[libc++] [test] Fix some GCC 11 errors/warnings in these tests. NFCI.

[ldionne]

Good catch on the end.cpp rename - we were not running that test.

LGTM if CI passes.

[• Quuxplusone]

Last update. This should fix all the outstanding issues, except for the -Wmaybe-uninitialized diagnostic in "libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_is_lock_free.pass.cpp".

libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/contiguous_iterator.compile.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // UNSUPPORTED: libcpp-no-concepts
 // UNSUPPORTED: gcc-10
 
 // template<class T>
 // concept contiguous_iterator;
 
 #include <iterator>
+#include <compare>
 
 #include "test_iterators.h"
 
-static_assert(!std::contiguous_iterator<cpp17_input_iterator<int*> >);
-static_assert(!std::contiguous_iterator<cpp20_input_iterator<int*> >);
-static_assert(!std::contiguous_iterator<forward_iterator<int*> >);
-static_assert(!std::contiguous_iterator<bidirectional_iterator<int*> >);
-static_assert(!std::contiguous_iterator<random_access_iterator<int*> >);
-static_assert(std::contiguous_iterator<contiguous_iterator<int*> >);
+static_assert(!std::contiguous_iterator<cpp17_input_iterator<int*>>);
+static_assert(!std::contiguous_iterator<cpp20_input_iterator<int*>>);
+static_assert(!std::contiguous_iterator<forward_iterator<int*>>);
+static_assert(!std::contiguous_iterator<bidirectional_iterator<int*>>);
+static_assert(!std::contiguous_iterator<random_access_iterator<int*>>);
+static_assert(std::contiguous_iterator<contiguous_iterator<int*>>);
 
 static_assert(std::contiguous_iterator<int*>);
 static_assert(std::contiguous_iterator<int const*>);
 static_assert(std::contiguous_iterator<int volatile*>);
 static_assert(std::contiguous_iterator<int const volatile*>);
 
 struct simple_contiguous_iterator {
     typedef std::contiguous_iterator_tag    iterator_category;
     typedef int                             value_type;
     typedef int                             element_type;
     typedef std::ptrdiff_t                  difference_type;
     typedef int*                            pointer;
     typedef int&                            reference;
     typedef simple_contiguous_iterator      self;
 
     simple_contiguous_iterator();
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self& y);
-    friend bool operator< (const self&, const self& y);
-    friend bool operator<=(const self&, const self& y);
-    friend bool operator> (const self&, const self& y);
-    friend bool operator>=(const self&, const self& y);
+    auto operator<=>(const self&) const = default;
 
     self& operator++();
     self operator++(int);
 
     self& operator--();
     self operator--(int);
 
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
 
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self& n) const;
 
     reference operator[](difference_type n) const;
 };
 
 static_assert(std::random_access_iterator<simple_contiguous_iterator>);
 static_assert(std::contiguous_iterator<simple_contiguous_iterator>);
 
-struct missmatch_value_iter_ref_t {
+struct mismatch_value_iter_ref_t {
     typedef std::contiguous_iterator_tag    iterator_category;
     typedef short                           value_type;
     typedef std::ptrdiff_t                  difference_type;
     typedef int*                            pointer;
     typedef int&                            reference;
-    typedef missmatch_value_iter_ref_t      self;
+    typedef mismatch_value_iter_ref_t       self;
 
-    missmatch_value_iter_ref_t();
+    mismatch_value_iter_ref_t();
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self& y);
-    friend bool operator< (const self&, const self& y);
-    friend bool operator<=(const self&, const self& y);
-    friend bool operator> (const self&, const self& y);
-    friend bool operator>=(const self&, const self& y);
+    auto operator<=>(const self&) const = default;
 
     self& operator++();
     self operator++(int);
 
     self& operator--();
     self operator--(int);
 
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
 
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self& n) const;
 
     reference operator[](difference_type n) const;
 };
 
