xref: /freebsd/contrib/llvm-project/clang/lib/Analysis/UninitializedValues.cpp (revision e1e636193db45630c7881246d25902e57c43d24e)
1 //===- UninitializedValues.cpp - Find Uninitialized Values ----------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements uninitialized values analysis for source-level CFGs.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "clang/Analysis/Analyses/UninitializedValues.h"
14 #include "clang/AST/Attr.h"
15 #include "clang/AST/Decl.h"
16 #include "clang/AST/DeclBase.h"
17 #include "clang/AST/Expr.h"
18 #include "clang/AST/OperationKinds.h"
19 #include "clang/AST/Stmt.h"
20 #include "clang/AST/StmtObjC.h"
21 #include "clang/AST/StmtVisitor.h"
22 #include "clang/AST/Type.h"
23 #include "clang/Analysis/Analyses/PostOrderCFGView.h"
24 #include "clang/Analysis/AnalysisDeclContext.h"
25 #include "clang/Analysis/CFG.h"
26 #include "clang/Analysis/DomainSpecific/ObjCNoReturn.h"
27 #include "clang/Analysis/FlowSensitive/DataflowWorklist.h"
28 #include "clang/Basic/LLVM.h"
29 #include "llvm/ADT/BitVector.h"
30 #include "llvm/ADT/DenseMap.h"
31 #include "llvm/ADT/PackedVector.h"
32 #include "llvm/ADT/SmallBitVector.h"
33 #include "llvm/ADT/SmallVector.h"
34 #include "llvm/Support/Casting.h"
35 #include <algorithm>
36 #include <cassert>
37 #include <optional>
38 
39 using namespace clang;
40 
41 #define DEBUG_LOGGING 0
42 
43 static bool recordIsNotEmpty(const RecordDecl *RD) {
44   // We consider a record decl to be empty if it contains only unnamed bit-
45   // fields, zero-width fields, and fields of empty record type.
46   for (const auto *FD : RD->fields()) {
47     if (FD->isUnnamedBitfield())
48       continue;
49     if (FD->isZeroSize(FD->getASTContext()))
50       continue;
51     // The only case remaining to check is for a field declaration of record
52     // type and whether that record itself is empty.
53     if (const auto *FieldRD = FD->getType()->getAsRecordDecl();
54         !FieldRD || recordIsNotEmpty(FieldRD))
55       return true;
56   }
57   return false;
58 }
59 
60 static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
61   if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
62       !vd->isExceptionVariable() && !vd->isInitCapture() && !vd->isImplicit() &&
63       vd->getDeclContext() == dc) {
64     QualType ty = vd->getType();
65     if (const auto *RD = ty->getAsRecordDecl())
66       return recordIsNotEmpty(RD);
67     return ty->isScalarType() || ty->isVectorType() || ty->isRVVSizelessBuiltinType();
68   }
69   return false;
70 }
71 
72 //------------------------------------------------------------------------====//
73 // DeclToIndex: a mapping from Decls we track to value indices.
74 //====------------------------------------------------------------------------//
75 
76 namespace {
77 
78 class DeclToIndex {
79   llvm::DenseMap<const VarDecl *, unsigned> map;
80 
81 public:
82   DeclToIndex() = default;
83 
84   /// Compute the actual mapping from declarations to bits.
85   void computeMap(const DeclContext &dc);
86 
87   /// Return the number of declarations in the map.
88   unsigned size() const { return map.size(); }
89 
90   /// Returns the bit vector index for a given declaration.
91   std::optional<unsigned> getValueIndex(const VarDecl *d) const;
92 };
93 
94 } // namespace
95 
96 void DeclToIndex::computeMap(const DeclContext &dc) {
97   unsigned count = 0;
98   DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
99                                                E(dc.decls_end());
100   for ( ; I != E; ++I) {
101     const VarDecl *vd = *I;
102     if (isTrackedVar(vd, &dc))
103       map[vd] = count++;
104   }
105 }
106 
107 std::optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
108   llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
109   if (I == map.end())
110     return std::nullopt;
111   return I->second;
112 }
113 
114 //------------------------------------------------------------------------====//
115 // CFGBlockValues: dataflow values for CFG blocks.
116 //====------------------------------------------------------------------------//
117 
118 // These values are defined in such a way that a merge can be done using
119 // a bitwise OR.
