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 using namespace brw;
33
34 /* Look for and eliminate dead control flow:
35 *
36 * - if/endif
37 * - else in else/endif
38 * - then in if/else/endif
39 */
40 bool
dead_control_flow_eliminate(backend_shader * s)41 dead_control_flow_eliminate(backend_shader *s)
42 {
43 bool progress = false;
44
45 foreach_block_safe (block, s->cfg) {
46 bblock_t *prev_block = block->prev();
47
48 if (!prev_block)
49 continue;
50
51 backend_instruction *const inst = block->start();
52 backend_instruction *const prev_inst = prev_block->end();
53
54 /* ENDIF instructions, by definition, can only be found at the start of
55 * basic blocks.
56 */
57 if (inst->opcode == BRW_OPCODE_ENDIF &&
58 prev_inst->opcode == BRW_OPCODE_ELSE) {
59 bblock_t *const else_block = prev_block;
60 backend_instruction *const else_inst = prev_inst;
61
62 else_inst->remove(else_block);
63 progress = true;
64 } else if (inst->opcode == BRW_OPCODE_ENDIF &&
65 prev_inst->opcode == BRW_OPCODE_IF) {
66 bblock_t *const endif_block = block;
67 bblock_t *const if_block = prev_block;
68 backend_instruction *const endif_inst = inst;
69 backend_instruction *const if_inst = prev_inst;
70
71 bblock_t *earlier_block = NULL, *later_block = NULL;
72
73 if (if_block->start_ip == if_block->end_ip) {
74 earlier_block = if_block->prev();
75 } else {
76 earlier_block = if_block;
77 }
78 if_inst->remove(if_block);
79
80 if (endif_block->start_ip == endif_block->end_ip) {
81 later_block = endif_block->next();
82 } else {
83 later_block = endif_block;
84 }
85 endif_inst->remove(endif_block);
86
87 assert((earlier_block == NULL) == (later_block == NULL));
88 if (earlier_block && earlier_block->can_combine_with(later_block)) {
89 earlier_block->combine_with(later_block);
90
91 /* If ENDIF was in its own block, then we've now deleted it and
92 * merged the two surrounding blocks, the latter of which the
93 * __next block pointer was pointing to.
94 */
95 if (endif_block != later_block) {
96 __next = earlier_block->next();
97 }
98 }
99
100 progress = true;
101 } else if (inst->opcode == BRW_OPCODE_ELSE &&
102 prev_inst->opcode == BRW_OPCODE_IF) {
103 bblock_t *const else_block = block;
104 backend_instruction *const if_inst = prev_inst;
105 backend_instruction *const else_inst = inst;
106
107 /* Since the else-branch is becoming the new then-branch, the
108 * condition has to be inverted.
109 */
110 if_inst->predicate_inverse = !if_inst->predicate_inverse;
111 else_inst->remove(else_block);
112
113 progress = true;
114 }
115 }
116
117 if (progress)
118 s->invalidate_analysis(DEPENDENCY_BLOCKS | DEPENDENCY_INSTRUCTIONS);
119
120 return progress;
121 }
122