1/*
2 * Copyright © 2010 Intel Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
21 * DEALINGS IN THE SOFTWARE.
22 */
23
24/**
25 * \file opt_constant_variable.cpp
26 *
27 * Marks variables assigned a single constant value over the course
28 * of the program as constant.
29 *
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.
33 */
34
35#include "ir.h"
36#include "ir_visitor.h"
37#include "ir_optimization.h"
38#include "glsl_types.h"
39
40struct assignment_entry {
41   exec_node link;
42   int assignment_count;
43   ir_variable *var;
44   ir_constant *constval;
45   bool our_scope;
46};
47
48class ir_constant_variable_visitor : public ir_hierarchical_visitor {
49public:
50   virtual ir_visitor_status visit_enter(ir_dereference_variable *);
51   virtual ir_visitor_status visit(ir_variable *);
52   virtual ir_visitor_status visit_enter(ir_assignment *);
53   virtual ir_visitor_status visit_enter(ir_call *);
54
55   exec_list list;
56};
57
58static struct assignment_entry *
59get_assignment_entry(ir_variable *var, exec_list *list)
60{
61   struct assignment_entry *entry;
62
63   foreach_list_typed(struct assignment_entry, entry, link, list) {
64      if (entry->var == var)
65	 return entry;
66   }
67
68   entry = (struct assignment_entry *)calloc(1, sizeof(*entry));
69   entry->var = var;
70   list->push_head(&entry->link);
71   return entry;
72}
73
74ir_visitor_status
75ir_constant_variable_visitor::visit(ir_variable *ir)
76{
77   struct assignment_entry *entry = get_assignment_entry(ir, &this->list);
78   entry->our_scope = true;
79   return visit_continue;
80}
81
82/* Skip derefs of variables so that we can detect declarations. */
83ir_visitor_status
84ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
85{
86   (void)ir;
87   return visit_continue_with_parent;
88}
89
90ir_visitor_status
91ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
92{
93   ir_constant *constval;
94   struct assignment_entry *entry;
95
96   entry = get_assignment_entry(ir->lhs->variable_referenced(), &this->list);
97   assert(entry);
98   entry->assignment_count++;
99
100   /* If it's already constant, don't do the work. */
101   if (entry->var->constant_value)
102      return visit_continue;
103
104   /* OK, now find if we actually have all the right conditions for
105    * this to be a constant value assigned to the var.
106    */
107   if (ir->condition) {
108      constval = ir->condition->constant_expression_value();
109      if (!constval || !constval->value.b[0])
110	 return visit_continue;
111   }
112
113   ir_variable *var = ir->whole_variable_written();
114   if (!var)
115      return visit_continue;
116
117   constval = ir->rhs->constant_expression_value();
118   if (!constval)
119      return visit_continue;
120
121   /* Mark this entry as having a constant assignment (if the
122    * assignment count doesn't go >1).  do_constant_variable will fix
123    * up the variable with the constant value later.
124    */
125   entry->constval = constval;
126
127   return visit_continue;
128}
129
130ir_visitor_status
131ir_constant_variable_visitor::visit_enter(ir_call *ir)
132{
133   exec_list_iterator sig_iter = ir->get_callee()->parameters.iterator();
134   foreach_iter(exec_list_iterator, iter, *ir) {
135      ir_rvalue *param_rval = (ir_rvalue *)iter.get();
136      ir_variable *param = (ir_variable *)sig_iter.get();
137
138      if (param->mode == ir_var_out ||
139	  param->mode == ir_var_inout) {
140	 ir_variable *var = param_rval->variable_referenced();
141	 struct assignment_entry *entry;
142
143	 assert(var);
144	 entry = get_assignment_entry(var, &this->list);
145	 entry->assignment_count++;
146      }
147      sig_iter.next();
148   }
149   return visit_continue;
150}
151
152/**
153 * Does a copy propagation pass on the code present in the instruction stream.
154 */
155bool
156do_constant_variable(exec_list *instructions)
157{
158   bool progress = false;
159   ir_constant_variable_visitor v;
160
161   v.run(instructions);
162
163   while (!v.list.is_empty()) {
164
165      struct assignment_entry *entry;
166      entry = exec_node_data(struct assignment_entry, v.list.head, link);
167
168      if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
169	 entry->var->constant_value = entry->constval;
170	 progress = true;
171      }
172      entry->link.remove();
173      free(entry);
174   }
175
176   return progress;
177}
178
179bool
180do_constant_variable_unlinked(exec_list *instructions)
181{
182   bool progress = false;
183
184   foreach_iter(exec_list_iterator, iter, *instructions) {
185      ir_instruction *ir = (ir_instruction *)iter.get();
186      ir_function *f = ir->as_function();
187      if (f) {
188	 foreach_iter(exec_list_iterator, sigiter, *f) {
189	    ir_function_signature *sig =
190	       (ir_function_signature *) sigiter.get();
191	    if (do_constant_variable(&sig->body))
192	       progress = true;
193	 }
194      }
195   }
196
197   return progress;
198}
199