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[libc++][NFC] Use early returns in a few basic_string functions #137299

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Merged
merged 1 commit into from
Aug 20, 2025
+144 −133
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[libc++][NFC] Use early returns in a few basic_string functions #137299

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277 changes: 144 additions & 133 deletions libcxx/include/string
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Original file line number Diff line number Diff line change
Expand Up @@ -1417,20 +1417,21 @@ public:
size_type __sz = size();
size_type __cap = capacity();
size_type __n = static_cast<size_type>(std::distance(__first, __last));
if (__n) {
if (__string_is_trivial_iterator_v<_ForwardIterator> && !__addr_in_range(*__first)) {
if (__cap - __sz < __n)
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __sz, 0);
__annotate_increase(__n);
auto __end = __copy_non_overlapping_range(__first, __last, std::__to_address(__get_pointer() + __sz));
traits_type::assign(*__end, value_type());
__set_size(__sz + __n);
} else {
const basic_string __temp(__first, __last, __alloc_);
append(__temp.data(), __temp.size());
}
if (__n == 0)
return *this;

if (__string_is_trivial_iterator_v<_ForwardIterator> && !__addr_in_range(*__first)) {
if (__cap - __sz < __n)
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __sz, 0);
__annotate_increase(__n);
auto __end = __copy_non_overlapping_range(__first, __last, std::__to_address(__get_pointer() + __sz));
traits_type::assign(*__end, value_type());
__set_size(__sz + __n);
return *this;
} else {
const basic_string __temp(__first, __last, __alloc_);
return append(__temp.data(), __temp.size());
}
return *this;
}

# if _LIBCPP_STD_VER >= 23
Expand Down Expand Up @@ -2790,24 +2791,23 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_NOINLINE basic_string<_CharT, _Traits, _Al
basic_string<_CharT, _Traits, _Allocator>::__assign_no_alias(const value_type* __s, size_type __n) {
const auto __cap = __is_short ? static_cast<size_type>(__min_cap) : __get_long_cap();
const auto __size = __is_short ? __get_short_size() : __get_long_size();
if (__n < __cap) {
if (__n > __size)
__annotate_increase(__n - __size);
pointer __p;
if (__is_short) {
__p = __get_short_pointer();
__set_short_size(__n);
} else {
__p = __get_long_pointer();
__set_long_size(__n);
}
traits_type::copy(std::__to_address(__p), __s, __n);
traits_type::assign(__p[__n], value_type());
if (__size > __n)
__annotate_shrink(__size);
} else {
if (__n >= __cap) {
__grow_by_and_replace(__cap - 1, __n - __cap + 1, __size, 0, __size, __n, __s);
return *this;
}

__annotate_delete();
auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
pointer __p;
if (__is_short) {
__p = __get_short_pointer();
__set_short_size(__n);
} else {
__p = __get_long_pointer();
__set_long_size(__n);
}
traits_type::copy(std::__to_address(__p), __s, __n);
traits_type::assign(__p[__n], value_type());
return *this;
}

Expand Down Expand Up @@ -3021,52 +3021,56 @@ basic_string<_CharT, _Traits, _Allocator>::append(const value_type* __s, size_ty
_LIBCPP_ASSERT_NON_NULL(__n == 0 || __s != nullptr, "string::append received nullptr");
size_type __cap = capacity();
size_type __sz = size();
if (__cap - __sz >= __n) {
if (__n) {
__annotate_increase(__n);
value_type* __p = std::__to_address(__get_pointer());
traits_type::copy(__p + __sz, __s, __n);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
}
} else
if (__cap - __sz < __n) {
__grow_by_and_replace(__cap, __sz + __n - __cap, __sz, __sz, 0, __n, __s);
return *this;
}

if (__n == 0)
return *this;
Comment on lines +3029 to +3030
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We probably don't want to optimize for the case where we're appending an empty string. Should we remove this special case? Let's look at the assembly.


