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 #include "util/debug.h"
27
28 /**
29 * This file implements the lowering required for VK_KHR_multiview.
30 *
31 * When possible, Primitive Replication is used and the shader is modified to
32 * make gl_Position an array and fill it with values for each view.
33 *
34 * Otherwise we implement multiview using instanced rendering. The number of
35 * instances in each draw call is multiplied by the number of views in the
36 * subpass. Then, in the shader, we divide gl_InstanceId by the number of
37 * views and use gl_InstanceId % view_count to compute the actual ViewIndex.
38 */
39
40 struct lower_multiview_state {
41 nir_builder builder;
42
43 uint32_t view_mask;
44
45 nir_ssa_def *instance_id;
46 nir_ssa_def *view_index;
47 };
48
49 static nir_ssa_def *
build_instance_id(struct lower_multiview_state * state)50 build_instance_id(struct lower_multiview_state *state)
51 {
52 assert(state->builder.shader->info.stage == MESA_SHADER_VERTEX);
53
54 if (state->instance_id == NULL) {
55 nir_builder *b = &state->builder;
56
57 b->cursor = nir_before_block(nir_start_block(b->impl));
58
59 /* We use instancing for implementing multiview. The actual instance id
60 * is given by dividing instance_id by the number of views in this
61 * subpass.
62 */
63 state->instance_id =
64 nir_idiv(b, nir_load_instance_id(b),
65 nir_imm_int(b, util_bitcount(state->view_mask)));
66 }
67
68 return state->instance_id;
69 }
70
71 static nir_ssa_def *
build_view_index(struct lower_multiview_state * state)72 build_view_index(struct lower_multiview_state *state)
73 {
74 if (state->view_index == NULL) {
75 nir_builder *b = &state->builder;
76
77 b->cursor = nir_before_block(nir_start_block(b->impl));
78
79 assert(state->view_mask != 0);
80 if (util_bitcount(state->view_mask) == 1) {
81 /* Set the view index directly. */
82 state->view_index = nir_imm_int(b, ffs(state->view_mask) - 1);
83 } else if (state->builder.shader->info.stage == MESA_SHADER_VERTEX) {
84 /* We only support 16 viewports */
85 assert((state->view_mask & 0xffff0000) == 0);
86
87 /* We use instancing for implementing multiview. The compacted view
88 * id is given by instance_id % view_count. We then have to convert
89 * that to an actual view id.
90 */
91 nir_ssa_def *compacted =
92 nir_umod(b, nir_load_instance_id(b),
93 nir_imm_int(b, util_bitcount(state->view_mask)));
94
95 if (util_is_power_of_two_or_zero(state->view_mask + 1)) {
96 /* If we have a full view mask, then compacted is what we want */
97 state->view_index = compacted;
98 } else {
99 /* Now we define a map from compacted view index to the actual
100 * view index that's based on the view_mask. The map is given by
101 * 16 nibbles, each of which is a value from 0 to 15.
102 */
103 uint64_t remap = 0;
104 uint32_t bit, i = 0;
105 for_each_bit(bit, state->view_mask) {
106 assert(bit < 16);
107 remap |= (uint64_t)bit << (i++ * 4);
108 }
109
110 nir_ssa_def *shift = nir_imul(b, compacted, nir_imm_int(b, 4));
111
112 /* One of these days, when we have int64 everywhere, this will be
113 * easier.
114 */
115 nir_ssa_def *shifted;
116 if (remap <= UINT32_MAX) {
117 shifted = nir_ushr(b, nir_imm_int(b, remap), shift);
118 } else {
119 nir_ssa_def *shifted_low =
120 nir_ushr(b, nir_imm_int(b, remap), shift);
121 nir_ssa_def *shifted_high =
122 nir_ushr(b, nir_imm_int(b, remap >> 32),
123 nir_isub(b, shift, nir_imm_int(b, 32)));
124 shifted = nir_bcsel(b, nir_ilt(b, shift, nir_imm_int(b, 32)),
125 shifted_low, shifted_high);
126 }
127 state->view_index = nir_iand(b, shifted, nir_imm_int(b, 0xf));
128 }
129 } else {
130 const struct glsl_type *type = glsl_int_type();
131 if (b->shader->info.stage == MESA_SHADER_TESS_CTRL ||
132 b->shader->info.stage == MESA_SHADER_GEOMETRY)
133 type = glsl_array_type(type, 1, 0);
134
135 nir_variable *idx_var =
136 nir_variable_create(b->shader, nir_var_shader_in,
137 type, "view index");
138 idx_var->data.location = VARYING_SLOT_VIEW_INDEX;
139 if (b->shader->info.stage == MESA_SHADER_FRAGMENT)
140 idx_var->data.interpolation = INTERP_MODE_FLAT;
141
142 nir_deref_instr *deref = nir_build_deref_var(b, idx_var);
143 if (glsl_type_is_array(type))
144 deref = nir_build_deref_array_imm(b, deref, 0);
145
146 state->view_index = nir_load_deref(b, deref);
147 }
148 }
149
150 return state->view_index;
151 }
152
153 bool
anv_nir_lower_multiview(nir_shader * shader,struct anv_graphics_pipeline * pipeline)154 anv_nir_lower_multiview(nir_shader *shader,
155 struct anv_graphics_pipeline *pipeline)
156 {
157 assert(shader->info.stage != MESA_SHADER_COMPUTE);
158 uint32_t view_mask = pipeline->subpass->view_mask;
159
160 /* If multiview isn't enabled, we have nothing to do. */
161 if (view_mask == 0)
162 return false;
163
164 /* This pass assumes a single entrypoint */
165 nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
166
167 /* Primitive Replication allows a shader to write different positions for
168 * each view in the same execution. If only the position depends on the
169 * view, then it is possible to use the feature instead of instancing to
170 * implement multiview.
