| //===- UninitializedValues.cpp - Find Uninitialized Values ----------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements uninitialized values analysis for source-level CFGs. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "clang/Analysis/Analyses/UninitializedValues.h" |
| #include "clang/AST/Attr.h" |
| #include "clang/AST/Decl.h" |
| #include "clang/AST/DeclBase.h" |
| #include "clang/AST/Expr.h" |
| #include "clang/AST/OperationKinds.h" |
| #include "clang/AST/Stmt.h" |
| #include "clang/AST/StmtObjC.h" |
| #include "clang/AST/StmtVisitor.h" |
| #include "clang/AST/Type.h" |
| #include "clang/Analysis/Analyses/PostOrderCFGView.h" |
| #include "clang/Analysis/AnalysisDeclContext.h" |
| #include "clang/Analysis/CFG.h" |
| #include "clang/Analysis/DomainSpecific/ObjCNoReturn.h" |
| #include "clang/Basic/LLVM.h" |
| #include "llvm/ADT/BitVector.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/None.h" |
| #include "llvm/ADT/Optional.h" |
| #include "llvm/ADT/PackedVector.h" |
| #include "llvm/ADT/SmallBitVector.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/Support/Casting.h" |
| #include <algorithm> |
| #include <cassert> |
| |
| using namespace clang; |
| |
| #define DEBUG_LOGGING 0 |
| |
| static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) { |
| if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() && |
| !vd->isExceptionVariable() && !vd->isInitCapture() && |
| !vd->isImplicit() && vd->getDeclContext() == dc) { |
| QualType ty = vd->getType(); |
| return ty->isScalarType() || ty->isVectorType() || ty->isRecordType(); |
| } |
| return false; |
| } |
| |
| //------------------------------------------------------------------------====// |
| // DeclToIndex: a mapping from Decls we track to value indices. |
| //====------------------------------------------------------------------------// |
| |
| namespace { |
| |
| class DeclToIndex { |
| llvm::DenseMap<const VarDecl *, unsigned> map; |
| |
| public: |
| DeclToIndex() = default; |
| |
| /// 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. |
| Optional<unsigned> getValueIndex(const VarDecl *d) const; |
| }; |
| |
| } // namespace |
| |
| 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++; |
| } |
| } |
| |
| Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const { |
| llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d); |
| if (I == map.end()) |
| return None; |
| 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 { |
| |
| using ValueVector = llvm::PackedVector<Value, 2, llvm::SmallBitVector>; |
| |
| class CFGBlockValues { |
| const CFG &cfg; |
| SmallVector<ValueVector, 8> vals; |
| ValueVector scratch; |
| DeclToIndex declToIndex; |
| |
| public: |
| CFGBlockValues(const CFG &cfg); |
| |
| unsigned getNumEntries() const { return declToIndex.size(); } |
| |
| void computeSetOfDeclarations(const DeclContext &dc); |
| |
| ValueVector &getValueVector(const CFGBlock *block) { |
| return vals[block->getBlockID()]; |
| } |
| |
| void setAllScratchValues(Value V); |
| void mergeIntoScratch(ValueVector const &source, bool isFirst); |
| bool updateValueVectorWithScratch(const CFGBlock *block); |
| |
| bool hasNoDeclarations() const { |
| return declToIndex.size() == 0; |
| } |
| |
| void resetScratch(); |
| |
| ValueVector::reference operator[](const VarDecl *vd); |
| |
| Value getValue(const CFGBlock *block, const CFGBlock *dstBlock, |
| const VarDecl *vd) { |
| const Optional<unsigned> &idx = declToIndex.getValueIndex(vd); |
| assert(idx.hasValue()); |
| return getValueVector(block)[idx.getValue()]; |
| } |
| }; |
| |
| } // namespace |
| |
| CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {} |
