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 "llvm/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 CFGElement front = block->front();
172 const CFGStmt *cstmt = front.getAs<CFGStmt>();
176 const BinaryOperator *b = dyn_cast_or_null<BinaryOperator>(cstmt->getStmt());
178 if (!b || !b->isLogicalOp())
181 if (block->pred_size() == 2) {
182 if (block->getTerminatorCondition() == b) {
183 if (block->succ_size() == 2)
186 else if (block->size() == 1)
193 ValueVector &CFGBlockValues::getValueVector(const CFGBlock *block,
194 const CFGBlock *dstBlock) {
195 unsigned idx = block->getBlockID();
196 if (dstBlock && getLogicalOperatorInChain(block)) {
197 if (*block->succ_begin() == dstBlock)
198 return lazyCreate(vals[idx].first);
199 assert(*(block->succ_begin()+1) == dstBlock);
200 return lazyCreate(vals[idx].second);
203 assert(vals[idx].second == 0);
204 return lazyCreate(vals[idx].first);
207 BVPair &CFGBlockValues::getValueVectors(const clang::CFGBlock *block,
208 bool shouldLazyCreate) {
209 unsigned idx = block->getBlockID();
210 lazyCreate(vals[idx].first);
211 if (shouldLazyCreate)
212 lazyCreate(vals[idx].second);
217 static void printVector(const CFGBlock *block, ValueVector &bv,
220 llvm::errs() << block->getBlockID() << " :";
221 for (unsigned i = 0; i < bv.size(); ++i) {
222 llvm::errs() << ' ' << bv[i];
224 llvm::errs() << " : " << num << '\n';
227 static void printVector(const char *name, ValueVector const &bv) {
228 llvm::errs() << name << " : ";
229 for (unsigned i = 0; i < bv.size(); ++i) {
230 llvm::errs() << ' ' << bv[i];
232 llvm::errs() << "\n";
236 void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
244 bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
245 ValueVector &dst = getValueVector(block, 0);
246 bool changed = (dst != scratch);
250 printVector(block, scratch, 0);
255 bool CFGBlockValues::updateValueVectors(const CFGBlock *block,
256 const BVPair &newVals) {
257 BVPair &vals = getValueVectors(block, true);
258 bool changed = *newVals.first != *vals.first ||
259 *newVals.second != *vals.second;
260 *vals.first = *newVals.first;
261 *vals.second = *newVals.second;
263 printVector(block, *vals.first, 1);
264 printVector(block, *vals.second, 2);
269 void CFGBlockValues::resetScratch() {
273 ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
274 const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
275 assert(idx.hasValue());
276 return scratch[idx.getValue()];
279 //------------------------------------------------------------------------====//
280 // Worklist: worklist for dataflow analysis.
281 //====------------------------------------------------------------------------//
284 class DataflowWorklist {
285 SmallVector<const CFGBlock *, 20> worklist;
286 llvm::BitVector enqueuedBlocks;
288 DataflowWorklist(const CFG &cfg) : enqueuedBlocks(cfg.getNumBlockIDs()) {}
290 void enqueueSuccessors(const CFGBlock *block);
291 const CFGBlock *dequeue();
295 void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
296 unsigned OldWorklistSize = worklist.size();
297 for (CFGBlock::const_succ_iterator I = block->succ_begin(),
298 E = block->succ_end(); I != E; ++I) {
299 const CFGBlock *Successor = *I;
300 if (!Successor || enqueuedBlocks[Successor->getBlockID()])
302 worklist.push_back(Successor);
303 enqueuedBlocks[Successor->getBlockID()] = true;
305 if (OldWorklistSize == 0 || OldWorklistSize == worklist.size())
308 // Rotate the newly added blocks to the start of the worklist so that it forms
309 // a proper queue when we pop off the end of the worklist.
310 std::rotate(worklist.begin(), worklist.begin() + OldWorklistSize,
314 const CFGBlock *DataflowWorklist::dequeue() {
315 if (worklist.empty())
317 const CFGBlock *b = worklist.back();
319 enqueuedBlocks[b->getBlockID()] = false;
323 //------------------------------------------------------------------------====//
324 // Transfer function for uninitialized values analysis.
