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

[Paul Eggert]

On 5/30/20 11:11 AM, Eli Zaretskii wrote:
> So any pointer whose alignment is the same as 'struct Lisp_Symbol'
> will pass the test, regardless of the tag bits?  That's basically most
> of the struct pointers on those architectures, no?

Yes, pretty much.

This is an inevitable consequence of the problem at hand. For aligned 
pointers we must consult the red-black tree no matter what solution we 
pick, because the compiler may have aligned a pointer for us.

Just to make sure we're on the same page here. This stuff is only about 
how to improve performance (compared to the patch proposed for emacs-27 
in Bug#41321#332) by doing fast checks on words before giving them to 
the red-black search.