UninitializedValues.cpp revision dd4286b5b7b02b8bb962e4b996b8f36cb7935d4f 
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 "clang/Analysis/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  bool hasEntry(const VarDecl *vd) const {
128    return declToIndex.getValueIndex(vd).hasValue();
129  }
130
131  bool hasValues(const CFGBlock *block);
132
133  void resetScratch();
134  ValueVector &getScratch() { return scratch; }
135
136  ValueVector::reference operator[](const VarDecl *vd);
137};
138} // end anonymous namespace
139
140CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {
141  unsigned n = cfg.getNumBlockIDs();
142  if (!n)
143    return;
144  vals = new std::pair<ValueVector*, ValueVector*>[n];
145  memset((void*)vals, 0, sizeof(*vals) * n);
146}
147
148CFGBlockValues::~CFGBlockValues() {
149  unsigned n = cfg.getNumBlockIDs();
150  if (n == 0)
151    return;
152  for (unsigned i = 0; i < n; ++i) {
153    delete vals[i].first;
154    delete vals[i].second;
155  }
156  delete [] vals;
157}
158
159void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
160  declToIndex.computeMap(dc);
161  scratch.resize(declToIndex.size());
162}
163
164ValueVector &CFGBlockValues::lazyCreate(ValueVector *&bv) {
165  if (!bv)
166    bv = new ValueVector(declToIndex.size());
167  return *bv;
168}
169
170/// This function pattern matches for a '&&' or '||' that appears at
171/// the beginning of a CFGBlock that also (1) has a terminator and
172/// (2) has no other elements.  If such an expression is found, it is returned.
173static BinaryOperator *getLogicalOperatorInChain(const CFGBlock *block) {
174  if (block->empty())
175    return 0;
176
177  const CFGStmt *cstmt = block->front().getAs<CFGStmt>();
178  if (!cstmt)
179    return 0;
180
181  BinaryOperator *b = llvm::dyn_cast_or_null<BinaryOperator>(cstmt->getStmt());
182
183  if (!b || !b->isLogicalOp())
184    return 0;
185
186  if (block->pred_size() == 2) {
187    if (block->getTerminatorCondition() == b) {
188      if (block->succ_size() == 2)
189      return b;
190    }
191    else if (block->size() == 1)
192      return b;
193  }
194
195  return 0;
196}
197
198ValueVector &CFGBlockValues::getValueVector(const CFGBlock *block,
199                                            const CFGBlock *dstBlock) {
200  unsigned idx = block->getBlockID();
201  if (dstBlock && getLogicalOperatorInChain(block)) {
202    if (*block->succ_begin() == dstBlock)
203      return lazyCreate(vals[idx].first);
204    assert(*(block->succ_begin()+1) == dstBlock);
205    return lazyCreate(vals[idx].second);
206  }
207
208  assert(vals[idx].second == 0);
209  return lazyCreate(vals[idx].first);
210}
211
212bool CFGBlockValues::hasValues(const CFGBlock *block) {
213  unsigned idx = block->getBlockID();
214  return vals[idx].second != 0;
215}
216
217BVPair &CFGBlockValues::getValueVectors(const clang::CFGBlock *block,
218                                        bool shouldLazyCreate) {
219  unsigned idx = block->getBlockID();
220  lazyCreate(vals[idx].first);
221  if (shouldLazyCreate)
222    lazyCreate(vals[idx].second);
223  return vals[idx];
224}
225
226void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
227                                      bool isFirst) {
228  if (isFirst)
229    scratch = source;
230  else
231    scratch |= source;
232}
233#if 0
234static void printVector(const CFGBlock *block, ValueVector &bv,
235                        unsigned num) {
236
237  llvm::errs() << block->getBlockID() << " :";
238  for (unsigned i = 0; i < bv.size(); ++i) {
239    llvm::errs() << ' ' << bv[i];
240  }
241  llvm::errs() << " : " << num << '\n';
242}
243#endif
244
245bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
246  ValueVector &dst = getValueVector(block, 0);
247  bool changed = (dst != scratch);
248  if (changed)
249    dst = scratch;
250#if 0
251  printVector(block, scratch, 0);
252#endif
253  return changed;
254}
255
256bool CFGBlockValues::updateValueVectors(const CFGBlock *block,
257                                      const BVPair &newVals) {
258  BVPair &vals = getValueVectors(block, true);
259  bool changed = *newVals.first != *vals.first ||
260                 *newVals.second != *vals.second;
261  *vals.first = *newVals.first;
262  *vals.second = *newVals.second;
263#if 0
264  printVector(block, *vals.first, 1);
265  printVector(block, *vals.second, 2);
266#endif
267  return changed;
268}
269
270void CFGBlockValues::resetScratch() {
271  scratch.reset();
272}
273
274ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
275  const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
276  assert(idx.hasValue());
277  return scratch[idx.getValue()];
278}
279
280//------------------------------------------------------------------------====//
281// Worklist: worklist for dataflow analysis.
