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

15 files changed, 1052 insertions, 3 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 02be981..8a8ec14 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,25 @@
+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.
diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index 3fe80f3..b8b786d 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/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 \
diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
index b675d35..cd1e9df 100644
--- a/libstdc++-v3/include/Makefile.in
+++ b/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 \
diff --git a/libstdc++-v3/include/bits/range_access.h b/libstdc++-v3/include/bits/range_access.h
index d1e7471..44b9c6c 100644
--- a/libstdc++-v3/include/bits/range_access.h
+++ b/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
 
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 8ab0d72..e29775a 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/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)
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
new file mode 100644
index 0000000..4ce2f31
--- /dev/null
+++ b/libstdc++-v3/include/std/span
@@ -0,0 +1,521 @@
+// Components for manipulating non-owning sequences of objects -*- C++ -*-
+
+// 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.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file span
+ *  This is a Standard C++ Library header.
+ */
+
+//
+// P0122 span library
+// Contributed by ThePhD
+//
+
+#ifndef _GLIBCXX_SPAN
+#define _GLIBCXX_SPAN 1
+
+#pragma GCC system_header
+
+#if __cplusplus > 201703L
+
+#include <type_traits>
+#include <tuple>
+#include <utility>
+#include <array>
+#include <bits/stl_iterator.h>
+#include <bits/range_access.h>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+// FIXME: they forgot this feature test macro
+// get on someone's back about it in Belfast!!!
+#define __cpp_lib_span 201911
+
+  inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);
+
+  namespace __detail
+  {
+    template<typename _Element, typename _ToElement>
+      static constexpr inline bool __is_base_derived_safe_convertible_v
+	= is_convertible_v<_Element (*)[], _ToElement (*)[]>;
+
+    template<typename _Tp>
+      inline constexpr bool __is_std_array_v = false;
+
+    template<typename _Tp, size_t _Num>
+      inline constexpr bool
+      __is_std_array_v<_GLIBCXX_STD_C::array<_Tp, _Num>> = true;
+
+#ifdef _GLIBCXX_DEBUG
+    template<typename _Tp, size_t _Num>
+      inline constexpr bool
+      __is_std_array_v<std::__debug::array<_Tp, _Num>> = true;
+#endif // debug/array
+
+    template<size_t _Extent>
+      class __extent_storage
+      {
+      public:
+	constexpr
+	__extent_storage() noexcept = default;
+
+	constexpr
+	__extent_storage(size_t) noexcept
+	{ }
+
+	static constexpr size_t
+	_M_extent() noexcept
+	{ return _Extent; }
+      };
+
+    template<>
+      class __extent_storage<static_cast<size_t>(-1)>
+      {
+      public:
+	constexpr
+	__extent_storage() noexcept : _M_extent_value(0)
+	{ };
+
+	constexpr
+	__extent_storage(size_t __extent) noexcept
+	: _M_extent_value(__extent)
+	{ }
+
+	constexpr size_t
+	_M_extent() const noexcept
+	{ return this->_M_extent_value; }
+
+      private:
+	size_t _M_extent_value;
+      };
+
+  } // namespace __detail
+
+  template<typename _Type, size_t _Extent = dynamic_extent>
+    class span : private __detail::__extent_storage<_Extent>
+    {
+    public:
+      // member types
+      using value_type             = remove_cv_t<_Type>;
+      using element_type           = _Type;
+      using index_type             = size_t;
+      using reference              = element_type&;
+      using const_reference        = const element_type&;
+      using pointer                = _Type*;
+      using const_pointer          = const _Type*;
+      using iterator
+	= __gnu_cxx::__normal_iterator<pointer, span>;
+      using const_iterator
+	= __gnu_cxx::__normal_iterator<const_pointer, span>;
+      using reverse_iterator       = std::reverse_iterator<iterator>;
+      using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+      using difference_type        = ptrdiff_t;
+      // Official wording has no size_type -- why??
