clang  3.7.0
UninitializedValues.cpp
Go to the documentation of this file.
1 //==- UninitializedValues.cpp - Find Uninitialized Values -------*- C++ --*-==//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements uninitialized values analysis for source-level CFGs.
11 //
12 //===----------------------------------------------------------------------===//
13 
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"
22 #include "clang/Analysis/CFG.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"
30 #include <utility>
31 
32 using namespace clang;
33 
34 #define DEBUG_LOGGING 0
35 
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();
42  }
43  return false;
44 }
45 
46 //------------------------------------------------------------------------====//
47 // DeclToIndex: a mapping from Decls we track to value indices.
48 //====------------------------------------------------------------------------//
49 
50 namespace {
51 class DeclToIndex {
52  llvm::DenseMap<const VarDecl *, unsigned> map;
53 public:
54  DeclToIndex() {}
55 
56  /// Compute the actual mapping from declarations to bits.
57  void computeMap(const DeclContext &dc);
58 
59  /// Return the number of declarations in the map.
60  unsigned size() const { return map.size(); }
61 
62  /// Returns the bit vector index for a given declaration.
63  Optional<unsigned> getValueIndex(const VarDecl *d) const;
64 };
65 }
66 
67 void DeclToIndex::computeMap(const DeclContext &dc) {
68  unsigned count = 0;
70  E(dc.decls_end());
71  for ( ; I != E; ++I) {
72  const VarDecl *vd = *I;
73  if (isTrackedVar(vd, &dc))
74  map[vd] = count++;
75  }
76 }
77 
78 Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
79  llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
80  if (I == map.end())
81  return None;
82  return I->second;
83 }
84 
85 //------------------------------------------------------------------------====//
86 // CFGBlockValues: dataflow values for CFG blocks.
87 //====------------------------------------------------------------------------//
88 
89 // These values are defined in such a way that a merge can be done using
90 // a bitwise OR.
91 enum Value { Unknown = 0x0, /* 00 */
92  Initialized = 0x1, /* 01 */
93  Uninitialized = 0x2, /* 10 */
94  MayUninitialized = 0x3 /* 11 */ };
95 
96 static bool isUninitialized(const Value v) {
97  return v >= Uninitialized;
98 }
99 static bool isAlwaysUninit(const Value v) {
100  return v == Uninitialized;
101 }
102 
103 namespace {
104 
105 typedef llvm::PackedVector<Value, 2, llvm::SmallBitVector> ValueVector;
106 
107 class CFGBlockValues {
108  const CFG &cfg;
110  ValueVector scratch;
111  DeclToIndex declToIndex;
112 public:
113  CFGBlockValues(const CFG &cfg);
114 
115  unsigned getNumEntries() const { return declToIndex.size(); }
116 
117  void computeSetOfDeclarations(const DeclContext &dc);
118  ValueVector &getValueVector(const CFGBlock *block) {
119  return vals[block->getBlockID()];
120  }
121 
122  void setAllScratchValues(Value V);
123  void mergeIntoScratch(ValueVector const &source, bool isFirst);
124  bool updateValueVectorWithScratch(const CFGBlock *block);
125 
126  bool hasNoDeclarations() const {
127  return declToIndex.size() == 0;
128  }
129 
130  void resetScratch();
131 
132  ValueVector::reference operator[](const VarDecl *vd);
133 
134  Value getValue(const CFGBlock *block, const CFGBlock *dstBlock,
135  const VarDecl *vd) {
136  const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
137  assert(idx.hasValue());
138  return getValueVector(block)[idx.getValue()];
139  }
140 };
141 } // end anonymous namespace
142 
143 CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {}
144 
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();
150  if (!n)
151  return;
152  vals.resize(n);
153  for (unsigned i = 0; i < n; ++i)
154  vals[i].resize(decls);
155 }
156 
157 #if DEBUG_LOGGING
158 static void printVector(const CFGBlock *block, ValueVector &bv,
159  unsigned num) {
160  llvm::errs() << block->getBlockID() << " :";
161  for (unsigned i = 0; i < bv.size(); ++i) {
162  llvm::errs() << ' ' << bv[i];
163  }
164  llvm::errs() << " : " << num << '\n';
165 }
166 #endif
167 
168 void CFGBlockValues::setAllScratchValues(Value V) {
169  for (unsigned I = 0, E = scratch.size(); I != E; ++I)
170  scratch[I] = V;
171 }
172 
173 void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
174  bool isFirst) {
175  if (isFirst)
176  scratch = source;
177  else
178  scratch |= source;
179 }
180 
181 bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
182  ValueVector &dst = getValueVector(block);
183  bool changed = (dst != scratch);
184  if (changed)
185  dst = scratch;
186 #if DEBUG_LOGGING
187  printVector(block, scratch, 0);
188 #endif
189  return changed;
190 }
191 
192 void CFGBlockValues::resetScratch() {
193  scratch.reset();
194 }
195 
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()];
200 }
201 
202 //------------------------------------------------------------------------====//
203 // Worklist: worklist for dataflow analysis.
