1 //===- ExplodedGraph.cpp - Local, Path-Sens. "Exploded Graph" -------------===//
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 the template classes ExplodedNode and ExplodedGraph,
10 // which represent a path-sensitive, intra-procedural "exploded graph."
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
15 #include "clang/AST/Expr.h"
16 #include "clang/AST/ExprObjC.h"
17 #include "clang/AST/ParentMap.h"
18 #include "clang/AST/Stmt.h"
19 #include "clang/Analysis/ProgramPoint.h"
20 #include "clang/Analysis/Support/BumpVector.h"
21 #include "clang/Basic/LLVM.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
24 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState_Fwd.h"
25 #include "llvm/ADT/DenseSet.h"
26 #include "llvm/ADT/FoldingSet.h"
27 #include "llvm/ADT/Optional.h"
28 #include "llvm/ADT/PointerUnion.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/Support/Casting.h"
31 #include <cassert>
32 #include <memory>
33
34 using namespace clang;
35 using namespace ento;
36
37 //===----------------------------------------------------------------------===//
38 // Cleanup.
39 //===----------------------------------------------------------------------===//
40
41 ExplodedGraph::ExplodedGraph() = default;
42
43 ExplodedGraph::~ExplodedGraph() = default;
44
45 //===----------------------------------------------------------------------===//
46 // Node reclamation.
47 //===----------------------------------------------------------------------===//
48
isInterestingLValueExpr(const Expr * Ex)49 bool ExplodedGraph::isInterestingLValueExpr(const Expr *Ex) {
50 if (!Ex->isLValue())
51 return false;
52 return isa<DeclRefExpr>(Ex) ||
53 isa<MemberExpr>(Ex) ||
54 isa<ObjCIvarRefExpr>(Ex);
55 }
56
shouldCollect(const ExplodedNode * node)57 bool ExplodedGraph::shouldCollect(const ExplodedNode *node) {
58 // First, we only consider nodes for reclamation of the following
59 // conditions apply:
60 //
61 // (1) 1 predecessor (that has one successor)
62 // (2) 1 successor (that has one predecessor)
63 //
64 // If a node has no successor it is on the "frontier", while a node
65 // with no predecessor is a root.
66 //
67 // After these prerequisites, we discard all "filler" nodes that
68 // are used only for intermediate processing, and are not essential
69 // for analyzer history:
70 //
71 // (a) PreStmtPurgeDeadSymbols
72 //
73 // We then discard all other nodes where *all* of the following conditions
74 // apply:
75 //
76 // (3) The ProgramPoint is for a PostStmt, but not a PostStore.
77 // (4) There is no 'tag' for the ProgramPoint.
78 // (5) The 'store' is the same as the predecessor.
79 // (6) The 'GDM' is the same as the predecessor.
80 // (7) The LocationContext is the same as the predecessor.
81 // (8) Expressions that are *not* lvalue expressions.
82 // (9) The PostStmt isn't for a non-consumed Stmt or Expr.
83 // (10) The successor is neither a CallExpr StmtPoint nor a CallEnter or
84 // PreImplicitCall (so that we would be able to find it when retrying a
85 // call with no inlining).
86 // FIXME: It may be safe to reclaim PreCall and PostCall nodes as well.
87
88 // Conditions 1 and 2.
89 if (node->pred_size() != 1 || node->succ_size() != 1)
90 return false;
91
92 const ExplodedNode *pred = *(node->pred_begin());
93 if (pred->succ_size() != 1)
94 return false;
95
96 const ExplodedNode *succ = *(node->succ_begin());
97 if (succ->pred_size() != 1)
98 return false;
99
100 // Now reclaim any nodes that are (by definition) not essential to
101 // analysis history and are not consulted by any client code.
102 ProgramPoint progPoint = node->getLocation();
103 if (progPoint.getAs<PreStmtPurgeDeadSymbols>())
104 return !progPoint.getTag();
105
106 // Condition 3.
