[Mesa-dev] [PATCH 02/11] nir/algebraic: sign(x)*x*x is abs(x)*x

[Thomas Helland]

Den tir. 11. sep. 2018 kl. 01:30 skrev Ian Romanick <idr at freedesktop.org>:
>
> From: Ian Romanick <ian.d.romanick at intel.com>
>

Reviewed-by: Thomas Helland<thomashelland90 at gmail.com>

> shader-db results:
>
> All Gen7+ platforms had similar results. (Skylake shown)
> total instructions in shared programs: 15106023 -> 15105981 (<.01%)
> instructions in affected programs: 300 -> 258 (-14.00%)
> helped: 6
> HURT: 0
> helped stats (abs) min: 7 max: 7 x̄: 7.00 x̃: 7
> helped stats (rel) min: 14.00% max: 14.00% x̄: 14.00% x̃: 14.00%
> 95% mean confidence interval for instructions value: -7.00 -7.00
> 95% mean confidence interval for instructions %-change: -14.00% -14.00%
> Instructions are helped.
>
> total cycles in shared programs: 566050327 -> 566050075 (<.01%)
> cycles in affected programs: 2826 -> 2574 (-8.92%)
> helped: 6
> HURT: 0
> helped stats (abs) min: 40 max: 44 x̄: 42.00 x̃: 42
> helped stats (rel) min: 8.89% max: 8.94% x̄: 8.92% x̃: 8.92%
> 95% mean confidence interval for cycles value: -44.30 -39.70
> 95% mean confidence interval for cycles %-change: -8.95% -8.88%
> Cycles are helped.
>
> No changes on Gen6 or earlier.
>
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> ---
>  src/compiler/nir/nir_opt_algebraic.py | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
> index ae1261f8744..3267e93a583 100644
> --- a/src/compiler/nir/nir_opt_algebraic.py
> +++ b/src/compiler/nir/nir_opt_algebraic.py
> @@ -105,6 +105,11 @@ optimizations = [
>     (('imul', a, 1), a),
>     (('fmul', a, -1.0), ('fneg', a)),
>     (('imul', a, -1), ('ineg', a)),
> +   # If a < 0: fsign(a)*a*a => -1*a*a => -a*a => abs(a)*a
> +   # If a > 0: fsign(a)*a*a => 1*a*a => a*a => abs(a)*a
> +   # If a == 0: fsign(a)*a*a => 0*0*0 => abs(0)*0
> +   (('fmul', ('fsign', a), ('fmul', a, a)), ('fmul', ('fabs', a), a)),
> +   (('fmul', ('fmul', ('fsign', a), a), a), ('fmul', ('fabs', a), a)),
>     (('~ffma', 0.0, a, b), b),
>     (('~ffma', a, 0.0, b), b),
>     (('~ffma', a, b, 0.0), ('fmul', a, b)),
> --
> 2.14.4
>
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