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