llvm/examples/Kaleidoscope/Chapter4/toy.cpp

   1 #include "../include/KaleidoscopeJIT.h"
   2 #include "llvm/ADT/APFloat.h"
   3 #include "llvm/ADT/STLExtras.h"
   4 #include "llvm/IR/BasicBlock.h"
   5 #include "llvm/IR/Constants.h"
   6 #include "llvm/IR/DerivedTypes.h"
   7 #include "llvm/IR/Function.h"
   8 #include "llvm/IR/IRBuilder.h"
   9 #include "llvm/IR/LLVMContext.h"
  10 #include "llvm/IR/LegacyPassManager.h"
  11 #include "llvm/IR/Module.h"
  12 #include "llvm/IR/Type.h"
  13 #include "llvm/IR/Verifier.h"
  14 #include "llvm/Support/TargetSelect.h"
  15 #include "llvm/Target/TargetMachine.h"
  16 #include "llvm/Transforms/InstCombine/InstCombine.h"
  17 #include "llvm/Transforms/Scalar.h"
  18 #include "llvm/Transforms/Scalar/GVN.h"
  19 #include <algorithm>
  20 #include <cassert>
  21 #include <cctype>
  22 #include <cstdint>
  23 #include <cstdio>
  24 #include <cstdlib>
  25 #include <map>
  26 #include <memory>
  27 #include <string>
  28 #include <vector>
  29
  30 using namespace llvm;
  31 using namespace llvm::orc;
  32
  33 //===----------------------------------------------------------------------===//
  34 // Lexer
  35 //===----------------------------------------------------------------------===//
  36
  37 // The lexer returns tokens [0-255] if it is an unknown character, otherwise one
  38 // of these for known things.
  39 enum Token {
  40   tok_eof = -1,
  41
  42   // commands
  43   tok_def = -2,
  44   tok_extern = -3,
  45
  46   // primary
  47   tok_identifier = -4,
  48   tok_number = -5
  49 };
  50
  51 static std::string IdentifierStr; // Filled in if tok_identifier
  52 static double NumVal;             // Filled in if tok_number
  53
  54 /// gettok - Return the next token from standard input.
  55 static int gettok() {
  56   static int LastChar = ' ';
  57
  58   // Skip any whitespace.
  59   while (isspace(LastChar))
  60     LastChar = getchar();
  61
  62   if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
  63     IdentifierStr = LastChar;
  64     while (isalnum((LastChar = getchar())))
  65       IdentifierStr += LastChar;
  66
  67     if (IdentifierStr == "def")
  68       return tok_def;
  69     if (IdentifierStr == "extern")
  70       return tok_extern;
  71     return tok_identifier;
  72   }
  73
  74   if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
  75     std::string NumStr;
  76     do {
  77       NumStr += LastChar;
  78       LastChar = getchar();
  79     } while (isdigit(LastChar) || LastChar == '.');
  80
  81     NumVal = strtod(NumStr.c_str(), nullptr);
  82     return tok_number;
  83   }
  84
  85   if (LastChar == '#') {
  86     // Comment until end of line.
  87     do
  88       LastChar = getchar();
  89     while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
  90
  91     if (LastChar != EOF)
  92       return gettok();
  93   }
  94
  95   // Check for end of file.  Don't eat the EOF.
  96   if (LastChar == EOF)
  97     return tok_eof;
  98
  99   // Otherwise, just return the character as its ascii value.
 100   int ThisChar = LastChar;
 101   LastChar = getchar();
 102   return ThisChar;
 103 }
 104
 105 //===----------------------------------------------------------------------===//
 106 // Abstract Syntax Tree (aka Parse Tree)
 107 //===----------------------------------------------------------------------===//
 108
 109 namespace {
 110
 111 /// ExprAST - Base class for all expression nodes.
 112 class ExprAST {
 113 public:
 114   virtual ~ExprAST() = default;
 115
 116   virtual Value *codegen() = 0;
 117 };
 118
 119 /// NumberExprAST - Expression class for numeric literals like "1.0".
 120 class NumberExprAST : public ExprAST {
 121   double Val;
 122
 123 public:
 124   NumberExprAST(double Val) : Val(Val) {}
 125
 126   Value *codegen() override;
 127 };
 128
 129 /// VariableExprAST - Expression class for referencing a variable, like "a".
