UninitializedValues.cpp revision cfa88f893915ceb8ae4ce2f17c46c24a4d67502f 
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/Analysis/Analyses/PostOrderCFGView.h"
18#include "clang/Analysis/Analyses/UninitializedValues.h"
19#include "clang/Analysis/AnalysisContext.h"
20#include "clang/Analysis/CFG.h"
21#include "clang/Analysis/DomainSpecific/ObjCNoReturn.h"
22#include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h"
23#include "llvm/ADT/DenseMap.h"
24#include "llvm/ADT/Optional.h"
25#include "llvm/ADT/PackedVector.h"
26#include "llvm/ADT/SmallBitVector.h"
27#include "llvm/ADT/SmallVector.h"
28#include "llvm/Support/SaveAndRestore.h"
29#include <utility>
30
31using namespace clang;
32
33#define DEBUG_LOGGING 0
34
35static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
36  if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
37      !vd->isExceptionVariable() &&
38      vd->getDeclContext() == dc) {
39    QualType ty = vd->getType();
40    return ty->isScalarType() || ty->isVectorType();
41  }
42  return false;
43}
44
45//------------------------------------------------------------------------====//
46// DeclToIndex: a mapping from Decls we track to value indices.
47//====------------------------------------------------------------------------//
48
49namespace {
50class DeclToIndex {
51  llvm::DenseMap<const VarDecl *, unsigned> map;
52public:
53  DeclToIndex() {}
54
55  /// Compute the actual mapping from declarations to bits.
56  void computeMap(const DeclContext &dc);
57
58  /// Return the number of declarations in the map.
59  unsigned size() const { return map.size(); }
60
61  /// Returns the bit vector index for a given declaration.
62  llvm::Optional<unsigned> getValueIndex(const VarDecl *d) const;
63};
64}
65
66void DeclToIndex::computeMap(const DeclContext &dc) {
67  unsigned count = 0;
68  DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
69                                               E(dc.decls_end());
70  for ( ; I != E; ++I) {
71    const VarDecl *vd = *I;
72    if (isTrackedVar(vd, &dc))
73      map[vd] = count++;
74  }
75}
76
77llvm::Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
78  llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
79  if (I == map.end())
80    return llvm::Optional<unsigned>();
81  return I->second;
82}
83
84//------------------------------------------------------------------------====//
85// CFGBlockValues: dataflow values for CFG blocks.
86//====------------------------------------------------------------------------//
87
88// These values are defined in such a way that a merge can be done using
89// a bitwise OR.
90enum Value { Unknown = 0x0,         /* 00 */
91             Initialized = 0x1,     /* 01 */
92             Uninitialized = 0x2,   /* 10 */
93             MayUninitialized = 0x3 /* 11 */ };
94
95static bool isUninitialized(const Value v) {
96  return v >= Uninitialized;
97}
98static bool isAlwaysUninit(const Value v) {
99  return v == Uninitialized;
100}
101
102namespace {
103
104typedef llvm::PackedVector<Value, 2, llvm::SmallBitVector> ValueVector;
105
106class CFGBlockValues {
107  const CFG &cfg;
108  SmallVector<ValueVector, 8> vals;
109  ValueVector scratch;
110  DeclToIndex declToIndex;
111public:
112  CFGBlockValues(const CFG &cfg);
113
114  unsigned getNumEntries() const { return declToIndex.size(); }
115
116  void computeSetOfDeclarations(const DeclContext &dc);
117  ValueVector &getValueVector(const CFGBlock *block) {
118    return vals[block->getBlockID()];
119  }
120
121  void setAllScratchValues(Value V);
122  void mergeIntoScratch(ValueVector const &source, bool isFirst);
123  bool updateValueVectorWithScratch(const CFGBlock *block);
124
125  bool hasNoDeclarations() const {
126    return declToIndex.size() == 0;
127  }
128
129  void resetScratch();
130
131  ValueVector::reference operator[](const VarDecl *vd);
132
133  Value getValue(const CFGBlock *block, const CFGBlock *dstBlock,
134                 const VarDecl *vd) {
135    const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
136    assert(idx.hasValue());
137    return getValueVector(block)[idx.getValue()];
138  }
139};
140} // end anonymous namespace
141
142CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {}
143
144void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
145  declToIndex.computeMap(dc);
146  unsigned decls = declToIndex.size();
147  scratch.resize(decls);
148  unsigned n = cfg.getNumBlockIDs();
149  if (!n)
150    return;
151  vals.resize(n);
152  for (unsigned i = 0; i < n; ++i)
153    vals[i].resize(decls);
154}
155
156#if DEBUG_LOGGING
157static void printVector(const CFGBlock *block, ValueVector &bv,
158                        unsigned num) {
