)
+    return Builder.SetCurrentDebugLocation(DebugLoc());
+  DIScope *Scope;
+  if (LexicalBlocks.empty())
+    Scope = TheCU;
+  else
+    Scope = LexicalBlocks.back();
+  Builder.SetCurrentDebugLocation(
+      DebugLoc::get(AST->getLine(), AST->getCol(), Scope));
+}
+
+static DISubroutineType *CreateFunctionType(unsigned NumArgs, DIFile *Unit) {
+  SmallVector<Metadata *, 8> EltTys;
+  DIType *DblTy = KSDbgInfo.getDoubleTy();
+
+  // Add the result type.
+  EltTys.push_back(DblTy);
+
+  for (unsigned i = 0, e = NumArgs; i != e; ++i)
+    EltTys.push_back(DblTy);
+
+  return DBuilder->createSubroutineType(DBuilder->getOrCreateTypeArray(EltTys));
+}
+
+//===----------------------------------------------------------------------===//
+// Code Generation
+//===----------------------------------------------------------------------===//
+
+static std::unique_ptr<Module> TheModule;
+static std::map<std::string, AllocaInst *> NamedValues;
+static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+static std::map<std::string, std::unique_ptr<PrototypeAST>> FunctionProtos;
+
+Value *LogErrorV(const char *Str) {
+  LogError(Str);
+  return nullptr;
+}
+
+Function *getFunction(std::string Name) {
+  // First, see if the function has already been added to the current module.
+  if (auto *F = TheModule->getFunction(Name))
+    return F;
+
+  // If not, check whether we can codegen the declaration from some existing
+  // prototype.
+  auto FI = FunctionProtos.find(Name);
+  if (FI != FunctionProtos.end())
+    return FI->second->codegen();
+
+  // If no existing prototype exists, return null.
+  return nullptr;
+}
+
+/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
+/// the function.  This is used for mutable variables etc.
+static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
+                                          const std::string &VarName) {
+  IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
+                   TheFunction->getEntryBlock().begin());
+  return TmpB.CreateAlloca(Type::getDoubleTy(TheContext), nullptr,
+                           VarName.c_str());
+}
+
+Value *NumberExprAST::codegen() {
+  KSDbgInfo.emitLocation(this);
+  return ConstantFP::get(TheContext, APFloat(Val));
+}
+
+Value *VariableExprAST::codegen() {
+  // Look this variable up in the function.
+  Value *V = NamedValues[Name];
+  if (!V)
+    return LogErrorV("Unknown variable name");
+
+  KSDbgInfo.emitLocation(this);
+  // Load the value.
+  return Builder.CreateLoad(V, Name.c_str());
+}
+
+Value *UnaryExprAST::codegen() {
+  Value *OperandV = Operand->codegen();
+  if (!OperandV)
+    return nullptr;
+
+  Function *F = getFunction(std::string("unary") + Opcode);
+  if (!F)
+    return LogErrorV("Unknown unary operator");
+
+  KSDbgInfo.emitLocation(this);
+  return Builder.CreateCall(F, OperandV, "unop");
+}
+
+Value *BinaryExprAST::codegen() {
+  KSDbgInfo.emitLocation(this);
+
+  // Special case '=' because we don't want to emit the LHS as an expression.
+  if (Op == '=') {
+    // Assignment requires the LHS to be an identifier.
+    // This assume we're building without RTTI because LLVM builds that way by
+    // default.  If you build LLVM with RTTI this can be changed to a
+    // dynamic_cast for automatic error checking.
+    VariableExprAST *LHSE = static_cast<VariableExprAST *>(LHS.get());
+    if (!LHSE)
+      return LogErrorV("destination of '=' must be a variable");
+    // Codegen the RHS.
+    Value *Val = RHS->codegen();
+    if (!Val)
+      return nullptr;
+
+    // Look up the name.
