[m-rev.] more LLDS accurate GC fixes

[Peter Moulder]

On Tue, Oct 14, 2003 at 02:34:59AM +1000, Fergus Henderson wrote:

> runtime/mercury_deep_copy_body.h:
> 	Don't abort when trying to copy foreign types,
> 	unless the foreign type happens to point into the Mercury heap.

Excuse my not looking too hard at the nature of this change; I'll just
ask a question to which hopefully the answer is simply "not a problem".

Could this create a problem for foreign types that are pointers, where
the implementor of the foreign code was using uniqueness on the mercury side
to keep a pure semantics?

I.e. does it allow the following code to run without a runtime error?

	copy(!.Ptr, !:PtrCopy),
	write_to_the_memory_pointed_to_by(!Ptr),
	read_from_the_memory_pointed_to_by(!.PtrCopy, X)

where

  :- mode write_to_the_memory_pointed_to_by(di, uo) is det.
  :- mode read_from_the_memory_pointed_to_by(ui, out) is det.


If that code is broken after this change (or even if it was broken even
before this change), what is the right way of implementing a foreign
type too big for pass-by-value, or for variable-size foreign types?

pjm.
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