tools/llvm-diff/DifferenceEngine.cpp

   1 //===-- DifferenceEngine.cpp - Structural function/module comparison ------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This header defines the implementation of the LLVM difference
  11 // engine, which structurally compares global values within a module.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "DifferenceEngine.h"
  16 #include "llvm/ADT/DenseMap.h"
  17 #include "llvm/ADT/DenseSet.h"
  18 #include "llvm/ADT/SmallVector.h"
  19 #include "llvm/ADT/StringSet.h"
  20 #include "llvm/IR/CFG.h"
  21 #include "llvm/IR/CallSite.h"
  22 #include "llvm/IR/Constants.h"
  23 #include "llvm/IR/Function.h"
  24 #include "llvm/IR/Instructions.h"
  25 #include "llvm/IR/Module.h"
  26 #include "llvm/Support/ErrorHandling.h"
  27 #include "llvm/Support/raw_ostream.h"
  28 #include "llvm/Support/type_traits.h"
  29 #include <utility>
  30
  31 using namespace llvm;
  32
  33 namespace {
  34
  35 /// A priority queue, implemented as a heap.
  36 template <class T, class Sorter, unsigned InlineCapacity>
  37 class PriorityQueue {
  38   Sorter Precedes;
  39   llvm::SmallVector<T, InlineCapacity> Storage;
  40
  41 public:
  42   PriorityQueue(const Sorter &Precedes) : Precedes(Precedes) {}
  43
  44   /// Checks whether the heap is empty.
  45   bool empty() const { return Storage.empty(); }
  46
  47   /// Insert a new value on the heap.
  48   void insert(const T &V) {
  49     unsigned Index = Storage.size();
  50     Storage.push_back(V);
  51     if (Index == 0) return;
  52
  53     T *data = Storage.data();
  54     while (true) {
  55       unsigned Target = (Index + 1) / 2 - 1;
  56       if (!Precedes(data[Index], data[Target])) return;
  57       std::swap(data[Index], data[Target]);
  58       if (Target == 0) return;
  59       Index = Target;
  60     }
  61   }
  62
  63   /// Remove the minimum value in the heap.  Only valid on a non-empty heap.
  64   T remove_min() {
  65     assert(!empty());
  66     T tmp = Storage[0];
  67
  68     unsigned NewSize = Storage.size() - 1;
  69     if (NewSize) {
  70       // Move the slot at the end to the beginning.
  71       if (isPodLike<T>::value)
  72         Storage[0] = Storage[NewSize];
  73       else
  74         std::swap(Storage[0], Storage[NewSize]);
  75
  76       // Bubble the root up as necessary.
  77       unsigned Index = 0;
  78       while (true) {
  79         // With a 1-based index, the children would be Index*2 and Index*2+1.
  80         unsigned R = (Index + 1) * 2;
  81         unsigned L = R - 1;
  82
  83         // If R is out of bounds, we're done after this in any case.
  84         if (R >= NewSize) {
  85           // If L is also out of bounds, we're done immediately.
  86           if (L >= NewSize) break;
  87
  88           // Otherwise, test whether we should swap L and Index.
  89           if (Precedes(Storage[L], Storage[Index]))
  90             std::swap(Storage[L], Storage[Index]);
  91           break;
  92         }
  93
  94         // Otherwise, we need to compare with the smaller of L and R.
  95         // Prefer R because it's closer to the end of the array.
  96         unsigned IndexToTest = (Precedes(Storage[L], Storage[R]) ? L : R);
  97
  98         // If Index is >= the min of L and R, then heap ordering is restored.
  99         if (!Precedes(Storage[IndexToTest], Storage[Index]))
 100           break;
 101
 102         // Otherwise, keep bubbling up.
 103         std::swap(Storage[IndexToTest], Storage[Index]);
 104         Index = IndexToTest;
 105       }
 106     }
 107     Storage.pop_back();
 108
 109     return tmp;
 110   }
 111 };
 112
 113 /// A function-scope difference engine.
 114 class FunctionDifferenceEngine {
 115   DifferenceEngine &Engine;
 116
 117   /// The current mapping from old local values to new local values.
 118   DenseMap<Value*, Value*> Values;
 119
 120   /// The current mapping from old blocks to new blocks.
