libstdc++: Add comparison operators to std::shared_ptr (PR 94562)

This also implements the proposed resolution to LWG issue 3247, so that
the ill-formed <=> expression with nullptr is not used.

	PR libstdc++/94562
	* include/bits/shared_ptr.h (operator<=>): Define for C++20.
	* include/bits/shared_ptr_base.h (operator<=>): Likewise.
	* include/bits/unique_ptr.h (operator<=>): Add inline specifier.
	* testsuite/20_util/shared_ptr/comparison/cmp_c++20.cc: New test.
	* testsuite/20_util/shared_ptr/comparison/less.cc: Do not expect
	std::less<A*> to be used when comparing std::shared_ptr<A> objects in
	C++20.

6 files changed, 158 insertions, 2 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 085ca6a..417c8c4 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,14 @@
 2020-04-14  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/94562
+	* include/bits/shared_ptr.h (operator<=>): Define for C++20.
+	* include/bits/shared_ptr_base.h (operator<=>): Likewise.
+	* include/bits/unique_ptr.h (operator<=>): Add inline specifier.
+	* testsuite/20_util/shared_ptr/comparison/cmp_c++20.cc: New test.
+	* testsuite/20_util/shared_ptr/comparison/less.cc: Do not expect
+	std::less<A*> to be used when comparing std::shared_ptr<A> objects in
+	C++20.
+
 	PR libstdc++/94565
 	* libsupc++/compare (__unspec): Add noexcept-specifier to constructor.
 	* testsuite/18_support/comparisons/categories/94565.cc: New test.
diff --git a/libstdc++-v3/include/bits/shared_ptr.h b/libstdc++-v3/include/bits/shared_ptr.h
index c4df358..0c393e2 100644
--- a/libstdc++-v3/include/bits/shared_ptr.h
+++ b/libstdc++-v3/include/bits/shared_ptr.h
@@ -442,6 +442,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
     { return !__a; }
 
+#ifdef __cpp_lib_three_way_comparison
+  template<typename _Tp, typename _Up>
+    inline strong_ordering
+    operator<=>(const shared_ptr<_Tp>& __a,
+		const shared_ptr<_Up>& __b) noexcept
+    { return compare_three_way()(__a.get(), __b.get()); }
+
+  template<typename _Tp>
+    inline strong_ordering
+    operator<=>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
+    {
+      using pointer = typename shared_ptr<_Tp>::element_type*;
+      return compare_three_way()(__a.get(), static_cast<pointer>(nullptr));
+    }
+#else
   /// shared_ptr comparison with nullptr
   template<typename _Tp>
     _GLIBCXX_NODISCARD inline bool
@@ -548,6 +563,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     _GLIBCXX_NODISCARD inline bool
     operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     { return !(nullptr < __a); }
+#endif
 
   // 20.7.2.2.8 shared_ptr specialized algorithms.
 
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index c9017ed..ff578e6 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -54,6 +54,9 @@
 #include <bits/refwrap.h>
 #include <bits/stl_function.h>
 #include <ext/aligned_buffer.h>
+#if __cplusplus > 201703L
+# include <compare>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -1442,6 +1445,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator==(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
     { return !__a; }
 
+#ifdef __cpp_lib_three_way_comparison
+  template<typename _Tp, typename _Up, _Lock_policy _Lp>
+    inline strong_ordering
+    operator<=>(const __shared_ptr<_Tp, _Lp>& __a,
+		const __shared_ptr<_Up, _Lp>& __b) noexcept
+    { return compare_three_way()(__a.get(), __b.get()); }
+
+  template<typename _Tp, _Lock_policy _Lp>
+    inline strong_ordering
+    operator<=>(const __shared_ptr<_Tp, _Lp>& __a, nullptr_t) noexcept
+    {
+      using pointer = typename __shared_ptr<_Tp, _Lp>::element_type*;
+      return compare_three_way()(__a.get(), static_cast<pointer>(nullptr));
+    }
+#else
   template<typename _Tp, _Lock_policy _Lp>
     inline bool
     operator==(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
@@ -1537,6 +1555,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline bool
     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
     { return !(nullptr < __a); }
+#endif // three-way comparison
 
   // 20.7.2.2.8 shared_ptr specialized algorithms.
   template<typename _Tp, _Lock_policy _Lp>
diff --git a/libstdc++-v3/include/bits/unique_ptr.h b/libstdc++-v3/include/bits/unique_ptr.h
index 53c8def..3695214 100644
--- a/libstdc++-v3/include/bits/unique_ptr.h
+++ b/libstdc++-v3/include/bits/unique_ptr.h
@@ -888,6 +888,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   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>
+    inline
     compare_three_way_result_t<typename unique_ptr<_Tp, _Dp>::pointer,
 			       typename unique_ptr<_Up, _Ep>::pointer>
     operator<=>(const unique_ptr<_Tp, _Dp>& __x,
@@ -896,11 +897,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _Tp, typename _Dp>
     requires three_way_comparable<typename unique_ptr<_Tp, _Dp>::pointer>
+    inline
     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));
+      return compare_three_way()(__x.get(), static_cast<pointer>(nullptr));
     }
 #endif
   // @} relates unique_ptr
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/cmp_c++20.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/cmp_c++20.cc
new file mode 100644
index 0000000..5600bbf
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/cmp_c++20.cc
@@ -0,0 +1,106 @@
+// 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::shared_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::shared_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::shared_ptr<int> p11 = p1;
+  VERIFY( p11 == p1 );
+  VERIFY( !(p11 < p1) );
+  VERIFY( !(p11 > p1) );
+  VERIFY( p11 <= p1 );
+  VERIFY( p11 >= p1 );
+  VERIFY( std::is_eq(p11 <=> p1) );
+
+  std::shared_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::shared_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::shared_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();
+}
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/less.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/less.cc
index 8b42b3a..9ee65ff 100644
--- a/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/less.cc
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/less.cc
@@ -46,7 +46,11 @@ test01()
   std::shared_ptr<A> p1;
   std::shared_ptr<A> p2;
   VERIFY( !less(p1, p2) && !less(p2, p1) );
+#ifndef __cpp_lib_three_way_comparison
+// In C++20 std::less<std::shared_ptr<A>> uses the operator< synthesized
+// from operator<=>, which uses std::compare_three_way not std::less<A*>.
   VERIFY( std::less<A*>::count == 2 );
+#endif
   return 0;
 }
 
@@ -86,7 +90,7 @@ test03()
 
   return 0;
 }
-int 
+int
 main()
 {
   test01();