204 //====------------------------------------------------------------------------//
205 
206 namespace {
207 class DataflowWorklist {
208  PostOrderCFGView::iterator PO_I, PO_E;
210  llvm::BitVector enqueuedBlocks;
211 public:
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.
216  if (PO_I != PO_E) {
217  assert(*PO_I == &cfg.getEntry());
218  enqueuedBlocks[(*PO_I)->getBlockID()] = false;
219  ++PO_I;
220  }
221  }
222 
223  void enqueueSuccessors(const CFGBlock *block);
224  const CFGBlock *dequeue();
225 };
226 }
227 
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()])
233  continue;
234  worklist.push_back(Successor);
235  enqueuedBlocks[Successor->getBlockID()] = true;
236  }
237 }
238 
239 const CFGBlock *DataflowWorklist::dequeue() {
240  const CFGBlock *B = nullptr;
241 
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();
246 
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) {
250  B = *PO_I;
251  ++PO_I;
252  }
253  else {
254  return nullptr;
255  }
256 
257  assert(enqueuedBlocks[B->getBlockID()] == true);
258  enqueuedBlocks[B->getBlockID()] = false;
259  return B;
260 }
261 
262 //------------------------------------------------------------------------====//
263 // Classification of DeclRefExprs as use or initialization.
264 //====------------------------------------------------------------------------//
265 
266 namespace {
267 class FindVarResult {
268  const VarDecl *vd;
269  const DeclRefExpr *dr;
270 public:
271  FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {}
272 
273  const DeclRefExpr *getDeclRefExpr() const { return dr; }
274  const VarDecl *getDecl() const { return vd; }
275 };
276 
277 static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
278  while (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();
283  continue;
284  }
285  }
286  break;
287  }
288  return Ex;
289 }
290 
291 /// If E is an expression comprising a reference to a single variable, find that
292 /// variable.
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);
300 }
301 
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> {
306 public:
307  enum Class {
308  Init,
309  Use,
310  SelfInit,
311  Ignore
312  };
313 
314 private:
315  const DeclContext *DC;
316  llvm::DenseMap<const DeclRefExpr*, Class> Classification;
317 
318  bool isTrackedVar(const VarDecl *VD) const {
319  return ::isTrackedVar(VD, DC);
320  }
321 
322  void classify(const Expr *E, Class C);
323 
324 public:
325  ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {}
326 
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);
332 
333  void operator()(Stmt *S) { Visit(S); }
334 
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())
339  return I->second;
340 
341  const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl());
342  if (!VD || !isTrackedVar(VD))
343  return Ignore;
344 
345  return Init;
346  }
347 };
348 }
349 
350 static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
351  if (VD->getType()->isRecordType()) return nullptr;
352  if (Expr *Init = VD->getInit()) {
353  const DeclRefExpr *DRE
354  = dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
355  if (DRE && DRE->getDecl() == VD)
356  return DRE;
357  }
358  return nullptr;
359 }
360 
361 void ClassifyRefs::classify(const Expr *E, Class C) {
362  // The result of a ?: could also be an lvalue.
