clang-tools 8.0.0

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