clang-tools 10.0.0

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
9 #include "TooSmallLoopVariableCheck.h"
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<unsigned>(
34 "MagnitudeBitsUpperLimit", 16)) {}
35
36 void TooSmallLoopVariableCheck::storeOptions(
37 ClangTidyOptions::OptionMap &Opts) {
38 Options.store(Opts, "MagnitudeBitsUpperLimit", MagnitudeBitsUpperLimit);
39 }
40
41 /// The matcher for loops with suspicious integer loop variable.
42 ///
43 /// In this general example, assuming 'j' and 'k' are of integral type:
44 /// \code
45 /// for (...; j < 3 + 2; ++k) { ... }
46 /// \endcode
47 /// The following string identifiers are bound to these parts of the AST:
48 /// LoopVarName: 'j' (as a VarDecl)
49 /// LoopVarCastName: 'j' (after implicit conversion)
50 /// LoopUpperBoundName: '3 + 2' (as an Expr)
51 /// LoopIncrementName: 'k' (as an Expr)
52 /// LoopName: The entire for loop (as a ForStmt)
53 ///
54 void TooSmallLoopVariableCheck::registerMatchers(MatchFinder *Finder) {
55 StatementMatcher LoopVarMatcher =
56 expr(
57 ignoringParenImpCasts(declRefExpr(to(varDecl(hasType(isInteger()))))))
58 .bind(LoopVarName);
59
60 // We need to catch only those comparisons which contain any integer cast.
61 StatementMatcher LoopVarConversionMatcher =
62 implicitCastExpr(hasImplicitDestinationType(isInteger()),
63 has(ignoringParenImpCasts(LoopVarMatcher)))
64 .bind(LoopVarCastName);
65
66 // We are interested in only those cases when the loop bound is a variable
67 // value (not const, enum, etc.).
68 StatementMatcher LoopBoundMatcher =
69 expr(ignoringParenImpCasts(allOf(hasType(isInteger()),
70 unless(integerLiteral()),
71 unless(hasType(isConstQualified())),
72 unless(hasType(enumType())))))
73 .bind(LoopUpperBoundName);
74
75 // We use the loop increment expression only to make sure we found the right
76 // loop variable.
77 StatementMatcher IncrementMatcher =
78 expr(ignoringParenImpCasts(hasType(isInteger()))).bind(LoopIncrementName);
79
80 Finder->addMatcher(
81 forStmt(
82 hasCondition(anyOf(
83 binaryOperator(hasOperatorName("<"),
84 hasLHS(LoopVarConversionMatcher),
85 hasRHS(LoopBoundMatcher)),
86 binaryOperator(hasOperatorName("<="),
87 hasLHS(LoopVarConversionMatcher),
88 hasRHS(LoopBoundMatcher)),
89 binaryOperator(hasOperatorName(">"), hasLHS(LoopBoundMatcher),
90 hasRHS(LoopVarConversionMatcher)),
91 binaryOperator(hasOperatorName(">="), hasLHS(LoopBoundMatcher),
92 hasRHS(LoopVarConversionMatcher)))),
93 hasIncrement(IncrementMatcher))
94 .bind(LoopName),
95 this);
96 }
97
98 /// Returns the magnitude bits of an integer type.
99 static unsigned calcMagnitudeBits(const ASTContext &Context,
100 const QualType &IntExprType) {
101 assert(IntExprType->isIntegerType());
102
103 return IntExprType->isUnsignedIntegerType()
104 ? Context.getIntWidth(IntExprType)
105 : Context.getIntWidth(IntExprType) - 1;
106 }
107
108 /// Calculate the upper bound expression's magnitude bits, but ignore
109 /// constant like values to reduce false positives.
110 static unsigned calcUpperBoundMagnitudeBits(const ASTContext &Context,
111 const Expr *UpperBound,
112 const QualType &UpperBoundType) {
113 // Ignore casting caused by constant values inside a binary operator.
114 // We are interested in variable values' magnitude bits.
115 if (const auto *BinOperator = dyn_cast<BinaryOperator>(UpperBound)) {
116 const Expr *RHSE = BinOperator->getRHS()->IgnoreParenImpCasts();
117 const Expr *LHSE = BinOperator->getLHS()->IgnoreParenImpCasts();
118
119 QualType RHSEType = RHSE->getType();
120 QualType LHSEType = LHSE->getType();
121
122 if (!RHSEType->isIntegerType() || !LHSEType->isIntegerType())
123 return 0;
124
125 bool RHSEIsConstantValue = RHSEType->isEnumeralType() ||
126 RHSEType.isConstQualified() ||
127 isa<IntegerLiteral>(RHSE);
128 bool LHSEIsConstantValue = LHSEType->isEnumeralType() ||
129 LHSEType.isConstQualified() ||
130 isa<IntegerLiteral>(LHSE);
131
132 // Avoid false positives produced by two constant values.
