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* [committed 1/2] libstdc++: Add [[nodiscard]] to iterators and related utilities
@ 2021-08-04 11:55 Jonathan Wakely
  2021-08-04 11:56 ` [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers Jonathan Wakely
  2021-08-05 14:19 ` [committed] libstdc++: Move attributes that follow requires-clauses [PR101782] Jonathan Wakely
  0 siblings, 2 replies; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-04 11:55 UTC (permalink / raw)
  To: libstdc++, gcc-patches

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This adds [[nodiscard]] throughout <iterator>, as proposed by P2377R0
(with some minor corrections).

The attribute is added for all modes from C++11 up, using
[[__nodiscard__]] or _GLIBCXX_NODISCARD where C++17 [[nodiscard]] can't
be used directly.



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commit 240b01b0215f9e46ecf04267c8a3faeb19d4fe3c
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Aug 3 18:06:27 2021

    libstdc++: Add [[nodiscard]] to iterators and related utilities
    
    This adds [[nodiscard]] throughout <iterator>, as proposed by P2377R0
    (with some minor corrections).
    
    The attribute is added for all modes from C++11 up, using
    [[__nodiscard__]] or _GLIBCXX_NODISCARD where C++17 [[nodiscard]] can't
    be used directly.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/iterator_concepts.h (iter_move): Add
            [[nodiscard]].
            * include/bits/range_access.h (begin, end, cbegin, cend)
            (rbegin, rend, crbegin, crend, size, data, ssize): Likewise.
            * include/bits/ranges_base.h (ranges::begin, ranges::end)
            (ranges::cbegin, ranges::cend, ranges::rbegin, ranges::rend)
            (ranges::crbegin, ranges::crend, ranges::size, ranges::ssize)
            (ranges::empty, ranges::data, ranges::cdata): Likewise.
            * include/bits/stl_iterator.h (reverse_iterator, __normal_iterator)
            (back_insert_iterator, front_insert_iterator, insert_iterator)
            (move_iterator, move_sentinel, common_iterator)
            (counted_iterator): Likewise.
            * include/bits/stl_iterator_base_funcs.h (distance, next, prev):
            Likewise.
            * include/bits/stream_iterator.h (istream_iterator)
            (ostream_iterartor): Likewise.
            * include/bits/streambuf_iterator.h (istreambuf_iterator)
            (ostreambuf_iterator): Likewise.
            * include/std/ranges (views::single, views::iota, views::all)
            (views::filter, views::transform, views::take, views::take_while)
            (views::drop, views::drop_while, views::join, views::lazy_split)
            (views::split, views::counted, views::common, views::reverse)
            (views::elements): Likewise.
            * testsuite/20_util/rel_ops.cc: Use -Wno-unused-result.
            * testsuite/24_iterators/move_iterator/greedy_ops.cc: Likewise.
            * testsuite/24_iterators/normal_iterator/greedy_ops.cc:
            Likewise.
            * testsuite/24_iterators/reverse_iterator/2.cc: Likewise.
            * testsuite/24_iterators/reverse_iterator/greedy_ops.cc:
            Likewise.
            * testsuite/21_strings/basic_string/range_access/char/1.cc:
            Cast result to void.
            * testsuite/21_strings/basic_string/range_access/wchar_t/1.cc:
            Likewise.
            * testsuite/21_strings/basic_string_view/range_access/char/1.cc:
            Likewise.
            * testsuite/21_strings/basic_string_view/range_access/wchar_t/1.cc:
            Likewise.
            * testsuite/23_containers/array/range_access.cc: Likewise.
            * testsuite/23_containers/deque/range_access.cc: Likewise.
            * testsuite/23_containers/forward_list/range_access.cc:
            Likewise.
            * testsuite/23_containers/list/range_access.cc: Likewise.
            * testsuite/23_containers/map/range_access.cc: Likewise.
            * testsuite/23_containers/multimap/range_access.cc: Likewise.
            * testsuite/23_containers/multiset/range_access.cc: Likewise.
            * testsuite/23_containers/set/range_access.cc: Likewise.
            * testsuite/23_containers/unordered_map/range_access.cc:
            Likewise.
            * testsuite/23_containers/unordered_multimap/range_access.cc:
            Likewise.
            * testsuite/23_containers/unordered_multiset/range_access.cc:
            Likewise.
            * testsuite/23_containers/unordered_set/range_access.cc:
            Likewise.
            * testsuite/23_containers/vector/range_access.cc: Likewise.
            * testsuite/24_iterators/customization_points/iter_move.cc:
            Likewise.
            * testsuite/24_iterators/istream_iterator/sentinel.cc:
            Likewise.
            * testsuite/24_iterators/istreambuf_iterator/sentinel.cc:
            Likewise.
            * testsuite/24_iterators/move_iterator/dr2061.cc: Likewise.
            * testsuite/24_iterators/operations/prev_neg.cc: Likewise.
            * testsuite/24_iterators/ostreambuf_iterator/2.cc: Likewise.
            * testsuite/24_iterators/range_access/range_access.cc:
            Likewise.
            * testsuite/24_iterators/range_operations/100768.cc: Likewise.
            * testsuite/26_numerics/valarray/range_access2.cc: Likewise.
            * testsuite/28_regex/range_access.cc: Likewise.
            * testsuite/experimental/string_view/range_access/char/1.cc:
            Likewise.
            * testsuite/experimental/string_view/range_access/wchar_t/1.cc:
            Likewise.
            * testsuite/ext/vstring/range_access.cc: Likewise.
            * testsuite/std/ranges/adaptors/take.cc: Likewise.
            * testsuite/std/ranges/p2259.cc: Likewise.

diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
index 9c28ebfb345..739017aaaad 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -120,6 +120,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  using __type = typename __result<_Tp>::type;
 
 	template<std::__detail::__dereferenceable _Tp>
+	  [[nodiscard]]
 	  constexpr __type<_Tp>
 	  operator()(_Tp&& __e) const
 	  noexcept(_S_noexcept<_Tp>())
diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index 71ad28c3ab0..ab2d4f8652c 100644
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/libstdc++-v3/include/bits/range_access.h
@@ -47,6 +47,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     begin(_Container& __cont) -> decltype(__cont.begin())
     { return __cont.begin(); }
@@ -57,6 +58,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     begin(const _Container& __cont) -> decltype(__cont.begin())
     { return __cont.begin(); }
@@ -67,6 +69,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     end(_Container& __cont) -> decltype(__cont.end())
     { return __cont.end(); }
@@ -77,6 +80,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     end(const _Container& __cont) -> decltype(__cont.end())
     { return __cont.end(); }
@@ -86,6 +90,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __arr  Array.
    */
   template<typename _Tp, size_t _Nm>
+    [[__nodiscard__]]
     inline _GLIBCXX14_CONSTEXPR _Tp*
     begin(_Tp (&__arr)[_Nm]) noexcept
     { return __arr; }
@@ -96,6 +101,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __arr  Array.
    */
   template<typename _Tp, size_t _Nm>
+    [[__nodiscard__]]
     inline _GLIBCXX14_CONSTEXPR _Tp*
     end(_Tp (&__arr)[_Nm]) noexcept
     { return __arr + _Nm; }
@@ -115,6 +121,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline constexpr auto
     cbegin(const _Container& __cont) noexcept(noexcept(std::begin(__cont)))
       -> decltype(std::begin(__cont))
@@ -126,6 +133,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline constexpr auto
     cend(const _Container& __cont) noexcept(noexcept(std::end(__cont)))
       -> decltype(std::end(__cont))
@@ -137,6 +145,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     rbegin(_Container& __cont) -> decltype(__cont.rbegin())
     { return __cont.rbegin(); }
@@ -147,6 +156,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     rbegin(const _Container& __cont) -> decltype(__cont.rbegin())
     { return __cont.rbegin(); }
@@ -157,6 +167,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     rend(_Container& __cont) -> decltype(__cont.rend())
     { return __cont.rend(); }
@@ -167,6 +178,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     rend(const _Container& __cont) -> decltype(__cont.rend())
     { return __cont.rend(); }
@@ -177,6 +189,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __arr  Array.
    */
   template<typename _Tp, size_t _Nm>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Tp*>
     rbegin(_Tp (&__arr)[_Nm]) noexcept
     { return reverse_iterator<_Tp*>(__arr + _Nm); }
@@ -187,6 +200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __arr  Array.
    */
   template<typename _Tp, size_t _Nm>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Tp*>
     rend(_Tp (&__arr)[_Nm]) noexcept
     { return reverse_iterator<_Tp*>(__arr); }
@@ -197,6 +211,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __il  initializer_list.
    */
   template<typename _Tp>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR reverse_iterator<const _Tp*>
     rbegin(initializer_list<_Tp> __il) noexcept
     { return reverse_iterator<const _Tp*>(__il.end()); }
@@ -207,6 +222,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __il  initializer_list.
    */
   template<typename _Tp>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR reverse_iterator<const _Tp*>
     rend(initializer_list<_Tp> __il) noexcept
     { return reverse_iterator<const _Tp*>(__il.begin()); }
@@ -217,6 +233,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     crbegin(const _Container& __cont) -> decltype(std::rbegin(__cont))
     { return std::rbegin(__cont); }
@@ -227,6 +244,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template<typename _Container>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     crend(const _Container& __cont) -> decltype(std::rend(__cont))
     { return std::rend(__cont); }
@@ -241,6 +259,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template <typename _Container>
+    [[nodiscard]]
     constexpr auto
     size(const _Container& __cont) noexcept(noexcept(__cont.size()))
     -> decltype(__cont.size())
@@ -250,6 +269,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @brief  Return the size of an array.
    */
   template <typename _Tp, size_t _Nm>
+    [[nodiscard]]
     constexpr size_t
     size(const _Tp (&)[_Nm]) noexcept
     { return _Nm; }
@@ -286,6 +306,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template <typename _Container>
+    [[nodiscard]]
     constexpr auto
     data(_Container& __cont) noexcept(noexcept(__cont.data()))
     -> decltype(__cont.data())
@@ -296,6 +317,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __cont  Container.
    */
   template <typename _Container>
+    [[nodiscard]]
     constexpr auto
     data(const _Container& __cont) noexcept(noexcept(__cont.data()))
     -> decltype(__cont.data())
@@ -306,6 +328,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __array  Array.
    */
   template <typename _Tp, size_t _Nm>
+    [[nodiscard]]
     constexpr _Tp*
     data(_Tp (&__array)[_Nm]) noexcept
     { return __array; }
@@ -315,6 +338,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @param  __il  Initializer list.
    */
   template <typename _Tp>
+    [[nodiscard]]
     constexpr const _Tp*
     data(initializer_list<_Tp> __il) noexcept
     { return __il.begin(); }
@@ -322,6 +346,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if __cplusplus > 201703L
 #define __cpp_lib_ssize 201902L
   template<typename _Container>
+    [[nodiscard]]
     constexpr auto
     ssize(const _Container& __cont)
     noexcept(noexcept(__cont.size()))
@@ -332,6 +357,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, ptrdiff_t _Num>
+    [[nodiscard]]
     constexpr ptrdiff_t
     ssize(const _Tp (&)[_Num]) noexcept
     { return _Num; }
diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index 9d749c8d9b7..614b6edf9df 100644
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -110,6 +110,7 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires is_array_v<remove_reference_t<_Tp>> || __member_begin<_Tp>
 	  || __adl_begin<_Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
@@ -161,6 +162,7 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_end<_Tp> || __adl_end<_Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
@@ -192,6 +194,7 @@ namespace ranges
     struct _CBegin
     {
       template<typename _Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __e) const
 	noexcept(noexcept(_Begin{}(__cust_access::__as_const<_Tp>(__e))))
@@ -204,6 +207,7 @@ namespace ranges
     struct _CEnd final
     {
       template<typename _Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __e) const
 	noexcept(noexcept(_End{}(__cust_access::__as_const<_Tp>(__e))))
@@ -263,6 +267,7 @@ namespace ranges
     public:
       template<__maybe_borrowed_range _Tp>
 	requires __member_rbegin<_Tp> || __adl_rbegin<_Tp> || __reversable<_Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
@@ -321,6 +326,7 @@ namespace ranges
     public:
       template<__maybe_borrowed_range _Tp>
 	requires __member_rend<_Tp> || __adl_rend<_Tp> || __reversable<_Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
@@ -337,6 +343,7 @@ namespace ranges
     struct _CRBegin
     {
       template<typename _Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __e) const
 	noexcept(noexcept(_RBegin{}(__cust_access::__as_const<_Tp>(__e))))
@@ -349,6 +356,7 @@ namespace ranges
     struct _CREnd
     {
       template<typename _Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __e) const
 	noexcept(noexcept(_REnd{}(__cust_access::__as_const<_Tp>(__e))))
@@ -408,6 +416,7 @@ namespace ranges
       template<typename _Tp>
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_size<_Tp> || __adl_size<_Tp> || __sentinel_size<_Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
@@ -428,6 +437,7 @@ namespace ranges
       // 3403. Domain of ranges::ssize(E) doesn't match ranges::size(E)
       template<typename _Tp>
 	requires requires (_Tp& __t) { _Size{}(__t); }
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
 	{
@@ -487,6 +497,7 @@ namespace ranges
       template<typename _Tp>
 	requires __member_empty<_Tp> || __size0_empty<_Tp>
 	  || __eq_iter_empty<_Tp>
+	[[nodiscard]]
 	constexpr bool
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
@@ -528,6 +539,7 @@ namespace ranges
     public:
       template<__maybe_borrowed_range _Tp>
 	requires __member_data<_Tp> || __begin_data<_Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp>())
 	{
@@ -541,6 +553,7 @@ namespace ranges
     struct _CData
     {
       template<typename _Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __e) const
 	noexcept(noexcept(_Data{}(__cust_access::__as_const<_Tp>(__e))))
@@ -782,6 +795,7 @@ namespace ranges
   struct __distance_fn final
   {
     template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+      [[nodiscard]]
       constexpr iter_difference_t<_It>
       operator()(_It __first, _Sent __last) const
       {
@@ -800,6 +814,7 @@ namespace ranges
       }
 
     template<range _Range>
+      [[nodiscard]]
       constexpr range_difference_t<_Range>
       operator()(_Range&& __r) const
       {
@@ -817,6 +832,7 @@ namespace ranges
   struct __next_fn final
   {
     template<input_or_output_iterator _It>
+      [[nodiscard]]
       constexpr _It
       operator()(_It __x) const
       {
@@ -825,6 +841,7 @@ namespace ranges
       }
 
     template<input_or_output_iterator _It>
+      [[nodiscard]]
       constexpr _It
       operator()(_It __x, iter_difference_t<_It> __n) const
       {
@@ -833,6 +850,7 @@ namespace ranges
       }
 
     template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+      [[nodiscard]]
       constexpr _It
       operator()(_It __x, _Sent __bound) const
       {
@@ -841,6 +859,7 @@ namespace ranges
       }
 
     template<input_or_output_iterator _It, sentinel_for<_It> _Sent>
+      [[nodiscard]]
       constexpr _It
       operator()(_It __x, iter_difference_t<_It> __n, _Sent __bound) const
       {
@@ -856,6 +875,7 @@ namespace ranges
   struct __prev_fn final
   {
     template<bidirectional_iterator _It>
+      [[nodiscard]]
       constexpr _It
       operator()(_It __x) const
       {
@@ -864,6 +884,7 @@ namespace ranges
       }
 
     template<bidirectional_iterator _It>
+      [[nodiscard]]
       constexpr _It
       operator()(_It __x, iter_difference_t<_It> __n) const
       {
@@ -872,6 +893,7 @@ namespace ranges
       }
 
     template<bidirectional_iterator _It>
+      [[nodiscard]]
       constexpr _It
       operator()(_It __x, iter_difference_t<_It> __n, _It __bound) const
       {
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 7fe727d8093..3773d600b8f 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -223,6 +223,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       /**
        *  @return  @c current, the %iterator used for underlying work.
       */
+      _GLIBCXX_NODISCARD
       _GLIBCXX17_CONSTEXPR iterator_type
       base() const
       { return current; }
@@ -237,6 +238,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *           @c *x remains valid after @c x has been modified or
        *           destroyed. This is a bug: http://gcc.gnu.org/PR51823
       */
+      _GLIBCXX_NODISCARD
       _GLIBCXX17_CONSTEXPR reference
       operator*() const
       {
@@ -249,6 +251,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *
        *  This requires that @c --current is dereferenceable.
       */
+      _GLIBCXX_NODISCARD
       _GLIBCXX17_CONSTEXPR pointer
       operator->() const
 #if __cplusplus > 201703L && __cpp_concepts >= 201907L
@@ -318,6 +321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *
        *  The underlying iterator must be a Random Access Iterator.
       */
+      _GLIBCXX_NODISCARD
       _GLIBCXX17_CONSTEXPR reverse_iterator
       operator+(difference_type __n) const
       { return reverse_iterator(current - __n); }
@@ -340,6 +344,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *
        *  The underlying iterator must be a Random Access Iterator.
       */
+      _GLIBCXX_NODISCARD
       _GLIBCXX17_CONSTEXPR reverse_iterator
       operator-(difference_type __n) const
       { return reverse_iterator(current + __n); }
@@ -362,11 +367,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *
        *  The underlying iterator must be a Random Access Iterator.
       */
+      _GLIBCXX_NODISCARD
       _GLIBCXX17_CONSTEXPR reference
       operator[](difference_type __n) const
       { return *(*this + __n); }
 
 #if __cplusplus > 201703L && __cpp_lib_concepts
+      [[nodiscard]]
       friend constexpr iter_rvalue_reference_t<_Iterator>
       iter_move(const reverse_iterator& __i)
       noexcept(is_nothrow_copy_constructible_v<_Iterator>
@@ -415,36 +422,42 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   */
 #if __cplusplus <= 201703L || ! defined __cpp_lib_concepts
   template<typename _Iterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator==(const reverse_iterator<_Iterator>& __x,
 	       const reverse_iterator<_Iterator>& __y)
     { return __x.base() == __y.base(); }
 
   template<typename _Iterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator<(const reverse_iterator<_Iterator>& __x,
 	      const reverse_iterator<_Iterator>& __y)
     { return __y.base() < __x.base(); }
 
   template<typename _Iterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator!=(const reverse_iterator<_Iterator>& __x,
 	       const reverse_iterator<_Iterator>& __y)
     { return !(__x == __y); }
 
   template<typename _Iterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator>(const reverse_iterator<_Iterator>& __x,
 	      const reverse_iterator<_Iterator>& __y)
     { return __y < __x; }
 
   template<typename _Iterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator<=(const reverse_iterator<_Iterator>& __x,
 	       const reverse_iterator<_Iterator>& __y)
     { return !(__y < __x); }
 
   template<typename _Iterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator>=(const reverse_iterator<_Iterator>& __x,
 	       const reverse_iterator<_Iterator>& __y)
@@ -454,24 +467,28 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // DR 280. Comparison of reverse_iterator to const reverse_iterator.
 
   template<typename _IteratorL, typename _IteratorR>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator==(const reverse_iterator<_IteratorL>& __x,
 	       const reverse_iterator<_IteratorR>& __y)
     { return __x.base() == __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator<(const reverse_iterator<_IteratorL>& __x,
 	      const reverse_iterator<_IteratorR>& __y)
     { return __x.base() > __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator!=(const reverse_iterator<_IteratorL>& __x,
 	       const reverse_iterator<_IteratorR>& __y)
     { return __x.base() != __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator>(const reverse_iterator<_IteratorL>& __x,
 	      const reverse_iterator<_IteratorR>& __y)
@@ -484,12 +501,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() >= __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR bool
     operator>=(const reverse_iterator<_IteratorL>& __x,
 	       const reverse_iterator<_IteratorR>& __y)
     { return __x.base() <= __y.base(); }
 #else // C++20
   template<typename _IteratorL, typename _IteratorR>
+    [[nodiscard]]
     constexpr bool
     operator==(const reverse_iterator<_IteratorL>& __x,
 	       const reverse_iterator<_IteratorR>& __y)
@@ -497,6 +516,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() == __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[nodiscard]]
     constexpr bool
     operator!=(const reverse_iterator<_IteratorL>& __x,
 	       const reverse_iterator<_IteratorR>& __y)
@@ -504,6 +524,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() != __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[nodiscard]]
     constexpr bool
     operator<(const reverse_iterator<_IteratorL>& __x,
 	      const reverse_iterator<_IteratorR>& __y)
@@ -511,6 +532,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() > __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[nodiscard]]
     constexpr bool
     operator>(const reverse_iterator<_IteratorL>& __x,
 	      const reverse_iterator<_IteratorR>& __y)
@@ -518,6 +540,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() < __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[nodiscard]]
     constexpr bool
     operator<=(const reverse_iterator<_IteratorL>& __x,
 	       const reverse_iterator<_IteratorR>& __y)
@@ -525,6 +548,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() >= __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[nodiscard]]
     constexpr bool
     operator>=(const reverse_iterator<_IteratorL>& __x,
 	       const reverse_iterator<_IteratorR>& __y)
@@ -533,6 +557,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _IteratorL,
 	   three_way_comparable_with<_IteratorL> _IteratorR>
+    [[nodiscard]]
     constexpr compare_three_way_result_t<_IteratorL, _IteratorR>
     operator<=>(const reverse_iterator<_IteratorL>& __x,
 		const reverse_iterator<_IteratorR>& __y)
@@ -556,6 +581,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // DR 685. reverse_iterator/move_iterator difference has invalid signatures
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     operator-(const reverse_iterator<_IteratorL>& __x,
 	      const reverse_iterator<_IteratorR>& __y)
@@ -564,6 +590,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _Iterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Iterator>
     operator+(typename reverse_iterator<_Iterator>::difference_type __n,
 	      const reverse_iterator<_Iterator>& __x)
@@ -583,6 +610,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // DR 2285. make_reverse_iterator
   /// Generator function for reverse_iterator.
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR reverse_iterator<_Iterator>
     make_reverse_iterator(_Iterator __i)
     { return reverse_iterator<_Iterator>(__i); }
@@ -683,7 +711,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
       /// Simply returns *this.
-      _GLIBCXX20_CONSTEXPR
+      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
       back_insert_iterator&
       operator*()
       { return *this; }
@@ -713,7 +741,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  types for you.
   */
   template<typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline back_insert_iterator<_Container>
     back_inserter(_Container& __x)
     { return back_insert_iterator<_Container>(__x); }
@@ -784,7 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
       /// Simply returns *this.
-      _GLIBCXX20_CONSTEXPR
+      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
       front_insert_iterator&
       operator*()
       { return *this; }
@@ -814,7 +842,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  types for you.
   */
   template<typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline front_insert_iterator<_Container>
     front_inserter(_Container& __x)
     { return front_insert_iterator<_Container>(__x); }
@@ -914,7 +942,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
       /// Simply returns *this.
-      _GLIBCXX20_CONSTEXPR
+      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
       insert_iterator&
       operator*()
       { return *this; }
@@ -946,11 +974,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   */
 #if __cplusplus > 201703L && defined __cpp_lib_concepts
   template<typename _Container>
+    [[nodiscard]]
     constexpr insert_iterator<_Container>
     inserter(_Container& __x, std::__detail::__range_iter_t<_Container> __i)
     { return insert_iterator<_Container>(__x, __i); }
 #else
   template<typename _Container>
+    _GLIBCXX_NODISCARD
     inline insert_iterator<_Container>
     inserter(_Container& __x, typename _Container::iterator __i)
     { return insert_iterator<_Container>(__x, __i); }
@@ -1090,6 +1120,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _IteratorL, typename _IteratorR, typename _Container>
     requires requires (_IteratorL __lhs, _IteratorR __rhs)
     { { __lhs == __rhs } -> std::convertible_to<bool>; }
+    [[nodiscard]]
     constexpr bool
     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1097,6 +1128,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    [[nodiscard]]
     constexpr std::__detail::__synth3way_t<_IteratorR, _IteratorL>
     operator<=>(const __normal_iterator<_IteratorL, _Container>& __lhs,
 		const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1105,7 +1137,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #else
    // Forward iterator requirements
   template<typename _IteratorL, typename _IteratorR, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1113,7 +1145,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator==(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -1121,7 +1153,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator!=(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1129,7 +1161,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() != __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator!=(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -1138,6 +1170,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // Random access iterator requirements
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	      const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1145,7 +1178,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() < __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator<(const __normal_iterator<_Iterator, _Container>& __lhs,
 	      const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -1153,6 +1186,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() < __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	      const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1160,7 +1194,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() > __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator>(const __normal_iterator<_Iterator, _Container>& __lhs,
 	      const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -1168,6 +1202,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() > __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<=(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1175,7 +1210,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() <= __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator<=(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -1183,6 +1218,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() <= __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>=(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -1190,7 +1226,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() >= __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     operator>=(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -1205,7 +1241,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _IteratorL, typename _IteratorR, typename _Container>
 #if __cplusplus >= 201103L
     // DR 685.
-    _GLIBCXX20_CONSTEXPR
+    [[__nodiscard__]] _GLIBCXX20_CONSTEXPR
     inline auto
     operator-(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	      const __normal_iterator<_IteratorR, _Container>& __rhs) noexcept
@@ -1218,7 +1254,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() - __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline typename __normal_iterator<_Iterator, _Container>::difference_type
     operator-(const __normal_iterator<_Iterator, _Container>& __lhs,
 	      const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -1226,7 +1262,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() - __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline __normal_iterator<_Iterator, _Container>
     operator+(typename __normal_iterator<_Iterator, _Container>::difference_type
 	      __n, const __normal_iterator<_Iterator, _Container>& __i)
@@ -1284,6 +1320,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  return *this;
 	}
 
