CoreEngine.cpp revision 2ac58b7c09938bb28c51c7cd2deada609b75f94c 
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#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
16#include "clang/StaticAnalyzer/Core/PathSensitive/CoreEngine.h"
17#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
18#include "clang/Index/TranslationUnit.h"
19#include "clang/AST/Expr.h"
20#include "clang/AST/StmtCXX.h"
21#include "llvm/Support/Casting.h"
22#include "llvm/ADT/DenseMap.h"
23using namespace clang;
24using namespace ento;
25
26//===----------------------------------------------------------------------===//
27// Worklist classes for exploration of reachable states.
28//===----------------------------------------------------------------------===//
29
30WorkList::Visitor::~Visitor() {}
31
32namespace {
33class DFS : public WorkList {
34  SmallVector<WorkListUnit,20> Stack;
35public:
36  virtual bool hasWork() const {
37    return !Stack.empty();
38  }
39
40  virtual void enqueue(const WorkListUnit& U) {
41    Stack.push_back(U);
42  }
43
44  virtual WorkListUnit dequeue() {
45    assert (!Stack.empty());
46    const WorkListUnit& U = Stack.back();
47    Stack.pop_back(); // This technically "invalidates" U, but we are fine.
48    return U;
49  }
50
51  virtual bool visitItemsInWorkList(Visitor &V) {
52    for (SmallVectorImpl<WorkListUnit>::iterator
53         I = Stack.begin(), E = Stack.end(); I != E; ++I) {
54      if (V.visit(*I))
55        return true;
56    }
57    return false;
58  }
59};
60
61class BFS : public WorkList {
62  std::deque<WorkListUnit> Queue;
63public:
64  virtual bool hasWork() const {
65    return !Queue.empty();
66  }
67
68  virtual void enqueue(const WorkListUnit& U) {
69    Queue.push_front(U);
70  }
71
72  virtual WorkListUnit dequeue() {
73    WorkListUnit U = Queue.front();
74    Queue.pop_front();
75    return U;
76  }
77
78  virtual bool visitItemsInWorkList(Visitor &V) {
79    for (std::deque<WorkListUnit>::iterator
80         I = Queue.begin(), E = Queue.end(); I != E; ++I) {
81      if (V.visit(*I))
82        return true;
83    }
84    return false;
85  }
86};
87
88} // end anonymous namespace
89
90// Place the dstor for WorkList here because it contains virtual member
91// functions, and we the code for the dstor generated in one compilation unit.
92WorkList::~WorkList() {}
93
94WorkList *WorkList::makeDFS() { return new DFS(); }
95WorkList *WorkList::makeBFS() { return new BFS(); }
96
97namespace {
98  class BFSBlockDFSContents : public WorkList {
99    std::deque<WorkListUnit> Queue;
100    SmallVector<WorkListUnit,20> Stack;
101  public:
102    virtual bool hasWork() const {
103      return !Queue.empty() || !Stack.empty();
104    }
105
106    virtual void enqueue(const WorkListUnit& U) {
107      if (isa<BlockEntrance>(U.getNode()->getLocation()))
108        Queue.push_front(U);
109      else
110        Stack.push_back(U);
111    }
112
113    virtual WorkListUnit dequeue() {
114      // Process all basic blocks to completion.
115      if (!Stack.empty()) {
116        const WorkListUnit& U = Stack.back();
117        Stack.pop_back(); // This technically "invalidates" U, but we are fine.
118        return U;
119      }
120
121      assert(!Queue.empty());
122      // Don't use const reference.  The subsequent pop_back() might make it
123      // unsafe.
124      WorkListUnit U = Queue.front();
125      Queue.pop_front();
126      return U;
127    }
128    virtual bool visitItemsInWorkList(Visitor &V) {
129      for (SmallVectorImpl<WorkListUnit>::iterator
130           I = Stack.begin(), E = Stack.end(); I != E; ++I) {
131        if (V.visit(*I))
132          return true;
133      }
134      for (std::deque<WorkListUnit>::iterator
135           I = Queue.begin(), E = Queue.end(); I != E; ++I) {
136        if (V.visit(*I))
137          return true;
138      }
139      return false;
140    }
141
142  };
143} // end anonymous namespace
144
145WorkList* WorkList::makeBFSBlockDFSContents() {
146  return new BFSBlockDFSContents();
147}
148
149//===----------------------------------------------------------------------===//
150// Core analysis engine.
151//===----------------------------------------------------------------------===//
152
153/// ExecuteWorkList - Run the worklist algorithm for a maximum number of steps.
