Re: Some experience with the igc branch

[Helmut Eller <eller.helmut@gmail.com>]

On Mon, Dec 23 2024, Pip Cet wrote:

>> sxhash_eq doesn't fly with headerless objects.
>
> Which objects would that be?
>
> Right now all IGC objects have headers, right?  Did I miss any?

Right, but I'd like to keep that option on the table.

>> It should be obsoleted, IMO.

[...]
> That leaves conses.  My guess so far was that you wanted to implement a
> hack where a headerless cons is a two-word object that would turn into a
> tagged pointer to another two-word object with a header as soon as its
> hash value is taken.  That requires slowing down either XCAR or XCDR, I
> think, and that's sufficient reason for me not to do it, but I guess I
> misunderstood your plans.  This would also mean sxhash_eq would allocate
> memory, so it couldn't be called from a signal handler without yet
> another workaround.

I would go the obvious way: use segregated allocation.  Each Lisp_Type
gets its own MPS pool, without igc-headers.  The dflt pool would only
contain non-lisp types, like IGC_OBJ_STRING_DATA, with igc-headers.
That wouldn't slow down XCAR, but it requires that hash tables use MPS's
location dependencies.

Helmut