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 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>(Ex) || 54 isa<MemberExpr>(Ex) || 55 isa<ObjCIvarRefExpr>(Ex); 56 } 57 58 bool ExplodedGraph::shouldCollect(const ExplodedNode *node) { 59 // First, we only consider nodes for reclamation of the following 60 // conditions apply: 61 // 62 // (1) 1 predecessor (that has one successor) 63 // (2) 1 successor (that has one predecessor) 64 // 65 // If a node has no successor it is on the "frontier", while a node 66 // with no predecessor is a root. 67 // 68 // After these prerequisites, we discard all "filler" nodes that 69 // are used only for intermediate processing, and are not essential 70 // for analyzer history: 71 // 72 // (a) PreStmtPurgeDeadSymbols 73 // 74 // We then discard all other nodes where *all* of the following conditions 75 // apply: 76 // 77 // (3) The ProgramPoint is for a PostStmt, but not a PostStore. 78 // (4) There is no 'tag' for the ProgramPoint. 79 // (5) The 'store' is the same as the predecessor. 80 // (6) The 'GDM' is the same as the predecessor. 81 // (7) The LocationContext is the same as the predecessor. 82 // (8) Expressions that are *not* lvalue expressions. 83 // (9) The PostStmt isn't for a non-consumed Stmt or Expr. 84 // (10) The successor is neither a CallExpr StmtPoint nor a CallEnter or 85 // PreImplicitCall (so that we would be able to find it when retrying a 86 // call with no inlining). 87 // FIXME: It may be safe to reclaim PreCall and PostCall nodes as well. 88 89 // Conditions 1 and 2. 90 if (node->pred_size() != 1 || node->succ_size() != 1) 91 return false; 92 93 const ExplodedNode *pred = *(node->pred_begin()); 94 if (pred->succ_size() != 1) 95 return false; 96 97 const ExplodedNode *succ = *(node->succ_begin()); 98 if (succ->pred_size() != 1) 99 return false; 100 101 // Now reclaim any nodes that are (by definition) not essential to 102 // analysis history and are not consulted by any client code. 103 ProgramPoint progPoint = node->getLocation(); 104 if (progPoint.getAs<PreStmtPurgeDeadSymbols>()) 105 return !progPoint.getTag(); 106 107 // Condition 3. 108 if (!progPoint.getAs<PostStmt>() || progPoint.getAs<PostStore>()) 109 return false; 110 111 // Condition 4. 112 if (progPoint.getTag()) 113 return false; 114 115 // Conditions 5, 6, and 7. 116 ProgramStateRef state = node->getState(); 117 ProgramStateRef pred_state = pred->getState(); 118 if (state->store != pred_state->store || state->GDM != pred_state->GDM || 119 progPoint.getLocationContext() != pred->getLocationContext()) 120 return false; 121 122 // All further checks require expressions. As per #3, we know that we have 123 // a PostStmt. 124 const Expr *Ex = dyn_cast<Expr>(progPoint.castAs<PostStmt>().getStmt()); 125 if (!Ex) 126 return false; 127 128 // Condition 8. 129 // Do not collect nodes for "interesting" lvalue expressions since they are 130 // used extensively for generating path diagnostics. 131 if (isInterestingLValueExpr(Ex)) 132 return false; 133 134 // Condition 9. 135 // Do not collect nodes for non-consumed Stmt or Expr to ensure precise 136 // diagnostic generation; specifically, so that we could anchor arrows 137 // pointing to the beginning of statements (as written in code). 138 const ParentMap &PM = progPoint.getLocationContext()->getParentMap(); 139 if (!PM.isConsumedExpr(Ex)) 140 return false; 141 142 // Condition 10. 143 const ProgramPoint SuccLoc = succ->getLocation(); 144 if (Optional<StmtPoint> SP = SuccLoc.getAs<StmtPoint>()) 145 if (CallEvent::isCallStmt(SP->getStmt())) 146 return false; 147 148 // Condition 10, continuation. 149 if (SuccLoc.getAs<CallEnter>() || SuccLoc.getAs<PreImplicitCall>()) 150 return false; 151 152 return true; 153 } 154 155 void ExplodedGraph::collectNode(ExplodedNode *node) { 156 // Removing a node means: 157 // (a) changing the predecessors successor to the successor of this node 158 // (b) changing the successors predecessor to the predecessor of this node 159 // (c) Putting 'node' onto freeNodes. 