nir: Use a system value for gl_PrimitiveIDIn.

At least on Intel hardware, gl_PrimitiveIDIn comes in as a special part
of the payload rather than a normal input.  This is typically what we
use system values for.  Dave and Ilia also agree that a system value
would be nicer.

At some point, we should change it at the GLSL IR level as well.  But
that requires changing most of the drivers.  For now, let's at least
make NIR do the right thing, which is easy.

v2: Add a comment about not creating a temporary (suggested by Iago).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_gs_nir.cpp b/src/mesa/drivers/dri/i965/brw_vec4_gs_nir.cpp
index 4f4e1e1..64a90e5 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_gs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_gs_nir.cpp
@@ -72,6 +72,10 @@ vec4_gs_visitor::nir_setup_system_value_intrinsic(nir_intrinsic_instr *instr)
    dst_reg *reg;
 
    switch (instr->intrinsic) {
+   case nir_intrinsic_load_primitive_id:
+      /* We'll just read g1 directly; don't create a temporary. */
+      break;
+
    case nir_intrinsic_load_invocation_id:
       reg = &this->nir_system_values[SYSTEM_VALUE_INVOCATION_ID];
       if (reg->file == BAD_FILE)
@@ -111,6 +115,12 @@ vec4_gs_visitor::nir_emit_intrinsic(nir_intrinsic_instr *instr)
          retype(get_nir_src(instr->src[0], 1), BRW_REGISTER_TYPE_UD);
       break;
 
+   case nir_intrinsic_load_primitive_id:
+      assert(c->prog_data.include_primitive_id);
+      dest = get_nir_dest(instr->dest, BRW_REGISTER_TYPE_D);
+      emit(MOV(dest, retype(brw_vec4_grf(1, 0), BRW_REGISTER_TYPE_D)));
+      break;
+
    case nir_intrinsic_load_invocation_id: {
       src_reg invocation_id =
          src_reg(nir_system_values[SYSTEM_VALUE_INVOCATION_ID]);