[m-rev.] for review: enumeration argument packing

[Julien Fischer]

On Mon, 4 Jul 2011, Peter Wang wrote:

> On 2011-07-01, Julien Fischer <juliensf at csse.unimelb.edu.au> wrote:
>>
>> Hi Peter,
>>
>> On Mon, 27 Jun 2011, Peter Wang wrote:
>>
>>> Branches: main
>>>
>>> Pack consecutive enumeration arguments in discriminated union types into a
>>> single word to reduce cell sizes.  Argument packing is only enabled on C
>>> back-ends, and reordering arguments to improve opportunities for packing is
>>> not yet attempted.  The RTTI implementations for other back-ends will need to
>>> be updated, but that is best left until after any argument reordering change.
>>>
>>> Modules which import abstract enumeration types are notified so by writing
>>> declarations of the form:
>>>
>>> 	:- type foo where type_is_abstract_enum(NumBits).
>>>
>>> into the interface file for the module which defines the type.
>>
>> I have a couple of questions regarding this:
>>
>> * Is this option safe in the presence (possibly, by disabling it) of
>>   --cross-compiling?
>
> I don't know what effect --cross-compiling should have, if any.

--cross-compiling disables all optimizations that rely on features of
a specific machine, e.g. the word size of that machine.

> The packing uses the --bits-per-word option to know how many arguments
> can be packed together.

In which case, --cross-compiling should imply --no-allow-argument
packing.

>> * Do the C grades in which the optimization is supported include grades
>>   in which --highlevel-data is enabled?  e.g. the hl.gc grade.
>
> Presumably if you wanted high-level data, you wouldn't want to deal with
> argument packing yourself.  In hl grades we might want to use C
> bit-field syntax. For now I will make --highlevel-data imply
> --no-allow-argument-packing.

Ok.

Julien.
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