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 //===----------------------------------------------------------------------===//
15 #include "llvm/ADT/Optional.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/PackedVector.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "clang/AST/Decl.h"
20 #include "clang/Analysis/CFG.h"
21 #include "clang/Analysis/AnalysisContext.h"
22 #include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h"
23 #include "clang/Analysis/Analyses/UninitializedValues.h"
24 #include "clang/Analysis/Support/SaveAndRestore.h"
26 using namespace clang;
28 static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
29 if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
30 !vd->isExceptionVariable() &&
31 vd->getDeclContext() == dc) {
32 QualType ty = vd->getType();
33 return ty->isScalarType() || ty->isVectorType();
38 //------------------------------------------------------------------------====//
39 // DeclToIndex: a mapping from Decls we track to value indices.
40 //====------------------------------------------------------------------------//
44 llvm::DenseMap<const VarDecl *, unsigned> map;
48 /// Compute the actual mapping from declarations to bits.
49 void computeMap(const DeclContext &dc);
51 /// Return the number of declarations in the map.
52 unsigned size() const { return map.size(); }
54 /// Returns the bit vector index for a given declaration.
55 llvm::Optional<unsigned> getValueIndex(const VarDecl *d) const;
59 void DeclToIndex::computeMap(const DeclContext &dc) {
61 DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
63 for ( ; I != E; ++I) {
64 const VarDecl *vd = *I;
65 if (isTrackedVar(vd, &dc))
70 llvm::Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
71 llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
73 return llvm::Optional<unsigned>();
77 //------------------------------------------------------------------------====//
78 // CFGBlockValues: dataflow values for CFG blocks.
79 //====------------------------------------------------------------------------//
81 // These values are defined in such a way that a merge can be done using
83 enum Value { Unknown = 0x0, /* 00 */
84 Initialized = 0x1, /* 01 */
85 Uninitialized = 0x2, /* 10 */
86 MayUninitialized = 0x3 /* 11 */ };
88 static bool isUninitialized(const Value v) {
89 return v >= Uninitialized;
91 static bool isAlwaysUninit(const Value v) {
92 return v == Uninitialized;
97 typedef llvm::PackedVector<Value, 2> ValueVector;
98 typedef std::pair<ValueVector *, ValueVector *> BVPair;
100 class CFGBlockValues {
104 DeclToIndex declToIndex;
106 ValueVector &lazyCreate(ValueVector *&bv);
108 CFGBlockValues(const CFG &cfg);
111 unsigned getNumEntries() const { return declToIndex.size(); }
113 void computeSetOfDeclarations(const DeclContext &dc);
114 ValueVector &getValueVector(const CFGBlock *block,
115 const CFGBlock *dstBlock);
117 BVPair &getValueVectors(const CFGBlock *block, bool shouldLazyCreate);
119 void mergeIntoScratch(ValueVector const &source, bool isFirst);
120 bool updateValueVectorWithScratch(const CFGBlock *block);
121 bool updateValueVectors(const CFGBlock *block, const BVPair &newVals);
123 bool hasNoDeclarations() const {
124 return declToIndex.size() == 0;
128 ValueVector &getScratch() { return scratch; }
130 ValueVector::reference operator[](const VarDecl *vd);
132 } // end anonymous namespace
134 CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {
135 unsigned n = cfg.getNumBlockIDs();
138 vals = new std::pair<ValueVector*, ValueVector*>[n];
139 memset((void*)vals, 0, sizeof(*vals) * n);
142 CFGBlockValues::~CFGBlockValues() {
143 unsigned n = cfg.getNumBlockIDs();
146 for (unsigned i = 0; i < n; ++i) {
147 delete vals[i].first;
148 delete vals[i].second;
153 void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
154 declToIndex.computeMap(dc);
155 scratch.resize(declToIndex.size());
158 ValueVector &CFGBlockValues::lazyCreate(ValueVector *&bv) {
160 bv = new ValueVector(declToIndex.size());
164 /// This function pattern matches for a '&&' or '||' that appears at
165 /// the beginning of a CFGBlock that also (1) has a terminator and
166 /// (2) has no other elements. If such an expression is found, it is returned.
