diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst --- a/clang/docs/LanguageExtensions.rst +++ b/clang/docs/LanguageExtensions.rst @@ -1621,6 +1621,10 @@ materialized temporary object. If ``T`` is not a reference type the result is false. Note this trait will also return false when the initialization of ``T`` from ``U`` is ill-formed. + Deprecated, use ``__reference_constructs_from_temporary``. +* ``__reference_constructs_from_temporary(T, U)`` (C++) + Returns true if a reference ``T`` can be constructed from a temporary of type + a non-cv-qualified ``U``. * ``__underlying_type`` (C++, GNU, Microsoft) In addition, the following expression traits are supported: diff --git a/clang/include/clang/Basic/TokenKinds.def b/clang/include/clang/Basic/TokenKinds.def --- a/clang/include/clang/Basic/TokenKinds.def +++ b/clang/include/clang/Basic/TokenKinds.def @@ -531,6 +531,7 @@ TYPE_TRAIT_1(__is_referenceable, IsReferenceable, KEYCXX) TYPE_TRAIT_1(__can_pass_in_regs, CanPassInRegs, KEYCXX) TYPE_TRAIT_2(__reference_binds_to_temporary, ReferenceBindsToTemporary, KEYCXX) +TYPE_TRAIT_2(__reference_constructs_from_temporary, ReferenceConstructsFromTemporary, KEYCXX) // Embarcadero Expression Traits EXPRESSION_TRAIT(__is_lvalue_expr, IsLValueExpr, KEYCXX) diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp --- a/clang/lib/Lex/PPMacroExpansion.cpp +++ b/clang/lib/Lex/PPMacroExpansion.cpp @@ -1695,6 +1695,7 @@ .Case("__array_rank", true) .Case("__array_extent", true) .Case("__reference_binds_to_temporary", true) + .Case("__reference_constructs_from_temporary", true) #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) .Case("__" #Trait, true) #include "clang/Basic/TransformTypeTraits.def" .Default(false); diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp --- a/clang/lib/Parse/ParseDeclCXX.cpp +++ b/clang/lib/Parse/ParseDeclCXX.cpp @@ -1655,7 +1655,9 @@ tok::kw___is_union, tok::kw___is_unsigned, tok::kw___is_void, - tok::kw___is_volatile)) + tok::kw___is_volatile, + tok::kw___reference_binds_to_temporary, + tok::kw___reference_constructs_from_temporary)) // GNU libstdc++ 4.2 and libc++ use certain intrinsic names as the // name of struct templates, but some are keywords in GCC >= 4.3 // and Clang. Therefore, when we see the token sequence "struct diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp --- a/clang/lib/Parse/ParseExpr.cpp +++ b/clang/lib/Parse/ParseExpr.cpp @@ -1128,6 +1128,8 @@ REVERTIBLE_TYPE_TRAIT(__is_unsigned); REVERTIBLE_TYPE_TRAIT(__is_void); REVERTIBLE_TYPE_TRAIT(__is_volatile); + REVERTIBLE_TYPE_TRAIT(__reference_binds_to_temporary); + REVERTIBLE_TYPE_TRAIT(__reference_constructs_from_temporary); #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) \ REVERTIBLE_TYPE_TRAIT(RTT_JOIN(__, Trait)); #include "clang/Basic/TransformTypeTraits.def" diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp --- a/clang/lib/Sema/SemaExprCXX.cpp +++ b/clang/lib/Sema/SemaExprCXX.cpp @@ -5410,14 +5410,15 @@ if (Kind <= UTT_Last) return EvaluateUnaryTypeTrait(S, Kind, KWLoc, Args[0]->getType()); - // Evaluate BTT_ReferenceBindsToTemporary alongside the IsConstructible - // traits to avoid duplication. - if (Kind <= BTT_Last && Kind != BTT_ReferenceBindsToTemporary) + // Evaluate ReferenceBindsToTemporary and ReferenceConstructsFromTemporary + // alongside the IsConstructible traits to avoid duplication. + if (Kind <= BTT_Last && Kind != BTT_ReferenceBindsToTemporary && Kind != BTT_ReferenceConstructsFromTemporary) return EvaluateBinaryTypeTrait(S, Kind, Args[0]->getType(), Args[1]->getType(), RParenLoc); switch (Kind) { case clang::BTT_ReferenceBindsToTemporary: + case clang::BTT_ReferenceConstructsFromTemporary: case clang::TT_IsConstructible: case clang::TT_IsNothrowConstructible: case clang::TT_IsTriviallyConstructible: { @@ -5494,11 +5495,23 @@ if (Kind == clang::TT_IsConstructible) return true; - if (Kind == clang::BTT_ReferenceBindsToTemporary) { + if (Kind == clang::BTT_ReferenceBindsToTemporary || Kind == clang::BTT_ReferenceConstructsFromTemporary) { if (!T->isReferenceType()) return false; - return !Init.isDirectReferenceBinding(); + if (!Init.isDirectReferenceBinding()) + return true; + + if (Kind == clang::BTT_ReferenceBindsToTemporary) + return false; + + QualType U = Args[1]->getType(); + if (U->isReferenceType()) + return false; + + QualType TPtr = S.Context.getPointerType(S.BuiltinRemoveReference(T, UnaryTransformType::RemoveCVRef, {})); + QualType UPtr = S.Context.getPointerType(S.BuiltinRemoveReference(U, UnaryTransformType::RemoveCVRef, {})); + return EvaluateBinaryTypeTrait(S, TypeTrait::BTT_IsConvertibleTo, UPtr, TPtr, RParenLoc); } if (Kind == clang::TT_IsNothrowConstructible) diff --git a/clang/test/SemaCXX/type-traits.cpp b/clang/test/SemaCXX/type-traits.cpp --- a/clang/test/SemaCXX/type-traits.cpp +++ b/clang/test/SemaCXX/type-traits.cpp @@ -2542,6 +2542,51 @@ { int arr[T((__reference_binds_to_temporary(const int &, long)))]; } } +void reference_constructs_from_temporary_checks() { + static_assert(!__reference_constructs_from_temporary(int &, int &), ""); + static_assert(!__reference_constructs_from_temporary(int &, int &&), ""); + + static_assert(!__reference_constructs_from_temporary(int const &, int &), ""); + static_assert(!__reference_constructs_from_temporary(int const &, int const &), ""); + static_assert(!__reference_constructs_from_temporary(int const &, int &&), ""); + + static_assert(!__reference_constructs_from_temporary(int &, long &), ""); // doesn't construct + + static_assert(__reference_constructs_from_temporary(int const &, long &), ""); + static_assert(__reference_constructs_from_temporary(int const &, long &&), ""); + static_assert(__reference_constructs_from_temporary(int &&, long &), ""); + + using LRef = ConvertsToRef; + using RRef = ConvertsToRef; + using CLRef = ConvertsToRef; + using LongRef = ConvertsToRef; + static_assert(__is_constructible(int &, LRef), ""); + static_assert(!__reference_constructs_from_temporary(int &, LRef), ""); + + static_assert(__is_constructible(int &&, RRef), ""); + static_assert(!__reference_constructs_from_temporary(int &&, RRef), ""); + + static_assert(__is_constructible(int const &, CLRef), ""); + static_assert(!__reference_constructs_from_temporary(int &&, CLRef), ""); + + static_assert(__is_constructible(int const &, LongRef), ""); + static_assert(__reference_constructs_from_temporary(int const &, LongRef), ""); + + // Test that it doesn't accept non-reference types as input. + static_assert(!__reference_constructs_from_temporary(int, long), ""); + + static_assert(__reference_constructs_from_temporary(const int &, long), ""); + + // Additional checks + static_assert(__reference_constructs_from_temporary(POD const&, Derives), ""); + static_assert(__reference_constructs_from_temporary(int&&, int), ""); + static_assert(__reference_constructs_from_temporary(const int&, int), ""); + static_assert(!__reference_constructs_from_temporary(int&&, int&&), ""); + static_assert(!__reference_constructs_from_temporary(const int&, int&&), ""); + static_assert(__reference_constructs_from_temporary(int&&, long&&), ""); + static_assert(__reference_constructs_from_temporary(int&&, long), ""); +} + void array_rank() { int t01[T(__array_rank(IntAr) == 1)]; int t02[T(__array_rank(ConstIntArAr) == 2)]; diff --git a/clang/www/cxx_status.html b/clang/www/cxx_status.html --- a/clang/www/cxx_status.html +++ b/clang/www/cxx_status.html @@ -292,10 +292,9 @@ P2255R2
Partial - Clang provides a __reference_binds_to_temporary type trait - builtin, with which the library facility can be partially implemented. - Both __reference_constructs_from_temporary and - __reference_converts_from_temporary builtins should be + Clang provides __reference_constructs_from_temporary type + trait builtin, with which std::reference_constructs_from_temporary + is implemented. __reference_converts_from_temporary needs to be provided, following the normal cross-vendor convention to implement traits requiring compiler support directly.