120 enum Value { Unknown = 0x0,         /* 00 */
121              Initialized = 0x1,     /* 01 */
122              Uninitialized = 0x2,   /* 10 */
123              MayUninitialized = 0x3 /* 11 */ };
124 
125 static bool isUninitialized(const Value v) {
126   return v >= Uninitialized;
127 }
128 
129 static bool isAlwaysUninit(const Value v) {
130   return v == Uninitialized;
131 }
132 
133 namespace {
134 
135 using ValueVector = llvm::PackedVector<Value, 2, llvm::SmallBitVector>;
136 
137 class CFGBlockValues {
138   const CFG &cfg;
139   SmallVector<ValueVector, 8> vals;
140   ValueVector scratch;
141   DeclToIndex declToIndex;
142 
143 public:
144   CFGBlockValues(const CFG &cfg);
145 
146   unsigned getNumEntries() const { return declToIndex.size(); }
147 
148   void computeSetOfDeclarations(const DeclContext &dc);
149 
150   ValueVector &getValueVector(const CFGBlock *block) {
151     return vals[block->getBlockID()];
152   }
153 
154   void setAllScratchValues(Value V);
155   void mergeIntoScratch(ValueVector const &source, bool isFirst);
156   bool updateValueVectorWithScratch(const CFGBlock *block);
157 
158   bool hasNoDeclarations() const {
159     return declToIndex.size() == 0;
160   }
161 
162   void resetScratch();
163 
164   ValueVector::reference operator[](const VarDecl *vd);
165 
166   Value getValue(const CFGBlock *block, const CFGBlock *dstBlock,
167                  const VarDecl *vd) {
168     std::optional<unsigned> idx = declToIndex.getValueIndex(vd);
169     return getValueVector(block)[*idx];
170   }
171 };
172 
173 } // namespace
174 
175 CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {}
176 
177 void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
178   declToIndex.computeMap(dc);
179   unsigned decls = declToIndex.size();
180   scratch.resize(decls);
181   unsigned n = cfg.getNumBlockIDs();
182   if (!n)
183     return;
184   vals.resize(n);
185   for (auto &val : vals)
186     val.resize(decls);
187 }
188 
189 #if DEBUG_LOGGING
190 static void printVector(const CFGBlock *block, ValueVector &bv,
191                         unsigned num) {
192   llvm::errs() << block->getBlockID() << " :";
193   for (const auto &i : bv)
194     llvm::errs() << ' ' << i;
195   llvm::errs() << " : " << num << '\n';
196 }
197 #endif
198 
199 void CFGBlockValues::setAllScratchValues(Value V) {
200   for (unsigned I = 0, E = scratch.size(); I != E; ++I)
201     scratch[I] = V;
202 }
203 
204 void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
205                                       bool isFirst) {
206   if (isFirst)
207     scratch = source;
208   else
209     scratch |= source;
210 }
211 
212 bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
213   ValueVector &dst = getValueVector(block);
214   bool changed = (dst != scratch);
215   if (changed)
216     dst = scratch;
217 #if DEBUG_LOGGING
218   printVector(block, scratch, 0);
219 #endif
220   return changed;
221 }
222 
223 void CFGBlockValues::resetScratch() {
224   scratch.reset();
225 }
226 
227 ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
228   return scratch[*declToIndex.getValueIndex(vd)];
229 }
230 
231 //------------------------------------------------------------------------====//
232 // Classification of DeclRefExprs as use or initialization.
233 //====------------------------------------------------------------------------//
234 
235 namespace {
236 
237 class FindVarResult {
238   const VarDecl *vd;
239   const DeclRefExpr *dr;
240 
241 public:
242   FindVarResult(const VarDecl *vd, const DeclRefExpr *dr) : vd(vd), dr(dr) {}
243 
244   const DeclRefExpr *getDeclRefExpr() const { return dr; }
245   const VarDecl *getDecl() const { return vd; }
246 };
247 
248 } // namespace
249 
250 static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
251   while (Ex) {
252     Ex = Ex->IgnoreParenNoopCasts(C);
253     if (const auto *CE = dyn_cast<CastExpr>(Ex)) {
254       if (CE->getCastKind() == CK_LValueBitCast) {
255         Ex = CE->getSubExpr();
256         continue;
257       }
258     }
259     break;
260   }
261   return Ex;
262 }
263 
264 /// If E is an expression comprising a reference to a single variable, find that
265 /// variable.
266 static FindVarResult findVar(const Expr *E, const DeclContext *DC) {
267   if (const auto *DRE =
268           dyn_cast<DeclRefExpr>(stripCasts(DC->getParentASTContext(), E)))
269     if (const auto *VD = dyn_cast<VarDecl>(DRE->getDecl()))
270       if (isTrackedVar(VD, DC))
271         return FindVarResult(VD, DRE);
272   return FindVarResult(nullptr, nullptr);
273 }
274 
275 namespace {
276 
277 /// Classify each DeclRefExpr as an initialization or a use. Any
278 /// DeclRefExpr which isn't explicitly classified will be assumed to have
279 /// escaped the analysis and will be treated as an initialization.
