[Mesa-dev] [PATCH] i965/vec4: dead_code_eliminate: update writemask on null_regs based on flag_live

[Francisco Jerez]

Alejandro Piñeiro <apinheiro at igalia.com> writes:

> ---
>
> This patch implements the idea proposed by Francisco Jerez. With this
> change, even adding the new condition pointed by Matt Turner on the
> "2/5 i965/vec4: adding vec4_cmod_propagation optimization", the shader-db
> numbers remain the same. So this patch would go before the optimization
> (so in this series it would be the patch 1.5).
>
> Note: Im not resending the patch 2/5, as Matt pointed that he granted
> the reviewed status with his suggested change. I can send it if needed
> in any case.
>
>  .../drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp    | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp b/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
> index 8fc7a36..31ea128 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_dead_code_eliminate.cpp
> @@ -78,13 +78,19 @@ vec4_visitor::dead_code_eliminate()
>               sizeof(BITSET_WORD));
>  
>        foreach_inst_in_block_reverse(vec4_instruction, inst, block) {
> -         if (inst->dst.file == GRF && !inst->has_side_effects()) {
> +         if ((inst->dst.file == GRF && !inst->has_side_effects()) ||
> +             (inst->dst.is_null() && inst->writes_flag())){
>              bool result_live[4] = { false };
>  
> -            for (unsigned i = 0; i < inst->regs_written; i++) {
> -               for (int c = 0; c < 4; c++)
> -                  result_live[c] |= BITSET_TEST(
> -                     live, var_from_reg(alloc, offset(inst->dst, i), c));
> +            if (inst->dst.file == GRF) {
> +               for (unsigned i = 0; i < inst->regs_written; i++) {
> +                  for (int c = 0; c < 4; c++)
> +                     result_live[c] |= BITSET_TEST(
> +                        live, var_from_reg(alloc, offset(inst->dst, i), c));
> +               }
> +            } else {
> +               for (unsigned c = 0; c < 4; c++)
> +                  result_live[c] |= BITSET_TEST(flag_live, c);

Sadly flag liveness is not kept track of per component -- I.e. the
flag_live bit-set and the flag live-out bitset calculated by liveness
analysis have only one bit representing the union of all components.
This won't work unless you fix that too.

>              }
>  
>              /* If the instruction can't do writemasking, then it's all or
> -- 
> 2.1.4
>
> _______________________________________________
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