diff --git a/libcxx/.clang-tidy b/libcxx/.clang-tidy
--- a/libcxx/.clang-tidy
+++ b/libcxx/.clang-tidy
@@ -12,6 +12,7 @@
 
   modernize-loop-convert,
   modernize-redundant-void-arg,
+  modernize-use-override,
 
   readability-duplicate-include,
   readability-function-cognitive-complexity,
@@ -39,7 +40,6 @@
 # modernize-use-equals-default,
 # modernize-use-equals-delete,
 # modernize-use-nullptr,
-# modernize-use-override,
 # portability-restrict-system-includes,
 # readability-function-cognitive-complexity,
 # readability-implicit-bool-conversion,
diff --git a/libcxx/include/__format/format_error.h b/libcxx/include/__format/format_error.h
--- a/libcxx/include/__format/format_error.h
+++ b/libcxx/include/__format/format_error.h
@@ -31,7 +31,7 @@
       : runtime_error(__s) {}
   _LIBCPP_HIDE_FROM_ABI explicit format_error(const char* __s)
       : runtime_error(__s) {}
-  virtual ~format_error() noexcept;
+  ~format_error() noexcept override;
 };
 
 _LIBCPP_NORETURN inline _LIBCPP_HIDE_FROM_ABI void
diff --git a/libcxx/include/__functional/function.h b/libcxx/include/__functional/function.h
--- a/libcxx/include/__functional/function.h
+++ b/libcxx/include/__functional/function.h
@@ -45,7 +45,7 @@
 #ifdef _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
     virtual ~bad_function_call() _NOEXCEPT;
 #else
-    virtual ~bad_function_call() _NOEXCEPT {}
+    ~bad_function_call() _NOEXCEPT override {}
 #endif
 
 #ifdef _LIBCPP_ABI_BAD_FUNCTION_CALL_GOOD_WHAT_MESSAGE
diff --git a/libcxx/include/__locale b/libcxx/include/__locale
--- a/libcxx/include/__locale
+++ b/libcxx/include/__locale
@@ -192,12 +192,12 @@
     explicit facet(size_t __refs = 0)
         : __shared_count(static_cast<long>(__refs)-1) {}
 
-    virtual ~facet();
+    ~facet() override;
 
 //    facet(const facet&) = delete;     // effectively done in __shared_count
 //    void operator=(const facet&) = delete;
 private:
-    virtual void __on_zero_shared() _NOEXCEPT;
+    void __on_zero_shared() _NOEXCEPT override;
 };
 
 class _LIBCPP_TYPE_VIS locale::id
@@ -292,7 +292,7 @@
     static locale::id id;
 
 protected:
-    ~collate();
+    ~collate() override;
     virtual int do_compare(const char_type* __lo1, const char_type* __hi1,
                            const char_type* __lo2, const char_type* __hi2) const;
     virtual string_type do_transform(const char_type* __lo, const char_type* __hi) const
@@ -360,10 +360,10 @@
     explicit collate_byname(const string& __n, size_t __refs = 0);
 
 protected:
-    ~collate_byname();
-    virtual int do_compare(const char_type* __lo1, const char_type* __hi1,
-                           const char_type* __lo2, const char_type* __hi2) const;
-    virtual string_type do_transform(const char_type* __lo, const char_type* __hi) const;
+    ~collate_byname() override;
+    int do_compare(const char_type* __lo1, const char_type* __hi1,
+                   const char_type* __lo2, const char_type* __hi2) const override;
+    string_type do_transform(const char_type* __lo, const char_type* __hi) const override;
 };
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
@@ -380,11 +380,11 @@
     explicit collate_byname(const string& __n, size_t __refs = 0);
 
 protected:
-    ~collate_byname();
+    ~collate_byname() override;
 
-    virtual int do_compare(const char_type* __lo1, const char_type* __hi1,
-                           const char_type* __lo2, const char_type* __hi2) const;
-    virtual string_type do_transform(const char_type* __lo, const char_type* __hi) const;
+    int do_compare(const char_type* __lo1, const char_type* __hi1,
+                   const char_type* __lo2, const char_type* __hi2) const override;
+    string_type do_transform(const char_type* __lo, const char_type* __hi) const override;
 };
 #endif
 
@@ -643,7 +643,7 @@
     static locale::id id;
 
 protected:
-    ~ctype();
+    ~ctype() override;
     virtual bool do_is(mask __m, char_type __c) const;
     virtual const char_type* do_is(const char_type* __low, const char_type* __high, mask* __vec) const;
     virtual const char_type* do_scan_is(mask __m, const char_type* __low, const char_type* __high) const;
@@ -773,7 +773,7 @@
 #endif
 
 protected:
-    ~ctype();
+    ~ctype() override;
     virtual char_type do_toupper(char_type __c) const;
     virtual const char_type* do_toupper(char_type* __low, const char_type* __high) const;
     virtual char_type do_tolower(char_type __c) const;
@@ -799,11 +799,11 @@
     explicit ctype_byname(const string&, size_t = 0);
 