280 class ClassifyRefs : public StmtVisitor<ClassifyRefs> {
281 public:
282   enum Class {
283     Init,
284     Use,
285     SelfInit,
286     ConstRefUse,
287     Ignore
288   };
289 
290 private:
291   const DeclContext *DC;
292   llvm::DenseMap<const DeclRefExpr *, Class> Classification;
293 
294   bool isTrackedVar(const VarDecl *VD) const {
295     return ::isTrackedVar(VD, DC);
296   }
297 
298   void classify(const Expr *E, Class C);
299 
300 public:
301   ClassifyRefs(AnalysisDeclContext &AC) : DC(cast<DeclContext>(AC.getDecl())) {}
302 
303   void VisitDeclStmt(DeclStmt *DS);
304   void VisitUnaryOperator(UnaryOperator *UO);
305   void VisitBinaryOperator(BinaryOperator *BO);
306   void VisitCallExpr(CallExpr *CE);
307   void VisitCastExpr(CastExpr *CE);
308   void VisitOMPExecutableDirective(OMPExecutableDirective *ED);
309 
310   void operator()(Stmt *S) { Visit(S); }
311 
312   Class get(const DeclRefExpr *DRE) const {
313     llvm::DenseMap<const DeclRefExpr*, Class>::const_iterator I
314         = Classification.find(DRE);
315     if (I != Classification.end())
316       return I->second;
317 
318     const auto *VD = dyn_cast<VarDecl>(DRE->getDecl());
319     if (!VD || !isTrackedVar(VD))
320       return Ignore;
321 
322     return Init;
323   }
324 };
325 
326 } // namespace
327 
328 static const DeclRefExpr *getSelfInitExpr(VarDecl *VD) {
329   if (VD->getType()->isRecordType())
330     return nullptr;
331   if (Expr *Init = VD->getInit()) {
332     const auto *DRE =
333         dyn_cast<DeclRefExpr>(stripCasts(VD->getASTContext(), Init));
334     if (DRE && DRE->getDecl() == VD)
335       return DRE;
336   }
337   return nullptr;
338 }
339 
340 void ClassifyRefs::classify(const Expr *E, Class C) {
341   // The result of a ?: could also be an lvalue.
342   E = E->IgnoreParens();
343   if (const auto *CO = dyn_cast<ConditionalOperator>(E)) {
344     classify(CO->getTrueExpr(), C);
345     classify(CO->getFalseExpr(), C);
346     return;
347   }
348 
349   if (const auto *BCO = dyn_cast<BinaryConditionalOperator>(E)) {
350     classify(BCO->getFalseExpr(), C);
351     return;
352   }
353 
354   if (const auto *OVE = dyn_cast<OpaqueValueExpr>(E)) {
355     classify(OVE->getSourceExpr(), C);
356     return;
357   }
358 
359   if (const auto *ME = dyn_cast<MemberExpr>(E)) {
360     if (const auto *VD = dyn_cast<VarDecl>(ME->getMemberDecl())) {
361       if (!VD->isStaticDataMember())
362         classify(ME->getBase(), C);
363     }
364     return;
365   }
366 
367   if (const auto *BO = dyn_cast<BinaryOperator>(E)) {
368     switch (BO->getOpcode()) {
369     case BO_PtrMemD:
370     case BO_PtrMemI:
371       classify(BO->getLHS(), C);
372       return;
373     case BO_Comma:
374       classify(BO->getRHS(), C);
375       return;
376     default:
377       return;
378     }
379   }
380 
381   FindVarResult Var = findVar(E, DC);
382   if (const DeclRefExpr *DRE = Var.getDeclRefExpr())
383     Classification[DRE] = std::max(Classification[DRE], C);
384 }
385 
386 void ClassifyRefs::VisitDeclStmt(DeclStmt *DS) {
387   for (auto *DI : DS->decls()) {
388     auto *VD = dyn_cast<VarDecl>(DI);
389     if (VD && isTrackedVar(VD))
390       if (const DeclRefExpr *DRE = getSelfInitExpr(VD))
391         Classification[DRE] = SelfInit;
392   }
393 }
394 
395 void ClassifyRefs::VisitBinaryOperator(BinaryOperator *BO) {
396   // Ignore the evaluation of a DeclRefExpr on the LHS of an assignment. If this
397   // is not a compound-assignment, we will treat it as initializing the variable
398   // when TransferFunctions visits it. A compound-assignment does not affect
399   // whether a variable is uninitialized, and there's no point counting it as a
400   // use.
