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
35using namespace clang;
36using namespace ento;
37
38//===----------------------------------------------------------------------===//
39// Cleanup.
40//===----------------------------------------------------------------------===//
41
42ExplodedGraph::ExplodedGraph() = default;
43
44ExplodedGraph::~ExplodedGraph() = default;
45
46//===----------------------------------------------------------------------===//
47// Node reclamation.
48//===----------------------------------------------------------------------===//
49
50bool 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
58bool 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
155void 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
171void 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.
203using ExplodedNodeVector = BumpVector<ExplodedNode *>;
204using GroupStorage = llvm::PointerUnion<ExplodedNode *, ExplodedNodeVector *>;
205
206void ExplodedNode::addPredecessor(ExplodedNode *V, ExplodedGraph &G) {
207  assert(!V->isSink());
208  Preds.addNode(V, G);
209  V->Succs.addNode(this, G);
210}
211
212void 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
221void 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
250unsigned 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
262ExplodedNode * 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
274ExplodedNode * 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
286bool ExplodedNode::isTrivial() const {
287  return pred_size() == 1 && succ_size() == 1 &&
288         getFirstPred()->getState()->getID() == getState()->getID() &&
289         getFirstPred()->succ_size() == 1;
290}
291
292const CFGBlock *ExplodedNode::getCFGBlock() const {
293  ProgramPoint P = getLocation();
294  if (auto BEP = P.getAs<BlockEntrance>())
295    return BEP->getBlock();
296
297  // Find the node's current statement in the CFG.
298  // FIXME: getStmtForDiagnostics() does nasty things in order to provide
299  // a valid statement for body farms, do we need this behavior here?
300  if (const Stmt *S = getStmtForDiagnostics())
301    return getLocationContext()
302        ->getAnalysisDeclContext()
303        ->getCFGStmtMap()
304        ->getBlock(S);
305
306  return nullptr;
307}
308
309static const LocationContext *
310findTopAutosynthesizedParentContext(const LocationContext *LC) {
311  assert(LC->getAnalysisDeclContext()->isBodyAutosynthesized());
312  const LocationContext *ParentLC = LC->getParent();
313  assert(ParentLC && "We don't start analysis from autosynthesized code");
314  while (ParentLC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
315    LC = ParentLC;
316    ParentLC = LC->getParent();
317    assert(ParentLC && "We don't start analysis from autosynthesized code");
318  }
319  return LC;
320}
321
322const Stmt *ExplodedNode::getStmtForDiagnostics() const {
323  // We cannot place diagnostics on autosynthesized code.
324  // Put them onto the call site through which we jumped into autosynthesized
325  // code for the first time.
326  const LocationContext *LC = getLocationContext();
327  if (LC->getAnalysisDeclContext()->isBodyAutosynthesized()) {
328    // It must be a stack frame because we only autosynthesize functions.
329    return cast<StackFrameContext>(findTopAutosynthesizedParentContext(LC))
330        ->getCallSite();
331  }
332  // Otherwise, see if the node's program point directly points to a statement.
333  // FIXME: Refactor into a ProgramPoint method?
334  ProgramPoint P = getLocation();
335  if (auto SP = P.getAs<StmtPoint>())
336    return SP->getStmt();
337  if (auto BE = P.getAs<BlockEdge>())
338    return BE->getSrc()->getTerminatorStmt();
339  if (auto CE = P.getAs<CallEnter>())
340    return CE->getCallExpr();
341  if (auto CEE = P.getAs<CallExitEnd>())
342    return CEE->getCalleeContext()->getCallSite();
343  if (auto PIPP = P.getAs<PostInitializer>())
344    return PIPP->getInitializer()->getInit();
345  if (auto CEB = P.getAs<CallExitBegin>())
346    return CEB->getReturnStmt();
347  if (auto FEP = P.getAs<FunctionExitPoint>())
348    return FEP->getStmt();
349
350  return nullptr;
351}
352
353const Stmt *ExplodedNode::getNextStmtForDiagnostics() const {
354  for (const ExplodedNode *N = getFirstSucc(); N; N = N->getFirstSucc()) {
355    if (const Stmt *S = N->getStmtForDiagnostics()) {
356      // Check if the statement is '?' or '&&'/'||'.  These are "merges",
357      // not actual statement points.
358      switch (S->getStmtClass()) {
359        case Stmt::ChooseExprClass:
360        case Stmt::BinaryConditionalOperatorClass:
361        case Stmt::ConditionalOperatorClass:
362          continue;
363        case Stmt::BinaryOperatorClass: {
364          BinaryOperatorKind Op = cast<BinaryOperator>(S)->getOpcode();
365          if (Op == BO_LAnd || Op == BO_LOr)
366            continue;
367          break;
368        }
369        default:
370          break;
371      }
372      // We found the statement, so return it.
373      return S;
374    }
375  }
376
377  return nullptr;
378}
379
380const Stmt *ExplodedNode::getPreviousStmtForDiagnostics() const {
381  for (const ExplodedNode *N = getFirstPred(); N; N = N->getFirstPred())
382    if (const Stmt *S = N->getStmtForDiagnostics())
383      return S;
384
385  return nullptr;
386}
387
388const Stmt *ExplodedNode::getCurrentOrPreviousStmtForDiagnostics() const {
389  if (const Stmt *S = getStmtForDiagnostics())
390    return S;
391
392  return getPreviousStmtForDiagnostics();
393}
394
395ExplodedNode *ExplodedGraph::getNode(const ProgramPoint &L,
396                                     ProgramStateRef State,
397                                     bool IsSink,
398                                     bool* IsNew) {
399  // Profile 'State' to determine if we already have an existing node.
