[Mesa-dev] [PATCH] i965: Reserve space for "Vertex Count" in GS outputs.

[Kenneth Graunke]

v2: Also increment ir->offset in the GS visitor, rather than at the
    final assembly generation stage (requested by Paul).

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_vec4_gs.c           | 6 ++++++
 src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp | 7 +++++++
 2 files changed, 13 insertions(+)

Hey Paul,

I think I implemented all of your feedback from last time.  (Previously,
I'd done this in gen8_vec4_generator, and you asked me to move it to the
visitor.  This patch does that - and it is indeed much nicer.)

 --Ken

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_gs.c b/src/mesa/drivers/dri/i965/brw_vec4_gs.c
index 018b0b6..c40112b 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_gs.c
+++ b/src/mesa/drivers/dri/i965/brw_vec4_gs.c
@@ -194,6 +194,12 @@ do_gs_prog(struct brw_context *brw,
       c.prog_data.output_vertex_size_hwords * 32 * gp->program.VerticesOut;
    output_size_bytes += 32 * c.prog_data.control_data_header_size_hwords;
 
+   /* Broadwell stores "Vertex Count" as a full 8 DWord (32 byte) URB output,
+    * which comes before the control header.
+    */
+   if (brw->gen >= 8)
+      output_size_bytes += 32;
+
    assert(output_size_bytes >= 1);
    if (output_size_bytes > GEN7_MAX_GS_URB_ENTRY_SIZE_BYTES)
       return false;
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp
index f33c80d..f0351ea 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp
@@ -267,6 +267,13 @@ vec4_gs_visitor::emit_urb_write_opcode(bool complete)
 
    vec4_instruction *inst = emit(GS_OPCODE_URB_WRITE);
    inst->offset = c->prog_data.control_data_header_size_hwords;
+
+   /* We need to increment Global Offset by 1 to make room for Broadwell's
+    * extra "Vertex Count" payload at the beginning of the URB entry.
+    */
+   if (brw->gen >= 8)
+      inst->offset++;
+
    inst->urb_write_flags = BRW_URB_WRITE_PER_SLOT_OFFSET;
    return inst;
 }
-- 
1.8.5.2