[Mesa-dev] [PATCH 5/5] i965/nir: use vectorization for non-scalar stages

[Connor Abbott]

Shader-db results on bdw with INTEL_DEBUG=vec4:

total instructions in shared programs: 1634044 -> 1612936 (-1.29%)
instructions in affected programs: 802502 -> 781394 (-2.63%)
helped: 5036
HURT: 1442

total cycles in shared programs: 9397790 -> 9355382 (-0.45%)
cycles in affected programs: 5078600 -> 5036192 (-0.84%)
helped: 3875
HURT: 2554

LOST:   0
GAINED: 0

Most of the hurt programs seem to be because we generate extra MOV's due
to vectorizing things. For example, in
shaders/non-free/steam/anomaly-2/158.shader_test, this:

add(8)          g116<1>.xyF     g12<4,4,1>.xyyyF g1.4<0,4,1>.xyyyF { align16 NoDDClr 1Q };
add(8)          g117<1>.xyF     g12<4,4,1>.xyyyF g1.4<0,4,1>.zwwwF { align16 NoDDClr 1Q };
add(8)          g116<1>.zwF     g12<4,4,1>.xxxyF -g1.4<0,4,1>.xxxyF { align16 NoDDChk 1Q };
add(8)          g117<1>.zwF     g12<4,4,1>.xxxyF -g1.4<0,4,1>.zzzwF { align16 NoDDChk 1Q };

Turns into this:

add(8)          g13<1>F         g12<4,4,1>.xyxyF g1.4<0,4,1>F   { align16 1Q };
add(8)          g14<1>F         g12<4,4,1>.xyxyF -g1.4<0,4,1>F  { align16 1Q };
mov(8)          g116<1>.xyD     g13<4,4,1>.xyyyD                { align16 NoDDClr 1Q };
mov(8)          g117<1>.xyD     g13<4,4,1>.zwwwD                { align16 NoDDClr 1Q };
mov(8)          g116<1>.zwD     g14<4,4,1>.xxxyD                { align16 NoDDChk 1Q };
mov(8)          g117<1>.zwD     g14<4,4,1>.zzzwD                { align16 NoDDChk 1Q };

So we eliminated two add's, but then had to introduce four mov's to
transpose the result. I don't think there's much we can do about this at
the NIR level, unfortunately.

Signed-off-by: Connor Abbott <cwabbott0 at gmail.com>
---
 src/mesa/drivers/dri/i965/brw_nir.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_nir.c b/src/mesa/drivers/dri/i965/brw_nir.c
index fe5cad4..29cafe6 100644
--- a/src/mesa/drivers/dri/i965/brw_nir.c
+++ b/src/mesa/drivers/dri/i965/brw_nir.c
@@ -198,6 +198,14 @@ nir_optimize(nir_shader *nir, bool is_scalar)
       nir_validate_shader(nir);
       progress |= nir_opt_cse(nir);
       nir_validate_shader(nir);
+
+      if (!is_scalar) {
+         progress |= nir_opt_vectorize(nir);
+         nir_validate_shader(nir);
+         progress |= nir_copy_prop(nir);
+         nir_validate_shader(nir);
+      }
+
       progress |= nir_opt_peephole_select(nir);
       nir_validate_shader(nir);
       progress |= nir_opt_algebraic(nir);
-- 
2.4.3