aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/libs/clang14/lib/Analysis/UninitializedValues.cpp
blob: 811146e50b45a13fc0392e935953bbfe93ae8f90 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
//===- UninitializedValues.cpp - Find Uninitialized Values ----------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements uninitialized values analysis for source-level CFGs.
//
//===----------------------------------------------------------------------===//

#include "clang/Analysis/Analyses/UninitializedValues.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/Expr.h"
#include "clang/AST/OperationKinds.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/Type.h"
#include "clang/Analysis/Analyses/PostOrderCFGView.h"
#include "clang/Analysis/AnalysisDeclContext.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/DomainSpecific/ObjCNoReturn.h"
#include "clang/Analysis/FlowSensitive/DataflowWorklist.h"
#include "clang/Basic/LLVM.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PackedVector.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Casting.h"
#include <algorithm>
#include <cassert>

using namespace clang;

#define DEBUG_LOGGING 0

static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
  if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
      !vd->isExceptionVariable() && !vd->isInitCapture() &&
      !vd->isImplicit() && vd->getDeclContext() == dc) {
    QualType ty = vd->getType();
    return ty->isScalarType() || ty->isVectorType() || ty->isRecordType();
  }
  return false;
}

//------------------------------------------------------------------------====//
// DeclToIndex: a mapping from Decls we track to value indices.
//====------------------------------------------------------------------------//

namespace {

class DeclToIndex {
  llvm::DenseMap<const VarDecl *, unsigned> map;

public:
  DeclToIndex() = default;

  /// Compute the actual mapping from declarations to bits.
  void computeMap(const DeclContext &dc);

  /// Return the number of declarations in the map.
  unsigned size() const { return map.size(); }

  /// Returns the bit vector index for a given declaration.
  Optional<unsigned> getValueIndex(const VarDecl *d) const;
};

} // namespace

void DeclToIndex::computeMap(const DeclContext &dc) {
  unsigned count = 0;
  DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
                                               E(dc.decls_end());
  for ( ; I != E; ++I) {
    const VarDecl *vd = *I;
    if (isTrackedVar(vd, &dc))
      map[vd] = count++;
  }
}

Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
  llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
  if (I == map.end())
    return None;
  return I->second;
}

//------------------------------------------------------------------------====//
// CFGBlockValues: dataflow values for CFG blocks.
//====------------------------------------------------------------------------//

// These values are defined in such a way that a merge can be done using
// a bitwise OR.
enum Value { Unknown = 0x0,         /* 00 */
             Initialized = 0x1,     /* 01 */
             Uninitialized = 0x2,   /* 10 */
             MayUninitialized = 0x3 /* 11 */ };

static bool isUninitialized(const Value v) {
  return v >= Uninitialized;
}

static bool isAlwaysUninit(const Value v) {
  return v == Uninitialized;
}

namespace {

using ValueVector = llvm::PackedVector<Value, 2, llvm::SmallBitVector>;

class CFGBlockValues {
  const CFG &cfg;
  SmallVector<ValueVector, 8> vals;
  ValueVector scratch;
  DeclToIndex declToIndex;

public:
  CFGBlockValues(const CFG &cfg);

  unsigned getNumEntries() const { return declToIndex.size(); }

  void computeSetOfDeclarations(const DeclContext &dc);

  ValueVector &getValueVector(const CFGBlock *block) {
    return vals[block->getBlockID()];
  }

  void setAllScratchValues(Value V);
  void mergeIntoScratch(ValueVector const &source, bool isFirst);
  bool updateValueVectorWithScratch(const CFGBlock *block);

  bool hasNoDeclarations() const {
    return declToIndex.size() == 0;
  }

  void resetScratch();

  ValueVector::reference operator[](const VarDecl *vd);

  Value getValue(const CFGBlock *block, const CFGBlock *dstBlock,
                 const VarDecl *vd) {
    const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
    assert(idx.hasValue());
    return getValueVector(block)[idx.getValue()];
  }
};

} // namespace

CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {}

void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
  declToIndex.computeMap(dc);
  unsigned decls = declToIndex.size();
  scratch.resize(decls);
  unsigned n = cfg.getNumBlockIDs();
  if (!n)
    return;
  vals.resize(n);
  for (auto &val : vals)
    val.resize(decls);
}

