tools/llvm-diff/DifferenceEngine.cpp

   1 //===-- DifferenceEngine.cpp - Structural function/module comparison ------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This header defines the implementation of the LLVM difference
  10 // engine, which structurally compares global values within a module.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "DifferenceEngine.h"
  15 #include "llvm/ADT/DenseMap.h"
  16 #include "llvm/ADT/DenseSet.h"
  17 #include "llvm/ADT/SmallVector.h"
  18 #include "llvm/ADT/StringSet.h"
  19 #include "llvm/IR/CFG.h"
  20 #include "llvm/IR/CallSite.h"
  21 #include "llvm/IR/Constants.h"
  22 #include "llvm/IR/Function.h"
  23 #include "llvm/IR/Instructions.h"
  24 #include "llvm/IR/Module.h"
  25 #include "llvm/Support/ErrorHandling.h"
  26 #include "llvm/Support/raw_ostream.h"
  27 #include "llvm/Support/type_traits.h"
  28 #include <utility>
  29
  30 using namespace llvm;
  31
  32 namespace {
  33
  34 /// A priority queue, implemented as a heap.
  35 template <class T, class Sorter, unsigned InlineCapacity>
  36 class PriorityQueue {
  37   Sorter Precedes;
  38   llvm::SmallVector<T, InlineCapacity> Storage;
  39
  40 public:
  41   PriorityQueue(const Sorter &Precedes) : Precedes(Precedes) {}
  42
  43   /// Checks whether the heap is empty.
  44   bool empty() const { return Storage.empty(); }
  45
  46   /// Insert a new value on the heap.
  47   void insert(const T &V) {
  48     unsigned Index = Storage.size();
  49     Storage.push_back(V);
  50     if (Index == 0) return;
  51
  52     T *data = Storage.data();
  53     while (true) {
  54       unsigned Target = (Index + 1) / 2 - 1;
  55       if (!Precedes(data[Index], data[Target])) return;
  56       std::swap(data[Index], data[Target]);
  57       if (Target == 0) return;
  58       Index = Target;
  59     }
  60   }
  61
  62   /// Remove the minimum value in the heap.  Only valid on a non-empty heap.
  63   T remove_min() {
  64     assert(!empty());
  65     T tmp = Storage[0];
  66
  67     unsigned NewSize = Storage.size() - 1;
  68     if (NewSize) {
  69       // Move the slot at the end to the beginning.
  70       if (is_trivially_copyable<T>::value)
  71         Storage[0] = Storage[NewSize];
  72       else
  73         std::swap(Storage[0], Storage[NewSize]);
  74
  75       // Bubble the root up as necessary.
  76       unsigned Index = 0;
  77       while (true) {
  78         // With a 1-based index, the children would be Index*2 and Index*2+1.
  79         unsigned R = (Index + 1) * 2;
  80         unsigned L = R - 1;
  81
  82         // If R is out of bounds, we're done after this in any case.
  83         if (R >= NewSize) {
  84           // If L is also out of bounds, we're done immediately.
  85           if (L >= NewSize) break;
  86
  87           // Otherwise, test whether we should swap L and Index.
  88           if (Precedes(Storage[L], Storage[Index]))
  89             std::swap(Storage[L], Storage[Index]);
  90           break;
  91         }
  92
  93         // Otherwise, we need to compare with the smaller of L and R.
  94         // Prefer R because it's closer to the end of the array.
  95         unsigned IndexToTest = (Precedes(Storage[L], Storage[R]) ? L : R);
  96
  97         // If Index is >= the min of L and R, then heap ordering is restored.
  98         if (!Precedes(Storage[IndexToTest], Storage[Index]))
  99           break;
 100
 101         // Otherwise, keep bubbling up.
 102         std::swap(Storage[IndexToTest], Storage[Index]);
 103         Index = IndexToTest;
 104       }
 105     }
 106     Storage.pop_back();
 107
 108     return tmp;
 109   }
 110 };
 111
 112 /// A function-scope difference engine.
 113 class FunctionDifferenceEngine {
 114   DifferenceEngine &Engine;
 115
 116   /// The current mapping from old local values to new local values.