363  E = E->IgnoreParens();
364  if (const ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
365  classify(CO->getTrueExpr(), C);
366  classify(CO->getFalseExpr(), C);
367  return;
368  }
369 
370  if (const BinaryConditionalOperator *BCO =
371  dyn_cast<BinaryConditionalOperator>(E)) {
372  classify(BCO->getFalseExpr(), C);
373  return;
374  }
375 
376  if (const OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(E)) {
377  classify(OVE->getSourceExpr(), C);
378  return;
379  }
380 
381  if (const MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
382  if (VarDecl *VD = dyn_cast<VarDecl>(ME->getMemberDecl())) {
383  if (!VD->isStaticDataMember())
384  classify(ME->getBase(), C);
385  }
386  return;
387  }
388 
389  if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
390  switch (BO->getOpcode()) {
391  case BO_PtrMemD:
392  case BO_PtrMemI:
393  classify(BO->getLHS(), C);
394  return;
395  case BO_Comma:
396  classify(BO->getRHS(), C);
397  return;
398  default:
399  return;
400  }
401  }
402 
403  FindVarResult Var = findVar(E, DC);
404  if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
405  Classification[DRE] = std::max(Classification[DRE], C);
406 }
407 
408 void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
409  for (auto *DI : DS->decls()) {
410  VarDecl *VD = dyn_cast<VarDecl>(DI);
411  if (VD && isTrackedVar(VD))
412  if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
413  Classification[DRE] = SelfInit;
414  }
415 }
416 
417 void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
418  // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
419  // is not a compound-assignment, we will treat it as initializing the variable
420  // when TransferFunctions visits it. A compound-assignment does not affect
421  // whether a variable is uninitialized, and there's no point counting it as a
422  // use.
423  if (BO->isCompoundAssignmentOp())
424  classify(BO->getLHS(), Use);
425  else if (BO->getOpcode() == BO_Assign || BO->getOpcode() == BO_Comma)
426  classify(BO->getLHS(), Ignore);
427 }
428 
429 void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
430  // Increment and decrement are uses despite there being no lvalue-to-rvalue
431  // conversion.
432  if (UO->isIncrementDecrementOp())
433  classify(UO->getSubExpr(), Use);
434 }
435 
436 static bool isPointerToConst(const QualType &QT) {
437  return QT->isAnyPointerType() && QT->getPointeeType().isConstQualified();
438 }
439 
440 void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
441  // Classify arguments to std::move as used.
442  if (CE->getNumArgs() == 1) {
443  if (FunctionDecl *FD = CE->getDirectCallee()) {
444  if (FD->isInStdNamespace() && FD->getIdentifier() &&
445  FD->getIdentifier()->isStr("move")) {
446  // RecordTypes are handled in SemaDeclCXX.cpp.
447  if (!CE->getArg(0)->getType()->isRecordType())
448  classify(CE->getArg(0), Use);
449  return;
450  }
451  }
452  }
453 
454  // If a value is passed by const pointer or by const reference to a function,
455  // we should not assume that it is initialized by the call, and we
456  // conservatively do not assume that it is used.
457  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
458  I != E; ++I) {
459  if ((*I)->isGLValue()) {
460  if ((*I)->getType().isConstQualified())
461  classify((*I), Ignore);
462  } else if (isPointerToConst((*I)->getType())) {
463  const Expr *Ex = stripCasts(DC->getParentASTContext(), *I);
464  const UnaryOperator *UO = dyn_cast<UnaryOperator>(Ex);
465  if (UO && UO->getOpcode() == UO_AddrOf)
466  Ex = UO->getSubExpr();
467  classify(Ex, Ignore);
468  }
469  }
470 }
471 
472 void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
473  if (CE->getCastKind() == CK_LValueToRValue)
474  classify(CE->getSubExpr(), Use);
475  else if (CStyleCastExpr *CSE = dyn_cast<CStyleCastExpr>(CE)) {
476  if (CSE->getType()->isVoidType()) {
477  // Squelch any detected load of an uninitialized value if
478  // we cast it to void.
479  // e.g. (void) x;
480  classify(CSE->getSubExpr(), Ignore);
481  }
482  }
483 }
484 
485 //------------------------------------------------------------------------====//
486 // Transfer function for uninitialized values analysis.
