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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 "compiler/glsl_types.h"
39 #include "util/hash_table.h"
43 struct assignment_entry
{
46 ir_constant
*constval
;
50 class ir_constant_variable_visitor
: public ir_hierarchical_visitor
{
52 using ir_hierarchical_visitor::visit
;
53 using ir_hierarchical_visitor::visit_enter
;
55 virtual ir_visitor_status
visit_enter(ir_dereference_variable
*);
56 virtual ir_visitor_status
visit(ir_variable
*);
57 virtual ir_visitor_status
visit_enter(ir_assignment
*);
58 virtual ir_visitor_status
visit_enter(ir_call
*);
60 struct hash_table
*ht
;
63 } /* unnamed namespace */
65 static struct assignment_entry
*
66 get_assignment_entry(ir_variable
*var
, struct hash_table
*ht
)
68 struct hash_entry
*hte
= _mesa_hash_table_search(ht
, var
);
69 struct assignment_entry
*entry
;
72 entry
= (struct assignment_entry
*) hte
->data
;
74 entry
= (struct assignment_entry
*) calloc(1, sizeof(*entry
));
76 _mesa_hash_table_insert(ht
, var
, entry
);
83 ir_constant_variable_visitor::visit(ir_variable
*ir
)
85 struct assignment_entry
*entry
= get_assignment_entry(ir
, this->ht
);
86 entry
->our_scope
= true;
87 return visit_continue
;
90 /* Skip derefs of variables so that we can detect declarations. */
92 ir_constant_variable_visitor::visit_enter(ir_dereference_variable
*ir
)
95 return visit_continue_with_parent
;
99 ir_constant_variable_visitor::visit_enter(ir_assignment
*ir
)
101 ir_constant
*constval
;
102 struct assignment_entry
*entry
;
104 entry
= get_assignment_entry(ir
->lhs
->variable_referenced(), this->ht
);
106 entry
->assignment_count
++;
108 /* If there's more than one assignment, don't bother - we won't do anything
109 * with this variable anyway, and continuing just wastes memory cloning
110 * constant expressions.
112 if (entry
->assignment_count
> 1)
113 return visit_continue
;
115 /* If it's already constant, don't do the work. */
116 if (entry
->var
->constant_value
)
117 return visit_continue
;
119 /* OK, now find if we actually have all the right conditions for
120 * this to be a constant value assigned to the var.
123 return visit_continue
;
125 ir_variable
*var
= ir
->whole_variable_written();
127 return visit_continue
;
129 /* Ignore buffer variables, since the underlying storage is shared
130 * and we can't be sure that this variable won't be written by another
133 if (var
->data
.mode
== ir_var_shader_storage
||
134 var
->data
.mode
== ir_var_shader_shared
)
135 return visit_continue
;
137 constval
= ir
->rhs
->constant_expression_value(ralloc_parent(ir
));
139 return visit_continue
;
141 /* Mark this entry as having a constant assignment (if the
142 * assignment count doesn't go >1). do_constant_variable will fix
143 * up the variable with the constant value later.
145 entry
->constval
= constval
;
147 return visit_continue
;
151 ir_constant_variable_visitor::visit_enter(ir_call
*ir
)
153 /* Mark any out parameters as assigned to */
154 foreach_two_lists(formal_node
, &ir
->callee
->parameters
,
155 actual_node
, &ir
->actual_parameters
) {
156 ir_rvalue
*param_rval
= (ir_rvalue
*) actual_node
;
157 ir_variable
*param
= (ir_variable
*) formal_node
;
159 if (param
->data
.mode
== ir_var_function_out
||
160 param
->data
.mode
== ir_var_function_inout
) {
161 ir_variable
*var
= param_rval
->variable_referenced();
162 struct assignment_entry
*entry
;
165 entry
= get_assignment_entry(var
, this->ht
);
166 entry
->assignment_count
++;
169 /* We don't know if the variable passed to this function has been
170 * assigned a value or if it is undefined, so for now we always assume
171 * it has been assigned a value. Once functions have been inlined any
172 * further potential optimisations will be taken care of.
174 struct assignment_entry
*entry
;
175 entry
= get_assignment_entry(param
, this->ht
);
176 entry
->assignment_count
++;
179 /* Mark the return storage as having been assigned to */
180 if (ir
->return_deref
!= NULL
) {
181 ir_variable
*var
= ir
->return_deref
->variable_referenced();
182 struct assignment_entry
*entry
;
185 entry
= get_assignment_entry(var
, this->ht
);
186 entry
->assignment_count
++;
189 return visit_continue
;
193 * Does a copy propagation pass on the code present in the instruction stream.
196 do_constant_variable(exec_list
*instructions
)
198 bool progress
= false;
199 ir_constant_variable_visitor v
;
201 v
.ht
= _mesa_pointer_hash_table_create(NULL
);
204 hash_table_foreach(v
.ht
, hte
) {
205 struct assignment_entry
*entry
= (struct assignment_entry
*) hte
->data
;
207 if (entry
->assignment_count
== 1 && entry
->constval
&& entry
->our_scope
) {
208 entry
->var
->constant_value
= entry
->constval
;
214 _mesa_hash_table_destroy(v
.ht
, NULL
);
220 do_constant_variable_unlinked(exec_list
*instructions
)
222 bool progress
= false;
224 foreach_in_list(ir_instruction
, ir
, instructions
) {
225 ir_function
*f
= ir
->as_function();
227 foreach_in_list(ir_function_signature
, sig
, &f
->signatures
) {
228 if (do_constant_variable(&sig
->body
))