 117   DenseMap<Value*, Value*> Values;
 118
 119   /// The current mapping from old blocks to new blocks.
 120   DenseMap<BasicBlock*, BasicBlock*> Blocks;
 121
 122   DenseSet<std::pair<Value*, Value*> > TentativeValues;
 123
 124   unsigned getUnprocPredCount(BasicBlock *Block) const {
 125     unsigned Count = 0;
 126     for (pred_iterator I = pred_begin(Block), E = pred_end(Block); I != E; ++I)
 127       if (!Blocks.count(*I)) Count++;
 128     return Count;
 129   }
 130
 131   typedef std::pair<BasicBlock*, BasicBlock*> BlockPair;
 132
 133   /// A type which sorts a priority queue by the number of unprocessed
 134   /// predecessor blocks it has remaining.
 135   ///
 136   /// This is actually really expensive to calculate.
 137   struct QueueSorter {
 138     const FunctionDifferenceEngine &fde;
 139     explicit QueueSorter(const FunctionDifferenceEngine &fde) : fde(fde) {}
 140
 141     bool operator()(const BlockPair &Old, const BlockPair &New) {
 142       return fde.getUnprocPredCount(Old.first)
 143            < fde.getUnprocPredCount(New.first);
 144     }
 145   };
 146
 147   /// A queue of unified blocks to process.
 148   PriorityQueue<BlockPair, QueueSorter, 20> Queue;
 149
 150   /// Try to unify the given two blocks.  Enqueues them for processing
 151   /// if they haven't already been processed.
 152   ///
 153   /// Returns true if there was a problem unifying them.
 154   bool tryUnify(BasicBlock *L, BasicBlock *R) {
 155     BasicBlock *&Ref = Blocks[L];
 156
 157     if (Ref) {
 158       if (Ref == R) return false;
 159
 160       Engine.logf("successor %l cannot be equivalent to %r; "
 161                   "it's already equivalent to %r")
 162         << L << R << Ref;
 163       return true;
 164     }
 165
 166     Ref = R;
 167     Queue.insert(BlockPair(L, R));
 168     return false;
 169   }
 170
 171   /// Unifies two instructions, given that they're known not to have
 172   /// structural differences.
 173   void unify(Instruction *L, Instruction *R) {
 174     DifferenceEngine::Context C(Engine, L, R);
 175
 176     bool Result = diff(L, R, true, true);
 177     assert(!Result && "structural differences second time around?");
 178     (void) Result;
 179     if (!L->use_empty())
 180       Values[L] = R;
 181   }
 182
 183   void processQueue() {
 184     while (!Queue.empty()) {
 185       BlockPair Pair = Queue.remove_min();
 186       diff(Pair.first, Pair.second);
 187     }
 188   }
 189
 190   void diff(BasicBlock *L, BasicBlock *R) {
 191     DifferenceEngine::Context C(Engine, L, R);
 192
 193     BasicBlock::iterator LI = L->begin(), LE = L->end();
 194     BasicBlock::iterator RI = R->begin();
 195
 196     do {
 197       assert(LI != LE && RI != R->end());
 198       Instruction *LeftI = &*LI, *RightI = &*RI;
 199
 200       // If the instructions differ, start the more sophisticated diff
 201       // algorithm at the start of the block.
 202       if (diff(LeftI, RightI, false, false)) {
 203         TentativeValues.clear();
 204         return runBlockDiff(L->begin(), R->begin());
 205       }
 206
 207       // Otherwise, tentatively unify them.
 208       if (!LeftI->use_empty())
 209         TentativeValues.insert(std::make_pair(LeftI, RightI));
 210
 211       ++LI;
 212       ++RI;
 213     } while (LI != LE); // This is sufficient: we can't get equality of
 214                         // terminators if there are residual instructions.
 215
 216     // Unify everything in the block, non-tentatively this time.