487 //====------------------------------------------------------------------------//
488 
489 namespace {
490 class TransferFunctions : public StmtVisitor<TransferFunctions> {
491  CFGBlockValues &vals;
492  const CFG &cfg;
493  const CFGBlock *block;
495  const ClassifyRefs &classification;
496  ObjCNoReturn objCNoRet;
497  UninitVariablesHandler &handler;
498 
499 public:
500  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
501  const CFGBlock *block, AnalysisDeclContext &ac,
502  const ClassifyRefs &classification,
503  UninitVariablesHandler &handler)
504  : vals(vals), cfg(cfg), block(block), ac(ac),
505  classification(classification), objCNoRet(ac.getASTContext()),
506  handler(handler) {}
507 
508  void reportUse(const Expr *ex, const VarDecl *vd);
509 
510  void VisitBinaryOperator(BinaryOperator *bo);
511  void VisitBlockExpr(BlockExpr *be);
512  void VisitCallExpr(CallExpr *ce);
513  void VisitDeclRefExpr(DeclRefExpr *dr);
514  void VisitDeclStmt(DeclStmt *ds);
515  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
516  void VisitObjCMessageExpr(ObjCMessageExpr *ME);
517 
518  bool isTrackedVar(const VarDecl *vd) {
519  return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
520  }
521 
522  FindVarResult findVar(const Expr *ex) {
523  return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
524  }
525 
526  UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
527  UninitUse Use(ex, isAlwaysUninit(v));
528 
529  assert(isUninitialized(v));
530  if (Use.getKind() == UninitUse::Always)
531  return Use;
532 
533  // If an edge which leads unconditionally to this use did not initialize
534  // the variable, we can say something stronger than 'may be uninitialized':
535  // we can say 'either it's used uninitialized or you have dead code'.
536  //
537  // We track the number of successors of a node which have been visited, and
538  // visit a node once we have visited all of its successors. Only edges where
539  // the variable might still be uninitialized are followed. Since a variable
540  // can't transfer from being initialized to being uninitialized, this will
541  // trace out the subgraph which inevitably leads to the use and does not
542  // initialize the variable. We do not want to skip past loops, since their
543  // non-termination might be correlated with the initialization condition.
544  //
545  // For example:
546  //
547  // void f(bool a, bool b) {
548  // block1: int n;
549  // if (a) {
550  // block2: if (b)
551  // block3: n = 1;
552  // block4: } else if (b) {
553  // block5: while (!a) {
554  // block6: do_work(&a);
555  // n = 2;
556  // }
557  // }
558  // block7: if (a)
559  // block8: g();
560  // block9: return n;
561  // }
562  //
563  // Starting from the maybe-uninitialized use in block 9:
564  // * Block 7 is not visited because we have only visited one of its two
565  // successors.
566  // * Block 8 is visited because we've visited its only successor.
567  // From block 8:
568  // * Block 7 is visited because we've now visited both of its successors.
569  // From block 7:
570  // * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
571  // of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
572  // * Block 3 is not visited because it initializes 'n'.
573  // Now the algorithm terminates, having visited blocks 7 and 8, and having
574  // found the frontier is blocks 2, 4, and 5.
575  //
576  // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
577  // and 4), so we report that any time either of those edges is taken (in
578  // each case when 'b == false'), 'n' is used uninitialized.
580  SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
581  Queue.push_back(block);
582  // Specify that we've already visited all successors of the starting block.
583  // This has the dual purpose of ensuring we never add it to the queue, and
584  // of marking it as not being a candidate element of the frontier.
585  SuccsVisited[block->getBlockID()] = block->succ_size();
586  while (!Queue.empty()) {
587  const CFGBlock *B = Queue.pop_back_val();
588 
589  // If the use is always reached from the entry block, make a note of that.
590  if (B == &cfg.getEntry())
591  Use.setUninitAfterCall();
592 
593  for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
594  I != E; ++I) {
595  const CFGBlock *Pred = *I;
596  if (!Pred)
597  continue;
598 
599  Value AtPredExit = vals.getValue(Pred, B, vd);
600  if (AtPredExit == Initialized)
601  // This block initializes the variable.
602  continue;
603  if (AtPredExit == MayUninitialized &&
604  vals.getValue(B, nullptr, vd) == Uninitialized) {
605  // This block declares the variable (uninitialized), and is reachable
606  // from a block that initializes the variable. We can't guarantee to
607  // give an earlier location for the diagnostic (and it appears that
608  // this code is intended to be reachable) so give a diagnostic here
609  // and go no further down this path.
