src/compiler/nir/nir_lower_interpolation.c

/*
 * Copyright © 2019 Google, Inc.
 *
 * 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.
 */

/*
 * This lower pass lowers load_interpolated_input for various interpolation
 * modes (as configured via nir_lower_interpolation_options bitmask) into
 * load_attribute_deltas plus alu instructions:
 *
 *    vec3 ad = load_attribute_deltas(varying_slot)
 *    float result = ad.x + ad.y * j + ad.z * i
 *
 */

#include "nir.h"
#include "nir_builder.h"

static bool
nir_lower_interpolation_block(nir_block *block, nir_builder *b,
                              nir_lower_interpolation_options options)
{
   bool progress = false;

   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_load_interpolated_input)
         continue;

      assert(intr->dest.is_ssa);
      assert(intr->src[0].is_ssa);
      assert(intr->src[1].is_ssa);

      nir_intrinsic_instr *bary_intrinsic =
         nir_instr_as_intrinsic(intr->src[0].ssa->parent_instr);

      /* Leave VARYING_SLOT_POS alone */
      if (nir_intrinsic_base(intr) == VARYING_SLOT_POS)
         continue;

      const enum glsl_interp_mode interp_mode =
         nir_intrinsic_interp_mode(bary_intrinsic);

      /* We need actual interpolation modes by the time we get here */
      assert(interp_mode != INTERP_MODE_NONE);

      /* Only lower for inputs that need interpolation */
      if (interp_mode != INTERP_MODE_SMOOTH &&
          interp_mode != INTERP_MODE_NOPERSPECTIVE)
         continue;

      nir_intrinsic_op op = bary_intrinsic->intrinsic;

      switch (op) {
      case nir_intrinsic_load_barycentric_at_sample:
         if (options & nir_lower_interpolation_at_sample)
            break;
         continue;
      case nir_intrinsic_load_barycentric_at_offset:
         if (options & nir_lower_interpolation_at_offset)
            break;
         continue;
      case nir_intrinsic_load_barycentric_centroid:
         if (options & nir_lower_interpolation_centroid)
            break;
         continue;
      case nir_intrinsic_load_barycentric_pixel:
         if (options & nir_lower_interpolation_pixel)
            break;
         continue;
      case nir_intrinsic_load_barycentric_sample:
         if (options & nir_lower_interpolation_sample)
            break;
         continue;
      default:
         continue;
      }

      b->cursor = nir_before_instr(instr);

      nir_ssa_def *comps[NIR_MAX_VEC_COMPONENTS];
      for (int i = 0; i < intr->num_components; i++) {
         nir_intrinsic_instr *load_iid =
            nir_intrinsic_instr_create(b->shader,
                                       nir_intrinsic_load_fs_input_interp_deltas);
         load_iid->src[0] = nir_src_for_ssa(intr->src[1].ssa);
         nir_ssa_dest_init(&load_iid->instr, &load_iid->dest,
                           3, 32, NULL);
         nir_intrinsic_set_base(load_iid, nir_intrinsic_base(intr));
         nir_intrinsic_set_component(load_iid,
                                     nir_intrinsic_component(intr) + i);
         nir_intrinsic_set_io_semantics(load_iid,
                                        nir_intrinsic_io_semantics(intr));
         nir_builder_instr_insert(b, &load_iid->instr);

         nir_ssa_def *iid = &load_iid->dest.ssa;
         nir_ssa_def *bary = intr->src[0].ssa;
         nir_ssa_def *val;

         val = nir_ffma(b, nir_channel(b, bary, 1),
                           nir_channel(b, iid, 1),
                           nir_channel(b, iid, 0));
         val = nir_ffma(b, nir_channel(b, bary, 0),
                           nir_channel(b, iid, 2),
                           val);

         comps[i] = val;
      }
      nir_ssa_def *vec = nir_vec(b, comps, intr->num_components);
      nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(vec));

      progress = true;
   }

   return progress;
}

static bool
nir_lower_interpolation_impl(nir_function_impl *impl,
                             nir_lower_interpolation_options options)
{
   bool progress = false;
   nir_builder builder;
   nir_builder_init(&builder, impl);

   nir_foreach_block(block, impl) {
      progress |= nir_lower_interpolation_block(block, &builder, options);
   }

   nir_metadata_preserve(impl, nir_metadata_block_index |
                               nir_metadata_dominance);
   return progress;
}

bool
nir_lower_interpolation(nir_shader *shader, nir_lower_interpolation_options options)
{
   bool progress = false;

   nir_foreach_function(function, shader) {
      if (function->impl)
         progress |= nir_lower_interpolation_impl(function->impl, options);
   }

   return progress;
}