bug#41357: 28.0.50; GC may miss to mark calle safe register content

[Eli Zaretskii]

> Cc: bug-gnu-emacs@gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sun, 17 May 2020 10:08:00 -0700
> 
> It's a low-level problem in which the garbage collector is not seeing some
> objects that it should see, because at the machine level the object addresses
> are in registers that the garbage collector hasn't saved and thus won't see 
> when
> it scans memory.

Since we write in C and in Lisp, not in assembly, I struggle to see
how a Lisp object could appear in a register without leaving any trace
on the stack.  I'm probably missing something.