src/intel/vulkan/anv_nir_lower_multiview.c

   1 /*
   2  * Copyright © 2016 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "anv_nir.h"
  25 #include "nir/nir_builder.h"
  26
  27 /**
  28  * This file implements the lowering required for VK_KHR_multiview.  We
  29  * implement multiview using instanced rendering.  The number of instances in
  30  * each draw call is multiplied by the number of views in the subpass.  Then,
  31  * in the shader, we divide gl_InstanceId by the number of views and use
  32  * gl_InstanceId % view_count to compute the actual ViewIndex.
  33  */
  34
  35 struct lower_multiview_state {
  36    nir_builder builder;
  37
  38    uint32_t view_mask;
  39
  40    nir_ssa_def *instance_id;
  41    nir_ssa_def *view_index;
  42 };
  43
  44 static nir_ssa_def *
  45 build_instance_id(struct lower_multiview_state *state)
  46 {
  47    assert(state->builder.shader->info.stage == MESA_SHADER_VERTEX);
  48
  49    if (state->instance_id == NULL) {
  50       nir_builder *b = &state->builder;
  51
  52       b->cursor = nir_before_block(nir_start_block(b->impl));
  53
  54       /* We use instancing for implementing multiview.  The actual instance id
  55        * is given by dividing instance_id by the number of views in this
  56        * subpass.
  57        */
  58       state->instance_id =
  59          nir_idiv(b, nir_load_instance_id(b),
  60                      nir_imm_int(b, _mesa_bitcount(state->view_mask)));
  61    }
  62
  63    return state->instance_id;
  64 }
  65
  66 static nir_ssa_def *
  67 build_view_index(struct lower_multiview_state *state)
  68 {
  69    if (state->view_index == NULL) {
  70       nir_builder *b = &state->builder;
  71
  72       b->cursor = nir_before_block(nir_start_block(b->impl));
  73
  74       assert(state->view_mask != 0);
  75       if (_mesa_bitcount(state->view_mask) == 1) {
  76          /* Set the view index directly. */
  77          state->view_index = nir_imm_int(b, ffs(state->view_mask) - 1);
  78       } else if (state->builder.shader->info.stage == MESA_SHADER_VERTEX) {
  79          /* We only support 16 viewports */
  80          assert((state->view_mask & 0xffff0000) == 0);
  81
  82          /* We use instancing for implementing multiview.  The compacted view
  83           * id is given by instance_id % view_count.  We then have to convert
  84           * that to an actual view id.
  85           */
  86          nir_ssa_def *compacted =
  87             nir_umod(b, nir_load_instance_id(b),
  88                         nir_imm_int(b, _mesa_bitcount(state->view_mask)));
  89
  90          if (util_is_power_of_two(state->view_mask + 1)) {
  91             /* If we have a full view mask, then compacted is what we want */
  92             state->view_index = compacted;
  93          } else {
  94             /* Now we define a map from compacted view index to the actual
  95              * view index that's based on the view_mask.  The map is given by
  96              * 16 nibbles, each of which is a value from 0 to 15.
  97              */
  98             uint64_t remap = 0;
  99             uint32_t bit, i = 0;
 100             for_each_bit(bit, state->view_mask) {
 101                assert(bit < 16);
 102                remap |= (uint64_t)bit << (i++ * 4);
 103             }
 104
 105             nir_ssa_def *shift = nir_imul(b, compacted, nir_imm_int(b, 4));
 106
 107             /* One of these days, when we have int64 everywhere, this will be
 108              * easier.
