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, 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 (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 = 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 } 247 248 unsigned 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 } 259 260 ExplodedNode * 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 } 271 272 ExplodedNode * 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 } 283 284 bool ExplodedNode::isTrivial() const { 285 return pred_size() == 1 && succ_size() == 1 && 286 getFirstPred()->getState()->getID() == getState()->getID() && 287 getFirstPred()->succ_size() == 1; 288 } 289 290 const 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 } 306 307 static const LocationContext * 308 findTopAutosynthesizedParentContext(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 } 319 320 const 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 } 350 351 const 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 } 377 378 const 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 } 385 386 const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const { 387 if (const Stmt *S = getStmtForDiagnostics()) 388 return S; 389 390 return getPreviousStmtForDiagnostics(); 391 } 392 393 ExplodedNode *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 } 430 431 ExplodedNode *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 } 439 440 std::unique_ptr<ExplodedGraph> 441 ExplodedGraph::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