r328680 - [ObjC] Make C++ triviality type traits available to non-trivial C

Wed Apr 4 16:24:05 PDT 2018

> On Apr 4, 2018, at 3:38 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> 
> Hi Akira,
> 
> This change has broken the C++ versions of these type traits for classes with volatile members. Such classes are required to claim to be trivial per C++ DR 2094 (http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2094 <http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2094>) but return false from isNonTrivialToPrimitiveCopy().
> 

Oh that’s right. The function returns false when isNonTrivialToPrimitiveCopy() returns PCK_VolatileTrivial. That is wrong.

> Also, exposing these __has_* traits more widely seems like a backwards step to me: these traits are deprecated, near-useless, and we're trying to remove them. No code should be using them under any circumstances; the __is_* traits should be used instead.
> 

The __is_* traits (is_trivially_copy_constructible, etc.) are templates defined in libcxx, so it seems that we can’t use them when compiling in C mode. Is it OK to add their definitions to TokenKinds.def as non-C++ keywords?

> On 27 March 2018 at 17:12, Akira Hatanaka via cfe-commits <cfe-commits at lists.llvm.org <mailto:cfe-commits at lists.llvm.org>> wrote:
> Author: ahatanak
> Date: Tue Mar 27 17:12:08 2018
> New Revision: 328680
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=328680&view=rev <http://llvm.org/viewvc/llvm-project?rev=328680&view=rev>
> Log:
> [ObjC] Make C++ triviality type traits available to non-trivial C
> structs.
> 
> r326307 and r327870 made changes that allowed using non-trivial C
> structs with fields qualified with __strong or __weak. This commit makes
> the following C++ triviality type traits available to non-trivial C
> structs:
> 
> __has_trivial_assign
> __has_trivial_move_assign
> __has_trivial_copy
> __has_trivial_move_constructor
> __has_trivial_constructor
> __has_trivial_destructor
> 
> rdar://problem/33599681
> 
> Differential Revision: https://reviews.llvm.org/D44913 <https://reviews.llvm.org/D44913>
> 
> Added:
>     cfe/trunk/test/SemaObjC/non-trivial-struct-traits.m
> Modified:
>     cfe/trunk/include/clang/Basic/TokenKinds.def
>     cfe/trunk/lib/Sema/SemaExprCXX.cpp
> 
> Modified: cfe/trunk/include/clang/Basic/TokenKinds.def
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/TokenKinds.def?rev=328680&r1=328679&r2=328680&view=diff <http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/TokenKinds.def?rev=328680&r1=328679&r2=328680&view=diff>
> ==============================================================================
> --- cfe/trunk/include/clang/Basic/TokenKinds.def (original)
> +++ cfe/trunk/include/clang/Basic/TokenKinds.def Tue Mar 27 17:12:08 2018
> @@ -433,12 +433,12 @@ TYPE_TRAIT_1(__has_nothrow_assign, HasNo
>  TYPE_TRAIT_1(__has_nothrow_move_assign, HasNothrowMoveAssign, KEYCXX)
>  TYPE_TRAIT_1(__has_nothrow_copy, HasNothrowCopy, KEYCXX)
>  TYPE_TRAIT_1(__has_nothrow_constructor, HasNothrowConstructor, KEYCXX)
> -TYPE_TRAIT_1(__has_trivial_assign, HasTrivialAssign, KEYCXX)
> -TYPE_TRAIT_1(__has_trivial_move_assign, HasTrivialMoveAssign, KEYCXX)
> -TYPE_TRAIT_1(__has_trivial_copy, HasTrivialCopy, KEYCXX)
> -TYPE_TRAIT_1(__has_trivial_constructor, HasTrivialDefaultConstructor, KEYCXX)
> -TYPE_TRAIT_1(__has_trivial_move_constructor, HasTrivialMoveConstructor, KEYCXX)
> -TYPE_TRAIT_1(__has_trivial_destructor, HasTrivialDestructor, KEYCXX)
> +TYPE_TRAIT_1(__has_trivial_assign, HasTrivialAssign, KEYALL)
> +TYPE_TRAIT_1(__has_trivial_move_assign, HasTrivialMoveAssign, KEYALL)
> +TYPE_TRAIT_1(__has_trivial_copy, HasTrivialCopy, KEYALL)
> +TYPE_TRAIT_1(__has_trivial_constructor, HasTrivialDefaultConstructor, KEYALL)
> +TYPE_TRAIT_1(__has_trivial_move_constructor, HasTrivialMoveConstructor, KEYALL)
> +TYPE_TRAIT_1(__has_trivial_destructor, HasTrivialDestructor, KEYALL)
>  TYPE_TRAIT_1(__has_virtual_destructor, HasVirtualDestructor, KEYCXX)
>  TYPE_TRAIT_1(__is_abstract, IsAbstract, KEYCXX)
>  TYPE_TRAIT_1(__is_aggregate, IsAggregate, KEYCXX)
> 
> Modified: cfe/trunk/lib/Sema/SemaExprCXX.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExprCXX.cpp?rev=328680&r1=328679&r2=328680&view=diff <http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExprCXX.cpp?rev=328680&r1=328679&r2=328680&view=diff>
> ==============================================================================
> --- cfe/trunk/lib/Sema/SemaExprCXX.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaExprCXX.cpp Tue Mar 27 17:12:08 2018
> @@ -4513,6 +4513,8 @@ static bool EvaluateUnaryTypeTrait(Sema
>      // does not correctly compute triviality in the presence of multiple special
>      // members of the same kind. Revisit this once the g++ bug is fixed.
