[Mesa-dev] [PATCH 1/7] gallium: add CONSTBUF type to tgsi_file_type

[Nicolai Hähnle]

On 23.08.2017 15:49, Ilia Mirkin wrote:
> On Wed, Aug 23, 2017 at 9:20 AM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>> On 22.08.2017 16:56, Ilia Mirkin wrote:
>>>
>>> On Tue, Aug 22, 2017 at 10:51 AM, Roland Scheidegger <sroland at vmware.com>
>>> wrote:
>>>>
>>>> I am probably missing something here, but why do you need a new register
>>>> file? Since you couldn't use LOAD with TGSI_FILE_CONSTANT before, can't
>>>> you just allow LOAD with TGSI_FILE_CONSTANT and achieve the same thing?
>>>> Or do you need to know how it's going to be accessed in advance?
>>>
>>>
>>> With bindless, LOAD can take a CONST I believe [which contains the
>>> value of the bindless id]. I think it's nice to keep those concepts
>>> separate... having CONST sometimes mean the value and other times mean
>>> the address is a bit weird. This way CONSTBUF[0] is the address of the
>>> 0th constbuf.
>>
>>
>> I'm still not quite convinced. The levels of indirection should clarify the
>> meaning, shouldn't they?
>>
>> You get
>>
>>    LOAD dst, CONST[0][0], IMM[0]
>>
>> when loading from offset IMM[0] of a bindless buffer whose handle is at the
>> beginning of the buffer CONST[0].
>>
>> You get
>>
>>    LOAD dst, CONST[0], IMM[0]
>>
>> when loading from offset IMM[0] of non-bindless buffer 0.
>>
>> Is there ever really a situation where the two could be confused?
> 
> I always considered CONST[0] == CONST[0][0]. Technically they're not,
> since once has the second dimension in the TGSI encoding while the
> other doesn't. But practically,
> 
> MOV TEMP[0], CONST[0]
> 
> and
> 
> MOV TEMP[0], CONST[0][0]
> 
> are in every way identical. Currently st/mesa will just use CONST[0]
> everywhere, never adding the 2nd dimension. As such, I don't think we
> should start having behavioural differences for those on some
> instructions.

Oh, you're right, CONST[n] and CONST[0][n] are treated the same. That's 
pretty inconsistent and unfortunate :/

I suppose the CONSTBUF thing is fine, then.

Cheers,