 217     TentativeValues.clear();
 218     for (LI = L->begin(), RI = R->begin(); LI != LE; ++LI, ++RI)
 219       unify(&*LI, &*RI);
 220   }
 221
 222   bool matchForBlockDiff(Instruction *L, Instruction *R);
 223   void runBlockDiff(BasicBlock::iterator LI, BasicBlock::iterator RI);
 224
 225   bool diffCallSites(CallSite L, CallSite R, bool Complain) {
 226     // FIXME: call attributes
 227     if (!equivalentAsOperands(L.getCalledValue(), R.getCalledValue())) {
 228       if (Complain) Engine.log("called functions differ");
 229       return true;
 230     }
 231     if (L.arg_size() != R.arg_size()) {
 232       if (Complain) Engine.log("argument counts differ");
 233       return true;
 234     }
 235     for (unsigned I = 0, E = L.arg_size(); I != E; ++I)
 236       if (!equivalentAsOperands(L.getArgument(I), R.getArgument(I))) {
 237         if (Complain)
 238           Engine.logf("arguments %l and %r differ")
 239             << L.getArgument(I) << R.getArgument(I);
 240         return true;
 241       }
 242     return false;
 243   }
 244
 245   bool diff(Instruction *L, Instruction *R, bool Complain, bool TryUnify) {
 246     // FIXME: metadata (if Complain is set)
 247
 248     // Different opcodes always imply different operations.
 249     if (L->getOpcode() != R->getOpcode()) {
 250       if (Complain) Engine.log("different instruction types");
 251       return true;
 252     }
 253
 254     if (isa<CmpInst>(L)) {
 255       if (cast<CmpInst>(L)->getPredicate()
 256             != cast<CmpInst>(R)->getPredicate()) {
 257         if (Complain) Engine.log("different predicates");
 258         return true;
 259       }
 260     } else if (isa<CallInst>(L)) {
 261       return diffCallSites(CallSite(L), CallSite(R), Complain);
 262     } else if (isa<PHINode>(L)) {
 263       // FIXME: implement.
 264
 265       // This is really weird;  type uniquing is broken?
 266       if (L->getType() != R->getType()) {
 267         if (!L->getType()->isPointerTy() || !R->getType()->isPointerTy()) {
 268           if (Complain) Engine.log("different phi types");
 269           return true;
 270         }
 271       }
 272       return false;
 273
 274     // Terminators.
 275     } else if (isa<InvokeInst>(L)) {
 276       InvokeInst *LI = cast<InvokeInst>(L);
 277       InvokeInst *RI = cast<InvokeInst>(R);
 278       if (diffCallSites(CallSite(LI), CallSite(RI), Complain))
 279         return true;
 280
 281       if (TryUnify) {
 282         tryUnify(LI->getNormalDest(), RI->getNormalDest());
 283         tryUnify(LI->getUnwindDest(), RI->getUnwindDest());
 284       }
 285       return false;
 286
 287     } else if (isa<BranchInst>(L)) {
 288       BranchInst *LI = cast<BranchInst>(L);
 289       BranchInst *RI = cast<BranchInst>(R);
 290       if (LI->isConditional() != RI->isConditional()) {
 291         if (Complain) Engine.log("branch conditionality differs");
 292         return true;
 293       }
 294
 295       if (LI->isConditional()) {
 296         if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) {
 297           if (Complain) Engine.log("branch conditions differ");
 298           return true;
 299         }
 300         if (TryUnify) tryUnify(LI->getSuccessor(1), RI->getSuccessor(1));
 301       }
 302       if (TryUnify) tryUnify(LI->getSuccessor(0), RI->getSuccessor(0));
 303       return false;
 304
 305     } else if (isa<IndirectBrInst>(L)) {
 306       IndirectBrInst *LI = cast<IndirectBrInst>(L);
 307       IndirectBrInst *RI = cast<IndirectBrInst>(R);
 308       if (LI->getNumDestinations() != RI->getNumDestinations()) {
 309         if (Complain) Engine.log("indirectbr # of destinations differ");
