commit 5b074864f8c593fd4bccee788a023a37b446b2ed
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Apr 9 21:10:32 2020 +0100

    libstdc++: Add comparison operators to std::unique_ptr
    
    Some more C++20 changes from P1614R2, "The Mothership has Landed".
    
    This includes the proposed resolution for LWG 3426 to fix the three-way
    comparison with nullptr_t.
    
    The existing tests for unique_ptr comparisons don't actually check the
    results, only that the expressions compile and are convertible to bool.
    This also adds a test for the results of those comparisons for C++11 and
    up.
    
            * include/bits/unique_ptr.h (operator<=>): Define for C++20.
            * testsuite/20_util/default_delete/48631_neg.cc: Adjust dg-error line.
            * testsuite/20_util/default_delete/void_neg.cc: Likewise.
            * testsuite/20_util/unique_ptr/comparison/compare.cc: New test.
            * testsuite/20_util/unique_ptr/comparison/compare_c++20.cc: New test.

diff --git a/libstdc++-v3/include/bits/unique_ptr.h b/libstdc++-v3/include/bits/unique_ptr.h
index d03266c1878..53c8def627d 100644
--- a/libstdc++-v3/include/bits/unique_ptr.h
+++ b/libstdc++-v3/include/bits/unique_ptr.h
@@ -37,6 +37,9 @@
 #include <tuple>
 #include <bits/stl_function.h>
 #include <bits/functional_hash.h>
+#if __cplusplus > 201703L
+# include <compare>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -756,6 +759,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator==(const unique_ptr<_Tp, _Dp>& __x, nullptr_t) noexcept
     { return !__x; }
 
+#ifndef __cpp_lib_three_way_comparison
   /// unique_ptr comparison with nullptr
   template<typename _Tp, typename _Dp>
     _GLIBCXX_NODISCARD inline bool
@@ -781,6 +785,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     _GLIBCXX_NODISCARD inline bool
     operator!=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x) noexcept
     { return (bool)__x; }
+#endif // three way comparison
 
   /// Relational operator for unique_ptr objects, compares the owned pointers
   template<typename _Tp, typename _Dp,
@@ -878,6 +883,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     _GLIBCXX_NODISCARD inline bool
     operator>=(nullptr_t, const unique_ptr<_Tp, _Dp>& __x)
     { return !(nullptr < __x); }
+
+#ifdef __cpp_lib_three_way_comparison
+  template<typename _Tp, typename _Dp, typename _Up, typename _Ep>
+    requires three_way_comparable_with<typename unique_ptr<_Tp, _Dp>::pointer,
+				       typename unique_ptr<_Up, _Ep>::pointer>
+    compare_three_way_result_t<typename unique_ptr<_Tp, _Dp>::pointer,
+			       typename unique_ptr<_Up, _Ep>::pointer>
+    operator<=>(const unique_ptr<_Tp, _Dp>& __x,
+		const unique_ptr<_Up, _Ep>& __y)
+    { return compare_three_way()(__x.get(), __y.get()); }
+
+  template<typename _Tp, typename _Dp>
+    requires three_way_comparable<typename unique_ptr<_Tp, _Dp>::pointer>
+    compare_three_way_result_t<typename unique_ptr<_Tp, _Dp>::pointer>
+    operator<=>(const unique_ptr<_Tp, _Dp>& __x, nullptr_t)
+    {
+      using pointer = typename unique_ptr<_Tp, _Dp>::pointer;
+      return compare_three_way()(__x.get(), pointer(nullptr));
+    }
+#endif
   // @} relates unique_ptr
 
