UninitializedValues.cpp revision 235864 
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 <utility>
15#include "llvm/ADT/Optional.h"
16#include "llvm/ADT/SmallVector.h"
17#include "llvm/ADT/PackedVector.h"
18#include "llvm/ADT/DenseMap.h"
19#include "clang/AST/Decl.h"
20#include "clang/Analysis/CFG.h"
21#include "clang/Analysis/AnalysisContext.h"
22#include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h"
23#include "clang/Analysis/Analyses/UninitializedValues.h"
24#include "llvm/Support/SaveAndRestore.h"
25
26using namespace clang;
27
28static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
29  if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
30      !vd->isExceptionVariable() &&
31      vd->getDeclContext() == dc) {
32    QualType ty = vd->getType();
33    return ty->isScalarType() || ty->isVectorType();
34  }
35  return false;
36}
37
38//------------------------------------------------------------------------====//
39// DeclToIndex: a mapping from Decls we track to value indices.
40//====------------------------------------------------------------------------//
41
42namespace {
43class DeclToIndex {
44  llvm::DenseMap<const VarDecl *, unsigned> map;
45public:
46  DeclToIndex() {}
47
48  /// Compute the actual mapping from declarations to bits.
49  void computeMap(const DeclContext &dc);
50
51  /// Return the number of declarations in the map.
52  unsigned size() const { return map.size(); }
53
54  /// Returns the bit vector index for a given declaration.
55  llvm::Optional<unsigned> getValueIndex(const VarDecl *d) const;
56};
57}
58
59void DeclToIndex::computeMap(const DeclContext &dc) {
60  unsigned count = 0;
61  DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
62                                               E(dc.decls_end());
63  for ( ; I != E; ++I) {
64    const VarDecl *vd = *I;
65    if (isTrackedVar(vd, &dc))
66      map[vd] = count++;
67  }
68}
69
70llvm::Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
71  llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
72  if (I == map.end())
73    return llvm::Optional<unsigned>();
74  return I->second;
75}
76
77//------------------------------------------------------------------------====//
78// CFGBlockValues: dataflow values for CFG blocks.
79//====------------------------------------------------------------------------//
80
81// These values are defined in such a way that a merge can be done using
82// a bitwise OR.
83enum Value { Unknown = 0x0,         /* 00 */
84             Initialized = 0x1,     /* 01 */
85             Uninitialized = 0x2,   /* 10 */
86             MayUninitialized = 0x3 /* 11 */ };
87
88static bool isUninitialized(const Value v) {
89  return v >= Uninitialized;
90}
91static bool isAlwaysUninit(const Value v) {
92  return v == Uninitialized;
93}
94
95namespace {
96
97typedef llvm::PackedVector<Value, 2> ValueVector;
98typedef std::pair<ValueVector *, ValueVector *> BVPair;
99
100class CFGBlockValues {
101  const CFG &cfg;
102  BVPair *vals;
103  ValueVector scratch;
104  DeclToIndex declToIndex;
105
106  ValueVector &lazyCreate(ValueVector *&bv);
107public:
108  CFGBlockValues(const CFG &cfg);
109  ~CFGBlockValues();
110
111  unsigned getNumEntries() const { return declToIndex.size(); }
112
113  void computeSetOfDeclarations(const DeclContext &dc);
114  ValueVector &getValueVector(const CFGBlock *block,
115                                const CFGBlock *dstBlock);
116
117  BVPair &getValueVectors(const CFGBlock *block, bool shouldLazyCreate);
118
119  void mergeIntoScratch(ValueVector const &source, bool isFirst);
120  bool updateValueVectorWithScratch(const CFGBlock *block);
121  bool updateValueVectors(const CFGBlock *block, const BVPair &newVals);
122
123  bool hasNoDeclarations() const {
124    return declToIndex.size() == 0;
125  }
126
127  void resetScratch();
128  ValueVector &getScratch() { return scratch; }
129
130  ValueVector::reference operator[](const VarDecl *vd);
131};
132} // end anonymous namespace
133
134CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {
135  unsigned n = cfg.getNumBlockIDs();
136  if (!n)
137    return;
138  vals = new std::pair<ValueVector*, ValueVector*>[n];
139  memset((void*)vals, 0, sizeof(*vals) * n);
140}
141
142CFGBlockValues::~CFGBlockValues() {
143  unsigned n = cfg.getNumBlockIDs();
144  if (n == 0)
145    return;
146  for (unsigned i = 0; i < n; ++i) {
147    delete vals[i].first;
148    delete vals[i].second;
149  }
150  delete [] vals;
151}
152
153void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
154  declToIndex.computeMap(dc);
155  scratch.resize(declToIndex.size());
156}
157
158ValueVector &CFGBlockValues::lazyCreate(ValueVector *&bv) {
159  if (!bv)
160    bv = new ValueVector(declToIndex.size());
161  return *bv;
162}
163
164/// This function pattern matches for a '&&' or '||' that appears at
165/// the beginning of a CFGBlock that also (1) has a terminator and
166/// (2) has no other elements.  If such an expression is found, it is returned.
