1 //==- UninitializedValues.cpp - Find Uninitialized Values -------*- C++ --*-==//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements uninitialized values analysis for source-level CFGs.
12 //===----------------------------------------------------------------------===//
14 #include "clang/AST/ASTContext.h"
15 #include "clang/AST/Attr.h"
16 #include "clang/AST/Decl.h"
17 #include "clang/AST/DeclCXX.h"
18 #include "clang/AST/StmtVisitor.h"
19 #include "clang/Analysis/Analyses/PostOrderCFGView.h"
20 #include "clang/Analysis/Analyses/UninitializedValues.h"
21 #include "clang/Analysis/AnalysisDeclContext.h"
22 #include "clang/Analysis/CFG.h"
23 #include "clang/Analysis/DomainSpecific/ObjCNoReturn.h"
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/Optional.h"
26 #include "llvm/ADT/PackedVector.h"
27 #include "llvm/ADT/SmallBitVector.h"
28 #include "llvm/ADT/SmallVector.h"
29 #include "llvm/Support/SaveAndRestore.h"
32 using namespace clang;
34 #define DEBUG_LOGGING 0
36 static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
37 if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
38 !vd->isExceptionVariable() && !vd->isInitCapture() &&
39 !vd->isImplicit() && vd->getDeclContext() == dc) {
40 QualType ty = vd->getType();
41 return ty->isScalarType() || ty->isVectorType() || ty->isRecordType();
46 //------------------------------------------------------------------------====//
47 // DeclToIndex: a mapping from Decls we track to value indices.
48 //====------------------------------------------------------------------------//
52 llvm::DenseMap<const VarDecl *, unsigned> map;
56 /// Compute the actual mapping from declarations to bits.
57 void computeMap(const DeclContext &dc);
59 /// Return the number of declarations in the map.
60 unsigned size() const { return map.size(); }
62 /// Returns the bit vector index for a given declaration.
63 Optional<unsigned> getValueIndex(const VarDecl *d) const;
67 void DeclToIndex::computeMap(const DeclContext &dc) {
69 DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
71 for ( ; I != E; ++I) {
72 const VarDecl *vd = *I;
73 if (isTrackedVar(vd, &dc))
78 Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
79 llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
85 //------------------------------------------------------------------------====//
86 // CFGBlockValues: dataflow values for CFG blocks.
87 //====------------------------------------------------------------------------//
89 // These values are defined in such a way that a merge can be done using
91 enum Value { Unknown = 0x0, /* 00 */
92 Initialized = 0x1, /* 01 */
93 Uninitialized = 0x2, /* 10 */
94 MayUninitialized = 0x3 /* 11 */ };
96 static bool isUninitialized(const Value v) {
97 return v >= Uninitialized;
99 static bool isAlwaysUninit(const Value v) {
100 return v == Uninitialized;
105 typedef llvm::PackedVector<Value, 2, llvm::SmallBitVector> ValueVector;
107 class CFGBlockValues {
109 SmallVector<ValueVector, 8> vals;
111 DeclToIndex declToIndex;
113 CFGBlockValues(const CFG &cfg);
115 unsigned getNumEntries() const { return declToIndex.size(); }
117 void computeSetOfDeclarations(const DeclContext &dc);
118 ValueVector &getValueVector(const CFGBlock *block) {
119 return vals[block->getBlockID()];
122 void setAllScratchValues(Value V);
123 void mergeIntoScratch(ValueVector const &source, bool isFirst);
124 bool updateValueVectorWithScratch(const CFGBlock *block);
126 bool hasNoDeclarations() const {
127 return declToIndex.size() == 0;
132 ValueVector::reference operator[](const VarDecl *vd);
134 Value getValue(const CFGBlock *block, const CFGBlock *dstBlock,
136 const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
137 assert(idx.hasValue());
138 return getValueVector(block)[idx.getValue()];
141 } // end anonymous namespace
143 CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {}
145 void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
146 declToIndex.computeMap(dc);
147 unsigned decls = declToIndex.size();
148 scratch.resize(decls);
149 unsigned n = cfg.getNumBlockIDs();
153 for (unsigned i = 0; i < n; ++i)
154 vals[i].resize(decls);
158 static void printVector(const CFGBlock *block, ValueVector &bv,
160 llvm::errs() << block->getBlockID() << " :";
161 for (unsigned i = 0; i < bv.size(); ++i) {
162 llvm::errs() << ' ' << bv[i];
164 llvm::errs() << " : " << num << '\n';
168 void CFGBlockValues::setAllScratchValues(Value V) {
169 for (unsigned I = 0, E = scratch.size(); I != E; ++I)
173 void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
181 bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
182 ValueVector &dst = getValueVector(block);
183 bool changed = (dst != scratch);
187 printVector(block, scratch, 0);
192 void CFGBlockValues::resetScratch() {
196 ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
197 const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
198 assert(idx.hasValue());
199 return scratch[idx.getValue()];
202 //------------------------------------------------------------------------====//
203 // Worklist: worklist for dataflow analysis.
