DifferenceEngine.cpp revision b82b4339d1dded9c7e36afac80aac2ca73918e51
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 17#include "llvm/Function.h" 18#include "llvm/Instructions.h" 19#include "llvm/Module.h" 20#include "llvm/ADT/DenseMap.h" 21#include "llvm/ADT/DenseSet.h" 22#include "llvm/ADT/SmallVector.h" 23#include "llvm/ADT/StringRef.h" 24#include "llvm/ADT/StringSet.h" 25#include "llvm/Support/CallSite.h" 26#include "llvm/Support/CFG.h" 27#include "llvm/Support/ErrorHandling.h" 28#include "llvm/Support/raw_ostream.h" 29#include "llvm/Support/type_traits.h" 30 31#include <utility> 32 33using namespace llvm; 34 35namespace { 36 37/// A priority queue, implemented as a heap. 38template <class T, class Sorter, unsigned InlineCapacity> 39class PriorityQueue { 40 Sorter Precedes; 41 llvm::SmallVector<T, InlineCapacity> Storage; 42 43public: 44 PriorityQueue(const Sorter &Precedes) : Precedes(Precedes) {} 45 46 /// Checks whether the heap is empty. 47 bool empty() const { return Storage.empty(); } 48 49 /// Insert a new value on the heap. 50 void insert(const T &V) { 51 unsigned Index = Storage.size(); 52 Storage.push_back(V); 53 if (Index == 0) return; 54 55 T *data = Storage.data(); 56 while (true) { 57 unsigned Target = (Index + 1) / 2 - 1; 58 if (!Precedes(data[Index], data[Target])) return; 59 std::swap(data[Index], data[Target]); 60 if (Target == 0) return; 61 Index = Target; 62 } 63 } 64 65 /// Remove the minimum value in the heap. Only valid on a non-empty heap. 66 T remove_min() { 67 assert(!empty()); 68 T tmp = Storage[0]; 69 70 unsigned NewSize = Storage.size() - 1; 71 if (NewSize) { 72 // Move the slot at the end to the beginning. 73 if (isPodLike<T>::value) 74 Storage[0] = Storage[NewSize]; 75 else 76 std::swap(Storage[0], Storage[NewSize]); 77 78 // Bubble the root up as necessary. 79 unsigned Index = 0; 80 while (true) { 81 // With a 1-based index, the children would be Index*2 and Index*2+1. 82 unsigned R = (Index + 1) * 2; 83 unsigned L = R - 1; 84 85 // If R is out of bounds, we're done after this in any case. 86 if (R >= NewSize) { 87 // If L is also out of bounds, we're done immediately. 88 if (L >= NewSize) break; 89 90 // Otherwise, test whether we should swap L and Index. 91 if (Precedes(Storage[L], Storage[Index])) 92 std::swap(Storage[L], Storage[Index]); 93 break; 94 } 95 96 // Otherwise, we need to compare with the smaller of L and R. 97 // Prefer R because it's closer to the end of the array. 98 unsigned IndexToTest = (Precedes(Storage[L], Storage[R]) ? L : R); 99 100 // If Index is >= the min of L and R, then heap ordering is restored. 101 if (!Precedes(Storage[IndexToTest], Storage[Index])) 102 break; 103 104 // Otherwise, keep bubbling up. 105 std::swap(Storage[IndexToTest], Storage[Index]); 106 Index = IndexToTest; 107 } 108 } 109 Storage.pop_back(); 110 111 return tmp; 112 } 113}; 114 115/// A function-scope difference engine. 116class FunctionDifferenceEngine { 117 DifferenceEngine &Engine; 118 119 /// The current mapping from old local values to new local values. 120 DenseMap<Value*, Value*> Values; 121 122 /// The current mapping from old blocks to new blocks. 