-static_assert(std::random_access_iterator<missmatch_value_iter_ref_t>);
-static_assert(!std::contiguous_iterator<missmatch_value_iter_ref_t>);
+static_assert(std::random_access_iterator<mismatch_value_iter_ref_t>);
+static_assert(!std::contiguous_iterator<mismatch_value_iter_ref_t>);
 
 struct wrong_iter_reference_t {
     typedef std::contiguous_iterator_tag    iterator_category;
     typedef short                           value_type;
     typedef std::ptrdiff_t                  difference_type;
     typedef int*                            pointer;
     typedef short&                          reference;
     typedef wrong_iter_reference_t          self;
 
     wrong_iter_reference_t();
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self& y);
-    friend bool operator< (const self&, const self& y);
-    friend bool operator<=(const self&, const self& y);
-    friend bool operator> (const self&, const self& y);
-    friend bool operator>=(const self&, const self& y);
+    auto operator<=>(const self&) const = default;
 
     self& operator++();
     self operator++(int);
 
     self& operator--();
     self operator--(int);
 
     self& operator+=(difference_type n);
struct no_element_type {
     typedef int*                            pointer;
     typedef int&                            reference;
     typedef no_element_type                 self;
 
     no_element_type();
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self& y);
-    friend bool operator< (const self&, const self& y);
-    friend bool operator<=(const self&, const self& y);
-    friend bool operator> (const self&, const self& y);
-    friend bool operator>=(const self&, const self& y);
+    auto operator<=>(const self&) const = default;
 
     self& operator++();
     self operator++(int);
 
     self& operator--();
     self operator--(int);
 
     self& operator+=(difference_type n);
struct to_address_wrong_return_type {
     typedef int*                            pointer;
     typedef int&                            reference;
     typedef to_address_wrong_return_type    self;
 
     to_address_wrong_return_type();
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self& y);
-    friend bool operator< (const self&, const self& y);
-    friend bool operator<=(const self&, const self& y);
-    friend bool operator> (const self&, const self& y);
-    friend bool operator>=(const self&, const self& y);
+    auto operator<=>(const self&) const = default;
 
     self& operator++();
     self operator++(int);
 
     self& operator--();
     self operator--(int);
 
     self& operator+=(difference_type n);
struct template_and_no_element_type {
     typedef int*                            pointer;
     typedef int&                            reference;
     typedef template_and_no_element_type    self;
 
     template_and_no_element_type();
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self& y);
-    friend bool operator< (const self&, const self& y);
-    friend bool operator<=(const self&, const self& y);
-    friend bool operator> (const self&, const self& y);
-    friend bool operator>=(const self&, const self& y);
+    auto operator<=>(const self&) const = default;
 
     self& operator++();
     self operator++(int);
 
     self& operator--();
     self operator--(int);
 
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
-    friend self operator+(difference_type n, self x);
+    friend self operator+(difference_type, self) { return self{}; }
 
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self& n) const;
 
     reference operator[](difference_type n) const;
 };
 
 // Template param is used instead of element_type.
 static_assert(std::random_access_iterator<template_and_no_element_type<int>>);
 static_assert(std::contiguous_iterator<template_and_no_element_type<int>>);

libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/random_access_iterator.compile.pass.cpp

 // template<class T>
 // concept random_access_iterator;
 
 #include <iterator>
 
 #include "test_iterators.h"
 #include "test_macros.h"
 
-static_assert(!std::random_access_iterator<cpp17_input_iterator<int*> >);
-static_assert(!std::random_access_iterator<cpp20_input_iterator<int*> >);
-static_assert(!std::random_access_iterator<forward_iterator<int*> >);
-static_assert(!std::random_access_iterator<bidirectional_iterator<int*> >);
-static_assert( std::random_access_iterator<random_access_iterator<int*> >);
-static_assert( std::random_access_iterator<contiguous_iterator<int*> >);
+static_assert(!std::random_access_iterator<cpp17_input_iterator<int*>>);
+static_assert(!std::random_access_iterator<cpp20_input_iterator<int*>>);
+static_assert(!std::random_access_iterator<forward_iterator<int*>>);
+static_assert(!std::random_access_iterator<bidirectional_iterator<int*>>);
+static_assert( std::random_access_iterator<random_access_iterator<int*>>);
+static_assert( std::random_access_iterator<contiguous_iterator<int*>>);
 
