1 /*
2 * Copyright © 2018 Valve Corporation
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 #ifndef ACO_DOMINANCE_CPP
26 #define ACO_DOMINANCE_CPP
27
28 #include "aco_ir.h"
29
30 /*
31 * Implements the algorithms for computing the dominator tree from
32 * "A Simple, Fast Dominance Algorithm" by Cooper, Harvey, and Kennedy.
33 *
34 * Different from the paper, our CFG allows to compute the dominator tree
35 * in a single pass as it is guaranteed that the dominating predecessors
36 * are processed before the current block.
37 */
38
39 namespace aco {
40
41 void
dominator_tree(Program * program)42 dominator_tree(Program* program)
43 {
44 for (unsigned i = 0; i < program->blocks.size(); i++) {
45 Block& block = program->blocks[i];
46
47 /* If this block has no predecessor, it dominates itself by definition */
48 if (block.linear_preds.empty()) {
49 block.linear_idom = block.index;
50 block.logical_idom = block.index;
51 continue;
52 }
53
54 int new_logical_idom = -1;
55 int new_linear_idom = -1;
56 for (unsigned pred_idx : block.logical_preds) {
57 if ((int)program->blocks[pred_idx].logical_idom == -1)
58 continue;
59
60 if (new_logical_idom == -1) {
61 new_logical_idom = pred_idx;
62 continue;
63 }
64
65 while ((int)pred_idx != new_logical_idom) {
66 if ((int)pred_idx > new_logical_idom)
67 pred_idx = program->blocks[pred_idx].logical_idom;
68 if ((int)pred_idx < new_logical_idom)
69 new_logical_idom = program->blocks[new_logical_idom].logical_idom;
70 }
71 }
72
73 for (unsigned pred_idx : block.linear_preds) {
74 if ((int)program->blocks[pred_idx].linear_idom == -1)
75 continue;
76
77 if (new_linear_idom == -1) {
78 new_linear_idom = pred_idx;
79 continue;
80 }
81
82 while ((int)pred_idx != new_linear_idom) {
83 if ((int)pred_idx > new_linear_idom)
84 pred_idx = program->blocks[pred_idx].linear_idom;
85 if ((int)pred_idx < new_linear_idom)
86 new_linear_idom = program->blocks[new_linear_idom].linear_idom;
87 }
88 }
89
90 block.logical_idom = new_logical_idom;
91 block.linear_idom = new_linear_idom;
92 }
93 }
94
95 } // namespace aco
96 #endif
97