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[libc++][modules] Get rid of <cstddef> dependency in __datasizeof (#107394)

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All the compilers we support also provide __builtin_offsetof, so avoid
using this macro and use the builtin directly instead. This allows
removing a dependency on `<cstddef>`, which is heavier than we need.
This commit is contained in:
Louis Dionne
2024-09-05 12:42:55 -04:00
committed by GitHub
parent 953af0e7f1
commit eee2f02e4e
1 changed files with 5 additions and 5 deletions
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10
libcxx/include/__type_traits/datasizeof.h
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@@ -10,9 +10,9 @@
#define _LIBCPP___TYPE_TRAITS_DATASIZEOF_H
#include <__config>
#include <__cstddef/size_t.h>
#include <__type_traits/is_class.h>
#include <__type_traits/is_final.h>
#include <cstddef>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
@@ -37,15 +37,15 @@ struct _FirstPaddingByte {
char __first_padding_byte_;
};
// _FirstPaddingByte<> is sometimes non-standard layout. Using `offsetof` is UB in that case, but GCC and Clang allow
// the use as an extension.
// _FirstPaddingByte<> is sometimes non-standard layout.
// It is conditionally-supported to use __builtin_offsetof in that case, but GCC and Clang allow it.
_LIBCPP_DIAGNOSTIC_PUSH
_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Winvalid-offsetof")
_LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Winvalid-offsetof")
template <class _Tp>
inline const size_t __datasizeof_v = offsetof(_FirstPaddingByte<_Tp>, __first_padding_byte_);
inline const size_t __datasizeof_v = __builtin_offsetof(_FirstPaddingByte<_Tp>, __first_padding_byte_);
_LIBCPP_DIAGNOSTIC_POP
#endif // __has_extension(datasizeof)
#endif // __has_extension(datasizeof)
_LIBCPP_END_NAMESPACE_STD