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[libc++] Make __allocate_long_buffer a constructor of __long #166451

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[libc++] Make __allocate_long_buffer a constructor of __long #166451

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106 changes: 43 additions & 63 deletions libcxx/include/string
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Original file line number Diff line number Diff line change
Expand Up @@ -825,31 +825,44 @@ public:
private:
static_assert(CHAR_BIT == 8, "This implementation assumes that one byte contains 8 bits");

# ifdef _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT

// Attribute 'packed' is used to keep the layout compatible with the
// previous definition that did not use bit fields. This is because on
// some platforms bit fields have a default size rather than the actual
// size used, e.g., it is 4 bytes on AIX. See D128285 for details.
struct __long {
__long() = default;

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __long(__alloc_result __alloc, size_type __size)
: __data_(__alloc.ptr), __size_(__size), __cap_(__alloc.count / __endian_factor), __is_long_(true) {
_LIBCPP_ASSERT_INTERNAL(!__fits_in_sso(__alloc.count), "Long capacity should always be larger than the SSO");
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __long(_Allocator& __alloc, size_type __size)
: __is_long_(true), __size_(__size) {
_LIBCPP_ASSERT_INTERNAL(!__fits_in_sso(__size), "Long capacity should always be larger than the SSO");
auto __allocation = std::__allocate_at_least(__alloc, __recommend(__size) + 1);

__cap_ = __allocation.count / __endian_factor;
__data_ = __allocation.ptr;

if (__libcpp_is_constant_evaluated()) {
for (size_type __i = 0; __i != __allocation.count; ++__i)
std::__construct_at(std::addressof(__allocation.ptr[__i]));
}
}

# ifdef _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT
pointer __data_;
size_type __size_;
size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
size_type __is_long_ : 1;
# else
struct _LIBCPP_PACKED {
size_type __is_long_ : 1;
size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
};
size_type __size_;
pointer __data_;
# endif // _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT
};

enum { __min_cap = (sizeof(__long) - 1) / sizeof(value_type) > 2 ? (sizeof(__long) - 1) / sizeof(value_type) : 2 };

struct __short {
value_type __data_[__min_cap];
_LIBCPP_NO_UNIQUE_ADDRESS __padding<sizeof(value_type) - 1> __padding_;
unsigned char __size_ : 7;
unsigned char __is_long_ : 1;
};

// The __endian_factor is required because the field we use to store the size
// has one fewer bit than it would if it were not a bitfield.
//
Expand All @@ -862,42 +875,22 @@ private:
// If the MSB is used for the short-flag, the max_size() is numeric_limits<size_type>::max() / 2.
// This does not impact the short string representation, since we never need the MSB
// for representing the size of a short string anyway.

# ifdef _LIBCPP_BIG_ENDIAN
#if defined(_LIBCPP_BIG_ENDIAN) == defined(_LIBCPP_ABI_ALTERNATE_STRING_LAYOUT)
static const size_type __endian_factor = 2;
# else
static const size_type __endian_factor = 1;
# endif

# else // _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT

# ifdef _LIBCPP_BIG_ENDIAN
#else
static const size_type __endian_factor = 1;
# else
static const size_type __endian_factor = 2;
# endif

// Attribute 'packed' is used to keep the layout compatible with the
// previous definition that did not use bit fields. This is because on
// some platforms bit fields have a default size rather than the actual
// size used, e.g., it is 4 bytes on AIX. See D128285 for details.
struct __long {
__long() = default;
#endif

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __long(__alloc_result __alloc, size_type __size)
: __is_long_(true), __cap_(__alloc.count / __endian_factor), __size_(__size), __data_(__alloc.ptr) {
_LIBCPP_ASSERT_INTERNAL(!__fits_in_sso(__alloc.count), "Long capacity should always be larger than the SSO");
}
# ifdef _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT

struct _LIBCPP_PACKED {
size_type __is_long_ : 1;
size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
};
size_type __size_;
pointer __data_;
struct __short {
value_type __data_[__min_cap];
_LIBCPP_NO_UNIQUE_ADDRESS __padding<sizeof(value_type) - 1> __padding_;
unsigned char __size_ : 7;
unsigned char __is_long_ : 1;
};

enum { __min_cap = (sizeof(__long) - 1) / sizeof(value_type) > 2 ? (sizeof(__long) - 1) / sizeof(value_type) : 2 };
# else // _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT

struct __short {
struct _LIBCPP_PACKED {
Expand Down Expand Up @@ -2255,19 +2248,6 @@ private:
// These functions are only responsible for managing the buffer itself, not the value inside the buffer. As such,
// none of these facilities ensure that there is a null terminator at `data()[size()]`.