282//====------------------------------------------------------------------------//
283
284namespace {
285class DataflowWorklist {
286  llvm::SmallVector<const CFGBlock *, 20> worklist;
287  llvm::BitVector enqueuedBlocks;
288public:
289  DataflowWorklist(const CFG &cfg) : enqueuedBlocks(cfg.getNumBlockIDs()) {}
290
291  void enqueueSuccessors(const CFGBlock *block);
292  const CFGBlock *dequeue();
293};
294}
295
296void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
297  unsigned OldWorklistSize = worklist.size();
298  for (CFGBlock::const_succ_iterator I = block->succ_begin(),
299       E = block->succ_end(); I != E; ++I) {
300    const CFGBlock *Successor = *I;
301    if (!Successor || enqueuedBlocks[Successor->getBlockID()])
302      continue;
303    worklist.push_back(Successor);
304    enqueuedBlocks[Successor->getBlockID()] = true;
305  }
306  if (OldWorklistSize == 0 || OldWorklistSize == worklist.size())
307    return;
308
309  // Rotate the newly added blocks to the start of the worklist so that it forms
310  // a proper queue when we pop off the end of the worklist.
311  std::rotate(worklist.begin(), worklist.begin() + OldWorklistSize,
312              worklist.end());
313}
314
315const CFGBlock *DataflowWorklist::dequeue() {
316  if (worklist.empty())
317    return 0;
318  const CFGBlock *b = worklist.back();
319  worklist.pop_back();
320  enqueuedBlocks[b->getBlockID()] = false;
321  return b;
322}
323
324//------------------------------------------------------------------------====//
325// Transfer function for uninitialized values analysis.
326//====------------------------------------------------------------------------//
327
328namespace {
329class FindVarResult {
330  const VarDecl *vd;
331  const DeclRefExpr *dr;
332public:
333  FindVarResult(VarDecl *vd, DeclRefExpr *dr) : vd(vd), dr(dr) {}
334
335  const DeclRefExpr *getDeclRefExpr() const { return dr; }
336  const VarDecl *getDecl() const { return vd; }
337};
338
339class TransferFunctions : public StmtVisitor<TransferFunctions> {
340  CFGBlockValues &vals;
341  const CFG &cfg;
342  AnalysisContext &ac;
343  UninitVariablesHandler *handler;
344  const bool flagBlockUses;
345
346  /// The last DeclRefExpr seen when analyzing a block.  Used to
347  /// cheat when detecting cases when the address of a variable is taken.
348  DeclRefExpr *lastDR;
349
350  /// The last lvalue-to-rvalue conversion of a variable whose value
351  /// was uninitialized.  Normally this results in a warning, but it is
352  /// possible to either silence the warning in some cases, or we
353  /// propagate the uninitialized value.