 protected:
-    ~ctype_byname();
-    virtual char_type do_toupper(char_type) const;
-    virtual const char_type* do_toupper(char_type* __low, const char_type* __high) const;
-    virtual char_type do_tolower(char_type) const;
-    virtual const char_type* do_tolower(char_type* __low, const char_type* __high) const;
+    ~ctype_byname() override;
+    char_type do_toupper(char_type) const override;
+    const char_type* do_toupper(char_type* __low, const char_type* __high) const override;
+    char_type do_tolower(char_type) const override;
+    const char_type* do_tolower(char_type* __low, const char_type* __high) const override;
 };
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
@@ -818,19 +818,19 @@
     explicit ctype_byname(const string&, size_t = 0);
 
 protected:
-    ~ctype_byname();
-    virtual bool do_is(mask __m, char_type __c) const;
-    virtual const char_type* do_is(const char_type* __low, const char_type* __high, mask* __vec) const;
-    virtual const char_type* do_scan_is(mask __m, const char_type* __low, const char_type* __high) const;
-    virtual const char_type* do_scan_not(mask __m, const char_type* __low, const char_type* __high) const;
-    virtual char_type do_toupper(char_type) const;
-    virtual const char_type* do_toupper(char_type* __low, const char_type* __high) const;
-    virtual char_type do_tolower(char_type) const;
-    virtual const char_type* do_tolower(char_type* __low, const char_type* __high) const;
-    virtual char_type do_widen(char) const;
-    virtual const char* do_widen(const char* __low, const char* __high, char_type* __dest) const;
-    virtual char do_narrow(char_type, char __dfault) const;
-    virtual const char_type* do_narrow(const char_type* __low, const char_type* __high, char __dfault, char* __dest) const;
+    ~ctype_byname() override;
+    bool do_is(mask __m, char_type __c) const override;
+    const char_type* do_is(const char_type* __low, const char_type* __high, mask* __vec) const override;
+    const char_type* do_scan_is(mask __m, const char_type* __low, const char_type* __high) const override;
+    const char_type* do_scan_not(mask __m, const char_type* __low, const char_type* __high) const override;
+    char_type do_toupper(char_type) const override;
+    const char_type* do_toupper(char_type* __low, const char_type* __high) const override;
+    char_type do_tolower(char_type) const override;
+    const char_type* do_tolower(char_type* __low, const char_type* __high) const override;
+    char_type do_widen(char) const override;
+    const char* do_widen(const char* __low, const char* __high, char_type* __dest) const override;
+    char do_narrow(char_type, char __dfault) const override;
+    const char_type* do_narrow(const char_type* __low, const char_type* __high, char __dfault, char* __dest) const override;
 };
 #endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
 
@@ -1021,7 +1021,7 @@
     explicit codecvt(const char*, size_t __refs = 0)
         : locale::facet(__refs) {}
 
-    ~codecvt();
+    ~codecvt() override;
 
     virtual result do_out(state_type& __st,
                           const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
@@ -1105,7 +1105,7 @@
 protected:
     explicit codecvt(const char*, size_t __refs = 0);
 
-    ~codecvt();
+    ~codecvt() override;
 
     virtual result do_out(state_type& __st,
                           const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
@@ -1192,7 +1192,7 @@
     explicit codecvt(const char*, size_t __refs = 0)
         : locale::facet(__refs) {}
 
-    ~codecvt();
+    ~codecvt() override;
 
     virtual result do_out(state_type& __st,
                           const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
@@ -1280,7 +1280,7 @@
     explicit codecvt(const char*, size_t __refs = 0)
         : locale::facet(__refs) {}
 
-    ~codecvt();
+    ~codecvt() override;
 
     virtual result do_out(state_type& __st,
                           const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
@@ -1368,7 +1368,7 @@
     explicit codecvt(const char*, size_t __refs = 0)
         : locale::facet(__refs) {}
 
-    ~codecvt();
+    ~codecvt() override;
 
     virtual result do_out(state_type& __st,
                           const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
@@ -1456,7 +1456,7 @@
     explicit codecvt(const char*, size_t __refs = 0)
         : locale::facet(__refs) {}
 
-    ~codecvt();
+    ~codecvt() override;
 
     virtual result do_out(state_type& __st,
                           const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
@@ -1488,7 +1488,7 @@
     explicit codecvt_byname(const string& __nm, size_t __refs = 0)
         : codecvt<_InternT, _ExternT, _StateT>(__nm.c_str(), __refs) {}
 protected:
-    ~codecvt_byname();
+    ~codecvt_byname() override;
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
@@ -1540,7 +1540,7 @@
     __narrow_to_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    ~__narrow_to_utf8();
+    ~__narrow_to_utf8() override;
 
     template <class _OutputIterator, class _CharT>
     _LIBCPP_INLINE_VISIBILITY
@@ -1576,7 +1576,7 @@
     __narrow_to_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    ~__narrow_to_utf8();
+    ~__narrow_to_utf8() override;
 
     template <class _OutputIterator, class _CharT>
     _LIBCPP_INLINE_VISIBILITY
@@ -1634,7 +1634,7 @@
     __widen_from_utf8() : codecvt<char16_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    ~__widen_from_utf8();
+    ~__widen_from_utf8() override;
 
     template <class _OutputIterator>
     _LIBCPP_INLINE_VISIBILITY
@@ -1670,7 +1670,7 @@
     __widen_from_utf8() : codecvt<char32_t, char, mbstate_t>(1) {}
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-    ~__widen_from_utf8();
+    ~__widen_from_utf8() override;
 
     template <class _OutputIterator>
     _LIBCPP_INLINE_VISIBILITY
@@ -1720,7 +1720,7 @@
     static locale::id id;
 