| |
| void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) { |
| declToIndex.computeMap(dc); |
| unsigned decls = declToIndex.size(); |
| scratch.resize(decls); |
| unsigned n = cfg.getNumBlockIDs(); |
| if (!n) |
| return; |
| vals.resize(n); |
| for (auto &val : vals) |
| val.resize(decls); |
| } |
| |
| #if DEBUG_LOGGING |
| static void printVector(const CFGBlock *block, ValueVector &bv, |
| unsigned num) { |
| llvm::errs() << block->getBlockID() << " :"; |
| for (const auto &i : bv) |
| llvm::errs() << ' ' << i; |
| llvm::errs() << " : " << num << '\n'; |
| } |
| #endif |
| |
| void CFGBlockValues::setAllScratchValues(Value V) { |
| for (unsigned I = 0, E = scratch.size(); I != E; ++I) |
| scratch[I] = V; |
| } |
| |
| 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); |
| bool changed = (dst != scratch); |
| if (changed) |
| dst = scratch; |
| #if DEBUG_LOGGING |
| printVector(block, scratch, 0); |
| #endif |
| return changed; |
| } |
| |
| void CFGBlockValues::resetScratch() { |
| scratch.reset(); |
| } |
| |
| ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) { |
| const Optional<unsigned> &idx = declToIndex.getValueIndex(vd); |
| assert(idx.hasValue()); |
| return scratch[idx.getValue()]; |
| } |
| |
| //------------------------------------------------------------------------====// |
| // Worklist: worklist for dataflow analysis. |
| //====------------------------------------------------------------------------// |
| |
| namespace { |
| |
| class DataflowWorklist { |
| PostOrderCFGView::iterator PO_I, PO_E; |
| SmallVector<const CFGBlock *, 20> worklist; |
| llvm::BitVector enqueuedBlocks; |
| |
| public: |
| DataflowWorklist(const CFG &cfg, PostOrderCFGView &view) |
| : PO_I(view.begin()), PO_E(view.end()), |
| enqueuedBlocks(cfg.getNumBlockIDs(), true) { |
| // Treat the first block as already analyzed. |
| if (PO_I != PO_E) { |
| assert(*PO_I == &cfg.getEntry()); |
| enqueuedBlocks[(*PO_I)->getBlockID()] = false; |
| ++PO_I; |
| } |
| } |
| |
| void enqueueSuccessors(const CFGBlock *block); |
| const CFGBlock *dequeue(); |
| }; |
| |
| } // namespace |
| |
| void DataflowWorklist::enqueueSuccessors(const CFGBlock *block) { |
| 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; |
| } |
| } |
| |
| const CFGBlock *DataflowWorklist::dequeue() { |
| const CFGBlock *B = nullptr; |
| |
| // First dequeue from the worklist. This can represent |
| // updates along backedges that we want propagated as quickly as possible. |
| if (!worklist.empty()) |
| B = worklist.pop_back_val(); |
| |
| // Next dequeue from the initial reverse post order. This is the |
| // theoretical ideal in the presence of no back edges. |
| else if (PO_I != PO_E) { |
| B = *PO_I; |
| ++PO_I; |
| } |
| else |
| return nullptr; |
| |
| assert(enqueuedBlocks[B->getBlockID()] == true); |
| enqueuedBlocks[B->getBlockID()] = false; |
| return B; |
| } |
| |
| //------------------------------------------------------------------------====// |
| // Classification of DeclRefExprs as use or initialization. |
| //====------------------------------------------------------------------------// |
| |
| namespace { |
| |
| class FindVarResult { |
| const VarDecl *vd; |
| const DeclRefExpr *dr; |
| |
| public: |
| FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {} |
| |
| const DeclRefExpr *getDeclRefExpr() const { return dr; } |
| const VarDecl *getDecl() const { return vd; } |
| }; |
| |
| } // namespace |
| |
| static const Expr *stripCasts(ASTContext &C, const Expr *Ex) { |
| while (Ex) { |
| Ex = Ex->IgnoreParenNoopCasts(C); |
| if (const auto *CE = dyn_cast<CastExpr>(Ex)) { |
