[Mesa-dev] [PATCH] i965/fs: Eliminate pointless self-moves.

[Matt Turner]

On Sat, Nov 3, 2012 at 8:44 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> We sometimes generate these, and they're so easy to remove...
>
> shader-db results:
> total instructions in shared programs: 1394522 -> 1394500 (-0.00%)
> instructions in affected programs:     6533 -> 6511 (-0.34%)
>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/brw_fs.cpp | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 777879e..711cde7 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -1379,9 +1379,15 @@ fs_visitor::dead_code_eliminate()
>     foreach_list_safe(node, &this->instructions) {
>        fs_inst *inst = (fs_inst *)node;
>
> -      if (inst->dst.file == GRF && this->virtual_grf_use[inst->dst.reg] <= pc) {
> -        inst->remove();
> -        progress = true;
> +      bool self_move =
> +         inst->opcode == BRW_OPCODE_MOV && !inst->saturate &&
> +         inst->dst.equals(inst->src[0]);
> +      bool never_used =
> +         inst->dst.file == GRF && this->virtual_grf_use[inst->dst.reg] <= pc;
> +
> +      if (self_move || never_used) {
> +         inst->remove();
> +         progress = true;
>        }
>
>        pc++;
> --
> 1.8.0

Makes sense to me.

Reviewed-by: Matt Turner <mattst88 at gmail.com>