CoreEngine.cpp revision 239462 
1//==- CoreEngine.cpp - Path-Sensitive Dataflow Engine ------------*- C++ -*-//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10//  This file defines a generic engine for intraprocedural, path-sensitive,
11//  dataflow analysis via graph reachability engine.
12//
13//===----------------------------------------------------------------------===//
14
15#define DEBUG_TYPE "CoreEngine"
16
17#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/CoreEngine.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
20#include "clang/AST/Expr.h"
21#include "clang/AST/StmtCXX.h"
22#include "llvm/Support/Casting.h"
23#include "llvm/ADT/DenseMap.h"
24#include "llvm/ADT/Statistic.h"
25
26using namespace clang;
27using namespace ento;
28
29STATISTIC(NumSteps,
30            "The # of steps executed.");
31STATISTIC(NumReachedMaxSteps,
32            "The # of times we reached the max number of steps.");
33STATISTIC(NumPathsExplored,
34            "The # of paths explored by the analyzer.");
35
36//===----------------------------------------------------------------------===//
37// Worklist classes for exploration of reachable states.
38//===----------------------------------------------------------------------===//
39
40WorkList::Visitor::~Visitor() {}
41
42namespace {
43class DFS : public WorkList {
44  SmallVector<WorkListUnit,20> Stack;
45public:
46  virtual bool hasWork() const {
47    return !Stack.empty();
48  }
49
50  virtual void enqueue(const WorkListUnit& U) {
51    Stack.push_back(U);
52  }
53
54  virtual WorkListUnit dequeue() {
55    assert (!Stack.empty());
56    const WorkListUnit& U = Stack.back();
57    Stack.pop_back(); // This technically "invalidates" U, but we are fine.
58    return U;
59  }
60
61  virtual bool visitItemsInWorkList(Visitor &V) {
62    for (SmallVectorImpl<WorkListUnit>::iterator
63         I = Stack.begin(), E = Stack.end(); I != E; ++I) {
64      if (V.visit(*I))
65        return true;
66    }
67    return false;
68  }
69};
70
71class BFS : public WorkList {
72  std::deque<WorkListUnit> Queue;
73public:
74  virtual bool hasWork() const {
75    return !Queue.empty();
76  }
77
78  virtual void enqueue(const WorkListUnit& U) {
79    Queue.push_back(U);
80  }
81
82  virtual WorkListUnit dequeue() {
83    WorkListUnit U = Queue.front();
84    Queue.pop_front();
85    return U;
86  }
87
88  virtual bool visitItemsInWorkList(Visitor &V) {
89    for (std::deque<WorkListUnit>::iterator
90         I = Queue.begin(), E = Queue.end(); I != E; ++I) {
91      if (V.visit(*I))
92        return true;
93    }
94    return false;
95  }
96};
97
98} // end anonymous namespace
99
100// Place the dstor for WorkList here because it contains virtual member
101// functions, and we the code for the dstor generated in one compilation unit.
102WorkList::~WorkList() {}
103
104WorkList *WorkList::makeDFS() { return new DFS(); }
105WorkList *WorkList::makeBFS() { return new BFS(); }
106
107namespace {
108  class BFSBlockDFSContents : public WorkList {
109    std::deque<WorkListUnit> Queue;
110    SmallVector<WorkListUnit,20> Stack;
111  public:
112    virtual bool hasWork() const {
113      return !Queue.empty() || !Stack.empty();
114    }
115
116    virtual void enqueue(const WorkListUnit& U) {
117      if (isa<BlockEntrance>(U.getNode()->getLocation()))
118        Queue.push_front(U);
119      else
120        Stack.push_back(U);
121    }
122
123    virtual WorkListUnit dequeue() {
124      // Process all basic blocks to completion.
125      if (!Stack.empty()) {
126        const WorkListUnit& U = Stack.back();
127        Stack.pop_back(); // This technically "invalidates" U, but we are fine.
128        return U;
129      }
130
131      assert(!Queue.empty());
132      // Don't use const reference.  The subsequent pop_back() might make it
133      // unsafe.
