diff --git a/libcxx/include/__string/extern_template_lists.h b/libcxx/include/__string/extern_template_lists.h
--- a/libcxx/include/__string/extern_template_lists.h
+++ b/libcxx/include/__string/extern_template_lists.h
@@ -28,34 +28,34 @@
 // functions supporting new c++ version / API changes. Typically entries
 // must never be removed from the stable list.
 #define _LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST(_Func, _CharType) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, value_type const*, size_type)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::rfind(value_type const*, size_type, size_type) const) \
-  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init(value_type const*, size_type, size_type)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, value_type const* _Nullable, size_type)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::rfind(value_type const* _Nonnull, size_type, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init(value_type const* _Null_unspecified, size_type, size_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::basic_string(basic_string const&)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, value_type const*)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, value_type const* _Nonnull)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::basic_string(basic_string const&, allocator<_CharType> const&)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_last_not_of(value_type const*, size_type, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_last_not_of(value_type const* _Nonnull, size_type, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::~basic_string()) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_first_not_of(value_type const*, size_type, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_first_not_of(value_type const* _Nonnull, size_type, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::insert(size_type, size_type, value_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::operator=(value_type)) \
-  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init(value_type const*, size_type)) \
+  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init(value_type const* _Null_unspecified, size_type)) \
   _Func(_LIBCPP_FUNC_VIS const _CharType& basic_string<_CharType>::at(size_type) const) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::insert(size_type, value_type const*, size_type)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_first_of(value_type const*, size_type, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::insert(size_type, value_type const* _Null_unspecified, size_type)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_first_of(value_type const* _Nonnull, size_type, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, size_type, value_type)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::assign(value_type const*, size_type)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::assign(value_type const* _Nullable, size_type)) \
   _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::reserve(size_type)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(value_type const*, size_type)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(value_type const* _Nullable, size_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::assign(basic_string const&, size_type, size_type)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::copy(value_type*, size_type, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::copy(value_type* _Null_unspecified, size_type, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::basic_string(basic_string const&, size_type, size_type, allocator<_CharType> const&)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find(value_type, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__init(size_type, value_type)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::insert(size_type, value_type const*)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_last_of(value_type const*, size_type, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::insert(size_type, value_type const* _Nonnull)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find_last_of(value_type const* _Nonnull, size_type, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__grow_by(size_type, size_type, size_type, size_type, size_type, size_type)) \
-  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__grow_by_and_replace(size_type, size_type, size_type, size_type, size_type, size_type, value_type const*)) \
+  _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::__grow_by_and_replace(size_type, size_type, size_type, size_type, size_type, size_type, value_type const* _Null_unspecified)) \
   _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::push_back(value_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(size_type, value_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::rfind(value_type, size_type) const) \
@@ -63,15 +63,15 @@
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::assign(size_type, value_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::erase(size_type, size_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(basic_string const&, size_type, size_type)) \
-  _Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(value_type const*) const) \
-  _Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(size_type, size_type, value_type const*) const) \
+  _Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(value_type const* _Nonnull) const) \
+  _Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(size_type, size_type, value_type const* _Nonnull) const) \
   _Func(_LIBCPP_FUNC_VIS _CharType& basic_string<_CharType>::at(size_type)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::assign(value_type const*)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find(value_type const*, size_type, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::assign(value_type const* _Nonnull)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::size_type basic_string<_CharType>::find(value_type const* _Nonnull, size_type, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(size_type, size_type, basic_string const&, size_type, size_type) const) \
-  _Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(size_type, size_type, value_type const*, size_type) const) \
+  _Func(_LIBCPP_FUNC_VIS int basic_string<_CharType>::compare(size_type, size_type, value_type const* _Nullable, size_type) const) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::operator=(basic_string const&)) \
-  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(value_type const*)) \
+  _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::append(value_type const* _Nonnull)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>& basic_string<_CharType>::replace(size_type, size_type, basic_string const&, size_type, size_type)) \
   _Func(_LIBCPP_FUNC_VIS basic_string<_CharType>::iterator basic_string<_CharType>::insert(basic_string::const_iterator, value_type)) \
   _Func(_LIBCPP_FUNC_VIS void basic_string<_CharType>::resize(size_type, value_type)) \
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -610,7 +610,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDDEN _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>
-operator+(const _CharT* __x, const basic_string<_CharT,_Traits,_Allocator>& __y);
+operator+(const _CharT* _Null_unspecified __x, const basic_string<_CharT,_Traits,_Allocator>& __y);
 
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -620,14 +620,14 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>
-operator+(const basic_string<_CharT, _Traits, _Allocator>& __x, const _CharT* __y);
+operator+(const basic_string<_CharT, _Traits, _Allocator>& __x, const _CharT* _Null_unspecified __y);
 
