[Mesa-dev] [PATCH 1/5] i965: Add writes_accumulator flag

[Matt Turner]

On Fri, Mar 28, 2014 at 6:28 AM, Juha-Pekka Heikkila
<juhapekka.heikkila at gmail.com> wrote:
> diff --git a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> index a951459..492ee0d 100644
> --- a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
> @@ -818,7 +818,7 @@ fs_instruction_scheduler::calculate_deps()
>          }
>        }
>
> -      if (inst->reads_flag()) {
> +      if (inst->reads_flag() || inst->writes_accumulator) {
>          add_dep(last_conditional_mod[inst->flag_subreg], n);

last_conditional_mod tracks the last instructions to write f0.0 and
f0.1, so we don't want to use it to also track writes to the
accumulator. Add another variable

  schedule_node *last_accumulator_write = NULL;

and use it like we do with last_conditional_mod

  if (inst->writes_accumulator || inst->dst.is_accumulator()) {
      ...
  }

You'll need to add an is_accumulator method to the FS backend's fs_reg
class, and to the vec4 backend's reg class. You can tell if a register
is the accumulator if

  reg.file == HW_REG &&
  reg.fixed_hw_reg.file == BRW_ARCHITECTURE_REGISTER_FILE &&
  reg.fixed_hw_reg.nr == BRW_ARF_ACCUMULATOR