 static_assert(std::random_access_iterator<int*>);
 static_assert(std::random_access_iterator<int const*>);
 static_assert(std::random_access_iterator<int volatile*>);
 static_assert(std::random_access_iterator<int const volatile*>);
 
 struct wrong_iterator_category {
     typedef std::bidirectional_iterator_tag iterator_category;
     typedef int                             value_type;
     typedef std::ptrdiff_t                  difference_type;
     typedef int*                            pointer;
     typedef int&                            reference;
     typedef wrong_iterator_category         self;
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self&);
-    friend bool operator< (const self&, const self&);
-    friend bool operator<=(const self&, const self&);
-    friend bool operator> (const self&, const self&);
-    friend bool operator>=(const self&, const self&);
+    auto operator<=>(const self&) const = default;
 
     self& operator++();
     self operator++(int);
 
     self& operator--();
     self operator--(int);
 
     self& operator+=(difference_type n);
struct common_base {
     typedef int                             value_type;
     typedef std::ptrdiff_t                  difference_type;
     typedef int*                            pointer;
     typedef int&                            reference;
     typedef Child                           self;
 
     reference operator*() const;
     pointer operator->() const;
-    friend bool operator==(const self&, const self&);
-    friend bool operator< (const self&, const self&);
-    friend bool operator<=(const self&, const self&);
-    friend bool operator> (const self&, const self&);
-    friend bool operator>=(const self&, const self&);
-
     self& operator++();
     self operator++(int);
-
     self& operator--();
     self operator--(int);
+    auto operator<=>(const common_base&) const = default;
 };
 
-struct simple_random_access_iterator
-  : common_base<simple_random_access_iterator> {
-
+struct simple_random_access_iterator : common_base<simple_random_access_iterator> {
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
-
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self&) const;
-
     reference operator[](difference_type n) const;
+    auto operator<=>(const self&) const = default;
 };
 static_assert(std::bidirectional_iterator<simple_random_access_iterator>);
 static_assert(std::random_access_iterator<simple_random_access_iterator>);
 
-struct no_plus_equals
-  : common_base<no_plus_equals> {
-
+struct no_plus_equals : common_base<no_plus_equals> {
  /* self& operator+=(difference_type n); */
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
-
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self&) const;
-
     reference operator[](difference_type n) const;
+    auto operator<=>(const self&) const = default;
 };
 static_assert( std::bidirectional_iterator<no_plus_equals>);
 static_assert(!std::random_access_iterator<no_plus_equals>);
 
-struct no_plus_difference_type
-  : common_base<no_plus_difference_type> {
-
+struct no_plus_difference_type : common_base<no_plus_difference_type> {
     self& operator+=(difference_type n);
  /* self operator+(difference_type n) const; */
     friend self operator+(difference_type n, self x);
-
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self&) const;
-
     reference operator[](difference_type n) const;
+    auto operator<=>(const self&) const = default;
 };
 static_assert( std::bidirectional_iterator<no_plus_difference_type>);
 static_assert(!std::random_access_iterator<no_plus_difference_type>);
 
-struct difference_type_no_plus
-  : common_base<difference_type_no_plus> {
-
+struct difference_type_no_plus : common_base<difference_type_no_plus> {
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
  /* friend self operator+(difference_type n, self x); */
-
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self&) const;
-
     reference operator[](difference_type n) const;
+    auto operator<=>(const self&) const = default;
 };
 static_assert( std::bidirectional_iterator<difference_type_no_plus>);
 static_assert(!std::random_access_iterator<difference_type_no_plus>);
 
-struct no_minus_equals
-  : common_base<no_minus_equals> {
-
+struct no_minus_equals : common_base<no_minus_equals> {
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
-
  /* self& operator-=(difference_type n); */
     self operator-(difference_type n) const;
     difference_type operator-(const self&) const;
-
     reference operator[](difference_type n) const;
+    auto operator<=>(const self&) const = default;
 };
 static_assert( std::bidirectional_iterator<no_minus_equals>);
 static_assert(!std::random_access_iterator<no_minus_equals>);
 
