================
@@ -8340,8 +8340,54 @@ void Sema::checkInitializerLifetime(const
InitializedEntity &Entity,
<< Entity.getType()->isReferenceType() << CLE->getInitializer() <<
2
<< DiagRange;
} else {
- Diag(DiagLoc, diag::warn_ret_local_temp_addr_ref)
- << Entity.getType()->isReferenceType() << DiagRange;
+ // P2748R5: Disallow Binding a Returned Glvalue to a Temporary.
+ // [stmt.return]/p6: In a function whose return type is a reference,
+ // other than an invented function for std::is_convertible
([meta.rel]),
+ // a return statement that binds the returned reference to a temporary
+ // expression ([class.temporary]) is ill-formed.
+ //
+ // C++0x [meta.rel]p4:
+ // Given the following function prototype:
+ //
+ // template <class T>
+ // typename add_rvalue_reference<T>::type create();
+ //
+ // the predicate condition for a template specialization
+ // is_convertible<From, To> shall be satisfied if and only if
+ // the return expression in the following code would be
+ // well-formed, including any implicit conversions to the return
+ // type of the function:
+ //
+ // To test() {
+ // return create<From>();
+ // }
+ //
+ // Access checking is performed as if in a context unrelated to To
and
+ // From. Only the validity of the immediate context of the expression
+ // of the return-statement (including conversions to the return type)
+ // is considered.
+ //
+ // We skip to check whether we are evaluating one of {__is_convertible,
+ // __is_nothrow_convertible, __is_convertible_to} type traits
+ // expression, because we model the initialization as a
+ // copy-initialization of a temporary of the appropriate type, which
for
+ // this expression is identical to the return statement (since NRVO
+ // doesn't apply), and not really build a `return create<From>()` in
+ // type traits expression evaluation. Therefor, P2748R5 has no impact
+ // for evaluation of {__is_convertible, __is_nothrow_convertible,
+ // __is_convertible_to}.
+ //
+ // Clang can correctly handle cases like the following:
+ //
+ // static_assert(__is_convertible(int, const int &));
+ // static_assert(__is_nothrow_convertible(int, const int &));
+ // static_assert(__is_convertible_to(int, const int &));
----------------
cor3ntin wrote:
I don't think this comment is useful in this context at this point in time.
If we ever need to do further surgery here, we can add the comment back
https://github.com/llvm/llvm-project/pull/89942
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