clang-tools  12.0.0git
UseAfterMoveCheck.cpp
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1 //===--- UseAfterMoveCheck.cpp - clang-tidy -------------------------------===//
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 #include "UseAfterMoveCheck.h"
10 
11 #include "clang/AST/Expr.h"
12 #include "clang/AST/ExprCXX.h"
13 #include "clang/AST/ExprConcepts.h"
14 #include "clang/ASTMatchers/ASTMatchers.h"
15 #include "clang/Analysis/CFG.h"
16 #include "clang/Lex/Lexer.h"
17 
18 #include "../utils/ExprSequence.h"
19 
20 using namespace clang::ast_matchers;
21 using namespace clang::tidy::utils;
22 
23 
24 namespace clang {
25 namespace tidy {
26 namespace bugprone {
27 
28 namespace {
29 
30 AST_MATCHER(Expr, hasUnevaluatedContext) {
31  if (isa<CXXNoexceptExpr>(Node) || isa<RequiresExpr>(Node))
32  return true;
33  if (const auto *UnaryExpr = dyn_cast<UnaryExprOrTypeTraitExpr>(&Node)) {
34  switch (UnaryExpr->getKind()) {
35  case UETT_SizeOf:
36  case UETT_AlignOf:
37  return true;
38  default:
39  return false;
40  }
41  }
42  if (const auto *TypeIDExpr = dyn_cast<CXXTypeidExpr>(&Node))
43  return !TypeIDExpr->isPotentiallyEvaluated();
44  return false;
45 }
46 
47 /// Contains information about a use-after-move.
48 struct UseAfterMove {
49  // The DeclRefExpr that constituted the use of the object.
50  const DeclRefExpr *DeclRef;
51 
52  // Is the order in which the move and the use are evaluated undefined?
54 };
55 
56 /// Finds uses of a variable after a move (and maintains state required by the
57 /// various internal helper functions).
58 class UseAfterMoveFinder {
59 public:
60  UseAfterMoveFinder(ASTContext *TheContext);
61 
62  // Within the given function body, finds the first use of 'MovedVariable' that
63  // occurs after 'MovingCall' (the expression that performs the move). If a
64  // use-after-move is found, writes information about it to 'TheUseAfterMove'.
65  // Returns whether a use-after-move was found.
66  bool find(Stmt *FunctionBody, const Expr *MovingCall,
67  const ValueDecl *MovedVariable, UseAfterMove *TheUseAfterMove);
68 
69 private:
70  bool findInternal(const CFGBlock *Block, const Expr *MovingCall,
71  const ValueDecl *MovedVariable,
72  UseAfterMove *TheUseAfterMove);
73  void getUsesAndReinits(const CFGBlock *Block, const ValueDecl *MovedVariable,
74  llvm::SmallVectorImpl<const DeclRefExpr *> *Uses,
75  llvm::SmallPtrSetImpl<const Stmt *> *Reinits);
76  void getDeclRefs(const CFGBlock *Block, const Decl *MovedVariable,
77  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs);
78  void getReinits(const CFGBlock *Block, const ValueDecl *MovedVariable,
79  llvm::SmallPtrSetImpl<const Stmt *> *Stmts,
80  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs);
81 
82  ASTContext *Context;
83  std::unique_ptr<ExprSequence> Sequence;
84  std::unique_ptr<StmtToBlockMap> BlockMap;
85  llvm::SmallPtrSet<const CFGBlock *, 8> Visited;
86 };
87 
88 } // namespace
89 
90 
91 // Matches nodes that are
92 // - Part of a decltype argument or class template argument (we check this by
93 // seeing if they are children of a TypeLoc), or
94 // - Part of a function template argument (we check this by seeing if they are
95 // children of a DeclRefExpr that references a function template).
96 // DeclRefExprs that fulfill these conditions should not be counted as a use or
97 // move.
98 static StatementMatcher inDecltypeOrTemplateArg() {
99  return anyOf(hasAncestor(typeLoc()),
100  hasAncestor(declRefExpr(
101  to(functionDecl(ast_matchers::isTemplateInstantiation())))),
102  hasAncestor(expr(hasUnevaluatedContext())));
103 }
104 
105 UseAfterMoveFinder::UseAfterMoveFinder(ASTContext *TheContext)
106  : Context(TheContext) {}
107 
108 bool UseAfterMoveFinder::find(Stmt *FunctionBody, const Expr *MovingCall,
109  const ValueDecl *MovedVariable,
110  UseAfterMove *TheUseAfterMove) {
111  // Generate the CFG manually instead of through an AnalysisDeclContext because
112  // it seems the latter can't be used to generate a CFG for the body of a
113  // lambda.