160 assert(node->pred_size() == 1 || node->succ_size() == 1); 161 ExplodedNode *pred = *(node->pred_begin()); 162 ExplodedNode *succ = *(node->succ_begin()); 163 pred->replaceSuccessor(succ); 164 succ->replacePredecessor(pred); 165 FreeNodes.push_back(node); 166 Nodes.RemoveNode(node); 167 --NumNodes; 168 node->~ExplodedNode(); 169 } 170 171 void ExplodedGraph::reclaimRecentlyAllocatedNodes() { 172 if (ChangedNodes.empty()) 173 return; 174 175 // Only periodically reclaim nodes so that we can build up a set of 176 // nodes that meet the reclamation criteria. Freshly created nodes 177 // by definition have no successor, and thus cannot be reclaimed (see below). 178 assert(ReclaimCounter > 0); 179 if (--ReclaimCounter != 0) 180 return; 181 ReclaimCounter = ReclaimNodeInterval; 182 183 for (const auto node : ChangedNodes) 184 if (shouldCollect(node)) 185 collectNode(node); 186 ChangedNodes.clear(); 187 } 188 189 //===----------------------------------------------------------------------===// 190 // ExplodedNode. 191 //===----------------------------------------------------------------------===// 192 193 // An NodeGroup's storage type is actually very much like a TinyPtrVector: 194 // it can be either a pointer to a single ExplodedNode, or a pointer to a 195 // BumpVector allocated with the ExplodedGraph's allocator. This allows the 196 // common case of single-node NodeGroups to be implemented with no extra memory. 197 // 198 // Consequently, each of the NodeGroup methods have up to four cases to handle: 199 // 1. The flag is set and this group does not actually contain any nodes. 200 // 2. The group is empty, in which case the storage value is null. 201 // 3. The group contains a single node. 202 // 4. The group contains more than one node. 203 using ExplodedNodeVector = BumpVector<ExplodedNode *>; 204 using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>; 205 206 void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) { 207 assert(!V->isSink()); 208 Preds.addNode(V, G); 209 V->Succs.addNode(this, G); 210 } 211 212 void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) { 213 assert(!getFlag()); 214 215 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P); 216 assert(Storage.is<ExplodedNode *>()); 217 Storage = node; 218 assert(Storage.is<ExplodedNode *>()); 219 } 220 221 void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) { 222 assert(!getFlag()); 223 224 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P); 225 if (Storage.isNull()) { 226 Storage = N; 227 assert(Storage.is<ExplodedNode *>()); 228 return; 229 } 230 231 ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>(); 232 233 if (!V) { 234 // Switch from single-node to multi-node representation. 235 ExplodedNode *Old = Storage.get<ExplodedNode *>(); 236 237 BumpVectorContext &Ctx = G.getNodeAllocator(); 238 V = G.getAllocator().Allocate<ExplodedNodeVector>(); 239 new (V) ExplodedNodeVector(Ctx, 4); 240 V->push_back(Old, Ctx); 241 242 Storage = V; 243 assert(!getFlag()); 244 assert(Storage.is<ExplodedNodeVector *>()); 245 } 246 247 V->push_back(N, G.getNodeAllocator()); 248 } 249 250 unsigned ExplodedNode::NodeGroup::size() const { 251 if (getFlag()) 252 return 0; 253 254 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P); 255 if (Storage.isNull()) 256 return 0; 257 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>()) 258 return V->size(); 259 return 1; 260 } 261 262 ExplodedNode * const *ExplodedNode::NodeGroup::begin() const { 263 if (getFlag()) 264 return nullptr; 265 266 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P); 267 if (Storage.isNull()) 268 return nullptr; 269 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>()) 270 return V->begin(); 271 return Storage.getAddrOfPtr1(); 272 } 273 274 ExplodedNode * const *ExplodedNode::NodeGroup::end() const { 275 if (getFlag()) 276 return nullptr; 277 278 const GroupStorage &Storage = reinterpret_cast<const GroupStorage &>(P); 279 if (Storage.isNull()) 280 return nullptr; 281 if (ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>()) 282 return V->end(); 283 return Storage.getAddrOfPtr1() + 1; 284 } 285 286 int64_t ExplodedNode::getID(ExplodedGraph *G) const { 287 return G->getAllocator().identifyKnownAlignedObject<ExplodedNode>(this); 