llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-clang @llvm/pr-subscribers-libcxx Author: Mital Ashok (MitalAshok) <details> <summary>Changes</summary> Closes #<!-- -->77638, #<!-- -->24186 Rebased from <https://reviews.llvm.org/D156032>, see there for more information. Implements wording change in [CWG2137](https://wg21.link/CWG2137) in the first commit. This also implements an approach to [CWG2311](https://wg21.link/CWG2311) in the second commit, because too much code that relies on `T{ T_prvalue }` being an elision would break. Because that issue is still open and the CWG issue doesn't provide wording to fix the issue, there may be different behaviours on other compilers. --- Full diff: https://github.com/llvm/llvm-project/pull/77768.diff 8 Files Affected: - (modified) clang/docs/ReleaseNotes.rst (+5) - (modified) clang/lib/Sema/SemaInit.cpp (+30-10) - (modified) clang/lib/Sema/SemaOverload.cpp (+28-10) - (modified) clang/test/CXX/drs/dr14xx.cpp (-10) - (modified) clang/test/CXX/drs/dr21xx.cpp (+40) - (modified) clang/test/CXX/drs/dr23xx.cpp (+84) - (modified) clang/www/cxx_dr_status.html (+2-2) - (modified) libcxx/test/std/utilities/utility/pairs/pairs.pair/ctor.pair_U_V_move.pass.cpp (+20-1) ``````````diff diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 59732962caac65..66d388bb954bda 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -199,6 +199,11 @@ C++2c Feature Support Resolutions to C++ Defect Reports ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +- Implemented `CWG2137 <https://wg21.link/CWG2137>`_ which allows + list-initialization from objects of the same type. +- Implemented `CWG2311 <https://wg21.link/CWG2311>`_: given a prvalue ``e`` of object type + ``T``, ``T{e}`` will try to resolve an initializer list constructor and will use it if successful (CWG2137). + Otherwise, if there is no initializer list constructor, the copy will be elided as if it was ``T(e)``. C Language Changes ------------------ diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp index 408ee5f775804b..2822a8d5d78b3e 100644 --- a/clang/lib/Sema/SemaInit.cpp +++ b/clang/lib/Sema/SemaInit.cpp @@ -4199,7 +4199,7 @@ static OverloadingResult ResolveConstructorOverload( /// \param IsListInit Is this list-initialization? /// \param IsInitListCopy Is this non-list-initialization resulting from a /// list-initialization from {x} where x is the same -/// type as the entity? +/// aggregate type as the entity? static void TryConstructorInitialization(Sema &S, const InitializedEntity &Entity, const InitializationKind &Kind, @@ -4229,6 +4229,14 @@ static void TryConstructorInitialization(Sema &S, Entity.getKind() != InitializedEntity::EK_LambdaToBlockConversionBlockElement); + bool CopyElisionPossible = false; + auto ElideConstructor = [&] { + // Convert qualifications if necessary. + Sequence.AddQualificationConversionStep(DestType, VK_PRValue); + if (ILE) + Sequence.RewrapReferenceInitList(DestType, ILE); + }; + // C++17 [dcl.init]p17: // - If the initializer expression is a prvalue and the cv-unqualified // version of the source type is the same class as the class of the @@ -4241,11 +4249,17 @@ static void TryConstructorInitialization(Sema &S, if (S.getLangOpts().CPlusPlus17 && !RequireActualConstructor && UnwrappedArgs.size() == 1 && UnwrappedArgs[0]->isPRValue() && S.Context.hasSameUnqualifiedType(UnwrappedArgs[0]->getType(), DestType)) { - // Convert qualifications if necessary. - Sequence.AddQualificationConversionStep(DestType, VK_PRValue); - if (ILE) - Sequence.RewrapReferenceInitList(DestType, ILE); - return; + if (ILE && !DestType->isAggregateType()) { + // CWG2311: T{ prvalue_of_type_T } is not eligible for copy elision + // Make this an elision if this won't call an initializer-list + // constructor. (Always on an aggregate type or check constructors first.) + assert(!IsInitListCopy && + "IsInitListCopy only possible with aggregate types"); + CopyElisionPossible = true; + } else { + ElideConstructor(); + return; + } } const RecordType *DestRecordType = DestType->getAs<RecordType>(); @@ -4290,6 +4304,12 @@ static void TryConstructorInitialization(Sema &S, S, Kind.getLocation(), Args, CandidateSet, DestType, Ctors, Best, CopyInitialization, AllowExplicit, /*OnlyListConstructors=*/true, IsListInit, RequireActualConstructor); + + if (CopyElisionPossible && Result == OR_No_Viable_Function) { + // No initializer list candidate + ElideConstructor(); + return; + } } // C++11 [over.match.list]p1: @@ -4571,9 +4591,9 @@ static void TryListInitialization(Sema &S, return; } - // C++11 [dcl.init.list]p3, per DR1467: - // - If T is a class type and the initializer list has a single element of - // type cv U, where U is T or a class derived from T, the object is + // C++11 [dcl.init.list]p3, per DR1467 and DR2137: + // - If T is an aggregate class and the initializer list has a single element + // of type cv U, where U is T or a class derived from T, the object is // initialized from that element (by copy-initialization for // copy-list-initialization, or by direct-initialization for // direct-list-initialization). @@ -4584,7 +4604,7 @@ static void TryListInitialization(Sema &S, // - Otherwise, if T is an aggregate, [...] (continue below). if (S.getLangOpts().CPlusPlus11 && InitList->getNumInits() == 1 && !IsDesignatedInit) { - if (DestType->isRecordType()) { + if (DestType->isRecordType() && DestType->isAggregateType()) { QualType InitType = InitList->getInit(0)->getType(); if (S.Context.hasSameUnqualifiedType(InitType, DestType) || S.IsDerivedFrom(InitList->getBeginLoc(), InitType, DestType)) { diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp index 64bc3851980272..30bc2036cf781c 100644 --- a/clang/lib/Sema/SemaOverload.cpp +++ b/clang/lib/Sema/SemaOverload.cpp @@ -1562,19 +1562,37 @@ TryUserDefinedConversion(Sema &S, Expr *From, QualType ToType, // called for those cases. if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(ICS.UserDefined.ConversionFunction)) { - QualType FromCanon - = S.Context.getCanonicalType(From->getType().getUnqualifiedType()); + QualType FromType; + SourceLocation FromLoc; + // C++11 [over.ics.list]p6, per DR2137: + // C++17 [over.ics.list]p6: + // If C is not an initializer-list constructor and the initializer list + // has a single element of type cv U, where U is X or a class derived + // from X, the implicit conversion sequence has Exact Match rank if U is + // X, or Conversion rank if U is derived from X. + if (const auto *InitList = dyn_cast<InitListExpr>(From); + InitList && InitList->getNumInits() == 1 && + !S.isInitListConstructor(Constructor)) { + const Expr *SingleInit = InitList->getInit(0); + FromType = SingleInit->getType(); + FromLoc = SingleInit->getBeginLoc(); + } else { + FromType = From->getType(); + FromLoc = From->getBeginLoc(); + } + QualType FromCanon = + S.Context.getCanonicalType(FromType.getUnqualifiedType()); QualType ToCanon = S.Context.getCanonicalType(ToType).getUnqualifiedType(); if (Constructor->isCopyConstructor() && (FromCanon == ToCanon || - S.IsDerivedFrom(From->getBeginLoc(), FromCanon, ToCanon))) { + S.IsDerivedFrom(FromLoc, FromCanon, ToCanon))) { // Turn this into a "standard" conversion sequence, so that it // gets ranked with standard conversion sequences. DeclAccessPair Found = ICS.UserDefined.FoundConversionFunction; ICS.setStandard(); ICS.Standard.setAsIdentityConversion(); - ICS.Standard.setFromType(From->getType()); + ICS.Standard.setFromType(FromType); ICS.Standard.setAllToTypes(ToType); ICS.Standard.CopyConstructor = Constructor; ICS.Standard.FoundCopyConstructor = Found; @@ -5320,18 +5338,18 @@ TryListConversion(Sema &S, InitListExpr *From, QualType ToType, IsDesignatedInit) return Result; - // Per DR1467: - // If the parameter type is a class X and the initializer list has a single - // element of type cv U, where U is X or a class derived from X, the - // implicit conversion sequence is the one required to convert the element - // to the parameter type. + // Per DR1467 and DR2137: + // If the parameter type is an aggregate class X and the initializer list + // has a single element of type cv U, where U is X or a class derived from + // X, the implicit conversion sequence is the one required to convert the + // element to the parameter type. // // Otherwise, if the parameter type is a character array [... ] // and the initializer list has a single element that is an // appropriately-typed string