UninitializedValues.cpp revision 344472ebeded2fca2ed5013b9e87f81d09bfa908 
1//==- UninitializedValues.cpp - Find Uninitialized Values -------*- C++ --*-==//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements uninitialized values analysis for source-level CFGs.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/AST/ASTContext.h"
15#include "clang/AST/Attr.h"
16#include "clang/AST/Decl.h"
17#include "clang/AST/StmtVisitor.h"
18#include "clang/Analysis/Analyses/PostOrderCFGView.h"
19#include "clang/Analysis/Analyses/UninitializedValues.h"
20#include "clang/Analysis/AnalysisContext.h"
21#include "clang/Analysis/CFG.h"
22#include "clang/Analysis/DomainSpecific/ObjCNoReturn.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  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
77Optional<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 None;
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 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 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.pop_back_val();
245
246  // Next dequeue from the initial reverse post order.  This is the
247  // theoretical ideal in the presence of no back edges.
248  else if (PO_I != PO_E) {
249    B = *PO_I;
250    ++PO_I;
251  }
252  else {
253    return 0;
254  }
255
256  assert(enqueuedBlocks[B->getBlockID()] == true);
257  enqueuedBlocks[B->getBlockID()] = false;
258  return B;
259}
260
261//------------------------------------------------------------------------====//
262// Classification of DeclRefExprs as use or initialization.
263//====------------------------------------------------------------------------//
264
265namespace {
266class FindVarResult {
267  const VarDecl *vd;
268  const DeclRefExpr *dr;
269public:
270  FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {}
271
272  const DeclRefExpr *getDeclRefExpr() const { return dr; }
273  const VarDecl *getDecl() const { return vd; }
274};
275
276static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
277  while (Ex) {
278    Ex = Ex->IgnoreParenNoopCasts(C);
279    if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) {
280      if (CE->getCastKind() == CK_LValueBitCast) {
281        Ex = CE->getSubExpr();
282        continue;
283      }
284    }
285    break;
286  }
287  return Ex;
288}
289
290/// If E is an expression comprising a reference to a single variable, find that
291/// variable.
292static FindVarResult findVar(const Expr *E, const DeclContext *DC) {
293  if (const DeclRefExpr *DRE =
294        dyn_cast<DeclRefExpr>(stripCasts(DC->getParentASTContext(), E)))
295    if (const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl()))
296      if (isTrackedVar(VD, DC))
297        return FindVarResult(VD, DRE);
298  return FindVarResult(0, 0);
299}
300
301/// \brief Classify each DeclRefExpr as an initialization or a use. Any
302/// DeclRefExpr which isn't explicitly classified will be assumed to have
303/// escaped the analysis and will be treated as an initialization.
304class ClassifyRefs : public StmtVisitor<ClassifyRefs> {
305public:
306  enum Class {
307    Init,
308    Use,
309    SelfInit,
310    Ignore
311  };
312
313private:
314  const DeclContext *DC;
315  llvm::DenseMap<const DeclRefExpr*, Class> Classification;
316
317  bool isTrackedVar(const VarDecl *VD) const {
318    return ::isTrackedVar(VD, DC);
319  }
320
321  void classify(const Expr *E, Class C);
322
323public:
324  ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {}
325
326  void VisitDeclStmt(DeclStmt *DS);
327  void VisitUnaryOperator(UnaryOperator *UO);
328  void VisitBinaryOperator(BinaryOperator *BO);
329  void VisitCallExpr(CallExpr *CE);
330  void VisitCastExpr(CastExpr *CE);
331
332  void operator()(Stmt *S) { Visit(S); }
333
334  Class get(const DeclRefExpr *DRE) const {
335    llvm::DenseMap<const DeclRefExpr*, Class>::const_iterator I
336        = Classification.find(DRE);
337    if (I != Classification.end())
338      return I->second;
339
340    const VarDecl *VD = dyn_cast<VarDecl>(DRE->getDecl());
341    if (!VD || !isTrackedVar(VD))
342      return Ignore;
343
344    return Init;
345  }
346};
347}
348
349static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
350  if (Expr *Init = VD->getInit()) {
351    const DeclRefExpr *DRE
352      = dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
353    if (DRE && DRE->getDecl() == VD)
354      return DRE;
355  }
356  return 0;
357}
358
359void ClassifyRefs::classify(const Expr *E, Class C) {
360  // The result of a ?: could also be an lvalue.
