clang-tools 8.0.0

UnnecessaryValueParamCheck.cpp
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1 //===--- UnnecessaryValueParamCheck.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 "UnnecessaryValueParamCheck.h"
11
12 #include "../utils/DeclRefExprUtils.h"
13 #include "../utils/FixItHintUtils.h"
14 #include "../utils/Matchers.h"
15 #include "../utils/OptionsUtils.h"
16 #include "../utils/TypeTraits.h"
17 #include "clang/Frontend/CompilerInstance.h"
18 #include "clang/Lex/Lexer.h"
19 #include "clang/Lex/Preprocessor.h"
20
21 using namespace clang::ast_matchers;
22
23 namespace clang {
24 namespace tidy {
25 namespace performance {
26
27 namespace {
28
29 std::string paramNameOrIndex(StringRef Name, size_t Index) {
30 return (Name.empty() ? llvm::Twine('#') + llvm::Twine(Index + 1)
31 : llvm::Twine('\'') + Name + llvm::Twine('\''))
32 .str();
33 }
34
35 bool isReferencedOutsideOfCallExpr(const FunctionDecl &Function,
36 ASTContext &Context) {
37 auto Matches = match(declRefExpr(to(functionDecl(equalsNode(&Function))),
38 unless(hasAncestor(callExpr()))),
39 Context);
40 return !Matches.empty();
41 }
42
43 bool hasLoopStmtAncestor(const DeclRefExpr &DeclRef, const Decl &Decl,
44 ASTContext &Context) {
45 auto Matches =
46 match(decl(forEachDescendant(declRefExpr(
47 equalsNode(&DeclRef),
48 unless(hasAncestor(stmt(anyOf(forStmt(), cxxForRangeStmt(),
49 whileStmt(), doStmt()))))))),
50 Decl, Context);
51 return Matches.empty();
52 }
53
54 bool isExplicitTemplateSpecialization(const FunctionDecl &Function) {
55 if (const auto *SpecializationInfo = Function.getTemplateSpecializationInfo())
56 if (SpecializationInfo->getTemplateSpecializationKind() ==
57 TSK_ExplicitSpecialization)
58 return true;
59 if (const auto *Method = llvm::dyn_cast<CXXMethodDecl>(&Function))
60 if (Method->getTemplatedKind() == FunctionDecl::TK_MemberSpecialization &&
61 Method->getMemberSpecializationInfo()->isExplicitSpecialization())
62 return true;
63 return false;
64 }
65
66 } // namespace
67
68 UnnecessaryValueParamCheck::UnnecessaryValueParamCheck(
69 StringRef Name, ClangTidyContext *Context)
70 : ClangTidyCheck(Name, Context),
71 IncludeStyle(utils::IncludeSorter::parseIncludeStyle(
72 Options.getLocalOrGlobal("IncludeStyle", "llvm"))),
73 AllowedTypes(
74 utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
75
76 void UnnecessaryValueParamCheck::registerMatchers(MatchFinder *Finder) {
77 // This check is specific to C++ and doesn't apply to languages like
78 // Objective-C.
79 if (!getLangOpts().CPlusPlus)
80 return;
81 const auto ExpensiveValueParamDecl = parmVarDecl(
82 hasType(qualType(
83 hasCanonicalType(matchers::isExpensiveToCopy()),
84 unless(anyOf(hasCanonicalType(referenceType()),
85 hasDeclaration(namedDecl(
86 matchers::matchesAnyListedName(AllowedTypes))))))),
87 decl().bind("param"));
88 Finder->addMatcher(
89 functionDecl(hasBody(stmt()), isDefinition(), unless(isImplicit()),
90 unless(cxxMethodDecl(anyOf(isOverride(), isFinal()))),
91 has(typeLoc(forEach(ExpensiveValueParamDecl))),
92 unless(isInstantiated()), decl().bind("functionDecl")),
93 this);
94 }
95
96 void UnnecessaryValueParamCheck::check(const MatchFinder::MatchResult &Result) {
97 const auto *Param = Result.Nodes.getNodeAs<ParmVarDecl>("param");
98 const auto *Function = Result.Nodes.getNodeAs<FunctionDecl>("functionDecl");
99
100 FunctionParmMutationAnalyzer &Analyzer =
101 MutationAnalyzers.try_emplace(Function, *Function, *Result.Context)
102 .first->second;
103 if (Analyzer.isMutated(Param))
104 return;
105
106 const bool IsConstQualified =
107 Param->getType().getCanonicalType().isConstQualified();
108
109 // If the parameter is non-const, check if it has a move constructor and is
110 // only referenced once to copy-construct another object or whether it has a
111 // move assignment operator and is only referenced once when copy-assigned.
112 // In this case wrap DeclRefExpr with std::move() to avoid the unnecessary
113 // copy.