 130 class VariableExprAST : public ExprAST {
 131   std::string Name;
 132
 133 public:
 134   VariableExprAST(const std::string &Name) : Name(Name) {}
 135
 136   Value *codegen() override;
 137 };
 138
 139 /// BinaryExprAST - Expression class for a binary operator.
 140 class BinaryExprAST : public ExprAST {
 141   char Op;
 142   std::unique_ptr<ExprAST> LHS, RHS;
 143
 144 public:
 145   BinaryExprAST(char Op, std::unique_ptr<ExprAST> LHS,
 146                 std::unique_ptr<ExprAST> RHS)
 147       : Op(Op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
 148
 149   Value *codegen() override;
 150 };
 151
 152 /// CallExprAST - Expression class for function calls.
 153 class CallExprAST : public ExprAST {
 154   std::string Callee;
 155   std::vector<std::unique_ptr<ExprAST>> Args;
 156
 157 public:
 158   CallExprAST(const std::string &Callee,
 159               std::vector<std::unique_ptr<ExprAST>> Args)
 160       : Callee(Callee), Args(std::move(Args)) {}
 161
 162   Value *codegen() override;
 163 };
 164
 165 /// PrototypeAST - This class represents the "prototype" for a function,
 166 /// which captures its name, and its argument names (thus implicitly the number
 167 /// of arguments the function takes).
 168 class PrototypeAST {
 169   std::string Name;
 170   std::vector<std::string> Args;
 171
 172 public:
 173   PrototypeAST(const std::string &Name, std::vector<std::string> Args)
 174       : Name(Name), Args(std::move(Args)) {}
 175
 176   Function *codegen();
 177   const std::string &getName() const { return Name; }
 178 };
 179
 180 /// FunctionAST - This class represents a function definition itself.
 181 class FunctionAST {
 182   std::unique_ptr<PrototypeAST> Proto;
 183   std::unique_ptr<ExprAST> Body;
 184
 185 public:
 186   FunctionAST(std::unique_ptr<PrototypeAST> Proto,
 187               std::unique_ptr<ExprAST> Body)
 188       : Proto(std::move(Proto)), Body(std::move(Body)) {}
 189
 190   Function *codegen();
 191 };
 192
 193 } // end anonymous namespace
 194
 195 //===----------------------------------------------------------------------===//
 196 // Parser
 197 //===----------------------------------------------------------------------===//
 198
 199 /// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current
 200 /// token the parser is looking at.  getNextToken reads another token from the
 201 /// lexer and updates CurTok with its results.
 202 static int CurTok;
 203 static int getNextToken() { return CurTok = gettok(); }
 204
 205 /// BinopPrecedence - This holds the precedence for each binary operator that is
 206 /// defined.
 207 static std::map<char, int> BinopPrecedence;
 208
 209 /// GetTokPrecedence - Get the precedence of the pending binary operator token.
 210 static int GetTokPrecedence() {
 211   if (!isascii(CurTok))
 212     return -1;
 213
 214   // Make sure it's a declared binop.
 215   int TokPrec = BinopPrecedence[CurTok];
 216   if (TokPrec <= 0)
 217     return -1;
 218   return TokPrec;
 219 }
 220
 221 /// LogError* - These are little helper functions for error handling.
 222 std::unique_ptr<ExprAST> LogError(const char *Str) {
 223   fprintf(stderr, "Error: %s\n", Str);
 224   return nullptr;
 225 }
 226
 227 std::unique_ptr<PrototypeAST> LogErrorP(const char *Str) {
 228   LogError(Str);
 229   return nullptr;
 230 }
 231
 232 static std::unique_ptr<ExprAST> ParseExpression();
 233
 234 /// numberexpr ::= number
 235 static std::unique_ptr<ExprAST> ParseNumberExpr() {
 236   auto Result = std::make_unique<NumberExprAST>(NumVal);
 237   getNextToken(); // consume the number
 238   return std::move(Result);
 239 }
 240
 241 /// parenexpr ::= '(' expression ')'
 242 static std::unique_ptr<ExprAST> ParseParenExpr() {
 243   getNextToken(); // eat (.
