Implement std::span for C++20

2019-09-05  JeanHeyd Meneide  <phdofthehouse@gmail.com>

	* include/Makefile.am: Add <span> header.
	* include/Makefile.in: Regenerate.
	* include/bits/range_access.h (__adl_begin, __adl_end, __adl_cbegin)
	(__adl_cend, __adl_rbegin, __adl_rend, __adl_crbegin, __adl_crend)
	(__adl_data, __adl_cdata, __adl_size, __adl_empty, __adl_to_address):
	New functions for performing argument-dependent lookup of range
	customization points.
	* include/bits/stl_iterator.h (__normal_iterator): Add
	_GLIBCXX20_CONSTEXPR to all functions.
	* include/std/span: New header.
	* include/std/version (__cpp_lib_span): Define feature test macro.
	* testsuite/23_containers/span/contiguous_range_neg.cc: New test.
	* testsuite/23_containers/span/everything.cc: New test.
	* testsuite/23_containers/span/get_neg.cc: New test.
	* testsuite/23_containers/span/last_neg.cc: New test.
	* testsuite/23_containers/span/subspan_neg.cc: New test.
	* testsuite/23_containers/span/tuple_element_dynamic_neg.cc: New test.
	* testsuite/23_containers/span/tuple_element_oob_neg.cc: New test.
	* testsuite/23_containers/span/tuple_size_neg.cc: New test.

From-SVN: r275403

libstdc++-v3/ChangeLog

+2019-09-05  JeanHeyd Meneide  <phdofthehouse@gmail.com>
+
+	* include/Makefile.am: Add <span> header.
+	* include/Makefile.in: Regenerate.
+	* include/bits/range_access.h (__adl_begin, __adl_end, __adl_cbegin)
+	(__adl_cend, __adl_rbegin, __adl_rend, __adl_crbegin, __adl_crend)
+	(__adl_data, __adl_cdata, __adl_size, __adl_empty, __adl_to_address):
+	New functions for performing argument-dependent lookup of range
+	customization points.
+	* include/bits/stl_iterator.h (__normal_iterator): Add
+	_GLIBCXX20_CONSTEXPR to all functions.
+	* include/std/span: New header.
+	* include/std/version (__cpp_lib_span): Define feature test macro.
+	* testsuite/23_containers/span/contiguous_range_neg.cc: New test.
+	* testsuite/23_containers/span/everything.cc: New test.
+	* testsuite/23_containers/span/get_neg.cc: New test.
+	* testsuite/23_containers/span/last_neg.cc: New test.
+	* testsuite/23_containers/span/subspan_neg.cc: New test.
+	* testsuite/23_containers/span/tuple_element_dynamic_neg.cc: New test.
+	* testsuite/23_containers/span/tuple_element_oob_neg.cc: New test.
+	* testsuite/23_containers/span/tuple_size_neg.cc: New test.
+
 2019-09-05  Jonathan Wakely  <jwakely@redhat.com>
 
 	* doc/xml/manual/allocator.xml: Remove URL for bibliography entry.

libstdc++-v3/include/Makefile.am

@@ -68,6 +68,7 @@ std_headers = \
 	${std_srcdir}/scoped_allocator \
 	${std_srcdir}/set \
 	${std_srcdir}/shared_mutex \
+	${std_srcdir}/span \
 	${std_srcdir}/sstream \
 	${std_srcdir}/stack \
 	${std_srcdir}/stdexcept \

libstdc++-v3/include/Makefile.in

@@ -412,6 +412,7 @@ std_headers = \
 	${std_srcdir}/scoped_allocator \
 	${std_srcdir}/set \
 	${std_srcdir}/shared_mutex \
+	${std_srcdir}/span \
 	${std_srcdir}/sstream \
 	${std_srcdir}/stack \
 	${std_srcdir}/stdexcept \

libstdc++-v3/include/bits/range_access.h

@@ -318,6 +318,78 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #endif // C++17
 
