[CVS ci] don't trace system areas in sweep opcode

[Leopold Toetsch]

After a thorough discussion at the Parrot BOF at Paris, we got a
solution for timely destruction vs trace system areas and bogus objects.

To clean up on scope exit (and after a Perl C<undef> ins), the HL emits
a C<sweep 0> opcode. This doesn't do C<trace_system_areas> anymore,
because there is nothing unanchored and alive beyond the runloop's stack.
A DOD run triggered from any resources lackage still does trace the
system areas, so infant mortality shouldn't be an issue either (at least
when e.g. processor registers are scanned correctly too).

s. also e.g. "Timely destruction and "TRACE_SYSTEM_AREAS" in the
summary, http://xrl.us/l6c and various bug reports WRT io_2.

leo

[Brent Dax]

Leopold Toetsch:

> To clean up on scope exit (and after a Perl C<undef> ins), the HL emits
> a C<sweep 0> opcode. This doesn't do C<trace_system_areas> anymore,
> because there is nothing unanchored and alive beyond the runloop's stack.

Have I mentioned lately that you guys are geniuses?

--Brent Dax <br...@brentdax.com>
Perl and Parrot hacker

[Piers Cawley]

"Brent Dax" <br...@brentdax.com> writes:

> Leopold Toetsch:
>> To clean up on scope exit (and after a Perl C<undef> ins), the HL emits
>> a C<sweep 0> opcode. This doesn't do C<trace_system_areas> anymore,
>> because there is nothing unanchored and alive beyond the runloop's stack.
>
> Have I mentioned lately that you guys are geniuses?

You weren't at the BOF. We went 'round the loop about 5 times before
we finally got to this solution.