clang-tools  12.0.0git
ForRangeCopyCheck.cpp
Go to the documentation of this file.
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 LoopVar =
49  varDecl(HasReferenceOrPointerTypeOrIsAllowed,
50  unless(hasInitializer(expr(hasDescendant(expr(anyOf(
51  materializeTemporaryExpr(), IteratorReturnsValueType)))))));
52  Finder->addMatcher(
53  traverse(ast_type_traits::TK_AsIs,
54  cxxForRangeStmt(hasLoopVariable(LoopVar.bind("loopVar")))
55  .bind("forRange")),
56  this);
57 }
58 
59 void ForRangeCopyCheck::check(const MatchFinder::MatchResult &Result) {
60  const auto *Var = Result.Nodes.getNodeAs<VarDecl>("loopVar");
61 
62  // Ignore code in macros since we can't place the fixes correctly.
63  if (Var->getBeginLoc().isMacroID())
64  return;
65  if (handleConstValueCopy(*Var, *Result.Context))
66  return;
67  const auto *ForRange = Result.Nodes.getNodeAs<CXXForRangeStmt>("forRange");
68  handleCopyIsOnlyConstReferenced(*Var, *ForRange, *Result.Context);
69 }
70 
71 bool ForRangeCopyCheck::handleConstValueCopy(const VarDecl &LoopVar,
72  ASTContext &Context) {
73  if (WarnOnAllAutoCopies) {
74  // For aggressive check just test that loop variable has auto type.
75  if (!isa<AutoType>(LoopVar.getType()))
76  return false;
77  } else if (!LoopVar.getType().isConstQualified()) {
78  return false;
79  }
80  llvm::Optional<bool> Expensive =
81  utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
82  if (!Expensive || !*Expensive)
83  return false;
84  auto Diagnostic =
85  diag(LoopVar.getLocation(),
86  "the loop variable's type is not a reference type; this creates a "
87  "copy in each iteration; consider making this a reference")
88  << utils::fixit::changeVarDeclToReference(LoopVar, Context);
89  if (!LoopVar.getType().isConstQualified()) {
90  if (llvm::Optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
91  LoopVar, Context, DeclSpec::TQ::TQ_const))
92  Diagnostic << *Fix;
93  }
94  return true;
95 }
96 
97 bool ForRangeCopyCheck::handleCopyIsOnlyConstReferenced(
98  const VarDecl &LoopVar, const CXXForRangeStmt &ForRange,
99  ASTContext &Context) {
100  llvm::Optional<bool> Expensive =
101  utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
102  if (LoopVar.getType().isConstQualified() || !Expensive || !*Expensive)
103  return false;
104  // We omit the case where the loop variable is not used in the loop body. E.g.
105  //
106  // for (auto _ : benchmark_state) {
107  // }
108  //
109  // Because the fix (changing to `const auto &`) will introduce an unused
110  // compiler warning which can't be suppressed.
111  // Since this case is very rare, it is safe to ignore it.
112  if (!ExprMutationAnalyzer(*ForRange.getBody(), Context).isMutated(&LoopVar) &&
113  !utils::decl_ref_expr::allDeclRefExprs(LoopVar, *ForRange.getBody(),
114  Context)
115  .empty()) {
116  auto Diag = diag(
117  LoopVar.getLocation(),
118  "loop variable is copied but only used as const reference; consider "
119  "making it a const reference");
120 
121  if (llvm::Optional<FixItHint> Fix = utils::fixit::addQualifierToVarDecl(
122  LoopVar, Context, DeclSpec::TQ::TQ_const))
123  Diag << *Fix << utils::fixit::changeVarDeclToReference(LoopVar, Context);
124 
125  return true;
126  }
127  return false;
128 }
129 
130 } // namespace performance
131 } // namespace tidy
132 } // namespace clang
std::string serializeStringList(ArrayRef< std::string > Strings)
Serialize a sequence of names that can be parsed by parseStringList.
SmallPtrSet< const DeclRefExpr *, 16 > allDeclRefExprs(const VarDecl &VarDecl, const Stmt &Stmt, ASTContext &Context)
Returns set of all DeclRefExprs to VarDecl within Stmt.
Base class for all clang-tidy checks.
std::vector< std::string > parseStringList(StringRef Option)
Parse a semicolon separated list of strings.
llvm::Optional< bool > isExpensiveToCopy(QualType Type, const ASTContext &Context)
Returns true if Type is expensive to copy.
Definition: TypeTraits.cpp:41
DiagnosticCallback Diagnostic
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
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.
static constexpr llvm::StringLiteral Name
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
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.
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))
std::map< std::string, ClangTidyValue > OptionMap
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.
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check&#39;s name.
FixItHint changeVarDeclToReference(const VarDecl &Var, ASTContext &Context)
Creates fix to make VarDecl a reference by adding &.