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
40namespace {
41
42struct assignment_entry {
43   exec_node link;
44   int assignment_count;
45   ir_variable *var;
46   ir_constant *constval;
47   bool our_scope;
48};
49
50class ir_constant_variable_visitor : public ir_hierarchical_visitor {
51public:
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 *);
56
57   exec_list list;
58};
59
60} /* unnamed namespace */
61
62static struct assignment_entry *
63get_assignment_entry(ir_variable *var, exec_list *list)
64{
65   struct assignment_entry *entry;
66
67   foreach_list_typed(struct assignment_entry, entry, link, list) {
68      if (entry->var == var)
69	 return entry;
70   }
71
72   entry = (struct assignment_entry *)calloc(1, sizeof(*entry));
73   entry->var = var;
74   list->push_head(&entry->link);
75   return entry;
76}
77
78ir_visitor_status
79ir_constant_variable_visitor::visit(ir_variable *ir)
80{
81   struct assignment_entry *entry = get_assignment_entry(ir, &this->list);
82   entry->our_scope = true;
83   return visit_continue;
84}
85
86/* Skip derefs of variables so that we can detect declarations. */
87ir_visitor_status
88ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
89{
90   (void)ir;
91   return visit_continue_with_parent;
92}
93
94ir_visitor_status
95ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
96{
97   ir_constant *constval;
98   struct assignment_entry *entry;
99
100   entry = get_assignment_entry(ir->lhs->variable_referenced(), &this->list);
101   assert(entry);
102   entry->assignment_count++;
103
104   /* If it's already constant, don't do the work. */
105   if (entry->var->constant_value)
106      return visit_continue;
107
108   /* OK, now find if we actually have all the right conditions for
109    * this to be a constant value assigned to the var.
110    */
111   if (ir->condition)
112      return visit_continue;
113
114   ir_variable *var = ir->whole_variable_written();
115   if (!var)
116      return visit_continue;
117
118   constval = ir->rhs->constant_expression_value();
119   if (!constval)
120      return visit_continue;
121
122   /* Mark this entry as having a constant assignment (if the
123    * assignment count doesn't go >1).  do_constant_variable will fix
124    * up the variable with the constant value later.
125    */
126   entry->constval = constval;
127
128   return visit_continue;
129}
130
131ir_visitor_status
132ir_constant_variable_visitor::visit_enter(ir_call *ir)
133{
134   /* Mark any out parameters as assigned to */
135   exec_list_iterator sig_iter = ir->callee->parameters.iterator();
136   foreach_iter(exec_list_iterator, iter, *ir) {
137      ir_rvalue *param_rval = (ir_rvalue *)iter.get();
138      ir_variable *param = (ir_variable *)sig_iter.get();
139
140      if (param->mode == ir_var_out ||
141	  param->mode == ir_var_inout) {
142	 ir_variable *var = param_rval->variable_referenced();
143	 struct assignment_entry *entry;
144
145	 assert(var);
146	 entry = get_assignment_entry(var, &this->list);
147	 entry->assignment_count++;
148      }
149      sig_iter.next();
150   }
151
152   /* Mark the return storage as having been assigned to */
153   if (ir->return_deref != NULL) {
154      ir_variable *var = ir->return_deref->variable_referenced();
155      struct assignment_entry *entry;
156
157      assert(var);
158      entry = get_assignment_entry(var, &this->list);
159      entry->assignment_count++;
160   }
161
162   return visit_continue;
163}
164
165/**
166 * Does a copy propagation pass on the code present in the instruction stream.
167 */
168bool
169do_constant_variable(exec_list *instructions)
170{
171   bool progress = false;
172   ir_constant_variable_visitor v;
173
174   v.run(instructions);
175
176   while (!v.list.is_empty()) {
177
178      struct assignment_entry *entry;
179      entry = exec_node_data(struct assignment_entry, v.list.head, link);
180
181      if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
182	 entry->var->constant_value = entry->constval;
183	 progress = true;
184      }
185      entry->link.remove();
186      free(entry);
187   }
188
189   return progress;
190}
191
192bool
193do_constant_variable_unlinked(exec_list *instructions)
194{
195   bool progress = false;
196
197   foreach_iter(exec_list_iterator, iter, *instructions) {
198      ir_instruction *ir = (ir_instruction *)iter.get();
199      ir_function *f = ir->as_function();
200      if (f) {
201	 foreach_iter(exec_list_iterator, sigiter, *f) {
202	    ir_function_signature *sig =
203	       (ir_function_signature *) sigiter.get();
204	    if (do_constant_variable(&sig->body))
205	       progress = true;
206	 }
207      }
208   }
209
210   return progress;
211}
212