PR libstdc++/86537 remove less<shared_ptr<T>> partial specialization

Message ID 20180716171339.GA9544@redhat.com
State New
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Series
  • PR libstdc++/86537 remove less<shared_ptr<T>> partial specialization
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Commit Message

Jonathan Wakely July 16, 2018, 5:13 p.m.
The standard doesn't specify this partial specialization (it was
required after the changes in N2637 but then should have been removed
following LWG 1262). Its presence is observable because it causes
different results when operator< has been overloaded for a shared_ptr
specialization.

	PR libstdc++/86537
	* include/bits/shared_ptr.h (less<shared_ptr<_Tp>>): Remove
	non-standard partial specialization.
	* include/bits/shared_ptr_base.h (_Sp_less): Remove class definition.
	(less<__shared_ptr<_Tp, _Lp>): Remove partial specialization.
	* testsuite/20_util/shared_ptr/comparison/86537.cc: New test.

Tested powerpc64le-linux, committed to trunk.
commit 1c48999500e277c2ff1e742214857faef842f80c
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jul 16 16:52:19 2018 +0100

    PR libstdc++/86537 remove less<shared_ptr<T>> partial specialization
    
    The standard doesn't specify this partial specialization (it was
    required after the changes in N2637 but then should have been removed
    following LWG 1262). Its presence is observable because it causes
    different results when operator< has been overloaded for a shared_ptr
    specialization.
    
            PR libstdc++/86537
            * include/bits/shared_ptr.h (less<shared_ptr<_Tp>>): Remove
            non-standard partial specialization.
            * include/bits/shared_ptr_base.h (_Sp_less): Remove class definition.
            (less<__shared_ptr<_Tp, _Lp>): Remove partial specialization.
            * testsuite/20_util/shared_ptr/comparison/86537.cc: New test.

Patch

diff --git a/libstdc++-v3/include/bits/shared_ptr.h b/libstdc++-v3/include/bits/shared_ptr.h
index 2a54145083d..2a82f186328 100644
--- a/libstdc++-v3/include/bits/shared_ptr.h
+++ b/libstdc++-v3/include/bits/shared_ptr.h
@@ -480,10 +480,6 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
     { return !(nullptr < __a); }
 
-  template<typename _Tp>
-    struct less<shared_ptr<_Tp>> : public _Sp_less<shared_ptr<_Tp>>
-    { };
-
   // 20.7.2.2.8 shared_ptr specialized algorithms.
   template<typename _Tp>
     inline void
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index 887edbd7879..f3994da158f 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -1502,22 +1502,6 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     operator>=(nullptr_t, const __shared_ptr<_Tp, _Lp>& __a) noexcept
     { return !(nullptr < __a); }
 
-  template<typename _Sp>
-    struct _Sp_less : public binary_function<_Sp, _Sp, bool>
-    {
-      bool
-      operator()(const _Sp& __lhs, const _Sp& __rhs) const noexcept
-      {
-	typedef typename _Sp::element_type element_type;
-	return std::less<element_type*>()(__lhs.get(), __rhs.get());
-      }
-    };
-
-  template<typename _Tp, _Lock_policy _Lp>
-    struct less<__shared_ptr<_Tp, _Lp>>
-    : public _Sp_less<__shared_ptr<_Tp, _Lp>>
-    { };
-
   // 20.7.2.2.8 shared_ptr specialized algorithms.
   template<typename _Tp, _Lock_policy _Lp>
     inline void
diff --git a/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/86537.cc b/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/86537.cc
new file mode 100644
index 00000000000..c8440a38ad0
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/shared_ptr/comparison/86537.cc
@@ -0,0 +1,69 @@ 
+// Copyright (C) 2018 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>
+
+struct Should_not_happen { };
+
+struct X { };
+
+namespace std {
+  template<> struct less<X*> {
+    bool operator()(X*, X*) const { throw Should_not_happen(); }
+  };
+}
+
+bool custom_op_called = false;
+
+bool
+operator<(const std::shared_ptr<X>&, const std::shared_ptr<X>&)
+{
+  custom_op_called = true;
+  return false;
+}
+
+void
+test01()
+{
+  const std::shared_ptr<X> sp;
+  bool b = sp < sp;
+  VERIFY( !b );
+  VERIFY( custom_op_called );
+
+  std::less<std::shared_ptr<X>> lt;
+  custom_op_called = false;
+  b = lt(sp, sp);
+  VERIFY( !b );
+  VERIFY( custom_op_called ); // PR libstdc++/86537 and LWG DR 1262
+
+#if __cplusplus >= 201402L
+  std::less<> ltv;
+  custom_op_called = false;
+  b = ltv(sp, sp);
+  VERIFY( !b );
+  VERIFY( custom_op_called );
+#endif
+}
+
+int
+main()
+{
+  test01();
+}