1 //===- CoreEngine.cpp - Path-Sensitive Dataflow Engine --------------------===//
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 defines a generic engine for intraprocedural, path-sensitive,
10 //  dataflow analysis via graph reachability engine.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "clang/StaticAnalyzer/Core/PathSensitive/CoreEngine.h"
15 #include "clang/AST/Expr.h"
16 #include "clang/AST/ExprCXX.h"
17 #include "clang/AST/Stmt.h"
18 #include "clang/AST/StmtCXX.h"
19 #include "clang/Analysis/AnalysisDeclContext.h"
20 #include "clang/Analysis/CFG.h"
21 #include "clang/Analysis/ProgramPoint.h"
22 #include "clang/Basic/LLVM.h"
23 #include "clang/StaticAnalyzer/Core/AnalyzerOptions.h"
24 #include "clang/StaticAnalyzer/Core/PathSensitive/BlockCounter.h"
25 #include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
26 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
27 #include "clang/StaticAnalyzer/Core/PathSensitive/FunctionSummary.h"
28 #include "clang/StaticAnalyzer/Core/PathSensitive/WorkList.h"
29 #include "llvm/ADT/Optional.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/Support/Casting.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include <algorithm>
35 #include <cassert>
36 #include <memory>
37 #include <utility>
38 
39 using namespace clang;
40 using namespace ento;
41 
42 #define DEBUG_TYPE "CoreEngine"
43 
44 STATISTIC(NumSteps,
45             "The # of steps executed.");
46 STATISTIC(NumSTUSteps, "The # of STU steps executed.");
47 STATISTIC(NumCTUSteps, "The # of CTU steps executed.");
48 STATISTIC(NumReachedMaxSteps,
49             "The # of times we reached the max number of steps.");
50 STATISTIC(NumPathsExplored,
51             "The # of paths explored by the analyzer.");
52 
53 //===----------------------------------------------------------------------===//
54 // Core analysis engine.
55 //===----------------------------------------------------------------------===//
56 
57 static std::unique_ptr<WorkList> generateWorkList(AnalyzerOptions &Opts) {
58   switch (Opts.getExplorationStrategy()) {
59     case ExplorationStrategyKind::DFS:
60       return WorkList::makeDFS();
61     case ExplorationStrategyKind::BFS:
62       return WorkList::makeBFS();
63     case ExplorationStrategyKind::BFSBlockDFSContents:
64       return WorkList::makeBFSBlockDFSContents();
65     case ExplorationStrategyKind::UnexploredFirst:
66       return WorkList::makeUnexploredFirst();
67     case ExplorationStrategyKind::UnexploredFirstQueue:
68       return WorkList::makeUnexploredFirstPriorityQueue();
69     case ExplorationStrategyKind::UnexploredFirstLocationQueue:
70       return WorkList::makeUnexploredFirstPriorityLocationQueue();
71   }
72   llvm_unreachable("Unknown AnalyzerOptions::ExplorationStrategyKind");
73 }
74 
75 CoreEngine::CoreEngine(ExprEngine &exprengine, FunctionSummariesTy *FS,
76                        AnalyzerOptions &Opts)
77     : ExprEng(exprengine), WList(generateWorkList(Opts)),
78       CTUWList(Opts.IsNaiveCTUEnabled ? generateWorkList(Opts) : nullptr),
79       BCounterFactory(G.getAllocator()), FunctionSummaries(FS) {}
80 
81 void CoreEngine::setBlockCounter(BlockCounter C) {
82   WList->setBlockCounter(C);
83   if (CTUWList)
84     CTUWList->setBlockCounter(C);
85 }
86 
87 /// ExecuteWorkList - Run the worklist algorithm for a maximum number of steps.
88 bool CoreEngine::ExecuteWorkList(const LocationContext *L, unsigned MaxSteps,
89                                  ProgramStateRef InitState) {
90   if (G.num_roots() == 0) { // Initialize the analysis by constructing
91     // the root if none exists.
92 
93     const CFGBlock *Entry = &(L->getCFG()->getEntry());
94 
95     assert(Entry->empty() && "Entry block must be empty.");
96 
97     assert(Entry->succ_size() == 1 && "Entry block must have 1 successor.");
98 
99     // Mark the entry block as visited.