literal (8.5.2 [dcl.init.string]), the // implicit conversion sequence is the identity conversion. if (From->getNumInits() == 1 && !IsDesignatedInit) { - if (ToType->isRecordType()) { + if (ToType->isRecordType() && ToType->isAggregateType()) { QualType InitType = From->getInit(0)->getType(); if (S.Context.hasSameUnqualifiedType(InitType, ToType) || S.IsDerivedFrom(From->getBeginLoc(), InitType, ToType)) diff --git a/clang/test/CXX/drs/dr14xx.cpp b/clang/test/CXX/drs/dr14xx.cpp index d262f6f9dcab79..4c29d03a6e117a 100644 --- a/clang/test/CXX/drs/dr14xx.cpp +++ b/clang/test/CXX/drs/dr14xx.cpp @@ -488,16 +488,6 @@ namespace dr1467 { // dr1467: 3.7 c++11 } } // nonaggregate - namespace SelfInitIsNotListInit { - struct S { - S(); - explicit S(S &); - S(const S &); - }; - S s1; - S s2 = {s1}; // ok, not list-initialization so we pick the non-explicit constructor - } - struct NestedInit { int a, b, c; }; NestedInit ni[1] = {{NestedInit{1, 2, 3}}}; diff --git a/clang/test/CXX/drs/dr21xx.cpp b/clang/test/CXX/drs/dr21xx.cpp index a7e50df3f374be..9d2016262712d1 100644 --- a/clang/test/CXX/drs/dr21xx.cpp +++ b/clang/test/CXX/drs/dr21xx.cpp @@ -11,6 +11,16 @@ // cxx98-error@-1 {{variadic macros are a C99 feature}} #endif +namespace std { + __extension__ typedef __SIZE_TYPE__ size_t; + + template<typename E> struct initializer_list { + const E *p; size_t n; + initializer_list(const E *p, size_t n); + initializer_list(); + }; +} + namespace dr2100 { // dr2100: 12 template<const int *P, bool = true> struct X {}; template<typename T> struct A { @@ -132,6 +142,36 @@ namespace dr2126 { // dr2126: 12 #endif } +namespace dr2137 { // dr2137: 18 +#if __cplusplus >= 201103L + struct Q { + Q(); + Q(Q&&); + Q(std::initializer_list<Q>) = delete; // expected-note 2 {{has been explicitly marked deleted here}} + }; + + Q x = Q { Q() }; // expected-error {{call to deleted constructor}} + + int f(Q); // expected-note {{passing argument to parameter here}} + int y = f({ Q() }); // expected-error {{call to deleted constructor}} + + struct U { + U(); + U(const U&); + }; + + struct Derived : U { + Derived(); + Derived(const Derived&); + } d; + + int g(Derived); + int g(U(&&)[1]) = delete; + + int z = g({ d }); +#endif +} + namespace dr2140 { // dr2140: 9 #if __cplusplus >= 201103L union U { int a; decltype(nullptr) b; }; diff --git a/clang/test/CXX/drs/dr23xx.cpp b/clang/test/CXX/drs/dr23xx.cpp index d2f4e7652ab568..8aa04c917846fa 100644 --- a/clang/test/CXX/drs/dr23xx.cpp +++ b/clang/test/CXX/drs/dr23xx.cpp @@ -6,6 +6,16 @@ // RUN: %clang_cc1 -std=c++23 %s -verify=expected,since-cxx11,since-cxx14,since-cxx17,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors 2>&1 | FileCheck %s // RUN: %clang_cc1 -std=c++2c %s -verify=expected,since-cxx11,since-cxx14,since-cxx17,since-cxx20 -fexceptions -fcxx-exceptions -pedantic-errors 2>&1 | FileCheck %s +namespace std { + __extension__ typedef __SIZE_TYPE__ size_t; + + template<typename E> struct initializer_list { + const E *p; size_t n; + initializer_list(const E *p, size_t n); + initializer_list(); + }; +} + #if __cplusplus >= 201103L namespace dr2303 { // dr2303: 12 template <typename... T> @@ -47,6 +57,80 @@ void g() { } //namespace dr2303 #endif +namespace dr2311 { // dr2311: 18 open +#if __cplusplus >= 201707L +template<typename T> +void test() { + // Ensure none of these expressions try to call a move constructor. + T a = T{T(0)}; + T b{T(0)}; + auto c{T(0)}; + T d = {T(0)}; + auto e = {T(0)}; +#if __cplusplus >= 202302L + auto f = auto{T(0)}; +#endif + void(*fn)(T); + fn({T(0)}); +} + +struct NonMovable { + NonMovable(int); + NonMovable(NonMovable&&) = delete; +}; +struct NonMovableNonApplicableIList { + NonMovableNonApplicableIList(int); + NonMovableNonApplicableIList(NonMovableNonApplicableIList&&) = delete; + NonMovableNonApplicableIList(std::initializer_list<int>); +}; +struct ExplicitMovable { + ExplicitMovable(int); + explicit ExplicitMovable(ExplicitMovable&&); +}; +struct ExplicitNonMovable { + ExplicitNonMovable(int); + explicit ExplicitNonMovable(ExplicitNonMovable&&) = delete; +}; +struct ExplicitNonMovableNonApplicableIList { + ExplicitNonMovableNonApplicableIList(int); + explicit