* [PATCH 1/2] libstdc++: Optimize is_void and is_null_pointer
@ 2022-09-07 0:45 Patrick Palka
2022-09-07 0:45 ` [PATCH 2/2] libstdc++: Optimize is_reference Patrick Palka
2022-09-07 8:19 ` [PATCH 1/2] libstdc++: Optimize is_void and is_null_pointer Jonathan Wakely
0 siblings, 2 replies; 4+ messages in thread
From: Patrick Palka @ 2022-09-07 0:45 UTC (permalink / raw)
To: gcc-patches; +Cc: libstdc++, Patrick Palka
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH 2/2] libstdc++: Optimize is_reference
2022-09-07 0:45 [PATCH 1/2] libstdc++: Optimize is_void and is_null_pointer Patrick Palka
@ 2022-09-07 0:45 ` 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
1 sibling, 1 reply; 4+ messages in thread
From: Patrick Palka @ 2022-09-07 0:45 UTC (permalink / raw)
To: gcc-patches; +Cc: libstdc++, Patrick Palka
Instead of defining is_reference in terms of is_lvalue_reference
and is_rvalue_reference, just define it directly.
Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
This reduces memory usage of join.cc by 1%.
libstdc++-v3/ChangeLog:
* include/std/type_traits (is_reference): Make the primary
template derive from false_type. Define two partial
specializations that derive from true_type.
---
libstdc++-v3/include/std/type_traits | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index b83e7257a9f..94e73eafd2f 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -611,8 +611,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// is_reference
template<typename _Tp>
struct is_reference
- : public __or_<is_lvalue_reference<_Tp>,
- is_rvalue_reference<_Tp>>::type
+ : public false_type
+ { };
+
+ template<typename _Tp>
+ struct is_reference<_Tp&>
+ : public true_type
+ { };
+
+ template<typename _Tp>
+ struct is_reference<_Tp&&>
+ : public true_type
{ };
/// is_arithmetic
--
2.37.3.518.g79f2338b37
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 2/2] libstdc++: Optimize is_reference
2022-09-07 0:45 ` [PATCH 2/2] libstdc++: Optimize is_reference Patrick Palka
@ 2022-09-07 8:00 ` Jonathan Wakely
0 siblings, 0 replies; 4+ messages in thread
From: Jonathan Wakely @ 2022-09-07 8:00 UTC (permalink / raw)
To: Patrick Palka; +Cc: gcc-patches, libstdc++
On Wed, 7 Sept 2022 at 01:46, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Instead of defining is_reference in terms of is_lvalue_reference
> and is_rvalue_reference, just define it directly.
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
Yes, thanks (I already did this for the std::is_reference_v variable
template, but for some reason left this equivalent change in the local
branch where I was doing the traits refactoring).
> This reduces memory usage of join.cc by 1%.
Now that many of the variable templates have been optimized to avoid
instantiating class templates, I wonder if the <ranges> code (and
anything else that's only defined for C++17 or later) would benefit
from using foo_v<T> && bar_v<T> instead of __and_<foo<T>, bar<T>>.
With your improvements to __and_ maybe it doesn't make so much
difference.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/type_traits (is_reference): Make the primary
> template derive from false_type. Define two partial
> specializations that derive from true_type.
> ---
> libstdc++-v3/include/std/type_traits | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
> index b83e7257a9f..94e73eafd2f 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -611,8 +611,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> /// is_reference
> template<typename _Tp>
> struct is_reference
> - : public __or_<is_lvalue_reference<_Tp>,
> - is_rvalue_reference<_Tp>>::type
> + : public false_type
> + { };
> +
> + template<typename _Tp>
> + struct is_reference<_Tp&>
> + : public true_type
> + { };
> +
> + template<typename _Tp>
> + struct is_reference<_Tp&&>
> + : public true_type
> { };
>
> /// is_arithmetic
> --
> 2.37.3.518.g79f2338b37
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 1/2] libstdc++: Optimize is_void and is_null_pointer
2022-09-07 0:45 [PATCH 1/2] libstdc++: Optimize is_void and is_null_pointer Patrick Palka
2022-09-07 0:45 ` [PATCH 2/2] libstdc++: Optimize is_reference Patrick Palka
@ 2022-09-07 8:19 ` Jonathan Wakely
1 sibling, 0 replies; 4+ messages in thread
From: Jonathan Wakely @ 2022-09-07 8:19 UTC (permalink / raw)
To: Patrick Palka; +Cc: gcc-patches, libstdc++
On Wed, 7 Sept 2022 at 01:46, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> 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?
Yes, and we should do the same for is_void_v and is_null_pointer_v.
Even though the class templates they instantiate will be cheaper now,
they can still avoid any class template instantiation.
> The is_void change alone reduces memory usage for join.cc by
> almost 1%.
Also in my queue of trait refactoring, but I haven't tested if these
are worth doing yet:
template<typename T>
struct is_object : is_const<const T>::type { };
template<>
struct is_object<void> : false_type { };
template<>
struct is_object<const void> : false_type { };
// and so on for volatile and const volatile
And we could define is_object_v as simply is_const_v<const T> && is_void_v<T>.
Improving is_object should benefit <ranges> and also the is_scalar
change proposed at
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96710#c2
^ permalink raw reply [flat|nested] 4+ messages in thread
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