+      [[nodiscard]]
       constexpr _Sent
       base() const
       noexcept(is_nothrow_copy_constructible_v<_Sent>)
@@ -1397,19 +1434,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	}
 
 #if __cplusplus <= 201703L
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR iterator_type
       base() const
       { return _M_current; }
 #else
+      [[nodiscard]]
       constexpr const iterator_type&
       base() const & noexcept
       { return _M_current; }
 
+      [[nodiscard]]
       constexpr iterator_type
       base() &&
       { return std::move(_M_current); }
 #endif
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR reference
       operator*() const
 #if __cplusplus > 201703L && __cpp_lib_concepts
@@ -1418,6 +1459,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return static_cast<reference>(*_M_current); }
 #endif
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR pointer
       operator->() const
       { return _M_current; }
@@ -1458,6 +1500,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return __tmp;
       }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR move_iterator
       operator+(difference_type __n) const
       { return move_iterator(_M_current + __n); }
@@ -1469,6 +1512,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR move_iterator
       operator-(difference_type __n) const
       { return move_iterator(_M_current - __n); }
@@ -1480,6 +1524,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR reference
       operator[](difference_type __n) const
 #if __cplusplus > 201703L && __cpp_lib_concepts
@@ -1490,20 +1535,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cplusplus > 201703L && __cpp_lib_concepts
       template<sentinel_for<_Iterator> _Sent>
+	[[nodiscard]]
 	friend constexpr bool
 	operator==(const move_iterator& __x, const move_sentinel<_Sent>& __y)
 	{ return __x.base() == __y.base(); }
 
       template<sized_sentinel_for<_Iterator> _Sent>
+	[[nodiscard]]
 	friend constexpr iter_difference_t<_Iterator>
 	operator-(const move_sentinel<_Sent>& __x, const move_iterator& __y)
 	{ return __x.base() - __y.base(); }
 
       template<sized_sentinel_for<_Iterator> _Sent>
+	[[nodiscard]]
 	friend constexpr iter_difference_t<_Iterator>
 	operator-(const move_iterator& __x, const move_sentinel<_Sent>& __y)
 	{ return __x.base() - __y.base(); }
 
+      [[nodiscard]]
       friend constexpr iter_rvalue_reference_t<_Iterator>
       iter_move(const move_iterator& __i)
       noexcept(noexcept(ranges::iter_move(__i._M_current)))
@@ -1518,6 +1567,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     };
 
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator==(const move_iterator<_IteratorL>& __x,
 	       const move_iterator<_IteratorR>& __y)
@@ -1529,12 +1579,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if __cpp_lib_three_way_comparison
   template<typename _IteratorL,
 	   three_way_comparable_with<_IteratorL> _IteratorR>
+    [[__nodiscard__]]
     constexpr compare_three_way_result_t<_IteratorL, _IteratorR>
     operator<=>(const move_iterator<_IteratorL>& __x,
 		const move_iterator<_IteratorR>& __y)
     { return __x.base() <=> __y.base(); }
 #else
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator!=(const move_iterator<_IteratorL>& __x,
 	       const move_iterator<_IteratorR>& __y)
@@ -1542,6 +1594,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator<(const move_iterator<_IteratorL>& __x,
 	      const move_iterator<_IteratorR>& __y)
@@ -1551,6 +1604,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() < __y.base(); }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator<=(const move_iterator<_IteratorL>& __x,
 	       const move_iterator<_IteratorR>& __y)
@@ -1560,6 +1614,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return !(__y < __x); }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator>(const move_iterator<_IteratorL>& __x,
 	      const move_iterator<_IteratorR>& __y)
@@ -1569,6 +1624,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __y < __x; }
 
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator>=(const move_iterator<_IteratorL>& __x,
 	       const move_iterator<_IteratorR>& __y)
@@ -1586,36 +1642,42 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // prefer them to greedy unconstrained function templates.
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator==(const move_iterator<_Iterator>& __x,
 	       const move_iterator<_Iterator>& __y)
     { return __x.base() == __y.base(); }
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator!=(const move_iterator<_Iterator>& __x,
 	       const move_iterator<_Iterator>& __y)
     { return !(__x == __y); }
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator<(const move_iterator<_Iterator>& __x,
 	      const move_iterator<_Iterator>& __y)
     { return __x.base() < __y.base(); }
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator<=(const move_iterator<_Iterator>& __x,
 	       const move_iterator<_Iterator>& __y)
     { return !(__y < __x); }
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator>(const move_iterator<_Iterator>& __x,
 	      const move_iterator<_Iterator>& __y)
     { return __y < __x; }
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR bool
     operator>=(const move_iterator<_Iterator>& __x,
 	       const move_iterator<_Iterator>& __y)
@@ -1624,6 +1686,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // DR 685.
   template<typename _IteratorL, typename _IteratorR>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR auto
     operator-(const move_iterator<_IteratorL>& __x,
 	      const move_iterator<_IteratorR>& __y)
@@ -1631,12 +1694,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __x.base() - __y.base(); }
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR move_iterator<_Iterator>
     operator+(typename move_iterator<_Iterator>::difference_type __n,
 	      const move_iterator<_Iterator>& __x)
     { return __x + __n; }
 
   template<typename _Iterator>
+    [[__nodiscard__]]
     inline _GLIBCXX17_CONSTEXPR move_iterator<_Iterator>
     make_move_iterator(_Iterator __i)
     { return move_iterator<_Iterator>(std::move(__i)); }
@@ -1857,6 +1922,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	}
     }
 
+    [[nodiscard]]
     decltype(auto)
     operator*()
     {
@@ -1864,6 +1930,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return *_M_it;
     }
 
+    [[nodiscard]]
     decltype(auto)
     operator*() const requires __detail::__dereferenceable<const _It>
     {
@@ -1871,6 +1938,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return *_M_it;
     }
 
+    [[nodiscard]]
     decltype(auto)
     operator->() const requires __detail::__common_iter_has_arrow<_It>
     {
@@ -1916,6 +1984,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2>
+      [[nodiscard]]
       friend bool
       operator==(const common_iterator& __x,
 		 const common_iterator<_It2, _Sent2>& __y)
@@ -1938,6 +2007,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2> && equality_comparable_with<_It, _It2>
+      [[nodiscard]]
       friend bool
       operator==(const common_iterator& __x,
 		 const common_iterator<_It2, _Sent2>& __y)
@@ -1961,6 +2031,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<sized_sentinel_for<_It> _It2, sized_sentinel_for<_It> _Sent2>
       requires sized_sentinel_for<_Sent, _It2>
+      [[nodiscard]]
       friend iter_difference_t<_It2>
       operator-(const common_iterator& __x,
 		const common_iterator<_It2, _Sent2>& __y)
@@ -1982,6 +2053,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  }
       }
 
+    [[nodiscard]]
     friend iter_rvalue_reference_t<_It>
     iter_move(const common_iterator& __i)
     noexcept(noexcept(ranges::iter_move(std::declval<const _It&>())))
@@ -2132,18 +2204,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  return *this;
 	}
 
+      [[nodiscard]]
       constexpr const _It&
       base() const & noexcept
       { return _M_current; }
 
+      [[nodiscard]]
       constexpr _It
       base() &&
       noexcept(is_nothrow_move_constructible_v<_It>)
       { return std::move(_M_current); }
 
+      [[nodiscard]]
       constexpr iter_difference_t<_It>
       count() const noexcept { return _M_length; }
 
+      [[nodiscard]]
       constexpr decltype(auto)
       operator*()
       noexcept(noexcept(*_M_current))
@@ -2152,6 +2228,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *_M_current;
       }
 
+      [[nodiscard]]
       constexpr decltype(auto)
       operator*() const
       noexcept(noexcept(*_M_current))
@@ -2161,6 +2238,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *_M_current;
       }
 
+      [[nodiscard]]
       constexpr auto
       operator->() const noexcept
       requires contiguous_iterator<_It>
@@ -2214,11 +2292,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return __tmp;
       }
 
+      [[nodiscard]]
       constexpr counted_iterator
       operator+(iter_difference_t<_It> __n) const
 	requires random_access_iterator<_It>
       { return counted_iterator(_M_current + __n, _M_length - __n); }
 
+      [[nodiscard]]
       friend constexpr counted_iterator
       operator+(iter_difference_t<_It> __n, const counted_iterator& __x)
       requires random_access_iterator<_It>
@@ -2234,21 +2314,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+      [[nodiscard]]
       constexpr counted_iterator
       operator-(iter_difference_t<_It> __n) const
       requires random_access_iterator<_It>
       { return counted_iterator(_M_current - __n, _M_length + __n); }
 
       template<common_with<_It> _It2>
+	[[nodiscard]]
 	friend constexpr iter_difference_t<_It2>
 	operator-(const counted_iterator& __x,
 		  const counted_iterator<_It2>& __y)
 	{ return __y._M_length - __x._M_length; }
 
+      [[nodiscard]]
       friend constexpr iter_difference_t<_It>
       operator-(const counted_iterator& __x, default_sentinel_t)
       { return -__x._M_length; }
 
+      [[nodiscard]]
       friend constexpr iter_difference_t<_It>
       operator-(default_sentinel_t, const counted_iterator& __y)
       { return __y._M_length; }
@@ -2263,6 +2347,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+      [[nodiscard]]
       constexpr decltype(auto)
       operator[](iter_difference_t<_It> __n) const
       noexcept(noexcept(_M_current[__n]))
@@ -2273,21 +2358,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
       template<common_with<_It> _It2>
+	[[nodiscard]]
 	friend constexpr bool
 	operator==(const counted_iterator& __x,
 		   const counted_iterator<_It2>& __y)
 	{ return __x._M_length == __y._M_length; }
 
+      [[nodiscard]]
       friend constexpr bool
       operator==(const counted_iterator& __x, default_sentinel_t)
       { return __x._M_length == 0; }
 
       template<common_with<_It> _It2>
+	[[nodiscard]]
 	friend constexpr strong_ordering
 	operator<=>(const counted_iterator& __x,
 		    const counted_iterator<_It2>& __y)
 	{ return __y._M_length <=> __x._M_length; }
 
+      [[nodiscard]]
       friend constexpr iter_rvalue_reference_t<_It>
       iter_move(const counted_iterator& __i)
       noexcept(noexcept(ranges::iter_move(__i._M_current)))
diff --git a/libstdc++-v3/include/bits/stl_iterator_base_funcs.h b/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
index fa8474f23c6..e5afab7f4fd 100644
--- a/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
+++ b/libstdc++-v3/include/bits/stl_iterator_base_funcs.h
@@ -133,6 +133,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
    *  and are constant time.  For other %iterator classes they are linear time.
   */
   template<typename _InputIterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR
     typename iterator_traits<_InputIterator>::difference_type
     distance(_InputIterator __first, _InputIterator __last)
@@ -209,6 +210,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
 #if __cplusplus >= 201103L
 
   template<typename _InputIterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR _InputIterator
     next(_InputIterator __x, typename
 	 iterator_traits<_InputIterator>::difference_type __n = 1)
@@ -220,6 +222,7 @@ _GLIBCXX_END_NAMESPACE_CONTAINER
     }
 
   template<typename _BidirectionalIterator>
+    _GLIBCXX_NODISCARD
     inline _GLIBCXX17_CONSTEXPR _BidirectionalIterator
     prev(_BidirectionalIterator __x, typename
 	 iterator_traits<_BidirectionalIterator>::difference_type __n = 1) 
diff --git a/libstdc++-v3/include/bits/stream_iterator.h b/libstdc++-v3/include/bits/stream_iterator.h
index d07474d4996..d74c158f342 100644
--- a/libstdc++-v3/include/bits/stream_iterator.h
+++ b/libstdc++-v3/include/bits/stream_iterator.h
@@ -89,6 +89,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       ~istream_iterator() = default;
 #endif
 
+      _GLIBCXX_NODISCARD
       const _Tp&
       operator*() const
       {
@@ -98,6 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return _M_value;
       }
 
+      _GLIBCXX_NODISCARD
       const _Tp*
       operator->() const { return std::__addressof((operator*())); }
 
@@ -143,17 +145,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       /// Return true if the iterators refer to the same stream,
       /// or are both at end-of-stream.
+      _GLIBCXX_NODISCARD
       friend bool
       operator==(const istream_iterator& __x, const istream_iterator& __y)
       { return __x._M_equal(__y); }
 
+#if __cpp_impl_three_way_comparison < 201907L
       /// Return true if the iterators refer to different streams,
       /// or if one is at end-of-stream and the other is not.
+      _GLIBCXX_NODISCARD
       friend bool
       operator!=(const istream_iterator& __x, const istream_iterator& __y)
       { return !__x._M_equal(__y); }
+#endif
 
 #if __cplusplus > 201703L && __cpp_lib_concepts
+      [[nodiscard]]
       friend bool
       operator==(const istream_iterator& __i, default_sentinel_t)
       { return !__i._M_stream; }
@@ -231,6 +238,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+      _GLIBCXX_NODISCARD
       ostream_iterator&
       operator*()
       { return *this; }
diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h b/libstdc++-v3/include/bits/streambuf_iterator.h
index cda596af40f..0a77d1a3da4 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -141,6 +141,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       ///  Return the current character pointed to by iterator.  This returns
       ///  streambuf.sgetc().  It cannot be assigned.  NB: The result of
       ///  operator*() on an end of stream is undefined.
+      _GLIBCXX_NODISCARD
       char_type
       operator*() const
       {
@@ -189,6 +190,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       // 110 istreambuf_iterator::equal not const
       // NB: there is also number 111 (NAD) relevant to this function.
       /// Return true both iterators are end or both are not end.
+      _GLIBCXX_NODISCARD
       bool
       equal(const istreambuf_iterator& __b) const
       { return _M_at_eof() == __b._M_at_eof(); }
@@ -215,6 +217,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
 #if __cplusplus > 201703L && __cpp_lib_concepts
+      [[nodiscard]]
       friend bool
       operator==(const istreambuf_iterator& __i, default_sentinel_t __s)
       { return __i._M_at_eof(); }
@@ -222,16 +225,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     };
 
   template<typename _CharT, typename _Traits>
+    _GLIBCXX_NODISCARD
     inline bool
     operator==(const istreambuf_iterator<_CharT, _Traits>& __a,
 	       const istreambuf_iterator<_CharT, _Traits>& __b)
     { return __a.equal(__b); }
 
+#if __cpp_impl_three_way_comparison < 201907L
   template<typename _CharT, typename _Traits>
+    _GLIBCXX_NODISCARD
     inline bool
     operator!=(const istreambuf_iterator<_CharT, _Traits>& __a,
 	       const istreambuf_iterator<_CharT, _Traits>& __b)
     { return !__a.equal(__b); }
+#endif
 
   /// Provides output iterator semantics for streambufs.
   template<typename _CharT, typename _Traits>
@@ -288,6 +295,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
       /// Return *this.
+      _GLIBCXX_NODISCARD
       ostreambuf_iterator&
       operator*()
       { return *this; }
@@ -303,6 +311,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return *this; }
 
       /// Return true if previous operator=() failed.
+      _GLIBCXX_NODISCARD
       bool
       failed() const _GLIBCXX_USE_NOEXCEPT
       { return _M_failed; }
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 5bdcd445a9e..03a3778bb52 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -645,6 +645,7 @@ namespace views
   struct _Single
   {
     template<typename _Tp>
+      [[nodiscard]]
       constexpr auto
       operator()(_Tp&& __e) const
       noexcept(noexcept(single_view<decay_t<_Tp>>(std::forward<_Tp>(__e))))
@@ -656,11 +657,13 @@ namespace views
   struct _Iota
   {
     template<typename _Tp>
+      [[nodiscard]]
       constexpr auto
       operator()(_Tp&& __e) const
       { return iota_view(std::forward<_Tp>(__e)); }
 
     template<typename _Tp, typename _Up>
+      [[nodiscard]]
       constexpr auto
       operator()(_Tp&& __e, _Up&& __f) const
       { return iota_view(std::forward<_Tp>(__e), std::forward<_Up>(__f)); }
@@ -1123,6 +1126,7 @@ namespace views::__adaptor
 	requires view<decay_t<_Range>>
 	  || __detail::__can_ref_view<_Range>
 	  || __detail::__can_subrange<_Range>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
 	noexcept(_S_noexcept<_Range>())
@@ -1549,6 +1553,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_filter_view<_Range, _Pred>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pred&& __p) const
 	{
@@ -1926,6 +1931,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Fp>
 	requires __detail::__can_transform_view<_Range, _Fp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Fp&& __f) const
 	{
@@ -2107,6 +2113,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_take_view<_Range, _Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Tp&& __n) const
 	{
@@ -2234,6 +2241,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_take_while_view<_Range, _Pred>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pred&& __p) const
 	{
@@ -2354,6 +2362,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_drop_view<_Range, _Tp>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Tp&& __n) const
 	{
@@ -2442,6 +2451,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_drop_while_view<_Range, _Pred>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pred&& __p) const
 	{
@@ -2804,6 +2814,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range>
 	requires __detail::__can_join_view<_Range>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
 	{
@@ -3255,6 +3266,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_lazy_split_view<_Range, _Pattern>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pattern&& __f) const
 	{
@@ -3463,6 +3475,7 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_split_view<_Range, _Pattern>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pattern&& __f) const
 	{
@@ -3484,6 +3497,7 @@ namespace views::__adaptor
     struct _Counted
     {
       template<input_or_output_iterator _Iter>
+      [[nodiscard]]
       constexpr auto
       operator()(_Iter __i, iter_difference_t<_Iter> __n) const
       {
@@ -3605,6 +3619,7 @@ namespace views::__adaptor
       template<viewable_range _Range>
 	requires __detail::__already_common<_Range>
 	  || __detail::__can_common_view<_Range>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
 	{
@@ -3727,6 +3742,7 @@ namespace views::__adaptor
 	requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
 	  || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
 	  || __detail::__can_reverse_view<_Range>
+	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
 	{
@@ -4125,6 +4141,7 @@ namespace views::__adaptor
       {
 	template<viewable_range _Range>
 	  requires __detail::__can_elements_view<_Nm, _Range>
+	  [[nodiscard]]
 	  constexpr auto
 	  operator()(_Range&& __r) const
 	  {
diff --git a/libstdc++-v3/testsuite/20_util/rel_ops.cc b/libstdc++-v3/testsuite/20_util/rel_ops.cc
index 4726462e64e..dd2c14650ae 100644
--- a/libstdc++-v3/testsuite/20_util/rel_ops.cc
+++ b/libstdc++-v3/testsuite/20_util/rel_ops.cc
@@ -17,6 +17,8 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
+// { dg-options "-Wno-unused-result" }
+
 // 20.2.1 Operators
 
