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
|
/*
* 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_if_simplification.cpp
*
* Moves constant branches of if statements out to the surrounding
* instruction stream, and inverts if conditionals to avoid empty
* "then" blocks.
*/
#include "ir.h"
namespace {
class ir_if_simplification_visitor : public ir_hierarchical_visitor {
public:
ir_if_simplification_visitor()
{
this->made_progress = false;
}
ir_visitor_status visit_leave(ir_if *);
ir_visitor_status visit_enter(ir_assignment *);
bool made_progress;
};
} /* unnamed namespace */
/* We only care about the top level "if" instructions, so don't
* descend into expressions.
*/
ir_visitor_status
ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
{
(void) ir;
return visit_continue_with_parent;
}
bool
do_if_simplification(exec_list *instructions)
{
ir_if_simplification_visitor v;
v.run(instructions);
return v.made_progress;
}
ir_visitor_status
ir_if_simplification_visitor::visit_leave(ir_if *ir)
{
/* If the if statement has nothing on either side, remove it. */
if (ir->then_instructions.is_empty() &&
ir->else_instructions.is_empty()) {
ir->remove();
this->made_progress = true;
return visit_continue;
}
/* FINISHME: Ideally there would be a way to note that the condition results
* FINISHME: in a constant before processing both of the other subtrees.
* FINISHME: This can probably be done with some flags, but it would take
* FINISHME: some work to get right.
*/
ir_constant *condition_constant = ir->condition->constant_expression_value();
if (condition_constant) {
/* Move the contents of the one branch of the conditional
* that matters out.
*/
if (condition_constant->value.b[0]) {
foreach_list_safe(n, &ir->then_instructions) {
ir_instruction *then_ir = (ir_instruction *) n;
ir->insert_before(then_ir);
}
} else {
foreach_list_safe(n, &ir->else_instructions) {
ir_instruction *else_ir = (ir_instruction *) n;
ir->insert_before(else_ir);
}
}
ir->remove();
this->made_progress = true;
return visit_continue;
}
/* Turn:
*
* if (cond) {
* } else {
* do_work();
* }
*
* into :
*
* if (!cond)
* do_work();
*
* which avoids control flow for "else" (which is usually more
* expensive than normal operations), and the "not" can usually be
* folded into the generation of "cond" anyway.
*/
if (ir->then_instructions.is_empty()) {
ir->condition = new(ralloc_parent(ir->condition))
ir_expression(ir_unop_logic_not, ir->condition);
ir->else_instructions.move_nodes_to(&ir->then_instructions);
this->made_progress = true;
}
return visit_continue;
}
|