+#if __cplusplus > 201703L
+  // "why are these in namespace std:: and not __gnu_cxx:: ?"
+  // because if we don't put them here it's impossible to
+  // have implicit ADL with "using std::begin/end/size/data;".
+  template <typename _Container>
+    constexpr auto
+    __adl_begin(_Container& __cont) noexcept(noexcept(begin(__cont)))
+    { return begin(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_end(_Container& __cont) noexcept(noexcept(end(__cont)))
+    { return end(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_cbegin(_Container& __cont) noexcept(noexcept(cbegin(__cont)))
+    { return cbegin(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_cend(_Container& __cont) noexcept(noexcept(cend(__cont)))
+    { return cend(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_rbegin(_Container& __cont) noexcept(noexcept(rbegin(__cont)))
+    { return rbegin(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_rend(_Container& __cont) noexcept(noexcept(rend(__cont)))
+    { return rend(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_crbegin(_Container& __cont) noexcept(noexcept(crbegin(__cont)))
+    { return crbegin(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_crend(_Container& __cont) noexcept(noexcept(crend(__cont)))
+    { return crend(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_data(_Container& __cont) noexcept(noexcept(data(__cont)))
+    { return data(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_cdata(_Container& __cont) noexcept(noexcept(cdata(__cont)))
+    { return cdata(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_size(_Container& __cont) noexcept(noexcept(size(__cont)))
+    { return size(__cont); }
+
+  template <typename _Container>
+    constexpr auto
+    __adl_empty(_Container& __cont) noexcept(noexcept(empty(__cont)))
+    { return empty(__cont); }
+
+#if defined(_GLIBCXX_P1394) && _GLIBCXX_P1394
+  template <typename _Container>
+    constexpr auto
+    __adl_to_address(_Container& __cont) noexcept(noexcept(to_address(__cont)))
+    { return to_address(__cont); }
+#endif // P1394 and new contiguous_iterator requirements [iterator.concept.contiguous]
+#endif // C++20
+
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 

libstdc++-v3/include/bits/stl_iterator.h

@@ -446,7 +446,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cplusplus >= 201103L
   template<typename _Iterator>
-    _GLIBCXX20_CONSTEXPR auto
+    _GLIBCXX20_CONSTEXPR
+    auto
     __niter_base(reverse_iterator<_Iterator> __it)
     -> decltype(__make_reverse_iterator(__niter_base(__it.base())))
     { return __make_reverse_iterator(__niter_base(__it.base())); }
@@ -457,7 +458,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
 
   template<typename _Iterator>
-    _GLIBCXX20_CONSTEXPR auto
+    _GLIBCXX20_CONSTEXPR
+    auto
     __miter_base(reverse_iterator<_Iterator> __it)
     -> decltype(__make_reverse_iterator(__miter_base(__it.base())))
     { return __make_reverse_iterator(__miter_base(__it.base())); }
@@ -802,12 +804,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _GLIBCXX_CONSTEXPR __normal_iterator() _GLIBCXX_NOEXCEPT
       : _M_current(_Iterator()) { }
 
-      explicit
+      explicit _GLIBCXX20_CONSTEXPR
       __normal_iterator(const _Iterator& __i) _GLIBCXX_NOEXCEPT
       : _M_current(__i) { }
 
       // Allow iterator to const_iterator conversion
       template<typename _Iter>
+        _GLIBCXX20_CONSTEXPR
         __normal_iterator(const __normal_iterator<_Iter,
 			  typename __enable_if<
       	       (std::__are_same<_Iter, typename _Container::pointer>::__value),
@@ -815,14 +818,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         : _M_current(__i.base()) { }
 
       // Forward iterator requirements
+      _GLIBCXX20_CONSTEXPR
       reference
       operator*() const _GLIBCXX_NOEXCEPT
       { return *_M_current; }
 
+      _GLIBCXX20_CONSTEXPR
       pointer
       operator->() const _GLIBCXX_NOEXCEPT
       { return _M_current; }
 