ExplicitNonMovableNonApplicableIList(ExplicitNonMovableNonApplicableIList&&) = delete; + ExplicitNonMovableNonApplicableIList(std::initializer_list<int>); +}; +struct CopyOnly { + CopyOnly(int); + CopyOnly(const CopyOnly&); + CopyOnly(CopyOnly&&) = delete; +}; +struct ExplicitCopyOnly { + ExplicitCopyOnly(int); + explicit ExplicitCopyOnly(const ExplicitCopyOnly&); + explicit ExplicitCopyOnly(ExplicitCopyOnly&&) = delete; +}; + +template void test<NonMovable>(); +template void test<NonMovableNonApplicableIList>(); +template void test<ExplicitMovable>(); +template void test<ExplicitNonMovable>(); +template void test<ExplicitNonMovableNonApplicableIList>(); +template void test<CopyOnly>(); +template void test<ExplicitCopyOnly>(); + +struct any { + template<typename T> + any(T&&); +}; + +template<typename T> +struct X { + X(); + X(T) = delete; // expected-note {{'X' has been explicitly marked deleted here}} +}; + +X<std::initializer_list<any>> x{ X<std::initializer_list<any>>() }; // expected-error {{call to deleted constructor of 'X<std::initializer_list<any>>'}} + +#endif +} + // dr2331: na #if __cplusplus >= 201103L diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html index 4a3ed19161f9a5..391c611480820c 100755 --- a/clang/www/cxx_dr_status.html +++ b/clang/www/cxx_dr_status.html @@ -12630,7 +12630,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2> <td><a href="https://cplusplus.github.io/CWG/issues/2137.html";>2137</a></td> <td>CD4</td> <td>List-initialization from object of same type</td> - <td class="unknown" align="center">Unknown</td> + <td class="unreleased" align="center">Clang 18</td> </tr> <tr id="2138"> <td><a href="https://cplusplus.github.io/CWG/issues/2138.html";>2138</a></td> @@ -13674,7 +13674,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2> <td><a href="https://cplusplus.github.io/CWG/issues/2311.html";>2311</a></td> <td>open</td> <td>Missed case for guaranteed copy elision</td> - <td align="center">Not resolved</td> + <td class="unreleased" align="center">Clang 18</td> </tr> <tr id="2312"> <td><a href="https://cplusplus.github.io/CWG/issues/2312.html";>2312</a></td> diff --git a/libcxx/test/std/utilities/utility/pairs/pairs.pair/ctor.pair_U_V_move.pass.cpp b/libcxx/test/std/utilities/utility/pairs/pairs.pair/ctor.pair_U_V_move.pass.cpp index 3b2d093eb34d49..30fdb19fd3aebe 100644 --- a/libcxx/test/std/utilities/utility/pairs/pairs.pair/ctor.pair_U_V_move.pass.cpp +++ b/libcxx/test/std/utilities/utility/pairs/pairs.pair/ctor.pair_U_V_move.pass.cpp @@ -121,7 +121,26 @@ int main(int, char**) test_pair_rv<CopyOnly, CopyOnly&>(); test_pair_rv<CopyOnly, CopyOnly&&>(); - test_pair_rv<ExplicitTypes::CopyOnly, ExplicitTypes::CopyOnly>(); + /* For ExplicitTypes::CopyOnly, two of the viable candidates for initializing from a non-const xvalue are: + * pair(const pair&); // (defaulted copy constructor) + * template<class U1, class U2> explicit pair(const pair<U1, U2>&&); [U1 = ExplicitTypes::CopyOnly, U2 = int] + * This results in diverging behavior for test_convertible which uses copy-list-initialization + * Prior to CWG2137, this would have selected the first (non-explicit) ctor as explicit ctors would not be considered + * Afterwards, it should select the second since it is a better match, and then failed because it is explicit + * + * This may change with future defect reports, and some compilers only have partial support for CWG2137, + * so use std::is_convertible directly to avoid a copy-list-initialization + */ + { + using P1 = std::pair<ExplicitTypes::CopyOnly, int>; + using P2 = std::pair<int, ExplicitTypes::CopyOnly>; + using UP1 = std::pair<ExplicitTypes::CopyOnly, int>&&; + using UP2 = std::pair<int, ExplicitTypes::CopyOnly>&&; + static_assert(std::is_constructible<P1, UP1>::value, ""); + static_assert(std::is_convertible<P1, UP1>::value, ""); + static_assert(std::is_constructible<P2, UP2>::value, ""); + static_assert(std::is_convertible<P2, UP2>::value, ""); + } test_pair_rv<ExplicitTypes::CopyOnly, ExplicitTypes::CopyOnly&, true, false>(); test_pair_rv<ExplicitTypes::CopyOnly, ExplicitTypes::CopyOnly&&, true, false>(); `````````` </details> https://github.com/llvm/llvm-project/pull/77768 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
