Fix after P0600.

gcc/testsuite/ChangeLog
2019-02-20  Ulrich Drepper  <drepper@redhat.com>

	Fix after P0600.
	* g++.dg/init/new39.C: Don't just ignore result of new.

libstdc++/ChangeLog
2019-02-20  Ulrich Drepper  <drepper@redhat.com>

	Implement C++20 P0600r1.
	* include/backward/hash_map: Add nodiscard attribute to empty.
	* include/backward/hash_set: Likewise.
	* backward/hashtable.h: Likewise.
	* include/bits/basic_string.h: Likewise.
	* include/bits/forward_list.h: Likewise.
	* include/bits/hashtable.h: Likewise.
	* include/bits/regex.h: Likewise.
	* include/bits/stl_deque.h: Likewise.
	* include/bits/stl_list.h: Likewise.
	* include/bits/stl_map.h: Likewise.
	* include/bits/stl_multimap.h: Likewise.
	* include/bits/stl_multiset.h: Likewise.
	* include/bits/stl_queue.h: Likewise.
	* include/bits/stl_set.h: Likewise.
	* include/bits/stl_stack.h: Likewise.
	* include/bits/stl_tree.h: Likewise.
	* include/bits/stl_vector.h: Likewise.
	* include/bits/unordered_map.h: Likewise.
	* include/bits/unordered_set.h: Likewise.
	* include/debug/array: Likewise.
	* include/experimental/any: Likewise.
	* include/experimental/bits/fs_path.h: Likewise.
	* include/experimental/internet: Likewise.
	* include/experimental/string_view: Likewise.
	* include/ext/pb_ds/detail/bin_search_tree_/info_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/binary_heap_/binary_heap_.hpp:
	Likewise.
	* include/ext/pb_ds/detail/binary_heap_/info_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/cc_hash_table_map_/cc_ht_map_.hpp:
	Likewise.
	* include/ext/pb_ds/detail/cc_hash_table_map_/info_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/cc_hash_table_map_/size_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/gp_hash_table_map_/gp_ht_map_.hpp:
	Likewise.
	* include/ext/pb_ds/detail/gp_hash_table_map_/info_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/left_child_next_sibling_heap_/info_fn_imps.hpp:
	Likewise.
	*
include/ext/pb_ds/detail/left_child_next_sibling_heap_/left_child_next_sibling_heap_.hpp:
	Likewise.
	* include/ext/pb_ds/detail/list_update_map_/info_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/list_update_map_/lu_map_.hpp:
	Likewise.
	* include/ext/pb_ds/detail/ov_tree_map_/info_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/ov_tree_map_/ov_tree_map_.hp:
	Likewise.
	* include/ext/pb_ds/detail/pat_trie_/info_fn_imps.hpp:
	Likewise.
	* include/ext/pb_ds/detail/pat_trie_/pat_trie_.hpp:
	Likewise.
	* include/ext/pb_ds/detail/rc_binomial_heap_/rc.hpp:
	Likewise.
	* include/ext/pb_ds/detail/tree_trace_base.hpp: Likewise.
	* include/ext/pb_ds/trie_policy.hpp: Likewise.
	* include/ext/rope: Likewise.
	* include/ext/slist: Likewise.
	* include/ext/vstring.h: Likewise.
	* include/profile/array: Likewise.
	* include/std/array: Likewise.
	* include/tr1/array: Likewise.
	* include/tr1/hashtable.h: Likewise.
	* include/tr1/regex: Likewise.
	* include/tr2/dynamic_bitset: Likewise.
	* include/bits/alloc_traits.h: Add nodiscard attribute to
	allocate.
	* include/experimental/memory_resource: Likewise.
	* include/ext/alloc_traits.h: Likewise.
	* include/ext/array_allocator.h: Likewise.
	* include/ext/bitmap_allocator.h: Likewise.
	* include/ext/debug_allocator.h: Likewise.
	* include/ext/extptr_allocator.h: Likewise.
	* include/ext/mt_allocator.h: Likewise.
	* include/ext/new_allocator.h: Likewise.
	* include/ext/pool_allocator.h: Likewise.
	* include/ext/throw_allocator.h: Likewise.
	* include/std/scoped_allocator: Likewise.
	* libsupc++/eh_alloc.cc: Likewise.
	* include/std/future: Add nodiscard attribute to async.
	* libsupc++/new: Add nodiscard attribute to new.