204 //====------------------------------------------------------------------------//
207 class DataflowWorklist {
208 PostOrderCFGView::iterator PO_I, PO_E;
209 SmallVector<const CFGBlock *, 20> worklist;
210 llvm::BitVector enqueuedBlocks;
212 DataflowWorklist(const CFG &cfg, PostOrderCFGView &view)
213 : PO_I(view.begin()), PO_E(view.end()),
214 enqueuedBlocks(cfg.getNumBlockIDs(), true) {
215 // Treat the first block as already analyzed.
217 assert(*PO_I == &cfg.getEntry());
218 enqueuedBlocks[(*PO_I)->getBlockID()] = false;
223 void enqueueSuccessors(const CFGBlock *block);
224 const CFGBlock *dequeue();
228 void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
229 for (CFGBlock::const_succ_iterator I = block->succ_begin(),
230 E = block->succ_end(); I != E; ++I) {
231 const CFGBlock *Successor = *I;
232 if (!Successor || enqueuedBlocks[Successor->getBlockID()])
234 worklist.push_back(Successor);
235 enqueuedBlocks[Successor->getBlockID()] = true;
239 const CFGBlock *DataflowWorklist::dequeue() {
240 const CFGBlock *B = nullptr;
242 // First dequeue from the worklist. This can represent
243 // updates along backedges that we want propagated as quickly as possible.
244 if (!worklist.empty())
245 B = worklist.pop_back_val();
247 // Next dequeue from the initial reverse post order. This is the
248 // theoretical ideal in the presence of no back edges.
249 else if (PO_I != PO_E) {
257 assert(enqueuedBlocks[B->getBlockID()] == true);
258 enqueuedBlocks[B->getBlockID()] = false;
262 //------------------------------------------------------------------------====//
263 // Classification of DeclRefExprs as use or initialization.
264 //====------------------------------------------------------------------------//
267 class FindVarResult {
269 const DeclRefExpr *dr;
271 FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {}
273 const DeclRefExpr *getDeclRefExpr() const { return dr; }
274 const VarDecl *getDecl() const { return vd; }
277 static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
279 Ex = Ex->IgnoreParenNoopCasts(C);
280 if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) {
281 if (CE->getCastKind() == CK_LValueBitCast) {
282 Ex = CE->getSubExpr();
291 /// If E is an expression comprising a reference to a single variable, find that
293 static FindVarResult findVar(const Expr *E, const DeclContext *DC) {
294 if (const DeclRefExpr *DRE =
295 dyn_cast<DeclRefExpr>(stripCasts(DC->getParentASTContext(), E)))
296 if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
297 if (isTrackedVar(VD, DC))
298 return FindVarResult(VD, DRE);
299 return FindVarResult(nullptr, nullptr);
302 /// \brief Classify each DeclRefExpr as an initialization or a use. Any
303 /// DeclRefExpr which isn't explicitly classified will be assumed to have
304 /// escaped the analysis and will be treated as an initialization.
305 class ClassifyRefs : public StmtVisitor<ClassifyRefs> {
315 const DeclContext *DC;
316 llvm::DenseMap<const DeclRefExpr*, Class> Classification;
318 bool isTrackedVar(const VarDecl *VD) const {
319 return ::isTrackedVar(VD, DC);
322 void classify(const Expr *E, Class C);
325 ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {}
327 void VisitDeclStmt(DeclStmt *DS);
328 void VisitUnaryOperator(UnaryOperator *UO);
329 void VisitBinaryOperator(BinaryOperator *BO);
330 void VisitCallExpr(CallExpr *CE);
331 void VisitCastExpr(CastExpr *CE);
333 void operator()(Stmt *S) { Visit(S); }
335 Class get(const DeclRefExpr *DRE) const {
336 llvm::DenseMap<const DeclRefExpr*, Class>::const_iterator I
337 = Classification.find(DRE);
338 if (I != Classification.end())
341 const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl());
342 if (!VD || !isTrackedVar(VD))
350 static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
351 if (VD->getType()->isRecordType())
353 if (Expr *Init = VD->getInit()) {
354 const DeclRefExpr *DRE
355 = dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
356 if (DRE && DRE->getDecl() == VD)
362 void ClassifyRefs::classify(const Expr *E, Class C) {
363 // The result of a ?: could also be an lvalue.
