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25 * \file opt_constant_variable.cpp
27 * Marks variables assigned a single constant value over the course
28 * of the program as constant.
30 * The goal here is to trigger further constant folding and then dead
31 * code elimination. This is common with vector/matrix constructors
32 * and calls to builtin functions.
36 #include "ir_visitor.h"
37 #include "ir_optimization.h"
38 #include "glsl_types.h"
42 struct assignment_entry
{
46 ir_constant
*constval
;
50 class ir_constant_variable_visitor
: public ir_hierarchical_visitor
{
52 virtual ir_visitor_status
visit_enter(ir_dereference_variable
*);
53 virtual ir_visitor_status
visit(ir_variable
*);
54 virtual ir_visitor_status
visit_enter(ir_assignment
*);
55 virtual ir_visitor_status
visit_enter(ir_call
*);
60 } /* unnamed namespace */
62 static struct assignment_entry
*
63 get_assignment_entry(ir_variable
*var
, exec_list
*list
)
65 struct assignment_entry
*entry
;
67 foreach_list_typed(struct assignment_entry
, entry
, link
, list
) {
68 if (entry
->var
== var
)
72 entry
= (struct assignment_entry
*)calloc(1, sizeof(*entry
));
74 list
->push_head(&entry
->link
);
79 ir_constant_variable_visitor::visit(ir_variable
*ir
)
81 struct assignment_entry
*entry
= get_assignment_entry(ir
, &this->list
);
82 entry
->our_scope
= true;
83 return visit_continue
;
86 /* Skip derefs of variables so that we can detect declarations. */
88 ir_constant_variable_visitor::visit_enter(ir_dereference_variable
*ir
)
91 return visit_continue_with_parent
;
95 ir_constant_variable_visitor::visit_enter(ir_assignment
*ir
)
97 ir_constant
*constval
;
98 struct assignment_entry
*entry
;
100 entry
= get_assignment_entry(ir
->lhs
->variable_referenced(), &this->list
);
102 entry
->assignment_count
++;
104 /* If it's already constant, don't do the work. */
105 if (entry
->var
->constant_value
)
106 return visit_continue
;
108 /* OK, now find if we actually have all the right conditions for
109 * this to be a constant value assigned to the var.
112 return visit_continue
;
114 ir_variable
*var
= ir
->whole_variable_written();
116 return visit_continue
;
118 /* Ignore buffer variables, since the underlying storage is shared
119 * and we can't be sure that this variable won't be written by another
122 if (var
->data
.mode
== ir_var_shader_storage
)
123 return visit_continue
;
125 constval
= ir
->rhs
->constant_expression_value();
127 return visit_continue
;
129 /* Mark this entry as having a constant assignment (if the
130 * assignment count doesn't go >1). do_constant_variable will fix
131 * up the variable with the constant value later.
133 entry
->constval
= constval
;
135 return visit_continue
;
139 ir_constant_variable_visitor::visit_enter(ir_call
*ir
)
141 /* Mark any out parameters as assigned to */
142 foreach_two_lists(formal_node
, &ir
->callee
->parameters
,
143 actual_node
, &ir
->actual_parameters
) {
144 ir_rvalue
*param_rval
= (ir_rvalue
*) actual_node
;
145 ir_variable
*param
= (ir_variable
*) formal_node
;
147 if (param
->data
.mode
== ir_var_function_out
||
148 param
->data
.mode
== ir_var_function_inout
) {
149 ir_variable
*var
= param_rval
->variable_referenced();
150 struct assignment_entry
*entry
;
153 entry
= get_assignment_entry(var
, &this->list
);
154 entry
->assignment_count
++;
158 /* Mark the return storage as having been assigned to */
159 if (ir
->return_deref
!= NULL
) {
160 ir_variable
*var
= ir
->return_deref
->variable_referenced();
161 struct assignment_entry
*entry
;
164 entry
= get_assignment_entry(var
, &this->list
);
165 entry
->assignment_count
++;
168 return visit_continue
;
172 * Does a copy propagation pass on the code present in the instruction stream.
175 do_constant_variable(exec_list
*instructions
)
177 bool progress
= false;
178 ir_constant_variable_visitor v
;
182 while (!v
.list
.is_empty()) {
184 struct assignment_entry
*entry
;
185 entry
= exec_node_data(struct assignment_entry
, v
.list
.head
, link
);
187 if (entry
->assignment_count
== 1 && entry
->constval
&& entry
->our_scope
) {
188 entry
->var
->constant_value
= entry
->constval
;
191 entry
->link
.remove();
199 do_constant_variable_unlinked(exec_list
*instructions
)
201 bool progress
= false;
203 foreach_in_list(ir_instruction
, ir
, instructions
) {
204 ir_function
*f
= ir
->as_function();
206 foreach_in_list(ir_function_signature
, sig
, &f
->signatures
) {
207 if (do_constant_variable(&sig
->body
))