 244   auto V = ParseExpression();
 245   if (!V)
 246     return nullptr;
 247
 248   if (CurTok != ')')
 249     return LogError("expected ')'");
 250   getNextToken(); // eat ).
 251   return V;
 252 }
 253
 254 /// identifierexpr
 255 ///   ::= identifier
 256 ///   ::= identifier '(' expression* ')'
 257 static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
 258   std::string IdName = IdentifierStr;
 259
 260   getNextToken(); // eat identifier.
 261
 262   if (CurTok != '(') // Simple variable ref.
 263     return std::make_unique<VariableExprAST>(IdName);
 264
 265   // Call.
 266   getNextToken(); // eat (
 267   std::vector<std::unique_ptr<ExprAST>> Args;
 268   if (CurTok != ')') {
 269     while (true) {
 270       if (auto Arg = ParseExpression())
 271         Args.push_back(std::move(Arg));
 272       else
 273         return nullptr;
 274
 275       if (CurTok == ')')
 276         break;
 277
 278       if (CurTok != ',')
 279         return LogError("Expected ')' or ',' in argument list");
 280       getNextToken();
 281     }
 282   }
 283
 284   // Eat the ')'.
 285   getNextToken();
 286
 287   return std::make_unique<CallExprAST>(IdName, std::move(Args));
 288 }
 289
 290 /// primary
 291 ///   ::= identifierexpr
 292 ///   ::= numberexpr
 293 ///   ::= parenexpr
 294 static std::unique_ptr<ExprAST> ParsePrimary() {
 295   switch (CurTok) {
 296   default:
 297     return LogError("unknown token when expecting an expression");
 298   case tok_identifier:
 299     return ParseIdentifierExpr();
 300   case tok_number:
 301     return ParseNumberExpr();
 302   case '(':
 303     return ParseParenExpr();
 304   }
 305 }
 306
 307 /// binoprhs
 308 ///   ::= ('+' primary)*
 309 static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
 310                                               std::unique_ptr<ExprAST> LHS) {
 311   // If this is a binop, find its precedence.
 312   while (true) {
 313     int TokPrec = GetTokPrecedence();
 314
 315     // If this is a binop that binds at least as tightly as the current binop,
 316     // consume it, otherwise we are done.
 317     if (TokPrec < ExprPrec)
 318       return LHS;
 319
 320     // Okay, we know this is a binop.
 321     int BinOp = CurTok;
 322     getNextToken(); // eat binop
 323
 324     // Parse the primary expression after the binary operator.
 325     auto RHS = ParsePrimary();
 326     if (!RHS)
 327       return nullptr;
 328
 329     // If BinOp binds less tightly with RHS than the operator after RHS, let
 330     // the pending operator take RHS as its LHS.
 331     int NextPrec = GetTokPrecedence();
 332     if (TokPrec < NextPrec) {
 333       RHS = ParseBinOpRHS(TokPrec + 1, std::move(RHS));
 334       if (!RHS)
 335         return nullptr;
 336     }
 337
 338     // Merge LHS/RHS.
 339     LHS =
 340         std::make_unique<BinaryExprAST>(BinOp, std::move(LHS), std::move(RHS));
 341   }
 342 }
 343
 344 /// expression
 345 ///   ::= primary binoprhs
 346 ///
 347 static std::unique_ptr<ExprAST> ParseExpression() {
 348   auto LHS = ParsePrimary();
 349   if (!LHS)
 350     return nullptr;
 351
 352   return ParseBinOpRHS(0, std::move(LHS));
 353 }
 354
 355 /// prototype
 356 ///   ::= id '(' id* ')'
 357 static std::unique_ptr<PrototypeAST> ParsePrototype() {
 358   if (CurTok != tok_identifier)
 359     return LogErrorP("Expected function name in prototype");
 360
 361   std::string FnName = IdentifierStr;
 362   getNextToken();
 363
 364   if (CurTok != '(')
 365     return LogErrorP("Expected '(' in prototype");
 366
 367   std::vector<std::string> ArgNames;
 368   while (getNextToken() == tok_identifier)
 369     ArgNames.push_back(IdentifierStr);
 370   if (CurTok != ')')
 371     return LogErrorP("Expected ')' in prototype");
 372
 373   // success.
