[libc++] Merge basic_string::__{replace,reset}_internal_buffer

Author: philnik777

libcxx/include/string

@@ -914,6 +914,10 @@ private:
   union __rep {
     __short __s;
     __long __l;
+
+    __rep() = default;
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __rep(__short __r) : __s(__r) {}
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __rep(__long __r) : __l(__r) {}
   };
 
   _LIBCPP_COMPRESSED_PAIR(__rep, __rep_, allocator_type, __alloc_);
@@ -2259,18 +2263,12 @@ private:
     return __long(__buffer, __capacity);
   }
 
-  // Deallocate the long buffer if it exists and clear the short buffer so we are an empty string
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __reset_internal_buffer() {
+  // Replace the current buffer with __new_rep. Deallocate the old long buffer if it exists.
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __reset_internal_buffer(__rep __new_rep = __short()) {
     __annotate_delete();
     if (__is_long())
       __alloc_traits::deallocate(__alloc_, __get_long_pointer(), __get_long_cap());
-    __rep_.__s = __short();
-  }
-
-  // Replace the current buffer with __alloc; the first __size elements constitute a string
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __replace_internal_buffer(__long __alloc) {
-    __reset_internal_buffer();
-    __rep_.__l = __alloc;
+    __rep_ = __new_rep;
   }
 
   // Initialize the internal buffer to hold __size elements
@@ -2444,7 +2442,7 @@ private:
         __annotate_delete();
         auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
         auto __alloc = __str.__alloc_;
-        __replace_internal_buffer(__allocate_long_buffer(__alloc, __str.size()));
+        __reset_internal_buffer(__allocate_long_buffer(__alloc, __str.size()));
         __alloc_ = std::move(__alloc);
       }
     }
@@ -2710,7 +2708,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void basic_string<_CharT, _Traits, _Allocator>::__
                       __sec_cp_sz);
   __buffer.__size_ = __n_copy + __n_add + __sec_cp_sz;
   traits_type::assign(__buffer.__data_[__buffer.__size_], value_type());
-  __replace_internal_buffer(__buffer);
+  __reset_internal_buffer(__buffer);
 }
 
 // __grow_by is deprecated because it does not set the size. It may not update the size when the size is changed, and it
@@ -2746,7 +2744,7 @@ _LIBCPP_DEPRECATED_("use __grow_by_without_replace") basic_string<_CharT, _Trait
   // This is -1 to make sure the caller sets the size properly, since old versions of this function didn't set the size
   // at all.
   __buffer.__size_ = -1;
-  __replace_internal_buffer(__buffer);
+  __reset_internal_buffer(__buffer);
 }
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -3394,7 +3392,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void basic_string<_CharT, _Traits, _Allocator>::re
   __long __buffer  = __allocate_long_buffer(__alloc_, __requested_capacity);
   __buffer.__size_ = size();
   traits_type::copy(std::__to_address(__buffer.__data_), data(), __buffer.__size_ + 1);
-  __replace_internal_buffer(__buffer);
+  __reset_internal_buffer(__buffer);
 }
 
 template <class _CharT, class _Traits, class _Allocator>
@@ -3433,7 +3431,7 @@ inline _LIBCPP_CONSTEXPR_SINCE_CXX20 void basic_string<_CharT, _Traits, _Allocat
     }
 
     traits_type::copy(std::__to_address(__buffer.__data_), std::__to_address(__get_long_pointer()), __size + 1);
-    __replace_internal_buffer(__buffer);
+    __reset_internal_buffer(__buffer);
 #  if _LIBCPP_HAS_EXCEPTIONS
   } catch (...) {
     return;