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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
*);
103 find_unconditional_discard(exec_list
&instructions
)
105 foreach_list(n
, &instructions
) {
106 ir_discard
*ir
= ((ir_instruction
*) n
)->as_discard();
107 if (ir
!= NULL
&& ir
->condition
== NULL
)
114 is_only_instruction(ir_discard
*discard
)
116 return (discard
->prev
->is_head_sentinel() &&
117 discard
->next
->is_tail_sentinel());
121 discard_simplifier::visit_enter(ir_if
*ir
)
123 ir_discard
*then_discard
= find_unconditional_discard(ir
->then_instructions
);
124 ir_discard
*else_discard
= find_unconditional_discard(ir
->else_instructions
);
126 if (then_discard
== NULL
&& else_discard
== NULL
)
127 return visit_continue
;
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
;
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
);
147 visit_list_elements(this, &ir
->then_instructions
);
148 return visit_continue_with_parent
;
152 discard_simplifier::visit_enter(ir_loop
*ir
)
154 ir_discard
*discard
= find_unconditional_discard(ir
->body_instructions
);
157 ir
->replace_with(discard
);
158 return visit_continue_with_parent
;
161 return visit_continue
;
165 do_discard_simplification(exec_list
*instructions
)
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
);
175 discard_simplifier v
;
177 visit_list_elements(&v
, instructions
);