+    Value *Variable = NamedValues[LHSE->getName()];
+    if (!Variable)
+      return LogErrorV("Unknown variable name");
+
+    Builder.CreateStore(Val, Variable);
+    return Val;
+  }
+
+  Value *L = LHS->codegen();
+  Value *R = RHS->codegen();
+  if (!L || !R)
+    return nullptr;
+
+  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(TheContext), "booltmp");
+  default:
+    break;
+  }
+
+  // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+  // a call to it.
+  Function *F = getFunction(std::string("binary") + Op);
+  assert(F && "binary operator not found!");
+
+  Value *Ops[] = {L, R};
+  return Builder.CreateCall(F, Ops, "binop");
+}
+
+Value *CallExprAST::codegen() {
+  KSDbgInfo.emitLocation(this);
+
+  // Look up the name in the global module table.
+  Function *CalleeF = getFunction(Callee);
+  if (!CalleeF)
+    return LogErrorV("Unknown function referenced");
+
+  // If argument mismatch error.
+  if (CalleeF->arg_size() != Args.size())
+    return LogErrorV("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())
+      return nullptr;
+  }
+
+  return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+}
+
+Value *IfExprAST::codegen() {
+  KSDbgInfo.emitLocation(this);
+
+  Value *CondV = Cond->codegen();
+  if (!CondV)
+    return nullptr;
+
+  // Convert condition to a bool by comparing equal to 0.0.
+  CondV = Builder.CreateFCmpONE(
+      CondV, ConstantFP::get(TheContext, APFloat(0.0)), "ifcond");
+
+  Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+  // Create blocks for the then and else cases.  Insert the 'then' block at the
+  // end of the function.
+  BasicBlock *ThenBB = BasicBlock::Create(TheContext, "then", TheFunction);
+  BasicBlock *ElseBB = BasicBlock::Create(TheContext, "else");
+  BasicBlock *MergeBB = BasicBlock::Create(TheContext, "ifcont");
+
+  Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+  // Emit then value.
+  Builder.SetInsertPoint(ThenBB);
+
+  Value *ThenV = Then->codegen();
+  if (!ThenV)
+    return nullptr;
+
+  Builder.CreateBr(MergeBB);
+  // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+  ThenBB = Builder.GetInsertBlock();
+
+  // Emit else block.
+  TheFunction->getBasicBlockList().push_back(ElseBB);
+  Builder.SetInsertPoint(ElseBB);
+
+  Value *ElseV = Else->codegen();
+  if (!ElseV)
+    return nullptr;
+
+  Builder.CreateBr(MergeBB);
+  // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
+  ElseBB = Builder.GetInsertBlock();
+
+  // Emit merge block.
+  TheFunction->getBasicBlockList().push_back(MergeBB);
+  Builder.SetInsertPoint(MergeBB);
+  PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(TheContext), 2, "iftmp");
+
+  PN->addIncoming(ThenV, ThenBB);
+  PN->addIncoming(ElseV, ElseBB);
+  return PN;
+}
+
+// Output for-loop as:
+//   var = alloca double
+//   ...
+//   start = startexpr
+//   store start -> var
+//   goto loop
+// loop:
+//   ...
+//   bodyexpr
+//   ...
+// loopend:
+//   step = stepexpr
+//   endcond = endexpr
+//
+//   curvar = load var
+//   nextvar = curvar + step
+//   store nextvar -> var
+//   br endcond, loop, endloop
+// outloop:
+Value *ForExprAST::codegen() {
+  Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+  // Create an alloca for the variable in the entry block.
+  AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+
+  KSDbgInfo.emitLocation(this);
+
+  // Emit the start code first, without 'variable' in scope.
+  Value *StartVal = Start->codegen();
+  if (!StartVal)
+    return nullptr;
+
+  // Store the value into the alloca.
+  Builder.CreateStore(StartVal, Alloca);
+
+  // Make the new basic block for the loop header, inserting after current
+  // block.