#if DEBUG_LOGGING
static void printVector(const CFGBlock *block, ValueVector &bv,
                        unsigned num) {
  llvm::errs() << block->getBlockID() << " :";
  for (const auto &i : bv)
    llvm::errs() << ' ' << i;
  llvm::errs() << " : " << num << '\n';
}
#endif

void CFGBlockValues::setAllScratchValues(Value V) {
  for (unsigned I = 0, E = scratch.size(); I != E; ++I)
    scratch[I] = V;
}

void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
                                      bool isFirst) {
  if (isFirst)
    scratch = source;
  else
    scratch |= source;
}

bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
  ValueVector &dst = getValueVector(block);
  bool changed = (dst != scratch);
  if (changed)
    dst = scratch;
#if DEBUG_LOGGING
  printVector(block, scratch, 0);
#endif
  return changed;
}

void CFGBlockValues::resetScratch() {
  scratch.reset();
}

ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
  const Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
  assert(idx.hasValue());
  return scratch[idx.getValue()];
}

//------------------------------------------------------------------------====//
// Classification of DeclRefExprs as use or initialization.
//====------------------------------------------------------------------------//

namespace {

class FindVarResult {
  const VarDecl *vd;
  const DeclRefExpr *dr;

public:
  FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {}

  const DeclRefExpr *getDeclRefExpr() const { return dr; }
  const VarDecl *getDecl() const { return vd; }
};

} // namespace

static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
  while (Ex) {
    Ex = Ex->IgnoreParenNoopCasts(C);
    if (const auto *CE = dyn_cast<CastExpr>(Ex)) {
      if (CE->getCastKind() == CK_LValueBitCast) {
        Ex = CE->getSubExpr();
        continue;
      }
    }
    break;
  }
  return Ex;
}

/// If E is an expression comprising a reference to a single variable, find that
/// variable.
static FindVarResult findVar(const Expr *E, const DeclContext *DC) {
  if (const auto *DRE =
          dyn_cast<DeclRefExpr>(stripCasts(DC->getParentASTContext(), E)))
    if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl()))
      if (isTrackedVar(VD, DC))
        return FindVarResult(VD, DRE);
  return FindVarResult(nullptr, nullptr);
}

namespace {

/// Classify each DeclRefExpr as an initialization or a use. Any
/// DeclRefExpr which isn't explicitly classified will be assumed to have
/// escaped the analysis and will be treated as an initialization.
class ClassifyRefs : public StmtVisitor<ClassifyRefs> {
public:
  enum Class {
    Init,
    Use,
    SelfInit,
    ConstRefUse,
    Ignore
  };

private:
  const DeclContext *DC;
  llvm::DenseMap<const DeclRefExpr *, Class> Classification;

  bool isTrackedVar(const VarDecl *VD) const {
    return ::isTrackedVar(VD, DC);
  }

  void classify(const Expr *E, Class C);

public:
  ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {}

  void VisitDeclStmt(DeclStmt *DS);
  void VisitUnaryOperator(UnaryOperator *UO);
  void VisitBinaryOperator(BinaryOperator *BO);
  void VisitCallExpr(CallExpr *CE);
  void VisitCastExpr(CastExpr *CE);
  void VisitOMPExecutableDirective(OMPExecutableDirective *ED);

  void operator()(Stmt *S) { Visit(S); }

  Class get(const DeclRefExpr *DRE) const {
    llvm::DenseMap<const DeclRefExpr*, Class>::const_iterator I
        = Classification.find(DRE);
    if (I != Classification.end())
      return I->second;

    const auto *VD = dyn_cast<VarDecl>(DRE->getDecl());
    if (!VD || !isTrackedVar(VD))
      return Ignore;

    return Init;
  }
};

} // namespace

static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
  if (VD->getType()->isRecordType())
    return nullptr;
  if (Expr *Init = VD->getInit()) {
    const auto *DRE =
        dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
    if (DRE && DRE->getDecl() == VD)
      return DRE;
  }
  return nullptr;
}

void ClassifyRefs::classify(const Expr *E, Class C) {
  // The result of a ?: could also be an lvalue.
  E = E->IgnoreParens();
  if (const auto *CO = dyn_cast<ConditionalOperator>(E)) {
    classify(CO->getTrueExpr(), C);
    classify(CO->getFalseExpr(), C);
    return;
  }

  if (const auto *BCO = dyn_cast<BinaryConditionalOperator>(E)) {
    classify(BCO->getFalseExpr(), C);
    return;
  }

