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 lower_discard.cpp
26 *
27 * This pass moves discards out of if-statements.
28 *
29 * Case 1: The "then" branch contains a conditional discard:
30 * ---------------------------------------------------------
31 *
32 * if (cond1) {
33 * s1;
34 * discard cond2;
35 * s2;
36 * } else {
37 * s3;
38 * }
39 *
40 * becomes:
41 *
42 * temp = false;
43 * if (cond1) {
44 * s1;
45 * temp = cond2;
46 * s2;
47 * } else {
48 * s3;
49 * }
50 * discard temp;
51 *
52 * Case 2: The "else" branch contains a conditional discard:
53 * ---------------------------------------------------------
54 *
55 * if (cond1) {
56 * s1;
57 * } else {
58 * s2;
59 * discard cond2;
60 * s3;
61 * }
62 *
63 * becomes:
64 *
65 * temp = false;
66 * if (cond1) {
67 * s1;
68 * } else {
69 * s2;
70 * temp = cond2;
71 * s3;
72 * }
73 * discard temp;
74 *
75 * Case 3: Both branches contain a conditional discard:
76 * ----------------------------------------------------
77 *
78 * if (cond1) {
79 * s1;
80 * discard cond2;
81 * s2;
82 * } else {
83 * s3;
84 * discard cond3;
85 * s4;
86 * }
87 *
88 * becomes:
89 *
90 * temp = false;
91 * if (cond1) {
92 * s1;
93 * temp = cond2;
94 * s2;
95 * } else {
96 * s3;
97 * temp = cond3;
98 * s4;
99 * }
100 * discard temp;
101 *
102 * If there are multiple conditional discards, we need only deal with one of
103 * them. Repeatedly applying this pass will take care of the others.
104 *
105 * Unconditional discards are treated as having a condition of "true".
106 */
107
108 #include "compiler/glsl_types.h"
109 #include "ir.h"
110
111 namespace {
112
113 class lower_discard_visitor : public ir_hierarchical_visitor {
114 public:
lower_discard_visitor()115 lower_discard_visitor()
116 {
117 this->progress = false;
118 }
119
120 ir_visitor_status visit_leave(ir_if *);
121
122 bool progress;
123 };
124
125 } /* anonymous namespace */
126
127 bool
lower_discard(exec_list * instructions)128 lower_discard(exec_list *instructions)
129 {
130 lower_discard_visitor v;
131
132 visit_list_elements(&v, instructions);
133
134 return v.progress;
135 }
136
137
138 static ir_discard *
find_discard(exec_list & instructions)139 find_discard(exec_list &instructions)
140 {
141 foreach_in_list(ir_instruction, node, &instructions) {
142 ir_discard *ir = node->as_discard();
143 if (ir != NULL)
144 return ir;
145 }
146 return NULL;
147 }
148
149
150 static void
replace_discard(void * mem_ctx,ir_variable * var,ir_discard * ir)151 replace_discard(void *mem_ctx, ir_variable *var, ir_discard *ir)
152 {
153 ir_rvalue *condition = ir->condition;
154
155 /* For unconditional discards, use "true" as the condition. */
156 if (condition == NULL)
157 condition = new(mem_ctx) ir_constant(true);
158
159 ir_assignment *assignment =
160 new(mem_ctx) ir_assignment(new(mem_ctx) ir_dereference_variable(var),
161 condition, NULL);
162
163 ir->replace_with(assignment);
164 }
165
166
167 ir_visitor_status
visit_leave(ir_if * ir)168 lower_discard_visitor::visit_leave(ir_if *ir)
169 {
170 ir_discard *then_discard = find_discard(ir->then_instructions);
171 ir_discard *else_discard = find_discard(ir->else_instructions);
172
173 if (then_discard == NULL && else_discard == NULL)
174 return visit_continue;
175
176 void *mem_ctx = ralloc_parent(ir);
177
178 ir_variable *temp = new(mem_ctx) ir_variable(glsl_type::bool_type,
179 "discard_cond_temp",
180 ir_var_temporary);
181 ir_assignment *temp_initializer =
182 new(mem_ctx) ir_assignment(new(mem_ctx) ir_dereference_variable(temp),
183 new(mem_ctx) ir_constant(false), NULL);
184
185 ir->insert_before(temp);
186 ir->insert_before(temp_initializer);
187
188 if (then_discard != NULL)
189 replace_discard(mem_ctx, temp, then_discard);
190
191 if (else_discard != NULL)
192 replace_discard(mem_ctx, temp, else_discard);
193
194 ir_discard *discard = then_discard != NULL ? then_discard : else_discard;
195 discard->condition = new(mem_ctx) ir_dereference_variable(temp);
196 ir->insert_after(discard);
197
198 this->progress = true;
199
200 return visit_continue;
201 }
202