[RFC] PPC64: Vector Function ABI for Power Architecture

[Bill Schmidt]

On 11/22/19 2:58 PM, GT wrote:
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Friday, November 22, 2019 3:34 PM, Bill Schmidt <wschmidt@linux.ibm.com> wrote:
>
>> On 11/22/19 2:27 PM, Tulio Magno Quites Machado Filho wrote:
>>
>>> GT tnggil@protonmail.com writes:
>>>
>>>> 1.  The document is hosted at URL: https://github.com/power8-abi-doc
>>>> 2.  Bill Schmidt, cc'ed here, is the IBMer ultimately responsible for the document.
>>>>
>>>> The pdf does not render quite right - so for feedback regarding visual presentation of the document, first download the html and open it in a browser. Please use the ABI's rendering in a browser as the basis for any recommendations on its formatting.
>>>> In section "Vector Function Name Mangling", I'm afraid we can't leave the <isa>
>>>> with an entry as generic as VSX.
>>> There are VSX instructions included in ISA 3.0 that will not execute in ISA
>>> 2.07. So, I think we need 2 <isa> entries there:
>>>
>>> 1.  ISA 2.07, which is the minimum ISA required in this document.
>>> 2.  ISA 3.0
> We have not used any instructions introduced in ISA 3.0. Can I simply have a single
> entry indicating ISA 2.07? Or should it be ISA 2.07+ (i.e. ISA at or above v2.07)?
> Or do we still really need 2 separate entries?
>
> Thanks.
> Bert.

ABI decisions shouldn't be based only on the current implementation.  
It's possible that we would later want to make use of ISA 3.0 
instructions in a future implementation of these same interfaces.  
Furthermore, it becomes even more likely as we move ahead into later 
versions of the ISA.  So I think it's best to be flexible and assign 
2.07 and 3.0 today, with the understanding that we will continue to add 
to this as ISA levels are released.

For today's implementations, the VSX/2.07 mangling would be the only one 
in use, so we're not asking for any changes in the implementation.

Thanks!
Bill