1//===--- UnnecessaryValueParamCheck.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 "UnnecessaryValueParamCheck.h"
10#include "../utils/DeclRefExprUtils.h"
11#include "../utils/FixItHintUtils.h"
12#include "../utils/Matchers.h"
13#include "../utils/OptionsUtils.h"
14#include "../utils/TypeTraits.h"
15#include "clang/Frontend/CompilerInstance.h"
16#include "clang/Lex/Lexer.h"
17#include "clang/Lex/Preprocessor.h"
18#include <optional>
19
20using namespace clang::ast_matchers;
21
22namespace clang::tidy::performance {
23
24namespace {
25
26std::string paramNameOrIndex(StringRef Name, size_t Index) {
27 return (Name.empty() ? llvm::Twine('#') + llvm::Twine(Index + 1)
28 : llvm::Twine('\'') + Name + llvm::Twine('\''))
29 .str();
30}
31
32bool hasLoopStmtAncestor(const DeclRefExpr &DeclRef, const Decl &Decl,
33 ASTContext &Context) {
34 auto Matches = match(
35 traverse(TK_AsIs,
36 decl(forEachDescendant(declRefExpr(
37 equalsNode(&DeclRef),
38 unless(hasAncestor(stmt(anyOf(forStmt(), cxxForRangeStmt(),
39 whileStmt(), doStmt())))))))),
40 Decl, Context);
41 return Matches.empty();
42}
43
44} // namespace
45
46UnnecessaryValueParamCheck::UnnecessaryValueParamCheck(
47 StringRef Name, ClangTidyContext *Context)
48 : ClangTidyCheck(Name, Context),
49 Inserter(Options.getLocalOrGlobal(LocalName: "IncludeStyle",
50 Default: utils::IncludeSorter::IS_LLVM),
51 areDiagsSelfContained()),
52 AllowedTypes(
53 utils::options::parseStringList(Option: Options.get(LocalName: "AllowedTypes", Default: ""))) {}
54
55void UnnecessaryValueParamCheck::registerMatchers(MatchFinder *Finder) {
56 const auto ExpensiveValueParamDecl = parmVarDecl(
57 hasType(InnerMatcher: qualType(
58 hasCanonicalType(InnerMatcher: matchers::isExpensiveToCopy()),
59 unless(anyOf(hasCanonicalType(InnerMatcher: referenceType()),
60 hasDeclaration(InnerMatcher: namedDecl(
61 matchers::matchesAnyListedName(NameList: AllowedTypes))))))),
62 decl().bind(ID: "param"));
63 Finder->addMatcher(
64 NodeMatch: traverse(
65 TK: TK_AsIs,
66 InnerMatcher: functionDecl(hasBody(InnerMatcher: stmt()), isDefinition(), unless(isImplicit()),
67 unless(cxxMethodDecl(anyOf(isOverride(), isFinal()))),
68 has(typeLoc(forEach(ExpensiveValueParamDecl))),
69 decl().bind(ID: "functionDecl"))),
70 Action: this);
71}
72
73void UnnecessaryValueParamCheck::check(const MatchFinder::MatchResult &Result) {
74 const auto *Param = Result.Nodes.getNodeAs<ParmVarDecl>(ID: "param");
75 const auto *Function = Result.Nodes.getNodeAs<FunctionDecl>(ID: "functionDecl");
76
77 TraversalKindScope RAII(*Result.Context, TK_AsIs);
78
79 FunctionParmMutationAnalyzer *Analyzer =
80 FunctionParmMutationAnalyzer::getFunctionParmMutationAnalyzer(
81 Func: *Function, Context&: *Result.Context, Memorized&: MutationAnalyzerCache);
82 if (Analyzer->isMutated(Parm: Param))
83 return;
84
85 const bool IsConstQualified =
86 Param->getType().getCanonicalType().isConstQualified();
87
88 // If the parameter is non-const, check if it has a move constructor and is
89 // only referenced once to copy-construct another object or whether it has a
90 // move assignment operator and is only referenced once when copy-assigned.
91 // In this case wrap DeclRefExpr with std::move() to avoid the unnecessary
92 // copy.