610  Use.setUninitAfterDecl();
611  continue;
612  }
613 
614  unsigned &SV = SuccsVisited[Pred->getBlockID()];
615  if (!SV) {
616  // When visiting the first successor of a block, mark all NULL
617  // successors as having been visited.
618  for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
619  SE = Pred->succ_end();
620  SI != SE; ++SI)
621  if (!*SI)
622  ++SV;
623  }
624 
625  if (++SV == Pred->succ_size())
626  // All paths from this block lead to the use and don't initialize the
627  // variable.
628  Queue.push_back(Pred);
629  }
630  }
631 
632  // Scan the frontier, looking for blocks where the variable was
633  // uninitialized.
634  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
635  const CFGBlock *Block = *BI;
636  unsigned BlockID = Block->getBlockID();
637  const Stmt *Term = Block->getTerminator();
638  if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
639  Term) {
640  // This block inevitably leads to the use. If we have an edge from here
641  // to a post-dominator block, and the variable is uninitialized on that
642  // edge, we have found a bug.
643  for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
644  E = Block->succ_end(); I != E; ++I) {
645  const CFGBlock *Succ = *I;
646  if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
647  vals.getValue(Block, Succ, vd) == Uninitialized) {
648  // Switch cases are a special case: report the label to the caller
649  // as the 'terminator', not the switch statement itself. Suppress
650  // situations where no label matched: we can't be sure that's
651  // possible.
652  if (isa<SwitchStmt>(Term)) {
653  const Stmt *Label = Succ->getLabel();
654  if (!Label || !isa<SwitchCase>(Label))
655  // Might not be possible.
656  continue;
657  UninitUse::Branch Branch;
658  Branch.Terminator = Label;
659  Branch.Output = 0; // Ignored.
660  Use.addUninitBranch(Branch);
661  } else {
662  UninitUse::Branch Branch;
663  Branch.Terminator = Term;
664  Branch.Output = I - Block->succ_begin();
665  Use.addUninitBranch(Branch);
666  }
667  }
668  }
669  }
670  }
671 
672  return Use;
673  }
674 };
675 }
676 
677 void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
678  Value v = vals[vd];
679  if (isUninitialized(v))
680  handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
681 }
682 
683 void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
684  // This represents an initialization of the 'element' value.
685  if (DeclStmt *DS = dyn_cast<DeclStmt>(FS->getElement())) {
686  const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
687  if (isTrackedVar(VD))
688  vals[VD] = Initialized;
689  }
690 }
691 
692 void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
693  const BlockDecl *bd = be->getBlockDecl();
694  for (const auto &I : bd->captures()) {
695  const VarDecl *vd = I.getVariable();
696  if (!isTrackedVar(vd))
697  continue;
698  if (I.isByRef()) {
699  vals[vd] = Initialized;
700  continue;
701  }
702  reportUse(be, vd);
703  }
704 }
705 
706 void TransferFunctions::VisitCallExpr(CallExpr *ce) {
707  if (Decl *Callee = ce->getCalleeDecl()) {
708  if (Callee->hasAttr<ReturnsTwiceAttr>()) {
709  // After a call to a function like setjmp or vfork, any variable which is
710  // initialized anywhere within this function may now be initialized. For
711  // now, just assume such a call initializes all variables. FIXME: Only
712  // mark variables as initialized if they have an initializer which is
713  // reachable from here.
714  vals.setAllScratchValues(Initialized);
715  }
716  else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
717  // Functions labeled like "analyzer_noreturn" are often used to denote
718  // "panic" functions that in special debug situations can still return,
719  // but for the most part should not be treated as returning. This is a
720  // useful annotation borrowed from the static analyzer that is useful for
721  // suppressing branch-specific false positives when we call one of these
722  // functions but keep pretending the path continues (when in reality the
723  // user doesn't care).
