1 //===--- InefficientAlgorithmCheck.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 "InefficientAlgorithmCheck.h"
11 #include "clang/AST/ASTContext.h"
12 #include "clang/ASTMatchers/ASTMatchFinder.h"
13 #include "clang/Lex/Lexer.h"
14 
15 using namespace clang::ast_matchers;
16 
17 namespace clang {
18 namespace tidy {
19 namespace performance {
20 
21 static bool areTypesCompatible(QualType Left, QualType Right) {
22   if (const auto *LeftRefType = Left->getAs<ReferenceType>())
23     Left = LeftRefType->getPointeeType();
24   if (const auto *RightRefType = Right->getAs<ReferenceType>())
25     Right = RightRefType->getPointeeType();
26   return Left->getCanonicalTypeUnqualified() ==
27          Right->getCanonicalTypeUnqualified();
28 }
29 
30 void InefficientAlgorithmCheck::registerMatchers(MatchFinder *Finder) {
31   // Only register the matchers for C++; the functionality currently does not
32   // provide any benefit to other languages, despite being benign.
33   if (!getLangOpts().CPlusPlus)
34     return;
35 
36   const auto Algorithms =
37       hasAnyName("::std::find", "::std::count", "::std::equal_range",
38                  "::std::lower_bound", "::std::upper_bound");
39   const auto ContainerMatcher = classTemplateSpecializationDecl(hasAnyName(
40       "::std::set", "::std::map", "::std::multiset", "::std::multimap",
41       "::std::unordered_set", "::std::unordered_map",
42       "::std::unordered_multiset", "::std::unordered_multimap"));
43 
44   const auto Matcher =
45       callExpr(
46           callee(functionDecl(Algorithms)),
47           hasArgument(
48               0, cxxConstructExpr(has(ignoringParenImpCasts(cxxMemberCallExpr(
49                      callee(cxxMethodDecl(hasName("begin"))),
50                      on(declRefExpr(
51                             hasDeclaration(decl().bind("IneffContObj")),
52                             anyOf(hasType(ContainerMatcher.bind("IneffCont")),
53                                   hasType(pointsTo(
54                                       ContainerMatcher.bind("IneffContPtr")))))
55                             .bind("IneffContExpr"))))))),
56           hasArgument(
57               1, cxxConstructExpr(has(ignoringParenImpCasts(cxxMemberCallExpr(
58                      callee(cxxMethodDecl(hasName("end"))),
59                      on(declRefExpr(
60                          hasDeclaration(equalsBoundNode("IneffContObj"))))))))),
61           hasArgument(2, expr().bind("AlgParam")),
62           unless(isInTemplateInstantiation()))
63           .bind("IneffAlg");
64 
65   Finder->addMatcher(Matcher, this);
66 }
67 
68 void InefficientAlgorithmCheck::check(const MatchFinder::MatchResult &Result) {
69   const auto *AlgCall = Result.Nodes.getNodeAs<CallExpr>("IneffAlg");
70   const auto *IneffCont =
71       Result.Nodes.getNodeAs<ClassTemplateSpecializationDecl>("IneffCont");
72   bool PtrToContainer = false;
73   if (!IneffCont) {
74     IneffCont =
75         Result.Nodes.getNodeAs<ClassTemplateSpecializationDecl>("IneffContPtr");
76     PtrToContainer = true;
77   }
78   const llvm::StringRef IneffContName = IneffCont->getName();
79   const bool Unordered =
80       IneffContName.find("unordered") != llvm::StringRef::npos;
81   const bool Maplike = IneffContName.find("map") != llvm::StringRef::npos;
82 
83   // Store if the key type of the container is compatible with the value
84   // that is searched for.
85   QualType ValueType = AlgCall->getArg(2)->getType();
86   QualType KeyType =
87       IneffCont->getTemplateArgs()[0].getAsType().getCanonicalType();
88   const bool CompatibleTypes = areTypesCompatible(KeyType, ValueType);
89 
90   // Check if the comparison type for the algorithm and the container matches.
91   if (AlgCall->getNumArgs() == 4 && !Unordered) {
92     const Expr *Arg = AlgCall->getArg(3);
93     const QualType AlgCmp =
94         Arg->getType().getUnqualifiedType().getCanonicalType();
95     const unsigned CmpPosition =
96         (IneffContName.find("map") == llvm::StringRef::npos) ? 1 : 2;
97     const QualType ContainerCmp = IneffCont->getTemplateArgs()[CmpPosition]
98                                       .getAsType()
99                                       .getUnqualifiedType()
100                                       .getCanonicalType();
101     if (AlgCmp != ContainerCmp) {
102       diag(Arg->getLocStart(),
103            "different comparers used in the algorithm and the container");
104       return;
105     }
106   }
107 
108   const auto *AlgDecl = AlgCall->getDirectCallee();
109   if (!AlgDecl)
110     return;
111 
112   if (Unordered && AlgDecl->getName().find("bound") != llvm::StringRef::npos)
113     return;
114 
115   const auto *AlgParam = Result.Nodes.getNodeAs<Expr>("AlgParam");
116   const auto *IneffContExpr = Result.Nodes.getNodeAs<Expr>("IneffContExpr");
117   FixItHint Hint;
118 
119   SourceManager &SM = *Result.SourceManager;
120   LangOptions LangOpts = getLangOpts();
121 
122   CharSourceRange CallRange =
123       CharSourceRange::getTokenRange(AlgCall->getSourceRange());
124 
125   // FIXME: Create a common utility to extract a file range that the given token
126   // sequence is exactly spelled at (without macro argument expansions etc.).
127   // We can't use Lexer::makeFileCharRange here, because for
128   //
129   //   #define F(x) x
130   //   x(a b c);
131   //
132   // it will return "x(a b c)", when given the range "a"-"c". It makes sense for
133   // removals, but not for replacements.
134   //
135   // This code is over-simplified, but works for many real cases.
136   if (SM.isMacroArgExpansion(CallRange.getBegin()) &&
137       SM.isMacroArgExpansion(CallRange.getEnd())) {
138     CallRange.setBegin(SM.getSpellingLoc(CallRange.getBegin()));
139     CallRange.setEnd(SM.getSpellingLoc(CallRange.getEnd()));
140   }
141 
142   if (!CallRange.getBegin().isMacroID() && !Maplike && CompatibleTypes) {
143     StringRef ContainerText = Lexer::getSourceText(
144         CharSourceRange::getTokenRange(IneffContExpr->getSourceRange()), SM,
145         LangOpts);
146     StringRef ParamText = Lexer::getSourceText(
147         CharSourceRange::getTokenRange(AlgParam->getSourceRange()), SM,
148         LangOpts);
149     std::string ReplacementText =
150         (llvm::Twine(ContainerText) + (PtrToContainer ? "->" : ".") +
151          AlgDecl->getName() + "(" + ParamText + ")")
152             .str();
153     Hint = FixItHint::CreateReplacement(CallRange, ReplacementText);
154   }
155 
156   diag(AlgCall->getLocStart(),
157        "this STL algorithm call should be replaced with a container method")
158       << Hint;
159 }
160 
161 } // namespace performance
162 } // namespace tidy
163 } // namespace clang
164