| if (CE->getCastKind() == CK_LValueBitCast) { |
| Ex = CE->getSubExpr(); |
| continue; |
| } |
| } |
| break; |
| } |
| return Ex; |
| } |
| |
| /// If E is an expression comprising a reference to a single variable, find that |
| /// variable. |
| static FindVarResult findVar(const Expr *E, const DeclContext *DC) { |
| if (const auto *DRE = |
| dyn_cast<DeclRefExpr>(stripCasts(DC->getParentASTContext(), E))) |
| if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl())) |
| if (isTrackedVar(VD, DC)) |
| return FindVarResult(VD, DRE); |
| return FindVarResult(nullptr, nullptr); |
| } |
| |
| namespace { |
| |
| /// Classify each DeclRefExpr as an initialization or a use. Any |
| /// DeclRefExpr which isn't explicitly classified will be assumed to have |
| /// escaped the analysis and will be treated as an initialization. |
| class ClassifyRefs : public StmtVisitor<ClassifyRefs> { |
| public: |
| enum Class { |
| Init, |
| Use, |
| SelfInit, |
| Ignore |
| }; |
| |
| private: |
| const DeclContext *DC; |
| llvm::DenseMap<const DeclRefExpr *, Class> Classification; |
| |
| bool isTrackedVar(const VarDecl *VD) const { |
| return ::isTrackedVar(VD, DC); |
| } |
| |
| void classify(const Expr *E, Class C); |
| |
| public: |
| ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {} |
| |
| void VisitDeclStmt(DeclStmt *DS); |
| void VisitUnaryOperator(UnaryOperator *UO); |
| void VisitBinaryOperator(BinaryOperator *BO); |
| void VisitCallExpr(CallExpr *CE); |
| void VisitCastExpr(CastExpr *CE); |
| void VisitOMPExecutableDirective(OMPExecutableDirective *ED); |
| |
| void operator()(Stmt *S) { Visit(S); } |
| |
| Class get(const DeclRefExpr *DRE) const { |
| llvm::DenseMap<const DeclRefExpr*, Class>::const_iterator I |
| = Classification.find(DRE); |
| if (I != Classification.end()) |
| return I->second; |
| |
| const auto *VD = dyn_cast<VarDecl>(DRE->getDecl()); |
| if (!VD || !isTrackedVar(VD)) |
| return Ignore; |
| |
| return Init; |
| } |
| }; |
| |
| } // namespace |
| |
| static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) { |
| if (VD->getType()->isRecordType()) |
| return nullptr; |
| if (Expr *Init = VD->getInit()) { |
| const auto *DRE = |
| dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init)); |
| if (DRE && DRE->getDecl() == VD) |
| return DRE; |
| } |
| return nullptr; |
| } |
| |
| void ClassifyRefs::classify(const Expr *E, Class C) { |
| // The result of a ?: could also be an lvalue. |
| E = E->IgnoreParens(); |
| if (const auto *CO = dyn_cast<ConditionalOperator>(E)) { |
| classify(CO->getTrueExpr(), C); |
| classify(CO->getFalseExpr(), C); |
| return; |
| } |
| |
| if (const auto *BCO = dyn_cast<BinaryConditionalOperator>(E)) { |
| classify(BCO->getFalseExpr(), C); |
| return; |
| } |
| |
| if (const auto *OVE = dyn_cast<OpaqueValueExpr>(E)) { |
| classify(OVE->getSourceExpr(), C); |
| return; |
| } |
| |
| if (const auto *ME = dyn_cast<MemberExpr>(E)) { |
| if (const auto *VD = dyn_cast<VarDecl>(ME->getMemberDecl())) { |
| if (!VD->isStaticDataMember()) |
| classify(ME->getBase(), C); |
| } |
| return; |
| } |
| |
| if (const auto *BO = dyn_cast<BinaryOperator>(E)) { |
| switch (BO->getOpcode()) { |
| case BO_PtrMemD: |
| case BO_PtrMemI: |
| classify(BO->getLHS(), C); |
| return; |
| case BO_Comma: |
| classify(BO->getRHS(), C); |
| return; |
| default: |
| return; |
| } |
| } |
| |
| FindVarResult Var = findVar(E, DC); |
| if (const DeclRefExpr *DRE = Var.getDeclRefExpr()) |
| Classification[DRE] = std::max(Classification[DRE], C); |
| } |
| |
| void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) { |
| for (auto *DI : DS->decls()) { |
| auto *VD = dyn_cast<VarDecl>(DI); |
| if (VD && isTrackedVar(VD)) |
| if (const DeclRefExpr *DRE = getSelfInitExpr(VD)) |
| Classification[DRE] = SelfInit; |
| } |
| } |
| |
| void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) { |
| // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this |
| // is not a compound-assignment, we will treat it as initializing the variable |
| // when TransferFunctions visits it. A compound-assignment does not affect |
| // whether a variable is uninitialized, and there's no point counting it as a |
| // use. |
| if (BO->isCompoundAssignmentOp()) |
| classify(BO->getLHS(), Use); |
| else if (BO->getOpcode() == BO_Assign || BO->getOpcode() == BO_Comma) |
| classify(BO->getLHS(), Ignore); |
| } |
| |
| void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) { |
| // Increment and decrement are uses despite there being no lvalue-to-rvalue |
| // conversion. |
| if (UO->isIncrementDecrementOp()) |
| classify(UO->getSubExpr(), Use); |
| } |
| |
| void ClassifyRefs::VisitOMPExecutableDirective(OMPExecutableDirective *ED) { |
| for (Stmt *S : OMPExecutableDirective::used_clauses_children(ED->clauses())) |
| classify(cast<Expr>(S), Use); |
| } |
| |
| static bool isPointerToConst(const QualType &QT) { |
| return QT->isAnyPointerType() && QT->getPointeeType().isConstQualified(); |
| } |
| |
| void ClassifyRefs::VisitCallExpr(CallExpr *CE) { |
| // Classify arguments to std::move as used. |
| if (CE->isCallToStdMove()) { |
| // RecordTypes are handled in SemaDeclCXX.cpp. |
| if (!CE->getArg(0)->getType()->isRecordType()) |
| classify(CE->getArg(0), Use); |
| return; |
| } |
| |
| // If a value is passed by const pointer or by const reference to a function, |
| // we should not assume that it is initialized by the call, and we |
| // conservatively do not assume that it is used. |
| for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end(); |
| I != E; ++I) { |
| if ((*I)->isGLValue()) { |
| if ((*I)->getType().isConstQualified()) |
| classify((*I), Ignore); |
| } else if (isPointerToConst((*I)->getType())) { |
| const Expr *Ex = stripCasts(DC->getParentASTContext(), *I); |
| const auto *UO = dyn_cast<UnaryOperator>(Ex); |
| if (UO && UO->getOpcode() == UO_AddrOf) |
| Ex = UO->getSubExpr(); |
| classify(Ex, Ignore); |
| } |
| } |
| } |
| |
| void ClassifyRefs::VisitCastExpr(CastExpr *CE) { |
| if (CE->getCastKind() == CK_LValueToRValue) |
| classify(CE->getSubExpr(), Use); |
| else if (const auto *CSE = dyn_cast<CStyleCastExpr>(CE)) { |
| if (CSE->getType()->isVoidType()) { |
| // Squelch any detected load of an uninitialized value if |
| // we cast it to void. |
| // e.g. (void) x; |
| classify(CSE->getSubExpr(), Ignore); |
| } |
| } |
| } |
| |
| //------------------------------------------------------------------------====// |
| // Transfer function for uninitialized values analysis. |
| //====------------------------------------------------------------------------// |
| |
| namespace { |
| |
| class TransferFunctions : public StmtVisitor<TransferFunctions> { |
| CFGBlockValues &vals; |
| const CFG &cfg; |
| const CFGBlock *block; |
| AnalysisDeclContext ∾ |
| const ClassifyRefs &classification; |
| ObjCNoReturn objCNoRet; |
| UninitVariablesHandler &handler; |
| |
| public: |
| TransferFunctions(CFGBlockValues &vals, const CFG &cfg, |
| const CFGBlock *block, AnalysisDeclContext &ac, |
| const ClassifyRefs &classification, |
| UninitVariablesHandler &handler) |
| : vals(vals), cfg(cfg), block(block), ac(ac), |
| classification(classification), objCNoRet(ac.getASTContext()), |
| handler(handler) {} |
| |
| void reportUse(const Expr *ex, const VarDecl *vd); |
