Re: Conservative GC isn't safe

[Eli Zaretskii]

> Cc: address@hidden, address@hidden
> From: Daniel Colascione <address@hidden>
> Date: Mon, 28 Nov 2016 11:40:22 -0800
> 
> > I already answered that up-thread: it will be dead code, and thus will
> > likely do the wrong thing if it ever runs.
> 
> We'll always have stray pointers to object interiors that will exercise 
> these code paths. I've broken enough of them recently enough to know.

We are not talking about broken code.  It's easy to get yourself hung
in Emacs by writing bad code.  Writing additions to GC to detect bad
code is not a good use of CPU cycles and of our time.

> > I also suggested what to do instead: add assertions that express what
> > we believe should never happen.  Stefan says doing that is unlikely to
> > be justified by the dangers, but if we think so, then we shouldn't be
> > afraid of the problem in the first place.  If we are, then adding
> > assertions is the way to go.
> 
> It's not possible to assert, statically or dynamically, that we don't 
> have this problem.

If we cannot assert the invariants, either we don't really understand
the problem, or the problem doesn't exist in the first place (or
both).