1 //===--- InefficientAlgorithmCheck.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 "InefficientAlgorithmCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 #include "clang/Lex/Lexer.h"
13 
14 using namespace clang::ast_matchers;
15 
16 namespace clang {
17 namespace tidy {
18 namespace performance {
19 
20 static bool areTypesCompatible(QualType Left, QualType Right) {
21   if (const auto *LeftRefType = Left->getAs<ReferenceType>())
22     Left = LeftRefType->getPointeeType();
23   if (const auto *RightRefType = Right->getAs<ReferenceType>())
24     Right = RightRefType->getPointeeType();
25   return Left->getCanonicalTypeUnqualified() ==
26          Right->getCanonicalTypeUnqualified();
27 }
28 
29 void InefficientAlgorithmCheck::registerMatchers(MatchFinder *Finder) {
30   const auto Algorithms =
31       hasAnyName("::std::find", "::std::count", "::std::equal_range",
32                  "::std::lower_bound", "::std::upper_bound");
33   const auto ContainerMatcher = classTemplateSpecializationDecl(hasAnyName(
34       "::std::set", "::std::map", "::std::multiset", "::std::multimap",
35       "::std::unordered_set", "::std::unordered_map",
36       "::std::unordered_multiset", "::std::unordered_multimap"));
37 
38   const auto Matcher =
39       callExpr(
40           callee(functionDecl(Algorithms)),
41           hasArgument(
42               0, cxxMemberCallExpr(
43                      callee(cxxMethodDecl(hasName("begin"))),
44                      on(declRefExpr(
45                             hasDeclaration(decl().bind("IneffContObj")),
46                             anyOf(hasType(ContainerMatcher.bind("IneffCont")),
47                                   hasType(pointsTo(
48                                       ContainerMatcher.bind("IneffContPtr")))))
49                             .bind("IneffContExpr")))),
50           hasArgument(
51               1, cxxMemberCallExpr(callee(cxxMethodDecl(hasName("end"))),
52                                    on(declRefExpr(hasDeclaration(
53                                        equalsBoundNode("IneffContObj")))))),
54           hasArgument(2, expr().bind("AlgParam")))
55           .bind("IneffAlg");
56 
57   Finder->addMatcher(Matcher, this);
58 }
59 
60 void InefficientAlgorithmCheck::check(const MatchFinder::MatchResult &Result) {
61   const auto *AlgCall = Result.Nodes.getNodeAs<CallExpr>("IneffAlg");
62   const auto *IneffCont =
63       Result.Nodes.getNodeAs<ClassTemplateSpecializationDecl>("IneffCont");
64   bool PtrToContainer = false;
65   if (!IneffCont) {
66     IneffCont =
67         Result.Nodes.getNodeAs<ClassTemplateSpecializationDecl>("IneffContPtr");
68     PtrToContainer = true;
69   }
70   const llvm::StringRef IneffContName = IneffCont->getName();
71   const bool Unordered =
72       IneffContName.find("unordered") != llvm::StringRef::npos;
73   const bool Maplike = IneffContName.find("map") != llvm::StringRef::npos;
74 
75   // Store if the key type of the container is compatible with the value
76   // that is searched for.
77   QualType ValueType = AlgCall->getArg(2)->getType();
78   QualType KeyType =
79       IneffCont->getTemplateArgs()[0].getAsType().getCanonicalType();
80   const bool CompatibleTypes = areTypesCompatible(KeyType, ValueType);
81 
82   // Check if the comparison type for the algorithm and the container matches.
83   if (AlgCall->getNumArgs() == 4 && !Unordered) {
84     const Expr *Arg = AlgCall->getArg(3);
85     const QualType AlgCmp =
86         Arg->getType().getUnqualifiedType().getCanonicalType();
87     const unsigned CmpPosition =
88         (IneffContName.find("map") == llvm::StringRef::npos) ? 1 : 2;
89     const QualType ContainerCmp = IneffCont->getTemplateArgs()[CmpPosition]
90                                       .getAsType()
91                                       .getUnqualifiedType()
92                                       .getCanonicalType();
93     if (AlgCmp != ContainerCmp) {
94       diag(Arg->getBeginLoc(),
95            "different comparers used in the algorithm and the container");
96       return;
97     }
98   }
99 
100   const auto *AlgDecl = AlgCall->getDirectCallee();
101   if (!AlgDecl)
102     return;
103 
104   if (Unordered && AlgDecl->getName().find("bound") != llvm::StringRef::npos)
105     return;
106 
107   const auto *AlgParam = Result.Nodes.getNodeAs<Expr>("AlgParam");
108   const auto *IneffContExpr = Result.Nodes.getNodeAs<Expr>("IneffContExpr");
109   FixItHint Hint;
110 
111   SourceManager &SM = *Result.SourceManager;
112   LangOptions LangOpts = getLangOpts();
113 
114   CharSourceRange CallRange =
115       CharSourceRange::getTokenRange(AlgCall->getSourceRange());
116 
117   // FIXME: Create a common utility to extract a file range that the given token
118   // sequence is exactly spelled at (without macro argument expansions etc.).
119   // We can't use Lexer::makeFileCharRange here, because for
120   //
121   //   #define F(x) x
122   //   x(a b c);
123   //
124   // it will return "x(a b c)", when given the range "a"-"c". It makes sense for
125   // removals, but not for replacements.
126   //
127   // This code is over-simplified, but works for many real cases.
128   if (SM.isMacroArgExpansion(CallRange.getBegin()) &&
129       SM.isMacroArgExpansion(CallRange.getEnd())) {
130     CallRange.setBegin(SM.getSpellingLoc(CallRange.getBegin()));
131     CallRange.setEnd(SM.getSpellingLoc(CallRange.getEnd()));
132   }
133 
134   if (!CallRange.getBegin().isMacroID() && !Maplike && CompatibleTypes) {
135     StringRef ContainerText = Lexer::getSourceText(
136         CharSourceRange::getTokenRange(IneffContExpr->getSourceRange()), SM,
137         LangOpts);
138     StringRef ParamText = Lexer::getSourceText(
139         CharSourceRange::getTokenRange(AlgParam->getSourceRange()), SM,
140         LangOpts);
141     std::string ReplacementText =
142         (llvm::Twine(ContainerText) + (PtrToContainer ? "->" : ".") +
143          AlgDecl->getName() + "(" + ParamText + ")")
144             .str();
145     Hint = FixItHint::CreateReplacement(CallRange, ReplacementText);
146   }
147 
148   diag(AlgCall->getBeginLoc(),
149        "this STL algorithm call should be replaced with a container method")
150       << Hint;
151 }
152 
153 } // namespace performance
154 } // namespace tidy
155 } // namespace clang
156