100     FunctionSummaries->markVisitedBasicBlock(Entry->getBlockID(),
101                                              L->getDecl(),
102                                              L->getCFG()->getNumBlockIDs());
103 
104     // Get the solitary successor.
105     const CFGBlock *Succ = *(Entry->succ_begin());
106 
107     // Construct an edge representing the
108     // starting location in the function.
109     BlockEdge StartLoc(Entry, Succ, L);
110 
111     // Set the current block counter to being empty.
112     setBlockCounter(BCounterFactory.GetEmptyCounter());
113 
114     if (!InitState)
115       InitState = ExprEng.getInitialState(L);
116 
117     bool IsNew;
118     ExplodedNode *Node = G.getNode(StartLoc, InitState, false, &IsNew);
119     assert(IsNew);
120     G.addRoot(Node);
121 
122     NodeBuilderContext BuilderCtx(*this, StartLoc.getDst(), Node);
123     ExplodedNodeSet DstBegin;
124     ExprEng.processBeginOfFunction(BuilderCtx, Node, DstBegin, StartLoc);
125 
126     enqueue(DstBegin);
127   }
128 
129   // Check if we have a steps limit
130   bool UnlimitedSteps = MaxSteps == 0;
131 
132   // Cap our pre-reservation in the event that the user specifies
133   // a very large number of maximum steps.
134   const unsigned PreReservationCap = 4000000;
135   if(!UnlimitedSteps)
136     G.reserve(std::min(MaxSteps, PreReservationCap));
137 
138   auto ProcessWList = [this, UnlimitedSteps](unsigned MaxSteps) {
139     unsigned Steps = MaxSteps;
140     while (WList->hasWork()) {
141       if (!UnlimitedSteps) {
142         if (Steps == 0) {
143           NumReachedMaxSteps++;
144           break;
145         }
146         --Steps;
147       }
148 
149       NumSteps++;
150 
151       const WorkListUnit &WU = WList->dequeue();
152 
153       // Set the current block counter.
154       setBlockCounter(WU.getBlockCounter());
155 
156       // Retrieve the node.
157       ExplodedNode *Node = WU.getNode();
158 
159       dispatchWorkItem(Node, Node->getLocation(), WU);
160     }
161     return MaxSteps - Steps;
162   };
163   const unsigned STUSteps = ProcessWList(MaxSteps);
164 
165   if (CTUWList) {
166     NumSTUSteps += STUSteps;
167     const unsigned MinCTUSteps =
168         this->ExprEng.getAnalysisManager().options.CTUMaxNodesMin;
169     const unsigned Pct =
170         this->ExprEng.getAnalysisManager().options.CTUMaxNodesPercentage;
171     unsigned MaxCTUSteps = std::max(STUSteps * Pct / 100, MinCTUSteps);
172 
173     WList = std::move(CTUWList);
174     const unsigned CTUSteps = ProcessWList(MaxCTUSteps);
175     NumCTUSteps += CTUSteps;
176   }
177 
178   ExprEng.processEndWorklist();
179   return WList->hasWork();
180 }
181 
182 void CoreEngine::dispatchWorkItem(ExplodedNode* Pred, ProgramPoint Loc,
183                                   const WorkListUnit& WU) {
184   // Dispatch on the location type.