-struct no_minus
-  : common_base<no_minus> {
-
+struct no_minus : common_base<no_minus> {
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
-
     self& operator-=(difference_type n);
  /* self operator-(difference_type n) const; */
     difference_type operator-(const self&) const;
-
     reference operator[](difference_type n) const;
+    auto operator<=>(const self&) const = default;
 };
 static_assert( std::bidirectional_iterator<no_minus>);
 static_assert(!std::random_access_iterator<no_minus>);
 
-struct not_sized_sentinel
-  : common_base<not_sized_sentinel> {
-
+struct not_sized_sentinel : common_base<not_sized_sentinel> {
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
-
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
  /* difference_type operator-(const self&) const; */
-
     reference operator[](difference_type n) const;
+    auto operator<=>(const self&) const = default;
 };
 static_assert( std::bidirectional_iterator<not_sized_sentinel>);
 static_assert(!std::random_access_iterator<not_sized_sentinel>);
 
-struct no_subscript
-  : common_base<no_subscript> {
-
+struct no_subscript : common_base<no_subscript> {
     self& operator+=(difference_type n);
     self operator+(difference_type n) const;
     friend self operator+(difference_type n, self x);
-
     self& operator-=(difference_type n);
     self operator-(difference_type n) const;
     difference_type operator-(const self&) const;
-
  /* reference operator[](difference_type n) const; */
+    auto operator<=>(const self&) const = default;
 };
 static_assert( std::bidirectional_iterator<no_subscript>);
 static_assert(!std::random_access_iterator<no_subscript>);

libcxx/test/std/ranges/range.access/range.access.begin/begin.pass.cpp

 static_assert( std::is_invocable_v<RangeCBeginT, BeginFunction &>);
 
 struct BeginFunctionWithDataMember {
   int x;
   int begin;
   friend constexpr const int *begin(BeginFunctionWithDataMember const& bf) { return &bf.x; }
 };
 
-struct BeginFunctionWithPrivateBeginMember : private BeginMember {
+struct BeginFunctionWithPrivateBeginMember {
   int y;
   friend constexpr const int *begin(BeginFunctionWithPrivateBeginMember const& bf) { return &bf.y; }
+private:
+  constexpr const int *begin() const { return nullptr; }
 };
 
 struct BeginFunctionReturnsEmptyPtr {
   Empty x;
   friend constexpr const Empty *begin(BeginFunctionReturnsEmptyPtr const& bf) { return &bf.x; }
 };
 
 struct BeginFunctionByValue {

 
 struct BeginFunctionReturnsInt {
   friend constexpr int begin(BeginFunctionReturnsInt const&);
 };
 
 static_assert(!std::is_invocable_v<RangeBeginT, BeginFunctionReturnsInt const&>);
 
 struct BeginFunctionReturnsVoidPtr {
-  friend constexpr void *begin(BeginFunctionReturnsVoidPtr const&);
+  friend void *begin(BeginFunctionReturnsVoidPtr const&);
 };
 
 static_assert(!std::is_invocable_v<RangeBeginT, BeginFunctionReturnsVoidPtr const&>);
 
 struct BeginFunctionReturnsEmpty {
   friend constexpr Empty begin(BeginFunctionReturnsEmpty const&);
 };
 
 static_assert(!std::is_invocable_v<RangeBeginT, BeginFunctionReturnsEmpty const&>);
 
 struct BeginFunctionReturnsPtrConvertible {
-  friend constexpr PtrConvertible begin(BeginFunctionReturnsPtrConvertible const&);
+  friend PtrConvertible begin(BeginFunctionReturnsPtrConvertible const&);
 };
 
 static_assert(!std::is_invocable_v<RangeBeginT, BeginFunctionReturnsPtrConvertible const&>);
 
 constexpr bool testBeginFunction() {
-  const BeginFunction a{};
+  BeginFunction a{};
   assert(std::ranges::begin(a) == &a.x);
-  BeginFunction aa{};
-  assert(std::ranges::cbegin(aa) == &aa.x);
+  assert(std::ranges::cbegin(a) == &a.x);
 
