[m-rev.] diff/for post-commit review: no stack slots for dummy types

[Fergus Henderson]

On 02-Sep-2004, Zoltan Somogyi <zs at cs.mu.OZ.AU> wrote:
> trace/mercury_trace.c:
> 	Adapt the test for whether a retry is across I/O. We used to base the
> 	test on whether the retried predicate has any I/O state arguments,
> 	and if so, whether the original I/O state variable is still around
> 	on the stack. After this change, the answer to the second half of
> 	that question would always be "no", so we now use only the first half:
> 	whether the retried predicate has any I/O state arguments. This
> 	requires us to consider more retries to be retries across I/O, but
> 	from the point of view of a user who may not remember whether the I/O
> 	predicate has done any I/O so far or not, is arguably more consistent
> 	than our previous policy.
> 
> 	Allow retries even if a value of type store.store is missing, since
> 	store.store is a dummy type just as io.state is.

Allowing retries if a value of type store.store is missing is not safe,
in the same sort of way that retrying I/O is not safe.  Actually more so,
because I/O is more often used for diagnostics than for storing and
retrieving values, whereas store.store is *always* used for storing and
retrieving values.  So allowing retries across procedures that have di-moded
store.store arguments doesn't sound like a good idea to me.

-- 
Fergus Henderson                    |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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