 protected:
-    ~numpunct();
+    ~numpunct() override;
     virtual char_type do_decimal_point() const;
     virtual char_type do_thousands_sep() const;
     virtual string do_grouping() const;
@@ -1752,7 +1752,7 @@
     static locale::id id;
 
 protected:
-    ~numpunct();
+    ~numpunct() override;
     virtual char_type do_decimal_point() const;
     virtual char_type do_thousands_sep() const;
     virtual string do_grouping() const;
@@ -1781,7 +1781,7 @@
     explicit numpunct_byname(const string& __nm, size_t __refs = 0);
 
 protected:
-    ~numpunct_byname();
+    ~numpunct_byname() override;
 
 private:
     void __init(const char*);
@@ -1800,7 +1800,7 @@
     explicit numpunct_byname(const string& __nm, size_t __refs = 0);
 
 protected:
-    ~numpunct_byname();
+    ~numpunct_byname() override;
 
 private:
     void __init(const char*);
diff --git a/libcxx/include/__memory/shared_ptr.h b/libcxx/include/__memory/shared_ptr.h
--- a/libcxx/include/__memory/shared_ptr.h
+++ b/libcxx/include/__memory/shared_ptr.h
@@ -130,8 +130,8 @@
 public:
     bad_weak_ptr() _NOEXCEPT = default;
     bad_weak_ptr(const bad_weak_ptr&) _NOEXCEPT = default;
-    virtual ~bad_weak_ptr() _NOEXCEPT;
-    virtual const char* what() const  _NOEXCEPT;
+    ~bad_weak_ptr() _NOEXCEPT override;
+     const char* what() const  _NOEXCEPT override;
 };
 
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
@@ -196,7 +196,7 @@
         : __shared_count(__refs),
           __shared_weak_owners_(__refs) {}
 protected:
-    virtual ~__shared_weak_count();
+    ~__shared_weak_count() override;
 
 public:
 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
@@ -239,12 +239,12 @@
         :  __data_(__compressed_pair<_Tp, _Dp>(__p, _VSTD::move(__d)), _VSTD::move(__a)) {}
 
 #ifndef _LIBCPP_NO_RTTI
-    virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;
+    const void* __get_deleter(const type_info&) const _NOEXCEPT override;
 #endif
 
 private:
-    virtual void __on_zero_shared() _NOEXCEPT;
-    virtual void __on_zero_shared_weak() _NOEXCEPT;
+    void __on_zero_shared() _NOEXCEPT override;
+    void __on_zero_shared_weak() _NOEXCEPT override;
 };
 
 #ifndef _LIBCPP_NO_RTTI
@@ -304,7 +304,7 @@
     _Tp* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
 
 private:
-    virtual void __on_zero_shared() _NOEXCEPT {
+    void __on_zero_shared() _NOEXCEPT override {
 #if _LIBCPP_STD_VER > 17
         using _TpAlloc = typename __allocator_traits_rebind<_Alloc, _Tp>::type;
         _TpAlloc __tmp(*__get_alloc());
@@ -314,7 +314,7 @@
 #endif
     }
 
-    virtual void __on_zero_shared_weak() _NOEXCEPT {
+    void __on_zero_shared_weak() _NOEXCEPT override {
         using _ControlBlockAlloc = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
         using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
         _ControlBlockAlloc __tmp(*__get_alloc());
diff --git a/libcxx/include/any b/libcxx/include/any
--- a/libcxx/include/any
+++ b/libcxx/include/any
@@ -101,7 +101,7 @@
 class _LIBCPP_EXCEPTION_ABI _LIBCPP_AVAILABILITY_BAD_ANY_CAST bad_any_cast : public bad_cast
 {
 public:
-    virtual const char* what() const _NOEXCEPT;
+    const char* what() const _NOEXCEPT override;
 };
 } // namespace std
 
diff --git a/libcxx/include/codecvt b/libcxx/include/codecvt
--- a/libcxx/include/codecvt
+++ b/libcxx/include/codecvt
@@ -94,22 +94,18 @@
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+    result do_out(state_type& __st,
+                  const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                  extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+    result do_in(state_type& __st,
+                 const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                 intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+    result do_unshift(state_type& __st,
+                      extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+    int do_encoding() const _NOEXCEPT override;
+    bool do_always_noconv() const _NOEXCEPT override;
+    int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+    int do_max_length() const _NOEXCEPT override;
 };
 #endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
 
@@ -133,22 +129,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
@@ -171,22 +163,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 template <class _Elem, unsigned long _Maxcode = 0x10ffff,
@@ -225,22 +213,19 @@
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
+                          size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 template <>
@@ -260,22 +245,18 @@
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 #endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
 
@@ -299,22 +280,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
@@ -337,22 +314,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
@@ -375,22 +348,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
@@ -413,22 +382,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 template <class _Elem, unsigned long _Maxcode = 0x10ffff,
@@ -467,22 +432,18 @@
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 #endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
 