159  llvm::errs() << block->getBlockID() << " :";
160  for (unsigned i = 0; i < bv.size(); ++i) {
161    llvm::errs() << ' ' << bv[i];
162  }
163  llvm::errs() << " : " << num << '\n';
164}
165#endif
166
167void CFGBlockValues::setAllScratchValues(Value V) {
168  for (unsigned I = 0, E = scratch.size(); I != E; ++I)
169    scratch[I] = V;
170}
171
172void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
173                                      bool isFirst) {
174  if (isFirst)
175    scratch = source;
176  else
177    scratch |= source;
178}
179
180bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
181  ValueVector &dst = getValueVector(block);
182  bool changed = (dst != scratch);
183  if (changed)
184    dst = scratch;
185#if DEBUG_LOGGING
186  printVector(block, scratch, 0);
187#endif
188  return changed;
189}
190
191void CFGBlockValues::resetScratch() {
192  scratch.reset();
193}
194
195ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
196  const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
197  assert(idx.hasValue());
198  return scratch[idx.getValue()];
199}
200
201//------------------------------------------------------------------------====//
202// Worklist: worklist for dataflow analysis.
203//====------------------------------------------------------------------------//
204
205namespace {
206class DataflowWorklist {
207  PostOrderCFGView::iterator PO_I, PO_E;
208  SmallVector<const CFGBlock *, 20> worklist;
209  llvm::BitVector enqueuedBlocks;
210public:
211  DataflowWorklist(const CFG &cfg, PostOrderCFGView &view)
212    : PO_I(view.begin()), PO_E(view.end()),
213      enqueuedBlocks(cfg.getNumBlockIDs(), true) {
214        // Treat the first block as already analyzed.
215        if (PO_I != PO_E) {
216          assert(*PO_I == &cfg.getEntry());
217          enqueuedBlocks[(*PO_I)->getBlockID()] = false;
218          ++PO_I;
219        }
220      }
221
222  void enqueueSuccessors(const CFGBlock *block);
223  const CFGBlock *dequeue();
224};
225}
226
227void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
228  for (CFGBlock::const_succ_iterator I = block->succ_begin(),
229       E = block->succ_end(); I != E; ++I) {
230    const CFGBlock *Successor = *I;
231    if (!Successor || enqueuedBlocks[Successor->getBlockID()])
232      continue;
233    worklist.push_back(Successor);
234    enqueuedBlocks[Successor->getBlockID()] = true;
235  }
236}
237
238const CFGBlock *DataflowWorklist::dequeue() {
239  const CFGBlock *B = 0;
240
241  // First dequeue from the worklist.  This can represent
242  // updates along backedges that we want propagated as quickly as possible.
243  if (!worklist.empty()) {
244    B = worklist.back();
245    worklist.pop_back();
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 0;
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
266namespace {
267class FindVarResult {
268  const VarDecl *vd;
269  const DeclRefExpr *dr;
270public:
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
277static 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.
293static 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(0, 0);
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.
305class ClassifyRefs : public StmtVisitor<ClassifyRefs> {
306public:
307  enum Class {
308    Init,
309    Use,
310    SelfInit,
311    Ignore
312  };
313
314private:
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
324public:
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
350static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
351  if (Expr *Init = VD->getInit()) {
352    const DeclRefExpr *DRE
353      = dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
354    if (DRE && DRE->getDecl() == VD)
355      return DRE;
356  }
357  return 0;
358}
359
360void ClassifyRefs::classify(const Expr *E, Class C) {
361  FindVarResult Var = findVar(E, DC);
362  if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
363    Classification[DRE] = std::max(Classification[DRE], C);
364}
365
366void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
367  for (DeclStmt::decl_iterator DI = DS->decl_begin(), DE = DS->decl_end();
368       DI != DE; ++DI) {
369    VarDecl *VD = dyn_cast<VarDecl>(*DI);
370    if (VD && isTrackedVar(VD))
371      if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
372        Classification[DRE] = SelfInit;
373  }
374}
375
376void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
377  // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
378  // is not a compound-assignment, we will treat it as initializing the variable
379  // when TransferFunctions visits it. A compound-assignment does not affect
380  // whether a variable is uninitialized, and there's no point counting it as a
381  // use.