 121   DenseMap<BasicBlock*, BasicBlock*> Blocks;
 122
 123   DenseSet<std::pair<Value*, Value*> > TentativeValues;
 124
 125   unsigned getUnprocPredCount(BasicBlock *Block) const {
 126     unsigned Count = 0;
 127     for (pred_iterator I = pred_begin(Block), E = pred_end(Block); I != E; ++I)
 128       if (!Blocks.count(*I)) Count++;
 129     return Count;
 130   }
 131
 132   typedef std::pair<BasicBlock*, BasicBlock*> BlockPair;
 133
 134   /// A type which sorts a priority queue by the number of unprocessed
 135   /// predecessor blocks it has remaining.
 136   ///
 137   /// This is actually really expensive to calculate.
 138   struct QueueSorter {
 139     const FunctionDifferenceEngine &fde;
 140     explicit QueueSorter(const FunctionDifferenceEngine &fde) : fde(fde) {}
 141
 142     bool operator()(const BlockPair &Old, const BlockPair &New) {
 143       return fde.getUnprocPredCount(Old.first)
 144            < fde.getUnprocPredCount(New.first);
 145     }
 146   };
 147
 148   /// A queue of unified blocks to process.
 149   PriorityQueue<BlockPair, QueueSorter, 20> Queue;
 150
 151   /// Try to unify the given two blocks.  Enqueues them for processing
 152   /// if they haven't already been processed.
 153   ///
 154   /// Returns true if there was a problem unifying them.
 155   bool tryUnify(BasicBlock *L, BasicBlock *R) {
 156     BasicBlock *&Ref = Blocks[L];
 157
 158     if (Ref) {
 159       if (Ref == R) return false;
 160
 161       Engine.logf("successor %l cannot be equivalent to %r; "
 162                   "it's already equivalent to %r")
 163         << L << R << Ref;
 164       return true;
 165     }
 166
 167     Ref = R;
 168     Queue.insert(BlockPair(L, R));
 169     return false;
 170   }
 171
 172   /// Unifies two instructions, given that they're known not to have
 173   /// structural differences.
 174   void unify(Instruction *L, Instruction *R) {
 175     DifferenceEngine::Context C(Engine, L, R);
 176
 177     bool Result = diff(L, R, true, true);
 178     assert(!Result && "structural differences second time around?");
 179     (void) Result;
 180     if (!L->use_empty())
 181       Values[L] = R;
 182   }
 183
 184   void processQueue() {
 185     while (!Queue.empty()) {
 186       BlockPair Pair = Queue.remove_min();
 187       diff(Pair.first, Pair.second);
 188     }
 189   }
 190
 191   void diff(BasicBlock *L, BasicBlock *R) {
 192     DifferenceEngine::Context C(Engine, L, R);
 193
 194     BasicBlock::iterator LI = L->begin(), LE = L->end();
 195     BasicBlock::iterator RI = R->begin();
 196
 197     do {
 198       assert(LI != LE && RI != R->end());
 199       Instruction *LeftI = &*LI, *RightI = &*RI;
 200
 201       // If the instructions differ, start the more sophisticated diff
 202       // algorithm at the start of the block.
 203       if (diff(LeftI, RightI, false, false)) {
 204         TentativeValues.clear();
 205         return runBlockDiff(L->begin(), R->begin());
 206       }
 207
 208       // Otherwise, tentatively unify them.
 209       if (!LeftI->use_empty())
 210         TentativeValues.insert(std::make_pair(LeftI, RightI));
 211
 212       ++LI;
 213       ++RI;
 214     } while (LI != LE); // This is sufficient: we can't get equality of
 215                         // terminators if there are residual instructions.
 216
 217     // Unify everything in the block, non-tentatively this time.
 218     TentativeValues.clear();
 219     for (LI = L->begin(), RI = R->begin(); LI != LE; ++LI, ++RI)
 220       unify(&*LI, &*RI);
 221   }
 222
 223   bool matchForBlockDiff(Instruction *L, Instruction *R);
 224   void runBlockDiff(BasicBlock::iterator LI, BasicBlock::iterator RI);
 225
 226   bool diffCallSites(CallSite L, CallSite R, bool Complain) {
 227     // FIXME: call attributes
 228     if (!equivalentAsOperands(L.getCalledValue(), R.getCalledValue())) {
 229       if (Complain) Engine.log("called functions differ");
 230       return true;
 231     }
 232     if (L.arg_size() != R.arg_size()) {
 233       if (Complain) Engine.log("argument counts differ");
 234       return true;
 235     }
 236     for (unsigned I = 0, E = L.arg_size(); I != E; ++I)
 237       if (!equivalentAsOperands(L.getArgument(I), R.getArgument(I))) {
 238         if (Complain)
 239           Engine.logf("arguments %l and %r differ")
 240             << L.getArgument(I) << R.getArgument(I);
 241         return true;
 242       }
 243     return false;
 244   }
 245
 246   bool diff(Instruction *L, Instruction *R, bool Complain, bool TryUnify) {
 247     // FIXME: metadata (if Complain is set)
 248
 249     // Different opcodes always imply different operations.