134      WorkListUnit U = Queue.front();
135      Queue.pop_front();
136      return U;
137    }
138    virtual bool visitItemsInWorkList(Visitor &V) {
139      for (SmallVectorImpl<WorkListUnit>::iterator
140           I = Stack.begin(), E = Stack.end(); I != E; ++I) {
141        if (V.visit(*I))
142          return true;
143      }
144      for (std::deque<WorkListUnit>::iterator
145           I = Queue.begin(), E = Queue.end(); I != E; ++I) {
146        if (V.visit(*I))
147          return true;
148      }
149      return false;
150    }
151
152  };
153} // end anonymous namespace
154
155WorkList* WorkList::makeBFSBlockDFSContents() {
156  return new BFSBlockDFSContents();
157}
158
159//===----------------------------------------------------------------------===//
160// Core analysis engine.
161//===----------------------------------------------------------------------===//
162
163/// ExecuteWorkList - Run the worklist algorithm for a maximum number of steps.
164bool CoreEngine::ExecuteWorkList(const LocationContext *L, unsigned Steps,
165                                   ProgramStateRef InitState) {
166
167  if (G->num_roots() == 0) { // Initialize the analysis by constructing
168    // the root if none exists.
169
170    const CFGBlock *Entry = &(L->getCFG()->getEntry());
171
172    assert (Entry->empty() &&
173            "Entry block must be empty.");
174
175    assert (Entry->succ_size() == 1 &&
176            "Entry block must have 1 successor.");
177
178    // Mark the entry block as visited.
179    FunctionSummaries->markVisitedBasicBlock(Entry->getBlockID(),
180                                             L->getDecl(),
181                                             L->getCFG()->getNumBlockIDs());
182
183    // Get the solitary successor.
184    const CFGBlock *Succ = *(Entry->succ_begin());
185
186    // Construct an edge representing the
187    // starting location in the function.
188    BlockEdge StartLoc(Entry, Succ, L);
189
190    // Set the current block counter to being empty.
191    WList->setBlockCounter(BCounterFactory.GetEmptyCounter());
192
193    if (!InitState)
194      // Generate the root.
195      generateNode(StartLoc, SubEng.getInitialState(L), 0);
196    else
197      generateNode(StartLoc, InitState, 0);
198  }
199
200  // Check if we have a steps limit
201  bool UnlimitedSteps = Steps == 0;
202
203  while (WList->hasWork()) {
204    if (!UnlimitedSteps) {
205      if (Steps == 0) {
206        NumReachedMaxSteps++;
207        break;
208      }
209      --Steps;
210    }
211
212    NumSteps++;
213
214    const WorkListUnit& WU = WList->dequeue();
215
216    // Set the current block counter.
217    WList->setBlockCounter(WU.getBlockCounter());
218
219    // Retrieve the node.
220    ExplodedNode *Node = WU.getNode();
221
222    dispatchWorkItem(Node, Node->getLocation(), WU);
223  }
224  SubEng.processEndWorklist(hasWorkRemaining());
225  return WList->hasWork();
226}
227
228void CoreEngine::dispatchWorkItem(ExplodedNode* Pred, ProgramPoint Loc,
229                                  const WorkListUnit& WU) {
230  // Dispatch on the location type.