114 if (!IsConstQualified) {
115 auto AllDeclRefExprs = utils::decl_ref_expr::allDeclRefExprs(
116 *Param, *Function, *Result.Context);
117 if (AllDeclRefExprs.size() == 1) {
118 auto CanonicalType = Param->getType().getCanonicalType();
119 const auto &DeclRefExpr = **AllDeclRefExprs.begin();
120
121 if (!hasLoopStmtAncestor(DeclRefExpr, *Function, *Result.Context) &&
122 ((utils::type_traits::hasNonTrivialMoveConstructor(CanonicalType) &&
123 utils::decl_ref_expr::isCopyConstructorArgument(
124 DeclRefExpr, *Function, *Result.Context)) ||
125 (utils::type_traits::hasNonTrivialMoveAssignment(CanonicalType) &&
126 utils::decl_ref_expr::isCopyAssignmentArgument(
127 DeclRefExpr, *Function, *Result.Context)))) {
128 handleMoveFix(*Param, DeclRefExpr, *Result.Context);
129 return;
130 }
131 }
132 }
133
134 const size_t Index = std::find(Function->parameters().begin(),
135 Function->parameters().end(), Param) -
136 Function->parameters().begin();
137
138 auto Diag =
139 diag(Param->getLocation(),
140 IsConstQualified ? "the const qualified parameter %0 is "
141 "copied for each invocation; consider "
142 "making it a reference"
143 : "the parameter %0 is copied for each "
144 "invocation but only used as a const reference; "
145 "consider making it a const reference")
146 << paramNameOrIndex(Param->getName(), Index);
147 // Do not propose fixes when:
148 // 1. the ParmVarDecl is in a macro, since we cannot place them correctly
149 // 2. the function is virtual as it might break overrides
150 // 3. the function is referenced outside of a call expression within the
151 // compilation unit as the signature change could introduce build errors.
152 // 4. the function is an explicit template specialization.
153 const auto *Method = llvm::dyn_cast<CXXMethodDecl>(Function);
154 if (Param->getBeginLoc().isMacroID() || (Method && Method->isVirtual()) ||
155 isReferencedOutsideOfCallExpr(*Function, *Result.Context) ||
156 isExplicitTemplateSpecialization(*Function))
157 return;
158 for (const auto *FunctionDecl = Function; FunctionDecl != nullptr;
159 FunctionDecl = FunctionDecl->getPreviousDecl()) {
160 const auto &CurrentParam = *FunctionDecl->getParamDecl(Index);
161 Diag << utils::fixit::changeVarDeclToReference(CurrentParam,
162 *Result.Context);
163 // The parameter of each declaration needs to be checked individually as to
164 // whether it is const or not as constness can differ between definition and
165 // declaration.
166 if (!CurrentParam.getType().getCanonicalType().isConstQualified())
167 Diag << utils::fixit::changeVarDeclToConst(CurrentParam);
168 }
169 }
170
171 void UnnecessaryValueParamCheck::registerPPCallbacks(
172 CompilerInstance &Compiler) {
173 Inserter.reset(new utils::IncludeInserter(
174 Compiler.getSourceManager(), Compiler.getLangOpts(), IncludeStyle));
175 Compiler.getPreprocessor().addPPCallbacks(Inserter->CreatePPCallbacks());
176 }
177
178 void UnnecessaryValueParamCheck::storeOptions(
179 ClangTidyOptions::OptionMap &Opts) {
180 Options.store(Opts, "IncludeStyle",
181 utils::IncludeSorter::toString(IncludeStyle));
182 Options.store(Opts, "AllowedTypes",
183 utils::options::serializeStringList(AllowedTypes));
184 }
185
186 void UnnecessaryValueParamCheck::onEndOfTranslationUnit() {
187 MutationAnalyzers.clear();
188 }
189
190 void UnnecessaryValueParamCheck::handleMoveFix(const ParmVarDecl &Var,
191 const DeclRefExpr &CopyArgument,
192 const ASTContext &Context) {
193 auto Diag = diag(CopyArgument.getBeginLoc(),
194 "parameter %0 is passed by value and only copied once; "
195 "consider moving it to avoid unnecessary copies")
196 << &Var;
197 // Do not propose fixes in macros since we cannot place them correctly.
198 if (CopyArgument.getBeginLoc().isMacroID())
199 return;
200 const auto &SM = Context.getSourceManager();
201 auto EndLoc = Lexer::getLocForEndOfToken(CopyArgument.getLocation(), 0, SM,
202 Context.getLangOpts());
203 Diag << FixItHint::CreateInsertion(CopyArgument.getBeginLoc(), "std::move(")
204 << FixItHint::CreateInsertion(EndLoc, ")");
205 if (auto IncludeFixit = Inserter->CreateIncludeInsertion(
206 SM.getFileID(CopyArgument.getBeginLoc()), "utility",
207 /*IsAngled=*/true))
208 Diag << *IncludeFixit;
209 }
210
211 } // namespace performance
212 } // namespace tidy
213 } // namespace clang
clang::ast_matchers
Definition: AbseilMatcher.h:15
clang::tidy::OptionsView::store
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:473
llvm
Some operations such as code completion produce a set of candidates.
Definition: YAMLGenerator.cpp:28
clang::tidy::utils::options::serializeStringList
std::string serializeStringList(ArrayRef< std::string > Strings)
Serialize a sequence of names that can be parsed by parseStringList.