  if (const auto *OVE = dyn_cast<OpaqueValueExpr>(E)) {
    classify(OVE->getSourceExpr(), C);
    return;
  }

  if (const auto *ME = dyn_cast<MemberExpr>(E)) {
    if (const auto *VD = dyn_cast<VarDecl>(ME->getMemberDecl())) {
      if (!VD->isStaticDataMember())
        classify(ME->getBase(), C);
    }
    return;
  }

  if (const auto *BO = dyn_cast<BinaryOperator>(E)) {
    switch (BO->getOpcode()) {
    case BO_PtrMemD:
    case BO_PtrMemI:
      classify(BO->getLHS(), C);
      return;
    case BO_Comma:
      classify(BO->getRHS(), C);
      return;
    default:
      return;
    }
  }

  FindVarResult Var = findVar(E, DC);
  if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
    Classification[DRE] = std::max(Classification[DRE], C);
}

void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
  for (auto *DI : DS->decls()) {
    auto *VD = dyn_cast<VarDecl>(DI);
    if (VD && isTrackedVar(VD))
      if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
        Classification[DRE] = SelfInit;
  }
}

void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
  // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
  // is not a compound-assignment, we will treat it as initializing the variable
  // when TransferFunctions visits it. A compound-assignment does not affect
  // whether a variable is uninitialized, and there's no point counting it as a
  // use.
  if (BO->isCompoundAssignmentOp())
    classify(BO->getLHS(), Use);
  else if (BO->getOpcode() == BO_Assign || BO->getOpcode() == BO_Comma)
    classify(BO->getLHS(), Ignore);
}

void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
  // Increment and decrement are uses despite there being no lvalue-to-rvalue
  // conversion.
  if (UO->isIncrementDecrementOp())
    classify(UO->getSubExpr(), Use);
}

void ClassifyRefs::VisitOMPExecutableDirective(OMPExecutableDirective *ED) {
  for (Stmt *S : OMPExecutableDirective::used_clauses_children(ED->clauses()))
    classify(cast<Expr>(S), Use);
}

static bool isPointerToConst(const QualType &QT) {
  return QT->isAnyPointerType() && QT->getPointeeType().isConstQualified();
}

static bool hasTrivialBody(CallExpr *CE) {
  if (FunctionDecl *FD = CE->getDirectCallee()) {
    if (FunctionTemplateDecl *FTD = FD->getPrimaryTemplate())
      return FTD->getTemplatedDecl()->hasTrivialBody();
    return FD->hasTrivialBody();
  }
  return false;
}

void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
  // Classify arguments to std::move as used.
  if (CE->isCallToStdMove()) {
    // RecordTypes are handled in SemaDeclCXX.cpp.
    if (!CE->getArg(0)->getType()->isRecordType())
      classify(CE->getArg(0), Use);
    return;
  }
  bool isTrivialBody = hasTrivialBody(CE);
  // If a value is passed by const pointer to a function,
  // we should not assume that it is initialized by the call, and we
  // conservatively do not assume that it is used.
  // If a value is passed by const reference to a function,
  // it should already be initialized.
  for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
       I != E; ++I) {
    if ((*I)->isGLValue()) {
      if ((*I)->getType().isConstQualified())
        classify((*I), isTrivialBody ? Ignore : ConstRefUse);
    } else if (isPointerToConst((*I)->getType())) {
      const Expr *Ex = stripCasts(DC->getParentASTContext(), *I);
      const auto *UO = dyn_cast<UnaryOperator>(Ex);
      if (UO && UO->getOpcode() == UO_AddrOf)
        Ex = UO->getSubExpr();
      classify(Ex, Ignore);
    }
  }
}

void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
  if (CE->getCastKind() == CK_LValueToRValue)
    classify(CE->getSubExpr(), Use);
  else if (const auto *CSE = dyn_cast<CStyleCastExpr>(CE)) {
    if (CSE->getType()->isVoidType()) {
      // Squelch any detected load of an uninitialized value if
      // we cast it to void.
      // e.g. (void) x;
      classify(CSE->getSubExpr(), Ignore);
    }
  }
}

