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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;