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 <cassert>
30#include <memory>
31#include <optional>
32
33using namespace clang;
34using namespace ento;
35
36//===----------------------------------------------------------------------===//
37// Cleanup.
38//===----------------------------------------------------------------------===//
39
40ExplodedGraph::ExplodedGraph() = default;
41
42ExplodedGraph::~ExplodedGraph() = default;
43
44//===----------------------------------------------------------------------===//
45// Node reclamation.
46//===----------------------------------------------------------------------===//
47
48bool ExplodedGraph::isInterestingLValueExpr(const Expr *Ex) {
49 if (!Ex->isLValue())
50 return false;
51 return isa<DeclRefExpr, MemberExpr, ObjCIvarRefExpr, ArraySubscriptExpr>(Val: Ex);
52}
53
54bool ExplodedGraph::shouldCollect(const ExplodedNode *node) {
55 // First, we only consider nodes for reclamation of the following
56 // conditions apply:
57 //
58 // (1) 1 predecessor (that has one successor)
59 // (2) 1 successor (that has one predecessor)
60 //
61 // If a node has no successor it is on the "frontier", while a node
62 // with no predecessor is a root.
63 //
64 // After these prerequisites, we discard all "filler" nodes that
65 // are used only for intermediate processing, and are not essential
66 // for analyzer history:
67 //
68 // (a) PreStmtPurgeDeadSymbols
69 //
70 // We then discard all other nodes where *all* of the following conditions
71 // apply:
72 //
73 // (3) The ProgramPoint is for a PostStmt, but not a PostStore.
74 // (4) There is no 'tag' for the ProgramPoint.
75 // (5) The 'store' is the same as the predecessor.
76 // (6) The 'GDM' is the same as the predecessor.
77 // (7) The LocationContext is the same as the predecessor.
78 // (8) Expressions that are *not* lvalue expressions.
79 // (9) The PostStmt isn't for a non-consumed Stmt or Expr.
80 // (10) The successor is neither a CallExpr StmtPoint nor a CallEnter or
81 // PreImplicitCall (so that we would be able to find it when retrying a
82 // call with no inlining).
83 // FIXME: It may be safe to reclaim PreCall and PostCall nodes as well.
84
85 // Conditions 1 and 2.
86 if (node->pred_size() != 1 || node->succ_size() != 1)
87 return false;
88
89 const ExplodedNode *pred = *(node->pred_begin());
90 if (pred->succ_size() != 1)
91 return false;
92
93 const ExplodedNode *succ = *(node->succ_begin());
94 if (succ->pred_size() != 1)
95 return false;
96
97 // Now reclaim any nodes that are (by definition) not essential to
98 // analysis history and are not consulted by any client code.
99 ProgramPoint progPoint = node->getLocation();
100 if (progPoint.getAs<PreStmtPurgeDeadSymbols>())
101 return !progPoint.getTag();
102
103 // Condition 3.
104 if (!progPoint.getAs<PostStmt>() || progPoint.getAs<PostStore>())
105 return false;
106
107 // Condition 4.
108 if (progPoint.getTag())
109 return false;
110
111 // Conditions 5, 6, and 7.
112 ProgramStateRef state = node->getState();
113 ProgramStateRef pred_state = pred->getState();
114 if (state->store != pred_state->store || state->GDM != pred_state->GDM ||
115 progPoint.getLocationContext() != pred->getLocationContext())
116 return false;
117
118 // All further checks require expressions. As per #3, we know that we have
119 // a PostStmt.
120 const Expr *Ex = dyn_cast<Expr>(Val: progPoint.castAs<PostStmt>().getStmt());
121 if (!Ex)
122 return false;
123
124 // Condition 8.
125 // Do not collect nodes for "interesting" lvalue expressions since they are
126 // used extensively for generating path diagnostics.
127 if (isInterestingLValueExpr(Ex))
128 return false;
129
130 // Condition 9.
131 // Do not collect nodes for non-consumed Stmt or Expr to ensure precise
132 // diagnostic generation; specifically, so that we could anchor arrows
133 // pointing to the beginning of statements (as written in code).