185   switch (Loc.getKind()) {
186     case ProgramPoint::BlockEdgeKind:
187       HandleBlockEdge(Loc.castAs<BlockEdge>(), Pred);
188       break;
189 
190     case ProgramPoint::BlockEntranceKind:
191       HandleBlockEntrance(Loc.castAs<BlockEntrance>(), Pred);
192       break;
193 
194     case ProgramPoint::BlockExitKind:
195       assert(false && "BlockExit location never occur in forward analysis.");
196       break;
197 
198     case ProgramPoint::CallEnterKind:
199       HandleCallEnter(Loc.castAs<CallEnter>(), Pred);
200       break;
201 
202     case ProgramPoint::CallExitBeginKind:
203       ExprEng.processCallExit(Pred);
204       break;
205 
206     case ProgramPoint::EpsilonKind: {
207       assert(Pred->hasSinglePred() &&
208              "Assume epsilon has exactly one predecessor by construction");
209       ExplodedNode *PNode = Pred->getFirstPred();
210       dispatchWorkItem(Pred, PNode->getLocation(), WU);
211       break;
212     }
213     default:
214       assert(Loc.getAs<PostStmt>() ||
215              Loc.getAs<PostInitializer>() ||
216              Loc.getAs<PostImplicitCall>() ||
217              Loc.getAs<CallExitEnd>() ||
218              Loc.getAs<LoopExit>() ||
219              Loc.getAs<PostAllocatorCall>());
220       HandlePostStmt(WU.getBlock(), WU.getIndex(), Pred);
221       break;
222   }
223 }
224 
225 bool CoreEngine::ExecuteWorkListWithInitialState(const LocationContext *L,
226                                                  unsigned Steps,
227                                                  ProgramStateRef InitState,
228                                                  ExplodedNodeSet &Dst) {
229   bool DidNotFinish = ExecuteWorkList(L, Steps, InitState);
230   for (ExplodedGraph::eop_iterator I = G.eop_begin(), E = G.eop_end(); I != E;
231        ++I) {
232     Dst.Add(*I);
233   }
234   return DidNotFinish;
235 }
236 
237 void CoreEngine::HandleBlockEdge(const BlockEdge &L, ExplodedNode *Pred) {
238   const CFGBlock *Blk = L.getDst();
239   NodeBuilderContext BuilderCtx(*this, Blk, Pred);
240 
241   // Mark this block as visited.
242   const LocationContext *LC = Pred->getLocationContext();
243   FunctionSummaries->markVisitedBasicBlock(Blk->getBlockID(),
244                                            LC->getDecl(),
245                                            LC->getCFG()->getNumBlockIDs());
246 
247   // Display a prunable path note to the user if it's a virtual bases branch
248   // and we're taking the path that skips virtual base constructors.
249   if (L.getSrc()->getTerminator().isVirtualBaseBranch() &&
250       L.getDst() == *L.getSrc()->succ_begin()) {
251     ProgramPoint P = L.withTag(getDataTags().make<NoteTag>(
252         [](BugReporterContext &, PathSensitiveBugReport &) -> std::string {
253           // TODO: Just call out the name of the most derived class
254           // when we know it.
255           return "Virtual base initialization skipped because "
256                  "it has already been handled by the most derived class";
257         },
258         /*IsPrunable=*/true));
259     // Perform the transition.
260     ExplodedNodeSet Dst;
261     NodeBuilder Bldr(Pred, Dst, BuilderCtx);
262     Pred = Bldr.generateNode(P, Pred->getState(), Pred);
263     if (!Pred)
264       return;
265   }
266 
267   // Check if we are entering the EXIT block.
268   if (Blk == &(L.getLocationContext()->getCFG()->getExit())) {
269     assert(L.getLocationContext()->getCFG()->getExit().empty() &&
270            "EXIT block cannot contain Stmts.");
271 
272     // Get return statement..
273     const ReturnStmt *RS = nullptr;
274     if (!L.getSrc()->empty()) {
275       CFGElement LastElement = L.getSrc()->back();
276       if (Optional<CFGStmt> LastStmt = LastElement.getAs<CFGStmt>()) {
277         RS = dyn_cast<ReturnStmt>(LastStmt->getStmt());
278       } else if (Optional<CFGAutomaticObjDtor> AutoDtor =
279                  LastElement.getAs<CFGAutomaticObjDtor>()) {
280         RS = dyn_cast<ReturnStmt>(AutoDtor->getTriggerStmt());
281       }
282     }
283 
284     // Process the final state transition.
285     ExprEng.processEndOfFunction(BuilderCtx, Pred, RS);
286 
287     // This path is done. Don't enqueue any more nodes.
288     return;
289   }
290 
291   // Call into the ExprEngine to process entering the CFGBlock.
292   ExplodedNodeSet dstNodes;
293   BlockEntrance BE(Blk, Pred->getLocationContext());
294   NodeBuilderWithSinks nodeBuilder(Pred, dstNodes, BuilderCtx, BE);
295   ExprEng.processCFGBlockEntrance(L, nodeBuilder, Pred);
296 
297   // Auto-generate a node.
298   if (!nodeBuilder.hasGeneratedNodes()) {
299     nodeBuilder.generateNode(Pred->State, Pred);
300   }
301 
302   // Enqueue nodes onto the worklist.
303   enqueue(dstNodes);
304 }
305 
306 void CoreEngine::HandleBlockEntrance(const BlockEntrance &L,
307                                        ExplodedNode *Pred) {
308   // Increment the block counter.