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator&
       operator++() _GLIBCXX_NOEXCEPT
       {
@@ -830,11 +836,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator
       operator++(int) _GLIBCXX_NOEXCEPT
       { return __normal_iterator(_M_current++); }
 
       // Bidirectional iterator requirements
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator&
       operator--() _GLIBCXX_NOEXCEPT
       {
@@ -842,31 +850,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return *this;
       }
 
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator
       operator--(int) _GLIBCXX_NOEXCEPT
       { return __normal_iterator(_M_current--); }
 
       // Random access iterator requirements
+      _GLIBCXX20_CONSTEXPR
       reference
       operator[](difference_type __n) const _GLIBCXX_NOEXCEPT
       { return _M_current[__n]; }
 
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator&
       operator+=(difference_type __n) _GLIBCXX_NOEXCEPT
       { _M_current += __n; return *this; }
 
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator
       operator+(difference_type __n) const _GLIBCXX_NOEXCEPT
       { return __normal_iterator(_M_current + __n); }
 
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator&
       operator-=(difference_type __n) _GLIBCXX_NOEXCEPT
       { _M_current -= __n; return *this; }
 
+      _GLIBCXX20_CONSTEXPR
       __normal_iterator
       operator-(difference_type __n) const _GLIBCXX_NOEXCEPT
       { return __normal_iterator(_M_current - __n); }
 
+      _GLIBCXX20_CONSTEXPR
       const _Iterator&
       base() const _GLIBCXX_NOEXCEPT
       { return _M_current; }
@@ -882,6 +897,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // Forward iterator requirements
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator==(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -889,6 +905,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator==(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -896,6 +913,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() == __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator!=(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -903,6 +921,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() != __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator!=(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -911,6 +930,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // Random access iterator requirements
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator<(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	      const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -918,6 +938,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() < __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator<(const __normal_iterator<_Iterator, _Container>& __lhs,
 	      const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -925,6 +946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() < __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator>(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	      const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -932,6 +954,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() > __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator>(const __normal_iterator<_Iterator, _Container>& __lhs,
 	      const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -939,6 +962,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() > __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator<=(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -946,6 +970,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() <= __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator<=(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -953,6 +978,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() <= __rhs.base(); }
 
   template<typename _IteratorL, typename _IteratorR, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator>=(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	       const __normal_iterator<_IteratorR, _Container>& __rhs)
@@ -960,6 +986,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() >= __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     operator>=(const __normal_iterator<_Iterator, _Container>& __lhs,
 	       const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -973,6 +1000,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _IteratorL, typename _IteratorR, typename _Container>
 #if __cplusplus >= 201103L
     // DR 685.
+    _GLIBCXX20_CONSTEXPR
     inline auto
     operator-(const __normal_iterator<_IteratorL, _Container>& __lhs,
 	      const __normal_iterator<_IteratorR, _Container>& __rhs) noexcept
@@ -985,6 +1013,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() - __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline typename __normal_iterator<_Iterator, _Container>::difference_type
     operator-(const __normal_iterator<_Iterator, _Container>& __lhs,
 	      const __normal_iterator<_Iterator, _Container>& __rhs)
@@ -992,6 +1021,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __lhs.base() - __rhs.base(); }
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     inline __normal_iterator<_Iterator, _Container>
     operator+(typename __normal_iterator<_Iterator, _Container>::difference_type
 	      __n, const __normal_iterator<_Iterator, _Container>& __i)
@@ -1006,6 +1036,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _Iterator, typename _Container>
+    _GLIBCXX20_CONSTEXPR
     _Iterator
     __niter_base(__gnu_cxx::__normal_iterator<_Iterator, _Container> __it)
     _GLIBCXX_NOEXCEPT_IF(std::is_nothrow_copy_constructible<_Iterator>::value)