| |
| void VisitBinaryOperator(BinaryOperator *bo); |
| void VisitBlockExpr(BlockExpr *be); |
| void VisitCallExpr(CallExpr *ce); |
| void VisitDeclRefExpr(DeclRefExpr *dr); |
| void VisitDeclStmt(DeclStmt *ds); |
| void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS); |
| void VisitObjCMessageExpr(ObjCMessageExpr *ME); |
| void VisitOMPExecutableDirective(OMPExecutableDirective *ED); |
| |
| bool isTrackedVar(const VarDecl *vd) { |
| return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl())); |
| } |
| |
| FindVarResult findVar(const Expr *ex) { |
| return ::findVar(ex, cast<DeclContext>(ac.getDecl())); |
| } |
| |
| UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) { |
| UninitUse Use(ex, isAlwaysUninit(v)); |
| |
| assert(isUninitialized(v)); |
| if (Use.getKind() == UninitUse::Always) |
| return Use; |
| |
| // If an edge which leads unconditionally to this use did not initialize |
| // the variable, we can say something stronger than 'may be uninitialized': |
| // we can say 'either it's used uninitialized or you have dead code'. |
| // |
| // We track the number of successors of a node which have been visited, and |
| // visit a node once we have visited all of its successors. Only edges where |
| // the variable might still be uninitialized are followed. Since a variable |
| // can't transfer from being initialized to being uninitialized, this will |
| // trace out the subgraph which inevitably leads to the use and does not |
| // initialize the variable. We do not want to skip past loops, since their |
| // non-termination might be correlated with the initialization condition. |
| // |
| // For example: |
| // |
| // void f(bool a, bool b) { |
| // block1: int n; |
| // if (a) { |
| // block2: if (b) |
| // block3: n = 1; |
| // block4: } else if (b) { |
| // block5: while (!a) { |
| // block6: do_work(&a); |
| // n = 2; |
| // } |
| // } |
| // block7: if (a) |
| // block8: g(); |
| // block9: return n; |
| // } |
| // |
| // Starting from the maybe-uninitialized use in block 9: |
| // * Block 7 is not visited because we have only visited one of its two |
| // successors. |
| // * Block 8 is visited because we've visited its only successor. |
| // From block 8: |
| // * Block 7 is visited because we've now visited both of its successors. |
| // From block 7: |
| // * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all |
| // of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively). |
| // * Block 3 is not visited because it initializes 'n'. |
| // Now the algorithm terminates, having visited blocks 7 and 8, and having |
| // found the frontier is blocks 2, 4, and 5. |
| // |
| // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2 |
| // and 4), so we report that any time either of those edges is taken (in |
| // each case when 'b == false'), 'n' is used uninitialized. |
| SmallVector<const CFGBlock*, 32> Queue; |
| SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0); |
| Queue.push_back(block); |
| // Specify that we've already visited all successors of the starting block. |
| // This has the dual purpose of ensuring we never add it to the queue, and |
| // of marking it as not being a candidate element of the frontier. |
| SuccsVisited[block->getBlockID()] = block->succ_size(); |
| while (!Queue.empty()) { |
| const CFGBlock *B = Queue.pop_back_val(); |
| |
| // If the use is always reached from the entry block, make a note of that. |
| if (B == &cfg.getEntry()) |
| Use.setUninitAfterCall(); |
| |
| for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end(); |
| I != E; ++I) { |
| const CFGBlock *Pred = *I; |
