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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 "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_assignment
*ir
);
54 virtual ir_visitor_status
visit_enter(ir_call
*ir
);
56 virtual void handle_rvalue(ir_rvalue
**rvalue
);
61 } /* unnamed namespace */
64 ir_constant_folding_visitor::handle_rvalue(ir_rvalue
**rvalue
)
66 if (*rvalue
== NULL
|| (*rvalue
)->ir_type
== ir_type_constant
)
69 /* Note that we do rvalue visitoring on leaving. So if an
70 * expression has a non-constant operand, no need to go looking
71 * down it to find if it's constant. This cuts the time of this
72 * pass down drastically.
74 ir_expression
*expr
= (*rvalue
)->as_expression();
76 for (unsigned int i
= 0; i
< expr
->get_num_operands(); i
++) {
77 if (!expr
->operands
[i
]->as_constant())
82 ir_constant
*constant
= (*rvalue
)->constant_expression_value();
85 this->progress
= true;
87 (*rvalue
)->accept(this);
92 ir_constant_folding_visitor::visit_enter(ir_assignment
*ir
)
94 ir
->rhs
->accept(this);
95 handle_rvalue(&ir
->rhs
);
98 ir
->condition
->accept(this);
99 handle_rvalue(&ir
->condition
);
101 ir_constant
*const_val
= ir
->condition
->as_constant();
102 /* If the condition is constant, either remove the condition or
103 * remove the never-executed assignment.
106 if (const_val
->value
.b
[0])
107 ir
->condition
= NULL
;
110 this->progress
= true;
114 /* Don't descend into the LHS because we want it to stay as a
115 * variable dereference. FINISHME: We probably should to get array
118 return visit_continue_with_parent
;
122 ir_constant_folding_visitor::visit_enter(ir_call
*ir
)
124 /* Attempt to constant fold parameters */
125 exec_list_iterator sig_iter
= ir
->callee
->parameters
.iterator();
126 foreach_iter(exec_list_iterator
, iter
, *ir
) {
127 ir_rvalue
*param_rval
= (ir_rvalue
*)iter
.get();
128 ir_variable
*sig_param
= (ir_variable
*)sig_iter
.get();
130 if (sig_param
->mode
== ir_var_in
|| sig_param
->mode
== ir_var_const_in
) {
131 ir_rvalue
*new_param
= param_rval
;
133 handle_rvalue(&new_param
);
134 if (new_param
!= param_rval
) {
135 param_rval
->replace_with(new_param
);
141 /* Next, see if the call can be replaced with an assignment of a constant */
142 ir_constant
*const_val
= ir
->constant_expression_value();
144 if (const_val
!= NULL
) {
145 ir_assignment
*assignment
=
146 new(ralloc_parent(ir
)) ir_assignment(ir
->return_deref
, const_val
);
147 ir
->replace_with(assignment
);
150 return visit_continue_with_parent
;
154 do_constant_folding(exec_list
*instructions
)
156 ir_constant_folding_visitor constant_folding
;
158 visit_list_elements(&constant_folding
, instructions
);
160 return constant_folding
.progress
;