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
13using namespace clang::ast_matchers;
14
15namespace clang::tidy::bugprone {
16
17static constexpr llvm::StringLiteral LoopName =
18 llvm::StringLiteral("forLoopName");
19static constexpr llvm::StringLiteral LoopVarName =
20 llvm::StringLiteral("loopVar");
21static constexpr llvm::StringLiteral LoopVarCastName =
22 llvm::StringLiteral("loopVarCast");
23static constexpr llvm::StringLiteral LoopUpperBoundName =
24 llvm::StringLiteral("loopUpperBound");
25static constexpr llvm::StringLiteral LoopIncrementName =
26 llvm::StringLiteral("loopIncrement");
27
28namespace {
29
30struct MagnitudeBits {
31 unsigned WidthWithoutSignBit = 0U;
32 unsigned BitFieldWidth = 0U;
33
34 bool operator<(const MagnitudeBits &Other) const noexcept {
35 return WidthWithoutSignBit < Other.WidthWithoutSignBit;
36 }
37
38 bool operator!=(const MagnitudeBits &Other) const noexcept {
39 return WidthWithoutSignBit != Other.WidthWithoutSignBit ||
40 BitFieldWidth != Other.BitFieldWidth;
41 }
42};
43
44} // namespace
45
46TooSmallLoopVariableCheck::TooSmallLoopVariableCheck(StringRef Name,
47 ClangTidyContext *Context)
48 : ClangTidyCheck(Name, Context),
49 MagnitudeBitsUpperLimit(Options.get(LocalName: "MagnitudeBitsUpperLimit", Default: 16U)) {}
50
51void TooSmallLoopVariableCheck::storeOptions(
52 ClangTidyOptions::OptionMap &Opts) {
53 Options.store(Options&: Opts, LocalName: "MagnitudeBitsUpperLimit", Value: MagnitudeBitsUpperLimit);
54}
55
56/// The matcher for loops with suspicious integer loop variable.
57///
58/// In this general example, assuming 'j' and 'k' are of integral type:
59/// \code
60/// for (...; j < 3 + 2; ++k) { ... }
61/// \endcode
62/// The following string identifiers are bound to these parts of the AST:
63/// LoopVarName: 'j' (as a VarDecl)
64/// LoopVarCastName: 'j' (after implicit conversion)
65/// LoopUpperBoundName: '3 + 2' (as an Expr)
66/// LoopIncrementName: 'k' (as an Expr)
67/// LoopName: The entire for loop (as a ForStmt)
68///
69void TooSmallLoopVariableCheck::registerMatchers(MatchFinder *Finder) {
70 StatementMatcher LoopVarMatcher =
71 expr(ignoringParenImpCasts(
72 InnerMatcher: anyOf(declRefExpr(to(InnerMatcher: varDecl(hasType(InnerMatcher: isInteger())))),
73 memberExpr(member(InnerMatcher: fieldDecl(hasType(InnerMatcher: isInteger())))))))
74 .bind(ID: LoopVarName);
75
76 // We need to catch only those comparisons which contain any integer cast.
77 StatementMatcher LoopVarConversionMatcher = traverse(
78 TK: TK_AsIs, InnerMatcher: implicitCastExpr(hasImplicitDestinationType(InnerMatcher: isInteger()),
79 has(ignoringParenImpCasts(InnerMatcher: LoopVarMatcher)))
80 .bind(ID: LoopVarCastName));
81
82 // We are interested in only those cases when the loop bound is a variable
83 // value (not const, enum, etc.).
84 StatementMatcher LoopBoundMatcher =
85 expr(ignoringParenImpCasts(InnerMatcher: allOf(
86 hasType(InnerMatcher: isInteger()), unless(integerLiteral()),
87 unless(allOf(
88 hasType(InnerMatcher: isConstQualified()),
89 declRefExpr(to(InnerMatcher: varDecl(anyOf(
90 hasInitializer(InnerMatcher: ignoringParenImpCasts(InnerMatcher: integerLiteral())),
91 isConstexpr(), isConstinit())))))),
92 unless(hasType(InnerMatcher: enumType())))))
93 .bind(ID: LoopUpperBoundName);
94
95 // We use the loop increment expression only to make sure we found the right
96 // loop variable.
97 StatementMatcher IncrementMatcher =
98 expr(ignoringParenImpCasts(InnerMatcher: hasType(InnerMatcher: isInteger()))).bind(ID: LoopIncrementName);
99
100 Finder->addMatcher(
101 NodeMatch: forStmt(
102 hasCondition(InnerMatcher: anyOf(
103 binaryOperator(hasOperatorName(Name: "<"),
104 hasLHS(InnerMatcher: LoopVarConversionMatcher),
105 hasRHS(InnerMatcher: LoopBoundMatcher)),
106 binaryOperator(hasOperatorName(Name: "<="),
107 hasLHS(InnerMatcher: LoopVarConversionMatcher),
108 hasRHS(InnerMatcher: LoopBoundMatcher)),
109 binaryOperator(hasOperatorName(Name: ">"), hasLHS(InnerMatcher: LoopBoundMatcher),
110 hasRHS(InnerMatcher: LoopVarConversionMatcher)),
111 binaryOperator(hasOperatorName(Name: ">="), hasLHS(InnerMatcher: LoopBoundMatcher),
112 hasRHS(InnerMatcher: LoopVarConversionMatcher)))),
113 hasIncrement(InnerMatcher: IncrementMatcher))
114 .bind(ID: LoopName),
115 Action: this);
116}
117
118/// Returns the magnitude bits of an integer type.
