On Mon, 11 Apr 2022 at 18:03, Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>         // Precondition: _M_frames == nullptr
>         pointer
>         _M_allocate(allocator_type& __alloc, size_type __n) noexcept
>         {
>           __try
>             {
> -             _M_frames = __n ? __alloc.allocate(__n) : nullptr;
> -             _M_capacity = __n;
> +             if (0 < __n && __n <= _S_max_size(__alloc)) [[unlikely]]

I originally changed this to return early if the size isn't OK:

  if (unlikely condition)
    return nullptr;

but in the version I pushed it's:

  if (likely condition)
    // do allocation

but forgot to change the attribute to match.

Fixed by the attached. Tested x86_64-linux and pushed to trunk.

I have further improvements to stacktrace::current coming tomorrow.