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

[Ilia Mirkin]

On Tue, Aug 22, 2017 at 7:25 PM, Timothy Arceri <tarceri at itsqueeze.com> wrote:
>
>
> On 23/08/17 09:08, Ilia Mirkin wrote:
>>
>> On Tue, Aug 22, 2017 at 6:55 PM, Timothy Arceri <tarceri at itsqueeze.com>
>> wrote:
>>>
>>>
>>>
>>> On 23/08/17 00:56, 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.
>>>
>>>
>>>
>>> Yeah. I think we also may need another type for bindless as I'm planning
>>> to
>>> use TGSI_FILE_CONSTANT for regular uniforms. The plan is to use LOAD for
>>> supporting packed uniforms rather than padding everything to vec4.
>>
>>
>> Shouldn't be necessary... we can think of CONST (and TEMP and IMM) as
>> "value" registers, and MEMORY/IMAGE/BUFFER/CONSTBUF as "address"
>> registers. If LOAD receives a value, then it's a bindless image
>> handle, otherwise it should work based on which of the address
>> registers it receives.
>
>
> But how do you tell the difference between a bindless image handle and a
> non-indirect uniform where the "value" is just the index of the uniform?

Easy - if the first arg is a CONSTBUF[], it's a uniform load. If it's
a value, then it's a bindless image handle. A uniform load becomes

LOAD dst, CONSTBUF[1], IMM[0].x

which would be identical to doing

MOV dst, CONST[1][5] (if IMM[0].x == 5)