114  //
115  // We include implicit and temporary destructors in the CFG so that
116  // destructors marked [[noreturn]] are handled correctly in the control flow
117  // analysis. (These are used in some styles of assertion macros.)
118  CFG::BuildOptions Options;
119  Options.AddImplicitDtors = true;
120  Options.AddTemporaryDtors = true;
121  std::unique_ptr<CFG> TheCFG =
122  CFG::buildCFG(nullptr, FunctionBody, Context, Options);
123  if (!TheCFG)
124  return false;
125 
126  Sequence =
127  std::make_unique<ExprSequence>(TheCFG.get(), FunctionBody, Context);
128  BlockMap = std::make_unique<StmtToBlockMap>(TheCFG.get(), Context);
129  Visited.clear();
130 
131  const CFGBlock *Block = BlockMap->blockContainingStmt(MovingCall);
132  if (!Block)
133  return false;
134 
135  return findInternal(Block, MovingCall, MovedVariable, TheUseAfterMove);
136 }
137 
138 bool UseAfterMoveFinder::findInternal(const CFGBlock *Block,
139  const Expr *MovingCall,
140  const ValueDecl *MovedVariable,
141  UseAfterMove *TheUseAfterMove) {
142  if (Visited.count(Block))
143  return false;
144 
145  // Mark the block as visited (except if this is the block containing the
146  // std::move() and it's being visited the first time).
147  if (!MovingCall)
148  Visited.insert(Block);
149 
150  // Get all uses and reinits in the block.
151  llvm::SmallVector<const DeclRefExpr *, 1> Uses;
152  llvm::SmallPtrSet<const Stmt *, 1> Reinits;
153  getUsesAndReinits(Block, MovedVariable, &Uses, &Reinits);
154 
155  // Ignore all reinitializations where the move potentially comes after the
156  // reinit.
157  llvm::SmallVector<const Stmt *, 1> ReinitsToDelete;
158  for (const Stmt *Reinit : Reinits) {
159  if (MovingCall && Sequence->potentiallyAfter(MovingCall, Reinit))
160  ReinitsToDelete.push_back(Reinit);
161  }
162  for (const Stmt *Reinit : ReinitsToDelete) {
163  Reinits.erase(Reinit);
164  }
165 
166  // Find all uses that potentially come after the move.
167  for (const DeclRefExpr *Use : Uses) {
168  if (!MovingCall || Sequence->potentiallyAfter(Use, MovingCall)) {
169  // Does the use have a saving reinit? A reinit is saving if it definitely
170  // comes before the use, i.e. if there's no potential that the reinit is
171  // after the use.
172  bool HaveSavingReinit = false;
173  for (const Stmt *Reinit : Reinits) {
174  if (!Sequence->potentiallyAfter(Reinit, Use))
175  HaveSavingReinit = true;
176  }
177 
178  if (!HaveSavingReinit) {
179  TheUseAfterMove->DeclRef = Use;
180 
181  // Is this a use-after-move that depends on order of evaluation?
182  // This is the case if the move potentially comes after the use (and we
183  // already know that use potentially comes after the move, which taken
184  // together tells us that the ordering is unclear).
185  TheUseAfterMove->EvaluationOrderUndefined =
186  MovingCall != nullptr &&
187  Sequence->potentiallyAfter(MovingCall, Use);
188 
189  return true;
190  }
191  }
192  }
193 
194  // If the object wasn't reinitialized, call ourselves recursively on all
195  // successors.
