1 //===- ExplodedGraph.cpp - Local, Path-Sens. "Exploded Graph" -------------===//
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/AST/Expr.h"
17 #include "clang/AST/ExprObjC.h"
18 #include "clang/AST/ParentMap.h"
19 #include "clang/AST/Stmt.h"
20 #include "clang/Analysis/ProgramPoint.h"
21 #include "clang/Analysis/Support/BumpVector.h"
22 #include "clang/Basic/LLVM.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
24 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
25 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState_Fwd.h"
26 #include "llvm/ADT/DenseSet.h"
27 #include "llvm/ADT/FoldingSet.h"
28 #include "llvm/ADT/Optional.h"
29 #include "llvm/ADT/PointerUnion.h"
30 #include "llvm/ADT/SmallVector.h"
31 #include "llvm/Support/Casting.h"
32 #include <cassert>
33 #include <memory>
34
35 using namespace clang;
36 using namespace ento;
37
38 //===----------------------------------------------------------------------===//
39 // Node auditing.
40 //===----------------------------------------------------------------------===//
41
42 // An out of line virtual method to provide a home for the class vtable.
43 ExplodedNode::Auditor::~Auditor() = default;
44
45 #ifndef NDEBUG
46 static ExplodedNode::Auditor* NodeAuditor = nullptr;
47 #endif
48
SetAuditor(ExplodedNode::Auditor * A)49 void ExplodedNode::SetAuditor(ExplodedNode::Auditor* A) {
50 #ifndef NDEBUG
51 NodeAuditor = A;
52 #endif
53 }
54
55 //===----------------------------------------------------------------------===//
56 // Cleanup.
57 //===----------------------------------------------------------------------===//
58
59 ExplodedGraph::ExplodedGraph() = default;
60
61 ExplodedGraph::~ExplodedGraph() = default;
62
63 //===----------------------------------------------------------------------===//
64 // Node reclamation.
65 //===----------------------------------------------------------------------===//
66
isInterestingLValueExpr(const Expr * Ex)67 bool ExplodedGraph::isInterestingLValueExpr(const Expr *Ex) {
68 if (!Ex->isLValue())
69 return false;
70 return isa<DeclRefExpr>(Ex) ||
71 isa<MemberExpr>(Ex) ||
72 isa<ObjCIvarRefExpr>(Ex);
73 }
74
shouldCollect(const ExplodedNode * node)75 bool ExplodedGraph::shouldCollect(const ExplodedNode *node) {
76 // First, we only consider nodes for reclamation of the following
77 // conditions apply:
78 //
79 // (1) 1 predecessor (that has one successor)
80 // (2) 1 successor (that has one predecessor)
81 //
82 // If a node has no successor it is on the "frontier", while a node
83 // with no predecessor is a root.
84 //
85 // After these prerequisites, we discard all "filler" nodes that
86 // are used only for intermediate processing, and are not essential
87 // for analyzer history:
88 //
89 // (a) PreStmtPurgeDeadSymbols
90 //
91 // We then discard all other nodes where *all* of the following conditions
92 // apply:
93 //
94 // (3) The ProgramPoint is for a PostStmt, but not a PostStore.
95 // (4) There is no 'tag' for the ProgramPoint.
96 // (5) The 'store' is the same as the predecessor.
97 // (6) The 'GDM' is the same as the predecessor.
98 // (7) The LocationContext is the same as the predecessor.
99 // (8) Expressions that are *not* lvalue expressions.
100 // (9) The PostStmt isn't for a non-consumed Stmt or Expr.
101 // (10) The successor is neither a CallExpr StmtPoint nor a CallEnter or
102 // PreImplicitCall (so that we would be able to find it when retrying a
103 // call with no inlining).
104 // FIXME: It may be safe to reclaim PreCall and PostCall nodes as well.
105
106 // Conditions 1 and 2.