288 } 289 290 bool ExplodedNode::isTrivial() const { 291 return pred_size() == 1 && succ_size() == 1 && 292 getFirstPred()->getState()->getID() == getState()->getID() && 293 getFirstPred()->succ_size() == 1; 294 } 295 296 const CFGBlock *ExplodedNode::getCFGBlock() const { 297 ProgramPoint P = getLocation(); 298 if (auto BEP = P.getAs<BlockEntrance>()) 299 return BEP->getBlock(); 300 301 // Find the node's current statement in the CFG. 302 // FIXME: getStmtForDiagnostics() does nasty things in order to provide 303 // a valid statement for body farms, do we need this behavior here? 304 if (const Stmt *S = getStmtForDiagnostics()) 305 return getLocationContext() 306 ->getAnalysisDeclContext() 307 ->getCFGStmtMap() 308 ->getBlock(S); 309 310 return nullptr; 311 } 312 313 static const LocationContext * 314 findTopAutosynthesizedParentContext(const LocationContext *LC) { 315 assert(LC->getAnalysisDeclContext()->isBodyAutosynthesized()); 316 const LocationContext *ParentLC = LC->getParent(); 317 assert(ParentLC && "We don't start analysis from autosynthesized code"); 318 while (ParentLC->getAnalysisDeclContext()->isBodyAutosynthesized()) { 319 LC = ParentLC; 320 ParentLC = LC->getParent(); 321 assert(ParentLC && "We don't start analysis from autosynthesized code"); 322 } 323 return LC; 324 } 325 326 const Stmt *ExplodedNode::getStmtForDiagnostics() const { 327 // We cannot place diagnostics on autosynthesized code. 328 // Put them onto the call site through which we jumped into autosynthesized 329 // code for the first time. 330 const LocationContext *LC = getLocationContext(); 331 if (LC->getAnalysisDeclContext()->isBodyAutosynthesized()) { 332 // It must be a stack frame because we only autosynthesize functions. 333 return cast<StackFrameContext>(findTopAutosynthesizedParentContext(LC)) 334 ->getCallSite(); 335 } 336 // Otherwise, see if the node's program point directly points to a statement. 337 // FIXME: Refactor into a ProgramPoint method? 338 ProgramPoint P = getLocation(); 339 if (auto SP = P.getAs<StmtPoint>()) 340 return SP->getStmt(); 341 if (auto BE = P.getAs<BlockEdge>()) 342 return BE->getSrc()->getTerminatorStmt(); 343 if (auto CE = P.getAs<CallEnter>()) 344 return CE->getCallExpr(); 345 if (auto CEE = P.getAs<CallExitEnd>()) 346 return CEE->getCalleeContext()->getCallSite(); 347 if (auto PIPP = P.getAs<PostInitializer>()) 348 return PIPP->getInitializer()->getInit(); 349 if (auto CEB = P.getAs<CallExitBegin>()) 350 return CEB->getReturnStmt(); 351 if (auto FEP = P.getAs<FunctionExitPoint>()) 352 return FEP->getStmt(); 353 354 return nullptr; 355 } 356 357 const Stmt *ExplodedNode::getNextStmtForDiagnostics() const { 358 for (const ExplodedNode *N = getFirstSucc(); N; N = N->getFirstSucc()) { 359 if (const Stmt *S = N->getStmtForDiagnostics()) { 360 // Check if the statement is '?' or '&&'/'||'. These are "merges", 361 // not actual statement points. 362 switch (S->getStmtClass()) { 363 case Stmt::ChooseExprClass: 364 case Stmt::BinaryConditionalOperatorClass: 365 case Stmt::ConditionalOperatorClass: 366 continue; 367 case Stmt::BinaryOperatorClass: { 368 BinaryOperatorKind Op = cast<BinaryOperator>(S)->getOpcode(); 369 if (Op == BO_LAnd || Op == BO_LOr) 370 continue; 371 break; 372 } 373 default: 374 break; 375 } 376 // We found the statement, so return it. 377 return S; 378 } 379 } 380 381 return nullptr; 382 } 383 384 const Stmt *ExplodedNode::getPreviousStmtForDiagnostics() const { 385 for (const ExplodedNode *N = getFirstPred(); N; N = N->getFirstPred()) 386 if (const Stmt *S = N->getStmtForDiagnostics()) 387 return S; 388 389 return nullptr; 390 } 391 392 const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const { 393 if (const Stmt *S = getStmtForDiagnostics()) 394 return S; 395 396 return getPreviousStmtForDiagnostics(); 397 } 398 399 ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L, 400 ProgramStateRef State, 401 bool IsSink, 402 bool* IsNew) { 403 // Profile 'State' to determine if we already have an existing node. 404 llvm::FoldingSetNodeID profile; 405 void *InsertPos = nullptr; 406 407 