231  switch (Loc.getKind()) {
232    case ProgramPoint::BlockEdgeKind:
233      HandleBlockEdge(cast<BlockEdge>(Loc), Pred);
234      break;
235
236    case ProgramPoint::BlockEntranceKind:
237      HandleBlockEntrance(cast<BlockEntrance>(Loc), Pred);
238      break;
239
240    case ProgramPoint::BlockExitKind:
241      assert (false && "BlockExit location never occur in forward analysis.");
242      break;
243
244    case ProgramPoint::CallEnterKind: {
245      CallEnter CEnter = cast<CallEnter>(Loc);
246      if (AnalyzedCallees)
247        if (const CallExpr* CE =
248            dyn_cast_or_null<CallExpr>(CEnter.getCallExpr()))
249          if (const Decl *CD = CE->getCalleeDecl())
250            AnalyzedCallees->insert(CD);
251      SubEng.processCallEnter(CEnter, Pred);
252      break;
253    }
254
255    case ProgramPoint::CallExitBeginKind:
256      SubEng.processCallExit(Pred);
257      break;
258
259    case ProgramPoint::EpsilonKind: {
260      assert(Pred->hasSinglePred() &&
261             "Assume epsilon has exactly one predecessor by construction");
262      ExplodedNode *PNode = Pred->getFirstPred();
263      dispatchWorkItem(Pred, PNode->getLocation(), WU);
264      break;
265    }
266    default:
267      assert(isa<PostStmt>(Loc) ||
268             isa<PostInitializer>(Loc) ||
269             isa<PostImplicitCall>(Loc) ||
270             isa<CallExitEnd>(Loc));
271      HandlePostStmt(WU.getBlock(), WU.getIndex(), Pred);
272      break;
273  }
274}
275
276bool CoreEngine::ExecuteWorkListWithInitialState(const LocationContext *L,
277                                                 unsigned Steps,
278                                                 ProgramStateRef InitState,
279                                                 ExplodedNodeSet &Dst) {
280  bool DidNotFinish = ExecuteWorkList(L, Steps, InitState);
281  for (ExplodedGraph::eop_iterator I = G->eop_begin(),
282                                   E = G->eop_end(); I != E; ++I) {
283    Dst.Add(*I);
284  }
285  return DidNotFinish;
286}
287
288void CoreEngine::HandleBlockEdge(const BlockEdge &L, ExplodedNode *Pred) {
289
290  const CFGBlock *Blk = L.getDst();
291  NodeBuilderContext BuilderCtx(*this, Blk, Pred);
292
293  // Mark this block as visited.
294  const LocationContext *LC = Pred->getLocationContext();
295  FunctionSummaries->markVisitedBasicBlock(Blk->getBlockID(),
296                                           LC->getDecl(),
297                                           LC->getCFG()->getNumBlockIDs());
298
299  // Check if we are entering the EXIT block.
300  if (Blk == &(L.getLocationContext()->getCFG()->getExit())) {
301
302    assert (L.getLocationContext()->getCFG()->getExit().size() == 0
303            && "EXIT block cannot contain Stmts.");
304
305    // Process the final state transition.
306    SubEng.processEndOfFunction(BuilderCtx);
307
308    // This path is done. Don't enqueue any more nodes.
309    return;
310  }
311
312  // Call into the SubEngine to process entering the CFGBlock.
313  ExplodedNodeSet dstNodes;
314  BlockEntrance BE(Blk, Pred->getLocationContext());
315  NodeBuilderWithSinks nodeBuilder(Pred, dstNodes, BuilderCtx, BE);
316  SubEng.processCFGBlockEntrance(L, nodeBuilder);
317
318  // Auto-generate a node.
319  if (!nodeBuilder.hasGeneratedNodes()) {
320    nodeBuilder.generateNode(Pred->State, Pred);
321  }
322
323  // Enqueue nodes onto the worklist.
324  enqueue(dstNodes);
325}
326
327void CoreEngine::HandleBlockEntrance(const BlockEntrance &L,
328                                       ExplodedNode *Pred) {
329
330  // Increment the block counter.
331  const LocationContext *LC = Pred->getLocationContext();
332  unsigned BlockId = L.getBlock()->getBlockID();
333  BlockCounter Counter = WList->getBlockCounter();
334  Counter = BCounterFactory.IncrementCount(Counter, LC->getCurrentStackFrame(),
335                                           BlockId);
336  WList->setBlockCounter(Counter);
337
338  // Process the entrance of the block.
339  if (CFGElement E = L.getFirstElement()) {
340    NodeBuilderContext Ctx(*this, L.getBlock(), Pred);
341    SubEng.processCFGElement(E, Pred, 0, &Ctx);
342  }
343  else
344    HandleBlockExit(L.getBlock(), Pred);
345}
346
347void CoreEngine::HandleBlockExit(const CFGBlock * B, ExplodedNode *Pred) {
348
349  if (const Stmt *Term = B->getTerminator()) {
350    switch (Term->getStmtClass()) {
351      default:
352        llvm_unreachable("Analysis for this terminator not implemented.");
353
354      case Stmt::BinaryOperatorClass: // '&&' and '||'
355        HandleBranch(cast<BinaryOperator>(Term)->getLHS(), Term, B, Pred);
356        return;
357
358      case Stmt::BinaryConditionalOperatorClass:
359      case Stmt::ConditionalOperatorClass:
360        HandleBranch(cast<AbstractConditionalOperator>(Term)->getCond(),
361                     Term, B, Pred);
362        return;
363
364        // FIXME: Use constant-folding in CFG construction to simplify this
365        // case.
