1 /*
2 * Copyright © 2013 Intel 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 /** @file brw_dead_control_flow.cpp
25 *
26 * This file implements the dead control flow elimination optimization pass.
27 */
28
29 #include "brw_shader.h"
30 #include "brw_cfg.h"
31
32 /* Look for and eliminate dead control flow:
33 *
34 * - if/endif
35 * - else in else/endif
36 * - then in if/else/endif
37 */
38 bool
dead_control_flow_eliminate(backend_shader * s)39 dead_control_flow_eliminate(backend_shader *s)
40 {
41 bool progress = false;
42
43 foreach_block_safe (block, s->cfg) {
44 bblock_t *prev_block = block->prev();
45
46 if (!prev_block)
47 continue;
48
49 backend_instruction *const inst = block->start();
50 backend_instruction *const prev_inst = prev_block->end();
51
52 /* ENDIF instructions, by definition, can only be found at the start of
53 * basic blocks.
54 */
55 if (inst->opcode == BRW_OPCODE_ENDIF &&
56 prev_inst->opcode == BRW_OPCODE_ELSE) {
57 bblock_t *const else_block = prev_block;
58 backend_instruction *const else_inst = prev_inst;
59
60 else_inst->remove(else_block);
61 progress = true;
62 } else if (inst->opcode == BRW_OPCODE_ENDIF &&
63 prev_inst->opcode == BRW_OPCODE_IF) {
64 bblock_t *const endif_block = block;
65 bblock_t *const if_block = prev_block;
66 backend_instruction *const endif_inst = inst;
67 backend_instruction *const if_inst = prev_inst;
68
69 bblock_t *earlier_block = NULL, *later_block = NULL;
70
71 if (if_block->start_ip == if_block->end_ip) {
72 earlier_block = if_block->prev();
73 } else {
74 earlier_block = if_block;
75 }
76 if_inst->remove(if_block);
77
78 if (endif_block->start_ip == endif_block->end_ip) {
79 later_block = endif_block->next();
80 } else {
81 later_block = endif_block;
82 }
83 endif_inst->remove(endif_block);
84
85 assert((earlier_block == NULL) == (later_block == NULL));
86 if (earlier_block && earlier_block->can_combine_with(later_block)) {
87 earlier_block->combine_with(later_block);
88
89 /* If ENDIF was in its own block, then we've now deleted it and
90 * merged the two surrounding blocks, the latter of which the
91 * __next block pointer was pointing to.
92 */
93 if (endif_block != later_block) {
94 __next = earlier_block->next();
95 }
96 }
97
98 progress = true;
99 } else if (inst->opcode == BRW_OPCODE_ELSE &&
100 prev_inst->opcode == BRW_OPCODE_IF) {
101 bblock_t *const else_block = block;
102 backend_instruction *const if_inst = prev_inst;
103 backend_instruction *const else_inst = inst;
104
105 /* Since the else-branch is becoming the new then-branch, the
106 * condition has to be inverted.
107 */
108 if_inst->predicate_inverse = !if_inst->predicate_inverse;
109 else_inst->remove(else_block);
110
111 progress = true;
112 }
113 }
114
115 if (progress)
116 s->invalidate_live_intervals();
117
118 return progress;
119 }
120