382  if (BO->isCompoundAssignmentOp())
383    classify(BO->getLHS(), Use);
384  else if (BO->getOpcode() == BO_Assign)
385    classify(BO->getLHS(), Ignore);
386}
387
388void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
389  // Increment and decrement are uses despite there being no lvalue-to-rvalue
390  // conversion.
391  if (UO->isIncrementDecrementOp())
392    classify(UO->getSubExpr(), Use);
393}
394
395void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
396  // If a value is passed by const reference to a function, we should not assume
397  // that it is initialized by the call, and we conservatively do not assume
398  // that it is used.
399  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
400       I != E; ++I)
401    if ((*I)->getType().isConstQualified() && (*I)->isGLValue())
402      classify(*I, Ignore);
403}
404
405void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
406  if (CE->getCastKind() == CK_LValueToRValue)
407    classify(CE->getSubExpr(), Use);
408  else if (CStyleCastExpr *CSE = dyn_cast<CStyleCastExpr>(CE)) {
409    if (CSE->getType()->isVoidType()) {
410      // Squelch any detected load of an uninitialized value if
411      // we cast it to void.
412      // e.g. (void) x;
413      classify(CSE->getSubExpr(), Ignore);
414    }
415  }
416}
417
418//------------------------------------------------------------------------====//
419// Transfer function for uninitialized values analysis.
420//====------------------------------------------------------------------------//
421
422namespace {
423class TransferFunctions : public StmtVisitor<TransferFunctions> {
424  CFGBlockValues &vals;
425  const CFG &cfg;
426  const CFGBlock *block;
427  AnalysisDeclContext &ac;
428  const ClassifyRefs &classification;
429  ObjCNoReturn objCNoRet;
430  UninitVariablesHandler &handler;
431
432public:
433  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
434                    const CFGBlock *block, AnalysisDeclContext &ac,
435                    const ClassifyRefs &classification,
436                    UninitVariablesHandler &handler)
437    : vals(vals), cfg(cfg), block(block), ac(ac),
438      classification(classification), objCNoRet(ac.getASTContext()),
439      handler(handler) {}
440
441  void reportUse(const Expr *ex, const VarDecl *vd);
442
443  void VisitBinaryOperator(BinaryOperator *bo);
444  void VisitBlockExpr(BlockExpr *be);
445  void VisitCallExpr(CallExpr *ce);
446  void VisitDeclRefExpr(DeclRefExpr *dr);
447  void VisitDeclStmt(DeclStmt *ds);
448  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
449  void VisitObjCMessageExpr(ObjCMessageExpr *ME);
450
451  bool isTrackedVar(const VarDecl *vd) {
452    return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
453  }
454
455  FindVarResult findVar(const Expr *ex) {
456    return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
457  }
458
459  UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
460    UninitUse Use(ex, isAlwaysUninit(v));
461
462    assert(isUninitialized(v));
463    if (Use.getKind() == UninitUse::Always)
464      return Use;
465
466    // If an edge which leads unconditionally to this use did not initialize
467    // the variable, we can say something stronger than 'may be uninitialized':
468    // we can say 'either it's used uninitialized or you have dead code'.
469    //
470    // We track the number of successors of a node which have been visited, and
471    // visit a node once we have visited all of its successors. Only edges where
472    // the variable might still be uninitialized are followed. Since a variable
473    // can't transfer from being initialized to being uninitialized, this will
474    // trace out the subgraph which inevitably leads to the use and does not
475    // initialize the variable. We do not want to skip past loops, since their
476    // non-termination might be correlated with the initialization condition.