134 const ParentMap &PM = progPoint.getLocationContext()->getParentMap();
135 if (!PM.isConsumedExpr(E: Ex))
136 return false;
137
138 // Condition 10.
139 const ProgramPoint SuccLoc = succ->getLocation();
140 if (std::optional<StmtPoint> SP = SuccLoc.getAs<StmtPoint>())
141 if (CallEvent::isCallStmt(S: SP->getStmt()))
142 return false;
143
144 // Condition 10, continuation.
145 if (SuccLoc.getAs<CallEnter>() || SuccLoc.getAs<PreImplicitCall>())
146 return false;
147
148 return true;
149}
150
151void ExplodedGraph::collectNode(ExplodedNode *node) {
152 // Removing a node means:
153 // (a) changing the predecessors successor to the successor of this node
154 // (b) changing the successors predecessor to the predecessor of this node
155 // (c) Putting 'node' onto freeNodes.
156 assert(node->pred_size() == 1 || node->succ_size() == 1);
157 ExplodedNode *pred = *(node->pred_begin());
158 ExplodedNode *succ = *(node->succ_begin());
159 pred->replaceSuccessor(node: succ);
160 succ->replacePredecessor(node: pred);
161 FreeNodes.push_back(x: node);
162 Nodes.RemoveNode(N: node);
163 --NumNodes;
164 node->~ExplodedNode();
165}
166
167void ExplodedGraph::reclaimRecentlyAllocatedNodes() {
168 if (ChangedNodes.empty())
169 return;
170
171 // Only periodically reclaim nodes so that we can build up a set of
172 // nodes that meet the reclamation criteria. Freshly created nodes
173 // by definition have no successor, and thus cannot be reclaimed (see below).
174 assert(ReclaimCounter > 0);
175 if (--ReclaimCounter != 0)
176 return;
177 ReclaimCounter = ReclaimNodeInterval;
178
179 for (const auto node : ChangedNodes)
180 if (shouldCollect(node))
181 collectNode(node);
182 ChangedNodes.clear();
183}
184
185//===----------------------------------------------------------------------===//
186// ExplodedNode.
187//===----------------------------------------------------------------------===//
188
189// An NodeGroup's storage type is actually very much like a TinyPtrVector:
190// it can be either a pointer to a single ExplodedNode, or a pointer to a
191// BumpVector allocated with the ExplodedGraph's allocator. This allows the
192// common case of single-node NodeGroups to be implemented with no extra memory.
193//
194// Consequently, each of the NodeGroup methods have up to four cases to handle:
195// 1. The flag is set and this group does not actually contain any nodes.
196// 2. The group is empty, in which case the storage value is null.
197// 3. The group contains a single node.
198// 4. The group contains more than one node.
199using ExplodedNodeVector = BumpVector<ExplodedNode *>;
200using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>;
201
202void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
203 assert(!V->isSink());
204 Preds.addNode(N: V, G);
205 V->Succs.addNode(N: this, G);
206}
207
208void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) {
209 assert(!getFlag());
210
211 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
212 assert(isa<ExplodedNode *>(Storage));
213 Storage = node;
214 assert(isa<ExplodedNode *>(Storage));
215}
216
217void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) {
218 assert(!getFlag());
219
220 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
221 if (Storage.isNull()) {
222 Storage = N;
223 assert(isa<ExplodedNode *>(Storage));
224 return;
225 }
226
227 ExplodedNodeVector *V = dyn_cast<ExplodedNodeVector *>(Val&: Storage);
228
229 if (!V) {
230 // Switch from single-node to multi-node representation.