 250     if (L->getOpcode() != R->getOpcode()) {
 251       if (Complain) Engine.log("different instruction types");
 252       return true;
 253     }
 254
 255     if (isa<CmpInst>(L)) {
 256       if (cast<CmpInst>(L)->getPredicate()
 257             != cast<CmpInst>(R)->getPredicate()) {
 258         if (Complain) Engine.log("different predicates");
 259         return true;
 260       }
 261     } else if (isa<CallInst>(L)) {
 262       return diffCallSites(CallSite(L), CallSite(R), Complain);
 263     } else if (isa<PHINode>(L)) {
 264       // FIXME: implement.
 265
 266       // This is really weird;  type uniquing is broken?
 267       if (L->getType() != R->getType()) {
 268         if (!L->getType()->isPointerTy() || !R->getType()->isPointerTy()) {
 269           if (Complain) Engine.log("different phi types");
 270           return true;
 271         }
 272       }
 273       return false;
 274
 275     // Terminators.
 276     } else if (isa<InvokeInst>(L)) {
 277       InvokeInst *LI = cast<InvokeInst>(L);
 278       InvokeInst *RI = cast<InvokeInst>(R);
 279       if (diffCallSites(CallSite(LI), CallSite(RI), Complain))
 280         return true;
 281
 282       if (TryUnify) {
 283         tryUnify(LI->getNormalDest(), RI->getNormalDest());
 284         tryUnify(LI->getUnwindDest(), RI->getUnwindDest());
 285       }
 286       return false;
 287
 288     } else if (isa<BranchInst>(L)) {
 289       BranchInst *LI = cast<BranchInst>(L);
 290       BranchInst *RI = cast<BranchInst>(R);
 291       if (LI->isConditional() != RI->isConditional()) {
 292         if (Complain) Engine.log("branch conditionality differs");
 293         return true;
 294       }
 295
 296       if (LI->isConditional()) {
 297         if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) {
 298           if (Complain) Engine.log("branch conditions differ");
 299           return true;
 300         }
 301         if (TryUnify) tryUnify(LI->getSuccessor(1), RI->getSuccessor(1));
 302       }
 303       if (TryUnify) tryUnify(LI->getSuccessor(0), RI->getSuccessor(0));
 304       return false;
 305
 306     } else if (isa<SwitchInst>(L)) {
 307       SwitchInst *LI = cast<SwitchInst>(L);
 308       SwitchInst *RI = cast<SwitchInst>(R);
 309       if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) {
 310         if (Complain) Engine.log("switch conditions differ");
 311         return true;
 312       }
 313       if (TryUnify) tryUnify(LI->getDefaultDest(), RI->getDefaultDest());
 314
 315       bool Difference = false;
 316
 317       DenseMap<ConstantInt*,BasicBlock*> LCases;
 318       for (auto Case : LI->cases())
 319         LCases[Case.getCaseValue()] = Case.getCaseSuccessor();
 320
 321       for (auto Case : RI->cases()) {
 322         ConstantInt *CaseValue = Case.getCaseValue();
 323         BasicBlock *LCase = LCases[CaseValue];
 324         if (LCase) {
 325           if (TryUnify)
 326             tryUnify(LCase, Case.getCaseSuccessor());
 327           LCases.erase(CaseValue);
 328         } else if (Complain || !Difference) {
 329           if (Complain)
 330             Engine.logf("right switch has extra case %r") << CaseValue;
 331           Difference = true;
 332         }
 333       }
 334       if (!Difference)
 335         for (DenseMap<ConstantInt*,BasicBlock*>::iterator
 336                I = LCases.begin(), E = LCases.end(); I != E; ++I) {
 337           if (Complain)
 338             Engine.logf("left switch has extra case %l") << I->first;
 339           Difference = true;
 340         }
 341       return Difference;
 342     } else if (isa<UnreachableInst>(L)) {
 343       return false;
 344     }
 345
 346     if (L->getNumOperands() != R->getNumOperands()) {
 347       if (Complain) Engine.log("instructions have different operand counts");
 348       return true;
 349     }
 350
 351     for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I) {
 352       Value *LO = L->getOperand(I), *RO = R->getOperand(I);
 353       if (!equivalentAsOperands(LO, RO)) {
 354         if (Complain) Engine.logf("operands %l and %r differ") << LO << RO;
 355         return true;
 356       }
 357     }
 358
 359     return false;
 360   }
 361
 362   bool equivalentAsOperands(Constant *L, Constant *R) {
 363     // Use equality as a preliminary filter.
