diff --git a/libcxx/include/__string b/libcxx/include/__string
--- a/libcxx/include/__string
+++ b/libcxx/include/__string
@@ -953,7 +953,7 @@
 template <class _CharT, class _Traits>
 inline _LIBCPP_CONSTEXPR_AFTER_CXX11 const _CharT *
 __search_substring(const _CharT *__first1, const _CharT *__last1,
-                   const _CharT *__first2, const _CharT *__last2) {
+                   const _CharT *__first2, const _CharT *__last2) _NOEXCEPT {
   // Take advantage of knowing source and pattern lengths.
   // Stop short when source is smaller than pattern.
   const ptrdiff_t __len2 = __last2 - __first2;
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1296,7 +1296,7 @@
             __can_be_converted_to_string_view<_CharT, _Traits, _Tp>::value,
             size_type
         >
-              rfind(const _Tp& __t, size_type __pos = npos) const;
+              rfind(const _Tp& __t, size_type __pos = npos) const _NOEXCEPT;
     size_type rfind(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY
     size_type rfind(const value_type* __s, size_type __pos = npos) const _NOEXCEPT;
@@ -1312,7 +1312,7 @@
             __can_be_converted_to_string_view<_CharT, _Traits, _Tp>::value,
             size_type
         >
-              find_first_of(const _Tp& __t, size_type __pos = 0) const;
+              find_first_of(const _Tp& __t, size_type __pos = 0) const _NOEXCEPT;
     size_type find_first_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY
     size_type find_first_of(const value_type* __s, size_type __pos = 0) const _NOEXCEPT;
@@ -1329,7 +1329,7 @@
             __can_be_converted_to_string_view<_CharT, _Traits, _Tp>::value,
             size_type
         >
-              find_last_of(const _Tp& __t, size_type __pos = npos) const;
+              find_last_of(const _Tp& __t, size_type __pos = npos) const _NOEXCEPT;
     size_type find_last_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY
     size_type find_last_of(const value_type* __s, size_type __pos = npos) const _NOEXCEPT;
@@ -1346,7 +1346,7 @@
             __can_be_converted_to_string_view<_CharT, _Traits, _Tp>::value,
             size_type
         >
-              find_first_not_of(const _Tp &__t, size_type __pos = 0) const;
+              find_first_not_of(const _Tp &__t, size_type __pos = 0) const _NOEXCEPT;
     size_type find_first_not_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY
     size_type find_first_not_of(const value_type* __s, size_type __pos = 0) const _NOEXCEPT;
@@ -1363,7 +1363,7 @@
             __can_be_converted_to_string_view<_CharT, _Traits, _Tp>::value,
             size_type
         >
-              find_last_not_of(const _Tp& __t, size_type __pos = npos) const;
+              find_last_not_of(const _Tp& __t, size_type __pos = npos) const _NOEXCEPT;
     size_type find_last_not_of(const value_type* __s, size_type __pos, size_type __n) const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY
     size_type find_last_not_of(const value_type* __s, size_type __pos = npos) const _NOEXCEPT;
@@ -1380,7 +1380,7 @@
             __can_be_converted_to_string_view<_CharT, _Traits, _Tp>::value,
             int
         >
-        compare(const _Tp &__t) const;
+        compare(const _Tp &__t) const _NOEXCEPT;
 
     template <class _Tp>
     _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
@@ -3583,7 +3583,7 @@
     typename basic_string<_CharT, _Traits, _Allocator>::size_type
 >
 basic_string<_CharT, _Traits, _Allocator>::rfind(const _Tp& __t,
-                                                size_type __pos) const
+                                                size_type __pos) const _NOEXCEPT
 {
     __self_view __sv = __t;
     return __str_rfind<value_type, size_type, traits_type, npos>
@@ -3641,7 +3641,7 @@
     typename basic_string<_CharT, _Traits, _Allocator>::size_type
 >
 basic_string<_CharT, _Traits, _Allocator>::find_first_of(const _Tp& __t,
-                                                size_type __pos) const
+                                                size_type __pos) const _NOEXCEPT
 {
     __self_view __sv = __t;
     return __str_find_first_of<value_type, size_type, traits_type, npos>
@@ -3699,7 +3699,7 @@
     typename basic_string<_CharT, _Traits, _Allocator>::size_type
 >
 basic_string<_CharT, _Traits, _Allocator>::find_last_of(const _Tp& __t,
-                                                size_type __pos) const
+                                                size_type __pos) const _NOEXCEPT
 {
     __self_view __sv = __t;
     return __str_find_last_of<value_type, size_type, traits_type, npos>
@@ -3757,7 +3757,7 @@
     typename basic_string<_CharT, _Traits, _Allocator>::size_type
 >
 basic_string<_CharT, _Traits, _Allocator>::find_first_not_of(const _Tp& __t,
-                                                size_type __pos) const
+                                                size_type __pos) const _NOEXCEPT
 {
     __self_view __sv = __t;
     return __str_find_first_not_of<value_type, size_type, traits_type, npos>
@@ -3816,7 +3816,7 @@
     typename basic_string<_CharT, _Traits, _Allocator>::size_type
 >
 basic_string<_CharT, _Traits, _Allocator>::find_last_not_of(const _Tp& __t,
-                                                size_type __pos) const