   /// @cond undocumented
diff --git a/libstdc++-v3/testsuite/20_util/default_delete/48631_neg.cc b/libstdc++-v3/testsuite/20_util/default_delete/48631_neg.cc
index 57d7e62c310..6da5a52e28b 100644
--- a/libstdc++-v3/testsuite/20_util/default_delete/48631_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/default_delete/48631_neg.cc
@@ -26,4 +26,4 @@ struct D : B { };
 D d;
 std::default_delete<B[]> db;
 typedef decltype(db(&d)) type; // { dg-error "no match" }
-// { dg-error "no type" "" { target *-*-* } 112 }
+// { dg-error "no type" "" { target *-*-* } 115 }
diff --git a/libstdc++-v3/testsuite/20_util/default_delete/void_neg.cc b/libstdc++-v3/testsuite/20_util/default_delete/void_neg.cc
index 0c5a09e1e9d..149b699d106 100644
--- a/libstdc++-v3/testsuite/20_util/default_delete/void_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/default_delete/void_neg.cc
@@ -25,5 +25,5 @@ void test01()
 {
   std::default_delete<void> d;
   d(nullptr);   // { dg-error "here" }
-  // { dg-error "incomplete" "" { target *-*-* } 77 }
+  // { dg-error "incomplete" "" { target *-*-* } 80 }
 }
diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/comparison/compare.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/comparison/compare.cc
new file mode 100644
index 00000000000..e293b27904e
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/unique_ptr/comparison/compare.cc
@@ -0,0 +1,88 @@
+// 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/>.
+
+// { dg-do run { target c++11 } }
+
+#include <memory>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::unique_ptr<int> p0, p00;
+  VERIFY( p0 == p00 );
+  VERIFY( !(p0 < p00) );
+  VERIFY( !(p0 > p00) );
+  VERIFY( p0 <= p00 );
+  VERIFY( p0 >= p00 );
+
+  std::unique_ptr<int> p1(new int(1));
+  VERIFY( p1 == p1 );
+  VERIFY( !(p1 < p1) );
+  VERIFY( !(p1 > p1) );
+  VERIFY( p1 <= p1 );
+  VERIFY( p1 >= p1 );
+
+  std::unique_ptr<const int> p2(new int(1));
+  VERIFY( p1 >= p1 );
+  VERIFY( p1 != p2 );
+  VERIFY( (p1 < p2) || (p1 > p2) );
+  VERIFY( (p1 <= p2) || (p1 >= p2) );
+
+  VERIFY( p1 != p0 );
+  VERIFY( !(p1 < p0) );
+  VERIFY( p1 > p0 );
+  VERIFY( !(p1 <= p0) );
+  VERIFY( p1 >= p0 );
+}
+
+void
+test02()
+{
+  std::unique_ptr<int> p0;
+  VERIFY( p0 == nullptr );
+  VERIFY( !(p0 < nullptr) );
+  VERIFY( !(p0 > nullptr) );
+  VERIFY( p0 <= nullptr );
+  VERIFY( p0 >= nullptr );
+
+  VERIFY( nullptr == p0 );
+  VERIFY( !(nullptr < p0) );
+  VERIFY( !(nullptr > p0) );
+  VERIFY( nullptr <= p0 );
+  VERIFY( nullptr >= p0 );
+
+  std::unique_ptr<int> p1(new int(1));
+  VERIFY( p1 != nullptr );
+  VERIFY( !(p1 < nullptr) );
+  VERIFY( p1 > nullptr );
+  VERIFY( !(p1 <= nullptr) );
+  VERIFY( p1 >= nullptr );
+
+  VERIFY( nullptr != p1 );
+  VERIFY( nullptr < p1 );
+  VERIFY( !(nullptr > p1) );
+  VERIFY( nullptr <= p1 );
+  VERIFY( !(nullptr >= p1) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}
diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/comparison/compare_c++20.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/comparison/compare_c++20.cc
new file mode 100644
index 00000000000..be9819f8de1
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/unique_ptr/comparison/compare_c++20.cc
@@ -0,0 +1,98 @@
+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <memory>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::unique_ptr<int> p0, p00;
+  VERIFY( p0 == p00 );
+  VERIFY( !(p0 < p00) );
+  VERIFY( !(p0 > p00) );
+  VERIFY( p0 <= p00 );
+  VERIFY( p0 >= p00 );
+  VERIFY( std::is_eq(p0 <=> p00) );
+
+  std::unique_ptr<int> p1(new int(1));
+  VERIFY( p1 == p1 );
+  VERIFY( !(p1 < p1) );
+  VERIFY( !(p1 > p1) );
+  VERIFY( p1 <= p1 );
+  VERIFY( p1 >= p1 );
+  VERIFY( std::is_eq(p1 <=> p1) );
+
+  std::unique_ptr<const int> p2(new int(1));
+  VERIFY( p1 >= p1 );
+  VERIFY( p1 != p2 );
+  VERIFY( (p1 < p2) || (p1 > p2) );
+  VERIFY( (p1 <= p2) || (p1 >= p2) );
+  VERIFY( std::is_neq(p1 <=> p2) );
+
+  VERIFY( p1 != p0 );
+  VERIFY( !(p1 < p0) );
+  VERIFY( p1 > p0 );
+  VERIFY( !(p1 <= p0) );
+  VERIFY( p1 >= p0 );
+  VERIFY( std::is_gt(p1 <=> p0) );
+  VERIFY( std::is_lt(p0 <=> p1) );
+}
+
+void
+test02()
+{
+  std::unique_ptr<int> p0;
+  VERIFY( p0 == nullptr );
+  VERIFY( !(p0 < nullptr) );
+  VERIFY( !(p0 > nullptr) );
+  VERIFY( p0 <= nullptr );
+  VERIFY( p0 >= nullptr );
+  VERIFY( std::is_eq(p0 <=> nullptr) );
+
+  VERIFY( nullptr == p0 );
+  VERIFY( !(nullptr < p0) );
+  VERIFY( !(nullptr > p0) );
+  VERIFY( nullptr <= p0 );
+  VERIFY( nullptr >= p0 );
+  VERIFY( std::is_eq(nullptr <=> p0) );
+
+  std::unique_ptr<int> p1(new int(1));
+  VERIFY( p1 != nullptr );
+  VERIFY( !(p1 < nullptr) );
+  VERIFY( p1 > nullptr );
+  VERIFY( !(p1 <= nullptr) );
+  VERIFY( p1 >= nullptr );
+  VERIFY( std::is_gt(p1 <=> nullptr) );
+
+  VERIFY( nullptr != p1 );
+  VERIFY( nullptr < p1 );
+  VERIFY( !(nullptr > p1) );
+  VERIFY( nullptr <= p1 );
+  VERIFY( !(nullptr >= p1) );
+  VERIFY( std::is_lt(nullptr <=> p1) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}