364 E = E->IgnoreParens();
365 if (const ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
366 classify(CO->getTrueExpr(), C);
367 classify(CO->getFalseExpr(), C);
371 if (const BinaryConditionalOperator *BCO =
372 dyn_cast<BinaryConditionalOperator>(E)) {
373 classify(BCO->getFalseExpr(), C);
377 if (const OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(E)) {
378 classify(OVE->getSourceExpr(), C);
382 if (const MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
383 if (VarDecl *VD = dyn_cast<VarDecl>(ME->getMemberDecl())) {
384 if (!VD->isStaticDataMember())
385 classify(ME->getBase(), C);
390 if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
391 switch (BO->getOpcode()) {
394 classify(BO->getLHS(), C);
397 classify(BO->getRHS(), C);
404 FindVarResult Var = findVar(E, DC);
405 if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
406 Classification[DRE] = std::max(Classification[DRE], C);
409 void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
410 for (auto *DI : DS->decls()) {
411 VarDecl *VD = dyn_cast<VarDecl>(DI);
412 if (VD && isTrackedVar(VD))
413 if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
414 Classification[DRE] = SelfInit;
418 void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
419 // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
420 // is not a compound-assignment, we will treat it as initializing the variable
421 // when TransferFunctions visits it. A compound-assignment does not affect
422 // whether a variable is uninitialized, and there's no point counting it as a
424 if (BO->isCompoundAssignmentOp())
425 classify(BO->getLHS(), Use);
426 else if (BO->getOpcode() == BO_Assign || BO->getOpcode() == BO_Comma)
427 classify(BO->getLHS(), Ignore);
430 void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
431 // Increment and decrement are uses despite there being no lvalue-to-rvalue
433 if (UO->isIncrementDecrementOp())
434 classify(UO->getSubExpr(), Use);
437 static bool isPointerToConst(const QualType &QT) {
438 return QT->isAnyPointerType() && QT->getPointeeType().isConstQualified();
441 void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
442 // Classify arguments to std::move as used.
443 if (CE->isCallToStdMove()) {
444 // RecordTypes are handled in SemaDeclCXX.cpp.
445 if (!CE->getArg(0)->getType()->isRecordType())
446 classify(CE->getArg(0), Use);
450 // If a value is passed by const pointer or by const reference to a function,
451 // we should not assume that it is initialized by the call, and we
452 // conservatively do not assume that it is used.
453 for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
455 if ((*I)->isGLValue()) {
456 if ((*I)->getType().isConstQualified())
457 classify((*I), Ignore);
458 } else if (isPointerToConst((*I)->getType())) {
459 const Expr *Ex = stripCasts(DC->getParentASTContext(), *I);
460 const UnaryOperator *UO = dyn_cast<UnaryOperator>(Ex);
461 if (UO && UO->getOpcode() == UO_AddrOf)
462 Ex = UO->getSubExpr();
463 classify(Ex, Ignore);
468 void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
469 if (CE->getCastKind() == CK_LValueToRValue)
470 classify(CE->getSubExpr(), Use);
471 else if (CStyleCastExpr *CSE = dyn_cast<CStyleCastExpr>(CE)) {
472 if (CSE->getType()->isVoidType()) {
473 // Squelch any detected load of an uninitialized value if
474 // we cast it to void.
476 classify(CSE->getSubExpr(), Ignore);
481 //------------------------------------------------------------------------====//
482 // Transfer function for uninitialized values analysis.