+      // using size_type = size_t;
+
+      // member constants
+      static inline constexpr size_t extent = _Extent;
+
+    private:
+      using __base_t = __detail::__extent_storage<extent>;
+
+    public:
+      // constructors
+
+      template <typename _Dummy = _Type,
+		enable_if_t<is_same_v<_Dummy, _Type>
+		  && (_Extent == dynamic_extent || _Extent == 0)>* = nullptr>
+	constexpr
+	span() noexcept : __base_t(0), _M_ptr(nullptr)
+	{ }
+
+      constexpr
+      span(const span&) noexcept = default;
+
+      template<size_t _ArrayExtent,
+	enable_if_t<
+	  (_Extent == dynamic_extent || _ArrayExtent == _Extent)
+	  && __detail::__is_base_derived_safe_convertible_v<
+	    remove_pointer_t<decltype(::std::__adl_data(
+	      ::std::declval<element_type (&)[_ArrayExtent]>()))>,
+	    element_type>>* = nullptr>
+	constexpr span(element_type (&__arr)[_ArrayExtent])
+	noexcept(noexcept(::std::__adl_data(__arr)))
+	: span(::std::__adl_data(__arr), _ArrayExtent)
+	{ }
+
+      template<size_t _ArrayExtent,
+	enable_if_t<
+	  (_Extent == dynamic_extent || _ArrayExtent == _Extent)
+	  && __detail::__is_base_derived_safe_convertible_v<
+	    remove_pointer_t<decltype(::std::__adl_data(
+	      ::std::declval<const array<value_type, _ArrayExtent>&>()))>,
+	    element_type>>* = nullptr>
+	constexpr
+	span(array<value_type, _ArrayExtent>& __arr)
+	noexcept(noexcept(::std::__adl_data(__arr)))
+	: span(::std::__adl_data(__arr), _ArrayExtent)
+	{ }
+
+      template<size_t _ArrayExtent,
+	enable_if_t<
+	  (_Extent == dynamic_extent || _ArrayExtent == _Extent)
+	  && __detail::__is_base_derived_safe_convertible_v<
+	    remove_pointer_t<decltype(::std::__adl_data(
+	      ::std::declval<const array<value_type, _ArrayExtent>&>()))>,
+	    element_type>>* = nullptr>
+	constexpr
+	span(const array<value_type, _ArrayExtent>& __arr)
+	noexcept(noexcept(::std::__adl_data(__arr)))
+	: span(::std::__adl_data(__arr), _ArrayExtent)
+	{ }
+
+      // NOTE: when the time comes, and P1394 -
+      // range constructors for std::span - ships in
+      // the standard, delete the #else block and remove
+      // the conditional
+      // if the paper fails, delete #if block
+      // and keep the crappy #else block
+      // and then cry that NB comments failed C++20...
+      // but maybe for C++23?
+#if defined(_GLIBCXX_P1394) && _GLIBCXX_P1394
+      template<typename _Range,
+	enable_if_t<
+	  (_Extent == dynamic_extent)
+	  && !is_same_v<remove_cvref_t<_Range>, span>
+	  && !__detail::__is_std_array_v<remove_cvref_t<_Range>>
+	  && !is_array_v<remove_cvref_t<_Range>>
+	  && __detail::__is_base_derived_safe_convertible_v<
+	    remove_pointer_t<decltype(
+	      ::std::__adl_data(::std::declval<_Range&>())
+	      + ::std::__adl_size(::std::declval<_Range&>()))>,
+	    element_type>>* = nullptr>
+	constexpr
+	span(_Range&& __range)
+	noexcept(noexcept(::std::__adl_data(__range))
+		  && noexcept(::std::__adl_size(__range)))
+	: span(::std::__adl_data(__range), ::std::__adl_size(__range))
+	{ }
+
+      template<typename _ContiguousIterator, typename _Sentinel,
+	enable_if_t<!is_convertible_v<_Sentinel, index_type>
+	  && __detail::__is_base_derived_safe_convertible_v<
+	    remove_reference_t<typename
+	      iterator_traits<_ContiguousIterator>::reference>,
+	  element_type>>* = nullptr>
+	constexpr
+	span(_ContiguousIterator __first, _Sentinel __last)
+	: span(::std::move(__first), static_cast<index_type>(__last - __first))
+	{ }
+
+      template<typename _ContiguousIterator>
+	constexpr
+	span(_ContiguousIterator __first, index_type __count)
+	noexcept(noexcept(::std::__adl_to_address(__first)))
+	: __base_t(__count), _M_ptr(::std::__adl_to_address(__first))
+	{ __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }
+
+#else
+
+      template<typename _Container,
+	enable_if_t<