724  vals.setAllScratchValues(Unknown);
725  }
726  }
727 }
728 
729 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
730  switch (classification.get(dr)) {
731  case ClassifyRefs::Ignore:
732  break;
733  case ClassifyRefs::Use:
734  reportUse(dr, cast<VarDecl>(dr->getDecl()));
735  break;
736  case ClassifyRefs::Init:
737  vals[cast<VarDecl>(dr->getDecl())] = Initialized;
738  break;
739  case ClassifyRefs::SelfInit:
740  handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
741  break;
742  }
743 }
744 
745 void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
746  if (BO->getOpcode() == BO_Assign) {
747  FindVarResult Var = findVar(BO->getLHS());
748  if (const VarDecl *VD = Var.getDecl())
749  vals[VD] = Initialized;
750  }
751 }
752 
753 void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
754  for (auto *DI : DS->decls()) {
755  VarDecl *VD = dyn_cast<VarDecl>(DI);
756  if (VD && isTrackedVar(VD)) {
757  if (getSelfInitExpr(VD)) {
758  // If the initializer consists solely of a reference to itself, we
759  // explicitly mark the variable as uninitialized. This allows code
760  // like the following:
761  //
762  // int x = x;
763  //
764  // to deliberately leave a variable uninitialized. Different analysis
765  // clients can detect this pattern and adjust their reporting
766  // appropriately, but we need to continue to analyze subsequent uses
767  // of the variable.
768  vals[VD] = Uninitialized;
769  } else if (VD->getInit()) {
770  // Treat the new variable as initialized.
771  vals[VD] = Initialized;
772  } else {
773  // No initializer: the variable is now uninitialized. This matters
774  // for cases like:
775  // while (...) {
776  // int n;
777  // use(n);
778  // n = 0;
779  // }
780  // FIXME: Mark the variable as uninitialized whenever its scope is
781  // left, since its scope could be re-entered by a jump over the
782  // declaration.
783  vals[VD] = Uninitialized;
784  }
785  }
786  }
787 }
788 
789 void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
790  // If the Objective-C message expression is an implicit no-return that
791  // is not modeled in the CFG, set the tracked dataflow values to Unknown.
792  if (objCNoRet.isImplicitNoReturn(ME)) {
793  vals.setAllScratchValues(Unknown);
794  }
795 }
796 
797 //------------------------------------------------------------------------====//
798 // High-level "driver" logic for uninitialized values analysis.
799 //====------------------------------------------------------------------------//
800 
801 static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
802  AnalysisDeclContext &ac, CFGBlockValues &vals,
803  const ClassifyRefs &classification,
804  llvm::BitVector &wasAnalyzed,
805  UninitVariablesHandler &handler) {
806  wasAnalyzed[block->getBlockID()] = true;
807  vals.resetScratch();
808  // Merge in values of predecessor blocks.
809  bool isFirst = true;
810  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
811  E = block->pred_end(); I != E; ++I) {
812  const CFGBlock *pred = *I;
813  if (!pred)
814  continue;
815  if (wasAnalyzed[pred->getBlockID()]) {
816  vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
817  isFirst = false;
818  }
819  }
820  // Apply the transfer function.
821  TransferFunctions tf(vals, cfg, block, ac, classification, handler);
822  for (CFGBlock::const_iterator I = block->begin(), E = block->end();
823  I != E; ++I) {
824  if (Optional<CFGStmt> cs = I->getAs<CFGStmt>())
825  tf.Visit(const_cast<Stmt*>(cs->getStmt()));
826  }
827  return vals.updateValueVectorWithScratch(block);
828 }
829 
830 /// PruneBlocksHandler is a special UninitVariablesHandler that is used
831 /// to detect when a CFGBlock has any *potential* use of an uninitialized
832 /// variable. It is mainly used to prune out work during the final
833 /// reporting pass.
834 namespace {
835 struct PruneBlocksHandler : public UninitVariablesHandler {
836  PruneBlocksHandler(unsigned numBlocks)
837  : hadUse(numBlocks, false), hadAnyUse(false),
838  currentBlock(0) {}
839 
840  ~PruneBlocksHandler() override {}
841 
842  /// Records if a CFGBlock had a potential use of an uninitialized variable.
843  llvm::BitVector hadUse;
844 
845  /// Records if any CFGBlock had a potential use of an uninitialized variable.