325 //====------------------------------------------------------------------------//
328 class FindVarResult {
330 const DeclRefExpr *dr;
332 FindVarResult(VarDecl *vd, DeclRefExpr *dr) : vd(vd), dr(dr) {}
334 const DeclRefExpr *getDeclRefExpr() const { return dr; }
335 const VarDecl *getDecl() const { return vd; }
338 class TransferFunctions : public StmtVisitor<TransferFunctions> {
339 CFGBlockValues &vals;
341 AnalysisDeclContext ∾
342 UninitVariablesHandler *handler;
344 /// The last DeclRefExpr seen when analyzing a block. Used to
345 /// cheat when detecting cases when the address of a variable is taken.
348 /// The last lvalue-to-rvalue conversion of a variable whose value
349 /// was uninitialized. Normally this results in a warning, but it is
350 /// possible to either silence the warning in some cases, or we
351 /// propagate the uninitialized value.
354 /// For some expressions, we want to ignore any post-processing after
356 bool skipProcessUses;
359 TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
360 AnalysisDeclContext &ac,
361 UninitVariablesHandler *handler)
362 : vals(vals), cfg(cfg), ac(ac), handler(handler),
363 lastDR(0), lastLoad(0),
364 skipProcessUses(false) {}
366 void reportUninit(const DeclRefExpr *ex, const VarDecl *vd,
367 bool isAlwaysUninit);
369 void VisitBlockExpr(BlockExpr *be);
370 void VisitDeclStmt(DeclStmt *ds);
371 void VisitDeclRefExpr(DeclRefExpr *dr);
372 void VisitUnaryOperator(UnaryOperator *uo);
373 void VisitBinaryOperator(BinaryOperator *bo);
374 void VisitCastExpr(CastExpr *ce);
375 void VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs);
378 bool isTrackedVar(const VarDecl *vd) {
379 return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
382 FindVarResult findBlockVarDecl(Expr *ex);
384 void ProcessUses(Stmt *s = 0);
388 static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
390 Ex = Ex->IgnoreParenNoopCasts(C);
391 if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) {
392 if (CE->getCastKind() == CK_LValueBitCast) {
393 Ex = CE->getSubExpr();
402 void TransferFunctions::reportUninit(const DeclRefExpr *ex,
403 const VarDecl *vd, bool isAlwaysUnit) {
404 if (handler) handler->handleUseOfUninitVariable(ex, vd, isAlwaysUnit);
407 FindVarResult TransferFunctions::findBlockVarDecl(Expr *ex) {
408 if (DeclRefExpr *dr = dyn_cast<DeclRefExpr>(ex->IgnoreParenCasts()))
409 if (VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
410 if (isTrackedVar(vd))
411 return FindVarResult(vd, dr);
412 return FindVarResult(0, 0);
415 void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs) {
416 // This represents an initialization of the 'element' value.
417 Stmt *element = fs->getElement();
418 const VarDecl *vd = 0;
420 if (DeclStmt *ds = dyn_cast<DeclStmt>(element)) {
421 vd = cast<VarDecl>(ds->getSingleDecl());
422 if (!isTrackedVar(vd))
425 // Initialize the value of the reference variable.
426 const FindVarResult &res = findBlockVarDecl(cast<Expr>(element));
431 vals[vd] = Initialized;
434 void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
435 const BlockDecl *bd = be->getBlockDecl();
436 for (BlockDecl::capture_const_iterator i = bd->capture_begin(),
437 e = bd->capture_end() ; i != e; ++i) {
438 const VarDecl *vd = i->getVariable();
439 if (!isTrackedVar(vd))
442 vals[vd] = Initialized;
446 if (handler && isUninitialized(v))
447 handler->handleUseOfUninitVariable(be, vd, isAlwaysUninit(v));
451 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
452 // Record the last DeclRefExpr seen. This is an lvalue computation.
453 // We use this value to later detect if a variable "escapes" the analysis.
