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 35 using namespace clang; 36 using namespace ento; 37 38 //===----------------------------------------------------------------------===// 39 // Cleanup. 40 //===----------------------------------------------------------------------===// 41 42 ExplodedGraph::ExplodedGraph() = default; 43 44 ExplodedGraph::~ExplodedGraph() = default; 45 46 //===----------------------------------------------------------------------===// 47 // Node reclamation. 48 //===----------------------------------------------------------------------===// 49 50 bool ExplodedGraph::isInterestingLValueExpr(const Expr *Ex) { 51 if (!Ex->isLValue()) 52 return false; 53 return isa<DeclRefExpr, MemberExpr, ObjCIvarRefExpr, ArraySubscriptExpr>(Ex); 54 } 55 56 bool 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 (std::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 } 152 153 void 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 } 168 169 void 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. 201 using ExplodedNodeVector = BumpVector<ExplodedNode *>; 202 using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>; 203 204 void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) { 205 assert(!V->isSink()); 206 Preds.addNode(V, G); 207 V->Succs.addNode(this, G); 208 } 209 210 void 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 } 218 219 void 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(Old, Ctx); 238 239 Storage = V; 240 assert(!getFlag()); 241 assert(Storage.is<ExplodedNodeVector *>()); 242 } 243 244 V->push_back(N, G.getNodeAllocator()); 245 } 246 247 unsigned 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 } 258 259 ExplodedNode * 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 } 270 271 ExplodedNode * 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 } 282 283 bool ExplodedNode::isTrivial() const { 284 return pred_size() == 1 && succ_size() == 1 && 285 getFirstPred()->getState()->getID() == getState()->getID() && 286 getFirstPred()->succ_size() == 1; 287 } 288 289 const 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 } 305 306 static const LocationContext * 307 findTopAutosynthesizedParentContext(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 } 318 319 const 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>(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 } 349 350 const 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>(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 } 376 377 const 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 } 384 385 const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const { 386 if (const Stmt *S = getStmtForDiagnostics()) 387 return S; 388 389 return getPreviousStmtForDiagnostics(); 390 } 391 392 ExplodedNode *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(profile, L, State, IsSink); 401 NodeTy* V = Nodes.FindNodeOrInsertPos(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(V); 418 419 // Insert the node into the node set and return it. 420 Nodes.InsertNode(V, InsertPos); 421 422 if (IsNew) *IsNew = true; 423 } 424 else 425 if (IsNew) *IsNew = false; 426 427 return V; 428 } 429 430 ExplodedNode *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 } 438 439 std::unique_ptr<ExplodedGraph> 440 ExplodedGraph::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(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(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(N); 471 continue; 472 } 473 474 // Visit our predecessors and enqueue them. 475 WL1.append(N->Preds.begin(), 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(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(N->getLocation(), N->State, 496 N->getID(), 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(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(Pred); 513 if (PI == Pass2.end()) 514 continue; 515 516 NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *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(Succ); 525 if (PI != Pass2.end()) { 526 const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G); 527 continue; 528 } 529 530 // Enqueue nodes to the worklist that were marked during pass 1. 531 if (Pass1.count(Succ)) 532 WL2.push_back(Succ); 533 } 534 } 535 536 return G; 537 } 538