 374   getNextToken(); // eat ')'.
 375
 376   return std::make_unique<PrototypeAST>(FnName, std::move(ArgNames));
 377 }
 378
 379 /// definition ::= 'def' prototype expression
 380 static std::unique_ptr<FunctionAST> ParseDefinition() {
 381   getNextToken(); // eat def.
 382   auto Proto = ParsePrototype();
 383   if (!Proto)
 384     return nullptr;
 385
 386   if (auto E = ParseExpression())
 387     return std::make_unique<FunctionAST>(std::move(Proto), std::move(E));
 388   return nullptr;
 389 }
 390
 391 /// toplevelexpr ::= expression
 392 static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
 393   if (auto E = ParseExpression()) {
 394     // Make an anonymous proto.
 395     auto Proto = std::make_unique<PrototypeAST>("__anon_expr",
 396                                                  std::vector<std::string>());
 397     return std::make_unique<FunctionAST>(std::move(Proto), std::move(E));
 398   }
 399   return nullptr;
 400 }
 401
 402 /// external ::= 'extern' prototype
 403 static std::unique_ptr<PrototypeAST> ParseExtern() {
 404   getNextToken(); // eat extern.
 405   return ParsePrototype();
 406 }
 407
 408 //===----------------------------------------------------------------------===//
 409 // Code Generation
 410 //===----------------------------------------------------------------------===//
 411
 412 static std::unique_ptr<LLVMContext> TheContext;
 413 static std::unique_ptr<Module> TheModule;
 414 static std::unique_ptr<IRBuilder<>> Builder;
 415 static std::map<std::string, Value *> NamedValues;
 416 static std::unique_ptr<legacy::FunctionPassManager> TheFPM;
 417 static std::unique_ptr<KaleidoscopeJIT> TheJIT;
 418 static std::map<std::string, std::unique_ptr<PrototypeAST>> FunctionProtos;
 419 static ExitOnError ExitOnErr;
 420
 421 Value *LogErrorV(const char *Str) {
 422   LogError(Str);
 423   return nullptr;
 424 }
 425
 426 Function *getFunction(std::string Name) {
 427   // First, see if the function has already been added to the current module.
 428   if (auto *F = TheModule->getFunction(Name))
 429     return F;
 430
 431   // If not, check whether we can codegen the declaration from some existing
 432   // prototype.
 433   auto FI = FunctionProtos.find(Name);
 434   if (FI != FunctionProtos.end())
 435     return FI->second->codegen();
 436
 437   // If no existing prototype exists, return null.
 438   return nullptr;
 439 }
 440
 441 Value *NumberExprAST::codegen() {
 442   return ConstantFP::get(*TheContext, APFloat(Val));
 443 }
 444
 445 Value *VariableExprAST::codegen() {
 446   // Look this variable up in the function.
 447   Value *V = NamedValues[Name];
 448   if (!V)
 449     return LogErrorV("Unknown variable name");
 450   return V;
 451 }
 452
 453 Value *BinaryExprAST::codegen() {
 454   Value *L = LHS->codegen();
 455   Value *R = RHS->codegen();
 456   if (!L || !R)
 457     return nullptr;
 458
 459   switch (Op) {
 460   case '+':
 461     return Builder->CreateFAdd(L, R, "addtmp");
 462   case '-':
 463     return Builder->CreateFSub(L, R, "subtmp");
 464   case '*':
 465     return Builder->CreateFMul(L, R, "multmp");
 466   case '<':
 467     L = Builder->CreateFCmpULT(L, R, "cmptmp");
 468     // Convert bool 0/1 to double 0.0 or 1.0
 469     return Builder->CreateUIToFP(L, Type::getDoubleTy(*TheContext), "booltmp");
 470   default:
 471     return LogErrorV("invalid binary operator");
 472   }
 473 }
 474
 475 Value *CallExprAST::codegen() {
 476   // Look up the name in the global module table.
 477   Function *CalleeF = getFunction(Callee);
 478   if (!CalleeF)
 479     return LogErrorV("Unknown function referenced");
 480
 481   // If argument mismatch error.