107 if (node->pred_size() != 1 || node->succ_size() != 1)
108 return false;
109
110 const ExplodedNode *pred = *(node->pred_begin());
111 if (pred->succ_size() != 1)
112 return false;
113
114 const ExplodedNode *succ = *(node->succ_begin());
115 if (succ->pred_size() != 1)
116 return false;
117
118 // Now reclaim any nodes that are (by definition) not essential to
119 // analysis history and are not consulted by any client code.
120 ProgramPoint progPoint = node->getLocation();
121 if (progPoint.getAs<PreStmtPurgeDeadSymbols>())
122 return !progPoint.getTag();
123
124 // Condition 3.
125 if (!progPoint.getAs<PostStmt>() || progPoint.getAs<PostStore>())
126 return false;
127
128 // Condition 4.
129 if (progPoint.getTag())
130 return false;
131
132 // Conditions 5, 6, and 7.
133 ProgramStateRef state = node->getState();
134 ProgramStateRef pred_state = pred->getState();
135 if (state->store != pred_state->store || state->GDM != pred_state->GDM ||
136 progPoint.getLocationContext() != pred->getLocationContext())
137 return false;
138
139 // All further checks require expressions. As per #3, we know that we have
140 // a PostStmt.
141 const Expr *Ex = dyn_cast<Expr>(progPoint.castAs<PostStmt>().getStmt());
142 if (!Ex)
143 return false;
144
145 // Condition 8.
146 // Do not collect nodes for "interesting" lvalue expressions since they are
147 // used extensively for generating path diagnostics.
148 if (isInterestingLValueExpr(Ex))
149 return false;
150
151 // Condition 9.
152 // Do not collect nodes for non-consumed Stmt or Expr to ensure precise
153 // diagnostic generation; specifically, so that we could anchor arrows
154 // pointing to the beginning of statements (as written in code).
155 ParentMap &PM = progPoint.getLocationContext()->getParentMap();
156 if (!PM.isConsumedExpr(Ex))
157 return false;
158
159 // Condition 10.
160 const ProgramPoint SuccLoc = succ->getLocation();
161 if (Optional<StmtPoint> SP = SuccLoc.getAs<StmtPoint>())
162 if (CallEvent::isCallStmt(SP->getStmt()))
163 return false;
164
165 // Condition 10, continuation.
166 if (SuccLoc.getAs<CallEnter>() || SuccLoc.getAs<PreImplicitCall>())
167 return false;
168
169 return true;
170 }
171
collectNode(ExplodedNode * node)172 void ExplodedGraph::collectNode(ExplodedNode *node) {
173 // Removing a node means:
174 // (a) changing the predecessors successor to the successor of this node
175 // (b) changing the successors predecessor to the predecessor of this node
176 // (c) Putting 'node' onto freeNodes.
177 assert(node->pred_size() == 1 || node->succ_size() == 1);
178 ExplodedNode *pred = *(node->pred_begin());
179 ExplodedNode *succ = *(node->succ_begin());
180 pred->replaceSuccessor(succ);
181 succ->replacePredecessor(pred);
182 FreeNodes.push_back(node);
183 Nodes.RemoveNode(node);
184 --NumNodes;
185 node->~ExplodedNode();
186 }
187
reclaimRecentlyAllocatedNodes()188 void ExplodedGraph::reclaimRecentlyAllocatedNodes() {
189 if (ChangedNodes.empty())
190 return;
191
192 // Only periodically reclaim nodes so that we can build up a set of
193 // nodes that meet the reclamation criteria. Freshly created nodes
194 // by definition have no successor, and thus cannot be reclaimed (see below).
195 assert(ReclaimCounter > 0);
196 if (--ReclaimCounter != 0)
197 return;
198 ReclaimCounter = ReclaimNodeInterval;
199
200 for (const auto node : ChangedNodes)
201 if (shouldCollect(node))
202 collectNode(node);
203 ChangedNodes.clear();
204 }
205
206 //===----------------------------------------------------------------------===//
207 // ExplodedNode.
