text: /*
   * Copyright © 2015 Broadcom
   *
   * 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.
   */
  
  /**
   * Implements most of the fixed function fragment pipeline in shader code.
   *
   * VC4 doesn't have any hardware support for blending, alpha test, logic ops,
   * or color mask.  Instead, you read the current contents of the destination
   * from the tile buffer after having waited for the scoreboard (which is
   * handled by vc4_qpu_emit.c), then do math using your output color and that
   * destination value, and update the output color appropriately.
   *
   * Once this pass is done, the color write will either have one component (for
   * single sample) with packed argb8888, or 4 components with the per-sample
   * argb8888 result.
   */
  
  /**
   * Lowers fixed-function blending to a load of the destination color and a
   * series of ALU operations before the store of the output.
   */
  #include "util/u_format.h"
  #include "vc4_qir.h"
  #include "compiler/nir/nir_builder.h"
  #include "vc4_context.h"
  
  static bool
  blend_depends_on_dst_color(struct vc4_compile *c)
  {
          return (c->fs_key->blend.blend_enable ||
                  c->fs_key->blend.colormask != 0xf ||
                  c->fs_key->logicop_func != PIPE_LOGICOP_COPY);
  }
  
  /** Emits a load of the previous fragment color from the tile buffer. */
  static nir_ssa_def *
  vc4_nir_get_dst_color(nir_builder *b, int sample)
  {
          nir_intrinsic_instr *load =
                  nir_intrinsic_instr_create(b->shader,
                                             nir_intrinsic_load_input);
          load->num_components = 1;
          nir_intrinsic_set_base(load, VC4_NIR_TLB_COLOR_READ_INPUT + sample);
          load->src[0] = nir_src_for_ssa(nir_imm_int(b, 0));
          nir_ssa_dest_init(&load->instr, &load->dest, 1, 32, NULL);
          nir_builder_instr_insert(b, &load->instr);
          return &load->dest.ssa;
  }
  
  static  nir_ssa_def *
  vc4_nir_srgb_decode(nir_builder *b, nir_ssa_def *srgb)
  {
          nir_ssa_def *is_low = nir_flt(b, srgb, nir_imm_float(b, 0.04045));
          nir_ssa_def *low = nir_fmul(b, srgb, nir_imm_float(b, 1.0 / 12.92));
          nir_ssa_def *high = nir_fpow(b,
                                       nir_fmul(b,
                                                nir_fadd(b, srgb,
                                                         nir_imm_float(b, 0.055)),
                                                nir_imm_float(b, 1.0 / 1.055)),
                                       nir_imm_float(b, 2.4));
  
          return nir_bcsel(b, is_low, low, high);
  }
  
  static  nir_ssa_def *
  vc4_nir_srgb_encode(nir_builder *b, nir_ssa_def *linear)
  {
          nir_ssa_def *is_low = nir_flt(b, linear, nir_imm_float(b, 0.0031308));
          nir_ssa_def *low = nir_fmul(b, linear, nir_imm_float(b, 12.92));
          nir_ssa_def *high = nir_fsub(b,
                                       nir_fmul(b,
                                                nir_imm_float(b, 1.055),
                                                nir_fpow(b,
                                                         linear,
                                                         nir_imm_float(b, 0.41666))),
                                       nir_imm_float(b, 0.055));
  