123 DenseMap<BasicBlock*, BasicBlock*> Blocks; 124 125 DenseSet<std::pair<Value*, Value*> > TentativeValues; 126 127 unsigned getUnprocPredCount(BasicBlock *Block) const { 128 unsigned Count = 0; 129 for (pred_iterator I = pred_begin(Block), E = pred_end(Block); I != E; ++I) 130 if (!Blocks.count(*I)) Count++; 131 return Count; 132 } 133 134 typedef std::pair<BasicBlock*, BasicBlock*> BlockPair; 135 136 /// A type which sorts a priority queue by the number of unprocessed 137 /// predecessor blocks it has remaining. 138 /// 139 /// This is actually really expensive to calculate. 140 struct QueueSorter { 141 const FunctionDifferenceEngine &fde; 142 explicit QueueSorter(const FunctionDifferenceEngine &fde) : fde(fde) {} 143 144 bool operator()(const BlockPair &Old, const BlockPair &New) { 145 return fde.getUnprocPredCount(Old.first) 146 < fde.getUnprocPredCount(New.first); 147 } 148 }; 149 150 /// A queue of unified blocks to process. 151 PriorityQueue<BlockPair, QueueSorter, 20> Queue; 152 153 /// Try to unify the given two blocks. Enqueues them for processing 154 /// if they haven't already been processed. 155 /// 156 /// Returns true if there was a problem unifying them. 157 bool tryUnify(BasicBlock *L, BasicBlock *R) { 158 BasicBlock *&Ref = Blocks[L]; 159 160 if (Ref) { 161 if (Ref == R) return false; 162 163 Engine.logf("successor %l cannot be equivalent to %r; " 164 "it's already equivalent to %r") 165 << L << R << Ref; 166 return true; 167 } 168 169 Ref = R; 170 Queue.insert(BlockPair(L, R)); 171 return false; 172 } 173 174 /// Unifies two instructions, given that they're known not to have 175 /// structural differences. 176 void unify(Instruction *L, Instruction *R) { 177 DifferenceEngine::Context C(Engine, L, R); 178 179 bool Result = diff(L, R, true, true); 180 assert(!Result && "structural differences second time around?"); 181 (void) Result; 182 if (!L->use_empty()) 183 Values[L] = R; 184 } 185 186 void processQueue() { 187 while (!Queue.empty()) { 188 BlockPair Pair = Queue.remove_min(); 189 diff(Pair.first, Pair.second); 190 } 191 } 192 193 void diff(BasicBlock *L, BasicBlock *R) { 194 DifferenceEngine::Context C(Engine, L, R); 195 196 BasicBlock::iterator LI = L->begin(), LE = L->end(); 197 BasicBlock::iterator RI = R->begin(), RE = R->end(); 198 199 llvm::SmallVector<std::pair<Instruction*,Instruction*>, 20> TentativePairs; 200 201 do { 202 assert(LI != LE && RI != RE); 203 Instruction *LeftI = &*LI, *RightI = &*RI; 204 205 // If the instructions differ, start the more sophisticated diff 206 // algorithm at the start of the block. 207 if (diff(LeftI, RightI, false, false)) { 208 TentativeValues.clear(); 209 return runBlockDiff(L->begin(), R->begin()); 210 } 211 212 // Otherwise, tentatively unify them. 213 if (!LeftI->use_empty()) 214 TentativeValues.insert(std::make_pair(LeftI, RightI)); 215 216 ++LI, ++RI; 217 } while (LI != LE); // This is sufficient: we can't get equality of 218 // terminators if there are residual instructions. 219 220 // Unify everything in the block, non-tentatively this time. 221 TentativeValues.clear(); 222 for (LI = L->begin(), RI = R->begin(); LI != LE; ++LI, ++RI) 223 unify(&*LI, &*RI); 224 } 225 226 bool matchForBlockDiff(Instruction *L, Instruction *R); 227 void runBlockDiff(BasicBlock::iterator LI, BasicBlock::iterator RI); 228 229 bool diffCallSites(CallSite L, CallSite R, bool Complain) { 230 // FIXME: call attributes 231 if (!equivalentAsOperands(L.getCalledValue(), R.getCalledValue())) { 232 if (Complain) Engine.log("called functions differ"); 233 return true; 234 } 235 if (L.arg_size() != R.arg_size()) { 