167static const BinaryOperator *getLogicalOperatorInChain(const CFGBlock *block) {
168  if (block->empty())
169    return 0;
170
171  CFGElement front = block->front();
172  const CFGStmt *cstmt = front.getAs<CFGStmt>();
173  if (!cstmt)
174    return 0;
175
176  const BinaryOperator *b = dyn_cast_or_null<BinaryOperator>(cstmt->getStmt());
177
178  if (!b || !b->isLogicalOp())
179    return 0;
180
181  if (block->pred_size() == 2) {
182    if (block->getTerminatorCondition() == b) {
183      if (block->succ_size() == 2)
184      return b;
185    }
186    else if (block->size() == 1)
187      return b;
188  }
189
190  return 0;
191}
192
193ValueVector &CFGBlockValues::getValueVector(const CFGBlock *block,
194                                            const CFGBlock *dstBlock) {
195  unsigned idx = block->getBlockID();
196  if (dstBlock && getLogicalOperatorInChain(block)) {
197    if (*block->succ_begin() == dstBlock)
198      return lazyCreate(vals[idx].first);
199    assert(*(block->succ_begin()+1) == dstBlock);
200    return lazyCreate(vals[idx].second);
201  }
202
203  assert(vals[idx].second == 0);
204  return lazyCreate(vals[idx].first);
205}
206
207BVPair &CFGBlockValues::getValueVectors(const clang::CFGBlock *block,
208                                        bool shouldLazyCreate) {
209  unsigned idx = block->getBlockID();
210  lazyCreate(vals[idx].first);
211  if (shouldLazyCreate)
212    lazyCreate(vals[idx].second);
213  return vals[idx];
214}
215
216#if 0
217static void printVector(const CFGBlock *block, ValueVector &bv,
218                        unsigned num) {
219
220  llvm::errs() << block->getBlockID() << " :";
221  for (unsigned i = 0; i < bv.size(); ++i) {
222    llvm::errs() << ' ' << bv[i];
223  }
224  llvm::errs() << " : " << num << '\n';
225}
226
227static void printVector(const char *name, ValueVector const &bv) {
228  llvm::errs() << name << " : ";
229  for (unsigned i = 0; i < bv.size(); ++i) {
230    llvm::errs() << ' ' << bv[i];
231  }
232  llvm::errs() << "\n";
233}
234#endif
235
236void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
237                                      bool isFirst) {
238  if (isFirst)
239    scratch = source;
240  else
241    scratch |= source;
242}
243
244bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
245  ValueVector &dst = getValueVector(block, 0);
246  bool changed = (dst != scratch);
247  if (changed)
248    dst = scratch;
249#if 0
250  printVector(block, scratch, 0);
251#endif
252  return changed;
253}
254
255bool CFGBlockValues::updateValueVectors(const CFGBlock *block,
256                                      const BVPair &newVals) {
257  BVPair &vals = getValueVectors(block, true);
258  bool changed = *newVals.first != *vals.first ||
259                 *newVals.second != *vals.second;
260  *vals.first = *newVals.first;
261  *vals.second = *newVals.second;
262#if 0
263  printVector(block, *vals.first, 1);
264  printVector(block, *vals.second, 2);
265#endif
266  return changed;
267}
268
269void CFGBlockValues::resetScratch() {
270  scratch.reset();
271}
272
273ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
274  const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
275  assert(idx.hasValue());
276  return scratch[idx.getValue()];
277}
278
279//------------------------------------------------------------------------====//
280// Worklist: worklist for dataflow analysis.