 310         return true;
 311       }
 312
 313       if (!equivalentAsOperands(LI->getAddress(), RI->getAddress())) {
 314         if (Complain) Engine.log("indirectbr addresses differ");
 315         return true;
 316       }
 317
 318       if (TryUnify) {
 319         for (unsigned i = 0; i < LI->getNumDestinations(); i++) {
 320           tryUnify(LI->getDestination(i), RI->getDestination(i));
 321         }
 322       }
 323       return false;
 324
 325     } else if (isa<SwitchInst>(L)) {
 326       SwitchInst *LI = cast<SwitchInst>(L);
 327       SwitchInst *RI = cast<SwitchInst>(R);
 328       if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) {
 329         if (Complain) Engine.log("switch conditions differ");
 330         return true;
 331       }
 332       if (TryUnify) tryUnify(LI->getDefaultDest(), RI->getDefaultDest());
 333
 334       bool Difference = false;
 335
 336       DenseMap<ConstantInt*,BasicBlock*> LCases;
 337       for (auto Case : LI->cases())
 338         LCases[Case.getCaseValue()] = Case.getCaseSuccessor();
 339
 340       for (auto Case : RI->cases()) {
 341         ConstantInt *CaseValue = Case.getCaseValue();
 342         BasicBlock *LCase = LCases[CaseValue];
 343         if (LCase) {
 344           if (TryUnify)
 345             tryUnify(LCase, Case.getCaseSuccessor());
 346           LCases.erase(CaseValue);
 347         } else if (Complain || !Difference) {
 348           if (Complain)
 349             Engine.logf("right switch has extra case %r") << CaseValue;
 350           Difference = true;
 351         }
 352       }
 353       if (!Difference)
 354         for (DenseMap<ConstantInt*,BasicBlock*>::iterator
 355                I = LCases.begin(), E = LCases.end(); I != E; ++I) {
 356           if (Complain)
 357             Engine.logf("left switch has extra case %l") << I->first;
 358           Difference = true;
 359         }
 360       return Difference;
 361     } else if (isa<UnreachableInst>(L)) {
 362       return false;
 363     }
 364
 365     if (L->getNumOperands() != R->getNumOperands()) {
 366       if (Complain) Engine.log("instructions have different operand counts");
 367       return true;
 368     }
 369
 370     for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I) {
 371       Value *LO = L->getOperand(I), *RO = R->getOperand(I);
 372       if (!equivalentAsOperands(LO, RO)) {
 373         if (Complain) Engine.logf("operands %l and %r differ") << LO << RO;
 374         return true;
 375       }
 376     }
 377
 378     return false;
 379   }
 380
 381   bool equivalentAsOperands(Constant *L, Constant *R) {
 382     // Use equality as a preliminary filter.
 383     if (L == R)
 384       return true;
 385
 386     if (L->getValueID() != R->getValueID())
 387       return false;
 388
 389     // Ask the engine about global values.
 390     if (isa<GlobalValue>(L))
 391       return Engine.equivalentAsOperands(cast<GlobalValue>(L),
 392                                          cast<GlobalValue>(R));
 393
 394     // Compare constant expressions structurally.
 395     if (isa<ConstantExpr>(L))
 396       return equivalentAsOperands(cast<ConstantExpr>(L),
 397                                   cast<ConstantExpr>(R));
 398
 399     // Constants of the "same type" don't always actually have the same
 400     // type; I don't know why.  Just white-list them.
 401     if (isa<ConstantPointerNull>(L) || isa<UndefValue>(L) || isa<ConstantAggregateZero>(L))
 402       return true;
 403
 404     // Block addresses only match if we've already encountered the
 405     // block.  FIXME: tentative matches?
