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25 * \file opt_constant_folding.cpp
26 * Replace constant-valued expressions with references to constant values.
30 #include "ir_visitor.h"
31 #include "ir_rvalue_visitor.h"
32 #include "ir_optimization.h"
33 #include "compiler/glsl_types.h"
38 * Visitor class for replacing expressions with ir_constant values.
41 class ir_constant_folding_visitor
: public ir_rvalue_visitor
{
43 ir_constant_folding_visitor()
45 this->progress
= false;
48 virtual ~ir_constant_folding_visitor()
53 virtual ir_visitor_status
visit_enter(ir_discard
*ir
);
54 virtual ir_visitor_status
visit_enter(ir_assignment
*ir
);
55 virtual ir_visitor_status
visit_enter(ir_call
*ir
);
57 virtual void handle_rvalue(ir_rvalue
**rvalue
);
62 } /* unnamed namespace */
65 ir_constant_fold(ir_rvalue
**rvalue
)
67 if (*rvalue
== NULL
|| (*rvalue
)->ir_type
== ir_type_constant
)
70 /* Note that we do rvalue visitoring on leaving. So if an
71 * expression has a non-constant operand, no need to go looking
72 * down it to find if it's constant. This cuts the time of this
73 * pass down drastically.
75 ir_expression
*expr
= (*rvalue
)->as_expression();
77 for (unsigned int i
= 0; i
< expr
->get_num_operands(); i
++) {
78 if (!expr
->operands
[i
]->as_constant())
83 /* Ditto for swizzles. */
84 ir_swizzle
*swiz
= (*rvalue
)->as_swizzle();
85 if (swiz
&& !swiz
->val
->as_constant())
88 /* Ditto for array dereferences */
89 ir_dereference_array
*array_ref
= (*rvalue
)->as_dereference_array();
90 if (array_ref
&& (!array_ref
->array
->as_constant() ||
91 !array_ref
->array_index
->as_constant()))
94 /* No constant folding can be performed on variable dereferences. We need
95 * to explicitly avoid them, as calling constant_expression_value() on a
96 * variable dereference will return a clone of var->constant_value. This
97 * would make us propagate the value into the tree, which isn't our job.
99 ir_dereference_variable
*var_ref
= (*rvalue
)->as_dereference_variable();
103 ir_constant
*constant
= (*rvalue
)->constant_expression_value();
112 ir_constant_folding_visitor::handle_rvalue(ir_rvalue
**rvalue
)
114 if (ir_constant_fold(rvalue
))
115 this->progress
= true;
119 ir_constant_folding_visitor::visit_enter(ir_discard
*ir
)
122 ir
->condition
->accept(this);
123 handle_rvalue(&ir
->condition
);
125 ir_constant
*const_val
= ir
->condition
->as_constant();
126 /* If the condition is constant, either remove the condition or
127 * remove the never-executed assignment.
130 if (const_val
->value
.b
[0])
131 ir
->condition
= NULL
;
134 this->progress
= true;
138 return visit_continue_with_parent
;
142 ir_constant_folding_visitor::visit_enter(ir_assignment
*ir
)
144 ir
->rhs
->accept(this);
145 handle_rvalue(&ir
->rhs
);
148 ir
->condition
->accept(this);
149 handle_rvalue(&ir
->condition
);
151 ir_constant
*const_val
= ir
->condition
->as_constant();
152 /* If the condition is constant, either remove the condition or
153 * remove the never-executed assignment.
156 if (const_val
->value
.b
[0])
157 ir
->condition
= NULL
;
160 this->progress
= true;
164 /* Don't descend into the LHS because we want it to stay as a
165 * variable dereference. FINISHME: We probably should to get array
168 return visit_continue_with_parent
;
172 ir_constant_folding_visitor::visit_enter(ir_call
*ir
)
174 /* Attempt to constant fold parameters */
175 foreach_two_lists(formal_node
, &ir
->callee
->parameters
,
176 actual_node
, &ir
->actual_parameters
) {
177 ir_rvalue
*param_rval
= (ir_rvalue
*) actual_node
;
178 ir_variable
*sig_param
= (ir_variable
*) formal_node
;
180 if (sig_param
->data
.mode
== ir_var_function_in
181 || sig_param
->data
.mode
== ir_var_const_in
) {
182 ir_rvalue
*new_param
= param_rval
;
184 handle_rvalue(&new_param
);
185 if (new_param
!= param_rval
) {
186 param_rval
->replace_with(new_param
);
191 /* Next, see if the call can be replaced with an assignment of a constant */
192 ir_constant
*const_val
= ir
->constant_expression_value();
194 if (const_val
!= NULL
) {
195 ir_assignment
*assignment
=
196 new(ralloc_parent(ir
)) ir_assignment(ir
->return_deref
, const_val
);
197 ir
->replace_with(assignment
);
200 return visit_continue_with_parent
;
204 do_constant_folding(exec_list
*instructions
)
206 ir_constant_folding_visitor constant_folding
;
208 visit_list_elements(&constant_folding
, instructions
);
210 return constant_folding
.progress
;