167 static const BinaryOperator *getLogicalOperatorInChain(const CFGBlock *block) {
171 const CFGStmt *cstmt = block->front().getAs<CFGStmt>();
175 const BinaryOperator *b = dyn_cast_or_null<BinaryOperator>(cstmt->getStmt());
177 if (!b || !b->isLogicalOp())
180 if (block->pred_size() == 2) {
181 if (block->getTerminatorCondition() == b) {
182 if (block->succ_size() == 2)
185 else if (block->size() == 1)
192 ValueVector &CFGBlockValues::getValueVector(const CFGBlock *block,
193 const CFGBlock *dstBlock) {
194 unsigned idx = block->getBlockID();
195 if (dstBlock && getLogicalOperatorInChain(block)) {
196 if (*block->succ_begin() == dstBlock)
197 return lazyCreate(vals[idx].first);
198 assert(*(block->succ_begin()+1) == dstBlock);
199 return lazyCreate(vals[idx].second);
202 assert(vals[idx].second == 0);
203 return lazyCreate(vals[idx].first);
206 BVPair &CFGBlockValues::getValueVectors(const clang::CFGBlock *block,
207 bool shouldLazyCreate) {
208 unsigned idx = block->getBlockID();
209 lazyCreate(vals[idx].first);
210 if (shouldLazyCreate)
211 lazyCreate(vals[idx].second);
216 static void printVector(const CFGBlock *block, ValueVector &bv,
219 llvm::errs() << block->getBlockID() << " :";
220 for (unsigned i = 0; i < bv.size(); ++i) {
221 llvm::errs() << ' ' << bv[i];
223 llvm::errs() << " : " << num << '\n';
226 static void printVector(const char *name, ValueVector const &bv) {
227 llvm::errs() << name << " : ";
228 for (unsigned i = 0; i < bv.size(); ++i) {
229 llvm::errs() << ' ' << bv[i];
231 llvm::errs() << "\n";
235 void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
243 bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
244 ValueVector &dst = getValueVector(block, 0);
245 bool changed = (dst != scratch);
249 printVector(block, scratch, 0);
254 bool CFGBlockValues::updateValueVectors(const CFGBlock *block,
255 const BVPair &newVals) {
256 BVPair &vals = getValueVectors(block, true);
257 bool changed = *newVals.first != *vals.first ||
258 *newVals.second != *vals.second;
259 *vals.first = *newVals.first;
260 *vals.second = *newVals.second;
262 printVector(block, *vals.first, 1);
263 printVector(block, *vals.second, 2);
268 void CFGBlockValues::resetScratch() {
272 ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
273 const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
274 assert(idx.hasValue());
275 return scratch[idx.getValue()];
278 //------------------------------------------------------------------------====//
279 // Worklist: worklist for dataflow analysis.
280 //====------------------------------------------------------------------------//
283 class DataflowWorklist {
284 SmallVector<const CFGBlock *, 20> worklist;
285 llvm::BitVector enqueuedBlocks;
287 DataflowWorklist(const CFG &cfg) : enqueuedBlocks(cfg.getNumBlockIDs()) {}
289 void enqueueSuccessors(const CFGBlock *block);
290 const CFGBlock *dequeue();
294 void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
295 unsigned OldWorklistSize = worklist.size();
296 for (CFGBlock::const_succ_iterator I = block->succ_begin(),
297 E = block->succ_end(); I != E; ++I) {
298 const CFGBlock *Successor = *I;
299 if (!Successor || enqueuedBlocks[Successor->getBlockID()])
301 worklist.push_back(Successor);
302 enqueuedBlocks[Successor->getBlockID()] = true;
304 if (OldWorklistSize == 0 || OldWorklistSize == worklist.size())
307 // Rotate the newly added blocks to the start of the worklist so that it forms
308 // a proper queue when we pop off the end of the worklist.
309 std::rotate(worklist.begin(), worklist.begin() + OldWorklistSize,
313 const CFGBlock *DataflowWorklist::dequeue() {
314 if (worklist.empty())
316 const CFGBlock *b = worklist.back();
318 enqueuedBlocks[b->getBlockID()] = false;
322 //------------------------------------------------------------------------====//
323 // Transfer function for uninitialized values analysis.
