Allocation of PASM registers (in PASM mode)

[Will Coleda]

On Sat, Jan 10, 2009 at 11:28 PM, Allison Randal <allison at parrot.org> wrote:
> Klaas-Jan Stol wrote:
>> hi,
>>
>> There is one minor detail on register allocation unclear to me,
>> regarding PASM registers (in PASM files).
>> When using/specifying PASM registers in PASM code, must these exact
>> registers be used, or should the PASM compiler do the allocation?
>>
>> So, when writing:
>>
>> new P42, 'Integer'
>> set P42, 100
>> print P42
>>
>> Should P42 be mapped to P0 (i.e. the first available register), or
>> should P42 be used (thus allocating at least 43 (counting from 0)
>> registers).
>> It's the difference between full power to the user (s/he might know what
>> s/he's doing), or doing the allocation for the user.
>>
>> IMCC was originally written to handle the register allocation, as the
>> default assembler did not handle that (which basically implies that
>> register allocation should not be done in PASM mode). I do  not intend
>> to change the implementation of IMCC (which, AFAIK, does register
>> allocation even in PASM mode), but for PIRC, I can go either way: submit
>> the PASM registers to the register allocator/optimizer, or use the
>> registers as specified by the user.
>
> As far as the user is concerned, they have no guarantee that P42 is
> allocated to any particular register. The only guarantee they have is
> that P42 will hold the value they stored in it for as long as that value
> is used within the program. This allows us to plug in any number of
> allocation schemes behind the scenes.
>
> In PIRC you're free to do whatever you want, but I prefer option B):
> intelligently allocate registers, and don't allocate 1000 registers just
> because someone used P999.
>
> Allison
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>

If P42 in PASM acts the same way as $P42 in PIR, why do we have two
different ways to say the same thing?



-- 
Will "Coke" Coleda