On Tue, Jan 20, 2015 at 12:53 AM, Kenneth Graunke <kenn...@whitecape.org> wrote:
> On Monday, January 19, 2015 03:31:09 PM Matt Turner wrote:
>> ---
>> src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
>> b/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
>> index 81be4de..d66808b 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp
>> @@ -85,6 +85,17 @@ fs_visitor::dead_code_eliminate()
>> }
>> }
>>
>> + if ((inst->opcode != BRW_OPCODE_IF &&
>> + inst->opcode != BRW_OPCODE_WHILE) &&
>> + inst->dst.is_null() &&
>> + !inst->has_side_effects() &&
>> + !inst->writes_flag() &&
>> + !inst->writes_accumulator) {
>> + inst->opcode = BRW_OPCODE_NOP;
>> + progress = true;
>> + continue;
>> + }
>> +
>> if (inst->dst.file == GRF) {
>> if (!inst->is_partial_write()) {
>> int var = live_intervals->var_from_reg(inst->dst);
>>
>
> Seems like these should be handled too...
>
> - BRW_OPCODE_ELSE
> - FS_OPCODE_DISCARD_JUMP
> - FS_OPCODE_PLACEHOLDER_HALT
> - SHADER_OPCODE_SHADER_TIME_ADD
These have BAD_FILE destinations.
> - SHADER_OPCODE_GEN4_SCRATCH_READ
> - SHADER_OPCODE_GEN4_SCRATCH_WRITE
> - SHADER_OPCODE_GEN7_SCRATCH_READ
The READs have non-null destinations (they have to return the data somewhere).
And we only emit SCRATCH_* from spilling registers as part of register
allocation. We can't ever call dead code elimination after we've
assigned registers. (Not only do we not, but it couldn't work)
> Maybe some of these should be added to has_side_effects()?
>
> I'm kind of surprised you didn't see regressions in Piglit...maybe I'm
> missing something.
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