nir: add two-sided-color lowering pass

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/glsl/Makefile.sources

@@ -47,6 +47,7 @@ NIR_FILES = \
 	nir/nir_lower_system_values.c \
 	nir/nir_lower_tex.c \
 	nir/nir_lower_to_source_mods.c \
+	nir/nir_lower_two_sided_color.c \
 	nir/nir_lower_vars_to_ssa.c \
 	nir/nir_lower_var_copies.c \
 	nir/nir_lower_vec_to_movs.c \

src/glsl/nir/nir.h

@@ -1878,6 +1878,8 @@ void nir_lower_idiv(nir_shader *shader);
 void nir_lower_clip_vs(nir_shader *shader, unsigned ucp_enables);
 void nir_lower_clip_fs(nir_shader *shader, unsigned ucp_enables);
 
+void nir_lower_two_sided_color(nir_shader *shader);
+
 void nir_lower_atomics(nir_shader *shader);
 void nir_lower_to_source_mods(nir_shader *shader);
 

src/glsl/nir/nir_lower_two_sided_color.c

@@ -0,0 +1,208 @@
+/*
+ * Copyright © 2015 Red Hat
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Authors:
+ *    Rob Clark <robclark@freedesktop.org>
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+
+#define MAX_COLORS 2  /* VARYING_SLOT_COL0/COL1 */
+
+typedef struct {
+   nir_builder   b;
+   nir_shader   *shader;
+   nir_variable *face;
+   struct {
+      nir_variable *front;        /* COLn */
+      nir_variable *back;         /* BFCn */
+   } colors[MAX_COLORS];
+   int colors_count;
+} lower_2side_state;
+
+
+/* Lowering pass for fragment shaders to emulated two-sided-color.  For
+ * each COLOR input, a corresponding BCOLOR input is created, and bcsel
+ * instruction used to select front or back color based on FACE.
+ */
+
+static nir_variable *
+create_input(nir_shader *shader, unsigned drvloc, gl_varying_slot slot)
+{
+   nir_variable *var = rzalloc(shader, nir_variable);
+
+   var->data.driver_location = drvloc;
+   var->type = glsl_vec4_type();
+   var->data.mode = nir_var_shader_in;
+   var->name = ralloc_asprintf(var, "in_%d", drvloc);
+   var->data.index = 0;
+   var->data.location = slot;
+
+   exec_list_push_tail(&shader->inputs, &var->node);
+
+   return var;
+}
+
+static nir_ssa_def *
+load_input(nir_builder *b, nir_variable *in)
+{
+   nir_intrinsic_instr *load;
+
+   load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
+   load->num_components = 4;
+   load->const_index[0] = in->data.driver_location;
+   nir_ssa_dest_init(&load->instr, &load->dest, 4, NULL);
+   nir_builder_instr_insert(b, &load->instr);
+
+   return &load->dest.ssa;
+}
+
+static int
+setup_inputs(lower_2side_state *state)
+{
+   int maxloc = -1;
+
+   /* find color/face inputs: */
+   foreach_list_typed(nir_variable, var, node, &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:
+       */
+      maxloc = MAX2(maxloc, loc);
+
+      switch (var->data.location) {
+      case VARYING_SLOT_COL0:
+      case VARYING_SLOT_COL1:
+         assert(state->colors_count < ARRAY_SIZE(state->colors));
+         state->colors[state->colors_count].front = var;
+         state->colors_count++;
+         break;
+      case VARYING_SLOT_FACE:
+         state->face = var;
+         break;
+      }
+   }
+
+   /* if we don't have any color inputs, nothing to do: */
+   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_QUALIFIER_FLAT;
+   }
+
+   /* add required back-face color inputs: */
+   for (int i = 0; i < state->colors_count; i++) {
+      gl_varying_slot slot;
+
+      if (state->colors[i].front->data.location == VARYING_SLOT_COL0)
+         slot = VARYING_SLOT_BFC0;
+      else
+         slot = VARYING_SLOT_BFC1;
+
+      state->colors[i].back = create_input(state->shader, ++maxloc, slot);
+   }
+
+   return 0;
+}
+
+static bool
+nir_lower_two_sided_color_block(nir_block *block, void *void_state)
+{
+   lower_2side_state *state = void_state;
+   nir_builder *b = &state->b;
+
+   nir_foreach_instr_safe(block, instr) {
+      if (instr->type != nir_instr_type_intrinsic)
+         continue;
+
+      nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+
+      if (intr->intrinsic != nir_intrinsic_load_input)
+         continue;
+
+      int idx;
+      for (idx = 0; idx < state->colors_count; idx++) {
+         unsigned drvloc =
+            state->colors[idx].front->data.driver_location;
+         if (intr->const_index[0] == drvloc) {
+            break;
+         }
+      }
+
+      if (idx == state->colors_count)
+         continue;
+
+      /* replace load_input(COLn) with
+       * bcsel(load_input(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 *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);
+
+      assert(intr->dest.is_ssa);
+      nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(color));
+   }
+
+   return true;
+}
+
+static void
+nir_lower_two_sided_color_impl(nir_function_impl *impl,
+                               lower_2side_state *state)
+{
+   nir_builder *b = &state->b;
+
+   nir_builder_init(b, impl);
+
+   nir_foreach_block(impl, nir_lower_two_sided_color_block, state);
+
+   nir_metadata_preserve(impl, nir_metadata_block_index |
+                               nir_metadata_dominance);
+}
+
+void
+nir_lower_two_sided_color(nir_shader *shader)
+{
+   lower_2side_state state = {
+      .shader = shader,
+   };
+
+   if (shader->stage != MESA_SHADER_FRAGMENT)
+      return;
+
+   if (setup_inputs(&state) != 0)
+      return;
+
+   nir_foreach_overload(shader, overload) {
+      if (overload->impl)
+         nir_lower_two_sided_color_impl(overload->impl, &state);
+   }
+
+}