196  if (Reinits.empty()) {
197  for (const auto &Succ : Block->succs()) {
198  if (Succ && findInternal(Succ, nullptr, MovedVariable, TheUseAfterMove))
199  return true;
200  }
201  }
202 
203  return false;
204 }
205 
206 void UseAfterMoveFinder::getUsesAndReinits(
207  const CFGBlock *Block, const ValueDecl *MovedVariable,
208  llvm::SmallVectorImpl<const DeclRefExpr *> *Uses,
209  llvm::SmallPtrSetImpl<const Stmt *> *Reinits) {
210  llvm::SmallPtrSet<const DeclRefExpr *, 1> DeclRefs;
211  llvm::SmallPtrSet<const DeclRefExpr *, 1> ReinitDeclRefs;
212 
213  getDeclRefs(Block, MovedVariable, &DeclRefs);
214  getReinits(Block, MovedVariable, Reinits, &ReinitDeclRefs);
215 
216  // All references to the variable that aren't reinitializations are uses.
217  Uses->clear();
218  for (const DeclRefExpr *DeclRef : DeclRefs) {
219  if (!ReinitDeclRefs.count(DeclRef))
220  Uses->push_back(DeclRef);
221  }
222 
223  // Sort the uses by their occurrence in the source code.
224  std::sort(Uses->begin(), Uses->end(),
225  [](const DeclRefExpr *D1, const DeclRefExpr *D2) {
226  return D1->getExprLoc() < D2->getExprLoc();
227  });
228 }
229 
230 bool isStandardSmartPointer(const ValueDecl *VD) {
231  const Type *TheType = VD->getType().getNonReferenceType().getTypePtrOrNull();
232  if (!TheType)
233  return false;
234 
235  const CXXRecordDecl *RecordDecl = TheType->getAsCXXRecordDecl();
236  if (!RecordDecl)
237  return false;
238 
239  const IdentifierInfo *ID = RecordDecl->getIdentifier();
240  if (!ID)
241  return false;
242 
243  StringRef Name = ID->getName();
244  if (Name != "unique_ptr" && Name != "shared_ptr" && Name != "weak_ptr")
245  return false;
246 
247  return RecordDecl->getDeclContext()->isStdNamespace();
248 }
249 
250 void UseAfterMoveFinder::getDeclRefs(
251  const CFGBlock *Block, const Decl *MovedVariable,
252  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs) {
253  DeclRefs->clear();
254  for (const auto &Elem : *Block) {
255  Optional<CFGStmt> S = Elem.getAs<CFGStmt>();
256  if (!S)
257  continue;
258 
259  auto addDeclRefs = [this, Block,
260  DeclRefs](const ArrayRef<BoundNodes> Matches) {
261  for (const auto &Match : Matches) {
262  const auto *DeclRef = Match.getNodeAs<DeclRefExpr>("declref");
263  const auto *Operator = Match.getNodeAs<CXXOperatorCallExpr>("operator");
264  if (DeclRef && BlockMap->blockContainingStmt(DeclRef) == Block) {
265  // Ignore uses of a standard smart pointer that don't dereference the
266  // pointer.
267  if (Operator || !isStandardSmartPointer(DeclRef->getDecl())) {
268  DeclRefs->insert(DeclRef);
269  }
270  }
271  }
272  };
273 
274  auto DeclRefMatcher = declRefExpr(hasDeclaration(equalsNode(MovedVariable)),
275  unless(inDecltypeOrTemplateArg()))
276  .bind("declref");
277 
278  addDeclRefs(
279  match(traverse(ast_type_traits::TK_AsIs, findAll(DeclRefMatcher)),
280  *S->getStmt(), *Context));
281  addDeclRefs(match(findAll(cxxOperatorCallExpr(
282  hasAnyOverloadedOperatorName("*", "->", "[]"),
283  hasArgument(0, DeclRefMatcher))
284  .bind("operator")),
285  *S->getStmt(), *Context));
286  }
287 }
288 
289 void UseAfterMoveFinder::getReinits(
290  const CFGBlock *Block, const ValueDecl *MovedVariable,
291  llvm::SmallPtrSetImpl<const Stmt *> *Stmts,
292  llvm::SmallPtrSetImpl<const DeclRefExpr *> *DeclRefs) {
293  auto DeclRefMatcher =
294  declRefExpr(hasDeclaration(equalsNode(MovedVariable))).bind("declref");
295 
296  auto StandardContainerTypeMatcher = hasType(hasUnqualifiedDesugaredType(
297  recordType(hasDeclaration(cxxRecordDecl(hasAnyName(
298  "::std::basic_string", "::std::vector", "::std::deque",
299  "::std::forward_list", "::std::list", "::std::set", "::std::map",
300  "::std::multiset", "::std::multimap", "::std::unordered_set",
301  "::std::unordered_map", "::std::unordered_multiset",
302  "::std::unordered_multimap"))))));
303 
304  auto StandardSmartPointerTypeMatcher = hasType(hasUnqualifiedDesugaredType(
305  recordType(hasDeclaration(cxxRecordDecl(hasAnyName(
306  "::std::unique_ptr", "::std::shared_ptr", "::std::weak_ptr"))))));
307 
308  // Matches different types of reinitialization.
