i965: Implement "Static Vertex Count" geometry shader optimization.

Broadwell's 3DSTATE_GS contains new "Static Output" and "Static Vertex
Count" fields, which control a new optimization.  Normally, geometry
shaders can output arbitrary numbers of vertices, which means that
resource allocation has to be done on the fly.  However, if the number
of vertices is statically known, the hardware can pre-allocate resources
up front, which is more efficient.

Thanks to the new NIR GS intrinsics, this is easy.  We just call the
function introduced in the previous commit to get the vertex count.
If it obtains a count, we stop emitting the extra 32-bit "Vertex Count"
field in the VUE, and instead fill out the 3DSTATE_GS fields.

Improves performance of Gl32GSCloth by 5.16347% +/- 0.12611% (n=91)
on my Lenovo X250 laptop (Broadwell GT2) at 1024x768.

shader-db statistics for geometry shaders only:

total instructions in shared programs: 3227 -> 3207 (-0.62%)
instructions in affected programs:     242 -> 222 (-8.26%)
helped:                                10

v2: Don't break non-NIR paths (just skip this optimization).

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Jordan Justen <[email protected]>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
index 7045d2ce043..393f17ac98c 100644
--- a/src/mesa/drivers/dri/i965/brw_defines.h
+++ b/src/mesa/drivers/dri/i965/brw_defines.h
@@ -1964,6 +1964,11 @@ enum brw_message_target {
 # define GEN6_GS_SVBI_POSTINCREMENT_VALUE_MASK		INTEL_MASK(25, 16)
 # define GEN6_GS_ENABLE					(1 << 15)
 
+/* Gen8+ DW8 */
+# define GEN8_GS_STATIC_OUTPUT                          (1 << 30)
+# define GEN8_GS_STATIC_VERTEX_COUNT_SHIFT              16
+# define GEN8_GS_STATIC_VERTEX_COUNT_MASK               INTEL_MASK(26, 16)
+
 /* Gen8+ DW9 */
 # define GEN8_GS_URB_ENTRY_OUTPUT_OFFSET_SHIFT          21
 # define GEN8_GS_URB_OUTPUT_LENGTH_SHIFT                16