clang  10.0.0svn
UninitializedValues.cpp
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1 //===- UninitializedValues.cpp - Find Uninitialized Values ----------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements uninitialized values analysis for source-level CFGs.
10 //
11 //===----------------------------------------------------------------------===//
12 
14 #include "clang/AST/Attr.h"
15 #include "clang/AST/Decl.h"
16 #include "clang/AST/DeclBase.h"
17 #include "clang/AST/Expr.h"
19 #include "clang/AST/Stmt.h"
20 #include "clang/AST/StmtObjC.h"
21 #include "clang/AST/StmtVisitor.h"
22 #include "clang/AST/Type.h"
25 #include "clang/Analysis/CFG.h"
27 #include "clang/Basic/LLVM.h"
28 #include "llvm/ADT/BitVector.h"
29 #include "llvm/ADT/DenseMap.h"
30 #include "llvm/ADT/None.h"
31 #include "llvm/ADT/Optional.h"
32 #include "llvm/ADT/PackedVector.h"
33 #include "llvm/ADT/SmallBitVector.h"
34 #include "llvm/ADT/SmallVector.h"
35 #include "llvm/Support/Casting.h"
36 #include <algorithm>
37 #include <cassert>
38 
39 using namespace clang;
40 
41 #define DEBUG_LOGGING 0
42 
43 static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
44  if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
45  !vd->isExceptionVariable() && !vd->isInitCapture() &&
46  !vd->isImplicit() && vd->getDeclContext() == dc) {
47  QualType ty = vd->getType();
48  return ty->isScalarType() || ty->isVectorType() || ty->isRecordType();
49  }
50  return false;
51 }
52 
53 //------------------------------------------------------------------------====//
54 // DeclToIndex: a mapping from Decls we track to value indices.
55 //====------------------------------------------------------------------------//
56 
57 namespace {
58 
59 class DeclToIndex {
60  llvm::DenseMap<const VarDecl *, unsigned> map;
61 
62 public:
63  DeclToIndex() = default;
64 
65  /// Compute the actual mapping from declarations to bits.
66  void computeMap(const DeclContext &dc);
67 
68  /// Return the number of declarations in the map.
69  unsigned size() const { return map.size(); }
70 
71  /// Returns the bit vector index for a given declaration.
72  Optional<unsigned> getValueIndex(const VarDecl *d) const;
73 };
74 
75 } // namespace
76 
77 void DeclToIndex::computeMap(const DeclContext &dc) {
78  unsigned count = 0;
80  E(dc.decls_end());
81  for ( ; I != E; ++I) {
82  const VarDecl *vd = *I;
83  if (isTrackedVar(vd, &dc))
84  map[vd] = count++;
85  }
86 }
87 
88 Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
89  llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
90  if (I == map.end())
91  return None;
92  return I->second;
93 }
94 
95 //------------------------------------------------------------------------====//
96 // CFGBlockValues: dataflow values for CFG blocks.
97 //====------------------------------------------------------------------------//
98 
99 // These values are defined in such a way that a merge can be done using
100 // a bitwise OR.
101 enum Value { Unknown = 0x0, /* 00 */
102  Initialized = 0x1, /* 01 */
103  Uninitialized = 0x2, /* 10 */
104  MayUninitialized = 0x3 /* 11 */ };
105 
106 static bool isUninitialized(const Value v) {
107  return v >= Uninitialized;
108 }
109 
110 static bool isAlwaysUninit(const Value v) {
111  return v == Uninitialized;
112 }
113 
114 namespace {
115 
116 using ValueVector = llvm::PackedVector<Value, 2, llvm::SmallBitVector>;
117 
118 class CFGBlockValues {
119  const CFG &cfg;
121  ValueVector scratch;
122  DeclToIndex declToIndex;
123 
124 public:
125  CFGBlockValues(const CFG &cfg);
126 
127  unsigned getNumEntries() const { return declToIndex.size(); }
128 
129  void computeSetOfDeclarations(const DeclContext &dc);
130 
131  ValueVector &getValueVector(const CFGBlock *block) {
132  return vals[block->getBlockID()];
133  }
134 
135  void setAllScratchValues(Value V);
136  void mergeIntoScratch(ValueVector const &source, bool isFirst);
137  bool updateValueVectorWithScratch(const CFGBlock *block);
138 
139  bool hasNoDeclarations() const {
140  return declToIndex.size() == 0;
141  }
142 
143  void resetScratch();
144 
145  ValueVector::reference operator[](const VarDecl *vd);
146 
147  Value getValue(const CFGBlock *block, const CFGBlock *dstBlock,
148  const VarDecl *vd) {
149  const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
150  assert(idx.hasValue());
151  return getValueVector(block)[idx.getValue()];
152  }
153 };
154 
155 } // namespace
156 
157 CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {}
158 
159 void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
160  declToIndex.computeMap(dc);
161  unsigned decls = declToIndex.size();
162  scratch.resize(decls);
163  unsigned n = cfg.getNumBlockIDs();
164  if (!n)
165  return;
166  vals.resize(n);
167  for (auto &val : vals)
168  val.resize(decls);
169 }
170 
171 #if DEBUG_LOGGING
172 static void printVector(const CFGBlock *block, ValueVector &bv,
173  unsigned num) {
174  llvm::errs() << block->getBlockID() << " :";
175  for (const auto &i : bv)
176  llvm::errs() << ' ' << i;
177  llvm::errs() << " : " << num << '\n';
178 }
179 #endif
180 
181 void CFGBlockValues::setAllScratchValues(Value V) {
182  for (unsigned I = 0, E = scratch.size(); I != E; ++I)
183  scratch[I] = V;
184 }
185 
186 void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
187  bool isFirst) {
188  if (isFirst)
189  scratch = source;
190  else
191  scratch |= source;
192 }
193 
194 bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
195  ValueVector &dst = getValueVector(block);
196  bool changed = (dst != scratch);
197  if (changed)
198  dst = scratch;
199 #if DEBUG_LOGGING
200  printVector(block, scratch, 0);
201 #endif
202  return changed;
203 }
204 
205 void CFGBlockValues::resetScratch() {
206  scratch.reset();
207 }
208 
209 ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
210  const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
211  assert(idx.hasValue());
212  return scratch[idx.getValue()];
213 }
214 
215 //------------------------------------------------------------------------====//
216 // Worklist: worklist for dataflow analysis.
