clang-tools  3.9.0
ForRangeCopyCheck.cpp
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1 //===--- ForRangeCopyCheck.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 "ForRangeCopyCheck.h"
11 #include "../utils/DeclRefExprUtils.h"
12 #include "../utils/FixItHintUtils.h"
13 #include "../utils/TypeTraits.h"
14 
15 using namespace clang::ast_matchers;
16 
17 namespace clang {
18 namespace tidy {
19 namespace performance {
20 
21 ForRangeCopyCheck::ForRangeCopyCheck(StringRef Name, ClangTidyContext *Context)
22  : ClangTidyCheck(Name, Context),
23  WarnOnAllAutoCopies(Options.get("WarnOnAllAutoCopies", 0)) {}
24 
26  Options.store(Opts, "WarnOnAllAutoCopies", WarnOnAllAutoCopies);
27 }
28 
30  // Match loop variables that are not references or pointers or are already
31  // initialized through MaterializeTemporaryExpr which indicates a type
32  // conversion.
33  auto LoopVar = varDecl(
34  hasType(hasCanonicalType(unless(anyOf(referenceType(), pointerType())))),
35  unless(hasInitializer(expr(hasDescendant(materializeTemporaryExpr())))));
36  Finder->addMatcher(cxxForRangeStmt(hasLoopVariable(LoopVar.bind("loopVar")))
37  .bind("forRange"),
38  this);
39 }
40 
41 void ForRangeCopyCheck::check(const MatchFinder::MatchResult &Result) {
42  const auto *Var = Result.Nodes.getNodeAs<VarDecl>("loopVar");
43  // Ignore code in macros since we can't place the fixes correctly.
44  if (Var->getLocStart().isMacroID())
45  return;
46  if (handleConstValueCopy(*Var, *Result.Context))
47  return;
48  const auto *ForRange = Result.Nodes.getNodeAs<CXXForRangeStmt>("forRange");
49  handleCopyIsOnlyConstReferenced(*Var, *ForRange, *Result.Context);
50 }
51 
52 bool ForRangeCopyCheck::handleConstValueCopy(const VarDecl &LoopVar,
53  ASTContext &Context) {
54  if (WarnOnAllAutoCopies) {
55  // For aggressive check just test that loop variable has auto type.
56  if (!isa<AutoType>(LoopVar.getType()))
57  return false;
58  } else if (!LoopVar.getType().isConstQualified()) {
59  return false;
60  }
61  llvm::Optional<bool> Expensive =
62  utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
63  if (!Expensive || !*Expensive)
64  return false;
65  auto Diagnostic =
66  diag(LoopVar.getLocation(),
67  "the loop variable's type is not a reference type; this creates a "
68  "copy in each iteration; consider making this a reference")
69  << utils::fixit::changeVarDeclToReference(LoopVar, Context);
70  if (!LoopVar.getType().isConstQualified())
71  Diagnostic << utils::fixit::changeVarDeclToConst(LoopVar);
72  return true;
73 }
74 
75 bool ForRangeCopyCheck::handleCopyIsOnlyConstReferenced(
76  const VarDecl &LoopVar, const CXXForRangeStmt &ForRange,
77  ASTContext &Context) {
78  llvm::Optional<bool> Expensive =
79  utils::type_traits::isExpensiveToCopy(LoopVar.getType(), Context);
80  if (LoopVar.getType().isConstQualified() || !Expensive || !*Expensive)
81  return false;
82  if (!utils::decl_ref_expr::isOnlyUsedAsConst(LoopVar, *ForRange.getBody(),
83  Context))
84  return false;
85  diag(LoopVar.getLocation(),
86  "loop variable is copied but only used as const reference; consider "
87  "making it a const reference")
89  << utils::fixit::changeVarDeclToReference(LoopVar, Context);
90  return true;
91 }
92 
93 } // namespace performance
94 } // namespace tidy
95 } // namespace clang
const std::string Name
Definition: USRFinder.cpp:140
std::unique_ptr< ast_matchers::MatchFinder > Finder
Definition: ClangTidy.cpp:210
bool isOnlyUsedAsConst(const VarDecl &Var, const Stmt &Stmt, ASTContext &Context)
Returns true if all DeclRefExpr to the variable within Stmt do not modify it.
Base class for all clang-tidy checks.
Definition: ClangTidy.h:110
llvm::Optional< bool > isExpensiveToCopy(QualType Type, const ASTContext &Context)
Returns true if Type is expensive to copy.
Definition: TypeTraits.cpp:42
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.
Definition: ClangTidy.cpp:385
std::map< std::string, std::string > OptionMap
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
ClangTidyContext & Context
Definition: ClangTidy.cpp:93
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.
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check's name.
Definition: ClangTidy.cpp:352
FixItHint changeVarDeclToConst(const VarDecl &Var)
Creates fix to make VarDecl const qualified.
const NamedDecl * Result
Definition: USRFinder.cpp:137
FixItHint changeVarDeclToReference(const VarDecl &Var, ASTContext &Context)
Creates fix to make VarDecl a reference by adding &.