483 //====------------------------------------------------------------------------//
486 class TransferFunctions : public StmtVisitor<TransferFunctions> {
487 CFGBlockValues &vals;
489 const CFGBlock *block;
490 AnalysisDeclContext ∾
491 const ClassifyRefs &classification;
492 ObjCNoReturn objCNoRet;
493 UninitVariablesHandler &handler;
496 TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
497 const CFGBlock *block, AnalysisDeclContext &ac,
498 const ClassifyRefs &classification,
499 UninitVariablesHandler &handler)
500 : vals(vals), cfg(cfg), block(block), ac(ac),
501 classification(classification), objCNoRet(ac.getASTContext()),
504 void reportUse(const Expr *ex, const VarDecl *vd);
506 void VisitBinaryOperator(BinaryOperator *bo);
507 void VisitBlockExpr(BlockExpr *be);
508 void VisitCallExpr(CallExpr *ce);
509 void VisitDeclRefExpr(DeclRefExpr *dr);
510 void VisitDeclStmt(DeclStmt *ds);
511 void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
512 void VisitObjCMessageExpr(ObjCMessageExpr *ME);
514 bool isTrackedVar(const VarDecl *vd) {
515 return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
518 FindVarResult findVar(const Expr *ex) {
519 return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
522 UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
523 UninitUse Use(ex, isAlwaysUninit(v));
525 assert(isUninitialized(v));
526 if (Use.getKind() == UninitUse::Always)
529 // If an edge which leads unconditionally to this use did not initialize
530 // the variable, we can say something stronger than 'may be uninitialized':
531 // we can say 'either it's used uninitialized or you have dead code'.
533 // We track the number of successors of a node which have been visited, and
534 // visit a node once we have visited all of its successors. Only edges where
535 // the variable might still be uninitialized are followed. Since a variable
536 // can't transfer from being initialized to being uninitialized, this will
537 // trace out the subgraph which inevitably leads to the use and does not
538 // initialize the variable. We do not want to skip past loops, since their
539 // non-termination might be correlated with the initialization condition.
543 // void f(bool a, bool b) {
548 // block4: } else if (b) {
549 // block5: while (!a) {
550 // block6: do_work(&a);
559 // Starting from the maybe-uninitialized use in block 9:
560 // * Block 7 is not visited because we have only visited one of its two
562 // * Block 8 is visited because we've visited its only successor.
564 // * Block 7 is visited because we've now visited both of its successors.
566 // * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
567 // of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
568 // * Block 3 is not visited because it initializes 'n'.
569 // Now the algorithm terminates, having visited blocks 7 and 8, and having
570 // found the frontier is blocks 2, 4, and 5.
572 // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
573 // and 4), so we report that any time either of those edges is taken (in
574 // each case when 'b == false'), 'n' is used uninitialized.
575 SmallVector<const CFGBlock*, 32> Queue;
576 SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
577 Queue.push_back(block);
578 // Specify that we've already visited all successors of the starting block.
579 // This has the dual purpose of ensuring we never add it to the queue, and
580 // of marking it as not being a candidate element of the frontier.
581 SuccsVisited[block->getBlockID()] = block->succ_size();
582 while (!Queue.empty()) {
583 const CFGBlock *B = Queue.pop_back_val();
585 // If the use is always reached from the entry block, make a note of that.
586 if (B == &cfg.getEntry())
587 Use.setUninitAfterCall();
589 for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
591 const CFGBlock *Pred = *I;
595 Value AtPredExit = vals.getValue(Pred, B, vd);
596 if (AtPredExit == Initialized)
597 // This block initializes the variable.
599 if (AtPredExit == MayUninitialized &&
600 vals.getValue(B, nullptr, vd) == Uninitialized) {
601 // This block declares the variable (uninitialized), and is reachable
602 // from a block that initializes the variable. We can't guarantee to
603 // give an earlier location for the diagnostic (and it appears that
604 // this code is intended to be reachable) so give a diagnostic here
605 // and go no further down this path.
606 Use.setUninitAfterDecl();
610 unsigned &SV = SuccsVisited[Pred->getBlockID()];
612 // When visiting the first successor of a block, mark all NULL
613 // successors as having been visited.
614 for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
615 SE = Pred->succ_end();
621 if (++SV == Pred->succ_size())
622 // All paths from this block lead to the use and don't initialize the
624 Queue.push_back(Pred);
628 // Scan the frontier, looking for blocks where the variable was
630 for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
631 const CFGBlock *Block = *BI;
632 unsigned BlockID = Block->getBlockID();
633 const Stmt *Term = Block->getTerminator();
634 if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
636 // This block inevitably leads to the use. If we have an edge from here
637 // to a post-dominator block, and the variable is uninitialized on that
638 // edge, we have found a bug.