281//====------------------------------------------------------------------------//
282
283namespace {
284class DataflowWorklist {
285  SmallVector<const CFGBlock *, 20> worklist;
286  llvm::BitVector enqueuedBlocks;
287public:
288  DataflowWorklist(const CFG &cfg) : enqueuedBlocks(cfg.getNumBlockIDs()) {}
289
290  void enqueueSuccessors(const CFGBlock *block);
291  const CFGBlock *dequeue();
292};
293}
294
295void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
296  unsigned OldWorklistSize = worklist.size();
297  for (CFGBlock::const_succ_iterator I = block->succ_begin(),
298       E = block->succ_end(); I != E; ++I) {
299    const CFGBlock *Successor = *I;
300    if (!Successor || enqueuedBlocks[Successor->getBlockID()])
301      continue;
302    worklist.push_back(Successor);
303    enqueuedBlocks[Successor->getBlockID()] = true;
304  }
305  if (OldWorklistSize == 0 || OldWorklistSize == worklist.size())
306    return;
307
308  // Rotate the newly added blocks to the start of the worklist so that it forms
309  // a proper queue when we pop off the end of the worklist.
310  std::rotate(worklist.begin(), worklist.begin() + OldWorklistSize,
311              worklist.end());
312}
313
314const CFGBlock *DataflowWorklist::dequeue() {
315  if (worklist.empty())
316    return 0;
317  const CFGBlock *b = worklist.back();
318  worklist.pop_back();
319  enqueuedBlocks[b->getBlockID()] = false;
320  return b;
321}
322
323//------------------------------------------------------------------------====//
324// Transfer function for uninitialized values analysis.
325//====------------------------------------------------------------------------//
326
327namespace {
328class FindVarResult {
329  const VarDecl *vd;
330  const DeclRefExpr *dr;
331public:
332  FindVarResult(VarDecl *vd, DeclRefExpr *dr) : vd(vd), dr(dr) {}
333
334  const DeclRefExpr *getDeclRefExpr() const { return dr; }
335  const VarDecl *getDecl() const { return vd; }
336};
337
338class TransferFunctions : public StmtVisitor<TransferFunctions> {
339  CFGBlockValues &vals;
340  const CFG &cfg;
341  AnalysisDeclContext &ac;
342  UninitVariablesHandler *handler;
343
344  /// The last DeclRefExpr seen when analyzing a block.  Used to
345  /// cheat when detecting cases when the address of a variable is taken.
346  DeclRefExpr *lastDR;
347
348  /// The last lvalue-to-rvalue conversion of a variable whose value
349  /// was uninitialized.  Normally this results in a warning, but it is
350  /// possible to either silence the warning in some cases, or we
351  /// propagate the uninitialized value.
352  CastExpr *lastLoad;
353
354  /// For some expressions, we want to ignore any post-processing after
355  /// visitation.
