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/PointerUnion.h"
29#include "llvm/ADT/SmallVector.h"
30#include "llvm/Support/Casting.h"
31#include <cassert>
32#include <memory>
33#include <optional>
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>(Val: 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>(Val: 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(E: Ex))
138 return false;
139
140 // Condition 10.
141 const ProgramPoint SuccLoc = succ->getLocation();
142 if (std::optional<StmtPoint> SP = SuccLoc.getAs<StmtPoint>())
143 if (CallEvent::isCallStmt(S: 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(node: succ);
162 succ->replacePredecessor(node: pred);
163 FreeNodes.push_back(x: node);
164 Nodes.RemoveNode(N: 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(N: V, G);
207 V->Succs.addNode(N: 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 = new (G.getAllocator()) ExplodedNodeVector(Ctx, 4);
237 V->push_back(Elt: Old, C&: Ctx);
238
239 Storage = V;
240 assert(!getFlag());
241 assert(Storage.is<ExplodedNodeVector *>());
242 }
243
244 V->push_back(Elt: N, C&: G.getNodeAllocator());
245}
246
247unsigned ExplodedNode::NodeGroup::size() const {
248 if (getFlag())
249 return 0;
250
251 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
252 if (Storage.isNull())
253 return 0;
254 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
255 return V->size();
256 return 1;
257}
258
259ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
260 if (getFlag())
261 return nullptr;
262
263 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
264 if (Storage.isNull())
265 return nullptr;
266 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
267 return V->begin();
268 return Storage.getAddrOfPtr1();
269}
270
271ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
272 if (getFlag())
273 return nullptr;
274
275 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
276 if (Storage.isNull())
277 return nullptr;
278 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>())
279 return V->end();
280 return Storage.getAddrOfPtr1() + 1;
281}
282
283bool ExplodedNode::isTrivial() const {
284 return pred_size() == 1 && succ_size() == 1 &&
285 getFirstPred()->getState()->getID() == getState()->getID() &&
286 getFirstPred()->succ_size() == 1;
287}
288
289const CFGBlock *ExplodedNode::getCFGBlock() const {
290 ProgramPoint P = getLocation();
291 if (auto BEP = P.getAs<BlockEntrance>())
292 return BEP->getBlock();
293
294 // Find the node's current statement in the CFG.
295 // FIXME: getStmtForDiagnostics() does nasty things in order to provide
296 // a valid statement for body farms, do we need this behavior here?
297 if (const Stmt *S = getStmtForDiagnostics())
298 return getLocationContext()
299 ->getAnalysisDeclContext()
300 ->getCFGStmtMap()
301 ->getBlock(S);
302
303 return nullptr;
304}
305
306static const LocationContext *
307findTopAutosynthesizedParentContext(const LocationContext *LC) {
308 assert(LC->getAnalysisDeclContext()->isBodyAutosynthesized());
309 const LocationContext *ParentLC = LC->getParent();
310 assert(ParentLC && "We don't start analysis from autosynthesized code");
311 while (ParentLC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
312 LC = ParentLC;
313 ParentLC = LC->getParent();
314 assert(ParentLC && "We don't start analysis from autosynthesized code");
315 }
316 return LC;
317}
318
319const Stmt *ExplodedNode::getStmtForDiagnostics() const {
320 // We cannot place diagnostics on autosynthesized code.
321 // Put them onto the call site through which we jumped into autosynthesized
322 // code for the first time.
323 const LocationContext *LC = getLocationContext();
324 if (LC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
325 // It must be a stack frame because we only autosynthesize functions.
326 return cast<StackFrameContext>(Val: findTopAutosynthesizedParentContext(LC))
327 ->getCallSite();
328 }
329 // Otherwise, see if the node's program point directly points to a statement.
330 // FIXME: Refactor into a ProgramPoint method?
331 ProgramPoint P = getLocation();
332 if (auto SP = P.getAs<StmtPoint>())
333 return SP->getStmt();
334 if (auto BE = P.getAs<BlockEdge>())
335 return BE->getSrc()->getTerminatorStmt();
336 if (auto CE = P.getAs<CallEnter>())
337 return CE->getCallExpr();
338 if (auto CEE = P.getAs<CallExitEnd>())
339 return CEE->getCalleeContext()->getCallSite();
340 if (auto PIPP = P.getAs<PostInitializer>())
341 return PIPP->getInitializer()->getInit();
342 if (auto CEB = P.getAs<CallExitBegin>())
343 return CEB->getReturnStmt();
344 if (auto FEP = P.getAs<FunctionExitPoint>())
345 return FEP->getStmt();
346
347 return nullptr;
348}
349
350const Stmt *ExplodedNode::getNextStmtForDiagnostics() const {
351 for (const ExplodedNode *N = getFirstSucc(); N; N = N->getFirstSucc()) {
352 if (const Stmt *S = N->getStmtForDiagnostics()) {
353 // Check if the statement is '?' or '&&'/'||'. These are "merges",
354 // not actual statement points.
355 switch (S->getStmtClass()) {
356 case Stmt::ChooseExprClass:
357 case Stmt::BinaryConditionalOperatorClass:
358 case Stmt::ConditionalOperatorClass:
359 continue;
360 case Stmt::BinaryOperatorClass: {
361 BinaryOperatorKind Op = cast<BinaryOperator>(Val: S)->getOpcode();
362 if (Op == BO_LAnd || Op == BO_LOr)
363 continue;
364 break;
365 }
366 default:
367 break;
368 }
369 // We found the statement, so return it.