309   const LocationContext *LC = Pred->getLocationContext();
310   unsigned BlockId = L.getBlock()->getBlockID();
311   BlockCounter Counter = WList->getBlockCounter();
312   Counter = BCounterFactory.IncrementCount(Counter, LC->getStackFrame(),
313                                            BlockId);
314   setBlockCounter(Counter);
315 
316   // Process the entrance of the block.
317   if (Optional<CFGElement> E = L.getFirstElement()) {
318     NodeBuilderContext Ctx(*this, L.getBlock(), Pred);
319     ExprEng.processCFGElement(*E, Pred, 0, &Ctx);
320   }
321   else
322     HandleBlockExit(L.getBlock(), Pred);
323 }
324 
325 void CoreEngine::HandleBlockExit(const CFGBlock * B, ExplodedNode *Pred) {
326   if (const Stmt *Term = B->getTerminatorStmt()) {
327     switch (Term->getStmtClass()) {
328       default:
329         llvm_unreachable("Analysis for this terminator not implemented.");
330 
331       case Stmt::CXXBindTemporaryExprClass:
332         HandleCleanupTemporaryBranch(
333             cast<CXXBindTemporaryExpr>(Term), B, Pred);
334         return;
335 
336       // Model static initializers.
337       case Stmt::DeclStmtClass:
338         HandleStaticInit(cast<DeclStmt>(Term), B, Pred);
339         return;
340 
341       case Stmt::BinaryOperatorClass: // '&&' and '||'
342         HandleBranch(cast<BinaryOperator>(Term)->getLHS(), Term, B, Pred);
343         return;
344 
345       case Stmt::BinaryConditionalOperatorClass:
346       case Stmt::ConditionalOperatorClass:
347         HandleBranch(cast<AbstractConditionalOperator>(Term)->getCond(),
348                      Term, B, Pred);
349         return;
350 
351         // FIXME: Use constant-folding in CFG construction to simplify this
352         // case.
353 
354       case Stmt::ChooseExprClass:
355         HandleBranch(cast<ChooseExpr>(Term)->getCond(), Term, B, Pred);
356         return;
357 
358       case Stmt::CXXTryStmtClass:
359         // Generate a node for each of the successors.
360         // Our logic for EH analysis can certainly be improved.
361         for (CFGBlock::const_succ_iterator it = B->succ_begin(),
362              et = B->succ_end(); it != et; ++it) {
363           if (const CFGBlock *succ = *it) {
364             generateNode(BlockEdge(B, succ, Pred->getLocationContext()),
365                          Pred->State, Pred);
366           }
367         }
368         return;
369 
370       case Stmt::DoStmtClass:
371         HandleBranch(cast<DoStmt>(Term)->getCond(), Term, B, Pred);
372         return;
373 
374       case Stmt::CXXForRangeStmtClass:
375         HandleBranch(cast<CXXForRangeStmt>(Term)->getCond(), Term, B, Pred);
376         return;
377 
378       case Stmt::ForStmtClass:
379         HandleBranch(cast<ForStmt>(Term)->getCond(), Term, B, Pred);
380         return;
381 
382       case Stmt::SEHLeaveStmtClass:
383       case Stmt::ContinueStmtClass:
384       case Stmt::BreakStmtClass:
385       case Stmt::GotoStmtClass:
386         break;
387 
388       case Stmt::IfStmtClass:
389         HandleBranch(cast<IfStmt>(Term)->getCond(), Term, B, Pred);
390         return;
391 
392       case Stmt::IndirectGotoStmtClass: {
393         // Only 1 successor: the indirect goto dispatch block.
394         assert(B->succ_size() == 1);
395 
396         IndirectGotoNodeBuilder
397            builder(Pred, B, cast<IndirectGotoStmt>(Term)->getTarget(),
398                    *(B->succ_begin()), this);
399 
400         ExprEng.processIndirectGoto(builder);
401         return;
402       }
403 
404       case Stmt::ObjCForCollectionStmtClass:
405         // In the case of ObjCForCollectionStmt, it appears twice in a CFG:
406         //
407         //  (1) inside a basic block, which represents the binding of the
408         //      'element' variable to a value.
409         //  (2) in a terminator, which represents the branch.