          return nir_bcsel(b, is_low, low, high);
  }
  
  static nir_ssa_def *
  vc4_blend_channel_f(nir_builder *b,
                      nir_ssa_def **src,
                      nir_ssa_def **dst,
                      unsigned factor,
                      int channel)
  {
          switch(factor) {
          case PIPE_BLENDFACTOR_ONE:
                  return nir_imm_float(b, 1.0);
          case PIPE_BLENDFACTOR_SRC_COLOR:
                  return src[channel];
          case PIPE_BLENDFACTOR_SRC_ALPHA:
                  return src[3];
          case PIPE_BLENDFACTOR_DST_ALPHA:
                  return dst[3];
          case PIPE_BLENDFACTOR_DST_COLOR:
                  return dst[channel];
          case PIPE_BLENDFACTOR_SRC_ALPHA_SATURATE:
                  if (channel != 3) {
                          return nir_fmin(b,
                                          src[3],
                                          nir_fsub(b,
                                                   nir_imm_float(b, 1.0),
                                                   dst[3]));
                  } else {
                          return nir_imm_float(b, 1.0);
                  }
          case PIPE_BLENDFACTOR_CONST_COLOR:
                  return nir_load_system_value(b,
                                               nir_intrinsic_load_blend_const_color_r_float +
                                               channel,
                                               0);
          case PIPE_BLENDFACTOR_CONST_ALPHA:
                  return nir_load_blend_const_color_a_float(b);
          case PIPE_BLENDFACTOR_ZERO:
                  return nir_imm_float(b, 0.0);
          case PIPE_BLENDFACTOR_INV_SRC_COLOR:
                  return nir_fsub(b, nir_imm_float(b, 1.0), src[channel]);
          case PIPE_BLENDFACTOR_INV_SRC_ALPHA:
                  return nir_fsub(b, nir_imm_float(b, 1.0), src[3]);
          case PIPE_BLENDFACTOR_INV_DST_ALPHA:
                  return nir_fsub(b, nir_imm_float(b, 1.0), dst[3]);
          case PIPE_BLENDFACTOR_INV_DST_COLOR:
                  return nir_fsub(b, nir_imm_float(b, 1.0), dst[channel]);
          case PIPE_BLENDFACTOR_INV_CONST_COLOR:
                  return nir_fsub(b, nir_imm_float(b, 1.0),
                                  nir_load_system_value(b,
                                                        nir_intrinsic_load_blend_const_color_r_float +
                                                        channel,
                                                        0));
          case PIPE_BLENDFACTOR_INV_CONST_ALPHA:
                  return nir_fsub(b, nir_imm_float(b, 1.0),
                                  nir_load_blend_const_color_a_float(b));
  
          default:
          case PIPE_BLENDFACTOR_SRC1_COLOR:
          case PIPE_BLENDFACTOR_SRC1_ALPHA:
          case PIPE_BLENDFACTOR_INV_SRC1_COLOR:
          case PIPE_BLENDFACTOR_INV_SRC1_ALPHA:
                  /* Unsupported. */
                  fprintf(stderr, "Unknown blend factor %d\n", factor);
                  return nir_imm_float(b, 1.0);
          }
  }
  
  static nir_ssa_def *
  vc4_nir_set_packed_chan(nir_builder *b, nir_ssa_def *src0, nir_ssa_def *src1,
                          int chan)
  {
          unsigned chan_mask = 0xff << (chan * 8);
          return nir_ior(b,
                         nir_iand(b, src0, nir_imm_int(b, ~chan_mask)),
                         nir_iand(b, src1, nir_imm_int(b, chan_mask)));
  }
  
  static nir_ssa_def *
  vc4_blend_channel_i(nir_builder *b,
                      nir_ssa_def *src,
                      nir_ssa_def *dst,
                      nir_ssa_def *src_a,
                      nir_ssa_def *dst_a,
                      unsigned factor,
                      int a_chan)
  {
          switch (factor) {
          case PIPE_BLENDFACTOR_ONE:
                  return nir_imm_int(b, ~0);
          case PIPE_BLENDFACTOR_SRC_COLOR:
                  return src;
          case PIPE_BLENDFACTOR_SRC_ALPHA:
                  return src_a;
          case PIPE_BLENDFACTOR_DST_ALPHA:
                  return dst_a;
          case PIPE_BLENDFACTOR_DST_COLOR:
                  return dst;
          case PIPE_BLENDFACTOR_SRC_ALPHA_SATURATE:
                  return vc4_nir_set_packed_chan(b,
                                                 nir_umin_4x8(b,
                                                              src_a,
                                                              nir_inot(b, dst_a)),
                                                 nir_imm_int(b, ~0),
                                                 a_chan);
          case PIPE_BLENDFACTOR_CONST_COLOR:
                  return nir_load_blend_const_color_rgba8888_unorm(b);
          case PIPE_BLENDFACTOR_CONST_ALPHA:
                  return nir_load_blend_const_color_aaaa8888_unorm(b);
          case PIPE_BLENDFACTOR_ZERO:
                  return nir_imm_int(b, 0);
          case PIPE_BLENDFACTOR_INV_SRC_COLOR:
                  return nir_inot(b, src);
          case PIPE_BLENDFACTOR_INV_SRC_ALPHA:
                  return nir_inot(b, src_a);
          case PIPE_BLENDFACTOR_INV_DST_ALPHA:
                  return nir_inot(b, dst_a);
          case PIPE_BLENDFACTOR_INV_DST_COLOR:
                  return nir_inot(b, dst);
          case PIPE_BLENDFACTOR_INV_CONST_COLOR:
                  return nir_inot(b,
                                  nir_load_blend_const_color_rgba8888_unorm(b));
          case PIPE_BLENDFACTOR_INV_CONST_ALPHA:
                  return nir_inot(b,
                                  nir_load_blend_const_color_aaaa8888_unorm(b));
  
