clang-tools  14.0.0git
TooSmallLoopVariableCheck.cpp
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1 //===--- TooSmallLoopVariableCheck.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 
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 
13 using namespace clang::ast_matchers;
14 
15 namespace clang {
16 namespace tidy {
17 namespace bugprone {
18 
19 static constexpr llvm::StringLiteral LoopName =
20  llvm::StringLiteral("forLoopName");
21 static constexpr llvm::StringLiteral LoopVarName =
22  llvm::StringLiteral("loopVar");
23 static constexpr llvm::StringLiteral LoopVarCastName =
24  llvm::StringLiteral("loopVarCast");
25 static constexpr llvm::StringLiteral LoopUpperBoundName =
26  llvm::StringLiteral("loopUpperBound");
27 static constexpr llvm::StringLiteral LoopIncrementName =
28  llvm::StringLiteral("loopIncrement");
29 
30 TooSmallLoopVariableCheck::TooSmallLoopVariableCheck(StringRef Name,
31  ClangTidyContext *Context)
32  : ClangTidyCheck(Name, Context),
33  MagnitudeBitsUpperLimit(Options.get("MagnitudeBitsUpperLimit", 16U)) {}
34 
37  Options.store(Opts, "MagnitudeBitsUpperLimit", MagnitudeBitsUpperLimit);
38 }
39 
40 /// The matcher for loops with suspicious integer loop variable.
41 ///
42 /// In this general example, assuming 'j' and 'k' are of integral type:
43 /// \code
44 /// for (...; j < 3 + 2; ++k) { ... }
45 /// \endcode
46 /// The following string identifiers are bound to these parts of the AST:
47 /// LoopVarName: 'j' (as a VarDecl)
48 /// LoopVarCastName: 'j' (after implicit conversion)
49 /// LoopUpperBoundName: '3 + 2' (as an Expr)
50 /// LoopIncrementName: 'k' (as an Expr)
51 /// LoopName: The entire for loop (as a ForStmt)
52 ///
54  StatementMatcher LoopVarMatcher =
55  expr(
56  ignoringParenImpCasts(declRefExpr(to(varDecl(hasType(isInteger()))))))
57  .bind(LoopVarName);
58 
59  // We need to catch only those comparisons which contain any integer cast.
60  StatementMatcher LoopVarConversionMatcher = traverse(
61  TK_AsIs, implicitCastExpr(hasImplicitDestinationType(isInteger()),
62  has(ignoringParenImpCasts(LoopVarMatcher)))
63  .bind(LoopVarCastName));
64 
65  // We are interested in only those cases when the loop bound is a variable
66  // value (not const, enum, etc.).
67  StatementMatcher LoopBoundMatcher =
68  expr(ignoringParenImpCasts(allOf(hasType(isInteger()),
69  unless(integerLiteral()),
70  unless(hasType(isConstQualified())),
71  unless(hasType(enumType())))))
72  .bind(LoopUpperBoundName);
73 
74  // We use the loop increment expression only to make sure we found the right
75  // loop variable.
76  StatementMatcher IncrementMatcher =
77  expr(ignoringParenImpCasts(hasType(isInteger()))).bind(LoopIncrementName);
78 
79  Finder->addMatcher(
80  forStmt(
81  hasCondition(anyOf(
82  binaryOperator(hasOperatorName("<"),
83  hasLHS(LoopVarConversionMatcher),
84  hasRHS(LoopBoundMatcher)),
85  binaryOperator(hasOperatorName("<="),
86  hasLHS(LoopVarConversionMatcher),
87  hasRHS(LoopBoundMatcher)),
88  binaryOperator(hasOperatorName(">"), hasLHS(LoopBoundMatcher),
89  hasRHS(LoopVarConversionMatcher)),
90  binaryOperator(hasOperatorName(">="), hasLHS(LoopBoundMatcher),
91  hasRHS(LoopVarConversionMatcher)))),
92  hasIncrement(IncrementMatcher))
93  .bind(LoopName),
94  this);
95 }
96 
97 /// Returns the magnitude bits of an integer type.
98 static unsigned calcMagnitudeBits(const ASTContext &Context,
99  const QualType &IntExprType) {
100  assert(IntExprType->isIntegerType());
101 
102  return IntExprType->isUnsignedIntegerType()
103  ? Context.getIntWidth(IntExprType)
104  : Context.getIntWidth(IntExprType) - 1;
105 }
106 
107 /// Calculate the upper bound expression's magnitude bits, but ignore
108 /// constant like values to reduce false positives.
109 static unsigned calcUpperBoundMagnitudeBits(const ASTContext &Context,
110  const Expr *UpperBound,
111  const QualType &UpperBoundType) {
112  // Ignore casting caused by constant values inside a binary operator.
113  // We are interested in variable values' magnitude bits.
114  if (const auto *BinOperator = dyn_cast<BinaryOperator>(UpperBound)) {
115  const Expr *RHSE = BinOperator->getRHS()->IgnoreParenImpCasts();
116  const Expr *LHSE = BinOperator->getLHS()->IgnoreParenImpCasts();
117 
118  QualType RHSEType = RHSE->getType();
119  QualType LHSEType = LHSE->getType();
120 
121  if (!RHSEType->isIntegerType() || !LHSEType->isIntegerType())
122  return 0;
123 
124  bool RHSEIsConstantValue = RHSEType->isEnumeralType() ||
125  RHSEType.isConstQualified() ||
126  isa<IntegerLiteral>(RHSE);
127  bool LHSEIsConstantValue = LHSEType->isEnumeralType() ||
128  LHSEType.isConstQualified() ||
129  isa<IntegerLiteral>(LHSE);
130 
131  // Avoid false positives produced by two constant values.
