[MLIR] Removing dead values for branches (#117501)
[llvm-project.git] / clang / lib / StaticAnalyzer / Core / ExplodedGraph.cpp
blobc4af02f21f4943f927080f03c576171bbffe79b3
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."
12 //===----------------------------------------------------------------------===//
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>
35 using namespace clang;
36 using namespace ento;
38 //===----------------------------------------------------------------------===//
39 // Cleanup.
40 //===----------------------------------------------------------------------===//
42 ExplodedGraph::ExplodedGraph() = default;
44 ExplodedGraph::~ExplodedGraph() = default;
46 //===----------------------------------------------------------------------===//
47 // Node reclamation.
48 //===----------------------------------------------------------------------===//
50 bool ExplodedGraph::isInterestingLValueExpr(const Expr *Ex) {
51 if (!Ex->isLValue())
52 return false;
53 return isa<DeclRefExpr, MemberExpr, ObjCIvarRefExpr, ArraySubscriptExpr>(Ex);
56 bool ExplodedGraph::shouldCollect(const ExplodedNode *node) {
57 // First, we only consider nodes for reclamation of the following
58 // conditions apply:
60 // (1) 1 predecessor (that has one successor)
61 // (2) 1 successor (that has one predecessor)
63 // If a node has no successor it is on the "frontier", while a node
64 // with no predecessor is a root.
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:
70 // (a) PreStmtPurgeDeadSymbols
72 // We then discard all other nodes where *all* of the following conditions
73 // apply:
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.
87 // Conditions 1 and 2.
88 if (node->pred_size() != 1 || node->succ_size() != 1)
89 return false;
91 const ExplodedNode *pred = *(node->pred_begin());
92 if (pred->succ_size() != 1)
93 return false;
95 const ExplodedNode *succ = *(node->succ_begin());
96 if (succ->pred_size() != 1)
97 return false;
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();
105 // Condition 3.
106 if (!progPoint.getAs<PostStmt>() || progPoint.getAs<PostStore>())
107 return false;
109 // Condition 4.
110 if (progPoint.getTag())
111 return false;
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;
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;
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;
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;
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;
146 // Condition 10, continuation.
147 if (SuccLoc.getAs<CallEnter>() || SuccLoc.getAs<PreImplicitCall>())
148 return false;
150 return true;
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();
169 void ExplodedGraph::reclaimRecentlyAllocatedNodes() {
170 if (ChangedNodes.empty())
171 return;
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;
181 for (const auto node : ChangedNodes)
182 if (shouldCollect(node))
183 collectNode(node);
184 ChangedNodes.clear();
187 //===----------------------------------------------------------------------===//
188 // ExplodedNode.
189 //===----------------------------------------------------------------------===//
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.
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 *>;
204 void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
205 assert(!V->isSink());
206 Preds.addNode(V, G);
207 V->Succs.addNode(this, G);
210 void ExplodedNode::NodeGroup::replaceNode(ExplodedNode *node) {
211 assert(!getFlag());
213 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
214 assert(isa<ExplodedNode *>(Storage));
215 Storage = node;
216 assert(isa<ExplodedNode *>(Storage));
219 void ExplodedNode::NodeGroup::addNode(ExplodedNode *N, ExplodedGraph &G) {
220 assert(!getFlag());
222 GroupStorage &Storage = reinterpret_cast<GroupStorage&>(P);
223 if (Storage.isNull()) {
224 Storage = N;
225 assert(isa<ExplodedNode *>(Storage));
226 return;
229 ExplodedNodeVector *V = Storage.dyn_cast<ExplodedNodeVector *>();
231 if (!V) {
232 // Switch from single-node to multi-node representation.
233 auto *Old = cast<ExplodedNode *>(Storage);
235 BumpVectorContext &Ctx = G.getNodeAllocator();
236 V = new (G.getAllocator()) ExplodedNodeVector(Ctx, 4);
237 V->push_back(Old, Ctx);
239 Storage = V;
240 assert(!getFlag());
241 assert(isa<ExplodedNodeVector *>(Storage));
244 V->push_back(N, G.getNodeAllocator());
247 unsigned ExplodedNode::NodeGroup::size() const {
248 if (getFlag())
249 return 0;
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;
259 ExplodedNode * const *ExplodedNode::NodeGroup::begin() const {
260 if (getFlag())
261 return nullptr;
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();
271 ExplodedNode * const *ExplodedNode::NodeGroup::end() const {
272 if (getFlag())
273 return nullptr;
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;
283 bool ExplodedNode::isTrivial() const {
284 return pred_size() == 1 && succ_size() == 1 &&
285 getFirstPred()->getState()->getID() == getState()->getID() &&
286 getFirstPred()->succ_size() == 1;
289 const CFGBlock *ExplodedNode::getCFGBlock() const {
290 ProgramPoint P = getLocation();
291 if (auto BEP = P.getAs<BlockEntrance>())
292 return BEP->getBlock();
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);
303 return nullptr;
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");
316 return LC;
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();
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();
347 return nullptr;
350 const Stmt *ExplodedNode::getNextStmtForDiagnostics() const {
351 for (const ExplodedNode *N = getFirstSucc(); N; N = N->getFirstSucc()) {
352 if (N->getLocation().isPurgeKind())
353 continue;
354 if (const Stmt *S = N->getStmtForDiagnostics()) {
355 // Check if the statement is '?' or '&&'/'||'. These are "merges",
356 // not actual statement points.