356  bool skipProcessUses;
357
358public:
359  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
360                    AnalysisDeclContext &ac,
361                    UninitVariablesHandler *handler)
362    : vals(vals), cfg(cfg), ac(ac), handler(handler),
363      lastDR(0), lastLoad(0),
364      skipProcessUses(false) {}
365
366  void reportUninit(const DeclRefExpr *ex, const VarDecl *vd,
367                    bool isAlwaysUninit);
368
369  void VisitBlockExpr(BlockExpr *be);
370  void VisitDeclStmt(DeclStmt *ds);
371  void VisitDeclRefExpr(DeclRefExpr *dr);
372  void VisitUnaryOperator(UnaryOperator *uo);
373  void VisitBinaryOperator(BinaryOperator *bo);
374  void VisitCastExpr(CastExpr *ce);
375  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs);
376  void Visit(Stmt *s);
377
378  bool isTrackedVar(const VarDecl *vd) {
379    return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
380  }
381
382  FindVarResult findBlockVarDecl(Expr *ex);
383
384  void ProcessUses(Stmt *s = 0);
385};
386}
387
388static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
389  while (Ex) {
390    Ex = Ex->IgnoreParenNoopCasts(C);
391    if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) {
392      if (CE->getCastKind() == CK_LValueBitCast) {
393        Ex = CE->getSubExpr();
394        continue;
395      }
396    }
397    break;
398  }
399  return Ex;
400}
401
402void TransferFunctions::reportUninit(const DeclRefExpr *ex,
403                                     const VarDecl *vd, bool isAlwaysUnit) {
404  if (handler) handler->handleUseOfUninitVariable(ex, vd, isAlwaysUnit);
405}
406
407FindVarResult TransferFunctions::findBlockVarDecl(Expr *ex) {
408  if (DeclRefExpr *dr = dyn_cast<DeclRefExpr>(ex->IgnoreParenCasts()))
409    if (VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
410      if (isTrackedVar(vd))
411        return FindVarResult(vd, dr);
412  return FindVarResult(0, 0);
413}
414
415void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs) {
416  // This represents an initialization of the 'element' value.
417  Stmt *element = fs->getElement();
418  const VarDecl *vd = 0;
419
420  if (DeclStmt *ds = dyn_cast<DeclStmt>(element)) {
421    vd = cast<VarDecl>(ds->getSingleDecl());
422    if (!isTrackedVar(vd))
423      vd = 0;
424  } else {
425    // Initialize the value of the reference variable.
426    const FindVarResult &res = findBlockVarDecl(cast<Expr>(element));
427    vd = res.getDecl();
428  }
429
430  if (vd)
431    vals[vd] = Initialized;
432}
433
434void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
435  const BlockDecl *bd = be->getBlockDecl();
436  for (BlockDecl::capture_const_iterator i = bd->capture_begin(),
437        e = bd->capture_end() ; i != e; ++i) {
438    const VarDecl *vd = i->getVariable();
439    if (!isTrackedVar(vd))
440      continue;
441    if (i->isByRef()) {
442      vals[vd] = Initialized;
443      continue;
444    }
445    Value v = vals[vd];
446    if (handler && isUninitialized(v))
447      handler->handleUseOfUninitVariable(be, vd, isAlwaysUninit(v));
448  }
449}
450
451void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
452  // Record the last DeclRefExpr seen.  This is an lvalue computation.
453  // We use this value to later detect if a variable "escapes" the analysis.
454  if (const VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
455    if (isTrackedVar(vd)) {
456      ProcessUses();
457      lastDR = dr;
458    }
459}
460
461void TransferFunctions::VisitDeclStmt(DeclStmt *ds) {
462  for (DeclStmt::decl_iterator DI = ds->decl_begin(), DE = ds->decl_end();
463       DI != DE; ++DI) {
464    if (VarDecl *vd = dyn_cast<VarDecl>(*DI)) {
465      if (isTrackedVar(vd)) {
466        if (Expr *init = vd->getInit()) {
467          // If the initializer consists solely of a reference to itself, we
468          // explicitly mark the variable as uninitialized. This allows code
469          // like the following:
470          //
471          //   int x = x;
472          //
473          // to deliberately leave a variable uninitialized. Different analysis
474          // clients can detect this pattern and adjust their reporting
475          // appropriately, but we need to continue to analyze subsequent uses
476          // of the variable.
477          if (init == lastLoad) {
478            const DeclRefExpr *DR
479              = cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
480                                             lastLoad->getSubExpr()));
481            if (DR->getDecl() == vd) {
482              // int x = x;
483              // Propagate uninitialized value, but don't immediately report
484              // a problem.
485              vals[vd] = Uninitialized;
486              lastLoad = 0;
487              lastDR = 0;
488              if (handler)
489                handler->handleSelfInit(vd);
490              return;
491            }
492          }
493
494          // All other cases: treat the new variable as initialized.
495          // This is a minor optimization to reduce the propagation
496          // of the analysis, since we will have already reported
497          // the use of the uninitialized value (which visiting the
498          // initializer).