366
367      case Stmt::ChooseExprClass:
368        HandleBranch(cast<ChooseExpr>(Term)->getCond(), Term, B, Pred);
369        return;
370
371      case Stmt::CXXTryStmtClass: {
372        // Generate a node for each of the successors.
373        // Our logic for EH analysis can certainly be improved.
374        for (CFGBlock::const_succ_iterator it = B->succ_begin(),
375             et = B->succ_end(); it != et; ++it) {
376          if (const CFGBlock *succ = *it) {
377            generateNode(BlockEdge(B, succ, Pred->getLocationContext()),
378                         Pred->State, Pred);
379          }
380        }
381        return;
382      }
383
384      case Stmt::DoStmtClass:
385        HandleBranch(cast<DoStmt>(Term)->getCond(), Term, B, Pred);
386        return;
387
388      case Stmt::CXXForRangeStmtClass:
389        HandleBranch(cast<CXXForRangeStmt>(Term)->getCond(), Term, B, Pred);
390        return;
391
392      case Stmt::ForStmtClass:
393        HandleBranch(cast<ForStmt>(Term)->getCond(), Term, B, Pred);
394        return;
395
396      case Stmt::ContinueStmtClass:
397      case Stmt::BreakStmtClass:
398      case Stmt::GotoStmtClass:
399        break;
400
401      case Stmt::IfStmtClass:
402        HandleBranch(cast<IfStmt>(Term)->getCond(), Term, B, Pred);
403        return;
404
405      case Stmt::IndirectGotoStmtClass: {
406        // Only 1 successor: the indirect goto dispatch block.
407        assert (B->succ_size() == 1);
408
409        IndirectGotoNodeBuilder
410           builder(Pred, B, cast<IndirectGotoStmt>(Term)->getTarget(),
411                   *(B->succ_begin()), this);
412
413        SubEng.processIndirectGoto(builder);
414        return;
415      }
416
417      case Stmt::ObjCForCollectionStmtClass: {
418        // In the case of ObjCForCollectionStmt, it appears twice in a CFG:
419        //
420        //  (1) inside a basic block, which represents the binding of the
421        //      'element' variable to a value.
422        //  (2) in a terminator, which represents the branch.
423        //
424        // For (1), subengines will bind a value (i.e., 0 or 1) indicating
425        // whether or not collection contains any more elements.  We cannot
426        // just test to see if the element is nil because a container can
427        // contain nil elements.
428        HandleBranch(Term, Term, B, Pred);
429        return;
430      }
431
432      case Stmt::SwitchStmtClass: {
433        SwitchNodeBuilder builder(Pred, B, cast<SwitchStmt>(Term)->getCond(),
434                                    this);
435
436        SubEng.processSwitch(builder);
437        return;
438      }
439
440      case Stmt::WhileStmtClass:
441        HandleBranch(cast<WhileStmt>(Term)->getCond(), Term, B, Pred);
442        return;
443    }
444  }
445
446  assert (B->succ_size() == 1 &&
447          "Blocks with no terminator should have at most 1 successor.");
448
449  generateNode(BlockEdge(B, *(B->succ_begin()), Pred->getLocationContext()),
450               Pred->State, Pred);
451}
452
453void CoreEngine::HandleBranch(const Stmt *Cond, const Stmt *Term,
454                                const CFGBlock * B, ExplodedNode *Pred) {
455  assert(B->succ_size() == 2);
456  NodeBuilderContext Ctx(*this, B, Pred);
457  ExplodedNodeSet Dst;
458  SubEng.processBranch(Cond, Term, Ctx, Pred, Dst,
459                       *(B->succ_begin()), *(B->succ_begin()+1));
460  // Enqueue the new frontier onto the worklist.