From-SVN: r268111

31 files changed, 38 insertions, 29 deletions

diff --git a/libstdc++-v3/include/ext/alloc_traits.h b/libstdc++-v3/include/ext/alloc_traits.h
index 5571d26..65fa3de 100644
--- a/libstdc++-v3/include/ext/alloc_traits.h
+++ b/libstdc++-v3/include/ext/alloc_traits.h
@@ -128,7 +128,7 @@ template<typename _Alloc, typename = typename _Alloc::value_type>
     typedef typename _Alloc::size_type              size_type;
     typedef typename _Alloc::difference_type        difference_type;
 
-    static pointer
+    _GLIBCXX_NODISCARD static pointer
     allocate(_Alloc& __a, size_type __n)
     { return __a.allocate(__n); }
 
diff --git a/libstdc++-v3/include/ext/array_allocator.h b/libstdc++-v3/include/ext/array_allocator.h
index 6dd23cd..c0d4a34 100644
--- a/libstdc++-v3/include/ext/array_allocator.h
+++ b/libstdc++-v3/include/ext/array_allocator.h
@@ -151,7 +151,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       ~array_allocator() _GLIBCXX_USE_NOEXCEPT { }
 
-      pointer
+      _GLIBCXX_NODISCARD pointer
       allocate(size_type __n, const void* = 0)
       {
 	if (_M_array == 0 || _M_used + __n > _M_array->size())
diff --git a/libstdc++-v3/include/ext/bitmap_allocator.h b/libstdc++-v3/include/ext/bitmap_allocator.h
index 400030b..532bad2 100644
--- a/libstdc++-v3/include/ext/bitmap_allocator.h
+++ b/libstdc++-v3/include/ext/bitmap_allocator.h
@@ -90,7 +90,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	_M_space_left() const throw()
 	{ return _M_end_of_storage - _M_finish; }
 
-	pointer
+	_GLIBCXX_NODISCARD pointer
 	allocate(size_type __n)
 	{ return static_cast<pointer>(::operator new(__n * sizeof(_Tp))); }
 
@@ -1009,7 +1009,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       ~bitmap_allocator() _GLIBCXX_USE_NOEXCEPT
       { }
 
-      pointer 
+      _GLIBCXX_NODISCARD pointer 
       allocate(size_type __n)
       {
 	if (__n > this->max_size())
@@ -1033,7 +1033,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  }
       }
 
-      pointer 
+      _GLIBCXX_NODISCARD pointer 
       allocate(size_type __n, typename bitmap_allocator<void>::const_pointer)
       { return allocate(__n); }
 
diff --git a/libstdc++-v3/include/ext/debug_allocator.h b/libstdc++-v3/include/ext/debug_allocator.h
index bf86470..c5fc57e 100644
--- a/libstdc++-v3/include/ext/debug_allocator.h
+++ b/libstdc++-v3/include/ext/debug_allocator.h
@@ -118,7 +118,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       debug_allocator(const _Alloc& __a)
       : _M_allocator(__a), _M_extra(_S_extra()) { }
 
-      pointer
+      _GLIBCXX_NODISCARD pointer
       allocate(size_type __n)
       {
         pointer __res = _M_allocator.allocate(__n + _M_extra);      
@@ -127,7 +127,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         return __res + _M_extra;
       }
 