libstdc++-v3/include/std/version

@@ -167,6 +167,9 @@
 #define __cpp_lib_list_remove_return_type 201806L
 #define __cpp_lib_math_constants 201907L
 #define __cpp_lib_to_array 201907L
+// FIXME: they forgot this feature test macro
+// get on someone's back about it in Belfast!!!
+#define __cpp_lib_span 201911
 #endif // C++2a
 #endif // C++17
 #endif // C++14

libstdc++-v3/testsuite/23_containers/span/contiguous_range_neg.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <span>
+#include <deque>
+
+int
+main()
+{
+  std::deque<int> d{};
+  std::span<int, std::dynamic_extent> myspan(d); // { dg-error "no match" }
+}
+
+// { dg-prune-output "data" }
+// { dg-prune-output "invalid operands" }

libstdc++-v3/testsuite/23_containers/span/everything.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do run { target c++2a } }
+
+#include <testsuite_hooks.h>
+
+#include <span>
+#include <type_traits>
+#include <cstdint>
+#include <vector>
+#include <algorithm>
+#include <cassert>
+
+int
+main()
+{
+  struct alignas(256) strawman
+  {
+    int x;
+    int y;
+    bool z;
+    int w;
+  };
+
+  struct naked_span
+  {
+    char* p;
+    std::size_t n;
+  };
+
+  struct strawman_span
+  {
+    strawman* p;
+    std::size_t n;
+  };
+
+  static_assert(sizeof(std::span<char, 0>) <= sizeof(char*));
+  static_assert(sizeof(std::span<const char, 0>) <= sizeof(const char*));
+  static_assert(sizeof(std::span<strawman, 0>) <= sizeof(strawman*));
+  static_assert(sizeof(std::span<strawman, 1>) <= sizeof(strawman*));
+  static_assert(sizeof(std::span<char>) <= sizeof(naked_span));
+  static_assert(sizeof(std::span<strawman>) <= sizeof(strawman_span));
+
+  constexpr static std::array<int, 9> arr_data{ 0, 1, 2, 3, 4, 5, 6, 7, 8 };
+  constexpr auto arr_data_span = std::span(arr_data);
+  static_assert(arr_data_span.size() == 9);
+  static_assert(arr_data_span.size_bytes() == 9 * sizeof(int));
+  static_assert(*arr_data_span.begin() == 0);
+  static_assert(*arr_data_span.data() == 0);
+  static_assert(arr_data_span.front() == 0);
+  static_assert(arr_data_span.back() == 8);
+  static_assert(arr_data_span[0] == 0);
+  static_assert(arr_data_span[1] == 1);
+  static_assert(arr_data_span[2] == 2);
+  static_assert(arr_data_span[3] == 3);
+  static_assert(arr_data_span[4] == 4);
+  static_assert(arr_data_span[5] == 5);
+  static_assert(arr_data_span[6] == 6);
+  static_assert(arr_data_span[7] == 7);
+  static_assert(arr_data_span[8] == 8);
+  static_assert(!arr_data_span.empty());
+  static_assert(decltype(arr_data_span)::extent == 9);
+
+  constexpr static int data[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8 };
+  constexpr auto data_span    = std::span(data);
+  static_assert(data_span.size() == 9);
+  static_assert(data_span.size_bytes() == 9 * sizeof(int));
+  static_assert(*data_span.begin() == 0);
+  static_assert(*data_span.data() == 0);
+  static_assert(data_span.front() == 0);
+  static_assert(data_span.back() == 8);
+  static_assert(data_span[0] == 0);
+  static_assert(data_span[1] == 1);
+  static_assert(data_span[2] == 2);
+  static_assert(data_span[3] == 3);
+  static_assert(data_span[4] == 4);
+  static_assert(data_span[5] == 5);
+  static_assert(data_span[6] == 6);
+  static_assert(data_span[7] == 7);
+  static_assert(data_span[8] == 8);
+  static_assert(!data_span.empty());
+  static_assert(decltype(data_span)::extent == 9);
+
+  constexpr auto data_span_first = data_span.first<3>();
+  static_assert(
+    std::is_same_v<std::remove_cv_t<decltype(data_span_first)>, std::span<const int, 3>>);
+  static_assert(decltype(data_span_first)::extent == 3);
+  static_assert(data_span_first.size() == 3);
+  static_assert(data_span_first.front() == 0);
+  static_assert(data_span_first.back() == 2);
+  static_assert(std::tuple_size_v<decltype(data_span_first)> == 3);
+  static_assert(std::is_same_v<std::tuple_element_t<0, decltype(data_span_first)>, const int>);
+
+  constexpr auto data_span_first_dyn = data_span.first(4);
+  static_assert(
+    std::is_same_v<std::remove_cv_t<decltype(data_span_first_dyn)>, std::span<const int>>);
+  static_assert(decltype(data_span_first_dyn)::extent == std::dynamic_extent);
+  static_assert(data_span_first_dyn.size() == 4);
+  static_assert(data_span_first_dyn.front() == 0);
+  static_assert(data_span_first_dyn.back() == 3);
+
+  constexpr auto data_span_last = data_span.last<5>();
+  static_assert(