          default:
          case PIPE_BLENDFACTOR_SRC1_COLOR:
          case PIPE_BLENDFACTOR_SRC1_ALPHA:
          case PIPE_BLENDFACTOR_INV_SRC1_COLOR:
          case PIPE_BLENDFACTOR_INV_SRC1_ALPHA:
                  /* Unsupported. */
                  fprintf(stderr, "Unknown blend factor %d\n", factor);
                  return nir_imm_int(b, ~0);
          }
  }
  
  static nir_ssa_def *
  vc4_blend_func_f(nir_builder *b, nir_ssa_def *src, nir_ssa_def *dst,
                   unsigned func)
  {
          switch (func) {
          case PIPE_BLEND_ADD:
                  return nir_fadd(b, src, dst);
          case PIPE_BLEND_SUBTRACT:
                  return nir_fsub(b, src, dst);
          case PIPE_BLEND_REVERSE_SUBTRACT:
                  return nir_fsub(b, dst, src);
          case PIPE_BLEND_MIN:
                  return nir_fmin(b, src, dst);
          case PIPE_BLEND_MAX:
                  return nir_fmax(b, src, dst);
  
          default:
                  /* Unsupported. */
                  fprintf(stderr, "Unknown blend func %d\n", func);
                  return src;
  
          }
  }
  
  static nir_ssa_def *
  vc4_blend_func_i(nir_builder *b, nir_ssa_def *src, nir_ssa_def *dst,
                   unsigned func)
  {
          switch (func) {
          case PIPE_BLEND_ADD:
                  return nir_usadd_4x8(b, src, dst);
          case PIPE_BLEND_SUBTRACT:
                  return nir_ussub_4x8(b, src, dst);
          case PIPE_BLEND_REVERSE_SUBTRACT:
                  return nir_ussub_4x8(b, dst, src);
          case PIPE_BLEND_MIN:
                  return nir_umin_4x8(b, src, dst);
          case PIPE_BLEND_MAX:
                  return nir_umax_4x8(b, src, dst);
  
          default:
                  /* Unsupported. */
                  fprintf(stderr, "Unknown blend func %d\n", func);
                  return src;
  
          }
  }
  
  static void
  vc4_do_blending_f(struct vc4_compile *c, nir_builder *b, nir_ssa_def **result,
                    nir_ssa_def **src_color, nir_ssa_def **dst_color)
  {
          struct pipe_rt_blend_state *blend = &c->fs_key->blend;
  
          if (!blend->blend_enable) {
                  for (int i = 0; i < 4; i++)
                          result[i] = src_color[i];
                  return;
          }
  
          /* Clamp the src color to [0, 1].  Dest is already clamped. */
          for (int i = 0; i < 4; i++)
                  src_color[i] = nir_fsat(b, src_color[i]);
  
          nir_ssa_def *src_blend[4], *dst_blend[4];
          for (int i = 0; i < 4; i++) {
                  int src_factor = ((i != 3) ? blend->rgb_src_factor :
                                    blend->alpha_src_factor);
                  int dst_factor = ((i != 3) ? blend->rgb_dst_factor :
                                    blend->alpha_dst_factor);
                  src_blend[i] = nir_fmul(b, src_color[i],
                                          vc4_blend_channel_f(b,
                                                              src_color, dst_color,
                                                              src_factor, i));
                  dst_blend[i] = nir_fmul(b, dst_color[i],
                                          vc4_blend_channel_f(b,
                                                              src_color, dst_color,
                                                              dst_factor, i));
          }
  
