[Mesa-dev] [PATCH 2/4] gallium: Add PIPE_SHADER_CAP_INDIRECT_TEMP_ARRAY_ADDR

[Christoph Bumiller]

On 25.11.2012 23:31, Marek Olšák wrote:
> On Thu, Nov 8, 2012 at 7:08 PM, Christoph Bumiller
> <e0425955 at student.tuwien.ac.at> wrote:
>> DCL TEMP[0..3] = "array" without indirect access (registers)
>> DCL TEMP[4..12] = indirectly accessed array
>> DCL TEMP[12..20] = another indirectly accessed array
>> DCL IMM[0] { -2, 0, 0, 0 }
>>
>> fill with data:
>> MOV TEMP[4], IN[1]
>> MOV TEMP[5], IN[2]
>> etc.
>>
>> indirect move with address (IN[0].x - 2) from array TEMP[4..12] to output:
>> UADD TEMP[0].x, IN[0].x, IMM[0].x <- added here explicitly instead of
>> using (4 - IMM[0].x == 2) in the MOV below
>> UARL ADDR[0].x, TEMP[0].x
>> MOV OUT[1], TEMP[ADDR[0].x + 4] <- must be 4 here to identify the
>> array/range (iff there is indirect addressing)
> I don't like this. It looks hackish. I think it would be better to
> have the array clearly specified in the declaration and in the
> instruction. For example like this:
Of course it looks hackish, if you want to add a new (3rd) index field
to TGSI sources and declarations you're welcome to do so.
I really want a solution that doesn't just work for TEMPs but also the
other files, especially INPUT and OUTPUT, where the 2nd index is already
taken (vertex index, in geometry and tessellation shaders), otherwise
someone will have to do this all over again at a later point.

Btw. for non-vec4 arrays we can use the UsageMask and e.g. declare a
scalar array with TEMP[0][0..3].x so the driver can pack it.

>
> DCL TEMP[0][0..3] = "array" without indirect access (registers)
> DCL TEMP[1][0..7] = indirectly accessed array
> DCL TEMP[2][0..7] = another indirectly accessed array
> DCL TEMP[3] = ill-formed declaration
>
> And in the instruction:
>
> MOV OUT[1], TEMP[1][ADDR[0].x]
>
> That said, I don't know how the temporary array file is implemented in
> TGSI. I would have to see some TGSI shader code first. If it's
> implemented just like my example shows, then I'm all for it and we can
> later deprecate the TEMPORARY file once all drivers support
> TEMPORARY_ARRAY.
>
> Marek