clang-tools  7.0.0
UseAfterMoveCheck.cpp
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1 //===--- UseAfterMoveCheck.cpp - clang-tidy -------------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "UseAfterMoveCheck.h"
11 
12 #include "clang/Analysis/CFG.h"
13 #include "clang/Lex/Lexer.h"
14 
15 #include "../utils/ExprSequence.h"
16 
17 using namespace clang::ast_matchers;
18 using namespace clang::tidy::utils;
19 
20 
21 namespace clang {
22 namespace tidy {
23 namespace bugprone {
24 
25 namespace {
26 
27 /// Contains information about a use-after-move.
28 struct UseAfterMove {
29  // The DeclRefExpr that constituted the use of the object.
30  const DeclRefExpr *DeclRef;
31 
32  // Is the order in which the move and the use are evaluated undefined?
34 };
35 
36 /// Finds uses of a variable after a move (and maintains state required by the
37 /// various internal helper functions).
38 class UseAfterMoveFinder {
39 public:
40  UseAfterMoveFinder(ASTContext *TheContext);
41 
42  // Within the given function body, finds the first use of 'MovedVariable' that
43  // occurs after 'MovingCall' (the expression that performs the move). If a
44  // use-after-move is found, writes information about it to 'TheUseAfterMove'.
45  // Returns whether a use-after-move was found.
46  bool find(Stmt *FunctionBody, const Expr *MovingCall,
47  const ValueDecl *MovedVariable, UseAfterMove *TheUseAfterMove);
48 
49 private:
50  bool findInternal(const CFGBlock *Block, const Expr *MovingCall,
51  const ValueDecl *MovedVariable,
52  UseAfterMove *TheUseAfterMove);
53  void getUsesAndReinits(const CFGBlock *Block, const ValueDecl *MovedVariable,
54  llvm::SmallVectorImpl<const DeclRefExpr *> *Uses,
55  llvm::SmallPtrSetImpl<const Stmt *> *Reinits);
56  void getDeclRefs(const CFGBlock *Block, const Decl *MovedVariable,
57  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs);
58  void getReinits(const CFGBlock *Block, const ValueDecl *MovedVariable,
59  llvm::SmallPtrSetImpl<const Stmt *> *Stmts,
60  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs);
61 
62  ASTContext *Context;
63  std::unique_ptr<ExprSequence> Sequence;
64  std::unique_ptr<StmtToBlockMap> BlockMap;
65  llvm::SmallPtrSet<const CFGBlock *, 8> Visited;
66 };
67 
68 } // namespace
69 
70 
71 // Matches nodes that are
72 // - Part of a decltype argument or class template argument (we check this by
73 // seeing if they are children of a TypeLoc), or
74 // - Part of a function template argument (we check this by seeing if they are
75 // children of a DeclRefExpr that references a function template).
76 // DeclRefExprs that fulfill these conditions should not be counted as a use or
77 // move.
78 static StatementMatcher inDecltypeOrTemplateArg() {
79  return anyOf(hasAncestor(typeLoc()),
80  hasAncestor(declRefExpr(
81  to(functionDecl(ast_matchers::isTemplateInstantiation())))));
82 }
83 
84 UseAfterMoveFinder::UseAfterMoveFinder(ASTContext *TheContext)
85  : Context(TheContext) {}
86 
87 bool UseAfterMoveFinder::find(Stmt *FunctionBody, const Expr *MovingCall,
88  const ValueDecl *MovedVariable,
89  UseAfterMove *TheUseAfterMove) {
90  // Generate the CFG manually instead of through an AnalysisDeclContext because
91  // it seems the latter can't be used to generate a CFG for the body of a
92  // labmda.
93  //
94  // We include implicit and temporary destructors in the CFG so that
95  // destructors marked [[noreturn]] are handled correctly in the control flow
96  // analysis. (These are used in some styles of assertion macros.)