+	  (_Extent == dynamic_extent)
+	  && !is_same_v<remove_cvref_t<_Container>, span>
+	  && !__detail::__is_std_array_v<remove_cvref_t<_Container>>
+	  && !is_array_v<remove_cvref_t<_Container>>
+	  && __detail::__is_base_derived_safe_convertible_v<
+	    remove_pointer_t<decltype(
+	      ::std::__adl_data(::std::declval<_Container&>())
+	      + ::std::__adl_size(::std::declval<_Container&>()))>,
+	    element_type>>* = nullptr>
+	constexpr
+	span(_Container& __range)
+	noexcept(noexcept(::std::__adl_data(__range))
+		  && noexcept(::std::__adl_size(__range)))
+	: span(::std::__adl_data(__range), ::std::__adl_size(__range))
+	{ }
+
+      template<typename _Container,
+	enable_if_t<
+	  (_Extent == dynamic_extent)
+	  && !is_same_v<remove_cvref_t<_Container>, span>
+	  && !__detail::__is_std_array_v<remove_cvref_t<_Container>>
+	  && !is_array_v<remove_cvref_t<_Container>>
+	  && __detail::__is_base_derived_safe_convertible_v<
+	    remove_pointer_t<decltype(
+	      ::std::__adl_data(::std::declval<_Container&>())
+	      + ::std::__adl_size(::std::declval<_Container&>()))>,
+	    element_type>>* = nullptr>
+	constexpr span(const _Container& __range)
+	noexcept(noexcept(::std::__adl_data(__range))
+		  && noexcept(::std::__adl_size(__range)))
+	: span(::std::__adl_data(__range), ::std::__adl_size(__range))
+	{ }
+
+      constexpr
+      span(pointer __first, index_type __count) noexcept
+      : __base_t(__count), _M_ptr(static_cast<pointer>(__first))
+      { __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }
+
+      constexpr
+      span(pointer __first, pointer __last) noexcept
+      : span(::std::move(__first), static_cast<index_type>(__last - __first))
+      { }
+#endif // P1394
+
+      // assignment
+
+      constexpr span&
+      operator=(const span&) noexcept = default;
+
+      // observers: element access
+
+      constexpr reference
+      front() const noexcept
+      { return *this->begin(); }
+
+      constexpr reference
+      back() const noexcept
+      {
+	iterator __it = this->end();
+	--__it;
+	return *__it;
+      }
+
+      constexpr reference
+      operator[](index_type __idx) const noexcept
+      { return *(this->_M_ptr + __idx); }
+
+      constexpr pointer
+      data() const noexcept
+      { return this->_M_ptr; }
+
+      constexpr index_type
+      size() const noexcept
+      { return this->__base_t::_M_extent(); }
+
+      constexpr index_type
+      size_bytes() const noexcept
+      { return this->__base_t::_M_extent() * sizeof(element_type); }
+
+      constexpr bool
+      empty() const noexcept
+      { return size() == 0; }
+
+      // observers: iterator support
+      constexpr iterator
+      begin() const noexcept
+      { return iterator(this->_M_ptr); }
+
+      constexpr const_iterator
+      cbegin() const noexcept
+      { return const_iterator(this->_M_ptr); }
+
+      constexpr iterator
+      end() const noexcept
+      { return iterator(this->_M_ptr + this->size()); }
+
+      constexpr const_iterator
+      cend() const noexcept
+      { return const_iterator(this->_M_ptr + this->size()); }
+
+      constexpr reverse_iterator
+      rbegin() const noexcept
+      { return reverse_iterator(this->end()); }
+
+      constexpr const_reverse_iterator
+      crbegin() const noexcept
+      { return const_reverse_iterator(this->cend()); }
+
+      constexpr reverse_iterator
+      rend() const noexcept
+      { return reverse_iterator(this->begin()); }
+
+      constexpr const_reverse_iterator
+      crend() const noexcept
+      { return const_reverse_iterator(this->cbegin()); }
+
+      // observers: subranges
+      template<size_t _Count>
+	constexpr span<element_type, _Count>
+	first() const
+	{
+	  __glibcxx_assert(_Count < size());
+	  return { this->data(), _Count };
+	}
+