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>
 operator+(const basic_string<_CharT, _Traits, _Allocator>& __x, _CharT __y);
 
-extern template _LIBCPP_FUNC_VIS string operator+<char, char_traits<char>, allocator<char> >(char const*, string const&);
+extern template _LIBCPP_FUNC_VIS string operator+<char, char_traits<char>, allocator<char> >(char const* _Nonnull, string const&);
 
 template <class _Iter>
 struct __string_is_trivial_iterator : public false_type {};
@@ -875,7 +875,7 @@
 #endif // _LIBCPP_CXX03_LANG
 
   template <class = __enable_if_t<__is_allocator<_Allocator>::value, nullptr_t> >
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* __s)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* _Nonnull __s)
       : __r_(__default_init_tag(), __default_init_tag()) {
     _LIBCPP_ASSERT(__s != nullptr, "basic_string(const char*) detected nullptr");
     __init(__s, traits_type::length(__s));
@@ -883,13 +883,13 @@
   }
 
   template <class = __enable_if_t<__is_allocator<_Allocator>::value, nullptr_t> >
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* __s, const _Allocator& __a);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* _Nonnull __s, const _Allocator& __a);
 
 #if _LIBCPP_STD_VER > 20
   basic_string(nullptr_t) = delete;
 #endif
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* __s, size_type __n)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string(const _CharT* _Nullable __s, size_type __n)
       : __r_(__default_init_tag(), __default_init_tag()) {
     _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "basic_string(const char*, n) detected nullptr");
     __init(__s, __n);
@@ -897,7 +897,7 @@
   }
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-  basic_string(const _CharT* __s, size_type __n, const _Allocator& __a)
+  basic_string(const _CharT* _Nullable __s, size_type __n, const _Allocator& __a)
       : __r_(__default_init_tag(), __a) {
     _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "basic_string(const char*, n, allocator) detected nullptr");
     __init(__s, __n);
@@ -995,7 +995,7 @@
     basic_string& operator=(initializer_list<value_type> __il) {return assign(__il.begin(), __il.size());}
 #endif
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string& operator=(const value_type* __s) {return assign(__s);}
+    basic_string& operator=(const value_type* _Nonnull __s) {return assign(__s);}
 #if _LIBCPP_STD_VER > 20
     basic_string& operator=(nullptr_t) = delete;
 #endif
@@ -1094,7 +1094,7 @@
         __self_view __sv = __t; return append(__sv);
     }
 
-    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& operator+=(const value_type* __s) {
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& operator+=(const value_type* _Nonnull __s) {
         return append(__s);
     }
 
@@ -1130,8 +1130,8 @@
             basic_string&
         >
                   append(const _Tp& __t, size_type __pos, size_type __n=npos);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& append(const value_type* __s, size_type __n);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& append(const value_type* __s);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& append(const value_type* _Nullable __s, size_type __n);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& append(const value_type* _Nonnull __s);
     _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& append(size_type __n, value_type __c);
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -1198,8 +1198,8 @@
             basic_string&
         >
                   assign(const _Tp & __t, size_type __pos, size_type __n=npos);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& assign(const value_type* __s, size_type __n);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& assign(const value_type* __s);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& assign(const value_type* _Nullable __s, size_type __n);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& assign(const value_type* _Nonnull __s);
     _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& assign(size_type __n, value_type __c);
     template<class _InputIterator>
     _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -1245,8 +1245,8 @@
                   insert(size_type __pos1, const _Tp& __t, size_type __pos2, size_type __n=npos);
     _LIBCPP_CONSTEXPR_SINCE_CXX20
     basic_string& insert(size_type __pos1, const basic_string& __str, size_type __pos2, size_type __n=npos);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& insert(size_type __pos, const value_type* __s, size_type __n);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& insert(size_type __pos, const value_type* __s);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& insert(size_type __pos, const value_type* _Nullable __s, size_type __n);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& insert(size_type __pos, const value_type* _Nonnull __s);
     _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& insert(size_type __pos, size_type __n, value_type __c);
     _LIBCPP_CONSTEXPR_SINCE_CXX20 iterator      insert(const_iterator __pos, value_type __c);
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -1301,8 +1301,8 @@
         >
                   replace(size_type __pos1, size_type __n1, const _Tp& __t, size_type __pos2, size_type __n2=npos);
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string& replace(size_type __pos, size_type __n1, const value_type* __s, size_type __n2);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& replace(size_type __pos, size_type __n1, const value_type* __s);
+    basic_string& replace(size_type __pos, size_type __n1, const value_type* _Nullable __s, size_type __n2);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& replace(size_type __pos, size_type __n1, const value_type* _Nonnull __s);
     _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& replace(size_type __pos, size_type __n1, size_type __n2, value_type __c);
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     basic_string& replace(const_iterator __i1, const_iterator __i2, const basic_string& __str);
@@ -1317,9 +1317,9 @@
                   replace(const_iterator __i1, const_iterator __i2, const _Tp& __t) { __self_view __sv = __t; return replace(__i1 - begin(), __i2 - __i1, __sv); }
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string& replace(const_iterator __i1, const_iterator __i2, const value_type* __s, size_type __n);
+    basic_string& replace(const_iterator __i1, const_iterator __i2, const value_type* _Null_unspecified __s, size_type __n);
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string& replace(const_iterator __i1, const_iterator __i2, const value_type* __s);
+    basic_string& replace(const_iterator __i1, const_iterator __i2, const value_type* _Null_unspecified __s);
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     basic_string& replace(const_iterator __i1, const_iterator __i2, size_type __n, value_type __c);
     template<class _InputIterator>
@@ -1336,7 +1336,7 @@
         {return replace(__i1, __i2, __il.begin(), __il.end());}
 #endif // _LIBCPP_CXX03_LANG
 
