[Mesa-dev] [PATCH 2/3] nir: Use the system-value front face for twoside lowering.

[Eric Anholt]

GLSL-to-NIR generates system value usage, and vc4/freedreno would both
like the system value instead of the varying, so switch this pass over to
it.
---
 src/compiler/nir/nir_lower_two_sided_color.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/src/compiler/nir/nir_lower_two_sided_color.c b/src/compiler/nir/nir_lower_two_sided_color.c
index 3e666691a691..5bb95f66e729 100644
--- a/src/compiler/nir/nir_lower_two_sided_color.c
+++ b/src/compiler/nir/nir_lower_two_sided_color.c
@@ -32,7 +32,6 @@
 typedef struct {
    nir_builder   b;
    nir_shader   *shader;
-   nir_variable *face;
    struct {
       nir_variable *front;        /* COLn */
       nir_variable *back;         /* BFCn */
@@ -85,12 +84,12 @@ setup_inputs(lower_2side_state *state)
 {
    int maxloc = -1;
 
-   /* find color/face inputs: */
+   /* find color inputs: */
    nir_foreach_variable(var, &state->shader->inputs) {
       int loc = var->data.driver_location;
 
       /* keep track of last used driver-location.. we'll be
-       * appending BCLr/FACE after last existing input:
+       * appending BCLr after last existing input:
        */
       maxloc = MAX2(maxloc, loc);
 
@@ -101,9 +100,6 @@ setup_inputs(lower_2side_state *state)
          state->colors[state->colors_count].front = var;
          state->colors_count++;
          break;
-      case VARYING_SLOT_FACE:
-         state->face = var;
-         break;
       }
    }
 
@@ -111,12 +107,6 @@ setup_inputs(lower_2side_state *state)
    if (state->colors_count == 0)
       return -1;
 
-   /* if we don't already have one, insert a FACE input: */
-   if (!state->face) {
-      state->face = create_input(state->shader, ++maxloc, VARYING_SLOT_FACE);
-      state->face->data.interpolation = INTERP_MODE_FLAT;
-   }
-
    /* add required back-face color inputs: */
    for (int i = 0; i < state->colors_count; i++) {
       gl_varying_slot slot;
@@ -161,14 +151,15 @@ nir_lower_two_sided_color_block(nir_block *block,
          continue;
 
       /* replace load_input(COLn) with
-       * bcsel(load_input(FACE), load_input(COLn), load_input(BFCn))
+       * bcsel(load_system_value(FACE), load_input(COLn), load_input(BFCn))
        */
       b->cursor = nir_before_instr(&intr->instr);
-      nir_ssa_def *face  = nir_channel(b, load_input(b, state->face), 0);
+      nir_ssa_def *face  = nir_load_system_value(b,
+                                                 nir_intrinsic_load_front_face,
+                                                 0);
       nir_ssa_def *front = load_input(b, state->colors[idx].front);
       nir_ssa_def *back  = load_input(b, state->colors[idx].back);
-      nir_ssa_def *cond  = nir_flt(b, face, nir_imm_float(b, 0.0));
-      nir_ssa_def *color = nir_bcsel(b, cond, back, front);
+      nir_ssa_def *color = nir_bcsel(b, face, front, back);
 
       assert(intr->dest.is_ssa);
       nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(color));
-- 
2.8.1