208 //===----------------------------------------------------------------------===//
209
210 // An NodeGroup's storage type is actually very much like a TinyPtrVector:
211 // it can be either a pointer to a single ExplodedNode, or a pointer to a
212 // BumpVector allocated with the ExplodedGraph's allocator. This allows the
213 // common case of single-node NodeGroups to be implemented with no extra memory.
214 //
215 // Consequently, each of the NodeGroup methods have up to four cases to handle:
216 // 1. The flag is set and this group does not actually contain any nodes.
217 // 2. The group is empty, in which case the storage value is null.
218 // 3. The group contains a single node.
219 // 4. The group contains more than one node.
220 using ExplodedNodeVector = BumpVector<ExplodedNode *>;
221 using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>;
222
addPredecessor(ExplodedNode * V,ExplodedGraph & G)223 void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
224 assert(!V->isSink());
225 Preds.addNode(V, G);
226 V->Succs.addNode(this, G);
227 #ifndef NDEBUG
228 if (NodeAuditor) NodeAuditor->AddEdge(V, this);
229 #endif
230 }
231
replaceNode(ExplodedNode * node)232 void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) {
233 assert(!getFlag());
234
235 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
236 assert(Storage.is<ExplodedNode *>());
237 Storage = node;
238 assert(Storage.is<ExplodedNode *>());
239 }
240
addNode(ExplodedNode * N,ExplodedGraph & G)241 void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) {
242 assert(!getFlag());
243
244 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
245 if (Storage.isNull()) {
246 Storage = N;
247 assert(Storage.is<ExplodedNode *>());
248 return;
249 }
250
251 ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>();
252
253 if (!V) {
254 // Switch from single-node to multi-node representation.
255 ExplodedNode *Old = Storage.get<ExplodedNode *>();
256
257 BumpVectorContext &Ctx = G.getNodeAllocator();
258 V = G.getAllocator().Allocate<ExplodedNodeVector>();
259 new (V) ExplodedNodeVector(Ctx, 4);
260 V->push_back(Old, Ctx);
261
262 Storage = V;
263 assert(!getFlag());
264 assert(Storage.is<ExplodedNodeVector *>());
265 }
266
267 V->push_back(N, G.getNodeAllocator());
268 }
269
size() const270 unsigned ExplodedNode::NodeGroup::size() const {
271 if (getFlag())
272 return 0;
273
274 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
275 if (Storage.isNull())
276 return 0;
277 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
278 return V->size();
279 return 1;
280 }
281
begin() const282 ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
283 if (getFlag())
284 return nullptr;
285
286 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
287 if (Storage.isNull())
288 return nullptr;
289 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
290 return V->begin();
291 return Storage.getAddrOfPtr1();
292 }
293
end() const294 ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
295 if (getFlag())
296 return nullptr;
297
298 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
299 if (Storage.isNull())
300 return nullptr;
301 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
302 return V->end();
303 return Storage.getAddrOfPtr1() + 1;
304 }
305
getNode(const ProgramPoint & L,ProgramStateRef State,bool IsSink,bool * IsNew)306 ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
307 ProgramStateRef State,
308 bool IsSink,
309 bool* IsNew) {
310 // Profile 'State' to determine if we already have an existing node.
311 llvm::FoldingSetNodeID profile;
312 void *InsertPos = nullptr;
313
314 NodeTy::Profile(profile, L, State, IsSink);
315 NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos);
316
317 if (!V) {
318 if (!FreeNodes.empty()) {
319 V = FreeNodes.back();
320 FreeNodes.pop_back();
321 }
322 else {
323 // Allocate a new node.
324 V = (NodeTy*) getAllocator().Allocate<NodeTy>();
325 }
326
327 new (V) NodeTy(L, State, IsSink);
328
329 if (ReclaimNodeInterval)
330 ChangedNodes.push_back(V);
331
332 // Insert the node into the node set and return it.