309  auto ReinitMatcher =
310  stmt(anyOf(
311  // Assignment. In addition to the overloaded assignment operator,
312  // test for built-in assignment as well, since template functions
313  // may be instantiated to use std::move() on built-in types.
314  binaryOperator(hasOperatorName("="), hasLHS(DeclRefMatcher)),
315  cxxOperatorCallExpr(hasOverloadedOperatorName("="),
316  hasArgument(0, DeclRefMatcher)),
317  // Declaration. We treat this as a type of reinitialization too,
318  // so we don't need to treat it separately.
319  declStmt(hasDescendant(equalsNode(MovedVariable))),
320  // clear() and assign() on standard containers.
321  cxxMemberCallExpr(
322  on(expr(DeclRefMatcher, StandardContainerTypeMatcher)),
323  // To keep the matcher simple, we check for assign() calls
324  // on all standard containers, even though only vector,
325  // deque, forward_list and list have assign(). If assign()
326  // is called on any of the other containers, this will be
327  // flagged by a compile error anyway.
328  callee(cxxMethodDecl(hasAnyName("clear", "assign")))),
329  // reset() on standard smart pointers.
330  cxxMemberCallExpr(
331  on(expr(DeclRefMatcher, StandardSmartPointerTypeMatcher)),
332  callee(cxxMethodDecl(hasName("reset")))),
333  // Methods that have the [[clang::reinitializes]] attribute.
334  cxxMemberCallExpr(
335  on(DeclRefMatcher),
336  callee(cxxMethodDecl(hasAttr(clang::attr::Reinitializes)))),
337  // Passing variable to a function as a non-const pointer.
338  callExpr(forEachArgumentWithParam(
339  unaryOperator(hasOperatorName("&"),
340  hasUnaryOperand(DeclRefMatcher)),
341  unless(parmVarDecl(hasType(pointsTo(isConstQualified())))))),
342  // Passing variable to a function as a non-const lvalue reference
343  // (unless that function is std::move()).
344  callExpr(forEachArgumentWithParam(
345  traverse(ast_type_traits::TK_AsIs, DeclRefMatcher),
346  unless(parmVarDecl(hasType(
347  references(qualType(isConstQualified())))))),
348  unless(callee(functionDecl(hasName("::std::move")))))))
349  .bind("reinit");
350 
351  Stmts->clear();
352  DeclRefs->clear();
353  for (const auto &Elem : *Block) {
354  Optional<CFGStmt> S = Elem.getAs<CFGStmt>();
355  if (!S)
356  continue;
357 
358  SmallVector<BoundNodes, 1> Matches =
359  match(findAll(ReinitMatcher), *S->getStmt(), *Context);
360 
361  for (const auto &Match : Matches) {
362  const auto *TheStmt = Match.getNodeAs<Stmt>("reinit");
363  const auto *TheDeclRef = Match.getNodeAs<DeclRefExpr>("declref");
364  if (TheStmt && BlockMap->blockContainingStmt(TheStmt) == Block) {
365  Stmts->insert(TheStmt);
366 
367  // We count DeclStmts as reinitializations, but they don't have a
368  // DeclRefExpr associated with them -- so we need to check 'TheDeclRef'
369  // before adding it to the set.