//------------------------------------------------------------------------====//
// Transfer function for uninitialized values analysis.
//====------------------------------------------------------------------------//

namespace {

class TransferFunctions : public StmtVisitor<TransferFunctions> {
  CFGBlockValues &vals;
  const CFG &cfg;
  const CFGBlock *block;
  AnalysisDeclContext &ac;
  const ClassifyRefs &classification;
  ObjCNoReturn objCNoRet;
  UninitVariablesHandler &handler;

public:
  TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
                    const CFGBlock *block, AnalysisDeclContext &ac,
                    const ClassifyRefs &classification,
                    UninitVariablesHandler &handler)
      : vals(vals), cfg(cfg), block(block), ac(ac),
        classification(classification), objCNoRet(ac.getASTContext()),
        handler(handler) {}

  void reportUse(const Expr *ex, const VarDecl *vd);
  void reportConstRefUse(const Expr *ex, const VarDecl *vd);

  void VisitBinaryOperator(BinaryOperator *bo);
  void VisitBlockExpr(BlockExpr *be);
  void VisitCallExpr(CallExpr *ce);
  void VisitDeclRefExpr(DeclRefExpr *dr);
  void VisitDeclStmt(DeclStmt *ds);
  void VisitGCCAsmStmt(GCCAsmStmt *as);
  void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
  void VisitObjCMessageExpr(ObjCMessageExpr *ME);
  void VisitOMPExecutableDirective(OMPExecutableDirective *ED);

  bool isTrackedVar(const VarDecl *vd) {
    return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
  }

  FindVarResult findVar(const Expr *ex) {
    return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
  }

  UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
    UninitUse Use(ex, isAlwaysUninit(v));

    assert(isUninitialized(v));
    if (Use.getKind() == UninitUse::Always)
      return Use;

    // If an edge which leads unconditionally to this use did not initialize
    // the variable, we can say something stronger than 'may be uninitialized':
    // we can say 'either it's used uninitialized or you have dead code'.
    //
    // We track the number of successors of a node which have been visited, and
    // visit a node once we have visited all of its successors. Only edges where
    // the variable might still be uninitialized are followed. Since a variable
    // can't transfer from being initialized to being uninitialized, this will
    // trace out the subgraph which inevitably leads to the use and does not
    // initialize the variable. We do not want to skip past loops, since their
    // non-termination might be correlated with the initialization condition.
    //
    // For example:
    //
    //         void f(bool a, bool b) {
    // block1:   int n;
    //           if (a) {
    // block2:     if (b)
    // block3:       n = 1;
    // block4:   } else if (b) {
    // block5:     while (!a) {
    // block6:       do_work(&a);
    //               n = 2;
    //             }
    //           }
    // block7:   if (a)
    // block8:     g();
    // block9:   return n;
    //         }
    //
    // Starting from the maybe-uninitialized use in block 9:
    //  * Block 7 is not visited because we have only visited one of its two
    //    successors.
    //  * Block 8 is visited because we've visited its only successor.
    // From block 8:
    //  * Block 7 is visited because we've now visited both of its successors.
    // From block 7:
    //  * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
    //    of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
    //  * Block 3 is not visited because it initializes 'n'.
    // Now the algorithm terminates, having visited blocks 7 and 8, and having
    // found the frontier is blocks 2, 4, and 5.
    //
    // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
    // and 4), so we report that any time either of those edges is taken (in
    // each case when 'b == false'), 'n' is used uninitialized.
    SmallVector<const CFGBlock*, 32> Queue;
    SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
    Queue.push_back(block);
    // Specify that we've already visited all successors of the starting block.
    // This has the dual purpose of ensuring we never add it to the queue, and
    // of marking it as not being a candidate element of the frontier.
    SuccsVisited[block->getBlockID()] = block->succ_size();
    while (!Queue.empty()) {
      const CFGBlock *B = Queue.pop_back_val();

      // If the use is always reached from the entry block, make a note of that.
      if (B == &cfg.getEntry())
        Use.setUninitAfterCall();

      for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
           I != E; ++I) {
        const CFGBlock *Pred = *I;
        if (!Pred)
          continue;