          for (int i = 0; i < 4; i++) {
                  result[i] = vc4_blend_func_f(b, src_blend[i], dst_blend[i],
                                               ((i != 3) ? blend->rgb_func :
                                                blend->alpha_func));
          }
  }
  
  static nir_ssa_def *
  vc4_nir_splat(nir_builder *b, nir_ssa_def *src)
  {
          nir_ssa_def *or1 = nir_ior(b, src, nir_ishl(b, src, nir_imm_int(b, 8)));
          return nir_ior(b, or1, nir_ishl(b, or1, nir_imm_int(b, 16)));
  }
  
  static nir_ssa_def *
  vc4_do_blending_i(struct vc4_compile *c, nir_builder *b,
                    nir_ssa_def *src_color, nir_ssa_def *dst_color,
                    nir_ssa_def *src_float_a)
  {
          struct pipe_rt_blend_state *blend = &c->fs_key->blend;
  
          if (!blend->blend_enable)
                  return src_color;
  
          enum pipe_format color_format = c->fs_key->color_format;
          const uint8_t *format_swiz = vc4_get_format_swizzle(color_format);
          nir_ssa_def *imm_0xff = nir_imm_int(b, 0xff);
          nir_ssa_def *src_a = nir_pack_unorm_4x8(b, src_float_a);
          nir_ssa_def *dst_a;
          int alpha_chan;
          for (alpha_chan = 0; alpha_chan < 4; alpha_chan++) {
                  if (format_swiz[alpha_chan] == 3)
                          break;
          }
          if (alpha_chan != 4) {
                  nir_ssa_def *shift = nir_imm_int(b, alpha_chan * 8);
                  dst_a = vc4_nir_splat(b, nir_iand(b, nir_ushr(b, dst_color,
                                                                shift), imm_0xff));
          } else {
                  dst_a = nir_imm_int(b, ~0);
          }
  
          nir_ssa_def *src_factor = vc4_blend_channel_i(b,
                                                        src_color, dst_color,
                                                        src_a, dst_a,
                                                        blend->rgb_src_factor,
                                                        alpha_chan);
          nir_ssa_def *dst_factor = vc4_blend_channel_i(b,
                                                        src_color, dst_color,
                                                        src_a, dst_a,
                                                        blend->rgb_dst_factor,
                                                        alpha_chan);
  
          if (alpha_chan != 4 &&
              blend->alpha_src_factor != blend->rgb_src_factor) {
                  nir_ssa_def *src_alpha_factor =
                          vc4_blend_channel_i(b,
                                              src_color, dst_color,
                                              src_a, dst_a,
                                              blend->alpha_src_factor,
                                              alpha_chan);
                  src_factor = vc4_nir_set_packed_chan(b, src_factor,
                                                       src_alpha_factor,
                                                       alpha_chan);
          }
          if (alpha_chan != 4 &&
              blend->alpha_dst_factor != blend->rgb_dst_factor) {
                  nir_ssa_def *dst_alpha_factor =
                          vc4_blend_channel_i(b,
                                              src_color, dst_color,
                                              src_a, dst_a,
                                              blend->alpha_dst_factor,
                                              alpha_chan);
                  dst_factor = vc4_nir_set_packed_chan(b, dst_factor,
                                                       dst_alpha_factor,
                                                       alpha_chan);
          }
          nir_ssa_def *src_blend = nir_umul_unorm_4x8(b, src_color, src_factor);
          nir_ssa_def *dst_blend = nir_umul_unorm_4x8(b, dst_color, dst_factor);
  
          nir_ssa_def *result =
                  vc4_blend_func_i(b, src_blend, dst_blend, blend->rgb_func);
          if (alpha_chan != 4 && blend->alpha_func != blend->rgb_func) {
                  nir_ssa_def *result_a = vc4_blend_func_i(b,
                                                           src_blend,
                                                           dst_blend,
                                                           blend->alpha_func);
                  result = vc4_nir_set_packed_chan(b, result, result_a,
                                                   alpha_chan);
          }
          return result;
  }
  