361  E = E->IgnoreParens();
362  if (const ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E)) {
363    const Expr *TrueExpr = CO->getTrueExpr();
364    if (!isa<OpaqueValueExpr>(TrueExpr))
365      classify(TrueExpr, C);
366    classify(CO->getFalseExpr(), C);
367    return;
368  }
369
370  FindVarResult Var = findVar(E, DC);
371  if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
372    Classification[DRE] = std::max(Classification[DRE], C);
373}
374
375void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
376  for (DeclStmt::decl_iterator DI = DS->decl_begin(), DE = DS->decl_end();
377       DI != DE; ++DI) {
378    VarDecl *VD = dyn_cast<VarDecl>(*DI);
379    if (VD && isTrackedVar(VD))
380      if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
381        Classification[DRE] = SelfInit;
382  }
383}
384
385void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
386  // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
387  // is not a compound-assignment, we will treat it as initializing the variable
388  // when TransferFunctions visits it. A compound-assignment does not affect
389  // whether a variable is uninitialized, and there's no point counting it as a
390  // use.
391  if (BO->isCompoundAssignmentOp())
392    classify(BO->getLHS(), Use);
393  else if (BO->getOpcode() == BO_Assign)
394    classify(BO->getLHS(), Ignore);
395}
396
397void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
398  // Increment and decrement are uses despite there being no lvalue-to-rvalue
399  // conversion.
400  if (UO->isIncrementDecrementOp())
401    classify(UO->getSubExpr(), Use);
402}
403
404void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
405  // If a value is passed by const reference to a function, we should not assume
406  // that it is initialized by the call, and we conservatively do not assume
407  // that it is used.
408  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
409       I != E; ++I)
410    if ((*I)->getType().isConstQualified() && (*I)->isGLValue())
411      classify(*I, Ignore);
412}
413
414void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
415  if (CE->getCastKind() == CK_LValueToRValue)
416    classify(CE->getSubExpr(), Use);
417  else if (CStyleCastExpr *CSE = dyn_cast<CStyleCastExpr>(CE)) {
418    if (CSE->getType()->isVoidType()) {
419      // Squelch any detected load of an uninitialized value if
420      // we cast it to void.
421      // e.g. (void) x;
422      classify(CSE->getSubExpr(), Ignore);
423    }
424  }
425}
426
427//------------------------------------------------------------------------====//
428// Transfer function for uninitialized values analysis.
429//====------------------------------------------------------------------------//
430
431namespace {
432class TransferFunctions : public StmtVisitor<TransferFunctions> {
433  CFGBlockValues &vals;
434  const CFG &cfg;
435  const CFGBlock *block;
436  AnalysisDeclContext &ac;
437  const ClassifyRefs &classification;
438  ObjCNoReturn objCNoRet;
439  UninitVariablesHandler &handler;
440
441public:
442  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
443                    const CFGBlock *block, AnalysisDeclContext &ac,
444                    const ClassifyRefs &classification,
445                    UninitVariablesHandler &handler)
446    : vals(vals), cfg(cfg), block(block), ac(ac),
447      classification(classification), objCNoRet(ac.getASTContext()),
448      handler(handler) {}
449
450  void reportUse(const Expr *ex, const VarDecl *vd);
451
452  void VisitBinaryOperator(BinaryOperator *bo);
453  void VisitBlockExpr(BlockExpr *be);
454  void VisitCallExpr(CallExpr *ce);
455  void VisitDeclRefExpr(DeclRefExpr *dr);
456  void VisitDeclStmt(DeclStmt *ds);
457  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
458  void VisitObjCMessageExpr(ObjCMessageExpr *ME);
459
460  bool isTrackedVar(const VarDecl *vd) {
461    return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
462  }
463
464  FindVarResult findVar(const Expr *ex) {
465    return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
466  }
467
468  UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
469    UninitUse Use(ex, isAlwaysUninit(v));
470
471    assert(isUninitialized(v));
472    if (Use.getKind() == UninitUse::Always)
473      return Use;
474
475    // If an edge which leads unconditionally to this use did not initialize
476    // the variable, we can say something stronger than 'may be uninitialized':
477    // we can say 'either it's used uninitialized or you have dead code'.