454 if (const VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
455 if (isTrackedVar(vd)) {
461 void TransferFunctions::VisitDeclStmt(DeclStmt *ds) {
462 for (DeclStmt::decl_iterator DI = ds->decl_begin(), DE = ds->decl_end();
464 if (VarDecl *vd = dyn_cast<VarDecl>(*DI)) {
465 if (isTrackedVar(vd)) {
466 if (Expr *init = vd->getInit()) {
467 // If the initializer consists solely of a reference to itself, we
468 // explicitly mark the variable as uninitialized. This allows code
469 // like the following:
473 // to deliberately leave a variable uninitialized. Different analysis
474 // clients can detect this pattern and adjust their reporting
475 // appropriately, but we need to continue to analyze subsequent uses
477 if (init == lastLoad) {
478 const DeclRefExpr *DR
479 = cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
480 lastLoad->getSubExpr()));
481 if (DR->getDecl() == vd) {
483 // Propagate uninitialized value, but don't immediately report
485 vals[vd] = Uninitialized;
489 handler->handleSelfInit(vd);
494 // All other cases: treat the new variable as initialized.
495 // This is a minor optimization to reduce the propagation
496 // of the analysis, since we will have already reported
497 // the use of the uninitialized value (which visiting the
499 vals[vd] = Initialized;
506 void TransferFunctions::VisitBinaryOperator(clang::BinaryOperator *bo) {
507 if (bo->isAssignmentOp()) {
508 const FindVarResult &res = findBlockVarDecl(bo->getLHS());
509 if (const VarDecl *vd = res.getDecl()) {
510 ValueVector::reference val = vals[vd];
511 if (isUninitialized(val)) {
512 if (bo->getOpcode() != BO_Assign)
513 reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
521 void TransferFunctions::VisitUnaryOperator(clang::UnaryOperator *uo) {
522 switch (uo->getOpcode()) {
523 case clang::UO_PostDec:
524 case clang::UO_PostInc:
525 case clang::UO_PreDec:
526 case clang::UO_PreInc: {
527 const FindVarResult &res = findBlockVarDecl(uo->getSubExpr());
528 if (const VarDecl *vd = res.getDecl()) {
529 assert(res.getDeclRefExpr() == lastDR);
530 // We null out lastDR to indicate we have fully processed it
531 // and we don't want the auto-value setting in Visit().
534 ValueVector::reference val = vals[vd];
535 if (isUninitialized(val))
536 reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
545 void TransferFunctions::VisitCastExpr(clang::CastExpr *ce) {
546 if (ce->getCastKind() == CK_LValueToRValue) {
547 const FindVarResult &res = findBlockVarDecl(ce->getSubExpr());
549 assert(res.getDeclRefExpr() == lastDR);
553 else if (ce->getCastKind() == CK_NoOp ||
554 ce->getCastKind() == CK_LValueBitCast) {
555 skipProcessUses = true;
557 else if (CStyleCastExpr *cse = dyn_cast<CStyleCastExpr>(ce)) {
558 if (cse->getType()->isVoidType()) {
560 if (lastLoad == cse->getSubExpr()) {
561 // Squelch any detected load of an uninitialized value if
562 // we cast it to void.
570 void TransferFunctions::Visit(clang::Stmt *s) {
571 skipProcessUses = false;
572 StmtVisitor<TransferFunctions>::Visit(s);
573 if (!skipProcessUses)
577 void TransferFunctions::ProcessUses(Stmt *s) {
578 // This method is typically called after visiting a CFGElement statement
579 // in the CFG. We delay processing of reporting many loads of uninitialized
580 // values until here.
582 // If we just visited the lvalue-to-rvalue cast, there is nothing
587 const DeclRefExpr *DR =
588 cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
589 lastLoad->getSubExpr()));
590 const VarDecl *VD = cast<VarDecl>(DR->getDecl());
592 // If we reach here, we may have seen a load of an uninitialized value
593 // and it hasn't been casted to void or otherwise handled. In this
594 // situation, report the incident.
595 if (isUninitialized(vals[VD]))
596 reportUninit(DR, VD, isAlwaysUninit(vals[VD]));
606 // Any other uses of 'lastDR' involve taking an lvalue of variable.
607 // In this case, it "escapes" the analysis.