@@ -506,22 +467,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
@@ -544,22 +501,18 @@
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
 protected:
-    virtual result
-        do_out(state_type& __st,
-               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
-               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual result
-        do_in(state_type& __st,
-              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
-              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
-    virtual result
-        do_unshift(state_type& __st,
-                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
-    virtual int do_encoding() const _NOEXCEPT;
-    virtual bool do_always_noconv() const _NOEXCEPT;
-    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
-                          size_t __mx) const;
-    virtual int do_max_length() const _NOEXCEPT;
+     result do_out(state_type& __st,
+                   const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     result do_in(state_type& __st,
+                  const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+                  intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const override;
+     result do_unshift(state_type& __st,
+                       extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const override;
+     int do_encoding() const _NOEXCEPT override;
+     bool do_always_noconv() const _NOEXCEPT override;
+     int do_length(state_type&, const extern_type* __frm, const extern_type* __end, size_t __mx) const override;
+     int do_max_length() const _NOEXCEPT override;
 };
 
 template <class _Elem, unsigned long _Maxcode = 0x10ffff,
diff --git a/libcxx/include/exception b/libcxx/include/exception
--- a/libcxx/include/exception
+++ b/libcxx/include/exception
@@ -112,8 +112,8 @@
 {
 public:
     _LIBCPP_INLINE_VISIBILITY bad_exception() _NOEXCEPT {}
-    virtual ~bad_exception() _NOEXCEPT;
-    virtual const char* what() const _NOEXCEPT;
+    ~bad_exception() _NOEXCEPT override;
+    const char* what() const _NOEXCEPT override;
 };
 #endif // !_LIBCPP_ABI_VCRUNTIME
 
diff --git a/libcxx/include/experimental/memory_resource b/libcxx/include/experimental/memory_resource
--- a/libcxx/include/experimental/memory_resource
+++ b/libcxx/include/experimental/memory_resource
@@ -379,7 +379,7 @@
 
 // 8.7.3, memory.resource.adaptor.mem
 private:
-    virtual void * do_allocate(size_t __bytes, size_t)
+    void * do_allocate(size_t __bytes, size_t) override
     {
         if (__bytes > __max_size())
             __throw_bad_array_new_length();
@@ -387,7 +387,7 @@
         return __alloc_.allocate(__s);
     }
 
-    virtual void do_deallocate(void * __p, size_t __bytes, size_t)
+    void do_deallocate(void * __p, size_t __bytes, size_t) override
     {
         _LIBCPP_ASSERT(__bytes <= __max_size(),
             "do_deallocate called for size which exceeds the maximum allocation size");
@@ -395,7 +395,7 @@
         __alloc_.deallocate((_ValueType*)__p, __s);
     }
 
-    virtual bool do_is_equal(memory_resource const & __other) const _NOEXCEPT {
+    bool do_is_equal(memory_resource const & __other) const _NOEXCEPT override {
         __resource_adaptor_imp const * __p
           = dynamic_cast<__resource_adaptor_imp const *>(&__other);
         return __p  ? __alloc_ == __p->__alloc_ : false;
diff --git a/libcxx/include/future b/libcxx/include/future
--- a/libcxx/include/future
+++ b/libcxx/include/future
@@ -514,7 +514,7 @@
     const error_code& code() const _NOEXCEPT {return __ec_;}
 
     future_error(const future_error&) _NOEXCEPT = default;
-    virtual ~future_error() _NOEXCEPT;
+    ~future_error() _NOEXCEPT override;
 };
 
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
@@ -540,7 +540,7 @@
     mutable condition_variable __cv_;
     unsigned __state_;
 
-    virtual void __on_zero_shared() _NOEXCEPT;
+    void __on_zero_shared() _NOEXCEPT override;
     void __sub_wait(unique_lock<mutex>& __lk);
 public:
     enum
@@ -627,7 +627,7 @@
 protected:
     _Up __value_;
 
-    virtual void __on_zero_shared() _NOEXCEPT;
+    void __on_zero_shared() _NOEXCEPT override;
 public:
 
     template <class _Arg>
@@ -707,7 +707,7 @@
 protected:
     _Up __value_;
 
-    virtual void __on_zero_shared() _NOEXCEPT;
+    void __on_zero_shared() _NOEXCEPT override;
 public:
 
     void set_value(_Rp& __arg);
@@ -819,7 +819,7 @@
     typedef __assoc_sub_state base;
     _Alloc __alloc_;
 
-    virtual void __on_zero_shared() _NOEXCEPT;
+    void __on_zero_shared() _NOEXCEPT override;
 public:
     _LIBCPP_INLINE_VISIBILITY
     explicit __assoc_sub_state_alloc(const _Alloc& __a)
@@ -891,7 +891,7 @@
     _LIBCPP_INLINE_VISIBILITY
     explicit __deferred_assoc_state(_Fp&& __f);
 
-    virtual void __execute();
+    void __execute() override;
 };
 
 template <class _Fp>
@@ -978,12 +978,12 @@
 
     _Fp __func_;
 
-    virtual void __on_zero_shared() _NOEXCEPT;
+    void __on_zero_shared() _NOEXCEPT override;
 public:
     _LIBCPP_INLINE_VISIBILITY
     explicit __async_assoc_state(_Fp&& __f);
 
-    virtual void __execute();
+    void __execute() override;
 };
 
 template <class _Fp>
diff --git a/libcxx/include/ios b/libcxx/include/ios
--- a/libcxx/include/ios
+++ b/libcxx/include/ios
@@ -434,7 +434,7 @@
     explicit failure(const string& __msg, const error_code& __ec = io_errc::stream);
     explicit failure(const char* __msg, const error_code& __ec = io_errc::stream);
     failure(const failure&) _NOEXCEPT = default;
-    virtual ~failure() _NOEXCEPT;
+    ~failure() _NOEXCEPT override;
 };
 
