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   using ir_hierarchical_visitor::visit;
53   using ir_hierarchical_visitor::visit_enter;
54
55   virtual ir_visitor_status visit_enter(ir_dereference_variable *);
56   virtual ir_visitor_status visit(ir_variable *);
57   virtual ir_visitor_status visit_enter(ir_assignment *);
58   virtual ir_visitor_status visit_enter(ir_call *);
59
60   struct hash_table *ht;
61};
62
63} /* unnamed namespace */
64
65static struct assignment_entry *
66get_assignment_entry(ir_variable *var, struct hash_table *ht)
67{
68   struct hash_entry *hte = _mesa_hash_table_search(ht, var);
69   struct assignment_entry *entry;
70
71   if (hte) {
72      entry = (struct assignment_entry *) hte->data;
73   } else {
74      entry = (struct assignment_entry *) calloc(1, sizeof(*entry));
75      entry->var = var;
76      _mesa_hash_table_insert(ht, var, entry);
77   }
78
79   return entry;
80}
81
82ir_visitor_status
83ir_constant_variable_visitor::visit(ir_variable *ir)
84{
85   struct assignment_entry *entry = get_assignment_entry(ir, this->ht);
86   entry->our_scope = true;
87   return visit_continue;
88}
89
90/* Skip derefs of variables so that we can detect declarations. */
91ir_visitor_status
92ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
93{
94   (void)ir;
95   return visit_continue_with_parent;
96}
97
98ir_visitor_status
99ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
100{
101   ir_constant *constval;
102   struct assignment_entry *entry;
103
104   entry = get_assignment_entry(ir->lhs->variable_referenced(), this->ht);
105   assert(entry);
106   entry->assignment_count++;
107
108   /* If there's more than one assignment, don't bother - we won't do anything
109    * with this variable anyway, and continuing just wastes memory cloning
110    * constant expressions.
111    */
112   if (entry->assignment_count > 1)
113      return visit_continue;
114
115   /* If it's already constant, don't do the work. */
116   if (entry->var->constant_value)
117      return visit_continue;
118
119   /* OK, now find if we actually have all the right conditions for
120    * this to be a constant value assigned to the var.
121    */
122   if (ir->condition)
123      return visit_continue;
124
125   ir_variable *var = ir->whole_variable_written();
126   if (!var)
127      return visit_continue;
128
129   /* Ignore buffer variables, since the underlying storage is shared
130    * and we can't be sure that this variable won't be written by another
131    * thread.
132    */
133   if (var->data.mode == ir_var_shader_storage ||
134       var->data.mode == ir_var_shader_shared)
135      return visit_continue;
136
137   constval = ir->rhs->constant_expression_value(ralloc_parent(ir));
138   if (!constval)
139      return visit_continue;
140
141   /* Mark this entry as having a constant assignment (if the
142    * assignment count doesn't go >1).  do_constant_variable will fix
143    * up the variable with the constant value later.
144    */
145   entry->constval = constval;
146
147   return visit_continue;
148}
149
150ir_visitor_status
151ir_constant_variable_visitor::visit_enter(ir_call *ir)
152{
153   /* Mark any out parameters as assigned to */
154   foreach_two_lists(formal_node, &ir->callee->parameters,
155                     actual_node, &ir->actual_parameters) {
156      ir_rvalue *param_rval = (ir_rvalue *) actual_node;
157      ir_variable *param = (ir_variable *) formal_node;
158
159      if (param->data.mode == ir_var_function_out ||
160	  param->data.mode == ir_var_function_inout) {
161	 ir_variable *var = param_rval->variable_referenced();
162	 struct assignment_entry *entry;
163
164	 assert(var);
165	 entry = get_assignment_entry(var, this->ht);
166	 entry->assignment_count++;
167      }
168
169      /* We don't know if the variable passed to this function has been
170       * assigned a value or if it is undefined, so for now we always assume
171       * it has been assigned a value. Once functions have been inlined any
172       * further potential optimisations will be taken care of.
173       */
174      struct assignment_entry *entry;
175      entry = get_assignment_entry(param, this->ht);
176      entry->assignment_count++;
177   }
178
179   /* Mark the return storage as having been assigned to */
180   if (ir->return_deref != NULL) {
181      ir_variable *var = ir->return_deref->variable_referenced();
182      struct assignment_entry *entry;
183
184      assert(var);
185      entry = get_assignment_entry(var, this->ht);
186      entry->assignment_count++;
187   }
188
189   return visit_continue;
190}
191
192/**
193 * Does a copy propagation pass on the code present in the instruction stream.
194 */
195bool
196do_constant_variable(exec_list *instructions)
197{
198   bool progress = false;
199   ir_constant_variable_visitor v;
200
201   v.ht = _mesa_pointer_hash_table_create(NULL);
202   v.run(instructions);
203
204   hash_table_foreach(v.ht, hte) {
205      struct assignment_entry *entry = (struct assignment_entry *) hte->data;
206
207      if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
208	 entry->var->constant_value = entry->constval;
209	 progress = true;
210      }
211      hte->data = NULL;
212      free(entry);
213   }
214   _mesa_hash_table_destroy(v.ht, NULL);
215
216   return progress;
217}
218
219bool
220do_constant_variable_unlinked(exec_list *instructions)
221{
222   bool progress = false;
223
224   foreach_in_list(ir_instruction, ir, instructions) {
225      ir_function *f = ir->as_function();
226      if (f) {
227	 foreach_in_list(ir_function_signature, sig, &f->signatures) {
228	    if (do_constant_variable(&sig->body))
229	       progress = true;
230	 }
231      }
232   }
233
234   return progress;
235}
236