+    std::is_same_v<std::remove_cv_t<decltype(data_span_last)>, std::span<const int, 5>>);
+  static_assert(decltype(data_span_last)::extent == 5);
+  static_assert(data_span_last.size() == 5);
+  static_assert(data_span_last.front() == 4);
+  static_assert(data_span_last.back() == 8);
+  static_assert(std::tuple_size_v<decltype(data_span_last)> == 5);
+  static_assert(std::is_same_v<std::tuple_element_t<0, decltype(data_span_last)>, const int>);
+
+  constexpr auto data_span_last_dyn = data_span.last(6);
+  static_assert(
+    std::is_same_v<std::remove_cv_t<decltype(data_span_last_dyn)>, std::span<const int>>);
+  static_assert(decltype(data_span_last_dyn)::extent == std::dynamic_extent);
+  static_assert(data_span_last_dyn.size() == 6);
+  static_assert(data_span_last_dyn.front() == 3);
+  static_assert(data_span_last_dyn.back() == 8);
+
+  constexpr auto data_span_subspan = data_span.subspan<1, 3>();
+  static_assert(
+    std::is_same_v<std::remove_cv_t<decltype(data_span_subspan)>, std::span<const int, 3>>);
+  static_assert(decltype(data_span_subspan)::extent == 3);
+  static_assert(data_span_subspan.size() == 3);
+  static_assert(data_span_subspan.front() == 1);
+  static_assert(data_span_subspan.back() == 3);
+
+  constexpr auto data_span_subspan_offset = data_span.subspan<8>();
+  static_assert(
+    std::is_same_v<std::remove_cv_t<decltype(data_span_subspan_offset)>, std::span<const int, 1>>);
+  static_assert(decltype(data_span_subspan_offset)::extent == 1);
+  static_assert(data_span_subspan_offset.size() == 1);
+  static_assert(data_span_subspan_offset.front() == 8);
+  static_assert(data_span_subspan_offset.back() == 8);
+
+  constexpr auto data_span_subspan_empty = data_span.subspan(9, 0);
+  static_assert(
+    std::is_same_v<std::remove_cv_t<decltype(data_span_subspan_empty)>, std::span<const int>>);
+  static_assert(decltype(data_span_subspan_empty)::extent == std::dynamic_extent);
+  static_assert(data_span_subspan_empty.size() == 0);
+
+  constexpr auto data_span_subspan_empty_static = data_span.subspan<9>();
+  static_assert(std::is_same_v<std::remove_cv_t<decltype(data_span_subspan_empty_static)>,
+    std::span<const int, 0>>);
+  static_assert(decltype(data_span_subspan_empty_static)::extent == 0);
+  static_assert(data_span_subspan_empty.size() == 0);
+
+  std::span<short> shorts{};
+  bool really_empty0 = shorts.empty();
+  bool really_empty1 = std::empty(shorts);
+  bool really_empty2 = shorts.data() == nullptr;
+  bool really_empty3 = shorts.begin() == shorts.end();
+  bool really_empty4 = shorts.cbegin() == shorts.cend();
+  bool really_empty =
+    really_empty0 && really_empty1 && really_empty2 && really_empty3 && really_empty4;
+  (void)really_empty;
+  VERIFY(really_empty);
+
+  std::vector<std::int_least32_t> value{ 0 };
+  std::span<int32_t> muh_span(value);
+  VERIFY(muh_span.size() == 1);
+  std::byte* original_bytes                  = reinterpret_cast<std::byte*>(value.data());
+  original_bytes[0]                          = static_cast<std::byte>(1);
+  original_bytes[1]                          = static_cast<std::byte>(2);
+  original_bytes[2]                          = static_cast<std::byte>(3);
+  original_bytes[3]                          = static_cast<std::byte>(4);
+  std::span<const std::byte> muh_byte_span   = std::as_bytes(muh_span);
+  std::span<std::byte> muh_mutable_byte_span = std::as_writable_bytes(muh_span);
+  std::span<std::byte> muh_original_byte_span(original_bytes, original_bytes + 4);
+  bool definitely_reinterpret_casted0 = std::equal(muh_byte_span.cbegin(), muh_byte_span.cend(),
+    muh_original_byte_span.cbegin(), muh_original_byte_span.cend());
+  bool definitely_reinterpret_casted1 = std::equal(muh_mutable_byte_span.cbegin(),
+    muh_mutable_byte_span.cend(), muh_original_byte_span.cbegin(), muh_original_byte_span.cend());
+  bool definitely_reinterpret_casted =
+    definitely_reinterpret_casted0 && definitely_reinterpret_casted1;
+  (void)definitely_reinterpret_casted;
+  VERIFY(definitely_reinterpret_casted);
+
+  std::span<std::byte> muh_original_byte_span_ptr_size(original_bytes, 4);
+  bool definitely_equivalent =
+    std::equal(muh_original_byte_span_ptr_size.cbegin(), muh_original_byte_span_ptr_size.cend(),
+      muh_original_byte_span.cbegin(), muh_original_byte_span.cend());
+  (void)definitely_equivalent;
+  VERIFY(definitely_equivalent);
+
+  return definitely_equivalent && definitely_reinterpret_casted && really_empty ? 0 : 1;
+}