608 if (lastDR && lastDR != s) {
609 vals[cast<VarDecl>(lastDR->getDecl())] = Initialized;
614 //------------------------------------------------------------------------====//
615 // High-level "driver" logic for uninitialized values analysis.
616 //====------------------------------------------------------------------------//
618 static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
619 AnalysisDeclContext &ac, CFGBlockValues &vals,
620 llvm::BitVector &wasAnalyzed,
621 UninitVariablesHandler *handler = 0) {
623 wasAnalyzed[block->getBlockID()] = true;
625 if (const BinaryOperator *b = getLogicalOperatorInChain(block)) {
626 CFGBlock::const_pred_iterator itr = block->pred_begin();
627 BVPair vA = vals.getValueVectors(*itr, false);
629 BVPair vB = vals.getValueVectors(*itr, false);
633 if (b->getOpcode() == BO_LAnd) {
634 // Merge the 'F' bits from the first and second.
635 vals.mergeIntoScratch(*(vA.second ? vA.second : vA.first), true);
636 vals.mergeIntoScratch(*(vB.second ? vB.second : vB.first), false);
637 valsAB.first = vA.first;
638 valsAB.second = &vals.getScratch();
640 // Merge the 'T' bits from the first and second.
641 assert(b->getOpcode() == BO_LOr);
642 vals.mergeIntoScratch(*vA.first, true);
643 vals.mergeIntoScratch(*vB.first, false);
644 valsAB.first = &vals.getScratch();
645 valsAB.second = vA.second ? vA.second : vA.first;
647 return vals.updateValueVectors(block, valsAB);
650 // Default behavior: merge in values of predecessor blocks.
653 for (CFGBlock::const_pred_iterator I = block->pred_begin(),
654 E = block->pred_end(); I != E; ++I) {
655 const CFGBlock *pred = *I;
656 if (wasAnalyzed[pred->getBlockID()]) {
657 vals.mergeIntoScratch(vals.getValueVector(pred, block), isFirst);
661 // Apply the transfer function.
662 TransferFunctions tf(vals, cfg, ac, handler);
663 for (CFGBlock::const_iterator I = block->begin(), E = block->end();
665 if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) {
666 tf.Visit(const_cast<Stmt*>(cs->getStmt()));
670 return vals.updateValueVectorWithScratch(block);
673 void clang::runUninitializedVariablesAnalysis(
674 const DeclContext &dc,
676 AnalysisDeclContext &ac,
677 UninitVariablesHandler &handler,
678 UninitVariablesAnalysisStats &stats) {
679 CFGBlockValues vals(cfg);
680 vals.computeSetOfDeclarations(dc);
681 if (vals.hasNoDeclarations())
684 stats.NumVariablesAnalyzed = vals.getNumEntries();
686 // Mark all variables uninitialized at the entry.
687 const CFGBlock &entry = cfg.getEntry();
688 for (CFGBlock::const_succ_iterator i = entry.succ_begin(),
689 e = entry.succ_end(); i != e; ++i) {
690 if (const CFGBlock *succ = *i) {
691 ValueVector &vec = vals.getValueVector(&entry, succ);
692 const unsigned n = vals.getNumEntries();
693 for (unsigned j = 0; j < n ; ++j) {
694 vec[j] = Uninitialized;
699 // Proceed with the workist.
700 DataflowWorklist worklist(cfg);
701 llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
702 worklist.enqueueSuccessors(&cfg.getEntry());
703 llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
704 wasAnalyzed[cfg.getEntry().getBlockID()] = true;
706 while (const CFGBlock *block = worklist.dequeue()) {
707 // Did the block change?
708 bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed);
709 ++stats.NumBlockVisits;
710 if (changed || !previouslyVisited[block->getBlockID()])
711 worklist.enqueueSuccessors(block);
712 previouslyVisited[block->getBlockID()] = true;
715 // Run through the blocks one more time, and report uninitialized variabes.
716 for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
717 const CFGBlock *block = *BI;
718 if (wasAnalyzed[block->getBlockID()]) {
719 runOnBlock(block, cfg, ac, vals, wasAnalyzed, &handler);
720 ++stats.NumBlockVisits;
725 UninitVariablesHandler::~UninitVariablesHandler() {}