-      pointer
+      _GLIBCXX_NODISCARD pointer
       allocate(size_type __n, const void* __hint)
       {
         pointer __res = _M_allocator.allocate(__n + _M_extra, __hint);
diff --git a/libstdc++-v3/include/ext/extptr_allocator.h b/libstdc++-v3/include/ext/extptr_allocator.h
index 388edb2..2ce87b60 100644
--- a/libstdc++-v3/include/ext/extptr_allocator.h
+++ b/libstdc++-v3/include/ext/extptr_allocator.h
@@ -92,7 +92,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       const_pointer address(const_reference __x) const _GLIBCXX_NOEXCEPT
       { return std::__addressof(__x); }
 
-      pointer allocate(size_type __n, void* __hint = 0)
+      _GLIBCXX_NODISCARD pointer allocate(size_type __n, void* __hint = 0)
       { return _M_real_alloc.allocate(__n,__hint); }
 
       void deallocate(pointer __p, size_type __n)
diff --git a/libstdc++-v3/include/ext/mt_allocator.h b/libstdc++-v3/include/ext/mt_allocator.h
index 7b07533..43e84f4 100644
--- a/libstdc++-v3/include/ext/mt_allocator.h
+++ b/libstdc++-v3/include/ext/mt_allocator.h
@@ -665,7 +665,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       ~__mt_alloc() _GLIBCXX_USE_NOEXCEPT { }
 
-      pointer
+      _GLIBCXX_NODISCARD pointer
       allocate(size_type __n, const void* = 0);
 
       void
@@ -684,7 +684,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     };
 
   template<typename _Tp, typename _Poolp>
-    typename __mt_alloc<_Tp, _Poolp>::pointer
+    _GLIBCXX_NODISCARD typename __mt_alloc<_Tp, _Poolp>::pointer
     __mt_alloc<_Tp, _Poolp>::
     allocate(size_type __n, const void*)
     {
diff --git a/libstdc++-v3/include/ext/new_allocator.h b/libstdc++-v3/include/ext/new_allocator.h
index 04db4bb..e245391 100644
--- a/libstdc++-v3/include/ext/new_allocator.h
+++ b/libstdc++-v3/include/ext/new_allocator.h
@@ -98,7 +98,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // NB: __n is permitted to be 0.  The C++ standard says nothing
       // about what the return value is when __n == 0.
-      pointer
+      _GLIBCXX_NODISCARD pointer
       allocate(size_type __n, const void* = static_cast<const void*>(0))
       {
 	if (__n > this->max_size())
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/info_fn_imps.hpp
index 5e73955..4019f86 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/info_fn_imps.hpp
@@ -39,6 +39,7 @@
  */
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/binary_heap_.hpp b/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/binary_heap_.hpp
index 40ddeed5..dbfd612 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/binary_heap_.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/binary_heap_.hpp
@@ -144,7 +144,7 @@ namespace __gnu_pbds
 
       ~binary_heap();
 
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       inline size_type
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/info_fn_imps.hpp
index 29612fa..d81d550 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/binary_heap_/info_fn_imps.hpp
@@ -39,6 +39,7 @@
  */
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/cc_ht_map_.hpp b/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/cc_ht_map_.hpp
index 6706c1a..1a6affc 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/cc_ht_map_.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/cc_ht_map_.hpp
@@ -271,7 +271,7 @@ namespace __gnu_pbds
       max_size() const;
 
       /// True if size() == 0.
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       /// Return current hash_fn.
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/info_fn_imps.hpp
index 7b5318b..9d38890 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/info_fn_imps.hpp
@@ -52,6 +52,7 @@ max_size() const
 { return m_entry_allocator.max_size(); }
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/size_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/size_fn_imps.hpp
index 500b92f..bcc1fc4 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/size_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/cc_hash_table_map_/size_fn_imps.hpp
@@ -46,6 +46,7 @@ size() const
 { return m_num_used_e; }
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/gp_ht_map_.hpp b/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/gp_ht_map_.hpp
index bcac913..90dfd50 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/gp_ht_map_.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/gp_ht_map_.hpp
@@ -279,7 +279,7 @@ namespace __gnu_pbds
       max_size() const;
 
