[Mesa-dev] [PATCH 1/3] i965/fs: Properly handle sign(-abs(x))

[Caio Marcelo de Oliveira Filho]

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com>

Tested the patch with the shaders mentioned.

Do you think would be worth to have a pass at NIR level to perform
these transformations?


Thanks,
Caio


On Wed, Jun 27, 2018 at 07:37:57AM -0700, Ian Romanick wrote:
> From: Ian Romanick <ian.d.romanick at intel.com>
> 
> Fixes new piglit tests:
> 
>  - glsl-1.10/execution/fs-sign-neg-abs.shader_test
>  - glsl-1.10/execution/fs-sign-sat-neg-abs.shader_test
>  - glsl-1.10/execution/vs-sign-neg-abs.shader_test
>  - glsl-1.10/execution/vs-sign-sat-neg-abs.shader_test
> 
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/intel/compiler/brw_fs_nir.cpp | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/src/intel/compiler/brw_fs_nir.cpp b/src/intel/compiler/brw_fs_nir.cpp
> index 0abb4798e70..2ad7a2d0dfc 100644
> --- a/src/intel/compiler/brw_fs_nir.cpp
> +++ b/src/intel/compiler/brw_fs_nir.cpp
> @@ -807,11 +807,20 @@ fs_visitor::nir_emit_alu(const fs_builder &bld, nir_alu_instr *instr)
>  
>     case nir_op_fsign: {
>        if (op[0].abs) {
> -         /* Straightforward since the source can be assumed to be
> -          * non-negative.
> +         /* Straightforward since the source can be assumed to be either
> +          * strictly >= 0 or strictly <= 0 depending on the setting of the
> +          * negate flag.
>            */
>           set_condmod(BRW_CONDITIONAL_NZ, bld.MOV(result, op[0]));
> -         set_predicate(BRW_PREDICATE_NORMAL, bld.MOV(result, brw_imm_f(1.0f)));
> +
> +         inst = (op[0].negate)
> +            ? bld.MOV(result, brw_imm_f(-1.0f))
> +            : bld.MOV(result, brw_imm_f(1.0f));
> +
> +         set_predicate(BRW_PREDICATE_NORMAL, inst);
> +
> +         if (instr->dest.saturate)
> +            inst->saturate = true;
>  
>        } else if (type_sz(op[0].type) < 8) {
>           /* AND(val, 0x80000000) gives the sign bit.
> -- 
> 2.14.4
> 
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