   BeginFunctionByValue b;
   assert(std::ranges::begin(b) == &globalBuff[1]);
   assert(std::ranges::cbegin(b) == &globalBuff[1]);
 
   BeginFunctionEnabledBorrowing c;
   assert(std::ranges::begin(std::move(c)) == &globalBuff[2]);
+  assert(std::ranges::cbegin(std::move(c)) == &globalBuff[2]);
+
+  const BeginFunctionEnabledBorrowing cc;
+  assert(std::ranges::begin(std::move(cc)) == &globalBuff[2]);
+  assert(std::ranges::cbegin(std::move(cc)) == &globalBuff[2]);
 
-  const BeginFunctionReturnsEmptyPtr d{};
+  BeginFunctionReturnsEmptyPtr d{};
   assert(std::ranges::begin(d) == &d.x);
-  BeginFunctionReturnsEmptyPtr dd{};
-  assert(std::ranges::cbegin(dd) == &dd.x);
+  assert(std::ranges::cbegin(d) == &d.x);
 
-  const BeginFunctionWithDataMember e{};
+  BeginFunctionWithDataMember e{};
   assert(std::ranges::begin(e) == &e.x);
-  BeginFunctionWithDataMember ee{};
-  assert(std::ranges::cbegin(ee) == &ee.x);
+  assert(std::ranges::cbegin(e) == &e.x);
 
-  const BeginFunctionWithPrivateBeginMember f{};
+  BeginFunctionWithPrivateBeginMember f{};
   assert(std::ranges::begin(f) == &f.y);
-  BeginFunctionWithPrivateBeginMember ff{};
-  assert(std::ranges::cbegin(ff) == &ff.y);
+  assert(std::ranges::cbegin(f) == &f.y);
 
   return true;
 }
 
 template<class T>
 struct NoThrowMemberBegin {
   T begin() noexcept;
   T begin() const noexcept;
 };
 
 template<class T>
 struct NoThrowADLBegin {
   friend T begin(NoThrowADLBegin&) noexcept;
   friend T begin(NoThrowADLBegin const&) noexcept;
 };
 ASSERT_NOEXCEPT(std::ranges::begin(std::declval<int (&)[10]>()));
 ASSERT_NOEXCEPT(std::ranges::begin(std::declval<NoThrowMemberBegin<int*>&>()));
-ASSERT_NOT_NOEXCEPT(std::ranges::begin(std::declval<NoThrowMemberBegin<ThrowingIterator<int> >&>()));
+ASSERT_NOT_NOEXCEPT(std::ranges::begin(std::declval<NoThrowMemberBegin<ThrowingIterator<int>>&>()));
 ASSERT_NOEXCEPT(std::ranges::begin(std::declval<NoThrowADLBegin<int*>&>()));
-ASSERT_NOT_NOEXCEPT(std::ranges::begin(std::declval<NoThrowADLBegin<ThrowingIterator<int> >&>()));
+ASSERT_NOT_NOEXCEPT(std::ranges::begin(std::declval<NoThrowADLBegin<ThrowingIterator<int>>&>()));
 
 
 int main(int, char**) {
   testArray();
   static_assert(testArray());
 
   testBeginMember();
   static_assert(testBeginMember());
 
   testBeginFunction();
   static_assert(testBeginFunction());
 
   return 0;
 }

libcxx/test/std/ranges/range.utility/range.subrange/subrange_test_types.h

struct ConditionallyConvertibleBase {
 
     int *base_ = nullptr;
 
     constexpr ConditionallyConvertibleBase() = default;
     constexpr explicit ConditionallyConvertibleBase(int *ptr) : base_(ptr) {}
 
     constexpr int *base() const { return base_; }
 
-    friend bool operator==(const self&, const self&);
+    friend bool operator==(const self&, const self&) = default;
 