231 auto *Old = cast<ExplodedNode *>(Val&: Storage);
232
233 BumpVectorContext &Ctx = G.getNodeAllocator();
234 V = new (G.getAllocator()) ExplodedNodeVector(Ctx, 4);
235 V->push_back(Elt: Old, C&: Ctx);
236
237 Storage = V;
238 assert(!getFlag());
239 assert(isa<ExplodedNodeVector *>(Storage));
240 }
241
242 V->push_back(Elt: N, C&: G.getNodeAllocator());
243}
244
245unsigned ExplodedNode::NodeGroup::size() const {
246 if (getFlag())
247 return 0;
248
249 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
250 if (Storage.isNull())
251 return 0;
252 if (ExplodedNodeVector *V = dyn_cast<ExplodedNodeVector *>(Val: Storage))
253 return V->size();
254 return 1;
255}
256
257ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
258 if (getFlag())
259 return nullptr;
260
261 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
262 if (Storage.isNull())
263 return nullptr;
264 if (ExplodedNodeVector *V = dyn_cast<ExplodedNodeVector *>(Val: Storage))
265 return V->begin();
266 return Storage.getAddrOfPtr1();
267}
268
269ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
270 if (getFlag())
271 return nullptr;
272
273 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P);
274 if (Storage.isNull())
275 return nullptr;
276 if (ExplodedNodeVector *V = dyn_cast<ExplodedNodeVector *>(Val: Storage))
277 return V->end();
278 return Storage.getAddrOfPtr1() + 1;
279}
280
281bool ExplodedNode::isTrivial() const {
282 return pred_size() == 1 && succ_size() == 1 &&
283 getFirstPred()->getState()->getID() == getState()->getID() &&
284 getFirstPred()->succ_size() == 1;
285}
286
287const CFGBlock *ExplodedNode::getCFGBlock() const {
288 ProgramPoint P = getLocation();
289 if (auto BEP = P.getAs<BlockEntrance>())
290 return BEP->getBlock();
291
292 // Find the node's current statement in the CFG.
293 // FIXME: getStmtForDiagnostics() does nasty things in order to provide
294 // a valid statement for body farms, do we need this behavior here?
295 if (const Stmt *S = getStmtForDiagnostics())
296 return getLocationContext()
297 ->getAnalysisDeclContext()
298 ->getCFGStmtMap()
299 ->getBlock(S);
300
301 return nullptr;
302}
303
304static const LocationContext *
305findTopAutosynthesizedParentContext(const LocationContext *LC) {
306 assert(LC->getAnalysisDeclContext()->isBodyAutosynthesized());
307 const LocationContext *ParentLC = LC->getParent();
308 assert(ParentLC && "We don't start analysis from autosynthesized code");
309 while (ParentLC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
310 LC = ParentLC;
311 ParentLC = LC->getParent();
312 assert(ParentLC && "We don't start analysis from autosynthesized code");
313 }
314 return LC;
315}
316
317const Stmt *ExplodedNode::getStmtForDiagnostics() const {
318 // We cannot place diagnostics on autosynthesized code.
319 // Put them onto the call site through which we jumped into autosynthesized
320 // code for the first time.
321 const LocationContext *LC = getLocationContext();
322 if (LC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
323 // It must be a stack frame because we only autosynthesize functions.
324 return cast<StackFrameContext>(Val: findTopAutosynthesizedParentContext(LC))
325 ->getCallSite();
326 }
327 // Otherwise, see if the node's program point directly points to a statement.
328 // FIXME: Refactor into a ProgramPoint method?
329 ProgramPoint P = getLocation();
330 if (auto SP = P.getAs<StmtPoint>())
331 return SP->getStmt();
332 if (auto BE = P.getAs<BlockEdge>())
333 return BE->getSrc()->getTerminatorStmt();
334 if (auto CE = P.getAs<CallEnter>())
335 return CE->getCallExpr();
336 if (auto CEE = P.getAs<CallExitEnd>())
337 return CEE->getCalleeContext()->getCallSite();
338 if (auto PIPP = P.getAs<PostInitializer>())
339 return PIPP->getInitializer()->getInit();
340 if (auto CEB = P.getAs<CallExitBegin>())
341 return CEB->getReturnStmt();
342 if (auto FEP = P.getAs<FunctionExitPoint>())
343 return FEP->getStmt();
344
345 return nullptr;
346}
347
348const Stmt *ExplodedNode::getNextStmtForDiagnostics() const {
349 for (const ExplodedNode *N = getFirstSucc(); N; N = N->getFirstSucc()) {
350 if (N->getLocation().isPurgeKind())
351 continue;
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(); S && !isa<CompoundStmt>(Val: S))
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 // FIXME: The two-pass algorithm of this function (which was introduced in
444 // 2008) is terribly overcomplicated and should be replaced by a single
445 // (backward) pass.