478    //
479    // We track the number of successors of a node which have been visited, and
480    // visit a node once we have visited all of its successors. Only edges where
481    // the variable might still be uninitialized are followed. Since a variable
482    // can't transfer from being initialized to being uninitialized, this will
483    // trace out the subgraph which inevitably leads to the use and does not
484    // initialize the variable. We do not want to skip past loops, since their
485    // non-termination might be correlated with the initialization condition.
486    //
487    // For example:
488    //
489    //         void f(bool a, bool b) {
490    // block1:   int n;
491    //           if (a) {
492    // block2:     if (b)
493    // block3:       n = 1;
494    // block4:   } else if (b) {
495    // block5:     while (!a) {
496    // block6:       do_work(&a);
497    //               n = 2;
498    //             }
499    //           }
500    // block7:   if (a)
501    // block8:     g();
502    // block9:   return n;
503    //         }
504    //
505    // Starting from the maybe-uninitialized use in block 9:
506    //  * Block 7 is not visited because we have only visited one of its two
507    //    successors.
508    //  * Block 8 is visited because we've visited its only successor.
509    // From block 8:
510    //  * Block 7 is visited because we've now visited both of its successors.
511    // From block 7:
512    //  * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
513    //    of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
514    //  * Block 3 is not visited because it initializes 'n'.
515    // Now the algorithm terminates, having visited blocks 7 and 8, and having
516    // found the frontier is blocks 2, 4, and 5.
517    //
518    // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
519    // and 4), so we report that any time either of those edges is taken (in
520    // each case when 'b == false'), 'n' is used uninitialized.
521    SmallVector<const CFGBlock*, 32> Queue;
522    SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
523    Queue.push_back(block);
524    // Specify that we've already visited all successors of the starting block.
525    // This has the dual purpose of ensuring we never add it to the queue, and
526    // of marking it as not being a candidate element of the frontier.
527    SuccsVisited[block->getBlockID()] = block->succ_size();
528    while (!Queue.empty()) {
529      const CFGBlock *B = Queue.pop_back_val();
530      for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
531           I != E; ++I) {
532        const CFGBlock *Pred = *I;
533        if (vals.getValue(Pred, B, vd) == Initialized)
534          // This block initializes the variable.
535          continue;
536
537        unsigned &SV = SuccsVisited[Pred->getBlockID()];
538        if (!SV) {
539          // When visiting the first successor of a block, mark all NULL
540          // successors as having been visited.
541          for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
542                                             SE = Pred->succ_end();
543               SI != SE; ++SI)
544            if (!*SI)
545              ++SV;
546        }
547
548        if (++SV == Pred->succ_size())
549          // All paths from this block lead to the use and don't initialize the
550          // variable.
551          Queue.push_back(Pred);
552      }
553    }
554
555    // Scan the frontier, looking for blocks where the variable was
556    // uninitialized.
557    for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
558      const CFGBlock *Block = *BI;
559      unsigned BlockID = Block->getBlockID();
560      const Stmt *Term = Block->getTerminator();
561      if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
562          Term) {
563        // This block inevitably leads to the use. If we have an edge from here
564        // to a post-dominator block, and the variable is uninitialized on that
565        // edge, we have found a bug.
566        for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
567             E = Block->succ_end(); I != E; ++I) {
568          const CFGBlock *Succ = *I;
569          if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
570              vals.getValue(Block, Succ, vd) == Uninitialized) {
571            // Switch cases are a special case: report the label to the caller
572            // as the 'terminator', not the switch statement itself. Suppress
573            // situations where no label matched: we can't be sure that's
574            // possible.
575            if (isa<SwitchStmt>(Term)) {
576              const Stmt *Label = Succ->getLabel();
577              if (!Label || !isa<SwitchCase>(Label))
578                // Might not be possible.
579                continue;
580              UninitUse::Branch Branch;
581              Branch.Terminator = Label;
582              Branch.Output = 0; // Ignored.
583              Use.addUninitBranch(Branch);
584            } else {
585              UninitUse::Branch Branch;
586              Branch.Terminator = Term;
587              Branch.Output = I - Block->succ_begin();
588              Use.addUninitBranch(Branch);
589            }
590          }
591        }
592      }
593    }
594
595    return Use;
596  }
597};
598}
599
600void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
601  Value v = vals[vd];
602  if (isUninitialized(v))
603    handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
604}
605
606void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
607  // This represents an initialization of the 'element' value.
