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//==- UninitializedValues.cpp - Find Uninitialized Values -------*- C++ --*-==// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements uninitialized values analysis for source-level CFGs. // //===----------------------------------------------------------------------===// #include <utility> #include "llvm/ADT/Optional.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/PackedVector.h" #include "llvm/ADT/DenseMap.h" #include "clang/AST/Decl.h" #include "clang/Analysis/CFG.h" #include "clang/Analysis/AnalysisContext.h" #include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h" #include "clang/Analysis/Analyses/UninitializedValues.h" #include "llvm/Support/SaveAndRestore.h" using namespace clang; static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) { if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() && !vd->isExceptionVariable() && vd->getDeclContext() == dc) { QualType ty = vd->getType(); return ty->isScalarType() || ty->isVectorType(); } return false; } //------------------------------------------------------------------------====// // DeclToIndex: a mapping from Decls we track to value indices. //====------------------------------------------------------------------------// namespace { class DeclToIndex { llvm::DenseMap<const VarDecl *, unsigned> map; public: DeclToIndex() {} /// Compute the actual mapping from declarations to bits. void computeMap(const DeclContext &dc); /// Return the number of declarations in the map. unsigned size() const { return map.size(); } /// Returns the bit vector index for a given declaration. llvm::Optional<unsigned> getValueIndex(const VarDecl *d) const; }; } void DeclToIndex::computeMap(const DeclContext &dc) { unsigned count = 0; DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()), E(dc.decls_end()); for ( ; I != E; ++I) { const VarDecl *vd = *I; if (isTrackedVar(vd, &dc)) map[vd] = count++; } } llvm::Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const { llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d); if (I == map.end()) return llvm::Optional<unsigned>(); return I->second; } //------------------------------------------------------------------------====// // CFGBlockValues: dataflow values for CFG blocks. //====------------------------------------------------------------------------// // These values are defined in such a way that a merge can be done using // a bitwise OR. enum Value { Unknown = 0x0, /* 00 */ Initialized = 0x1, /* 01 */ Uninitialized = 0x2, /* 10 */ MayUninitialized = 0x3 /* 11 */ }; static bool isUninitialized(const Value v) { return v >= Uninitialized; } static bool isAlwaysUninit(const Value v) { return v == Uninitialized; } namespace { typedef llvm::PackedVector<Value, 2> ValueVector; typedef std::pair<ValueVector *, ValueVector *> BVPair; class CFGBlockValues { const CFG &cfg; BVPair *vals; ValueVector scratch; DeclToIndex declToIndex; ValueVector &lazyCreate(ValueVector *&bv); public: CFGBlockValues(const CFG &cfg); ~CFGBlockValues(); unsigned getNumEntries() const { return declToIndex.size(); } void computeSetOfDeclarations(const DeclContext &dc); ValueVector &getValueVector(const CFGBlock *block, const CFGBlock *dstBlock); BVPair &getValueVectors(const CFGBlock *block, bool shouldLazyCreate); void mergeIntoScratch(ValueVector const &source, bool isFirst); bool updateValueVectorWithScratch(const CFGBlock *block); bool updateValueVectors(const CFGBlock *block, const BVPair &newVals); bool hasNoDeclarations() const { return declToIndex.size() == 0; } void resetScratch(); ValueVector &getScratch() { return scratch; } ValueVector::reference operator[](const VarDecl *vd); }; } // end anonymous namespace CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) { unsigned n = cfg.getNumBlockIDs(); if (!n) return; vals = new std::pair<ValueVector*, ValueVector*>[n]; memset((void*)vals, 0, sizeof(*vals) * n); } CFGBlockValues::~CFGBlockValues() { unsigned n = cfg.getNumBlockIDs(); if (n == 0) return; for (unsigned i = 0; i < n; ++i) { delete vals[i].first; delete vals[i].second; } delete [] vals; } void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) { declToIndex.computeMap(dc); scratch.resize(declToIndex.size()); } ValueVector &CFGBlockValues::lazyCreate(ValueVector *&bv) { if (!bv) bv = new ValueVector(declToIndex.size()); return *bv; } /// This function pattern matches for a '&&' or '||' that appears at /// the beginning of a CFGBlock that also (1) has a terminator and /// (2) has no other elements. If such an expression is found, it is returned. static const BinaryOperator *getLogicalOperatorInChain(const CFGBlock *block) { if (block->empty()) return 0; CFGElement front = block->front(); const CFGStmt *cstmt = front.getAs<CFGStmt>(); if (!cstmt) return 0; const BinaryOperator *b = dyn_cast_or_null<BinaryOperator>(cstmt->getStmt()); if (!b || !b->isLogicalOp()) return 0; if (block->pred_size() == 2) { if (block->getTerminatorCondition() == b) { if (block->succ_size() == 2) return b; } else if (block->size() == 1) return b; } return 0; } ValueVector &CFGBlockValues::getValueVector(const CFGBlock *block, const CFGBlock *dstBlock) { unsigned idx = block->getBlockID(); if (dstBlock && getLogicalOperatorInChain(block)) { if (*block->succ_begin() == dstBlock) return lazyCreate(vals[idx].first); assert(*(block->succ_begin()+1) == dstBlock); return lazyCreate(vals[idx].second); } assert(vals[idx].second == 0); return lazyCreate(vals[idx].first); } BVPair &CFGBlockValues::getValueVectors(const clang::CFGBlock *block, bool shouldLazyCreate) { unsigned idx = block->getBlockID(); lazyCreate(vals[idx].first); if (shouldLazyCreate) lazyCreate(vals[idx].second); return vals[idx]; } #if 0 static void printVector(const CFGBlock *block, ValueVector &bv, unsigned num) { llvm::errs() << block->getBlockID() << " :"; for (unsigned i = 0; i < bv.size(); ++i) { llvm::errs() << ' ' << bv[i]; } llvm::errs() << " : " << num << '\n'; } static void printVector(const char *name, ValueVector const &bv) { llvm::errs() << name << " : "; for (unsigned i = 0; i < bv.size(); ++i) { llvm::errs() << ' ' << bv[i]; } llvm::errs() << "\n"; } #endif void CFGBlockValues::mergeIntoScratch(ValueVector const &source, bool isFirst) { if (isFirst) scratch = source; else scratch |= source; } bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) { ValueVector &dst = getValueVector(block, 0); bool changed = (dst != scratch); if (changed) dst = scratch; #if 0 printVector(block, scratch, 0); #endif return changed; } bool CFGBlockValues::updateValueVectors(const CFGBlock *block, const BVPair &newVals) { BVPair &vals = getValueVectors(block, true); bool changed = *newVals.first != *vals.first || *newVals.second != *vals.second; *vals.first = *newVals.first; *vals.second = *newVals.second; #if 0 printVector(block, *vals.first, 1); printVector(block, *vals.second, 2); #endif return changed; } void CFGBlockValues::resetScratch() { scratch.reset(); } ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) { const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd); assert(idx.hasValue()); return scratch[idx.getValue()]; } //------------------------------------------------------------------------====// // Worklist: worklist for dataflow analysis. //====------------------------------------------------------------------------// namespace { class DataflowWorklist { SmallVector<const CFGBlock *, 20> worklist; llvm::BitVector enqueuedBlocks; public: DataflowWorklist(const CFG &cfg) : enqueuedBlocks(cfg.getNumBlockIDs()) {} void enqueueSuccessors(const CFGBlock *block); const CFGBlock *dequeue(); }; } void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) { unsigned OldWorklistSize = worklist.size(); for (CFGBlock::const_succ_iterator I = block->succ_begin(), E = block->succ_end(); I != E; ++I) { const CFGBlock *Successor = *I; if (!Successor || enqueuedBlocks[Successor->getBlockID()]) continue; worklist.push_back(Successor); enqueuedBlocks[Successor->getBlockID()] = true; } if (OldWorklistSize == 0 || OldWorklistSize == worklist.size()) return; // Rotate the newly added blocks to the start of the worklist so that it forms // a proper queue when we pop off the end of the worklist. std::rotate(worklist.begin(), worklist.begin() + OldWorklistSize, worklist.end()); } const CFGBlock *DataflowWorklist::dequeue() { if (worklist.empty()) return 0; const CFGBlock *b = worklist.back(); worklist.pop_back(); enqueuedBlocks[b->getBlockID()] = false; return b; } //------------------------------------------------------------------------====// // Transfer function for uninitialized values analysis. //====------------------------------------------------------------------------// namespace { class FindVarResult { const VarDecl *vd; const DeclRefExpr *dr; public: FindVarResult(VarDecl *vd, DeclRefExpr *dr) : vd(vd), dr(dr) {} const DeclRefExpr *getDeclRefExpr() const { return dr; } const VarDecl *getDecl() const { return vd; } }; class TransferFunctions : public StmtVisitor<TransferFunctions> { CFGBlockValues &vals; const CFG &cfg; AnalysisDeclContext ∾ UninitVariablesHandler *handler; /// The last DeclRefExpr seen when analyzing a block. Used to /// cheat when detecting cases when the address of a variable is taken. DeclRefExpr *lastDR; /// The last lvalue-to-rvalue conversion of a variable whose value /// was uninitialized. Normally this results in a warning, but it is /// possible to either silence the warning in some cases, or we /// propagate the uninitialized value. CastExpr *lastLoad; /// For some expressions, we want to ignore any post-processing after /// visitation. bool skipProcessUses; public: TransferFunctions(CFGBlockValues &vals, const CFG &cfg, AnalysisDeclContext &ac, UninitVariablesHandler *handler) : vals(vals), cfg(cfg), ac(ac), handler(handler), lastDR(0), lastLoad(0), skipProcessUses(false) {} void reportUninit(const DeclRefExpr *ex, const VarDecl *vd, bool isAlwaysUninit); void VisitBlockExpr(BlockExpr *be); void VisitDeclStmt(DeclStmt *ds); void VisitDeclRefExpr(DeclRefExpr *dr); void VisitUnaryOperator(UnaryOperator *uo); void VisitBinaryOperator(BinaryOperator *bo); void VisitCastExpr(CastExpr *ce); void VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs); void Visit(Stmt *s); bool isTrackedVar(const VarDecl *vd) { return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl())); } FindVarResult findBlockVarDecl(Expr *ex); void ProcessUses(Stmt *s = 0); }; } static const Expr *stripCasts(ASTContext &C, const Expr *Ex) { while (Ex) { Ex = Ex->IgnoreParenNoopCasts(C); if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) { if (CE->getCastKind() == CK_LValueBitCast) { Ex = CE->getSubExpr(); continue; } } break; } return Ex; } void TransferFunctions::reportUninit(const DeclRefExpr *ex, const VarDecl *vd, bool isAlwaysUnit) { if (handler) handler->handleUseOfUninitVariable(ex, vd, isAlwaysUnit); } FindVarResult TransferFunctions::findBlockVarDecl(Expr *ex) { if (DeclRefExpr *dr = dyn_cast<DeclRefExpr>(ex->IgnoreParenCasts())) if (VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl())) if (isTrackedVar(vd)) return FindVarResult(vd, dr); return FindVarResult(0, 0); } void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs) { // This represents an initialization of the 'element' value. Stmt *element = fs->getElement(); const VarDecl *vd = 0; if (DeclStmt *ds = dyn_cast<DeclStmt>(element)) { vd = cast<VarDecl>(ds->getSingleDecl()); if (!isTrackedVar(vd)) vd = 0; } else { // Initialize the value of the reference variable. const FindVarResult &res = findBlockVarDecl(cast<Expr>(element)); vd = res.getDecl(); } if (vd) vals[vd] = Initialized; } void TransferFunctions::VisitBlockExpr(BlockExpr *be) { const BlockDecl *bd = be->getBlockDecl(); for (BlockDecl::capture_const_iterator i = bd->capture_begin(), e = bd->capture_end() ; i != e; ++i) { const VarDecl *vd = i->getVariable(); if (!isTrackedVar(vd)) continue; if (i->isByRef()) { vals[vd] = Initialized; continue; } Value v = vals[vd]; if (handler && isUninitialized(v)) handler->handleUseOfUninitVariable(be, vd, isAlwaysUninit(v)); } } void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) { // Record the last DeclRefExpr seen. This is an lvalue computation. // We use this value to later detect if a variable "escapes" the analysis. if (const VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl())) if (isTrackedVar(vd)) { ProcessUses(); lastDR = dr; } } void TransferFunctions::VisitDeclStmt(DeclStmt *ds) { for (DeclStmt::decl_iterator DI = ds->decl_begin(), DE = ds->decl_end(); DI != DE; ++DI) { if (VarDecl *vd = dyn_cast<VarDecl>(*DI)) { if (isTrackedVar(vd)) { if (Expr *init = vd->getInit()) { // If the initializer consists solely of a reference to itself, we // explicitly mark the variable as uninitialized. This allows code // like the following: // // int x = x; // // to deliberately leave a variable uninitialized. Different analysis // clients can detect this pattern and adjust their reporting // appropriately, but we need to continue to analyze subsequent uses // of the variable. if (init == lastLoad) { const DeclRefExpr *DR = cast<DeclRefExpr>(stripCasts(ac.getASTContext(), lastLoad->getSubExpr())); if (DR->getDecl() == vd) { // int x = x; // Propagate uninitialized value, but don't immediately report // a problem. vals[vd] = Uninitialized; lastLoad = 0; lastDR = 0; if (handler) handler->handleSelfInit(vd); return; } } // All other cases: treat the new variable as initialized. // This is a minor optimization to reduce the propagation // of the analysis, since we will have already reported // the use of the uninitialized value (which visiting the // initializer). vals[vd] = Initialized; } } } } } void TransferFunctions::VisitBinaryOperator(clang::BinaryOperator *bo) { if (bo->isAssignmentOp()) { const FindVarResult &res = findBlockVarDecl(bo->getLHS()); if (const VarDecl *vd = res.getDecl()) { ValueVector::reference val = vals[vd]; if (isUninitialized(val)) { if (bo->getOpcode() != BO_Assign) reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val)); else val = Initialized; } } } } void TransferFunctions::VisitUnaryOperator(clang::UnaryOperator *uo) { switch (uo->getOpcode()) { case clang::UO_PostDec: case clang::UO_PostInc: case clang::UO_PreDec: case clang::UO_PreInc: { const FindVarResult &res = findBlockVarDecl(uo->getSubExpr()); if (const VarDecl *vd = res.getDecl()) { assert(res.getDeclRefExpr() == lastDR); // We null out lastDR to indicate we have fully processed it // and we don't want the auto-value setting in Visit(). lastDR = 0; ValueVector::reference val = vals[vd]; if (isUninitialized(val)) reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val)); } break; } default: break; } } void TransferFunctions::VisitCastExpr(clang::CastExpr *ce) { if (ce->getCastKind() == CK_LValueToRValue) { const FindVarResult &res = findBlockVarDecl(ce->getSubExpr()); if (res.getDecl()) { assert(res.getDeclRefExpr() == lastDR); lastLoad = ce; } } else if (ce->getCastKind() == CK_NoOp || ce->getCastKind() == CK_LValueBitCast) { skipProcessUses = true; } else if (CStyleCastExpr *cse = dyn_cast<CStyleCastExpr>(ce)) { if (cse->getType()->isVoidType()) { // e.g. (void) x; if (lastLoad == cse->getSubExpr()) { // Squelch any detected load of an uninitialized value if // we cast it to void. lastLoad = 0; lastDR = 0; } } } } void TransferFunctions::Visit(clang::Stmt *s) { skipProcessUses = false; StmtVisitor<TransferFunctions>::Visit(s); if (!skipProcessUses) ProcessUses(s); } void TransferFunctions::ProcessUses(Stmt *s) { // This method is typically called after visiting a CFGElement statement // in the CFG. We delay processing of reporting many loads of uninitialized // values until here. if (lastLoad) { // If we just visited the lvalue-to-rvalue cast, there is nothing // left to do. if (lastLoad == s) return; const DeclRefExpr *DR = cast<DeclRefExpr>(stripCasts(ac.getASTContext(), lastLoad->getSubExpr())); const VarDecl *VD = cast<VarDecl>(DR->getDecl()); // If we reach here, we may have seen a load of an uninitialized value // and it hasn't