+  BasicBlock *LoopBB = BasicBlock::Create(TheContext, "loop", TheFunction);
+
+  // Insert an explicit fall through from the current block to the LoopBB.
+  Builder.CreateBr(LoopBB);
+
+  // Start insertion in LoopBB.
+  Builder.SetInsertPoint(LoopBB);
+
+  // Within the loop, the variable is defined equal to the PHI node.  If it
+  // shadows an existing variable, we have to restore it, so save it now.
+  AllocaInst *OldVal = NamedValues[VarName];
+  NamedValues[VarName] = Alloca;
+
+  // Emit the body of the loop.  This, like any other expr, can change the
+  // current BB.  Note that we ignore the value computed by the body, but don't
+  // allow an error.
+  if (!Body->codegen())
+    return nullptr;
+
+  // Emit the step value.
+  Value *StepVal = nullptr;
+  if (Step) {
+    StepVal = Step->codegen();
+    if (!StepVal)
+      return nullptr;
+  } else {
+    // If not specified, use 1.0.
+    StepVal = ConstantFP::get(TheContext, APFloat(1.0));
+  }
+
+  // Compute the end condition.
+  Value *EndCond = End->codegen();
+  if (!EndCond)
+    return nullptr;
+
+  // Reload, increment, and restore the alloca.  This handles the case where
+  // the body of the loop mutates the variable.
+  Value *CurVar = Builder.CreateLoad(Alloca, VarName.c_str());
+  Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
+  Builder.CreateStore(NextVar, Alloca);
+
+  // Convert condition to a bool by comparing equal to 0.0.
+  EndCond = Builder.CreateFCmpONE(
+      EndCond, ConstantFP::get(TheContext, APFloat(0.0)), "loopcond");
+
+  // Create the "after loop" block and insert it.
+  BasicBlock *AfterBB =
+      BasicBlock::Create(TheContext, "afterloop", TheFunction);
+
+  // Insert the conditional branch into the end of LoopEndBB.
+  Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+  // Any new code will be inserted in AfterBB.
+  Builder.SetInsertPoint(AfterBB);
+
+  // Restore the unshadowed variable.
+  if (OldVal)
+    NamedValues[VarName] = OldVal;
+  else
+    NamedValues.erase(VarName);
+
+  // for expr always returns 0.0.
+  return Constant::getNullValue(Type::getDoubleTy(TheContext));
+}
+
+Value *VarExprAST::codegen() {
+  std::vector<AllocaInst *> OldBindings;
+
+  Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+  // Register all variables and emit their initializer.
+  for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
+    const std::string &VarName = VarNames[i].first;
+    ExprAST *Init = VarNames[i].second.get();
+
+    // Emit the initializer before adding the variable to scope, this prevents
+    // the initializer from referencing the variable itself, and permits stuff
+    // like this:
+    //  var a = 1 in
+    //    var a = a in ...   # refers to outer 'a'.
+    Value *InitVal;
+    if (Init) {
+      InitVal = Init->codegen();
+      if (!InitVal)
+        return nullptr;
+    } else { // If not specified, use 0.0.
+      InitVal = ConstantFP::get(TheContext, APFloat(0.0));
+    }
+
+    AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+    Builder.CreateStore(InitVal, Alloca);
+
+    // Remember the old variable binding so that we can restore the binding when
+    // we unrecurse.
+    OldBindings.push_back(NamedValues[VarName]);
+
+    // Remember this binding.
+    NamedValues[VarName] = Alloca;
+  }
+
+  KSDbgInfo.emitLocation(this);
+
+  // Codegen the body, now that all vars are in scope.
+  Value *BodyVal = Body->codegen();
+  if (!BodyVal)
+    return nullptr;
+
+  // Pop all our variables from scope.
+  for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
+    NamedValues[VarNames[i].first] = OldBindings[i];
+
+  // Return the body computation.
+  return BodyVal;
+}
+
+Function *PrototypeAST::codegen() {
+  // Make the function type:  double(double,double) etc.