477    //
478    // For example:
479    //
480    //         void f(bool a, bool b) {
481    // block1:   int n;
482    //           if (a) {
483    // block2:     if (b)
484    // block3:       n = 1;
485    // block4:   } else if (b) {
486    // block5:     while (!a) {
487    // block6:       do_work(&a);
488    //               n = 2;
489    //             }
490    //           }
491    // block7:   if (a)
492    // block8:     g();
493    // block9:   return n;
494    //         }
495    //
496    // Starting from the maybe-uninitialized use in block 9:
497    //  * Block 7 is not visited because we have only visited one of its two
498    //    successors.
499    //  * Block 8 is visited because we've visited its only successor.
500    // From block 8:
501    //  * Block 7 is visited because we've now visited both of its successors.
502    // From block 7:
503    //  * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
504    //    of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
505    //  * Block 3 is not visited because it initializes 'n'.
506    // Now the algorithm terminates, having visited blocks 7 and 8, and having
507    // found the frontier is blocks 2, 4, and 5.
508    //
509    // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
510    // and 4), so we report that any time either of those edges is taken (in
511    // each case when 'b == false'), 'n' is used uninitialized.
512    SmallVector<const CFGBlock*, 32> Queue;
513    SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
514    Queue.push_back(block);
515    // Specify that we've already visited all successors of the starting block.
516    // This has the dual purpose of ensuring we never add it to the queue, and
517    // of marking it as not being a candidate element of the frontier.
518    SuccsVisited[block->getBlockID()] = block->succ_size();
519    while (!Queue.empty()) {
520      const CFGBlock *B = Queue.back();
521      Queue.pop_back();
522      for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
523           I != E; ++I) {
524        const CFGBlock *Pred = *I;
525        if (vals.getValue(Pred, B, vd) == Initialized)
526          // This block initializes the variable.
527          continue;
528
529        unsigned &SV = SuccsVisited[Pred->getBlockID()];
530        if (!SV) {
531          // When visiting the first successor of a block, mark all NULL
532          // successors as having been visited.
533          for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
534                                             SE = Pred->succ_end();
535               SI != SE; ++SI)
536            if (!*SI)
537              ++SV;
538        }
539
540        if (++SV == Pred->succ_size())
541          // All paths from this block lead to the use and don't initialize the
542          // variable.
543          Queue.push_back(Pred);
544      }
545    }
546
547    // Scan the frontier, looking for blocks where the variable was
548    // uninitialized.
549    for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
550      const CFGBlock *Block = *BI;
551      unsigned BlockID = Block->getBlockID();
552      const Stmt *Term = Block->getTerminator();
553      if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
554          Term) {
555        // This block inevitably leads to the use. If we have an edge from here
556        // to a post-dominator block, and the variable is uninitialized on that
557        // edge, we have found a bug.
558        for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
559             E = Block->succ_end(); I != E; ++I) {
560          const CFGBlock *Succ = *I;
561          if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
562              vals.getValue(Block, Succ, vd) == Uninitialized) {
563            // Switch cases are a special case: report the label to the caller
564            // as the 'terminator', not the switch statement itself. Suppress
565            // situations where no label matched: we can't be sure that's
566            // possible.
567            if (isa<SwitchStmt>(Term)) {
568              const Stmt *Label = Succ->getLabel();
569              if (!Label || !isa<SwitchCase>(Label))
570                // Might not be possible.
571                continue;
572              UninitUse::Branch Branch;
573              Branch.Terminator = Label;
574              Branch.Output = 0; // Ignored.
575              Use.addUninitBranch(Branch);
576            } else {
577              UninitUse::Branch Branch;
578              Branch.Terminator = Term;
579              Branch.Output = I - Block->succ_begin();
580              Use.addUninitBranch(Branch);
581            }
582          }
583        }
584      }
585    }
586
587    return Use;
588  }
589};
590}
591
592void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
593  Value v = vals[vd];
594  if (isUninitialized(v))
595    handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
596}
597
598void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
599  // This represents an initialization of the 'element' value.
