1 //===-- DifferenceEngine.cpp - Structural function/module comparison ------===//
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
7 //===----------------------------------------------------------------------===//
9 // This header defines the implementation of the LLVM difference
10 // engine, which structurally compares global values within a module.
12 //===----------------------------------------------------------------------===//
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"
34 /// A priority queue, implemented as a heap.
35 template <class T, class Sorter, unsigned InlineCapacity>
38 llvm::SmallVector<T, InlineCapacity> Storage;
41 PriorityQueue(const Sorter &Precedes) : Precedes(Precedes) {}
43 /// Checks whether the heap is empty.
44 bool empty() const { return Storage.empty(); }
46 /// Insert a new value on the heap.
47 void insert(const T &V) {
48 unsigned Index = Storage.size();
50 if (Index == 0) return;
52 T *data = Storage.data();
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;
62 /// Remove the minimum value in the heap. Only valid on a non-empty heap.
67 unsigned NewSize = Storage.size() - 1;
69 // Move the slot at the end to the beginning.
70 if (is_trivially_copyable<T>::value)
71 Storage[0] = Storage[NewSize];
73 std::swap(Storage[0], Storage[NewSize]);
75 // Bubble the root up as necessary.
78 // With a 1-based index, the children would be Index*2 and Index*2+1.
79 unsigned R = (Index + 1) * 2;
82 // If R is out of bounds, we're done after this in any case.
84 // If L is also out of bounds, we're done immediately.
85 if (L >= NewSize) break;
87 // Otherwise, test whether we should swap L and Index.
88 if (Precedes(Storage[L], Storage[Index]))
89 std::swap(Storage[L], Storage[Index]);
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);
97 // If Index is >= the min of L and R, then heap ordering is restored.
98 if (!Precedes(Storage[IndexToTest], Storage[Index]))
101 // Otherwise, keep bubbling up.
102 std::swap(Storage[IndexToTest], Storage[Index]);
112 /// A function-scope difference engine.
113 class FunctionDifferenceEngine {
114 DifferenceEngine &Engine;
116 /// The current mapping from old local values to new local values.
117 DenseMap<Value*, Value*> Values;
119 /// The current mapping from old blocks to new blocks.
120 DenseMap<BasicBlock*, BasicBlock*> Blocks;
122 DenseSet<std::pair<Value*, Value*> > TentativeValues;
124 unsigned getUnprocPredCount(BasicBlock *Block) const {
126 for (pred_iterator I = pred_begin(Block), E = pred_end(Block); I != E; ++I)
127 if (!Blocks.count(*I)) Count++;
131 typedef std::pair<BasicBlock*, BasicBlock*> BlockPair;
133 /// A type which sorts a priority queue by the number of unprocessed
134 /// predecessor blocks it has remaining.
136 /// This is actually really expensive to calculate.
138 const FunctionDifferenceEngine &fde;
139 explicit QueueSorter(const FunctionDifferenceEngine &fde) : fde(fde) {}
141 bool operator()(const BlockPair &Old, const BlockPair &New) {
142 return fde.getUnprocPredCount(Old.first)
143 < fde.getUnprocPredCount(New.first);
147 /// A queue of unified blocks to process.
148 PriorityQueue<BlockPair, QueueSorter, 20> Queue;
150 /// Try to unify the given two blocks. Enqueues them for processing
151 /// if they haven't already been processed.
153 /// Returns true if there was a problem unifying them.
154 bool tryUnify(BasicBlock *L, BasicBlock *R) {
155 BasicBlock *&Ref = Blocks[L];
158 if (Ref == R) return false;
160 Engine.logf("successor %l cannot be equivalent to %r; "
161 "it's already equivalent to %r")
167 Queue.insert(BlockPair(L, R));
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);
176 bool Result = diff(L, R, true, true);
177 assert(!Result && "structural differences second time around?");
183 void processQueue() {
184 while (!Queue.empty()) {
185 BlockPair Pair = Queue.remove_min();
186 diff(Pair.first, Pair.second);
190 void diff(BasicBlock *L, BasicBlock *R) {
191 DifferenceEngine::Context C(Engine, L, R);
193 BasicBlock::iterator LI = L->begin(), LE = L->end();
194 BasicBlock::iterator RI = R->begin();
197 assert(LI != LE && RI != R->end());
198 Instruction *LeftI = &*LI, *RightI = &*RI;
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());
207 // Otherwise, tentatively unify them.
208 if (!LeftI->use_empty())
209 TentativeValues.insert(std::make_pair(LeftI, RightI));
213 } while (LI != LE); // This is sufficient: we can't get equality of
214 // terminators if there are residual instructions.