+  std::vector<Type *> Doubles(Args.size(), Type::getDoubleTy(TheContext));
+  FunctionType *FT =
+      FunctionType::get(Type::getDoubleTy(TheContext), Doubles, false);
+
+  Function *F =
+      Function::Create(FT, Function::ExternalLinkage, Name, TheModule.get());
+
+  // Set names for all arguments.
+  unsigned Idx = 0;
+  for (auto &Arg : F->args())
+    Arg.setName(Args[Idx++]);
+
+  return F;
+}
+
+Function *FunctionAST::codegen() {
+  // Transfer ownership of the prototype to the FunctionProtos map, but keep a
+  // reference to it for use below.
+  auto &P = *Proto;
+  FunctionProtos[Proto->getName()] = std::move(Proto);
+  Function *TheFunction = getFunction(P.getName());
+  if (!TheFunction)
+    return nullptr;
+
+  // If this is an operator, install it.
+  if (P.isBinaryOp())
+    BinopPrecedence[P.getOperatorName()] = P.getBinaryPrecedence();
+
+  // Create a new basic block to start insertion into.
+  BasicBlock *BB = BasicBlock::Create(TheContext, "entry", TheFunction);
+  Builder.SetInsertPoint(BB);
+
+  // Create a subprogram DIE for this function.
+  DIFile *Unit = DBuilder->createFile(KSDbgInfo.TheCU->getFilename(),
+                                      KSDbgInfo.TheCU->getDirectory());
+  DIScope *FContext = Unit;
+  unsigned LineNo = P.getLine();
+  unsigned ScopeLine = LineNo;
+  DISubprogram *SP = DBuilder->createFunction(
+      FContext, P.getName(), StringRef(), Unit, LineNo,
+      CreateFunctionType(TheFunction->arg_size(), Unit),
+      false /* internal linkage */, true /* definition */, ScopeLine,
+      DINode::FlagPrototyped, false);
+  TheFunction->setSubprogram(SP);
+
+  // Push the current scope.
+  KSDbgInfo.LexicalBlocks.push_back(SP);
+
+  // Unset the location for the prologue emission (leading instructions with no
+  // location in a function are considered part of the prologue and the debugger
+  // will run past them when breaking on a function)
+  KSDbgInfo.emitLocation(nullptr);
+
+  // Record the function arguments in the NamedValues map.
+  NamedValues.clear();
+  unsigned ArgIdx = 0;
+  for (auto &Arg : TheFunction->args()) {
+    // Create an alloca for this variable.
+    AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, Arg.getName());
+
+    // Create a debug descriptor for the variable.
+    DILocalVariable *D = DBuilder->createParameterVariable(
+        SP, Arg.getName(), ++ArgIdx, Unit, LineNo, KSDbgInfo.getDoubleTy(),
+        true);
+
+    DBuilder->insertDeclare(Alloca, D, DBuilder->createExpression(),
+                            DebugLoc::get(LineNo, 0, SP),
+                            Builder.GetInsertBlock());
+
+    // Store the initial value into the alloca.
+    Builder.CreateStore(&Arg, Alloca);
+
+    // Add arguments to variable symbol table.
+    NamedValues[Arg.getName()] = Alloca;
+  }
+
+  KSDbgInfo.emitLocation(Body.get());
+
+  if (Value *RetVal = Body->codegen()) {
+    // Finish off the function.
+    Builder.CreateRet(RetVal);
+
+    // Pop off the lexical block for the function.
+    KSDbgInfo.LexicalBlocks.pop_back();
+
+    // Validate the generated code, checking for consistency.
+    verifyFunction(*TheFunction);
+
+    return TheFunction;
+  }
+
+  // Error reading body, remove function.
+  TheFunction->eraseFromParent();
+
+  if (P.isBinaryOp())
+    BinopPrecedence.erase(Proto->getOperatorName());
+
+  // Pop off the lexical block for the function since we added it
+  // unconditionally.