 #include <utility>
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/range_access/char/1.cc b/libstdc++-v3/testsuite/21_strings/basic_string/range_access/char/1.cc
index 90574d2a811..d37b1cb4c4e 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/range_access/char/1.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/range_access/char/1.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::string s("Hello, World!");
-  std::begin(s);
-  std::end(s);
+  (void) std::begin(s);
+  (void) std::end(s);
 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/range_access/wchar_t/1.cc b/libstdc++-v3/testsuite/21_strings/basic_string/range_access/wchar_t/1.cc
index beab3110ca2..56169150089 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/range_access/wchar_t/1.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/range_access/wchar_t/1.cc
@@ -26,7 +26,7 @@ test01()
 {
 #ifdef _GLIBCXX_USE_WCHAR_T
   std::wstring ws(L"Hello, World!");
-  std::begin(ws);
-  std::end(ws);
+  (void) std::begin(ws);
+  (void) std::end(ws);
 #endif
 }
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/char/1.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/char/1.cc
index 856aafde552..4a3595663b8 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/char/1.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/char/1.cc
@@ -25,10 +25,10 @@ void
 test01()
 {
   std::string_view s("Hello, World!");
-  std::begin(s);
-  std::end(s);
-  std::rbegin(s);
-  std::rend(s);
+  (void) std::begin(s);
+  (void) std::end(s);
+  (void) std::rbegin(s);
+  (void) std::rend(s);
 }
 
 void
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/wchar_t/1.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/wchar_t/1.cc
index c6d83c47bfd..f8ecd1a84cd 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/wchar_t/1.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/range_access/wchar_t/1.cc
@@ -25,10 +25,10 @@ void
 test01()
 {
   std::wstring_view ws(L"Hello, World!");
-  std::begin(ws);
-  std::end(ws);
-  std::rbegin(ws);
-  std::rend(ws);
+  (void) std::begin(ws);
+  (void) std::end(ws);
+  (void) std::rbegin(ws);
+  (void) std::rend(ws);
 }
 
 void
diff --git a/libstdc++-v3/testsuite/23_containers/array/range_access.cc b/libstdc++-v3/testsuite/23_containers/array/range_access.cc
index 38116888a6c..807ccdb2b01 100644
--- a/libstdc++-v3/testsuite/23_containers/array/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::array<int, 3> a{{1, 2, 3}};
-  std::begin(a);
-  std::end(a);
+  (void) std::begin(a);
+  (void) std::end(a);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/deque/range_access.cc b/libstdc++-v3/testsuite/23_containers/deque/range_access.cc
index fed56a48414..990fc0d573b 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::deque<int> d{1, 2, 3};
-  std::begin(d);
-  std::end(d);
+  (void) std::begin(d);
+  (void) std::end(d);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/forward_list/range_access.cc b/libstdc++-v3/testsuite/23_containers/forward_list/range_access.cc
index 0b70ff02131..6398240e126 100644
--- a/libstdc++-v3/testsuite/23_containers/forward_list/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/forward_list/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::forward_list<int> fl{1, 2, 3};
-  std::begin(fl);
-  std::end(fl);
+  (void) std::begin(fl);
+  (void) std::end(fl);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/list/range_access.cc b/libstdc++-v3/testsuite/23_containers/list/range_access.cc
index de845d446f0..15047ec755d 100644
--- a/libstdc++-v3/testsuite/23_containers/list/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/list/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::list<int> l{1, 2, 3};
-  std::begin(l);
-  std::end(l);
+  (void) std::begin(l);
+  (void) std::end(l);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/map/range_access.cc b/libstdc++-v3/testsuite/23_containers/map/range_access.cc
index dc0bdbb9a74..3c6b00128ca 100644
--- a/libstdc++-v3/testsuite/23_containers/map/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/map/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::map<int, double> m{{1, 1.0}, {2, 2.0}, {3, 3.0}};
-  std::begin(m);
-  std::end(m);
+  (void) std::begin(m);
+  (void) std::end(m);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/multimap/range_access.cc b/libstdc++-v3/testsuite/23_containers/multimap/range_access.cc
index 32ffa3b2651..020a7a9e627 100644
--- a/libstdc++-v3/testsuite/23_containers/multimap/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/multimap/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::multimap<int, double> mm{{1, 1.0}, {2, 2.0}, {3, 3.0}};
-  std::begin(mm);
-  std::end(mm);
+  (void) std::begin(mm);
+  (void) std::end(mm);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/multiset/range_access.cc b/libstdc++-v3/testsuite/23_containers/multiset/range_access.cc
index 2d08ba40a59..7e66bfa24aa 100644
--- a/libstdc++-v3/testsuite/23_containers/multiset/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/multiset/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::multiset<int> ms{1, 2, 3};
-  std::begin(ms);
-  std::end(ms);
+  (void) std::begin(ms);
+  (void) std::end(ms);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/set/range_access.cc b/libstdc++-v3/testsuite/23_containers/set/range_access.cc
index 35703e2a7be..66099b39df4 100644
--- a/libstdc++-v3/testsuite/23_containers/set/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/set/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::set<int> s{1, 2, 3};
-  std::begin(s);
-  std::end(s);
+  (void) std::begin(s);
+  (void) std::end(s);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_map/range_access.cc b/libstdc++-v3/testsuite/23_containers/unordered_map/range_access.cc
index edb06d06894..ad20c1da942 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_map/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_map/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::unordered_map<int, double> um{{1, 1.0}, {2, 2.0}, {3, 3.0}};
-  std::begin(um);
-  std::end(um);
+  (void) std::begin(um);
+  (void) std::end(um);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_multimap/range_access.cc b/libstdc++-v3/testsuite/23_containers/unordered_multimap/range_access.cc
index e19e825a042..4bb126e34f9 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_multimap/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_multimap/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::unordered_multimap<int, double> umm{{1, 1.0}, {2, 2.0}, {3, 3.0}};
-  std::begin(umm);
-  std::end(umm);
+  (void) std::begin(umm);
+  (void) std::end(umm);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_multiset/range_access.cc b/libstdc++-v3/testsuite/23_containers/unordered_multiset/range_access.cc
index 574012bee32..899b74af35c 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_multiset/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_multiset/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::unordered_multiset<int> ums{1, 2, 3};
-  std::begin(ums);
-  std::end(ums);
+  (void) std::begin(ums);
+  (void) std::end(ums);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/unordered_set/range_access.cc b/libstdc++-v3/testsuite/23_containers/unordered_set/range_access.cc
index 033653a37ec..4f9e8857113 100644
--- a/libstdc++-v3/testsuite/23_containers/unordered_set/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/unordered_set/range_access.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::unordered_set<int> us{1, 2, 3};
-  std::begin(us);
-  std::end(us);
+  (void) std::begin(us);
+  (void) std::end(us);
 }
diff --git a/libstdc++-v3/testsuite/23_containers/vector/range_access.cc b/libstdc++-v3/testsuite/23_containers/vector/range_access.cc
index a36975cac72..0dd761b71f1 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/range_access.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/range_access.cc
@@ -25,10 +25,10 @@ void
 test01()
 {
   std::vector<double> v{1.0, 2.0, 3.0};
-  std::begin(v);
-  std::end(v);
+  (void) std::begin(v);
+  (void) std::end(v);
 
   std::vector<bool> vb{true, false, true};
-  std::begin(vb);
-  std::end(vb);
+  (void) std::begin(vb);
+  (void) std::end(vb);
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/customization_points/iter_move.cc b/libstdc++-v3/testsuite/24_iterators/customization_points/iter_move.cc
index a43448581f3..40a084b918c 100644
--- a/libstdc++-v3/testsuite/24_iterators/customization_points/iter_move.cc
+++ b/libstdc++-v3/testsuite/24_iterators/customization_points/iter_move.cc
@@ -51,7 +51,7 @@ constexpr bool
 test_X(int i, int j)
 {
   X x1{i}, x2{j};
-  std::ranges::iter_move(&x1); // no-op
+  (void) std::ranges::iter_move(&x1); // no-op
   x1 = std::ranges::iter_move(&x2);
   return x1.value == j &&  x2.value == -1;
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/istream_iterator/sentinel.cc b/libstdc++-v3/testsuite/24_iterators/istream_iterator/sentinel.cc
index 7e1fd173877..f8f16375bf0 100644
--- a/libstdc++-v3/testsuite/24_iterators/istream_iterator/sentinel.cc
+++ b/libstdc++-v3/testsuite/24_iterators/istream_iterator/sentinel.cc
@@ -43,9 +43,9 @@ test02()
   VERIFY( iter != std::default_sentinel );
   VERIFY( std::default_sentinel != iter );
 
-  *iter++;
-  *iter++;
-  *iter++;
+  (void) *iter++;
+  (void) *iter++;
+  (void) *iter++;
   VERIFY( iter == std::default_sentinel );
   VERIFY( std::default_sentinel == iter );
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/sentinel.cc b/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/sentinel.cc
index 4961ddaf793..b7cdd44677d 100644
--- a/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/sentinel.cc
+++ b/libstdc++-v3/testsuite/24_iterators/istreambuf_iterator/sentinel.cc
@@ -41,7 +41,7 @@ test02()
   VERIFY( iter != std::default_sentinel );
   VERIFY( std::default_sentinel != iter );
 
-  std::next(iter, 3);
+  (void) std::next(iter, 3);
   VERIFY( iter == std::default_sentinel );
   VERIFY( std::default_sentinel == iter );
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/dr2061.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/dr2061.cc
index 0af4b16b7f4..c9bd3d677e5 100644
--- a/libstdc++-v3/testsuite/24_iterators/move_iterator/dr2061.cc
+++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/dr2061.cc
@@ -23,6 +23,6 @@
 void test01()
 {
   int a[] = { 1, 2, 3, 4 };
-  std::make_move_iterator(a + 4);
-  std::make_move_iterator(a);
+  (void) std::make_move_iterator(a + 4);
+  (void) std::make_move_iterator(a);
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/move_iterator/greedy_ops.cc b/libstdc++-v3/testsuite/24_iterators/move_iterator/greedy_ops.cc
index 93b3d7dbcd4..ce50e34a5a6 100644
--- a/libstdc++-v3/testsuite/24_iterators/move_iterator/greedy_ops.cc
+++ b/libstdc++-v3/testsuite/24_iterators/move_iterator/greedy_ops.cc
@@ -1,4 +1,6 @@
 // { dg-do compile { target c++11 } }
+// { dg-options "-Wno-unused-result" }
+
 // Copyright (C) 2010-2021 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
diff --git a/libstdc++-v3/testsuite/24_iterators/normal_iterator/greedy_ops.cc b/libstdc++-v3/testsuite/24_iterators/normal_iterator/greedy_ops.cc
index 557dfacbf24..29ff7266d07 100644
--- a/libstdc++-v3/testsuite/24_iterators/normal_iterator/greedy_ops.cc
+++ b/libstdc++-v3/testsuite/24_iterators/normal_iterator/greedy_ops.cc
@@ -1,4 +1,6 @@
 // { dg-do compile }
+// { dg-options "-Wno-unused-result" }
+
 // Copyright (C) 2010-2021 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
@@ -33,7 +35,7 @@ void test01()
 				       greedy_ops::C> iterator_type;
 
   iterator_type it(0);
-  
+
   it == it;
   it != it;
   it < it;
@@ -45,8 +47,8 @@ void test01()
   1 + it;
 }
 
-int main() 
-{ 
+int main()
+{
   test01();
   return 0;
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/operations/prev_neg.cc b/libstdc++-v3/testsuite/24_iterators/operations/prev_neg.cc
index 1d421bbcb2d..cafafc4b651 100644
--- a/libstdc++-v3/testsuite/24_iterators/operations/prev_neg.cc
+++ b/libstdc++-v3/testsuite/24_iterators/operations/prev_neg.cc
@@ -37,6 +37,6 @@ void
 test02()
 {
   const Y array[1] = { };
-  std::prev(array + 1);
+  (void) std::prev(array + 1);
   // { dg-error "forward_iterator" "" { target *-*-* } 223 }
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/ostreambuf_iterator/2.cc b/libstdc++-v3/testsuite/24_iterators/ostreambuf_iterator/2.cc
index 847f4352739..a962cd58236 100644
--- a/libstdc++-v3/testsuite/24_iterators/ostreambuf_iterator/2.cc
+++ b/libstdc++-v3/testsuite/24_iterators/ostreambuf_iterator/2.cc
@@ -45,7 +45,7 @@ void test02(void)
   VERIFY( !ostrb_it01.failed() );
   ostrb_it01 = 'a';
   VERIFY( !ostrb_it01.failed() );
-  *ostrb_it01;
+  (void) *ostrb_it01;
   VERIFY( !ostrb_it01.failed() );
 
   costreambuf_iter ostrb_it02(0);
@@ -53,11 +53,11 @@ void test02(void)
   ostrb_it02++;
   ++ostrb_it02;
   VERIFY( ostrb_it02.failed() );
-  *ostrb_it02;
+  (void) *ostrb_it02;
   VERIFY( ostrb_it02.failed() );
   ostrb_it02 = 'a';
   VERIFY( ostrb_it02.failed() );
-  
+
   // charT operator*() const
   // ostreambuf_iterator& operator++();
   // ostreambuf_iterator& operator++(int);
diff --git a/libstdc++-v3/testsuite/24_iterators/range_access/range_access.cc b/libstdc++-v3/testsuite/24_iterators/range_access/range_access.cc
index b0b379c6ea5..e679f24e75b 100644
--- a/libstdc++-v3/testsuite/24_iterators/range_access/range_access.cc
+++ b/libstdc++-v3/testsuite/24_iterators/range_access/range_access.cc
@@ -25,8 +25,8 @@ void
 test01()
 {
   int arr[3] = {1, 2, 3};
-  std::begin(arr);
-  std::end(arr);
+  (void) std::begin(arr);
+  (void) std::end(arr);
 
   static_assert( noexcept(std::begin(arr)), "LWG 2280" );
   static_assert( noexcept(std::end(arr)), "LWG 2280" );
diff --git a/libstdc++-v3/testsuite/24_iterators/range_operations/100768.cc b/libstdc++-v3/testsuite/24_iterators/range_operations/100768.cc
index bbcfcece5ff..d4deedd82f6 100644
--- a/libstdc++-v3/testsuite/24_iterators/range_operations/100768.cc
+++ b/libstdc++-v3/testsuite/24_iterators/range_operations/100768.cc
@@ -114,15 +114,15 @@ test01()
   // deleted overloads in namespace ns3 (because it is an associated namespace
   // and those functions are exact matches for the arguments).
   using namespace std::ranges;
-  advance(iter, 1);
-  advance(iter, 3, sentinel);
-  distance(iter, sentinel);
-  distance(range);
-  next(iter);
-  next(iter, -1);
-  next(iter, sentinel);
-  next(iter, 5, sentinel);
-  prev(iter);
-  prev(iter, 0);
-  prev(iter, 0, sentinel);
+  (void) advance(iter, 1);
+  (void) advance(iter, 3, sentinel);
+  (void) distance(iter, sentinel);
+  (void) distance(range);
+  (void) next(iter);
+  (void) next(iter, -1);
+  (void) next(iter, sentinel);
+  (void) next(iter, 5, sentinel);
+  (void) prev(iter);
+  (void) prev(iter, 0);
+  (void) prev(iter, 0, sentinel);
 }
diff --git a/libstdc++-v3/testsuite/24_iterators/reverse_iterator/2.cc b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/2.cc
index 633c1426b96..bd8b20d877d 100644
--- a/libstdc++-v3/testsuite/24_iterators/reverse_iterator/2.cc
+++ b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/2.cc
@@ -17,6 +17,8 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
+// { dg-options "-Wno-unused-result" }
+
 // 24.4.1.2 Reverse iterators
 
 #include <iterator>
diff --git a/libstdc++-v3/testsuite/24_iterators/reverse_iterator/greedy_ops.cc b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/greedy_ops.cc
index 012f0082751..e5e6dd25027 100644
--- a/libstdc++-v3/testsuite/24_iterators/reverse_iterator/greedy_ops.cc
+++ b/libstdc++-v3/testsuite/24_iterators/reverse_iterator/greedy_ops.cc
@@ -1,4 +1,6 @@
 // { dg-do compile }
+// { dg-options "-Wno-unused-result" }
+
 // Copyright (C) 2010-2021 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
diff --git a/libstdc++-v3/testsuite/26_numerics/valarray/range_access2.cc b/libstdc++-v3/testsuite/26_numerics/valarray/range_access2.cc
index a7ce1332117..cf5418a61d1 100644
--- a/libstdc++-v3/testsuite/26_numerics/valarray/range_access2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/valarray/range_access2.cc
@@ -27,9 +27,9 @@ void
 test01()
 {
   std::valarray<double> va{1.0, 2.0, 3.0};
-  std::cbegin(va);
-  std::cend(va);
+  (void) std::cbegin(va);
+  (void) std::cend(va);
   const auto& cva = va;
-  std::cbegin(cva);
-  std::cend(cva);
+  (void) std::cbegin(cva);
+  (void) std::cend(cva);
 }
diff --git a/libstdc++-v3/testsuite/28_regex/range_access.cc b/libstdc++-v3/testsuite/28_regex/range_access.cc
index 46ef3c64391..6baefbfb673 100644
--- a/libstdc++-v3/testsuite/28_regex/range_access.cc
+++ b/libstdc++-v3/testsuite/28_regex/range_access.cc
@@ -26,6 +26,6 @@ void
 test01()
 {
   std::smatch sm;
-  std::begin(sm);
-  std::end(sm);
+  (void) std::begin(sm);
+  (void) std::end(sm);
 }
diff --git a/libstdc++-v3/testsuite/experimental/string_view/range_access/char/1.cc b/libstdc++-v3/testsuite/experimental/string_view/range_access/char/1.cc
index c750430d6af..1c456920e5b 100644
--- a/libstdc++-v3/testsuite/experimental/string_view/range_access/char/1.cc
+++ b/libstdc++-v3/testsuite/experimental/string_view/range_access/char/1.cc
@@ -25,6 +25,6 @@ void
 test01()
 {
   std::experimental::string_view s("Hello, World!");
-  std::begin(s);
-  std::end(s);
+  (void) std::begin(s);
+  (void) std::end(s);
 }
diff --git a/libstdc++-v3/testsuite/experimental/string_view/range_access/wchar_t/1.cc b/libstdc++-v3/testsuite/experimental/string_view/range_access/wchar_t/1.cc
index 1dd926333c3..f19e455a606 100644
--- a/libstdc++-v3/testsuite/experimental/string_view/range_access/wchar_t/1.cc
+++ b/libstdc++-v3/testsuite/experimental/string_view/range_access/wchar_t/1.cc
@@ -26,7 +26,7 @@ test01()
 {
 #ifdef _GLIBCXX_USE_WCHAR_T
   std::experimental::wstring_view ws(L"Hello, World!");
-  std::begin(ws);
-  std::end(ws);
+  (void) std::begin(ws);
+  (void) std::end(ws);
 #endif
 }
diff --git a/libstdc++-v3/testsuite/ext/vstring/range_access.cc b/libstdc++-v3/testsuite/ext/vstring/range_access.cc
index 8219eeabed1..7b381ffd956 100644
--- a/libstdc++-v3/testsuite/ext/vstring/range_access.cc
+++ b/libstdc++-v3/testsuite/ext/vstring/range_access.cc
@@ -25,12 +25,12 @@ void
 test01()
 {
   __gnu_cxx::__vstring s("Hello, World!");
-  std::begin(s);
-  std::end(s);
+  (void) std::begin(s);
+  (void) std::end(s);
 
 #ifdef _GLIBCXX_USE_WCHAR_T
   __gnu_cxx::__wvstring ws(L"Hello, World!");
-  std::begin(ws);
-  std::end(ws);
+  (void) std::begin(ws);
+  (void) std::end(ws);
 #endif
 }
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/take.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/take.cc
index 55f74824737..d79d451478d 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/take.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/take.cc
@@ -62,7 +62,7 @@ test03()
   int x[] = {0,1,2,3,4,5};
   auto is_odd = [] (int i) { return i%2 == 1; };
   auto v = x | views::filter(is_odd) | views::take(3);
-  ranges::begin(v);
+  (void) ranges::begin(v);
   using R = decltype(v);
   static_assert(ranges::view<R>);
   static_assert(!ranges::sized_range<R>);
diff --git a/libstdc++-v3/testsuite/std/ranges/p2259.cc b/libstdc++-v3/testsuite/std/ranges/p2259.cc
index 0ec7e21f657..89234e246a0 100644
--- a/libstdc++-v3/testsuite/std/ranges/p2259.cc
+++ b/libstdc++-v3/testsuite/std/ranges/p2259.cc
@@ -64,7 +64,7 @@ test01()
 
   // Verify the changes to common_iterator.
   only_cxx20_input_range auto v6 = v0 | views::common;
-  *(v6.begin()++);
+  (void) *(v6.begin()++);
 
   // Verify the changes to iota_view.
   only_cxx20_input_range auto v8 = ranges::iota_view{v0.begin()};
@@ -77,7 +77,7 @@ test01()
   static_assert(std::contiguous_iterator<decltype(i10)>);
   static_assert(std::same_as<std::iterator_traits<decltype(i10)>::iterator_category,
 			     std::random_access_iterator_tag>);
-  i10.operator->();
+  (void) i10.operator->();
   __iter_without_category auto i11 = std::counted_iterator{v0.begin(), 5};
 }
 

^ permalink raw reply	[flat|nested] 12+ messages in thread

* [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers
  2021-08-04 11:55 [committed 1/2] libstdc++: Add [[nodiscard]] to iterators and related utilities Jonathan Wakely
@ 2021-08-04 11:56 ` Jonathan Wakely
  2021-08-04 12:00   ` Jonathan Wakely
  2021-08-05 14:19 ` [committed] libstdc++: Move attributes that follow requires-clauses [PR101782] Jonathan Wakely
  1 sibling, 1 reply; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-04 11:56 UTC (permalink / raw)
  To: libstdc++, gcc-patches

[-- Attachment #1: Type: text/plain, Size: 272 bytes --]

... and container adaptors.

This adds the [[nodiscard]] attribute to functions with no side-effects
for the sequence containers and their iterators, and the debug versions
of those containers, and the container adaptors,

Tested powerpc64le-linux, committed to trunk.




[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 88076 bytes --]

commit 0d04fe49239d91787850036599164788f1c87785
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Aug 3 20:50:52 2021

    libstdc++: Add [[nodiscard]] to sequence containers
    
    ... and container adaptors.
    
    This adds the [[nodiscard]] attribute to functions with no side-effects
    for the sequence containers and their iterators, and the debug versions
    of those containers, and the container adaptors,
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/forward_list.h: Add [[nodiscard]] to functions
            with no side-effects.
            * include/bits/stl_bvector.h: Likewise.
            * include/bits/stl_deque.h: Likewise.
            * include/bits/stl_list.h: Likewise.
            * include/bits/stl_queue.h: Likewise.
            * include/bits/stl_stack.h: Likewise.
            * include/bits/stl_vector.h: Likewise.
            * include/debug/deque: Likewise.
            * include/debug/forward_list: Likewise.
            * include/debug/list: Likewise.
            * include/debug/safe_iterator.h: Likewise.
            * include/debug/vector: Likewise.
            * include/std/array: Likewise.
            * testsuite/23_containers/array/creation/3_neg.cc: Use
            -Wno-unused-result.
            * testsuite/23_containers/array/debug/back1_neg.cc: Cast result
            to void.
            * testsuite/23_containers/array/debug/back2_neg.cc: Likewise.
            * testsuite/23_containers/array/debug/front1_neg.cc: Likewise.
            * testsuite/23_containers/array/debug/front2_neg.cc: Likewise.
            * testsuite/23_containers/array/debug/square_brackets_operator1_neg.cc:
            Likewise.
            * testsuite/23_containers/array/debug/square_brackets_operator2_neg.cc:
            Likewise.
            * testsuite/23_containers/array/tuple_interface/get_neg.cc:
            Adjust dg-error line numbers.
            * testsuite/23_containers/deque/cons/clear_allocator.cc: Cast
            result to void.
            * testsuite/23_containers/deque/debug/invalidation/4.cc:
            Likewise.
            * testsuite/23_containers/deque/types/1.cc: Use
            -Wno-unused-result.
            * testsuite/23_containers/list/types/1.cc: Cast result to void.
            * testsuite/23_containers/priority_queue/members/7161.cc:
            Likewise.
            * testsuite/23_containers/queue/members/7157.cc: Likewise.
            * testsuite/23_containers/vector/59829.cc: Likewise.
            * testsuite/23_containers/vector/ext_pointer/types/1.cc:
            Likewise.
            * testsuite/23_containers/vector/ext_pointer/types/2.cc:
            Likewise.
            * testsuite/23_containers/vector/types/1.cc: Use
            -Wno-unused-result.

diff --git a/libstdc++-v3/include/bits/forward_list.h b/libstdc++-v3/include/bits/forward_list.h
index e61746848f6..ab6d9389194 100644
--- a/libstdc++-v3/include/bits/forward_list.h
+++ b/libstdc++-v3/include/bits/forward_list.h
@@ -150,10 +150,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _Fwd_list_iterator(_Fwd_list_node_base* __n) noexcept
       : _M_node(__n) { }
 
+      [[__nodiscard__]]
       reference
       operator*() const noexcept
       { return *static_cast<_Node*>(this->_M_node)->_M_valptr(); }
 
+      [[__nodiscard__]]
       pointer
       operator->() const noexcept
       { return static_cast<_Node*>(this->_M_node)->_M_valptr(); }
@@ -176,6 +178,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       /**
        *  @brief  Forward list iterator equality comparison.
        */
+      [[__nodiscard__]]
       friend bool
       operator==(const _Self& __x, const _Self& __y) noexcept
       { return __x._M_node == __y._M_node; }
@@ -184,6 +187,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       /**
        *  @brief  Forward list iterator inequality comparison.
        */
+      [[__nodiscard__]]
       friend bool
       operator!=(const _Self& __x, const _Self& __y) noexcept
       { return __x._M_node != __y._M_node; }
@@ -229,10 +233,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _Fwd_list_const_iterator(const iterator& __iter) noexcept
       : _M_node(__iter._M_node) { }
 
+      [[__nodiscard__]]
       reference
       operator*() const noexcept
       { return *static_cast<_Node*>(this->_M_node)->_M_valptr(); }
 