846  bool hadAnyUse;
847 
848  /// The current block to scribble use information.
849  unsigned currentBlock;
850 
851  void handleUseOfUninitVariable(const VarDecl *vd,
852  const UninitUse &use) override {
853  hadUse[currentBlock] = true;
854  hadAnyUse = true;
855  }
856 
857  /// Called when the uninitialized variable analysis detects the
858  /// idiom 'int x = x'. All other uses of 'x' within the initializer
859  /// are handled by handleUseOfUninitVariable.
860  void handleSelfInit(const VarDecl *vd) override {
861  hadUse[currentBlock] = true;
862  hadAnyUse = true;
863  }
864 };
865 }
866 
868  const DeclContext &dc,
869  const CFG &cfg,
871  UninitVariablesHandler &handler,
873  CFGBlockValues vals(cfg);
874  vals.computeSetOfDeclarations(dc);
875  if (vals.hasNoDeclarations())
876  return;
877 
878  stats.NumVariablesAnalyzed = vals.getNumEntries();
879 
880  // Precompute which expressions are uses and which are initializations.
881  ClassifyRefs classification(ac);
882  cfg.VisitBlockStmts(classification);
883 
884  // Mark all variables uninitialized at the entry.
885  const CFGBlock &entry = cfg.getEntry();
886  ValueVector &vec = vals.getValueVector(&entry);
887  const unsigned n = vals.getNumEntries();
888  for (unsigned j = 0; j < n ; ++j) {
889  vec[j] = Uninitialized;
890  }
891 
892  // Proceed with the workist.
893  DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>());
894  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
895  worklist.enqueueSuccessors(&cfg.getEntry());
896  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
897  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
898  PruneBlocksHandler PBH(cfg.getNumBlockIDs());
899 
900  while (const CFGBlock *block = worklist.dequeue()) {
901  PBH.currentBlock = block->getBlockID();
902 
903  // Did the block change?
904  bool changed = runOnBlock(block, cfg, ac, vals,
905  classification, wasAnalyzed, PBH);
906  ++stats.NumBlockVisits;
907  if (changed || !previouslyVisited[block->getBlockID()])
908  worklist.enqueueSuccessors(block);
909  previouslyVisited[block->getBlockID()] = true;
910  }
911 
912  if (!PBH.hadAnyUse)
913  return;
914 
915  // Run through the blocks one more time, and report uninitialized variables.
916  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
917  const CFGBlock *block = *BI;
918  if (PBH.hadUse[block->getBlockID()]) {
919  runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
920  ++stats.NumBlockVisits;
921  }
922  }
923 }
924 
925 UninitVariablesHandler::~UninitVariablesHandler() {}
Defines the clang::ASTContext interface.
CastKind getCastKind() const
Definition: Expr.h:2709
pred_iterator pred_end()
Definition: CFG.h:533
Expr * getArg(unsigned Arg)
getArg - Return the specified argument.
Definition: Expr.h:2216
succ_iterator succ_begin()
Definition: CFG.h:542
CFGBlock & getEntry()
Definition: CFG.h:863
static bool isPointerToConst(const QualType &QT)
bool isRecordType() const
Definition: Type.h:5289
iterator begin()
Definition: CFG.h:506
const Expr * getInit() const
Definition: Decl.h:1068
static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc)
unsigned succ_size() const
Definition: CFG.h:552
bool hasGlobalStorage() const
Returns true for all variables that do not have local storage.
