[Mesa-dev] [PATCH] radeonsi/nir: disable GLSL IR loop unrolling

[Ilia Mirkin]

On Tue, Feb 20, 2018 at 8:35 PM, Timothy Arceri <tarceri at itsqueeze.com> wrote:
> Delaying unrolling and allowing NIR to do it instead has been shown
> to result in better code in drivers such as i965. shader-db results
> appear to should the same is true for radeonsi.
>
> The other advantage is that using NIR unrolling improves compile
> times significantly.
>
> Totals from affected shaders:
> SGPRS: 9624 -> 10016 (4.07 %)
> VGPRS: 6800 -> 6464 (-4.94 %)
> Spilled SGPRs: 0 -> 2 (0.00 %)
> Spilled VGPRs: 0 -> 0 (0.00 %)
> Private memory VGPRs: 0 -> 0 (0.00 %)
> Scratch size: 0 -> 0 (0.00 %) dwords per thread
> Code Size: 359176 -> 332264 (-7.49 %) bytes

This basically means that fewer loops were unrolled. I don't know if
this is the right metric to look at when comparing loop unroll
efficacy.

IOW, you might want to look at actual perf of some of the affected
games. (For all I know it really does improve. My point is that this
isn't a good measure of that.)

> LDS: 0 -> 0 (0.00 %) blocks
> Max Waves: 1355 -> 1432 (5.68 %)
> Wait states: 0 -> 0 (0.00 %)
> ---
>  src/gallium/drivers/radeonsi/si_get.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/src/gallium/drivers/radeonsi/si_get.c b/src/gallium/drivers/radeonsi/si_get.c
> index ef03a962d1..18d9cec414 100644
> --- a/src/gallium/drivers/radeonsi/si_get.c
> +++ b/src/gallium/drivers/radeonsi/si_get.c
> @@ -437,6 +437,8 @@ static int si_get_shader_param(struct pipe_screen* pscreen,
>         case PIPE_SHADER_CAP_MAX_SHADER_IMAGES:
>                 return SI_NUM_IMAGES;
>         case PIPE_SHADER_CAP_MAX_UNROLL_ITERATIONS_HINT:
> +               if (sscreen->debug_flags & DBG(NIR))
> +                       return 0;
>                 return 32;
>         case PIPE_SHADER_CAP_PREFERRED_IR:
>                 if (sscreen->debug_flags & DBG(NIR))
> --
> 2.14.3
>
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