1 /*
2 * Copyright (C) 2021 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 "agx_compiler.h"
26 #include "util/u_memory.h"
27 #include "util/list.h"
28 #include "util/set.h"
29
30 /* Liveness analysis is a backwards-may dataflow analysis pass. Within a block,
31 * we compute live_out from live_in. The intrablock pass is linear-time. It
32 * returns whether progress was made. */
33
34 /* live_in[s] = GEN[s] + (live_out[s] - KILL[s]) */
35
36 void
agx_liveness_ins_update(BITSET_WORD * live,agx_instr * I)37 agx_liveness_ins_update(BITSET_WORD *live, agx_instr *I)
38 {
39 agx_foreach_dest(I, d) {
40 if (I->dest[d].type == AGX_INDEX_NORMAL)
41 BITSET_CLEAR(live, I->dest[d].value);
42 }
43
44 agx_foreach_src(I, s) {
45 if (I->src[s].type == AGX_INDEX_NORMAL) {
46 /* If the source is not live after this instruction, but becomes live
47 * at this instruction, this is the use that kills the source */
48 I->src[s].kill = !BITSET_TEST(live, I->src[s].value);
49 BITSET_SET(live, I->src[s].value);
50 }
51 }
52 }
53
54 /* Globally, liveness analysis uses a fixed-point algorithm based on a
55 * worklist. We initialize a work list with the exit block. We iterate the work
56 * list to compute live_in from live_out for each block on the work list,
57 * adding the predecessors of the block to the work list if we made progress.
58 */
59
60 void
agx_compute_liveness(agx_context * ctx)61 agx_compute_liveness(agx_context *ctx)
62 {
63 u_worklist worklist;
64 u_worklist_init(&worklist, ctx->num_blocks, NULL);
65
66 /* Free any previous liveness, and allocate */
67 unsigned words = BITSET_WORDS(ctx->alloc);
68
69 agx_foreach_block(ctx, block) {
70 if (block->live_in)
71 ralloc_free(block->live_in);
72
73 if (block->live_out)
74 ralloc_free(block->live_out);
75
76 block->live_in = rzalloc_array(block, BITSET_WORD, words);
77 block->live_out = rzalloc_array(block, BITSET_WORD, words);
78
79 agx_worklist_push_head(&worklist, block);
80 }
81
82 /* Iterate the work list */
83 while(!u_worklist_is_empty(&worklist)) {
84 /* Pop in reverse order since liveness is a backwards pass */
85 agx_block *blk = agx_worklist_pop_head(&worklist);
86
87 /* Update its liveness information */
88 memcpy(blk->live_in, blk->live_out, words * sizeof(BITSET_WORD));
89
90 agx_foreach_instr_in_block_rev(blk, I) {
91 /* Phi nodes are handled separately, so we skip them. As phi nodes are at
92 * the beginning and we're iterating backwards, we stop as soon as we hit
93 * a phi node.
94 */
95 if (I->op == AGX_OPCODE_PHI)
96 break;
97
98 agx_liveness_ins_update(blk->live_in, I);
99 }
100
101 /* Propagate the live in of the successor (blk) to the live out of
102 * predecessors.
103 *
104 * Phi nodes are logically on the control flow edge and act in parallel. To
105 * handle when propagating, we kill writes from phis and make live the
106 * corresponding sources.
107 */
108 agx_foreach_predecessor(blk, pred) {
109 BITSET_WORD *live = ralloc_array(blk, BITSET_WORD, words);
110 memcpy(live, blk->live_in, words * sizeof(BITSET_WORD));
111
112 /* Kill write */
113 agx_foreach_instr_in_block(blk, I) {
114 if (I->op != AGX_OPCODE_PHI) break;
115
116 assert(I->dest[0].type == AGX_INDEX_NORMAL);
117 BITSET_CLEAR(live, I->dest[0].value);
118 }
119
120 /* Make live the corresponding source */
121 agx_foreach_instr_in_block(blk, I) {
122 if (I->op != AGX_OPCODE_PHI) break;
123
124 agx_index operand = I->src[agx_predecessor_index(blk, *pred)];
125 assert(operand.type == AGX_INDEX_NORMAL);
126 BITSET_SET(live, operand.value);
127 }
128
129 bool progress = false;
130
131 for (unsigned i = 0; i < words; ++i) {
132 progress |= live[i] & ~((*pred)->live_out[i]);
133 (*pred)->live_out[i] |= live[i];
134 }
135
136 if (progress)
137 agx_worklist_push_tail(&worklist, *pred);
138 }
139 }
140
141 u_worklist_fini(&worklist);
142 }
143