1 /*
2 * Copyright © 2016 Intel Corporation
3 * Copyright © 2020 Valve Corporation
4 *
5 * Permission is hereby granted, free of charge, to any person obtaining a
6 * copy of this software and associated documentation files (the "Software"),
7 * to deal in the Software without restriction, including without limitation
8 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
9 * and/or sell copies of the Software, and to permit persons to whom the
10 * Software is furnished to do so, subject to the following conditions:
11 *
12 * The above copyright notice and this permission notice (including the next
13 * paragraph) shall be included in all copies or substantial portions of the
14 * Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
21 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
22 * IN THE SOFTWARE.
23 */
24
25 #include "nir_control_flow.h"
26 #include "nir_builder.h"
27
28 /**
29 * This file implements an optimization for multiview. Some GPU's have a
30 * special mode which allows the vertex shader (or last stage in the geometry
31 * pipeline) to create multiple primitives in different layers of the
32 * framebuffer at once by writing multiple copies of gl_Position. The
33 * assumption is that in most uses of multiview, the only use of gl_ViewIndex
34 * is to change the position to implement the parallax effect, and other
35 * varyings will be the same between the different views. We put the body of
36 * the original vertex shader in a loop, writing to a different copy of
37 * gl_Position each loop iteration, and then let other optimizations clean up
38 * the mess.
39 */
40
41 static bool
shader_writes_to_memory(nir_shader * shader)42 shader_writes_to_memory(nir_shader *shader)
43 {
44 /* With multiview, we would need to ensure that memory writes happen either
45 * once or once per view. Since combination of multiview and memory writes
46 * is not expected, we'll just skip this optimization in this case.
47 */
48
49 nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
50
51 nir_foreach_block(block, entrypoint) {
52 nir_foreach_instr(instr, block) {
53 if (instr->type != nir_instr_type_intrinsic)
54 continue;
55 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
56
57 switch (intrin->intrinsic) {
58 case nir_intrinsic_deref_atomic_add:
59 case nir_intrinsic_deref_atomic_imin:
60 case nir_intrinsic_deref_atomic_umin:
61 case nir_intrinsic_deref_atomic_imax:
62 case nir_intrinsic_deref_atomic_umax:
63 case nir_intrinsic_deref_atomic_and:
64 case nir_intrinsic_deref_atomic_or:
65 case nir_intrinsic_deref_atomic_xor:
66 case nir_intrinsic_deref_atomic_exchange:
67 case nir_intrinsic_deref_atomic_comp_swap:
68 case nir_intrinsic_store_ssbo:
69 case nir_intrinsic_ssbo_atomic_add:
70 case nir_intrinsic_ssbo_atomic_imin:
71 case nir_intrinsic_ssbo_atomic_umin:
72 case nir_intrinsic_ssbo_atomic_imax:
73 case nir_intrinsic_ssbo_atomic_umax:
74 case nir_intrinsic_ssbo_atomic_and:
75 case nir_intrinsic_ssbo_atomic_or:
76 case nir_intrinsic_ssbo_atomic_xor:
77 case nir_intrinsic_ssbo_atomic_exchange:
78 case nir_intrinsic_ssbo_atomic_comp_swap:
79 case nir_intrinsic_store_shared:
80 case nir_intrinsic_store_shared2_amd:
81 case nir_intrinsic_shared_atomic_add:
82 case nir_intrinsic_shared_atomic_imin:
83 case nir_intrinsic_shared_atomic_umin:
84 case nir_intrinsic_shared_atomic_imax:
85 case nir_intrinsic_shared_atomic_umax:
86 case nir_intrinsic_shared_atomic_and:
87 case nir_intrinsic_shared_atomic_or:
88 case nir_intrinsic_shared_atomic_xor:
89 case nir_intrinsic_shared_atomic_exchange:
90 case nir_intrinsic_shared_atomic_comp_swap:
91 case nir_intrinsic_task_payload_atomic_add:
92 case nir_intrinsic_task_payload_atomic_imin:
93 case nir_intrinsic_task_payload_atomic_umin:
94 case nir_intrinsic_task_payload_atomic_imax:
95 case nir_intrinsic_task_payload_atomic_umax:
96 case nir_intrinsic_task_payload_atomic_and:
97 case nir_intrinsic_task_payload_atomic_or:
98 case nir_intrinsic_task_payload_atomic_xor:
99 case nir_intrinsic_task_payload_atomic_exchange:
100 case nir_intrinsic_task_payload_atomic_comp_swap:
101 case nir_intrinsic_task_payload_atomic_fadd:
102 case nir_intrinsic_task_payload_atomic_fmin:
103 case nir_intrinsic_task_payload_atomic_fmax:
104 case nir_intrinsic_task_payload_atomic_fcomp_swap:
105 case nir_intrinsic_image_deref_store:
106 case nir_intrinsic_image_deref_atomic_add:
107 case nir_intrinsic_image_deref_atomic_fadd:
108 case nir_intrinsic_image_deref_atomic_umin:
109 case nir_intrinsic_image_deref_atomic_umax:
110 case nir_intrinsic_image_deref_atomic_imin:
111 case nir_intrinsic_image_deref_atomic_imax:
112 case nir_intrinsic_image_deref_atomic_fmin:
113 case nir_intrinsic_image_deref_atomic_fmax:
114 case nir_intrinsic_image_deref_atomic_and:
115 case nir_intrinsic_image_deref_atomic_or:
116 case nir_intrinsic_image_deref_atomic_xor:
117 case nir_intrinsic_image_deref_atomic_exchange:
118 case nir_intrinsic_image_deref_atomic_comp_swap:
119 return true;
120
121 default:
122 /* Keep walking. */
123 break;
124 }
125 }
126 }
127
128 return false;
129 }
130
131 bool
nir_shader_uses_view_index(nir_shader * shader)132 nir_shader_uses_view_index(nir_shader *shader)
133 {
134 nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
135
136 nir_foreach_block(block, entrypoint) {
137 nir_foreach_instr(instr, block) {
138 if (instr->type != nir_instr_type_intrinsic)
139 continue;
140
141 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
142 if (intrin->intrinsic == nir_intrinsic_load_view_index)
143 return true;
144 }
145 }
146
147 return false;
148 }
149
150 static bool
shader_only_position_uses_view_index(nir_shader * shader)151 shader_only_position_uses_view_index(nir_shader *shader)
152 {
153 nir_shader *shader_no_position = nir_shader_clone(NULL, shader);
154 nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader_no_position);
155
156 /* Remove the store position from a cloned shader. */
157 nir_foreach_block(block, entrypoint) {
158 nir_foreach_instr_safe(instr, block) {
159 if (instr->type != nir_instr_type_intrinsic)
160 continue;
161
162 nir_intrinsic_instr *store = nir_instr_as_intrinsic(instr);
163 if (store->intrinsic != nir_intrinsic_store_deref)
164 continue;
165
166 nir_variable *var = nir_intrinsic_get_var(store, 0);
167 if (var->data.location != VARYING_SLOT_POS)
168 continue;
169
170 nir_instr_remove(&store->instr);
171 }
172 }
173
174 /* Clean up shader so unused load_view_index intrinsics are removed. */
175 bool progress;
176 do {
177 progress = false;
178 progress |= nir_opt_dead_cf(shader_no_position);
179
180 /* Peephole select will drop if-blocks that have then and else empty,
181 * which will remove the usage of an SSA in the condition.
182 */
183 progress |= nir_opt_peephole_select(shader_no_position, 0, false, false);
184
185 progress |= nir_opt_dce(shader_no_position);
186 } while (progress);
187
188 bool uses_view_index = nir_shader_uses_view_index(shader_no_position);
189
190 ralloc_free(shader_no_position);
191 return !uses_view_index;
192 }
193
194 /* Return true if it's safe to call nir_lower_multiview() on this vertex
195 * shader. Note that this only handles driver-agnostic checks, i.e. things
196 * which would make nir_lower_multiview() incorrect. Any driver-specific
197 * checks, e.g. for sufficient varying space or performance considerations,
198 * should be handled in the driver.
199 *
200 * Note that we don't handle the more complex checks needed for lowering
201 * pipelines with geometry or tessellation shaders.
202 */
203
204 bool
nir_can_lower_multiview(nir_shader * shader)205 nir_can_lower_multiview(nir_shader *shader)
206 {
207 bool writes_position = false;
208 nir_foreach_shader_out_variable(var, shader) {
209 if (var->data.location == VARYING_SLOT_POS) {
210 writes_position = true;
211 break;
212 }
213 }
214
215 /* Don't bother handling this edge case. */
216 if (!writes_position)
217 return false;
218
219 return !shader_writes_to_memory(shader) &&
220 shader_only_position_uses_view_index(shader);
221 }
222
223 /**
224 * The lowering. Call with the last active geometry stage.
