Mesa (main): lima: enable PIPE_CAP_PREFER_POT_ALIGNED_VARYINGS

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Module: Mesa
Branch: main
Commit: 15013958d0794205bab086645a0d8c619a8f9038
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=15013958d0794205bab086645a0d8c619a8f9038

Author: Vasily Khoruzhick <anarsoul at gmail.com>
Date:   Fri Oct  1 06:32:52 2021 -0700

lima: enable PIPE_CAP_PREFER_POT_ALIGNED_VARYINGS

Mali4x0 PP doesn't have a swizzle for load_input, so use POT-aligned
varyings to avoid unnecessary movs for vec3 and precision downgrade
in case if this vec3 is coordinates for a sampler

shader-db:

total instructions in shared programs: 15707 -> 15623 (-0.53%)
instructions in affected programs: 3906 -> 3822 (-2.15%)
helped: 47
HURT: 18
helped stats (abs) min: 1 max: 9 x̄: 3.09 x̃: 2
helped stats (rel) min: 1.49% max: 23.53% x̄: 8.20% x̃: 6.45%
HURT stats (abs)   min: 1 max: 7 x̄: 3.39 x̃: 3
HURT stats (rel)   min: 0.78% max: 20.59% x̄: 10.45% x̃: 10.97%
95% mean confidence interval for instructions value: -2.18 -0.41
95% mean confidence interval for instructions %-change: -5.70% -0.38%
Instructions are helped.

total spills in shared programs: 146 -> 136 (-6.85%)
spills in affected programs: 39 -> 29 (-25.64%)
helped: 6
HURT: 0

total fills in shared programs: 617 -> 598 (-3.08%)
fills in affected programs: 125 -> 106 (-15.20%)
helped: 6
HURT: 0

HURT shaders are vertex shaders where we may need more instructions
for non-packed vec3s. It's acceptable trade-off since we don't get
precision downgrade if this varying is coordinates for a sampler.

Reviewed-by: Erico Nunes <nunes.erico at gmail.com>
Signed-off-by: Vasily Khoruzhick <anarsoul at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13151>

---

 src/gallium/drivers/lima/lima_screen.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/gallium/drivers/lima/lima_screen.c b/src/gallium/drivers/lima/lima_screen.c
index a68ef81876d..baa1d6be472 100644
--- a/src/gallium/drivers/lima/lima_screen.c
+++ b/src/gallium/drivers/lima/lima_screen.c
@@ -161,6 +161,13 @@ lima_screen_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
    case PIPE_CAP_FRAGMENT_SHADER_DERIVATIVES:
       return 1;
 
+   /* Mali4x0 PP doesn't have a swizzle for load_input, so use POT-aligned
+    * varyings to avoid unnecessary movs for vec3 and precision downgrade
+    * in case if this vec3 is coordinates for a sampler
+    */
+   case PIPE_CAP_PREFER_POT_ALIGNED_VARYINGS:
+      return 1;
+
    default:
       return u_pipe_screen_get_param_defaults(pscreen, param);
    }