357 switch (S->getStmtClass()) {
358 case Stmt::ChooseExprClass:
359 case Stmt::BinaryConditionalOperatorClass:
360 case Stmt::ConditionalOperatorClass:
361 continue;
362 case Stmt::BinaryOperatorClass: {
363 BinaryOperatorKind Op = cast<BinaryOperator>(S)->getOpcode();
364 if (Op == BO_LAnd || Op == BO_LOr)
365 continue;
366 break;
368 default:
369 break;
371 // We found the statement, so return it.
372 return S;
376 return nullptr;
379 const Stmt *ExplodedNode::getPreviousStmtForDiagnostics() const {
380 for (const ExplodedNode *N = getFirstPred(); N; N = N->getFirstPred())
381 if (const Stmt *S = N->getStmtForDiagnostics(); S && !isa<CompoundStmt>(S))
382 return S;
384 return nullptr;
387 const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const {
388 if (const Stmt *S = getStmtForDiagnostics())
389 return S;
391 return getPreviousStmtForDiagnostics();
394 ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
395 ProgramStateRef State,
396 bool IsSink,
397 bool* IsNew) {
398 // Profile 'State' to determine if we already have an existing node.
399 llvm::FoldingSetNodeID profile;
400 void *InsertPos = nullptr;
402 NodeTy::Profile(profile, L, State, IsSink);
403 NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos);
405 if (!V) {
406 if (!FreeNodes.empty()) {
407 V = FreeNodes.back();
408 FreeNodes.pop_back();
410 else {
411 // Allocate a new node.
412 V = getAllocator().Allocate<NodeTy>();
415 ++NumNodes;
416 new (V) NodeTy(L, State, NumNodes, IsSink);
418 if (ReclaimNodeInterval)
419 ChangedNodes.push_back(V);
421 // Insert the node into the node set and return it.
422 Nodes.InsertNode(V, InsertPos);
424 if (IsNew) *IsNew = true;
426 else
427 if (IsNew) *IsNew = false;
429 return V;
432 ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
433 ProgramStateRef State,
434 int64_t Id,
435 bool IsSink) {
436 NodeTy *V = getAllocator().Allocate<NodeTy>();
437 new (V) NodeTy(L, State, Id, IsSink);
438 return V;
441 std::unique_ptr<ExplodedGraph>
442 ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks,
443 InterExplodedGraphMap *ForwardMap,
444 InterExplodedGraphMap *InverseMap) const {
445 if (Nodes.empty())
446 return nullptr;
448 using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
449 Pass1Ty Pass1;
451 using Pass2Ty = InterExplodedGraphMap;
452 InterExplodedGraphMap Pass2Scratch;
453 Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
455 SmallVector<const ExplodedNode*, 10> WL1, WL2;
457 // ===- Pass 1 (reverse DFS) -===
458 for (const auto Sink : Sinks)
459 if (Sink)
460 WL1.push_back(Sink);
462 // Process the first worklist until it is empty.
463 while (!WL1.empty()) {
464 const ExplodedNode *N = WL1.pop_back_val();
466 // Have we already visited this node? If so, continue to the next one.
467 if (!Pass1.insert(N).second)
468 continue;
470 // If this is a root enqueue it to the second worklist.
471 if (N->Preds.empty()) {
472 WL2.push_back(N);
473 continue;
476 // Visit our predecessors and enqueue them.
477 WL1.append(N->Preds.begin(), N->Preds.end());
480 // We didn't hit a root? Return with a null pointer for the new graph.
481 if (WL2.empty())
482 return nullptr;
484 // Create an empty graph.
485 std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph();
487 // ===- Pass 2 (forward DFS to construct the new graph) -===
488 while (!WL2.empty()) {
489 const ExplodedNode *N = WL2.pop_back_val();
491 // Skip this node if we have already processed it.
492 if (Pass2.contains(N))
493 continue;
495 // Create the corresponding node in the new graph and record the mapping
496 // from the old node to the new node.
497 ExplodedNode *NewN = G->createUncachedNode(N->getLocation(), N->State,
498 N->getID(), N->isSink());
499 Pass2[N] = NewN;
501 // Also record the reverse mapping from the new node to the old node.
502 if (InverseMap) (*InverseMap)[NewN] = N;
504 // If this node is a root, designate it as such in the graph.
505 if (N->Preds.empty())
506 G->addRoot(NewN);
508 // In the case that some of the intended predecessors of NewN have already
509 // been created, we should hook them up as predecessors.
511 // Walk through the predecessors of 'N' and hook up their corresponding
512 // nodes in the new graph (if any) to the freshly created node.
513 for (const ExplodedNode *Pred : N->Preds) {
514 Pass2Ty::iterator PI = Pass2.find(Pred);
515 if (PI == Pass2.end())
516 continue;
518 NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *G);
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 (const ExplodedNode *Succ : N->Succs) {
526 Pass2Ty::iterator PI = Pass2.find(Succ);
527 if (PI != Pass2.end()) {
528 const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G);
529 continue;
532 // Enqueue nodes to the worklist that were marked during pass 1.
533 if (Pass1.count(Succ))
534 WL2.push_back(Succ);
538 return G;