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 size_type copy(value_type* __s, size_type __n, size_type __pos = 0) const;
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 size_type copy(value_type* _Null_unspecified __s, size_type __n, size_type __pos = 0) const;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     basic_string substr(size_type __pos = 0, size_type __n = npos) const;
 
@@ -1350,12 +1350,12 @@
 #endif
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    const value_type* c_str() const _NOEXCEPT {return data();}
+    const value_type* _Nonnull c_str() const _NOEXCEPT {return data();}
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    const value_type* data() const _NOEXCEPT  {return std::__to_address(__get_pointer());}
+    const value_type* _Nonnull data() const _NOEXCEPT  {return std::__to_address(__get_pointer());}
 #if _LIBCPP_STD_VER > 14 || defined(_LIBCPP_BUILDING_LIBRARY)
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    value_type* data()             _NOEXCEPT  {return std::__to_address(__get_pointer());}
+    value_type* _Nonnull data()             _NOEXCEPT  {return std::__to_address(__get_pointer());}
 #endif
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -1373,9 +1373,9 @@
         >
               find(const _Tp& __t, size_type __pos = 0) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
+    size_type find(const value_type* _Nullable __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find(const value_type* __s, size_type __pos = 0) const _NOEXCEPT;
+    size_type find(const value_type* _Nonnull __s, size_type __pos = 0) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20 size_type find(value_type __c, size_type __pos = 0) const _NOEXCEPT;
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -1390,9 +1390,9 @@
         >
               rfind(const _Tp& __t, size_type __pos = npos) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type rfind(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
+    size_type rfind(const value_type* _Nullable __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type rfind(const value_type* __s, size_type __pos = npos) const _NOEXCEPT;
+    size_type rfind(const value_type* _Nonnull __s, size_type __pos = npos) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20 size_type rfind(value_type __c, size_type __pos = npos) const _NOEXCEPT;
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -1407,9 +1407,9 @@
         >
               find_first_of(const _Tp& __t, size_type __pos = 0) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_first_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
+    size_type find_first_of(const value_type* _Nullable __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_first_of(const value_type* __s, size_type __pos = 0) const _NOEXCEPT;
+    size_type find_first_of(const value_type* _Nonnull __s, size_type __pos = 0) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     size_type find_first_of(value_type __c, size_type __pos = 0) const _NOEXCEPT;
 
@@ -1425,9 +1425,9 @@
         >
               find_last_of(const _Tp& __t, size_type __pos = npos) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_last_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
+    size_type find_last_of(const value_type* _Nullable __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_last_of(const value_type* __s, size_type __pos = npos) const _NOEXCEPT;
+    size_type find_last_of(const value_type* _Nonnull __s, size_type __pos = npos) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     size_type find_last_of(value_type __c, size_type __pos = npos) const _NOEXCEPT;
 
@@ -1443,9 +1443,9 @@
         >
               find_first_not_of(const _Tp &__t, size_type __pos = 0) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_first_not_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
+    size_type find_first_not_of(const value_type* _Nullable __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_first_not_of(const value_type* __s, size_type __pos = 0) const _NOEXCEPT;
+    size_type find_first_not_of(const value_type* _Nonnull __s, size_type __pos = 0) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     size_type find_first_not_of(value_type __c, size_type __pos = 0) const _NOEXCEPT;
 
@@ -1461,9 +1461,9 @@
         >
               find_last_not_of(const _Tp& __t, size_type __pos = npos) const _NOEXCEPT;
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_last_not_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
+    size_type find_last_not_of(const value_type* _Nullable __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    size_type find_last_not_of(const value_type* __s, size_type __pos = npos) const _NOEXCEPT;
+    size_type find_last_not_of(const value_type* _Nonnull __s, size_type __pos = npos) const _NOEXCEPT;
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     size_type find_last_not_of(value_type __c, size_type __pos = npos) const _NOEXCEPT;
 