 _LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
@@ -634,7 +634,7 @@
     // 27.5.4.1 Constructor/destructor:
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_ios(basic_streambuf<char_type,traits_type>* __sb);
-    virtual ~basic_ios();
+    ~basic_ios() override;
 
     // 27.5.4.2 Members:
     _LIBCPP_INLINE_VISIBILITY
diff --git a/libcxx/include/istream b/libcxx/include/istream
--- a/libcxx/include/istream
+++ b/libcxx/include/istream
@@ -191,7 +191,7 @@
     inline _LIBCPP_HIDE_FROM_ABI_AFTER_V1
     explicit basic_istream(basic_streambuf<char_type, traits_type>* __sb) : __gc_(0)
     { this->init(__sb); }
-    virtual ~basic_istream();
+    ~basic_istream() override;
 protected:
     inline _LIBCPP_INLINE_VISIBILITY
     basic_istream(basic_istream&& __rhs);
@@ -1407,7 +1407,7 @@
       : basic_istream<_CharT, _Traits>(__sb)
     {}
 
-    virtual ~basic_iostream();
+    ~basic_iostream() override;
 protected:
     inline _LIBCPP_INLINE_VISIBILITY
     basic_iostream(basic_iostream&& __rhs);
diff --git a/libcxx/include/locale b/libcxx/include/locale
--- a/libcxx/include/locale
+++ b/libcxx/include/locale
@@ -675,8 +675,7 @@
     static locale::id id;
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~num_get() {}
+    _LIBCPP_HIDE_FROM_ABI ~num_get() override {}
 
     template <class _Fp>
     _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
@@ -1346,8 +1345,7 @@
     static locale::id id;
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~num_put() {}
+    _LIBCPP_HIDE_FROM_ABI ~num_put() override {}
 
     virtual iter_type do_put(iter_type __s, ios_base& __iob, char_type __fl,
                              bool __v) const;
@@ -1792,8 +1790,7 @@
     static locale::id id;
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~time_get() {}
+    _LIBCPP_HIDE_FROM_ABI ~time_get() override {}
 
     virtual dateorder do_date_order() const;
     virtual iter_type do_get_time(iter_type __b, iter_type __e, ios_base& __iob,
@@ -2410,26 +2407,25 @@
           __time_get_storage<_CharT>(__nm) {}
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~time_get_byname() {}
+    _LIBCPP_HIDE_FROM_ABI ~time_get_byname() override {}
 
     _LIBCPP_INLINE_VISIBILITY
-    virtual dateorder do_date_order() const {return this->__do_date_order();}
+     dateorder do_date_order() const override {return this->__do_date_order();}
 private:
     _LIBCPP_INLINE_VISIBILITY
-    virtual const string_type* __weeks() const  {return this->__weeks_;}
+     const string_type* __weeks() const override  {return this->__weeks_;}
     _LIBCPP_INLINE_VISIBILITY
-    virtual const string_type* __months() const {return this->__months_;}
+     const string_type* __months() const override {return this->__months_;}
     _LIBCPP_INLINE_VISIBILITY
-    virtual const string_type* __am_pm() const  {return this->__am_pm_;}
+     const string_type* __am_pm() const override  {return this->__am_pm_;}
     _LIBCPP_INLINE_VISIBILITY
-    virtual const string_type& __c() const      {return this->__c_;}
+     const string_type& __c() const override      {return this->__c_;}
     _LIBCPP_INLINE_VISIBILITY
-    virtual const string_type& __r() const      {return this->__r_;}
+     const string_type& __r() const override      {return this->__r_;}
     _LIBCPP_INLINE_VISIBILITY
-    virtual const string_type& __x() const      {return this->__x_;}
+     const string_type& __x() const override      {return this->__x_;}
     _LIBCPP_INLINE_VISIBILITY
-    virtual const string_type& __X() const      {return this->__X_;}
+     const string_type& __X() const override      {return this->__X_;}
 };
 
 _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get_byname<char>)
@@ -2477,8 +2473,7 @@
     static locale::id id;
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~time_put() {}
+    _LIBCPP_HIDE_FROM_ABI ~time_put() override {}
     virtual iter_type do_put(iter_type __s, ios_base&, char_type, const tm* __tm,
                              char __fmt, char __mod) const;
 
@@ -2566,8 +2561,7 @@
         : time_put<_CharT, _OutputIterator>(__nm, __refs) {}
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~time_put_byname() {}
+    _LIBCPP_HIDE_FROM_ABI ~time_put_byname() override {}
 };
 
