ExplodedGraph.cpp revision 4d9e497a2b1eab3b1214848216050c64fc3acfd6
1//=-- ExplodedGraph.cpp - Local, Path-Sens. "Exploded Graph" -*- 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 the template classes ExplodedNode and ExplodedGraph,
11//  which represent a path-sensitive, intra-procedural "exploded graph."
12//
13//===----------------------------------------------------------------------===//
14
15#include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
16#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
17#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
18#include "clang/AST/Stmt.h"
19#include "clang/AST/ParentMap.h"
20#include "llvm/ADT/DenseSet.h"
21#include "llvm/ADT/DenseMap.h"
22#include "llvm/ADT/SmallVector.h"
23#include "llvm/ADT/Statistic.h"
24#include <vector>
25
26using namespace clang;
27using namespace ento;
28
29//===----------------------------------------------------------------------===//
30// Node auditing.
31//===----------------------------------------------------------------------===//
32
33// An out of line virtual method to provide a home for the class vtable.
34ExplodedNode::Auditor::~Auditor() {}
35
36#ifndef NDEBUG
37static ExplodedNode::Auditor* NodeAuditor = 0;
38#endif
39
40void ExplodedNode::SetAuditor(ExplodedNode::Auditor* A) {
41#ifndef NDEBUG
42  NodeAuditor = A;
43#endif
44}
45
46//===----------------------------------------------------------------------===//
47// Cleanup.
48//===----------------------------------------------------------------------===//
49
50ExplodedGraph::ExplodedGraph()
51  : NumNodes(0), ReclaimNodeInterval(0) {}
52
53ExplodedGraph::~ExplodedGraph() {}
54
55//===----------------------------------------------------------------------===//
56// Node reclamation.
57//===----------------------------------------------------------------------===//
58
59bool ExplodedGraph::shouldCollect(const ExplodedNode *node) {
60  // Reclaim all nodes that match *all* the following criteria:
61  //
62  // (1) 1 predecessor (that has one successor)
63  // (2) 1 successor (that has one predecessor)
64  // (3) The ProgramPoint is for a PostStmt.
65  // (4) There is no 'tag' for the ProgramPoint.
66  // (5) The 'store' is the same as the predecessor.
67  // (6) The 'GDM' is the same as the predecessor.
68  // (7) The LocationContext is the same as the predecessor.
69  // (8) The PostStmt isn't for a non-consumed Stmt or Expr.
70  // (9) The successor is not a CallExpr StmtPoint (so that we would be able to
71  //     find it when retrying a call with no inlining).
72  // FIXME: It may be safe to reclaim PreCall and PostCall nodes as well.
73
74  // Conditions 1 and 2.
75  if (node->pred_size() != 1 || node->succ_size() != 1)
76    return false;
77
78  const ExplodedNode *pred = *(node->pred_begin());
79  if (pred->succ_size() != 1)
80    return false;
81
82  const ExplodedNode *succ = *(node->succ_begin());
83  if (succ->pred_size() != 1)
84    return false;
85
86  // Condition 3.
87  ProgramPoint progPoint = node->getLocation();
88  if (!isa<PostStmt>(progPoint))
89    return false;
90
91  // Condition 4.
92  PostStmt ps = cast<PostStmt>(progPoint);
93  if (ps.getTag())
94    return false;
95
96  // Conditions 5, 6, and 7.
97  ProgramStateRef state = node->getState();
98  ProgramStateRef pred_state = pred->getState();
99  if (state->store != pred_state->store || state->GDM != pred_state->GDM ||
100      progPoint.getLocationContext() != pred->getLocationContext())
101    return false;
102
103  // Condition 8.
104  // Do not collect nodes for non-consumed Stmt or Expr to ensure precise
105  // diagnostic generation; specifically, so that we could anchor arrows
106  // pointing to the beginning of statements (as written in code).
107  if (!isa<Expr>(ps.getStmt()))
108    return false;
109
110  if (const Expr *Ex = dyn_cast<Expr>(ps.getStmt())) {
111    ParentMap &PM = progPoint.getLocationContext()->getParentMap();
112    if (!PM.isConsumedExpr(Ex))
113      return false;
114  }
115
116  // Condition 9.
117  const ProgramPoint SuccLoc = succ->getLocation();
118  if (const StmtPoint *SP = dyn_cast<StmtPoint>(&SuccLoc))
119    if (CallEvent::isCallStmt(SP->getStmt()))
120      return false;
121
122  return true;
123}
124
125void ExplodedGraph::collectNode(ExplodedNode *node) {
126  // Removing a node means:
127  // (a) changing the predecessors successor to the successor of this node
128  // (b) changing the successors predecessor to the predecessor of this node
129  // (c) Putting 'node' onto freeNodes.