 406     if (isa<BlockAddress>(L))
 407       return Blocks[cast<BlockAddress>(L)->getBasicBlock()]
 408                  == cast<BlockAddress>(R)->getBasicBlock();
 409
 410     // If L and R are ConstantVectors, compare each element
 411     if (isa<ConstantVector>(L)) {
 412       ConstantVector *CVL = cast<ConstantVector>(L);
 413       ConstantVector *CVR = cast<ConstantVector>(R);
 414       if (CVL->getType()->getNumElements() != CVR->getType()->getNumElements())
 415         return false;
 416       for (unsigned i = 0; i < CVL->getType()->getNumElements(); i++) {
 417         if (!equivalentAsOperands(CVL->getOperand(i), CVR->getOperand(i)))
 418           return false;
 419       }
 420       return true;
 421     }
 422
 423     return false;
 424   }
 425
 426   bool equivalentAsOperands(ConstantExpr *L, ConstantExpr *R) {
 427     if (L == R)
 428       return true;
 429     if (L->getOpcode() != R->getOpcode())
 430       return false;
 431
 432     switch (L->getOpcode()) {
 433     case Instruction::ICmp:
 434     case Instruction::FCmp:
 435       if (L->getPredicate() != R->getPredicate())
 436         return false;
 437       break;
 438
 439     case Instruction::GetElementPtr:
 440       // FIXME: inbounds?
 441       break;
 442
 443     default:
 444       break;
 445     }
 446
 447     if (L->getNumOperands() != R->getNumOperands())
 448       return false;
 449
 450     for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I)
 451       if (!equivalentAsOperands(L->getOperand(I), R->getOperand(I)))
 452         return false;
 453
 454     return true;
 455   }
 456
 457   bool equivalentAsOperands(Value *L, Value *R) {
 458     // Fall out if the values have different kind.
 459     // This possibly shouldn't take priority over oracles.
 460     if (L->getValueID() != R->getValueID())
 461       return false;
 462
 463     // Value subtypes:  Argument, Constant, Instruction, BasicBlock,
 464     //                  InlineAsm, MDNode, MDString, PseudoSourceValue
 465
 466     if (isa<Constant>(L))
 467       return equivalentAsOperands(cast<Constant>(L), cast<Constant>(R));
 468
 469     if (isa<Instruction>(L))
 470       return Values[L] == R || TentativeValues.count(std::make_pair(L, R));
 471
 472     if (isa<Argument>(L))
 473       return Values[L] == R;
 474
 475     if (isa<BasicBlock>(L))
 476       return Blocks[cast<BasicBlock>(L)] != R;
 477
 478     // Pretend everything else is identical.
 479     return true;
 480   }
 481
 482   // Avoid a gcc warning about accessing 'this' in an initializer.
 483   FunctionDifferenceEngine *this_() { return this; }
 484
 485 public:
 486   FunctionDifferenceEngine(DifferenceEngine &Engine) :
 487     Engine(Engine), Queue(QueueSorter(*this_())) {}
 488
 489   void diff(Function *L, Function *R) {
 490     if (L->arg_size() != R->arg_size())
 491       Engine.log("different argument counts");
 492
 493     // Map the arguments.
 494     for (Function::arg_iterator
 495            LI = L->arg_begin(), LE = L->arg_end(),
 496            RI = R->arg_begin(), RE = R->arg_end();
 497          LI != LE && RI != RE; ++LI, ++RI)
 498       Values[&*LI] = &*RI;
 499
 500     tryUnify(&*L->begin(), &*R->begin());
 501     processQueue();
 502   }
 503 };
 504
 505 struct DiffEntry {
 506   DiffEntry() : Cost(0) {}
 507
 508   unsigned Cost;
 509   llvm::SmallVector<char, 8> Path; // actually of DifferenceEngine::DiffChange
 510 };
 511
 512 bool FunctionDifferenceEngine::matchForBlockDiff(Instruction *L,
 513                                                  Instruction *R) {
 514   return !diff(L, R, false, false);
 515 }
 516
 517 void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart,
 518                                             BasicBlock::iterator RStart) {
 519   BasicBlock::iterator LE = LStart->getParent()->end();
 520   BasicBlock::iterator RE = RStart->getParent()->end();
 521
 522   unsigned NL = std::distance(LStart, LE);
 523
 524   SmallVector<DiffEntry, 20> Paths1(NL+1);
 525   SmallVector<DiffEntry, 20> Paths2(NL+1);
 526
 527   DiffEntry *Cur = Paths1.data();
 528   DiffEntry *Next = Paths2.data();
 529
 530   const unsigned LeftCost = 2;
 531   const unsigned RightCost = 2;
 532   const unsigned MatchCost = 0;
 533
 534   assert(TentativeValues.empty());
 535
 536   // Initialize the first column.