217 //====------------------------------------------------------------------------//
218 
219 namespace {
220 
221 class DataflowWorklist {
222  PostOrderCFGView::iterator PO_I, PO_E;
224  llvm::BitVector enqueuedBlocks;
225 
226 public:
227  DataflowWorklist(const CFG &cfg, PostOrderCFGView &view)
228  : PO_I(view.begin()), PO_E(view.end()),
229  enqueuedBlocks(cfg.getNumBlockIDs(), true) {
230  // Treat the first block as already analyzed.
231  if (PO_I != PO_E) {
232  assert(*PO_I == &cfg.getEntry());
233  enqueuedBlocks[(*PO_I)->getBlockID()] = false;
234  ++PO_I;
235  }
236  }
237 
238  void enqueueSuccessors(const CFGBlock *block);
239  const CFGBlock *dequeue();
240 };
241 
242 } // namespace
243 
244 void DataflowWorklist::enqueueSuccessors(const CFGBlock *block) {
245  for (CFGBlock::const_succ_iterator I = block->succ_begin(),
246  E = block->succ_end(); I != E; ++I) {
247  const CFGBlock *Successor = *I;
248  if (!Successor || enqueuedBlocks[Successor->getBlockID()])
249  continue;
250  worklist.push_back(Successor);
251  enqueuedBlocks[Successor->getBlockID()] = true;
252  }
253 }
254 
255 const CFGBlock *DataflowWorklist::dequeue() {
256  const CFGBlock *B = nullptr;
257 
258  // First dequeue from the worklist. This can represent
259  // updates along backedges that we want propagated as quickly as possible.
260  if (!worklist.empty())
261  B = worklist.pop_back_val();
262 
263  // Next dequeue from the initial reverse post order. This is the
264  // theoretical ideal in the presence of no back edges.
265  else if (PO_I != PO_E) {
266  B = *PO_I;
267  ++PO_I;
268  }
269  else
270  return nullptr;
271 
272  assert(enqueuedBlocks[B->getBlockID()] == true);
273  enqueuedBlocks[B->getBlockID()] = false;
274  return B;
275 }
276 
277 //------------------------------------------------------------------------====//
278 // Classification of DeclRefExprs as use or initialization.
279 //====------------------------------------------------------------------------//
280 
281 namespace {
282 
283 class FindVarResult {
284  const VarDecl *vd;
285  const DeclRefExpr *dr;
286 
287 public:
288  FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {}
289 
290  const DeclRefExpr *getDeclRefExpr() const { return dr; }
291  const VarDecl *getDecl() const { return vd; }
292 };
293 
294 } // namespace
295 
296 static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
297  while (Ex) {
298  Ex = Ex->IgnoreParenNoopCasts(C);
299  if (const auto *CE = dyn_cast<CastExpr>(Ex)) {
300  if (CE->getCastKind() == CK_LValueBitCast) {
301  Ex = CE->getSubExpr();
302  continue;
303  }
304  }
305  break;
306  }
307  return Ex;
308 }
309 
310 /// If E is an expression comprising a reference to a single variable, find that
311 /// variable.
312 static FindVarResult findVar(const Expr *E, const DeclContext *DC) {
313  if (const auto *DRE =
314  dyn_cast<DeclRefExpr>(stripCasts(DC->getParentASTContext(), E)))
315  if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl()))
316  if (isTrackedVar(VD, DC))
317  return FindVarResult(VD, DRE);
318  return FindVarResult(nullptr, nullptr);
319 }
320 
321 namespace {
322 
323 /// Classify each DeclRefExpr as an initialization or a use. Any
324 /// DeclRefExpr which isn't explicitly classified will be assumed to have
325 /// escaped the analysis and will be treated as an initialization.
