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

[Eli Zaretskii]

> Cc: Pip Cet <pipcet@gmail.com>, Eli Zaretskii <eliz@gnu.org>,
>  41321@debbugs.gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Fri, 29 May 2020 13:40:33 -0700
> 
>   (USE_LSB_TAG
>    ? (uintptr_t) word % GCALIGNMENT == Lisp_Symbol
>    : (uintptr_t) word % alignof (struct Lisp_Symbol) == 0)

I don't understand how this will work, given that Lisp object on the
stack can be pushed as 2 non-contiguous 32-bit words.  Can you
explain?