171 */
172 if (pipeline->use_primitive_replication) {
173 if (shader->info.stage == MESA_SHADER_FRAGMENT)
174 return false;
175
176 bool progress = nir_lower_multiview(shader, pipeline->subpass->view_mask);
177
178 if (progress) {
179 nir_builder b;
180 nir_builder_init(&b, entrypoint);
181 b.cursor = nir_before_cf_list(&entrypoint->body);
182
183 /* Fill Layer ID with zero. Replication will use that as base to
184 * apply the RTAI offsets.
185 */
186 nir_variable *layer_id_out =
187 nir_variable_create(shader, nir_var_shader_out,
188 glsl_int_type(), "layer ID");
189 layer_id_out->data.location = VARYING_SLOT_LAYER;
190 nir_store_var(&b, layer_id_out, nir_imm_zero(&b, 1, 32), 0x1);
191 }
192
193 return progress;
194 }
195
196 struct lower_multiview_state state = {
197 .view_mask = view_mask,
198 };
199
200 nir_builder_init(&state.builder, entrypoint);
201
202 bool progress = false;
203 nir_foreach_block(block, entrypoint) {
204 nir_foreach_instr_safe(instr, block) {
205 if (instr->type != nir_instr_type_intrinsic)
206 continue;
207
208 nir_intrinsic_instr *load = nir_instr_as_intrinsic(instr);
209
210 if (load->intrinsic != nir_intrinsic_load_instance_id &&
211 load->intrinsic != nir_intrinsic_load_view_index)
212 continue;
213
214 assert(load->dest.is_ssa);
215
216 nir_ssa_def *value;
217 if (load->intrinsic == nir_intrinsic_load_instance_id) {
218 value = build_instance_id(&state);
219 } else {
220 assert(load->intrinsic == nir_intrinsic_load_view_index);
221 value = build_view_index(&state);
222 }
223
224 nir_ssa_def_rewrite_uses(&load->dest.ssa, nir_src_for_ssa(value));
225
226 nir_instr_remove(&load->instr);
227 progress = true;
228 }
229 }
230
231 /* The view index is available in all stages but the instance id is only
232 * available in the VS. If it's not a fragment shader, we need to pass
233 * the view index on to the next stage.
234 */
235 if (shader->info.stage != MESA_SHADER_FRAGMENT) {
236 nir_ssa_def *view_index = build_view_index(&state);
237
238 nir_builder *b = &state.builder;
239
240 assert(view_index->parent_instr->block == nir_start_block(entrypoint));
241 b->cursor = nir_after_instr(view_index->parent_instr);
242
243 /* Unless there is only one possible view index (that would be set
244 * directly), pass it to the next stage. */
245 if (util_bitcount(state.view_mask) != 1) {
246 nir_variable *view_index_out =
247 nir_variable_create(shader, nir_var_shader_out,
248 glsl_int_type(), "view index");
249 view_index_out->data.location = VARYING_SLOT_VIEW_INDEX;
250 nir_store_var(b, view_index_out, view_index, 0x1);
251 }
252
253 nir_variable *layer_id_out =
254 nir_variable_create(shader, nir_var_shader_out,
255 glsl_int_type(), "layer ID");
256 layer_id_out->data.location = VARYING_SLOT_LAYER;
257 nir_store_var(b, layer_id_out, view_index, 0x1);
258
259 progress = true;
260 }
261
262 if (progress) {
263 nir_metadata_preserve(entrypoint, nir_metadata_block_index |
264 nir_metadata_dominance);
265 }
266
267 return progress;
268 }
269
270 bool
anv_check_for_primitive_replication(nir_shader ** shaders,struct anv_graphics_pipeline * pipeline)271 anv_check_for_primitive_replication(nir_shader **shaders,
272 struct anv_graphics_pipeline *pipeline)
273 {
274 assert(pipeline->base.device->info.gen >= 12);
275
276 static int primitive_replication_max_views = -1;
277 if (primitive_replication_max_views < 0) {
278 /* TODO: Figure out why we are not getting same benefits for larger than
279 * 2 views. For now use Primitive Replication just for the 2-view case
280 * by default.
281 */
282 const unsigned default_max_views = 2;
283
284 primitive_replication_max_views =
285 MIN2(MAX_VIEWS_FOR_PRIMITIVE_REPLICATION,
286 env_var_as_unsigned("ANV_PRIMITIVE_REPLICATION_MAX_VIEWS",
287 default_max_views));
288 }
289
290 /* TODO: We should be able to support replication at 'geometry' stages
291 * later than Vertex. In that case only the last stage can refer to
292 * gl_ViewIndex.
293 */
294 if (pipeline->active_stages != (VK_SHADER_STAGE_VERTEX_BIT |
295 VK_SHADER_STAGE_FRAGMENT_BIT)) {
296 return false;
297 }
298
299 uint32_t view_mask = pipeline->subpass->view_mask;
300 int view_count = util_bitcount(view_mask);
301 if (view_count == 1 || view_count > primitive_replication_max_views)
302 return false;
303
304 /* We can't access the view index in the fragment shader. */
305 if (nir_shader_uses_view_index(shaders[MESA_SHADER_FRAGMENT]))
306 return false;
307
308 return nir_can_lower_multiview(shaders[MESA_SHADER_VERTEX]);
309 }
310