132  if (RHSEIsConstantValue && LHSEIsConstantValue)
133  return 0;
134  if (RHSEIsConstantValue)
135  return calcMagnitudeBits(Context, LHSEType);
136  if (LHSEIsConstantValue)
137  return calcMagnitudeBits(Context, RHSEType);
138 
139  return std::max(calcMagnitudeBits(Context, LHSEType),
140  calcMagnitudeBits(Context, RHSEType));
141  }
142 
143  return calcMagnitudeBits(Context, UpperBoundType);
144 }
145 
146 void TooSmallLoopVariableCheck::check(const MatchFinder::MatchResult &Result) {
147  const auto *LoopVar = Result.Nodes.getNodeAs<Expr>(LoopVarName);
148  const auto *UpperBound =
149  Result.Nodes.getNodeAs<Expr>(LoopUpperBoundName)->IgnoreParenImpCasts();
150  const auto *LoopIncrement =
151  Result.Nodes.getNodeAs<Expr>(LoopIncrementName)->IgnoreParenImpCasts();
152 
153  // We matched the loop variable incorrectly.
154  if (LoopVar->getType() != LoopIncrement->getType())
155  return;
156 
157  QualType LoopVarType = LoopVar->getType();
158  QualType UpperBoundType = UpperBound->getType();
159 
160  ASTContext &Context = *Result.Context;
161 
162  unsigned LoopVarMagnitudeBits = calcMagnitudeBits(Context, LoopVarType);
163  unsigned UpperBoundMagnitudeBits =
164  calcUpperBoundMagnitudeBits(Context, UpperBound, UpperBoundType);
165 
166  if (UpperBoundMagnitudeBits == 0)
167  return;
168 
169  if (LoopVarMagnitudeBits > MagnitudeBitsUpperLimit)
170  return;
171 
172  if (LoopVarMagnitudeBits < UpperBoundMagnitudeBits)
173  diag(LoopVar->getBeginLoc(), "loop variable has narrower type %0 than "
174  "iteration's upper bound %1")
175  << LoopVarType << UpperBoundType;
176 }
177 
178 } // namespace bugprone
179 } // namespace tidy
180 } // namespace clang
clang::tidy::bugprone::LoopIncrementName
static constexpr llvm::StringLiteral LoopIncrementName
Definition: TooSmallLoopVariableCheck.cpp:27
clang::tidy::ClangTidyOptions::OptionMap
llvm::StringMap< ClangTidyValue > OptionMap
Definition: ClangTidyOptions.h:115
clang::tidy::bugprone::LoopVarName
static constexpr llvm::StringLiteral LoopVarName
Definition: TooSmallLoopVariableCheck.cpp:21
clang::tidy::bugprone::LoopName
static constexpr llvm::StringLiteral LoopName
Definition: TooSmallLoopVariableCheck.cpp:19
clang::tidy::bugprone::TooSmallLoopVariableCheck::registerMatchers
void registerMatchers(ast_matchers::MatchFinder *Finder) override
The matcher for loops with suspicious integer loop variable.
Definition: TooSmallLoopVariableCheck.cpp:53
clang::tidy::ClangTidyCheck
Base class for all clang-tidy checks.
Definition: ClangTidyCheck.h:54
clang::tidy::bugprone::TooSmallLoopVariableCheck::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: TooSmallLoopVariableCheck.cpp:35
clang::tidy::bugprone::TooSmallLoopVariableCheck::check
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
Definition: TooSmallLoopVariableCheck.cpp:146
clang::ast_matchers
Definition: AbseilMatcher.h:14
clang::tidy::bugprone::LoopUpperBoundName
static constexpr llvm::StringLiteral LoopUpperBoundName
Definition: TooSmallLoopVariableCheck.cpp:25
clang::tidy::bugprone::LoopVarCastName
static constexpr llvm::StringLiteral LoopVarCastName
Definition: TooSmallLoopVariableCheck.cpp:23
clang::tidy::ClangTidyCheck::Options
OptionsView Options
Definition: ClangTidyCheck.h:416
clang::tidy::ClangTidyContext
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
Definition: ClangTidyDiagnosticConsumer.h:71
Name
static constexpr llvm::StringLiteral Name
Definition: UppercaseLiteralSuffixCheck.cpp:28
TooSmallLoopVariableCheck.h
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
clang::tidy::bugprone::calcMagnitudeBits
static unsigned calcMagnitudeBits(const ASTContext &Context, const QualType &IntExprType)
Returns the magnitude bits of an integer type.
Definition: TooSmallLoopVariableCheck.cpp:98
clang::tidy::bugprone::calcUpperBoundMagnitudeBits
static unsigned calcUpperBoundMagnitudeBits(const ASTContext &Context, const Expr *UpperBound, const QualType &UpperBoundType)
Calculate the upper bound expression's magnitude bits, but ignore constant like values to reduce fals...
Definition: TooSmallLoopVariableCheck.cpp:109
clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ApplyReplacements.h:27
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:120