// Allocate a buffer of __capacity size with __alloc and return it
_LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX20 __long
__allocate_long_buffer(_Allocator& __alloc, size_type __capacity) {
auto __buffer = std::__allocate_at_least(__alloc, __recommend(__capacity) + 1);

if (__libcpp_is_constant_evaluated()) {
for (size_type __i = 0; __i != __buffer.count; ++__i)
std::__construct_at(std::addressof(__buffer.ptr[__i]));
}

return __long(__buffer, __capacity);
}

// 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();
Expand All @@ -2290,7 +2270,7 @@ private:
__annotate_new(__size);
return __get_short_pointer();
} else {
__rep_.__l = __allocate_long_buffer(__alloc_, __size);
__rep_ = __long(__alloc_, __size);
__annotate_new(__size);
return __get_long_pointer();
}
Expand Down Expand Up @@ -2447,7 +2427,7 @@ private:
__annotate_delete();
auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
auto __alloc = __str.__alloc_;
__reset_internal_buffer(__allocate_long_buffer(__alloc, __str.size()));
__reset_internal_buffer(__long(__alloc, __str.size()));
__alloc_ = std::move(__alloc);
}
}
Expand Down Expand Up @@ -2700,8 +2680,8 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void basic_string<_CharT, _Traits, _Allocator>::__
size_type __cap =
__old_cap < __ms / 2 - __alignment ? __recommend(std::max(__old_cap + __delta_cap, 2 * __old_cap)) : __ms;
__annotate_delete();
auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
__long __buffer = __allocate_long_buffer(__alloc_, __cap);
auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
__long __buffer(__alloc_, __cap);
if (__n_copy != 0)
traits_type::copy(std::__to_address(__buffer.__data_), std::__to_address(__old_p), __n_copy);
if (__n_add != 0)
Expand Down Expand Up @@ -2737,7 +2717,7 @@ _LIBCPP_DEPRECATED_("use __grow_by_without_replace") basic_string<_CharT, _Trait
pointer __old_p = __get_pointer();
size_type __cap =
__old_cap < __ms / 2 - __alignment ? __recommend(std::max(__old_cap + __delta_cap, 2 * __old_cap)) : __ms;
__long __buffer = __allocate_long_buffer(__alloc_, __cap);
__long __buffer(__alloc_, __cap);
if (__n_copy != 0)
traits_type::copy(std::__to_address(__buffer.__data_), std::__to_address(__old_p), __n_copy);
size_type __sec_cp_sz = __old_sz - __n_del - __n_copy;
Expand Down Expand Up @@ -3394,7 +3374,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void basic_string<_CharT, _Traits, _Allocator>::re
return;

__annotation_guard __g(*this);
__long __buffer = __allocate_long_buffer(__alloc_, __requested_capacity);
__long __buffer(__alloc_, __requested_capacity);
__buffer.__size_ = size();
traits_type::copy(std::__to_address(__buffer.__data_), data(), __buffer.__size_ + 1);
__reset_internal_buffer(__buffer);
Expand Down Expand Up @@ -3425,7 +3405,7 @@ inline _LIBCPP_CONSTEXPR_SINCE_CXX20 void basic_string<_CharT, _Traits, _Allocat
try {
# endif // _LIBCPP_HAS_EXCEPTIONS
__annotation_guard __g(*this);
__long __buffer = __allocate_long_buffer(__alloc_, __size);
__long __buffer(__alloc_, __size);

// The Standard mandates shrink_to_fit() does not increase the capacity.
// With equal capacity keep the existing buffer. This avoids extra work
Expand Down
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