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/*
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 PeepholeOptimiser.h
* Performs local optimising code changes to assembly.
*/
#include "PeepholeOptimiser.h"
#include <libevmasm/AssemblyItem.h>
#include <libevmasm/SemanticInformation.h>
using namespace std;
using namespace dev::eth;
using namespace dev;
// TODO: Extend this to use the tools from ExpressionClasses.cpp
struct Identity
{
static size_t windowSize() { return 1; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
*_out = *_in;
return true;
}
};
struct PushPop
{
static size_t windowSize() { return 2; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
{
auto t = _in[0].type();
if (_in[1] == Instruction::POP && (
SemanticInformation::isDupInstruction(_in[0]) ||
t == Push || t == PushString || t == PushTag || t == PushSub ||
t == PushSubSize || t == PushProgramSize || t == PushData || t == PushLibraryAddress
))
return true;
else
return false;
}
};
struct DoubleSwap
{
static size_t windowSize() { return 2; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems>)
{
if (_in[0] == _in[1] && SemanticInformation::isSwapInstruction(_in[0]))
return true;
else
return false;
}
};
struct JumpToNext
{
static size_t windowSize() { return 3; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
if (
_in[0].type() == PushTag &&
(_in[1] == Instruction::JUMP || _in[1] == Instruction::JUMPI) &&
_in[2].type() == Tag &&
_in[0].data() == _in[2].data()
)
{
if (_in[1] == Instruction::JUMPI)
*_out = AssemblyItem(Instruction::POP, _in[1].location());
*_out = _in[2];
return true;
}
else
return false;
}
};
struct TagConjunctions
{
static size_t windowSize() { return 3; }
static bool apply(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
if (
_in[0].type() == PushTag &&
_in[2] == Instruction::AND &&
_in[1].type() == Push &&
(_in[1].data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
)
{
*_out = _in[0];
return true;
}
else
return false;
}
};
struct OptimiserState
{
AssemblyItems const& items;
size_t i;
std::back_insert_iterator<AssemblyItems> out;
};
void applyMethods(OptimiserState&)
{
assertThrow(false, OptimizerException, "Peephole optimizer failed to apply identity.");
}
template <typename Method, typename... OtherMethods>
void applyMethods(OptimiserState& _state, Method, OtherMethods... _other)
{
if (_state.i + Method::windowSize() <= _state.items.size() && Method::apply(_state.items.begin() + _state.i, _state.out))
_state.i += Method::windowSize();
else
applyMethods(_state, _other...);
}
bool PeepholeOptimiser::optimise()
{
OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
while (state.i < m_items.size())
applyMethods(state, PushPop(), DoubleSwap(), JumpToNext(), TagConjunctions(), Identity());
if (m_optimisedItems.size() < m_items.size())
{
m_items = std::move(m_optimisedItems);
return true;
}
else
return false;
}
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