326 class ClassifyRefs : public StmtVisitor<ClassifyRefs> {
327 public:
328  enum Class {
329  Init,
330  Use,
331  SelfInit,
332  Ignore
333  };
334 
335 private:
336  const DeclContext *DC;
337  llvm::DenseMap<const DeclRefExpr *, Class> Classification;
338 
339  bool isTrackedVar(const VarDecl *VD) const {
340  return ::isTrackedVar(VD, DC);
341  }
342 
343  void classify(const Expr *E, Class C);
344 
345 public:
346  ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {}
347 
348  void VisitDeclStmt(DeclStmt *DS);
349  void VisitUnaryOperator(UnaryOperator *UO);
350  void VisitBinaryOperator(BinaryOperator *BO);
351  void VisitCallExpr(CallExpr *CE);
352  void VisitCastExpr(CastExpr *CE);
353  void VisitOMPExecutableDirective(OMPExecutableDirective *ED);
354 
355  void operator()(Stmt *S) { Visit(S); }
356 
357  Class get(const DeclRefExpr *DRE) const {
358  llvm::DenseMap<const DeclRefExpr*, Class>::const_iterator I
359  = Classification.find(DRE);
360  if (I != Classification.end())
361  return I->second;
362 
363  const auto *VD = dyn_cast<VarDecl>(DRE->getDecl());
364  if (!VD || !isTrackedVar(VD))
365  return Ignore;
366 
367  return Init;
368  }
369 };
370 
371 } // namespace
372 
373 static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
374  if (VD->getType()->isRecordType())
375  return nullptr;
376  if (Expr *Init = VD->getInit()) {
377  const auto *DRE =
378  dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
379  if (DRE && DRE->getDecl() == VD)
380  return DRE;
381  }
382  return nullptr;
383 }
384 
385 void ClassifyRefs::classify(const Expr *E, Class C) {
386  // The result of a ?: could also be an lvalue.
387  E = E->IgnoreParens();
388  if (const auto *CO = dyn_cast<ConditionalOperator>(E)) {
389  classify(CO->getTrueExpr(), C);
390  classify(CO->getFalseExpr(), C);
391  return;
392  }
393 
394  if (const auto *BCO = dyn_cast<BinaryConditionalOperator>(E)) {
395  classify(BCO->getFalseExpr(), C);
396  return;
397  }
398 
399  if (const auto *OVE = dyn_cast<OpaqueValueExpr>(E)) {
400  classify(OVE->getSourceExpr(), C);
401  return;
402  }
403 
404  if (const auto *ME = dyn_cast<MemberExpr>(E)) {
405  if (const auto *VD = dyn_cast<VarDecl>(ME->getMemberDecl())) {
406  if (!VD->isStaticDataMember())
407  classify(ME->getBase(), C);
408  }
409  return;
410  }
411 
412  if (const auto *BO = dyn_cast<BinaryOperator>(E)) {
413  switch (BO->getOpcode()) {
414  case BO_PtrMemD:
415  case BO_PtrMemI:
416  classify(BO->getLHS(), C);
417  return;
418  case BO_Comma:
419  classify(BO->getRHS(), C);
420  return;
421  default:
422  return;
423  }
424  }
425 
426  FindVarResult Var = findVar(E, DC);
427  if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
428  Classification[DRE] = std::max(Classification[DRE], C);
429 }
430 
431 void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
432  for (auto *DI : DS->decls()) {
433  auto *VD = dyn_cast<VarDecl>(DI);
434  if (VD && isTrackedVar(VD))
435  if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
436  Classification[DRE] = SelfInit;
437  }
438 }
439 
440 void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
441  // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
442  // is not a compound-assignment, we will treat it as initializing the variable
443  // when TransferFunctions visits it. A compound-assignment does not affect
444  // whether a variable is uninitialized, and there's no point counting it as a
445  // use.
446  if (BO->isCompoundAssignmentOp())
447  classify(BO->getLHS(), Use);
448  else if (BO->getOpcode() == BO_Assign || BO->getOpcode() == BO_Comma)
449  classify(BO->getLHS(), Ignore);
450 }
451 
452 void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
453  // Increment and decrement are uses despite there being no lvalue-to-rvalue
454  // conversion.
455  if (UO->isIncrementDecrementOp())
456  classify(UO->getSubExpr(), Use);
457 }
458 
459 void ClassifyRefs::VisitOMPExecutableDirective(OMPExecutableDirective *ED) {
461  classify(cast<Expr>(S), Use);
462 }
463 
464 static bool isPointerToConst(const QualType &QT) {
465  return QT->isAnyPointerType() && QT->getPointeeType().isConstQualified();
466 }
467 
468 void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
469  // Classify arguments to std::move as used.
470  if (CE->isCallToStdMove()) {
471  // RecordTypes are handled in SemaDeclCXX.cpp.
472  if (!CE->getArg(0)->getType()->isRecordType())
473  classify(CE->getArg(0), Use);
474  return;
475  }
476 
477  // If a value is passed by const pointer or by const reference to a function,
478  // we should not assume that it is initialized by the call, and we
479  // conservatively do not assume that it is used.
