[Mesa-dev] [PATCH 10/10] i965/fs: Add algebraic optimizations for MAD.

[Matt Turner]

On Mon, Feb 9, 2015 at 6:00 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> On Wednesday, February 04, 2015 08:21:27 PM Matt Turner wrote:
>> total instructions in shared programs: 5764176 -> 5763808 (-0.01%)
>> instructions in affected programs:     25121 -> 24753 (-1.46%)
>> helped:                                164
>> HURT:                                  2
>> ---
>>  src/mesa/drivers/dri/i965/brw_fs.cpp | 26 ++++++++++++++++++++++++++
>>  1 file changed, 26 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> index 69602a7..6f36e39 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> @@ -2417,6 +2417,32 @@ fs_visitor::opt_algebraic()
>>              }
>>           }
>>           break;
>> +      case BRW_OPCODE_MAD:
>> +         if (inst->src[1].is_zero() || inst->src[2].is_zero()) {
>> +            inst->opcode = BRW_OPCODE_MOV;
>> +            inst->src[1] = reg_undef;
>> +            inst->src[2] = reg_undef;
>> +            progress = true;
>> +         } else if (inst->src[0].is_zero()) {
>> +            inst->opcode = BRW_OPCODE_MUL;
>> +            inst->src[0] = inst->src[2];
>> +            inst->src[2] = reg_undef;
>> +         } else if (inst->src[1].is_one()) {
>> +            inst->opcode = BRW_OPCODE_ADD;
>> +            inst->src[1] = inst->src[2];
>> +            inst->src[2] = reg_undef;
>> +            progress = true;
>> +         } else if (inst->src[2].is_one()) {
>> +            inst->opcode = BRW_OPCODE_ADD;
>> +            inst->src[2] = reg_undef;
>> +            progress = true;
>> +         } else if (inst->src[1].file == IMM && inst->src[2].file == IMM) {
>> +            inst->opcode = BRW_OPCODE_MUL;
>
> Shouldn't this be BRW_OPCODE_ADD?
>
> MAD is src0 + src1 * src2.  If src1 and src2 are IMM, then we should
> make this ADD src0 (src1 * src2).
>
> With that fixed, and the shader-db numbers confirmed, patches 9-10 are:
> Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

Whoops. Yes indeed.

Thanks!