 482   if (CalleeF->arg_size() != Args.size())
 483     return LogErrorV("Incorrect # arguments passed");
 484
 485   std::vector<Value *> ArgsV;
 486   for (unsigned i = 0, e = Args.size(); i != e; ++i) {
 487     ArgsV.push_back(Args[i]->codegen());
 488     if (!ArgsV.back())
 489       return nullptr;
 490   }
 491
 492   return Builder->CreateCall(CalleeF, ArgsV, "calltmp");
 493 }
 494
 495 Function *PrototypeAST::codegen() {
 496   // Make the function type:  double(double,double) etc.
 497   std::vector<Type *> Doubles(Args.size(), Type::getDoubleTy(*TheContext));
 498   FunctionType *FT =
 499       FunctionType::get(Type::getDoubleTy(*TheContext), Doubles, false);
 500
 501   Function *F =
 502       Function::Create(FT, Function::ExternalLinkage, Name, TheModule.get());
 503
 504   // Set names for all arguments.
 505   unsigned Idx = 0;
 506   for (auto &Arg : F->args())
 507     Arg.setName(Args[Idx++]);
 508
 509   return F;
 510 }
 511
 512 Function *FunctionAST::codegen() {
 513   // Transfer ownership of the prototype to the FunctionProtos map, but keep a
 514   // reference to it for use below.
 515   auto &P = *Proto;
 516   FunctionProtos[Proto->getName()] = std::move(Proto);
 517   Function *TheFunction = getFunction(P.getName());
 518   if (!TheFunction)
 519     return nullptr;
 520
 521   // Create a new basic block to start insertion into.
 522   BasicBlock *BB = BasicBlock::Create(*TheContext, "entry", TheFunction);
 523   Builder->SetInsertPoint(BB);
 524
 525   // Record the function arguments in the NamedValues map.
 526   NamedValues.clear();
 527   for (auto &Arg : TheFunction->args())
 528     NamedValues[std::string(Arg.getName())] = &Arg;
 529
 530   if (Value *RetVal = Body->codegen()) {
 531     // Finish off the function.
 532     Builder->CreateRet(RetVal);
 533
 534     // Validate the generated code, checking for consistency.
 535     verifyFunction(*TheFunction);
 536
 537     // Run the optimizer on the function.
 538     TheFPM->run(*TheFunction);
 539
 540     return TheFunction;
 541   }
 542
 543   // Error reading body, remove function.
 544   TheFunction->eraseFromParent();
 545   return nullptr;
 546 }
 547
 548 //===----------------------------------------------------------------------===//
 549 // Top-Level parsing and JIT Driver
 550 //===----------------------------------------------------------------------===//
 551
 552 static void InitializeModuleAndPassManager() {
 553   // Open a new context and module.
 554   TheContext = std::make_unique<LLVMContext>();
 555   TheModule = std::make_unique<Module>("my cool jit", *TheContext);
 556   TheModule->setDataLayout(TheJIT->getDataLayout());
 557
 558   // Create a new builder for the module.
 559   Builder = std::make_unique<IRBuilder<>>(*TheContext);
 560
 561   // Create a new pass manager attached to it.
 562   TheFPM = std::make_unique<legacy::FunctionPassManager>(TheModule.get());
 563
 564   // Do simple "peephole" optimizations and bit-twiddling optzns.
 565   TheFPM->add(createInstructionCombiningPass());
 566   // Reassociate expressions.
 567   TheFPM->add(createReassociatePass());
 568   // Eliminate Common SubExpressions.
 569   TheFPM->add(createGVNPass());
 570   // Simplify the control flow graph (deleting unreachable blocks, etc).
 571   TheFPM->add(createCFGSimplificationPass());
 572
 573   TheFPM->doInitialization();
 574 }
 575
 576 static void HandleDefinition() {
 577   if (auto FnAST = ParseDefinition()) {
 578     if (auto *FnIR = FnAST->codegen()) {
 579       fprintf(stderr, "Read function definition:");
 580       FnIR->print(errs());
 581       fprintf(stderr, "\n");
 582       ExitOnErr(TheJIT->addModule(
 583           ThreadSafeModule(std::move(TheModule), std::move(TheContext))));
 584       InitializeModuleAndPassManager();
 585     }
 586   } else {
 587     // Skip token for error recovery.