400  llvm::FoldingSetNodeID profile;
401  void *InsertPos = nullptr;
402
403  NodeTy::Profile(profile, L, State, IsSink);
404  NodeTy* V = Nodes.FindNodeOrInsertPos(profile, InsertPos);
405
406  if (!V) {
407    if (!FreeNodes.empty()) {
408      V = FreeNodes.back();
409      FreeNodes.pop_back();
410    }
411    else {
412      // Allocate a new node.
413      V = (NodeTy*) getAllocator().Allocate<NodeTy>();
414    }
415
416    ++NumNodes;
417    new (V) NodeTy(L, State, NumNodes, IsSink);
418
419    if (ReclaimNodeInterval)
420      ChangedNodes.push_back(V);
421
422    // Insert the node into the node set and return it.
423    Nodes.InsertNode(V, InsertPos);
424
425    if (IsNew) *IsNew = true;
426  }
427  else
428    if (IsNew) *IsNew = false;
429
430  return V;
431}
432
433ExplodedNode *ExplodedGraph::createUncachedNode(const ProgramPoint &L,
434                                                ProgramStateRef State,
435                                                int64_t Id,
436                                                bool IsSink) {
437  NodeTy *V = (NodeTy *) getAllocator().Allocate<NodeTy>();
438  new (V) NodeTy(L, State, Id, IsSink);
439  return V;
440}
441
442std::unique_ptr<ExplodedGraph>
443ExplodedGraph::trim(ArrayRef<const NodeTy *> Sinks,
444                    InterExplodedGraphMap *ForwardMap,
445                    InterExplodedGraphMap *InverseMap) const {
446  if (Nodes.empty())
447    return nullptr;
448
449  using Pass1Ty = llvm::DenseSet<const ExplodedNode *>;
450  Pass1Ty Pass1;
451
452  using Pass2Ty = InterExplodedGraphMap;
453  InterExplodedGraphMap Pass2Scratch;
454  Pass2Ty &Pass2 = ForwardMap ? *ForwardMap : Pass2Scratch;
455
456  SmallVector<const ExplodedNode*, 10> WL1, WL2;
457
458  // ===- Pass 1 (reverse DFS) -===
459  for (const auto Sink : Sinks)
460    if (Sink)
461      WL1.push_back(Sink);
462
463  // Process the first worklist until it is empty.
464  while (!WL1.empty()) {
465    const ExplodedNode *N = WL1.pop_back_val();
466
467    // Have we already visited this node?  If so, continue to the next one.
468    if (!Pass1.insert(N).second)
469      continue;
470
471    // If this is a root enqueue it to the second worklist.
472    if (N->Preds.empty()) {
473      WL2.push_back(N);
474      continue;
475    }
476
477    // Visit our predecessors and enqueue them.
478    WL1.append(N->Preds.begin(), N->Preds.end());
479  }
480
481  // We didn't hit a root? Return with a null pointer for the new graph.
482  if (WL2.empty())
483    return nullptr;
484
485  // Create an empty graph.
486  std::unique_ptr<ExplodedGraph> G = MakeEmptyGraph();
487
488  // ===- Pass 2 (forward DFS to construct the new graph) -===
489  while (!WL2.empty()) {
490    const ExplodedNode *N = WL2.pop_back_val();
491
492    // Skip this node if we have already processed it.
493    if (Pass2.find(N) != Pass2.end())
494      continue;
495
496    // Create the corresponding node in the new graph and record the mapping
497    // from the old node to the new node.
498    ExplodedNode *NewN = G->createUncachedNode(N->getLocation(), N->State,
499                                               N->getID(), N->isSink());
500    Pass2[N] = NewN;
501
502    // Also record the reverse mapping from the new node to the old node.
503    if (InverseMap) (*InverseMap)[NewN] = N;
504
505    // If this node is a root, designate it as such in the graph.
506    if (N->Preds.empty())
507      G->addRoot(NewN);
508
509    // In the case that some of the intended predecessors of NewN have already
510    // been created, we should hook them up as predecessors.
511
512    // Walk through the predecessors of 'N' and hook up their corresponding
513    // nodes in the new graph (if any) to the freshly created node.
514    for (ExplodedNode::pred_iterator I = N->Preds.begin(), E = N->Preds.end();
515         I != E; ++I) {
516      Pass2Ty::iterator PI = Pass2.find(*I);
517      if (PI == Pass2.end())
518        continue;
519
520      NewN->addPredecessor(const_cast<ExplodedNode *>(PI->second), *G);
521    }
522
523    // In the case that some of the intended successors of NewN have already
524    // been created, we should hook them up as successors.  Otherwise, enqueue
525    // the new nodes from the original graph that should have nodes created
526    // in the new graph.
527    for (ExplodedNode::succ_iterator I = N->Succs.begin(), E = N->Succs.end();
528         I != E; ++I) {
529      Pass2Ty::iterator PI = Pass2.find(*I);
530      if (PI != Pass2.end()) {
531        const_cast<ExplodedNode *>(PI->second)->addPredecessor(NewN, *G);
532        continue;
533      }
534
535      // Enqueue nodes to the worklist that were marked during pass 1.
536      if (Pass1.count(*I))
537        WL2.push_back(*I);
538    }
539  }
540
541  return G;
542}
543