639 for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
640 E = Block->succ_end(); I != E; ++I) {
641 const CFGBlock *Succ = *I;
642 if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
643 vals.getValue(Block, Succ, vd) == Uninitialized) {
644 // Switch cases are a special case: report the label to the caller
645 // as the 'terminator', not the switch statement itself. Suppress
646 // situations where no label matched: we can't be sure that's
648 if (isa<SwitchStmt>(Term)) {
649 const Stmt *Label = Succ->getLabel();
650 if (!Label || !isa<SwitchCase>(Label))
651 // Might not be possible.
653 UninitUse::Branch Branch;
654 Branch.Terminator = Label;
655 Branch.Output = 0; // Ignored.
656 Use.addUninitBranch(Branch);
658 UninitUse::Branch Branch;
659 Branch.Terminator = Term;
660 Branch.Output = I - Block->succ_begin();
661 Use.addUninitBranch(Branch);
673 void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
675 if (isUninitialized(v))
676 handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
679 void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
680 // This represents an initialization of the 'element' value.
681 if (DeclStmt *DS = dyn_cast<DeclStmt>(FS->getElement())) {
682 const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
683 if (isTrackedVar(VD))
684 vals[VD] = Initialized;
688 void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
689 const BlockDecl *bd = be->getBlockDecl();
690 for (const auto &I : bd->captures()) {
691 const VarDecl *vd = I.getVariable();
692 if (!isTrackedVar(vd))
695 vals[vd] = Initialized;
702 void TransferFunctions::VisitCallExpr(CallExpr *ce) {
703 if (Decl *Callee = ce->getCalleeDecl()) {
704 if (Callee->hasAttr<ReturnsTwiceAttr>()) {
705 // After a call to a function like setjmp or vfork, any variable which is
706 // initialized anywhere within this function may now be initialized. For
707 // now, just assume such a call initializes all variables. FIXME: Only
708 // mark variables as initialized if they have an initializer which is
709 // reachable from here.
710 vals.setAllScratchValues(Initialized);
712 else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
713 // Functions labeled like "analyzer_noreturn" are often used to denote
714 // "panic" functions that in special debug situations can still return,
715 // but for the most part should not be treated as returning. This is a
716 // useful annotation borrowed from the static analyzer that is useful for
717 // suppressing branch-specific false positives when we call one of these
718 // functions but keep pretending the path continues (when in reality the
719 // user doesn't care).
720 vals.setAllScratchValues(Unknown);
725 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
726 switch (classification.get(dr)) {
727 case ClassifyRefs::Ignore:
729 case ClassifyRefs::Use:
730 reportUse(dr, cast<VarDecl>(dr->getDecl()));
732 case ClassifyRefs::Init:
733 vals[cast<VarDecl>(dr->getDecl())] = Initialized;
735 case ClassifyRefs::SelfInit:
736 handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
741 void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
742 if (BO->getOpcode() == BO_Assign) {
743 FindVarResult Var = findVar(BO->getLHS());
744 if (const VarDecl *VD = Var.getDecl())
745 vals[VD] = Initialized;
749 void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
750 for (auto *DI : DS->decls()) {
751 VarDecl *VD = dyn_cast<VarDecl>(DI);
752 if (VD && isTrackedVar(VD)) {
753 if (getSelfInitExpr(VD)) {
754 // If the initializer consists solely of a reference to itself, we
755 // explicitly mark the variable as uninitialized. This allows code
756 // like the following:
760 // to deliberately leave a variable uninitialized. Different analysis
761 // clients can detect this pattern and adjust their reporting
762 // appropriately, but we need to continue to analyze subsequent uses
764 vals[VD] = Uninitialized;
765 } else if (VD->getInit()) {
766 // Treat the new variable as initialized.
767 vals[VD] = Initialized;
769 // No initializer: the variable is now uninitialized. This matters
776 // FIXME: Mark the variable as uninitialized whenever its scope is
777 // left, since its scope could be re-entered by a jump over the
779 vals[VD] = Uninitialized;
785 void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
786 // If the Objective-C message expression is an implicit no-return that
787 // is not modeled in the CFG, set the tracked dataflow values to Unknown.
