[gcc r14-6973] libstdc++: Optimize std::is_trivially_destructible_v

[Jonathan Wakely]

https://gcc.gnu.org/g:7af436ada243bbb6ae601c85bd47ea908c71fb41

commit r14-6973-g7af436ada243bbb6ae601c85bd47ea908c71fb41
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Nov 22 15:09:24 2023 +0000

    libstdc++: Optimize std::is_trivially_destructible_v
    
    This reduces the overhead of using std::is_trivially_destructible_v and
    as a result fixes some recent regressions seen with a non-default
    GLIBCXX_TESTSUITE_STDS env var:
    FAIL: 20_util/variant/87619.cc  -std=gnu++20 (test for excess errors)
    FAIL: 20_util/variant/87619.cc  -std=gnu++23 (test for excess errors)
    FAIL: 20_util/variant/87619.cc  -std=gnu++26 (test for excess errors)
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_trivially_destructible_v): Use
            built-in directly when concepts are supported.
            * testsuite/20_util/is_trivially_destructible/value_v.cc: New
            test.

Diff:
---
 libstdc++-v3/include/std/type_traits               | 19 ++++++++++
 .../20_util/is_trivially_destructible/value_v.cc   | 40 ++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 3b1b419bbbb..1cec0822b73 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -3410,9 +3410,28 @@ template <typename _Tp>
   inline constexpr bool is_trivially_move_assignable_v
     = __is_trivially_assignable(__add_lval_ref_t<_Tp>,
 				__add_rval_ref_t<_Tp>);
+
+#if __cpp_concepts
+template <typename _Tp>
+  inline constexpr bool is_trivially_destructible_v = false;
+
+template <typename _Tp>
+  requires (!is_reference_v<_Tp>) && requires (_Tp& __t) { __t.~_Tp(); }
+  inline constexpr bool is_trivially_destructible_v<_Tp>
+    = __has_trivial_destructor(_Tp);
+template <typename _Tp>
+  inline constexpr bool is_trivially_destructible_v<_Tp&> = true;
+template <typename _Tp>
+  inline constexpr bool is_trivially_destructible_v<_Tp&&> = true;
+template <typename _Tp, size_t _Nm>
+  inline constexpr bool is_trivially_destructible_v<_Tp[_Nm]>
+    = is_trivially_destructible_v<_Tp>;
+#else
 template <typename _Tp>
   inline constexpr bool is_trivially_destructible_v =
     is_trivially_destructible<_Tp>::value;
+#endif
+
 template <typename _Tp, typename... _Args>
   inline constexpr bool is_nothrow_constructible_v
     = __is_nothrow_constructible(_Tp, _Args...);
diff --git a/libstdc++-v3/testsuite/20_util/is_trivially_destructible/value_v.cc b/libstdc++-v3/testsuite/20_util/is_trivially_destructible/value_v.cc
new file mode 100644
index 00000000000..7db098a2c4d
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_trivially_destructible/value_v.cc
@@ -0,0 +1,40 @@
+// { dg-do compile { target c++17 } }
+#include <type_traits>
+#include <testsuite_tr1.h>
+
+template<typename T>
+constexpr void test_cv()
+{
+  static_assert(std::is_trivially_destructible_v<const T>
+      == std::is_trivially_destructible_v<T>);
+  static_assert(std::is_trivially_destructible_v<volatile T>
+      == std::is_trivially_destructible_v<T>);
+  static_assert(std::is_trivially_destructible_v<const volatile T>
+      == std::is_trivially_destructible_v<T>);
+}
+
+template<typename T, bool Expected>
+void test()
+{
+  static_assert(std::is_trivially_destructible_v<T> == Expected);
+  test_cv<T>();
+}
+
+void test01()
+{
+  using namespace __gnu_test;
+
+  test<int, true>();
+  test<int&, true>();
+  test<int&&, true>();
+  test<int[1], true>();
+  test<TType, true>();
+  test<TType[1], true>();
+  test<PODType, true>();
+  test<PODType[1], true>();
+  test<NType, false>();
+  test<SLType, false>();
+  test<int(), false>();
+  test<void, false>();
+  test<int[], false>();
+}