119static MagnitudeBits calcMagnitudeBits(const ASTContext &Context,
120 const QualType &IntExprType,
121 const Expr *IntExpr) {
122 assert(IntExprType->isIntegerType());
123
124 unsigned SignedBits = IntExprType->isUnsignedIntegerType() ? 0U : 1U;
125
126 if (const auto *BitField = IntExpr->getSourceBitField()) {
127 unsigned BitFieldWidth = BitField->getBitWidthValue();
128 return {.WidthWithoutSignBit: BitFieldWidth - SignedBits, .BitFieldWidth: BitFieldWidth};
129 }
130
131 unsigned IntWidth = Context.getIntWidth(T: IntExprType);
132 return {.WidthWithoutSignBit: IntWidth - SignedBits, .BitFieldWidth: 0U};
133}
134
135/// Calculate the upper bound expression's magnitude bits, but ignore
136/// constant like values to reduce false positives.
137static MagnitudeBits
138calcUpperBoundMagnitudeBits(const ASTContext &Context, const Expr *UpperBound,
139 const QualType &UpperBoundType) {
140 // Ignore casting caused by constant values inside a binary operator.
141 // We are interested in variable values' magnitude bits.
142 if (const auto *BinOperator = dyn_cast<BinaryOperator>(Val: UpperBound)) {
143 const Expr *RHSE = BinOperator->getRHS()->IgnoreParenImpCasts();
144 const Expr *LHSE = BinOperator->getLHS()->IgnoreParenImpCasts();
145
146 QualType RHSEType = RHSE->getType();
147 QualType LHSEType = LHSE->getType();
148
149 if (!RHSEType->isIntegerType() || !LHSEType->isIntegerType())
150 return {};
151
152 bool RHSEIsConstantValue = RHSEType->isEnumeralType() ||
153 RHSEType.isConstQualified() ||
154 isa<IntegerLiteral>(Val: RHSE);
155 bool LHSEIsConstantValue = LHSEType->isEnumeralType() ||
156 LHSEType.isConstQualified() ||
157 isa<IntegerLiteral>(Val: LHSE);
158
159 // Avoid false positives produced by two constant values.
160 if (RHSEIsConstantValue && LHSEIsConstantValue)
161 return {};
162 if (RHSEIsConstantValue)
163 return calcMagnitudeBits(Context, IntExprType: LHSEType, IntExpr: LHSE);
164 if (LHSEIsConstantValue)
165 return calcMagnitudeBits(Context, IntExprType: RHSEType, IntExpr: RHSE);
166
167 return std::max(a: calcMagnitudeBits(Context, IntExprType: LHSEType, IntExpr: LHSE),
168 b: calcMagnitudeBits(Context, IntExprType: RHSEType, IntExpr: RHSE));
169 }
170
171 return calcMagnitudeBits(Context, IntExprType: UpperBoundType, IntExpr: UpperBound);
172}
173
174static std::string formatIntegralType(const QualType &Type,
175 const MagnitudeBits &Info) {
176 std::string Name = Type.getAsString();
177 if (!Info.BitFieldWidth)
178 return Name;
179
180 Name += ':';
181 Name += std::to_string(val: Info.BitFieldWidth);
182 return Name;
183}
184
185void TooSmallLoopVariableCheck::check(const MatchFinder::MatchResult &Result) {
186 const auto *LoopVar = Result.Nodes.getNodeAs<Expr>(ID: LoopVarName);
187 const auto *UpperBound =
188 Result.Nodes.getNodeAs<Expr>(ID: LoopUpperBoundName)->IgnoreParenImpCasts();
189 const auto *LoopIncrement =
190 Result.Nodes.getNodeAs<Expr>(ID: LoopIncrementName)->IgnoreParenImpCasts();
191
192 // We matched the loop variable incorrectly.
193 if (LoopVar->getType() != LoopIncrement->getType())
194 return;
195
196 ASTContext &Context = *Result.Context;
197
198 const QualType LoopVarType = LoopVar->getType();
199 const MagnitudeBits LoopVarMagnitudeBits =
200 calcMagnitudeBits(Context, IntExprType: LoopVarType, IntExpr: LoopVar);
201
202 const MagnitudeBits LoopIncrementMagnitudeBits =
203 calcMagnitudeBits(Context, IntExprType: LoopIncrement->getType(), IntExpr: LoopIncrement);
204 // We matched the loop variable incorrectly.
205 if (LoopIncrementMagnitudeBits != LoopVarMagnitudeBits)
206 return;
207
208 const QualType UpperBoundType = UpperBound->getType();
209 const MagnitudeBits UpperBoundMagnitudeBits =
210 calcUpperBoundMagnitudeBits(Context, UpperBound, UpperBoundType);
211
212 if ((0U == UpperBoundMagnitudeBits.WidthWithoutSignBit) ||
213 (LoopVarMagnitudeBits.WidthWithoutSignBit > MagnitudeBitsUpperLimit) ||
214 (LoopVarMagnitudeBits.WidthWithoutSignBit >=
215 UpperBoundMagnitudeBits.WidthWithoutSignBit))
216 return;
217
218 diag(LoopVar->getBeginLoc(),
219 "loop variable has narrower type '%0' than iteration's upper bound '%1'")
220 << formatIntegralType(Type: LoopVarType, Info: LoopVarMagnitudeBits)
221 << formatIntegralType(Type: UpperBoundType, Info: UpperBoundMagnitudeBits);
222}
223
224} // namespace clang::tidy::bugprone
225

source code of clang-tools-extra/clang-tidy/bugprone/TooSmallLoopVariableCheck.cpp