        Value AtPredExit = vals.getValue(Pred, B, vd);
        if (AtPredExit == Initialized)
          // This block initializes the variable.
          continue;
        if (AtPredExit == MayUninitialized &&
            vals.getValue(B, nullptr, vd) == Uninitialized) {
          // This block declares the variable (uninitialized), and is reachable
          // from a block that initializes the variable. We can't guarantee to
          // give an earlier location for the diagnostic (and it appears that
          // this code is intended to be reachable) so give a diagnostic here
          // and go no further down this path.
          Use.setUninitAfterDecl();
          continue;
        }

        if (AtPredExit == MayUninitialized) {
          // If the predecessor's terminator is an "asm goto" that initializes
          // the variable, then don't count it as "initialized" on the indirect
          // paths.
          CFGTerminator term = Pred->getTerminator();
          if (const auto *as = dyn_cast_or_null<GCCAsmStmt>(term.getStmt())) {
            const CFGBlock *fallthrough = *Pred->succ_begin();
            if (as->isAsmGoto() &&
                llvm::any_of(as->outputs(), [&](const Expr *output) {
                    return vd == findVar(output).getDecl() &&
                        llvm::any_of(as->labels(),
                                     [&](const AddrLabelExpr *label) {
                          return label->getLabel()->getStmt() == B->Label &&
                              B != fallthrough;
                        });
                })) {
              Use.setUninitAfterDecl();
              continue;
            }
          }
        }

        unsigned &SV = SuccsVisited[Pred->getBlockID()];
        if (!SV) {
          // When visiting the first successor of a block, mark all NULL
          // successors as having been visited.
          for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
                                             SE = Pred->succ_end();
               SI != SE; ++SI)
            if (!*SI)
              ++SV;
        }

        if (++SV == Pred->succ_size())
          // All paths from this block lead to the use and don't initialize the
          // variable.
          Queue.push_back(Pred);
      }
    }

    // Scan the frontier, looking for blocks where the variable was
    // uninitialized.
    for (const auto *Block : cfg) {
      unsigned BlockID = Block->getBlockID();
      const Stmt *Term = Block->getTerminatorStmt();
      if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
          Term) {
        // This block inevitably leads to the use. If we have an edge from here
        // to a post-dominator block, and the variable is uninitialized on that
        // edge, we have found a bug.
        for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
             E = Block->succ_end(); I != E; ++I) {
          const CFGBlock *Succ = *I;
          if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
              vals.getValue(Block, Succ, vd) == Uninitialized) {
            // Switch cases are a special case: report the label to the caller
            // as the 'terminator', not the switch statement itself. Suppress
            // situations where no label matched: we can't be sure that's
            // possible.
            if (isa<SwitchStmt>(Term)) {
              const Stmt *Label = Succ->getLabel();
              if (!Label || !isa<SwitchCase>(Label))
                // Might not be possible.
                continue;
              UninitUse::Branch Branch;
              Branch.Terminator = Label;
              Branch.Output = 0; // Ignored.
              Use.addUninitBranch(Branch);
            } else {
              UninitUse::Branch Branch;
              Branch.Terminator = Term;
              Branch.Output = I - Block->succ_begin();
              Use.addUninitBranch(Branch);
            }
          }
        }
      }
    }

    return Use;
  }
};

} // namespace

void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
  Value v = vals[vd];
  if (isUninitialized(v))
    handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
}

void TransferFunctions::reportConstRefUse(const Expr *ex, const VarDecl *vd) {
  Value v = vals[vd];
  if (isAlwaysUninit(v))
    handler.handleConstRefUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
}

void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
  // This represents an initialization of the 'element' value.
  if (const auto *DS = dyn_cast<DeclStmt>(FS->getElement())) {
    const auto *VD = cast<VarDecl>(DS->getSingleDecl());
    if (isTrackedVar(VD))
      vals[VD] = Initialized;
  }
}

void TransferFunctions::VisitOMPExecutableDirective(
    OMPExecutableDirective *ED) {
  for (Stmt *S : OMPExecutableDirective::used_clauses_children(ED->clauses())) {
    assert(S && "Expected non-null used-in-clause child.");
    Visit(S);
  }
  if (!ED->isStandaloneDirective())
    Visit(ED->getStructuredBlock());
}

void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
  const BlockDecl *bd = be->getBlockDecl();
  for (const auto &I : bd->captures()) {
    const VarDecl *vd = I.getVariable();
    if (!isTrackedVar(vd))
      continue;
    if (I.isByRef()) {
      vals[vd] = Initialized;
      continue;
    }
    reportUse(be, vd);
  }
}