333 Nodes.InsertNode(V, InsertPos);
334 ++NumNodes;
335
336 if (IsNew) *IsNew = true;
337 }
338 else
339 if (IsNew) *IsNew = false;
340
341 return V;
342 }
343
createUncachedNode(const ProgramPoint & L,ProgramStateRef State,bool IsSink)344 ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
345 ProgramStateRef State,
346 bool IsSink) {
347 NodeTy *V = (NodeTy *) getAllocator().Allocate<NodeTy>();
348 new (V) NodeTy(L, State, IsSink);
349 return V;
350 }
351
352 std::unique_ptr<ExplodedGraph>
trim(ArrayRef<const NodeTy * > Sinks,InterExplodedGraphMap * ForwardMap,InterExplodedGraphMap * InverseMap) const353 ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks,
354 InterExplodedGraphMap *ForwardMap,
355 InterExplodedGraphMap *InverseMap) const {
356 if (Nodes.empty())
357 return nullptr;
358
359 using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
360 Pass1Ty Pass1;
361
362 using Pass2Ty = InterExplodedGraphMap;
363 InterExplodedGraphMap Pass2Scratch;
364 Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
365
366 SmallVector<const ExplodedNode*, 10> WL1, WL2;
367
368 // ===- Pass 1 (reverse DFS) -===
369 for (const auto Sink : Sinks)
370 if (Sink)
371 WL1.push_back(Sink);
372
373 // Process the first worklist until it is empty.
374 while (!WL1.empty()) {
375 const ExplodedNode *N = WL1.pop_back_val();
376
377 // Have we already visited this node? If so, continue to the next one.
378 if (!Pass1.insert(N).second)
379 continue;
380
381 // If this is a root enqueue it to the second worklist.
382 if (N->Preds.empty()) {
383 WL2.push_back(N);
384 continue;
385 }
386
387 // Visit our predecessors and enqueue them.
388 WL1.append(N->Preds.begin(), N->Preds.end());
389 }
390
391 // We didn't hit a root? Return with a null pointer for the new graph.
392 if (WL2.empty())
393 return nullptr;
394
395 // Create an empty graph.
396 std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph();
397
398 // ===- Pass 2 (forward DFS to construct the new graph) -===
399 while (!WL2.empty()) {
400 const ExplodedNode *N = WL2.pop_back_val();
401
402 // Skip this node if we have already processed it.
403 if (Pass2.find(N) != Pass2.end())
404 continue;
405
406 // Create the corresponding node in the new graph and record the mapping
407 // from the old node to the new node.
408 ExplodedNode *NewN = G->createUncachedNode(N->getLocation(), N->State, N->isSink());
409 Pass2[N] = NewN;
410
411 // Also record the reverse mapping from the new node to the old node.
412 if (InverseMap) (*InverseMap)[NewN] = N;
413
414 // If this node is a root, designate it as such in the graph.
415 if (N->Preds.empty())
416 G->addRoot(NewN);
417
418 // In the case that some of the intended predecessors of NewN have already
419 // been created, we should hook them up as predecessors.
420
421 // Walk through the predecessors of 'N' and hook up their corresponding
422 // nodes in the new graph (if any) to the freshly created node.
423 for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end();
424 I != E; ++I) {
425 Pass2Ty::iterator PI = Pass2.find(*I);
426 if (PI == Pass2.end())
427 continue;
428
429 NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *G);
430 }
431
432 // In the case that some of the intended successors of NewN have already
433 // been created, we should hook them up as successors. Otherwise, enqueue
434 // the new nodes from the original graph that should have nodes created
435 // in the new graph.
436 for (ExplodedNode::succ_iterator I = N->Succs.begin(), E = N->Succs.end();
437 I != E; ++I) {
438 Pass2Ty::iterator PI = Pass2.find(*I);
439 if (PI != Pass2.end()) {
440 const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G);
441 continue;
442 }
443
444 // Enqueue nodes to the worklist that were marked during pass 1.
445 if (Pass1.count(*I))
446 WL2.push_back(*I);
447 }
448 }
449
450 return G;
451 }
452