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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 ConstantOptimiser.cpp
* @author Christian <c@ethdev.com>
* @date 2015
*/
#pragma once
#include <vector>
#include <libdevcore/CommonData.h>
#include <libdevcore/CommonIO.h>
namespace dev
{
namespace eth
{
class AssemblyItem;
using AssemblyItems = std::vector<AssemblyItem>;
class Assembly;
/**
* Abstract base class for one way to change how constants are represented in the code.
*/
class ConstantOptimisationMethod
{
public:
/// Tries to optimised how constants are represented in the source code and modifies
/// @a _assembly and its @a _items.
/// @returns zero if no optimisations could be performed.
static unsigned optimiseConstants(
bool _isCreation,
size_t _runs,
Assembly& _assembly,
AssemblyItems& _items
);
struct Params
{
bool isCreation; ///< Whether this is called during contract creation or runtime.
size_t runs; ///< Estimated number of calls per opcode oven the lifetime of the contract.
size_t multiplicity; ///< Number of times the constant appears in the code.
};
explicit ConstantOptimisationMethod(Params const& _params, u256 const& _value):
m_params(_params), m_value(_value) {}
virtual bigint gasNeeded() = 0;
virtual void execute(Assembly& _assembly, AssemblyItems& _items) = 0;
protected:
size_t dataSize() const { return std::max<size_t>(1, dev::bytesRequired(m_value)); }
/// @returns the run gas for the given items ignoring special gas costs
static bigint simpleRunGas(AssemblyItems const& _items);
/// @returns the gas needed to store the given data literally
bigint dataGas(bytes const& _data) const;
/// @returns the gas needed to store the value literally
bigint dataGas() const { return dataGas(toCompactBigEndian(m_value, 1)); }
static size_t bytesRequired(AssemblyItems const& _items);
/// @returns the combined estimated gas usage taking @a m_params into account.
bigint combineGas(
bigint const& _runGas,
bigint const& _repeatedDataGas,
bigint const& _uniqueDataGas
)
{
// _runGas is not multiplied by _multiplicity because the runs are "per opcode"
return m_params.runs * _runGas + m_params.multiplicity * _repeatedDataGas + _uniqueDataGas;
}
/// Replaces the constant by the code given in @a _replacement.
void replaceConstants(AssemblyItems& _items, AssemblyItems const& _replacement) const;
Params m_params;
u256 const& m_value;
};
/**
* Optimisation method that pushes the constant to the stack literally. This is the default method,
* i.e. executing it does not alter the Assembly.
*/
class LiteralMethod: public ConstantOptimisationMethod
{
public:
explicit LiteralMethod(Params const& _params, u256 const& _value):
ConstantOptimisationMethod(_params, _value) {}
virtual bigint gasNeeded() override;
virtual void execute(Assembly&, AssemblyItems&) override {}
};
/**
* Method that stores the data in the .data section of the code and copies it to the stack.
*/
class CodeCopyMethod: public ConstantOptimisationMethod
{
public:
explicit CodeCopyMethod(Params const& _params, u256 const& _value);
virtual bigint gasNeeded() override;
virtual void execute(Assembly& _assembly, AssemblyItems& _items) override;
protected:
AssemblyItems m_copyRoutine;
};
/**
* Method that tries to compute the constant.
*/
class ComputeMethod: public ConstantOptimisationMethod
{
public:
explicit ComputeMethod(Params const& _params, u256 const& _value):
ConstantOptimisationMethod(_params, _value)
{
m_routine = findRepresentation(m_value);
}
virtual bigint gasNeeded() override { return gasNeeded(m_routine); }
virtual void execute(Assembly&, AssemblyItems& _items) override
{
replaceConstants(_items, m_routine);
}
protected:
/// Tries to recursively find a way to compute @a _value.
AssemblyItems findRepresentation(u256 const& _value);
bigint gasNeeded(AssemblyItems const& _routine);
AssemblyItems m_routine;
};
}
}
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