[Mesa-dev] [PATCH] i965: Relax accumulator dependency scheduling on Gen < 6

[Matt Turner]

Nice work.

On Tue, May 6, 2014 at 1:16 AM, Iago Toral Quiroga <itoral at igalia.com> wrote:
> diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
> index 6e74803..37d3eab 100644
> --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> @@ -676,6 +676,13 @@ backend_instruction::reads_accumulator_implicitly() const
>  }
>
>  bool
> +backend_instruction::writes_accumulator_implicitly(int gen) const
> +{
> +   return writes_accumulator ||
> +          (gen < 6 && opcode >= BRW_OPCODE_ADD && opcode != BRW_OPCODE_NOP);

Since our virtual instruction opcodes are > BRW_OPCODE_NOP, they'll
also be classified as writing the accumulator, whereas before they
weren't.

I think the only ones (that are used on gen < 6) that generate
hardware instructions that write the accumulator are

   FS_OPCODE_DDX
   FS_OPCODE_DDY
   FS_OPCODE_PIXEL_X
   FS_OPCODE_PIXEL_Y
   FS_OPCODE_CINTERP
   FS_OPCODE_LINTERP

If you update this function with these and it still passes piglit on
gen < 6, then this patch is

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