1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
|
/*
* Copyright © 2010 Intel Corporation
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
* DEALINGS IN THE SOFTWARE.
*/
/**
* \file opt_constant_folding.cpp
* Replace constant-valued expressions with references to constant values.
*/
#include "ir.h"
#include "ir_visitor.h"
#include "ir_rvalue_visitor.h"
#include "ir_optimization.h"
#include "compiler/glsl_types.h"
namespace {
/**
* Visitor class for replacing expressions with ir_constant values.
*/
class ir_constant_folding_visitor : public ir_rvalue_visitor {
public:
ir_constant_folding_visitor()
{
this->progress = false;
}
virtual ~ir_constant_folding_visitor()
{
/* empty */
}
virtual ir_visitor_status visit_enter(ir_discard *ir);
virtual ir_visitor_status visit_enter(ir_assignment *ir);
virtual ir_visitor_status visit_enter(ir_call *ir);
virtual void handle_rvalue(ir_rvalue **rvalue);
bool progress;
};
} /* unnamed namespace */
bool
ir_constant_fold(ir_rvalue **rvalue)
{
if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
return false;
/* Note that we do rvalue visitoring on leaving. So if an
* expression has a non-constant operand, no need to go looking
* down it to find if it's constant. This cuts the time of this
* pass down drastically.
*/
ir_expression *expr = (*rvalue)->as_expression();
if (expr) {
for (unsigned int i = 0; i < expr->num_operands; i++) {
if (!expr->operands[i]->as_constant())
return false;
}
}
/* Ditto for swizzles. */
ir_swizzle *swiz = (*rvalue)->as_swizzle();
if (swiz && !swiz->val->as_constant())
return false;
/* Ditto for array dereferences */
ir_dereference_array *array_ref = (*rvalue)->as_dereference_array();
if (array_ref && (!array_ref->array->as_constant() ||
!array_ref->array_index->as_constant()))
return false;
/* No constant folding can be performed on variable dereferences. We need
* to explicitly avoid them, as calling constant_expression_value() on a
* variable dereference will return a clone of var->constant_value. This
* would make us propagate the value into the tree, which isn't our job.
*/
ir_dereference_variable *var_ref = (*rvalue)->as_dereference_variable();
if (var_ref)
return false;
ir_constant *constant =
(*rvalue)->constant_expression_value(ralloc_parent(*rvalue));
if (constant) {
*rvalue = constant;
return true;
}
return false;
}
void
ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
{
if (ir_constant_fold(rvalue))
this->progress = true;
}
ir_visitor_status
ir_constant_folding_visitor::visit_enter(ir_discard *ir)
{
if (ir->condition) {
ir->condition->accept(this);
handle_rvalue(&ir->condition);
ir_constant *const_val = ir->condition->as_constant();
/* If the condition is constant, either remove the condition or
* remove the never-executed assignment.
*/
if (const_val) {
if (const_val->value.b[0])
ir->condition = NULL;
else
ir->remove();
this->progress = true;
}
}
return visit_continue_with_parent;
}
ir_visitor_status
ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
{
ir->rhs->accept(this);
handle_rvalue(&ir->rhs);
if (ir->condition) {
ir->condition->accept(this);
handle_rvalue(&ir->condition);
ir_constant *const_val = ir->condition->as_constant();
/* If the condition is constant, either remove the condition or
* remove the never-executed assignment.
*/
if (const_val) {
if (const_val->value.b[0])
ir->condition = NULL;
else
ir->remove();
this->progress = true;
}
}
/* Don't descend into the LHS because we want it to stay as a
* variable dereference. FINISHME: We probably should to get array
* indices though.
*/
return visit_continue_with_parent;
}
ir_visitor_status
ir_constant_folding_visitor::visit_enter(ir_call *ir)
{
/* Attempt to constant fold parameters */
foreach_two_lists(formal_node, &ir->callee->parameters,
actual_node, &ir->actual_parameters) {
ir_rvalue *param_rval = (ir_rvalue *) actual_node;
ir_variable *sig_param = (ir_variable *) formal_node;
if (sig_param->data.mode == ir_var_function_in
|| sig_param->data.mode == ir_var_const_in) {
ir_rvalue *new_param = param_rval;
handle_rvalue(&new_param);
if (new_param != param_rval) {
param_rval->replace_with(new_param);
}
}
}
/* Next, see if the call can be replaced with an assignment of a constant */
ir_constant *const_val = ir->constant_expression_value(ralloc_parent(ir));
if (const_val != NULL) {
ir_assignment *assignment =
new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
ir->replace_with(assignment);
}
return visit_continue_with_parent;
}
bool
do_constant_folding(exec_list *instructions)
{
ir_constant_folding_visitor constant_folding;
visit_list_elements(&constant_folding, instructions);
return constant_folding.progress;
}
|