154bool CoreEngine::ExecuteWorkList(const LocationContext *L, unsigned Steps,
155                                   ProgramStateRef InitState) {
156
157  if (G->num_roots() == 0) { // Initialize the analysis by constructing
158    // the root if none exists.
159
160    const CFGBlock *Entry = &(L->getCFG()->getEntry());
161
162    assert (Entry->empty() &&
163            "Entry block must be empty.");
164
165    assert (Entry->succ_size() == 1 &&
166            "Entry block must have 1 successor.");
167
168    // Get the solitary successor.
169    const CFGBlock *Succ = *(Entry->succ_begin());
170
171    // Construct an edge representing the
172    // starting location in the function.
173    BlockEdge StartLoc(Entry, Succ, L);
174
175    // Set the current block counter to being empty.
176    WList->setBlockCounter(BCounterFactory.GetEmptyCounter());
177
178    if (!InitState)
179      // Generate the root.
180      generateNode(StartLoc, SubEng.getInitialState(L), 0);
181    else
182      generateNode(StartLoc, InitState, 0);
183  }
184
185  // Check if we have a steps limit
186  bool UnlimitedSteps = Steps == 0;
187
188  while (WList->hasWork()) {
189    if (!UnlimitedSteps) {
190      if (Steps == 0)
191        break;
192      --Steps;
193    }
194
195    const WorkListUnit& WU = WList->dequeue();
196
197    // Set the current block counter.
198    WList->setBlockCounter(WU.getBlockCounter());
199
200    // Retrieve the node.
201    ExplodedNode *Node = WU.getNode();
202
203    // Dispatch on the location type.
204    switch (Node->getLocation().getKind()) {
205      case ProgramPoint::BlockEdgeKind:
206        HandleBlockEdge(cast<BlockEdge>(Node->getLocation()), Node);
207        break;
208
209      case ProgramPoint::BlockEntranceKind:
210        HandleBlockEntrance(cast<BlockEntrance>(Node->getLocation()), Node);
211        break;
212
213      case ProgramPoint::BlockExitKind:
214        assert (false && "BlockExit location never occur in forward analysis.");
215        break;
216
217      case ProgramPoint::CallEnterKind:
218        SubEng.processCallEnter(cast<CallEnter>(Node->getLocation()), Node);
219        break;
220
221      case ProgramPoint::CallExitKind:
222        SubEng.processCallExit(Node);
223        break;
224
225      default:
226        assert(isa<PostStmt>(Node->getLocation()) ||
227               isa<PostInitializer>(Node->getLocation()));
228        HandlePostStmt(WU.getBlock(), WU.getIndex(), Node);
229        break;
230    }
231  }
232
233  SubEng.processEndWorklist(hasWorkRemaining());
234  return WList->hasWork();
235}
236
237void CoreEngine::ExecuteWorkListWithInitialState(const LocationContext *L,
238                                                 unsigned Steps,
239                                                 ProgramStateRef InitState,
240                                                 ExplodedNodeSet &Dst) {
241  ExecuteWorkList(L, Steps, InitState);
242  for (ExplodedGraph::eop_iterator I = G->eop_begin(),
243                                   E = G->eop_end(); I != E; ++I) {
244    Dst.Add(*I);
245  }
246}
247
248void CoreEngine::HandleBlockEdge(const BlockEdge &L, ExplodedNode *Pred) {
249
250  const CFGBlock *Blk = L.getDst();
251  NodeBuilderContext BuilderCtx(*this, Blk, Pred);
252
253  // Check if we are entering the EXIT block.
254  if (Blk == &(L.getLocationContext()->getCFG()->getExit())) {
255
256    assert (L.getLocationContext()->getCFG()->getExit().size() == 0
257            && "EXIT block cannot contain Stmts.");
258
259    // Process the final state transition.
260    SubEng.processEndOfFunction(BuilderCtx);
261
262    // This path is done. Don't enqueue any more nodes.
263    return;
264  }
265
266  // Call into the SubEngine to process entering the CFGBlock.
267  ExplodedNodeSet dstNodes;
268  BlockEntrance BE(Blk, Pred->getLocationContext());
269  NodeBuilderWithSinks nodeBuilder(Pred, dstNodes, BuilderCtx, BE);
270  SubEng.processCFGBlockEntrance(nodeBuilder);
271
272  // Auto-generate a node.