Definition: Decl.h:922
capture_range captures()
Definition: Decl.h:3563
decl_iterator decls_end() const
Definition: DeclBase.h:1415
bool isScalarType() const
Definition: Type.h:5461
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:89
bool isAnyPointerType() const
Definition: Type.h:5235
static bool isIncrementDecrementOp(Opcode Op)
Definition: Expr.h:1733
Expr * getSubExpr()
Definition: Expr.h:2713
iterator end()
Definition: CFG.h:845
static bool isAlwaysUninit(const Value v)
Expr * getLHS() const
Definition: Expr.h:2964
static bool runOnBlock(const CFGBlock *block, const CFG &cfg, AnalysisDeclContext &ac, CFGBlockValues &vals, const ClassifyRefs &classification, llvm::BitVector &wasAnalyzed, UninitVariablesHandler &handler)
bool isImplicit() const
Definition: DeclBase.h:503
ElementList::const_iterator const_iterator
Definition: CFG.h:499
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:2918
decl_iterator decls_begin() const
Definition: DeclBase.cpp:1141
QualType getType() const
Definition: Decl.h:538
arg_iterator arg_end()
Definition: Expr.h:2247
Expr * IgnoreParenNoopCasts(ASTContext &Ctx) LLVM_READONLY
Definition: Expr.cpp:2559
QualType getPointeeType() const
Definition: Type.cpp:414
void VisitBlockStmts(CALLBACK &O) const
Definition: CFG.h:917
ASTContext & getParentASTContext() const
Definition: DeclBase.h:1203
virtual void handleSelfInit(const VarDecl *vd)
DeclContext * getDeclContext()
Definition: DeclBase.h:381
static SVal getValue(SVal val, SValBuilder &svalBuilder)
void runUninitializedVariablesAnalysis(const DeclContext &dc, const CFG &cfg, AnalysisDeclContext &ac, UninitVariablesHandler &handler, UninitVariablesAnalysisStats &stats)
AdjacentBlocks::const_iterator const_pred_iterator
Definition: CFG.h:523
Expr * getSubExpr() const
Definition: Expr.h:1699
bool isExceptionVariable() const
Determine whether this variable is the exception variable in a C++ catch statememt or an Objective-C ...
Definition: Decl.h:1184
unsigned getBlockID() const
Definition: CFG.h:639
An expression that sends a message to the given Objective-C object or class.
Definition: ExprObjC.h:858
ValueDecl * getDecl()
Definition: Expr.h:994
A use of a variable, which might be uninitialized.
do v
Definition: arm_acle.h:77
CFGTerminator getTerminator()
Definition: CFG.h:623
#define false
Definition: stdbool.h:33
Stmt * getLabel()
Definition: CFG.h:634
ASTContext & getASTContext() const LLVM_READONLY
Definition: DeclBase.cpp:284
bool isLocalVarDecl() const
Definition: Decl.h:951
virtual void handleUseOfUninitVariable(const VarDecl *vd, const UninitUse &use)
Called when the uninitialized variable is used at the given expression.
iterator begin()
Definition: CFG.h:844
bool isVectorType() const
Definition: Type.h:5298
succ_iterator succ_end()
Definition: CFG.h:543
const BlockDecl * getBlockDecl() const
Definition: Expr.h:4616
AdjacentBlocks::const_iterator const_succ_iterator
Definition: CFG.h:528
const Decl * getSingleDecl() const
Definition: Stmt.h:467
bool isInitCapture() const
Whether this variable is the implicit variable for a lambda init-capture.
Definition: Decl.h:1242
static const DeclRefExpr * getSelfInitExpr(VarDecl *VD)
QualType getType() const
Definition: Expr.h:125
pred_iterator pred_begin()
Definition: CFG.h:532
FunctionDecl * getDirectCallee()
If the callee is a FunctionDecl, return it. Otherwise return 0.
Definition: Expr.cpp:1184
unsigned getNumArgs() const
Definition: Expr.h:2205
Decl * getCalleeDecl()
Definition: Expr.cpp:1160
std::vector< const CFGBlock * >::reverse_iterator iterator
The use is always uninitialized.
Represents Objective-C's collection statement.
Definition: StmtObjC.h:24
arg_iterator arg_begin()
Definition: Expr.h:2246
decl_range decls()
Definition: Stmt.h:497
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
static bool isCompoundAssignmentOp(Opcode Opc)
Definition: Expr.h:3045
Opcode getOpcode() const
Definition: Expr.h:2961
A reference to a declared variable, function, enum, etc. [C99 6.5.1p2].
Definition: Expr.h:899
#define true
Definition: stdbool.h:32
iterator end()
Definition: CFG.h:507
bool isConstQualified() const
Determine whether this type is const-qualified.
Definition: Type.h:5075
unsigned getNumBlockIDs() const
Definition: CFG.h:932
Expr * IgnoreParens() LLVM_READONLY
Definition: Expr.cpp:2408
static bool isUninitialized(const Value v)