void TransferFunctions::VisitCallExpr(CallExpr *ce) {
  if (Decl *Callee = ce->getCalleeDecl()) {
    if (Callee->hasAttr<ReturnsTwiceAttr>()) {
      // After a call to a function like setjmp or vfork, any variable which is
      // initialized anywhere within this function may now be initialized. For
      // now, just assume such a call initializes all variables.  FIXME: Only
      // mark variables as initialized if they have an initializer which is
      // reachable from here.
      vals.setAllScratchValues(Initialized);
    }
    else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
      // Functions labeled like "analyzer_noreturn" are often used to denote
      // "panic" functions that in special debug situations can still return,
      // but for the most part should not be treated as returning.  This is a
      // useful annotation borrowed from the static analyzer that is useful for
      // suppressing branch-specific false positives when we call one of these
      // functions but keep pretending the path continues (when in reality the
      // user doesn't care).
      vals.setAllScratchValues(Unknown);
    }
  }
}

void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
  switch (classification.get(dr)) {
  case ClassifyRefs::Ignore:
    break;
  case ClassifyRefs::Use:
    reportUse(dr, cast<VarDecl>(dr->getDecl()));
    break;
  case ClassifyRefs::Init:
    vals[cast<VarDecl>(dr->getDecl())] = Initialized;
    break;
  case ClassifyRefs::SelfInit:
    handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
    break;
  case ClassifyRefs::ConstRefUse:
    reportConstRefUse(dr, cast<VarDecl>(dr->getDecl()));
    break;
  }
}

void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
  if (BO->getOpcode() == BO_Assign) {
    FindVarResult Var = findVar(BO->getLHS());
    if (const VarDecl *VD = Var.getDecl())
      vals[VD] = Initialized;
  }
}

void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
  for (auto *DI : DS->decls()) {
    auto *VD = dyn_cast<VarDecl>(DI);
    if (VD && isTrackedVar(VD)) {
      if (getSelfInitExpr(VD)) {
        // If the initializer consists solely of a reference to itself, we
        // explicitly mark the variable as uninitialized. This allows code
        // like the following:
        //
        //   int x = x;
        //
        // to deliberately leave a variable uninitialized. Different analysis
        // clients can detect this pattern and adjust their reporting
        // appropriately, but we need to continue to analyze subsequent uses
        // of the variable.
        vals[VD] = Uninitialized;
      } else if (VD->getInit()) {
        // Treat the new variable as initialized.
        vals[VD] = Initialized;
      } else {
        // No initializer: the variable is now uninitialized. This matters
        // for cases like:
        //   while (...) {
        //     int n;
        //     use(n);
        //     n = 0;
        //   }
        // FIXME: Mark the variable as uninitialized whenever its scope is
        // left, since its scope could be re-entered by a jump over the
        // declaration.
        vals[VD] = Uninitialized;
      }
    }
  }
}

void TransferFunctions::VisitGCCAsmStmt(GCCAsmStmt *as) {
  // An "asm goto" statement is a terminator that may initialize some variables.
  if (!as->isAsmGoto())
    return;

  ASTContext &C = ac.getASTContext();
  for (const Expr *O : as->outputs()) {
    const Expr *Ex = stripCasts(C, O);

    // Strip away any unary operators. Invalid l-values are reported by other
    // semantic analysis passes.
    while (const auto *UO = dyn_cast<UnaryOperator>(Ex))
      Ex = stripCasts(C, UO->getSubExpr());

    // Mark the variable as potentially uninitialized for those cases where
    // it's used on an indirect path, where it's not guaranteed to be
    // defined.
    if (const VarDecl *VD = findVar(Ex).getDecl())
      vals[VD] = MayUninitialized;
  }
}

void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
  // If the Objective-C message expression is an implicit no-return that
  // is not modeled in the CFG, set the tracked dataflow values to Unknown.
  if (objCNoRet.isImplicitNoReturn(ME)) {
    vals.setAllScratchValues(Unknown);
  }
}