__annotate_increase(__n);
value_type* __p = std::__to_address(__get_pointer());
traits_type::copy(__p + __sz, __s, __n);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
return *this;
}

template <class _CharT, class _Traits, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20 basic_string<_CharT, _Traits, _Allocator>&
basic_string<_CharT, _Traits, _Allocator>::append(size_type __n, value_type __c) {
if (__n) {
size_type __cap = capacity();
size_type __sz = size();
if (__cap - __sz < __n)
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __sz, 0);
__annotate_increase(__n);
pointer __p = __get_pointer();
traits_type::assign(std::__to_address(__p) + __sz, __n, __c);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
}
if (__n == 0)
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Same here.

return *this;

size_type __cap = capacity();
size_type __sz = size();
if (__cap - __sz < __n)
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __sz, 0);
__annotate_increase(__n);
pointer __p = __get_pointer();
traits_type::assign(std::__to_address(__p) + __sz, __n, __c);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
return *this;
}

template <class _CharT, class _Traits, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20 inline void
basic_string<_CharT, _Traits, _Allocator>::__append_default_init(size_type __n) {
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In a follow-up PR, let's merge this into __resize_default_init since that's the only place where it is used. And actually __resize_default_init can also be inlined into resize_in_overwrite which is its only usage point.

if (__n) {
size_type __cap = capacity();
size_type __sz = size();
if (__cap - __sz < __n)
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __sz, 0);
__annotate_increase(__n);
pointer __p = __get_pointer();
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
}
if (__n == 0)
return;
Comment on lines +3063 to +3064
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Same comment.

size_type __cap = capacity();
size_type __sz = size();
if (__cap - __sz < __n)
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __sz, 0);
__annotate_increase(__n);
pointer __p = __get_pointer();
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
}

template <class _CharT, class _Traits, class _Allocator>
Expand Down Expand Up @@ -3124,23 +3128,27 @@ basic_string<_CharT, _Traits, _Allocator>::insert(size_type __pos, const value_t
if (__pos > __sz)
this->__throw_out_of_range();
size_type __cap = capacity();
if (__cap - __sz >= __n) {
if (__n) {
__annotate_increase(__n);
value_type* __p = std::__to_address(__get_pointer());
size_type __n_move = __sz - __pos;
if (__n_move != 0) {
if (std::__is_pointer_in_range(__p + __pos, __p + __sz, __s))
__s += __n;
traits_type::move(__p + __pos + __n, __p + __pos, __n_move);
}
traits_type::move(__p + __pos, __s, __n);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
}
} else

if (__cap - __sz < __n) {
__grow_by_and_replace(__cap, __sz + __n - __cap, __sz, __pos, 0, __n, __s);
return *this;
}

if (__n == 0)
return *this;
Comment on lines +3137 to +3138
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Same comment. I suggest we tackle all of these removals in the same PR, as a follow-up to this one.


__annotate_increase(__n);
value_type* __p = std::__to_address(__get_pointer());
size_type __n_move = __sz - __pos;
if (__n_move != 0) {
if (std::__is_pointer_in_range(__p + __pos, __p + __sz, __s))
__s += __n;
traits_type::move(__p + __pos + __n, __p + __pos, __n_move);
}
traits_type::move(__p + __pos, __s, __n);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
return *this;
}

Expand All @@ -3150,24 +3158,26 @@ basic_string<_CharT, _Traits, _Allocator>::insert(size_type __pos, size_type __n
size_type __sz = size();
if (__pos > __sz)
this->__throw_out_of_range();
if (__n) {
size_type __cap = capacity();
value_type* __p;
if (__cap - __sz >= __n) {
__annotate_increase(__n);
__p = std::__to_address(__get_pointer());
size_type __n_move = __sz - __pos;
if (__n_move != 0)
traits_type::move(__p + __pos + __n, __p + __pos, __n_move);
} else {
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __pos, 0, __n);
__p = std::__to_address(__get_long_pointer());
}
traits_type::assign(__p + __pos, __n, __c);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());

if (__n == 0)
return *this;

size_type __cap = capacity();
value_type* __p;
if (__cap - __sz >= __n) {
__annotate_increase(__n);
__p = std::__to_address(__get_pointer());
size_type __n_move = __sz - __pos;
if (__n_move != 0)
traits_type::move(__p + __pos + __n, __p + __pos, __n_move);
} else {
__grow_by_without_replace(__cap, __sz + __n - __cap, __sz, __pos, 0, __n);
__p = std::__to_address(__get_long_pointer());
}
traits_type::assign(__p + __pos, __n, __c);
__sz += __n;
__set_size(__sz);
traits_type::assign(__p[__sz], value_type());
return *this;
}