 364     if (L == R)
 365       return true;
 366
 367     if (L->getValueID() != R->getValueID())
 368       return false;
 369
 370     // Ask the engine about global values.
 371     if (isa<GlobalValue>(L))
 372       return Engine.equivalentAsOperands(cast<GlobalValue>(L),
 373                                          cast<GlobalValue>(R));
 374
 375     // Compare constant expressions structurally.
 376     if (isa<ConstantExpr>(L))
 377       return equivalentAsOperands(cast<ConstantExpr>(L),
 378                                   cast<ConstantExpr>(R));
 379
 380     // Nulls of the "same type" don't always actually have the same
 381     // type; I don't know why.  Just white-list them.
 382     if (isa<ConstantPointerNull>(L))
 383       return true;
 384
 385     // Block addresses only match if we've already encountered the
 386     // block.  FIXME: tentative matches?
 387     if (isa<BlockAddress>(L))
 388       return Blocks[cast<BlockAddress>(L)->getBasicBlock()]
 389                  == cast<BlockAddress>(R)->getBasicBlock();
 390
 391     return false;
 392   }
 393
 394   bool equivalentAsOperands(ConstantExpr *L, ConstantExpr *R) {
 395     if (L == R)
 396       return true;
 397     if (L->getOpcode() != R->getOpcode())
 398       return false;
 399
 400     switch (L->getOpcode()) {
 401     case Instruction::ICmp:
 402     case Instruction::FCmp:
 403       if (L->getPredicate() != R->getPredicate())
 404         return false;
 405       break;
 406
 407     case Instruction::GetElementPtr:
 408       // FIXME: inbounds?
 409       break;
 410
 411     default:
 412       break;
 413     }
 414
 415     if (L->getNumOperands() != R->getNumOperands())
 416       return false;
 417
 418     for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I)
 419       if (!equivalentAsOperands(L->getOperand(I), R->getOperand(I)))
 420         return false;
 421
 422     return true;
 423   }
 424
 425   bool equivalentAsOperands(Value *L, Value *R) {
 426     // Fall out if the values have different kind.
 427     // This possibly shouldn't take priority over oracles.
 428     if (L->getValueID() != R->getValueID())
 429       return false;
 430
 431     // Value subtypes:  Argument, Constant, Instruction, BasicBlock,
 432     //                  InlineAsm, MDNode, MDString, PseudoSourceValue
 433
 434     if (isa<Constant>(L))
 435       return equivalentAsOperands(cast<Constant>(L), cast<Constant>(R));
 436
 437     if (isa<Instruction>(L))
 438       return Values[L] == R || TentativeValues.count(std::make_pair(L, R));
 439
 440     if (isa<Argument>(L))
 441       return Values[L] == R;
 442
 443     if (isa<BasicBlock>(L))
 444       return Blocks[cast<BasicBlock>(L)] != R;
 445
 446     // Pretend everything else is identical.
 447     return true;
 448   }
 449
 450   // Avoid a gcc warning about accessing 'this' in an initializer.
 451   FunctionDifferenceEngine *this_() { return this; }
 452
 453 public:
 454   FunctionDifferenceEngine(DifferenceEngine &Engine) :
 455     Engine(Engine), Queue(QueueSorter(*this_())) {}
 456
 457   void diff(Function *L, Function *R) {
 458     if (L->arg_size() != R->arg_size())
 459       Engine.log("different argument counts");
 460
 461     // Map the arguments.
