bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Eli Zaretskii]

> Cc: pipcet@gmail.com, 41321@debbugs.gnu.org, monnier@iro.umontreal.ca
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sat, 30 May 2020 11:12:49 -0700
> 
> On 5/30/20 10:22 AM, Eli Zaretskii wrote:
> >>>> That's not correct for !USE_LSB_TAG, where LISP_ALIGNMENT is merely the 
> >>>> native
> >>>> alignment (there's no need to align objects to 8 because the tags are at 
> >>>> the
> >>>> high end).
> >>> I'm using a !USE_LSB_TAG build, but LISP_ALIGNMENT is 8 nonetheless.
> >> That's true for your platform, since alignof (max_align_t) == 8 on your
> >> platform.
> > No, it's 16.  And I don't understand what does that have to do with
> > LISP_ALIGNMENT on the master branch, since we all but removed
> > max_align_t from there.
> 
> Oh, I thought you were talking about the emacs-27 branch which is still 
> using max_align_t.
> 
> You're right that LISP_ALIGNMENT is 8 on your platform on the master 
> branch. However, my comment "That's not correct for !USE_LSB_TAG ..." 
> (Bug#41321#305) was responding to Pip Cet's earlier comment "I would 
> prefer simply defining LISP_ALIGNMENT to be 8" (Bug#41321#272) which was 
> talking about the emacs-27 branch.

I'm still confused, because on current emacs-27, both LISP_ALIGNMENT
and alignof(max_align_t) are 16 in my builds.  And I still don't
understand why using LISP_ALIGNMENT of 8 is not right in this case (on
emacs-27).