788 if (objCNoRet.isImplicitNoReturn(ME)) {
789 vals.setAllScratchValues(Unknown);
793 //------------------------------------------------------------------------====//
794 // High-level "driver" logic for uninitialized values analysis.
795 //====------------------------------------------------------------------------//
797 static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
798 AnalysisDeclContext &ac, CFGBlockValues &vals,
799 const ClassifyRefs &classification,
800 llvm::BitVector &wasAnalyzed,
801 UninitVariablesHandler &handler) {
802 wasAnalyzed[block->getBlockID()] = true;
804 // Merge in values of predecessor blocks.
806 for (CFGBlock::const_pred_iterator I = block->pred_begin(),
807 E = block->pred_end(); I != E; ++I) {
808 const CFGBlock *pred = *I;
811 if (wasAnalyzed[pred->getBlockID()]) {
812 vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
816 // Apply the transfer function.
817 TransferFunctions tf(vals, cfg, block, ac, classification, handler);
818 for (CFGBlock::const_iterator I = block->begin(), E = block->end();
820 if (Optional<CFGStmt> cs = I->getAs<CFGStmt>())
821 tf.Visit(const_cast<Stmt*>(cs->getStmt()));
823 return vals.updateValueVectorWithScratch(block);
826 /// PruneBlocksHandler is a special UninitVariablesHandler that is used
827 /// to detect when a CFGBlock has any *potential* use of an uninitialized
828 /// variable. It is mainly used to prune out work during the final
831 struct PruneBlocksHandler : public UninitVariablesHandler {
832 PruneBlocksHandler(unsigned numBlocks)
833 : hadUse(numBlocks, false), hadAnyUse(false),
836 ~PruneBlocksHandler() override {}
838 /// Records if a CFGBlock had a potential use of an uninitialized variable.
839 llvm::BitVector hadUse;
841 /// Records if any CFGBlock had a potential use of an uninitialized variable.
844 /// The current block to scribble use information.
845 unsigned currentBlock;
847 void handleUseOfUninitVariable(const VarDecl *vd,
848 const UninitUse &use) override {
849 hadUse[currentBlock] = true;
853 /// Called when the uninitialized variable analysis detects the
854 /// idiom 'int x = x'. All other uses of 'x' within the initializer
855 /// are handled by handleUseOfUninitVariable.
856 void handleSelfInit(const VarDecl *vd) override {
857 hadUse[currentBlock] = true;
863 void clang::runUninitializedVariablesAnalysis(
864 const DeclContext &dc,
866 AnalysisDeclContext &ac,
867 UninitVariablesHandler &handler,
868 UninitVariablesAnalysisStats &stats) {
869 CFGBlockValues vals(cfg);
870 vals.computeSetOfDeclarations(dc);
871 if (vals.hasNoDeclarations())
874 stats.NumVariablesAnalyzed = vals.getNumEntries();
876 // Precompute which expressions are uses and which are initializations.
877 ClassifyRefs classification(ac);
878 cfg.VisitBlockStmts(classification);
880 // Mark all variables uninitialized at the entry.
881 const CFGBlock &entry = cfg.getEntry();
882 ValueVector &vec = vals.getValueVector(&entry);
883 const unsigned n = vals.getNumEntries();
884 for (unsigned j = 0; j < n ; ++j) {
885 vec[j] = Uninitialized;
888 // Proceed with the workist.
889 DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>());
890 llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
891 worklist.enqueueSuccessors(&cfg.getEntry());
892 llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
893 wasAnalyzed[cfg.getEntry().getBlockID()] = true;
894 PruneBlocksHandler PBH(cfg.getNumBlockIDs());
896 while (const CFGBlock *block = worklist.dequeue()) {
897 PBH.currentBlock = block->getBlockID();
899 // Did the block change?
900 bool changed = runOnBlock(block, cfg, ac, vals,
901 classification, wasAnalyzed, PBH);
902 ++stats.NumBlockVisits;
903 if (changed || !previouslyVisited[block->getBlockID()])
904 worklist.enqueueSuccessors(block);
905 previouslyVisited[block->getBlockID()] = true;
911 // Run through the blocks one more time, and report uninitialized variables.
912 for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
913 const CFGBlock *block = *BI;
914 if (PBH.hadUse[block->getBlockID()]) {
915 runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
916 ++stats.NumBlockVisits;
921 UninitVariablesHandler::~UninitVariablesHandler() {}