401   if (BO->isCompoundAssignmentOp())
402     classify(BO->getLHS(), Use);
403   else if (BO->getOpcode() == BO_Assign || BO->getOpcode() == BO_Comma)
404     classify(BO->getLHS(), Ignore);
405 }
406 
407 void ClassifyRefs::VisitUnaryOperator(UnaryOperator *UO) {
408   // Increment and decrement are uses despite there being no lvalue-to-rvalue
409   // conversion.
410   if (UO->isIncrementDecrementOp())
411     classify(UO->getSubExpr(), Use);
412 }
413 
414 void ClassifyRefs::VisitOMPExecutableDirective(OMPExecutableDirective *ED) {
415   for (Stmt *S : OMPExecutableDirective::used_clauses_children(ED->clauses()))
416     classify(cast<Expr>(S), Use);
417 }
418 
419 static bool isPointerToConst(const QualType &QT) {
420   return QT->isAnyPointerType() && QT->getPointeeType().isConstQualified();
421 }
422 
423 static bool hasTrivialBody(CallExpr *CE) {
424   if (FunctionDecl *FD = CE->getDirectCallee()) {
425     if (FunctionTemplateDecl *FTD = FD->getPrimaryTemplate())
426       return FTD->getTemplatedDecl()->hasTrivialBody();
427     return FD->hasTrivialBody();
428   }
429   return false;
430 }
431 
432 void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
433   // Classify arguments to std::move as used.
434   if (CE->isCallToStdMove()) {
435     // RecordTypes are handled in SemaDeclCXX.cpp.
436     if (!CE->getArg(0)->getType()->isRecordType())
437       classify(CE->getArg(0), Use);
438     return;
439   }
440   bool isTrivialBody = hasTrivialBody(CE);
441   // If a value is passed by const pointer to a function,
442   // we should not assume that it is initialized by the call, and we
443   // conservatively do not assume that it is used.
444   // If a value is passed by const reference to a function,
445   // it should already be initialized.
446   for (CallExpr::arg_iterator I = CE->arg_begin(), E = CE->arg_end();
447        I != E; ++I) {
448     if ((*I)->isGLValue()) {
449       if ((*I)->getType().isConstQualified())
450         classify((*I), isTrivialBody ? Ignore : ConstRefUse);
451     } else if (isPointerToConst((*I)->getType())) {
452       const Expr *Ex = stripCasts(DC->getParentASTContext(), *I);
453       const auto *UO = dyn_cast<UnaryOperator>(Ex);
454       if (UO && UO->getOpcode() == UO_AddrOf)
455         Ex = UO->getSubExpr();
456       classify(Ex, Ignore);
457     }
458   }
459 }
460 
461 void ClassifyRefs::VisitCastExpr(CastExpr *CE) {
462   if (CE->getCastKind() == CK_LValueToRValue)
463     classify(CE->getSubExpr(), Use);
464   else if (const auto *CSE = dyn_cast<CStyleCastExpr>(CE)) {
465     if (CSE->getType()->isVoidType()) {
466       // Squelch any detected load of an uninitialized value if
467       // we cast it to void.
468       // e.g. (void) x;
469       classify(CSE->getSubExpr(), Ignore);
470     }
471   }
472 }
473 
474 //------------------------------------------------------------------------====//
475 // Transfer function for uninitialized values analysis.
476 //====------------------------------------------------------------------------//
477 
478 namespace {
479 
480 class TransferFunctions : public StmtVisitor<TransferFunctions> {
481   CFGBlockValues &vals;
482   const CFG &cfg;
483   const CFGBlock *block;
484   AnalysisDeclContext &ac;
485   const ClassifyRefs &classification;
486   ObjCNoReturn objCNoRet;
487   UninitVariablesHandler &handler;
488 
489 public:
490   TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
491                     const CFGBlock *block, AnalysisDeclContext &ac,
492                     const ClassifyRefs &classification,
493                     UninitVariablesHandler &handler)
494       : vals(vals), cfg(cfg), block(block), ac(ac),
495         classification(classification), objCNoRet(ac.getASTContext()),
496         handler(handler) {}
497 
498   void reportUse(const Expr *ex, const VarDecl *vd);
499   void reportConstRefUse(const Expr *ex, const VarDecl *vd);
500 
501   void VisitBinaryOperator(BinaryOperator *bo);
502   void VisitBlockExpr(BlockExpr *be);
503   void VisitCallExpr(CallExpr *ce);
504   void VisitDeclRefExpr(DeclRefExpr *dr);
505   void VisitDeclStmt(DeclStmt *ds);
506   void VisitGCCAsmStmt(GCCAsmStmt *as);
507   void VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS);
508   void VisitObjCMessageExpr(ObjCMessageExpr *ME);
509   void VisitOMPExecutableDirective(OMPExecutableDirective *ED);
510 
511   bool isTrackedVar(const VarDecl *vd) {
512     return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
513   }
514 
515   FindVarResult findVar(const Expr *ex) {
516     return ::findVar(ex, cast<DeclContext>(ac.getDecl()));
517   }
518 
519   UninitUse getUninitUse(const Expr *ex, const VarDecl *vd, Value v) {
520     UninitUse Use(ex, isAlwaysUninit(v));
521 
522     assert(isUninitialized(v));
523     if (Use.getKind() == UninitUse::Always)
524       return Use;
525 
526     // If an edge which leads unconditionally to this use did not initialize
527     // the variable, we can say something stronger than 'may be uninitialized':
528     // we can say 'either it's used uninitialized or you have dead code'.
529     //
530     // We track the number of successors of a node which have been visited, and
531     // visit a node once we have visited all of its successors. Only edges where
532     // the variable might still be uninitialized are followed. Since a variable
533     // can't transfer from being initialized to being uninitialized, this will
534     // trace out the subgraph which inevitably leads to the use and does not
535     // initialize the variable. We do not want to skip past loops, since their
536     // non-termination might be correlated with the initialization condition.
537     //
538     // For example:
539     //
540     //         void f(bool a, bool b) {
541     // block1:   int n;
542     //           if (a) {
543     // block2:     if (b)
544     // block3:       n = 1;
545     // block4:   } else if (b) {
546     // block5:     while (!a) {
547     // block6:       do_work(&a);
548     //               n = 2;
549     //             }
550     //           }
551     // block7:   if (a)
552     // block8:     g();
553     // block9:   return n;
554     //         }
555     //
556     // Starting from the maybe-uninitialized use in block 9:
557     //  * Block 7 is not visited because we have only visited one of its two
558     //    successors.
559     //  * Block 8 is visited because we've visited its only successor.
560     // From block 8:
561     //  * Block 7 is visited because we've now visited both of its successors.
562     // From block 7:
563     //  * Blocks 1, 2, 4, 5, and 6 are not visited because we didn't visit all
564     //    of their successors (we didn't visit 4, 3, 5, 6, and 5, respectively).
565     //  * Block 3 is not visited because it initializes 'n'.
566     // Now the algorithm terminates, having visited blocks 7 and 8, and having
567     // found the frontier is blocks 2, 4, and 5.
568     //
569     // 'n' is definitely uninitialized for two edges into block 7 (from blocks 2
570     // and 4), so we report that any time either of those edges is taken (in
571     // each case when 'b == false'), 'n' is used uninitialized.
572     SmallVector<const CFGBlock*, 32> Queue;
573     SmallVector<unsigned, 32> SuccsVisited(cfg.getNumBlockIDs(), 0);
574     Queue.push_back(block);
575     // Specify that we've already visited all successors of the starting block.
576     // This has the dual purpose of ensuring we never add it to the queue, and
577     // of marking it as not being a candidate element of the frontier.
578     SuccsVisited[block->getBlockID()] = block->succ_size();
579     while (!Queue.empty()) {
580       const CFGBlock *B = Queue.pop_back_val();
581 
582       // If the use is always reached from the entry block, make a note of that.
583       if (B == &cfg.getEntry())
584         Use.setUninitAfterCall();
585 
586       for (CFGBlock::const_pred_iterator I = B->pred_begin(), E = B->pred_end();
587            I != E; ++I) {
588         const CFGBlock *Pred = *I;
589         if (!Pred)
590           continue;
591 
592         Value AtPredExit = vals.getValue(Pred, B, vd);
593         if (AtPredExit == Initialized)
594           // This block initializes the variable.
595           continue;
596         if (AtPredExit == MayUninitialized &&
597             vals.getValue(B, nullptr, vd) == Uninitialized) {
598           // This block declares the variable (uninitialized), and is reachable
599           // from a block that initializes the variable. We can't guarantee to
600           // give an earlier location for the diagnostic (and it appears that
601           // this code is intended to be reachable) so give a diagnostic here
602           // and go no further down this path.
603           Use.setUninitAfterDecl();
604           continue;
605         }
606 
607         unsigned &SV = SuccsVisited[Pred->getBlockID()];
608         if (!SV) {
609           // When visiting the first successor of a block, mark all NULL
610           // successors as having been visited.
