1 //===--- MoveConstArgCheck.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 "MoveConstArgCheck.h"
10 
11 #include "clang/Lex/Lexer.h"
12 
13 using namespace clang::ast_matchers;
14 
15 namespace clang {
16 namespace tidy {
17 namespace performance {
18 
19 static void ReplaceCallWithArg(const CallExpr *Call, DiagnosticBuilder &Diag,
20                                const SourceManager &SM,
21                                const LangOptions &LangOpts) {
22   const Expr *Arg = Call->getArg(0);
23 
24   CharSourceRange BeforeArgumentsRange = Lexer::makeFileCharRange(
25       CharSourceRange::getCharRange(Call->getBeginLoc(), Arg->getBeginLoc()),
26       SM, LangOpts);
27   CharSourceRange AfterArgumentsRange = Lexer::makeFileCharRange(
28       CharSourceRange::getCharRange(Call->getEndLoc(),
29                                     Call->getEndLoc().getLocWithOffset(1)),
30       SM, LangOpts);
31 
32   if (BeforeArgumentsRange.isValid() && AfterArgumentsRange.isValid()) {
33     Diag << FixItHint::CreateRemoval(BeforeArgumentsRange)
34          << FixItHint::CreateRemoval(AfterArgumentsRange);
35   }
36 }
37 
38 void MoveConstArgCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
39   Options.store(Opts, "CheckTriviallyCopyableMove", CheckTriviallyCopyableMove);
40 }
41 
42 void MoveConstArgCheck::registerMatchers(MatchFinder *Finder) {
43   auto MoveCallMatcher =
44       callExpr(callee(functionDecl(hasName("::std::move"))), argumentCountIs(1),
45                unless(isInTemplateInstantiation()))
46           .bind("call-move");
47 
48   Finder->addMatcher(MoveCallMatcher, this);
49 
50   auto ConstParamMatcher = forEachArgumentWithParam(
51       MoveCallMatcher, parmVarDecl(hasType(references(isConstQualified()))));
52 
53   Finder->addMatcher(callExpr(ConstParamMatcher).bind("receiving-expr"), this);
54   Finder->addMatcher(
55       traverse(ast_type_traits::TK_AsIs,
56                cxxConstructExpr(ConstParamMatcher).bind("receiving-expr")),
57       this);
58 }
59 
60 void MoveConstArgCheck::check(const MatchFinder::MatchResult &Result) {
61   const auto *CallMove = Result.Nodes.getNodeAs<CallExpr>("call-move");
62   const auto *ReceivingExpr = Result.Nodes.getNodeAs<Expr>("receiving-expr");
63   const Expr *Arg = CallMove->getArg(0);
64   SourceManager &SM = Result.Context->getSourceManager();
65 
66   CharSourceRange MoveRange =
67       CharSourceRange::getCharRange(CallMove->getSourceRange());
68   CharSourceRange FileMoveRange =
69       Lexer::makeFileCharRange(MoveRange, SM, getLangOpts());
70   if (!FileMoveRange.isValid())
71     return;
72 
73   bool IsConstArg = Arg->getType().isConstQualified();
74   bool IsTriviallyCopyable =
75       Arg->getType().isTriviallyCopyableType(*Result.Context);
76 
77   if (IsConstArg || IsTriviallyCopyable) {
78     if (const CXXRecordDecl *R = Arg->getType()->getAsCXXRecordDecl()) {
79       // According to [expr.prim.lambda]p3, "whether the closure type is
80       // trivially copyable" property can be changed by the implementation of
81       // the language, so we shouldn't rely on it when issuing diagnostics.
82       if (R->isLambda())
83         return;
84       // Don't warn when the type is not copyable.
85       for (const auto *Ctor : R->ctors()) {
86         if (Ctor->isCopyConstructor() && Ctor->isDeleted())
87           return;
88       }
89     }
90 
91     if (!IsConstArg && IsTriviallyCopyable && !CheckTriviallyCopyableMove)
92       return;
93 
94     bool IsVariable = isa<DeclRefExpr>(Arg);
95     const auto *Var =
96         IsVariable ? dyn_cast<DeclRefExpr>(Arg)->getDecl() : nullptr;
97     auto Diag = diag(FileMoveRange.getBegin(),
98                      "std::move of the %select{|const }0"
99                      "%select{expression|variable %4}1 "
100                      "%select{|of the trivially-copyable type %5 }2"
101                      "has no effect; remove std::move()"
102                      "%select{| or make the variable non-const}3")
103                 << IsConstArg << IsVariable << IsTriviallyCopyable
104                 << (IsConstArg && IsVariable && !IsTriviallyCopyable) << Var
105                 << Arg->getType();
106 
107     ReplaceCallWithArg(CallMove, Diag, SM, getLangOpts());
108   } else if (ReceivingExpr) {
109     auto Diag = diag(FileMoveRange.getBegin(),
110                      "passing result of std::move() as a const reference "
111                      "argument; no move will actually happen");
112 
113     ReplaceCallWithArg(CallMove, Diag, SM, getLangOpts());
114   }
115 }
116 
117 } // namespace performance
118 } // namespace tidy
119 } // namespace clang
120