     reference operator*() const;
     pointer operator->() const;
     self& operator++();
     self operator++(int);
     self& operator--();
     self operator--(int);
 

libcxx/test/std/ranges/range.utility/view.interface/view.interface.pass.cpp

 
 struct InputRange : std::ranges::view_interface<InputRange> {
   int buff[8] = {0, 1, 2, 3, 4, 5, 6, 7};
   constexpr InputIter begin() const { return InputIter(buff); }
   constexpr InputIter end() const { return InputIter(buff + 8); }
 };
 
 struct NotSizedSentinel {
-  using I = int*;
-  using value_type = std::iter_value_t<I>;
-  using difference_type = std::iter_difference_t<I>;
+  using value_type = int;
+  using difference_type = std::ptrdiff_t;
   using iterator_concept = std::forward_iterator_tag;
 
-  NotSizedSentinel() = default;
-  explicit constexpr NotSizedSentinel(I);
-
-  constexpr int &operator*() const { return *value; };
+  explicit NotSizedSentinel() = default;
+  explicit NotSizedSentinel(int*);
+  int& operator*() const;
   NotSizedSentinel& operator++();
   NotSizedSentinel operator++(int);
   bool operator==(NotSizedSentinel const&) const;
-
-  int *value;
 };
 static_assert(std::forward_iterator<NotSizedSentinel>);
 
 using ForwardIter = forward_iterator<int*>;
 
 // So that we conform to sized_sentinel_for.
 constexpr std::ptrdiff_t operator-(const ForwardIter& x, const ForwardIter& y) {
     return x.base() - y.base();

 template<bool IsNoexcept>
 struct BoolConvertibleComparison : std::ranges::view_interface<BoolConvertibleComparison<IsNoexcept>> {
   struct ResultType {
     bool value;
     constexpr operator bool() const noexcept(IsNoexcept) { return value; }
   };
 
   struct SentinelType {
-    int *base;
+    int *base_;
     SentinelType() = default;
-    explicit constexpr SentinelType(int *base) : base(base) {}
-    friend constexpr ResultType operator==(ForwardIter const& iter, SentinelType const& sent) noexcept { return {iter.base() == sent.base}; }
-    friend constexpr ResultType operator==(SentinelType const& sent, ForwardIter const& iter) noexcept { return {iter.base() == sent.base}; }
-    friend constexpr ResultType operator!=(ForwardIter const& iter, SentinelType const& sent) noexcept { return {iter.base() != sent.base}; }
-    friend constexpr ResultType operator!=(SentinelType const& sent, ForwardIter const& iter) noexcept { return {iter.base() != sent.base}; }
+    explicit constexpr SentinelType(int *base) : base_(base) {}
+    friend constexpr ResultType operator==(ForwardIter const& iter, SentinelType const& sent) noexcept { return {iter.base() == sent.base_}; }
+    friend constexpr ResultType operator==(SentinelType const& sent, ForwardIter const& iter) noexcept { return {iter.base() == sent.base_}; }
+    friend constexpr ResultType operator!=(ForwardIter const& iter, SentinelType const& sent) noexcept { return {iter.base() != sent.base_}; }
+    friend constexpr ResultType operator!=(SentinelType const& sent, ForwardIter const& iter) noexcept { return {iter.base() != sent.base_}; }
   };
 
   int buff[8] = {0, 1, 2, 3, 4, 5, 6, 7};
   constexpr ForwardIter begin() const noexcept { return ForwardIter(const_cast<int*>(buff)); }
   constexpr SentinelType end() const noexcept { return SentinelType(const_cast<int*>(buff) + 8); }
 };
 
 template<class T>

libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// XFAIL: gcc-10
+// XFAIL: gcc-10, gcc-11
 //     GCC's __builtin_strlen isn't constexpr yet
 // UNSUPPORTED: LIBCXX-DEBUG-FIXME
 
 // <string_view>
 
 // size_type copy(charT* s, size_type n, size_type pos = 0) const;
 
 // Throws: out_of_range if pos > size().