130  assert(node->pred_size() == 1 || node->succ_size() == 1);
131  ExplodedNode *pred = *(node->pred_begin());
132  ExplodedNode *succ = *(node->succ_begin());
133  pred->replaceSuccessor(succ);
134  succ->replacePredecessor(pred);
135  FreeNodes.push_back(node);
136  Nodes.RemoveNode(node);
137  --NumNodes;
138  node->~ExplodedNode();
139}
140
141void ExplodedGraph::reclaimRecentlyAllocatedNodes() {
142  if (ChangedNodes.empty())
143    return;
144
145  // Only periodically reclaim nodes so that we can build up a set of
146  // nodes that meet the reclamation criteria.  Freshly created nodes
147  // by definition have no successor, and thus cannot be reclaimed (see below).
148  assert(ReclaimCounter > 0);
149  if (--ReclaimCounter != 0)
150    return;
151  ReclaimCounter = ReclaimNodeInterval;
152
153  for (NodeVector::iterator it = ChangedNodes.begin(), et = ChangedNodes.end();
154       it != et; ++it) {
155    ExplodedNode *node = *it;
156    if (shouldCollect(node))
157      collectNode(node);
158  }
159  ChangedNodes.clear();
160}
161
162//===----------------------------------------------------------------------===//
163// ExplodedNode.
164//===----------------------------------------------------------------------===//
165
166// An NodeGroup's storage type is actually very much like a TinyPtrVector:
167// it can be either a pointer to a single ExplodedNode, or a pointer to a
168// BumpVector allocated with the ExplodedGraph's allocator. This allows the
169// common case of single-node NodeGroups to be implemented with no extra memory.
170//
171// Consequently, each of the NodeGroup methods have up to four cases to handle:
172// 1. The flag is set and this group does not actually contain any nodes.
173// 2. The group is empty, in which case the storage value is null.
174// 3. The group contains a single node.
175// 4. The group contains more than one node.
176typedef BumpVector<ExplodedNode *> ExplodedNodeVector;
177typedef llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *> GroupStorage;
178
179void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
180  assert (!V->isSink());
181  Preds.addNode(V, G);
182  V->Succs.addNode(this, G);
183#ifndef NDEBUG
184  if (NodeAuditor) NodeAuditor->AddEdge(V, this);
185#endif
186}
187
188void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) {
189  assert(!getFlag());
190
191  GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
192  assert(Storage.is<ExplodedNode *>());
193  Storage = node;
194  assert(Storage.is<ExplodedNode *>());
195}
196
197void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) {
198  assert(!getFlag());
199
200  GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
201  if (Storage.isNull()) {
202    Storage = N;
203    assert(Storage.is<ExplodedNode *>());
204    return;
205  }
206
207  ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>();
208
209  if (!V) {
210    // Switch from single-node to multi-node representation.
211    ExplodedNode *Old = Storage.get<ExplodedNode *>();
212
213    BumpVectorContext &Ctx = G.getNodeAllocator();
214    V = G.getAllocator().Allocate<ExplodedNodeVector>();
215    new (V) ExplodedNodeVector(Ctx, 4);
216    V->push_back(Old, Ctx);
217
218    Storage = V;
219    assert(!getFlag());
220    assert(Storage.is<ExplodedNodeVector *>());
221  }
222
223  V->push_back(N, G.getNodeAllocator());
224}
225
226unsigned ExplodedNode::NodeGroup::size() const {
227  if (getFlag())
228    return 0;
229
230  const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
231  if (Storage.isNull())
232    return 0;
233  if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
234    return V->size();
235  return 1;
236}
237
238ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
239  if (getFlag())
240    return 0;
241
242  const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
243  if (Storage.isNull())
244    return 0;
245  if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
246    return V->begin();
247  return Storage.getAddrOfPtr1();
248}
249
250ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
251  if (getFlag())
252    return 0;
253
254  const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
255  if (Storage.isNull())
256    return 0;
257  if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
258    return V->end();
259  return Storage.getAddrOfPtr1() + 1;
260}
261
262ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
263                                     ProgramStateRef State,
264                                     bool IsSink,
265                                     bool* IsNew) {
266  // Profile 'State' to determine if we already have an existing node.
267  llvm::FoldingSetNodeID profile;
268  void *InsertPos = 0;
269
270  NodeTy::Profile(profile, L, State, IsSink);
271  NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos);
272
273  if (!V) {
274    if (!FreeNodes.empty()) {
275      V = FreeNodes.back();
276      FreeNodes.pop_back();
277    }
278    else {
279      // Allocate a new node.
280      V = (NodeTy*) getAllocator().Allocate<NodeTy>();
281    }
282
283    new (V) NodeTy(L, State, IsSink);
284
285    if (ReclaimNodeInterval)
286      ChangedNodes.push_back(V);
287
288    // Insert the node into the node set and return it.
