clang-tools  6.0.0
PassByValueCheck.cpp
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1 //===--- PassByValueCheck.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 "PassByValueCheck.h"
11 #include "clang/AST/ASTContext.h"
12 #include "clang/AST/RecursiveASTVisitor.h"
13 #include "clang/ASTMatchers/ASTMatchFinder.h"
14 #include "clang/ASTMatchers/ASTMatchers.h"
15 #include "clang/Frontend/CompilerInstance.h"
16 #include "clang/Lex/Lexer.h"
17 #include "clang/Lex/Preprocessor.h"
18 
19 using namespace clang::ast_matchers;
20 using namespace llvm;
21 
22 namespace clang {
23 namespace tidy {
24 namespace modernize {
25 
26 /// \brief Matches move-constructible classes.
27 ///
28 /// Given
29 /// \code
30 /// // POD types are trivially move constructible.
31 /// struct Foo { int a; };
32 ///
33 /// struct Bar {
34 /// Bar(Bar &&) = deleted;
35 /// int a;
36 /// };
37 /// \endcode
38 /// recordDecl(isMoveConstructible())
39 /// matches "Foo".
40 AST_MATCHER(CXXRecordDecl, isMoveConstructible) {
41  for (const CXXConstructorDecl *Ctor : Node.ctors()) {
42  if (Ctor->isMoveConstructor() && !Ctor->isDeleted())
43  return true;
44  }
45  return false;
46 }
47 
48 static TypeMatcher constRefType() {
49  return lValueReferenceType(pointee(isConstQualified()));
50 }
51 
52 static TypeMatcher nonConstValueType() {
53  return qualType(unless(anyOf(referenceType(), isConstQualified())));
54 }
55 
56 /// \brief Whether or not \p ParamDecl is used exactly one time in \p Ctor.
57 ///
58 /// Checks both in the init-list and the body of the constructor.
59 static bool paramReferredExactlyOnce(const CXXConstructorDecl *Ctor,
60  const ParmVarDecl *ParamDecl) {
61  /// \brief \c clang::RecursiveASTVisitor that checks that the given
62  /// \c ParmVarDecl is used exactly one time.
63  ///
64  /// \see ExactlyOneUsageVisitor::hasExactlyOneUsageIn()
65  class ExactlyOneUsageVisitor
66  : public RecursiveASTVisitor<ExactlyOneUsageVisitor> {
67  friend class RecursiveASTVisitor<ExactlyOneUsageVisitor>;
68 
69  public:
70  ExactlyOneUsageVisitor(const ParmVarDecl *ParamDecl)
71  : ParamDecl(ParamDecl) {}
72 
73  /// \brief Whether or not the parameter variable is referred only once in
74  /// the
75  /// given constructor.
76  bool hasExactlyOneUsageIn(const CXXConstructorDecl *Ctor) {
77  Count = 0;
78  TraverseDecl(const_cast<CXXConstructorDecl *>(Ctor));
79  return Count == 1;
80  }
81 
82  private:
83  /// \brief Counts the number of references to a variable.
84  ///
85  /// Stops the AST traversal if more than one usage is found.
86  bool VisitDeclRefExpr(DeclRefExpr *D) {
87  if (const ParmVarDecl *To = dyn_cast<ParmVarDecl>(D->getDecl())) {
88  if (To == ParamDecl) {
89  ++Count;
90  if (Count > 1) {
91  // No need to look further, used more than once.
92  return false;
93  }
94  }
95  }
96  return true;
97  }
98 
99  const ParmVarDecl *ParamDecl;
100  unsigned Count;
101  };
102 
103  return ExactlyOneUsageVisitor(ParamDecl).hasExactlyOneUsageIn(Ctor);
104 }
105 
106 /// \brief Find all references to \p ParamDecl across all of the
107 /// redeclarations of \p Ctor.
108 static SmallVector<const ParmVarDecl *, 2>
109 collectParamDecls(const CXXConstructorDecl *Ctor,
110  const ParmVarDecl *ParamDecl) {
111  SmallVector<const ParmVarDecl *, 2> Results;
112  unsigned ParamIdx = ParamDecl->getFunctionScopeIndex();
113 
114  for (const FunctionDecl *Redecl : Ctor->redecls())
115  Results.push_back(Redecl->getParamDecl(ParamIdx));
116  return Results;
117 }
118 
119 PassByValueCheck::PassByValueCheck(StringRef Name, ClangTidyContext *Context)
120  : ClangTidyCheck(Name, Context),
121  IncludeStyle(utils::IncludeSorter::parseIncludeStyle(
122  Options.getLocalOrGlobal("IncludeStyle", "llvm"))),
123  ValuesOnly(Options.get("ValuesOnly", 0) != 0) {}
124 
126  Options.store(Opts, "IncludeStyle",
127  utils::IncludeSorter::toString(IncludeStyle));
128  Options.store(Opts, "ValuesOnly", ValuesOnly);
129 }
130 
131 void PassByValueCheck::registerMatchers(MatchFinder *Finder) {
132  // Only register the matchers for C++; the functionality currently does not
133  // provide any benefit to other languages, despite being benign.
134  if (!getLangOpts().CPlusPlus)
135  return;
136 
137  Finder->addMatcher(
138  cxxConstructorDecl(
139  forEachConstructorInitializer(
140  cxxCtorInitializer(
141  unless(isBaseInitializer()),
142  // Clang builds a CXXConstructExpr only when it knows which
143  // constructor will be called. In dependent contexts a
144  // ParenListExpr is generated instead of a CXXConstructExpr,
145  // filtering out templates automatically for us.