354  CastExpr *lastLoad;
355public:
356  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
357                    AnalysisContext &ac,
358                    UninitVariablesHandler *handler,
359                    bool flagBlockUses)
360    : vals(vals), cfg(cfg), ac(ac), handler(handler),
361      flagBlockUses(flagBlockUses), lastDR(0), lastLoad(0) {}
362
363  const CFG &getCFG() { return cfg; }
364  void reportUninit(const DeclRefExpr *ex, const VarDecl *vd,
365                    bool isAlwaysUninit);
366
367  void VisitBlockExpr(BlockExpr *be);
368  void VisitDeclStmt(DeclStmt *ds);
369  void VisitDeclRefExpr(DeclRefExpr *dr);
370  void VisitUnaryOperator(UnaryOperator *uo);
371  void VisitBinaryOperator(BinaryOperator *bo);
372  void VisitCastExpr(CastExpr *ce);
373  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs);
374  void Visit(Stmt *s);
375
376  bool isTrackedVar(const VarDecl *vd) {
377    return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
378  }
379
380  FindVarResult findBlockVarDecl(Expr *ex);
381
382  void ProcessUses(Stmt *s = 0);
383};
384}
385
386void TransferFunctions::reportUninit(const DeclRefExpr *ex,
387                                     const VarDecl *vd, bool isAlwaysUnit) {
388  if (handler) handler->handleUseOfUninitVariable(ex, vd, isAlwaysUnit);
389}
390
391FindVarResult TransferFunctions::findBlockVarDecl(Expr* ex) {
392  if (DeclRefExpr* dr = dyn_cast<DeclRefExpr>(ex->IgnoreParenCasts()))
393    if (VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
394      if (isTrackedVar(vd))
395        return FindVarResult(vd, dr);
396  return FindVarResult(0, 0);
397}
398
399void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs) {
400  // This represents an initialization of the 'element' value.
401  Stmt *element = fs->getElement();
402  const VarDecl* vd = 0;
403
404  if (DeclStmt* ds = dyn_cast<DeclStmt>(element)) {
405    vd = cast<VarDecl>(ds->getSingleDecl());
406    if (!isTrackedVar(vd))
407      vd = 0;
408  }
409  else {
410    // Initialize the value of the reference variable.
411    const FindVarResult &res = findBlockVarDecl(cast<Expr>(element));
412    vd = res.getDecl();
413  }
414
415  if (vd)
416    vals[vd] = Initialized;
417}
418
419void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
420  if (!flagBlockUses || !handler)
421    return;
422  const BlockDecl *bd = be->getBlockDecl();
423  for (BlockDecl::capture_const_iterator i = bd->capture_begin(),
424        e = bd->capture_end() ; i != e; ++i) {
425    const VarDecl *vd = i->getVariable();
426    if (!vd->hasLocalStorage())
427      continue;
428    if (!isTrackedVar(vd))
429      continue;
430    if (i->isByRef()) {
431      vals[vd] = Initialized;
432      continue;
433    }
434    Value v = vals[vd];
435    if (isUninitialized(v))
436      handler->handleUseOfUninitVariable(be, vd, isAlwaysUninit(v));
437  }
438}
439
440void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
441  // Record the last DeclRefExpr seen.  This is an lvalue computation.
442  // We use this value to later detect if a variable "escapes" the analysis.
443  if (const VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
444    if (isTrackedVar(vd)) {
445      ProcessUses();
446      lastDR = dr;
447    }
448}
449
450void TransferFunctions::VisitDeclStmt(DeclStmt *ds) {
451  for (DeclStmt::decl_iterator DI = ds->decl_begin(), DE = ds->decl_end();
452       DI != DE; ++DI) {
453    if (VarDecl *vd = dyn_cast<VarDecl>(*DI)) {
454      if (isTrackedVar(vd)) {
455        if (Expr *init = vd->getInit()) {
456          // If the initializer consists solely of a reference to itself, we
457          // explicitly mark the variable as uninitialized. This allows code
458          // like the following:
459          //
460          //   int x = x;
461          //
462          // to deliberately leave a variable uninitialized. Different analysis
463          // clients can detect this pattern and adjust their reporting
464          // appropriately, but we need to continue to analyze subsequent uses
465          // of the variable.
466          if (init == lastLoad) {
467            DeclRefExpr *DR =
468              cast<DeclRefExpr>(lastLoad->getSubExpr()->IgnoreParens());
469            if (DR->getDecl() == vd) {
470              // int x = x;
471              // Propagate uninitialized value, but don't immediately report
472              // a problem.
473              vals[vd] = Uninitialized;
474              lastLoad = 0;
475              lastDR = 0;
476              return;
477            }
478          }
479
480          // All other cases: treat the new variable as initialized.
