clang-tools  16.0.0git
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", false)),
27  AllowedTypes(
28  utils::options::parseStringList(Options.get("AllowedTypes", ""))) {}
29 
31  Options.store(Opts, "WarnOnAllAutoCopies", WarnOnAllAutoCopies);
32  Options.store(Opts, "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 HasReferenceOrPointerTypeOrIsAllowed = hasType(qualType(
41  unless(anyOf(hasCanonicalType(anyOf(referenceType(), pointerType())),
42  hasDeclaration(namedDecl(
43  matchers::matchesAnyListedName(AllowedTypes)))))));
44  auto IteratorReturnsValueType = cxxOperatorCallExpr(
45  hasOverloadedOperatorName("*"),
46  callee(
47  cxxMethodDecl(returns(unless(hasCanonicalType(referenceType()))))));
48  auto NotConstructedByCopy = cxxConstructExpr(
49  hasDeclaration(cxxConstructorDecl(unless(isCopyConstructor()))));
50  auto ConstructedByConversion = cxxMemberCallExpr(callee(cxxConversionDecl()));
51  auto LoopVar =
52  varDecl(HasReferenceOrPointerTypeOrIsAllowed,
53  unless(hasInitializer(expr(hasDescendant(expr(
54  anyOf(materializeTemporaryExpr(), IteratorReturnsValueType,
55  NotConstructedByCopy, ConstructedByConversion)))))));
56  Finder->addMatcher(
57  traverse(TK_AsIs,
58  cxxForRangeStmt(hasLoopVariable(LoopVar.bind("loopVar")))
59  .bind("forRange")),
60  this);
61 }
62 
63 void ForRangeCopyCheck::check(const MatchFinder::MatchResult &Result) {
64  const auto *Var = Result.Nodes.getNodeAs<VarDecl>("loopVar");
65 
66  // Ignore code in macros since we can't place the fixes correctly.
67  if (Var->getBeginLoc().isMacroID())
68  return;
69  if (handleConstValueCopy(*Var, *Result.Context))
70  return;
71  const auto *ForRange = Result.Nodes.getNodeAs<CXXForRangeStmt>("forRange");
72  handleCopyIsOnlyConstReferenced(*Var, *ForRange, *Result.Context);
73 }
74 
75 bool ForRangeCopyCheck::handleConstValueCopy(const VarDecl &LoopVar,
76  ASTContext &Context) {
77  if (WarnOnAllAutoCopies) {
78  // For aggressive check just test that loop variable has auto type.
79  if (!isa<AutoType>(LoopVar.getType()))
80  return false;
81  } else if (!LoopVar.getType().isConstQualified()) {
82  return false;
83  }
84  llvm::Optional<bool> Expensive =
85  utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
86  if (!Expensive || !*Expensive)
87  return false;
88  auto Diagnostic =
89  diag(LoopVar.getLocation(),
90  "the loop variable's type is not a reference type; this creates a "
91  "copy in each iteration; consider making this a reference")
92  << utils::fixit::changeVarDeclToReference(LoopVar, Context);
93  if (!LoopVar.getType().isConstQualified()) {
94  if (llvm::Optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
95  LoopVar, Context, DeclSpec::TQ::TQ_const))
96  Diagnostic << *Fix;
97  }
98  return true;
99 }
100 
101 bool ForRangeCopyCheck::handleCopyIsOnlyConstReferenced(
102  const VarDecl &LoopVar, const CXXForRangeStmt &ForRange,
103  ASTContext &Context) {
104  llvm::Optional<bool> Expensive =
105  utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
106  if (LoopVar.getType().isConstQualified() || !Expensive || !*Expensive)
107  return false;
108  // We omit the case where the loop variable is not used in the loop body. E.g.
109  //
110  // for (auto _ : benchmark_state) {
111  // }
112  //
113  // Because the fix (changing to `const auto &`) will introduce an unused
114  // compiler warning which can't be suppressed.
115  // Since this case is very rare, it is safe to ignore it.
116  if (!ExprMutationAnalyzer(*ForRange.getBody(), Context).isMutated(&LoopVar) &&
117  !utils::decl_ref_expr::allDeclRefExprs(LoopVar, *ForRange.getBody(),
118  Context)
119  .empty()) {
120  auto Diag = diag(
121  LoopVar.getLocation(),
122  "loop variable is copied but only used as const reference; consider "
123  "making it a const reference");
124 
125  if (llvm::Optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
126  LoopVar, Context, DeclSpec::TQ::TQ_const))
127  Diag << *Fix << utils::fixit::changeVarDeclToReference(LoopVar, Context);
128 
129  return true;
130  }
131  return false;
132 }
133 
134 } // namespace performance
135 } // namespace tidy
136 } // namespace clang
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:101
clang::tidy::ClangTidyOptions::OptionMap
llvm::StringMap< ClangTidyValue > OptionMap
Definition: ClangTidyOptions.h:115
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
Base class for all clang-tidy checks.
Definition: ClangTidyCheck.h:53
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::utils::fixit::changeVarDeclToReference
FixItHint changeVarDeclToReference(const VarDecl &Var, ASTContext &Context)
Creates fix to make VarDecl a reference by adding &.
Definition: FixItHintUtils.cpp:19
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::performance::ForRangeCopyCheck::registerMatchers
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
Definition: ForRangeCopyCheck.cpp:36
clang::ast_matchers
Definition: AbseilMatcher.h:14
Diagnostic
DiagnosticCallback Diagnostic
Definition: ConfigCompile.cpp:100
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:63
clang::tidy::ClangTidyCheck::Options
OptionsView Options
Definition: ClangTidyCheck.h:415
clang::tidy::ClangTidyContext
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
Definition: ClangTidyDiagnosticConsumer.h:67
clang::tidy::ClangTidyCheck::diag
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check's name.
Definition: ClangTidyCheck.cpp:25
Name
Token Name
Definition: MacroToEnumCheck.cpp:89
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::matchers::matchesAnyListedName
inline ::clang::ast_matchers::internal::Matcher< NamedDecl > matchesAnyListedName(llvm::ArrayRef< StringRef > NameList)
Definition: clang-tidy/utils/Matchers.h:119
clang::tidy::utils::options::serializeStringList
std::string serializeStringList(ArrayRef< StringRef > Strings)
Serialize a sequence of names that can be parsed by parseStringList.
Definition: OptionsUtils.cpp:62
clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ApplyReplacements.h:27
clang::tidy::utils::options::parseStringList
std::vector< StringRef > parseStringList(StringRef Option)
Parse a semicolon separated list of strings.
Definition: OptionsUtils.cpp:19
ForRangeCopyCheck.h
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:129