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 "compiler/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_discard *ir);
54 virtual ir_visitor_status visit_enter(ir_assignment *ir);
55 virtual ir_visitor_status visit_enter(ir_call *ir);
56
57 virtual void handle_rvalue(ir_rvalue **rvalue);
58
59 bool progress;
60 };
61
62 } /* unnamed namespace */
63
64 bool
ir_constant_fold(ir_rvalue ** rvalue)65 ir_constant_fold(ir_rvalue **rvalue)
66 {
67 if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
68 return false;
69
70 /* Note that we do rvalue visitoring on leaving. So if an
71 * expression has a non-constant operand, no need to go looking
72 * down it to find if it's constant. This cuts the time of this
73 * pass down drastically.
74 */
75 ir_expression *expr = (*rvalue)->as_expression();
76 if (expr) {
77 for (unsigned int i = 0; i < expr->num_operands; i++) {
78 if (!expr->operands[i]->as_constant())
79 return false;
80 }
81 }
82
83 /* Ditto for swizzles. */
84 ir_swizzle *swiz = (*rvalue)->as_swizzle();
85 if (swiz && !swiz->val->as_constant())
86 return false;
87
88 /* Ditto for array dereferences */
89 ir_dereference_array *array_ref = (*rvalue)->as_dereference_array();
90 if (array_ref && (!array_ref->array->as_constant() ||
91 !array_ref->array_index->as_constant()))
92 return false;
93
94 /* No constant folding can be performed on variable dereferences. We need
95 * to explicitly avoid them, as calling constant_expression_value() on a
96 * variable dereference will return a clone of var->constant_value. This
97 * would make us propagate the value into the tree, which isn't our job.
98 */
99 ir_dereference_variable *var_ref = (*rvalue)->as_dereference_variable();
100 if (var_ref)
101 return false;
102
103 ir_constant *constant =
104 (*rvalue)->constant_expression_value(ralloc_parent(*rvalue));
105 if (constant) {
106 *rvalue = constant;
107 return true;
108 }
109 return false;
110 }
111
112 void
handle_rvalue(ir_rvalue ** rvalue)113 ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
114 {
115 if (ir_constant_fold(rvalue))
116 this->progress = true;
117 }
118
119 ir_visitor_status
visit_enter(ir_discard * ir)120 ir_constant_folding_visitor::visit_enter(ir_discard *ir)
121 {
122 if (ir->condition) {
123 ir->condition->accept(this);
124 handle_rvalue(&ir->condition);
125
126 ir_constant *const_val = ir->condition->as_constant();
127 /* If the condition is constant, either remove the condition or
128 * remove the never-executed assignment.
129 */
130 if (const_val) {
131 if (const_val->value.b[0])
132 ir->condition = NULL;
133 else
134 ir->remove();
135 this->progress = true;
136 }
137 }
138
139 return visit_continue_with_parent;
140 }
141
142 ir_visitor_status
visit_enter(ir_assignment * ir)143 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
144 {
145 ir->rhs->accept(this);
146 handle_rvalue(&ir->rhs);
147
148 /* Don't descend into the LHS because we want it to stay as a
149 * variable dereference. FINISHME: We probably should to get array
150 * indices though.
151 */
152 return visit_continue_with_parent;
153 }
154
155 ir_visitor_status
visit_enter(ir_call * ir)156 ir_constant_folding_visitor::visit_enter(ir_call *ir)
157 {
158 /* Attempt to constant fold parameters */
159 foreach_two_lists(formal_node, &ir->callee->parameters,
160 actual_node, &ir->actual_parameters) {
161 ir_rvalue *param_rval = (ir_rvalue *) actual_node;
162 ir_variable *sig_param = (ir_variable *) formal_node;
163
164 if (sig_param->data.mode == ir_var_function_in
165 || sig_param->data.mode == ir_var_const_in) {
166 ir_rvalue *new_param = param_rval;
167
168 handle_rvalue(&new_param);
169 if (new_param != param_rval) {
170 param_rval->replace_with(new_param);
171 }
172 }
173 }
174
175 /* Next, see if the call can be replaced with an assignment of a constant */
176 ir_constant *const_val = ir->constant_expression_value(ralloc_parent(ir));
177
178 if (const_val != NULL) {
179 ir_assignment *assignment =
180 new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
181 ir->replace_with(assignment);
182 }
183
184 return visit_continue_with_parent;
185 }
186
187 bool
do_constant_folding(exec_list * instructions)188 do_constant_folding(exec_list *instructions)
189 {
190 ir_constant_folding_visitor constant_folding;
191
192 visit_list_elements(&constant_folding, instructions);
193
194 return constant_folding.progress;
195 }
196