+      constexpr span<element_type, dynamic_extent>
+      first(index_type __count) const
+      {
+	__glibcxx_assert(__count < size());
+	return { this->data(), __count };
+      }
+
+      template<size_t _Count>
+	constexpr span<element_type, _Count>
+	last() const
+	{
+	  static_assert(_Count == dynamic_extent ||
+			  _Extent == dynamic_extent || _Count <= _Extent,
+	    "Count or Extent are dynamic, "
+	    "or the Count is less than the static extent");
+	  __glibcxx_assert(_Count <= size());
+	  return { this->data() + (this->size() - _Count), _Count };
+	}
+
+      constexpr span<element_type, dynamic_extent>
+      last(index_type __count) const
+      {
+	__glibcxx_assert(__count < size());
+	index_type __offset = (this->size() - __count);
+	return { this->data() + __offset, __count };
+      }
+
+      template<size_t _Offset, size_t _Count = dynamic_extent>
+	constexpr auto
+	subspan() const
+	{
+	  static_assert(_Count == dynamic_extent ||
+			  _Extent == dynamic_extent ||
+			  (_Offset + _Count) <= _Extent,
+	    "Count or Extent are dynamic, "
+	    "or the Count + Offset is less than the static extent");
+	  constexpr size_t __span_extent =
+	    (_Count != dynamic_extent
+		? _Count
+		: (_Extent != dynamic_extent ? _Extent - _Offset
+						    : dynamic_extent));
+	  using __span_t = span<element_type, __span_extent>;
+	  if constexpr(_Count != dynamic_extent)
+	    {
+	      __glibcxx_assert((_Offset + _Count) < size());
+	    }
+	  return __span_t(this->data() + _Offset,
+	    (_Count == dynamic_extent ? this->size() - _Offset : _Count));
+	}
+
+      constexpr span<element_type, dynamic_extent>
+      subspan(index_type __offset, index_type __count = dynamic_extent) const
+      {
+	return {this->data() + __offset,
+	  __count == dynamic_extent ? this->size() - __offset : __count};
+      }
+
+      // observers: range helpers
+
+      friend constexpr iterator
+      begin(span __sp) noexcept
+      { return __sp.begin(); }
+
+      friend constexpr iterator
+      end(span __sp) noexcept
+      { return __sp.end(); }
+
+    private:
+      pointer _M_ptr;
+    };
+
+  // deduction guides
+  template<typename _Type, size_t _ArrayExtent>
+    span(_Type(&)[_ArrayExtent])->span<_Type, _ArrayExtent>;
+
+  template<typename _Type, size_t _ArrayExtent>
+    span(array<_Type, _ArrayExtent>&)->span<_Type, _ArrayExtent>;
+
+  template<typename _Type, size_t _ArrayExtent>
+    span(const array<_Type, _ArrayExtent>&)
+      ->span<const _Type, _ArrayExtent>;
+
+#if defined(_GLIBCXX_P1394) && _GLIBCXX_P1394
+
+  template<typename _ContiguousIterator, typename _Sentinel>
+    span(_ContiguousIterator, _Sentinel)
+      ->span<remove_reference_t<
+	typename iterator_traits<_ContiguousIterator>::reference>>;
+
+  template<typename _Range>
+    span(_Range &&)
+      ->span<remove_reference_t<typename iterator_traits<decltype(
+	::std::__adl_begin(::std::declval<_Range&>()))>::reference>>;
+
+#else
+
+  template<typename _Container>
+    span(_Container&)->span<typename _Container::value_type>;
+
+  template<typename _Container>
+    span(const _Container&)->span<const typename _Container::value_type>;
+
+#endif // P1394
+
+  template<typename _Type, size_t _Extent>
+    span<const byte, _Extent == dynamic_extent
+	? dynamic_extent : _Extent * sizeof(_Type)>
+    inline as_bytes(span<_Type, _Extent> __sp) noexcept
+    {
+      return {reinterpret_cast<const byte*>(__sp.data()), __sp.size_bytes()};
+    }
+
+  template<typename _Type, size_t _Extent>
+    span<byte, _Extent == dynamic_extent
+       ? dynamic_extent : _Extent * sizeof(_Type)>
+    as_writable_bytes(span<_Type, _Extent> __sp) noexcept
+    {
+      return {reinterpret_cast<byte*>(__sp.data()), __sp.size_bytes()};
+    }
+
+  // tuple helpers
+  template<size_t _Index, typename _Type, size_t _Extent>