600  if (DeclStmt *DS = dyn_cast<DeclStmt>(FS->getElement())) {
601    const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
602    if (isTrackedVar(VD))
603      vals[VD] = Initialized;
604  }
605}
606
607void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
608  const BlockDecl *bd = be->getBlockDecl();
609  for (BlockDecl::capture_const_iterator i = bd->capture_begin(),
610        e = bd->capture_end() ; i != e; ++i) {
611    const VarDecl *vd = i->getVariable();
612    if (!isTrackedVar(vd))
613      continue;
614    if (i->isByRef()) {
615      vals[vd] = Initialized;
616      continue;
617    }
618    reportUse(be, vd);
619  }
620}
621
622void TransferFunctions::VisitCallExpr(CallExpr *ce) {
623  if (Decl *Callee = ce->getCalleeDecl()) {
624    if (Callee->hasAttr<ReturnsTwiceAttr>()) {
625      // After a call to a function like setjmp or vfork, any variable which is
626      // initialized anywhere within this function may now be initialized. For
627      // now, just assume such a call initializes all variables.  FIXME: Only
628      // mark variables as initialized if they have an initializer which is
629      // reachable from here.
630      vals.setAllScratchValues(Initialized);
631    }
632    else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
633      // Functions labeled like "analyzer_noreturn" are often used to denote
634      // "panic" functions that in special debug situations can still return,
635      // but for the most part should not be treated as returning.  This is a
636      // useful annotation borrowed from the static analyzer that is useful for
637      // suppressing branch-specific false positives when we call one of these
638      // functions but keep pretending the path continues (when in reality the
639      // user doesn't care).
640      vals.setAllScratchValues(Unknown);
641    }
642  }
643}
644
645void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
646  switch (classification.get(dr)) {
647  case ClassifyRefs::Ignore:
648    break;
649  case ClassifyRefs::Use:
650    reportUse(dr, cast<VarDecl>(dr->getDecl()));
651    break;
652  case ClassifyRefs::Init:
653    vals[cast<VarDecl>(dr->getDecl())] = Initialized;
654    break;
655  case ClassifyRefs::SelfInit:
656      handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
657    break;
658  }
659}
660
661void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
662  if (BO->getOpcode() == BO_Assign) {
663    FindVarResult Var = findVar(BO->getLHS());
664    if (const VarDecl *VD = Var.getDecl())
665      vals[VD] = Initialized;
666  }
667}
668
669void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
670  for (DeclStmt::decl_iterator DI = DS->decl_begin(), DE = DS->decl_end();
671       DI != DE; ++DI) {
672    VarDecl *VD = dyn_cast<VarDecl>(*DI);
673    if (VD && isTrackedVar(VD)) {
674      if (getSelfInitExpr(VD)) {
675        // If the initializer consists solely of a reference to itself, we
676        // explicitly mark the variable as uninitialized. This allows code
677        // like the following:
678        //
679        //   int x = x;
680        //
681        // to deliberately leave a variable uninitialized. Different analysis
682        // clients can detect this pattern and adjust their reporting
683        // appropriately, but we need to continue to analyze subsequent uses
684        // of the variable.
685        vals[VD] = Uninitialized;
686      } else if (VD->getInit()) {
687        // Treat the new variable as initialized.
688        vals[VD] = Initialized;
689      } else {
690        // No initializer: the variable is now uninitialized. This matters
691        // for cases like:
692        //   while (...) {
693        //     int n;
694        //     use(n);
695        //     n = 0;
696        //   }
697        // FIXME: Mark the variable as uninitialized whenever its scope is
698        // left, since its scope could be re-entered by a jump over the
699        // declaration.
700        vals[VD] = Uninitialized;
701      }
702    }
703  }
704}
705
706void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
707  // If the Objective-C message expression is an implicit no-return that
708  // is not modeled in the CFG, set the tracked dataflow values to Unknown.
709  if (objCNoRet.isImplicitNoReturn(ME)) {
710    vals.setAllScratchValues(Unknown);
711  }
712}
713
714//------------------------------------------------------------------------====//
715// High-level "driver" logic for uninitialized values analysis.
716//====------------------------------------------------------------------------//
717
718static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
719                       AnalysisDeclContext &ac, CFGBlockValues &vals,
720                       const ClassifyRefs &classification,
721                       llvm::BitVector &wasAnalyzed,
722                       UninitVariablesHandler &handler) {
723  wasAnalyzed[block->getBlockID()] = true;
724  vals.resetScratch();
725  // Merge in values of predecessor blocks.