236 if (Complain) Engine.log("argument counts differ"); 237 return true; 238 } 239 for (unsigned I = 0, E = L.arg_size(); I != E; ++I) 240 if (!equivalentAsOperands(L.getArgument(I), R.getArgument(I))) { 241 if (Complain) 242 Engine.logf("arguments %l and %r differ") 243 << L.getArgument(I) << R.getArgument(I); 244 return true; 245 } 246 return false; 247 } 248 249 bool diff(Instruction *L, Instruction *R, bool Complain, bool TryUnify) { 250 // FIXME: metadata (if Complain is set) 251 252 // Different opcodes always imply different operations. 253 if (L->getOpcode() != R->getOpcode()) { 254 if (Complain) Engine.log("different instruction types"); 255 return true; 256 } 257 258 if (isa<CmpInst>(L)) { 259 if (cast<CmpInst>(L)->getPredicate() 260 != cast<CmpInst>(R)->getPredicate()) { 261 if (Complain) Engine.log("different predicates"); 262 return true; 263 } 264 } else if (isa<CallInst>(L)) { 265 return diffCallSites(CallSite(L), CallSite(R), Complain); 266 } else if (isa<PHINode>(L)) { 267 // FIXME: implement. 268 269 // This is really wierd; type uniquing is broken? 270 if (L->getType() != R->getType()) { 271 if (!L->getType()->isPointerTy() || !R->getType()->isPointerTy()) { 272 if (Complain) Engine.log("different phi types"); 273 return true; 274 } 275 } 276 return false; 277 278 // Terminators. 279 } else if (isa<InvokeInst>(L)) { 280 InvokeInst *LI = cast<InvokeInst>(L); 281 InvokeInst *RI = cast<InvokeInst>(R); 282 if (diffCallSites(CallSite(LI), CallSite(RI), Complain)) 283 return true; 284 285 if (TryUnify) { 286 tryUnify(LI->getNormalDest(), RI->getNormalDest()); 287 tryUnify(LI->getUnwindDest(), RI->getUnwindDest()); 288 } 289 return false; 290 291 } else if (isa<BranchInst>(L)) { 292 BranchInst *LI = cast<BranchInst>(L); 293 BranchInst *RI = cast<BranchInst>(R); 294 if (LI->isConditional() != RI->isConditional()) { 295 if (Complain) Engine.log("branch conditionality differs"); 296 return true; 297 } 298 299 if (LI->isConditional()) { 300 if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) { 301 if (Complain) Engine.log("branch conditions differ"); 302 return true; 303 } 304 if (TryUnify) tryUnify(LI->getSuccessor(1), RI->getSuccessor(1)); 305 } 306 if (TryUnify) tryUnify(LI->getSuccessor(0), RI->getSuccessor(0)); 307 return false; 308 309 } else if (isa<SwitchInst>(L)) { 310 SwitchInst *LI = cast<SwitchInst>(L); 311 SwitchInst *RI = cast<SwitchInst>(R); 312 if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) { 313 if (Complain) Engine.log("switch conditions differ"); 314 return true; 315 } 316 if (TryUnify) tryUnify(LI->getDefaultDest(), RI->getDefaultDest()); 317 318 bool Difference = false; 319 320 DenseMap<ConstantInt*,BasicBlock*> LCases; 321 for (unsigned I = 1, E = LI->getNumCases(); I != E; ++I) 322 LCases[LI->getCaseValue(I)] = LI->getSuccessor(I); 323 for (unsigned I = 1, E = RI->getNumCases(); I != E; ++I) { 324 ConstantInt *CaseValue = RI->getCaseValue(I); 325 BasicBlock *LCase = LCases[CaseValue]; 326 if (LCase) { 327 if (TryUnify) tryUnify(LCase, RI->getSuccessor(I)); 328 LCases.erase(CaseValue); 329 } else if (!Difference) { 330 if (Complain) 331 Engine.logf("right switch has extra case %r") << CaseValue; 332 Difference = true; 333 } 334 } 335 if (!Difference) 336 for (DenseMap<ConstantInt*,BasicBlock*>::iterator 337 I = LCases.begin(), E = LCases.end(); I != E; ++I) { 338 if (Complain) 339 Engine.logf("left switch has extra case %l") << I->first; 340 Difference = true; 341 } 342 return Difference; 343 } else if (isa<UnreachableInst>(L)) { 344 return false; 345 } 346 347 if (L->getNumOperands() != R->getNumOperands()) { 348 if (Complain) Engine.log("instructions have different operand counts"); 349 return true; 350 } 351 352 for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I) { 353 Value *LO = L->getOperand(I), *RO = R->getOperand(I); 354 if (!equivalentAsOperands(LO, RO)) { 355 if (Complain) Engine.logf("operands %l and %r differ") << LO << RO; 356 return true; 357 } 358 } 359 360 return false; 361 } 362 363 bool equivalentAsOperands(Constant *L, Constant *R) { 364 // Use equality as a preliminary filter. 365 if (L == R) 366 return true; 367 368 if (L->getValueID() != R->getValueID()) 369 return false; 370 371 // Ask the engine about global values. 372 if (isa<GlobalValue>(L)) 373 return Engine.equivalentAsOperands(cast<GlobalValue>(L), 374 cast<GlobalValue>(R)); 375 376 // Compare constant expressions structurally. 377 if (isa<ConstantExpr>(L)) 378 return equivalentAsOperands(cast<ConstantExpr>(L), 379 cast<ConstantExpr>(R)); 380 381 // Nulls of the "same type" don't always actually have the same 382 // type; I don't know why. Just white-list them. 383 if (isa<ConstantPointerNull>(L)) 384 return true; 385 386 // Block addresses only match if we've already encountered the 387 // block. FIXME: tentative matches? 388 if (isa<BlockAddress>(L)) 389 return Blocks[cast<BlockAddress>(L)->getBasicBlock()] 390 == cast<BlockAddress>(R)->getBasicBlock(); 391 392 return false; 393 } 394 395 bool equivalentAsOperands(ConstantExpr *L, ConstantExpr *R) { 396 if (L == R) 397 return true; 398 if (L->getOpcode() != R->getOpcode()) 399 return false; 400 401 switch (L->getOpcode()) { 402 case Instruction::ICmp: 403 case Instruction::FCmp: 404 if (L->getPredicate() != R->getPredicate()) 405 return false; 406 break; 407 408 case Instruction::GetElementPtr: 409 // FIXME: inbounds? 410 break; 411 412 default: 413 break; 414 } 415 416 if (L->getNumOperands() != R->getNumOperands()) 417 return false; 418 419 for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I) 420 if (!equivalentAsOperands(L->getOperand(I), R->getOperand(I))) 421 return false; 422 423 return true; 424 } 425 426 bool equivalentAsOperands(Value *L, Value *R) { 427 // Fall out if the values have different kind. 428 // This possibly shouldn't take priority over oracles. 429 if (L->getValueID() != R->getValueID()) 430 return false; 431 432 // Value subtypes: Argument, Constant, Instruction, BasicBlock, 433 // InlineAsm, MDNode, MDString, PseudoSourceValue 434 435 if (isa<Constant>(L)) 436 return equivalentAsOperands(cast<Constant>(L), cast<Constant>(R)); 437 438 if (isa<Instruction>(L)) 439 return Values[L] == R || TentativeValues.count(std::make_pair(L, R)); 440 441 if (isa<Argument>(L)) 442 return Values[L] == R; 443 444 if (isa<BasicBlock>(L)) 445 return Blocks[cast<BasicBlock>(L)] != R; 446 447 // Pretend everything else is identical. 448 return true; 449 } 450 451 // Avoid a gcc warning about accessing 'this' in an initializer. 452 FunctionDifferenceEngine *this_() { return this; } 453 454public: 455 FunctionDifferenceEngine(DifferenceEngine &Engine) : 456 Engine(Engine), Queue(QueueSorter(*this_())) {} 457 458 void diff(Function *L, Function *R) { 459 if (L->arg_size() != R->arg_size()) 460 Engine.log("different argument counts"); 461 462 // Map the arguments. 