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
213
214
215
216
217
218
219
220
221
222
223
224
225
|
/*
This file is part of cpp-ethereum.
cpp-ethereum is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
cpp-ethereum is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with cpp-ethereum. If not, see <http://www.gnu.org/licenses/>.
*/
/** @file ConstantOptimiser.cpp
* @author Christian <c@ethdev.com>
* @date 2015
*/
#include "libevmasm/ConstantOptimiser.h"
#include <libevmasm/Assembly.h>
#include <libevmasm/GasMeter.h>
using namespace std;
using namespace dev;
using namespace dev::eth;
unsigned ConstantOptimisationMethod::optimiseConstants(
bool _isCreation,
size_t _runs,
Assembly& _assembly,
AssemblyItems& _items
)
{
unsigned optimisations = 0;
map<AssemblyItem, size_t> pushes;
for (AssemblyItem const& item: _items)
if (item.type() == Push)
pushes[item]++;
for (auto it: pushes)
{
AssemblyItem const& item = it.first;
if (item.data() < 0x100)
continue;
Params params;
params.multiplicity = it.second;
params.isCreation = _isCreation;
params.runs = _runs;
LiteralMethod lit(params, item.data());
bigint literalGas = lit.gasNeeded();
CodeCopyMethod copy(params, item.data());
bigint copyGas = copy.gasNeeded();
ComputeMethod compute(params, item.data());
bigint computeGas = compute.gasNeeded();
if (copyGas < literalGas && copyGas < computeGas)
{
copy.execute(_assembly, _items);
optimisations++;
}
else if (computeGas < literalGas && computeGas < copyGas)
{
compute.execute(_assembly, _items);
optimisations++;
}
}
return optimisations;
}
bigint ConstantOptimisationMethod::simpleRunGas(AssemblyItems const& _items)
{
EVMSchedule schedule; // TODO: make relevant to context.
bigint gas = 0;
for (AssemblyItem const& item: _items)
if (item.type() == Push)
gas += GasMeter::runGas(Instruction::PUSH1, schedule);
else if (item.type() == Operation)
gas += GasMeter::runGas(item.instruction(), schedule);
return gas;
}
bigint ConstantOptimisationMethod::dataGas(bytes const& _data) const
{
if (m_params.isCreation)
{
bigint gas;
for (auto b: _data)
gas += b ? m_schedule.txDataNonZeroGas : m_schedule.txDataZeroGas;
return gas;
}
else
return m_schedule.createDataGas * dataSize();
}
size_t ConstantOptimisationMethod::bytesRequired(AssemblyItems const& _items)
{
size_t size = 0;
for (AssemblyItem const& item: _items)
size += item.bytesRequired(3); // assume 3 byte addresses
return size;
}
void ConstantOptimisationMethod::replaceConstants(
AssemblyItems& _items,
AssemblyItems const& _replacement
) const
{
assertThrow(_items.size() > 0, OptimizerException, "");
for (size_t i = 0; i < _items.size(); ++i)
{
if (_items.at(i) != AssemblyItem(m_value))
continue;
_items[i] = _replacement[0];
_items.insert(_items.begin() + i + 1, _replacement.begin() + 1, _replacement.end());
i += _replacement.size() - 1;
}
}
bigint LiteralMethod::gasNeeded()
{
return combineGas(
simpleRunGas({Instruction::PUSH1}),
// PUSHX plus data
(m_params.isCreation ? m_schedule.txDataNonZeroGas : m_schedule.createDataGas) + dataGas(),
0
);
}
CodeCopyMethod::CodeCopyMethod(Params const& _params, u256 const& _value):
ConstantOptimisationMethod(_params, _value)
{
m_copyRoutine = AssemblyItems{
u256(0),
Instruction::DUP1,
Instruction::MLOAD, // back up memory
u256(32),
AssemblyItem(PushData, u256(1) << 16), // has to be replaced
Instruction::DUP4,
Instruction::CODECOPY,
Instruction::DUP2,
Instruction::MLOAD,
Instruction::SWAP2,
Instruction::MSTORE
};
}
bigint CodeCopyMethod::gasNeeded()
{
return combineGas(
// Run gas: we ignore memory increase costs
simpleRunGas(m_copyRoutine) + m_schedule.copyGas,
// Data gas for copy routines: Some bytes are zero, but we ignore them.
bytesRequired(m_copyRoutine) * (m_params.isCreation ? m_schedule.txDataNonZeroGas : m_schedule.createDataGas),
// Data gas for data itself
dataGas(toBigEndian(m_value))
);
}
void CodeCopyMethod::execute(Assembly& _assembly, AssemblyItems& _items)
{
bytes data = toBigEndian(m_value);
m_copyRoutine[4] = _assembly.newData(data);
replaceConstants(_items, m_copyRoutine);
}
AssemblyItems ComputeMethod::findRepresentation(u256 const& _value)
{
if (_value < 0x10000)
// Very small value, not worth computing
return AssemblyItems{_value};
else if (dev::bytesRequired(~_value) < dev::bytesRequired(_value))
// Negated is shorter to represent
return findRepresentation(~_value) + AssemblyItems{Instruction::NOT};
else
{
// Decompose value into a * 2**k + b where abs(b) << 2**k
// Is not always better, try literal and decomposition method.
AssemblyItems routine{u256(_value)};
bigint bestGas = gasNeeded(routine);
for (unsigned bits = 255; bits > 8; --bits)
{
unsigned gapDetector = unsigned(_value >> (bits - 8)) & 0x1ff;
if (gapDetector != 0xff && gapDetector != 0x100)
continue;
u256 powerOfTwo = u256(1) << bits;
u256 upperPart = _value >> bits;
bigint lowerPart = _value & (powerOfTwo - 1);
if (abs(powerOfTwo - lowerPart) < lowerPart)
lowerPart = lowerPart - powerOfTwo; // make it negative
if (abs(lowerPart) >= (powerOfTwo >> 8))
continue;
AssemblyItems newRoutine;
if (lowerPart != 0)
newRoutine += findRepresentation(u256(abs(lowerPart)));
newRoutine += AssemblyItems{u256(bits), u256(2), Instruction::EXP};
if (upperPart != 1 && upperPart != 0)
newRoutine += findRepresentation(upperPart) + AssemblyItems{Instruction::MUL};
if (lowerPart > 0)
newRoutine += AssemblyItems{Instruction::ADD};
else if (lowerPart < 0)
newRoutine.push_back(Instruction::SUB);
bigint newGas = gasNeeded(newRoutine);
if (newGas < bestGas)
{
bestGas = move(newGas);
routine = move(newRoutine);
}
}
return routine;
}
}
bigint ComputeMethod::gasNeeded(AssemblyItems const& _routine)
{
size_t numExps = count(_routine.begin(), _routine.end(), Instruction::EXP);
return combineGas(
simpleRunGas(_routine) + numExps * (m_schedule.expGas + m_schedule.expByteGas),
// Data gas for routine: Some bytes are zero, but we ignore them.
bytesRequired(_routine) * (m_params.isCreation ? m_schedule.txDataNonZeroGas : m_schedule.createDataGas),
0
);
}
|