461  enqueue(Dst);
462}
463
464void CoreEngine::HandlePostStmt(const CFGBlock *B, unsigned StmtIdx,
465                                  ExplodedNode *Pred) {
466  assert(B);
467  assert(!B->empty());
468
469  if (StmtIdx == B->size())
470    HandleBlockExit(B, Pred);
471  else {
472    NodeBuilderContext Ctx(*this, B, Pred);
473    SubEng.processCFGElement((*B)[StmtIdx], Pred, StmtIdx, &Ctx);
474  }
475}
476
477/// generateNode - Utility method to generate nodes, hook up successors,
478///  and add nodes to the worklist.
479void CoreEngine::generateNode(const ProgramPoint &Loc,
480                              ProgramStateRef State,
481                              ExplodedNode *Pred) {
482
483  bool IsNew;
484  ExplodedNode *Node = G->getNode(Loc, State, false, &IsNew);
485
486  if (Pred)
487    Node->addPredecessor(Pred, *G);  // Link 'Node' with its predecessor.
488  else {
489    assert (IsNew);
490    G->addRoot(Node);  // 'Node' has no predecessor.  Make it a root.
491  }
492
493  // Only add 'Node' to the worklist if it was freshly generated.
494  if (IsNew) WList->enqueue(Node);
495}
496
497void CoreEngine::enqueueStmtNode(ExplodedNode *N,
498                                 const CFGBlock *Block, unsigned Idx) {
499  assert(Block);
500  assert (!N->isSink());
501
502  // Check if this node entered a callee.
503  if (isa<CallEnter>(N->getLocation())) {
504    // Still use the index of the CallExpr. It's needed to create the callee
505    // StackFrameContext.
506    WList->enqueue(N, Block, Idx);
507    return;
508  }
509
510  // Do not create extra nodes. Move to the next CFG element.
511  if (isa<PostInitializer>(N->getLocation()) ||
512      isa<PostImplicitCall>(N->getLocation())) {
513    WList->enqueue(N, Block, Idx+1);
514    return;
515  }
516
517  if (isa<EpsilonPoint>(N->getLocation())) {
518    WList->enqueue(N, Block, Idx);
519    return;
520  }
521
522  const CFGStmt *CS = (*Block)[Idx].getAs<CFGStmt>();
523  const Stmt *St = CS ? CS->getStmt() : 0;
524  PostStmt Loc(St, N->getLocationContext());
525
526  if (Loc == N->getLocation()) {
527    // Note: 'N' should be a fresh node because otherwise it shouldn't be
528    // a member of Deferred.
529    WList->enqueue(N, Block, Idx+1);
530    return;
531  }
532
533  bool IsNew;
534  ExplodedNode *Succ = G->getNode(Loc, N->getState(), false, &IsNew);
535  Succ->addPredecessor(N, *G);
536
537  if (IsNew)
538    WList->enqueue(Succ, Block, Idx+1);
539}
540
541ExplodedNode *CoreEngine::generateCallExitBeginNode(ExplodedNode *N) {
542  // Create a CallExitBegin node and enqueue it.
543  const StackFrameContext *LocCtx
544                         = cast<StackFrameContext>(N->getLocationContext());
545
546  // Use the callee location context.
547  CallExitBegin Loc(LocCtx);
548
549  bool isNew;
550  ExplodedNode *Node = G->getNode(Loc, N->getState(), false, &isNew);
551  Node->addPredecessor(N, *G);
552  return isNew ? Node : 0;
553}
554
555
556void CoreEngine::enqueue(ExplodedNodeSet &Set) {
557  for (ExplodedNodeSet::iterator I = Set.begin(),
558                                 E = Set.end(); I != E; ++I) {
559    WList->enqueue(*I);
560  }
561}
562
563void CoreEngine::enqueue(ExplodedNodeSet &Set,
564                         const CFGBlock *Block, unsigned Idx) {
565  for (ExplodedNodeSet::iterator I = Set.begin(),
566                                 E = Set.end(); I != E; ++I) {
567    enqueueStmtNode(*I, Block, Idx);
568  }
569}
570
571void CoreEngine::enqueueEndOfFunction(ExplodedNodeSet &Set) {
572  for (ExplodedNodeSet::iterator I = Set.begin(), E = Set.end(); I != E; ++I) {
573    ExplodedNode *N = *I;
574    // If we are in an inlined call, generate CallExitBegin node.