 109              */
 110             nir_ssa_def *shifted;
 111             if (remap <= UINT32_MAX) {
 112                shifted = nir_ushr(b, nir_imm_int(b, remap), shift);
 113             } else {
 114                nir_ssa_def *shifted_low =
 115                   nir_ushr(b, nir_imm_int(b, remap), shift);
 116                nir_ssa_def *shifted_high =
 117                   nir_ushr(b, nir_imm_int(b, remap >> 32),
 118                               nir_isub(b, shift, nir_imm_int(b, 32)));
 119                shifted = nir_bcsel(b, nir_ilt(b, shift, nir_imm_int(b, 32)),
 120                                       shifted_low, shifted_high);
 121             }
 122             state->view_index = nir_iand(b, shifted, nir_imm_int(b, 0xf));
 123          }
 124       } else {
 125          const struct glsl_type *type = glsl_int_type();
 126          if (b->shader->info.stage == MESA_SHADER_TESS_CTRL ||
 127              b->shader->info.stage == MESA_SHADER_GEOMETRY)
 128             type = glsl_array_type(type, 1);
 129
 130          nir_variable *idx_var =
 131             nir_variable_create(b->shader, nir_var_shader_in,
 132                                 type, "view index");
 133          idx_var->data.location = VARYING_SLOT_VIEW_INDEX;
 134          if (b->shader->info.stage == MESA_SHADER_FRAGMENT)
 135             idx_var->data.interpolation = INTERP_MODE_FLAT;
 136
 137          if (glsl_type_is_array(type)) {
 138             nir_deref_var *deref = nir_deref_var_create(b->shader, idx_var);
 139             nir_deref_array *arr = nir_deref_array_create(b->shader);
 140             arr->deref.type = glsl_int_type();
 141             arr->deref_array_type = nir_deref_array_type_direct;
 142             arr->base_offset = 0;
 143             deref->deref.child = &arr->deref;
 144
 145             state->view_index = nir_load_deref_var(b, deref);
 146          } else {
 147             state->view_index = nir_load_var(b, idx_var);
 148          }
 149       }
 150    }
 151
 152    return state->view_index;
 153 }
 154
 155 bool
 156 anv_nir_lower_multiview(nir_shader *shader, uint32_t view_mask)
 157 {
 158    assert(shader->info.stage != MESA_SHADER_COMPUTE);
 159
 160    /* If multiview isn't enabled, we have nothing to do. */
 161    if (view_mask == 0)
 162       return false;
 163
 164    struct lower_multiview_state state = {
 165       .view_mask = view_mask,
 166    };
 167
 168    /* This pass assumes a single entrypoint */
 169    nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
 170
 171    nir_builder_init(&state.builder, entrypoint);
 172
 173    bool progress = false;
 174    nir_foreach_block(block, entrypoint) {
 175       nir_foreach_instr_safe(instr, block) {
 176          if (instr->type != nir_instr_type_intrinsic)
 177             continue;
 178
 179          nir_intrinsic_instr *load = nir_instr_as_intrinsic(instr);
 180
 181          if (load->intrinsic != nir_intrinsic_load_instance_id &&
 182              load->intrinsic != nir_intrinsic_load_view_index)
 183             continue;
 184
 185          assert(load->dest.is_ssa);
 186
 187          nir_ssa_def *value;
 188          if (load->intrinsic == nir_intrinsic_load_instance_id) {
 189             value = build_instance_id(&state);
 190          } else {
 191             assert(load->intrinsic == nir_intrinsic_load_view_index);
 192             value = build_view_index(&state);
 193          }
 194
 195          nir_ssa_def_rewrite_uses(&load->dest.ssa, nir_src_for_ssa(value));
 196
 197          nir_instr_remove(&load->instr);
 198          progress = true;
 199       }
 200    }
 201
 202    /* The view index is available in all stages but the instance id is only
 203     * available in the VS.  If it's not a fragment shader, we need to pass
 204     * the view index on to the next stage.
 205     */
 206    if (shader->info.stage != MESA_SHADER_FRAGMENT) {
 207       nir_ssa_def *view_index = build_view_index(&state);
 208
 209       nir_builder *b = &state.builder;
 210
 211       assert(view_index->parent_instr->block == nir_start_block(entrypoint));
 212       b->cursor = nir_after_instr(view_index->parent_instr);
 213
 214       /* Unless there is only one possible view index (that would be set
 215        * directly), pass it to the next stage. */
 216       if (_mesa_bitcount(state.view_mask) != 1) {
 217          nir_variable *view_index_out =
 218             nir_variable_create(shader, nir_var_shader_out,
 219                                 glsl_int_type(), "view index");
 220          view_index_out->data.location = VARYING_SLOT_VIEW_INDEX;
 221          nir_store_var(b, view_index_out, view_index, 0x1);
 222       }
 223
 224       nir_variable *layer_id_out =
 225          nir_variable_create(shader, nir_var_shader_out,
 226                              glsl_int_type(), "layer ID");
 227       layer_id_out->data.location = VARYING_SLOT_LAYER;
 228       nir_store_var(b, layer_id_out, view_index, 0x1);
 229
 230       progress = true;
 231    }
 232
 233    if (progress) {
 234       nir_metadata_preserve(entrypoint, nir_metadata_block_index |
 235                                         nir_metadata_dominance);
 236    }
 237
 238    return progress;
 239 }