480  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
481  I != E; ++I) {
482  if ((*I)->isGLValue()) {
483  if ((*I)->getType().isConstQualified())
484  classify((*I), Ignore);
485  } else if (isPointerToConst((*I)->getType())) {
486  const Expr *Ex = stripCasts(DC->getParentASTContext(), *I);
487  const auto *UO = dyn_cast<UnaryOperator>(Ex);
488  if (UO && UO->getOpcode() == UO_AddrOf)
489  Ex = UO->getSubExpr();
490  classify(Ex, Ignore);
491  }
492  }
493 }
494 
495 void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
496  if (CE->getCastKind() == CK_LValueToRValue)
497  classify(CE->getSubExpr(), Use);
498  else if (const auto *CSE = dyn_cast<CStyleCastExpr>(CE)) {
499  if (CSE->getType()->isVoidType()) {
500  // Squelch any detected load of an uninitialized value if
501  // we cast it to void.
502  // e.g. (void) x;
503  classify(CSE->getSubExpr(), Ignore);
504  }
505  }
506 }
507 
508 //------------------------------------------------------------------------====//
509 // Transfer function for uninitialized values analysis.
510 //====------------------------------------------------------------------------//
511 
512 namespace {
513 
514 class TransferFunctions : public StmtVisitor<TransferFunctions> {
515  CFGBlockValues &vals;
516  const CFG &cfg;
517  const CFGBlock *block;
519  const ClassifyRefs &classification;
520  ObjCNoReturn objCNoRet;
521  UninitVariablesHandler &handler;
522 
523 public:
524  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
525  const CFGBlock *block, AnalysisDeclContext &ac,
526  const ClassifyRefs &classification,
527  UninitVariablesHandler &handler)
528  : vals(vals), cfg(cfg), block(block), ac(ac),
529  classification(classification), objCNoRet(ac.getASTContext()),
530  handler(handler) {}
531 
532  void reportUse(const Expr *ex, const VarDecl *vd);
533 
534  void VisitBinaryOperator(BinaryOperator *bo);
535  void VisitBlockExpr(BlockExpr *be);
536  void VisitCallExpr(CallExpr *ce);
537  void VisitDeclRefExpr(DeclRefExpr *dr);
538  void VisitDeclStmt(DeclStmt *ds);
539  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
540  void VisitObjCMessageExpr(ObjCMessageExpr *ME);
541  void VisitOMPExecutableDirective(OMPExecutableDirective *ED);
542 
543  bool isTrackedVar(const VarDecl *vd) {
544  return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
545  }
546 
547  FindVarResult findVar(const Expr *ex) {
548  return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
549  }
550 
551  UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
552  UninitUse Use(ex, isAlwaysUninit(v));
553 
554  assert(isUninitialized(v));
555  if (Use.getKind() == UninitUse::Always)
556  return Use;
557 
558  // If an edge which leads unconditionally to this use did not initialize
559  // the variable, we can say something stronger than 'may be uninitialized':
560  // we can say 'either it's used uninitialized or you have dead code'.
561  //
562  // We track the number of successors of a node which have been visited, and
563  // visit a node once we have visited all of its successors. Only edges where
564  // the variable might still be uninitialized are followed. Since a variable
565  // can't transfer from being initialized to being uninitialized, this will
566  // trace out the subgraph which inevitably leads to the use and does not
567  // initialize the variable. We do not want to skip past loops, since their
568  // non-termination might be correlated with the initialization condition.
569  //
570  // For example:
571  //
572  // void f(bool a, bool b) {
573  // block1: int n;
574  // if (a) {
575  // block2: if (b)
576  // block3: n = 1;
577  // block4: } else if (b) {
578  // block5: while (!a) {
579  // block6: do_work(&a);
580  // n = 2;
581  // }
582  // }
583  // block7: if (a)
584  // block8: g();
585  // block9: return n;
586  // }
587  //
588  // Starting from the maybe-uninitialized use in block 9:
589  // * Block 7 is not visited because we have only visited one of its two
590  // successors.
591  // * Block 8 is visited because we've visited its only successor.
592  // From block 8:
593  // * Block 7 is visited because we've now visited both of its successors.
594  // From block 7:
595  // * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
596  // of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
597  // * Block 3 is not visited because it initializes 'n'.
598  // Now the algorithm terminates, having visited blocks 7 and 8, and having
599  // found the frontier is blocks 2, 4, and 5.
600  //
601  // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
602  // and 4), so we report that any time either of those edges is taken (in
603  // each case when 'b == false'), 'n' is used uninitialized.
605  SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
606  Queue.push_back(block);
607  // Specify that we've already visited all successors of the starting block.
608  // This has the dual purpose of ensuring we never add it to the queue, and
609  // of marking it as not being a candidate element of the frontier.
610  SuccsVisited[block->getBlockID()] = block->succ_size();
611  while (!Queue.empty()) {
612  const CFGBlock *B = Queue.pop_back_val();
613 
614  // If the use is always reached from the entry block, make a note of that.