//------------------------------------------------------------------------====//
// High-level "driver" logic for uninitialized values analysis.
//====------------------------------------------------------------------------//

static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
                       AnalysisDeclContext &ac, CFGBlockValues &vals,
                       const ClassifyRefs &classification,
                       llvm::BitVector &wasAnalyzed,
                       UninitVariablesHandler &handler) {
  wasAnalyzed[block->getBlockID()] = true;
  vals.resetScratch();
  // Merge in values of predecessor blocks.
  bool isFirst = true;
  for (CFGBlock::const_pred_iterator I = block->pred_begin(),
       E = block->pred_end(); I != E; ++I) {
    const CFGBlock *pred = *I;
    if (!pred)
      continue;
    if (wasAnalyzed[pred->getBlockID()]) {
      vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
      isFirst = false;
    }
  }
  // Apply the transfer function.
  TransferFunctions tf(vals, cfg, block, ac, classification, handler);
  for (const auto &I : *block) {
    if (Optional<CFGStmt> cs = I.getAs<CFGStmt>())
      tf.Visit(const_cast<Stmt *>(cs->getStmt()));
  }
  CFGTerminator terminator = block->getTerminator();
  if (auto *as = dyn_cast_or_null<GCCAsmStmt>(terminator.getStmt()))
    if (as->isAsmGoto())
      tf.Visit(as);
  return vals.updateValueVectorWithScratch(block);
}

namespace {

/// PruneBlocksHandler is a special UninitVariablesHandler that is used
/// to detect when a CFGBlock has any *potential* use of an uninitialized
/// variable.  It is mainly used to prune out work during the final
/// reporting pass.
struct PruneBlocksHandler : public UninitVariablesHandler {
  /// Records if a CFGBlock had a potential use of an uninitialized variable.
  llvm::BitVector hadUse;

  /// Records if any CFGBlock had a potential use of an uninitialized variable.
  bool hadAnyUse = false;

  /// The current block to scribble use information.
  unsigned currentBlock = 0;

  PruneBlocksHandler(unsigned numBlocks) : hadUse(numBlocks, false) {}

  ~PruneBlocksHandler() override = default;

  void handleUseOfUninitVariable(const VarDecl *vd,
                                 const UninitUse &use) override {
    hadUse[currentBlock] = true;
    hadAnyUse = true;
  }

  void handleConstRefUseOfUninitVariable(const VarDecl *vd,
                                         const UninitUse &use) override {
    hadUse[currentBlock] = true;
    hadAnyUse = true;
  }
  
  /// Called when the uninitialized variable analysis detects the
  /// idiom 'int x = x'.  All other uses of 'x' within the initializer
  /// are handled by handleUseOfUninitVariable.
  void handleSelfInit(const VarDecl *vd) override {
    hadUse[currentBlock] = true;
    hadAnyUse = true;
  }
};

} // namespace

void clang::runUninitializedVariablesAnalysis(
    const DeclContext &dc,
    const CFG &cfg,
    AnalysisDeclContext &ac,
    UninitVariablesHandler &handler,
    UninitVariablesAnalysisStats &stats) {
  CFGBlockValues vals(cfg);
  vals.computeSetOfDeclarations(dc);
  if (vals.hasNoDeclarations())
    return;

  stats.NumVariablesAnalyzed = vals.getNumEntries();

  // Precompute which expressions are uses and which are initializations.
  ClassifyRefs classification(ac);
  cfg.VisitBlockStmts(classification);

  // Mark all variables uninitialized at the entry.
  const CFGBlock &entry = cfg.getEntry();
  ValueVector &vec = vals.getValueVector(&entry);
  const unsigned n = vals.getNumEntries();
  for (unsigned j = 0; j < n; ++j) {
    vec[j] = Uninitialized;
  }

  // Proceed with the workist.
  ForwardDataflowWorklist worklist(cfg, ac);
  llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
  worklist.enqueueSuccessors(&cfg.getEntry());
  llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
  wasAnalyzed[cfg.getEntry().getBlockID()] = true;
  PruneBlocksHandler PBH(cfg.getNumBlockIDs());

  while (const CFGBlock *block = worklist.dequeue()) {
    PBH.currentBlock = block->getBlockID();

    // Did the block change?
    bool changed = runOnBlock(block, cfg, ac, vals,
                              classification, wasAnalyzed, PBH);
    ++stats.NumBlockVisits;
    if (changed || !previouslyVisited[block->getBlockID()])
      worklist.enqueueSuccessors(block);
    previouslyVisited[block->getBlockID()] = true;
  }

  if (!PBH.hadAnyUse)
    return;

  // Run through the blocks one more time, and report uninitialized variables.
  for (const auto *block : cfg)
    if (PBH.hadUse[block->getBlockID()]) {
      runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
      ++stats.NumBlockVisits;
    }
}

UninitVariablesHandler::~UninitVariablesHandler() = default;