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 
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
static constexpr llvm::StringLiteral LoopVarName
static constexpr llvm::StringLiteral LoopName
static unsigned calcPositiveBits(const ASTContext &Context, const QualType &IntExprType)
Returns the positive part of the integer width for an integer type.
static constexpr llvm::StringLiteral LoopVarCastName
static constexpr llvm::StringLiteral LoopUpperBoundName
llvm::Optional< llvm::Expected< tooling::AtomicChanges > > Result
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
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...
static constexpr llvm::StringLiteral LoopIncrementName