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[libc++] Simplify the implementation of aligned_storage #162459

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[libc++] Simplify the implementation of aligned_storage #162459

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4 changes: 2 additions & 2 deletions libcxx/include/__config
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Original file line number Diff line number Diff line change
Expand Up @@ -339,7 +339,7 @@ _LIBCPP_HARDENING_MODE_DEBUG

# ifndef _LIBCPP_CXX03_LANG

# define _LIBCPP_ALIGNOF(_Tp) alignof(_Tp)
# define _LIBCPP_ALIGNOF(...) alignof(__VA_ARGS__)
# define _ALIGNAS_TYPE(x) alignas(x)
# define _ALIGNAS(x) alignas(x)
# define _NOEXCEPT noexcept
Expand All @@ -348,7 +348,7 @@ _LIBCPP_HARDENING_MODE_DEBUG

# else

# define _LIBCPP_ALIGNOF(_Tp) _Alignof(_Tp)
# define _LIBCPP_ALIGNOF(...) _Alignof(__VA_ARGS__)
# define _ALIGNAS_TYPE(x) __attribute__((__aligned__(_LIBCPP_ALIGNOF(x))))
# define _ALIGNAS(x) __attribute__((__aligned__(x)))
# define nullptr __nullptr
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53 changes: 13 additions & 40 deletions libcxx/include/__type_traits/aligned_storage.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,6 @@

#include <__config>
#include <__cstddef/size_t.h>
#include <__type_traits/integral_constant.h>
#include <__type_traits/type_list.h>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
Expand All @@ -21,10 +19,10 @@
_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp>
struct __align_type {
static const size_t value = _LIBCPP_PREFERRED_ALIGNOF(_Tp);
typedef _Tp type;
};
struct _ALIGNAS(_LIBCPP_PREFERRED_ALIGNOF(_Tp)) _AlignedAsT {};

template <class... _Args>
struct __max_align_impl : _AlignedAsT<_Args>... {};

struct __struct_double {
long double __lx;
Expand All @@ -33,41 +31,16 @@ struct __struct_double4 {
double __lx[4];
};

using __all_types _LIBCPP_NODEBUG =
__type_list<__align_type<unsigned char>,
__align_type<unsigned short>,
__align_type<unsigned int>,
__align_type<unsigned long>,
__align_type<unsigned long long>,
__align_type<double>,
__align_type<long double>,
__align_type<__struct_double>,
__align_type<__struct_double4>,
__align_type<int*> >;

template <class _TL, size_t _Len>
struct __find_max_align;

template <class _Head, size_t _Len>
struct __find_max_align<__type_list<_Head>, _Len> : public integral_constant<size_t, _Head::value> {};

template <size_t _Len, size_t _A1, size_t _A2>
struct __select_align {
private:
static const size_t __min = _A2 < _A1 ? _A2 : _A1;
static const size_t __max = _A1 < _A2 ? _A2 : _A1;

public:
static const size_t value = _Len < __max ? __min : __max;
};
inline const size_t __aligned_storage_max_align =
_LIBCPP_ALIGNOF(__max_align_impl<unsigned long long, double, long double, __struct_double, __struct_double4, int*>);

template <class _Head, class... _Tail, size_t _Len>
struct __find_max_align<__type_list<_Head, _Tail...>, _Len>
: public integral_constant<
size_t,
__select_align<_Len, _Head::value, __find_max_align<__type_list<_Tail...>, _Len>::value>::value> {};
template <size_t _Len>
inline const size_t __aligned_storage_alignment =
_Len > __aligned_storage_max_align
? __aligned_storage_max_align
: size_t(1) << ((sizeof(size_t) * __CHAR_BIT__) - __builtin_clzg(_Len) - 1);

template <size_t _Len, size_t _Align = __find_max_align<__all_types, _Len>::value>
template <size_t _Len, size_t _Align = __aligned_storage_alignment<_Len> >
struct _LIBCPP_DEPRECATED_IN_CXX23 _LIBCPP_NO_SPECIALIZATIONS aligned_storage {
union _ALIGNAS(_Align) type {
unsigned char __data[(_Len + _Align - 1) / _Align * _Align];
Expand All @@ -77,7 +50,7 @@ struct _LIBCPP_DEPRECATED_IN_CXX23 _LIBCPP_NO_SPECIALIZATIONS aligned_storage {
#if _LIBCPP_STD_VER >= 14

_LIBCPP_SUPPRESS_DEPRECATED_PUSH
template <size_t _Len, size_t _Align = __find_max_align<__all_types, _Len>::value>
template <size_t _Len, size_t _Align = __aligned_storage_alignment<_Len> >
using aligned_storage_t _LIBCPP_DEPRECATED_IN_CXX23 = typename aligned_storage<_Len, _Align>::type;
_LIBCPP_SUPPRESS_DEPRECATED_POP

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