@@ -1502,10 +1502,10 @@
             int
         >
         compare(size_type __pos1, size_type __n1, const _Tp& __t, size_type __pos2, size_type __n2=npos) const;
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 int compare(const value_type* __s) const _NOEXCEPT;
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 int compare(size_type __pos1, size_type __n1, const value_type* __s) const;
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 int compare(const value_type* _Nonnull __s) const _NOEXCEPT;
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 int compare(size_type __pos1, size_type __n1, const value_type* _Nonnull __s) const;
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    int compare(size_type __pos1, size_type __n1, const value_type* __s, size_type __n2) const;
+    int compare(size_type __pos1, size_type __n1, const value_type* _Nullable __s, size_type __n2) const;
 
 #if _LIBCPP_STD_VER > 17
     constexpr _LIBCPP_HIDE_FROM_ABI
@@ -1517,7 +1517,7 @@
     { return !empty() && _Traits::eq(front(), __c); }
 
     constexpr _LIBCPP_HIDE_FROM_ABI
-    bool starts_with(const value_type* __s) const noexcept
+    bool starts_with(const value_type* _Nonnull __s) const noexcept
     { return starts_with(__self_view(__s)); }
 
     constexpr _LIBCPP_HIDE_FROM_ABI
@@ -1529,7 +1529,7 @@
     { return !empty() && _Traits::eq(back(), __c); }
 
     constexpr _LIBCPP_HIDE_FROM_ABI
-    bool ends_with(const value_type* __s) const noexcept
+    bool ends_with(const value_type* _Nonnull __s) const noexcept
     { return ends_with(__self_view(__s)); }
 #endif
 
@@ -1543,7 +1543,7 @@
     { return __self_view(data(), size()).contains(__c); }
 
     constexpr _LIBCPP_HIDE_FROM_ABI
-    bool contains(const value_type* __s) const
+    bool contains(const value_type* _Nonnull __s) const
     { return __self_view(data(), size()).contains(__s); }
 #endif
 
@@ -1716,9 +1716,9 @@
     }
 
     inline _LIBCPP_CONSTEXPR_SINCE_CXX20
-    void __init(const value_type* __s, size_type __sz, size_type __reserve);
+    void __init(const value_type* _Null_unspecified __s, size_type __sz, size_type __reserve);
     inline _LIBCPP_CONSTEXPR_SINCE_CXX20
-    void __init(const value_type* __s, size_type __sz);
+    void __init(const value_type* _Null_unspecified __s, size_type __sz);
     inline _LIBCPP_CONSTEXPR_SINCE_CXX20
     void __init(size_type __n, value_type __c);
 
@@ -1730,7 +1730,7 @@
     // to call the __init() functions as those are marked as inline which may
     // result in over-aggressive inlining by the compiler, where our aim is
     // to only inline the fast path code directly in the ctor.
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 void __init_copy_ctor_external(const value_type* __s, size_type __sz);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 void __init_copy_ctor_external(const value_type* _Nonnull __s, size_type __sz);
 
     template <class _InputIterator>
     inline _LIBCPP_CONSTEXPR_SINCE_CXX20
@@ -1754,13 +1754,13 @@
     _LIBCPP_CONSTEXPR_SINCE_CXX20
     void __grow_by_and_replace(size_type __old_cap, size_type __delta_cap, size_type __old_sz,
                                size_type __n_copy,  size_type __n_del,
-                               size_type __n_add, const value_type* __p_new_stuff);
+                               size_type __n_add, const value_type* _Null_unspecified __p_new_stuff);
 
     // __assign_no_alias is invoked for assignment operations where we
     // have proof that the input does not alias the current instance.
     // For example, operator=(basic_string) performs a 'self' check.
     template <bool __is_short>
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& __assign_no_alias(const value_type* __s, size_type __n);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& __assign_no_alias(const value_type* _Null_unspecified __s, size_type __n);
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
     void __erase_to_end(size_type __pos);
@@ -1838,11 +1838,11 @@
         _NOEXCEPT
         {}
 
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& __assign_external(const value_type* __s);
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& __assign_external(const value_type* __s, size_type __n);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& __assign_external(const value_type* _Null_unspecified __s);
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string& __assign_external(const value_type* _Null_unspecified __s, size_type __n);
 
