Re: [Caml-list] Functor Performace Question

From: "Till Varoquaux" <till.varoquaux@gmail.com>
To: "Jim Grundy" <jim.d.grundy@intel.com>
Cc: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Functor Performace Question
Date: Wed, 11 Apr 2007 00:37:52 +0200	[thread overview]
Message-ID: <9d3ec8300704101537q30f1c5dsad0b72f0255b3b3d@mail.gmail.com> (raw)
In-Reply-To: <461C0C71.7060709@intel.com>

Functors are computed at run time... defunctorisation has been studied
for Ocaml before [1], however the current implementation of reccursive
modules relies on these modules not being defunctorised (The process
is being made in a lazy like way at runtime since fix point cannot
always be reached during compilation).

Like monorphisation defunctorisation is a whole program optimization
technique that relies on the existence of a finite number of cases.
However ocaml is not about whole program optimizations nor are we
dealing with finite universes (in the general case, although more than
90% of the ocaml programs don't uses these corner cases). I doubt we
will see these in a caml compiler any time soon.

Till

P.S.: You should take my answer with a grain of salt: I'm not
affiliated in anyways with ocaml development team.

[1]http://www.lri.fr/~signoles/publis/signoles06defun.ps.gz

On 4/11/07, Jim Grundy <jim.d.grundy@intel.com> wrote:
> I have a functor related performance issue.
>
> I have the following collection of modules and types that we are using
> in the implementation of a SAT solver:
>
> module type Map = sig .. end
>
> module Nat_map: Map with type key = int
>
> module type PriorityQueue = sig .. end
>
> module Make_priority_queue:
>    functor (M : Map) -> PriorityQueue with type elt = M.key
>
> module Nat_priority_queue: PriorityQueue  with type elt = int
>
> If we implement Nat_priority_queue in the "right" way as
>
> module Nat_priority_queue = Make_priority_queue (Nat_map)
>
> Then I pay about a 3% performance penalty over instantiating the functor
> by hand...
>
> module Nat_priority_queue  = struct
>    module M = Nat_map
>    (* same code as the body of Make_priority_queue *)
> end
>
> Is there some compiler switch or future version in the works that will
> save me from this?
>
> Thanks
>
> Jim
>
>
> --
> Jim Grundy, Research Scientist. Intel Corporation, Strategic CAD Labs
> Mail Stop RA2-451, 2501 NW 229th Ave, Hillsboro, OR 97124-5503, USA
> Phone: +1 971 214-1709   Fax: +1 971 214-1771
> http://www.intel.com/technology/techresearch/people/bios/grundy_j.htm
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>
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