| if (!Pred) |
| continue; |
| |
| Value AtPredExit = vals.getValue(Pred, B, vd); |
| if (AtPredExit == Initialized) |
| // This block initializes the variable. |
| continue; |
| if (AtPredExit == MayUninitialized && |
| vals.getValue(B, nullptr, vd) == Uninitialized) { |
| // This block declares the variable (uninitialized), and is reachable |
| // from a block that initializes the variable. We can't guarantee to |
| // give an earlier location for the diagnostic (and it appears that |
| // this code is intended to be reachable) so give a diagnostic here |
| // and go no further down this path. |
| Use.setUninitAfterDecl(); |
| continue; |
| } |
| |
| unsigned &SV = SuccsVisited[Pred->getBlockID()]; |
| if (!SV) { |
| // When visiting the first successor of a block, mark all NULL |
| // successors as having been visited. |
| for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(), |
| SE = Pred->succ_end(); |
| SI != SE; ++SI) |
| if (!*SI) |
| ++SV; |
| } |
| |
| if (++SV == Pred->succ_size()) |
| // All paths from this block lead to the use and don't initialize the |
| // variable. |
| Queue.push_back(Pred); |
| } |
| } |
| |
| // Scan the frontier, looking for blocks where the variable was |
| // uninitialized. |
| for (const auto *Block : cfg) { |
| unsigned BlockID = Block->getBlockID(); |
| const Stmt *Term = Block->getTerminatorStmt(); |
| if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() && |
| Term) { |
| // This block inevitably leads to the use. If we have an edge from here |
| // to a post-dominator block, and the variable is uninitialized on that |
| // edge, we have found a bug. |
| for (CFGBlock::const_succ_iterator I = Block->succ_begin(), |
| E = Block->succ_end(); I != E; ++I) { |
| const CFGBlock *Succ = *I; |
| if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() && |
| vals.getValue(Block, Succ, vd) == Uninitialized) { |
| // Switch cases are a special case: report the label to the caller |
| // as the 'terminator', not the switch statement itself. Suppress |
| // situations where no label matched: we can't be sure that's |
| // possible. |
| if (isa<SwitchStmt>(Term)) { |
| const Stmt *Label = Succ->getLabel(); |
| if (!Label || !isa<SwitchCase>(Label)) |
| // Might not be possible. |
| continue; |
| UninitUse::Branch Branch; |
| Branch.Terminator = Label; |
| Branch.Output = 0; // Ignored. |
| Use.addUninitBranch(Branch); |
| } else { |
| UninitUse::Branch Branch; |
| Branch.Terminator = Term; |
| Branch.Output = I - Block->succ_begin(); |
| Use.addUninitBranch(Branch); |
| } |
| } |
| } |
| } |
| } |
| |
| return Use; |
| } |
| }; |
| |
| } // namespace |
| |
| void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) { |
| Value v = vals[vd]; |
| if (isUninitialized(v)) |
| handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v)); |
| } |
| |
| void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) { |
| // This represents an initialization of the 'element' value. |
| if (const auto *DS = dyn_cast<DeclStmt>(FS->getElement())) { |
| const auto *VD = cast<VarDecl>(DS->getSingleDecl()); |
| if (isTrackedVar(VD)) |
| vals[VD] = Initialized; |
| } |
| } |
| |
| void TransferFunctions::VisitOMPExecutableDirective( |
| OMPExecutableDirective *ED) { |
| for (Stmt *S : OMPExecutableDirective::used_clauses_children(ED->clauses())) { |
| assert(S && "Expected non-null used-in-clause child."); |
| Visit(S); |
| } |
| if (!ED->isStandaloneDirective()) |
| Visit(ED->getStructuredBlock()); |
| } |
| |
| void TransferFunctions::VisitBlockExpr(BlockExpr *be) { |
| const BlockDecl *bd = be->getBlockDecl(); |
| for (const auto &I : bd->captures()) { |