  static nir_ssa_def *
  vc4_logicop(nir_builder *b, int logicop_func,
              nir_ssa_def *src, nir_ssa_def *dst)
  {
          switch (logicop_func) {
          case PIPE_LOGICOP_CLEAR:
                  return nir_imm_int(b, 0);
          case PIPE_LOGICOP_NOR:
                  return nir_inot(b, nir_ior(b, src, dst));
          case PIPE_LOGICOP_AND_INVERTED:
                  return nir_iand(b, nir_inot(b, src), dst);
          case PIPE_LOGICOP_COPY_INVERTED:
                  return nir_inot(b, src);
          case PIPE_LOGICOP_AND_REVERSE:
                  return nir_iand(b, src, nir_inot(b, dst));
          case PIPE_LOGICOP_INVERT:
                  return nir_inot(b, dst);
          case PIPE_LOGICOP_XOR:
                  return nir_ixor(b, src, dst);
          case PIPE_LOGICOP_NAND:
                  return nir_inot(b, nir_iand(b, src, dst));
          case PIPE_LOGICOP_AND:
                  return nir_iand(b, src, dst);
          case PIPE_LOGICOP_EQUIV:
                  return nir_inot(b, nir_ixor(b, src, dst));
          case PIPE_LOGICOP_NOOP:
                  return dst;
          case PIPE_LOGICOP_OR_INVERTED:
                  return nir_ior(b, nir_inot(b, src), dst);
          case PIPE_LOGICOP_OR_REVERSE:
                  return nir_ior(b, src, nir_inot(b, dst));
          case PIPE_LOGICOP_OR:
                  return nir_ior(b, src, dst);
          case PIPE_LOGICOP_SET:
                  return nir_imm_int(b, ~0);
          default:
                  fprintf(stderr, "Unknown logic op %d\n", logicop_func);
                  /* FALLTHROUGH */
          case PIPE_LOGICOP_COPY:
                  return src;
          }
  }
  
  static nir_ssa_def *
  vc4_nir_pipe_compare_func(nir_builder *b, int func,
                            nir_ssa_def *src0, nir_ssa_def *src1)
  {
          switch (func) {
          default:
                  fprintf(stderr, "Unknown compare func %d\n", func);
                  /* FALLTHROUGH */
          case PIPE_FUNC_NEVER:
                  return nir_imm_int(b, 0);
          case PIPE_FUNC_ALWAYS:
                  return nir_imm_int(b, ~0);
          case PIPE_FUNC_EQUAL:
                  return nir_feq(b, src0, src1);
          case PIPE_FUNC_NOTEQUAL:
                  return nir_fne(b, src0, src1);
          case PIPE_FUNC_GREATER:
                  return nir_flt(b, src1, src0);
          case PIPE_FUNC_GEQUAL:
                  return nir_fge(b, src0, src1);
          case PIPE_FUNC_LESS:
                  return nir_flt(b, src0, src1);
          case PIPE_FUNC_LEQUAL:
                  return nir_fge(b, src1, src0);
          }
  }
  
  static void
  vc4_nir_emit_alpha_test_discard(struct vc4_compile *c, nir_builder *b,
                                  nir_ssa_def *alpha)
  {
          if (!c->fs_key->alpha_test)
                  return;
  
          nir_ssa_def *condition =
                  vc4_nir_pipe_compare_func(b, c->fs_key->alpha_test_func,
                                            alpha,
                                            nir_load_alpha_ref_float(b));
  
          nir_intrinsic_instr *discard =
                  nir_intrinsic_instr_create(b->shader,
                                             nir_intrinsic_discard_if);
          discard->num_components = 1;
          discard->src[0] = nir_src_for_ssa(nir_inot(b, condition));
          nir_builder_instr_insert(b, &discard->instr);
          c->s->info.fs.uses_discard = true;
  }
  
  static nir_ssa_def *
  vc4_nir_swizzle_and_pack(struct vc4_compile *c, nir_builder *b,
                           nir_ssa_def **colors)
  {
          enum pipe_format color_format = c->fs_key->color_format;
          const uint8_t *format_swiz = vc4_get_format_swizzle(color_format);
  
          nir_ssa_def *swizzled[4];
          for (int i = 0; i < 4; i++) {
                  swizzled[i] = vc4_nir_get_swizzled_channel(b, colors,
                                                             format_swiz[i]);
          }
  
          return nir_pack_unorm_4x8(b,
                                    nir_vec4(b,
                                             swizzled[0], swizzled[1],
                                             swizzled[2], swizzled[3]));
  