133 if (RHSEIsConstantValue && LHSEIsConstantValue)
134 return 0;
135 if (RHSEIsConstantValue)
136 return calcMagnitudeBits(Context, LHSEType);
137 if (LHSEIsConstantValue)
138 return calcMagnitudeBits(Context, RHSEType);
139
140 return std::max(calcMagnitudeBits(Context, LHSEType),
141 calcMagnitudeBits(Context, RHSEType));
142 }
143
144 return calcMagnitudeBits(Context, UpperBoundType);
145 }
146
147 void TooSmallLoopVariableCheck::check(const MatchFinder::MatchResult &Result) {
148 const auto *LoopVar = Result.Nodes.getNodeAs<Expr>(LoopVarName);
149 const auto *UpperBound =
150 Result.Nodes.getNodeAs<Expr>(LoopUpperBoundName)->IgnoreParenImpCasts();
151 const auto *LoopIncrement =
152 Result.Nodes.getNodeAs<Expr>(LoopIncrementName)->IgnoreParenImpCasts();
153
154 // We matched the loop variable incorrectly.
155 if (LoopVar->getType() != LoopIncrement->getType())
156 return;
157
158 QualType LoopVarType = LoopVar->getType();
159 QualType UpperBoundType = UpperBound->getType();
160
161 ASTContext &Context = *Result.Context;
162
163 unsigned LoopVarMagnitudeBits = calcMagnitudeBits(Context, LoopVarType);
164 unsigned UpperBoundMagnitudeBits =
165 calcUpperBoundMagnitudeBits(Context, UpperBound, UpperBoundType);
166
167 if (UpperBoundMagnitudeBits == 0)
168 return;
169
170 if (LoopVarMagnitudeBits > MagnitudeBitsUpperLimit)
171 return;
172
173 if (LoopVarMagnitudeBits < UpperBoundMagnitudeBits)
174 diag(LoopVar->getBeginLoc(), "loop variable has narrower type %0 than "
175 "iteration's upper bound %1")
176 << LoopVarType << UpperBoundType;
177 }
178
179 } // namespace bugprone
180 } // namespace tidy
181 } // namespace clang
clang::ast_matchers
Definition: AbseilMatcher.h:14
clang::tidy::bugprone::LoopVarName
static constexpr llvm::StringLiteral LoopVarName
Definition: TooSmallLoopVariableCheck.cpp:21
clang::tidy::bugprone::TooSmallLoopVariableCheck::registerMatchers
void registerMatchers(ast_matchers::MatchFinder *Finder) override
The matcher for loops with suspicious integer loop variable.
Definition: TooSmallLoopVariableCheck.cpp:54
clang::tidy::bugprone::LoopName
static constexpr llvm::StringLiteral LoopName
Definition: TooSmallLoopVariableCheck.cpp:19
clang::tidy::ClangTidyCheck
Base class for all clang-tidy checks.
Definition: ClangTidyCheck.h:47
TooSmallLoopVariableCheck.h
clang::tidy::ClangTidyCheck::Options
OptionsView Options
Definition: ClangTidyCheck.h:184
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:36
clang::tidy::bugprone::LoopVarCastName
static constexpr llvm::StringLiteral LoopVarCastName
Definition: TooSmallLoopVariableCheck.cpp:23
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
clang::tidy::bugprone::LoopUpperBoundName
static constexpr llvm::StringLiteral LoopUpperBoundName
Definition: TooSmallLoopVariableCheck.cpp:25
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
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ApplyReplacements.h:27
clang::tidy::bugprone::calcMagnitudeBits
static unsigned calcMagnitudeBits(const ASTContext &Context, const QualType &IntExprType)
Returns the magnitude bits of an integer type.
Definition: TooSmallLoopVariableCheck.cpp:99
clang::tidy::bugprone::calcUpperBoundMagnitudeBits
static unsigned calcUpperBoundMagnitudeBits(const ASTContext &Context, const Expr *UpperBound, const QualType &UpperBoundType)
Calculate the upper bound expression&#39;s magnitude bits, but ignore constant like values to reduce fals...
Definition: TooSmallLoopVariableCheck.cpp:110
clang::tidy::ClangTidyContext
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
Definition: ClangTidyDiagnosticConsumer.h:77
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:147
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::bugprone::LoopIncrementName
static constexpr llvm::StringLiteral LoopIncrementName
Definition: TooSmallLoopVariableCheck.cpp:27