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Viewing changes to src/broadcom/compiler/vir_opt_dead_code.c

  • Committer: mmach
  • Date: 2022-09-22 19:56:13 UTC
  • Revision ID: netbit73@gmail.com-20220922195613-wtik9mmy20tmor0i
2022-09-22 21:17:09

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src/broadcom/compiler/vir_opt_dead_code.c
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
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
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
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
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
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
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
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
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
 
}