[Mesa-dev] [PATCH] nir: Use a system value for gl_PrimitiveIDIn.

[Kenneth Graunke]

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.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/glsl/nir/glsl_to_nir.cpp                  | 5 +++++
 src/glsl/nir/nir.c                            | 5 ++++-
 src/glsl/nir/nir_intrinsics.h                 | 1 +
 src/glsl/shader_enums.h                       | 2 +-
 src/mesa/drivers/dri/i965/brw_vec4_gs_nir.cpp | 9 +++++++++
 5 files changed, 20 insertions(+), 2 deletions(-)

I bypassed most of the system value boilerplate in the backend.  Notably,
this means we just access g1 directly rather than moving it to a VGRF at
the start of the program and using that later.  This means more HW_REG
usage, but it also means less seemingly pointless copies.

I'm hoping to simplify the handling of other system values too, but I'm
waiting until we delete the GLSL IR code paths first.

diff --git a/src/glsl/nir/glsl_to_nir.cpp b/src/glsl/nir/glsl_to_nir.cpp
index f03a107..c0b2634 100644
--- a/src/glsl/nir/glsl_to_nir.cpp
+++ b/src/glsl/nir/glsl_to_nir.cpp
@@ -271,6 +271,11 @@ nir_visitor::visit(ir_variable *ir)
          /* For whatever reason, GLSL IR makes gl_FrontFacing an input */
          var->data.location = SYSTEM_VALUE_FRONT_FACE;
          var->data.mode = nir_var_system_value;
+      } else if (shader->stage == MESA_SHADER_GEOMETRY &&
+                 ir->data.location == VARYING_SLOT_PRIMITIVE_ID) {
+         /* For whatever reason, GLSL IR makes gl_PrimitiveIDIn an input */
+         var->data.location = SYSTEM_VALUE_PRIMITIVE_ID;
+         var->data.mode = nir_var_system_value;
       } else {
          var->data.mode = nir_var_shader_in;
       }
diff --git a/src/glsl/nir/nir.c b/src/glsl/nir/nir.c
index 1206bb4..7f30b8a 100644
--- a/src/glsl/nir/nir.c
+++ b/src/glsl/nir/nir.c
@@ -1487,10 +1487,11 @@ nir_intrinsic_from_system_value(gl_system_value val)
       return nir_intrinsic_load_local_invocation_id;
    case SYSTEM_VALUE_WORK_GROUP_ID:
       return nir_intrinsic_load_work_group_id;
+   case SYSTEM_VALUE_PRIMITIVE_ID:
+      return nir_intrinsic_load_primitive_id;
    /* FINISHME: Add tessellation intrinsics.
    case SYSTEM_VALUE_TESS_COORD:
    case SYSTEM_VALUE_VERTICES_IN:
-   case SYSTEM_VALUE_PRIMITIVE_ID:
    case SYSTEM_VALUE_TESS_LEVEL_OUTER:
    case SYSTEM_VALUE_TESS_LEVEL_INNER:
     */
@@ -1525,6 +1526,8 @@ nir_system_value_from_intrinsic(nir_intrinsic_op intrin)
       return SYSTEM_VALUE_LOCAL_INVOCATION_ID;
    case nir_intrinsic_load_work_group_id:
       return SYSTEM_VALUE_WORK_GROUP_ID;
+   case nir_intrinsic_load_primitive_id:
+      return SYSTEM_VALUE_PRIMITIVE_ID;
    /* FINISHME: Add tessellation intrinsics.
       return SYSTEM_VALUE_TESS_COORD;
       return SYSTEM_VALUE_VERTICES_IN;
diff --git a/src/glsl/nir/nir_intrinsics.h b/src/glsl/nir/nir_intrinsics.h
index 06f1b02..0d93b12 100644
--- a/src/glsl/nir/nir_intrinsics.h
+++ b/src/glsl/nir/nir_intrinsics.h
@@ -194,6 +194,7 @@ SYSTEM_VALUE(instance_id, 1, 0)
 SYSTEM_VALUE(sample_id, 1, 0)
 SYSTEM_VALUE(sample_pos, 2, 0)
 SYSTEM_VALUE(sample_mask_in, 1, 0)
+SYSTEM_VALUE(primitive_id, 1, 0)
 SYSTEM_VALUE(invocation_id, 1, 0)
 SYSTEM_VALUE(local_invocation_id, 3, 0)
 SYSTEM_VALUE(work_group_id, 3, 0)
diff --git a/src/glsl/shader_enums.h b/src/glsl/shader_enums.h
index 3978007..f6b71a3 100644
--- a/src/glsl/shader_enums.h
+++ b/src/glsl/shader_enums.h
@@ -399,7 +399,7 @@ typedef enum
    /*@{*/
    SYSTEM_VALUE_TESS_COORD,
    SYSTEM_VALUE_VERTICES_IN,    /**< Tessellation vertices in input patch */
-   SYSTEM_VALUE_PRIMITIVE_ID,   /**< (currently not used by GS) */
+   SYSTEM_VALUE_PRIMITIVE_ID,
    SYSTEM_VALUE_TESS_LEVEL_OUTER, /**< TES input */
    SYSTEM_VALUE_TESS_LEVEL_INNER, /**< TES input */
    /*@}*/
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..26766a0 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 +72,9 @@ vec4_gs_visitor::nir_setup_system_value_intrinsic(nir_intrinsic_instr *instr)
    dst_reg *reg;
 
    switch (instr->intrinsic) {
+   case nir_intrinsic_load_primitive_id:
+      break;
+
    case nir_intrinsic_load_invocation_id:
       reg = &this->nir_system_values[SYSTEM_VALUE_INVOCATION_ID];
       if (reg->file == BAD_FILE)
@@ -111,6 +114,12 @@ 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]);
-- 
2.5.3