2 * Copyright © 2010 Intel Corporation
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:
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
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.
25 * \file opt_discard_simplification.cpp
27 * This pass simplifies if-statements and loops containing unconditional
30 * Case 1: Both branches contain unconditional discards:
31 * -----------------------------------------------------
47 * Case 2: The "then" clause contains an unconditional discard:
48 * ------------------------------------------------------------
66 * Case 3: The "else" clause contains an unconditional discard:
67 * ------------------------------------------------------------
86 #include "glsl_types.h"
89 class discard_simplifier : public ir_hierarchical_visitor {
93 this->progress = false;
96 ir_visitor_status visit_enter(ir_if *);
97 ir_visitor_status visit_enter(ir_loop *);
98 ir_visitor_status visit_enter(ir_assignment *);
104 find_unconditional_discard(exec_list &instructions)
106 foreach_list(n, &instructions) {
107 ir_instruction *ir = (ir_instruction *)n;
109 if (ir->ir_type == ir_type_return ||
110 ir->ir_type == ir_type_loop_jump)
113 /* So far, this code doesn't know how to look inside of flow
114 * control to see if a discard later on at this level is
117 if (ir->ir_type == ir_type_if ||
118 ir->ir_type == ir_type_loop)
121 ir_discard *discard = ir->as_discard();
122 if (discard != NULL && discard->condition == NULL)
129 is_only_instruction(ir_discard *discard)
131 return (discard->prev->is_head_sentinel() &&
132 discard->next->is_tail_sentinel());
135 /* We only care about the top level instructions, so don't descend
139 discard_simplifier::visit_enter(ir_assignment *ir)
141 return visit_continue_with_parent;
145 discard_simplifier::visit_enter(ir_if *ir)
147 ir_discard *then_discard = find_unconditional_discard(ir->then_instructions);
148 ir_discard *else_discard = find_unconditional_discard(ir->else_instructions);
150 if (then_discard == NULL && else_discard == NULL)
151 return visit_continue;
153 /* If both branches result in discard, replace whole if with discard. */
154 if (then_discard != NULL && else_discard != NULL) {
155 this->progress = true;
156 ir->replace_with(then_discard);
157 return visit_continue_with_parent;
160 /* Otherwise, one branch has a discard. */
161 if (then_discard != NULL && !is_only_instruction(then_discard)) {
162 this->progress = true;
163 ir->then_instructions.make_empty();
164 ir->then_instructions.push_tail(then_discard);
165 } else if (else_discard != NULL && !is_only_instruction(else_discard)) {
166 this->progress = true;
167 ir->else_instructions.make_empty();
168 ir->else_instructions.push_tail(else_discard);
171 visit_list_elements(this, &ir->then_instructions);
172 return visit_continue_with_parent;
176 discard_simplifier::visit_enter(ir_loop *ir)
178 ir_discard *discard = find_unconditional_discard(ir->body_instructions);
181 ir->replace_with(discard);
182 return visit_continue_with_parent;
185 return visit_continue;
189 do_discard_simplification(exec_list *instructions)
191 /* Look for a top-level unconditional discard */
192 ir_discard *discard = find_unconditional_discard(*instructions);
193 if (discard != NULL) {
194 instructions->make_empty();
195 instructions->push_tail(discard);
199 discard_simplifier v;
201 visit_list_elements(&v, instructions);