[Bug libstdc++/105258] New: std::get_temporary_buffer() does not respect alignment (affects std::stable_sort())

[wielkiegie at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105258

            Bug ID: 105258
           Summary: std::get_temporary_buffer() does not respect alignment
                    (affects std::stable_sort())
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wielkiegie at gmail dot com
  Target Milestone: ---

Created attachment 52795
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52795&action=edit
The reproducer

The `std::get_temporary_buffer()` function uses raw `operator new()` to
allocate enough memory for the `sizeof(T) * count` bytes. However, it does not
take `alignof(T)` into account.

While `std::get_temporary_buffer()` is deprecated in C++17 [1], it is still
used internally by `std::stable_sort()`.

The issue is reproducible on the gcc HEAD [2]. Please note that the alignment
issues might not be deterministic as the allocator can return an allocation of
correct alignment by accident.

For convenience, I have also attached the reproducer to this bug report.

[1] https://en.cppreference.com/w/cpp/memory/get_temporary_buffer
[2] https://wandbox.org/permlink/zZt6Weh3V1XWmUWt