370 return S;
371 }
372 }
373
374 return nullptr;
375}
376
377const Stmt *ExplodedNode::getPreviousStmtForDiagnostics() const {
378 for (const ExplodedNode *N = getFirstPred(); N; N = N->getFirstPred())
379 if (const Stmt *S = N->getStmtForDiagnostics())
380 return S;
381
382 return nullptr;
383}
384
385const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const {
386 if (const Stmt *S = getStmtForDiagnostics())
387 return S;
388
389 return getPreviousStmtForDiagnostics();
390}
391
392ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
393 ProgramStateRef State,
394 bool IsSink,
395 bool* IsNew) {
396 // Profile 'State' to determine if we already have an existing node.
397 llvm::FoldingSetNodeID profile;
398 void *InsertPos = nullptr;
399
400 NodeTy::Profile(ID&: profile, Loc: L, state: State, IsSink);
401 NodeTy* V = Nodes.FindNodeOrInsertPos(ID: profile, InsertPos);
402
403 if (!V) {
404 if (!FreeNodes.empty()) {
405 V = FreeNodes.back();
406 FreeNodes.pop_back();
407 }
408 else {
409 // Allocate a new node.
410 V = getAllocator().Allocate<NodeTy>();
411 }
412
413 ++NumNodes;
414 new (V) NodeTy(L, State, NumNodes, IsSink);
415
416 if (ReclaimNodeInterval)
417 ChangedNodes.push_back(x: V);
418
419 // Insert the node into the node set and return it.
420 Nodes.InsertNode(N: V, InsertPos);
421
422 if (IsNew) *IsNew = true;
423 }
424 else
425 if (IsNew) *IsNew = false;
426
427 return V;
428}
429
430ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
431 ProgramStateRef State,
432 int64_t Id,
433 bool IsSink) {
434 NodeTy *V = getAllocator().Allocate<NodeTy>();
435 new (V) NodeTy(L, State, Id, IsSink);
436 return V;
437}
438
439std::unique_ptr<ExplodedGraph>
440ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks,
441 InterExplodedGraphMap *ForwardMap,
442 InterExplodedGraphMap *InverseMap) const {
443 if (Nodes.empty())
444 return nullptr;
445
446 using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
447 Pass1Ty Pass1;
448
449 using Pass2Ty = InterExplodedGraphMap;
450 InterExplodedGraphMap Pass2Scratch;
451 Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
452
453 SmallVector<const ExplodedNode*, 10> WL1, WL2;
454
455 // ===- Pass 1 (reverse DFS) -===
456 for (const auto Sink : Sinks)
457 if (Sink)
458 WL1.push_back(Elt: Sink);
459
460 // Process the first worklist until it is empty.
461 while (!WL1.empty()) {
462 const ExplodedNode *N = WL1.pop_back_val();
463
464 // Have we already visited this node? If so, continue to the next one.
465 if (!Pass1.insert(V: N).second)
466 continue;
467
468 // If this is a root enqueue it to the second worklist.
469 if (N->Preds.empty()) {
470 WL2.push_back(Elt: N);
471 continue;
472 }
473
474 // Visit our predecessors and enqueue them.
475 WL1.append(in_start: N->Preds.begin(), in_end: N->Preds.end());
476 }
477
478 // We didn't hit a root? Return with a null pointer for the new graph.
479 if (WL2.empty())
480 return nullptr;
481
482 // Create an empty graph.
483 std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph();
484
485 // ===- Pass 2 (forward DFS to construct the new graph) -===
486 while (!WL2.empty()) {
487 const ExplodedNode *N = WL2.pop_back_val();
488
489 // Skip this node if we have already processed it.
490 if (Pass2.contains(Val: N))
491 continue;
492
493 // Create the corresponding node in the new graph and record the mapping
494 // from the old node to the new node.
495 ExplodedNode *NewN = G->createUncachedNode(L: N->getLocation(), State: N->State,
496 Id: N->getID(), IsSink: N->isSink());
497 Pass2[N] = NewN;
498
499 // Also record the reverse mapping from the new node to the old node.
500 if (InverseMap) (*InverseMap)[NewN] = N;
501
502 // If this node is a root, designate it as such in the graph.
503 if (N->Preds.empty())
504 G->addRoot(V: NewN);
505
506 // In the case that some of the intended predecessors of NewN have already
507 // been created, we should hook them up as predecessors.
508
509 // Walk through the predecessors of 'N' and hook up their corresponding
510 // nodes in the new graph (if any) to the freshly created node.
511 for (const ExplodedNode *Pred : N->Preds) {
512 Pass2Ty::iterator PI = Pass2.find(Val: Pred);
513 if (PI == Pass2.end())
514 continue;
515
516 NewN->addPredecessor(V: const_cast<ExplodedNode *>(PI->second), G&: *G);
517 }
518
519 // In the case that some of the intended successors of NewN have already
520 // been created, we should hook them up as successors. Otherwise, enqueue
521 // the new nodes from the original graph that should have nodes created
522 // in the new graph.
523 for (const ExplodedNode *Succ : N->Succs) {
524 Pass2Ty::iterator PI = Pass2.find(Val: Succ);
525 if (PI != Pass2.end()) {
526 const_cast<ExplodedNode *>(PI->second)->addPredecessor(V: NewN, G&: *G);
527 continue;
528 }
529
530 // Enqueue nodes to the worklist that were marked during pass 1.
531 if (Pass1.count(V: Succ))
532 WL2.push_back(Elt: Succ);
533 }
534 }
535
536 return G;
537}
538