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