Re: [Mesa-dev] [PATCH 1/9] i965/vec4: Don't emit MOVs for unused URB slots.

[Emil Velikov]

On 20 October 2015 at 05:08, Matt Turner  wrote:
> Otherwise we'd emit a MOV from the null register (which isn't allowed).
>
Would you say it's a good idea to push the check down to the MOV()
implementation ? If not perhaps we should add an assert() to easily
catch cases like these in the future ?

Thanks
Emil
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Re: [Mesa-dev] [PATCH 1/9] i965/vec4: Don't emit MOVs for unused URB slots.

[Matt Turner]

On Wed, Oct 21, 2015 at 1:52 PM, Emil Velikov  wrote:
> On 20 October 2015 at 05:08, Matt Turner  wrote:
>> Otherwise we'd emit a MOV from the null register (which isn't allowed).
>>
> Would you say it's a good idea to push the check down to the MOV()
> implementation ? If not perhaps we should add an assert() to easily
> catch cases like these in the future ?

Sort of, yes. :)

This series arose by writing an assembly validator that I plan to send today.
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Re: [Mesa-dev] [PATCH 1/9] i965/vec4: Don't emit MOVs for unused URB slots.

[Iago Toral]

On Mon, 2015-10-19 at 21:08 -0700, Matt Turner wrote:
> Otherwise we'd emit a MOV from the null register (which isn't allowed).
> 
> Helps 24 programs in shader-db (the geometry shaders in GSCloth):
> 
> instructions in affected programs: 302 -> 262 (-13.25%)

Makes sense to me,

Reviewed-by: Iago Toral Quiroga 

Out of curiosity, does moving from the null register have any actual
consequences?

Iago

> ---
>  src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp| 18 +-
>  src/mesa/drivers/dri/i965/brw_vec4_vs_visitor.cpp |  2 +-
>  2 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp 
> b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> index f891910..c39f97e 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> @@ -1221,6 +1221,9 @@ vec4_visitor::emit_untyped_surface_read(unsigned 
> surf_index, dst_reg dst,
>  void
>  vec4_visitor::emit_ndc_computation()
>  {
> +   if (output_reg[VARYING_SLOT_POS].file == BAD_FILE)
> +  return;
> +
> /* Get the position */
> src_reg pos = src_reg(output_reg[VARYING_SLOT_POS]);
>  
> @@ -1286,7 +1289,8 @@ vec4_visitor::emit_psiz_and_flags(dst_reg reg)
> * Later, clipping will detect ucp[6] and ensure the primitive is
> * clipped against all fixed planes.
> */
> -  if (devinfo->has_negative_rhw_bug) {
> +  if (devinfo->has_negative_rhw_bug &&
> +  output_reg[BRW_VARYING_SLOT_NDC].file != BAD_FILE) {
>   src_reg ndc_w = src_reg(output_reg[BRW_VARYING_SLOT_NDC]);
>   ndc_w.swizzle = BRW_SWIZZLE_;
>   emit(CMP(dst_null_f(), ndc_w, src_reg(0.0f), BRW_CONDITIONAL_L));
> @@ -1334,8 +1338,10 @@ vec4_visitor::emit_generic_urb_slot(dst_reg reg, int 
> varying)
> assert(varying < VARYING_SLOT_MAX);
> assert(output_reg[varying].type == reg.type);
> current_annotation = output_reg_annotation[varying];
> -   /* Copy the register, saturating if necessary */
> -   return emit(MOV(reg, src_reg(output_reg[varying])));
> +   if (output_reg[varying].file != BAD_FILE)
> +  return emit(MOV(reg, src_reg(output_reg[varying])));
> +   else
> +  return NULL;
>  }
>  
>  void
> @@ -1354,11 +1360,13 @@ vec4_visitor::emit_urb_slot(dst_reg reg, int varying)
> }
> case BRW_VARYING_SLOT_NDC:
>current_annotation = "NDC";
> -  emit(MOV(reg, src_reg(output_reg[BRW_VARYING_SLOT_NDC])));
> +  if (output_reg[BRW_VARYING_SLOT_NDC].file != BAD_FILE)
> + emit(MOV(reg, src_reg(output_reg[BRW_VARYING_SLOT_NDC])));
>break;
> case VARYING_SLOT_POS:
>current_annotation = "gl_Position";
> -  emit(MOV(reg, src_reg(output_reg[VARYING_SLOT_POS])));
> +  if (output_reg[VARYING_SLOT_POS].file != BAD_FILE)
> + emit(MOV(reg, src_reg(output_reg[VARYING_SLOT_POS])));
>break;
> case VARYING_SLOT_EDGE:
>/* This is present when doing unfilled polygons.  We're supposed to 
> copy
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_vs_visitor.cpp 
> b/src/mesa/drivers/dri/i965/brw_vec4_vs_visitor.cpp
> index 485a80e..5dd4f98 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_vs_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_vs_visitor.cpp
> @@ -217,7 +217,7 @@ vec4_vs_visitor::emit_urb_slot(dst_reg reg, int varying)
> * shader.
> */
>vec4_instruction *inst = emit_generic_urb_slot(reg, varying);
> -  if (key->clamp_vertex_color)
> +  if (inst && key->clamp_vertex_color)
>   inst->saturate = true;
>break;
> }


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Re: [Mesa-dev] [PATCH 1/9] i965/vec4: Don't emit MOVs for unused URB slots.

[Matt Turner]

On Tue, Oct 20, 2015 at 1:01 AM, Iago Toral  wrote:
> On Mon, 2015-10-19 at 21:08 -0700, Matt Turner wrote:
>> Otherwise we'd emit a MOV from the null register (which isn't allowed).
>>
>> Helps 24 programs in shader-db (the geometry shaders in GSCloth):
>>
>> instructions in affected programs: 302 -> 262 (-13.25%)
>
> Makes sense to me,
>
> Reviewed-by: Iago Toral Quiroga 
>
> Out of curiosity, does moving from the null register have any actual
> consequences?

The documentation says that it's not allowed, and I *think* I've seen
a case where it caused a GPU hang but I cannot remember for sure.
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