 588     getNextToken();
 589   }
 590 }
 591
 592 static void HandleExtern() {
 593   if (auto ProtoAST = ParseExtern()) {
 594     if (auto *FnIR = ProtoAST->codegen()) {
 595       fprintf(stderr, "Read extern: ");
 596       FnIR->print(errs());
 597       fprintf(stderr, "\n");
 598       FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
 599     }
 600   } else {
 601     // Skip token for error recovery.
 602     getNextToken();
 603   }
 604 }
 605
 606 static void HandleTopLevelExpression() {
 607   // Evaluate a top-level expression into an anonymous function.
 608   if (auto FnAST = ParseTopLevelExpr()) {
 609     if (FnAST->codegen()) {
 610       // Create a ResourceTracker to track JIT'd memory allocated to our
 611       // anonymous expression -- that way we can free it after executing.
 612       auto RT = TheJIT->getMainJITDylib().createResourceTracker();
 613
 614       auto TSM = ThreadSafeModule(std::move(TheModule), std::move(TheContext));
 615       ExitOnErr(TheJIT->addModule(std::move(TSM), RT));
 616       InitializeModuleAndPassManager();
 617
 618       // Search the JIT for the __anon_expr symbol.
 619       auto ExprSymbol = ExitOnErr(TheJIT->lookup("__anon_expr"));
 620
 621       // Get the symbol's address and cast it to the right type (takes no
 622       // arguments, returns a double) so we can call it as a native function.
 623       double (*FP)() = (double (*)())(intptr_t)ExprSymbol.getAddress();
 624       fprintf(stderr, "Evaluated to %f\n", FP());
 625
 626       // Delete the anonymous expression module from the JIT.
 627       ExitOnErr(RT->remove());
 628     }
 629   } else {
 630     // Skip token for error recovery.
 631     getNextToken();
 632   }
 633 }
 634
 635 /// top ::= definition | external | expression | ';'
 636 static void MainLoop() {
 637   while (true) {
 638     fprintf(stderr, "ready> ");
 639     switch (CurTok) {
 640     case tok_eof:
 641       return;
 642     case ';': // ignore top-level semicolons.
 643       getNextToken();
 644       break;
 645     case tok_def:
 646       HandleDefinition();
 647       break;
 648     case tok_extern:
 649       HandleExtern();
 650       break;
 651     default:
 652       HandleTopLevelExpression();
 653       break;
 654     }
 655   }
 656 }
 657
 658 //===----------------------------------------------------------------------===//
 659 // "Library" functions that can be "extern'd" from user code.
 660 //===----------------------------------------------------------------------===//
 661
 662 #ifdef _WIN32
 663 #define DLLEXPORT __declspec(dllexport)
 664 #else
 665 #define DLLEXPORT
 666 #endif
 667
 668 /// putchard - putchar that takes a double and returns 0.
 669 extern "C" DLLEXPORT double putchard(double X) {
 670   fputc((char)X, stderr);
 671   return 0;
 672 }
 673
 674 /// printd - printf that takes a double prints it as "%f\n", returning 0.
 675 extern "C" DLLEXPORT double printd(double X) {
 676   fprintf(stderr, "%f\n", X);
 677   return 0;
 678 }
 679
 680 //===----------------------------------------------------------------------===//
 681 // Main driver code.
 682 //===----------------------------------------------------------------------===//
 683
 684 int main() {
 685   InitializeNativeTarget();
 686   InitializeNativeTargetAsmPrinter();
 687   InitializeNativeTargetAsmParser();
 688
 689   // Install standard binary operators.
 690   // 1 is lowest precedence.
 691   BinopPrecedence['<'] = 10;
 692   BinopPrecedence['+'] = 20;
 693   BinopPrecedence['-'] = 20;
 694   BinopPrecedence['*'] = 40; // highest.
 695
 696   // Prime the first token.
 697   fprintf(stderr, "ready> ");
 698   getNextToken();
 699
 700   TheJIT = ExitOnErr(KaleidoscopeJIT::Create());
 701
 702   InitializeModuleAndPassManager();
 703
 704   // Run the main "interpreter loop" now.
 705   MainLoop();
 706
 707   return 0;
 708 }