+      [[__nodiscard__]]
       pointer
       operator->() const noexcept
       { return static_cast<_Node*>(this->_M_node)->_M_valptr(); }
@@ -255,6 +261,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       /**
        *  @brief  Forward list const_iterator equality comparison.
        */
+      [[__nodiscard__]]
       friend bool
       operator==(const _Self& __x, const _Self& __y) noexcept
       { return __x._M_node == __y._M_node; }
@@ -263,6 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       /**
        *  @brief  Forward list const_iterator inequality comparison.
        */
+      [[__nodiscard__]]
       friend bool
       operator!=(const _Self& __x, const _Self& __y) noexcept
       { return __x._M_node != __y._M_node; }
@@ -698,6 +706,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write iterator that points before the first element
        *  in the %forward_list.  Iteration is done in ordinary element order.
        */
+      [[__nodiscard__]]
       iterator
       before_begin() noexcept
       { return iterator(&this->_M_impl._M_head); }
@@ -707,6 +716,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  first element in the %forward_list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       before_begin() const noexcept
       { return const_iterator(&this->_M_impl._M_head); }
@@ -715,6 +725,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write iterator that points to the first element
        *  in the %forward_list.  Iteration is done in ordinary element order.
        */
+      [[__nodiscard__]]
       iterator
       begin() noexcept
       { return iterator(this->_M_impl._M_head._M_next); }
@@ -724,6 +735,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  element in the %forward_list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       begin() const noexcept
       { return const_iterator(this->_M_impl._M_head._M_next); }
@@ -733,6 +745,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  element in the %forward_list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       iterator
       end() noexcept
       { return iterator(nullptr); }
@@ -742,6 +755,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  element in the %forward_list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       end() const noexcept
       { return const_iterator(nullptr); }
@@ -751,6 +765,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  first element in the %forward_list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return const_iterator(this->_M_impl._M_head._M_next); }
@@ -760,6 +775,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  first element in the %forward_list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cbefore_begin() const noexcept
       { return const_iterator(&this->_M_impl._M_head); }
@@ -769,6 +785,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  the last element in the %forward_list.  Iteration is done in
        *  ordinary element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return const_iterator(nullptr); }
@@ -777,13 +794,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns true if the %forward_list is empty.  (Thus begin() would
        *  equal end().)
        */
-      _GLIBCXX_NODISCARD bool
+      [[__nodiscard__]]
+      bool
       empty() const noexcept
       { return this->_M_impl._M_head._M_next == nullptr; }
 
       /**
        *  Returns the largest possible number of elements of %forward_list.
        */
+      [[__nodiscard__]]
       size_type
       max_size() const noexcept
       { return _Node_alloc_traits::max_size(this->_M_get_Node_allocator()); }
@@ -794,6 +813,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write reference to the data at the first
        *  element of the %forward_list.
        */
+      [[__nodiscard__]]
       reference
       front()
       {
@@ -805,6 +825,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read-only (constant) reference to the data at the first
        *  element of the %forward_list.
        */
+      [[__nodiscard__]]
       const_reference
       front() const
       {
@@ -1425,6 +1446,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    *  if corresponding elements compare equal.
    */
   template<typename _Tp, typename _Alloc>
+    [[__nodiscard__]]
     bool
     operator==(const forward_list<_Tp, _Alloc>& __lx,
 	       const forward_list<_Tp, _Alloc>& __ly);
@@ -1442,6 +1464,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    *  `<` and `>=` etc.
   */
   template<typename _Tp, typename _Alloc>
+    [[nodiscard]]
     inline __detail::__synth3way_t<_Tp>
     operator<=>(const forward_list<_Tp, _Alloc>& __x,
 		const forward_list<_Tp, _Alloc>& __y)
@@ -1464,6 +1487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    *  See std::lexicographical_compare() for how the determination is made.
    */
   template<typename _Tp, typename _Alloc>
+    [[__nodiscard__]]
     inline bool
     operator<(const forward_list<_Tp, _Alloc>& __lx,
 	      const forward_list<_Tp, _Alloc>& __ly)
@@ -1472,6 +1496,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
   /// Based on operator==
   template<typename _Tp, typename _Alloc>
+    [[__nodiscard__]]
     inline bool
     operator!=(const forward_list<_Tp, _Alloc>& __lx,
 	       const forward_list<_Tp, _Alloc>& __ly)
@@ -1479,6 +1504,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    [[__nodiscard__]]
     inline bool
     operator>(const forward_list<_Tp, _Alloc>& __lx,
 	      const forward_list<_Tp, _Alloc>& __ly)
@@ -1486,6 +1512,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    [[__nodiscard__]]
     inline bool
     operator>=(const forward_list<_Tp, _Alloc>& __lx,
 	       const forward_list<_Tp, _Alloc>& __ly)
@@ -1493,6 +1520,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    [[__nodiscard__]]
     inline bool
     operator<=(const forward_list<_Tp, _Alloc>& __lx,
 	       const forward_list<_Tp, _Alloc>& __ly)
diff --git a/libstdc++-v3/include/bits/stl_bvector.h b/libstdc++-v3/include/bits/stl_bvector.h
index fadb6615102..a954890ff20 100644
--- a/libstdc++-v3/include/bits/stl_bvector.h
+++ b/libstdc++-v3/include/bits/stl_bvector.h
@@ -83,6 +83,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     _Bit_reference(const _Bit_reference&) = default;
 #endif
 
+    _GLIBCXX_NODISCARD
     operator bool() const _GLIBCXX_NOEXCEPT
     { return !!(*_M_p & _M_mask); }
 
@@ -100,10 +101,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     operator=(const _Bit_reference& __x) _GLIBCXX_NOEXCEPT
     { return *this = bool(__x); }
 
+    _GLIBCXX_NODISCARD
     bool
     operator==(const _Bit_reference& __x) const
     { return bool(*this) == bool(__x); }
 
+    _GLIBCXX_NODISCARD
     bool
     operator<(const _Bit_reference& __x) const
     { return !bool(*this) && bool(__x); }
@@ -182,11 +185,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _M_offset = static_cast<unsigned int>(__n);
     }
 
+    _GLIBCXX_NODISCARD
     friend _GLIBCXX20_CONSTEXPR bool
     operator==(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
     { return __x._M_p == __y._M_p && __x._M_offset == __y._M_offset; }
 
 #if __cpp_lib_three_way_comparison
+    [[nodiscard]]
     friend constexpr strong_ordering
     operator<=>(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
     noexcept
@@ -196,6 +201,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       return __x._M_offset <=> __y._M_offset;
     }
 #else
+    _GLIBCXX_NODISCARD
     friend bool
     operator<(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
     {
@@ -203,18 +209,22 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	    || (__x._M_p == __y._M_p && __x._M_offset < __y._M_offset);
     }
 
+    _GLIBCXX_NODISCARD
     friend bool
     operator!=(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
     { return !(__x == __y); }
 
+    _GLIBCXX_NODISCARD
     friend bool
     operator>(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
     { return __y < __x; }
 
+    _GLIBCXX_NODISCARD
     friend bool
     operator<=(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
     { return !(__y < __x); }
 
+    _GLIBCXX_NODISCARD
     friend bool
     operator>=(const _Bit_iterator_base& __x, const _Bit_iterator_base& __y)
     { return !(__x < __y); }
@@ -247,6 +257,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     _M_const_cast() const
     { return *this; }
 
+    _GLIBCXX_NODISCARD
     reference
     operator*() const
     { return reference(_M_p, 1UL << _M_offset); }
@@ -295,10 +306,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       return *this;
     }
 
+    _GLIBCXX_NODISCARD
     reference
     operator[](difference_type __i) const
     { return *(*this + __i); }
 
+    _GLIBCXX_NODISCARD
     friend iterator
     operator+(const iterator& __x, difference_type __n)
     {
@@ -307,10 +320,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       return __tmp;
     }
 
+    _GLIBCXX_NODISCARD
     friend iterator
     operator+(difference_type __n, const iterator& __x)
     { return __x + __n; }
 
+    _GLIBCXX_NODISCARD
     friend iterator
     operator-(const iterator& __x, difference_type __n)
     {
@@ -343,6 +358,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     _M_const_cast() const
     { return _Bit_iterator(_M_p, _M_offset); }
 
+    _GLIBCXX_NODISCARD
     const_reference
     operator*() const
     { return _Bit_reference(_M_p, 1UL << _M_offset); }
@@ -391,10 +407,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       return *this;
     }
 
+    _GLIBCXX_NODISCARD
     const_reference
     operator[](difference_type __i) const
     { return *(*this + __i); }
 
+    _GLIBCXX_NODISCARD
     friend const_iterator
     operator+(const const_iterator& __x, difference_type __n)
     {
@@ -403,6 +421,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       return __tmp;
     }
 
+    _GLIBCXX_NODISCARD
     friend const_iterator
     operator-(const const_iterator& __x, difference_type __n)
     {
@@ -411,6 +430,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       return __tmp;
     }
 
+    _GLIBCXX_NODISCARD
     friend const_iterator
     operator+(difference_type __n, const const_iterator& __x)
     { return __x + __n; }
@@ -827,60 +847,74 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       { _M_assign_aux(__l.begin(), __l.end(), random_access_iterator_tag()); }
 #endif
 
+      _GLIBCXX_NODISCARD
       iterator
       begin() _GLIBCXX_NOEXCEPT
       { return iterator(this->_M_impl._M_start._M_p, 0); }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
       { return const_iterator(this->_M_impl._M_start._M_p, 0); }
 
+      _GLIBCXX_NODISCARD
       iterator
       end() _GLIBCXX_NOEXCEPT
       { return this->_M_impl._M_finish; }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
       { return this->_M_impl._M_finish; }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rbegin() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rend() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(begin()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rend() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(begin()); }
 
 #if __cplusplus >= 201103L
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return const_iterator(this->_M_impl._M_start._M_p, 0); }
 
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return this->_M_impl._M_finish; }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(end()); }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(begin()); }
 #endif
 
+      _GLIBCXX_NODISCARD
       size_type
       size() const _GLIBCXX_NOEXCEPT
       { return size_type(end() - begin()); }
 
+      _GLIBCXX_NODISCARD
       size_type
       max_size() const _GLIBCXX_NOEXCEPT
       {
@@ -893,6 +927,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 		? __asize * int(_S_word_bit) : __isize);
       }
 
+      _GLIBCXX_NODISCARD
       size_type
       capacity() const _GLIBCXX_NOEXCEPT
       { return size_type(const_iterator(this->_M_impl._M_end_addr(), 0)
@@ -902,10 +937,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       empty() const _GLIBCXX_NOEXCEPT
       { return begin() == end(); }
 
+      _GLIBCXX_NODISCARD
       reference
       operator[](size_type __n)
       { return begin()[__n]; }
 
+      _GLIBCXX_NODISCARD
       const_reference
       operator[](size_type __n) const
       { return begin()[__n]; }
@@ -939,18 +976,22 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  _M_reallocate(__n);
       }
 
+      _GLIBCXX_NODISCARD
       reference
       front()
       { return *begin(); }
 
+      _GLIBCXX_NODISCARD
       const_reference
       front() const
       { return *begin(); }
 
+      _GLIBCXX_NODISCARD
       reference
       back()
       { return *(end() - 1); }
 
+      _GLIBCXX_NODISCARD
       const_reference
       back() const
       { return *(end() - 1); }
diff --git a/libstdc++-v3/include/bits/stl_deque.h b/libstdc++-v3/include/bits/stl_deque.h
index 20c73b4fc3c..6095498d440 100644
--- a/libstdc++-v3/include/bits/stl_deque.h
+++ b/libstdc++-v3/include/bits/stl_deque.h
@@ -176,10 +176,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _M_const_cast() const _GLIBCXX_NOEXCEPT
       { return iterator(_M_cur, _M_node); }
 
+      _GLIBCXX_NODISCARD
       reference
       operator*() const _GLIBCXX_NOEXCEPT
       { return *_M_cur; }
 
+      _GLIBCXX_NODISCARD
       pointer
       operator->() const _GLIBCXX_NOEXCEPT
       { return _M_cur; }
@@ -247,6 +249,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       operator-=(difference_type __n) _GLIBCXX_NOEXCEPT
       { return *this += -__n; }
 
+      _GLIBCXX_NODISCARD
       reference
       operator[](difference_type __n) const _GLIBCXX_NOEXCEPT
       { return *(*this + __n); }
@@ -264,6 +267,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	_M_last = _M_first + difference_type(_S_buffer_size());
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator==(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return __x._M_cur == __y._M_cur; }
@@ -272,6 +276,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       // order to avoid ambiguous overload resolution when std::rel_ops
       // operators are in scope (for additional details, see libstdc++/3628)
       template<typename _RefR, typename _PtrR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator==(const _Self& __x,
 		   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
@@ -279,6 +284,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	{ return __x._M_cur == __y._M_cur; }
 
 #if __cpp_lib_three_way_comparison
+      [[nodiscard]]
       friend strong_ordering
       operator<=>(const _Self& __x, const _Self& __y) noexcept
       {
@@ -287,17 +293,20 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	return __x._M_cur <=> __y._M_cur;
       }
 #else
+      _GLIBCXX_NODISCARD
       friend bool
       operator!=(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return !(__x == __y); }
 
       template<typename _RefR, typename _PtrR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator!=(const _Self& __x,
 		   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
 	_GLIBCXX_NOEXCEPT
 	{ return !(__x == __y); }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator<(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       {
@@ -306,6 +315,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       }
 
       template<typename _RefR, typename _PtrR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator<(const _Self& __x,
 		  const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
@@ -315,33 +325,39 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	    ? (__x._M_cur < __y._M_cur) : (__x._M_node < __y._M_node);
 	}
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator>(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return __y < __x; }
 
       template<typename _RefR, typename _PtrR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator>(const _Self& __x,
 		  const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
 	_GLIBCXX_NOEXCEPT
 	{ return __y < __x; }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator<=(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return !(__y < __x); }
 
       template<typename _RefR, typename _PtrR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator<=(const _Self& __x,
 		   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
 	_GLIBCXX_NOEXCEPT
 	{ return !(__y < __x); }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator>=(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return !(__x < __y); }
 
       template<typename _RefR, typename _PtrR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator>=(const _Self& __x,
 		   const _Deque_iterator<_Tp, _RefR, _PtrR>& __y)
@@ -349,6 +365,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	{ return !(__x < __y); }
 #endif // three-way comparison
 
+      _GLIBCXX_NODISCARD
       friend difference_type
       operator-(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       {
@@ -363,6 +380,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       // operators but also operator- must accept mixed iterator/const_iterator
       // parameters.
       template<typename _RefR, typename _PtrR>
+	_GLIBCXX_NODISCARD
 	friend difference_type
 	operator-(const _Self& __x,
 		  const _Deque_iterator<_Tp, _RefR, _PtrR>& __y) _GLIBCXX_NOEXCEPT
@@ -373,6 +391,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	    + (__y._M_last - __y._M_cur);
 	}
 
+      _GLIBCXX_NODISCARD
       friend _Self
       operator+(const _Self& __x, difference_type __n) _GLIBCXX_NOEXCEPT
       {
@@ -381,6 +400,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	return __tmp;
       }
 
+      _GLIBCXX_NODISCARD
       friend _Self
       operator-(const _Self& __x, difference_type __n) _GLIBCXX_NOEXCEPT
       {
@@ -389,6 +409,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	return __tmp;
       }
 
+      _GLIBCXX_NODISCARD
       friend _Self
       operator+(difference_type __n, const _Self& __x) _GLIBCXX_NOEXCEPT
       { return __x + __n; }
@@ -1114,6 +1135,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 #endif
 
       /// Get a copy of the memory allocation object.
+      _GLIBCXX_NODISCARD
       allocator_type
       get_allocator() const _GLIBCXX_NOEXCEPT
       { return _Base::get_allocator(); }
@@ -1123,6 +1145,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write iterator that points to the first element in the
        *  %deque.  Iteration is done in ordinary element order.
        */
+      _GLIBCXX_NODISCARD
       iterator
       begin() _GLIBCXX_NOEXCEPT
       { return this->_M_impl._M_start; }
@@ -1131,6 +1154,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read-only (constant) iterator that points to the first
        *  element in the %deque.  Iteration is done in ordinary element order.
        */
+      _GLIBCXX_NODISCARD
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
       { return this->_M_impl._M_start; }
@@ -1140,6 +1164,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  element in the %deque.  Iteration is done in ordinary
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       iterator
       end() _GLIBCXX_NOEXCEPT
       { return this->_M_impl._M_finish; }
@@ -1149,6 +1174,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  the last element in the %deque.  Iteration is done in
        *  ordinary element order.
        */
+      _GLIBCXX_NODISCARD
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
       { return this->_M_impl._M_finish; }
@@ -1158,6 +1184,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  last element in the %deque.  Iteration is done in reverse
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(this->_M_impl._M_finish); }
@@ -1167,6 +1194,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to the last element in the %deque.  Iteration is done in
        *  reverse element order.
        */
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rbegin() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(this->_M_impl._M_finish); }
@@ -1176,6 +1204,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  before the first element in the %deque.  Iteration is done
        *  in reverse element order.
        */
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rend() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(this->_M_impl._M_start); }
@@ -1185,6 +1214,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to one before the first element in the %deque.  Iteration is
        *  done in reverse element order.
        */
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rend() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(this->_M_impl._M_start); }
@@ -1194,6 +1224,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read-only (constant) iterator that points to the first
        *  element in the %deque.  Iteration is done in ordinary element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return this->_M_impl._M_start; }
@@ -1203,6 +1234,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  the last element in the %deque.  Iteration is done in
        *  ordinary element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return this->_M_impl._M_finish; }
@@ -1212,6 +1244,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to the last element in the %deque.  Iteration is done in
        *  reverse element order.
        */
+      [[__nodiscard__]]
       const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(this->_M_impl._M_finish); }
@@ -1221,6 +1254,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to one before the first element in the %deque.  Iteration is
        *  done in reverse element order.
        */
+      [[__nodiscard__]]
       const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(this->_M_impl._M_start); }
@@ -1228,11 +1262,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
       // [23.2.1.2] capacity
       /**  Returns the number of elements in the %deque.  */
+      _GLIBCXX_NODISCARD
       size_type
       size() const _GLIBCXX_NOEXCEPT
       { return this->_M_impl._M_finish - this->_M_impl._M_start; }
 
       /**  Returns the size() of the largest possible %deque.  */
+      _GLIBCXX_NODISCARD
       size_type
       max_size() const _GLIBCXX_NOEXCEPT
       { return _S_max_size(_M_get_Tp_allocator()); }
@@ -1322,6 +1358,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  out_of_range lookups are not defined. (For checked lookups
        *  see at().)
        */
+      _GLIBCXX_NODISCARD
       reference
       operator[](size_type __n) _GLIBCXX_NOEXCEPT
       {
@@ -1340,6 +1377,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  out_of_range lookups are not defined. (For checked lookups
        *  see at().)
        */
+      _GLIBCXX_NODISCARD
       const_reference
       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
       {
@@ -1400,6 +1438,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write reference to the data at the first
        *  element of the %deque.
        */
+      _GLIBCXX_NODISCARD
       reference
       front() _GLIBCXX_NOEXCEPT
       {
@@ -1411,6 +1450,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read-only (constant) reference to the data at the first
        *  element of the %deque.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       front() const _GLIBCXX_NOEXCEPT
       {
@@ -1422,6 +1462,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write reference to the data at the last element of the
        *  %deque.
        */
+      _GLIBCXX_NODISCARD
       reference
       back() _GLIBCXX_NOEXCEPT
       {
@@ -1435,6 +1476,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read-only (constant) reference to the data at the last
        *  element of the %deque.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       back() const _GLIBCXX_NOEXCEPT
       {
@@ -2242,6 +2284,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    *  and if corresponding elements compare equal.
   */
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator==(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
     { return __x.size() == __y.size()
@@ -2260,6 +2303,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    *  `<` and `>=` etc.
   */
   template<typename _Tp, typename _Alloc>
+    [[nodiscard]]
     inline __detail::__synth3way_t<_Tp>
     operator<=>(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
     {
@@ -2280,6 +2324,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
    *  See std::lexicographical_compare() for how the determination is made.
   */
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
     { return std::lexicographical_compare(__x.begin(), __x.end(),
@@ -2287,24 +2332,28 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
   /// Based on operator==
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator!=(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
     { return !(__x == __y); }
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
     { return __y < __x; }
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<=(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
     { return !(__y < __x); }
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>=(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
     { return !(__x < __y); }
diff --git a/libstdc++-v3/include/bits/stl_list.h b/libstdc++-v3/include/bits/stl_list.h
index dbe05a9834b..9ae640ee692 100644
--- a/libstdc++-v3/include/bits/stl_list.h
+++ b/libstdc++-v3/include/bits/stl_list.h
@@ -205,10 +205,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       { return *this; }
 
       // Must downcast from _List_node_base to _List_node to get to value.
+      _GLIBCXX_NODISCARD
       reference
       operator*() const _GLIBCXX_NOEXCEPT
       { return *static_cast<_Node*>(_M_node)->_M_valptr(); }
 
+      _GLIBCXX_NODISCARD
       pointer
       operator->() const _GLIBCXX_NOEXCEPT
       { return static_cast<_Node*>(_M_node)->_M_valptr(); }
@@ -243,11 +245,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	return __tmp;
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator==(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return __x._M_node == __y._M_node; }
 
 #if __cpp_impl_three_way_comparison < 201907L
+      _GLIBCXX_NODISCARD
       friend bool
       operator!=(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return __x._M_node != __y._M_node; }
@@ -291,10 +295,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       { return iterator(const_cast<__detail::_List_node_base*>(_M_node)); }
 
       // Must downcast from List_node_base to _List_node to get to value.
+      _GLIBCXX_NODISCARD
       reference
       operator*() const _GLIBCXX_NOEXCEPT
       { return *static_cast<_Node*>(_M_node)->_M_valptr(); }
 
+      _GLIBCXX_NODISCARD
       pointer
       operator->() const _GLIBCXX_NOEXCEPT
       { return static_cast<_Node*>(_M_node)->_M_valptr(); }
@@ -329,11 +335,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	return __tmp;
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator==(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return __x._M_node == __y._M_node; }
 
 #if __cpp_impl_three_way_comparison < 201907L
+      _GLIBCXX_NODISCARD
       friend bool
       operator!=(const _Self& __x, const _Self& __y) _GLIBCXX_NOEXCEPT
       { return __x._M_node != __y._M_node; }
@@ -941,6 +949,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  Returns a read/write iterator that points to the first element in the
        *  %list.  Iteration is done in ordinary element order.
        */
+      _GLIBCXX_NODISCARD
       iterator
       begin() _GLIBCXX_NOEXCEPT
       { return iterator(this->_M_impl._M_node._M_next); }
@@ -950,6 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  first element in the %list.  Iteration is done in ordinary
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
       { return const_iterator(this->_M_impl._M_node._M_next); }
@@ -959,6 +969,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  element in the %list.  Iteration is done in ordinary element
        *  order.
        */
+      _GLIBCXX_NODISCARD
       iterator
       end() _GLIBCXX_NOEXCEPT
       { return iterator(&this->_M_impl._M_node); }
@@ -968,6 +979,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  the last element in the %list.  Iteration is done in ordinary
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
       { return const_iterator(&this->_M_impl._M_node); }
@@ -977,6 +989,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  element in the %list.  Iteration is done in reverse element
        *  order.
        */
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(end()); }
@@ -986,6 +999,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  the last element in the %list.  Iteration is done in reverse
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rbegin() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(end()); }
@@ -995,6 +1009,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  before the first element in the %list.  Iteration is done in
        *  reverse element order.
        */
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rend() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(begin()); }
@@ -1004,6 +1019,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  before the first element in the %list.  Iteration is done in reverse
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rend() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(begin()); }
@@ -1014,6 +1030,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  first element in the %list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return const_iterator(this->_M_impl._M_node._M_next); }
@@ -1023,6 +1040,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  the last element in the %list.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return const_iterator(&this->_M_impl._M_node); }
@@ -1032,6 +1050,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  the last element in the %list.  Iteration is done in reverse
        *  element order.
        */
+      [[__nodiscard__]]
       const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(end()); }
@@ -1041,6 +1060,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  before the first element in the %list.  Iteration is done in reverse
        *  element order.
        */
+      [[__nodiscard__]]
       const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(begin()); }
@@ -1056,11 +1076,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       { return this->_M_impl._M_node._M_next == &this->_M_impl._M_node; }
 
       /**  Returns the number of elements in the %list.  */
+      _GLIBCXX_NODISCARD
       size_type
       size() const _GLIBCXX_NOEXCEPT
       { return _M_node_count(); }
 