575    if (N->getLocationContext()->getParent()) {
576      N = generateCallExitBeginNode(N);
577      if (N)
578        WList->enqueue(N);
579    } else {
580      // TODO: We should run remove dead bindings here.
581      G->addEndOfPath(N);
582      NumPathsExplored++;
583    }
584  }
585}
586
587
588void NodeBuilder::anchor() { }
589
590ExplodedNode* NodeBuilder::generateNodeImpl(const ProgramPoint &Loc,
591                                            ProgramStateRef State,
592                                            ExplodedNode *FromN,
593                                            bool MarkAsSink) {
594  HasGeneratedNodes = true;
595  bool IsNew;
596  ExplodedNode *N = C.Eng.G->getNode(Loc, State, MarkAsSink, &IsNew);
597  N->addPredecessor(FromN, *C.Eng.G);
598  Frontier.erase(FromN);
599
600  if (!IsNew)
601    return 0;
602
603  if (!MarkAsSink)
604    Frontier.Add(N);
605
606  return N;
607}
608
609void NodeBuilderWithSinks::anchor() { }
610
611StmtNodeBuilder::~StmtNodeBuilder() {
612  if (EnclosingBldr)
613    for (ExplodedNodeSet::iterator I = Frontier.begin(),
614                                   E = Frontier.end(); I != E; ++I )
615      EnclosingBldr->addNodes(*I);
616}
617
618void BranchNodeBuilder::anchor() { }
619
620ExplodedNode *BranchNodeBuilder::generateNode(ProgramStateRef State,
621                                              bool branch,
622                                              ExplodedNode *NodePred) {
623  // If the branch has been marked infeasible we should not generate a node.
624  if (!isFeasible(branch))
625    return NULL;
626
627  ProgramPoint Loc = BlockEdge(C.Block, branch ? DstT:DstF,
628                               NodePred->getLocationContext());
629  ExplodedNode *Succ = generateNodeImpl(Loc, State, NodePred);
630  return Succ;
631}
632
633ExplodedNode*
634IndirectGotoNodeBuilder::generateNode(const iterator &I,
635                                      ProgramStateRef St,
636                                      bool IsSink) {
637  bool IsNew;
638  ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, I.getBlock(),
639                                      Pred->getLocationContext()), St,
640                                      IsSink, &IsNew);
641  Succ->addPredecessor(Pred, *Eng.G);
642
643  if (!IsNew)
644    return 0;
645
646  if (!IsSink)
647    Eng.WList->enqueue(Succ);
648
649  return Succ;
650}
651
652
653ExplodedNode*
654SwitchNodeBuilder::generateCaseStmtNode(const iterator &I,
655                                        ProgramStateRef St) {
656
657  bool IsNew;
658  ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, I.getBlock(),
659                                      Pred->getLocationContext()), St,
660                                      false, &IsNew);
661  Succ->addPredecessor(Pred, *Eng.G);
662  if (!IsNew)
663    return 0;
664
665  Eng.WList->enqueue(Succ);
666  return Succ;
667}
668
669
670ExplodedNode*
671SwitchNodeBuilder::generateDefaultCaseNode(ProgramStateRef St,
672                                           bool IsSink) {
673  // Get the block for the default case.
674  assert(Src->succ_rbegin() != Src->succ_rend());
675  CFGBlock *DefaultBlock = *Src->succ_rbegin();
676
677  // Sanity check for default blocks that are unreachable and not caught
678  // by earlier stages.
679  if (!DefaultBlock)
680    return NULL;
681
682  bool IsNew;
683  ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, DefaultBlock,
684                                      Pred->getLocationContext()), St,
685                                      IsSink, &IsNew);
686  Succ->addPredecessor(Pred, *Eng.G);
687
688  if (!IsNew)
689    return 0;
690
691  if (!IsSink)
692    Eng.WList->enqueue(Succ);
693
694  return Succ;
695}
696