[Mesa-dev] [PATCH] i965/vec4: Only zero out unused message components when there are any.

[Ian Romanick]

On 09/09/2013 01:38 PM, Kenneth Graunke wrote:
> Otherwise, coordinates with four components would result in a MOV
> with a destination writemask that has no channels enabled:
> 
> mov(8) g115<1>.F 0D { align16 WE_normal NoDDChk 1Q };
> 
> At best, this is stupid: we emit code that shouldn't do anything.
> Worse, it apparently causes GPU hangs (observable with Chris's
> textureGather test on CubeArrays.)
> 
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> Cc: Chris Forbes <chrisf at ijw.co.nz>
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> index ca52fd3..8cfe4e3 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> @@ -2245,8 +2245,10 @@ vec4_visitor::visit(ir_texture *ir)
>  	 emit(MOV(dst_reg(MRF, param_base, ir->coordinate->type, coord_mask),
>  		  coordinate));
>        }
> -      emit(MOV(dst_reg(MRF, param_base, ir->coordinate->type, zero_mask),
> -	       src_reg(0)));
> +      if (zero_mask != 0) {
> +         emit(MOV(dst_reg(MRF, param_base, ir->coordinate->type, zero_mask),
> +                  src_reg(0)));
> +      }

I'd be tempted to do this as:

    if (coord_mask != 0x0f) {
       const int zero_mask = 0x0f & ~coord_mask;

       emit(MOV(dst_reg(MRF, param_base, ir->coordinate->type, zero_mask),
                src_reg(0)));
    }

And delete the silly zero_mask loop above.

I'm also not sure why coord_mask is calculated by a loop, but I can
leave that bikeshed for another day...

Either way, the patch is

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

>        /* Load the shadow comparitor */
>        if (ir->shadow_comparitor && ir->op != ir_txd) {
>  	 emit(MOV(dst_reg(MRF, param_base + 1, ir->shadow_comparitor->type,