499          vals[vd] = Initialized;
500        }
501      }
502    }
503  }
504}
505
506void TransferFunctions::VisitBinaryOperator(clang::BinaryOperator *bo) {
507  if (bo->isAssignmentOp()) {
508    const FindVarResult &res = findBlockVarDecl(bo->getLHS());
509    if (const VarDecl *vd = res.getDecl()) {
510      ValueVector::reference val = vals[vd];
511      if (isUninitialized(val)) {
512        if (bo->getOpcode() != BO_Assign)
513          reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
514        else
515          val = Initialized;
516      }
517    }
518  }
519}
520
521void TransferFunctions::VisitUnaryOperator(clang::UnaryOperator *uo) {
522  switch (uo->getOpcode()) {
523    case clang::UO_PostDec:
524    case clang::UO_PostInc:
525    case clang::UO_PreDec:
526    case clang::UO_PreInc: {
527      const FindVarResult &res = findBlockVarDecl(uo->getSubExpr());
528      if (const VarDecl *vd = res.getDecl()) {
529        assert(res.getDeclRefExpr() == lastDR);
530        // We null out lastDR to indicate we have fully processed it
531        // and we don't want the auto-value setting in Visit().
532        lastDR = 0;
533
534        ValueVector::reference val = vals[vd];
535        if (isUninitialized(val))
536          reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
537      }
538      break;
539    }
540    default:
541      break;
542  }
543}
544
545void TransferFunctions::VisitCastExpr(clang::CastExpr *ce) {
546  if (ce->getCastKind() == CK_LValueToRValue) {
547    const FindVarResult &res = findBlockVarDecl(ce->getSubExpr());
548    if (res.getDecl()) {
549      assert(res.getDeclRefExpr() == lastDR);
550      lastLoad = ce;
551    }
552  }
553  else if (ce->getCastKind() == CK_NoOp ||
554           ce->getCastKind() == CK_LValueBitCast) {
555    skipProcessUses = true;
556  }
557  else if (CStyleCastExpr *cse = dyn_cast<CStyleCastExpr>(ce)) {
558    if (cse->getType()->isVoidType()) {
559      // e.g. (void) x;
560      if (lastLoad == cse->getSubExpr()) {
561        // Squelch any detected load of an uninitialized value if
562        // we cast it to void.
563        lastLoad = 0;
564        lastDR = 0;
565      }
566    }
567  }
568}
569
570void TransferFunctions::Visit(clang::Stmt *s) {
571  skipProcessUses = false;
572  StmtVisitor<TransferFunctions>::Visit(s);
573  if (!skipProcessUses)
574    ProcessUses(s);
575}
576
577void TransferFunctions::ProcessUses(Stmt *s) {
578  // This method is typically called after visiting a CFGElement statement
579  // in the CFG.  We delay processing of reporting many loads of uninitialized
580  // values until here.
581  if (lastLoad) {
582    // If we just visited the lvalue-to-rvalue cast, there is nothing
583    // left to do.
584    if (lastLoad == s)
585      return;
586
587    const DeclRefExpr *DR =
588      cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
589                                   lastLoad->getSubExpr()));
590    const VarDecl *VD = cast<VarDecl>(DR->getDecl());
591
592    // If we reach here, we may have seen a load of an uninitialized value
593    // and it hasn't been casted to void or otherwise handled.  In this
594    // situation, report the incident.
595    if (isUninitialized(vals[VD]))
596      reportUninit(DR, VD, isAlwaysUninit(vals[VD]));
597
598    lastLoad = 0;
599
600    if (DR == lastDR) {
601      lastDR = 0;
602      return;
603    }
604  }
605
606  // Any other uses of 'lastDR' involve taking an lvalue of variable.
607  // In this case, it "escapes" the analysis.
608  if (lastDR && lastDR != s) {
609    vals[cast<VarDecl>(lastDR->getDecl())] = Initialized;
610    lastDR = 0;
611  }
612}
613
614//------------------------------------------------------------------------====//
615// High-level "driver" logic for uninitialized values analysis.
