[Mesa-dev] [PATCH] glsl: Drop constant 0.0 components from dot products.

[Kenneth Graunke]

On Thursday, October 23, 2014 04:19:19 PM Matt Turner wrote:
> Helps a small number of vertex shaders in the games Dungeon Defenders
> and Shank, as well as an internal benchmark.
> 
> instructions in affected programs:     2801 -> 2719 (-2.93%)
> ---
>  src/glsl/opt_algebraic.cpp | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
> index 0cdb8ec..6976ee7 100644
> --- a/src/glsl/opt_algebraic.cpp
> +++ b/src/glsl/opt_algebraic.cpp
> @@ -553,6 +553,31 @@ ir_algebraic_visitor::handle_expression(ir_expression 
*ir)
>  	 }
>  	 return new(mem_ctx) ir_swizzle(ir->operands[0], component, 0, 0, 0, 1);
>        }
> +
> +      for (int i = 0; i < 2; i++) {
> +         if (!op_const[i])
> +            continue;
> +
> +         unsigned components[4] = { 0 }, count = 0;
> +
> +         for (unsigned c = 0; c < op_const[i]->type->vector_elements; c++) 
{
> +            if (op_const[i]->value.f[c] == 0.0)
> +               continue;
> +

               /* Store which channels have non-zero values. */

> +            components[count] = c;
> +            count++;
> +         }
> +

            /* No channels had zero values; bail. */

> +         if (count >= op_const[i]->type->vector_elements)
> +            break;

            /* Swizzle both operands to remove the channels that were zero. */

> +         return new(mem_ctx)
> +            ir_expression(ir_binop_dot, glsl_type::float_type,
> +                          new(mem_ctx) ir_swizzle(ir->operands[0],
> +                                                  components, count),
> +                          new(mem_ctx) ir_swizzle(ir->operands[1],
> +                                                  components, count));
> +      }
>        break;
>  
>     case ir_binop_less:

With or without the comments,
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
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