+                                                size_type __pos) const _NOEXCEPT
 {
     __self_view __sv = __t;
     return __str_find_last_not_of<value_type, size_type, traits_type, npos>
@@ -3853,7 +3853,7 @@
     __can_be_converted_to_string_view<_CharT, _Traits, _Tp>::value,
     int
 >
-basic_string<_CharT, _Traits, _Allocator>::compare(const _Tp& __t) const
+basic_string<_CharT, _Traits, _Allocator>::compare(const _Tp& __t) const _NOEXCEPT
 {
     __self_view __sv = __t;
     size_t __lhs_sz = size();
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -427,7 +427,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find(const _CharT* __s, size_type __pos, size_type __n) const
+    size_type find(const _CharT* __s, size_type __pos, size_type __n) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string_view::find(): received nullptr");
         return __str_find<value_type, size_type, traits_type, npos>
@@ -435,7 +435,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find(const _CharT* __s, size_type __pos = 0) const
+    size_type find(const _CharT* __s, size_type __pos = 0) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__s != nullptr, "string_view::find(): received nullptr");
         return __str_find<value_type, size_type, traits_type, npos>
@@ -459,7 +459,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type rfind(const _CharT* __s, size_type __pos, size_type __n) const
+    size_type rfind(const _CharT* __s, size_type __pos, size_type __n) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string_view::rfind(): received nullptr");
         return __str_rfind<value_type, size_type, traits_type, npos>
@@ -467,7 +467,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type rfind(const _CharT* __s, size_type __pos=npos) const
+    size_type rfind(const _CharT* __s, size_type __pos=npos) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__s != nullptr, "string_view::rfind(): received nullptr");
         return __str_rfind<value_type, size_type, traits_type, npos>
@@ -488,7 +488,7 @@
     { return find(__c, __pos); }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_first_of(const _CharT* __s, size_type __pos, size_type __n) const
+    size_type find_first_of(const _CharT* __s, size_type __pos, size_type __n) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string_view::find_first_of(): received nullptr");
         return __str_find_first_of<value_type, size_type, traits_type, npos>
@@ -496,7 +496,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_first_of(const _CharT* __s, size_type __pos=0) const
+    size_type find_first_of(const _CharT* __s, size_type __pos=0) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__s != nullptr, "string_view::find_first_of(): received nullptr");
         return __str_find_first_of<value_type, size_type, traits_type, npos>
@@ -517,7 +517,7 @@
     { return rfind(__c, __pos); }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_last_of(const _CharT* __s, size_type __pos, size_type __n) const
+    size_type find_last_of(const _CharT* __s, size_type __pos, size_type __n) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string_view::find_last_of(): received nullptr");
         return __str_find_last_of<value_type, size_type, traits_type, npos>
@@ -525,7 +525,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_last_of(const _CharT* __s, size_type __pos=npos) const
+    size_type find_last_of(const _CharT* __s, size_type __pos=npos) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__s != nullptr, "string_view::find_last_of(): received nullptr");
         return __str_find_last_of<value_type, size_type, traits_type, npos>
@@ -549,7 +549,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_first_not_of(const _CharT* __s, size_type __pos, size_type __n) const
+    size_type find_first_not_of(const _CharT* __s, size_type __pos, size_type __n) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string_view::find_first_not_of(): received nullptr");
         return __str_find_first_not_of<value_type, size_type, traits_type, npos>
@@ -557,7 +557,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_first_not_of(const _CharT* __s, size_type __pos=0) const
+    size_type find_first_not_of(const _CharT* __s, size_type __pos=0) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__s != nullptr, "string_view::find_first_not_of(): received nullptr");
         return __str_find_first_not_of<value_type, size_type, traits_type, npos>
@@ -581,7 +581,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_last_not_of(const _CharT* __s, size_type __pos, size_type __n) const
+    size_type find_last_not_of(const _CharT* __s, size_type __pos, size_type __n) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__n == 0 || __s != nullptr, "string_view::find_last_not_of(): received nullptr");
         return __str_find_last_not_of<value_type, size_type, traits_type, npos>
@@ -589,7 +589,7 @@
     }
 
     _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
-    size_type find_last_not_of(const _CharT* __s, size_type __pos=npos) const
+    size_type find_last_not_of(const _CharT* __s, size_type __pos=npos) const _NOEXCEPT
     {
         _LIBCPP_ASSERT(__s != nullptr, "string_view::find_last_not_of(): received nullptr");
         return __str_find_last_not_of<value_type, size_type, traits_type, npos>