 _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put_byname<char>)
@@ -2615,8 +2609,7 @@
     static const bool intl = _International;
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~moneypunct() {}
+    _LIBCPP_HIDE_FROM_ABI ~moneypunct() override {}
 
     virtual char_type   do_decimal_point() const {return numeric_limits<char_type>::max();}
     virtual char_type   do_thousands_sep() const {return numeric_limits<char_type>::max();}
@@ -2666,18 +2659,17 @@
         : moneypunct<_CharT, _International>(__refs) {init(__nm.c_str());}
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~moneypunct_byname() {}
-
-    virtual char_type   do_decimal_point() const {return __decimal_point_;}
-    virtual char_type   do_thousands_sep() const {return __thousands_sep_;}
-    virtual string      do_grouping()      const {return __grouping_;}
-    virtual string_type do_curr_symbol()   const {return __curr_symbol_;}
-    virtual string_type do_positive_sign() const {return __positive_sign_;}
-    virtual string_type do_negative_sign() const {return __negative_sign_;}
-    virtual int         do_frac_digits()   const {return __frac_digits_;}
-    virtual pattern     do_pos_format()    const {return __pos_format_;}
-    virtual pattern     do_neg_format()    const {return __neg_format_;}
+    _LIBCPP_HIDE_FROM_ABI ~moneypunct_byname() override {}
+
+     char_type   do_decimal_point() const override {return __decimal_point_;}
+     char_type   do_thousands_sep() const override {return __thousands_sep_;}
+     string      do_grouping()      const override {return __grouping_;}
+     string_type do_curr_symbol()   const override {return __curr_symbol_;}
+     string_type do_positive_sign() const override {return __positive_sign_;}
+     string_type do_negative_sign() const override {return __negative_sign_;}
+     int         do_frac_digits()   const override {return __frac_digits_;}
+     pattern     do_pos_format()    const override {return __pos_format_;}
+     pattern     do_neg_format()    const override {return __neg_format_;}
 
 private:
     char_type   __decimal_point_;
@@ -2795,9 +2787,7 @@
     static locale::id id;
 
 protected:
-
-    _LIBCPP_INLINE_VISIBILITY
-    ~money_get() {}
+    _LIBCPP_HIDE_FROM_ABI ~money_get() override {}
 
     virtual iter_type do_get(iter_type __b, iter_type __e, bool __intl,
                              ios_base& __iob, ios_base::iostate& __err,
@@ -3341,8 +3331,7 @@
     static locale::id id;
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~money_put() {}
+    _LIBCPP_HIDE_FROM_ABI ~money_put() override {}
 
     virtual iter_type do_put(iter_type __s, bool __intl, ios_base& __iob,
                              char_type __fl, long double __units) const;
@@ -3510,8 +3499,7 @@
     static locale::id id;
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~messages() {}
+    _LIBCPP_HIDE_FROM_ABI ~messages() override {}
 
     virtual catalog do_open(const basic_string<char>&, const locale&) const;
     virtual string_type do_get(catalog, int __set, int __msgid,
@@ -3600,8 +3588,7 @@
         : messages<_CharT>(__refs) {}
 
 protected:
-    _LIBCPP_INLINE_VISIBILITY
-    ~messages_byname() {}
+    _LIBCPP_HIDE_FROM_ABI ~messages_byname() override {}
 };
 
 _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages_byname<char>)
diff --git a/libcxx/include/new b/libcxx/include/new
--- a/libcxx/include/new
+++ b/libcxx/include/new
@@ -129,8 +129,8 @@
 {
 public:
     bad_alloc() _NOEXCEPT;
-    virtual ~bad_alloc() _NOEXCEPT;
-    virtual const char* what() const _NOEXCEPT;
+    ~bad_alloc() _NOEXCEPT override;
+    const char* what() const _NOEXCEPT override;
 };
 
 class _LIBCPP_EXCEPTION_ABI bad_array_new_length
@@ -138,8 +138,8 @@
 {
 public:
     bad_array_new_length() _NOEXCEPT;
-    virtual ~bad_array_new_length() _NOEXCEPT;
-    virtual const char* what() const _NOEXCEPT;
+    ~bad_array_new_length() _NOEXCEPT override;
+    const char* what() const _NOEXCEPT override;
 };
 
 typedef void (*new_handler)();
diff --git a/libcxx/include/optional b/libcxx/include/optional
--- a/libcxx/include/optional
+++ b/libcxx/include/optional
@@ -195,8 +195,8 @@
 {
 public:
     // Get the key function ~bad_optional_access() into the dylib
-    virtual ~bad_optional_access() _NOEXCEPT;
-    virtual const char* what() const _NOEXCEPT;
+    ~bad_optional_access() _NOEXCEPT override;
+    const char* what() const _NOEXCEPT override;
 };
 
 } // namespace std
diff --git a/libcxx/include/ostream b/libcxx/include/ostream
--- a/libcxx/include/ostream
+++ b/libcxx/include/ostream
@@ -165,7 +165,7 @@
     inline _LIBCPP_HIDE_FROM_ABI_AFTER_V1
     explicit basic_ostream(basic_streambuf<char_type, traits_type>* __sb)
     { this->init(__sb); }
-    virtual ~basic_ostream();
+    ~basic_ostream() override;
 protected:
     inline _LIBCPP_INLINE_VISIBILITY
     basic_ostream(basic_ostream&& __rhs);
diff --git a/libcxx/include/regex b/libcxx/include/regex
--- a/libcxx/include/regex
+++ b/libcxx/include/regex
@@ -990,8 +990,8 @@
 public:
     explicit regex_error(regex_constants::error_type __ecode);
     regex_error(const regex_error&) _NOEXCEPT = default;
-    virtual ~regex_error() _NOEXCEPT;
-     _LIBCPP_INLINE_VISIBILITY
+    ~regex_error() _NOEXCEPT override;
+    _LIBCPP_INLINE_VISIBILITY
     regex_constants::error_type code() const {return __code_;}
 };
 
@@ -1491,7 +1491,7 @@
     explicit __owns_one_state(__node<_CharT>* __s)
         : base(__s) {}
 
-    virtual ~__owns_one_state();
+    ~__owns_one_state() override;
 };
 
 template <class _CharT>
@@ -2180,7 +2180,7 @@
     __match_any_but_newline(__node<_CharT>* __s)
         : base(__s) {}
 
-    virtual void __exec(__state&) const;
+    void __exec(__state&) const override;
 };
 
 template <> _LIBCPP_FUNC_VIS void __match_any_but_newline<char>::__exec(__state&) const;
diff --git a/libcxx/include/stdexcept b/libcxx/include/stdexcept
--- a/libcxx/include/stdexcept
+++ b/libcxx/include/stdexcept
@@ -87,9 +87,9 @@
     logic_error(const logic_error&) _NOEXCEPT;
     logic_error& operator=(const logic_error&) _NOEXCEPT;
 
-    virtual ~logic_error() _NOEXCEPT;
+    ~logic_error() _NOEXCEPT override;
 
-    virtual const char* what() const _NOEXCEPT;
+    const char* what() const _NOEXCEPT override;
 #else
 public:
     explicit logic_error(const _VSTD::string&); // Symbol uses versioned std::string
@@ -110,9 +110,9 @@
     runtime_error(const runtime_error&) _NOEXCEPT;
     runtime_error& operator=(const runtime_error&) _NOEXCEPT;
 
-    virtual ~runtime_error() _NOEXCEPT;
+    ~runtime_error() _NOEXCEPT override;
 
-    virtual const char* what() const _NOEXCEPT;
+    const char* what() const _NOEXCEPT override;
 #else
 public:
    explicit runtime_error(const _VSTD::string&); // Symbol uses versioned std::string
@@ -129,7 +129,7 @@
 
 #ifndef _LIBCPP_ABI_VCRUNTIME
     domain_error(const domain_error&) _NOEXCEPT = default;
-    virtual ~domain_error() _NOEXCEPT;
+    ~domain_error() _NOEXCEPT override;
 #endif
 };
 
@@ -142,7 +142,7 @@
 
 #ifndef _LIBCPP_ABI_VCRUNTIME
     invalid_argument(const invalid_argument&) _NOEXCEPT = default;
-    virtual ~invalid_argument() _NOEXCEPT;
+    ~invalid_argument() _NOEXCEPT override;
 #endif
 };
 
@@ -154,7 +154,7 @@
     _LIBCPP_INLINE_VISIBILITY explicit length_error(const char* __s)   : logic_error(__s) {}
 #ifndef _LIBCPP_ABI_VCRUNTIME
     length_error(const length_error&) _NOEXCEPT = default;
-    virtual ~length_error() _NOEXCEPT;
+    ~length_error() _NOEXCEPT override;
 #endif
 };
 
@@ -167,7 +167,7 @@
 
 #ifndef _LIBCPP_ABI_VCRUNTIME
     out_of_range(const out_of_range&) _NOEXCEPT = default;
-    virtual ~out_of_range() _NOEXCEPT;
+    ~out_of_range() _NOEXCEPT override;
 #endif
 };
 
@@ -180,7 +180,7 @@
 
 #ifndef _LIBCPP_ABI_VCRUNTIME
     range_error(const range_error&) _NOEXCEPT = default;
-    virtual ~range_error() _NOEXCEPT;
+    ~range_error() _NOEXCEPT override;
 #endif
 };
 
@@ -193,7 +193,7 @@
 
 #ifndef _LIBCPP_ABI_VCRUNTIME
     overflow_error(const overflow_error&) _NOEXCEPT = default;
-    virtual ~overflow_error() _NOEXCEPT;
+    ~overflow_error() _NOEXCEPT override;
 #endif
 };
 
@@ -206,7 +206,7 @@
 
 #ifndef _LIBCPP_ABI_VCRUNTIME
     underflow_error(const underflow_error&) _NOEXCEPT = default;
-    virtual ~underflow_error() _NOEXCEPT;
+    ~underflow_error() _NOEXCEPT override;
 #endif
 };
 
diff --git a/libcxx/include/strstream b/libcxx/include/strstream
--- a/libcxx/include/strstream
+++ b/libcxx/include/strstream
@@ -167,7 +167,7 @@
     strstreambuf& operator=(strstreambuf&& __rhs);
 #endif // _LIBCPP_CXX03_LANG
 
-    virtual ~strstreambuf();
+    ~strstreambuf() override;
 
     void swap(strstreambuf& __rhs);
 
@@ -176,13 +176,13 @@
     int pcount() const;
 
 protected:
-    virtual int_type overflow (int_type __c = EOF);
-    virtual int_type pbackfail(int_type __c = EOF);
-    virtual int_type underflow();
-    virtual pos_type seekoff(off_type __off, ios_base::seekdir __way,
-                             ios_base::openmode __which = ios_base::in | ios_base::out);
-    virtual pos_type seekpos(pos_type __sp,
-                             ios_base::openmode __which = ios_base::in | ios_base::out);
+    int_type overflow (int_type __c = EOF) override;
+    int_type pbackfail(int_type __c = EOF) override;
+    int_type underflow() override;
+    pos_type seekoff(off_type __off, ios_base::seekdir __way,
+                     ios_base::openmode __which = ios_base::in | ios_base::out) override;
+    pos_type seekpos(pos_type __sp,
+                     ios_base::openmode __which = ios_base::in | ios_base::out) override;
 
 private:
     typedef unsigned __mode_type;
@@ -272,7 +272,7 @@
     }
 #endif // _LIBCPP_CXX03_LANG
 
-    virtual ~istrstream();
+    ~istrstream() override;
 
     _LIBCPP_INLINE_VISIBILITY
     void swap(istrstream& __rhs)
@@ -321,7 +321,7 @@
     }
 #endif // _LIBCPP_CXX03_LANG
 
-    virtual ~ostrstream();
+    ~ostrstream() override;
 
     _LIBCPP_INLINE_VISIBILITY
     void swap(ostrstream& __rhs)
@@ -381,7 +381,7 @@
     }
 #endif // _LIBCPP_CXX03_LANG
 
-    virtual ~strstream();
+    ~strstream() override;
 
     _LIBCPP_INLINE_VISIBILITY
     void swap(strstream& __rhs)
diff --git a/libcxx/include/system_error b/libcxx/include/system_error
--- a/libcxx/include/system_error
+++ b/libcxx/include/system_error
@@ -233,7 +233,7 @@
     : public error_category
 {
 public:
-    virtual string message(int ev) const;
+    string message(int ev) const override;
 };
 
 _LIBCPP_FUNC_VIS const error_category& generic_category() _NOEXCEPT;
@@ -469,7 +469,7 @@
     system_error(int __ev, const error_category& __ecat, const char* __what_arg);
     system_error(int __ev, const error_category& __ecat);
     system_error(const system_error&) _NOEXCEPT = default;
-    ~system_error() _NOEXCEPT;
+    ~system_error() _NOEXCEPT override;
 
     _LIBCPP_INLINE_VISIBILITY
     const error_code& code() const _NOEXCEPT {return __ec_;}
diff --git a/libcxx/include/typeinfo b/libcxx/include/typeinfo
--- a/libcxx/include/typeinfo
+++ b/libcxx/include/typeinfo
@@ -349,8 +349,8 @@
  public:
   bad_cast() _NOEXCEPT;
   bad_cast(const bad_cast&) _NOEXCEPT = default;
-  virtual ~bad_cast() _NOEXCEPT;
-  virtual const char* what() const _NOEXCEPT;
+  ~bad_cast() _NOEXCEPT override;
+  const char* what() const _NOEXCEPT override;
 };
 
 class _LIBCPP_EXCEPTION_ABI bad_typeid
@@ -358,8 +358,8 @@
 {
  public:
   bad_typeid() _NOEXCEPT;
-  virtual ~bad_typeid() _NOEXCEPT;
-  virtual const char* what() const _NOEXCEPT;
+  ~bad_typeid() _NOEXCEPT override;
+  const char* what() const _NOEXCEPT override;
 };
 
 } // namespace std
diff --git a/libcxx/include/variant b/libcxx/include/variant
--- a/libcxx/include/variant
+++ b/libcxx/include/variant
@@ -240,7 +240,7 @@
 
 class _LIBCPP_EXCEPTION_ABI _LIBCPP_AVAILABILITY_BAD_VARIANT_ACCESS bad_variant_access : public exception {
 public:
-  virtual const char* what() const _NOEXCEPT;
+   const char* what() const _NOEXCEPT override;
 };
 
 } // namespace std
diff --git a/libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.fail.cpp
--- a/libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.fail.cpp
+++ b/libcxx/test/libcxx/input.output/file.streams/fstreams/traits_mismatch.fail.cpp
@@ -18,8 +18,11 @@
 int main(int, char**)
 {
 	std::basic_fstream<char, std::char_traits<wchar_t> > f;
-//  expected-error-re@ios:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
-//  expected-error-re@streambuf:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+// expected-error-re@ios:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+// expected-error-re@streambuf:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+
+// expected-error@istream:* {{only virtual member functions can be marked 'override'}}
+// expected-error@istream:* {{only virtual member functions can be marked 'override'}}
 
 // FIXME: As of commit r324062 Clang incorrectly generates a diagnostic about mismatching
 // exception specifications for types which are already invalid for one reason or another.
diff --git a/libcxx/test/libcxx/input.output/iostream.format/input.streams/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/iostream.format/input.streams/traits_mismatch.fail.cpp
--- a/libcxx/test/libcxx/input.output/iostream.format/input.streams/traits_mismatch.fail.cpp
+++ b/libcxx/test/libcxx/input.output/iostream.format/input.streams/traits_mismatch.fail.cpp
@@ -26,6 +26,7 @@
 int main(int, char**)
 {
 //  expected-error-re@ios:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+//  expected-error@istream:* {{only virtual member functions can be marked 'override'}}
 
   return 0;
 }
diff --git a/libcxx/test/libcxx/input.output/iostream.format/output.streams/traits_mismatch.fail.cpp b/libcxx/test/libcxx/input.output/iostream.format/output.streams/traits_mismatch.fail.cpp
--- a/libcxx/test/libcxx/input.output/iostream.format/output.streams/traits_mismatch.fail.cpp
+++ b/libcxx/test/libcxx/input.output/iostream.format/output.streams/traits_mismatch.fail.cpp
@@ -26,6 +26,7 @@
 int main(int, char**)
 {
 //  expected-error-re@ios:* {{static_assert failed{{.*}} "traits_type::char_type must be the same type as CharT"}}
+//  expected-error@ostream:* {{only virtual member functions can be marked 'override'}}
 
   return 0;
 }