       /**  Returns the size() of the largest possible %list.  */
+      _GLIBCXX_NODISCARD
       size_type
       max_size() const _GLIBCXX_NOEXCEPT
       { return _Node_alloc_traits::max_size(_M_get_Node_allocator()); }
@@ -1110,6 +1132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  Returns a read/write reference to the data at the first
        *  element of the %list.
        */
+      _GLIBCXX_NODISCARD
       reference
       front() _GLIBCXX_NOEXCEPT
       { return *begin(); }
@@ -1118,6 +1141,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  Returns a read-only (constant) reference to the data at the first
        *  element of the %list.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       front() const _GLIBCXX_NOEXCEPT
       { return *begin(); }
@@ -1126,6 +1150,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  Returns a read/write reference to the data at the last element
        *  of the %list.
        */
+      _GLIBCXX_NODISCARD
       reference
       back() _GLIBCXX_NOEXCEPT
       {
@@ -1138,6 +1163,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
        *  Returns a read-only (constant) reference to the data at the last
        *  element of the %list.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       back() const _GLIBCXX_NOEXCEPT
       {
@@ -1991,6 +2017,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
    *  equal, and if corresponding elements compare equal.
   */
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator==(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     {
@@ -2026,6 +2053,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
    *  `<` and `>=` etc.
   */
   template<typename _Tp, typename _Alloc>
+    [[nodiscard]]
     inline __detail::__synth3way_t<_Tp>
     operator<=>(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     {
@@ -2046,6 +2074,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
    *  See std::lexicographical_compare() for how the determination is made.
   */
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     { return std::lexicographical_compare(__x.begin(), __x.end(),
@@ -2053,24 +2082,28 @@ _GLIBCXX_END_NAMESPACE_CXX11
 
   /// Based on operator==
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator!=(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     { return !(__x == __y); }
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     { return __y < __x; }
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<=(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     { return !(__y < __x); }
 
   /// Based on operator<
   template<typename _Tp, typename _Alloc>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>=(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
     { return !(__x < __y); }
diff --git a/libstdc++-v3/include/bits/stl_queue.h b/libstdc++-v3/include/bits/stl_queue.h
index 936cf0d2380..363868fe0a6 100644
--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -107,15 +107,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
       template<typename _Tp1, typename _Seq1>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator==(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 
       template<typename _Tp1, typename _Seq1>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator<(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 
 #if __cpp_lib_three_way_comparison
       template<typename _Tp1, three_way_comparable _Seq1>
+	[[nodiscard]]
 	friend compare_three_way_result_t<_Seq1>
 	operator<=>(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 #endif
@@ -204,6 +207,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return c.empty(); }
 
       /**  Returns the number of elements in the %queue.  */
+      _GLIBCXX_NODISCARD
       size_type
       size() const
       { return c.size(); }
@@ -212,6 +216,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns a read/write reference to the data at the first
        *  element of the %queue.
        */
+      _GLIBCXX_NODISCARD
       reference
       front()
       {
@@ -223,6 +228,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns a read-only (constant) reference to the data at the first
        *  element of the %queue.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       front() const
       {
@@ -234,6 +240,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns a read/write reference to the data at the last
        *  element of the %queue.
        */
+      _GLIBCXX_NODISCARD
       reference
       back()
       {
@@ -245,6 +252,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns a read-only (constant) reference to the data at the last
        *  element of the %queue.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       back() const
       {
@@ -340,6 +348,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  if their sequences compare equal.
   */
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator==(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return __x.c == __y.c; }
@@ -358,36 +367,42 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  determination.
   */
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return __x.c < __y.c; }
 
   /// Based on operator==
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator!=(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return !(__x == __y); }
 
   /// Based on operator<
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return __y < __x; }
 
   /// Based on operator<
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<=(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return !(__y < __x); }
 
   /// Based on operator<
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>=(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return !(__x < __y); }
 
 #if __cpp_lib_three_way_comparison
   template<typename _Tp, three_way_comparable _Seq>
+    [[nodiscard]]
     inline compare_three_way_result_t<_Seq>
     operator<=>(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
     { return __x.c <=> __y.c; }
@@ -613,6 +628,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return c.empty(); }
 
       /**  Returns the number of elements in the %queue.  */
+      _GLIBCXX_NODISCARD
       size_type
       size() const
       { return c.size(); }
@@ -621,6 +637,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns a read-only (constant) reference to the data at the first
        *  element of the %queue.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       top() const
       {
diff --git a/libstdc++-v3/include/bits/stl_stack.h b/libstdc++-v3/include/bits/stl_stack.h
index 2a460d2751a..85137b9d428 100644
--- a/libstdc++-v3/include/bits/stl_stack.h
+++ b/libstdc++-v3/include/bits/stl_stack.h
@@ -200,6 +200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return c.empty(); }
 
       /**  Returns the number of elements in the %stack.  */
+      _GLIBCXX_NODISCARD
       size_type
       size() const
       { return c.size(); }
@@ -208,6 +209,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns a read/write reference to the data at the first
        *  element of the %stack.
        */
+      _GLIBCXX_NODISCARD
       reference
       top()
       {
@@ -219,6 +221,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  Returns a read-only (constant) reference to the data at the first
        *  element of the %stack.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       top() const
       {
@@ -315,6 +318,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  equal.
   */
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator==(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return __x.c == __y.c; }
@@ -333,36 +337,42 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  determination.
   */
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return __x.c < __y.c; }
 
   /// Based on operator==
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator!=(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return !(__x == __y); }
 
   /// Based on operator<
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return __y < __x; }
 
   /// Based on operator<
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator<=(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return !(__y < __x); }
 
   /// Based on operator<
   template<typename _Tp, typename _Seq>
+    _GLIBCXX_NODISCARD
     inline bool
     operator>=(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return !(__x < __y); }
 
 #if __cpp_lib_three_way_comparison
   template<typename _Tp, three_way_comparable _Seq>
+    [[nodiscard]]
     inline compare_three_way_result_t<_Seq>
     operator<=>(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
     { return __x.c <=> __y.c; }
diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index 06abf01ab0e..296da43822a 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -807,6 +807,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  element in the %vector.  Iteration is done in ordinary
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       iterator
       begin() _GLIBCXX_NOEXCEPT
       { return iterator(this->_M_impl._M_start); }
@@ -816,6 +817,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  first element in the %vector.  Iteration is done in ordinary
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
       { return const_iterator(this->_M_impl._M_start); }
@@ -825,6 +827,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  element in the %vector.  Iteration is done in ordinary
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       iterator
       end() _GLIBCXX_NOEXCEPT
       { return iterator(this->_M_impl._M_finish); }
@@ -834,6 +837,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  the last element in the %vector.  Iteration is done in
        *  ordinary element order.
        */
+      _GLIBCXX_NODISCARD
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
       { return const_iterator(this->_M_impl._M_finish); }
@@ -843,6 +847,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  last element in the %vector.  Iteration is done in reverse
        *  element order.
        */
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(end()); }
@@ -852,6 +857,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to the last element in the %vector.  Iteration is done in
        *  reverse element order.
        */
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rbegin() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(end()); }
@@ -861,6 +867,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  before the first element in the %vector.  Iteration is done
        *  in reverse element order.
        */
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rend() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(begin()); }
@@ -870,6 +877,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to one before the first element in the %vector.  Iteration
        *  is done in reverse element order.
        */
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rend() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(begin()); }
@@ -880,6 +888,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  first element in the %vector.  Iteration is done in ordinary
        *  element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return const_iterator(this->_M_impl._M_start); }
@@ -889,6 +898,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  the last element in the %vector.  Iteration is done in
        *  ordinary element order.
        */
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return const_iterator(this->_M_impl._M_finish); }
@@ -898,6 +908,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to the last element in the %vector.  Iteration is done in
        *  reverse element order.
        */
+      [[__nodiscard__]]
       const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(end()); }
@@ -907,6 +918,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  to one before the first element in the %vector.  Iteration
        *  is done in reverse element order.
        */
+      [[__nodiscard__]]
       const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(begin()); }
@@ -914,11 +926,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
       // [23.2.4.2] capacity
       /**  Returns the number of elements in the %vector.  */
+      _GLIBCXX_NODISCARD
       size_type
       size() const _GLIBCXX_NOEXCEPT
       { return size_type(this->_M_impl._M_finish - this->_M_impl._M_start); }
 
       /**  Returns the size() of the largest possible %vector.  */
+      _GLIBCXX_NODISCARD
       size_type
       max_size() const _GLIBCXX_NOEXCEPT
       { return _S_max_size(_M_get_Tp_allocator()); }
@@ -994,6 +1008,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns the total number of elements that the %vector can
        *  hold before needing to allocate more memory.
        */
+      _GLIBCXX_NODISCARD
       size_type
       capacity() const _GLIBCXX_NOEXCEPT
       { return size_type(this->_M_impl._M_end_of_storage
@@ -1039,6 +1054,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  out_of_range lookups are not defined. (For checked lookups
        *  see at().)
        */
+      _GLIBCXX_NODISCARD
       reference
       operator[](size_type __n) _GLIBCXX_NOEXCEPT
       {
@@ -1057,6 +1073,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  out_of_range lookups are not defined. (For checked lookups
        *  see at().)
        */
+      _GLIBCXX_NODISCARD
       const_reference
       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
       {
@@ -1117,6 +1134,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write reference to the data at the first
        *  element of the %vector.
        */
+      _GLIBCXX_NODISCARD
       reference
       front() _GLIBCXX_NOEXCEPT
       {
@@ -1128,6 +1146,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read-only (constant) reference to the data at the first
        *  element of the %vector.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       front() const _GLIBCXX_NOEXCEPT
       {
@@ -1139,6 +1158,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read/write reference to the data at the last
        *  element of the %vector.
        */
+      _GLIBCXX_NODISCARD
       reference
       back() _GLIBCXX_NOEXCEPT
       {
@@ -1150,6 +1170,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *  Returns a read-only (constant) reference to the data at the
        *  last element of the %vector.
        */
+      _GLIBCXX_NODISCARD
       const_reference
       back() const _GLIBCXX_NOEXCEPT
       {
@@ -1164,10 +1185,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        *   Returns a pointer such that [data(), data() + size()) is a valid
        *   range.  For a non-empty %vector, data() == &front().
        */
+      _GLIBCXX_NODISCARD
       _Tp*
       data() _GLIBCXX_NOEXCEPT
       { return _M_data_ptr(this->_M_impl._M_start); }
 
+      _GLIBCXX_NODISCARD
       const _Tp*
       data() const _GLIBCXX_NOEXCEPT
       { return _M_data_ptr(this->_M_impl._M_start); }
diff --git a/libstdc++-v3/include/debug/deque b/libstdc++-v3/include/debug/deque
index 227d083da04..4257a1651bd 100644
--- a/libstdc++-v3/include/debug/deque
+++ b/libstdc++-v3/include/debug/deque
@@ -219,51 +219,63 @@ namespace __debug
       using _Base::get_allocator;
 
       // iterators:
+      _GLIBCXX_NODISCARD
       iterator
       begin() _GLIBCXX_NOEXCEPT
       { return iterator(_Base::begin(), this); }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
       { return const_iterator(_Base::begin(), this); }
 
+      _GLIBCXX_NODISCARD
       iterator
       end() _GLIBCXX_NOEXCEPT
       { return iterator(_Base::end(), this); }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
       { return const_iterator(_Base::end(), this); }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rbegin() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rend() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(begin()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rend() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(begin()); }
 
 #if __cplusplus >= 201103L
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return const_iterator(_Base::begin(), this); }
 
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return const_iterator(_Base::end(), this); }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(end()); }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(begin()); }
@@ -335,6 +347,7 @@ namespace __debug
       using _Base::empty;
 
       // element access:
+      _GLIBCXX_NODISCARD
       reference
       operator[](size_type __n) _GLIBCXX_NOEXCEPT
       {
@@ -342,6 +355,7 @@ namespace __debug
 	return _M_base()[__n];
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
       {
@@ -351,6 +365,7 @@ namespace __debug
 
       using _Base::at;
 
+      _GLIBCXX_NODISCARD
       reference
       front() _GLIBCXX_NOEXCEPT
       {
@@ -358,6 +373,7 @@ namespace __debug
 	return _Base::front();
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       front() const _GLIBCXX_NOEXCEPT
       {
@@ -365,6 +381,7 @@ namespace __debug
 	return _Base::front();
       }
 
+      _GLIBCXX_NODISCARD
       reference
       back() _GLIBCXX_NOEXCEPT
       {
@@ -372,6 +389,7 @@ namespace __debug
 	return _Base::back();
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       back() const _GLIBCXX_NOEXCEPT
       {
diff --git a/libstdc++-v3/include/debug/forward_list b/libstdc++-v3/include/debug/forward_list
index 16f0531dce7..9cc05e8129c 100644
--- a/libstdc++-v3/include/debug/forward_list
+++ b/libstdc++-v3/include/debug/forward_list
@@ -327,38 +327,47 @@ namespace __debug
 
       // iterators:
 
+      [[__nodiscard__]]
       iterator
       before_begin() noexcept
       { return { _Base::before_begin(), this }; }
 
+      [[__nodiscard__]]
       const_iterator
       before_begin() const noexcept
       { return { _Base::before_begin(), this }; }
 
+      [[__nodiscard__]]
       iterator
       begin() noexcept
       { return { _Base::begin(), this }; }
 
+      [[__nodiscard__]]
       const_iterator
       begin() const noexcept
       { return { _Base::begin(), this }; }
 
+      [[__nodiscard__]]
       iterator
       end() noexcept
       { return { _Base::end(), this }; }
 
+      [[__nodiscard__]]
       const_iterator
       end() const noexcept
       { return { _Base::end(), this }; }
 
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return { _Base::cbegin(), this }; }
 
+      [[__nodiscard__]]
       const_iterator
       cbefore_begin() const noexcept
       { return { _Base::cbefore_begin(), this }; }
 
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return { _Base::cend(), this }; }
@@ -368,6 +377,7 @@ namespace __debug
 
       // element access:
 
+      [[__nodiscard__]]
       reference
       front()
       {
@@ -375,6 +385,7 @@ namespace __debug
 	return _Base::front();
       }
 
+      [[__nodiscard__]]
       const_reference
       front() const
       {
diff --git a/libstdc++-v3/include/debug/list b/libstdc++-v3/include/debug/list
index 01fe43fc7df..83122f8248d 100644
--- a/libstdc++-v3/include/debug/list
+++ b/libstdc++-v3/include/debug/list
@@ -223,51 +223,63 @@ namespace __debug
       using _Base::get_allocator;
 
       // iterators:
+      _GLIBCXX_NODISCARD
       iterator
       begin() _GLIBCXX_NOEXCEPT
       { return iterator(_Base::begin(), this); }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
       { return const_iterator(_Base::begin(), this); }
 
+      _GLIBCXX_NODISCARD
       iterator
       end() _GLIBCXX_NOEXCEPT
       { return iterator(_Base::end(), this); }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
       { return const_iterator(_Base::end(), this); }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rbegin() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rend() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(begin()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rend() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(begin()); }
 
 #if __cplusplus >= 201103L
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return const_iterator(_Base::begin(), this); }
 
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return const_iterator(_Base::end(), this); }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(end()); }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(begin()); }
@@ -356,6 +368,7 @@ namespace __debug
 #endif
 
       // element access:
+      _GLIBCXX_NODISCARD
       reference
       front() _GLIBCXX_NOEXCEPT
       {
@@ -363,6 +376,7 @@ namespace __debug
 	return _Base::front();
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       front() const _GLIBCXX_NOEXCEPT
       {
@@ -370,6 +384,7 @@ namespace __debug
 	return _Base::front();
       }
 
+      _GLIBCXX_NODISCARD
       reference
       back() _GLIBCXX_NOEXCEPT
       {
@@ -377,6 +392,7 @@ namespace __debug
 	return _Base::back();
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       back() const _GLIBCXX_NOEXCEPT
       {
diff --git a/libstdc++-v3/include/debug/safe_iterator.h b/libstdc++-v3/include/debug/safe_iterator.h
index 8e138fd32e5..5584d06de5a 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -297,6 +297,7 @@ namespace __gnu_debug
        *  @brief Iterator dereference.
        *  @pre iterator is dereferenceable
        */
+      _GLIBCXX_NODISCARD
       reference
       operator*() const _GLIBCXX_NOEXCEPT
       {
@@ -310,6 +311,7 @@ namespace __gnu_debug
        *  @brief Iterator dereference.
        *  @pre iterator is dereferenceable
        */
+      _GLIBCXX_NODISCARD
       pointer
       operator->() const _GLIBCXX_NOEXCEPT
       {
@@ -463,6 +465,7 @@ namespace __gnu_debug
 
       typedef _Safe_iterator<_Iterator, _Sequence, iterator_category> _Self;
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator==(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -471,6 +474,7 @@ namespace __gnu_debug
       }
 
       template<typename _IteR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator==(const _Self& __lhs,
 	  const _Safe_iterator<_IteR, _Sequence, iterator_category>& __rhs)
@@ -481,6 +485,7 @@ namespace __gnu_debug
 	}
 
 #if ! __cpp_lib_three_way_comparison
+      _GLIBCXX_NODISCARD
       friend bool
       operator!=(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -489,6 +494,7 @@ namespace __gnu_debug
       }
 
       template<typename _IteR>
+	_GLIBCXX_NODISCARD
 	friend bool
 	operator!=(const _Self& __lhs,
 	  const _Safe_iterator<_IteR, _Sequence, iterator_category>& __rhs)
@@ -786,6 +792,7 @@ namespace __gnu_debug
       }
 
       // ------ Random access iterator requirements ------
+      _GLIBCXX_NODISCARD
       reference
       operator[](difference_type __n) const _GLIBCXX_NOEXCEPT
       {
@@ -819,6 +826,7 @@ namespace __gnu_debug
       }
 
 #if __cpp_lib_three_way_comparison
+      [[nodiscard]]
       friend auto
       operator<=>(const _Self& __lhs, const _Self& __rhs) noexcept
       {
@@ -826,6 +834,7 @@ namespace __gnu_debug
 	return __lhs.base() <=> __rhs.base();
       }
 
+      [[nodiscard]]
       friend auto
       operator<=>(const _Self& __lhs, const _OtherSelf& __rhs) noexcept
       {
@@ -833,6 +842,7 @@ namespace __gnu_debug
 	return __lhs.base() <=> __rhs.base();
       }
 #else
+      _GLIBCXX_NODISCARD
       friend bool
       operator<(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -840,6 +850,7 @@ namespace __gnu_debug
 	return __lhs.base() < __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator<(const _Self& __lhs, const _OtherSelf& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -847,6 +858,7 @@ namespace __gnu_debug
 	return __lhs.base() < __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator<=(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -854,6 +866,7 @@ namespace __gnu_debug
 	return __lhs.base() <= __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator<=(const _Self& __lhs, const _OtherSelf& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -861,6 +874,7 @@ namespace __gnu_debug
 	return __lhs.base() <= __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator>(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -868,6 +882,7 @@ namespace __gnu_debug
 	return __lhs.base() > __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator>(const _Self& __lhs, const _OtherSelf& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -875,6 +890,7 @@ namespace __gnu_debug
 	return __lhs.base() > __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator>=(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -882,6 +898,7 @@ namespace __gnu_debug
 	return __lhs.base() >= __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend bool
       operator>=(const _Self& __lhs, const _OtherSelf& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -894,6 +911,7 @@ namespace __gnu_debug
       // According to the resolution of DR179 not only the various comparison
       // operators but also operator- must accept mixed iterator/const_iterator
       // parameters.
+      _GLIBCXX_NODISCARD
       friend difference_type
       operator-(const _Self& __lhs, const _OtherSelf& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -901,6 +919,7 @@ namespace __gnu_debug
 	return __lhs.base() - __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend difference_type
       operator-(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -908,6 +927,7 @@ namespace __gnu_debug
 	return __lhs.base() - __rhs.base();
       }
 
+      _GLIBCXX_NODISCARD
       friend _Self
       operator+(const _Self& __x, difference_type __n) _GLIBCXX_NOEXCEPT
       {
@@ -917,6 +937,7 @@ namespace __gnu_debug
 	return _Safe_iterator(__x.base() + __n, __x._M_sequence);
       }
 
+      _GLIBCXX_NODISCARD
       friend _Self
       operator+(difference_type __n, const _Self& __x) _GLIBCXX_NOEXCEPT
       {
@@ -926,6 +947,7 @@ namespace __gnu_debug
 	return _Safe_iterator(__n + __x.base(), __x._M_sequence);
       }
 
+      _GLIBCXX_NODISCARD
       friend _Self
       operator-(const _Self& __x, difference_type __n) _GLIBCXX_NOEXCEPT
       {
diff --git a/libstdc++-v3/include/debug/vector b/libstdc++-v3/include/debug/vector
index 79ccf527dd6..55271384922 100644
--- a/libstdc++-v3/include/debug/vector
+++ b/libstdc++-v3/include/debug/vector
@@ -303,51 +303,63 @@ namespace __debug
       using _Base::get_allocator;
 
       // iterators:
+      _GLIBCXX_NODISCARD
       iterator
       begin() _GLIBCXX_NOEXCEPT
       { return iterator(_Base::begin(), this); }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       begin() const _GLIBCXX_NOEXCEPT
       { return const_iterator(_Base::begin(), this); }
 
+      _GLIBCXX_NODISCARD
       iterator
       end() _GLIBCXX_NOEXCEPT
       { return iterator(_Base::end(), this); }
 
+      _GLIBCXX_NODISCARD
       const_iterator
       end() const _GLIBCXX_NOEXCEPT
       { return const_iterator(_Base::end(), this); }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rbegin() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rbegin() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(end()); }
 
+      _GLIBCXX_NODISCARD
       reverse_iterator
       rend() _GLIBCXX_NOEXCEPT
       { return reverse_iterator(begin()); }
 
+      _GLIBCXX_NODISCARD
       const_reverse_iterator
       rend() const _GLIBCXX_NOEXCEPT
       { return const_reverse_iterator(begin()); }
 
 #if __cplusplus >= 201103L
+      [[__nodiscard__]]
       const_iterator
       cbegin() const noexcept
       { return const_iterator(_Base::begin(), this); }
 
+      [[__nodiscard__]]
       const_iterator
       cend() const noexcept
       { return const_iterator(_Base::end(), this); }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(end()); }
 
+      [[__nodiscard__]]
       const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(begin()); }
@@ -407,6 +419,7 @@ namespace __debug
       }
 #endif
 
+      _GLIBCXX_NODISCARD
       size_type
       capacity() const _GLIBCXX_NOEXCEPT
       {
@@ -431,6 +444,7 @@ namespace __debug
       }
 
       // element access:
+      _GLIBCXX_NODISCARD
       reference
       operator[](size_type __n) _GLIBCXX_NOEXCEPT
       {
@@ -438,6 +452,7 @@ namespace __debug
 	return _M_base()[__n];
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
       {
@@ -447,6 +462,7 @@ namespace __debug
 
       using _Base::at;
 
+      _GLIBCXX_NODISCARD
       reference
       front() _GLIBCXX_NOEXCEPT
       {
@@ -454,6 +470,7 @@ namespace __debug
 	return _Base::front();
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       front() const _GLIBCXX_NOEXCEPT
       {
@@ -461,6 +478,7 @@ namespace __debug
 	return _Base::front();
       }
 
+      _GLIBCXX_NODISCARD
       reference
       back() _GLIBCXX_NOEXCEPT
       {
@@ -468,6 +486,7 @@ namespace __debug
 	return _Base::back();
       }
 
+      _GLIBCXX_NODISCARD
       const_reference
       back() const _GLIBCXX_NOEXCEPT
       {
diff --git a/libstdc++-v3/include/std/array b/libstdc++-v3/include/std/array
index ea8d3cb5f2e..3e12d35157c 100644
--- a/libstdc++-v3/include/std/array
+++ b/libstdc++-v3/include/std/array
@@ -127,65 +127,81 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { std::swap_ranges(begin(), end(), __other.begin()); }
 