608  if (DeclStmt *DS = dyn_cast<DeclStmt>(FS->getElement())) {
609    const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
610    if (isTrackedVar(VD))
611      vals[VD] = Initialized;
612  }
613}
614
615void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
616  const BlockDecl *bd = be->getBlockDecl();
617  for (BlockDecl::capture_const_iterator i = bd->capture_begin(),
618        e = bd->capture_end() ; i != e; ++i) {
619    const VarDecl *vd = i->getVariable();
620    if (!isTrackedVar(vd))
621      continue;
622    if (i->isByRef()) {
623      vals[vd] = Initialized;
624      continue;
625    }
626    reportUse(be, vd);
627  }
628}
629
630void TransferFunctions::VisitCallExpr(CallExpr *ce) {
631  if (Decl *Callee = ce->getCalleeDecl()) {
632    if (Callee->hasAttr<ReturnsTwiceAttr>()) {
633      // After a call to a function like setjmp or vfork, any variable which is
634      // initialized anywhere within this function may now be initialized. For
635      // now, just assume such a call initializes all variables.  FIXME: Only
636      // mark variables as initialized if they have an initializer which is
637      // reachable from here.
638      vals.setAllScratchValues(Initialized);
639    }
640    else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
641      // Functions labeled like "analyzer_noreturn" are often used to denote
642      // "panic" functions that in special debug situations can still return,
643      // but for the most part should not be treated as returning.  This is a
644      // useful annotation borrowed from the static analyzer that is useful for
645      // suppressing branch-specific false positives when we call one of these
646      // functions but keep pretending the path continues (when in reality the
647      // user doesn't care).
648      vals.setAllScratchValues(Unknown);
649    }
650  }
651}
652
653void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
654  switch (classification.get(dr)) {
655  case ClassifyRefs::Ignore:
656    break;
657  case ClassifyRefs::Use:
658    reportUse(dr, cast<VarDecl>(dr->getDecl()));
659    break;
660  case ClassifyRefs::Init:
661    vals[cast<VarDecl>(dr->getDecl())] = Initialized;
662    break;
663  case ClassifyRefs::SelfInit:
664      handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
665    break;
666  }
667}
668
669void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
670  if (BO->getOpcode() == BO_Assign) {
671    FindVarResult Var = findVar(BO->getLHS());
672    if (const VarDecl *VD = Var.getDecl())
673      vals[VD] = Initialized;
674  }
675}
676
677void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
678  for (DeclStmt::decl_iterator DI = DS->decl_begin(), DE = DS->decl_end();
679       DI != DE; ++DI) {
680    VarDecl *VD = dyn_cast<VarDecl>(*DI);
681    if (VD && isTrackedVar(VD)) {
682      if (getSelfInitExpr(VD)) {
683        // If the initializer consists solely of a reference to itself, we
684        // explicitly mark the variable as uninitialized. This allows code
685        // like the following:
686        //
687        //   int x = x;
688        //
689        // to deliberately leave a variable uninitialized. Different analysis
690        // clients can detect this pattern and adjust their reporting
691        // appropriately, but we need to continue to analyze subsequent uses
692        // of the variable.
693        vals[VD] = Uninitialized;
694      } else if (VD->getInit()) {
695        // Treat the new variable as initialized.
696        vals[VD] = Initialized;
697      } else {
698        // No initializer: the variable is now uninitialized. This matters
699        // for cases like:
700        //   while (...) {
701        //     int n;
702        //     use(n);
703        //     n = 0;
704        //   }
705        // FIXME: Mark the variable as uninitialized whenever its scope is
706        // left, since its scope could be re-entered by a jump over the
707        // declaration.
708        vals[VD] = Uninitialized;
709      }
710    }
711  }
712}
713
714void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
715  // If the Objective-C message expression is an implicit no-return that
716  // is not modeled in the CFG, set the tracked dataflow values to Unknown.
717  if (objCNoRet.isImplicitNoReturn(ME)) {
718    vals.setAllScratchValues(Unknown);
719  }
720}
721
722//------------------------------------------------------------------------====//
723// High-level "driver" logic for uninitialized values analysis.
724//====------------------------------------------------------------------------//
725
726static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
727                       AnalysisDeclContext &ac, CFGBlockValues &vals,
728                       const ClassifyRefs &classification,
729                       llvm::BitVector &wasAnalyzed,
730                       UninitVariablesHandler &handler) {
731  wasAnalyzed[block->getBlockID()] = true;
732  vals.resetScratch();
733  // Merge in values of predecessor blocks.