611           for (CFGBlock::const_succ_iterator SI = Pred->succ_begin(),
612                                              SE = Pred->succ_end();
613                SI != SE; ++SI)
614             if (!*SI)
615               ++SV;
616         }
617 
618         if (++SV == Pred->succ_size())
619           // All paths from this block lead to the use and don't initialize the
620           // variable.
621           Queue.push_back(Pred);
622       }
623     }
624 
625     // Scan the frontier, looking for blocks where the variable was
626     // uninitialized.
627     for (const auto *Block : cfg) {
628       unsigned BlockID = Block->getBlockID();
629       const Stmt *Term = Block->getTerminatorStmt();
630       if (SuccsVisited[BlockID] && SuccsVisited[BlockID] < Block->succ_size() &&
631           Term) {
632         // This block inevitably leads to the use. If we have an edge from here
633         // to a post-dominator block, and the variable is uninitialized on that
634         // edge, we have found a bug.
635         for (CFGBlock::const_succ_iterator I = Block->succ_begin(),
636              E = Block->succ_end(); I != E; ++I) {
637           const CFGBlock *Succ = *I;
638           if (Succ && SuccsVisited[Succ->getBlockID()] >= Succ->succ_size() &&
639               vals.getValue(Block, Succ, vd) == Uninitialized) {
640             // Switch cases are a special case: report the label to the caller
641             // as the 'terminator', not the switch statement itself. Suppress
642             // situations where no label matched: we can't be sure that's
643             // possible.
644             if (isa<SwitchStmt>(Term)) {
645               const Stmt *Label = Succ->getLabel();
646               if (!Label || !isa<SwitchCase>(Label))
647                 // Might not be possible.
648                 continue;
649               UninitUse::Branch Branch;
650               Branch.Terminator = Label;
651               Branch.Output = 0; // Ignored.
652               Use.addUninitBranch(Branch);
653             } else {
654               UninitUse::Branch Branch;
655               Branch.Terminator = Term;
656               Branch.Output = I - Block->succ_begin();
657               Use.addUninitBranch(Branch);
658             }
659           }
660         }
661       }
662     }
663 
664     return Use;
665   }
666 };
667 
668 } // namespace
669 
670 void TransferFunctions::reportUse(const Expr *ex, const VarDecl *vd) {
671   Value v = vals[vd];
672   if (isUninitialized(v))
673     handler.handleUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
674 }
675 
676 void TransferFunctions::reportConstRefUse(const Expr *ex, const VarDecl *vd) {
677   Value v = vals[vd];
678   if (isAlwaysUninit(v))
679     handler.handleConstRefUseOfUninitVariable(vd, getUninitUse(ex, vd, v));
680 }
681 
682 void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *FS) {
683   // This represents an initialization of the 'element' value.
684   if (const auto *DS = dyn_cast<DeclStmt>(FS->getElement())) {
685     const auto *VD = cast<VarDecl>(DS->getSingleDecl());
686     if (isTrackedVar(VD))
687       vals[VD] = Initialized;
688   }
689 }
690 
691 void TransferFunctions::VisitOMPExecutableDirective(
692     OMPExecutableDirective *ED) {
693   for (Stmt *S : OMPExecutableDirective::used_clauses_children(ED->clauses())) {
694     assert(S && "Expected non-null used-in-clause child.");
695     Visit(S);
696   }
697   if (!ED->isStandaloneDirective())
698     Visit(ED->getStructuredBlock());
699 }
700 
701 void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
702   const BlockDecl *bd = be->getBlockDecl();
703   for (const auto &I : bd->captures()) {
704     const VarDecl *vd = I.getVariable();
705     if (!isTrackedVar(vd))
706       continue;
707     if (I.isByRef()) {
708       vals[vd] = Initialized;
709       continue;
710     }
711     reportUse(be, vd);
712   }
713 }
714 
715 void TransferFunctions::VisitCallExpr(CallExpr *ce) {
716   if (Decl *Callee = ce->getCalleeDecl()) {
717     if (Callee->hasAttr<ReturnsTwiceAttr>()) {
718       // After a call to a function like setjmp or vfork, any variable which is
719       // initialized anywhere within this function may now be initialized. For
720       // now, just assume such a call initializes all variables.  FIXME: Only
721       // mark variables as initialized if they have an initializer which is
722       // reachable from here.
723       vals.setAllScratchValues(Initialized);
724     }
725     else if (Callee->hasAttr<AnalyzerNoReturnAttr>()) {
726       // Functions labeled like "analyzer_noreturn" are often used to denote
727       // "panic" functions that in special debug situations can still return,
728       // but for the most part should not be treated as returning.  This is a
729       // useful annotation borrowed from the static analyzer that is useful for
730       // suppressing branch-specific false positives when we call one of these
731       // functions but keep pretending the path continues (when in reality the
732       // user doesn't care).