       // Iterators.
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR iterator
       begin() noexcept
       { return iterator(data()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_iterator
       begin() const noexcept
       { return const_iterator(data()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR iterator
       end() noexcept
       { return iterator(data() + _Nm); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_iterator
       end() const noexcept
       { return const_iterator(data() + _Nm); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR reverse_iterator
       rbegin() noexcept
       { return reverse_iterator(end()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_reverse_iterator
       rbegin() const noexcept
       { return const_reverse_iterator(end()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR reverse_iterator
       rend() noexcept
       { return reverse_iterator(begin()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_reverse_iterator
       rend() const noexcept
       { return const_reverse_iterator(begin()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_iterator
       cbegin() const noexcept
       { return const_iterator(data()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_iterator
       cend() const noexcept
       { return const_iterator(data() + _Nm); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_reverse_iterator
       crbegin() const noexcept
       { return const_reverse_iterator(end()); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_reverse_iterator
       crend() const noexcept
       { return const_reverse_iterator(begin()); }
 
       // Capacity.
+      [[__nodiscard__]]
       constexpr size_type
       size() const noexcept { return _Nm; }
 
+      [[__nodiscard__]]
       constexpr size_type
       max_size() const noexcept { return _Nm; }
 
-      _GLIBCXX_NODISCARD constexpr bool
+      [[__nodiscard__]]
+      constexpr bool
       empty() const noexcept { return size() == 0; }
 
       // Element access.
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR reference
       operator[](size_type __n) noexcept
       {
@@ -193,6 +209,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return _AT_Type::_S_ref(_M_elems, __n);
       }
 
+      [[__nodiscard__]]
       constexpr const_reference
       operator[](size_type __n) const noexcept
       {
@@ -224,6 +241,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	     _AT_Type::_S_ref(_M_elems, 0));
       }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR reference
       front() noexcept
       {
@@ -231,6 +249,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *begin();
       }
 
+      [[__nodiscard__]]
       constexpr const_reference
       front() const noexcept
       {
@@ -240,6 +259,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return _AT_Type::_S_ref(_M_elems, 0);
       }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR reference
       back() noexcept
       {
@@ -247,6 +267,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return _Nm ? *(end() - 1) : *end();
       }
 
+      [[__nodiscard__]]
       constexpr const_reference
       back() const noexcept
       {
@@ -257,10 +278,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
  	           : _AT_Type::_S_ref(_M_elems, 0);
       }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR pointer
       data() noexcept
       { return _AT_Type::_S_ptr(_M_elems); }
 
+      [[__nodiscard__]]
       _GLIBCXX17_CONSTEXPR const_pointer
       data() const noexcept
       { return _AT_Type::_S_ptr(_M_elems); }
@@ -275,6 +298,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // Array comparisons.
   template<typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     _GLIBCXX20_CONSTEXPR
     inline bool
     operator==(const array<_Tp, _Nm>& __one, const array<_Tp, _Nm>& __two)
@@ -282,6 +306,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cpp_lib_three_way_comparison && __cpp_lib_concepts
   template<typename _Tp, size_t _Nm>
+    [[nodiscard]]
     constexpr __detail::__synth3way_t<_Tp>
     operator<=>(const array<_Tp, _Nm>& __a, const array<_Tp, _Nm>& __b)
     {
@@ -304,12 +329,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 #else
   template<typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     _GLIBCXX20_CONSTEXPR
     inline bool
     operator!=(const array<_Tp, _Nm>& __one, const array<_Tp, _Nm>& __two)
     { return !(__one == __two); }
 
   template<typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     _GLIBCXX20_CONSTEXPR
     inline bool
     operator<(const array<_Tp, _Nm>& __a, const array<_Tp, _Nm>& __b)
@@ -319,18 +346,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     _GLIBCXX20_CONSTEXPR
     inline bool
     operator>(const array<_Tp, _Nm>& __one, const array<_Tp, _Nm>& __two)
     { return __two < __one; }
 
   template<typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     _GLIBCXX20_CONSTEXPR
     inline bool
     operator<=(const array<_Tp, _Nm>& __one, const array<_Tp, _Nm>& __two)
     { return !(__one > __two); }
 
   template<typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     _GLIBCXX20_CONSTEXPR
     inline bool
     operator>=(const array<_Tp, _Nm>& __one, const array<_Tp, _Nm>& __two)
@@ -361,6 +391,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<std::size_t _Int, typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     constexpr _Tp&
     get(array<_Tp, _Nm>& __arr) noexcept
     {
@@ -369,6 +400,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<std::size_t _Int, typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     constexpr _Tp&&
     get(array<_Tp, _Nm>&& __arr) noexcept
     {
@@ -377,6 +409,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<std::size_t _Int, typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     constexpr const _Tp&
     get(const array<_Tp, _Nm>& __arr) noexcept
     {
@@ -385,6 +418,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<std::size_t _Int, typename _Tp, std::size_t _Nm>
+    [[__nodiscard__]]
     constexpr const _Tp&&
     get(const array<_Tp, _Nm>&& __arr) noexcept
     {
@@ -406,6 +440,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, size_t _Nm>
+    [[nodiscard]]
     constexpr array<remove_cv_t<_Tp>, _Nm>
     to_array(_Tp (&__a)[_Nm])
     noexcept(is_nothrow_constructible_v<_Tp, _Tp&>)
@@ -418,6 +453,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _Tp, size_t _Nm>
+    [[nodiscard]]
     constexpr array<remove_cv_t<_Tp>, _Nm>
     to_array(_Tp (&&__a)[_Nm])
     noexcept(is_nothrow_move_constructible_v<_Tp>)
diff --git a/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc b/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc
index c286b35fd61..e3cb6990f59 100644
--- a/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/creation/3_neg.cc
@@ -1,4 +1,4 @@
-// { dg-options "-std=gnu++2a" }
+// { dg-options "-std=gnu++2a -Wno-unused-result" }
 // { dg-do compile { target c++2a } }
 
 // Copyright (C) 2019-2021 Free Software Foundation, Inc.
diff --git a/libstdc++-v3/testsuite/23_containers/array/debug/back1_neg.cc b/libstdc++-v3/testsuite/23_containers/array/debug/back1_neg.cc
index d384b7b2ff4..01c7c45784e 100644
--- a/libstdc++-v3/testsuite/23_containers/array/debug/back1_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/debug/back1_neg.cc
@@ -23,7 +23,7 @@
 void test01()
 {
   std::array<int, 0> a;
-  a.back();
+  (void) a.back();
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/23_containers/array/debug/back2_neg.cc b/libstdc++-v3/testsuite/23_containers/array/debug/back2_neg.cc
index b27f5f0bb03..db195e86411 100644
--- a/libstdc++-v3/testsuite/23_containers/array/debug/back2_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/debug/back2_neg.cc
@@ -23,7 +23,7 @@
 void test01()
 {
   constexpr std::array<int, 0> a;
-  a.back();
+  (void) a.back();
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/23_containers/array/debug/front1_neg.cc b/libstdc++-v3/testsuite/23_containers/array/debug/front1_neg.cc
index e0d86f1c07f..700f8524950 100644
--- a/libstdc++-v3/testsuite/23_containers/array/debug/front1_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/debug/front1_neg.cc
@@ -23,7 +23,7 @@
 void test01()
 {
   std::array<int, 0> a;
-  a.front();
+  (void) a.front();
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/23_containers/array/debug/front2_neg.cc b/libstdc++-v3/testsuite/23_containers/array/debug/front2_neg.cc
index dcbe5b6dd2e..d84b301fbf8 100644
--- a/libstdc++-v3/testsuite/23_containers/array/debug/front2_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/debug/front2_neg.cc
@@ -23,7 +23,7 @@
 void test01()
 {
   constexpr std::array<int, 0> a;
-  a.front();
+  (void) a.front();
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator1_neg.cc b/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator1_neg.cc
index 299ba85a5cf..bc5db43e123 100644
--- a/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator1_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator1_neg.cc
@@ -23,7 +23,7 @@
 void test01()
 {
   std::array<int, 0> a;
-  a[0];
+  (void) a[0];
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator2_neg.cc b/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator2_neg.cc
index 36d281af105..105952f36d9 100644
--- a/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator2_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/debug/square_brackets_operator2_neg.cc
@@ -23,7 +23,7 @@
 void test01()
 {
   constexpr std::array<int, 0> a;
-  a[0];
+  (void) a[0];
 }
 
 int main()
diff --git a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
index 423594dd2b3..70742c14a7d 100644
--- a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
@@ -26,6 +26,6 @@ int n1 = std::get<1>(a);
 int n2 = std::get<1>(std::move(a));
 int n3 = std::get<1>(ca);
 
-// { dg-error "static assertion failed" "" { target *-*-* } 367 }
-// { dg-error "static assertion failed" "" { target *-*-* } 375 }
-// { dg-error "static assertion failed" "" { target *-*-* } 383 }
+// { dg-error "static assertion failed" "" { target *-*-* } 398 }
+// { dg-error "static assertion failed" "" { target *-*-* } 407 }
+// { dg-error "static assertion failed" "" { target *-*-* } 416 }
diff --git a/libstdc++-v3/testsuite/23_containers/deque/cons/clear_allocator.cc b/libstdc++-v3/testsuite/23_containers/deque/cons/clear_allocator.cc
index 29fdd46115b..12063f53bb9 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/cons/clear_allocator.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/cons/clear_allocator.cc
@@ -5,12 +5,12 @@
 // 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/>.
@@ -22,12 +22,12 @@ using namespace std;
 using __gnu_cxx::new_allocator;
 
 template<typename T>
-  class clear_alloc : public new_allocator<T> 
+  class clear_alloc : public new_allocator<T>
   {
   public:
 
     template <typename T1>
-      struct rebind 
+      struct rebind
       { typedef clear_alloc<T1> other; };
 
     virtual void clear() throw()
@@ -35,10 +35,10 @@ template<typename T>
 
     clear_alloc() throw()
     { }
-    
-    clear_alloc(clear_alloc const&) throw() : new_allocator<T>() 
+
+    clear_alloc(clear_alloc const&) throw() : new_allocator<T>()
     { }
-    
+
     template<typename T1>
     clear_alloc(clear_alloc<T1> const&) throw()
       { }
@@ -51,7 +51,7 @@ template<typename T>
       this->clear();
       return new_allocator<T>::allocate(n, hint);
     }
-    
+
     void deallocate(T *ptr, typename new_allocator<T>::size_type n)
     {
       this->clear();
@@ -64,14 +64,14 @@ template<typename Container>
   {
     Container* pic = new Container;
     int x = 230;
-    
+
     while (x--)
       {
 	pic->push_back(x);
       }
-    
-    pic->get_allocator();
-    
+
+    (void) pic->get_allocator();
+
     // The following has led to infinite recursions or cores.
     pic->clear();
 
diff --git a/libstdc++-v3/testsuite/23_containers/deque/debug/invalidation/4.cc b/libstdc++-v3/testsuite/23_containers/deque/debug/invalidation/4.cc
index 6ec8b620422..aa98b7f6608 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/debug/invalidation/4.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/debug/invalidation/4.cc
@@ -58,7 +58,7 @@ void test04()
   before = v.begin();
   at = before + 3;
   v.erase(at, v.end());
-  *before;
+  (void) *before;
 
   // clear()
   before = v.begin();
diff --git a/libstdc++-v3/testsuite/23_containers/deque/types/1.cc b/libstdc++-v3/testsuite/23_containers/deque/types/1.cc
index a17b1d86ec9..144eb57e13a 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/types/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/types/1.cc
@@ -18,6 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
+// { dg-options "-Wno-unused-result" }
 
 #include <deque>
 #include <testsuite_greedy_ops.h>
diff --git a/libstdc++-v3/testsuite/23_containers/list/types/1.cc b/libstdc++-v3/testsuite/23_containers/list/types/1.cc
index 1e649963b84..45222b93bce 100644
--- a/libstdc++-v3/testsuite/23_containers/list/types/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/list/types/1.cc
@@ -25,7 +25,7 @@ int main()
   std::list<greedy_ops::X> l;
   const std::list<greedy_ops::X> cl;
 
-  l.size();
+  (void) l.size();
   l.insert(l.begin(), greedy_ops::X());
   l.insert(l.begin(), 1, greedy_ops::X());
   l.insert(l.begin(), cl.begin(), cl.end());
diff --git a/libstdc++-v3/testsuite/23_containers/priority_queue/members/7161.cc b/libstdc++-v3/testsuite/23_containers/priority_queue/members/7161.cc
index 951b667c555..3ab3d337f46 100644
--- a/libstdc++-v3/testsuite/23_containers/priority_queue/members/7161.cc
+++ b/libstdc++-v3/testsuite/23_containers/priority_queue/members/7161.cc
@@ -32,7 +32,7 @@ test03()
   for (int i = 0; i < 3; ++i)
     pq.push(data[i]);
 
-  pq.top();
+  (void) pq.top();
   for (int i = 0; i < 2; ++i)
     pq.pop();
 
diff --git a/libstdc++-v3/testsuite/23_containers/queue/members/7157.cc b/libstdc++-v3/testsuite/23_containers/queue/members/7157.cc
index b01201a968e..e3e5dda2ef0 100644
--- a/libstdc++-v3/testsuite/23_containers/queue/members/7157.cc
+++ b/libstdc++-v3/testsuite/23_containers/queue/members/7157.cc
@@ -29,7 +29,7 @@ test01()
   std::queue<int> q;
 
   q.push(1);
-  q.front();
+  (void) q.front();
   q.pop();
 }
 
diff --git a/libstdc++-v3/testsuite/23_containers/vector/59829.cc b/libstdc++-v3/testsuite/23_containers/vector/59829.cc
index 16bfb6fb327..7a7f577a643 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/59829.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/59829.cc
@@ -63,5 +63,5 @@ bool operator!=(Alloc<T> l, Alloc<T> r) { return false; }
 int main()
 {
   std::vector<int, Alloc<int>> a;
-  a.data();
+  (void) a.data();
 }
diff --git a/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/1.cc b/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/1.cc
index 3d2fe29389d..7656f840448 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/1.cc
@@ -46,10 +46,10 @@ int main()
   std::vector<N::X, __gnu_cxx::_ExtPtr_allocator<N::X> > v(5);
   const std::vector<N::X, __gnu_cxx::_ExtPtr_allocator<N::X> > w(1);
 
-  v[0];
-  w[0];
-  v.size();
-  v.capacity();
+  (void) v[0];
+  (void) w[0];
+  (void) v.size();
+  (void) v.capacity();
   v.resize(1);
   v.insert(v.begin(), N::X());
   v.insert(v.begin(), 1, N::X());
diff --git a/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/2.cc b/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/2.cc
index 9e01e8f607d..7329712a2a1 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/2.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/ext_pointer/types/2.cc
@@ -48,10 +48,10 @@ int main()
   std::vector<N::X, __gnu_cxx::_ExtPtr_allocator<N::X> > v(5);
   const std::vector<N::X, __gnu_cxx::_ExtPtr_allocator<N::X> > w(1);
 
-  v[0];
-  w[0];
-  v.size();
-  v.capacity();
+  (void) v[0];
+  (void) w[0];
+  (void) v.size();
+  (void) v.capacity();
   v.resize(1);
   v.insert(v.begin(), N::X());
   v.insert(v.begin(), 1, N::X());
diff --git a/libstdc++-v3/testsuite/23_containers/vector/types/1.cc b/libstdc++-v3/testsuite/23_containers/vector/types/1.cc
index 803f658eedd..7295a64a008 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/types/1.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/types/1.cc
@@ -18,6 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
+// { dg-options "-Wno-unused-result" }
 
 #include <vector>
 #include <testsuite_greedy_ops.h>

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers
  2021-08-04 11:56 ` [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers Jonathan Wakely
@ 2021-08-04 12:00   ` Jonathan Wakely
  2021-08-05 12:09     ` Christophe Lyon
  2021-08-05 14:38     ` Jonathan Wakely
  0 siblings, 2 replies; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-04 12:00 UTC (permalink / raw)
  To: libstdc++, gcc-patches

On 04/08/21 12:56 +0100, Jonathan Wakely wrote:
>... and container adaptors.
>
>This adds the [[nodiscard]] attribute to functions with no side-effects
>for the sequence containers and their iterators, and the debug versions
>of those containers, and the container adaptors,

I don't plan to add any more [[nodiscard]] attributes for now, but
these two commits should demonstrate how to do it for anybody who
wants to contribute similar patches.

I didn't add tests that verify we do actually warn on each of those
functions, because there are hundreds of them, and I know they're
working because I had to alter existing tests to not warn.



^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers
  2021-08-04 12:00   ` Jonathan Wakely
@ 2021-08-05 12:09     ` Christophe Lyon
  2021-08-05 12:13       ` Ville Voutilainen
  2021-08-05 14:38     ` Jonathan Wakely
  1 sibling, 1 reply; 12+ messages in thread
From: Christophe Lyon @ 2021-08-05 12:09 UTC (permalink / raw)
  To: Jonathan Wakely; +Cc: libstdc++, GCC Patches

Hi Jonathan,

On Wed, Aug 4, 2021 at 2:04 PM Jonathan Wakely via Gcc-patches <
gcc-patches@gcc.gnu.org> wrote:

> On 04/08/21 12:56 +0100, Jonathan Wakely wrote:
> >... and container adaptors.
> >
> >This adds the [[nodiscard]] attribute to functions with no side-effects
> >for the sequence containers and their iterators, and the debug versions
> >of those containers, and the container adaptors,
>
> I don't plan to add any more [[nodiscard]] attributes for now, but
> these two commits should demonstrate how to do it for anybody who
> wants to contribute similar patches.
>
> I didn't add tests that verify we do actually warn on each of those
> functions, because there are hundreds of them, and I know they're
> working because I had to alter existing tests to not warn.
>
>
I've noticed a regression on aarch64/arm:
FAIL: g++.old-deja/g++.other/inline7.C  -std=gnu++17 (test for excess
errors)
Excess errors:
/gcc/testsuite/g++.old-deja/g++.other/inline7.C:11:11: warning: ignoring
return value of 'std::__cxx11::list<_Tp, _Alloc>::size_type
std::__cxx11::list<_Tp, _Alloc>::size() const [with _Tp = int*; _Alloc =
std::allocator<int*>; std::__cxx11::list<_Tp, _Alloc>::size_type = long
unsigned int]', declared with attribute 'nodiscard' [-Wunused-result]

FAIL: g++.old-deja/g++.other/inline7.C  -std=gnu++2a (test for excess
errors)
Excess errors:
/gcc/testsuite/g++.old-deja/g++.other/inline7.C:11:11: warning: ignoring
return value of 'std::__cxx11::list<_Tp, _Alloc>::size_type
std::__cxx11::list<_Tp, _Alloc>::size() const [with _Tp = int*; _Alloc =
std::allocator<int*>; std::__cxx11::list<_Tp, _Alloc>::size_type = long
unsigned int]', declared with attribute 'nodiscard' [-Wunused-result]

Not sure why you didn't see it?

Christophe

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers
  2021-08-05 12:09     ` Christophe Lyon
@ 2021-08-05 12:13       ` Ville Voutilainen
  2021-08-05 14:21         ` Jonathan Wakely
  0 siblings, 1 reply; 12+ messages in thread
From: Ville Voutilainen @ 2021-08-05 12:13 UTC (permalink / raw)
  To: Christophe Lyon; +Cc: Jonathan Wakely, libstdc++, GCC Patches

On Thu, 5 Aug 2021 at 15:11, Christophe Lyon via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Hi Jonathan,
>
> On Wed, Aug 4, 2021 at 2:04 PM Jonathan Wakely via Gcc-patches <
> gcc-patches@gcc.gnu.org> wrote:
>
> > On 04/08/21 12:56 +0100, Jonathan Wakely wrote:
> > >... and container adaptors.
> > >
> > >This adds the [[nodiscard]] attribute to functions with no side-effects
> > >for the sequence containers and their iterators, and the debug versions
> > >of those containers, and the container adaptors,
> >
> > I don't plan to add any more [[nodiscard]] attributes for now, but
> > these two commits should demonstrate how to do it for anybody who
> > wants to contribute similar patches.
> >
> > I didn't add tests that verify we do actually warn on each of those
> > functions, because there are hundreds of them, and I know they're
> > working because I had to alter existing tests to not warn.
> >
> >
> I've noticed a regression on aarch64/arm:
> FAIL: g++.old-deja/g++.other/inline7.C  -std=gnu++17 (test for excess
> errors)
> Excess errors:
> /gcc/testsuite/g++.old-deja/g++.other/inline7.C:11:11: warning: ignoring
> return value of 'std::__cxx11::list<_Tp, _Alloc>::size_type
> std::__cxx11::list<_Tp, _Alloc>::size() const [with _Tp = int*; _Alloc =
> std::allocator<int*>; std::__cxx11::list<_Tp, _Alloc>::size_type = long
> unsigned int]', declared with attribute 'nodiscard' [-Wunused-result]
>
> FAIL: g++.old-deja/g++.other/inline7.C  -std=gnu++2a (test for excess
> errors)
> Excess errors:
> /gcc/testsuite/g++.old-deja/g++.other/inline7.C:11:11: warning: ignoring
> return value of 'std::__cxx11::list<_Tp, _Alloc>::size_type
> std::__cxx11::list<_Tp, _Alloc>::size() const [with _Tp = int*; _Alloc =
> std::allocator<int*>; std::__cxx11::list<_Tp, _Alloc>::size_type = long
> unsigned int]', declared with attribute 'nodiscard' [-Wunused-result]
>
> Not sure why you didn't see it?

That can easily happen when running just the library tests, rather
than all of them. :P

^ permalink raw reply	[flat|nested] 12+ messages in thread

* [committed] libstdc++: Move attributes that follow requires-clauses [PR101782]
  2021-08-04 11:55 [committed 1/2] libstdc++: Add [[nodiscard]] to iterators and related utilities Jonathan Wakely
  2021-08-04 11:56 ` [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers Jonathan Wakely
@ 2021-08-05 14:19 ` Jonathan Wakely
  2021-08-05 14:27   ` Ville Voutilainen
  2021-08-05 14:40   ` Jonathan Wakely
  1 sibling, 2 replies; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-05 14:19 UTC (permalink / raw)
  To: libstdc++, gcc-patches

[-- Attachment #1: Type: text/plain, Size: 422 bytes --]

On 04/08/21 12:55 +0100, Jonathan Wakely wrote:
>This adds [[nodiscard]] throughout <iterator>, as proposed by P2377R0
>(with some minor corrections).
>
>The attribute is added for all modes from C++11 up, using
>[[__nodiscard__]] or _GLIBCXX_NODISCARD where C++17 [[nodiscard]] can't
>be used directly.

This change causes errors when -fconcepts-ts is used. Fixed like so.

Tested powerpc64le-linux, committed to trunk.