     // Assigns the value in __s, guaranteed to be __n < __min_cap in length.
-    inline basic_string& __assign_short(const value_type* __s, size_type __n) {
+    inline basic_string& __assign_short(const value_type* _Null_unspecified __s, size_type __n) {
       pointer __p = __is_long()
                         ? (__set_long_size(__n), __get_long_pointer())
                         : (__set_short_size(__n), __get_short_pointer());
@@ -1852,7 +1852,7 @@
     }
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string& __null_terminate_at(value_type* __p, size_type __newsz) {
+    basic_string& __null_terminate_at(value_type* _Nonnull __p, size_type __newsz) {
       __set_size(__newsz);
       __invalidate_iterators_past(__newsz);
       traits_type::assign(__p[__newsz], value_type());
@@ -1882,9 +1882,9 @@
     }
 
     friend _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string operator+<>(const basic_string&, const basic_string&);
-    friend _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string operator+<>(const value_type*, const basic_string&);
+    friend _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string operator+<>(const value_type* _Null_unspecified, const basic_string&);
     friend _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string operator+<>(value_type, const basic_string&);
-    friend _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string operator+<>(const basic_string&, const value_type*);
+    friend _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string operator+<>(const basic_string&, const value_type* _Null_unspecified);
     friend _LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string operator+<>(const basic_string&, value_type);
 };
 
@@ -1965,7 +1965,7 @@
 
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
-void basic_string<_CharT, _Traits, _Allocator>::__init(const value_type* __s,
+void basic_string<_CharT, _Traits, _Allocator>::__init(const value_type* _Null_unspecified __s,
                                                        size_type __sz,
                                                        size_type __reserve)
 {
@@ -1995,7 +1995,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 void
-basic_string<_CharT, _Traits, _Allocator>::__init(const value_type* __s, size_type __sz)
+basic_string<_CharT, _Traits, _Allocator>::__init(const value_type* _Null_unspecified __s, size_type __sz)
 {
     if (__libcpp_is_constant_evaluated())
         __r_.first() = __rep();
@@ -2023,7 +2023,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 template <class>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
-basic_string<_CharT, _Traits, _Allocator>::basic_string(const _CharT* __s, const _Allocator& __a)
+basic_string<_CharT, _Traits, _Allocator>::basic_string(const _CharT* _Nonnull __s, const _Allocator& __a)
     : __r_(__default_init_tag(), __a)
 {
     _LIBCPP_ASSERT(__s != nullptr, "basic_string(const char*, allocator) detected nullptr");
@@ -2061,7 +2061,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 void basic_string<_CharT, _Traits, _Allocator>::__init_copy_ctor_external(
-    const value_type* __s, size_type __sz) {
+    const value_type* _Nonnull __s, size_type __sz) {
   if (__libcpp_is_constant_evaluated())
     __r_.first() = __rep();
 
@@ -2259,7 +2259,7 @@
 void
 basic_string<_CharT, _Traits, _Allocator>::__grow_by_and_replace
     (size_type __old_cap, size_type __delta_cap, size_type __old_sz,
-     size_type __n_copy,  size_type __n_del,     size_type __n_add, const value_type* __p_new_stuff)
+     size_type __n_copy,  size_type __n_del,     size_type __n_add, const value_type* _Null_unspecified __p_new_stuff)
 {
     size_type __ms = max_size();
     if (__delta_cap > __ms - __old_cap - 1)
@@ -2328,7 +2328,7 @@
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
 basic_string<_CharT, _Traits, _Allocator>::__assign_no_alias(
-    const value_type* __s, size_type __n) {
+    const value_type* _Null_unspecified __s, size_type __n) {
   size_type __cap = __is_short ? static_cast<size_type>(__min_cap) : __get_long_cap();
   if (__n < __cap) {
     pointer __p = __is_short ? __get_short_pointer() : __get_long_pointer();
@@ -2347,7 +2347,7 @@
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
 basic_string<_CharT, _Traits, _Allocator>::__assign_external(
-    const value_type* __s, size_type __n) {
+    const value_type* _Null_unspecified __s, size_type __n) {
   size_type __cap = capacity();
   if (__cap >= __n) {
     value_type* __p = std::__to_address(__get_pointer());
@@ -2363,7 +2363,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::assign(const value_type* __s, size_type __n)
+basic_string<_CharT, _Traits, _Allocator>::assign(const value_type* _Nullable __s, size_type __n)
 {
     _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string::assign received nullptr");
     return (__builtin_constant_p(__n) && __fits_in_sso(__n))
@@ -2571,14 +2571,14 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::__assign_external(const value_type* __s) {
+basic_string<_CharT, _Traits, _Allocator>::__assign_external(const value_type* _Null_unspecified __s) {
   return __assign_external(__s, traits_type::length(__s));
 }
 