615  if (B == &cfg.getEntry())
616  Use.setUninitAfterCall();
617 
618  for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
619  I != E; ++I) {
620  const CFGBlock *Pred = *I;
621  if (!Pred)
622  continue;
623 
624  Value AtPredExit = vals.getValue(Pred, B, vd);
625  if (AtPredExit == Initialized)
626  // This block initializes the variable.
627  continue;
628  if (AtPredExit == MayUninitialized &&
629  vals.getValue(B, nullptr, vd) == Uninitialized) {
630  // This block declares the variable (uninitialized), and is reachable
631  // from a block that initializes the variable. We can't guarantee to
632  // give an earlier location for the diagnostic (and it appears that
633  // this code is intended to be reachable) so give a diagnostic here
634  // and go no further down this path.
635  Use.setUninitAfterDecl();
636  continue;
637  }
638 
639  unsigned &SV = SuccsVisited[Pred->getBlockID()];
640  if (!SV) {
641  // When visiting the first successor of a block, mark all NULL
642  // successors as having been visited.
643  for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
644  SE = Pred->succ_end();
645  SI != SE; ++SI)
646  if (!*SI)
647  ++SV;
648  }
649 
650  if (++SV == Pred->succ_size())
651  // All paths from this block lead to the use and don't initialize the
652  // variable.
653  Queue.push_back(Pred);
654  }
655  }
656 
657  // Scan the frontier, looking for blocks where the variable was
658  // uninitialized.
659  for (const auto *Block : cfg) {
660  unsigned BlockID = Block->getBlockID();
661  const Stmt *Term = Block->getTerminatorStmt();
662  if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
663  Term) {
664  // This block inevitably leads to the use. If we have an edge from here
665  // to a post-dominator block, and the variable is uninitialized on that
666  // edge, we have found a bug.
667  for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
668  E = Block->succ_end(); I != E; ++I) {
669  const CFGBlock *Succ = *I;
670  if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
671  vals.getValue(Block, Succ, vd) == Uninitialized) {
672  // Switch cases are a special case: report the label to the caller
673  // as the 'terminator', not the switch statement itself. Suppress
674  // situations where no label matched: we can't be sure that's
675  // possible.
676  if (isa<SwitchStmt>(Term)) {
677  const Stmt *Label = Succ->getLabel();
678  if (!Label || !isa<SwitchCase>(Label))
679  // Might not be possible.
680  continue;
681  UninitUse::Branch Branch;
682  Branch.Terminator = Label;
683  Branch.Output = 0; // Ignored.
684  Use.addUninitBranch(Branch);
685  } else {
686  UninitUse::Branch Branch;
687  Branch.Terminator = Term;
688  Branch.Output = I - Block->succ_begin();
689  Use.addUninitBranch(Branch);
690  }
691  }
692  }
693  }
694  }
695 
696  return Use;
697  }
698 };
699 
700 } // namespace
701 
702 void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
703  Value v = vals[vd];
704  if (isUninitialized(v))
705  handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
706 }
707 
708 void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
709  // This represents an initialization of the 'element' value.
710  if (const auto *DS = dyn_cast<DeclStmt>(FS->getElement())) {
711  const auto *VD = cast<VarDecl>(DS->getSingleDecl());
712  if (isTrackedVar(VD))
713  vals[VD] = Initialized;
714  }
715 }
716 
717 void TransferFunctions::VisitOMPExecutableDirective(
720  assert(S && "Expected non-null used-in-clause child.");
721  Visit(S);
722  }
723  if (!ED->isStandaloneDirective())
724  Visit(ED->getStructuredBlock());
725 }
726 
727 void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
728  const BlockDecl *bd = be->getBlockDecl();
729  for (const auto &I : bd->captures()) {
730  const VarDecl *vd = I.getVariable();
731  if (!isTrackedVar(vd))
732  continue;
733  if (I.isByRef()) {
734  vals[vd] = Initialized;
735  continue;
736  }
737  reportUse(be, vd);
738  }
739 }
740 
741 void TransferFunctions::VisitCallExpr(CallExpr *ce) {
742  if (Decl *Callee = ce->getCalleeDecl()) {
743  if (Callee->hasAttr<ReturnsTwiceAttr>()) {
744  // After a call to a function like setjmp or vfork, any variable which is
745  // initialized anywhere within this function may now be initialized. For
746  // now, just assume such a call initializes all variables. FIXME: Only
747  // mark variables as initialized if they have an initializer which is
748  // reachable from here.
749  vals.setAllScratchValues(Initialized);
750  }
751  else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
752  // Functions labeled like "analyzer_noreturn" are often used to denote
753  // "panic" functions that in special debug situations can still return,
754  // but for the most part should not be treated as returning. This is a
755  // useful annotation borrowed from the static analyzer that is useful for
756  // suppressing branch-specific false positives when we call one of these
757  // functions but keep pretending the path continues (when in reality the
758  // user doesn't care).