273  if (!nodeBuilder.hasGeneratedNodes()) {
274    nodeBuilder.generateNode(Pred->State, Pred);
275  }
276
277  // Enqueue nodes onto the worklist.
278  enqueue(dstNodes);
279
280  // Make sink nodes as exhausted.
281  const SmallVectorImpl<ExplodedNode*> &Sinks =  nodeBuilder.getSinks();
282  for (SmallVectorImpl<ExplodedNode*>::const_iterator
283         I =Sinks.begin(), E = Sinks.end(); I != E; ++I) {
284    blocksExhausted.push_back(std::make_pair(L, *I));
285  }
286}
287
288void CoreEngine::HandleBlockEntrance(const BlockEntrance &L,
289                                       ExplodedNode *Pred) {
290
291  // Increment the block counter.
292  BlockCounter Counter = WList->getBlockCounter();
293  Counter = BCounterFactory.IncrementCount(Counter,
294                             Pred->getLocationContext()->getCurrentStackFrame(),
295                                           L.getBlock()->getBlockID());
296  WList->setBlockCounter(Counter);
297
298  // Process the entrance of the block.
299  if (CFGElement E = L.getFirstElement()) {
300    NodeBuilderContext Ctx(*this, L.getBlock(), Pred);
301    SubEng.processCFGElement(E, Pred, 0, &Ctx);
302  }
303  else
304    HandleBlockExit(L.getBlock(), Pred);
305}
306
307void CoreEngine::HandleBlockExit(const CFGBlock * B, ExplodedNode *Pred) {
308
309  if (const Stmt *Term = B->getTerminator()) {
310    switch (Term->getStmtClass()) {
311      default:
312        llvm_unreachable("Analysis for this terminator not implemented.");
313
314      case Stmt::BinaryOperatorClass: // '&&' and '||'
315        HandleBranch(cast<BinaryOperator>(Term)->getLHS(), Term, B, Pred);
316        return;
317
318      case Stmt::BinaryConditionalOperatorClass:
319      case Stmt::ConditionalOperatorClass:
320        HandleBranch(cast<AbstractConditionalOperator>(Term)->getCond(),
321                     Term, B, Pred);
322        return;
323
324        // FIXME: Use constant-folding in CFG construction to simplify this
325        // case.
326
327      case Stmt::ChooseExprClass:
328        HandleBranch(cast<ChooseExpr>(Term)->getCond(), Term, B, Pred);
329        return;
330
331      case Stmt::DoStmtClass:
332        HandleBranch(cast<DoStmt>(Term)->getCond(), Term, B, Pred);
333        return;
334
335      case Stmt::CXXForRangeStmtClass:
336        HandleBranch(cast<CXXForRangeStmt>(Term)->getCond(), Term, B, Pred);
337        return;
338
339      case Stmt::ForStmtClass:
340        HandleBranch(cast<ForStmt>(Term)->getCond(), Term, B, Pred);
341        return;
342
343      case Stmt::ContinueStmtClass:
344      case Stmt::BreakStmtClass:
345      case Stmt::GotoStmtClass:
346        break;
347
348      case Stmt::IfStmtClass:
349        HandleBranch(cast<IfStmt>(Term)->getCond(), Term, B, Pred);
350        return;
351
352      case Stmt::IndirectGotoStmtClass: {
353        // Only 1 successor: the indirect goto dispatch block.
354        assert (B->succ_size() == 1);
355
356        IndirectGotoNodeBuilder
357           builder(Pred, B, cast<IndirectGotoStmt>(Term)->getTarget(),
358                   *(B->succ_begin()), this);
359
360        SubEng.processIndirectGoto(builder);
361        return;
362      }
363
364      case Stmt::ObjCForCollectionStmtClass: {
365        // In the case of ObjCForCollectionStmt, it appears twice in a CFG:
366        //
367        //  (1) inside a basic block, which represents the binding of the
368        //      'element' variable to a value.
369        //  (2) in a terminator, which represents the branch.
370        //
371        // For (1), subengines will bind a value (i.e., 0 or 1) indicating
372        // whether or not collection contains any more elements.  We cannot
373        // just test to see if the element is nil because a container can
374        // contain nil elements.
