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[libcxx] adds a size-based representation for vector's unstable ABI #155330

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[libcxx] adds a size-based representation for vector's unstable ABI #155330

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1 change: 1 addition & 0 deletions libcxx/include/__configuration/abi.h
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,7 @@
# define _LIBCPP_ABI_NO_REVERSE_ITERATOR_SECOND_MEMBER
# define _LIBCPP_ABI_OPTIMIZED_FUNCTION
# define _LIBCPP_ABI_REGEX_CONSTANTS_NONZERO
# define _LIBCPP_ABI_SIZE_BASED_VECTOR
# define _LIBCPP_ABI_STRING_OPTIMIZED_EXTERNAL_INSTANTIATION
# define _LIBCPP_ABI_USE_WRAP_ITER_IN_STD_ARRAY
# define _LIBCPP_ABI_USE_WRAP_ITER_IN_STD_STRING_VIEW
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8 changes: 3 additions & 5 deletions libcxx/include/__split_buffer
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Original file line number Diff line number Diff line change
Expand Up @@ -268,7 +268,6 @@ public:
__set_valid_range(pointer __new_begin, pointer __new_end) _NOEXCEPT {
// Size-based __split_buffers track their size directly: we need to explicitly update the size
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@jyknight jyknight Dec 11, 2025

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Comment says you need to update the size, but said update was deleted by the PR?

// when the front is adjusted.
__size_ -= __new_begin - __begin_;
__begin_ = __new_begin;
__set_sentinel(__new_end);
}
Expand All @@ -277,7 +276,6 @@ public:
__set_valid_range(pointer __new_begin, size_type __new_size) _NOEXCEPT {
// Size-based __split_buffers track their size directly: we need to explicitly update the size
// when the front is adjusted.
__size_ -= __new_begin - __begin_;
__begin_ = __new_begin;
__set_sentinel(__new_size);
}
Expand Down Expand Up @@ -316,9 +314,9 @@ public:
}

_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __swap_without_allocator(
__split_buffer_pointer_layout<__split_buffer<value_type, __alloc_rr&, __split_buffer_pointer_layout>,
value_type,
__alloc_rr&>& __other) _NOEXCEPT {
__split_buffer_size_layout<__split_buffer<value_type, __alloc_rr&, __split_buffer_size_layout>,
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@jyknight jyknight Dec 11, 2025

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Maybe can be a separate commit; I'm presuming this is simply a bugfix to the previous change adding size-based __split_buffer?

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@cjdb cjdb Dec 11, 2025

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Yes, this was a bug-fix. We don't have a way to test that __split_buffer works with __split_buffer_size_layout without size-based vector (which is its only driver), so I'm kind of ambivalent on whether this happens in lock-step with vector or if it happens in a separate PR.

Again, the benefit of another commit is that it adds documentation, so I'm partial on that front.

value_type,
__alloc_rr&>& __other) _NOEXCEPT {
std::swap(__front_cap_, __other.__front_cap_);
std::swap(__begin_, __other.__begin_);
std::swap(__cap_, __other.__cap_);
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