146  withInitializer(cxxConstructExpr(
147  has(ignoringParenImpCasts(declRefExpr(to(
148  parmVarDecl(
149  hasType(qualType(
150  // Match only const-ref or a non-const value
151  // parameters. Rvalues and const-values
152  // shouldn't be modified.
153  ValuesOnly ? nonConstValueType()
154  : anyOf(constRefType(),
155  nonConstValueType()))))
156  .bind("Param"))))),
157  hasDeclaration(cxxConstructorDecl(
158  isCopyConstructor(), unless(isDeleted()),
159  hasDeclContext(
160  cxxRecordDecl(isMoveConstructible())))))))
161  .bind("Initializer")))
162  .bind("Ctor"),
163  this);
164 }
165 
166 void PassByValueCheck::registerPPCallbacks(CompilerInstance &Compiler) {
167  // Only register the preprocessor callbacks for C++; the functionality
168  // currently does not provide any benefit to other languages, despite being
169  // benign.
170  if (getLangOpts().CPlusPlus) {
171  Inserter.reset(new utils::IncludeInserter(
172  Compiler.getSourceManager(), Compiler.getLangOpts(), IncludeStyle));
173  Compiler.getPreprocessor().addPPCallbacks(Inserter->CreatePPCallbacks());
174  }
175 }
176 
177 void PassByValueCheck::check(const MatchFinder::MatchResult &Result) {
178  const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructorDecl>("Ctor");
179  const auto *ParamDecl = Result.Nodes.getNodeAs<ParmVarDecl>("Param");
180  const auto *Initializer =
181  Result.Nodes.getNodeAs<CXXCtorInitializer>("Initializer");
182  SourceManager &SM = *Result.SourceManager;
183 
184  // If the parameter is used or anything other than the copy, do not apply
185  // the changes.
186  if (!paramReferredExactlyOnce(Ctor, ParamDecl))
187  return;
188 
189  // If the parameter is trivial to copy, don't move it. Moving a trivivally
190  // copyable type will cause a problem with performance-move-const-arg
191  if (ParamDecl->getType().getNonReferenceType().isTriviallyCopyableType(
192  *Result.Context))
193  return;
194 
195  auto Diag = diag(ParamDecl->getLocStart(), "pass by value and use std::move");
196 
197  // Iterate over all declarations of the constructor.
198  for (const ParmVarDecl *ParmDecl : collectParamDecls(Ctor, ParamDecl)) {
199  auto ParamTL = ParmDecl->getTypeSourceInfo()->getTypeLoc();
200  auto RefTL = ParamTL.getAs<ReferenceTypeLoc>();
201 
202  // Do not replace if it is already a value, skip.
203  if (RefTL.isNull())
204  continue;
205 
206  TypeLoc ValueTL = RefTL.getPointeeLoc();
207  auto TypeRange = CharSourceRange::getTokenRange(ParmDecl->getLocStart(),
208  ParamTL.getLocEnd());
209  std::string ValueStr = Lexer::getSourceText(CharSourceRange::getTokenRange(
210  ValueTL.getSourceRange()),
211  SM, getLangOpts())
212  .str();
213  ValueStr += ' ';
214  Diag << FixItHint::CreateReplacement(TypeRange, ValueStr);
215  }
216 
217  // Use std::move in the initialization list.
218  Diag << FixItHint::CreateInsertion(Initializer->getRParenLoc(), ")")
219  << FixItHint::CreateInsertion(
220  Initializer->getLParenLoc().getLocWithOffset(1), "std::move(");
221 
222  if (auto IncludeFixit = Inserter->CreateIncludeInsertion(
223  Result.SourceManager->getFileID(Initializer->getSourceLocation()),
224  "utility",
225  /*IsAngled=*/true)) {
226  Diag << *IncludeFixit;
227  }
228 }
229 
230 } // namespace modernize
231 } // namespace tidy
232 } // namespace clang
static bool paramReferredExactlyOnce(const CXXConstructorDecl *Ctor, const ParmVarDecl *ParamDecl)
Whether or not ParamDecl is used exactly one time in Ctor.
void store(ClangTidyOptions::OptionMap &Options, StringRef LocalName, StringRef Value) const
Stores an option with the check-local name LocalName with string value Value to Options.
Definition: ClangTidy.cpp:449
static TypeMatcher constRefType()
StringHandle Name
LangOptions getLangOpts() const
Returns the language options from the context.
Definition: ClangTidy.h:187
static StringRef toString(IncludeStyle Style)
Converts IncludeStyle to string representation.
static TypeMatcher nonConstValueType()
Base class for all clang-tidy checks.
Definition: ClangTidy.h:127
void registerPPCallbacks(clang::CompilerInstance &Compiler) override
std::map< std::string, std::string > OptionMap
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
static SmallVector< const ParmVarDecl *, 2 > collectParamDecls(const CXXConstructorDecl *Ctor, const ParmVarDecl *ParamDecl)
Find all references to ParamDecl across all of the redeclarations of Ctor.
Produces fixes to insert specified includes to source files, if not yet present.
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
AST_MATCHER(VarDecl, isAsm)
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check&#39;s name.
Definition: ClangTidy.cpp:416