[Mesa-dev] [RFC v2 4/4] nir: add crude live range analysis to nir_compact_varyings()

[Timothy Arceri]

Using robs packing fix for the st I'm actually getting results for 
radeonsi now but they are pretty mixed for this patch:

Totals from affected shaders:
SGPRS: 35992 -> 35520 (-1.31 %)
VGPRS: 20688 -> 20808 (0.58 %)
Spilled SGPRs: 1926 -> 1996 (3.63 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 1053168 -> 1055452 (0.22 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 4636 -> 4616 (-0.43 %)
Wait states: 0 -> 0 (0.00 %)

On 10/12/18 11:31 am, Timothy Arceri wrote:
> vkpipeline-db results RADV (VEGA):
> 
> Totals from affected shaders:
> SGPRS: 27168 -> 27872 (2.59 %)
> VGPRS: 24180 -> 24056 (-0.51 %)
> Spilled SGPRs: 28 -> 24 (-14.29 %)
> Spilled VGPRs: 0 -> 0 (0.00 %)
> Private memory VGPRs: 0 -> 0 (0.00 %)
> Scratch size: 0 -> 0 (0.00 %) dwords per thread
> Code Size: 1584936 -> 1585552 (0.04 %) bytes
> LDS: 0 -> 0 (0.00 %) blocks
> Max Waves: 3804 -> 3824 (0.53 %)
> Wait states: 0 -> 0 (0.00 %)
> ---
>   src/compiler/nir/nir_linking_helpers.c | 45 ++++++++++++++++++++++++++
>   1 file changed, 45 insertions(+)
> 
> diff --git a/src/compiler/nir/nir_linking_helpers.c b/src/compiler/nir/nir_linking_helpers.c
> index 8bd4acc2ee..badda80979 100644
> --- a/src/compiler/nir/nir_linking_helpers.c
> +++ b/src/compiler/nir/nir_linking_helpers.c
> @@ -415,6 +415,8 @@ remap_slots_and_components(struct exec_list *var_list, gl_shader_stage stage,
>   
>   struct varying_component {
>      nir_variable *var;
> +   unsigned first_block_use;
> +   unsigned last_block_use;
>      uint8_t interp_type;
>      uint8_t interp_loc;
>      bool is_patch;
> @@ -441,10 +443,36 @@ cmp_varying_component(const void *comp1_v, const void *comp2_v)
>      if (comp1->interp_loc != comp2->interp_loc)
>         return comp1->interp_loc - comp2->interp_loc;
>   
> +   /* Attempt to reduce register pressure with crude live range analysis */
> +   if (comp1->first_block_use != comp2->first_block_use)
> +      return comp1->first_block_use - comp2->first_block_use;
> +   if (comp1->last_block_use != comp2->last_block_use)
> +      return comp1->last_block_use - comp2->last_block_use;
> +
>      /* If everything else matches just use the original location to sort */
>      return comp1->var->data.location - comp2->var->data.location;
>   }
>   
> +static void
> +set_block_use(struct varying_component *vc_info, nir_src *src,
> +              bool is_if_condition)
> +{
> +   nir_block *blk
> +      = nir_cursor_current_block(nir_before_src(src, is_if_condition));
> +
> +   if (vc_info->initialised) {
> +      if (vc_info->first_block_use > blk->index)
> +         vc_info->first_block_use = blk->index;
> +
> +      if (vc_info->last_block_use < blk->index)
> +         vc_info->last_block_use = blk->index;
> +   } else {
> +      vc_info->first_block_use = blk->index;
> +      vc_info->last_block_use = blk->index;
> +      vc_info->initialised = true;
> +   }
> +}
> +
>   static void
>   gather_varying_component_info(nir_shader *consumer,
>                                 struct varying_component **varying_comp_info,
> @@ -533,6 +561,14 @@ gather_varying_component_info(nir_shader *consumer,
>               vc_info->interp_loc = get_interp_loc(in_var);
>               vc_info->is_patch = in_var->data.patch;
>            }
> +
> +         nir_foreach_use(src, &intr->dest.ssa) {
> +            set_block_use(vc_info, src, false);
> +         }
> +
> +         nir_foreach_if_use(src, &intr->dest.ssa) {
> +            set_block_use(vc_info, src, true);
> +         }
>         }
>      }
>   }
> @@ -651,6 +687,12 @@ void
>   nir_compact_varyings(nir_shader *producer, nir_shader *consumer,
>                        bool default_to_smooth_interp)
>   {
> +   nir_function_impl *p_impl = nir_shader_get_entrypoint(producer);
> +   nir_function_impl *c_impl = nir_shader_get_entrypoint(consumer);
> +
> +   nir_metadata_require(p_impl, nir_metadata_block_index);
> +   nir_metadata_require(c_impl, nir_metadata_block_index);
> +
>      assert(producer->info.stage != MESA_SHADER_FRAGMENT);
>      assert(consumer->info.stage != MESA_SHADER_VERTEX);
>   
> @@ -665,6 +707,9 @@ nir_compact_varyings(nir_shader *producer, nir_shader *consumer,
>   
>      compact_components(producer, consumer, unmoveable_comps,
>                         default_to_smooth_interp);
> +
> +   nir_metadata_preserve(p_impl, nir_metadata_block_index);
> +   nir_metadata_preserve(c_impl, nir_metadata_block_index);
>   }
>   
>   /*
>