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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 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 *);
57 struct hash_table *ht;
60 } /* unnamed namespace */
62 static struct assignment_entry *
63 get_assignment_entry(ir_variable *var, struct hash_table *ht)
65 struct hash_entry *hte = _mesa_hash_table_search(ht, var);
66 struct assignment_entry *entry;
69 entry = (struct assignment_entry *) hte->data;
71 entry = (struct assignment_entry *) calloc(1, sizeof(*entry));
73 _mesa_hash_table_insert(ht, var, entry);
80 ir_constant_variable_visitor::visit(ir_variable *ir)
82 struct assignment_entry *entry = get_assignment_entry(ir, this->ht);
83 entry->our_scope = true;
84 return visit_continue;
87 /* Skip derefs of variables so that we can detect declarations. */
89 ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
92 return visit_continue_with_parent;
96 ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
98 ir_constant *constval;
99 struct assignment_entry *entry;
101 entry = get_assignment_entry(ir->lhs->variable_referenced(), this->ht);
103 entry->assignment_count++;
105 /* If there's more than one assignment, don't bother - we won't do anything
106 * with this variable anyway, and continuing just wastes memory cloning
107 * constant expressions.
109 if (entry->assignment_count > 1)
110 return visit_continue;
112 /* If it's already constant, don't do the work. */
113 if (entry->var->constant_value)
114 return visit_continue;
116 /* OK, now find if we actually have all the right conditions for
117 * this to be a constant value assigned to the var.
120 return visit_continue;
122 ir_variable *var = ir->whole_variable_written();
124 return visit_continue;
126 /* Ignore buffer variables, since the underlying storage is shared
127 * and we can't be sure that this variable won't be written by another
130 if (var->data.mode == ir_var_shader_storage ||
131 var->data.mode == ir_var_shader_shared)
132 return visit_continue;
134 constval = ir->rhs->constant_expression_value(ralloc_parent(ir));
136 return visit_continue;
138 /* Mark this entry as having a constant assignment (if the
139 * assignment count doesn't go >1). do_constant_variable will fix
140 * up the variable with the constant value later.
142 entry->constval = constval;
144 return visit_continue;
148 ir_constant_variable_visitor::visit_enter(ir_call *ir)
150 /* Mark any out parameters as assigned to */
151 foreach_two_lists(formal_node, &ir->callee->parameters,
152 actual_node, &ir->actual_parameters) {
153 ir_rvalue *param_rval = (ir_rvalue *) actual_node;
154 ir_variable *param = (ir_variable *) formal_node;
156 if (param->data.mode == ir_var_function_out ||
157 param->data.mode == ir_var_function_inout) {
158 ir_variable *var = param_rval->variable_referenced();
159 struct assignment_entry *entry;
162 entry = get_assignment_entry(var, this->ht);
163 entry->assignment_count++;
167 /* Mark the return storage as having been assigned to */
168 if (ir->return_deref != NULL) {
169 ir_variable *var = ir->return_deref->variable_referenced();
170 struct assignment_entry *entry;
173 entry = get_assignment_entry(var, this->ht);
174 entry->assignment_count++;
177 return visit_continue;
181 * Does a copy propagation pass on the code present in the instruction stream.
184 do_constant_variable(exec_list *instructions)
186 bool progress = false;
187 ir_constant_variable_visitor v;
189 v.ht = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
190 _mesa_key_pointer_equal);
193 struct hash_entry *hte;
194 hash_table_foreach(v.ht, hte) {
195 struct assignment_entry *entry = (struct assignment_entry *) hte->data;
197 if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
198 entry->var->constant_value = entry->constval;
204 _mesa_hash_table_destroy(v.ht, NULL);
210 do_constant_variable_unlinked(exec_list *instructions)
212 bool progress = false;
214 foreach_in_list(ir_instruction, ir, instructions) {
215 ir_function *f = ir->as_function();
217 foreach_in_list(ir_function_signature, sig, &f->signatures) {
218 if (do_constant_variable(&sig->body))