733       vals.setAllScratchValues(Unknown);
734     }
735   }
736 }
737 
738 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
739   switch (classification.get(dr)) {
740   case ClassifyRefs::Ignore:
741     break;
742   case ClassifyRefs::Use:
743     reportUse(dr, cast<VarDecl>(dr->getDecl()));
744     break;
745   case ClassifyRefs::Init:
746     vals[cast<VarDecl>(dr->getDecl())] = Initialized;
747     break;
748   case ClassifyRefs::SelfInit:
749     handler.handleSelfInit(cast<VarDecl>(dr->getDecl()));
750     break;
751   case ClassifyRefs::ConstRefUse:
752     reportConstRefUse(dr, cast<VarDecl>(dr->getDecl()));
753     break;
754   }
755 }
756 
757 void TransferFunctions::VisitBinaryOperator(BinaryOperator *BO) {
758   if (BO->getOpcode() == BO_Assign) {
759     FindVarResult Var = findVar(BO->getLHS());
760     if (const VarDecl *VD = Var.getDecl())
761       vals[VD] = Initialized;
762   }
763 }
764 
765 void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
766   for (auto *DI : DS->decls()) {
767     auto *VD = dyn_cast<VarDecl>(DI);
768     if (VD && isTrackedVar(VD)) {
769       if (getSelfInitExpr(VD)) {
770         // If the initializer consists solely of a reference to itself, we
771         // explicitly mark the variable as uninitialized. This allows code
772         // like the following:
773         //
774         //   int x = x;
775         //
776         // to deliberately leave a variable uninitialized. Different analysis
777         // clients can detect this pattern and adjust their reporting
778         // appropriately, but we need to continue to analyze subsequent uses
779         // of the variable.
780         vals[VD] = Uninitialized;
781       } else if (VD->getInit()) {
782         // Treat the new variable as initialized.
783         vals[VD] = Initialized;
784       } else {
785         // No initializer: the variable is now uninitialized. This matters
786         // for cases like:
787         //   while (...) {
788         //     int n;
789         //     use(n);
790         //     n = 0;
791         //   }
792         // FIXME: Mark the variable as uninitialized whenever its scope is
793         // left, since its scope could be re-entered by a jump over the
794         // declaration.
795         vals[VD] = Uninitialized;
796       }
797     }
798   }
799 }
800 
801 void TransferFunctions::VisitGCCAsmStmt(GCCAsmStmt *as) {
802   // An "asm goto" statement is a terminator that may initialize some variables.
803   if (!as->isAsmGoto())
804     return;
805 
806   ASTContext &C = ac.getASTContext();
807   for (const Expr *O : as->outputs()) {
808     const Expr *Ex = stripCasts(C, O);
809 
810     // Strip away any unary operators. Invalid l-values are reported by other
811     // semantic analysis passes.
812     while (const auto *UO = dyn_cast<UnaryOperator>(Ex))
813       Ex = stripCasts(C, UO->getSubExpr());
814 
815     // Mark the variable as potentially uninitialized for those cases where
816     // it's used on an indirect path, where it's not guaranteed to be
817     // defined.
818     if (const VarDecl *VD = findVar(Ex).getDecl())
819       if (vals[VD] != Initialized)
820         vals[VD] = MayUninitialized;
821   }
822 }
823 
824 void TransferFunctions::VisitObjCMessageExpr(ObjCMessageExpr *ME) {
825   // If the Objective-C message expression is an implicit no-return that
826   // is not modeled in the CFG, set the tracked dataflow values to Unknown.
827   if (objCNoRet.isImplicitNoReturn(ME)) {
828     vals.setAllScratchValues(Unknown);
829   }
830 }
831 
832 //------------------------------------------------------------------------====//
833 // High-level "driver" logic for uninitialized values analysis.
834 //====------------------------------------------------------------------------//
835 
836 static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
837                        AnalysisDeclContext &ac, CFGBlockValues &vals,
838                        const ClassifyRefs &classification,
839                        llvm::BitVector &wasAnalyzed,
840                        UninitVariablesHandler &handler) {
841   wasAnalyzed[block->getBlockID()] = true;
842   vals.resetScratch();
843   // Merge in values of predecessor blocks.
844   bool isFirst = true;
845   for (CFGBlock::const_pred_iterator I = block->pred_begin(),
846        E = block->pred_end(); I != E; ++I) {
847     const CFGBlock *pred = *I;
848     if (!pred)
849       continue;
850     if (wasAnalyzed[pred->getBlockID()]) {
851       vals.mergeIntoScratch(vals.getValueVector(pred), isFirst);
852       isFirst = false;
853     }
854   }
855   // Apply the transfer function.
