From: Patrick Palka <ppalka@redhat.com>
To: gcc-patches@gcc.gnu.org
Cc: libstdc++@gcc.gnu.org, Patrick Palka <ppalka@redhat.com>
Subject: [PATCH 1/2] libstdc++: Optimize is_void and is_null_pointer
Date: Tue, 6 Sep 2022 20:45:41 -0400 [thread overview]
Message-ID: <20220907004542.288365-1-ppalka@redhat.com> (raw)
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.
Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
The is_void change alone reduces memory usage for join.cc by
almost 1%.
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.
---
libstdc++-v3/include/std/type_traits | 48 ++++++++++++++++++----------
1 file changed, 31 insertions(+), 17 deletions(-)
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index e4d167939d9..b83e7257a9f 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -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
+ /// is_void
+ template<typename _Tp>
+ struct is_void
: public false_type { };
template<>
- struct __is_void_helper<void>
+ struct is_void<void>
: public true_type { };
- /// @endcond
- /// is_void
- template<typename _Tp>
- struct is_void
- : public __is_void_helper<__remove_cv_t<_Tp>>::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
+ /// is_null_pointer (LWG 2247).
+ template<typename _Tp>
+ struct is_null_pointer
: public false_type { };
template<>
- struct __is_null_pointer_helper<std::nullptr_t>
+ struct is_null_pointer<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
- { };
+ 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.
--
2.37.3.518.g79f2338b37
next reply other threads:[~2022-09-07 0:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-07 0:45 Patrick Palka [this message]
2022-09-07 0:45 ` [PATCH 2/2] libstdc++: Optimize is_reference Patrick Palka
2022-09-07 8:00 ` Jonathan Wakely
2022-09-07 8:19 ` [PATCH 1/2] libstdc++: Optimize is_void and is_null_pointer Jonathan Wakely
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