97  CFG::BuildOptions Options;
98  Options.AddImplicitDtors = true;
99  Options.AddTemporaryDtors = true;
100  std::unique_ptr<CFG> TheCFG =
101  CFG::buildCFG(nullptr, FunctionBody, Context, Options);
102  if (!TheCFG)
103  return false;
104 
105  Sequence.reset(new ExprSequence(TheCFG.get(), Context));
106  BlockMap.reset(new StmtToBlockMap(TheCFG.get(), Context));
107  Visited.clear();
108 
109  const CFGBlock *Block = BlockMap->blockContainingStmt(MovingCall);
110  if (!Block)
111  return false;
112 
113  return findInternal(Block, MovingCall, MovedVariable, TheUseAfterMove);
114 }
115 
116 bool UseAfterMoveFinder::findInternal(const CFGBlock *Block,
117  const Expr *MovingCall,
118  const ValueDecl *MovedVariable,
119  UseAfterMove *TheUseAfterMove) {
120  if (Visited.count(Block))
121  return false;
122 
123  // Mark the block as visited (except if this is the block containing the
124  // std::move() and it's being visited the first time).
125  if (!MovingCall)
126  Visited.insert(Block);
127 
128  // Get all uses and reinits in the block.
129  llvm::SmallVector<const DeclRefExpr *, 1> Uses;
130  llvm::SmallPtrSet<const Stmt *, 1> Reinits;
131  getUsesAndReinits(Block, MovedVariable, &Uses, &Reinits);
132 
133  // Ignore all reinitializations where the move potentially comes after the
134  // reinit.
135  llvm::SmallVector<const Stmt *, 1> ReinitsToDelete;
136  for (const Stmt *Reinit : Reinits) {
137  if (MovingCall && Sequence->potentiallyAfter(MovingCall, Reinit))
138  ReinitsToDelete.push_back(Reinit);
139  }
140  for (const Stmt *Reinit : ReinitsToDelete) {
141  Reinits.erase(Reinit);
142  }
143 
144  // Find all uses that potentially come after the move.
145  for (const DeclRefExpr *Use : Uses) {
146  if (!MovingCall || Sequence->potentiallyAfter(Use, MovingCall)) {
147  // Does the use have a saving reinit? A reinit is saving if it definitely
148  // comes before the use, i.e. if there's no potential that the reinit is
149  // after the use.
150  bool HaveSavingReinit = false;
151  for (const Stmt *Reinit : Reinits) {
152  if (!Sequence->potentiallyAfter(Reinit, Use))
153  HaveSavingReinit = true;
154  }
155 
156  if (!HaveSavingReinit) {
157  TheUseAfterMove->DeclRef = Use;
158 
159  // Is this a use-after-move that depends on order of evaluation?
160  // This is the case if the move potentially comes after the use (and we
161  // already know that use potentially comes after the move, which taken
162  // together tells us that the ordering is unclear).
163  TheUseAfterMove->EvaluationOrderUndefined =
164  MovingCall != nullptr &&
165  Sequence->potentiallyAfter(MovingCall, Use);
166 
167  return true;
168  }
169  }
170  }
171 
172  // If the object wasn't reinitialized, call ourselves recursively on all
173  // successors.
174  if (Reinits.empty()) {
175  for (const auto &Succ : Block->succs()) {
176  if (Succ && findInternal(Succ, nullptr, MovedVariable, TheUseAfterMove))
177  return true;
178  }
179  }
180 
181  return false;
182 }
183 
184 void UseAfterMoveFinder::getUsesAndReinits(
185  const CFGBlock *Block, const ValueDecl *MovedVariable,
186  llvm::SmallVectorImpl<const DeclRefExpr *> *Uses,
187  llvm::SmallPtrSetImpl<const Stmt *> *Reinits) {
188  llvm::SmallPtrSet<const DeclRefExpr *, 1> DeclRefs;
189  llvm::SmallPtrSet<const DeclRefExpr *, 1> ReinitDeclRefs;
190 
191  getDeclRefs(Block, MovedVariable, &DeclRefs);
192  getReinits(Block, MovedVariable, Reinits, &ReinitDeclRefs);
193 
194  // All references to the variable that aren't reinitializations are uses.