  }
  
  static nir_ssa_def *
  vc4_nir_blend_pipeline(struct vc4_compile *c, nir_builder *b, nir_ssa_def *src,
                         int sample)
  {
          enum pipe_format color_format = c->fs_key->color_format;
          const uint8_t *format_swiz = vc4_get_format_swizzle(color_format);
          bool srgb = util_format_is_srgb(color_format);
  
          /* Pull out the float src/dst color components. */
          nir_ssa_def *packed_dst_color = vc4_nir_get_dst_color(b, sample);
          nir_ssa_def *dst_vec4 = nir_unpack_unorm_4x8(b, packed_dst_color);
          nir_ssa_def *src_color[4], *unpacked_dst_color[4];
          for (unsigned i = 0; i < 4; i++) {
                  src_color[i] = nir_channel(b, src, i);
                  unpacked_dst_color[i] = nir_channel(b, dst_vec4, i);
          }
  
          if (c->fs_key->sample_alpha_to_one && c->fs_key->msaa)
                  src_color[3] = nir_imm_float(b, 1.0);
  
          vc4_nir_emit_alpha_test_discard(c, b, src_color[3]);
  
          nir_ssa_def *packed_color;
          if (srgb) {
                  /* Unswizzle the destination color. */
                  nir_ssa_def *dst_color[4];
                  for (unsigned i = 0; i < 4; i++) {
                          dst_color[i] = vc4_nir_get_swizzled_channel(b,
                                                                      unpacked_dst_color,
                                                                      format_swiz[i]);
                  }
  
                  /* Turn dst color to linear. */
                  for (int i = 0; i < 3; i++)
                          dst_color[i] = vc4_nir_srgb_decode(b, dst_color[i]);
  
                  nir_ssa_def *blend_color[4];
                  vc4_do_blending_f(c, b, blend_color, src_color, dst_color);
  
                  /* sRGB encode the output color */
                  for (int i = 0; i < 3; i++)
                          blend_color[i] = vc4_nir_srgb_encode(b, blend_color[i]);
  
                  packed_color = vc4_nir_swizzle_and_pack(c, b, blend_color);
          } else {
                  nir_ssa_def *packed_src_color =
                          vc4_nir_swizzle_and_pack(c, b, src_color);
  
                  packed_color =
                          vc4_do_blending_i(c, b,
                                            packed_src_color, packed_dst_color,
                                            src_color[3]);
          }
  
          packed_color = vc4_logicop(b, c->fs_key->logicop_func,
                                     packed_color, packed_dst_color);
  
          /* If the bit isn't set in the color mask, then just return the
           * original dst color, instead.
           */
          uint32_t colormask = 0xffffffff;
          for (int i = 0; i < 4; i++) {
                  if (format_swiz[i] < 4 &&
                      !(c->fs_key->blend.colormask & (1 << format_swiz[i]))) {
                          colormask &= ~(0xff << (i * 8));
                  }
          }
  
          return nir_ior(b,
                         nir_iand(b, packed_color,
                                  nir_imm_int(b, colormask)),
                         nir_iand(b, packed_dst_color,
                                  nir_imm_int(b, ~colormask)));
  }
  
  static int
  vc4_nir_next_output_driver_location(nir_shader *s)
  {
          int maxloc = -1;
  
          nir_foreach_variable(var, &s->outputs)
                  maxloc = MAX2(maxloc, (int)var->data.driver_location);
  
          return maxloc + 1;
  }
  
  static void
  vc4_nir_store_sample_mask(struct vc4_compile *c, nir_builder *b,
                            nir_ssa_def *val)
  {
          nir_variable *sample_mask = nir_variable_create(c->s, nir_var_shader_out,
                                                          glsl_uint_type(),
                                                          "sample_mask");
          sample_mask->data.driver_location =
                  vc4_nir_next_output_driver_location(c->s);
          sample_mask->data.location = FRAG_RESULT_SAMPLE_MASK;
  
          nir_intrinsic_instr *intr =
                  nir_intrinsic_instr_create(c->s, nir_intrinsic_store_output);
          intr->num_components = 1;
          nir_intrinsic_set_base(intr, sample_mask->data.driver_location);
  
