[Mesa-dev] [PATCH] i965: Delete most of the linked GLSL IR when using NIR.

[Jason Ekstrand]

On May 5, 2015 10:17 PM, "Tapani Pälli" <tapani.palli at intel.com> wrote:
>
>
> On 05/06/2015 04:57 AM, Kenneth Graunke wrote:
>>
>> Vertex shader attribute and fragment shader output queries rely on being
>> able to inspect top-level ir_variable objects.  So, we have to keep
>> those.  However, functions and global temporary variables can be deleted
>> with impunity.
>>
>> Saves 58MB of memory when replaying a Dota 2 trace on Broadwell.
>>
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
>> ---
>>   src/mesa/drivers/dri/i965/brw_shader.cpp | 43
+++++++++++++++++++++++++++++++-
>>   1 file changed, 42 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp
b/src/mesa/drivers/dri/i965/brw_shader.cpp
>> index c1fd859..6e4abb2 100644
>> --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
>> @@ -138,6 +138,45 @@ brw_lower_packing_builtins(struct brw_context *brw,
>>      lower_packing_builtins(ir, ops);
>>   }
>>
>> +static bool
>> +is_vert_input_or_frag_output(gl_shader_stage stage, ir_variable *var)
>
>
> I believe you'll need to save any input and output independent of shader
stage as with GL_ARB_program_interface_query application can query if some
input or output is referenced by a given stage. Did you encounter any
failures on Piglit tests?
>
> I've been working to get rid of ir_variable on the background but it has
taken a bit of time as there seems to be always something else to be worked
first 'priority wise' ... but I think this is a nice start anyways to get
rid of most IR in memory.

Do you have a branch somewhere with that work in it?  I would be interested
in taking a look at it.  I probably won't really work on it but i would, at
the very least, like to see where all the ir_variable's end up getting tied
in.
--Jason

>> +{
>> +   if (var) {
>> +      if (stage == MESA_SHADER_VERTEX) {
>> +         return var->data.mode == ir_var_shader_in ||
>> +                var->data.mode == ir_var_system_value;
>> +      }
>> +
>> +      if (stage == MESA_SHADER_FRAGMENT) {
>> +         return var->data.mode == ir_var_shader_out;
>> +      }
>> +   }
>> +   return false;
>> +}
>> +
>> +/**
>> + * Delete GLSL IR except for VS inputs and FS outputs.
>> + *
>> + * Once we've translated to NIR, we don't need most of the linked GLSL
IR anymore.
>> + * However, GL API calls for introspecting certain shader inputs/outputs
>> + * (shader_query.cpp) require us to keep some top-level ir_variables.
>> + */
>> +static void
>> +delete_most_glsl_ir(struct gl_shader *shader)
>> +{
>> +   void *mem_ctx = ralloc_context(NULL);
>> +   ralloc_adopt(mem_ctx, shader->ir);
>> +
>> +   foreach_in_list_safe(ir_instruction, ir, shader->ir) {
>> +      if (!is_vert_input_or_frag_output(shader->Stage,
ir->as_variable()))
>> +         ir->remove();
>> +   }
>> +
>> +   reparent_ir(shader->ir, shader->ir);
>> +   ralloc_free(mem_ctx);
>> +}
>> +
>> +
>>   static void
>>   process_glsl_ir(struct brw_context *brw,
>>                   struct gl_shader_program *shader_prog,
>> @@ -297,8 +336,10 @@ brw_link_shader(struct gl_context *ctx, struct
gl_shader_program *shProg)
>>
>>         brw_add_texrect_params(prog);
>>
>> -      if (options->NirOptions)
>> +      if (options->NirOptions) {
>>            prog->nir = brw_create_nir(brw, shProg, prog,
(gl_shader_stage) stage);
>> +         delete_most_glsl_ir(shader);
>> +      }
>>
>>         _mesa_reference_program(ctx, &prog, NULL);
>>      }
>>
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