463 for (Function::arg_iterator 464 LI = L->arg_begin(), LE = L->arg_end(), 465 RI = R->arg_begin(), RE = R->arg_end(); 466 LI != LE && RI != RE; ++LI, ++RI) 467 Values[&*LI] = &*RI; 468 469 tryUnify(&*L->begin(), &*R->begin()); 470 processQueue(); 471 } 472}; 473 474struct DiffEntry { 475 DiffEntry() : Cost(0) {} 476 477 unsigned Cost; 478 llvm::SmallVector<char, 8> Path; // actually of DifferenceEngine::DiffChange 479}; 480 481bool FunctionDifferenceEngine::matchForBlockDiff(Instruction *L, 482 Instruction *R) { 483 return !diff(L, R, false, false); 484} 485 486void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart, 487 BasicBlock::iterator RStart) { 488 BasicBlock::iterator LE = LStart->getParent()->end(); 489 BasicBlock::iterator RE = RStart->getParent()->end(); 490 491 unsigned NL = std::distance(LStart, LE); 492 493 SmallVector<DiffEntry, 20> Paths1(NL+1); 494 SmallVector<DiffEntry, 20> Paths2(NL+1); 495 496 DiffEntry *Cur = Paths1.data(); 497 DiffEntry *Next = Paths2.data(); 498 499 const unsigned LeftCost = 2; 500 const unsigned RightCost = 2; 501 const unsigned MatchCost = 0; 502 503 assert(TentativeValues.empty()); 504 505 // Initialize the first column. 506 for (unsigned I = 0; I != NL+1; ++I) { 507 Cur[I].Cost = I * LeftCost; 508 for (unsigned J = 0; J != I; ++J) 509 Cur[I].Path.push_back(DifferenceEngine::DC_left); 510 } 511 512 for (BasicBlock::iterator RI = RStart; RI != RE; ++RI) { 513 // Initialize the first row. 514 Next[0] = Cur[0]; 515 Next[0].Cost += RightCost; 516 Next[0].Path.push_back(DifferenceEngine::DC_right); 517 518 unsigned Index = 1; 519 for (BasicBlock::iterator LI = LStart; LI != LE; ++LI, ++Index) { 520 if (matchForBlockDiff(&*LI, &*RI)) { 521 Next[Index] = Cur[Index-1]; 522 Next[Index].Cost += MatchCost; 523 Next[Index].Path.push_back(DifferenceEngine::DC_match); 524 TentativeValues.insert(std::make_pair(&*LI, &*RI)); 525 } else if (Next[Index-1].Cost <= Cur[Index].Cost) { 526 Next[Index] = Next[Index-1]; 527 Next[Index].Cost += LeftCost; 528 Next[Index].Path.push_back(DifferenceEngine::DC_left); 529 } else { 530 Next[Index] = Cur[Index]; 531 Next[Index].Cost += RightCost; 532 Next[Index].Path.push_back(DifferenceEngine::DC_right); 533 } 534 } 535 536 std::swap(Cur, Next); 537 } 538 539 // We don't need the tentative values anymore; everything from here 540 // on out should be non-tentative. 541 TentativeValues.clear(); 542 543 SmallVectorImpl<char> &Path = Cur[NL].Path; 544 BasicBlock::iterator LI = LStart, RI = RStart; 545 546 DifferenceEngine::DiffLogBuilder Diff(Engine); 547 548 // Drop trailing matches. 549 while (Path.back() == DifferenceEngine::DC_match) 550 Path.pop_back(); 551 552 // Skip leading matches. 553 SmallVectorImpl<char>::iterator 554 PI = Path.begin(), PE = Path.end(); 555 while (PI != PE && *PI == DifferenceEngine::DC_match) { 556 unify(&*LI, &*RI); 557 ++PI, ++LI, ++RI; 558 } 559 560 for (; PI != PE; ++PI) { 561 switch (static_cast<DifferenceEngine::DiffChange>(*PI)) { 562 case DifferenceEngine::DC_match: 563 assert(LI != LE && RI != RE); 564 { 565 Instruction *L = &*LI, *R = &*RI; 566 unify(L, R); 567 Diff.addMatch(L, R); 568 } 569 ++LI; ++RI; 570 break; 571 572 case DifferenceEngine::DC_left: 573 assert(LI != LE); 574 Diff.addLeft(&*LI); 575 ++LI; 576 break; 577 578 case DifferenceEngine::DC_right: 579 assert(RI != RE); 580 Diff.addRight(&*RI); 581 ++RI; 582 break; 583 } 584 } 585 586 // Finishing unifying and complaining about the tails of the block, 587 // which should be matches all the way through. 