289    Nodes.InsertNode(V, InsertPos);
290    ++NumNodes;
291
292    if (IsNew) *IsNew = true;
293  }
294  else
295    if (IsNew) *IsNew = false;
296
297  return V;
298}
299
300std::pair<ExplodedGraph*, InterExplodedGraphMap*>
301ExplodedGraph::Trim(const NodeTy* const* NBeg, const NodeTy* const* NEnd,
302               llvm::DenseMap<const void*, const void*> *InverseMap) const {
303
304  if (NBeg == NEnd)
305    return std::make_pair((ExplodedGraph*) 0,
306                          (InterExplodedGraphMap*) 0);
307
308  assert (NBeg < NEnd);
309
310  OwningPtr<InterExplodedGraphMap> M(new InterExplodedGraphMap());
311
312  ExplodedGraph* G = TrimInternal(NBeg, NEnd, M.get(), InverseMap);
313
314  return std::make_pair(static_cast<ExplodedGraph*>(G), M.take());
315}
316
317ExplodedGraph*
318ExplodedGraph::TrimInternal(const ExplodedNode* const* BeginSources,
319                            const ExplodedNode* const* EndSources,
320                            InterExplodedGraphMap* M,
321                   llvm::DenseMap<const void*, const void*> *InverseMap) const {
322
323  typedef llvm::DenseSet<const ExplodedNode*> Pass1Ty;
324  Pass1Ty Pass1;
325
326  typedef llvm::DenseMap<const ExplodedNode*, ExplodedNode*> Pass2Ty;
327  Pass2Ty& Pass2 = M->M;
328
329  SmallVector<const ExplodedNode*, 10> WL1, WL2;
330
331  // ===- Pass 1 (reverse DFS) -===
332  for (const ExplodedNode* const* I = BeginSources; I != EndSources; ++I) {
333    if (*I)
334      WL1.push_back(*I);
335  }
336
337  // Process the first worklist until it is empty.  Because it is a std::list
338  // it acts like a FIFO queue.
339  while (!WL1.empty()) {
340    const ExplodedNode *N = WL1.back();
341    WL1.pop_back();
342
343    // Have we already visited this node?  If so, continue to the next one.
344    if (Pass1.count(N))
345      continue;
346
347    // Otherwise, mark this node as visited.
348    Pass1.insert(N);
349
350    // If this is a root enqueue it to the second worklist.
351    if (N->Preds.empty()) {
352      WL2.push_back(N);
353      continue;
354    }
355
356    // Visit our predecessors and enqueue them.
357    for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end();
358         I != E; ++I)
359      WL1.push_back(*I);
360  }
361
362  // We didn't hit a root? Return with a null pointer for the new graph.
363  if (WL2.empty())
364    return 0;
365
366  // Create an empty graph.
367  ExplodedGraph* G = MakeEmptyGraph();
368
369  // ===- Pass 2 (forward DFS to construct the new graph) -===
370  while (!WL2.empty()) {
371    const ExplodedNode *N = WL2.back();
372    WL2.pop_back();
373
374    // Skip this node if we have already processed it.
375    if (Pass2.find(N) != Pass2.end())
376      continue;
377
378    // Create the corresponding node in the new graph and record the mapping
379    // from the old node to the new node.
380    ExplodedNode *NewN = G->getNode(N->getLocation(), N->State, N->isSink(), 0);
381    Pass2[N] = NewN;
382
383    // Also record the reverse mapping from the new node to the old node.
384    if (InverseMap) (*InverseMap)[NewN] = N;
385
386    // If this node is a root, designate it as such in the graph.
387    if (N->Preds.empty())
388      G->addRoot(NewN);
389
390    // In the case that some of the intended predecessors of NewN have already
391    // been created, we should hook them up as predecessors.
392
393    // Walk through the predecessors of 'N' and hook up their corresponding
394    // nodes in the new graph (if any) to the freshly created node.
395    for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end();
396         I != E; ++I) {
397      Pass2Ty::iterator PI = Pass2.find(*I);
398      if (PI == Pass2.end())
399        continue;
400
401      NewN->addPredecessor(PI->second, *G);
402    }
403
404    // In the case that some of the intended successors of NewN have already
405    // been created, we should hook them up as successors.  Otherwise, enqueue
406    // the new nodes from the original graph that should have nodes created
407    // in the new graph.
408    for (ExplodedNode::succ_iterator I = N->Succs.begin(), E = N->Succs.end();
409         I != E; ++I) {
410      Pass2Ty::iterator PI = Pass2.find(*I);
411      if (PI != Pass2.end()) {
412        PI->second->addPredecessor(NewN, *G);
413        continue;
414      }
415
416      // Enqueue nodes to the worklist that were marked during pass 1.
417      if (Pass1.count(*I))
418        WL2.push_back(*I);
419    }
420  }
421
422  return G;
423}
424
425void InterExplodedGraphMap::anchor() { }
426
427ExplodedNode*
428InterExplodedGraphMap::getMappedNode(const ExplodedNode *N) const {
429  llvm::DenseMap<const ExplodedNode*, ExplodedNode*>::const_iterator I =
430    M.find(N);
431
432  return I == M.end() ? 0 : I->second;
433}
434
435