93 if (!IsConstQualified) {
94 auto AllDeclRefExprs = utils::decl_ref_expr::allDeclRefExprs(
95 *Param, *Function, *Result.Context);
96 if (AllDeclRefExprs.size() == 1) {
97 auto CanonicalType = Param->getType().getCanonicalType();
98 const auto &DeclRefExpr = **AllDeclRefExprs.begin();
99
100 if (!hasLoopStmtAncestor(DeclRefExpr, *Function, *Result.Context) &&
101 ((utils::type_traits::hasNonTrivialMoveConstructor(Type: CanonicalType) &&
102 utils::decl_ref_expr::isCopyConstructorArgument(
103 DeclRef: DeclRefExpr, Decl: *Function, Context&: *Result.Context)) ||
104 (utils::type_traits::hasNonTrivialMoveAssignment(Type: CanonicalType) &&
105 utils::decl_ref_expr::isCopyAssignmentArgument(
106 DeclRef: DeclRefExpr, Decl: *Function, Context&: *Result.Context)))) {
107 handleMoveFix(Param: *Param, CopyArgument: DeclRefExpr, Context&: *Result.Context);
108 return;
109 }
110 }
111 }
112
113 handleConstRefFix(Function: *Function, Param: *Param, Context&: *Result.Context);
114}
115
116void UnnecessaryValueParamCheck::registerPPCallbacks(
117 const SourceManager &SM, Preprocessor *PP, Preprocessor *ModuleExpanderPP) {
118 Inserter.registerPreprocessor(PP);
119}
120
121void UnnecessaryValueParamCheck::storeOptions(
122 ClangTidyOptions::OptionMap &Opts) {
123 Options.store(Options&: Opts, LocalName: "IncludeStyle", Value: Inserter.getStyle());
124 Options.store(Options&: Opts, LocalName: "AllowedTypes",
125 Value: utils::options::serializeStringList(Strings: AllowedTypes));
126}
127
128void UnnecessaryValueParamCheck::onEndOfTranslationUnit() {
129 MutationAnalyzerCache.clear();
130}
131
132void UnnecessaryValueParamCheck::handleConstRefFix(const FunctionDecl &Function,
133 const ParmVarDecl &Param,
134 ASTContext &Context) {
135 const size_t Index =
136 llvm::find(Range: Function.parameters(), Val: &Param) - Function.parameters().begin();
137 const bool IsConstQualified =
138 Param.getType().getCanonicalType().isConstQualified();
139
140 auto Diag =
141 diag(Param.getLocation(),
142 "the %select{|const qualified }0parameter %1 is copied for each "
143 "invocation%select{ but only used as a const reference|}0; consider "
144 "making it a %select{const |}0reference")
145 << IsConstQualified << paramNameOrIndex(Param.getName(), Index);
146 // Do not propose fixes when:
147 // 1. the ParmVarDecl is in a macro, since we cannot place them correctly
148 // 2. the function is virtual as it might break overrides
149 // 3. the function is an explicit template/ specialization.
150 const auto *Method = llvm::dyn_cast<CXXMethodDecl>(Val: &Function);
151 if (Param.getBeginLoc().isMacroID() || (Method && Method->isVirtual()) ||
152 Function.getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
153 return;
154 for (const auto *FunctionDecl = &Function; FunctionDecl != nullptr;
155 FunctionDecl = FunctionDecl->getPreviousDecl()) {
156 const auto &CurrentParam = *FunctionDecl->getParamDecl(i: Index);
157 Diag << utils::fixit::changeVarDeclToReference(CurrentParam, Context);
158 // The parameter of each declaration needs to be checked individually as to
159 // whether it is const or not as constness can differ between definition and
160 // declaration.
161 if (!CurrentParam.getType().getCanonicalType().isConstQualified()) {
162 if (std::optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
163 CurrentParam, Context, Qualifiers::Const))
164 Diag << *Fix;
165 }
166 }
167}
168
169void UnnecessaryValueParamCheck::handleMoveFix(const ParmVarDecl &Param,
170 const DeclRefExpr &CopyArgument,
171 ASTContext &Context) {
172 auto Diag = diag(Loc: CopyArgument.getBeginLoc(),
173 Description: "parameter %0 is passed by value and only copied once; "
174 "consider moving it to avoid unnecessary copies")
175 << &Param;
176 // Do not propose fixes in macros since we cannot place them correctly.
177 if (CopyArgument.getBeginLoc().isMacroID())
178 return;
179 const auto &SM = Context.getSourceManager();
180 auto EndLoc = Lexer::getLocForEndOfToken(Loc: CopyArgument.getLocation(), Offset: 0, SM,
181 LangOpts: Context.getLangOpts());
182 Diag << FixItHint::CreateInsertion(InsertionLoc: CopyArgument.getBeginLoc(), Code: "std::move(")
183 << FixItHint::CreateInsertion(InsertionLoc: EndLoc, Code: ")")
184 << Inserter.createIncludeInsertion(
185 FileID: SM.getFileID(SpellingLoc: CopyArgument.getBeginLoc()), Header: "<utility>");
186}
187
188} // namespace clang::tidy::performance
189

source code of clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp