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_folding.cpp
26 * Replace constant-valued expressions with references to constant values.
27 */
28
29#include "ir.h"
30#include "ir_visitor.h"
31#include "ir_rvalue_visitor.h"
32#include "ir_optimization.h"
33#include "glsl_types.h"
34
35/**
36 * Visitor class for replacing expressions with ir_constant values.
37 */
38
39class ir_constant_folding_visitor : public ir_rvalue_visitor {
40public:
41   ir_constant_folding_visitor()
42   {
43      this->progress = false;
44   }
45
46   virtual ~ir_constant_folding_visitor()
47   {
48      /* empty */
49   }
50
51   virtual ir_visitor_status visit_enter(ir_assignment *ir);
52   virtual ir_visitor_status visit_enter(ir_call *ir);
53
54   virtual void handle_rvalue(ir_rvalue **rvalue);
55
56   bool progress;
57};
58
59void
60ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
61{
62   if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
63      return;
64
65   /* Note that we do rvalue visitoring on leaving.  So if an
66    * expression has a non-constant operand, no need to go looking
67    * down it to find if it's constant.  This cuts the time of this
68    * pass down drastically.
69    */
70   ir_expression *expr = (*rvalue)->as_expression();
71   if (expr) {
72      for (unsigned int i = 0; i < expr->get_num_operands(); i++) {
73	 if (!expr->operands[i]->as_constant())
74	    return;
75      }
76   }
77
78   ir_constant *constant = (*rvalue)->constant_expression_value();
79   if (constant) {
80      *rvalue = constant;
81      this->progress = true;
82   } else {
83      (*rvalue)->accept(this);
84   }
85}
86
87ir_visitor_status
88ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
89{
90   ir->rhs->accept(this);
91   handle_rvalue(&ir->rhs);
92
93   if (ir->condition) {
94      ir->condition->accept(this);
95      handle_rvalue(&ir->condition);
96
97      ir_constant *const_val = ir->condition->as_constant();
98      /* If the condition is constant, either remove the condition or
99       * remove the never-executed assignment.
100       */
101      if (const_val) {
102	 if (const_val->value.b[0])
103	    ir->condition = NULL;
104	 else
105	    ir->remove();
106	 this->progress = true;
107      }
108   }
109
110   /* Don't descend into the LHS because we want it to stay as a
111    * variable dereference.  FINISHME: We probably should to get array
112    * indices though.
113    */
114   return visit_continue_with_parent;
115}
116
117ir_visitor_status
118ir_constant_folding_visitor::visit_enter(ir_call *ir)
119{
120   exec_list_iterator sig_iter = ir->get_callee()->parameters.iterator();
121   foreach_iter(exec_list_iterator, iter, *ir) {
122      ir_rvalue *param_rval = (ir_rvalue *)iter.get();
123      ir_variable *sig_param = (ir_variable *)sig_iter.get();
124
125      if (sig_param->mode == ir_var_in) {
126	 ir_rvalue *new_param = param_rval;
127
128	 handle_rvalue(&new_param);
129	 if (new_param != param_rval) {
130	    param_rval->replace_with(new_param);
131	 }
132      }
133      sig_iter.next();
134   }
135
136   return visit_continue_with_parent;
137}
138
139bool
140do_constant_folding(exec_list *instructions)
141{
142   ir_constant_folding_visitor constant_folding;
143
144   visit_list_elements(&constant_folding, instructions);
145
146   return constant_folding.progress;
147}
148