[Mesa-dev] [PATCH 2/4] i965: Turn not.nz x into cmp.z x,0.

[Kenneth Graunke]

On Monday, August 15, 2016 2:24:30 PM PDT Matt Turner wrote:
> This allow conditional mod propagation to handle it.
> 
> HSW:
> 
>    total instructions in shared programs: 8270006 -> 8269855 (-0.00%)
>    instructions in affected programs: 41552 -> 41401 (-0.36%)
>    helped: 136
> 
>    total cycles in shared programs: 82424584 -> 82420414 (-0.01%)
>    cycles in affected programs: 745390 -> 741220 (-0.56%)
>    helped: 86
>    HURT: 27
> 
> BDW:
> 
>    total instructions in shared programs: 11644113 -> 11643810 (-0.00%)
>    instructions in affected programs: 68405 -> 68102 (-0.44%)
>    helped: 278
> 
>    total cycles in shared programs: 144891558 -> 144883684 (-0.01%)
>    cycles in affected programs: 866424 -> 858550 (-0.91%)
>    helped: 226
>    HURT: 27
> 
> Also prevents regressions in "nir: Convert ineg(b2i(a)) to a if it's a
> boolean."
> ---
>  src/mesa/drivers/dri/i965/brw_fs.cpp   | 9 +++++++++
>  src/mesa/drivers/dri/i965/brw_vec4.cpp | 9 +++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index d1ac80a..7ee50e7 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -2301,6 +2301,15 @@ fs_visitor::opt_algebraic()
>              break;
>           }
>           break;
> +      case BRW_OPCODE_NOT:
> +         if (inst->dst.is_null() &&
> +             inst->conditional_mod == BRW_CONDITIONAL_NZ) {
> +            inst->opcode = BRW_OPCODE_CMP;
> +            inst->conditional_mod = BRW_CONDITIONAL_Z;
> +            inst->src[1] = retype(brw_imm_d(0), inst->src[0].type);
> +            progress = true;
> +         }
> +         break;
>        case BRW_OPCODE_LRP:
>           if (inst->src[1].equals(inst->src[2])) {
>              inst->opcode = BRW_OPCODE_MOV;
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> index 2cf0e17..337a363 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> @@ -746,6 +746,15 @@ vec4_visitor::opt_algebraic()
>              progress = true;
>  	 }
>  	 break;
> +      case BRW_OPCODE_NOT:
> +         if (inst->dst.is_null() &&
> +             inst->conditional_mod == BRW_CONDITIONAL_NZ) {
> +            inst->opcode = BRW_OPCODE_CMP;
> +            inst->conditional_mod = BRW_CONDITIONAL_Z;
> +            inst->src[1] = retype(brw_imm_d(0), inst->src[0].type);
> +            progress = true;
> +         }
> +         break;
>        case BRW_OPCODE_CMP:
>           if (inst->conditional_mod == BRW_CONDITIONAL_GE &&
>               inst->src[0].abs &&
> 

This works for boolean values, but I don't think it works in general:

    val       not val   not.nz val   cmp.z val 0
    0         ffffffff  yes          yes
    1         fffffffe  yes          no
    ffffffff  0         no           no
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