| const VarDecl *vd = I.getVariable(); |
| if (!isTrackedVar(vd)) |
| continue; |
| if (I.isByRef()) { |
| vals[vd] = Initialized; |
| continue; |
| } |
| reportUse(be, vd); |
| } |
| } |
| |
| void TransferFunctions::VisitCallExpr(CallExpr *ce) { |
| if (Decl *Callee = ce->getCalleeDecl()) { |
| if (Callee->hasAttr<ReturnsTwiceAttr>()) { |
| // After a call to a function like setjmp or vfork, any variable which is |
| // initialized anywhere within this function may now be initialized. For |
| // now, just assume such a call initializes all variables. FIXME: Only |
| // mark variables as initialized if they have an initializer which is |
| // reachable from here. |
| vals.setAllScratchValues(Initialized); |
| } |
| else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) { |
| // Functions labeled like "analyzer_noreturn" are often used to denote |
| // "panic" functions that in special debug situations can still return, |
| // but for the most part should not be treated as returning. This is a |
| // useful annotation borrowed from the static analyzer that is useful for |
| // suppressing branch-specific false positives when we call one of these |
| // functions but keep pretending the path continues (when in reality the |
| // user doesn't care). |
| vals.setAllScratchValues(Unknown); |
| } |
| } |
| } |
| |
| void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) { |
| switch (classification.get(dr)) { |
| case ClassifyRefs::Ignore: |
| break; |
| case ClassifyRefs::Use: |
| reportUse(dr, cast<VarDecl>(dr->getDecl())); |
| break; |
| case ClassifyRefs::Init: |
| vals[cast<VarDecl>(dr->getDecl())] = Initialized; |
| break; |
| case ClassifyRefs::SelfInit: |
| handler.handleSelfInit(cast<VarDecl>(dr->getDecl())); |
| break; |
| } |
| } |
| |
| void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) { |
| if (BO->getOpcode() == BO_Assign) { |
| FindVarResult Var = findVar(BO->getLHS()); |
| if (const VarDecl *VD = Var.getDecl()) |
| vals[VD] = Initialized; |
| } |
| } |
| |
| void TransferFunctions::VisitDeclStmt(DeclStmt *DS) { |
| for (auto *DI : DS->decls()) { |
| auto *VD = dyn_cast<VarDecl>(DI); |
| if (VD && isTrackedVar(VD)) { |
| if (getSelfInitExpr(VD)) { |
| // 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. |
| vals[VD] = Uninitialized; |
| } else if (VD->getInit()) { |
| // Treat the new variable as initialized. |
| vals[VD] = Initialized; |
| } else { |
| // No initializer: the variable is now uninitialized. This matters |
| // for cases like: |
| // while (...) { |
| // int n; |
| // use(n); |
| // n = 0; |
| // } |
| // FIXME: Mark the variable as uninitialized whenever its scope is |
| // left, since its scope could be re-entered by a jump over the |
| // declaration. |
| vals[VD] = Uninitialized; |
| } |
| } |
| } |
| } |
| |
| void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) { |
| // If the Objective-C message expression is an implicit no-return that |
| // is not modeled in the CFG, set the tracked dataflow values to Unknown. |
| if (objCNoRet.isImplicitNoReturn(ME)) { |
| vals.setAllScratchValues(Unknown); |
| } |
| } |
| |
| //------------------------------------------------------------------------====// |
| // High-level "driver" logic for uninitialized values analysis. |
| //====------------------------------------------------------------------------// |
| |
| static bool runOnBlock(const CFGBlock *block, const CFG &cfg, |
| AnalysisDeclContext &ac, CFGBlockValues &vals, |
| const ClassifyRefs &classification, |
| llvm::BitVector &wasAnalyzed, |
| UninitVariablesHandler &handler) { |
| wasAnalyzed[block->getBlockID()] = true; |
