Describe the bug
Currently, _Optimistic_temporary_buffer used for stable sorting algorithms relies on _Aligned_storage_t, which doesn't accept overaligned element types by default due to ABI compatibility issues.
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_Aligned_storage_t<sizeof(_Ty), alignof(_Ty)> _Stack_space[_Optimistic_count];
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template <size_t _Len, size_t _Align>
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struct _Aligned<_Len, _Align, double, false> {
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#ifdef _ENABLE_EXTENDED_ALIGNED_STORAGE
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struct type {
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alignas(_Align) char _Space[_Len];
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};
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#else // ^^^ defined(_ENABLE_EXTENDED_ALIGNED_STORAGE) / !defined(_ENABLE_EXTENDED_ALIGNED_STORAGE) vvv
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#ifndef _DISABLE_EXTENDED_ALIGNED_STORAGE
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static_assert(_Always_false<_Aligned>,
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"You've instantiated std::aligned_storage<Len, Align> with an extended alignment (in other "
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"words, Align > alignof(max_align_t)). Before VS 2017 15.8, the member \"type\" would "
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"non-conformingly have an alignment of only alignof(max_align_t). VS 2017 15.8 was fixed to "
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"handle this correctly, but the fix inherently changes layout and breaks binary compatibility "
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"(*only* for uses of aligned_storage with extended alignments). "
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"To suppress this error, please define either "
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"(1) _ENABLE_EXTENDED_ALIGNED_STORAGE to confirm that you want a type with an extended alignment, or "
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"(2) _DISABLE_EXTENDED_ALIGNED_STORAGE to get the old non-conforming behavior.");
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#endif // ^^^ !defined(_DISABLE_EXTENDED_ALIGNED_STORAGE) ^^^
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using type = _Align_type<max_align_t, _Len>;
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#endif // ^^^ !defined(_ENABLE_EXTENDED_ALIGNED_STORAGE) ^^^
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};
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Command-line test case
Godbolt link
#include <algorithm>
#include <array>
#include <iterator>
struct alignas(32) large_element {
std::array<unsigned char, 32> elems;
friend auto operator<=>(const large_element&, const large_element&) = default;
};
int main() {
large_element arr[42]{};
std::stable_sort(std::begin(arr), std::end(arr));
std::stable_partition(std::begin(arr), std::end(arr), [](const auto&) { return true; });
std::inplace_merge(std::begin(arr), std::begin(arr), std::end(arr));
std::ranges::stable_sort(arr);
std::ranges::stable_partition(arr, [](const auto&) { return true; });
std::ranges::inplace_merge(arr, std::ranges::begin(arr));
}Expected behavior
This program correctly compiles and runs.
STL version
Probably all versions with default error set for aligned_storage_t.
Additional context
As _Optimistic_temporary_buffer is only internally used and only used on the stack, perhaps it's safe to change the size and/or the alignment of the buffer with its name changed.
Describe the bug
Currently,
_Optimistic_temporary_bufferused for stable sorting algorithms relies on_Aligned_storage_t, which doesn't accept overaligned element types by default due to ABI compatibility issues.STL/stl/inc/algorithm
Line 491 in eb024e0
STL/stl/inc/type_traits
Lines 1246 to 1266 in eb024e0
Command-line test case
Godbolt link
Expected behavior
This program correctly compiles and runs.
STL version
Probably all versions with default error set for
aligned_storage_t.Additional context
As
_Optimistic_temporary_bufferis only internally used and only used on the stack, perhaps it's safe to change the size and/or the alignment of the buffer with its name changed.