 537   for (unsigned I = 0; I != NL+1; ++I) {
 538     Cur[I].Cost = I * LeftCost;
 539     for (unsigned J = 0; J != I; ++J)
 540       Cur[I].Path.push_back(DC_left);
 541   }
 542
 543   for (BasicBlock::iterator RI = RStart; RI != RE; ++RI) {
 544     // Initialize the first row.
 545     Next[0] = Cur[0];
 546     Next[0].Cost += RightCost;
 547     Next[0].Path.push_back(DC_right);
 548
 549     unsigned Index = 1;
 550     for (BasicBlock::iterator LI = LStart; LI != LE; ++LI, ++Index) {
 551       if (matchForBlockDiff(&*LI, &*RI)) {
 552         Next[Index] = Cur[Index-1];
 553         Next[Index].Cost += MatchCost;
 554         Next[Index].Path.push_back(DC_match);
 555         TentativeValues.insert(std::make_pair(&*LI, &*RI));
 556       } else if (Next[Index-1].Cost <= Cur[Index].Cost) {
 557         Next[Index] = Next[Index-1];
 558         Next[Index].Cost += LeftCost;
 559         Next[Index].Path.push_back(DC_left);
 560       } else {
 561         Next[Index] = Cur[Index];
 562         Next[Index].Cost += RightCost;
 563         Next[Index].Path.push_back(DC_right);
 564       }
 565     }
 566
 567     std::swap(Cur, Next);
 568   }
 569
 570   // We don't need the tentative values anymore; everything from here
 571   // on out should be non-tentative.
 572   TentativeValues.clear();
 573
 574   SmallVectorImpl<char> &Path = Cur[NL].Path;
 575   BasicBlock::iterator LI = LStart, RI = RStart;
 576
 577   DiffLogBuilder Diff(Engine.getConsumer());
 578
 579   // Drop trailing matches.
 580   while (Path.back() == DC_match)
 581     Path.pop_back();
 582
 583   // Skip leading matches.
 584   SmallVectorImpl<char>::iterator
 585     PI = Path.begin(), PE = Path.end();
 586   while (PI != PE && *PI == DC_match) {
 587     unify(&*LI, &*RI);
 588     ++PI;
 589     ++LI;
 590     ++RI;
 591   }
 592
 593   for (; PI != PE; ++PI) {
 594     switch (static_cast<DiffChange>(*PI)) {
 595     case DC_match:
 596       assert(LI != LE && RI != RE);
 597       {
 598         Instruction *L = &*LI, *R = &*RI;
 599         unify(L, R);
 600         Diff.addMatch(L, R);
 601       }
 602       ++LI; ++RI;
 603       break;
 604
 605     case DC_left:
 606       assert(LI != LE);
 607       Diff.addLeft(&*LI);
 608       ++LI;
 609       break;
 610
 611     case DC_right:
 612       assert(RI != RE);
 613       Diff.addRight(&*RI);
 614       ++RI;
 615       break;
 616     }
 617   }
 618
 619   // Finishing unifying and complaining about the tails of the block,
 620   // which should be matches all the way through.
 621   while (LI != LE) {
 622     assert(RI != RE);
 623     unify(&*LI, &*RI);
 624     ++LI;
 625     ++RI;
 626   }
 627
 628   // If the terminators have different kinds, but one is an invoke and the
 629   // other is an unconditional branch immediately following a call, unify
 630   // the results and the destinations.
