[Mesa-dev] [PATCH 3/3] st/mesa: skip lower_output_reads when possible

[Nicolai Hähnle]

On 29.11.2016 12:41, Marek Olšák wrote:
> For the series:
>
> Reviewed-by: Marek Olšák <marek.olsak at amd.com>
>
> It was a matter of time that this would resurface again. We used to
> have this, but some people didn't want it and removed it.

I can see how not reading from outputs might make life easier for some 
drivers, but with the way we use LLVM, it was just redundant.


> I wonder if radeonsi implements output indirect indexing exactly like
> temps, or if there are differences.

Not quite. TCS is completely different, but in other shader stages 
output indirect indexing uses the "fallback" path that builds an 
LLVM-level vector out of the relevant part of the output file, then does 
insertelement, then stores everything back to the output file.

Temporary indirect indexing should always use the path where the array 
is one big alloca (or one alloca per component), and we load/store from 
a pointer into that array. The fallback path should only be used when 
the state tracker doesn't provide ArrayIDs.

If indirect indexing of outputs becomes a problem, we could try to 
communicate ArrayIDs of outputs to improve that code.

Nicolai


>
> Marek
>
>
> On Tue, Nov 29, 2016 at 12:01 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>>
>> ---
>>  src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> index 8a247ea..7720edf 100644
>> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> @@ -6438,21 +6438,22 @@ get_mesa_program_tgsi(struct gl_context *ctx,
>>
>>     v->have_sqrt = pscreen->get_shader_param(pscreen, ptarget,
>>                                              PIPE_SHADER_CAP_TGSI_SQRT_SUPPORTED);
>>     v->have_fma = pscreen->get_shader_param(pscreen, ptarget,
>>                                             PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED);
>>
>>     _mesa_generate_parameters_list_for_uniforms(shader_program, shader,
>>                                                 prog->Parameters);
>>
>>     /* Remove reads from output registers. */
>> -   lower_output_reads(shader->Stage, shader->ir);
>> +   if (!pscreen->get_param(pscreen, PIPE_CAP_TGSI_CAN_READ_OUTPUTS))
>> +      lower_output_reads(shader->Stage, shader->ir);
>>
>>     /* Emit intermediate IR for main(). */
>>     visit_exec_list(shader->ir, v);
>>
>>  #if 0
>>     /* Print out some information (for debugging purposes) used by the
>>      * optimization passes. */
>>     {
>>        int i;
>>        int *first_writes = rzalloc_array(v->mem_ctx, int, v->next_temp);
>> --
>> 2.7.4
>>
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