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 "compiler/glsl_types.h"
39#include "util/hash_table.h"
40
41namespace {
42
43struct assignment_entry {
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   struct hash_table *ht;
58};
59
60} /* unnamed namespace */
61
62static struct assignment_entry *
63get_assignment_entry(ir_variable *var, struct hash_table *ht)
64{
65   struct hash_entry *hte = _mesa_hash_table_search(ht, var);
66   struct assignment_entry *entry;
67
68   if (hte) {
69      entry = (struct assignment_entry *) hte->data;
70   } else {
71      entry = (struct assignment_entry *) calloc(1, sizeof(*entry));
72      entry->var = var;
73      _mesa_hash_table_insert(ht, var, entry);
74   }
75
76   return entry;
77}
78
79ir_visitor_status
80ir_constant_variable_visitor::visit(ir_variable *ir)
81{
82   struct assignment_entry *entry = get_assignment_entry(ir, this->ht);
83   entry->our_scope = true;
84   return visit_continue;
85}
86
87/* Skip derefs of variables so that we can detect declarations. */
88ir_visitor_status
89ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
90{
91   (void)ir;
92   return visit_continue_with_parent;
93}
94
95ir_visitor_status
96ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
97{
98   ir_constant *constval;
99   struct assignment_entry *entry;
100
101   entry = get_assignment_entry(ir->lhs->variable_referenced(), this->ht);
102   assert(entry);
103   entry->assignment_count++;
104
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.
108    */
109   if (entry->assignment_count > 1)
110      return visit_continue;
111
112   /* If it's already constant, don't do the work. */
113   if (entry->var->constant_value)
114      return visit_continue;
115
116   /* OK, now find if we actually have all the right conditions for
117    * this to be a constant value assigned to the var.
118    */
119   if (ir->condition)
120      return visit_continue;
121
122   ir_variable *var = ir->whole_variable_written();
123   if (!var)
124      return visit_continue;
125
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
128    * thread.
129    */
130   if (var->data.mode == ir_var_shader_storage ||
131       var->data.mode == ir_var_shader_shared)
132      return visit_continue;
133
134   constval = ir->rhs->constant_expression_value(ralloc_parent(ir));
135   if (!constval)
136      return visit_continue;
137
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.
141    */
142   entry->constval = constval;
143
144   return visit_continue;
145}
146
147ir_visitor_status
148ir_constant_variable_visitor::visit_enter(ir_call *ir)
149{
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;
155
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;
160
161	 assert(var);
162	 entry = get_assignment_entry(var, this->ht);
163	 entry->assignment_count++;
164      }
165   }
166
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;
171
172      assert(var);
173      entry = get_assignment_entry(var, this->ht);
174      entry->assignment_count++;
175   }
176
177   return visit_continue;
178}
179
180/**
181 * Does a copy propagation pass on the code present in the instruction stream.
182 */
183bool
184do_constant_variable(exec_list *instructions)
185{
186   bool progress = false;
187   ir_constant_variable_visitor v;
188
189   v.ht = _mesa_pointer_hash_table_create(NULL);
190   v.run(instructions);
191
192   hash_table_foreach(v.ht, hte) {
193      struct assignment_entry *entry = (struct assignment_entry *) hte->data;
194
195      if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
196	 entry->var->constant_value = entry->constval;
197	 progress = true;
198      }
199      hte->data = NULL;
200      free(entry);
201   }
202   _mesa_hash_table_destroy(v.ht, NULL);
203
204   return progress;
205}
206
207bool
208do_constant_variable_unlinked(exec_list *instructions)
209{
210   bool progress = false;
211
212   foreach_in_list(ir_instruction, ir, instructions) {
213      ir_function *f = ir->as_function();
214      if (f) {
215	 foreach_in_list(ir_function_signature, sig, &f->signatures) {
216	    if (do_constant_variable(&sig->body))
217	       progress = true;
218	 }
219      }
220   }
221
222   return progress;
223}
224