libstdc++-v3/testsuite/23_containers/span/get_neg.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <span>
+#include <tuple>
+
+int
+main()
+{
+  std::span<int, std::dynamic_extent> myspan((int*)nullptr, 0ul);
+  std::get<0>(myspan); // { dg-error "here" }
+}
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }

libstdc++-v3/testsuite/23_containers/span/last_neg.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <span>
+
+int
+main()
+{
+  std::span<int, 2> myspan(nullptr, 2);
+  myspan.last<3>(); // { dg-error "here" }
+}
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }

libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <span>
+
+int
+main()
+{
+  std::span<int, 2> myspan(nullptr, 2);
+  myspan.subspan<3, 1>(); // { dg-error "here" }
+}
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }

libstdc++-v3/testsuite/23_containers/span/tuple_element_dynamic_neg.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <span>
+#include <tuple>
+
+std::tuple_element<0, std::span<int, std::dynamic_extent>> ts; // { dg-error "here" }
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }

libstdc++-v3/testsuite/23_containers/span/tuple_element_oob_neg.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <span>
+#include <tuple>
+
+std::tuple_element<3, std::span<int, 2>> te; // { dg-error "here" }
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }

libstdc++-v3/testsuite/23_containers/span/tuple_size_neg.cc

+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=c++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <span>
+#include <tuple>
+
+std::tuple_size<std::span<int, std::dynamic_extent>> ts; // { dg-error "here" }
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }