clang-tools 10.0.0

ForRangeCopyCheck.cpp
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1 //===--- ForRangeCopyCheck.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 "ForRangeCopyCheck.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/Analysis/Analyses/ExprMutationAnalyzer.h"
16 #include "clang/Basic/Diagnostic.h"
17
18 using namespace clang::ast_matchers;
19
20 namespace clang {
21 namespace tidy {
22 namespace performance {
23
24 ForRangeCopyCheck::ForRangeCopyCheck(StringRef Name, ClangTidyContext *Context)
25 : ClangTidyCheck(Name, Context),
26 WarnOnAllAutoCopies(Options.get("WarnOnAllAutoCopies", 0)),
27 AllowedTypes(
28 utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
29
30 void ForRangeCopyCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
31 Options.store(Opts, "WarnOnAllAutoCopies", WarnOnAllAutoCopies);
32 Options.store(Opts, "AllowedTypes",
33 utils::options::serializeStringList(AllowedTypes));
34 }
35
36 void ForRangeCopyCheck::registerMatchers(MatchFinder *Finder) {
37 // Match loop variables that are not references or pointers or are already
38 // initialized through MaterializeTemporaryExpr which indicates a type
39 // conversion.
40 auto LoopVar = varDecl(
41 hasType(qualType(
42 unless(anyOf(hasCanonicalType(anyOf(referenceType(), pointerType())),
43 hasDeclaration(namedDecl(
44 matchers::matchesAnyListedName(AllowedTypes))))))),
45 unless(hasInitializer(expr(hasDescendant(materializeTemporaryExpr())))));
46 Finder->addMatcher(cxxForRangeStmt(hasLoopVariable(LoopVar.bind("loopVar")))
47 .bind("forRange"),
48 this);
49 }
50
51 void ForRangeCopyCheck::check(const MatchFinder::MatchResult &Result) {
52 const auto *Var = Result.Nodes.getNodeAs<VarDecl>("loopVar");
53
54 // Ignore code in macros since we can't place the fixes correctly.
55 if (Var->getBeginLoc().isMacroID())
56 return;
57 if (handleConstValueCopy(*Var, *Result.Context))
58 return;
59 const auto *ForRange = Result.Nodes.getNodeAs<CXXForRangeStmt>("forRange");
60 handleCopyIsOnlyConstReferenced(*Var, *ForRange, *Result.Context);
61 }
62
63 bool ForRangeCopyCheck::handleConstValueCopy(const VarDecl &LoopVar,
64 ASTContext &Context) {
65 if (WarnOnAllAutoCopies) {
66 // For aggressive check just test that loop variable has auto type.
67 if (!isa<AutoType>(LoopVar.getType()))
68 return false;
69 } else if (!LoopVar.getType().isConstQualified()) {
70 return false;
71 }
72 llvm::Optional<bool> Expensive =
73 utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
74 if (!Expensive || !*Expensive)
75 return false;
76 auto Diagnostic =
77 diag(LoopVar.getLocation(),
78 "the loop variable's type is not a reference type; this creates a "
79 "copy in each iteration; consider making this a reference")
80 << utils::fixit::changeVarDeclToReference(LoopVar, Context);
81 if (!LoopVar.getType().isConstQualified()) {
82 if (llvm::Optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
83 LoopVar, Context, DeclSpec::TQ::TQ_const))
84 Diagnostic << *Fix;
85 }
86 return true;
87 }
88
89 bool ForRangeCopyCheck::handleCopyIsOnlyConstReferenced(
90 const VarDecl &LoopVar, const CXXForRangeStmt &ForRange,
91 ASTContext &Context) {
92 llvm::Optional<bool> Expensive =
93 utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
94 if (LoopVar.getType().isConstQualified() || !Expensive || !*Expensive)
95 return false;
96 // We omit the case where the loop variable is not used in the loop body. E.g.
97 //
98 // for (auto _ : benchmark_state) {
99 // }
100 //
101 // Because the fix (changing to `const auto &`) will introduce an unused
102 // compiler warning which can't be suppressed.
103 // Since this case is very rare, it is safe to ignore it.
104 if (!ExprMutationAnalyzer(*ForRange.getBody(), Context).isMutated(&LoopVar) &&
105 !utils::decl_ref_expr::allDeclRefExprs(LoopVar, *ForRange.getBody(),
106 Context)
107 .empty()) {
108 auto Diag = diag(
109 LoopVar.getLocation(),
110 "loop variable is copied but only used as const reference; consider "
111 "making it a const reference");
112
113 if (llvm::Optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
114 LoopVar, Context, DeclSpec::TQ::TQ_const))
115 Diag << *Fix << utils::fixit::changeVarDeclToReference(LoopVar, Context);
116
117 return true;
118 }
119 return false;
120 }
121
122 } // namespace performance
123 } // namespace tidy
124 } // namespace clang
clang::ast_matchers
Definition: AbseilMatcher.h:14
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:30
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:120
clang::tidy::ClangTidyCheck
Base class for all clang-tidy checks.
Definition: ClangTidyCheck.h:47
ForRangeCopyCheck.h
clang::tidy::utils::options::parseStringList
std::vector< std::string > parseStringList(StringRef Option)
Parse a semicolon separated list of strings.
Definition: OptionsUtils.cpp:18
clang::tidy::ClangTidyCheck::Options
OptionsView Options
Definition: ClangTidyCheck.h:184
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:41
clang::tidy::performance::ForRangeCopyCheck::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: ForRangeCopyCheck.cpp:30
clang::tidy::ClangTidyCheck::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: ClangTidyCheck.cpp:58
Name
static constexpr llvm::StringLiteral Name
Definition: UppercaseLiteralSuffixCheck.cpp:27
clang::tidy::ClangTidyOptions::OptionMap
std::map< std::string, std::string > OptionMap
Definition: ClangTidyOptions.h:97
clang::tidy::performance::ForRangeCopyCheck::registerMatchers
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
Definition: ForRangeCopyCheck.cpp:36
clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ApplyReplacements.h:27
clang::tidy::ClangTidyContext
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
Definition: ClangTidyDiagnosticConsumer.h:77
clang::tidy::performance::ForRangeCopyCheck::check
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
Definition: ForRangeCopyCheck.cpp:51
Fix
static cl::opt< bool > Fix("fix", cl::desc(R"( Apply suggested fixes. Without -fix-errors clang-tidy will bail out if any compilation errors were found. )"), cl::init(false), cl::cat(ClangTidyCategory))
clang::tidy::utils::fixit::addQualifierToVarDecl
Optional< FixItHint > addQualifierToVarDecl(const VarDecl &Var, const ASTContext &Context, DeclSpec::TQ Qualifier, QualifierTarget QualTarget, QualifierPolicy QualPolicy)
Creates fix to qualify VarDecl with the specified Qualifier.
Definition: FixItHintUtils.cpp:184
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: ClangTidyCheck.cpp:21
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