[libc++][NFC] Copy the whole union instead of a member; also remove __zero()

This doesn't affect code-gen

Reviewed By: ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D132951

Author: philnik777

libcxx/include/string

@@ -812,7 +812,7 @@ private:
         if (__size > max_size())
             __throw_length_error();
         if (__fits_in_sso(__size)) {
-            __zero();
+            __r_.first() = __rep();
             __set_short_size(__size);
         } else {
             auto __capacity = __recommend(__size) + 1;
@@ -1531,7 +1531,7 @@ private:
     }
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __default_init() {
-        __zero();
+        __r_.first() = __rep();
         if (__libcpp_is_constant_evaluated()) {
             size_type __sz = __recommend(0) + 1;
             pointer __ptr = __alloc_traits::allocate(__alloc(), __sz);
@@ -1638,11 +1638,6 @@ private:
     const_pointer __get_pointer() const _NOEXCEPT
         {return __is_long() ? __get_long_pointer() : __get_short_pointer();}
 
-    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-    void __zero() _NOEXCEPT {
-        __r_.first() = __rep();
-    }
-
     template <size_type __a> static
         _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
         size_type __align_it(size_type __s) _NOEXCEPT
@@ -1942,7 +1937,7 @@ void basic_string<_CharT, _Traits, _Allocator>::__init(const value_type* __s,
                                                        size_type __reserve)
 {
     if (__libcpp_is_constant_evaluated())
-        __zero();
+        __r_.first() = __rep();
     if (__reserve > max_size())
         __throw_length_error();
     pointer __p;
@@ -1970,7 +1965,7 @@ void
 basic_string<_CharT, _Traits, _Allocator>::__init(const value_type* __s, size_type __sz)
 {
     if (__libcpp_is_constant_evaluated())
-        __zero();
+        __r_.first() = __rep();
     if (__sz > max_size())
         __throw_length_error();
     pointer __p;
@@ -2029,7 +2024,7 @@ basic_string<_CharT, _Traits, _Allocator>::basic_string(const basic_string& __st
     : __r_(__default_init_tag(), __alloc_traits::select_on_container_copy_construction(__str.__alloc()))
 {
     if (!__str.__is_long())
-        __r_.first().__r = __str.__r_.first().__r;
+        __r_.first() = __str.__r_.first();
     else
         __init_copy_ctor_external(std::__to_address(__str.__get_long_pointer()),
                                   __str.__get_long_size());
@@ -2043,7 +2038,7 @@ basic_string<_CharT, _Traits, _Allocator>::basic_string(
     : __r_(__default_init_tag(), __a)
 {
     if (!__str.__is_long())
-        __r_.first().__r = __str.__r_.first().__r;
+        __r_.first() = __str.__r_.first();
     else
         __init_copy_ctor_external(std::__to_address(__str.__get_long_pointer()),
                                   __str.__get_long_size());
@@ -2055,7 +2050,8 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20
 void basic_string<_CharT, _Traits, _Allocator>::__init_copy_ctor_external(
     const value_type* __s, size_type __sz) {
   if (__libcpp_is_constant_evaluated())
-    __zero();
+    __r_.first() = __rep();
+
   pointer __p;
   if (__fits_in_sso(__sz)) {
     __p = __get_short_pointer();
@@ -2100,12 +2096,9 @@ basic_string<_CharT, _Traits, _Allocator>::basic_string(basic_string&& __str, co
         __init(std::__to_address(__str.__get_long_pointer()), __str.__get_long_size());
     else
     {
-        if (__libcpp_is_constant_evaluated()) {
-            __zero();
-            __r_.first().__l = __str.__r_.first().__l;
-        } else {
-            __r_.first().__r = __str.__r_.first().__r;
-        }
+        if (__libcpp_is_constant_evaluated())
+            __r_.first() = __rep();
+        __r_.first() = __str.__r_.first();
         __str.__default_init();
     }
     std::__debug_db_insert_c(this);
@@ -2121,7 +2114,8 @@ void
 basic_string<_CharT, _Traits, _Allocator>::__init(size_type __n, value_type __c)
 {
     if (__libcpp_is_constant_evaluated())
-        __zero();
+        __r_.first() = __rep();
+
     if (__n > max_size())
         __throw_length_error();
     pointer __p;
@@ -2261,7 +2255,7 @@ __enable_if_t
 basic_string<_CharT, _Traits, _Allocator>::__init(_ForwardIterator __first, _ForwardIterator __last)
 {
     if (__libcpp_is_constant_evaluated())
-        __zero();
+        __r_.first() = __rep();
     size_type __sz = static_cast<size_type>(std::distance(__first, __last));
     if (__sz > max_size())
         __throw_length_error();
@@ -2517,7 +2511,7 @@ basic_string<_CharT, _Traits, _Allocator>::operator=(const basic_string& __str)
     __copy_assign_alloc(__str);
     if (!__is_long()) {
       if (!__str.__is_long()) {
-        __r_.first().__r = __str.__r_.first().__r;
+        __r_.first() = __str.__r_.first();
       } else {
         return __assign_no_alias<true>(__str.data(), __str.size());
       }