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::assign(const value_type* __s)
+basic_string<_CharT, _Traits, _Allocator>::assign(const value_type* _Nonnull __s)
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::assign received nullptr");
     return __builtin_constant_p(*__s)
@@ -2592,7 +2592,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::append(const value_type* __s, size_type __n)
+basic_string<_CharT, _Traits, _Allocator>::append(const value_type* _Nullable __s, size_type __n)
 {
     _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string::append received nullptr");
     size_type __cap = capacity();
@@ -2763,7 +2763,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::append(const value_type* __s)
+basic_string<_CharT, _Traits, _Allocator>::append(const value_type* _Nonnull __s)
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::append received nullptr");
     return append(__s, traits_type::length(__s));
@@ -2774,7 +2774,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::insert(size_type __pos, const value_type* __s, size_type __n)
+basic_string<_CharT, _Traits, _Allocator>::insert(size_type __pos, const value_type* _Nullable __s, size_type __n)
 {
     _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string::insert received nullptr");
     size_type __sz = size();
@@ -2930,7 +2930,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::insert(size_type __pos, const value_type* __s)
+basic_string<_CharT, _Traits, _Allocator>::insert(size_type __pos, const value_type* _Nonnull __s)
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::insert received nullptr");
     return insert(__pos, __s, traits_type::length(__s));
@@ -2985,7 +2985,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::replace(size_type __pos, size_type __n1, const value_type* __s, size_type __n2)
+basic_string<_CharT, _Traits, _Allocator>::replace(size_type __pos, size_type __n1, const value_type* _Nullable __s, size_type __n2)
     _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK
 {
     _LIBCPP_ASSERT(__n2 == 0 || __s != nullptr, "string::replace received nullptr");
@@ -3122,7 +3122,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::replace(size_type __pos, size_type __n1, const value_type* __s)
+basic_string<_CharT, _Traits, _Allocator>::replace(size_type __pos, size_type __n1, const value_type* _Nonnull __s)
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::replace received nullptr");
     return replace(__pos, __n1, __s, traits_type::length(__s));
@@ -3140,7 +3140,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::replace(const_iterator __i1, const_iterator __i2, const value_type* __s, size_type __n)
+basic_string<_CharT, _Traits, _Allocator>::replace(const_iterator __i1, const_iterator __i2, const value_type* _Null_unspecified __s, size_type __n)
 {
     return replace(static_cast<size_type>(__i1 - begin()), static_cast<size_type>(__i2 - __i1), __s, __n);
 }
@@ -3148,7 +3148,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>&
-basic_string<_CharT, _Traits, _Allocator>::replace(const_iterator __i1, const_iterator __i2, const value_type* __s)
+basic_string<_CharT, _Traits, _Allocator>::replace(const_iterator __i1, const_iterator __i2, const value_type* _Null_unspecified __s)
 {
     return replace(static_cast<size_type>(__i1 - begin()), static_cast<size_type>(__i2 - __i1), __s);
 }
@@ -3475,7 +3475,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::copy(value_type* __s, size_type __n, size_type __pos) const
+basic_string<_CharT, _Traits, _Allocator>::copy(value_type* _Null_unspecified __s, size_type __n, size_type __pos) const
 {
     size_type __sz = size();
     if (__pos > __sz)
@@ -3532,7 +3532,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find(const value_type* _Nullable __s,
                                                 size_type __pos,
                                                 size_type __n) const _NOEXCEPT
 {
@@ -3570,7 +3570,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find(const value_type* _Nonnull __s,
                                                 size_type __pos) const _NOEXCEPT
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::find(): received nullptr");
@@ -3593,7 +3593,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::rfind(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::rfind(const value_type* _Nullable __s,
                                                  size_type __pos,
                                                  size_type __n) const _NOEXCEPT
 {
@@ -3631,7 +3631,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::rfind(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::rfind(const value_type* _Nonnull __s,
                                                  size_type __pos) const _NOEXCEPT
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::rfind(): received nullptr");
@@ -3654,7 +3654,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_first_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_first_of(const value_type* _Nullable __s,
                                                          size_type __pos,
                                                          size_type __n) const _NOEXCEPT
 {
@@ -3692,7 +3692,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_first_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_first_of(const value_type* _Nonnull __s,
                                                          size_type __pos) const _NOEXCEPT
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::find_first_of(): received nullptr");
@@ -3714,7 +3714,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_last_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_last_of(const value_type* _Nullable __s,
                                                         size_type __pos,
                                                         size_type __n) const _NOEXCEPT
 {
@@ -3752,7 +3752,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_last_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_last_of(const value_type* _Nonnull __s,
                                                         size_type __pos) const _NOEXCEPT
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::find_last_of(): received nullptr");
@@ -3774,7 +3774,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_first_not_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_first_not_of(const value_type* _Nullable __s,
                                                              size_type __pos,
                                                              size_type __n) const _NOEXCEPT
 {
@@ -3812,7 +3812,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_first_not_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_first_not_of(const value_type* _Nonnull __s,
                                                              size_type __pos) const _NOEXCEPT
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::find_first_not_of(): received nullptr");
@@ -3835,7 +3835,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_last_not_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_last_not_of(const value_type* _Nullable __s,
                                                             size_type __pos,
                                                             size_type __n) const _NOEXCEPT
 {
@@ -3873,7 +3873,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename basic_string<_CharT, _Traits, _Allocator>::size_type
-basic_string<_CharT, _Traits, _Allocator>::find_last_not_of(const value_type* __s,
+basic_string<_CharT, _Traits, _Allocator>::find_last_not_of(const value_type* _Nonnull __s,
                                                             size_type __pos) const _NOEXCEPT
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::find_last_not_of(): received nullptr");
@@ -3930,7 +3930,7 @@
 int
 basic_string<_CharT, _Traits, _Allocator>::compare(size_type __pos1,
                                                    size_type __n1,
-                                                   const value_type* __s,
+                                                   const value_type* _Nullable __s,
                                                    size_type __n2) const
 {
     _LIBCPP_ASSERT(__n2 == 0 || __s != nullptr, "string::compare(): received nullptr");
@@ -4009,7 +4009,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20
 int
-basic_string<_CharT, _Traits, _Allocator>::compare(const value_type* __s) const _NOEXCEPT
+basic_string<_CharT, _Traits, _Allocator>::compare(const value_type* _Nonnull __s) const _NOEXCEPT
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::compare(): received nullptr");
     return compare(0, npos, __s, traits_type::length(__s));
@@ -4020,7 +4020,7 @@
 int
 basic_string<_CharT, _Traits, _Allocator>::compare(size_type __pos1,
                                                    size_type __n1,
-                                                   const value_type* __s) const
+                                                   const value_type* _Nonnull __s) const
 {
     _LIBCPP_ASSERT(__s != nullptr, "string::compare(): received nullptr");
     return compare(__pos1, __n1, __s, traits_type::length(__s));
@@ -4115,7 +4115,7 @@
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI
 bool
 operator==(const basic_string<_CharT,_Traits,_Allocator>& __lhs,
-           const _CharT* __rhs) _NOEXCEPT
+           const _CharT* _Nonnull __rhs) _NOEXCEPT
 {
 #if _LIBCPP_STD_VER > 17
     return basic_string_view<_CharT, _Traits>(__lhs) == basic_string_view<_CharT, _Traits>(__rhs);
@@ -4139,7 +4139,7 @@
 