410         //
411         // For (1), ExprEngine will bind a value (i.e., 0 or 1) indicating
412         // whether or not collection contains any more elements.  We cannot
413         // just test to see if the element is nil because a container can
414         // contain nil elements.
415         HandleBranch(Term, Term, B, Pred);
416         return;
417 
418       case Stmt::SwitchStmtClass: {
419         SwitchNodeBuilder builder(Pred, B, cast<SwitchStmt>(Term)->getCond(),
420                                     this);
421 
422         ExprEng.processSwitch(builder);
423         return;
424       }
425 
426       case Stmt::WhileStmtClass:
427         HandleBranch(cast<WhileStmt>(Term)->getCond(), Term, B, Pred);
428         return;
429 
430       case Stmt::GCCAsmStmtClass:
431         assert(cast<GCCAsmStmt>(Term)->isAsmGoto() && "Encountered GCCAsmStmt without labels");
432         // TODO: Handle jumping to labels
433         return;
434     }
435   }
436 
437   if (B->getTerminator().isVirtualBaseBranch()) {
438     HandleVirtualBaseBranch(B, Pred);
439     return;
440   }
441 
442   assert(B->succ_size() == 1 &&
443          "Blocks with no terminator should have at most 1 successor.");
444 
445   generateNode(BlockEdge(B, *(B->succ_begin()), Pred->getLocationContext()),
446                Pred->State, Pred);
447 }
448 
449 void CoreEngine::HandleCallEnter(const CallEnter &CE, ExplodedNode *Pred) {
450   NodeBuilderContext BuilderCtx(*this, CE.getEntry(), Pred);
451   ExprEng.processCallEnter(BuilderCtx, CE, Pred);
452 }
453 
454 void CoreEngine::HandleBranch(const Stmt *Cond, const Stmt *Term,
455                                 const CFGBlock * B, ExplodedNode *Pred) {
456   assert(B->succ_size() == 2);
457   NodeBuilderContext Ctx(*this, B, Pred);
458   ExplodedNodeSet Dst;
459   ExprEng.processBranch(Cond, Ctx, Pred, Dst, *(B->succ_begin()),
460                        *(B->succ_begin() + 1));
461   // Enqueue the new frontier onto the worklist.
462   enqueue(Dst);
463 }
464 
465 void CoreEngine::HandleCleanupTemporaryBranch(const CXXBindTemporaryExpr *BTE,
466                                               const CFGBlock *B,
467                                               ExplodedNode *Pred) {
468   assert(B->succ_size() == 2);
469   NodeBuilderContext Ctx(*this, B, Pred);
470   ExplodedNodeSet Dst;
471   ExprEng.processCleanupTemporaryBranch(BTE, Ctx, Pred, Dst, *(B->succ_begin()),
472                                        *(B->succ_begin() + 1));
473   // Enqueue the new frontier onto the worklist.
474   enqueue(Dst);
475 }
476 
477 void CoreEngine::HandleStaticInit(const DeclStmt *DS, const CFGBlock *B,
478                                   ExplodedNode *Pred) {
479   assert(B->succ_size() == 2);
480   NodeBuilderContext Ctx(*this, B, Pred);
481   ExplodedNodeSet Dst;
482   ExprEng.processStaticInitializer(DS, Ctx, Pred, Dst,
483                                   *(B->succ_begin()), *(B->succ_begin()+1));
484   // Enqueue the new frontier onto the worklist.
485   enqueue(Dst);
486 }
487 
488 void CoreEngine::HandlePostStmt(const CFGBlock *B, unsigned StmtIdx,
489                                 ExplodedNode *Pred) {
490   assert(B);
491   assert(!B->empty());
492 
493   if (StmtIdx == B->size())
494     HandleBlockExit(B, Pred);
495   else {
496     NodeBuilderContext Ctx(*this, B, Pred);
497     ExprEng.processCFGElement((*B)[StmtIdx], Pred, StmtIdx, &Ctx);
498   }
499 }
500 
501 void CoreEngine::HandleVirtualBaseBranch(const CFGBlock *B,
502                                          ExplodedNode *Pred) {
503   const LocationContext *LCtx = Pred->getLocationContext();
504   if (const auto *CallerCtor = dyn_cast_or_null<CXXConstructExpr>(
505           LCtx->getStackFrame()->getCallSite())) {
506     switch (CallerCtor->getConstructionKind()) {
507     case CXXConstructExpr::CK_NonVirtualBase:
508     case CXXConstructExpr::CK_VirtualBase: {
509       BlockEdge Loc(B, *B->succ_begin(), LCtx);
510       HandleBlockEdge(Loc, Pred);
511       return;
512     }
513     default:
514       break;
515     }
516   }
517 
518   // We either don't see a parent stack frame because we're in the top frame,
519   // or the parent stack frame doesn't initialize our virtual bases.
