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libstdc++: Optimize is_void and is_null_pointer

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Instead of defining these in terms of a helper class template
and the relatively expensive __remove_cv_t, just declare four
explicit specializations of the main template, one for each choice
of cv-quals.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (__is_void_helper): Remove.
	(is_void): Make the primary template derive from false_type,
	and define four explicit specializations that derive from
	true_type.
	(__is_null_pointer_helper, is_null_pointer): Likewise.
This commit is contained in:
Patrick Palka 2022-09-07 10:21:45 -04:00
parent 873d395c29
commit 66af6e991b
1 changed files with 35 additions and 21 deletions
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56
libstdc++-v3/include/std/type_traits
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@ -289,23 +289,30 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// __remove_cv_t (std::remove_cv_t for C++11).
template<typename _Tp>
using __remove_cv_t = typename remove_cv<_Tp>::type;
/// @endcond
// Primary type categories.
template<typename>
struct __is_void_helper
: public false_type { };
template<>
struct __is_void_helper<void>
: public true_type { };
/// @endcond
/// is_void
template<typename _Tp>
struct is_void
: public __is_void_helper<__remove_cv_t<_Tp>>::type
{ };
: public false_type { };
template<>
struct is_void<void>
: public true_type { };
template<>
struct is_void<const void>
: public true_type { };
template<>
struct is_void<volatile void>
: public true_type { };
template<>
struct is_void<const volatile void>
: public true_type { };
/// @cond undocumented
template<typename>
@ -571,19 +578,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#define __cpp_lib_is_null_pointer 201309L
template<typename>
struct __is_null_pointer_helper
: public false_type { };
template<>
struct __is_null_pointer_helper<std::nullptr_t>
: public true_type { };
/// is_null_pointer (LWG 2247).
template<typename _Tp>
struct is_null_pointer
: public __is_null_pointer_helper<__remove_cv_t<_Tp>>::type
{ };
: public false_type { };
template<>
struct is_null_pointer<std::nullptr_t>
: public true_type { };
template<>
struct is_null_pointer<const std::nullptr_t>
: public true_type { };
template<>
struct is_null_pointer<volatile std::nullptr_t>
: public true_type { };
template<>
struct is_null_pointer<const volatile std::nullptr_t>
: public true_type { };
/// __is_nullptr_t (deprecated extension).
/// @deprecated Non-standard. Use `is_null_pointer` instead.