1 /*
2 * Copyright © 2010 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
21 * DEALINGS IN THE SOFTWARE.
22 */
23
24 /**
25 * \file opt_discard_simplification.cpp
26 *
27 * This pass simplifies if-statements and loops containing unconditional
28 * discards.
29 *
30 * Case 1: Both branches contain unconditional discards:
31 * -----------------------------------------------------
32 *
33 * if (cond) {
34 * s1;
35 * discard;
36 * s2;
37 * } else {
38 * s3;
39 * discard;
40 * s4;
41 * }
42 *
43 * becomes:
44 *
45 * discard
46 *
47 * Case 2: The "then" clause contains an unconditional discard:
48 * ------------------------------------------------------------
49 *
50 * if (cond) {
51 * s1;
52 * discard;
53 * s2;
54 * } else {
55 * s3;
56 * }
57 *
58 * becomes:
59 *
60 * if (cond) {
61 * discard;
62 * } else {
63 * s3;
64 * }
65 *
66 * Case 3: The "else" clause contains an unconditional discard:
67 * ------------------------------------------------------------
68 *
69 * if (cond) {
70 * s1;
71 * } else {
72 * s2;
73 * discard;
74 * s3;
75 * }
76 *
77 * becomes:
78 *
79 * if (cond) {
80 * s1;
81 * } else {
82 * discard;
83 * }
84 */
85
86 #include "glsl_types.h"
87 #include "ir.h"
88
89 class discard_simplifier : public ir_hierarchical_visitor {
90 public:
discard_simplifier()91 discard_simplifier()
92 {
93 this->progress = false;
94 }
95
96 ir_visitor_status visit_enter(ir_if *);
97 ir_visitor_status visit_enter(ir_loop *);
98
99 bool progress;
100 };
101
102 static ir_discard *
find_unconditional_discard(exec_list & instructions)103 find_unconditional_discard(exec_list &instructions)
104 {
105 foreach_list(n, &instructions) {
106 ir_discard *ir = ((ir_instruction *) n)->as_discard();
107 if (ir != NULL && ir->condition == NULL)
108 return ir;
109 }
110 return NULL;
111 }
112
113 static bool
is_only_instruction(ir_discard * discard)114 is_only_instruction(ir_discard *discard)
115 {
116 return (discard->prev->is_head_sentinel() &&
117 discard->next->is_tail_sentinel());
118 }
119
120 ir_visitor_status
visit_enter(ir_if * ir)121 discard_simplifier::visit_enter(ir_if *ir)
122 {
123 ir_discard *then_discard = find_unconditional_discard(ir->then_instructions);
124 ir_discard *else_discard = find_unconditional_discard(ir->else_instructions);
125
126 if (then_discard == NULL && else_discard == NULL)
127 return visit_continue;
128
129 /* If both branches result in discard, replace whole if with discard. */
130 if (then_discard != NULL && else_discard != NULL) {
131 this->progress = true;
132 ir->replace_with(then_discard);
133 return visit_continue_with_parent;
134 }
135
136 /* Otherwise, one branch has a discard. */
137 if (then_discard != NULL && !is_only_instruction(then_discard)) {
138 this->progress = true;
139 ir->then_instructions.make_empty();
140 ir->then_instructions.push_tail(then_discard);
141 } else if (else_discard != NULL && !is_only_instruction(else_discard)) {
142 this->progress = true;
143 ir->else_instructions.make_empty();
144 ir->else_instructions.push_tail(else_discard);
145 }
146
147 visit_list_elements(this, &ir->then_instructions);
148 return visit_continue_with_parent;
149 }
150
151 ir_visitor_status
visit_enter(ir_loop * ir)152 discard_simplifier::visit_enter(ir_loop *ir)
153 {
154 ir_discard *discard = find_unconditional_discard(ir->body_instructions);
155
156 if (discard) {
157 ir->replace_with(discard);
158 return visit_continue_with_parent;
159 }
160
161 return visit_continue;
162 }
163
164 bool
do_discard_simplification(exec_list * instructions)165 do_discard_simplification(exec_list *instructions)
166 {
167 /* Look for a top-level unconditional discard */
168 ir_discard *discard = find_unconditional_discard(*instructions);
169 if (discard != NULL) {
170 instructions->make_empty();
171 instructions->push_tail(discard);
172 return true;
173 }
174
175 discard_simplifier v;
176
177 visit_list_elements(&v, instructions);
178
179 return v.progress;
180 }
181