1 /*
2 * Copyright © 2014 Broadcom
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 /**
25 * @file v3d_opt_dead_code.c
26 *
27 * This is a simple dead code eliminator for SSA values in VIR.
28 *
29 * It walks all the instructions finding what temps are used, then walks again
30 * to remove instructions writing unused temps.
31 *
32 * This is an inefficient implementation if you have long chains of
33 * instructions where the entire chain is dead, but we expect those to have
34 * been eliminated at the NIR level, and here we're just cleaning up small
35 * problems produced by NIR->VIR.
36 */
37
38 #include "v3d_compiler.h"
39
40 static bool debug;
41
42 static void
dce(struct v3d_compile * c,struct qinst * inst)43 dce(struct v3d_compile *c, struct qinst *inst)
44 {
45 if (debug) {
46 fprintf(stderr, "Removing: ");
47 vir_dump_inst(c, inst);
48 fprintf(stderr, "\n");
49 }
50 assert(!v3d_qpu_writes_flags(&inst->qpu));
51 vir_remove_instruction(c, inst);
52 }
53
54 static bool
has_nonremovable_reads(struct v3d_compile * c,struct qinst * inst)55 has_nonremovable_reads(struct v3d_compile *c, struct qinst *inst)
56 {
57 for (int i = 0; i < vir_get_nsrc(inst); i++) {
58 if (inst->src[i].file == QFILE_VPM)
59 return true;
60 }
61
62 return false;
63 }
64
65 static bool
can_write_to_null(struct v3d_compile * c,struct qinst * inst)66 can_write_to_null(struct v3d_compile *c, struct qinst *inst)
67 {
68 /* The SFU instructions must write to a physical register. */
69 if (c->devinfo->ver >= 41 && v3d_qpu_uses_sfu(&inst->qpu))
70 return false;
71
72 return true;
73 }
74
75 static void
vir_dce_flags(struct v3d_compile * c,struct qinst * inst)76 vir_dce_flags(struct v3d_compile *c, struct qinst *inst)
77 {
78 if (debug) {
79 fprintf(stderr,
80 "Removing flags write from: ");
81 vir_dump_inst(c, inst);
82 fprintf(stderr, "\n");
83 }
84
85 assert(inst->qpu.type == V3D_QPU_INSTR_TYPE_ALU);
86
87 inst->qpu.flags.apf = V3D_QPU_PF_NONE;
88 inst->qpu.flags.mpf = V3D_QPU_PF_NONE;
89 inst->qpu.flags.auf = V3D_QPU_UF_NONE;
90 inst->qpu.flags.muf = V3D_QPU_UF_NONE;
91 }
92
93 static bool
check_last_ldunifa(struct v3d_compile * c,struct qinst * inst,struct qblock * block)94 check_last_ldunifa(struct v3d_compile *c,
95 struct qinst *inst,
96 struct qblock *block)
97 {
98 if (!inst->qpu.sig.ldunifa && !inst->qpu.sig.ldunifarf)
99 return false;
100
101 list_for_each_entry_from(struct qinst, scan_inst, inst->link.next,
102 &block->instructions, link) {
103 /* If we find a new write to unifa, then this was the last
104 * ldunifa in its sequence and is safe to remove.
105 */
106 if (scan_inst->dst.file == QFILE_MAGIC &&
107 scan_inst->dst.index == V3D_QPU_WADDR_UNIFA) {
108 return true;
109 }
110
111 /* If we find another ldunifa in the same sequence then we
112 * can't remove it.
113 */
114 if (scan_inst->qpu.sig.ldunifa || scan_inst->qpu.sig.ldunifarf)
115 return false;
116 }
117
118 return true;
119 }
120
121 static bool
check_first_ldunifa(struct v3d_compile * c,struct qinst * inst,struct qblock * block,struct qinst ** unifa)122 check_first_ldunifa(struct v3d_compile *c,
123 struct qinst *inst,
124 struct qblock *block,
125 struct qinst **unifa)
126 {
127 if (!inst->qpu.sig.ldunifa && !inst->qpu.sig.ldunifarf)
128 return false;
129
130 list_for_each_entry_from_rev(struct qinst, scan_inst, inst->link.prev,
131 &block->instructions, link) {
132 /* If we find a write to unifa, then this was the first
133 * ldunifa in its sequence and is safe to remove.
134 */
135 if (scan_inst->dst.file == QFILE_MAGIC &&
136 scan_inst->dst.index == V3D_QPU_WADDR_UNIFA) {
137 *unifa = scan_inst;
138 return true;
139 }
140
141 /* If we find another ldunifa in the same sequence then we
142 * can't remove it.
