commit c7b591f3868f778ce89b14cbfb81d8e96d0daad2
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Feb 7 20:28:06 2020 +0000

    libstdc++: Add <=> to thread::id
    
            * include/std/thread (thread::id::operator<=>): Define for C++20.
            * testsuite/30_threads/thread/id/70294.cc: Do not take addresses of
            functions in namespace std.
            * testsuite/30_threads/thread/id/operators_c++20.cc: New test.

diff --git a/libstdc++-v3/include/std/thread b/libstdc++-v3/include/std/thread
index b533bca578f..1f9c13ff7d1 100644
--- a/libstdc++-v3/include/std/thread
+++ b/libstdc++-v3/include/std/thread
@@ -45,7 +45,8 @@
 #include <tuple>  // std::tuple
 
 #if __cplusplus > 201703L
-# include <stop_token> // std::stop_source, std::stop_token, std::nostopstate
+# include <compare>	// std::strong_ordering
+# include <stop_token>	// std::stop_source, std::stop_token, std::nostopstate
 #endif
 
 #ifdef _GLIBCXX_USE_NANOSLEEP
@@ -96,17 +97,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     private:
       friend class thread;
-      friend class hash<thread::id>;
+      friend class hash<id>;
 
       friend bool
-      operator==(thread::id __x, thread::id __y) noexcept;
+      operator==(id __x, id __y) noexcept;
 
+#if __cpp_lib_three_way_comparison
+      friend strong_ordering
+      operator<=>(id __x, id __y) noexcept;
+#else
       friend bool
-      operator<(thread::id __x, thread::id __y) noexcept;
+      operator<(id __x, id __y) noexcept;
+#endif
 
       template<class _CharT, class _Traits>
 	friend basic_ostream<_CharT, _Traits>&
-	operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id);
+	operator<<(basic_ostream<_CharT, _Traits>& __out, id __id);
     };
 
   private:
@@ -180,7 +186,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     void
     detach();
 
-    thread::id
+    id
     get_id() const noexcept
     { return _M_id; }
 
@@ -296,6 +302,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     return __x._M_thread == __y._M_thread;
   }
 
+#if __cpp_lib_three_way_comparison
+  inline strong_ordering
+  operator<=>(thread::id __x, thread::id __y) noexcept
+  { return __x._M_thread <=> __y._M_thread; }
+#else
   inline bool
   operator!=(thread::id __x, thread::id __y) noexcept
   { return !(__x == __y); }
@@ -319,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   inline bool
   operator>=(thread::id __x, thread::id __y) noexcept
   { return !(__x < __y); }
+#endif // __cpp_lib_three_way_comparison
 
   // DR 889.
   /// std::hash specialization for thread::id.
@@ -424,8 +436,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   class jthread
   {
   public:
-    using id = std::thread::id;
-    using native_handle_type = std::thread::native_handle_type;
+    using id = thread::id;
+    using native_handle_type = thread::native_handle_type;
 
     jthread() noexcept
     : _M_stop_source{nostopstate}
@@ -498,7 +510,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     [[nodiscard]] static unsigned
     hardware_concurrency() noexcept
     {
-      return std::thread::hardware_concurrency();
+      return thread::hardware_concurrency();
     }
 
     [[nodiscard]] stop_source
@@ -544,7 +556,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
     stop_source _M_stop_source;
-    std::thread _M_thread;
+    thread _M_thread;
   };
 #endif // __cpp_lib_jthread
 _GLIBCXX_END_NAMESPACE_VERSION
diff --git a/libstdc++-v3/testsuite/30_threads/thread/id/70294.cc b/libstdc++-v3/testsuite/30_threads/thread/id/70294.cc
index ac3b58afa75..d9c61f74351 100644
--- a/libstdc++-v3/testsuite/30_threads/thread/id/70294.cc
+++ b/libstdc++-v3/testsuite/30_threads/thread/id/70294.cc
@@ -19,5 +19,14 @@
 
 #include <thread>
 
-bool (*lt)(std::thread::id, std::thread::id) = &std::operator<;
-bool (*eq)(std::thread::id, std::thread::id) = &std::operator==;
+struct T
+{
+  operator std::thread::id() const;
+} const t;
+
+using namespace std;
+
+// std::thread::id comparison operators are not hidden friends,
+// so should be candidates for these expressions:
+bool lt = t < t;
+bool eq = t == t;
diff --git a/libstdc++-v3/testsuite/30_threads/thread/id/operators.cc b/libstdc++-v3/testsuite/30_threads/thread/id/operators.cc
index fb6440bfc3d..3d84afafd15 100644
--- a/libstdc++-v3/testsuite/30_threads/thread/id/operators.cc
+++ b/libstdc++-v3/testsuite/30_threads/thread/id/operators.cc
@@ -20,16 +20,26 @@
 
 #include <thread>
 
+template<typename Expected, typename T>
+  struct check_type
+  : std::false_type
+  { };
+
+template<typename Expected>
+  struct check_type<Expected, Expected>
+  : std::true_type
+  { };
+
 void test01()
 {
   // thread::id operators
   std::thread::id id1;
   std::thread::id id2;
 
-  id1 == id2;
-  id1 != id2;
-  id1 < id2;
-  id1 > id2;
-  id1 >= id2;
-  id1 <= id2;
+  static_assert( check_type<bool, decltype(id1 == id2)>{} );
+  static_assert( check_type<bool, decltype(id1 != id2)>{} );
+  static_assert( check_type<bool, decltype(id1 < id2)>{} );
+  static_assert( check_type<bool, decltype(id1 > id2)>{} );
+  static_assert( check_type<bool, decltype(id1 >= id2)>{} );
+  static_assert( check_type<bool, decltype(id1 <= id2)>{} );
 }
diff --git a/libstdc++-v3/testsuite/30_threads/thread/id/operators_c++20.cc b/libstdc++-v3/testsuite/30_threads/thread/id/operators_c++20.cc
new file mode 100644
index 00000000000..6094b0e1501
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/thread/id/operators_c++20.cc
@@ -0,0 +1,48 @@
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+// { dg-require-gthreads "" }
+
+// 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 <thread>
+
+template<typename Expected, typename T>
+  struct check_type
+  : std::false_type
+  { };
+
+template<typename Expected>
+  struct check_type<Expected, Expected>
+  : std::true_type
+  { };
+
+void test01()
+{
+  // thread::id operators
+  std::thread::id id1;
+  std::thread::id id2;
+
+  static_assert( check_type<bool, decltype(id1 == id2)>{} );
+  static_assert( check_type<bool, decltype(id1 != id2)>{} );
+  static_assert( check_type<bool, decltype(id1 < id2)>{} );
+  static_assert( check_type<bool, decltype(id1 > id2)>{} );
+  static_assert( check_type<bool, decltype(id1 >= id2)>{} );
+  static_assert( check_type<bool, decltype(id1 <= id2)>{} );
+
+  static_assert( check_type<std::strong_ordering, decltype(id1 <=> id2)>{} );
+}