375        HandleBranch(Term, Term, B, Pred);
376        return;
377      }
378
379      case Stmt::SwitchStmtClass: {
380        SwitchNodeBuilder builder(Pred, B, cast<SwitchStmt>(Term)->getCond(),
381                                    this);
382
383        SubEng.processSwitch(builder);
384        return;
385      }
386
387      case Stmt::WhileStmtClass:
388        HandleBranch(cast<WhileStmt>(Term)->getCond(), Term, B, Pred);
389        return;
390    }
391  }
392
393  assert (B->succ_size() == 1 &&
394          "Blocks with no terminator should have at most 1 successor.");
395
396  generateNode(BlockEdge(B, *(B->succ_begin()), Pred->getLocationContext()),
397               Pred->State, Pred);
398}
399
400void CoreEngine::HandleBranch(const Stmt *Cond, const Stmt *Term,
401                                const CFGBlock * B, ExplodedNode *Pred) {
402  assert(B->succ_size() == 2);
403  NodeBuilderContext Ctx(*this, B, Pred);
404  ExplodedNodeSet Dst;
405  SubEng.processBranch(Cond, Term, Ctx, Pred, Dst,
406                       *(B->succ_begin()), *(B->succ_begin()+1));
407  // Enqueue the new frontier onto the worklist.
408  enqueue(Dst);
409}
410
411void CoreEngine::HandlePostStmt(const CFGBlock *B, unsigned StmtIdx,
412                                  ExplodedNode *Pred) {
413  assert(B);
414  assert(!B->empty());
415
416  if (StmtIdx == B->size())
417    HandleBlockExit(B, Pred);
418  else {
419    NodeBuilderContext Ctx(*this, B, Pred);
420    SubEng.processCFGElement((*B)[StmtIdx], Pred, StmtIdx, &Ctx);
421  }
422}
423
424/// generateNode - Utility method to generate nodes, hook up successors,
425///  and add nodes to the worklist.
426void CoreEngine::generateNode(const ProgramPoint &Loc,
427                              ProgramStateRef State,
428                              ExplodedNode *Pred) {
429
430  bool IsNew;
431  ExplodedNode *Node = G->getNode(Loc, State, false, &IsNew);
432
433  if (Pred)
434    Node->addPredecessor(Pred, *G);  // Link 'Node' with its predecessor.
435  else {
436    assert (IsNew);
437    G->addRoot(Node);  // 'Node' has no predecessor.  Make it a root.
438  }
439
440  // Only add 'Node' to the worklist if it was freshly generated.
441  if (IsNew) WList->enqueue(Node);
442}
443
444void CoreEngine::enqueueStmtNode(ExplodedNode *N,
445                                 const CFGBlock *Block, unsigned Idx) {
446  assert(Block);
447  assert (!N->isSink());
448
449  // Check if this node entered a callee.
450  if (isa<CallEnter>(N->getLocation())) {
451    // Still use the index of the CallExpr. It's needed to create the callee
452    // StackFrameContext.
453    WList->enqueue(N, Block, Idx);
454    return;
455  }
456
457  // Do not create extra nodes. Move to the next CFG element.
458  if (isa<PostInitializer>(N->getLocation())) {
459    WList->enqueue(N, Block, Idx+1);
460    return;
461  }
462
463  const CFGStmt *CS = (*Block)[Idx].getAs<CFGStmt>();
464  const Stmt *St = CS ? CS->getStmt() : 0;
465  PostStmt Loc(St, N->getLocationContext());
466
467  if (Loc == N->getLocation()) {
468    // Note: 'N' should be a fresh node because otherwise it shouldn't be
469    // a member of Deferred.
470    WList->enqueue(N, Block, Idx+1);
471    return;
472  }
473
474  bool IsNew;
475  ExplodedNode *Succ = G->getNode(Loc, N->getState(), false, &IsNew);
476  Succ->addPredecessor(N, *G);
477
478  if (IsNew)
479    WList->enqueue(Succ, Block, Idx+1);
480}
481
482ExplodedNode *CoreEngine::generateCallExitNode(ExplodedNode *N) {
483  // Create a CallExit node and enqueue it.
484  const StackFrameContext *LocCtx
485                         = cast<StackFrameContext>(N->getLocationContext());
486  const Stmt *CE = LocCtx->getCallSite();
487
488  // Use the the callee location context.