143 */
144 if (scan_inst->qpu.sig.ldunifa || scan_inst->qpu.sig.ldunifarf)
145 return false;
146 }
147
148 unreachable("could not find starting unifa for ldunifa sequence");
149 }
150
151 static bool
increment_unifa_address(struct v3d_compile * c,struct qblock * block,struct qinst * unifa)152 increment_unifa_address(struct v3d_compile *c, struct qblock *block, struct qinst *unifa)
153 {
154 struct qblock *current_block = c->cur_block;
155 if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU &&
156 unifa->qpu.alu.mul.op == V3D_QPU_M_MOV) {
157 c->cursor = vir_after_inst(unifa);
158 c->cur_block = block;
159 struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA);
160 vir_ADD_dest(c, unifa_reg, unifa->src[0], vir_uniform_ui(c, 4u));
161 vir_remove_instruction(c, unifa);
162 c->cur_block = current_block;
163 return true;
164 }
165
166 if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU &&
167 unifa->qpu.alu.add.op == V3D_QPU_A_ADD) {
168 c->cursor = vir_after_inst(unifa);
169 c->cur_block = block;
170 struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA);
171 struct qreg tmp =
172 vir_ADD(c, unifa->src[1], vir_uniform_ui(c, 4u));
173 vir_ADD_dest(c, unifa_reg, unifa->src[0], tmp);
174 vir_remove_instruction(c, unifa);
175 c->cur_block = current_block;
176 return true;
177 }
178
179 return false;
180 }
181
182 bool
vir_opt_dead_code(struct v3d_compile * c)183 vir_opt_dead_code(struct v3d_compile *c)
184 {
185 bool progress = false;
186 bool *used = calloc(c->num_temps, sizeof(bool));
187
188 /* Defuse the "are you removing the cursor?" assertion in the core.
189 * You'll need to set up a new cursor for any new instructions after
190 * doing DCE (which we would expect, anyway).
191 */
192 c->cursor.link = NULL;
193
194 vir_for_each_inst_inorder(inst, c) {
195 for (int i = 0; i < vir_get_nsrc(inst); i++) {
196 if (inst->src[i].file == QFILE_TEMP)
197 used[inst->src[i].index] = true;
198 }
199 }
200
201 vir_for_each_block(block, c) {
202 struct qinst *last_flags_write = NULL;
203
204 vir_for_each_inst_safe(inst, block) {
205 /* If this instruction reads the flags, we can't
206 * remove the flags generation for it.
207 */
208 if (v3d_qpu_reads_flags(&inst->qpu))
209 last_flags_write = NULL;
210
211 if (inst->dst.file != QFILE_NULL &&
212 !(inst->dst.file == QFILE_TEMP &&
213 !used[inst->dst.index])) {
214 continue;
215 }
216
217 const bool is_ldunifa = inst->qpu.sig.ldunifa ||
218 inst->qpu.sig.ldunifarf;
219
220 if (vir_has_side_effects(c, inst) && !is_ldunifa)
221 continue;
222
223 bool is_first_ldunifa = false;
224 bool is_last_ldunifa = false;
225 struct qinst *unifa = NULL;
226 if (is_ldunifa) {
227 is_last_ldunifa =
228 check_last_ldunifa(c, inst, block);
229
230 is_first_ldunifa =
231 check_first_ldunifa(c, inst, block, &unifa);
232 }
233
234 if (v3d_qpu_writes_flags(&inst->qpu)) {
235 /* If we obscure a previous flags write,
236 * drop it.
237 */
238 if (last_flags_write &&
239 (inst->qpu.flags.apf != V3D_QPU_PF_NONE ||
240 inst->qpu.flags.mpf != V3D_QPU_PF_NONE)) {
241 vir_dce_flags(c, last_flags_write);
242 progress = true;
243 }
244
245 last_flags_write = inst;
246 }
247
248 if (v3d_qpu_writes_flags(&inst->qpu) ||
249 has_nonremovable_reads(c, inst) ||
250 (is_ldunifa && !is_first_ldunifa && !is_last_ldunifa)) {
251 /* If we can't remove the instruction, but we
252 * don't need its destination value, just
253 * remove the destination. The register
254 * allocator would trivially color it and it
255 * wouldn't cause any register pressure, but
256 * it's nicer to read the VIR code without
257 * unused destination regs.
258 */
259 if (inst->dst.file == QFILE_TEMP &&
260 can_write_to_null(c, inst)) {
261 if (debug) {
262 fprintf(stderr,
263 "Removing dst from: ");
264 vir_dump_inst(c, inst);
265 fprintf(stderr, "\n");
266 }
267 c->defs[inst->dst.index] = NULL;
268 inst->dst.file = QFILE_NULL;
269 progress = true;
270 }
271 continue;
272 }
273
274 /* If we are removing the first ldunifa in a sequence
275 * we need to update the unifa address.
276 */
277 if (is_first_ldunifa) {
278 assert(unifa);
279 if (!increment_unifa_address(c, block, unifa))
280 continue;
281 }
282
283 assert(inst != last_flags_write);
284 dce(c, inst);
285 progress = true;
286 continue;
287 }
288 }
289
290 free(used);
291
292 return progress;
293 }
294