       /// True if size() == 0.
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       /// Return current hash_fn.
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/info_fn_imps.hpp
index 64fa975..464216e 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/gp_hash_table_map_/info_fn_imps.hpp
@@ -52,6 +52,7 @@ max_size() const
 { return s_entry_allocator.max_size(); }
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/info_fn_imps.hpp
index 8d31e5b..d12710a 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/info_fn_imps.hpp
@@ -39,6 +39,7 @@
  */
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/left_child_next_sibling_heap_.hpp b/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/left_child_next_sibling_heap_.hpp
index 746a3d8..32d67eb 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/left_child_next_sibling_heap_.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/left_child_next_sibling_heap_/left_child_next_sibling_heap_.hpp
@@ -144,7 +144,7 @@ namespace __gnu_pbds
 
       ~left_child_next_sibling_heap();
 
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       inline size_type
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/info_fn_imps.hpp
index 2c44a51..5d2e81f 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/info_fn_imps.hpp
@@ -51,6 +51,7 @@ max_size() const
 { return s_entry_allocator.max_size(); }
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/lu_map_.hpp b/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/lu_map_.hpp
index e3539a5..a3c0fb4 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/lu_map_.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/list_update_map_/lu_map_.hpp
@@ -198,7 +198,7 @@ namespace __gnu_pbds
       inline size_type
       max_size() const;
 
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       inline mapped_reference
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/info_fn_imps.hpp
index 26f33bf..81e7305 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/info_fn_imps.hpp
@@ -54,6 +54,7 @@ max_size() const
 { return s_value_alloc.max_size(); }
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/ov_tree_map_.hpp b/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/ov_tree_map_.hpp
index efebc35..0859da1 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/ov_tree_map_.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/ov_tree_map_/ov_tree_map_.hpp
@@ -239,7 +239,7 @@ namespace __gnu_pbds
       inline size_type
       max_size() const;
 
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       inline size_type
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/info_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/info_fn_imps.hpp
index 0f6eaf5..33fc3e1 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/info_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/info_fn_imps.hpp
@@ -39,6 +39,7 @@
  */
 
 PB_DS_CLASS_T_DEC
+_GLIBCXX_NODISCARD
 inline bool
 PB_DS_CLASS_C_DEC::
 empty() const
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/pat_trie_.hpp b/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/pat_trie_.hpp
index 13da3d4..3f7e054 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/pat_trie_.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/pat_trie_/pat_trie_.hpp
@@ -223,7 +223,7 @@ namespace __gnu_pbds
 	    }
 	}
 
-	inline bool
+	_GLIBCXX_NODISCARD inline bool
 	empty() const
 	{ return m_bag.empty(); }
       };
@@ -279,7 +279,7 @@ namespace __gnu_pbds
 
       ~PB_DS_PAT_TRIE_NAME();
 
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       inline size_type
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/rc_binomial_heap_/rc.hpp b/libstdc++-v3/include/ext/pb_ds/detail/rc_binomial_heap_/rc.hpp
index 2d1b4e7..5c996d1 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/rc_binomial_heap_/rc.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/rc_binomial_heap_/rc.hpp
@@ -87,7 +87,7 @@ namespace __gnu_pbds
       inline void
       pop();
 
-      inline bool
+      _GLIBCXX_NODISCARD inline bool
       empty() const;
 
       inline size_type
@@ -178,7 +178,7 @@ namespace __gnu_pbds
     }
 
     template<typename _Node, typename _Alloc>
-    inline bool
+    _GLIBCXX_NODISCARD inline bool
     rc<_Node, _Alloc>::
     empty() const
     {
diff --git a/libstdc++-v3/include/ext/pb_ds/detail/tree_trace_base.hpp b/libstdc++-v3/include/ext/pb_ds/detail/tree_trace_base.hpp
index 980ff97..3b349c7 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/tree_trace_base.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/tree_trace_base.hpp
@@ -80,7 +80,7 @@ namespace __gnu_pbds
       void
       trace_node(node_const_iterator, size_type) const;
 