225 */
226
227 bool
nir_lower_multiview(nir_shader * shader,uint32_t view_mask)228 nir_lower_multiview(nir_shader *shader, uint32_t view_mask)
229 {
230 assert(shader->info.stage != MESA_SHADER_FRAGMENT);
231 int view_count = util_bitcount(view_mask);
232
233 nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
234
235 /* Update position to refer to an array. */
236 nir_variable *pos_var = NULL;
237 nir_foreach_shader_out_variable(var, shader) {
238 if (var->data.location == VARYING_SLOT_POS) {
239 assert(var->type == glsl_vec4_type());
240 var->type = glsl_array_type(glsl_vec4_type(), view_count, 0);
241 var->data.per_view = true;
242 pos_var = var;
243 break;
244 }
245 }
246
247 assert(pos_var);
248
249 nir_cf_list body;
250 nir_cf_list_extract(&body, &entrypoint->body);
251
252 nir_builder b;
253 nir_builder_init(&b, entrypoint);
254 b.cursor = nir_after_cf_list(&entrypoint->body);
255
256 /* Loop Index will go from 0 to view_count. */
257 nir_variable *loop_index_var =
258 nir_local_variable_create(entrypoint, glsl_uint_type(), "loop_index");
259 nir_deref_instr *loop_index_deref = nir_build_deref_var(&b, loop_index_var);
260 nir_store_deref(&b, loop_index_deref, nir_imm_int(&b, 0), 1);
261
262 /* Array of view index values that are active in the loop. Note that the
263 * loop index only matches the view index if there are no gaps in the
264 * view_mask.
265 */
266 nir_variable *view_index_var = nir_local_variable_create(
267 entrypoint, glsl_array_type(glsl_uint_type(), view_count, 0), "view_index");
268 nir_deref_instr *view_index_deref = nir_build_deref_var(&b, view_index_var);
269 {
270 int array_position = 0;
271 uint32_t view_mask_temp = view_mask;
272 while (view_mask_temp) {
273 uint32_t view_index = u_bit_scan(&view_mask_temp);
274 nir_store_deref(&b, nir_build_deref_array_imm(&b, view_index_deref, array_position),
275 nir_imm_int(&b, view_index), 1);
276 array_position++;
277 }
278 }
279
280 /* Create the equivalent of
281 *
282 * while (true):
283 * if (loop_index >= view_count):
284 * break
285 *
286 * view_index = active_indices[loop_index]
287 * pos_deref = &pos[loop_index]
288 *
289 * # Placeholder for the body to be reinserted.
290 *
291 * loop_index += 1
292 *
293 * Later both `view_index` and `pos_deref` will be used to rewrite the
294 * original shader body.
295 */
296
297 nir_loop* loop = nir_push_loop(&b);
298
299 nir_ssa_def *loop_index = nir_load_deref(&b, loop_index_deref);
300 nir_ssa_def *cmp = nir_ige(&b, loop_index, nir_imm_int(&b, view_count));
301 nir_if *loop_check = nir_push_if(&b, cmp);
302 nir_jump(&b, nir_jump_break);
303 nir_pop_if(&b, loop_check);
304
305 nir_ssa_def *view_index =
306 nir_load_deref(&b, nir_build_deref_array(&b, view_index_deref, loop_index));
307 nir_deref_instr *pos_deref =
308 nir_build_deref_array(&b, nir_build_deref_var(&b, pos_var), loop_index);
309
310 nir_store_deref(&b, loop_index_deref, nir_iadd_imm(&b, loop_index, 1), 1);
311 nir_pop_loop(&b, loop);
312
313 /* Reinsert the body. */
314 b.cursor = nir_after_instr(&pos_deref->instr);
315 nir_cf_reinsert(&body, b.cursor);
316
317 nir_foreach_block(block, entrypoint) {
318 nir_foreach_instr_safe(instr, block) {
319 if (instr->type != nir_instr_type_intrinsic)
320 continue;
321
322 nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
323
324 switch (intrin->intrinsic) {
325 case nir_intrinsic_load_view_index: {
326 assert(intrin->dest.is_ssa);
327 nir_ssa_def_rewrite_uses(&intrin->dest.ssa, view_index);
328 break;
329 }
330
331 case nir_intrinsic_store_deref: {
332 nir_variable *var = nir_intrinsic_get_var(intrin, 0);
333 if (var == pos_var) {
334 nir_deref_instr *old_deref = nir_src_as_deref(intrin->src[0]);
335
336 nir_instr_rewrite_src(instr, &intrin->src[0],
337 nir_src_for_ssa(&pos_deref->dest.ssa));
338
339 /* Remove old deref since it has the wrong type. */
340 nir_deref_instr_remove_if_unused(old_deref);
341 }
342 break;
343 }
344
345 case nir_intrinsic_load_deref:
346 if (nir_intrinsic_get_var(intrin, 0) == pos_var) {
347 unreachable("Should have lowered I/O to temporaries "
348 "so no load_deref on position output is expected.");
349 }
350 break;
351
352 case nir_intrinsic_copy_deref:
353 unreachable("Should have lowered copy_derefs at this point");
354 break;
355
356 default:
357 /* Do nothing. */
358 break;
359 }
360 }
361 }
362
363 nir_metadata_preserve(entrypoint, nir_metadata_none);
364 return true;
365 }
366
367