Definition: OptionsUtils.cpp:31
clang::tidy::utils::decl_ref_expr::allDeclRefExprs
SmallPtrSet< const DeclRefExpr *, 16 > allDeclRefExprs(const VarDecl &VarDecl, const Stmt &Stmt, ASTContext &Context)
Returns set of all DeclRefExprs to VarDecl within Stmt.
Definition: DeclRefExprUtils.cpp:121
clang::tidy::ClangTidyCheck::getLangOpts
LangOptions getLangOpts() const
Returns the language options from the context.
Definition: ClangTidy.h:187
clang::tidy::utils::decl_ref_expr::isCopyConstructorArgument
bool isCopyConstructorArgument(const DeclRefExpr &DeclRef, const Decl &Decl, ASTContext &Context)
Returns true if DeclRefExpr is the argument of a copy-constructor call expression within Decl...
Definition: DeclRefExprUtils.cpp:141
clang::tidy::utils::IncludeSorter::toString
static StringRef toString(IncludeStyle Style)
Converts IncludeStyle to string representation.
Definition: IncludeSorter.cpp:284
clang::tidy::performance::UnnecessaryValueParamCheck::storeOptions
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
Definition: UnnecessaryValueParamCheck.cpp:178
clang::tidy::ClangTidyCheck
Base class for all clang-tidy checks.
Definition: ClangTidy.h:127
clang::tidy::utils::type_traits::hasNonTrivialMoveConstructor
bool hasNonTrivialMoveConstructor(QualType Type)
Returns true if Type has a non-trivial move constructor.
Definition: TypeTraits.cpp:135
clang::tidy::utils::options::parseStringList
std::vector< std::string > parseStringList(StringRef Option)
Parse a semicolon separated list of strings.
Definition: OptionsUtils.cpp:19
clang::tidy::ClangTidyCheck::Options
OptionsView Options
Definition: ClangTidy.h:183
clang::tidy::performance::UnnecessaryValueParamCheck::onEndOfTranslationUnit
void onEndOfTranslationUnit() override
Definition: UnnecessaryValueParamCheck.cpp:186
clang::tidy::utils::type_traits::isExpensiveToCopy
llvm::Optional< bool > isExpensiveToCopy(QualType Type, const ASTContext &Context)
Returns true if Type is expensive to copy.
Definition: TypeTraits.cpp:42
Name
static constexpr llvm::StringLiteral Name
Definition: UppercaseLiteralSuffixCheck.cpp:28
clang::tidy::ClangTidyOptions::OptionMap
std::map< std::string, std::string > OptionMap
Definition: ClangTidyOptions.h:98
Result
llvm::Optional< llvm::Expected< tooling::AtomicChanges > > Result
Definition: ClangdServer.cpp:60
clang::clangd::CompletionItemKind::Method
clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ChangeNamespace.cpp:18
clang::tidy::performance::UnnecessaryValueParamCheck::registerPPCallbacks
void registerPPCallbacks(CompilerInstance &Compiler) override
Override this to register PPCallbacks with Compiler.
Definition: UnnecessaryValueParamCheck.cpp:171
UnnecessaryValueParamCheck.h
clang::tidy::utils::IncludeInserter
Produces fixes to insert specified includes to source files, if not yet present.
Definition: IncludeInserter.h:57
clang::tidy::ClangTidyContext
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
Definition: ClangTidyDiagnosticConsumer.h:100
clang::tidy::performance::UnnecessaryValueParamCheck::check
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
Definition: UnnecessaryValueParamCheck.cpp:96
clang::tidy::utils::decl_ref_expr::isCopyAssignmentArgument
bool isCopyAssignmentArgument(const DeclRefExpr &DeclRef, const Decl &Decl, ASTContext &Context)
Returns true if DeclRefExpr is the argument of a copy-assignment operator CallExpr within Decl...
Definition: DeclRefExprUtils.cpp:155
DeclRef
const DeclRefExpr * DeclRef
Definition: UseAfterMoveCheck.cpp:30
clang::tidy::ClangTidyCheck::diag
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check&#39;s name.
Definition: ClangTidy.cpp:438
clang::tidy::utils::type_traits::hasNonTrivialMoveAssignment
bool hasNonTrivialMoveAssignment(QualType Type)
Return true if Type has a non-trivial move assignment operator.
Definition: TypeTraits.cpp:141
clang::tidy::utils::fixit::changeVarDeclToConst
FixItHint changeVarDeclToConst(const VarDecl &Var)
Creates fix to make VarDecl const qualified.
Definition: FixItHintUtils.cpp:30
clang::tidy::performance::UnnecessaryValueParamCheck::registerMatchers
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
Definition: UnnecessaryValueParamCheck.cpp:76
Index
const SymbolIndex * Index
Definition: Dexp.cpp:85
clang::tidy::utils::fixit::changeVarDeclToReference
FixItHint changeVarDeclToReference(const VarDecl &Var, ASTContext &Context)
Creates fix to make VarDecl a reference by adding &.
Definition: FixItHintUtils.cpp:19