 631   Instruction *LTerm = LStart->getParent()->getTerminator();
 632   Instruction *RTerm = RStart->getParent()->getTerminator();
 633   if (isa<BranchInst>(LTerm) && isa<InvokeInst>(RTerm)) {
 634     if (cast<BranchInst>(LTerm)->isConditional()) return;
 635     BasicBlock::iterator I = LTerm->getIterator();
 636     if (I == LStart->getParent()->begin()) return;
 637     --I;
 638     if (!isa<CallInst>(*I)) return;
 639     CallInst *LCall = cast<CallInst>(&*I);
 640     InvokeInst *RInvoke = cast<InvokeInst>(RTerm);
 641     if (!equivalentAsOperands(LCall->getCalledValue(), RInvoke->getCalledValue()))
 642       return;
 643     if (!LCall->use_empty())
 644       Values[LCall] = RInvoke;
 645     tryUnify(LTerm->getSuccessor(0), RInvoke->getNormalDest());
 646   } else if (isa<InvokeInst>(LTerm) && isa<BranchInst>(RTerm)) {
 647     if (cast<BranchInst>(RTerm)->isConditional()) return;
 648     BasicBlock::iterator I = RTerm->getIterator();
 649     if (I == RStart->getParent()->begin()) return;
 650     --I;
 651     if (!isa<CallInst>(*I)) return;
 652     CallInst *RCall = cast<CallInst>(I);
 653     InvokeInst *LInvoke = cast<InvokeInst>(LTerm);
 654     if (!equivalentAsOperands(LInvoke->getCalledValue(), RCall->getCalledValue()))
 655       return;
 656     if (!LInvoke->use_empty())
 657       Values[LInvoke] = RCall;
 658     tryUnify(LInvoke->getNormalDest(), RTerm->getSuccessor(0));
 659   }
 660 }
 661
 662 }
 663
 664 void DifferenceEngine::Oracle::anchor() { }
 665
 666 void DifferenceEngine::diff(Function *L, Function *R) {
 667   Context C(*this, L, R);
 668
 669   // FIXME: types
 670   // FIXME: attributes and CC
 671   // FIXME: parameter attributes
 672
 673   // If both are declarations, we're done.
 674   if (L->empty() && R->empty())
 675     return;
 676   else if (L->empty())
 677     log("left function is declaration, right function is definition");
 678   else if (R->empty())
 679     log("right function is declaration, left function is definition");
 680   else
 681     FunctionDifferenceEngine(*this).diff(L, R);
 682 }
 683
 684 void DifferenceEngine::diff(Module *L, Module *R) {
 685   StringSet<> LNames;
 686   SmallVector<std::pair<Function*,Function*>, 20> Queue;
 687
 688   unsigned LeftAnonCount = 0;
 689   unsigned RightAnonCount = 0;
 690
 691   for (Module::iterator I = L->begin(), E = L->end(); I != E; ++I) {
 692     Function *LFn = &*I;
 693     StringRef Name = LFn->getName();
 694     if (Name.empty()) {
 695       ++LeftAnonCount;
 696       continue;
 697     }
 698
 699     LNames.insert(Name);
 700
 701     if (Function *RFn = R->getFunction(LFn->getName()))
 702       Queue.push_back(std::make_pair(LFn, RFn));
 703     else
 704       logf("function %l exists only in left module") << LFn;
 705   }
 706
 707   for (Module::iterator I = R->begin(), E = R->end(); I != E; ++I) {
 708     Function *RFn = &*I;
 709     StringRef Name = RFn->getName();
 710     if (Name.empty()) {
 711       ++RightAnonCount;
 712       continue;
 713     }
 714
 715     if (!LNames.count(Name))
 716       logf("function %r exists only in right module") << RFn;
 717   }
 718
 719
 720   if (LeftAnonCount != 0 || RightAnonCount != 0) {
 721     SmallString<32> Tmp;
 722     logf(("not comparing " + Twine(LeftAnonCount) +
 723           " anonymous functions in the left module and " +
 724           Twine(RightAnonCount) + " in the right module")
 725              .toStringRef(Tmp));
 726   }
 727
 728   for (SmallVectorImpl<std::pair<Function*,Function*> >::iterator
 729          I = Queue.begin(), E = Queue.end(); I != E; ++I)
 730     diff(I->first, I->second);
 731 }
 732
 733 bool DifferenceEngine::equivalentAsOperands(GlobalValue *L, GlobalValue *R) {
 734   if (globalValueOracle) return (*globalValueOracle)(L, R);
 735   return L->getName() == R->getName();
 736 }