There is a whole series of things by Pal Balog dealing with layout too.

On Thu, Feb 27, 2020, 17:01 Arvid Norberg via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
On Thu, Feb 27, 2020 at 5:50 PM Brian Bi via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
On Thu, Feb 27, 2020 at 10:37 AM Ryan Nicholl via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
[...]
I think it's better to have the order of construction and destruction go according to the declaration order, and add some new feature to control the memory layout, rather than the reverse.

Rene Rivera wrote a paper for this that he presented in SG14.

https://raw.githack.com/grafikrobot/papers/master/wg21/member_layout/member_layout_D1605R0.html

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Arvid Norberg
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