[Mesa-dev] [PATCH] i965: Fix gl_InvocationID in dual object GS where invocations == 1.

[Kenneth Graunke]

dEQP-GLES31.functional.geometry_shading.instanced.geometry_1_invocations
draws using a geometry shader that specifies

   layout(points, invocations = 1) in;

and then uses gl_InvocationID.  According to the Haswell PRM, the
"GS Instance ID 0" (and 1) thread payload fields are undefined in
dual object mode:

   "If 'dispatch mode' is DUAL_OBJECT this field is not valid."

But there's no point in using them - if there's only one invocation,
the ID will be 0.  So just load a constant.

Cc: mesa-stable at lists.freedesktop.org
Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

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 c5886d4..59c7d21 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp
@@ -59,7 +59,10 @@ vec4_gs_visitor::make_reg_for_system_value(int location)
    switch (location) {
    case SYSTEM_VALUE_INVOCATION_ID:
       this->current_annotation = "initialize gl_InvocationID";
-      emit(GS_OPCODE_GET_INSTANCE_ID, *reg);
+      if (gs_prog_data->invocations > 1)
+         emit(GS_OPCODE_GET_INSTANCE_ID, *reg);
+      else
+         emit(MOV(*reg, brw_imm_ud(0)));
       break;
    default:
       unreachable("not reached");
-- 
2.10.0