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