Expand Down Expand Up @@ -3241,38 +3251,38 @@ basic_string<_CharT, _Traits, _Allocator>::replace(
this->__throw_out_of_range();
__n1 = std::min(__n1, __sz - __pos);
size_type __cap = capacity();
if (__cap - __sz + __n1 >= __n2) {
value_type* __p = std::__to_address(__get_pointer());
if (__n1 != __n2) {
if (__n2 > __n1)
__annotate_increase(__n2 - __n1);
size_type __n_move = __sz - __pos - __n1;
if (__n_move != 0) {
if (__n1 > __n2) {
traits_type::move(__p + __pos, __s, __n2);
traits_type::move(__p + __pos + __n2, __p + __pos + __n1, __n_move);
return __null_terminate_at(__p, __sz + (__n2 - __n1));
}
if (std::__is_pointer_in_range(__p + __pos + 1, __p + __sz, __s)) {
if (__p + __pos + __n1 <= __s)
__s += __n2 - __n1;
else // __p + __pos < __s < __p + __pos + __n1
{
traits_type::move(__p + __pos, __s, __n1);
__pos += __n1;
__s += __n2;
__n2 -= __n1;
__n1 = 0;
}
}
if (__cap - __sz + __n1 < __n2) {
__grow_by_and_replace(__cap, __sz - __n1 + __n2 - __cap, __sz, __pos, __n1, __n2, __s);
return *this;
}

value_type* __p = std::__to_address(__get_pointer());
if (__n1 != __n2) {
if (__n2 > __n1)
__annotate_increase(__n2 - __n1);
size_type __n_move = __sz - __pos - __n1;
if (__n_move != 0) {
if (__n1 > __n2) {
traits_type::move(__p + __pos, __s, __n2);
traits_type::move(__p + __pos + __n2, __p + __pos + __n1, __n_move);
return __null_terminate_at(__p, __sz + (__n2 - __n1));
}
if (std::__is_pointer_in_range(__p + __pos + 1, __p + __sz, __s)) {
if (__p + __pos + __n1 <= __s) {
__s += __n2 - __n1;
} else { // __p + __pos < __s < __p + __pos + __n1
traits_type::move(__p + __pos, __s, __n1);
__pos += __n1;
__s += __n2;
__n2 -= __n1;
__n1 = 0;
}
}
traits_type::move(__p + __pos + __n2, __p + __pos + __n1, __n_move);
}
traits_type::move(__p + __pos, __s, __n2);
return __null_terminate_at(__p, __sz + (__n2 - __n1));
} else
__grow_by_and_replace(__cap, __sz - __n1 + __n2 - __cap, __sz, __pos, __n1, __n2, __s);
return *this;
}
traits_type::move(__p + __pos, __s, __n2);
return __null_terminate_at(__p, __sz + (__n2 - __n1));
}

template <class _CharT, class _Traits, class _Allocator>
Expand Down Expand Up @@ -3325,15 +3335,16 @@ basic_string<_CharT, _Traits, _Allocator>::replace(size_type __pos, size_type __
template <class _CharT, class _Traits, class _Allocator>
_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_NOINLINE void
basic_string<_CharT, _Traits, _Allocator>::__erase_external_with_move(size_type __pos, size_type __n) {
if (__n) {
size_type __sz = size();
value_type* __p = std::__to_address(__get_pointer());
__n = std::min(__n, __sz - __pos);
size_type __n_move = __sz - __pos - __n;
if (__n_move != 0)
traits_type::move(__p + __pos, __p + __pos + __n, __n_move);
__null_terminate_at(__p, __sz - __n);
}
if (__n == 0)
return;

size_type __sz = size();
value_type* __p = std::__to_address(__get_pointer());
__n = std::min(__n, __sz - __pos);
size_type __n_move = __sz - __pos - __n;
if (__n_move != 0)
traits_type::move(__p + __pos, __p + __pos + __n, __n_move);
__null_terminate_at(__p, __sz - __n);
}

template <class _CharT, class _Traits, class _Allocator>
Expand Down
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