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 #include "brw_cfg.h"
25
26 using namespace brw;
27
28 /** @file brw_predicated_break.cpp
29 *
30 * Loops are often structured as
31 *
32 * loop:
33 * CMP.f0
34 * (+f0) IF
35 * BREAK
36 * ENDIF
37 * ...
38 * WHILE loop
39 *
40 * This peephole pass removes the IF and ENDIF instructions and predicates the
41 * BREAK, dropping two instructions from the loop body.
42 *
43 * If the loop was a DO { ... } WHILE loop, it looks like
44 *
45 * loop:
46 * ...
47 * CMP.f0
48 * (+f0) IF
49 * BREAK
50 * ENDIF
51 * WHILE loop
52 *
53 * and we can remove the BREAK instruction and predicate the WHILE.
54 */
55
56 bool
opt_predicated_break(backend_shader * s)57 opt_predicated_break(backend_shader *s)
58 {
59 bool progress = false;
60
61 foreach_block (block, s->cfg) {
62 if (block->start_ip != block->end_ip)
63 continue;
64
65 /* BREAK and CONTINUE instructions, by definition, can only be found at
66 * the ends of basic blocks.
67 */
68 backend_instruction *jump_inst = block->end();
69 if (jump_inst->opcode != BRW_OPCODE_BREAK &&
70 jump_inst->opcode != BRW_OPCODE_CONTINUE)
71 continue;
72
73 backend_instruction *if_inst = block->prev()->end();
74 if (if_inst->opcode != BRW_OPCODE_IF)
75 continue;
76
77 backend_instruction *endif_inst = block->next()->start();
78 if (endif_inst->opcode != BRW_OPCODE_ENDIF)
79 continue;
80
81 bblock_t *jump_block = block;
82 bblock_t *if_block = jump_block->prev();
83 bblock_t *endif_block = jump_block->next();
84
85 jump_inst->predicate = if_inst->predicate;
86 jump_inst->predicate_inverse = if_inst->predicate_inverse;
87
88 bblock_t *earlier_block = if_block;
89 if (if_block->start_ip == if_block->end_ip) {
90 earlier_block = if_block->prev();
91 }
92
93 if_inst->remove(if_block);
94
95 bblock_t *later_block = endif_block;
96 if (endif_block->start_ip == endif_block->end_ip) {
97 later_block = endif_block->next();
98 }
99 endif_inst->remove(endif_block);
100
101 if (!earlier_block->ends_with_control_flow()) {
102 earlier_block->children.make_empty();
103 earlier_block->add_successor(s->cfg->mem_ctx, jump_block);
104 }
105
106 if (!later_block->starts_with_control_flow()) {
107 later_block->parents.make_empty();
108 }
109 jump_block->add_successor(s->cfg->mem_ctx, later_block);
110
111 if (earlier_block->can_combine_with(jump_block)) {
112 earlier_block->combine_with(jump_block);
113
114 block = earlier_block;
115 }
116
117 /* Now look at the first instruction of the block following the BREAK. If
118 * it's a WHILE, we can delete the break, predicate the WHILE, and join
119 * the two basic blocks.
120 */
121 bblock_t *while_block = earlier_block->next();
122 backend_instruction *while_inst = while_block->start();
123
124 if (jump_inst->opcode == BRW_OPCODE_BREAK &&
125 while_inst->opcode == BRW_OPCODE_WHILE &&
126 while_inst->predicate == BRW_PREDICATE_NONE) {
127 jump_inst->remove(earlier_block);
128 while_inst->predicate = jump_inst->predicate;
129 while_inst->predicate_inverse = !jump_inst->predicate_inverse;
130
131 earlier_block->children.make_empty();
132 earlier_block->add_successor(s->cfg->mem_ctx, while_block);
133
134 assert(earlier_block->can_combine_with(while_block));
135 earlier_block->combine_with(while_block);
136
137 earlier_block->next()->parents.make_empty();
138 earlier_block->add_successor(s->cfg->mem_ctx, earlier_block->next());
139 }
140
141 progress = true;
142 }
143
144 if (progress)
145 s->invalidate_live_intervals();
146
147 return progress;
148 }
149