bi_opt_dce.c revision 7ec681f3 
1/*
2 * Copyright (C) 2018 Alyssa Rosenzweig
3 * Copyright (C) 2019-2020 Collabora, Ltd.
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 FROM,
21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 * SOFTWARE.
23 */
24
25#include "compiler.h"
26#include "util/u_memory.h"
27
28/* A simple liveness-based dead code elimination pass. */
29
30void
31bi_opt_dead_code_eliminate(bi_context *ctx)
32{
33        unsigned temp_count = bi_max_temp(ctx);
34
35        bi_invalidate_liveness(ctx);
36        bi_compute_liveness(ctx);
37
38        bi_foreach_block_rev(ctx, block) {
39                uint8_t *live = rzalloc_array(block, uint8_t, temp_count);
40
41                bi_foreach_successor(block, succ) {
42                        for (unsigned i = 0; i < temp_count; ++i)
43                                live[i] |= succ->live_in[i];
44                }
45
46                bi_foreach_instr_in_block_safe_rev(block, ins) {
47                        bool all_null = true;
48
49                        bi_foreach_dest(ins, d) {
50                                unsigned index = bi_get_node(ins->dest[d]);
51
52                                if (index < temp_count && !(live[index] & bi_writemask(ins, d)))
53                                        ins->dest[d] = bi_null();
54
55                                all_null &= bi_is_null(ins->dest[d]);
56                        }
57
58                        if (all_null && !bi_side_effects(ins->op))
59                                bi_remove_instruction(ins);
60                        else
61                                bi_liveness_ins_update(live, ins, temp_count);
62                }
63
64                ralloc_free(block->live_in);
65                block->live_in = live;
66        }
67}
68
69/* Post-RA liveness-based dead code analysis to clean up results of bundling */
70
71uint64_t
72bi_postra_liveness_ins(uint64_t live, bi_instr *ins)
73{
74        bi_foreach_dest(ins, d) {
75                if (ins->dest[d].type == BI_INDEX_REGISTER) {
76                        unsigned nr = bi_count_write_registers(ins, d);
77                        unsigned reg = ins->dest[d].value;
78                        live &= ~(BITFIELD64_MASK(nr) << reg);
79                }
80        }
81
82        bi_foreach_src(ins, s) {
83                if (ins->src[s].type == BI_INDEX_REGISTER) {
84                        unsigned nr = bi_count_read_registers(ins, s);
85                        unsigned reg = ins->src[s].value;
86                        live |= (BITFIELD64_MASK(nr) << reg);
87                }
88        }
89
90        return live;
91}
92
93static bool
94bi_postra_liveness_block(bi_block *blk)
95{
96        bi_foreach_successor(blk, succ)
97                blk->reg_live_out |= succ->reg_live_in;
98
99        uint64_t live = blk->reg_live_out;
100
101        bi_foreach_instr_in_block_rev(blk, ins)
102                live = bi_postra_liveness_ins(live, ins);
103
104        bool progress = blk->reg_live_in != live;
105        blk->reg_live_in = live;
106        return progress;
107}
108
109/* Globally, liveness analysis uses a fixed-point algorithm based on a
110 * worklist. We initialize a work list with the exit block. We iterate the work
111 * list to compute live_in from live_out for each block on the work list,
112 * adding the predecessors of the block to the work list if we made progress.
113 */
114
115void
116bi_postra_liveness(bi_context *ctx)
117{
118        struct set *work_list = _mesa_set_create(NULL,
119                        _mesa_hash_pointer,
120                        _mesa_key_pointer_equal);
121
122        struct set *visited = _mesa_set_create(NULL,
123                        _mesa_hash_pointer,
124                        _mesa_key_pointer_equal);
125
126        struct set_entry *cur;
127        cur = _mesa_set_add(work_list, pan_exit_block(&ctx->blocks));
128
129        bi_foreach_block(ctx, block) {
130                block->reg_live_out = block->reg_live_in = 0;
131        }
132
133        do {
134                bi_block *blk = (struct bi_block *) cur->key;
135                _mesa_set_remove(work_list, cur);
136
137                /* Update its liveness information */
138                bool progress = bi_postra_liveness_block(blk);
139
140                /* If we made progress, we need to process the predecessors */
141
142                if (progress || !_mesa_set_search(visited, blk)) {
143                        bi_foreach_predecessor((blk), pred)
144                                _mesa_set_add(work_list, pred);
145                }
146
147                _mesa_set_add(visited, blk);
148        } while((cur = _mesa_set_next_entry(work_list, NULL)) != NULL);
149
150        _mesa_set_destroy(visited, NULL);
151        _mesa_set_destroy(work_list, NULL);
152}
153
154void
155bi_opt_dce_post_ra(bi_context *ctx)
156{
157        bi_postra_liveness(ctx);
158
159        bi_foreach_block_rev(ctx, block) {
160                uint64_t live = block->reg_live_out;
161
162                bi_foreach_instr_in_block_rev(block, ins) {
163                        bi_foreach_dest(ins, d) {
164                                if (ins->dest[d].type != BI_INDEX_REGISTER)
165                                        continue;
166
167                                unsigned nr = bi_count_write_registers(ins, d);
168                                unsigned reg = ins->dest[d].value;
169                                uint64_t mask = (BITFIELD64_MASK(nr) << reg);
170                                bool cullable = (ins->op != BI_OPCODE_BLEND);
171
172                                if (!(live & mask) && cullable)
173                                        ins->dest[d] = bi_null();
174                        }
175
176                        live = bi_postra_liveness_ins(live, ins);
177                }
178        }
179}
180