324 //====------------------------------------------------------------------------//
327 class FindVarResult {
329 const DeclRefExpr *dr;
331 FindVarResult(VarDecl *vd, DeclRefExpr *dr) : vd(vd), dr(dr) {}
333 const DeclRefExpr *getDeclRefExpr() const { return dr; }
334 const VarDecl *getDecl() const { return vd; }
337 class TransferFunctions : public StmtVisitor<TransferFunctions> {
338 CFGBlockValues &vals;
341 UninitVariablesHandler *handler;
343 /// The last DeclRefExpr seen when analyzing a block. Used to
344 /// cheat when detecting cases when the address of a variable is taken.
347 /// The last lvalue-to-rvalue conversion of a variable whose value
348 /// was uninitialized. Normally this results in a warning, but it is
349 /// possible to either silence the warning in some cases, or we
350 /// propagate the uninitialized value.
353 /// For some expressions, we want to ignore any post-processing after
355 bool skipProcessUses;
358 TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
360 UninitVariablesHandler *handler)
361 : vals(vals), cfg(cfg), ac(ac), handler(handler),
362 lastDR(0), lastLoad(0),
363 skipProcessUses(false) {}
365 void reportUninit(const DeclRefExpr *ex, const VarDecl *vd,
366 bool isAlwaysUninit);
368 void VisitBlockExpr(BlockExpr *be);
369 void VisitDeclStmt(DeclStmt *ds);
370 void VisitDeclRefExpr(DeclRefExpr *dr);
371 void VisitUnaryOperator(UnaryOperator *uo);
372 void VisitBinaryOperator(BinaryOperator *bo);
373 void VisitCastExpr(CastExpr *ce);
374 void VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs);
377 bool isTrackedVar(const VarDecl *vd) {
378 return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
381 FindVarResult findBlockVarDecl(Expr *ex);
383 void ProcessUses(Stmt *s = 0);
387 static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
389 Ex = Ex->IgnoreParenNoopCasts(C);
390 if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) {
391 if (CE->getCastKind() == CK_LValueBitCast) {
392 Ex = CE->getSubExpr();
401 void TransferFunctions::reportUninit(const DeclRefExpr *ex,
402 const VarDecl *vd, bool isAlwaysUnit) {
403 if (handler) handler->handleUseOfUninitVariable(ex, vd, isAlwaysUnit);
406 FindVarResult TransferFunctions::findBlockVarDecl(Expr *ex) {
407 if (DeclRefExpr *dr = dyn_cast<DeclRefExpr>(ex->IgnoreParenCasts()))
408 if (VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
409 if (isTrackedVar(vd))
410 return FindVarResult(vd, dr);
411 return FindVarResult(0, 0);
414 void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs) {
415 // This represents an initialization of the 'element' value.
416 Stmt *element = fs->getElement();
417 const VarDecl *vd = 0;
419 if (DeclStmt *ds = dyn_cast<DeclStmt>(element)) {
420 vd = cast<VarDecl>(ds->getSingleDecl());
421 if (!isTrackedVar(vd))
424 // Initialize the value of the reference variable.
425 const FindVarResult &res = findBlockVarDecl(cast<Expr>(element));
430 vals[vd] = Initialized;
433 void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
434 const BlockDecl *bd = be->getBlockDecl();
435 for (BlockDecl::capture_const_iterator i = bd->capture_begin(),
436 e = bd->capture_end() ; i != e; ++i) {
437 const VarDecl *vd = i->getVariable();
438 if (!isTrackedVar(vd))
441 vals[vd] = Initialized;
445 if (handler && isUninitialized(v))
446 handler->handleUseOfUninitVariable(be, vd, isAlwaysUninit(v));
450 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
451 // Record the last DeclRefExpr seen. This is an lvalue computation.
452 // We use this value to later detect if a variable "escapes" the analysis.
