kf::vector resize method leads to the use of unsupported on old 32-bit systems (Windows XP-Windows 7) memcmp function

[maliysergey]

If use resize method with value for integer types, for example
kf::vector<int, PagedPool> test; test.resize(10, 1);
it leads to import the memcmp function to the resulting binary.

It occurs because resize internally calls _Uninitialized_fill_n method that use _Is_all_bits_zero method
template <class _Ty> _NODISCARD bool _Is_all_bits_zero(const _Ty& _Val) { // checks if scalar type has all bits set to zero _STL_INTERNAL_STATIC_ASSERT(is_scalar_v<_Ty> && !is_member_pointer_v<_Ty>); constexpr _Ty _Zero{}; return _CSTD memcmp(&_Val, &_Zero, sizeof(_Ty)) == 0; }

[SergiusTheBest]

@maliysergey Probably we need memcmp implementation for Windows XP?

[maliysergey]

or we can think how to change our allocator to fit to this constraint _Uses_default_construct, maybe only for integer types

[SergiusTheBest]

or we can think how to change our allocator to fit to this constraint _Uses_default_construct, maybe only for integer types

@maliysergey It satisfies already:

    if constexpr (_Fill_memset_is_safe<_Ty*, _Ty> && _Uses_default_construct<_Alloc, _Ty*, _Ty>::value) {
#if _HAS_CXX20
        if (!_STD is_constant_evaluated())
#endif // _HAS_CXX20
        {
            _Fill_memset(_Unfancy(_First), _Val, static_cast<size_t>(_Count));
            return _First + _Count;
        }
    } else if constexpr (_Fill_zero_memset_is_safe<_Ty*, _Ty> && _Uses_default_construct<_Alloc, _Ty*, _Ty>::value) {
#if _HAS_CXX20
        if (!_STD is_constant_evaluated())
#endif // _HAS_CXX20
        {
            if (_Is_all_bits_zero(_Val)) {
                _Fill_zero_memset(_Unfancy(_First), static_cast<size_t>(_Count));
                return _First + _Count;
            }
        }
    }

_Uses_default_construct is used in both branches, so it evaluates to true.

[SergiusTheBest]

@maliysergey I traced down it to 32-bit Windows XP-Windows 7. They all have no memcmp.

[SergiusTheBest]

Adding this to the code fixes the issue:

extern "C" _Check_return_ int __cdecl memcmp(
    _In_reads_bytes_(_Size) void const* _Buf1,
    _In_reads_bytes_(_Size) void const* _Buf2,
    _In_                    size_t      _Size
)
{
	return RtlCompareMemory(_Buf1, _Buf2, _Size); // implement returning of the correct value
}

I think we can add it unconditionally for all 32-bit code.