616//====------------------------------------------------------------------------//
617
618static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
619                       AnalysisDeclContext &ac, CFGBlockValues &vals,
620                       llvm::BitVector &wasAnalyzed,
621                       UninitVariablesHandler *handler = 0) {
622
623  wasAnalyzed[block->getBlockID()] = true;
624
625  if (const BinaryOperator *b = getLogicalOperatorInChain(block)) {
626    CFGBlock::const_pred_iterator itr = block->pred_begin();
627    BVPair vA = vals.getValueVectors(*itr, false);
628    ++itr;
629    BVPair vB = vals.getValueVectors(*itr, false);
630
631    BVPair valsAB;
632
633    if (b->getOpcode() == BO_LAnd) {
634      // Merge the 'F' bits from the first and second.
635      vals.mergeIntoScratch(*(vA.second ? vA.second : vA.first), true);
636      vals.mergeIntoScratch(*(vB.second ? vB.second : vB.first), false);
637      valsAB.first = vA.first;
638      valsAB.second = &vals.getScratch();
639    } else {
640      // Merge the 'T' bits from the first and second.
641      assert(b->getOpcode() == BO_LOr);
642      vals.mergeIntoScratch(*vA.first, true);
643      vals.mergeIntoScratch(*vB.first, false);
644      valsAB.first = &vals.getScratch();
645      valsAB.second = vA.second ? vA.second : vA.first;
646    }
647    return vals.updateValueVectors(block, valsAB);
648  }
649
650  // Default behavior: merge in values of predecessor blocks.
651  vals.resetScratch();
652  bool isFirst = true;
653  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
654       E = block->pred_end(); I != E; ++I) {
655    const CFGBlock *pred = *I;
656    if (wasAnalyzed[pred->getBlockID()]) {
657      vals.mergeIntoScratch(vals.getValueVector(pred, block), isFirst);
658      isFirst = false;
659    }
660  }
661  // Apply the transfer function.
662  TransferFunctions tf(vals, cfg, ac, handler);
663  for (CFGBlock::const_iterator I = block->begin(), E = block->end();
664       I != E; ++I) {
665    if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) {
666      tf.Visit(const_cast<Stmt*>(cs->getStmt()));
667    }
668  }
669  tf.ProcessUses();
670  return vals.updateValueVectorWithScratch(block);
671}
672
673void clang::runUninitializedVariablesAnalysis(
674    const DeclContext &dc,
675    const CFG &cfg,
676    AnalysisDeclContext &ac,
677    UninitVariablesHandler &handler,
678    UninitVariablesAnalysisStats &stats) {
679  CFGBlockValues vals(cfg);
680  vals.computeSetOfDeclarations(dc);
681  if (vals.hasNoDeclarations())
682    return;
683
684  stats.NumVariablesAnalyzed = vals.getNumEntries();
685
686  // Mark all variables uninitialized at the entry.
687  const CFGBlock &entry = cfg.getEntry();
688  for (CFGBlock::const_succ_iterator i = entry.succ_begin(),
689        e = entry.succ_end(); i != e; ++i) {
690    if (const CFGBlock *succ = *i) {
691      ValueVector &vec = vals.getValueVector(&entry, succ);
692      const unsigned n = vals.getNumEntries();
693      for (unsigned j = 0; j < n ; ++j) {
694        vec[j] = Uninitialized;
695      }
696    }
697  }
698
699  // Proceed with the workist.
700  DataflowWorklist worklist(cfg);
701  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
702  worklist.enqueueSuccessors(&cfg.getEntry());
703  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
704  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
705
706  while (const CFGBlock *block = worklist.dequeue()) {
707    // Did the block change?
708    bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed);
709    ++stats.NumBlockVisits;
710    if (changed || !previouslyVisited[block->getBlockID()])
711      worklist.enqueueSuccessors(block);
712    previouslyVisited[block->getBlockID()] = true;
713  }
714
715  // Run through the blocks one more time, and report uninitialized variabes.
716  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
717    const CFGBlock *block = *BI;
718    if (wasAnalyzed[block->getBlockID()]) {
719      runOnBlock(block, cfg, ac, vals, wasAnalyzed, &handler);
720      ++stats.NumBlockVisits;
721    }
722  }
723}
724
725UninitVariablesHandler::~UninitVariablesHandler() {}
726