 462     for (Function::arg_iterator
 463            LI = L->arg_begin(), LE = L->arg_end(),
 464            RI = R->arg_begin(), RE = R->arg_end();
 465          LI != LE && RI != RE; ++LI, ++RI)
 466       Values[&*LI] = &*RI;
 467
 468     tryUnify(&*L->begin(), &*R->begin());
 469     processQueue();
 470   }
 471 };
 472
 473 struct DiffEntry {
 474   DiffEntry() : Cost(0) {}
 475
 476   unsigned Cost;
 477   llvm::SmallVector<char, 8> Path; // actually of DifferenceEngine::DiffChange
 478 };
 479
 480 bool FunctionDifferenceEngine::matchForBlockDiff(Instruction *L,
 481                                                  Instruction *R) {
 482   return !diff(L, R, false, false);
 483 }
 484
 485 void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart,
 486                                             BasicBlock::iterator RStart) {
 487   BasicBlock::iterator LE = LStart->getParent()->end();
 488   BasicBlock::iterator RE = RStart->getParent()->end();
 489
 490   unsigned NL = std::distance(LStart, LE);
 491
 492   SmallVector<DiffEntry, 20> Paths1(NL+1);
 493   SmallVector<DiffEntry, 20> Paths2(NL+1);
 494
 495   DiffEntry *Cur = Paths1.data();
 496   DiffEntry *Next = Paths2.data();
 497
 498   const unsigned LeftCost = 2;
 499   const unsigned RightCost = 2;
 500   const unsigned MatchCost = 0;
 501
 502   assert(TentativeValues.empty());
 503
 504   // Initialize the first column.
 505   for (unsigned I = 0; I != NL+1; ++I) {
 506     Cur[I].Cost = I * LeftCost;
 507     for (unsigned J = 0; J != I; ++J)
 508       Cur[I].Path.push_back(DC_left);
 509   }
 510
 511   for (BasicBlock::iterator RI = RStart; RI != RE; ++RI) {
 512     // Initialize the first row.
 513     Next[0] = Cur[0];
 514     Next[0].Cost += RightCost;
 515     Next[0].Path.push_back(DC_right);
 516
 517     unsigned Index = 1;
 518     for (BasicBlock::iterator LI = LStart; LI != LE; ++LI, ++Index) {
 519       if (matchForBlockDiff(&*LI, &*RI)) {
 520         Next[Index] = Cur[Index-1];
 521         Next[Index].Cost += MatchCost;
 522         Next[Index].Path.push_back(DC_match);
 523         TentativeValues.insert(std::make_pair(&*LI, &*RI));
 524       } else if (Next[Index-1].Cost <= Cur[Index].Cost) {
 525         Next[Index] = Next[Index-1];
 526         Next[Index].Cost += LeftCost;
 527         Next[Index].Path.push_back(DC_left);
 528       } else {
 529         Next[Index] = Cur[Index];
 530         Next[Index].Cost += RightCost;
 531         Next[Index].Path.push_back(DC_right);
 532       }
 533     }
 534
 535     std::swap(Cur, Next);
 536   }
 537
 538   // We don't need the tentative values anymore; everything from here
 539   // on out should be non-tentative.
 540   TentativeValues.clear();
 541
 542   SmallVectorImpl<char> &Path = Cur[NL].Path;
 543   BasicBlock::iterator LI = LStart, RI = RStart;
 544
 545   DiffLogBuilder Diff(Engine.getConsumer());
 546
 547   // Drop trailing matches.
 548   while (Path.back() == DC_match)
 549     Path.pop_back();
 550
 551   // Skip leading matches.
 552   SmallVectorImpl<char>::iterator
 553     PI = Path.begin(), PE = Path.end();
 554   while (PI != PE && *PI == DC_match) {
 555     unify(&*LI, &*RI);
 556     ++PI;
 557     ++LI;
 558     ++RI;
 559   }
 560
 561   for (; PI != PE; ++PI) {
 562     switch (static_cast<DiffChange>(*PI)) {
 563     case DC_match:
 564       assert(LI != LE && RI != RE);
 565       {
 566         Instruction *L = &*LI, *R = &*RI;
 567         unify(L, R);
 568         Diff.addMatch(L, R);
 569       }
 570       ++LI; ++RI;
 571       break;
 572
 573     case DC_left:
 574       assert(LI != LE);
 575       Diff.addLeft(&*LI);
 576       ++LI;
 577       break;
 578
 579     case DC_right:
 580       assert(RI != RE);
 581       Diff.addRight(&*RI);
 582       ++RI;
 583       break;
 584     }
 585   }
 586
 587   // Finishing unifying and complaining about the tails of the block,
 588   // which should be matches all the way through.
