libstdc++: Add spaceship operator to std::type_index

Another C++20 change from P1614R2, "The Mothership has Landed".

	* include/std/typeindex (operator<=>): Define for C++20.
	* testsuite/20_util/typeindex/comparison_operators_c++20.cc: New test.

libstdc++-v3/ChangeLog

+2020-04-15  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/typeindex (operator<=>): Define for C++20.
+	* testsuite/20_util/typeindex/comparison_operators_c++20.cc: New test.
+
 2020-04-14  Jonathan Wakely  <jwakely@redhat.com>
 
 	* libsupc++/compare (compare_three_way): Fix constraint so that

libstdc++-v3/include/std/typeindex

@@ -36,6 +36,9 @@
 #else
 
 #include <typeinfo>
+#if __cplusplus > 201703L
+# include <compare>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -58,9 +61,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator==(const type_index& __rhs) const noexcept
     { return *_M_target == *__rhs._M_target; }
 
+#if ! __cpp_lib_three_way_comparison
     bool
     operator!=(const type_index& __rhs) const noexcept
     { return *_M_target != *__rhs._M_target; }
+#endif
 
     bool
     operator<(const type_index& __rhs) const noexcept
@@ -78,6 +83,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator>=(const type_index& __rhs) const noexcept
     { return !_M_target->before(*__rhs._M_target); }
 
+#if __cpp_lib_three_way_comparison
+    strong_ordering
+    operator<=>(const type_index& __rhs) const noexcept
+    {
+      if (*_M_target == *__rhs._M_target)
+	return strong_ordering::equal;
+      if (_M_target->before(*__rhs._M_target))
+	return strong_ordering::less;
+      return strong_ordering::greater;
+    }
+#endif
+
     size_t
     hash_code() const noexcept
     { return _M_target->hash_code(); }

libstdc++-v3/testsuite/20_util/typeindex/comparison_operators_c++20.cc

+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <typeindex>
+#include <testsuite_hooks.h>
+
+void test01()
+{
+  class Abraca { };
+  Abraca a1, a2_;
+  const Abraca a2 = a2_;
+
+  const std::type_index arr[] = {
+    typeid(int), typeid(double), typeid(Abraca), typeid(const Abraca),
+    typeid(const Abraca&), typeid(a1), typeid(a2)
+  };
+
+  for (const std::type_index& t1 : arr)
+    for (const std::type_index& t2 : arr)
+    {
+      VERIFY( (t1 == t2) == std::is_eq(t1 <=> t2) );
+      VERIFY( (t1 != t2) == std::is_neq(t1 <=> t2) );
+      VERIFY( (t1 < t2) == std::is_lt(t1 <=> t2) );
+      VERIFY( (t1 > t2) == std::is_gt(t1 <=> t2) );
+      VERIFY( (t1 <= t2) == std::is_lteq(t1 <=> t2) );
+      VERIFY( (t1 >= t2) == std::is_gteq(t1 <=> t2) );
+    }
+}
+
+int main()
+{
+  test01();
+}