734  bool isFirst = true;
735  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
736       E = block->pred_end(); I != E; ++I) {
737    const CFGBlock *pred = *I;
738    if (wasAnalyzed[pred->getBlockID()]) {
739      vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
740      isFirst = false;
741    }
742  }
743  // Apply the transfer function.
744  TransferFunctions tf(vals, cfg, block, ac, classification, handler);
745  for (CFGBlock::const_iterator I = block->begin(), E = block->end();
746       I != E; ++I) {
747    if (Optional<CFGStmt> cs = I->getAs<CFGStmt>())
748      tf.Visit(const_cast<Stmt*>(cs->getStmt()));
749  }
750  return vals.updateValueVectorWithScratch(block);
751}
752
753/// PruneBlocksHandler is a special UninitVariablesHandler that is used
754/// to detect when a CFGBlock has any *potential* use of an uninitialized
755/// variable.  It is mainly used to prune out work during the final
756/// reporting pass.
757namespace {
758struct PruneBlocksHandler : public UninitVariablesHandler {
759  PruneBlocksHandler(unsigned numBlocks)
760    : hadUse(numBlocks, false), hadAnyUse(false),
761      currentBlock(0) {}
762
763  virtual ~PruneBlocksHandler() {}
764
765  /// Records if a CFGBlock had a potential use of an uninitialized variable.
766  llvm::BitVector hadUse;
767
768  /// Records if any CFGBlock had a potential use of an uninitialized variable.
769  bool hadAnyUse;
770
771  /// The current block to scribble use information.
772  unsigned currentBlock;
773
774  virtual void handleUseOfUninitVariable(const VarDecl *vd,
775                                         const UninitUse &use) {
776    hadUse[currentBlock] = true;
777    hadAnyUse = true;
778  }
779
780  /// Called when the uninitialized variable analysis detects the
781  /// idiom 'int x = x'.  All other uses of 'x' within the initializer
782  /// are handled by handleUseOfUninitVariable.
783  virtual void handleSelfInit(const VarDecl *vd) {
784    hadUse[currentBlock] = true;
785    hadAnyUse = true;
786  }
787};
788}
789
790void clang::runUninitializedVariablesAnalysis(
791    const DeclContext &dc,
792    const CFG &cfg,
793    AnalysisDeclContext &ac,
794    UninitVariablesHandler &handler,
795    UninitVariablesAnalysisStats &stats) {
796  CFGBlockValues vals(cfg);
797  vals.computeSetOfDeclarations(dc);
798  if (vals.hasNoDeclarations())
799    return;
800
801  stats.NumVariablesAnalyzed = vals.getNumEntries();
802
803  // Precompute which expressions are uses and which are initializations.
804  ClassifyRefs classification(ac);
805  cfg.VisitBlockStmts(classification);
806
807  // Mark all variables uninitialized at the entry.
808  const CFGBlock &entry = cfg.getEntry();
809  ValueVector &vec = vals.getValueVector(&entry);
810  const unsigned n = vals.getNumEntries();
811  for (unsigned j = 0; j < n ; ++j) {
812    vec[j] = Uninitialized;
813  }
814
815  // Proceed with the workist.
816  DataflowWorklist worklist(cfg, *ac.getAnalysis<PostOrderCFGView>());
817  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
818  worklist.enqueueSuccessors(&cfg.getEntry());
819  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
820  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
821  PruneBlocksHandler PBH(cfg.getNumBlockIDs());
822
823  while (const CFGBlock *block = worklist.dequeue()) {
824    PBH.currentBlock = block->getBlockID();
825
826    // Did the block change?
827    bool changed = runOnBlock(block, cfg, ac, vals,
828                              classification, wasAnalyzed, PBH);
829    ++stats.NumBlockVisits;
830    if (changed || !previouslyVisited[block->getBlockID()])
831      worklist.enqueueSuccessors(block);
832    previouslyVisited[block->getBlockID()] = true;
833  }
834
835  if (!PBH.hadAnyUse)
836    return;
837
838  // Run through the blocks one more time, and report uninitialized variables.
839  for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
840    const CFGBlock *block = *BI;
841    if (PBH.hadUse[block->getBlockID()]) {
842      runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
843      ++stats.NumBlockVisits;
844    }
845  }
846}
847
848UninitVariablesHandler::~UninitVariablesHandler() {}
849