>    case UTT_HasTrivialDefaultConstructor:
> +    if (T.isNonTrivialToPrimitiveDefaultInitialize())
> +      return false;
>      // http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html <http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html>:
>      //   If __is_pod (type) is true then the trait is true, else if type is
>      //   a cv class or union type (or array thereof) with a trivial default
> @@ -4524,6 +4526,8 @@ static bool EvaluateUnaryTypeTrait(Sema
>               !RD->hasNonTrivialDefaultConstructor();
>      return false;
>    case UTT_HasTrivialMoveConstructor:
> +    if (T.isNonTrivialToPrimitiveDestructiveMove())
> +      return false;
>      //  This trait is implemented by MSVC 2012 and needed to parse the
>      //  standard library headers. Specifically this is used as the logic
>      //  behind std::is_trivially_move_constructible (20.9.4.3).
> @@ -4533,6 +4537,8 @@ static bool EvaluateUnaryTypeTrait(Sema
>        return RD->hasTrivialMoveConstructor() && !RD->hasNonTrivialMoveConstructor();
>      return false;
>    case UTT_HasTrivialCopy:
> +    if (T.isNonTrivialToPrimitiveCopy())
> +      return false;
>      // http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html <http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html>:
>      //   If __is_pod (type) is true or type is a reference type then
>      //   the trait is true, else if type is a cv class or union type
> @@ -4545,6 +4551,8 @@ static bool EvaluateUnaryTypeTrait(Sema
>               !RD->hasNonTrivialCopyConstructor();
>      return false;
>    case UTT_HasTrivialMoveAssign:
> +    if (T.isNonTrivialToPrimitiveDestructiveMove())
> +      return false;
>      //  This trait is implemented by MSVC 2012 and needed to parse the
>      //  standard library headers. Specifically it is used as the logic
>      //  behind std::is_trivially_move_assignable (20.9.4.3)
> @@ -4554,6 +4562,8 @@ static bool EvaluateUnaryTypeTrait(Sema
>        return RD->hasTrivialMoveAssignment() && !RD->hasNonTrivialMoveAssignment();
>      return false;
>    case UTT_HasTrivialAssign:
> +    if (T.isNonTrivialToPrimitiveCopy())
> +      return false;
>      // http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html <http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html>:
>      //   If type is const qualified or is a reference type then the
>      //   trait is false. Otherwise if __is_pod (type) is true then the
> @@ -4624,6 +4634,8 @@ static bool EvaluateUnaryTypeTrait(Sema
>      return true;
> 
>    case UTT_HasTrivialDestructor:
> +    if (T.isDestructedType() == QualType::DK_nontrivial_c_struct)
> +      return false;
>      // http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html <http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html>
>      //   If __is_pod (type) is true or type is a reference type
>      //   then the trait is true, else if type is a cv class or union
> 
> Added: cfe/trunk/test/SemaObjC/non-trivial-struct-traits.m
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaObjC/non-trivial-struct-traits.m?rev=328680&view=auto <http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaObjC/non-trivial-struct-traits.m?rev=328680&view=auto>
> ==============================================================================
> --- cfe/trunk/test/SemaObjC/non-trivial-struct-traits.m (added)
> +++ cfe/trunk/test/SemaObjC/non-trivial-struct-traits.m Tue Mar 27 17:12:08 2018
> @@ -0,0 +1,25 @@
> +// RUN: %clang_cc1 -fsyntax-only -fobjc-arc -verify %s
> +
> +// expected-no-diagnostics
> +
> +struct Trivial {
> +  int x;
> +};
> +
> +struct NonTrivial {
> +  id x;
> +};
> +
> +int trivial_assign[__has_trivial_assign(struct Trivial) ? 1 : -1];
> +int trivial_move_assign[__has_trivial_move_assign(struct Trivial) ? 1 : -1];
> +int trivial_copy_constructor[__has_trivial_copy(struct Trivial) ? 1 : -1];
> +int trivial_move_constructor[__has_trivial_move_constructor(struct Trivial) ? 1 : -1];
> +int trivial_constructor[__has_trivial_constructor(struct Trivial) ? 1 : -1];
> +int trivial_destructor[__has_trivial_destructor(struct Trivial) ? 1 : -1];
> +
> +int non_trivial_assign[__has_trivial_assign(struct NonTrivial) ? -1 : 1];
> +int non_trivial_move_assign[__has_trivial_move_assign(struct NonTrivial) ? -1 : 1];
> +int non_trivial_copy_constructor[__has_trivial_copy(struct NonTrivial) ? -1 : 1];
> +int non_trivial_move_constructor[__has_trivial_move_constructor(struct NonTrivial) ? -1 : 1];
> +int non_trivial_constructor[__has_trivial_constructor(struct NonTrivial) ? -1 : 1];
> +int non_trivial_destructor[__has_trivial_destructor(struct NonTrivial) ? -1 : 1];
> 
> 
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