520   BlockEdge Loc(B, *(B->succ_begin() + 1), LCtx);
521   HandleBlockEdge(Loc, Pred);
522 }
523 
524 /// generateNode - Utility method to generate nodes, hook up successors,
525 ///  and add nodes to the worklist.
526 void CoreEngine::generateNode(const ProgramPoint &Loc,
527                               ProgramStateRef State,
528                               ExplodedNode *Pred) {
529   bool IsNew;
530   ExplodedNode *Node = G.getNode(Loc, State, false, &IsNew);
531 
532   if (Pred)
533     Node->addPredecessor(Pred, G); // Link 'Node' with its predecessor.
534   else {
535     assert(IsNew);
536     G.addRoot(Node); // 'Node' has no predecessor.  Make it a root.
537   }
538 
539   // Only add 'Node' to the worklist if it was freshly generated.
540   if (IsNew) WList->enqueue(Node);
541 }
542 
543 void CoreEngine::enqueueStmtNode(ExplodedNode *N,
544                                  const CFGBlock *Block, unsigned Idx) {
545   assert(Block);
546   assert(!N->isSink());
547 
548   // Check if this node entered a callee.
549   if (N->getLocation().getAs<CallEnter>()) {
550     // Still use the index of the CallExpr. It's needed to create the callee
551     // StackFrameContext.
552     WList->enqueue(N, Block, Idx);
553     return;
554   }
555 
556   // Do not create extra nodes. Move to the next CFG element.
557   if (N->getLocation().getAs<PostInitializer>() ||
558       N->getLocation().getAs<PostImplicitCall>()||
559       N->getLocation().getAs<LoopExit>()) {
560     WList->enqueue(N, Block, Idx+1);
561     return;
562   }
563 
564   if (N->getLocation().getAs<EpsilonPoint>()) {
565     WList->enqueue(N, Block, Idx);
566     return;
567   }
568 
569   if ((*Block)[Idx].getKind() == CFGElement::NewAllocator) {
570     WList->enqueue(N, Block, Idx+1);
571     return;
572   }
573 
574   // At this point, we know we're processing a normal statement.
575   CFGStmt CS = (*Block)[Idx].castAs<CFGStmt>();
576   PostStmt Loc(CS.getStmt(), N->getLocationContext());
577 
578   if (Loc == N->getLocation().withTag(nullptr)) {
579     // Note: 'N' should be a fresh node because otherwise it shouldn't be
580     // a member of Deferred.
581     WList->enqueue(N, Block, Idx+1);
582     return;
583   }
584 
585   bool IsNew;
586   ExplodedNode *Succ = G.getNode(Loc, N->getState(), false, &IsNew);
587   Succ->addPredecessor(N, G);
588 
589   if (IsNew)
590     WList->enqueue(Succ, Block, Idx+1);
591 }
592 
593 ExplodedNode *CoreEngine::generateCallExitBeginNode(ExplodedNode *N,
594                                                     const ReturnStmt *RS) {
595   // Create a CallExitBegin node and enqueue it.
596   const auto *LocCtx = cast<StackFrameContext>(N->getLocationContext());
597 
598   // Use the callee location context.
599   CallExitBegin Loc(LocCtx, RS);
600 
601   bool isNew;
602   ExplodedNode *Node = G.getNode(Loc, N->getState(), false, &isNew);
603   Node->addPredecessor(N, G);
604   return isNew ? Node : nullptr;
605 }
606 
607 void CoreEngine::enqueue(ExplodedNodeSet &Set) {
608   for (const auto I : Set)
609     WList->enqueue(I);
610 }
611 
612 void CoreEngine::enqueue(ExplodedNodeSet &Set,
613                          const CFGBlock *Block, unsigned Idx) {
614   for (const auto I : Set)
615     enqueueStmtNode(I, Block, Idx);
616 }
617 
618 void CoreEngine::enqueueEndOfFunction(ExplodedNodeSet &Set, const ReturnStmt *RS) {
619   for (auto I : Set) {
620     // If we are in an inlined call, generate CallExitBegin node.