+    constexpr _Type&
+    get(span<_Type, _Extent> __sp) noexcept
+    {
+      static_assert(_Extent != dynamic_extent
+	&& (_Extent > 0) && (_Index < _Extent),
+	"std::get can only be used with a span of non-dynamic (fixed) extent");
+      return __sp[_Index];
+    }
+
+  template<typename _Type, size_t _Extent>
+    struct tuple_size<span<_Type, _Extent>>
+    : public integral_constant<size_t, _Extent>
+    {
+      static_assert(_Extent != dynamic_extent, "tuple_size can only "
+	"be used with a span of non-dynamic (fixed) extent");
+    };
+
+  template<size_t _Index, typename _Type, size_t _Extent>
+    struct tuple_element<_Index, span<_Type, _Extent>>
+    {
+      static_assert(_Extent != dynamic_extent, "tuple_size can only "
+	"be used with a span of non-dynamic (fixed) extent");
+      static_assert(_Index < _Extent, "Index is less than Extent");
+      using type = typename span<_Type, _Extent>::element_type;
+    };
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+
+#endif // C++20
+#endif // _GLIBCXX_SPAN
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 7f7d05f..4341c9f 100644
--- a/libstdc++-v3/include/std/version
+++ b/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
diff --git a/libstdc++-v3/testsuite/23_containers/span/contiguous_range_neg.cc b/libstdc++-v3/testsuite/23_containers/span/contiguous_range_neg.cc
new file mode 100644
index 0000000..475be1e
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/contiguous_range_neg.cc
@@ -0,0 +1,32 @@
+// 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" }
diff --git a/libstdc++-v3/testsuite/23_containers/span/everything.cc b/libstdc++-v3/testsuite/23_containers/span/everything.cc
new file mode 100644
index 0000000..719015a
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/everything.cc
@@ -0,0 +1,203 @@
+// 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;
+}
diff --git a/libstdc++-v3/testsuite/23_containers/span/get_neg.cc b/libstdc++-v3/testsuite/23_containers/span/get_neg.cc
new file mode 100644
index 0000000..37d188e
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/get_neg.cc
@@ -0,0 +1,30 @@
+// 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 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/last_neg.cc b/libstdc++-v3/testsuite/23_containers/span/last_neg.cc
new file mode 100644
index 0000000..8f0145f
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/last_neg.cc
@@ -0,0 +1,29 @@
+// 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 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc b/libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc
new file mode 100644
index 0000000..5ecbff9
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/subspan_neg.cc
@@ -0,0 +1,29 @@
+// 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 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/tuple_element_dynamic_neg.cc b/libstdc++-v3/testsuite/23_containers/span/tuple_element_dynamic_neg.cc
new file mode 100644
index 0000000..cf84360
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/tuple_element_dynamic_neg.cc
@@ -0,0 +1,25 @@
+// 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 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/tuple_element_oob_neg.cc b/libstdc++-v3/testsuite/23_containers/span/tuple_element_oob_neg.cc
new file mode 100644
index 0000000..bf97735
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/tuple_element_oob_neg.cc
@@ -0,0 +1,25 @@
+// 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 }
diff --git a/libstdc++-v3/testsuite/23_containers/span/tuple_size_neg.cc b/libstdc++-v3/testsuite/23_containers/span/tuple_size_neg.cc
new file mode 100644
index 0000000..99e95b3
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/span/tuple_size_neg.cc
@@ -0,0 +1,25 @@
+// 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 }