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/CFGStmtMap.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
35using namespace clang;
36using namespace ento;
37
38//===----------------------------------------------------------------------===//
39// Cleanup.
40//===----------------------------------------------------------------------===//
41
42ExplodedGraph::ExplodedGraph() = default;
43
44ExplodedGraph::~ExplodedGraph() = default;
45
46//===----------------------------------------------------------------------===//
47// Node reclamation.
48//===----------------------------------------------------------------------===//
49
50bool ExplodedGraph::isInterestingLValueExpr(const Expr *Ex) {
51 if (!Ex->isLValue())
52 return false;
53 return isa<DeclRefExpr, MemberExpr, ObjCIvarRefExpr, ArraySubscriptExpr>(Ex);
54}
55
56bool ExplodedGraph::shouldCollect(const ExplodedNode *node) {
57 // First, we only consider nodes for reclamation of the following
58 // conditions apply:
59 //
60 // (1) 1 predecessor (that has one successor)
61 // (2) 1 successor (that has one predecessor)
62 //
63 // If a node has no successor it is on the "frontier", while a node
64 // with no predecessor is a root.
65 //
66 // After these prerequisites, we discard all "filler" nodes that
67 // are used only for intermediate processing, and are not essential
68 // for analyzer history:
69 //
70 // (a) PreStmtPurgeDeadSymbols
71 //
72 // We then discard all other nodes where *all* of the following conditions
73 // apply:
74 //
75 // (3) The ProgramPoint is for a PostStmt, but not a PostStore.
76 // (4) There is no 'tag' for the ProgramPoint.
77 // (5) The 'store' is the same as the predecessor.
78 // (6) The 'GDM' is the same as the predecessor.
79 // (7) The LocationContext is the same as the predecessor.
80 // (8) Expressions that are *not* lvalue expressions.
81 // (9) The PostStmt isn't for a non-consumed Stmt or Expr.
82 // (10) The successor is neither a CallExpr StmtPoint nor a CallEnter or
83 // PreImplicitCall (so that we would be able to find it when retrying a
84 // call with no inlining).
85 // FIXME: It may be safe to reclaim PreCall and PostCall nodes as well.
86
87 // Conditions 1 and 2.
88 if (node->pred_size() != 1 || node->succ_size() != 1)
89 return false;
90
91 const ExplodedNode *pred = *(node->pred_begin());
92 if (pred->succ_size() != 1)
93 return false;
94
95 const ExplodedNode *succ = *(node->succ_begin());
96 if (succ->pred_size() != 1)
97 return false;
98
99 // Now reclaim any nodes that are (by definition) not essential to
100 // analysis history and are not consulted by any client code.
101 ProgramPoint progPoint = node->getLocation();
102 if (progPoint.getAs<PreStmtPurgeDeadSymbols>())
103 return !progPoint.getTag();
104
105 // Condition 3.
106 if (!progPoint.getAs<PostStmt>() || progPoint.getAs<PostStore>())
107 return false;
108
109 // Condition 4.
110 if (progPoint.getTag())
111 return false;
112
113 // Conditions 5, 6, and 7.
114 ProgramStateRef state = node->getState();
115 ProgramStateRef pred_state = pred->getState();
116 if (state->store != pred_state->store || state->GDM != pred_state->GDM ||
117 progPoint.getLocationContext() != pred->getLocationContext())
118 return false;
119
120 // All further checks require expressions. As per #3, we know that we have
121 // a PostStmt.
122 const Expr *Ex = dyn_cast<Expr>(progPoint.castAs<PostStmt>().getStmt());
123 if (!Ex)
124 return false;
125
126 // Condition 8.
127 // Do not collect nodes for "interesting" lvalue expressions since they are
128 // used extensively for generating path diagnostics.
129 if (isInterestingLValueExpr(Ex))
130 return false;
131
132 // Condition 9.
133 // Do not collect nodes for non-consumed Stmt or Expr to ensure precise
134 // diagnostic generation; specifically, so that we could anchor arrows
135 // pointing to the beginning of statements (as written in code).
136 const ParentMap &PM = progPoint.getLocationContext()->getParentMap();
137 if (!PM.isConsumedExpr(Ex))
138 return false;
139
140 // Condition 10.
141 const ProgramPoint SuccLoc = succ->getLocation();
142 if (Optional<StmtPoint> SP = SuccLoc.getAs<StmtPoint>())
143 if (CallEvent::isCallStmt(SP->getStmt()))
144 return false;
145
146 // Condition 10, continuation.
147 if (SuccLoc.getAs<CallEnter>() || SuccLoc.getAs<PreImplicitCall>())
148 return false;
149
150 return true;
151}
152
153void ExplodedGraph::collectNode(ExplodedNode *node) {
154 // Removing a node means:
155 // (a) changing the predecessors successor to the successor of this node
156 // (b) changing the successors predecessor to the predecessor of this node
157 // (c) Putting 'node' onto freeNodes.
158 assert(node->pred_size() == 1 || node->succ_size() == 1);
159 ExplodedNode *pred = *(node->pred_begin());
160 ExplodedNode *succ = *(node->succ_begin());
161 pred->replaceSuccessor(succ);
162 succ->replacePredecessor(pred);
163 FreeNodes.push_back(node);
164 Nodes.RemoveNode(node);
165 --NumNodes;
166 node->~ExplodedNode();
167}
168
169void ExplodedGraph::reclaimRecentlyAllocatedNodes() {
170 if (ChangedNodes.empty())
171 return;
172
173 // Only periodically reclaim nodes so that we can build up a set of
174 // nodes that meet the reclamation criteria. Freshly created nodes
175 // by definition have no successor, and thus cannot be reclaimed (see below).
176 assert(ReclaimCounter > 0);
177 if (--ReclaimCounter != 0)
178 return;
179 ReclaimCounter = ReclaimNodeInterval;
180
181 for (const auto node : ChangedNodes)
182 if (shouldCollect(node))
183 collectNode(node);
184 ChangedNodes.clear();
185}
186
187//===----------------------------------------------------------------------===//
188// ExplodedNode.
189//===----------------------------------------------------------------------===//
190
191// An NodeGroup's storage type is actually very much like a TinyPtrVector:
192// it can be either a pointer to a single ExplodedNode, or a pointer to a
193// BumpVector allocated with the ExplodedGraph's allocator. This allows the
194// common case of single-node NodeGroups to be implemented with no extra memory.
195//
196// Consequently, each of the NodeGroup methods have up to four cases to handle:
197// 1. The flag is set and this group does not actually contain any nodes.
198// 2. The group is empty, in which case the storage value is null.
199// 3. The group contains a single node.
200// 4. The group contains more than one node.
201using ExplodedNodeVector = BumpVector<ExplodedNode *>;
202using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>;
203
204void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
205 assert(!V->isSink());
206 Preds.addNode(V, G);
207 V->Succs.addNode(this, G);
208}
209
210void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) {
211 assert(!getFlag());
212
213 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
214 assert(Storage.is<ExplodedNode *>());
215 Storage = node;
216 assert(Storage.is<ExplodedNode *>());
217}
218
219void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) {
220 assert(!getFlag());
221
222 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
223 if (Storage.isNull()) {
224 Storage = N;
225 assert(Storage.is<ExplodedNode *>());
226 return;
227 }
228
229 ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>();
230
231 if (!V) {
232 // Switch from single-node to multi-node representation.
233 ExplodedNode *Old = Storage.get<ExplodedNode *>();
234
235 BumpVectorContext &Ctx = G.getNodeAllocator();
236 V = G.getAllocator().Allocate<ExplodedNodeVector>();
237 new (V) ExplodedNodeVector(Ctx, 4);
238 V->push_back(Old, Ctx);
239
240 Storage = V;
241 assert(!getFlag());
242 assert(Storage.is<ExplodedNodeVector *>());
243 }
244
245 V->push_back(N, G.getNodeAllocator());
246}
247
248unsigned ExplodedNode::NodeGroup::size() const {
249 if (getFlag())
250 return 0;
251
252 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
253 if (Storage.isNull())
254 return 0;
255 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
256 return V->size();
257 return 1;
258}
259
260ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
261 if (getFlag())
262 return nullptr;
263
264 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
265 if (Storage.isNull())
266 return nullptr;
267 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
268 return V->begin();
269 return Storage.getAddrOfPtr1();
270}
271
272ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
273 if (getFlag())
274 return nullptr;
275
276 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
277 if (Storage.isNull())
278 return nullptr;
279 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
280 return V->end();
281 return Storage.getAddrOfPtr1() + 1;
282}
283
284bool ExplodedNode::isTrivial() const {
285 return pred_size() == 1 && succ_size() == 1 &&
286 getFirstPred()->getState()->getID() == getState()->getID() &&
287 getFirstPred()->succ_size() == 1;
288}
289
290const CFGBlock *ExplodedNode::getCFGBlock() const {
291 ProgramPoint P = getLocation();
292 if (auto BEP = P.getAs<BlockEntrance>())
293 return BEP->getBlock();
294
295 // Find the node's current statement in the CFG.
296 // FIXME: getStmtForDiagnostics() does nasty things in order to provide
297 // a valid statement for body farms, do we need this behavior here?
298 if (const Stmt *S = getStmtForDiagnostics())
299 return getLocationContext()
300 ->getAnalysisDeclContext()
301 ->getCFGStmtMap()
302 ->getBlock(S);
303
304 return nullptr;
305}
306
307static const LocationContext *
308findTopAutosynthesizedParentContext(const LocationContext *LC) {
309 assert(LC->getAnalysisDeclContext()->isBodyAutosynthesized());
310 const LocationContext *ParentLC = LC->getParent();
311 assert(ParentLC && "We don't start analysis from autosynthesized code");
312 while (ParentLC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
313 LC = ParentLC;
314 ParentLC = LC->getParent();
315 assert(ParentLC && "We don't start analysis from autosynthesized code");
316 }
317 return LC;
318}
319
320const Stmt *ExplodedNode::getStmtForDiagnostics() const {
321 // We cannot place diagnostics on autosynthesized code.
322 // Put them onto the call site through which we jumped into autosynthesized
323 // code for the first time.
324 const LocationContext *LC = getLocationContext();
325 if (LC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
326 // It must be a stack frame because we only autosynthesize functions.
327 return cast<StackFrameContext>(findTopAutosynthesizedParentContext(LC))
328 ->getCallSite();
329 }
330 // Otherwise, see if the node's program point directly points to a statement.
331 // FIXME: Refactor into a ProgramPoint method?
332 ProgramPoint P = getLocation();
333 if (auto SP = P.getAs<StmtPoint>())
334 return SP->getStmt();
335 if (auto BE = P.getAs<BlockEdge>())
336 return BE->getSrc()->getTerminatorStmt();
337 if (auto CE = P.getAs<CallEnter>())
338 return CE->getCallExpr();
339 if (auto CEE = P.getAs<CallExitEnd>())
340 return CEE->getCalleeContext()->getCallSite();
341 if (auto PIPP = P.getAs<PostInitializer>())
342 return PIPP->getInitializer()->getInit();
343 if (auto CEB = P.getAs<CallExitBegin>())
344 return CEB->getReturnStmt();
345 if (auto FEP = P.getAs<FunctionExitPoint>())
346 return FEP->getStmt();
347
348 return nullptr;
349}
350
351const Stmt *ExplodedNode::getNextStmtForDiagnostics() const {
352 for (const ExplodedNode *N = getFirstSucc(); N; N = N->getFirstSucc()) {
353 if (const Stmt *S = N->getStmtForDiagnostics()) {
354 // Check if the statement is '?' or '&&'/'||'. These are "merges",
355 // not actual statement points.
356 switch (S->getStmtClass()) {
357 case Stmt::ChooseExprClass:
358 case Stmt::BinaryConditionalOperatorClass:
359 case Stmt::ConditionalOperatorClass:
360 continue;
361 case Stmt::BinaryOperatorClass: {
362 BinaryOperatorKind Op = cast<BinaryOperator>(S)->getOpcode();
363 if (Op == BO_LAnd || Op == BO_LOr)
364 continue;
365 break;
366 }
367 default:
368 break;
369 }
370 // We found the statement, so return it.
371 return S;
372 }
373 }
374
375 return nullptr;
376}
377
378const Stmt *ExplodedNode::getPreviousStmtForDiagnostics() const {
379 for (const ExplodedNode *N = getFirstPred(); N; N = N->getFirstPred())
380 if (const Stmt *S = N->getStmtForDiagnostics())
381 return S;
382
383 return nullptr;
384}
385
386const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const {
387 if (const Stmt *S = getStmtForDiagnostics())
388 return S;
389
390 return getPreviousStmtForDiagnostics();
391}
392
393ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
394 ProgramStateRef State,
395 bool IsSink,
396 bool* IsNew) {
397 // Profile 'State' to determine if we already have an existing node.
398 llvm::FoldingSetNodeID profile;
399 void *InsertPos = nullptr;
400
401 NodeTy::Profile(profile, L, State, IsSink);
402 NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos);
403
404 if (!V) {
405 if (!FreeNodes.empty()) {
406 V = FreeNodes.back();
407 FreeNodes.pop_back();
408 }
409 else {
410 // Allocate a new node.
411 V = (NodeTy*) getAllocator().Allocate<NodeTy>();
412 }
413
414 ++NumNodes;
415 new (V) NodeTy(L, State, NumNodes, IsSink);
416
417 if (ReclaimNodeInterval)
418 ChangedNodes.push_back(V);
419
420 // Insert the node into the node set and return it.
421 Nodes.InsertNode(V, InsertPos);
422
423 if (IsNew) *IsNew = true;
424 }
425 else
426 if (IsNew) *IsNew = false;
427
428 return V;
429}
430
431ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
432 ProgramStateRef State,
433 int64_t Id,
434 bool IsSink) {
435 NodeTy *V = (NodeTy *) getAllocator().Allocate<NodeTy>();
436 new (V) NodeTy(L, State, Id, IsSink);
437 return V;
438}
439
440std::unique_ptr<ExplodedGraph>
441ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks,
442 InterExplodedGraphMap *ForwardMap,
443 InterExplodedGraphMap *InverseMap) const {
444 if (Nodes.empty())
445 return nullptr;
446
447 using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
448 Pass1Ty Pass1;
449
450 using Pass2Ty = InterExplodedGraphMap;
451 InterExplodedGraphMap Pass2Scratch;
452 Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
453
454 SmallVector<const ExplodedNode*, 10> WL1, WL2;
455
456 // ===- Pass 1 (reverse DFS) -===
457 for (const auto Sink : Sinks)
458 if (Sink)
459 WL1.push_back(Sink);
460
461 // Process the first worklist until it is empty.
462 while (!WL1.empty()) {
463 const ExplodedNode *N = WL1.pop_back_val();
464
465 // Have we already visited this node? If so, continue to the next one.
466 if (!Pass1.insert(N).second)
467 continue;
468
469 // If this is a root enqueue it to the second worklist.
470 if (N->Preds.empty()) {
471 WL2.push_back(N);
472 continue;
473 }
474
475 // Visit our predecessors and enqueue them.
476 WL1.append(N->Preds.begin(), N->Preds.end());
477 }
478
479 // We didn't hit a root? Return with a null pointer for the new graph.
480 if (WL2.empty())
481 return nullptr;
482
483 // Create an empty graph.
484 std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph();
485
486 // ===- Pass 2 (forward DFS to construct the new graph) -===
487 while (!WL2.empty()) {
488 const ExplodedNode *N = WL2.pop_back_val();
489
490 // Skip this node if we have already processed it.
491 if (Pass2.find(N) != Pass2.end())
492 continue;
493
494 // Create the corresponding node in the new graph and record the mapping
495 // from the old node to the new node.
496 ExplodedNode *NewN = G->createUncachedNode(N->getLocation(), N->State,
497 N->getID(), N->isSink());
498 Pass2[N] = NewN;
499
500 // Also record the reverse mapping from the new node to the old node.
501 if (InverseMap) (*InverseMap)[NewN] = N;
502
503 // If this node is a root, designate it as such in the graph.
504 if (N->Preds.empty())
505 G->addRoot(NewN);
506
507 // In the case that some of the intended predecessors of NewN have already
508 // been created, we should hook them up as predecessors.
509
510 // Walk through the predecessors of 'N' and hook up their corresponding
511 // nodes in the new graph (if any) to the freshly created node.
512 for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end();
513 I != E; ++I) {
514 Pass2Ty::iterator PI = Pass2.find(*I);
515 if (PI == Pass2.end())
516 continue;
517
518 NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *G);
519 }
520
521 // In the case that some of the intended successors of NewN have already
522 // been created, we should hook them up as successors. Otherwise, enqueue
523 // the new nodes from the original graph that should have nodes created
524 // in the new graph.
525 for (ExplodedNode::succ_iterator I = N->Succs.begin(), E = N->Succs.end();
526 I != E; ++I) {
527 Pass2Ty::iterator PI = Pass2.find(*I);
528 if (PI != Pass2.end()) {
529 const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G);
530 continue;
531 }
532
533 // Enqueue nodes to the worklist that were marked during pass 1.
534 if (Pass1.count(*I))
535 WL2.push_back(*I);
536 }
537 }
538
539 return G;
540}
541

source code of clang/lib/StaticAnalyzer/Core/ExplodedGraph.cpp