195  Uses->clear();
196  for (const DeclRefExpr *DeclRef : DeclRefs) {
197  if (!ReinitDeclRefs.count(DeclRef))
198  Uses->push_back(DeclRef);
199  }
200 
201  // Sort the uses by their occurrence in the source code.
202  std::sort(Uses->begin(), Uses->end(),
203  [](const DeclRefExpr *D1, const DeclRefExpr *D2) {
204  return D1->getExprLoc() < D2->getExprLoc();
205  });
206 }
207 
208 bool isStandardSmartPointer(const ValueDecl *VD) {
209  const Type *TheType = VD->getType().getTypePtrOrNull();
210  if (!TheType)
211  return false;
212 
213  const CXXRecordDecl *RecordDecl = TheType->getAsCXXRecordDecl();
214  if (!RecordDecl)
215  return false;
216 
217  const IdentifierInfo *ID = RecordDecl->getIdentifier();
218  if (!ID)
219  return false;
220 
221  StringRef Name = ID->getName();
222  if (Name != "unique_ptr" && Name != "shared_ptr" && Name != "weak_ptr")
223  return false;
224 
225  return RecordDecl->getDeclContext()->isStdNamespace();
226 }
227 
228 void UseAfterMoveFinder::getDeclRefs(
229  const CFGBlock *Block, const Decl *MovedVariable,
230  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs) {
231  DeclRefs->clear();
232  for (const auto &Elem : *Block) {
233  Optional<CFGStmt> S = Elem.getAs<CFGStmt>();
234  if (!S)
235  continue;
236 
237  auto addDeclRefs = [this, Block,
238  DeclRefs](const ArrayRef<BoundNodes> Matches) {
239  for (const auto &Match : Matches) {
240  const auto *DeclRef = Match.getNodeAs<DeclRefExpr>("declref");
241  const auto *Operator = Match.getNodeAs<CXXOperatorCallExpr>("operator");
242  if (DeclRef && BlockMap->blockContainingStmt(DeclRef) == Block) {
243  // Ignore uses of a standard smart pointer that don't dereference the
244  // pointer.
245  if (Operator || !isStandardSmartPointer(DeclRef->getDecl())) {
246  DeclRefs->insert(DeclRef);
247  }
248  }
249  }
250  };
251 
252  auto DeclRefMatcher = declRefExpr(hasDeclaration(equalsNode(MovedVariable)),
253  unless(inDecltypeOrTemplateArg()))
254  .bind("declref");
255 
256  addDeclRefs(match(findAll(DeclRefMatcher), *S->getStmt(), *Context));
257  addDeclRefs(match(
258  findAll(cxxOperatorCallExpr(anyOf(hasOverloadedOperatorName("*"),
259  hasOverloadedOperatorName("->"),
260  hasOverloadedOperatorName("[]")),
261  hasArgument(0, DeclRefMatcher))
262  .bind("operator")),
263  *S->getStmt(), *Context));
264  }
265 }
266 
267 void UseAfterMoveFinder::getReinits(
268  const CFGBlock *Block, const ValueDecl *MovedVariable,
269  llvm::SmallPtrSetImpl<const Stmt *> *Stmts,
270  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs) {
271  auto DeclRefMatcher =
272  declRefExpr(hasDeclaration(equalsNode(MovedVariable))).bind("declref");
273 
274  auto StandardContainerTypeMatcher = hasType(hasUnqualifiedDesugaredType(
275  recordType(hasDeclaration(cxxRecordDecl(hasAnyName(
276  "::std::basic_string", "::std::vector", "::std::deque",
277  "::std::forward_list", "::std::list", "::std::set", "::std::map",
278  "::std::multiset", "::std::multimap", "::std::unordered_set",
279  "::std::unordered_map", "::std::unordered_multiset",
280  "::std::unordered_multimap"))))));
281 
282  auto StandardSmartPointerTypeMatcher = hasType(hasUnqualifiedDesugaredType(
283  recordType(hasDeclaration(cxxRecordDecl(hasAnyName(
284  "::std::unique_ptr", "::std::shared_ptr", "::std::weak_ptr"))))));
285 
286  // Matches different types of reinitialization.