856   TransferFunctions tf(vals, cfg, block, ac, classification, handler);
857   for (const auto &I : *block) {
858     if (std::optional<CFGStmt> cs = I.getAs<CFGStmt>())
859       tf.Visit(const_cast<Stmt *>(cs->getStmt()));
860   }
861   CFGTerminator terminator = block->getTerminator();
862   if (auto *as = dyn_cast_or_null<GCCAsmStmt>(terminator.getStmt()))
863     if (as->isAsmGoto())
864       tf.Visit(as);
865   return vals.updateValueVectorWithScratch(block);
866 }
867 
868 namespace {
869 
870 /// PruneBlocksHandler is a special UninitVariablesHandler that is used
871 /// to detect when a CFGBlock has any *potential* use of an uninitialized
872 /// variable.  It is mainly used to prune out work during the final
873 /// reporting pass.
874 struct PruneBlocksHandler : public UninitVariablesHandler {
875   /// Records if a CFGBlock had a potential use of an uninitialized variable.
876   llvm::BitVector hadUse;
877 
878   /// Records if any CFGBlock had a potential use of an uninitialized variable.
879   bool hadAnyUse = false;
880 
881   /// The current block to scribble use information.
882   unsigned currentBlock = 0;
883 
884   PruneBlocksHandler(unsigned numBlocks) : hadUse(numBlocks, false) {}
885 
886   ~PruneBlocksHandler() override = default;
887 
888   void handleUseOfUninitVariable(const VarDecl *vd,
889                                  const UninitUse &use) override {
890     hadUse[currentBlock] = true;
891     hadAnyUse = true;
892   }
893 
894   void handleConstRefUseOfUninitVariable(const VarDecl *vd,
895                                          const UninitUse &use) override {
896     hadUse[currentBlock] = true;
897     hadAnyUse = true;
898   }
899 
900   /// Called when the uninitialized variable analysis detects the
901   /// idiom 'int x = x'.  All other uses of 'x' within the initializer
902   /// are handled by handleUseOfUninitVariable.
903   void handleSelfInit(const VarDecl *vd) override {
904     hadUse[currentBlock] = true;
905     hadAnyUse = true;
906   }
907 };
908 
909 } // namespace
910 
911 void clang::runUninitializedVariablesAnalysis(
912     const DeclContext &dc,
913     const CFG &cfg,
914     AnalysisDeclContext &ac,
915     UninitVariablesHandler &handler,
916     UninitVariablesAnalysisStats &stats) {
917   CFGBlockValues vals(cfg);
918   vals.computeSetOfDeclarations(dc);
919   if (vals.hasNoDeclarations())
920     return;
921 
922   stats.NumVariablesAnalyzed = vals.getNumEntries();
923 
924   // Precompute which expressions are uses and which are initializations.
925   ClassifyRefs classification(ac);
926   cfg.VisitBlockStmts(classification);
927 
928   // Mark all variables uninitialized at the entry.
929   const CFGBlock &entry = cfg.getEntry();
930   ValueVector &vec = vals.getValueVector(&entry);
931   const unsigned n = vals.getNumEntries();
932   for (unsigned j = 0; j < n; ++j) {
933     vec[j] = Uninitialized;
934   }
935 
936   // Proceed with the workist.
937   ForwardDataflowWorklist worklist(cfg, ac);
938   llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
939   worklist.enqueueSuccessors(&cfg.getEntry());
940   llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
941   wasAnalyzed[cfg.getEntry().getBlockID()] = true;
942   PruneBlocksHandler PBH(cfg.getNumBlockIDs());
943 
944   while (const CFGBlock *block = worklist.dequeue()) {
945     PBH.currentBlock = block->getBlockID();
946 
947     // Did the block change?
948     bool changed = runOnBlock(block, cfg, ac, vals,
949                               classification, wasAnalyzed, PBH);
950     ++stats.NumBlockVisits;
951     if (changed || !previouslyVisited[block->getBlockID()])
952       worklist.enqueueSuccessors(block);
953     previouslyVisited[block->getBlockID()] = true;
954   }
955 
956   if (!PBH.hadAnyUse)
957     return;
958 
959   // Run through the blocks one more time, and report uninitialized variables.
960   for (const auto *block : cfg)
961     if (PBH.hadUse[block->getBlockID()]) {
962       runOnBlock(block, cfg, ac, vals, classification, wasAnalyzed, handler);
963       ++stats.NumBlockVisits;
964     }
965 }
966 
967 UninitVariablesHandler::~UninitVariablesHandler() = default;
968