[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 12719 bytes --]

commit 7b1de3eb9ed3f8dde54732d88520292c5ad1157d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Aug 5 13:34:00 2021

    libstdc++: Move attributes that follow requires-clauses [PR101782]
    
    As explained in the PR, the grammar in the Concepts TS means that a [
    token following a requires-clause is parsed as part of the
    logical-or-expression rather than the start of an attribute. That makes
    the following ill-formed when using -fconcepts-ts:
    
      template<typename T> requires foo<T> [[nodiscard]] int f(T);
    
    This change moves all attributes that follow a requires-clause to the
    end of the function declarator.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/101782
            * include/bits/ranges_base.h (ranges::begin, ranges::end)
            (ranges::rbegin, ranges::rend, ranges::size, ranges::ssize)
            (ranges::empty, ranges::data): Move attribute to the end of
            the declarator.
            * include/bits/stl_iterator.h (__gnu_cxx::__normal_iterator)
            (common_iterator): Likewise for non-member operator functions.
            * include/std/ranges (views::all, views::filter)
            (views::transform, views::take, views::take_while, views::drop)
            (views::drop_while, views::join, views::lazy_split)
            (views::split, views::counted, views::common, views::reverse)
            (views::elements): Likewise.
            * testsuite/std/ranges/access/101782.cc: New test.

diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index 614b6edf9df..1dac9680b4f 100644
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -110,9 +110,9 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires is_array_v<remove_reference_t<_Tp>> || __member_begin<_Tp>
 	  || __adl_begin<_Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
+	[[nodiscard]]
 	{
 	  if constexpr (is_array_v<remove_reference_t<_Tp>>)
 	    {
@@ -162,9 +162,9 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_end<_Tp> || __adl_end<_Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
+	[[nodiscard]]
 	{
 	  if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
 	    {
@@ -267,10 +267,10 @@ namespace ranges
     public:
       template<__maybe_borrowed_range _Tp>
 	requires __member_rbegin<_Tp> || __adl_rbegin<_Tp> || __reversable<_Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
+	[[nodiscard]]
 	{
 	  if constexpr (__member_rbegin<_Tp>)
 	    return __t.rbegin();
@@ -326,10 +326,10 @@ namespace ranges
     public:
       template<__maybe_borrowed_range _Tp>
 	requires __member_rend<_Tp> || __adl_rend<_Tp> || __reversable<_Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
+	[[nodiscard]]
 	{
 	  if constexpr (__member_rend<_Tp>)
 	    return __t.rend();
@@ -416,9 +416,9 @@ namespace ranges
       template<typename _Tp>
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_size<_Tp> || __adl_size<_Tp> || __sentinel_size<_Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
+	[[nodiscard]]
 	{
 	  if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
 	    return extent_v<remove_reference_t<_Tp>>;
@@ -437,9 +437,9 @@ namespace ranges
       // 3403. Domain of ranges::ssize(E) doesn't match ranges::size(E)
       template<typename _Tp>
 	requires requires (_Tp& __t) { _Size{}(__t); }
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
+	[[nodiscard]]
 	{
 	  auto __size = _Size{}(__t);
 	  using __size_type = decltype(__size);
@@ -497,9 +497,9 @@ namespace ranges
       template<typename _Tp>
 	requires __member_empty<_Tp> || __size0_empty<_Tp>
 	  || __eq_iter_empty<_Tp>
-	[[nodiscard]]
 	constexpr bool
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
+	[[nodiscard]]
 	{
 	  if constexpr (__member_empty<_Tp>)
 	    return bool(__t.empty());
@@ -539,9 +539,9 @@ namespace ranges
     public:
       template<__maybe_borrowed_range _Tp>
 	requires __member_data<_Tp> || __begin_data<_Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp>())
+	[[nodiscard]]
 	{
 	  if constexpr (__member_data<_Tp>)
 	    return __t.data();
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 3773d600b8f..053ae41e9c3 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1120,19 +1120,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _IteratorL, typename _IteratorR, typename _Container>
     requires requires (_IteratorL __lhs, _IteratorR __rhs)
     { { __lhs == __rhs } -> std::convertible_to<bool>; }
-    [[nodiscard]]
     constexpr bool
     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
     noexcept(noexcept(__lhs.base() == __rhs.base()))
+    [[nodiscard]]
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
-    [[nodiscard]]
     constexpr std::__detail::__synth3way_t<_IteratorR, _IteratorL>
     operator<=>(const __normal_iterator<_IteratorL, _Container>& __lhs,
 		const __normal_iterator<_IteratorR, _Container>& __rhs)
     noexcept(noexcept(std::__detail::__synth3way(__lhs.base(), __rhs.base())))
+    [[nodiscard]]
     { return std::__detail::__synth3way(__lhs.base(), __rhs.base()); }
 #else
    // Forward iterator requirements
@@ -1984,10 +1984,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2>
-      [[nodiscard]]
       friend bool
       operator==(const common_iterator& __x,
 		 const common_iterator<_It2, _Sent2>& __y)
+      [[nodiscard]]
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
@@ -2007,10 +2007,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2> && equality_comparable_with<_It, _It2>
-      [[nodiscard]]
       friend bool
       operator==(const common_iterator& __x,
 		 const common_iterator<_It2, _Sent2>& __y)
+      [[nodiscard]]
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
@@ -2031,10 +2031,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<sized_sentinel_for<_It> _It2, sized_sentinel_for<_It> _Sent2>
       requires sized_sentinel_for<_Sent, _It2>
-      [[nodiscard]]
       friend iter_difference_t<_It2>
       operator-(const common_iterator& __x,
 		const common_iterator<_It2, _Sent2>& __y)
+      [[nodiscard]]
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 03a3778bb52..71b7dc7d295 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1126,10 +1126,10 @@ namespace views::__adaptor
 	requires view<decay_t<_Range>>
 	  || __detail::__can_ref_view<_Range>
 	  || __detail::__can_subrange<_Range>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
 	noexcept(_S_noexcept<_Range>())
+	[[nodiscard]]
 	{
 	  if constexpr (view<decay_t<_Range>>)
 	    return std::forward<_Range>(__r);
@@ -1553,9 +1553,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_filter_view<_Range, _Pred>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pred&& __p) const
+	[[nodiscard]]
 	{
 	  return filter_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
 	}
@@ -1931,9 +1931,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Fp>
 	requires __detail::__can_transform_view<_Range, _Fp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Fp&& __f) const
+	[[nodiscard]]
 	{
 	  return transform_view(std::forward<_Range>(__r), std::forward<_Fp>(__f));
 	}
@@ -2113,9 +2113,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_take_view<_Range, _Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Tp&& __n) const
+	[[nodiscard]]
 	{
 	  return take_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
 	}
@@ -2241,9 +2241,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_take_while_view<_Range, _Pred>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pred&& __p) const
+	[[nodiscard]]
 	{
 	  return take_while_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
 	}
@@ -2362,9 +2362,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_drop_view<_Range, _Tp>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Tp&& __n) const
+	[[nodiscard]]
 	{
 	  return drop_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
 	}
@@ -2451,9 +2451,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_drop_while_view<_Range, _Pred>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pred&& __p) const
+	[[nodiscard]]
 	{
 	  return drop_while_view(std::forward<_Range>(__r),
 				 std::forward<_Pred>(__p));
@@ -2814,9 +2814,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range>
 	requires __detail::__can_join_view<_Range>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
+	[[nodiscard]]
 	{
 	  // _GLIBCXX_RESOLVE_LIB_DEFECTS
 	  // 3474. Nesting join_views is broken because of CTAD
@@ -3266,9 +3266,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_lazy_split_view<_Range, _Pattern>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pattern&& __f) const
+	[[nodiscard]]
 	{
 	  return lazy_split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
 	}
@@ -3475,9 +3475,9 @@ namespace views::__adaptor
     {
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_split_view<_Range, _Pattern>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r, _Pattern&& __f) const
+	[[nodiscard]]
 	{
 	  return split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
 	}
@@ -3497,9 +3497,9 @@ namespace views::__adaptor
     struct _Counted
     {
       template<input_or_output_iterator _Iter>
-      [[nodiscard]]
       constexpr auto
       operator()(_Iter __i, iter_difference_t<_Iter> __n) const
+      [[nodiscard]]
       {
 	if constexpr (random_access_iterator<_Iter>)
 	  return subrange(__i, __i + __n);
@@ -3619,9 +3619,9 @@ namespace views::__adaptor
       template<viewable_range _Range>
 	requires __detail::__already_common<_Range>
 	  || __detail::__can_common_view<_Range>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
+	[[nodiscard]]
 	{
 	  if constexpr (__detail::__already_common<_Range>)
 	    return views::all(std::forward<_Range>(__r));
@@ -3742,9 +3742,9 @@ namespace views::__adaptor
 	requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
 	  || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
 	  || __detail::__can_reverse_view<_Range>
-	[[nodiscard]]
 	constexpr auto
 	operator()(_Range&& __r) const
+	[[nodiscard]]
 	{
 	  using _Tp = remove_cvref_t<_Range>;
 	  if constexpr (__detail::__is_reverse_view<_Tp>)
@@ -4141,9 +4141,9 @@ namespace views::__adaptor
       {
 	template<viewable_range _Range>
 	  requires __detail::__can_elements_view<_Nm, _Range>
-	  [[nodiscard]]
 	  constexpr auto
 	  operator()(_Range&& __r) const
+	  [[nodiscard]]
 	  {
 	    return elements_view<all_t<_Range>, _Nm>{std::forward<_Range>(__r)};
 	  }
diff --git a/libstdc++-v3/testsuite/std/ranges/access/101782.cc b/libstdc++-v3/testsuite/std/ranges/access/101782.cc
new file mode 100644
index 00000000000..abb0c8dab0f
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/access/101782.cc
@@ -0,0 +1,9 @@
+// { dg-options "-std=gnu++20 -fconcepts-ts" }
+// { dg-do compile { target c++20 } }
+
+// PR testsuite/101782
+// attribute-specifier-seq cannot follow requires-clause with -fconcepts-ts
+
+#include <algorithm>
+#include <iterator>
+#include <ranges>

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers
  2021-08-05 12:13       ` Ville Voutilainen
@ 2021-08-05 14:21         ` Jonathan Wakely
  0 siblings, 0 replies; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-05 14:21 UTC (permalink / raw)
  To: Ville Voutilainen; +Cc: Christophe Lyon, libstdc++, GCC Patches

[-- Attachment #1: Type: text/plain, Size: 2285 bytes --]

On Thu, 5 Aug 2021 at 13:14, Ville Voutilainen
<ville.voutilainen@gmail.com> wrote:
>
> On Thu, 5 Aug 2021 at 15:11, Christophe Lyon via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > Hi Jonathan,
> >
> > On Wed, Aug 4, 2021 at 2:04 PM Jonathan Wakely via Gcc-patches <
> > gcc-patches@gcc.gnu.org> wrote:
> >
> > > On 04/08/21 12:56 +0100, Jonathan Wakely wrote:
> > > >... and container adaptors.
> > > >
> > > >This adds the [[nodiscard]] attribute to functions with no side-effects
> > > >for the sequence containers and their iterators, and the debug versions
> > > >of those containers, and the container adaptors,
> > >
> > > I don't plan to add any more [[nodiscard]] attributes for now, but
> > > these two commits should demonstrate how to do it for anybody who
> > > wants to contribute similar patches.
> > >
> > > I didn't add tests that verify we do actually warn on each of those
> > > functions, because there are hundreds of them, and I know they're
> > > working because I had to alter existing tests to not warn.
> > >
> > >
> > I've noticed a regression on aarch64/arm:
> > FAIL: g++.old-deja/g++.other/inline7.C  -std=gnu++17 (test for excess
> > errors)
> > Excess errors:
> > /gcc/testsuite/g++.old-deja/g++.other/inline7.C:11:11: warning: ignoring
> > return value of 'std::__cxx11::list<_Tp, _Alloc>::size_type
> > std::__cxx11::list<_Tp, _Alloc>::size() const [with _Tp = int*; _Alloc =
> > std::allocator<int*>; std::__cxx11::list<_Tp, _Alloc>::size_type = long
> > unsigned int]', declared with attribute 'nodiscard' [-Wunused-result]
> >
> > FAIL: g++.old-deja/g++.other/inline7.C  -std=gnu++2a (test for excess
> > errors)
> > Excess errors:
> > /gcc/testsuite/g++.old-deja/g++.other/inline7.C:11:11: warning: ignoring
> > return value of 'std::__cxx11::list<_Tp, _Alloc>::size_type
> > std::__cxx11::list<_Tp, _Alloc>::size() const [with _Tp = int*; _Alloc =
> > std::allocator<int*>; std::__cxx11::list<_Tp, _Alloc>::size_type = long
> > unsigned int]', declared with attribute 'nodiscard' [-Wunused-result]
> >
> > Not sure why you didn't see it?
>
> That can easily happen when running just the library tests, rather
> than all of them. :P

Right, I didn't run all the compiler tests.

Fixed with this patch, tested x86_64-linux, pushed to trunk.

[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 728 bytes --]

commit 03d47da7e1e91adddbde261ffefd2760df59a564
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Aug 5 14:00:35 2021

    testsuite: Fix warning introduced by nodiscard in libstdc++
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    gcc/testsuite/ChangeLog:
    
            * g++.old-deja/g++.other/inline7.C: Cast nodiscard call to void.

diff --git a/gcc/testsuite/g++.old-deja/g++.other/inline7.C b/gcc/testsuite/g++.old-deja/g++.other/inline7.C
index a3723cfba1e..626000039c5 100644
--- a/gcc/testsuite/g++.old-deja/g++.other/inline7.C
+++ b/gcc/testsuite/g++.old-deja/g++.other/inline7.C
@@ -8,7 +8,7 @@ std::list<int*> li;
 
 void f ()
 {
-  li.size ();
+  (void) li.size ();
 }
 
 int main ()

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed] libstdc++: Move attributes that follow requires-clauses [PR101782]
  2021-08-05 14:19 ` [committed] libstdc++: Move attributes that follow requires-clauses [PR101782] Jonathan Wakely
@ 2021-08-05 14:27   ` Ville Voutilainen
  2021-08-05 14:40   ` Jonathan Wakely
  1 sibling, 0 replies; 12+ messages in thread
From: Ville Voutilainen @ 2021-08-05 14:27 UTC (permalink / raw)
  To: Jonathan Wakely; +Cc: libstdc++, gcc-patches List

On Thu, 5 Aug 2021 at 17:21, Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On 04/08/21 12:55 +0100, Jonathan Wakely wrote:
> >This adds [[nodiscard]] throughout <iterator>, as proposed by P2377R0
> >(with some minor corrections).
> >
> >The attribute is added for all modes from C++11 up, using
> >[[__nodiscard__]] or _GLIBCXX_NODISCARD where C++17 [[nodiscard]] can't
> >be used directly.
>
> This change causes errors when -fconcepts-ts is used. Fixed like so.

But this makes the attribute appertain to the function type, not to
the function. It's also ill-formed:
"The attribute-token nodiscard may be applied to the declarator-id in
a function declaration or to the
declaration of a class or enumeration. " Your change makes nodiscard
be applied to the function declaration,
not to the declarator-id.

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers
  2021-08-04 12:00   ` Jonathan Wakely
  2021-08-05 12:09     ` Christophe Lyon
@ 2021-08-05 14:38     ` Jonathan Wakely
  1 sibling, 0 replies; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-05 14:38 UTC (permalink / raw)
  To: libstdc++, gcc-patches

[-- Attachment #1: Type: text/plain, Size: 623 bytes --]

On 04/08/21 13:00 +0100, Jonathan Wakely wrote:
>On 04/08/21 12:56 +0100, Jonathan Wakely wrote:
>>... and container adaptors.
>>
>>This adds the [[nodiscard]] attribute to functions with no side-effects
>>for the sequence containers and their iterators, and the debug versions
>>of those containers, and the container adaptors,
>
>I don't plan to add any more [[nodiscard]] attributes for now, but
>these two commits should demonstrate how to do it for anybody who
>wants to contribute similar patches.

OK, one more change in this vein, adding [[nodiscard]] to <compare>.

Tested powerpc64le-linux, committed to trunk.



[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 10719 bytes --]

commit 8dec72aeb54e98643c0fb3d53768cdb96cf1342a
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Aug 5 14:01:31 2021

    libstdc++: Add [[nodiscard]] to <compare>
    
    This adds the [[nodiscard]] attribute to all conversion operators,
    comparison operators, call operators and non-member functions in
    <compare>. Nothing in this header except constructors has side effects.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * libsupc++/compare (partial_ordering, weak_ordering)
            (strong_ordering, is_eq, is_neq, is_lt, is_lteq, is_gt, is_gteq)
            (compare_three_way, strong_order, weak_order, partial_order)
            (compare_strong_order_fallback, compare_weak_order_fallback)
            (compare_partial_order_fallback, __detail::__synth3way): Add
            nodiscard attribute.
            * testsuite/18_support/comparisons/categories/zero_neg.cc: Add
            -Wno-unused-result to options.

diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare
index dd0ec5fa36d..faeff641437 100644
--- a/libstdc++-v3/libsupc++/compare
+++ b/libstdc++-v3/libsupc++/compare
@@ -86,49 +86,61 @@ namespace std
     static const partial_ordering unordered;
 
     // comparisons
+    [[nodiscard]]
     friend constexpr bool
     operator==(partial_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value == 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator==(partial_ordering, partial_ordering) noexcept = default;
 
+    [[nodiscard]]
     friend constexpr bool
     operator< (partial_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value == -1; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator> (partial_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value == 1; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator<=(partial_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value <= 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator>=(partial_ordering __v, __cmp_cat::__unspec) noexcept
     { return __cmp_cat::type(__v._M_value & 1) == __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator< (__cmp_cat::__unspec, partial_ordering __v) noexcept
     { return __v._M_value == 1; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator> (__cmp_cat::__unspec, partial_ordering __v) noexcept
     { return __v._M_value == -1; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator<=(__cmp_cat::__unspec, partial_ordering __v) noexcept
     { return __cmp_cat::type(__v._M_value & 1) == __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator>=(__cmp_cat::__unspec, partial_ordering __v) noexcept
     { return 0 >= __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr partial_ordering
     operator<=>(partial_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v; }
 
+    [[nodiscard]]
     friend constexpr partial_ordering
     operator<=>(__cmp_cat::__unspec, partial_ordering __v) noexcept
     {
@@ -168,53 +180,66 @@ namespace std
     static const weak_ordering equivalent;
     static const weak_ordering greater;
 
+    [[nodiscard]]
     constexpr operator partial_ordering() const noexcept
     { return partial_ordering(__cmp_cat::_Ord(_M_value)); }
 
     // comparisons
+    [[nodiscard]]
     friend constexpr bool
     operator==(weak_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value == 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator==(weak_ordering, weak_ordering) noexcept = default;
 
+    [[nodiscard]]
     friend constexpr bool
     operator< (weak_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value < 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator> (weak_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value > 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator<=(weak_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value <= 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator>=(weak_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value >= 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator< (__cmp_cat::__unspec, weak_ordering __v) noexcept
     { return 0 < __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator> (__cmp_cat::__unspec, weak_ordering __v) noexcept
     { return 0 > __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator<=(__cmp_cat::__unspec, weak_ordering __v) noexcept
     { return 0 <= __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator>=(__cmp_cat::__unspec, weak_ordering __v) noexcept
     { return 0 >= __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr weak_ordering
     operator<=>(weak_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v; }
 
+    [[nodiscard]]
     friend constexpr weak_ordering
     operator<=>(__cmp_cat::__unspec, weak_ordering __v) noexcept
     { return weak_ordering(__cmp_cat::_Ord(-__v._M_value)); }
@@ -246,56 +271,70 @@ namespace std
     static const strong_ordering equivalent;
     static const strong_ordering greater;
 
+    [[nodiscard]]
     constexpr operator partial_ordering() const noexcept
     { return partial_ordering(__cmp_cat::_Ord(_M_value)); }
 
+    [[nodiscard]]
     constexpr operator weak_ordering() const noexcept
     { return weak_ordering(__cmp_cat::_Ord(_M_value)); }
 
     // comparisons
+    [[nodiscard]]
     friend constexpr bool
     operator==(strong_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value == 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator==(strong_ordering, strong_ordering) noexcept = default;
 
+    [[nodiscard]]
     friend constexpr bool
     operator< (strong_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value < 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator> (strong_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value > 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator<=(strong_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value <= 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator>=(strong_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v._M_value >= 0; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator< (__cmp_cat::__unspec, strong_ordering __v) noexcept
     { return 0 < __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator> (__cmp_cat::__unspec, strong_ordering __v) noexcept
     { return 0 > __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator<=(__cmp_cat::__unspec, strong_ordering __v) noexcept
     { return 0 <= __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr bool
     operator>=(__cmp_cat::__unspec, strong_ordering __v) noexcept
     { return 0 >= __v._M_value; }
 
+    [[nodiscard]]
     friend constexpr strong_ordering
     operator<=>(strong_ordering __v, __cmp_cat::__unspec) noexcept
     { return __v; }
 
+    [[nodiscard]]
     friend constexpr strong_ordering
     operator<=>(__cmp_cat::__unspec, strong_ordering __v) noexcept
     { return strong_ordering(__cmp_cat::_Ord(-__v._M_value)); }
@@ -316,26 +355,32 @@ namespace std
 
 
   // named comparison functions
+  [[nodiscard]]
   constexpr bool
   is_eq(partial_ordering __cmp) noexcept
   { return __cmp == 0; }
 
+  [[nodiscard]]
   constexpr bool
   is_neq(partial_ordering __cmp) noexcept
   { return __cmp != 0; }
 
+  [[nodiscard]]
   constexpr bool
   is_lt  (partial_ordering __cmp) noexcept
   { return __cmp < 0; }
 
+  [[nodiscard]]
   constexpr bool
   is_lteq(partial_ordering __cmp) noexcept
   { return __cmp <= 0; }
 
+  [[nodiscard]]
   constexpr bool
   is_gt  (partial_ordering __cmp) noexcept
   { return __cmp > 0; }
 
+  [[nodiscard]]
   constexpr bool
   is_gteq(partial_ordering __cmp) noexcept
   { return __cmp >= 0; }
@@ -505,6 +550,7 @@ namespace std
       constexpr auto
       operator()(_Tp&& __t, _Up&& __u) const
       noexcept(noexcept(std::declval<_Tp>() <=> std::declval<_Up>()))
+      [[nodiscard]]
       {
 	if constexpr (__detail::__3way_builtin_ptr_cmp<_Tp, _Up>)
 	  {
@@ -628,6 +674,7 @@ namespace std
 	constexpr strong_ordering
 	operator()(_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
+	[[nodiscard]]
 	{
 	  /* FIXME:
 	  if constexpr (floating_point<decay_t<_Tp>>)
@@ -675,6 +722,7 @@ namespace std
 	constexpr weak_ordering
 	operator()(_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
+	[[nodiscard]]
 	{
 	  if constexpr (floating_point<decay_t<_Tp>>)
 	    return __cmp_cust::__fp_weak_ordering(__e, __f);
@@ -720,6 +768,7 @@ namespace std
 	constexpr partial_ordering
 	operator()(_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
+	[[nodiscard]]
 	{
 	  if constexpr (__adl_partial<_Tp, _Up>)
 	    return partial_ordering(partial_order(static_cast<_Tp&&>(__e),
@@ -761,6 +810,7 @@ namespace std
 	constexpr strong_ordering
 	operator()(_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
+	[[nodiscard]]
 	{
 	  if constexpr (__strongly_ordered<_Tp, _Up>)
 	    return _Strong_order{}(static_cast<_Tp&&>(__e),
@@ -793,6 +843,7 @@ namespace std
 	constexpr weak_ordering
 	operator()(_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
+	[[nodiscard]]
 	{
 	  if constexpr (__weakly_ordered<_Tp, _Up>)
 	    return _Weak_order{}(static_cast<_Tp&&>(__e),
@@ -835,6 +886,7 @@ namespace std
 	constexpr partial_ordering
 	operator()(_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
+	[[nodiscard]]
 	{
 	  if constexpr (__partially_ordered<_Tp, _Up>)
 	    return _Partial_order{}(static_cast<_Tp&&>(__e),
@@ -886,6 +938,7 @@ namespace std
 	}
 
       template<typename _Tp, typename _Up>
+	[[nodiscard]]
 	constexpr auto
 	operator()(const _Tp& __t, const _Up& __u) const
 	noexcept(_S_noexcept<_Tp, _Up>())
diff --git a/libstdc++-v3/testsuite/18_support/comparisons/categories/zero_neg.cc b/libstdc++-v3/testsuite/18_support/comparisons/categories/zero_neg.cc
index 0ca7de0179c..f912ad399d0 100644
--- a/libstdc++-v3/testsuite/18_support/comparisons/categories/zero_neg.cc
+++ b/libstdc++-v3/testsuite/18_support/comparisons/categories/zero_neg.cc
@@ -15,7 +15,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// { dg-options "-std=gnu++2a" }
+// { dg-options "-std=gnu++2a -Wno-unused-result" }
 // { dg-do compile { target c++2a } }
 
 #include <compare>

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed] libstdc++: Move attributes that follow requires-clauses [PR101782]
  2021-08-05 14:19 ` [committed] libstdc++: Move attributes that follow requires-clauses [PR101782] Jonathan Wakely
  2021-08-05 14:27   ` Ville Voutilainen
@ 2021-08-05 14:40   ` Jonathan Wakely
  2021-08-05 18:02     ` Jonathan Wakely
  1 sibling, 1 reply; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-05 14:40 UTC (permalink / raw)
  To: libstdc++, gcc-patches

On 05/08/21 15:19 +0100, Jonathan Wakely wrote:
>On 04/08/21 12:55 +0100, Jonathan Wakely wrote:
>>This adds [[nodiscard]] throughout <iterator>, as proposed by P2377R0
>>(with some minor corrections).
>>
>>The attribute is added for all modes from C++11 up, using
>>[[__nodiscard__]] or _GLIBCXX_NODISCARD where C++17 [[nodiscard]] can't
>>be used directly.
>
>This change causes errors when -fconcepts-ts is used. Fixed like so.
>
>Tested powerpc64le-linux, committed to trunk.
>

>commit 7b1de3eb9ed3f8dde54732d88520292c5ad1157d
>Author: Jonathan Wakely <jwakely@redhat.com>
>Date:   Thu Aug 5 13:34:00 2021
>
>    libstdc++: Move attributes that follow requires-clauses [PR101782]
>    
>    As explained in the PR, the grammar in the Concepts TS means that a [
>    token following a requires-clause is parsed as part of the
>    logical-or-expression rather than the start of an attribute. That makes
>    the following ill-formed when using -fconcepts-ts:
>    
>      template<typename T> requires foo<T> [[nodiscard]] int f(T);
>    
>    This change moves all attributes that follow a requires-clause to the
>    end of the function declarator.