287  auto ReinitMatcher =
288  stmt(anyOf(
289  // Assignment. In addition to the overloaded assignment operator,
290  // test for built-in assignment as well, since template functions
291  // may be instantiated to use std::move() on built-in types.
292  binaryOperator(hasOperatorName("="), hasLHS(DeclRefMatcher)),
293  cxxOperatorCallExpr(hasOverloadedOperatorName("="),
294  hasArgument(0, DeclRefMatcher)),
295  // Declaration. We treat this as a type of reinitialization too,
296  // so we don't need to treat it separately.
297  declStmt(hasDescendant(equalsNode(MovedVariable))),
298  // clear() and assign() on standard containers.
299  cxxMemberCallExpr(
300  on(allOf(DeclRefMatcher, StandardContainerTypeMatcher)),
301  // To keep the matcher simple, we check for assign() calls
302  // on all standard containers, even though only vector,
303  // deque, forward_list and list have assign(). If assign()
304  // is called on any of the other containers, this will be
305  // flagged by a compile error anyway.
306  callee(cxxMethodDecl(hasAnyName("clear", "assign")))),
307  // reset() on standard smart pointers.
308  cxxMemberCallExpr(
309  on(allOf(DeclRefMatcher, StandardSmartPointerTypeMatcher)),
310  callee(cxxMethodDecl(hasName("reset")))),
311  // Passing variable to a function as a non-const pointer.
312  callExpr(forEachArgumentWithParam(
313  unaryOperator(hasOperatorName("&"),
314  hasUnaryOperand(DeclRefMatcher)),
315  unless(parmVarDecl(hasType(pointsTo(isConstQualified())))))),
316  // Passing variable to a function as a non-const lvalue reference
317  // (unless that function is std::move()).
318  callExpr(forEachArgumentWithParam(
319  DeclRefMatcher,
320  unless(parmVarDecl(hasType(
321  references(qualType(isConstQualified())))))),
322  unless(callee(functionDecl(hasName("::std::move")))))))
323  .bind("reinit");
324 
325  Stmts->clear();
326  DeclRefs->clear();
327  for (const auto &Elem : *Block) {
328  Optional<CFGStmt> S = Elem.getAs<CFGStmt>();
329  if (!S)
330  continue;
331 
332  SmallVector<BoundNodes, 1> Matches =
333  match(findAll(ReinitMatcher), *S->getStmt(), *Context);
334 
335  for (const auto &Match : Matches) {
336  const auto *TheStmt = Match.getNodeAs<Stmt>("reinit");
337  const auto *TheDeclRef = Match.getNodeAs<DeclRefExpr>("declref");
338  if (TheStmt && BlockMap->blockContainingStmt(TheStmt) == Block) {
339  Stmts->insert(TheStmt);
340 
341  // We count DeclStmts as reinitializations, but they don't have a
342  // DeclRefExpr associated with them -- so we need to check 'TheDeclRef'
343  // before adding it to the set.
