Re: [Caml-list] How much optimized is the 'a option type ?

[Yotam Barnoy <yotambarnoy@gmail.com>]

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That reminds me -- what is the situation regarding inlining? Is there work
being done on inlining from other modules? Is heavy inlining being done
within a module? Would it be possible to annotate with [@@inline] to give
hints to the compiler at some point?

-Yotam


On Fri, Jan 17, 2014 at 9:36 AM, Markus Mottl <markus.mottl@gmail.com>wrote:

> Others have already answered about memory representation, but there is
> one thing about allocations that many OCaml programmers may not yet be
> aware of and that can make a noticeable performance difference when
> used wisely: the OCaml compiler will inspect your code and, under the
> right conditions, batch together allocations.  E.g. consider this
> function (references are records, btw.):
>
>   let f n =
>     let x = ref (ref (Some (Some n))) in
>     [(x, n); (x, n)]
>
> One might naively assume that this would lead to seven or so
> allocations.  But if you inspect the assembly, you'll see only one
> allocation followed by mere initialization assignments.
>
> Such allocation batches can break if, for example, the code calls
> non-inlined (e.g. recursive or external) functions.  I'm not quite
> sure about all the rules there, but it's generally trivial to just
> look at the assembler output to find out what the compiler is doing.
> In some cases merely calling all functions before any allocations take
> place can speed up your code.  There are even cases where it may be
> more efficient to allocate several values in one chunk though only
> some may be needed depending on branches taken later.
>
> Regards,
> Markus
>
> On Fri, Jan 17, 2014 at 2:35 AM, Damien Guichard <alphablock@orange.fr>
> wrote:
> > Hello,
> >
> > Compared to the code :
> >
> > type 'a option = None | Some of 'a
> >
> > How do an 'a option value performs ?
> > Any allocation saved ?
> > Any indirection removed ?
> >
> > Is 'a option just like any sum type ?
> > Or is 'a option more like an ANSI C pointer type ?
> >
> > Regards,
> >
> > Damien Guichard
> >
> >
> >
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>
> --
> Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com
>
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