libstdc++: add std::is_virtual_base_of

Added by P2985R0 for C++26. This simply exposes the compiler
builtin, and adds the feature-testing macro.

libstdc++-v3/ChangeLog:

	* include/bits/version.def: Added the feature-testing macro.
	* include/bits/version.h: Regenerated.
	* include/std/type_traits: Add support for
	std::is_virtual_base_of and std::is_virtual_base_of_v,
	implemented in terms of the compiler builtin.
	* testsuite/20_util/is_virtual_base_of/value.cc: New test.

Signed-off-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index f2e28175b087ac5e7ddb2d03b9a121ad3ea21c3f..477651f358a29666abfe1a9eb5ab05a753c1c080 100644 (file)
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -1807,6 +1807,15 @@ ftms = {
   };
 };
 
+ftms = {
+  name = is_virtual_base_of;
+  values = {
+    v = 202406;
+    cxxmin = 26;
+    extra_cond = "__has_builtin(__builtin_is_virtual_base_of)";
+  };
+};
+
 ftms = {
   name = ranges_concat;
   values = {

diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index dcd93fd432da7275fb9413eec91dc57de70b72c1..342ee6b4c7a0d2770daf8d87edd91923c66d8f0e 100644 (file)
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2000,6 +2000,16 @@
 #endif /* !defined(__cpp_lib_fstream_native_handle) && defined(__glibcxx_want_fstream_native_handle) */
 #undef __glibcxx_want_fstream_native_handle
 
+#if !defined(__cpp_lib_is_virtual_base_of)
+# if (__cplusplus >  202302L) && (__has_builtin(__builtin_is_virtual_base_of))
+#  define __glibcxx_is_virtual_base_of 202406L
+#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_is_virtual_base_of)
+#   define __cpp_lib_is_virtual_base_of 202406L
+#  endif
+# endif
+#endif /* !defined(__cpp_lib_is_virtual_base_of) && defined(__glibcxx_want_is_virtual_base_of) */
+#undef __glibcxx_want_is_virtual_base_of
+
 #if !defined(__cpp_lib_ranges_concat)
 # if (__cplusplus >  202302L)
 #  define __glibcxx_ranges_concat 202403L

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 6e6778078dcf0286822aa78a44f058a333876bbe..17ae2c435b382e759ef5b8a639bd4689696f9f43 100644 (file)
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -53,6 +53,7 @@
 #define __glibcxx_want_is_pointer_interconvertible
 #define __glibcxx_want_is_scoped_enum
 #define __glibcxx_want_is_swappable
+#define __glibcxx_want_is_virtual_base_of
 #define __glibcxx_want_logical_traits
 #define __glibcxx_want_reference_from_temporary
 #define __glibcxx_want_remove_cvref
@@ -1541,6 +1542,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : public __bool_constant<__is_base_of(_Base, _Derived)>
     { };
 
+#ifdef __cpp_lib_is_virtual_base_of // C++ >= 26
+  /// is_virtual_base_of
+  /// @since C++26
+  template<typename _Base, typename _Derived>
+    struct is_virtual_base_of
+    : public bool_constant<__builtin_is_virtual_base_of(_Base, _Derived)>
+    { };
+#endif
+
 #if _GLIBCXX_USE_BUILTIN_TRAIT(__is_convertible)
   template<typename _From, typename _To>
     struct is_convertible
@@ -3636,6 +3646,10 @@ template <typename _Tp>
 #endif
 template <typename _Base, typename _Derived>
   inline constexpr bool is_base_of_v = __is_base_of(_Base, _Derived);
+#ifdef __cpp_lib_is_virtual_base_of // C++ >= 26
+template <typename _Base, typename _Derived>
+  inline constexpr bool is_virtual_base_of_v = __builtin_is_virtual_base_of(_Base, _Derived);
+#endif
 #if _GLIBCXX_USE_BUILTIN_TRAIT(__is_convertible)
 template <typename _From, typename _To>
   inline constexpr bool is_convertible_v = __is_convertible(_From, _To);

diff --git a/libstdc++-v3/testsuite/20_util/is_virtual_base_of/value.cc b/libstdc++-v3/testsuite/20_util/is_virtual_base_of/value.cc
new file mode 100644 (file)
index 0000000..5d83de0
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_virtual_base_of/value.cc
@@ -0,0 +1,34 @@
+// { dg-do compile { target c++26 } }
+
+#include <type_traits>
+
+#if !defined(__cpp_lib_is_virtual_base_of) || __cpp_lib_is_virtual_base_of < 202406L
+#error "__cpp_lib_is_virtual_base_of should have been defined to 202406L or more"
+#endif
+
+class B { };
+class X : virtual public B { };
+class Y : virtual public B { };
+class Z : public B { };
+class AA : public X, public Y, public Z { };
+
+template<typename Base, typename Derived>
+constexpr bool test()
+{
+  constexpr bool t1 = std::is_virtual_base_of<Base, Derived>::value;
+  constexpr bool t2 = std::is_virtual_base_of_v<Base, Derived>;
+  static_assert(t1 == t2);
+  return t1;
+}
+
+void test01()
+{
+  static_assert(!test<B, B>());
+  static_assert( test<B, X>());
+  static_assert( test<B, Y>());
+  static_assert(!test<B, Z>());
+  static_assert( test<B, AA>());
+  static_assert(!test<X, AA>());
+  static_assert(!test<Y, AA>());
+  static_assert(!test<Z, AA>());
+}