Except that as Jakub pointed out, putting it there doesn't work.

It needs to be:

   template<typename T> requires foo<T> int f [[nodiscard]] (T);

At least the testsuite isn't failing now, but the attributes I moved
have no effect. I'll fix it ... some time.




^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed] libstdc++: Move attributes that follow requires-clauses [PR101782]
  2021-08-05 14:40   ` Jonathan Wakely
@ 2021-08-05 18:02     ` Jonathan Wakely
  2021-08-06 13:29       ` Jonathan Wakely
  0 siblings, 1 reply; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-05 18:02 UTC (permalink / raw)
  To: libstdc++, gcc-patches

[-- Attachment #1: Type: text/plain, Size: 1550 bytes --]

On 05/08/21 15:40 +0100, Jonathan Wakely wrote:
>On 05/08/21 15:19 +0100, Jonathan Wakely wrote:
>>On 04/08/21 12:55 +0100, Jonathan Wakely wrote:
>>>This adds [[nodiscard]] throughout <iterator>, as proposed by P2377R0
>>>(with some minor corrections).
>>>
>>>The attribute is added for all modes from C++11 up, using
>>>[[__nodiscard__]] or _GLIBCXX_NODISCARD where C++17 [[nodiscard]] can't
>>>be used directly.
>>
>>This change causes errors when -fconcepts-ts is used. Fixed like so.
>>
>>Tested powerpc64le-linux, committed to trunk.
>>
>
>>commit 7b1de3eb9ed3f8dde54732d88520292c5ad1157d
>>Author: Jonathan Wakely <jwakely@redhat.com>
>>Date:   Thu Aug 5 13:34:00 2021
>>
>>   libstdc++: Move attributes that follow requires-clauses [PR101782]
>>   As explained in the PR, the grammar in the Concepts TS means that a [
>>   token following a requires-clause is parsed as part of the
>>   logical-or-expression rather than the start of an attribute. That makes
>>   the following ill-formed when using -fconcepts-ts:
>>     template<typename T> requires foo<T> [[nodiscard]] int f(T);
>>   This change moves all attributes that follow a requires-clause to the
>>   end of the function declarator.
>
>
>Except that as Jakub pointed out, putting it there doesn't work.
>
>It needs to be:
>
>  template<typename T> requires foo<T> int f [[nodiscard]] (T);
>
>At least the testsuite isn't failing now, but the attributes I moved
>have no effect. I'll fix it ... some time.

This should be correct now.

Tested powerpc64le-linux, pushed to trunk.



[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 14051 bytes --]

commit c8b024fa4b76bfd914e96dd3cecfbb6ee8e91316
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Aug 5 16:46:00 2021

    libstdc++: Move [[nodiscard]] attributes again [PR101782]
    
    Where I moved these nodiscard attributes to made them apply to the
    function type, not to the function. This meant they no longer generated
    the desired -Wunused-result warnings, and were ill-formed with Clang
    (but only a pedwarn with GCC).
    
    Clang also detected ill-formed attributes in <queue> which this fixes.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/101782
            * include/bits/ranges_base.h (ranges::begin, ranges::end)
            (ranges::rbegin, ranges::rend, ranges::size, ranges::ssize)
            (ranges::empty, ranges::data): Move attribute after the
            declarator-id instead of at the end of the declarator.
            * include/bits/stl_iterator.h (__gnu_cxx::__normal_iterator):
            Move attributes back to the start of the function declarator,
            but move the requires-clause to the end.
            (common_iterator): Move attribute after the declarator-id.
            * include/bits/stl_queue.h (queue): Remove ill-formed attributes
            from friend declaration that are not definitions.
            * include/std/ranges (views::all, views::filter)
            (views::transform, views::take, views::take_while,
            views::drop) (views::drop_while, views::join,
            views::lazy_split) (views::split, views::counted,
            views::common, views::reverse) (views::elements): Move
            attributes after the declarator-id.

diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index 1dac9680b4f..49c7d9c9f06 100644
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -111,8 +111,7 @@ namespace ranges
 	requires is_array_v<remove_reference_t<_Tp>> || __member_begin<_Tp>
 	  || __adl_begin<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (is_array_v<remove_reference_t<_Tp>>)
 	    {
@@ -163,8 +162,7 @@ namespace ranges
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_end<_Tp> || __adl_end<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
 	    {
@@ -268,9 +266,8 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires __member_rbegin<_Tp> || __adl_rbegin<_Tp> || __reversable<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const
+	operator()[[nodiscard]](_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
 	{
 	  if constexpr (__member_rbegin<_Tp>)
 	    return __t.rbegin();
@@ -327,9 +324,8 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires __member_rend<_Tp> || __adl_rend<_Tp> || __reversable<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const
+	operator()[[nodiscard]](_Tp&& __t) const
 	noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
 	{
 	  if constexpr (__member_rend<_Tp>)
 	    return __t.rend();
@@ -417,8 +413,7 @@ namespace ranges
 	requires is_bounded_array_v<remove_reference_t<_Tp>>
 	  || __member_size<_Tp> || __adl_size<_Tp> || __sentinel_size<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (is_bounded_array_v<remove_reference_t<_Tp>>)
 	    return extent_v<remove_reference_t<_Tp>>;
@@ -438,8 +433,7 @@ namespace ranges
       template<typename _Tp>
 	requires requires (_Tp& __t) { _Size{}(__t); }
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(noexcept(_Size{}(__t)))
 	{
 	  auto __size = _Size{}(__t);
 	  using __size_type = decltype(__size);
@@ -498,8 +492,7 @@ namespace ranges
 	requires __member_empty<_Tp> || __size0_empty<_Tp>
 	  || __eq_iter_empty<_Tp>
 	constexpr bool
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp&>())
 	{
 	  if constexpr (__member_empty<_Tp>)
 	    return bool(__t.empty());
@@ -540,8 +533,7 @@ namespace ranges
       template<__maybe_borrowed_range _Tp>
 	requires __member_data<_Tp> || __begin_data<_Tp>
 	constexpr auto
-	operator()(_Tp&& __t) const noexcept(_S_noexcept<_Tp>())
-	[[nodiscard]]
+	operator()[[nodiscard]](_Tp&& __t) const noexcept(_S_noexcept<_Tp>())
 	{
 	  if constexpr (__member_data<_Tp>)
 	    return __t.data();
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 053ae41e9c3..c5b02408c1c 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1118,21 +1118,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cpp_lib_three_way_comparison
   template<typename _IteratorL, typename _IteratorR, typename _Container>
-    requires requires (_IteratorL __lhs, _IteratorR __rhs)
-    { { __lhs == __rhs } -> std::convertible_to<bool>; }
+    [[nodiscard]]
     constexpr bool
     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
     noexcept(noexcept(__lhs.base() == __rhs.base()))
-    [[nodiscard]]
+    requires requires {
+      { __lhs.base() == __rhs.base() } -> std::convertible_to<bool>;
+    }
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    [[nodiscard]]
     constexpr std::__detail::__synth3way_t<_IteratorR, _IteratorL>
     operator<=>(const __normal_iterator<_IteratorL, _Container>& __lhs,
 		const __normal_iterator<_IteratorR, _Container>& __rhs)
     noexcept(noexcept(std::__detail::__synth3way(__lhs.base(), __rhs.base())))
-    [[nodiscard]]
     { return std::__detail::__synth3way(__lhs.base(), __rhs.base()); }
 #else
    // Forward iterator requirements
@@ -1985,9 +1986,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2>
       friend bool
-      operator==(const common_iterator& __x,
-		 const common_iterator<_It2, _Sent2>& __y)
-      [[nodiscard]]
+      operator== [[nodiscard]] (const common_iterator& __x,
+				const common_iterator<_It2, _Sent2>& __y)
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
@@ -2008,9 +2008,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _It2, sentinel_for<_It> _Sent2>
       requires sentinel_for<_Sent, _It2> && equality_comparable_with<_It, _It2>
       friend bool
-      operator==(const common_iterator& __x,
-		 const common_iterator<_It2, _Sent2>& __y)
-      [[nodiscard]]
+      operator== [[nodiscard]] (const common_iterator& __x,
+				const common_iterator<_It2, _Sent2>& __y)
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
@@ -2032,9 +2031,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<sized_sentinel_for<_It> _It2, sized_sentinel_for<_It> _Sent2>
       requires sized_sentinel_for<_Sent, _It2>
       friend iter_difference_t<_It2>
-      operator-(const common_iterator& __x,
-		const common_iterator<_It2, _Sent2>& __y)
-      [[nodiscard]]
+      operator- [[nodiscard]] (const common_iterator& __x,
+			       const common_iterator<_It2, _Sent2>& __y)
       {
 	switch(__x._M_index << 2 | __y._M_index)
 	  {
diff --git a/libstdc++-v3/include/bits/stl_queue.h b/libstdc++-v3/include/bits/stl_queue.h
index 363868fe0a6..41ffc50d380 100644
--- a/libstdc++-v3/include/bits/stl_queue.h
+++ b/libstdc++-v3/include/bits/stl_queue.h
@@ -107,18 +107,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
       template<typename _Tp1, typename _Seq1>
-	_GLIBCXX_NODISCARD
 	friend bool
 	operator==(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 
       template<typename _Tp1, typename _Seq1>
-	_GLIBCXX_NODISCARD
 	friend bool
 	operator<(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 
 #if __cpp_lib_three_way_comparison
       template<typename _Tp1, three_way_comparable _Seq1>
-	[[nodiscard]]
 	friend compare_three_way_result_t<_Seq1>
 	operator<=>(const queue<_Tp1, _Seq1>&, const queue<_Tp1, _Seq1>&);
 #endif
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 71b7dc7d295..fb8905fab08 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1127,9 +1127,8 @@ namespace views::__adaptor
 	  || __detail::__can_ref_view<_Range>
 	  || __detail::__can_subrange<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
+	operator() [[nodiscard]] (_Range&& __r) const
 	noexcept(_S_noexcept<_Range>())
-	[[nodiscard]]
 	{
 	  if constexpr (view<decay_t<_Range>>)
 	    return std::forward<_Range>(__r);
@@ -1554,8 +1553,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_filter_view<_Range, _Pred>
 	constexpr auto
-	operator()(_Range&& __r, _Pred&& __p) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pred&& __p) const
 	{
 	  return filter_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
 	}
@@ -1932,8 +1930,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Fp>
 	requires __detail::__can_transform_view<_Range, _Fp>
 	constexpr auto
-	operator()(_Range&& __r, _Fp&& __f) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Fp&& __f) const
 	{
 	  return transform_view(std::forward<_Range>(__r), std::forward<_Fp>(__f));
 	}
@@ -2114,8 +2111,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_take_view<_Range, _Tp>
 	constexpr auto
-	operator()(_Range&& __r, _Tp&& __n) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Tp&& __n) const
 	{
 	  return take_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
 	}
@@ -2242,8 +2238,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_take_while_view<_Range, _Pred>
 	constexpr auto
-	operator()(_Range&& __r, _Pred&& __p) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pred&& __p) const
 	{
 	  return take_while_view(std::forward<_Range>(__r), std::forward<_Pred>(__p));
 	}
@@ -2363,8 +2358,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Tp>
 	requires __detail::__can_drop_view<_Range, _Tp>
 	constexpr auto
-	operator()(_Range&& __r, _Tp&& __n) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Tp&& __n) const
 	{
 	  return drop_view(std::forward<_Range>(__r), std::forward<_Tp>(__n));
 	}
@@ -2452,8 +2446,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pred>
 	requires __detail::__can_drop_while_view<_Range, _Pred>
 	constexpr auto
-	operator()(_Range&& __r, _Pred&& __p) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pred&& __p) const
 	{
 	  return drop_while_view(std::forward<_Range>(__r),
 				 std::forward<_Pred>(__p));
@@ -2815,8 +2808,7 @@ namespace views::__adaptor
       template<viewable_range _Range>
 	requires __detail::__can_join_view<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r) const
 	{
 	  // _GLIBCXX_RESOLVE_LIB_DEFECTS
 	  // 3474. Nesting join_views is broken because of CTAD
@@ -3267,8 +3259,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_lazy_split_view<_Range, _Pattern>
 	constexpr auto
-	operator()(_Range&& __r, _Pattern&& __f) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pattern&& __f) const
 	{
 	  return lazy_split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
 	}
@@ -3476,8 +3467,7 @@ namespace views::__adaptor
       template<viewable_range _Range, typename _Pattern>
 	requires __detail::__can_split_view<_Range, _Pattern>
 	constexpr auto
-	operator()(_Range&& __r, _Pattern&& __f) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r, _Pattern&& __f) const
 	{
 	  return split_view(std::forward<_Range>(__r), std::forward<_Pattern>(__f));
 	}
@@ -3498,8 +3488,7 @@ namespace views::__adaptor
     {
       template<input_or_output_iterator _Iter>
       constexpr auto
-      operator()(_Iter __i, iter_difference_t<_Iter> __n) const
-      [[nodiscard]]
+      operator() [[nodiscard]] (_Iter __i, iter_difference_t<_Iter> __n) const
       {
 	if constexpr (random_access_iterator<_Iter>)
 	  return subrange(__i, __i + __n);
@@ -3620,8 +3609,7 @@ namespace views::__adaptor
 	requires __detail::__already_common<_Range>
 	  || __detail::__can_common_view<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r) const
 	{
 	  if constexpr (__detail::__already_common<_Range>)
 	    return views::all(std::forward<_Range>(__r));
@@ -3743,8 +3731,7 @@ namespace views::__adaptor
 	  || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
 	  || __detail::__can_reverse_view<_Range>
 	constexpr auto
-	operator()(_Range&& __r) const
-	[[nodiscard]]
+	operator() [[nodiscard]] (_Range&& __r) const
 	{
 	  using _Tp = remove_cvref_t<_Range>;
 	  if constexpr (__detail::__is_reverse_view<_Tp>)
@@ -4142,8 +4129,7 @@ namespace views::__adaptor
 	template<viewable_range _Range>
 	  requires __detail::__can_elements_view<_Nm, _Range>
 	  constexpr auto
-	  operator()(_Range&& __r) const
-	  [[nodiscard]]
+	  operator() [[nodiscard]] (_Range&& __r) const
 	  {
 	    return elements_view<all_t<_Range>, _Nm>{std::forward<_Range>(__r)};
 	  }

^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [committed] libstdc++: Move attributes that follow requires-clauses [PR101782]
  2021-08-05 18:02     ` Jonathan Wakely
@ 2021-08-06 13:29       ` Jonathan Wakely
  0 siblings, 0 replies; 12+ messages in thread
From: Jonathan Wakely @ 2021-08-06 13:29 UTC (permalink / raw)
  To: libstdc++, gcc-patches

[-- Attachment #1: Type: text/plain, Size: 1692 bytes --]

On 05/08/21 19:02 +0100, Jonathan Wakely wrote:
>On 05/08/21 15:40 +0100, Jonathan Wakely wrote:
>>On 05/08/21 15:19 +0100, Jonathan Wakely wrote:
>>>On 04/08/21 12:55 +0100, Jonathan Wakely wrote:
>>>>This adds [[nodiscard]] throughout <iterator>, as proposed by P2377R0
>>>>(with some minor corrections).
>>>>
>>>>The attribute is added for all modes from C++11 up, using
>>>>[[__nodiscard__]] or _GLIBCXX_NODISCARD where C++17 [[nodiscard]] can't
>>>>be used directly.
>>>
>>>This change causes errors when -fconcepts-ts is used. Fixed like so.
>>>
>>>Tested powerpc64le-linux, committed to trunk.
>>>
>>
>>>commit 7b1de3eb9ed3f8dde54732d88520292c5ad1157d
>>>Author: Jonathan Wakely <jwakely@redhat.com>
>>>Date:   Thu Aug 5 13:34:00 2021
>>>
>>>  libstdc++: Move attributes that follow requires-clauses [PR101782]
>>>  As explained in the PR, the grammar in the Concepts TS means that a [
>>>  token following a requires-clause is parsed as part of the
>>>  logical-or-expression rather than the start of an attribute. That makes
>>>  the following ill-formed when using -fconcepts-ts:
>>>    template<typename T> requires foo<T> [[nodiscard]] int f(T);
>>>  This change moves all attributes that follow a requires-clause to the
>>>  end of the function declarator.
>>
>>
>>Except that as Jakub pointed out, putting it there doesn't work.
>>
>>It needs to be:
>>
>> template<typename T> requires foo<T> int f [[nodiscard]] (T);
>>
>>At least the testsuite isn't failing now, but the attributes I moved
>>have no effect. I'll fix it ... some time.
>
>This should be correct now.

Except I needed to move the ones I added to <compare> as well.

Tested powerpc64le-linux, pushed to trunk.



[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 3707 bytes --]

commit c2a984a3570b908a44a35e43bb48f0a05196156a
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Aug 6 13:43:26 2021

    libstdc++: Also move the [[nodiscard]] attributes in <compare>
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * libsupc++/compare (compare_three_way, strong_order)
            (weak_order, partial_order, compare_strong_order_fallback)
            (compare_weak_order_fallback, compare_partial_order_fallback):
            Move nodiscard attributes to correct location.

diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare
index faeff641437..5aee89e3a6e 100644
--- a/libstdc++-v3/libsupc++/compare
+++ b/libstdc++-v3/libsupc++/compare
@@ -548,9 +548,8 @@ namespace std
     template<typename _Tp, typename _Up>
       requires three_way_comparable_with<_Tp, _Up>
       constexpr auto
-      operator()(_Tp&& __t, _Up&& __u) const
+      operator() [[nodiscard]] (_Tp&& __t, _Up&& __u) const
       noexcept(noexcept(std::declval<_Tp>() <=> std::declval<_Up>()))
-      [[nodiscard]]
       {
 	if constexpr (__detail::__3way_builtin_ptr_cmp<_Tp, _Up>)
 	  {
@@ -672,9 +671,8 @@ namespace std
       template<typename _Tp, __decayed_same_as<_Tp> _Up>
 	requires __strongly_ordered<_Tp, _Up>
 	constexpr strong_ordering
-	operator()(_Tp&& __e, _Up&& __f) const
+	operator() [[nodiscard]] (_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
-	[[nodiscard]]
 	{
 	  /* FIXME:
 	  if constexpr (floating_point<decay_t<_Tp>>)
@@ -720,9 +718,8 @@ namespace std
       template<typename _Tp, __decayed_same_as<_Tp> _Up>
 	requires __weakly_ordered<_Tp, _Up>
 	constexpr weak_ordering
-	operator()(_Tp&& __e, _Up&& __f) const
+	operator() [[nodiscard]] (_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
-	[[nodiscard]]
 	{
 	  if constexpr (floating_point<decay_t<_Tp>>)
 	    return __cmp_cust::__fp_weak_ordering(__e, __f);
@@ -766,9 +763,8 @@ namespace std
       template<typename _Tp, __decayed_same_as<_Tp> _Up>
 	requires __partially_ordered<_Tp, _Up>
 	constexpr partial_ordering
-	operator()(_Tp&& __e, _Up&& __f) const
+	operator() [[nodiscard]] (_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
-	[[nodiscard]]
 	{
 	  if constexpr (__adl_partial<_Tp, _Up>)
 	    return partial_ordering(partial_order(static_cast<_Tp&&>(__e),
@@ -808,9 +804,8 @@ namespace std
       template<typename _Tp, __decayed_same_as<_Tp> _Up>
 	requires __strongly_ordered<_Tp, _Up> || __op_eq_lt<_Tp, _Up>
 	constexpr strong_ordering
-	operator()(_Tp&& __e, _Up&& __f) const
+	operator() [[nodiscard]] (_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
-	[[nodiscard]]
 	{
 	  if constexpr (__strongly_ordered<_Tp, _Up>)
 	    return _Strong_order{}(static_cast<_Tp&&>(__e),
@@ -841,9 +836,8 @@ namespace std
       template<typename _Tp, __decayed_same_as<_Tp> _Up>
 	requires __weakly_ordered<_Tp, _Up> || __op_eq_lt<_Tp, _Up>
 	constexpr weak_ordering
-	operator()(_Tp&& __e, _Up&& __f) const
+	operator() [[nodiscard]] (_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
-	[[nodiscard]]
 	{
 	  if constexpr (__weakly_ordered<_Tp, _Up>)
 	    return _Weak_order{}(static_cast<_Tp&&>(__e),
@@ -884,9 +878,8 @@ namespace std
       template<typename _Tp, __decayed_same_as<_Tp> _Up>
 	requires __partially_ordered<_Tp, _Up> || __op_eq_lt_lt<_Tp, _Up>
 	constexpr partial_ordering
-	operator()(_Tp&& __e, _Up&& __f) const
+	operator() [[nodiscard]] (_Tp&& __e, _Up&& __f) const
 	noexcept(_S_noexcept<_Tp, _Up>())
-	[[nodiscard]]
 	{
 	  if constexpr (__partially_ordered<_Tp, _Up>)
 	    return _Partial_order{}(static_cast<_Tp&&>(__e),

^ permalink raw reply	[flat|nested] 12+ messages in thread

end of thread, other threads:[~2021-08-06 13:29 UTC | newest]

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-08-04 11:55 [committed 1/2] libstdc++: Add [[nodiscard]] to iterators and related utilities Jonathan Wakely
2021-08-04 11:56 ` [committed 2/2] libstdc++: Add [[nodiscard]] to sequence containers Jonathan Wakely
2021-08-04 12:00   ` Jonathan Wakely
2021-08-05 12:09     ` Christophe Lyon
2021-08-05 12:13       ` Ville Voutilainen
2021-08-05 14:21         ` Jonathan Wakely
2021-08-05 14:38     ` Jonathan Wakely
2021-08-05 14:19 ` [committed] libstdc++: Move attributes that follow requires-clauses [PR101782] Jonathan Wakely
2021-08-05 14:27   ` Ville Voutilainen
2021-08-05 14:40   ` Jonathan Wakely
2021-08-05 18:02     ` Jonathan Wakely
2021-08-06 13:29       ` Jonathan Wakely

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