+  KSDbgInfo.LexicalBlocks.pop_back();
+
+  return nullptr;
+}
+
+//===----------------------------------------------------------------------===//
+// Top-Level parsing and JIT Driver
+//===----------------------------------------------------------------------===//
+
+static void InitializeModule() {
+  // Open a new module.
+  TheModule = llvm::make_unique<Module>("my cool jit", TheContext);
+  TheModule->setDataLayout(TheJIT->getTargetMachine().createDataLayout());
+}
+
+static void HandleDefinition() {
+  if (auto FnAST = ParseDefinition()) {
+    if (!FnAST->codegen())
+      fprintf(stderr, "Error reading function definition:");
+  } else {
+    // Skip token for error recovery.
+    getNextToken();
+  }
+}
+
+static void HandleExtern() {
+  if (auto ProtoAST = ParseExtern()) {
+    if (!ProtoAST->codegen())
+      fprintf(stderr, "Error reading extern");
+    else
+      FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
+  } else {
+    // Skip token for error recovery.
+    getNextToken();
+  }
+}
+
+static void HandleTopLevelExpression() {
+  // Evaluate a top-level expression into an anonymous function.
+  if (auto FnAST = ParseTopLevelExpr()) {
+    if (!FnAST->codegen()) {
+      fprintf(stderr, "Error generating code for top level expr");
+    }
+  } else {
+    // Skip token for error recovery.
+    getNextToken();
+  }
+}
+
+/// top ::= definition | external | expression | ';'
+static void MainLoop() {
+  while (1) {
+    switch (CurTok) {
+    case tok_eof:
+      return;
+    case ';': // ignore top-level semicolons.
+      getNextToken();
+      break;
+    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) {
+  fputc((char)X, stderr);
+  return 0;
+}
+
+/// printd - printf that takes a double prints it as "%f\n", returning 0.
+extern "C" double printd(double X) {
+  fprintf(stderr, "%f\n", X);
+  return 0;
+}
+
+//===----------------------------------------------------------------------===//
+// Main driver code.
+//===----------------------------------------------------------------------===//
+
+int main() {
+  InitializeNativeTarget();
+  InitializeNativeTargetAsmPrinter();
+  InitializeNativeTargetAsmParser();
+
+  // Install standard binary operators.
+  // 1 is lowest precedence.
+  BinopPrecedence['='] = 2;
+  BinopPrecedence['<'] = 10;
+  BinopPrecedence['+'] = 20;
+  BinopPrecedence['-'] = 20;
+  BinopPrecedence['*'] = 40; // highest.
+
+  // Prime the first token.
+  getNextToken();
+
+  TheJIT = llvm::make_unique<KaleidoscopeJIT>();
+
+  InitializeModule();
+
+  // Add the current debug info version into the module.
+  TheModule->addModuleFlag(Module::Warning, "Debug Info Version",
+                           DEBUG_METADATA_VERSION);
+
+  // Darwin only supports dwarf2.
+  if (Triple(sys::getProcessTriple()).isOSDarwin())
+    TheModule->addModuleFlag(llvm::Module::Warning, "Dwarf Version", 2);
+
+  // Construct the DIBuilder, we do this here because we need the module.
+  DBuilder = llvm::make_unique<DIBuilder>(*TheModule);
+
+  // Create the compile unit for the module.
+  // Currently down as "fib.ks" as a filename since we're redirecting stdin
+  // but we'd like actual source locations.
+  KSDbgInfo.TheCU = DBuilder->createCompileUnit(
+      dwarf::DW_LANG_C, "fib.ks", ".", "Kaleidoscope Compiler", 0, "", 0);
+
+  // Run the main "interpreter loop" now.
+  MainLoop();
+
+  // Finalize the debug info.
+  DBuilder->finalize();
+
+  // Print out all of the generated code.
+  TheModule->dump();
+
+  return 0;
+}