759  vals.setAllScratchValues(Unknown);
760  }
761  }
762 }
763 
764 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
765  switch (classification.get(dr)) {
766  case ClassifyRefs::Ignore:
767  break;
768  case ClassifyRefs::Use:
769  reportUse(dr, cast<VarDecl>(dr->getDecl()));
770  break;
771  case ClassifyRefs::Init:
772  vals[cast<VarDecl>(dr->getDecl())] = Initialized;
773  break;
774  case ClassifyRefs::SelfInit:
775  handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
776  break;
777  }
778 }
779 
780 void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
781  if (BO->getOpcode() == BO_Assign) {
782  FindVarResult Var = findVar(BO->getLHS());
783  if (const VarDecl *VD = Var.getDecl())
784  vals[VD] = Initialized;
785  }
786 }
787 
788 void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
789  for (auto *DI : DS->decls()) {
790  auto *VD = dyn_cast<VarDecl>(DI);
791  if (VD && isTrackedVar(VD)) {
792  if (getSelfInitExpr(VD)) {
793  // If the initializer consists solely of a reference to itself, we
794  // explicitly mark the variable as uninitialized. This allows code
795  // like the following:
796  //
797  // int x = x;
798  //
799  // to deliberately leave a variable uninitialized. Different analysis
800  // clients can detect this pattern and adjust their reporting
801  // appropriately, but we need to continue to analyze subsequent uses
802  // of the variable.
803  vals[VD] = Uninitialized;
804  } else if (VD->getInit()) {
805  // Treat the new variable as initialized.
806  vals[VD] = Initialized;
807  } else {
808  // No initializer: the variable is now uninitialized. This matters
809  // for cases like:
810  // while (...) {
811  // int n;
812  // use(n);
813  // n = 0;
814  // }
815  // FIXME: Mark the variable as uninitialized whenever its scope is
816  // left, since its scope could be re-entered by a jump over the
817  // declaration.
818  vals[VD] = Uninitialized;
819  }
820  }
821  }
822 }
823 
824 void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
825  // If the Objective-C message expression is an implicit no-return that
826  // is not modeled in the CFG, set the tracked dataflow values to Unknown.
827  if (objCNoRet.isImplicitNoReturn(ME)) {
828  vals.setAllScratchValues(Unknown);
829  }
830 }
831 
832 //------------------------------------------------------------------------====//
833 // High-level "driver" logic for uninitialized values analysis.
834 //====------------------------------------------------------------------------//
835 
836 static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
837  AnalysisDeclContext &ac, CFGBlockValues &vals,
838  const ClassifyRefs &classification,
839  llvm::BitVector &wasAnalyzed,
840  UninitVariablesHandler &handler) {
841  wasAnalyzed[block->getBlockID()] = true;
842  vals.resetScratch();
843  // Merge in values of predecessor blocks.
844  bool isFirst = true;
845  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
846  E = block->pred_end(); I != E; ++I) {
847  const CFGBlock *pred = *I;
848  if (!pred)
849  continue;
850  if (wasAnalyzed[pred->getBlockID()]) {
851  vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
852  isFirst = false;
853  }
854  }
855  // Apply the transfer function.
856  TransferFunctions tf(vals, cfg, block, ac, classification, handler);
857  for (const auto &I : *block) {
858  if (Optional<CFGStmt> cs = I.getAs<CFGStmt>())
859  tf.Visit(const_cast<Stmt *>(cs->getStmt()));
860  }
861  return vals.updateValueVectorWithScratch(block);
862 }
863 
864 namespace {
865 
866 /// PruneBlocksHandler is a special UninitVariablesHandler that is used
867 /// to detect when a CFGBlock has any *potential* use of an uninitialized
868 /// variable. It is mainly used to prune out work during the final
869 /// reporting pass.
870 struct PruneBlocksHandler : public UninitVariablesHandler {
871  /// Records if a CFGBlock had a potential use of an uninitialized variable.
872  llvm::BitVector hadUse;
873 
874  /// Records if any CFGBlock had a potential use of an uninitialized variable.
875  bool hadAnyUse = false;
876 
877  /// The current block to scribble use information.
878  unsigned currentBlock = 0;
879 
880  PruneBlocksHandler(unsigned numBlocks) : hadUse(numBlocks, false) {}
881 
882  ~PruneBlocksHandler() override = default;
883 
884  void handleUseOfUninitVariable(const VarDecl *vd,
885  const UninitUse &use) override {
886  hadUse[currentBlock] = true;
887  hadAnyUse = true;
888  }
889 
890  /// Called when the uninitialized variable analysis detects the
891  /// idiom 'int x = x'. All other uses of 'x' within the initializer
892  /// are handled by handleUseOfUninitVariable.
893  void handleSelfInit(const VarDecl *vd) override {
894  hadUse[currentBlock] = true;
895  hadAnyUse = true;
896  }
897 };
898 
899 } // namespace
900 
902  const DeclContext &dc,
903  const CFG &cfg,
905  UninitVariablesHandler &handler,
907  CFGBlockValues vals(cfg);
908  vals.computeSetOfDeclarations(dc);
909  if (vals.hasNoDeclarations())
910  return;
911 
912  stats.NumVariablesAnalyzed = vals.getNumEntries();
913 
914  // Precompute which expressions are uses and which are initializations.