344  if (TheDeclRef)
345  DeclRefs->insert(TheDeclRef);
346  }
347  }
348  }
349 }
350 
351 static void emitDiagnostic(const Expr *MovingCall, const DeclRefExpr *MoveArg,
352  const UseAfterMove &Use, ClangTidyCheck *Check,
353  ASTContext *Context) {
354  SourceLocation UseLoc = Use.DeclRef->getExprLoc();
355  SourceLocation MoveLoc = MovingCall->getExprLoc();
356 
357  Check->diag(UseLoc, "'%0' used after it was moved")
358  << MoveArg->getDecl()->getName();
359  Check->diag(MoveLoc, "move occurred here", DiagnosticIDs::Note);
360  if (Use.EvaluationOrderUndefined) {
361  Check->diag(UseLoc,
362  "the use and move are unsequenced, i.e. there is no guarantee "
363  "about the order in which they are evaluated",
364  DiagnosticIDs::Note);
365  } else if (UseLoc < MoveLoc || Use.DeclRef == MoveArg) {
366  Check->diag(UseLoc,
367  "the use happens in a later loop iteration than the move",
368  DiagnosticIDs::Note);
369  }
370 }
371 
372 void UseAfterMoveCheck::registerMatchers(MatchFinder *Finder) {
373  if (!getLangOpts().CPlusPlus11)
374  return;
375 
376  auto CallMoveMatcher =
377  callExpr(callee(functionDecl(hasName("::std::move"))), argumentCountIs(1),
378  hasArgument(0, declRefExpr().bind("arg")),
379  anyOf(hasAncestor(lambdaExpr().bind("containing-lambda")),
380  hasAncestor(functionDecl().bind("containing-func"))),
381  unless(inDecltypeOrTemplateArg()))
382  .bind("call-move");
383 
384  Finder->addMatcher(
385  // To find the Stmt that we assume performs the actual move, we look for
386  // the direct ancestor of the std::move() that isn't one of the node
387  // types ignored by ignoringParenImpCasts().
388  stmt(forEach(expr(ignoringParenImpCasts(CallMoveMatcher))),
389  // Don't allow an InitListExpr to be the moving call. An InitListExpr
390  // has both a syntactic and a semantic form, and the parent-child
391  // relationships are different between the two. This could cause an
392  // InitListExpr to be analyzed as the moving call in addition to the
393  // Expr that we actually want, resulting in two diagnostics with
394  // different code locations for the same move.
395  unless(initListExpr()),
396  unless(expr(ignoringParenImpCasts(equalsBoundNode("call-move")))))
397  .bind("moving-call"),
398  this);
399 }
400 
401 void UseAfterMoveCheck::check(const MatchFinder::MatchResult &Result) {
402  const auto *ContainingLambda =
403  Result.Nodes.getNodeAs<LambdaExpr>("containing-lambda");
404  const auto *ContainingFunc =
405  Result.Nodes.getNodeAs<FunctionDecl>("containing-func");
406  const auto *CallMove = Result.Nodes.getNodeAs<CallExpr>("call-move");
407  const auto *MovingCall = Result.Nodes.getNodeAs<Expr>("moving-call");
408  const auto *Arg = Result.Nodes.getNodeAs<DeclRefExpr>("arg");
409 
410  if (!MovingCall || !MovingCall->getExprLoc().isValid())
411  MovingCall = CallMove;
412 
413  Stmt *FunctionBody = nullptr;
414  if (ContainingLambda)
415  FunctionBody = ContainingLambda->getBody();
416  else if (ContainingFunc)
417  FunctionBody = ContainingFunc->getBody();
418  else
419  return;
420 
421  // Ignore the std::move if the variable that was passed to it isn't a local
422  // variable.
423  if (!Arg->getDecl()->getDeclContext()->isFunctionOrMethod())
424  return;
425 
426  UseAfterMoveFinder finder(Result.Context);
427  UseAfterMove Use;
428  if (finder.find(FunctionBody, MovingCall, Arg->getDecl(), &Use))
429  emitDiagnostic(MovingCall, Arg, Use, this, Result.Context);
430 }
431 
432 } // namespace bugprone
433 } // namespace tidy
434 } // namespace clang
llvm::StringRef Name
Maps Stmts to the CFGBlock that contains them.
Definition: ExprSequence.h:104
Provides information about the evaluation order of (sub-)expressions within a CFGBlock.
Definition: ExprSequence.h:69
Base class for all clang-tidy checks.
Definition: ClangTidy.h:127
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
bool isStandardSmartPointer(const ValueDecl *VD)
static StatementMatcher inDecltypeOrTemplateArg()
bool EvaluationOrderUndefined
const DeclRefExpr * DeclRef
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check&#39;s name.
Definition: ClangTidy.cpp:427
static void emitDiagnostic(const Expr *MovingCall, const DeclRefExpr *MoveArg, const UseAfterMove &Use, ClangTidyCheck *Check, ASTContext *Context)