-      virtual bool
+      _GLIBCXX_NODISCARD virtual bool
       empty() const = 0;
 
       virtual node_const_iterator
diff --git a/libstdc++-v3/include/ext/pb_ds/trie_policy.hpp b/libstdc++-v3/include/ext/pb_ds/trie_policy.hpp
index 0b0683d..9c750aa 100644
--- a/libstdc++-v3/include/ext/pb_ds/trie_policy.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/trie_policy.hpp
@@ -315,7 +315,7 @@ namespace __gnu_pbds
     typedef typename __rebind_ma::reference 		metadata_reference;
 
     /// Returns true if the container is empty.
-    virtual bool
+    _GLIBCXX_NODISCARD virtual bool
     empty() const = 0;
 
     /// Returns the iterator associated with the trie's first element.
diff --git a/libstdc++-v3/include/ext/pool_allocator.h b/libstdc++-v3/include/ext/pool_allocator.h
index 460f55d..4b23727 100644
--- a/libstdc++-v3/include/ext/pool_allocator.h
+++ b/libstdc++-v3/include/ext/pool_allocator.h
@@ -188,7 +188,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       destroy(pointer __p) { __p->~_Tp(); }
 #endif
 
-      pointer
+      _GLIBCXX_NODISCARD pointer
       allocate(size_type __n, const void* = 0);
 
       void
@@ -210,7 +210,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __pool_alloc<_Tp>::_S_force_new;
 
   template<typename _Tp>
-    _Tp*
+    _GLIBCXX_NODISCARD _Tp*
     __pool_alloc<_Tp>::allocate(size_type __n, const void*)
     {
       pointer __ret = 0;
diff --git a/libstdc++-v3/include/ext/rope b/libstdc++-v3/include/ext/rope
index 4cc8285..127d113 100644
--- a/libstdc++-v3/include/ext/rope
+++ b/libstdc++-v3/include/ext/rope
@@ -1797,7 +1797,7 @@ protected:
       static int _S_compare(const _RopeRep* __x, const _RopeRep* __y);
       
     public:
-      bool
+      _GLIBCXX_NODISCARD bool
       empty() const
       { return 0 == this->_M_tree_ptr; }
       
diff --git a/libstdc++-v3/include/ext/slist b/libstdc++-v3/include/ext/slist
index 532235f..3b49ae2 100644
--- a/libstdc++-v3/include/ext/slist
+++ b/libstdc++-v3/include/ext/slist
@@ -458,7 +458,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       max_size() const
       { return size_type(-1); }
 
-      bool
+      _GLIBCXX_NODISCARD bool
       empty() const
       { return this->_M_head._M_next == 0; }
 
diff --git a/libstdc++-v3/include/ext/throw_allocator.h b/libstdc++-v3/include/ext/throw_allocator.h
index 52d58e6..38e80f7 100644
--- a/libstdc++-v3/include/ext/throw_allocator.h
+++ b/libstdc++-v3/include/ext/throw_allocator.h
@@ -829,7 +829,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       address(const_reference __x) const _GLIBCXX_NOEXCEPT
       { return std::__addressof(__x); }
 
-      pointer
+      _GLIBCXX_NODISCARD pointer
       allocate(size_type __n, std::allocator<void>::const_pointer hint = 0)
       {
 	if (__n > this->max_size())
diff --git a/libstdc++-v3/include/ext/vstring.h b/libstdc++-v3/include/ext/vstring.h
index ddffebf..5942218 100644
--- a/libstdc++-v3/include/ext/vstring.h
+++ b/libstdc++-v3/include/ext/vstring.h
@@ -518,7 +518,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns true if the %string is empty.  Equivalent to 
        *  <code>*this == ""</code>.
        */
-      bool
+      _GLIBCXX_NODISCARD bool
       empty() const _GLIBCXX_NOEXCEPT
       { return this->size() == 0; }