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 qinst * unifa)152 increment_unifa_address(struct v3d_compile *c, struct qinst *unifa)
153 {
154 if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU &&
155 unifa->qpu.alu.mul.op == V3D_QPU_M_MOV) {
156 c->cursor = vir_after_inst(unifa);
157 struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA);
158 vir_ADD_dest(c, unifa_reg, unifa->src[0], vir_uniform_ui(c, 4u));
159 vir_remove_instruction(c, unifa);
160 return true;
161 }
162
163 if (unifa->qpu.type == V3D_QPU_INSTR_TYPE_ALU &&
164 unifa->qpu.alu.add.op == V3D_QPU_A_ADD) {
165 c->cursor = vir_after_inst(unifa);
166 struct qreg unifa_reg = vir_reg(QFILE_MAGIC, V3D_QPU_WADDR_UNIFA);
167 struct qreg tmp =
168 vir_ADD(c, unifa->src[1], vir_uniform_ui(c, 4u));
169 vir_ADD_dest(c, unifa_reg, unifa->src[0], tmp);
170 vir_remove_instruction(c, unifa);
171 return true;
172 }
173
174 return false;
175 }
176
177 bool
vir_opt_dead_code(struct v3d_compile * c)178 vir_opt_dead_code(struct v3d_compile *c)
179 {
180 bool progress = false;
181 bool *used = calloc(c->num_temps, sizeof(bool));
182
183 /* Defuse the "are you removing the cursor?" assertion in the core.
184 * You'll need to set up a new cursor for any new instructions after
185 * doing DCE (which we would expect, anyway).
186 */
187 c->cursor.link = NULL;
188
189 vir_for_each_inst_inorder(inst, c) {
190 for (int i = 0; i < vir_get_nsrc(inst); i++) {
191 if (inst->src[i].file == QFILE_TEMP)
192 used[inst->src[i].index] = true;
193 }
194 }
195
196 vir_for_each_block(block, c) {
197 struct qinst *last_flags_write = NULL;
198 c->cur_block = block;
199 vir_for_each_inst_safe(inst, block) {
200 /* If this instruction reads the flags, we can't
201 * remove the flags generation for it.
202 */
203 if (v3d_qpu_reads_flags(&inst->qpu))
204 last_flags_write = NULL;
205
206 if (inst->dst.file != QFILE_NULL &&
207 !(inst->dst.file == QFILE_TEMP &&
208 !used[inst->dst.index])) {
209 continue;
210 }
211
212 const bool is_ldunifa = inst->qpu.sig.ldunifa ||
213 inst->qpu.sig.ldunifarf;
214
215 if (vir_has_side_effects(c, inst) && !is_ldunifa)
216 continue;
217
218 bool is_first_ldunifa = false;
219 bool is_last_ldunifa = false;
220 struct qinst *unifa = NULL;
221 if (is_ldunifa) {
222 is_last_ldunifa =
223 check_last_ldunifa(c, inst, block);
224
225 is_first_ldunifa =
226 check_first_ldunifa(c, inst, block, &unifa);
227 }
228
229 if (v3d_qpu_writes_flags(&inst->qpu)) {
230 /* If we obscure a previous flags write,
231 * drop it.
232 */
233 if (last_flags_write &&
234 (inst->qpu.flags.apf != V3D_QPU_PF_NONE ||
235 inst->qpu.flags.mpf != V3D_QPU_PF_NONE)) {
236 vir_dce_flags(c, last_flags_write);
237 progress = true;
238 }
239
240 last_flags_write = inst;
241 }
242
243 if (v3d_qpu_writes_flags(&inst->qpu) ||
244 has_nonremovable_reads(c, inst) ||
245 (is_ldunifa && !is_first_ldunifa && !is_last_ldunifa)) {
246 /* If we can't remove the instruction, but we
247 * don't need its destination value, just
248 * remove the destination. The register
249 * allocator would trivially color it and it
250 * wouldn't cause any register pressure, but
251 * it's nicer to read the VIR code without
252 * unused destination regs.
253 */
254 if (inst->dst.file == QFILE_TEMP &&
255 can_write_to_null(c, inst)) {
256 if (debug) {
257 fprintf(stderr,
258 "Removing dst from: ");
259 vir_dump_inst(c, inst);
260 fprintf(stderr, "\n");
261 }
262 c->defs[inst->dst.index] = NULL;
263 inst->dst.file = QFILE_NULL;
264 progress = true;
265 }
266 continue;
267 }
268
269 /* If we are removing the first ldunifa in a sequence
270 * we need to update the unifa address.
271 */
272 if (is_first_ldunifa) {
273 assert(unifa);
274 if (!increment_unifa_address(c, unifa))
275 continue;
276 }
277
278 assert(inst != last_flags_write);
279 dce(c, inst);
280 progress = true;
281 continue;
282 }
283 }
284
285 free(used);
286
287 return progress;
288 }
289