[m-rev.] for review: fix expand equivalence type for special preds bug

[Fergus Henderson]

On 08-Nov-2002, Peter Ross <pro at missioncriticalit.com> wrote:
> fjh wrote:
> > > compiler/rtti.m:
> > > Record the the actual argument types for a special predicate
> > > in the rtti_proc_label type.
> >
> > What was the rationale for this bit of the change?
>
> Because the expanded types are needed in ml_gen_proc_params_from_rtti.

Oh, I see.  I was confused by your terminology change from
"actual argument types" to "expanded argument types".

> > > compiler/ml_call_gen.m:
> > > compiler/ml_closure_gen.m:
> > > compiler/ml_code_gen.m:
> > > compiler/ml_code_util.m:
> > > Use the types where all the equivalence types have been
> > > eliminated.
> > >
> > > compiler/type_util.m:
> > > Add a utility predicate to expand out equivalence types.
> >
> > Hmm.  Expanding these on the fly all the time seems like it could be
> > a bit inefficient (as far as compile time is concerned).
>
> The results of the expansion could be cached in pred_info and proc_info
> structures,

That would probably be worse -- the memory size increase for the
extra field would probably slow things down considerably.

I don't see a better solution off-hand.  But it might be a good idea to
measure the effect of your patch on compilation time, so that we know
whether this is worth worrying about.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  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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