915  ClassifyRefs classification(ac);
916  cfg.VisitBlockStmts(classification);
917 
918  // Mark all variables uninitialized at the entry.
919  const CFGBlock &entry = cfg.getEntry();
920  ValueVector &vec = vals.getValueVector(&entry);
921  const unsigned n = vals.getNumEntries();
922  for (unsigned j = 0; j < n; ++j) {
923  vec[j] = Uninitialized;
924  }
925 
926  // Proceed with the workist.
927  DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>());
928  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
929  worklist.enqueueSuccessors(&cfg.getEntry());
930  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
931  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
932  PruneBlocksHandler PBH(cfg.getNumBlockIDs());
933 
934  while (const CFGBlock *block = worklist.dequeue()) {
935  PBH.currentBlock = block->getBlockID();
936 
937  // Did the block change?
938  bool changed = runOnBlock(block, cfg, ac, vals,
939  classification, wasAnalyzed, PBH);
940  ++stats.NumBlockVisits;
941  if (changed || !previouslyVisited[block->getBlockID()])
942  worklist.enqueueSuccessors(block);
943  previouslyVisited[block->getBlockID()] = true;
944  }
945 
946  if (!PBH.hadAnyUse)
947  return;
948 
949  // Run through the blocks one more time, and report uninitialized variables.
950  for (const auto *block : cfg)
951  if (PBH.hadUse[block->getBlockID()]) {
952  runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
953  ++stats.NumBlockVisits;
954  }
955 }
956 
const BlockDecl * getBlockDecl() const
Definition: Expr.h:5565
bool isCallToStdMove() const
Definition: Expr.h:2774
static llvm::iterator_range< used_clauses_child_iterator > used_clauses_children(ArrayRef< OMPClause *> Clauses)
Definition: StmtOpenMP.h:142
pred_iterator pred_end()
Definition: CFG.h:939
A (possibly-)qualified type.
Definition: Type.h:643
ArrayRef< OMPClause * > clauses()
Definition: StmtOpenMP.h:324
Expr * getArg(unsigned Arg)
getArg - Return the specified argument.
Definition: Expr.h:2677
AdjacentBlocks::const_iterator const_pred_iterator
Definition: CFG.h:925
succ_iterator succ_begin()
Definition: CFG.h:956
Stmt - This represents one statement.
Definition: Stmt.h:66
bool isStandaloneDirective() const
Returns whether or not this is a Standalone directive.
Definition: StmtOpenMP.cpp:25
CFGBlock & getEntry()
Definition: CFG.h:1316
QualType getPointeeType() const
If this is a pointer, ObjC object pointer, or block pointer, this returns the respective pointee...
Definition: Type.cpp:518
C Language Family Type Representation.
bool isRecordType() const
Definition: Type.h:6470
unsigned getBlockID() const
Definition: CFG.h:1075
static bool isPointerToConst(const QualType &QT)
Decl - This represents one declaration (or definition), e.g.
Definition: DeclBase.h:88
Opcode getOpcode() const
Definition: Expr.h:3444
static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc)
static const Expr * stripCasts(ASTContext &C, const Expr *Ex)
unsigned succ_size() const
Definition: CFG.h:974
Represents a variable declaration or definition.
Definition: Decl.h:812
ASTContext & getASTContext() const
Defines the Objective-C statement AST node classes.
Kind getKind() const
Get the kind of uninitialized use.
const Stmt * getStructuredBlock() const
Returns the AST node representing OpenMP structured-block of this OpenMP executable directive...
Definition: StmtOpenMP.cpp:36
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:160
AnalysisDeclContext contains the context data for the function or method under analysis.
static bool isIncrementDecrementOp(Opcode Op)
Definition: Expr.h:2094
__DEVICE__ int max(int __a, int __b)
Expr * getSubExpr()
Definition: Expr.h:3177
static bool isAlwaysUninit(const Value v)
AdjacentBlocks::const_iterator const_succ_iterator
Definition: CFG.h:932
static bool runOnBlock(const CFGBlock *block, const CFG &cfg, AnalysisDeclContext &ac, CFGBlockValues &vals, const ClassifyRefs &classification, llvm::BitVector &wasAnalyzed, UninitVariablesHandler &handler)
Forward-declares and imports various common LLVM datatypes that clang wants to use unqualified...
T * getAnalysis()
Return the specified analysis object, lazily running the analysis if necessary.
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:3409
CastExpr - Base class for type casts, including both implicit casts (ImplicitCastExpr) and explicit c...
Definition: Expr.h:3125
bool isScalarType() const
Definition: Type.h:6738
arg_iterator arg_end()
Definition: Expr.h:2722
Represents a single basic block in a source-level CFG.
Definition: CFG.h:576
Represents a block literal declaration, which is like an unnamed FunctionDecl.
Definition: Decl.h:3923
This represents one expression.
Definition: Expr.h:108
std::string Label
Represents a source-level, intra-procedural CFG that represents the control-flow of a Stmt...