481          vals[vd] = Initialized;
482        }
483      }
484    }
485  }
486}
487
488void TransferFunctions::VisitBinaryOperator(clang::BinaryOperator *bo) {
489  if (bo->isAssignmentOp()) {
490    const FindVarResult &res = findBlockVarDecl(bo->getLHS());
491    if (const VarDecl* vd = res.getDecl()) {
492      ValueVector::reference val = vals[vd];
493      if (isUninitialized(val)) {
494        if (bo->getOpcode() != BO_Assign)
495          reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
496        val = Initialized;
497      }
498    }
499  }
500}
501
502void TransferFunctions::VisitUnaryOperator(clang::UnaryOperator *uo) {
503  switch (uo->getOpcode()) {
504    case clang::UO_PostDec:
505    case clang::UO_PostInc:
506    case clang::UO_PreDec:
507    case clang::UO_PreInc: {
508      const FindVarResult &res = findBlockVarDecl(uo->getSubExpr());
509      if (const VarDecl *vd = res.getDecl()) {
510        assert(res.getDeclRefExpr() == lastDR);
511        // We null out lastDR to indicate we have fully processed it
512        // and we don't want the auto-value setting in Visit().
513        lastDR = 0;
514
515        ValueVector::reference val = vals[vd];
516        if (isUninitialized(val)) {
517          reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
518          // Don't cascade warnings.
519          val = Initialized;
520        }
521      }
522      break;
523    }
524    default:
525      break;
526  }
527}
528
529void TransferFunctions::VisitCastExpr(clang::CastExpr *ce) {
530  if (ce->getCastKind() == CK_LValueToRValue) {
531    const FindVarResult &res = findBlockVarDecl(ce->getSubExpr());
532    if (const VarDecl *vd = res.getDecl()) {
533      assert(res.getDeclRefExpr() == lastDR);
534      if (isUninitialized(vals[vd])) {
535        // Record this load of an uninitialized value.  Normally this
536        // results in a warning, but we delay reporting the issue
537        // in case it is wrapped in a void cast, etc.
538        lastLoad = ce;
539      }
540    }
541  }
542  else if (CStyleCastExpr *cse = dyn_cast<CStyleCastExpr>(ce)) {
543    if (cse->getType()->isVoidType()) {
544      // e.g. (void) x;
545      if (lastLoad == cse->getSubExpr()) {
546        // Squelch any detected load of an uninitialized value if
547        // we cast it to void.
548        lastLoad = 0;
549        lastDR = 0;
550      }
551    }
552  }
553}
554
555void TransferFunctions::Visit(clang::Stmt *s) {
556  StmtVisitor<TransferFunctions>::Visit(s);
557  ProcessUses(s);
558}
559
560void TransferFunctions::ProcessUses(Stmt *s) {
561  // This method is typically called after visiting a CFGElement statement
562  // in the CFG.  We delay processing of reporting many loads of uninitialized
563  // values until here.
564  if (lastLoad) {
565    // If we just visited the lvalue-to-rvalue cast, there is nothing
566    // left to do.
567    if (lastLoad == s)
568      return;
569
570    // If we reach here, we have seen a load of an uninitialized value
571    // and it hasn't been casted to void or otherwise handled.  In this
572    // situation, report the incident.
573    DeclRefExpr *DR = cast<DeclRefExpr>(lastLoad->getSubExpr()->IgnoreParens());
574    VarDecl *VD = cast<VarDecl>(DR->getDecl());
575    reportUninit(DR, VD, isAlwaysUninit(vals[VD]));
576    lastLoad = 0;
577
578    // Prevent cascade of warnings.
579    vals[VD] = Initialized;
580    if (DR == lastDR) {
581      lastDR = 0;
582      return;
583    }
584  }
585
586  // Any other uses of 'lastDR' involve taking an lvalue of variable.
587  // In this case, it "escapes" the analysis.
588  if (lastDR && lastDR != s) {
589    vals[cast<VarDecl>(lastDR->getDecl())] = Initialized;
590    lastDR = 0;
591  }
592}
593
594//------------------------------------------------------------------------====//
595// High-level "driver" logic for uninitialized values analysis.