          intr->src[0] = nir_src_for_ssa(val);
          intr->src[1] = nir_src_for_ssa(nir_imm_int(b, 0));
          nir_builder_instr_insert(b, &intr->instr);
  }
  
  static void
  vc4_nir_lower_blend_instr(struct vc4_compile *c, nir_builder *b,
                            nir_intrinsic_instr *intr)
  {
          nir_ssa_def *frag_color = intr->src[0].ssa;
  
          if (c->fs_key->sample_coverage) {
                  nir_intrinsic_instr *load =
                          nir_intrinsic_instr_create(b->shader,
                                                     nir_intrinsic_load_sample_mask_in);
                  load->num_components = 1;
                  nir_ssa_dest_init(&load->instr, &load->dest, 1, 32, NULL);
                  nir_builder_instr_insert(b, &load->instr);
  
                  nir_ssa_def *bitmask = &load->dest.ssa;
  
                  vc4_nir_store_sample_mask(c, b, bitmask);
          } else if (c->fs_key->sample_alpha_to_coverage) {
                  nir_ssa_def *a = nir_channel(b, frag_color, 3);
  
                  /* XXX: We should do a nice dither based on the fragment
                   * coordinate, instead.
                   */
                  nir_ssa_def *num_samples = nir_imm_float(b, VC4_MAX_SAMPLES);
                  nir_ssa_def *num_bits = nir_f2i(b, nir_fmul(b, a, num_samples));
                  nir_ssa_def *bitmask = nir_isub(b,
                                                  nir_ishl(b,
                                                           nir_imm_int(b, 1),
                                                           num_bits),
                                                  nir_imm_int(b, 1));
                  vc4_nir_store_sample_mask(c, b, bitmask);
          }
  
          /* The TLB color read returns each sample in turn, so if our blending
           * depends on the destination color, we're going to have to run the
           * blending function separately for each destination sample value, and
           * then output the per-sample color using TLB_COLOR_MS.
           */
          nir_ssa_def *blend_output;
          if (c->fs_key->msaa && blend_depends_on_dst_color(c)) {
                  c->msaa_per_sample_output = true;
  
                  nir_ssa_def *samples[4];
                  for (int i = 0; i < VC4_MAX_SAMPLES; i++)
                          samples[i] = vc4_nir_blend_pipeline(c, b, frag_color, i);
                  blend_output = nir_vec4(b,
                                          samples[0], samples[1],
                                          samples[2], samples[3]);
          } else {
                  blend_output = vc4_nir_blend_pipeline(c, b, frag_color, 0);
          }
  
          nir_instr_rewrite_src(&intr->instr, &intr->src[0],
                                nir_src_for_ssa(blend_output));
          intr->num_components = blend_output->num_components;
  }
  
  static bool
  vc4_nir_lower_blend_block(nir_block *block, struct vc4_compile *c)
  {
          nir_foreach_instr_safe(instr, block) {
                  if (instr->type != nir_instr_type_intrinsic)
                          continue;
                  nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
                  if (intr->intrinsic != nir_intrinsic_store_output)
                          continue;
  
                  nir_variable *output_var = NULL;
                  nir_foreach_variable(var, &c->s->outputs) {
                          if (var->data.driver_location ==
                              nir_intrinsic_base(intr)) {
                                  output_var = var;
                                  break;
                          }
                  }
                  assert(output_var);
  
                  if (output_var->data.location != FRAG_RESULT_COLOR &&
                      output_var->data.location != FRAG_RESULT_DATA0) {
                          continue;
                  }
  
                  nir_function_impl *impl =
                          nir_cf_node_get_function(&block->cf_node);
                  nir_builder b;
                  nir_builder_init(&b, impl);
                  b.cursor = nir_before_instr(&intr->instr);
                  vc4_nir_lower_blend_instr(c, &b, intr);
          }
          return true;
  }
  
  void
  vc4_nir_lower_blend(nir_shader *s, struct vc4_compile *c)
  {
          nir_foreach_function(function, s) {
                  if (function->impl) {
                          nir_foreach_block(block, function->impl) {
                                  vc4_nir_lower_blend_block(block, c);
                          }
  
                          nir_metadata_preserve(function->impl,
                                                nir_metadata_block_index |
                                                nir_metadata_dominance);
                  }
          }
  }
  