370  if (TheDeclRef)
371  DeclRefs->insert(TheDeclRef);
372  }
373  }
374  }
375 }
376 
377 static void emitDiagnostic(const Expr *MovingCall, const DeclRefExpr *MoveArg,
378  const UseAfterMove &Use, ClangTidyCheck *Check,
379  ASTContext *Context) {
380  SourceLocation UseLoc = Use.DeclRef->getExprLoc();
381  SourceLocation MoveLoc = MovingCall->getExprLoc();
382 
383  Check->diag(UseLoc, "'%0' used after it was moved")
384  << MoveArg->getDecl()->getName();
385  Check->diag(MoveLoc, "move occurred here", DiagnosticIDs::Note);
386  if (Use.EvaluationOrderUndefined) {
387  Check->diag(UseLoc,
388  "the use and move are unsequenced, i.e. there is no guarantee "
389  "about the order in which they are evaluated",
390  DiagnosticIDs::Note);
391  } else if (UseLoc < MoveLoc || Use.DeclRef == MoveArg) {
392  Check->diag(UseLoc,
393  "the use happens in a later loop iteration than the move",
394  DiagnosticIDs::Note);
395  }
396 }
397 
398 void UseAfterMoveCheck::registerMatchers(MatchFinder *Finder) {
399  auto CallMoveMatcher =
400  callExpr(callee(functionDecl(hasName("::std::move"))), argumentCountIs(1),
401  hasArgument(0, declRefExpr().bind("arg")),
402  anyOf(hasAncestor(lambdaExpr().bind("containing-lambda")),
403  hasAncestor(functionDecl().bind("containing-func"))),
404  unless(inDecltypeOrTemplateArg()))
405  .bind("call-move");
406 
407  Finder->addMatcher(
408  traverse(
409  ast_type_traits::TK_AsIs,
410  // To find the Stmt that we assume performs the actual move, we look
411  // for the direct ancestor of the std::move() that isn't one of the
412  // node types ignored by ignoringParenImpCasts().
413  stmt(
414  forEach(expr(ignoringParenImpCasts(CallMoveMatcher))),
415  // Don't allow an InitListExpr to be the moving call. An
416  // InitListExpr has both a syntactic and a semantic form, and the
417  // parent-child relationships are different between the two. This
418  // could cause an InitListExpr to be analyzed as the moving call
419  // in addition to the Expr that we actually want, resulting in two
420  // diagnostics with different code locations for the same move.
421  unless(initListExpr()),
422  unless(expr(ignoringParenImpCasts(equalsBoundNode("call-move")))))
423  .bind("moving-call")),
424  this);
425 }
426 
427 void UseAfterMoveCheck::check(const MatchFinder::MatchResult &Result) {
428  const auto *ContainingLambda =
429  Result.Nodes.getNodeAs<LambdaExpr>("containing-lambda");
430  const auto *ContainingFunc =
431  Result.Nodes.getNodeAs<FunctionDecl>("containing-func");
432  const auto *CallMove = Result.Nodes.getNodeAs<CallExpr>("call-move");
433  const auto *MovingCall = Result.Nodes.getNodeAs<Expr>("moving-call");
434  const auto *Arg = Result.Nodes.getNodeAs<DeclRefExpr>("arg");
435 
436  if (!MovingCall || !MovingCall->getExprLoc().isValid())
437  MovingCall = CallMove;
438 
439  Stmt *FunctionBody = nullptr;
440  if (ContainingLambda)
441  FunctionBody = ContainingLambda->getBody();
442  else if (ContainingFunc)
443  FunctionBody = ContainingFunc->getBody();
444  else
445  return;
446 
447  // Ignore the std::move if the variable that was passed to it isn't a local
448  // variable.
449  if (!Arg->getDecl()->getDeclContext()->isFunctionOrMethod())
450  return;
451 
452  UseAfterMoveFinder finder(Result.Context);
453  UseAfterMove Use;
454  if (finder.find(FunctionBody, MovingCall, Arg->getDecl(), &Use))
455  emitDiagnostic(MovingCall, Arg, Use, this, Result.Context);
456 }
457 
458 } // namespace bugprone
459 } // namespace tidy
460 } // namespace clang
const FunctionDecl * Decl
Base class for all clang-tidy checks.
std::vector< std::string > match(const SymbolIndex &I, const FuzzyFindRequest &Req, bool *Incomplete)
Definition: TestIndex.cpp:94
static constexpr llvm::StringLiteral Name
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
bool isStandardSmartPointer(const ValueDecl *VD)
static StatementMatcher inDecltypeOrTemplateArg()
bool EvaluationOrderUndefined
const DeclRefExpr * DeclRef
NodeType Type
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check&#39;s name.
static void emitDiagnostic(const Expr *MovingCall, const DeclRefExpr *MoveArg, const UseAfterMove &Use, ClangTidyCheck *Check, ASTContext *Context)