[Mesa-dev] [PATCH 3/7] glsl/lower_if: don't lower branches touching tess control outputs

[Marek Olšák]

On Wed, Nov 2, 2016 at 2:55 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> On 29.10.2016 01:13, Marek Olšák wrote:
>>
>> From: Marek Olšák <marek.olsak at amd.com>
>>
>> ---
>>  src/compiler/glsl/ir_optimization.h           |  3 ++-
>>  src/compiler/glsl/lower_if_to_cond_assign.cpp | 23
>> ++++++++++++++++++++---
>>  src/compiler/glsl/test_optpass.cpp            |  2 +-
>>  src/mesa/drivers/dri/i965/brw_link.cpp        |  2 +-
>>  src/mesa/program/ir_to_mesa.cpp               |  3 ++-
>>  src/mesa/state_tracker/st_glsl_to_tgsi.cpp    |  3 ++-
>>  6 files changed, 28 insertions(+), 8 deletions(-)
>>
> [snip]
>>
>> @@ -105,20 +109,33 @@ check_ir_node(ir_instruction *ir, void *data)
>>     case ir_type_call:
>>     case ir_type_discard:
>>     case ir_type_loop:
>>     case ir_type_loop_jump:
>>     case ir_type_return:
>>     case ir_type_emit_vertex:
>>     case ir_type_end_primitive:
>>     case ir_type_barrier:
>>        v->found_unsupported_op = true;
>>        break;
>> +
>> +   case ir_type_dereference_variable: {
>> +      ir_variable *var =
>> ir->as_dereference_variable()->variable_referenced();
>> +
>> +      /* Tess control shader outputs are like shared memory with complex
>> +       * side effects, so treat it that way.
>> +       */
>> +      if (v->stage == MESA_SHADER_TESS_CTRL &&
>> +          var->data.mode == ir_var_shader_out)
>> +         v->found_unsupported_op = true;
>> +      break;
>> +   }
>> +
>
>
> I don't understand this rationale. What side effects are there, and can you
> give an example where the transformation would be wrong?

Well I can't think of a case now where it would break something.

Marek