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDE_FROM_ABI constexpr auto
-operator<=>(const basic_string<_CharT, _Traits, _Allocator>& __lhs, const _CharT* __rhs) {
+operator<=>(const basic_string<_CharT, _Traits, _Allocator>& __lhs, const _CharT* _Nonnull __rhs) {
     return basic_string_view<_CharT, _Traits>(__lhs) <=> basic_string_view<_CharT, _Traits>(__rhs);
 }
 
@@ -4313,7 +4313,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDDEN _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>
-operator+(const _CharT* __lhs , const basic_string<_CharT,_Traits,_Allocator>& __rhs)
+operator+(const _CharT* _Null_unspecified __lhs , const basic_string<_CharT,_Traits,_Allocator>& __rhs)
 {
     using _String = basic_string<_CharT, _Traits, _Allocator>;
     auto __lhs_sz = _Traits::length(__lhs);
@@ -4348,7 +4348,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>
-operator+(const basic_string<_CharT, _Traits, _Allocator>& __lhs, const _CharT* __rhs)
+operator+(const basic_string<_CharT, _Traits, _Allocator>& __lhs, const _CharT* _Null_unspecified __rhs)
 {
     using _String = basic_string<_CharT, _Traits, _Allocator>;
     typename _String::size_type __lhs_sz = __lhs.size();
@@ -4409,7 +4409,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>
-operator+(const _CharT* __lhs , basic_string<_CharT,_Traits,_Allocator>&& __rhs)
+operator+(const _CharT* _Null_unspecified __lhs , basic_string<_CharT,_Traits,_Allocator>&& __rhs)
 {
     return std::move(__rhs.insert(0, __lhs));
 }
@@ -4426,7 +4426,7 @@
 template<class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 basic_string<_CharT, _Traits, _Allocator>
-operator+(basic_string<_CharT, _Traits, _Allocator>&& __lhs, const _CharT* __rhs)
+operator+(basic_string<_CharT, _Traits, _Allocator>&& __lhs, const _CharT* _Null_unspecified __rhs)
 {
     return std::move(__lhs.append(__rhs));
 }
@@ -4454,15 +4454,15 @@
     __lhs.swap(__rhs);
 }
 
-_LIBCPP_FUNC_VIS int                stoi  (const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS long               stol  (const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS unsigned long      stoul (const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS long long          stoll (const string& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS unsigned long long stoull(const string& __str, size_t* __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS int                stoi  (const string& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS long               stol  (const string& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS unsigned long      stoul (const string& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS long long          stoll (const string& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS unsigned long long stoull(const string& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
 
