[mercury-users] Compiler optimization for large number of factual clauses.

[Bartlomiej Szymczak]

On 7/3/07, Ralph Becket <rafe at csse.unimelb.edu.au> wrote:
> Bartlomiej Szymczak, Friday, 29 June 2007:
> > Hi.
> >
> > Consider the following Mercury code:
> >
> > :-type c --->
> >        c_1;
> >        c_2;
> > ....(thousands of entries)
> >        c_99999.
> >
> > :-pred rel(c,c).
> > :-mode rel(in,in) is semidet.
> > :-mode rel(in,out) is nondet.
> > :-mode rel(out,in) is nondet.
> >
> > rel(c_1,c_2).
> > rel(c_1,c_3).
> > rel(c_3,c_1).
> > ....(thousands of entries)
> > rel(c_99999,c_3).
> >
> > I want to ask how fast the "rel" predicate is. Will the compiler
> > optimize it by adding some hash table based lookup? Are all three
> > modes equivalently efficient? I need it to work as fast as possible,
> > as "rel" is called very often in the remaining code.
>
> The Mercury compiler goes to some lengths to compile switch based code
> efficiently.  Your c type data constructors will be represented as integers
> and some hash or tree scheme will be used to implement rel.
>
> I've just run some quick tests and  performance appears
> constant regardless of the number of constructors involved.
>
> -- Ralph
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>

That's amazing. It will save me some work then. Thanks!
-- 
Bartlomiej Antoni Szymczak

Gmail: rhywek at gmail.com
Work mail: bas at imm.dtu.dk
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