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)
222 bool matchForBlockDiff(Instruction *L, Instruction *R);
223 void runBlockDiff(BasicBlock::iterator LI, BasicBlock::iterator RI);
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");
231 if (L.arg_size() != R.arg_size()) {
232 if (Complain) Engine.log("argument counts differ");
235 for (unsigned I = 0, E = L.arg_size(); I != E; ++I)
236 if (!equivalentAsOperands(L.getArgument(I), R.getArgument(I))) {
238 Engine.logf("arguments %l and %r differ")
239 << L.getArgument(I) << R.getArgument(I);
245 bool diff(Instruction *L, Instruction *R, bool Complain, bool TryUnify) {
246 // FIXME: metadata (if Complain is set)
248 // Different opcodes always imply different operations.
249 if (L->getOpcode() != R->getOpcode()) {
250 if (Complain) Engine.log("different instruction types");
254 if (isa<CmpInst>(L)) {
255 if (cast<CmpInst>(L)->getPredicate()
256 != cast<CmpInst>(R)->getPredicate()) {
257 if (Complain) Engine.log("different predicates");
260 } else if (isa<CallInst>(L)) {
261 return diffCallSites(CallSite(L), CallSite(R), Complain);
262 } else if (isa<PHINode>(L)) {
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");
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))
282 tryUnify(LI->getNormalDest(), RI->getNormalDest());
283 tryUnify(LI->getUnwindDest(), RI->getUnwindDest());
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");
295 if (LI->isConditional()) {
296 if (!equivalentAsOperands(LI->getCondition(), RI->getCondition())) {
297 if (Complain) Engine.log("branch conditions differ");
300 if (TryUnify) tryUnify(LI->getSuccessor(1), RI->getSuccessor(1));
302 if (TryUnify) tryUnify(LI->getSuccessor(0), RI->getSuccessor(0));
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");
313 if (!equivalentAsOperands(LI->getAddress(), RI->getAddress())) {
314 if (Complain) Engine.log("indirectbr addresses differ");
319 for (unsigned i = 0; i < LI->getNumDestinations(); i++) {
320 tryUnify(LI->getDestination(i), RI->getDestination(i));
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");
332 if (TryUnify) tryUnify(LI->getDefaultDest(), RI->getDefaultDest());
334 bool Difference = false;
336 DenseMap<ConstantInt*,BasicBlock*> LCases;
337 for (auto Case : LI->cases())
338 LCases[Case.getCaseValue()] = Case.getCaseSuccessor();
340 for (auto Case : RI->cases()) {
341 ConstantInt *CaseValue = Case.getCaseValue();
342 BasicBlock *LCase = LCases[CaseValue];
345 tryUnify(LCase, Case.getCaseSuccessor());
346 LCases.erase(CaseValue);
347 } else if (Complain || !Difference) {
349 Engine.logf("right switch has extra case %r") << CaseValue;
354 for (DenseMap<ConstantInt*,BasicBlock*>::iterator
355 I = LCases.begin(), E = LCases.end(); I != E; ++I) {
357 Engine.logf("left switch has extra case %l") << I->first;
361 } else if (isa<UnreachableInst>(L)) {
365 if (L->getNumOperands() != R->getNumOperands()) {
366 if (Complain) Engine.log("instructions have different operand counts");
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;
381 bool equivalentAsOperands(Constant *L, Constant *R) {
382 // Use equality as a preliminary filter.
386 if (L->getValueID() != R->getValueID())
389 // Ask the engine about global values.
390 if (isa<GlobalValue>(L))
391 return Engine.equivalentAsOperands(cast<GlobalValue>(L),
392 cast<GlobalValue>(R));
394 // Compare constant expressions structurally.
395 if (isa<ConstantExpr>(L))
396 return equivalentAsOperands(cast<ConstantExpr>(L),
397 cast<ConstantExpr>(R));
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))
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();
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())
416 for (unsigned i = 0; i < CVL->getType()->getNumElements(); i++) {
417 if (!equivalentAsOperands(CVL->getOperand(i), CVR->getOperand(i)))
426 bool equivalentAsOperands(ConstantExpr *L, ConstantExpr *R) {
429 if (L->getOpcode() != R->getOpcode())
432 switch (L->getOpcode()) {
433 case Instruction::ICmp:
434 case Instruction::FCmp:
435 if (L->getPredicate() != R->getPredicate())
439 case Instruction::GetElementPtr:
447 if (L->getNumOperands() != R->getNumOperands())
450 for (unsigned I = 0, E = L->getNumOperands(); I != E; ++I)
451 if (!equivalentAsOperands(L->getOperand(I), R->getOperand(I)))
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())
463 // Value subtypes: Argument, Constant, Instruction, BasicBlock,
464 // InlineAsm, MDNode, MDString, PseudoSourceValue
466 if (isa<Constant>(L))
467 return equivalentAsOperands(cast<Constant>(L), cast<Constant>(R));
469 if (isa<Instruction>(L))
470 return Values[L] == R || TentativeValues.count(std::make_pair(L, R));
472 if (isa<Argument>(L))
473 return Values[L] == R;
475 if (isa<BasicBlock>(L))
476 return Blocks[cast<BasicBlock>(L)] != R;
478 // Pretend everything else is identical.
482 // Avoid a gcc warning about accessing 'this' in an initializer.
483 FunctionDifferenceEngine *this_() { return this; }
486 FunctionDifferenceEngine(DifferenceEngine &Engine) :
487 Engine(Engine), Queue(QueueSorter(*this_())) {}
489 void diff(Function *L, Function *R) {
490 if (L->arg_size() != R->arg_size())
491 Engine.log("different argument counts");
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)
500 tryUnify(&*L->begin(), &*R->begin());
506 DiffEntry() : Cost(0) {}
509 llvm::SmallVector<char, 8> Path; // actually of DifferenceEngine::DiffChange
512 bool FunctionDifferenceEngine::matchForBlockDiff(Instruction *L,
514 return !diff(L, R, false, false);
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();
522 unsigned NL = std::distance(LStart, LE);
524 SmallVector<DiffEntry, 20> Paths1(NL+1);
525 SmallVector<DiffEntry, 20> Paths2(NL+1);
527 DiffEntry *Cur = Paths1.data();
528 DiffEntry *Next = Paths2.data();
530 const unsigned LeftCost = 2;
531 const unsigned RightCost = 2;
532 const unsigned MatchCost = 0;
534 assert(TentativeValues.empty());
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);
543 for (BasicBlock::iterator RI = RStart; RI != RE; ++RI) {
544 // Initialize the first row.
546 Next[0].Cost += RightCost;
547 Next[0].Path.push_back(DC_right);
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);
561 Next[Index] = Cur[Index];
562 Next[Index].Cost += RightCost;
563 Next[Index].Path.push_back(DC_right);
567 std::swap(Cur, Next);
570 // We don't need the tentative values anymore; everything from here
571 // on out should be non-tentative.
572 TentativeValues.clear();
574 SmallVectorImpl<char> &Path = Cur[NL].Path;
575 BasicBlock::iterator LI = LStart, RI = RStart;
577 DiffLogBuilder Diff(Engine.getConsumer());
579 // Drop trailing matches.
580 while (Path.back() == DC_match)
583 // Skip leading matches.
584 SmallVectorImpl<char>::iterator
585 PI = Path.begin(), PE = Path.end();
586 while (PI != PE && *PI == DC_match) {
593 for (; PI != PE; ++PI) {
594 switch (static_cast<DiffChange>(*PI)) {
596 assert(LI != LE && RI != RE);
598 Instruction *L = &*LI, *R = &*RI;
619 // Finishing unifying and complaining about the tails of the block,
620 // which should be matches all the way through.
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;
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()))
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;
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()))
656 if (!LInvoke->use_empty())
657 Values[LInvoke] = RCall;
658 tryUnify(LInvoke->getNormalDest(), RTerm->getSuccessor(0));
664 void DifferenceEngine::Oracle::anchor() { }
666 void DifferenceEngine::diff(Function *L, Function *R) {
667 Context C(*this, L, R);
670 // FIXME: attributes and CC
671 // FIXME: parameter attributes
673 // If both are declarations, we're done.
674 if (L->empty() && R->empty())
677 log("left function is declaration, right function is definition");
679 log("right function is declaration, left function is definition");
681 FunctionDifferenceEngine(*this).diff(L, R);
684 void DifferenceEngine::diff(Module *L, Module *R) {
686 SmallVector<std::pair<Function*,Function*>, 20> Queue;
688 unsigned LeftAnonCount = 0;
689 unsigned RightAnonCount = 0;
691 for (Module::iterator I = L->begin(), E = L->end(); I != E; ++I) {
693 StringRef Name = LFn->getName();
701 if (Function *RFn = R->getFunction(LFn->getName()))
702 Queue.push_back(std::make_pair(LFn, RFn));
704 logf("function %l exists only in left module") << LFn;
707 for (Module::iterator I = R->begin(), E = R->end(); I != E; ++I) {
709 StringRef Name = RFn->getName();
715 if (!LNames.count(Name))
716 logf("function %r exists only in right module") << RFn;
720 if (LeftAnonCount != 0 || RightAnonCount != 0) {
722 logf(("not comparing " + Twine(LeftAnonCount) +
723 " anonymous functions in the left module and " +
724 Twine(RightAnonCount) + " in the right module")
728 for (SmallVectorImpl<std::pair<Function*,Function*> >::iterator
729 I = Queue.begin(), E = Queue.end(); I != E; ++I)
730 diff(I->first, I->second);
733 bool DifferenceEngine::equivalentAsOperands(GlobalValue *L, GlobalValue *R) {
734 if (globalValueOracle) return (*globalValueOracle)(L, R);
735 return L->getName() == R->getName();