596//====------------------------------------------------------------------------//
597
598static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
599                       AnalysisContext &ac, CFGBlockValues &vals,
600                       llvm::BitVector &wasAnalyzed,
601                       UninitVariablesHandler *handler = 0,
602                       bool flagBlockUses = false) {
603
604  wasAnalyzed[block->getBlockID()] = true;
605
606  if (const BinaryOperator *b = getLogicalOperatorInChain(block)) {
607    CFGBlock::const_pred_iterator itr = block->pred_begin();
608    BVPair vA = vals.getValueVectors(*itr, false);
609    ++itr;
610    BVPair vB = vals.getValueVectors(*itr, false);
611
612    BVPair valsAB;
613
614    if (b->getOpcode() == BO_LAnd) {
615      // Merge the 'F' bits from the first and second.
616      vals.mergeIntoScratch(*(vA.second ? vA.second : vA.first), true);
617      vals.mergeIntoScratch(*(vB.second ? vB.second : vB.first), false);
618      valsAB.first = vA.first;
619      valsAB.second = &vals.getScratch();
620    }
621    else {
622      // Merge the 'T' bits from the first and second.
623      assert(b->getOpcode() == BO_LOr);
624      vals.mergeIntoScratch(*vA.first, true);
625      vals.mergeIntoScratch(*vB.first, false);
626      valsAB.first = &vals.getScratch();
627      valsAB.second = vA.second ? vA.second : vA.first;
628    }
629    return vals.updateValueVectors(block, valsAB);
630  }
631
632  // Default behavior: merge in values of predecessor blocks.
633  vals.resetScratch();
634  bool isFirst = true;
635  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
636       E = block->pred_end(); I != E; ++I) {
637    vals.mergeIntoScratch(vals.getValueVector(*I, block), isFirst);
638    isFirst = false;
639  }
640  // Apply the transfer function.
641  TransferFunctions tf(vals, cfg, ac, handler, flagBlockUses);
642  for (CFGBlock::const_iterator I = block->begin(), E = block->end();
643       I != E; ++I) {
644    if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) {
645      tf.Visit(cs->getStmt());
646    }
647  }
648  tf.ProcessUses();
649  return vals.updateValueVectorWithScratch(block);
650}
651
652void clang::runUninitializedVariablesAnalysis(
653    const DeclContext &dc,
654    const CFG &cfg,
655    AnalysisContext &ac,
656    UninitVariablesHandler &handler,
657    UninitVariablesAnalysisStats &stats) {
658  CFGBlockValues vals(cfg);
659  vals.computeSetOfDeclarations(dc);
660  if (vals.hasNoDeclarations())
661    return;
662
663  stats.NumVariablesAnalyzed = vals.getNumEntries();
664
665  // Mark all variables uninitialized at the entry.
666  const CFGBlock &entry = cfg.getEntry();
667  for (CFGBlock::const_succ_iterator i = entry.succ_begin(),
668        e = entry.succ_end(); i != e; ++i) {
669    if (const CFGBlock *succ = *i) {
670      ValueVector &vec = vals.getValueVector(&entry, succ);
671      const unsigned n = vals.getNumEntries();
672      for (unsigned j = 0; j < n ; ++j) {
673        vec[j] = Uninitialized;
674      }
675    }
676  }
677
678  // Proceed with the workist.
679  DataflowWorklist worklist(cfg);
680  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
681  worklist.enqueueSuccessors(&cfg.getEntry());
682  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
683
684  while (const CFGBlock *block = worklist.dequeue()) {
685    // Did the block change?
686    bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed);
687    ++stats.NumBlockVisits;
688    if (changed || !previouslyVisited[block->getBlockID()])
689      worklist.enqueueSuccessors(block);
690    previouslyVisited[block->getBlockID()] = true;
691  }
692
693  // Run through the blocks one more time, and report uninitialized variabes.
694  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
695    if (wasAnalyzed[(*BI)->getBlockID()]) {
696      runOnBlock(*BI, cfg, ac, vals, wasAnalyzed, &handler,
697                 /* flagBlockUses */ true);
698      ++stats.NumBlockVisits;
699    }
700  }
701}
702
703UninitVariablesHandler::~UninitVariablesHandler() {}
704