Re: [Caml-list] Accelerating compilation

[Romain Bardou <romain.bardou@inria.fr>]

Le 06/09/2013 17:18, Gabriel Scherer a écrit :
> Those are all good points, but they would be just as appropriate as
> feature requests in the OCaml bugtracker (
> http://caml.inria.fr/mantis/ ).

Actually Xavier Clerc noticed me that there is already a related feature
request:
http://caml.inria.fr/mantis/view.php?id=6102

> I think it should not be too difficult to add a flag to the compiler
> to only produce .cmi files out of its source inputs, and not also a
> .cmo (or also a .cmx) as is currently done. If you (or anyone
> interested in contributing) are interested in providing a patch for
> this, I'm more than ready to review the patch to help upstream
> integration. I'd consider this "junior job" difficulty.

Thanks for your review proposal. I might actually consider doing this
the day it becomes too much of a pain. FR#6102 actually have a patch
attached which looks like a nice starting point.

> 
> Integrating this into build systems may be trickier because, as Markus
> noted, just asking for the .cmi of the main module of your project
> will recursively build .cmi from the .mli of its dependencies, without
> checking that the .ml matches them. You could add a phony rule/stamp
> .impl.cmi that is handled differently by the build system (basically
> like .cmo, except they would be empty).
> 
> Your points (2) and (3) are well noted. I've personally been thinking
> about an optional -use-timestamp option for ocamlbuild, but devoted my
> own contribution time to other things this summer.
> 
> 
> Markus Mottl wrote:
>> I'm not sure what you are referring to, OCamlBuild does already
>> support parallel builds.
> 
> While there is support for parallel compilation in ocamlbuild (...
> except on Windows, I'm afraid), I've often found out that it doesn't
> parallelize much in practice because of current implementation
> limitations -- but if you have success stories about this I'd be glad
> to hear about them. Improving on this is on the medium-term
> ocamlbuild-development TODO list.
> 
> On Fri, Sep 6, 2013 at 3:56 PM, Romain Bardou <romain.bardou@inria.fr> wrote:
>> Hello list,
>>
>> As my project grows bigger, it is becoming much less efficient to use
>> the type-checker to quickly find places in my code which must be updated
>> (e.g. pattern-matching). Here is a wishlist for improvements.
>>
>> 1) Separate typing and code generation, in ocamlc and in ocamlopt
>>
>> For instance, provide an option -typing-only which would mean "only
>> produce the .cmi but do not produce the .cmo or the .cmx". The compiler
>> would only need the .cmi of the dependencies, not their .cmo or .cmx.
>> This would make it possible to have a Makefile target, or an Ocamlbuild
>> option, to just type.
>>
>> Also, provide an option -do-not-retype which would mean "if the .cmi
>> exists, load it instead of type-checking again". This would allow the
>> build process to first type-check (using -typing-only) and then generate
>> the code without type-checking again (using -do-not-retype). Of course
>> the build system should be very careful to ensure the .cmi is
>> up-to-date. This option could also help when compiling both in bytecode
>> and in native code. This option is not necessary to just find errors
>> quickly, though.
>>
>> 2) Be able to disable Ocamlbuild's digest mechanism and use dates and
>> file sizes instead
>>
>> If I am not mistaken, this is one of the main reasons why Ocamlbuild is
>> slower that make. It does help to prevent useless recompilation, but
>> what good does it make to prevent a useless recompilation once in a
>> while if it is at the cost of losing a lot of time in all other cases?
>> I'm sure it is project-dependent though so it should only be an option,
>> say, -do-not-hash, or -comparison-mode dateandsize.
>>
>> 3) Parallel compilation in Ocamlbuild
>>
>> Of course it would help but it is not easy to implement so I'm just
>> putting it there to be exhaustive.
>>
>> I think the most important point is the first one, as the other two
>> depend on the build system, and they have been debated already. I'm not
>> aware of any discussion about separing typing and code generation
>> though. What do you think about that?
>>
>> Cheers,
>>
>> --
>> Romain Bardou
>>
>> --
>> Caml-list mailing list.  Subscription management and archives:
>> https://sympa.inria.fr/sympa/arc/caml-list
>> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>> Bug reports: http://caml.inria.fr/bin/caml-bugs
>