588 while (LI != LE) { 589 assert(RI != RE); 590 unify(&*LI, &*RI); 591 ++LI, ++RI; 592 } 593 594 // If the terminators have different kinds, but one is an invoke and the 595 // other is an unconditional branch immediately following a call, unify 596 // the results and the destinations. 597 TerminatorInst *LTerm = LStart->getParent()->getTerminator(); 598 TerminatorInst *RTerm = RStart->getParent()->getTerminator(); 599 if (isa<BranchInst>(LTerm) && isa<InvokeInst>(RTerm)) { 600 if (cast<BranchInst>(LTerm)->isConditional()) return; 601 BasicBlock::iterator I = LTerm; 602 if (I == LStart->getParent()->begin()) return; 603 --I; 604 if (!isa<CallInst>(*I)) return; 605 CallInst *LCall = cast<CallInst>(&*I); 606 InvokeInst *RInvoke = cast<InvokeInst>(RTerm); 607 if (!equivalentAsOperands(LCall->getCalledValue(), RInvoke->getCalledValue())) 608 return; 609 if (!LCall->use_empty()) 610 Values[LCall] = RInvoke; 611 tryUnify(LTerm->getSuccessor(0), RInvoke->getNormalDest()); 612 } else if (isa<InvokeInst>(LTerm) && isa<BranchInst>(RTerm)) { 613 if (cast<BranchInst>(RTerm)->isConditional()) return; 614 BasicBlock::iterator I = RTerm; 615 if (I == RStart->getParent()->begin()) return; 616 --I; 617 if (!isa<CallInst>(*I)) return; 618 CallInst *RCall = cast<CallInst>(I); 619 InvokeInst *LInvoke = cast<InvokeInst>(LTerm); 620 if (!equivalentAsOperands(LInvoke->getCalledValue(), RCall->getCalledValue())) 621 return; 622 if (!LInvoke->use_empty()) 623 Values[LInvoke] = RCall; 624 tryUnify(LInvoke->getNormalDest(), RTerm->getSuccessor(0)); 625 } 626} 627 628} 629 630void DifferenceEngine::diff(Function *L, Function *R) { 631 Context C(*this, L, R); 632 633 // FIXME: types 634 // FIXME: attributes and CC 635 // FIXME: parameter attributes 636 637 // If both are declarations, we're done. 638 if (L->empty() && R->empty()) 639 return; 640 else if (L->empty()) 641 log("left function is declaration, right function is definition"); 642 else if (R->empty()) 643 log("right function is declaration, left function is definition"); 644 else 645 FunctionDifferenceEngine(*this).diff(L, R); 646} 647 648void DifferenceEngine::diff(Module *L, Module *R) { 649 StringSet<> LNames; 650 SmallVector<std::pair<Function*,Function*>, 20> Queue; 651 652 for (Module::iterator I = L->begin(), E = L->end(); I != E; ++I) { 653 Function *LFn = &*I; 654 LNames.insert(LFn->getName()); 655 656 if (Function *RFn = R->getFunction(LFn->getName())) 657 Queue.push_back(std::make_pair(LFn, RFn)); 658 else 659 logf("function %l exists only in left module") << LFn; 660 } 661 662 for (Module::iterator I = R->begin(), E = R->end(); I != E; ++I) { 663 Function *RFn = &*I; 664 if (!LNames.count(RFn->getName())) 665 logf("function %r exists only in right module") << RFn; 666 } 667 668 for (SmallVectorImpl<std::pair<Function*,Function*> >::iterator 669 I = Queue.begin(), E = Queue.end(); I != E; ++I) 670 diff(I->first, I->second); 671} 672 673bool DifferenceEngine::equivalentAsOperands(GlobalValue *L, GlobalValue *R) { 674 if (globalValueOracle) return (*globalValueOracle)(L, R); 675 return L->getName() == R->getName(); 676} 677