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 namespace {
36
37 /**
38 * Visitor class for replacing expressions with ir_constant values.
39 */
40
41 class ir_constant_folding_visitor : public ir_rvalue_visitor {
42 public:
ir_constant_folding_visitor()43 ir_constant_folding_visitor()
44 {
45 this->progress = false;
46 }
47
~ir_constant_folding_visitor()48 virtual ~ir_constant_folding_visitor()
49 {
50 /* empty */
51 }
52
53 virtual ir_visitor_status visit_enter(ir_assignment *ir);
54 virtual ir_visitor_status visit_enter(ir_call *ir);
55
56 virtual void handle_rvalue(ir_rvalue **rvalue);
57
58 bool progress;
59 };
60
61 } /* unnamed namespace */
62
63 void
handle_rvalue(ir_rvalue ** rvalue)64 ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
65 {
66 if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
67 return;
68
69 /* Note that we do rvalue visitoring on leaving. So if an
70 * expression has a non-constant operand, no need to go looking
71 * down it to find if it's constant. This cuts the time of this
72 * pass down drastically.
73 */
74 ir_expression *expr = (*rvalue)->as_expression();
75 if (expr) {
76 for (unsigned int i = 0; i < expr->get_num_operands(); i++) {
77 if (!expr->operands[i]->as_constant())
78 return;
79 }
80 }
81
82 ir_constant *constant = (*rvalue)->constant_expression_value();
83 if (constant) {
84 *rvalue = constant;
85 this->progress = true;
86 } else {
87 (*rvalue)->accept(this);
88 }
89 }
90
91 ir_visitor_status
visit_enter(ir_assignment * ir)92 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
93 {
94 ir->rhs->accept(this);
95 handle_rvalue(&ir->rhs);
96
97 if (ir->condition) {
98 ir->condition->accept(this);
99 handle_rvalue(&ir->condition);
100
101 ir_constant *const_val = ir->condition->as_constant();
102 /* If the condition is constant, either remove the condition or
103 * remove the never-executed assignment.
104 */
105 if (const_val) {
106 if (const_val->value.b[0])
107 ir->condition = NULL;
108 else
109 ir->remove();
110 this->progress = true;
111 }
112 }
113
114 /* Don't descend into the LHS because we want it to stay as a
115 * variable dereference. FINISHME: We probably should to get array
116 * indices though.
117 */
118 return visit_continue_with_parent;
119 }
120
121 ir_visitor_status
visit_enter(ir_call * ir)122 ir_constant_folding_visitor::visit_enter(ir_call *ir)
123 {
124 /* Attempt to constant fold parameters */
125 exec_list_iterator sig_iter = ir->callee->parameters.iterator();
126 foreach_iter(exec_list_iterator, iter, *ir) {
127 ir_rvalue *param_rval = (ir_rvalue *)iter.get();
128 ir_variable *sig_param = (ir_variable *)sig_iter.get();
129
130 if (sig_param->mode == ir_var_in || sig_param->mode == ir_var_const_in) {
131 ir_rvalue *new_param = param_rval;
132
133 handle_rvalue(&new_param);
134 if (new_param != param_rval) {
135 param_rval->replace_with(new_param);
136 }
137 }
138 sig_iter.next();
139 }
140
141 /* Next, see if the call can be replaced with an assignment of a constant */
142 ir_constant *const_val = ir->constant_expression_value();
143
144 if (const_val != NULL) {
145 ir_assignment *assignment =
146 new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
147 ir->replace_with(assignment);
148 }
149
150 return visit_continue_with_parent;
151 }
152
153 bool
do_constant_folding(exec_list * instructions)154 do_constant_folding(exec_list *instructions)
155 {
156 ir_constant_folding_visitor constant_folding;
157
158 visit_list_elements(&constant_folding, instructions);
159
160 return constant_folding.progress;
161 }
162