[Mesa-dev] [PATCH] glsl_to_tgsi: Skip useless comparison instructions.

[Matt Turner]

On Tue, Dec 1, 2015 at 5:17 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Tue, Dec 1, 2015 at 8:12 PM, Matt Turner <mattst88 at gmail.com> wrote:
>> ---
>>  src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 16 ++++++++++++++--
>>  1 file changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> index 7f58b44..89ad6cd 100644
>> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
>> @@ -1655,7 +1655,13 @@ glsl_to_tgsi_visitor::visit(ir_expression *ir)
>>              st_dst_reg temp_dst = st_dst_reg(temp);
>>              st_src_reg temp1 = st_src_reg(temp), temp2 = st_src_reg(temp);
>>
>> -            emit_asm(ir, TGSI_OPCODE_SEQ, st_dst_reg(temp), op[0], op[1]);
>> +            if (ir->operands[0]->type->is_boolean() &&
>> +                ir->operands[1]->as_constant() &&
>> +                ir->operands[1]->as_constant()->is_one()) {
>> +               emit_asm(ir, TGSI_OPCODE_MOV, st_dst_reg(temp), op[0]);
>> +            } else {
>> +               emit_asm(ir, TGSI_OPCODE_SEQ, st_dst_reg(temp), op[0], op[1]);
>> +            }
>>
>>              /* Emit 1-3 AND operations to combine the SEQ results. */
>>              switch (ir->operands[0]->type->vector_elements) {
>> @@ -1708,7 +1714,13 @@ glsl_to_tgsi_visitor::visit(ir_expression *ir)
>>           st_src_reg temp = get_temp(native_integers ?
>>                                      glsl_type::uvec4_type :
>>                                      glsl_type::vec4_type);
>> -         emit_asm(ir, TGSI_OPCODE_SNE, st_dst_reg(temp), op[0], op[1]);
>> +         if (ir->operands[0]->type->is_boolean() &&
>> +             ir->operands[1]->as_constant() &&
>> +             ir->operands[1]->as_constant()->is_zero()) {
>> +            emit_asm(ir, TGSI_OPCODE_MOV, st_dst_reg(temp), op[0]);
>> +         } else {
>> +            emit_asm(ir, TGSI_OPCODE_SNE, st_dst_reg(temp), op[0], op[1]);
>> +         }
>>
>>           if (native_integers) {
>>              st_dst_reg temp_dst = st_dst_reg(temp);
>
> Reviewed-by: Ilia Mirkin <imirkin at alum.mit.edu>
>
> I'd feel a little better if you double-checked that a shader_test that
> hits this continues to pass with llvmpipe or softpipe.

I tested vs-all-bvec4-using-if.shader_test and
vs-any-bvec4-using-if.shader_test on llvmpipe. They both pass and drop
an instruction.