489  CallExit Loc(CE, LocCtx);
490
491  bool isNew;
492  ExplodedNode *Node = G->getNode(Loc, N->getState(), false, &isNew);
493  Node->addPredecessor(N, *G);
494  return isNew ? Node : 0;
495}
496
497
498void CoreEngine::enqueue(ExplodedNodeSet &Set) {
499  for (ExplodedNodeSet::iterator I = Set.begin(),
500                                 E = Set.end(); I != E; ++I) {
501    WList->enqueue(*I);
502  }
503}
504
505void CoreEngine::enqueue(ExplodedNodeSet &Set,
506                         const CFGBlock *Block, unsigned Idx) {
507  for (ExplodedNodeSet::iterator I = Set.begin(),
508                                 E = Set.end(); I != E; ++I) {
509    enqueueStmtNode(*I, Block, Idx);
510  }
511}
512
513void CoreEngine::enqueueEndOfFunction(ExplodedNodeSet &Set) {
514  for (ExplodedNodeSet::iterator I = Set.begin(), E = Set.end(); I != E; ++I) {
515    ExplodedNode *N = *I;
516    // If we are in an inlined call, generate CallExit node.
517    if (N->getLocationContext()->getParent()) {
518      N = generateCallExitNode(N);
519      if (N)
520        WList->enqueue(N);
521    } else
522      G->addEndOfPath(N);
523  }
524}
525
526
527void NodeBuilder::anchor() { }
528
529ExplodedNode* NodeBuilder::generateNodeImpl(const ProgramPoint &Loc,
530                                            ProgramStateRef State,
531                                            ExplodedNode *FromN,
532                                            bool MarkAsSink) {
533  HasGeneratedNodes = true;
534  bool IsNew;
535  ExplodedNode *N = C.Eng.G->getNode(Loc, State, MarkAsSink, &IsNew);
536  N->addPredecessor(FromN, *C.Eng.G);
537  Frontier.erase(FromN);
538
539  if (!IsNew)
540    return 0;
541
542  if (!MarkAsSink)
543    Frontier.Add(N);
544
545  return N;
546}
547
548void NodeBuilderWithSinks::anchor() { }
549
550StmtNodeBuilder::~StmtNodeBuilder() {
551  if (EnclosingBldr)
552    for (ExplodedNodeSet::iterator I = Frontier.begin(),
553                                   E = Frontier.end(); I != E; ++I )
554      EnclosingBldr->addNodes(*I);
555}
556
557void BranchNodeBuilder::anchor() { }
558
559ExplodedNode *BranchNodeBuilder::generateNode(ProgramStateRef State,
560                                              bool branch,
561                                              ExplodedNode *NodePred) {
562  // If the branch has been marked infeasible we should not generate a node.
563  if (!isFeasible(branch))
564    return NULL;
565
566  ProgramPoint Loc = BlockEdge(C.Block, branch ? DstT:DstF,
567                               NodePred->getLocationContext());
568  ExplodedNode *Succ = generateNodeImpl(Loc, State, NodePred);
569  return Succ;
570}
571
572ExplodedNode*
573IndirectGotoNodeBuilder::generateNode(const iterator &I,
574                                      ProgramStateRef St,
575                                      bool IsSink) {
576  bool IsNew;
577  ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, I.getBlock(),
578                                      Pred->getLocationContext()), St,
579                                      IsSink, &IsNew);
580  Succ->addPredecessor(Pred, *Eng.G);
581
582  if (!IsNew)
583    return 0;
584
585  if (!IsSink)
586    Eng.WList->enqueue(Succ);
587
588  return Succ;
589}
590
591
592ExplodedNode*
593SwitchNodeBuilder::generateCaseStmtNode(const iterator &I,
594                                        ProgramStateRef St) {
595
596  bool IsNew;
597  ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, I.getBlock(),
598                                      Pred->getLocationContext()), St,
599                                      false, &IsNew);
600  Succ->addPredecessor(Pred, *Eng.G);
601  if (!IsNew)
602    return 0;
603
604  Eng.WList->enqueue(Succ);
605  return Succ;
606}
607
608
609ExplodedNode*
610SwitchNodeBuilder::generateDefaultCaseNode(ProgramStateRef St,
611                                           bool IsSink) {
612  // Get the block for the default case.
613  assert(Src->succ_rbegin() != Src->succ_rend());
614  CFGBlock *DefaultBlock = *Src->succ_rbegin();
615
616  // Sanity check for default blocks that are unreachable and not caught
617  // by earlier stages.
618  if (!DefaultBlock)
619    return NULL;
620
621  bool IsNew;
622  ExplodedNode *Succ = Eng.G->getNode(BlockEdge(Src, DefaultBlock,
623                                      Pred->getLocationContext()), St,
624                                      IsSink, &IsNew);
625  Succ->addPredecessor(Pred, *Eng.G);
626
627  if (!IsNew)
628    return 0;
629
630  if (!IsSink)
631    Eng.WList->enqueue(Succ);
632
633  return Succ;
634}
635