621     if (I->getLocationContext()->getParent()) {
622       I = generateCallExitBeginNode(I, RS);
623       if (I)
624         WList->enqueue(I);
625     } else {
626       // TODO: We should run remove dead bindings here.
627       G.addEndOfPath(I);
628       NumPathsExplored++;
629     }
630   }
631 }
632 
633 void NodeBuilder::anchor() {}
634 
635 ExplodedNode* NodeBuilder::generateNodeImpl(const ProgramPoint &Loc,
636                                             ProgramStateRef State,
637                                             ExplodedNode *FromN,
638                                             bool MarkAsSink) {
639   HasGeneratedNodes = true;
640   bool IsNew;
641   ExplodedNode *N = C.Eng.G.getNode(Loc, State, MarkAsSink, &IsNew);
642   N->addPredecessor(FromN, C.Eng.G);
643   Frontier.erase(FromN);
644 
645   if (!IsNew)
646     return nullptr;
647 
648   if (!MarkAsSink)
649     Frontier.Add(N);
650 
651   return N;
652 }
653 
654 void NodeBuilderWithSinks::anchor() {}
655 
656 StmtNodeBuilder::~StmtNodeBuilder() {
657   if (EnclosingBldr)
658     for (const auto I : Frontier)
659       EnclosingBldr->addNodes(I);
660 }
661 
662 void BranchNodeBuilder::anchor() {}
663 
664 ExplodedNode *BranchNodeBuilder::generateNode(ProgramStateRef State,
665                                               bool branch,
666                                               ExplodedNode *NodePred) {
667   // If the branch has been marked infeasible we should not generate a node.
668   if (!isFeasible(branch))
669     return nullptr;
670 
671   ProgramPoint Loc = BlockEdge(C.Block, branch ? DstT:DstF,
672                                NodePred->getLocationContext());
673   ExplodedNode *Succ = generateNodeImpl(Loc, State, NodePred);
674   return Succ;
675 }
676 
677 ExplodedNode*
678 IndirectGotoNodeBuilder::generateNode(const iterator &I,
679                                       ProgramStateRef St,
680                                       bool IsSink) {
681   bool IsNew;
682   ExplodedNode *Succ =
683       Eng.G.getNode(BlockEdge(Src, I.getBlock(), Pred->getLocationContext()),
684                     St, IsSink, &IsNew);
685   Succ->addPredecessor(Pred, Eng.G);
686 
687   if (!IsNew)
688     return nullptr;
689 
690   if (!IsSink)
691     Eng.WList->enqueue(Succ);
692 
693   return Succ;
694 }
695 
696 ExplodedNode*
697 SwitchNodeBuilder::generateCaseStmtNode(const iterator &I,
698                                         ProgramStateRef St) {
699   bool IsNew;
700   ExplodedNode *Succ =
701       Eng.G.getNode(BlockEdge(Src, I.getBlock(), Pred->getLocationContext()),
702                     St, false, &IsNew);
703   Succ->addPredecessor(Pred, Eng.G);
704   if (!IsNew)
705     return nullptr;
706 
707   Eng.WList->enqueue(Succ);
708   return Succ;
709 }
710 
711 ExplodedNode*
712 SwitchNodeBuilder::generateDefaultCaseNode(ProgramStateRef St,
713                                            bool IsSink) {
714   // Get the block for the default case.
715   assert(Src->succ_rbegin() != Src->succ_rend());
716   CFGBlock *DefaultBlock = *Src->succ_rbegin();
717 
718   // Basic correctness check for default blocks that are unreachable and not
719   // caught by earlier stages.
720   if (!DefaultBlock)
721     return nullptr;
722 
723   bool IsNew;
724   ExplodedNode *Succ =
725       Eng.G.getNode(BlockEdge(Src, DefaultBlock, Pred->getLocationContext()),
726                     St, IsSink, &IsNew);
727   Succ->addPredecessor(Pred, Eng.G);
728 
729   if (!IsNew)
730     return nullptr;
731 
732   if (!IsSink)
733     Eng.WList->enqueue(Succ);
734 
735   return Succ;
736 }
737