Definition: CFG.h:1225
#define V(N, I)
Definition: ASTContext.h:2915
BlockExpr - Adaptor class for mixing a BlockDecl with expressions.
Definition: Expr.h:5551
bool isImplicit() const
isImplicit - Indicates whether the declaration was implicitly generated by the implementation.
Definition: DeclBase.h:558
bool isExceptionVariable() const
Determine whether this variable is the exception variable in a C++ catch statememt or an Objective-C ...
Definition: Decl.h:1319
DeclContext * getDeclContext()
Definition: DeclBase.h:438
static FindVarResult findVar(const Expr *E, const DeclContext *DC)
If E is an expression comprising a reference to a single variable, find that variable.
static SVal getValue(SVal val, SValBuilder &svalBuilder)
void runUninitializedVariablesAnalysis(const DeclContext &dc, const CFG &cfg, AnalysisDeclContext &ac, UninitVariablesHandler &handler, UninitVariablesAnalysisStats &stats)
QualType getType() const
Definition: Expr.h:137
An expression that sends a message to the given Objective-C object or class.
Definition: ExprObjC.h:950
UnaryOperator - This represents the unary-expression&#39;s (except sizeof and alignof), the postinc/postdec operators from postfix-expression, and various extensions.
Definition: Expr.h:2021
ValueDecl * getDecl()
Definition: Expr.h:1222
A use of a variable, which might be uninitialized.
do v
Definition: arm_acle.h:64
bool isConstQualified() const
Determine whether this type is const-qualified.
Definition: Type.h:6207
Stmt * getLabel()
Definition: CFG.h:1070
decl_iterator decls_begin() const
Definition: DeclBase.cpp:1385
Expr * getSubExpr() const
Definition: Expr.h:2051
This is a basic class for representing single OpenMP executable directive.
Definition: StmtOpenMP.h:32
CastKind getCastKind() const
Definition: Expr.h:3171
ASTContext & getASTContext() const LLVM_READONLY
Definition: DeclBase.cpp:377
DeclStmt - Adaptor class for mixing declarations with statements and expressions. ...
Definition: Stmt.h:1203
StmtVisitor - This class implements a simple visitor for Stmt subclasses.
Definition: StmtVisitor.h:182
bool hasGlobalStorage() const
Returns true for all variables that do not have local storage.
Definition: Decl.h:1077
const Decl * getDecl() const
bool isAnyPointerType() const
Definition: Type.h:6394
std::vector< const CFGBlock * >::reverse_iterator iterator
unsigned getNumBlockIDs() const
Returns the total number of BlockIDs allocated (which start at 0).
Definition: CFG.h:1392
bool isVectorType() const
Definition: Type.h:6482
succ_iterator succ_end()
Definition: CFG.h:957
Expr * getLHS() const
Definition: Expr.h:3449
static const DeclRefExpr * getSelfInitExpr(VarDecl *VD)
pred_iterator pred_begin()
Definition: CFG.h:938
Dataflow Directional Tag Classes.
void VisitBlockStmts(CALLBACK &O) const
Definition: CFG.h:1378
DeclContext - This is used only as base class of specific decl types that can act as declaration cont...
Definition: DeclBase.h:1271
ArrayRef< Capture > captures() const
Definition: Decl.h:4050
const Expr * getInit() const
Definition: Decl.h:1219
const Decl * getSingleDecl() const
Definition: Stmt.h:1218
bool isInitCapture() const
Whether this variable is the implicit variable for a lambda init-capture.
Definition: Decl.h:1403
specific_decl_iterator - Iterates over a subrange of declarations stored in a DeclContext, providing only those that are of type SpecificDecl (or a class derived from it).
Definition: DeclBase.h:2048
Iterator for iterating over Stmt * arrays that contain only T *.
Definition: Stmt.h:1042
The use is always uninitialized.
Represents Objective-C&#39;s collection statement.
Definition: StmtObjC.h:23
arg_iterator arg_begin()
Definition: Expr.h:2719
decl_range decls()
Definition: Stmt.h:1251
static bool isCompoundAssignmentOp(Opcode Opc)
Definition: Expr.h:3540
CallExpr - Represents a function call (C99 6.5.2.2, C++ [expr.call]).
Definition: Expr.h:2521
ASTContext & getParentASTContext() const
Definition: DeclBase.h:1808
A reference to a declared variable, function, enum, etc.
Definition: Expr.h:1146
bool isLocalVarDecl() const
Returns true for local variable declarations other than parameters.
Definition: Decl.h:1104
QualType getType() const
Definition: Decl.h:647
void addUninitBranch(Branch B)
Expr * IgnoreParenNoopCasts(const ASTContext &Ctx) LLVM_READONLY
Skip past any parenthese and casts which do not change the value (including ptr->int casts of the sam...
Definition: Expr.cpp:2993
Decl * getCalleeDecl()
Definition: Expr.h:2650
Expr * IgnoreParens() LLVM_READONLY
Skip past any parentheses which might surround this expression until reaching a fixed point...
Definition: Expr.cpp:2962
decl_iterator decls_end() const
Definition: DeclBase.h:2030
static bool isUninitialized(const Value v)