446
447 if (Nodes.empty())
448 return nullptr;
449
450 using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
451 Pass1Ty Pass1;
452
453 using Pass2Ty = InterExplodedGraphMap;
454 InterExplodedGraphMap Pass2Scratch;
455 Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
456
457 SmallVector<const ExplodedNode*, 10> WL1, WL2;
458
459 // ===- Pass 1 (reverse DFS) -===
460 for (const auto Sink : Sinks)
461 if (Sink)
462 WL1.push_back(Elt: Sink);
463
464 // Process the first worklist until it is empty.
465 while (!WL1.empty()) {
466 const ExplodedNode *N = WL1.pop_back_val();
467
468 // Have we already visited this node? If so, continue to the next one.
469 if (!Pass1.insert(V: N).second)
470 continue;
471
472 // If this is the root enqueue it to the second worklist.
473 if (N->Preds.empty()) {
474 assert(N == getRoot() && "Found non-root node with no predecessors!");
475 WL2.push_back(Elt: N);
476 continue;
477 }
478
479 // Visit our predecessors and enqueue them.
480 WL1.append(in_start: N->Preds.begin(), in_end: N->Preds.end());
481 }
482
483 // We didn't hit the root? Return with a null pointer for the new graph.
484 if (WL2.empty())
485 return nullptr;
486
487 assert(WL2.size() == 1 && "There must be only one root!");
488
489 // Create an empty graph.
490 std::unique_ptr<ExplodedGraph> G = std::make_unique<ExplodedGraph>();
491
492 // ===- Pass 2 (forward DFS to construct the new graph) -===
493 while (!WL2.empty()) {
494 const ExplodedNode *N = WL2.pop_back_val();
495
496 auto [Place, Inserted] = Pass2.try_emplace(Key: N);
497
498 // Skip this node if we have already processed it.
499 if (!Inserted)
500 continue;
501
502 // Create the corresponding node in the new graph and record the mapping
503 // from the old node to the new node.
504 ExplodedNode *NewN = G->createUncachedNode(L: N->getLocation(), State: N->State,
505 Id: N->getID(), IsSink: N->isSink());
506 Place->second = NewN;
507
508 // Also record the reverse mapping from the new node to the old node.
509 if (InverseMap) (*InverseMap)[NewN] = N;
510
511 // If this node is the root, designate it as such in the graph.
512 if (N->Preds.empty()) {
513 assert(N == getRoot());
514 G->designateAsRoot(V: NewN);
515 }
516
517 // In the case that some of the intended predecessors of NewN have already
518 // been created, we should hook them up as predecessors.
519
520 // Walk through the predecessors of 'N' and hook up their corresponding
521 // nodes in the new graph (if any) to the freshly created node.
522 for (const ExplodedNode *Pred : N->Preds) {
523 Pass2Ty::iterator PI = Pass2.find(Val: Pred);
524 if (PI == Pass2.end())
525 continue;
526
527 NewN->addPredecessor(V: const_cast<ExplodedNode *>(PI->second), G&: *G);
528 }
529
530 // In the case that some of the intended successors of NewN have already
531 // been created, we should hook them up as successors. Otherwise, enqueue
532 // the new nodes from the original graph that should have nodes created
533 // in the new graph.
534 for (const ExplodedNode *Succ : N->Succs) {
535 Pass2Ty::iterator PI = Pass2.find(Val: Succ);
536 if (PI != Pass2.end()) {
537 const_cast<ExplodedNode *>(PI->second)->addPredecessor(V: NewN, G&: *G);
538 continue;
539 }
540
541 // Enqueue nodes to the worklist that were marked during pass 1.
542 if (Pass1.count(V: Succ))
543 WL2.push_back(Elt: Succ);
544 }
545 }
546
547 return G;
548}
549