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
|
// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/compiler/dead-code-elimination.h"
#include "src/compiler/common-operator.h"
#include "src/compiler/graph.h"
#include "src/compiler/node-properties.h"
#include "src/compiler/operator-properties.h"
namespace v8 {
namespace internal {
namespace compiler {
DeadCodeElimination::DeadCodeElimination(Editor* editor, Graph* graph,
CommonOperatorBuilder* common)
: AdvancedReducer(editor),
graph_(graph),
common_(common),
dead_(graph->NewNode(common->Dead())) {}
Reduction DeadCodeElimination::Reduce(Node* node) {
switch (node->opcode()) {
case IrOpcode::kEnd:
return ReduceEnd(node);
case IrOpcode::kLoop:
case IrOpcode::kMerge:
return ReduceLoopOrMerge(node);
default:
return ReduceNode(node);
}
UNREACHABLE();
return NoChange();
}
Reduction DeadCodeElimination::ReduceEnd(Node* node) {
DCHECK_EQ(IrOpcode::kEnd, node->opcode());
int const input_count = node->InputCount();
DCHECK_LE(1, input_count);
int live_input_count = 0;
for (int i = 0; i < input_count; ++i) {
Node* const input = node->InputAt(i);
// Skip dead inputs.
if (input->opcode() == IrOpcode::kDead) continue;
// Compact live inputs.
if (i != live_input_count) node->ReplaceInput(live_input_count, input);
++live_input_count;
}
if (live_input_count == 0) {
return Replace(dead());
} else if (live_input_count < input_count) {
node->set_op(common()->End(live_input_count));
node->TrimInputCount(live_input_count);
return Changed(node);
}
DCHECK_EQ(input_count, live_input_count);
return NoChange();
}
Reduction DeadCodeElimination::ReduceLoopOrMerge(Node* node) {
DCHECK(IrOpcode::IsMergeOpcode(node->opcode()));
int const input_count = node->InputCount();
DCHECK_LE(1, input_count);
// Count the number of live inputs to {node} and compact them on the fly, also
// compacting the inputs of the associated {Phi} and {EffectPhi} uses at the
// same time. We consider {Loop}s dead even if only the first control input
// is dead.
int live_input_count = 0;
if (node->opcode() != IrOpcode::kLoop ||
node->InputAt(0)->opcode() != IrOpcode::kDead) {
for (int i = 0; i < input_count; ++i) {
Node* const input = node->InputAt(i);
// Skip dead inputs.
if (input->opcode() == IrOpcode::kDead) continue;
// Compact live inputs.
if (live_input_count != i) {
node->ReplaceInput(live_input_count, input);
for (Node* const use : node->uses()) {
if (NodeProperties::IsPhi(use)) {
DCHECK_EQ(input_count + 1, use->InputCount());
use->ReplaceInput(live_input_count, use->InputAt(i));
}
}
}
++live_input_count;
}
}
if (live_input_count == 0) {
return Replace(dead());
} else if (live_input_count == 1) {
// Due to compaction above, the live input is at offset 0.
for (Node* const use : node->uses()) {
if (NodeProperties::IsPhi(use)) {
Replace(use, use->InputAt(0));
} else if (use->opcode() == IrOpcode::kTerminate) {
DCHECK_EQ(IrOpcode::kLoop, node->opcode());
Replace(use, dead());
}
}
return Replace(node->InputAt(0));
}
DCHECK_LE(2, live_input_count);
DCHECK_LE(live_input_count, input_count);
// Trim input count for the {Merge} or {Loop} node.
if (live_input_count < input_count) {
// Trim input counts for all phi uses and revisit them.
for (Node* const use : node->uses()) {
if (NodeProperties::IsPhi(use)) {
use->ReplaceInput(live_input_count, node);
TrimMergeOrPhi(use, live_input_count);
Revisit(use);
}
}
TrimMergeOrPhi(node, live_input_count);
return Changed(node);
}
return NoChange();
}
Reduction DeadCodeElimination::ReduceNode(Node* node) {
// If {node} has exactly one control input and this is {Dead},
// replace {node} with {Dead}.
int const control_input_count = node->op()->ControlInputCount();
if (control_input_count == 0) return NoChange();
DCHECK_EQ(1, control_input_count);
Node* control = NodeProperties::GetControlInput(node);
if (control->opcode() == IrOpcode::kDead) return Replace(control);
return NoChange();
}
void DeadCodeElimination::TrimMergeOrPhi(Node* node, int size) {
const Operator* const op = common()->ResizeMergeOrPhi(node->op(), size);
node->TrimInputCount(OperatorProperties::GetTotalInputCount(op));
node->set_op(op);
}
} // namespace compiler
} // namespace internal
} // namespace v8
|