107 if (!progPoint.getAs<PostStmt>() || progPoint.getAs<PostStore>())
108 return false;
109
110 // Condition 4.
111 if (progPoint.getTag())
112 return false;
113
114 // Conditions 5, 6, and 7.
115 ProgramStateRef state = node->getState();
116 ProgramStateRef pred_state = pred->getState();
117 if (state->store != pred_state->store || state->GDM != pred_state->GDM ||
118 progPoint.getLocationContext() != pred->getLocationContext())
119 return false;
120
121 // All further checks require expressions. As per #3, we know that we have
122 // a PostStmt.
123 const Expr *Ex = dyn_cast<Expr>(progPoint.castAs<PostStmt>().getStmt());
124 if (!Ex)
125 return false;
126
127 // Condition 8.
128 // Do not collect nodes for "interesting" lvalue expressions since they are
129 // used extensively for generating path diagnostics.
130 if (isInterestingLValueExpr(Ex))
131 return false;
132
133 // Condition 9.
134 // Do not collect nodes for non-consumed Stmt or Expr to ensure precise
135 // diagnostic generation; specifically, so that we could anchor arrows
136 // pointing to the beginning of statements (as written in code).
137 ParentMap &PM = progPoint.getLocationContext()->getParentMap();
138 if (!PM.isConsumedExpr(Ex))
139 return false;
140
141 // Condition 10.
142 const ProgramPoint SuccLoc = succ->getLocation();
143 if (Optional<StmtPoint> SP = SuccLoc.getAs<StmtPoint>())
144 if (CallEvent::isCallStmt(SP->getStmt()))
145 return false;
146
147 // Condition 10, continuation.
148 if (SuccLoc.getAs<CallEnter>() || SuccLoc.getAs<PreImplicitCall>())
149 return false;
150
151 return true;
152 }
153
collectNode(ExplodedNode * node)154 void ExplodedGraph::collectNode(ExplodedNode *node) {
155 // Removing a node means:
156 // (a) changing the predecessors successor to the successor of this node
157 // (b) changing the successors predecessor to the predecessor of this node
158 // (c) Putting 'node' onto freeNodes.
159 assert(node->pred_size() == 1 || node->succ_size() == 1);
160 ExplodedNode *pred = *(node->pred_begin());
161 ExplodedNode *succ = *(node->succ_begin());
162 pred->replaceSuccessor(succ);
163 succ->replacePredecessor(pred);
164 FreeNodes.push_back(node);
165 Nodes.RemoveNode(node);
166 --NumNodes;
167 node->~ExplodedNode();
168 }
169
reclaimRecentlyAllocatedNodes()170 void ExplodedGraph::reclaimRecentlyAllocatedNodes() {
171 if (ChangedNodes.empty())
172 return;
173
174 // Only periodically reclaim nodes so that we can build up a set of
175 // nodes that meet the reclamation criteria. Freshly created nodes
176 // by definition have no successor, and thus cannot be reclaimed (see below).
177 assert(ReclaimCounter > 0);
178 if (--ReclaimCounter != 0)
179 return;
180 ReclaimCounter = ReclaimNodeInterval;
181
182 for (const auto node : ChangedNodes)
183 if (shouldCollect(node))
184 collectNode(node);
185 ChangedNodes.clear();
186 }
187
188 //===----------------------------------------------------------------------===//
189 // ExplodedNode.
190 //===----------------------------------------------------------------------===//
191
192 // An NodeGroup's storage type is actually very much like a TinyPtrVector:
193 // it can be either a pointer to a single ExplodedNode, or a pointer to a
194 // BumpVector allocated with the ExplodedGraph's allocator. This allows the
195 // common case of single-node NodeGroups to be implemented with no extra memory.
196 //
197 // Consequently, each of the NodeGroup methods have up to four cases to handle:
198 // 1. The flag is set and this group does not actually contain any nodes.
199 // 2. The group is empty, in which case the storage value is null.
200 // 3. The group contains a single node.
201 // 4. The group contains more than one node.
202 using ExplodedNodeVector = BumpVector<ExplodedNode *>;
203 using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>;
204
addPredecessor(ExplodedNode * V,ExplodedGraph & G)205 void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
206 assert(!V->isSink());
207 Preds.addNode(V, G);
208 V->Succs.addNode(this, G);
209 }
210
replaceNode(ExplodedNode * node)211 void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) {
212 assert(!getFlag());
213
214 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
215 assert(Storage.is<ExplodedNode *>());
216 Storage = node;
217 assert(Storage.is<ExplodedNode *>());
218 }
219
addNode(ExplodedNode * N,ExplodedGraph & G)220 void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) {
221 assert(!getFlag());
222
223 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
224 if (Storage.isNull()) {
225 Storage = N;
226 assert(Storage.is<ExplodedNode *>());
227 return;
228 }
229
230 ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>();
231
232 if (!V) {
233 // Switch from single-node to multi-node representation.
234 ExplodedNode *Old = Storage.get<ExplodedNode *>();
235
236 BumpVectorContext &Ctx = G.getNodeAllocator();
237 V = G.getAllocator().Allocate<ExplodedNodeVector>();
238 new (V) ExplodedNodeVector(Ctx, 4);
239 V->push_back(Old, Ctx);
240
241 Storage = V;
242 assert(!getFlag());
243 assert(Storage.is<ExplodedNodeVector *>());
244 }
245
246 V->push_back(N, G.getNodeAllocator());
247 }
248
size() const249 unsigned ExplodedNode::NodeGroup::size() const {
250 if (getFlag())
251 return 0;
252
253 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
254 if (Storage.isNull())
255 return 0;
256 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
257 return V->size();
258 return 1;
259 }
260
begin() const261 ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
262 if (getFlag())
263 return nullptr;
264
265 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
266 if (Storage.isNull())
267 return nullptr;
268 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
269 return V->begin();
270 return Storage.getAddrOfPtr1();
271 }
272
end() const273 ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
274 if (getFlag())
275 return nullptr;
276
277 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
278 if (Storage.isNull())
279 return nullptr;
280 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
281 return V->end();
282 return Storage.getAddrOfPtr1() + 1;
283 }
284
getID(ExplodedGraph * G) const285 int64_t ExplodedNode::getID(ExplodedGraph *G) const {
286 return G->getAllocator().identifyKnownAlignedObject<ExplodedNode>(this);
287 }
288
isTrivial() const289 bool ExplodedNode::isTrivial() const {
290 return pred_size() == 1 && succ_size() == 1 &&
291 getFirstPred()->getState()->getID() == getState()->getID() &&
292 getFirstPred()->succ_size() == 1;
293 }
294
getNode(const ProgramPoint & L,ProgramStateRef State,bool IsSink,bool * IsNew)295 ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
296 ProgramStateRef State,
297 bool IsSink,
298 bool* IsNew) {
299 // Profile 'State' to determine if we already have an existing node.
300 llvm::FoldingSetNodeID profile;
301 void *InsertPos = nullptr;
302
303 NodeTy::Profile(profile, L, State, IsSink);
304 NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos);
305
306 if (!V) {
307 if (!FreeNodes.empty()) {
308 V = FreeNodes.back();
309 FreeNodes.pop_back();
310 }
311 else {
312 // Allocate a new node.
313 V = (NodeTy*) getAllocator().Allocate<NodeTy>();
314 }
315
316 new (V) NodeTy(L, State, IsSink);
317
318 if (ReclaimNodeInterval)
319 ChangedNodes.push_back(V);
320
321 // Insert the node into the node set and return it.
322 Nodes.InsertNode(V, InsertPos);
323 ++NumNodes;
324
325 if (IsNew) *IsNew = true;
326 }
327 else
328 if (IsNew) *IsNew = false;
329
330 return V;
331 }
332
createUncachedNode(const ProgramPoint & L,ProgramStateRef State,bool IsSink)333 ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
334 ProgramStateRef State,
335 bool IsSink) {
336 NodeTy *V = (NodeTy *) getAllocator().Allocate<NodeTy>();
337 new (V) NodeTy(L, State, IsSink);
338 return V;
339 }
340
341 std::unique_ptr<ExplodedGraph>
trim(ArrayRef<const NodeTy * > Sinks,InterExplodedGraphMap * ForwardMap,InterExplodedGraphMap * InverseMap) const342 ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks,
343 InterExplodedGraphMap *ForwardMap,
344 InterExplodedGraphMap *InverseMap) const {
345 if (Nodes.empty())
346 return nullptr;
347
348 using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
349 Pass1Ty Pass1;
350
351 using Pass2Ty = InterExplodedGraphMap;
352 InterExplodedGraphMap Pass2Scratch;
353 Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
354
355 SmallVector<const ExplodedNode*, 10> WL1, WL2;
356
357 // ===- Pass 1 (reverse DFS) -===
358 for (const auto Sink : Sinks)
359 if (Sink)
360 WL1.push_back(Sink);
361
362 // Process the first worklist until it is empty.
363 while (!WL1.empty()) {
364 const ExplodedNode *N = WL1.pop_back_val();
365
366 // Have we already visited this node? If so, continue to the next one.
367 if (!Pass1.insert(N).second)
368 continue;
369
370 // If this is a root enqueue it to the second worklist.
371 if (N->Preds.empty()) {
372 WL2.push_back(N);
373 continue;
374 }
375
376 // Visit our predecessors and enqueue them.
377 WL1.append(N->Preds.begin(), N->Preds.end());
378 }
379
380 // We didn't hit a root? Return with a null pointer for the new graph.
381 if (WL2.empty())
382 return nullptr;
383
384 // Create an empty graph.
385 std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph();
386
387 // ===- Pass 2 (forward DFS to construct the new graph) -===
388 while (!WL2.empty()) {
389 const ExplodedNode *N = WL2.pop_back_val();
390
391 // Skip this node if we have already processed it.
392 if (Pass2.find(N) != Pass2.end())
393 continue;
394
395 // Create the corresponding node in the new graph and record the mapping
396 // from the old node to the new node.
397 ExplodedNode *NewN = G->createUncachedNode(N->getLocation(), N->State, N->isSink());
398 Pass2[N] = NewN;
399
400 // Also record the reverse mapping from the new node to the old node.
401 if (InverseMap) (*InverseMap)[NewN] = N;
402
403 // If this node is a root, designate it as such in the graph.
404 if (N->Preds.empty())
405 G->addRoot(NewN);
406
407 // In the case that some of the intended predecessors of NewN have already
408 // been created, we should hook them up as predecessors.
409
410 // Walk through the predecessors of 'N' and hook up their corresponding
411 // nodes in the new graph (if any) to the freshly created node.
412 for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end();
413 I != E; ++I) {
414 Pass2Ty::iterator PI = Pass2.find(*I);
415 if (PI == Pass2.end())
416 continue;
417
418 NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *G);
419 }
420
421 // In the case that some of the intended successors of NewN have already
422 // been created, we should hook them up as successors. Otherwise, enqueue
423 // the new nodes from the original graph that should have nodes created
424 // in the new graph.
425 for (ExplodedNode::succ_iterator I = N->Succs.begin(), E = N->Succs.end();
426 I != E; ++I) {
427 Pass2Ty::iterator PI = Pass2.find(*I);
428 if (PI != Pass2.end()) {
429 const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G);
430 continue;
431 }
432
433 // Enqueue nodes to the worklist that were marked during pass 1.
434 if (Pass1.count(*I))
435 WL2.push_back(*I);
436 }
437 }
438
439 return G;
440 }
441