d3d12: add pass to forward front-face

src/gallium/drivers/d3d12/d3d12_nir_passes.c

@@ -115,6 +115,53 @@ d3d12_lower_yflip(nir_shader *nir)
    }
 }
 
+static void
+lower_load_face(nir_builder *b, struct nir_instr *instr, nir_variable *var)
+{
+   if (instr->type != nir_instr_type_intrinsic)
+      return;
+
+   nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+   if (intr->intrinsic != nir_intrinsic_load_front_face)
+      return;
+
+   b->cursor = nir_before_instr(&intr->instr);
+
+   nir_ssa_def *load = nir_load_var(b, var);
+
+   nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(load));
+   nir_instr_remove(instr);
+}
+
+void
+d3d12_forward_front_face(nir_shader *nir)
+{
+   assert(nir->info.stage == MESA_SHADER_FRAGMENT);
+
+   nir_variable *var = nir_variable_create(nir, nir_var_shader_in,
+                                           glsl_bool_type(),
+                                           "gl_FrontFacing");
+   var->data.location = VARYING_SLOT_VAR12;
+   var->data.interpolation = INTERP_MODE_FLAT;
+
+
+   nir_foreach_function(function, nir) {
+      if (function->impl) {
+         nir_builder b;
+         nir_builder_init(&b, function->impl);
+
+         nir_foreach_block(block, function->impl) {
+            nir_foreach_instr_safe(instr, block) {
+               lower_load_face(&b, instr, var);
+            }
+         }
+
+         nir_metadata_preserve(function->impl, nir_metadata_block_index |
+                                               nir_metadata_dominance);
+      }
+   }
+}
+
 static void
 lower_pos_read(nir_builder *b, struct nir_instr *instr,
                nir_variable **depth_transform_var)

src/gallium/drivers/d3d12/d3d12_nir_passes.h

@@ -45,6 +45,9 @@ d3d12_lower_state_vars(struct nir_shader *s, struct d3d12_shader *shader);
 void
 d3d12_lower_yflip(nir_shader *s);
 
+void
+d3d12_forward_front_face(nir_shader *nir);
+
 void
 d3d12_lower_depth_range(nir_shader *nir);