[gcc r15-1289] libstdc++: Optimize std::is_pointer compilation performance

[Ken Matsui]

https://gcc.gnu.org/g:014879ea4c86b3b8ab6b61a1226ee5b31e816c8b

commit r15-1289-g014879ea4c86b3b8ab6b61a1226ee5b31e816c8b
Author: Ken Matsui <kmatsui@gcc.gnu.org>
Date:   Wed Jul 12 13:43:44 2023 -0700

    libstdc++: Optimize std::is_pointer compilation performance
    
    This patch optimizes the compilation performance of std::is_pointer
    by dispatching to the new __is_pointer built-in trait.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/cpp_type_traits.h (__is_pointer): Use
            __is_pointer built-in trait.
            * include/std/type_traits (is_pointer): Likewise.  Optimize its
            implementation.
            (is_pointer_v): Likewise.
    
    Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
    Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
    Reviewed-by: Patrick Palka <ppalka@redhat.com>
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

Diff:
---
 libstdc++-v3/include/bits/cpp_type_traits.h |  8 ++++++
 libstdc++-v3/include/std/type_traits        | 44 +++++++++++++++++++++++------
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h b/libstdc++-v3/include/bits/cpp_type_traits.h
index 59f1a1875eb8..679eee99b904 100644
--- a/libstdc++-v3/include/bits/cpp_type_traits.h
+++ b/libstdc++-v3/include/bits/cpp_type_traits.h
@@ -363,6 +363,13 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
   //
   // Pointer types
   //
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
+  template<typename _Tp, bool _IsPtr = __is_pointer(_Tp)>
+    struct __is_pointer : __truth_type<_IsPtr>
+    {
+      enum { __value = _IsPtr };
+    };
+#else
   template<typename _Tp>
     struct __is_pointer
     {
@@ -376,6 +383,7 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
       enum { __value = 1 };
       typedef __true_type __type;
     };
+#endif
 
   //
   // An arithmetic type is an integer type or a floating point type
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 8c8219b2697c..0ef112926575 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -542,19 +542,33 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public true_type { };
 #endif
 
-  template<typename>
-    struct __is_pointer_helper
+  /// is_pointer
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
+  template<typename _Tp>
+    struct is_pointer
+    : public __bool_constant<__is_pointer(_Tp)>
+    { };
+#else
+  template<typename _Tp>
+    struct is_pointer
     : public false_type { };
 
   template<typename _Tp>
-    struct __is_pointer_helper<_Tp*>
+    struct is_pointer<_Tp*>
     : public true_type { };
 
-  /// is_pointer
   template<typename _Tp>
-    struct is_pointer
-    : public __is_pointer_helper<__remove_cv_t<_Tp>>::type
-    { };
+    struct is_pointer<_Tp* const>
+    : public true_type { };
+
+  template<typename _Tp>
+    struct is_pointer<_Tp* volatile>
+    : public true_type { };
+
+  template<typename _Tp>
+    struct is_pointer<_Tp* const volatile>
+    : public true_type { };
+#endif
 
   /// is_lvalue_reference
   template<typename>
@@ -3306,8 +3320,22 @@ template <typename _Tp, size_t _Num>
   inline constexpr bool is_array_v<_Tp[_Num]> = true;
 #endif
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__is_pointer)
+template <typename _Tp>
+  inline constexpr bool is_pointer_v = __is_pointer(_Tp);
+#else
 template <typename _Tp>
-  inline constexpr bool is_pointer_v = is_pointer<_Tp>::value;
+  inline constexpr bool is_pointer_v = false;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp*> = true;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp* const> = true;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp* volatile> = true;
+template <typename _Tp>
+  inline constexpr bool is_pointer_v<_Tp* const volatile> = true;
+#endif
+
 template <typename _Tp>
   inline constexpr bool is_lvalue_reference_v = false;
 template <typename _Tp>