 589   while (LI != LE) {
 590     assert(RI != RE);
 591     unify(&*LI, &*RI);
 592     ++LI;
 593     ++RI;
 594   }
 595
 596   // If the terminators have different kinds, but one is an invoke and the
 597   // other is an unconditional branch immediately following a call, unify
 598   // the results and the destinations.
 599   TerminatorInst *LTerm = LStart->getParent()->getTerminator();
 600   TerminatorInst *RTerm = RStart->getParent()->getTerminator();
 601   if (isa<BranchInst>(LTerm) && isa<InvokeInst>(RTerm)) {
 602     if (cast<BranchInst>(LTerm)->isConditional()) return;
 603     BasicBlock::iterator I = LTerm->getIterator();
 604     if (I == LStart->getParent()->begin()) return;
 605     --I;
 606     if (!isa<CallInst>(*I)) return;
 607     CallInst *LCall = cast<CallInst>(&*I);
 608     InvokeInst *RInvoke = cast<InvokeInst>(RTerm);
 609     if (!equivalentAsOperands(LCall->getCalledValue(), RInvoke->getCalledValue()))
 610       return;
 611     if (!LCall->use_empty())
 612       Values[LCall] = RInvoke;
 613     tryUnify(LTerm->getSuccessor(0), RInvoke->getNormalDest());
 614   } else if (isa<InvokeInst>(LTerm) && isa<BranchInst>(RTerm)) {
 615     if (cast<BranchInst>(RTerm)->isConditional()) return;
 616     BasicBlock::iterator I = RTerm->getIterator();
 617     if (I == RStart->getParent()->begin()) return;
 618     --I;
 619     if (!isa<CallInst>(*I)) return;
 620     CallInst *RCall = cast<CallInst>(I);
 621     InvokeInst *LInvoke = cast<InvokeInst>(LTerm);
 622     if (!equivalentAsOperands(LInvoke->getCalledValue(), RCall->getCalledValue()))
 623       return;
 624     if (!LInvoke->use_empty())
 625       Values[LInvoke] = RCall;
 626     tryUnify(LInvoke->getNormalDest(), RTerm->getSuccessor(0));
 627   }
 628 }
 629
 630 }
 631
 632 void DifferenceEngine::Oracle::anchor() { }
 633
 634 void DifferenceEngine::diff(Function *L, Function *R) {
 635   Context C(*this, L, R);
 636
 637   // FIXME: types
 638   // FIXME: attributes and CC
 639   // FIXME: parameter attributes
 640
 641   // If both are declarations, we're done.
 642   if (L->empty() && R->empty())
 643     return;
 644   else if (L->empty())
 645     log("left function is declaration, right function is definition");
 646   else if (R->empty())
 647     log("right function is declaration, left function is definition");
 648   else
 649     FunctionDifferenceEngine(*this).diff(L, R);
 650 }
 651
 652 void DifferenceEngine::diff(Module *L, Module *R) {
 653   StringSet<> LNames;
 654   SmallVector<std::pair<Function*,Function*>, 20> Queue;
 655
 656   for (Module::iterator I = L->begin(), E = L->end(); I != E; ++I) {
 657     Function *LFn = &*I;
 658     LNames.insert(LFn->getName());
 659
 660     if (Function *RFn = R->getFunction(LFn->getName()))
 661       Queue.push_back(std::make_pair(LFn, RFn));
 662     else
 663       logf("function %l exists only in left module") << LFn;
 664   }
 665
 666   for (Module::iterator I = R->begin(), E = R->end(); I != E; ++I) {
 667     Function *RFn = &*I;
 668     if (!LNames.count(RFn->getName()))
 669       logf("function %r exists only in right module") << RFn;
 670   }
 671
 672   for (SmallVectorImpl<std::pair<Function*,Function*> >::iterator
 673          I = Queue.begin(), E = Queue.end(); I != E; ++I)
 674     diff(I->first, I->second);
 675 }
 676
 677 bool DifferenceEngine::equivalentAsOperands(GlobalValue *L, GlobalValue *R) {
 678   if (globalValueOracle) return (*globalValueOracle)(L, R);
 679   return L->getName() == R->getName();
 680 }