726  bool isFirst = true;
727  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
728       E = block->pred_end(); I != E; ++I) {
729    const CFGBlock *pred = *I;
730    if (wasAnalyzed[pred->getBlockID()]) {
731      vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
732      isFirst = false;
733    }
734  }
735  // Apply the transfer function.
736  TransferFunctions tf(vals, cfg, block, ac, classification, handler);
737  for (CFGBlock::const_iterator I = block->begin(), E = block->end();
738       I != E; ++I) {
739    if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) {
740      tf.Visit(const_cast<Stmt*>(cs->getStmt()));
741    }
742  }
743  return vals.updateValueVectorWithScratch(block);
744}
745
746/// PruneBlocksHandler is a special UninitVariablesHandler that is used
747/// to detect when a CFGBlock has any *potential* use of an uninitialized
748/// variable.  It is mainly used to prune out work during the final
749/// reporting pass.
750namespace {
751struct PruneBlocksHandler : public UninitVariablesHandler {
752  PruneBlocksHandler(unsigned numBlocks)
753    : hadUse(numBlocks, false), hadAnyUse(false),
754      currentBlock(0) {}
755
756  virtual ~PruneBlocksHandler() {}
757
758  /// Records if a CFGBlock had a potential use of an uninitialized variable.
759  llvm::BitVector hadUse;
760
761  /// Records if any CFGBlock had a potential use of an uninitialized variable.
762  bool hadAnyUse;
763
764  /// The current block to scribble use information.
765  unsigned currentBlock;
766
767  virtual void handleUseOfUninitVariable(const VarDecl *vd,
768                                         const UninitUse &use) {
769    hadUse[currentBlock] = true;
770    hadAnyUse = true;
771  }
772
773  /// Called when the uninitialized variable analysis detects the
774  /// idiom 'int x = x'.  All other uses of 'x' within the initializer
775  /// are handled by handleUseOfUninitVariable.
776  virtual void handleSelfInit(const VarDecl *vd) {
777    hadUse[currentBlock] = true;
778    hadAnyUse = true;
779  }
780};
781}
782
783void clang::runUninitializedVariablesAnalysis(
784    const DeclContext &dc,
785    const CFG &cfg,
786    AnalysisDeclContext &ac,
787    UninitVariablesHandler &handler,
788    UninitVariablesAnalysisStats &stats) {
789  CFGBlockValues vals(cfg);
790  vals.computeSetOfDeclarations(dc);
791  if (vals.hasNoDeclarations())
792    return;
793
794  stats.NumVariablesAnalyzed = vals.getNumEntries();
795
796  // Precompute which expressions are uses and which are initializations.
797  ClassifyRefs classification(ac);
798  cfg.VisitBlockStmts(classification);
799
800  // Mark all variables uninitialized at the entry.
801  const CFGBlock &entry = cfg.getEntry();
802  ValueVector &vec = vals.getValueVector(&entry);
803  const unsigned n = vals.getNumEntries();
804  for (unsigned j = 0; j < n ; ++j) {
805    vec[j] = Uninitialized;
806  }
807
808  // Proceed with the workist.
809  DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>());
810  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
811  worklist.enqueueSuccessors(&cfg.getEntry());
812  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
813  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
814  PruneBlocksHandler PBH(cfg.getNumBlockIDs());
815
816  while (const CFGBlock *block = worklist.dequeue()) {
817    PBH.currentBlock = block->getBlockID();
818
819    // Did the block change?
820    bool changed = runOnBlock(block, cfg, ac, vals,
821                              classification, wasAnalyzed, PBH);
822    ++stats.NumBlockVisits;
823    if (changed || !previouslyVisited[block->getBlockID()])
824      worklist.enqueueSuccessors(block);
825    previouslyVisited[block->getBlockID()] = true;
826  }
827
828  if (!PBH.hadAnyUse)
829    return;
830
831  // Run through the blocks one more time, and report uninitialized variables.
832  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
833    const CFGBlock *block = *BI;
834    if (PBH.hadUse[block->getBlockID()]) {
835      runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
836      ++stats.NumBlockVisits;
837    }
838  }
839}
840
841UninitVariablesHandler::~UninitVariablesHandler() {}
842