[PATCH] Add a way to define the bit range covered by a SubRegIndex.

[Ahmed Bougacha]

On Thu, May 30, 2013 at 4:26 PM, Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote:
>
> On May 30, 2013, at 2:44 PM, Ahmed Bougacha <ahmed.bougacha at gmail.com> wrote:
>
>> On Tue, May 28, 2013 at 1:48 PM, Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote:
>>>
>>>> -class SubRegIndex<list<SubRegIndex> comps = []> {
>>>> +class SubRegIndex<list<SubRegIndex> comps = [], int offset = -1, int size = -1> {
>>>
>>>
>>> I think we should flip these arguments around to be (size, offset, comps). That is more convenient for most targets. You can also make the offset default = 0, that is usually the right thing.
>>>
>>> In a second patch, I think it would make sense to make the size argument mandatory.
>>
>> OK then - quick update on the patch - what about this: Instead of
>> having the comps list, let ComposedOf only be settable by
>> ComposedSubRegIndex, a subclass of SubRegIndex. That way, SubRegIndex
>> only has size/offset, whereas ComposedSubRegIndex only has the A and B
>> elements of comps. (By the way, this lets us do some cleanup in
>> TableGen).
>
> I’m OK with removing the ‘comps’ argument, but we should just use:
>
> def foo : SubRegIndex<32, 32> { let ComposedOf = [a,b]; }

Well, the idea behind removing comps was that the subclass had two
(small) advantages:
- you don't have to specify the size/offset (as they can/should be
inferred from the pair)
- the fact that the list is a pair is enforced by the template
arguments instead of the TableGen code.

It's not a big deal anyway though.

-- Ahmed Bougacha

> /jakob
>