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This option allows callers to disable the warning from
https://clang.llvm.org/extra/clang-tidy/checks/performance-move-const-arg.html
that would warn on the following
cc
void f(const string &s);
string s;
f(std::move(s)); // ALLOWED if
performance-move-const-arg.CheckMoveToConstRef=false
The reason people might want to disable this check, is because it allows
callers to use `std::move()` or not based on local reasoning about the
argument, and without having to care about how the function `f` accepts
the argument. Indeed, `f` might accept the argument by const-ref today,
but change to by-value tomorrow, and if the caller had moved the
argument that they were finished with, the code would work as
efficiently as possible regardless of how `f` accepted the parameter.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D119370
Files:
clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.h
clang-tools-extra/test/clang-tidy/checkers/performance-move-const-arg-const-ref.cpp
Index: clang-tools-extra/test/clang-tidy/checkers/performance-move-const-arg-const-ref.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/checkers/performance-move-const-arg-const-ref.cpp
@@ -0,0 +1,80 @@
+// RUN: %check_clang_tidy %s performance-move-const-arg %t \
+// RUN: -config='{CheckOptions: \
+// RUN: [{key: performance-move-const-arg.CheckMoveToConstRef, value: false}]}'
+
+namespace std {
+template <typename>
+struct remove_reference;
+
+template <typename _Tp>
+struct remove_reference {
+ typedef _Tp type;
+};
+
+template <typename _Tp>
+struct remove_reference<_Tp &> {
+ typedef _Tp type;
+};
+
+template <typename _Tp>
+struct remove_reference<_Tp &&> {
+ typedef _Tp type;
+};
+
+template <typename _Tp>
+constexpr typename std::remove_reference<_Tp>::type &&move(_Tp &&__t) {
+ return static_cast<typename std::remove_reference<_Tp>::type &&>(__t);
+}
+
+template <typename _Tp>
+constexpr _Tp &&
+forward(typename remove_reference<_Tp>::type &__t) noexcept {
+ return static_cast<_Tp &&>(__t);
+}
+
+} // namespace std
+
+struct TriviallyCopyable {
+ int i;
+};
+
+void f(TriviallyCopyable) {}
+
+void g() {
+ TriviallyCopyable obj;
+ // Some basic test to ensure that other warnings from
+ // performance-move-const-arg are still working and enabled.
+ f(std::move(obj));
+ // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: std::move of the variable 'obj' of the trivially-copyable type 'TriviallyCopyable' has no effect; remove std::move() [performance-move-const-arg]
+ // CHECK-FIXES: f(obj);
+}
+
+class NoMoveSemantics {
+public:
+ NoMoveSemantics();
+ NoMoveSemantics(const NoMoveSemantics &);
+ NoMoveSemantics &operator=(const NoMoveSemantics &);
+};
+
+class MoveSemantics {
+public:
+ MoveSemantics();
+ MoveSemantics(MoveSemantics &&);
+
+ MoveSemantics &operator=(MoveSemantics &&);
+};
+
+void callByConstRef1(const NoMoveSemantics &);
+void callByConstRef2(const MoveSemantics &);
+
+void moveToConstReferencePositives() {
+ NoMoveSemantics a;
+
+ // This call is now allowed since CheckMoveToConstRef is false.
+ callByConstRef1(std::move(a));
+
+ MoveSemantics b;
+
+ // This call is now allowed since CheckMoveToConstRef is false.
+ callByConstRef2(std::move(b));
+}
Index: clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.h
===================================================================
--- clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.h
+++ clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.h
@@ -25,9 +25,9 @@
class MoveConstArgCheck : public ClangTidyCheck {
public:
MoveConstArgCheck(StringRef Name, ClangTidyContext *Context)
- : ClangTidyCheck(Name, Context),
- CheckTriviallyCopyableMove(
- Options.get("CheckTriviallyCopyableMove", true)) {}
+ : ClangTidyCheck(Name, Context), CheckTriviallyCopyableMove(Options.get(
+ "CheckTriviallyCopyableMove", true)),
+ CheckMoveToConstRef(Options.get("CheckMoveToConstRef", true)) {}
bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
return LangOpts.CPlusPlus;
}
@@ -37,6 +37,7 @@
private:
const bool CheckTriviallyCopyableMove;
+ const bool CheckMoveToConstRef;
llvm::DenseSet<const CallExpr *> AlreadyCheckedMoves;
};
Index: clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
+++ clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
@@ -37,6 +37,7 @@
void MoveConstArgCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "CheckTriviallyCopyableMove", CheckTriviallyCopyableMove);
+ Options.store(Opts, "CheckMoveToConstRef", CheckMoveToConstRef);
}
void MoveConstArgCheck::registerMatchers(MatchFinder *Finder) {
@@ -194,7 +195,7 @@
<< *InvocationParmType << ExpectParmTypeName;
}
} else if (ReceivingExpr) {
- if ((*InvocationParmType)->isRValueReferenceType())
+ if ((*InvocationParmType)->isRValueReferenceType() || !CheckMoveToConstRef)
return;
auto Diag = diag(FileMoveRange.getBegin(),
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