453 if (const VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
454 if (isTrackedVar(vd)) {
460 void TransferFunctions::VisitDeclStmt(DeclStmt *ds) {
461 for (DeclStmt::decl_iterator DI = ds->decl_begin(), DE = ds->decl_end();
463 if (VarDecl *vd = dyn_cast<VarDecl>(*DI)) {
464 if (isTrackedVar(vd)) {
465 if (Expr *init = vd->getInit()) {
466 // If the initializer consists solely of a reference to itself, we
467 // explicitly mark the variable as uninitialized. This allows code
468 // like the following:
472 // to deliberately leave a variable uninitialized. Different analysis
473 // clients can detect this pattern and adjust their reporting
474 // appropriately, but we need to continue to analyze subsequent uses
476 if (init == lastLoad) {
477 const DeclRefExpr *DR
478 = cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
479 lastLoad->getSubExpr()));
480 if (DR->getDecl() == vd) {
482 // Propagate uninitialized value, but don't immediately report
484 vals[vd] = Uninitialized;
488 handler->handleSelfInit(vd);
493 // All other cases: treat the new variable as initialized.
494 // This is a minor optimization to reduce the propagation
495 // of the analysis, since we will have already reported
496 // the use of the uninitialized value (which visiting the
498 vals[vd] = Initialized;
505 void TransferFunctions::VisitBinaryOperator(clang::BinaryOperator *bo) {
506 if (bo->isAssignmentOp()) {
507 const FindVarResult &res = findBlockVarDecl(bo->getLHS());
508 if (const VarDecl *vd = res.getDecl()) {
509 ValueVector::reference val = vals[vd];
510 if (isUninitialized(val)) {
511 if (bo->getOpcode() != BO_Assign)
512 reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
520 void TransferFunctions::VisitUnaryOperator(clang::UnaryOperator *uo) {
521 switch (uo->getOpcode()) {
522 case clang::UO_PostDec:
523 case clang::UO_PostInc:
524 case clang::UO_PreDec:
525 case clang::UO_PreInc: {
526 const FindVarResult &res = findBlockVarDecl(uo->getSubExpr());
527 if (const VarDecl *vd = res.getDecl()) {
528 assert(res.getDeclRefExpr() == lastDR);
529 // We null out lastDR to indicate we have fully processed it
530 // and we don't want the auto-value setting in Visit().
533 ValueVector::reference val = vals[vd];
534 if (isUninitialized(val))
535 reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
544 void TransferFunctions::VisitCastExpr(clang::CastExpr *ce) {
545 if (ce->getCastKind() == CK_LValueToRValue) {
546 const FindVarResult &res = findBlockVarDecl(ce->getSubExpr());
548 assert(res.getDeclRefExpr() == lastDR);
552 else if (ce->getCastKind() == CK_NoOp ||
553 ce->getCastKind() == CK_LValueBitCast) {
554 skipProcessUses = true;
556 else if (CStyleCastExpr *cse = dyn_cast<CStyleCastExpr>(ce)) {
557 if (cse->getType()->isVoidType()) {
559 if (lastLoad == cse->getSubExpr()) {
560 // Squelch any detected load of an uninitialized value if
561 // we cast it to void.
569 void TransferFunctions::Visit(clang::Stmt *s) {
570 skipProcessUses = false;
571 StmtVisitor<TransferFunctions>::Visit(s);
572 if (!skipProcessUses)
576 void TransferFunctions::ProcessUses(Stmt *s) {
577 // This method is typically called after visiting a CFGElement statement
578 // in the CFG. We delay processing of reporting many loads of uninitialized
579 // values until here.
581 // If we just visited the lvalue-to-rvalue cast, there is nothing
586 const DeclRefExpr *DR =
587 cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
588 lastLoad->getSubExpr()));
589 const VarDecl *VD = cast<VarDecl>(DR->getDecl());
591 // If we reach here, we may have seen a load of an uninitialized value
592 // and it hasn't been casted to void or otherwise handled. In this
593 // situation, report the incident.
594 if (isUninitialized(vals[VD]))
595 reportUninit(DR, VD, isAlwaysUninit(vals[VD]));
605 // Any other uses of 'lastDR' involve taking an lvalue of variable.
606 // In this case, it "escapes" the analysis.