NodeTy::Profile(profile, L, State, IsSink); 408 NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos); 409 410 if (!V) { 411 if (!FreeNodes.empty()) { 412 V = FreeNodes.back(); 413 FreeNodes.pop_back(); 414 } 415 else { 416 // Allocate a new node. 417 V = (NodeTy*) getAllocator().Allocate<NodeTy>(); 418 } 419 420 new (V) NodeTy(L, State, IsSink); 421 422 if (ReclaimNodeInterval) 423 ChangedNodes.push_back(V); 424 425 // Insert the node into the node set and return it. 426 Nodes.InsertNode(V, InsertPos); 427 ++NumNodes; 428 429 if (IsNew) *IsNew = true; 430 } 431 else 432 if (IsNew) *IsNew = false; 433 434 return V; 435 } 436 437 ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L, 438 ProgramStateRef State, 439 bool IsSink) { 440 NodeTy *V = (NodeTy *) getAllocator().Allocate<NodeTy>(); 441 new (V) NodeTy(L, State, IsSink); 442 return V; 443 } 444 445 std::unique_ptr<ExplodedGraph> 446 ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks, 447 InterExplodedGraphMap *ForwardMap, 448 InterExplodedGraphMap *InverseMap) const { 449 if (Nodes.empty()) 450 return nullptr; 451 452 using Pass1Ty = llvm::DenseSet<const ExplodedNode *>; 453 Pass1Ty Pass1; 454 455 using Pass2Ty = InterExplodedGraphMap; 456 InterExplodedGraphMap Pass2Scratch; 457 Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch; 458 459 SmallVector<const ExplodedNode*, 10> WL1, WL2; 460 461 // ===- Pass 1 (reverse DFS) -=== 462 for (const auto Sink : Sinks) 463 if (Sink) 464 WL1.push_back(Sink); 465 466 // Process the first worklist until it is empty. 467 while (!WL1.empty()) { 468 const ExplodedNode *N = WL1.pop_back_val(); 469 470 // Have we already visited this node? If so, continue to the next one. 471 if (!Pass1.insert(N).second) 472 continue; 473 474 // If this is a root enqueue it to the second worklist. 475 if (N->Preds.empty()) { 476 WL2.push_back(N); 477 continue; 478 } 479 480 // Visit our predecessors and enqueue them. 481 WL1.append(N->Preds.begin(), N->Preds.end()); 482 } 483 484 // We didn't hit a root? Return with a null pointer for the new graph. 485 if (WL2.empty()) 486 return nullptr; 487 488 // Create an empty graph. 489 std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph(); 490 491 // ===- Pass 2 (forward DFS to construct the new graph) -=== 492 while (!WL2.empty()) { 493 const ExplodedNode *N = WL2.pop_back_val(); 494 495 // Skip this node if we have already processed it. 496 if (Pass2.find(N) != Pass2.end()) 497 continue; 498 499 // Create the corresponding node in the new graph and record the mapping 500 // from the old node to the new node. 501 ExplodedNode *NewN = G->createUncachedNode(N->getLocation(), N->State, N->isSink()); 502 Pass2[N] = NewN; 503 504 // Also record the reverse mapping from the new node to the old node. 505 if (InverseMap) (*InverseMap)[NewN] = N; 506 507 // If this node is a root, designate it as such in the graph. 508 if (N->Preds.empty()) 509 G->addRoot(NewN); 510 511 // In the case that some of the intended predecessors of NewN have already 512 // been created, we should hook them up as predecessors. 513 514 // Walk through the predecessors of 'N' and hook up their corresponding 515 // nodes in the new graph (if any) to the freshly created node. 516 for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end(); 517 I != E; ++I) { 518 Pass2Ty::iterator PI = Pass2.find(*I); 519 if (PI == Pass2.end()) 520 continue; 521 522 NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *G); 523 } 524 525 // In the case that some of the intended successors of NewN have already 526 // been created, we should hook them up as successors. Otherwise, enqueue 527 // the new nodes from the original graph that should have nodes created 528 // in the new graph. 529 for (ExplodedNode::succ_iterator I = N->Succs.begin(), E = N->Succs.end(); 530 I != E; ++I) { 531 Pass2Ty::iterator PI = Pass2.find(*I); 532 if (PI != Pass2.end()) { 533 const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G); 534 continue; 535 } 536 537 // Enqueue nodes to the worklist that were marked during pass 1. 538 if (Pass1.count(*I)) 539 WL2.push_back(*I); 540 } 541 } 542 543 return G; 544 } 545