[Mesa-dev] [PATCH 2/2] radeonsi: move PSIZE and CLIPDIST unique IO indices after GENERIC

[Marek Olšák]

From: Marek Olšák <marek.olsak at amd.com>

Heaven LDS usage for LS+HS is below. The masks are "outputs_written"
for LS and HS. Note that 32K is the maximum size.

Before:
  heaven_x64: ls=1f1 tcs=1f1, lds=32K
  heaven_x64: ls=31 tcs=31, lds=24K
  heaven_x64: ls=71 tcs=71, lds=28K

After:
  heaven_x64: ls=3f tcs=3f, lds=24K
  heaven_x64: ls=7 tcs=7, lds=13K
  heaven_x64: ls=f tcs=f, lds=17K

All other apps have a similar decrease in LDS usage, because
the "outputs_written" masks are similar. Also, most apps don't write
POSITION in these shader stages, so there is room for improvement.
(tight per-component input/output packing might help even more)

It's unknown whether this improves performance.
---
 src/gallium/drivers/radeonsi/si_shader.c        | 18 +++++++++++-------
 src/gallium/drivers/radeonsi/si_state_shaders.c |  4 +++-
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
index ddfaa3b..3a86c0b 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -129,32 +129,36 @@ unsigned si_shader_io_get_unique_index_patch(unsigned semantic_name, unsigned in
 /**
  * Returns a unique index for a semantic name and index. The index must be
  * less than 64, so that a 64-bit bitmask of used inputs or outputs can be
  * calculated.
  */
 unsigned si_shader_io_get_unique_index(unsigned semantic_name, unsigned index)
 {
 	switch (semantic_name) {
 	case TGSI_SEMANTIC_POSITION:
 		return 0;
-	case TGSI_SEMANTIC_PSIZE:
-		return 1;
-	case TGSI_SEMANTIC_CLIPDIST:
-		assert(index <= 1);
-		return 2 + index;
 	case TGSI_SEMANTIC_GENERIC:
+		/* Since some shader stages use the the highest used IO index
+		 * to determine the size to allocate for inputs/outputs
+		 * (in LDS, tess and GS rings). GENERIC should be placed right
+		 * after POSITION to make that size as small as possible.
+		 */
 		if (index < SI_MAX_IO_GENERIC)
-			return 4 + index;
+			return 1 + index;
 
 		assert(!"invalid generic index");
 		return 0;
-
+	case TGSI_SEMANTIC_PSIZE:
+		return SI_MAX_IO_GENERIC + 1;
+	case TGSI_SEMANTIC_CLIPDIST:
+		assert(index <= 1);
+		return SI_MAX_IO_GENERIC + 2 + index;
 	case TGSI_SEMANTIC_FOG:
 		return SI_MAX_IO_GENERIC + 4;
 	case TGSI_SEMANTIC_LAYER:
 		return SI_MAX_IO_GENERIC + 5;
 	case TGSI_SEMANTIC_VIEWPORT_INDEX:
 		return SI_MAX_IO_GENERIC + 6;
 	case TGSI_SEMANTIC_PRIMID:
 		return SI_MAX_IO_GENERIC + 7;
 	case TGSI_SEMANTIC_COLOR: /* these alias */
 	case TGSI_SEMANTIC_BCOLOR:
diff --git a/src/gallium/drivers/radeonsi/si_state_shaders.c b/src/gallium/drivers/radeonsi/si_state_shaders.c
index 8ac4309..f36997b 100644
--- a/src/gallium/drivers/radeonsi/si_state_shaders.c
+++ b/src/gallium/drivers/radeonsi/si_state_shaders.c
@@ -1226,21 +1226,23 @@ static void si_shader_selector_key_hw_vs(struct si_context *sctx,
 		ps_disabled = sctx->queued.named.rasterizer->rasterizer_discard ||
 			      (!ps_colormask &&
 			       !ps_modifies_zs &&
 			       !ps->info.writes_memory);
 	}
 
 	/* Find out which VS outputs aren't used by the PS. */
 	uint64_t outputs_written = vs->outputs_written;
 	uint64_t inputs_read = 0;
 
-	outputs_written &= ~0x3; /* ignore POSITION, PSIZE */
+	/* ignore POSITION, PSIZE */
+	outputs_written &= ~((1ull << si_shader_io_get_unique_index(TGSI_SEMANTIC_POSITION, 0) |
+			     (1ull << si_shader_io_get_unique_index(TGSI_SEMANTIC_PSIZE, 0))));
 
 	if (!ps_disabled) {
 		inputs_read = ps->inputs_read;
 	}
 
 	uint64_t linked = outputs_written & inputs_read;
 
 	key->opt.hw_vs.kill_outputs = ~linked & outputs_written;
 }
 
-- 
2.7.4