-_LIBCPP_FUNC_VIS float       stof (const string& __str, size_t* __idx = nullptr);
-_LIBCPP_FUNC_VIS double      stod (const string& __str, size_t* __idx = nullptr);
-_LIBCPP_FUNC_VIS long double stold(const string& __str, size_t* __idx = nullptr);
+_LIBCPP_FUNC_VIS float       stof (const string& __str, size_t* _Nullable __idx = nullptr);
+_LIBCPP_FUNC_VIS double      stod (const string& __str, size_t* _Nullable __idx = nullptr);
+_LIBCPP_FUNC_VIS long double stold(const string& __str, size_t* _Nullable __idx = nullptr);
 
 _LIBCPP_FUNC_VIS string to_string(int __val);
 _LIBCPP_FUNC_VIS string to_string(unsigned __val);
@@ -4475,15 +4475,15 @@
 _LIBCPP_FUNC_VIS string to_string(long double __val);
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_FUNC_VIS int                stoi  (const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS long               stol  (const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS unsigned long      stoul (const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS long long          stoll (const wstring& __str, size_t* __idx = nullptr, int __base = 10);
-_LIBCPP_FUNC_VIS unsigned long long stoull(const wstring& __str, size_t* __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS int                stoi  (const wstring& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS long               stol  (const wstring& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS unsigned long      stoul (const wstring& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS long long          stoll (const wstring& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
+_LIBCPP_FUNC_VIS unsigned long long stoull(const wstring& __str, size_t* _Nullable __idx = nullptr, int __base = 10);
 
-_LIBCPP_FUNC_VIS float       stof (const wstring& __str, size_t* __idx = nullptr);
-_LIBCPP_FUNC_VIS double      stod (const wstring& __str, size_t* __idx = nullptr);
-_LIBCPP_FUNC_VIS long double stold(const wstring& __str, size_t* __idx = nullptr);
+_LIBCPP_FUNC_VIS float       stof (const wstring& __str, size_t* _Nullable __idx = nullptr);
+_LIBCPP_FUNC_VIS double      stod (const wstring& __str, size_t* _Nullable __idx = nullptr);
+_LIBCPP_FUNC_VIS long double stold(const wstring& __str, size_t* _Nullable __idx = nullptr);
 
 _LIBCPP_FUNC_VIS wstring to_wstring(int __val);
 _LIBCPP_FUNC_VIS wstring to_wstring(unsigned __val);
@@ -4626,14 +4626,14 @@
   inline namespace string_literals
   {
     inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string<char> operator "" s( const char *__str, size_t __len )
+    basic_string<char> operator "" s( const char* _Nullable __str, size_t __len )
     {
         return basic_string<char> (__str, __len);
     }
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
     inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string<wchar_t> operator "" s( const wchar_t *__str, size_t __len )
+    basic_string<wchar_t> operator "" s( const wchar_t* _Nullable __str, size_t __len )
     {
         return basic_string<wchar_t> (__str, __len);
     }
@@ -4641,20 +4641,20 @@
 
 #ifndef _LIBCPP_HAS_NO_CHAR8_T
     inline _LIBCPP_HIDE_FROM_ABI constexpr
-    basic_string<char8_t> operator "" s(const char8_t *__str, size_t __len)
+    basic_string<char8_t> operator "" s(const char8_t* _Nullable __str, size_t __len)
     {
         return basic_string<char8_t> (__str, __len);
     }
 #endif
 
     inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string<char16_t> operator "" s( const char16_t *__str, size_t __len )
+    basic_string<char16_t> operator "" s( const char16_t* _Nullable __str, size_t __len )
     {
         return basic_string<char16_t> (__str, __len);
     }
 
     inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    basic_string<char32_t> operator "" s( const char32_t *__str, size_t __len )
+    basic_string<char32_t> operator "" s( const char32_t* _Nullable __str, size_t __len )
     {
         return basic_string<char32_t> (__str, __len);
     }
diff --git a/libcxx/test/libcxx/strings/basic.string/string.cons/ptr.nonnull.verify.cpp b/libcxx/test/libcxx/strings/basic.string/string.cons/ptr.nonnull.verify.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/strings/basic.string/string.cons/ptr.nonnull.verify.cpp
@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <string>
+
+#include <string>
+
+void func() {
+  std::string s(static_cast<char*>(nullptr)); // Null passed to a callee that requires a non-null argument
+}
diff --git a/libcxx/test/std/strings/basic.string/string.cons/pointer_size_alloc.pass.cpp b/libcxx/test/std/strings/basic.string/string.cons/pointer_size_alloc.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.cons/pointer_size_alloc.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.cons/pointer_size_alloc.pass.cpp
@@ -52,6 +52,7 @@
   {
     typedef test_allocator<char> A;
 
+    test(static_cast<char*>(nullptr), 0);
     test("", 0);
     test("", 0, A(2));