solidity/libevmasm/PeepholeOptimiser.cpp

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/*
This file is part of solidity.
solidity 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.
solidity 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 solidity. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* @file PeepholeOptimiser.cpp
* 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 OptimiserState
{
AssemblyItems const& items;
size_t i;
std::back_insert_iterator<AssemblyItems> out;
};
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template <class Method, size_t Arguments>
struct ApplyRule
{
};
template <class Method>
struct ApplyRule<Method, 3>
{
static bool applyRule(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
return Method::applySimple(_in[0], _in[1], _in[2], _out);
}
};
template <class Method>
struct ApplyRule<Method, 2>
{
static bool applyRule(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
return Method::applySimple(_in[0], _in[1], _out);
}
};
template <class Method>
struct ApplyRule<Method, 1>
{
static bool applyRule(AssemblyItems::const_iterator _in, std::back_insert_iterator<AssemblyItems> _out)
{
return Method::applySimple(_in[0], _out);
}
};
template <class Method, size_t WindowSize>
struct SimplePeepholeOptimizerMethod
{
static bool apply(OptimiserState& _state)
{
if (
_state.i + WindowSize <= _state.items.size() &&
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ApplyRule<Method, WindowSize>::applyRule(_state.items.begin() + _state.i, _state.out)
)
{
_state.i += WindowSize;
return true;
}
else
return false;
}
};
struct Identity: SimplePeepholeOptimizerMethod<Identity, 1>
{
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static bool applySimple(AssemblyItem const& _item, std::back_insert_iterator<AssemblyItems> _out)
{
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*_out = _item;
return true;
}
};
struct PushPop: SimplePeepholeOptimizerMethod<PushPop, 2>
{
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static bool applySimple(AssemblyItem const& _push, AssemblyItem const& _pop, std::back_insert_iterator<AssemblyItems>)
{
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auto t = _push.type();
return _pop == Instruction::POP && (
SemanticInformation::isDupInstruction(_push) ||
t == Push || t == PushString || t == PushTag || t == PushSub ||
t == PushSubSize || t == PushProgramSize || t == PushData || t == PushLibraryAddress
);
}
};
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struct OpPop: SimplePeepholeOptimizerMethod<OpPop, 2>
{
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static bool applySimple(
AssemblyItem const& _op,
AssemblyItem const& _pop,
std::back_insert_iterator<AssemblyItems> _out
)
{
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if (_pop == Instruction::POP && _op.type() == Operation)
{
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Instruction instr = _op.instruction();
if (instructionInfo(instr).ret == 1 && !instructionInfo(instr).sideEffects)
{
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for (int j = 0; j < instructionInfo(instr).args; j++)
*_out = {Instruction::POP, _op.location()};
return true;
}
}
return false;
}
};
struct DoubleSwap: SimplePeepholeOptimizerMethod<DoubleSwap, 2>
{
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static size_t applySimple(AssemblyItem const& _s1, AssemblyItem const& _s2, std::back_insert_iterator<AssemblyItems>)
{
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return _s1 == _s2 && SemanticInformation::isSwapInstruction(_s1);
}
};
struct JumpToNext: SimplePeepholeOptimizerMethod<JumpToNext, 3>
{
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static size_t applySimple(
AssemblyItem const& _pushTag,
AssemblyItem const& _jump,
AssemblyItem const& _tag,
std::back_insert_iterator<AssemblyItems> _out
)
{
if (
_pushTag.type() == PushTag &&
(_jump == Instruction::JUMP || _jump == Instruction::JUMPI) &&
_tag.type() == Tag &&
_pushTag.data() == _tag.data()
)
{
if (_jump == Instruction::JUMPI)
*_out = AssemblyItem(Instruction::POP, _jump.location());
*_out = _tag;
return true;
}
else
return false;
}
};
struct TagConjunctions: SimplePeepholeOptimizerMethod<TagConjunctions, 3>
{
static bool applySimple(
AssemblyItem const& _pushTag,
AssemblyItem const& _pushConstant,
AssemblyItem const& _and,
std::back_insert_iterator<AssemblyItems> _out
)
{
if (
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_pushTag.type() == PushTag &&
_and == Instruction::AND &&
_pushConstant.type() == Push &&
(_pushConstant.data() & u256(0xFFFFFFFF)) == u256(0xFFFFFFFF)
)
{
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*_out = _pushTag;
return true;
}
else
return false;
}
};
/// Removes everything after a JUMP (or similar) until the next JUMPDEST.
struct UnreachableCode
{
static bool apply(OptimiserState& _state)
{
auto it = _state.items.begin() + _state.i;
auto end = _state.items.end();
if (it == end)
return false;
if (
it[0] != Instruction::JUMP &&
it[0] != Instruction::RETURN &&
it[0] != Instruction::STOP &&
it[0] != Instruction::INVALID &&
it[0] != Instruction::SELFDESTRUCT
)
return false;
size_t i = 1;
while (it + i != end && it[i].type() != Tag)
i++;
if (i > 1)
{
*_state.out = it[0];
_state.i += i;
return true;
}
else
return false;
}
};
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 (!Method::apply(_state))
applyMethods(_state, _other...);
}
bool PeepholeOptimiser::optimise()
{
OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
while (state.i < m_items.size())
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applyMethods(state, PushPop(), OpPop(), DoubleSwap(), JumpToNext(), UnreachableCode(), TagConjunctions(), Identity());
if (m_optimisedItems.size() < m_items.size())
{
m_items = std::move(m_optimisedItems);
return true;
}
else
return false;
}