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 
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 
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 ///
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
static constexpr llvm::StringLiteral LoopVarName
void registerMatchers(ast_matchers::MatchFinder *Finder) override
The matcher for loops with suspicious integer loop variable.
static constexpr llvm::StringLiteral LoopName
Base class for all clang-tidy checks.
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
static constexpr llvm::StringLiteral LoopVarCastName
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.
static constexpr llvm::StringLiteral LoopUpperBoundName
static constexpr llvm::StringLiteral Name
std::map< std::string, std::string > OptionMap
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
static unsigned calcMagnitudeBits(const ASTContext &Context, const QualType &IntExprType)
Returns the magnitude bits of an integer type.
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...
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&#39;s name.
static constexpr llvm::StringLiteral LoopIncrementName