been casted to void or otherwise handled. In this // situation, report the incident. if (isUninitialized(vals[VD])) reportUninit(DR, VD, isAlwaysUninit(vals[VD])); lastLoad = 0; if (DR == lastDR) { lastDR = 0; return; } } // Any other uses of 'lastDR' involve taking an lvalue of variable. // In this case, it "escapes" the analysis. if (lastDR && lastDR != s) { vals[cast<VarDecl>(lastDR->getDecl())] = Initialized; lastDR = 0; } } //------------------------------------------------------------------------====// // High-level "driver" logic for uninitialized values analysis. //====------------------------------------------------------------------------// static bool runOnBlock(const CFGBlock *block, const CFG &cfg, AnalysisDeclContext &ac, CFGBlockValues &vals, llvm::BitVector &wasAnalyzed, UninitVariablesHandler *handler = 0) { wasAnalyzed[block->getBlockID()] = true; if (const BinaryOperator *b = getLogicalOperatorInChain(block)) { CFGBlock::const_pred_iterator itr = block->pred_begin(); BVPair vA = vals.getValueVectors(*itr, false); ++itr; BVPair vB = vals.getValueVectors(*itr, false); BVPair valsAB; if (b->getOpcode() == BO_LAnd) { // Merge the 'F' bits from the first and second. vals.mergeIntoScratch(*(vA.second ? vA.second : vA.first), true); vals.mergeIntoScratch(*(vB.second ? vB.second : vB.first), false); valsAB.first = vA.first; valsAB.second = &vals.getScratch(); } else { // Merge the 'T' bits from the first and second. assert(b->getOpcode() == BO_LOr); vals.mergeIntoScratch(*vA.first, true); vals.mergeIntoScratch(*vB.first, false); valsAB.first = &vals.getScratch(); valsAB.second = vA.second ? vA.second : vA.first; } return vals.updateValueVectors(block, valsAB); } // Default behavior: merge in values of predecessor blocks. vals.resetScratch(); bool isFirst = true; for (CFGBlock::const_pred_iterator I = block->pred_begin(), E = block->pred_end(); I != E; ++I) { const CFGBlock *pred = *I; if (wasAnalyzed[pred->getBlockID()]) { vals.mergeIntoScratch(vals.getValueVector(pred, block), isFirst); isFirst = false; } } // Apply the transfer function. TransferFunctions tf(vals, cfg, ac, handler); for (CFGBlock::const_iterator I = block->begin(), E = block->end(); I != E; ++I) { if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) { tf.Visit(const_cast<Stmt*>(cs->getStmt())); } } tf.ProcessUses(); return vals.updateValueVectorWithScratch(block); } void clang::runUninitializedVariablesAnalysis( const DeclContext &dc, const CFG &cfg, AnalysisDeclContext &ac, UninitVariablesHandler &handler, UninitVariablesAnalysisStats &stats) { CFGBlockValues vals(cfg); vals.computeSetOfDeclarations(dc); if (vals.hasNoDeclarations()) return; stats.NumVariablesAnalyzed = vals.getNumEntries(); // Mark all variables uninitialized at the entry. const CFGBlock &entry = cfg.getEntry(); for (CFGBlock::const_succ_iterator i = entry.succ_begin(), e = entry.succ_end(); i != e; ++i) { if (const CFGBlock *succ = *i) { ValueVector &vec = vals.getValueVector(&entry, succ); const unsigned n = vals.getNumEntries(); for (unsigned j = 0; j < n ; ++j) { vec[j] = Uninitialized; } } } // Proceed with the workist. DataflowWorklist worklist(cfg); llvm::BitVector previouslyVisited(cfg.getNumBlockIDs()); worklist.enqueueSuccessors(&cfg.getEntry()); llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false); wasAnalyzed[cfg.getEntry().getBlockID()] = true; while (const CFGBlock *block = worklist.dequeue()) { // Did the block change? bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed); ++stats.NumBlockVisits; if (changed || !previouslyVisited[block->getBlockID()]) worklist.enqueueSuccessors(block); previouslyVisited[block->getBlockID()] = true; } // Run through the blocks one more time, and report uninitialized variabes. for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) { const CFGBlock *block = *BI; if (wasAnalyzed[block->getBlockID()]) { runOnBlock(block, cfg, ac, vals, wasAnalyzed, &handler); ++stats.NumBlockVisits; } } } UninitVariablesHandler::~UninitVariablesHandler() {}