607 if (lastDR && lastDR != s) {
608 vals[cast<VarDecl>(lastDR->getDecl())] = Initialized;
613 //------------------------------------------------------------------------====//
614 // High-level "driver" logic for uninitialized values analysis.
615 //====------------------------------------------------------------------------//
617 static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
618 AnalysisContext &ac, CFGBlockValues &vals,
619 llvm::BitVector &wasAnalyzed,
620 UninitVariablesHandler *handler = 0) {
622 wasAnalyzed[block->getBlockID()] = true;
624 if (const BinaryOperator *b = getLogicalOperatorInChain(block)) {
625 CFGBlock::const_pred_iterator itr = block->pred_begin();
626 BVPair vA = vals.getValueVectors(*itr, false);
628 BVPair vB = vals.getValueVectors(*itr, false);
632 if (b->getOpcode() == BO_LAnd) {
633 // Merge the 'F' bits from the first and second.
634 vals.mergeIntoScratch(*(vA.second ? vA.second : vA.first), true);
635 vals.mergeIntoScratch(*(vB.second ? vB.second : vB.first), false);
636 valsAB.first = vA.first;
637 valsAB.second = &vals.getScratch();
639 // Merge the 'T' bits from the first and second.
640 assert(b->getOpcode() == BO_LOr);
641 vals.mergeIntoScratch(*vA.first, true);
642 vals.mergeIntoScratch(*vB.first, false);
643 valsAB.first = &vals.getScratch();
644 valsAB.second = vA.second ? vA.second : vA.first;
646 return vals.updateValueVectors(block, valsAB);
649 // Default behavior: merge in values of predecessor blocks.
652 for (CFGBlock::const_pred_iterator I = block->pred_begin(),
653 E = block->pred_end(); I != E; ++I) {
654 const CFGBlock *pred = *I;
655 if (wasAnalyzed[pred->getBlockID()]) {
656 vals.mergeIntoScratch(vals.getValueVector(pred, block), isFirst);
660 // Apply the transfer function.
661 TransferFunctions tf(vals, cfg, ac, handler);
662 for (CFGBlock::const_iterator I = block->begin(), E = block->end();
664 if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) {
665 tf.Visit(const_cast<Stmt*>(cs->getStmt()));
669 return vals.updateValueVectorWithScratch(block);
672 void clang::runUninitializedVariablesAnalysis(
673 const DeclContext &dc,
676 UninitVariablesHandler &handler,
677 UninitVariablesAnalysisStats &stats) {
678 CFGBlockValues vals(cfg);
679 vals.computeSetOfDeclarations(dc);
680 if (vals.hasNoDeclarations())
683 stats.NumVariablesAnalyzed = vals.getNumEntries();
685 // Mark all variables uninitialized at the entry.
686 const CFGBlock &entry = cfg.getEntry();
687 for (CFGBlock::const_succ_iterator i = entry.succ_begin(),
688 e = entry.succ_end(); i != e; ++i) {
689 if (const CFGBlock *succ = *i) {
690 ValueVector &vec = vals.getValueVector(&entry, succ);
691 const unsigned n = vals.getNumEntries();
692 for (unsigned j = 0; j < n ; ++j) {
693 vec[j] = Uninitialized;
698 // Proceed with the workist.
699 DataflowWorklist worklist(cfg);
700 llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
701 worklist.enqueueSuccessors(&cfg.getEntry());
702 llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
703 wasAnalyzed[cfg.getEntry().getBlockID()] = true;
705 while (const CFGBlock *block = worklist.dequeue()) {
706 // Did the block change?
707 bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed);
708 ++stats.NumBlockVisits;
709 if (changed || !previouslyVisited[block->getBlockID()])
710 worklist.enqueueSuccessors(block);
711 previouslyVisited[block->getBlockID()] = true;
714 // Run through the blocks one more time, and report uninitialized variabes.
715 for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
716 const CFGBlock *block = *BI;
717 if (wasAnalyzed[block->getBlockID()]) {
718 runOnBlock(block, cfg, ac, vals, wasAnalyzed, &handler);
719 ++stats.NumBlockVisits;
724 UninitVariablesHandler::~UninitVariablesHandler() {}