| vals.resetScratch(); |
| // Merge in values of predecessor blocks. |
| bool isFirst = true; |
| for (CFGBlock::const_pred_iterator I = block->pred_begin(), |
| E = block->pred_end(); I != E; ++I) { |
| const CFGBlock *pred = *I; |
| if (!pred) |
| continue; |
| if (wasAnalyzed[pred->getBlockID()]) { |
| vals.mergeIntoScratch(vals.getValueVector(pred), isFirst); |
| isFirst = false; |
| } |
| } |
| // Apply the transfer function. |
| TransferFunctions tf(vals, cfg, block, ac, classification, handler); |
| for (const auto &I : *block) { |
| if (Optional<CFGStmt> cs = I.getAs<CFGStmt>()) |
| tf.Visit(const_cast<Stmt *>(cs->getStmt())); |
| } |
| return vals.updateValueVectorWithScratch(block); |
| } |
| |
| namespace { |
| |
| /// PruneBlocksHandler is a special UninitVariablesHandler that is used |
| /// to detect when a CFGBlock has any *potential* use of an uninitialized |
| /// variable. It is mainly used to prune out work during the final |
| /// reporting pass. |
| struct PruneBlocksHandler : public UninitVariablesHandler { |
| /// Records if a CFGBlock had a potential use of an uninitialized variable. |
| llvm::BitVector hadUse; |
| |
| /// Records if any CFGBlock had a potential use of an uninitialized variable. |
| bool hadAnyUse = false; |
| |
| /// The current block to scribble use information. |
| unsigned currentBlock = 0; |
| |
| PruneBlocksHandler(unsigned numBlocks) : hadUse(numBlocks, false) {} |
| |
| ~PruneBlocksHandler() override = default; |
| |
| void handleUseOfUninitVariable(const VarDecl *vd, |
| const UninitUse &use) override { |
| hadUse[currentBlock] = true; |
| hadAnyUse = true; |
| } |
| |
| /// Called when the uninitialized variable analysis detects the |
| /// idiom 'int x = x'. All other uses of 'x' within the initializer |
| /// are handled by handleUseOfUninitVariable. |
| void handleSelfInit(const VarDecl *vd) override { |
| hadUse[currentBlock] = true; |
| hadAnyUse = true; |
| } |
| }; |
| |
| } // namespace |
| |
| 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(); |
| |
| // Precompute which expressions are uses and which are initializations. |
| ClassifyRefs classification(ac); |
| cfg.VisitBlockStmts(classification); |
| |
| // Mark all variables uninitialized at the entry. |
| const CFGBlock &entry = cfg.getEntry(); |
| ValueVector &vec = vals.getValueVector(&entry); |
| const unsigned n = vals.getNumEntries(); |
| for (unsigned j = 0; j < n; ++j) { |
| vec[j] = Uninitialized; |
| } |
| |
| // Proceed with the workist. |
| DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>()); |
| llvm::BitVector previouslyVisited(cfg.getNumBlockIDs()); |
| worklist.enqueueSuccessors(&cfg.getEntry()); |
| llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false); |
| wasAnalyzed[cfg.getEntry().getBlockID()] = true; |
| PruneBlocksHandler PBH(cfg.getNumBlockIDs()); |
| |
| while (const CFGBlock *block = worklist.dequeue()) { |
| PBH.currentBlock = block->getBlockID(); |
| |
| // Did the block change? |
| bool changed = runOnBlock(block, cfg, ac, vals, |
| classification, wasAnalyzed, PBH); |
| ++stats.NumBlockVisits; |
| if (changed || !previouslyVisited[block->getBlockID()]) |
| worklist.enqueueSuccessors(block); |
| previouslyVisited[block->getBlockID()] = true; |
| } |
| |
| if (!PBH.hadAnyUse) |
| return; |
| |
| // Run through the blocks one more time, and report uninitialized variables. |
| for (const auto *block : cfg) |
| if (PBH.hadUse[block->getBlockID()]) { |
| runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler); |
| ++stats.NumBlockVisits; |
| } |
| } |
| |
| UninitVariablesHandler::~UninitVariablesHandler() = default; |