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https://github.com/ethereum/solidity
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Constant optimiser for Yul.
This commit is contained in:
chriseth
@@ -0,0 +1,169 @@
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/*
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This file is part of solidity.
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solidity is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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solidity is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with solidity. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* Optimisation stage that replaces constants by expressions that compute them.
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*/
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#include <libyul/optimiser/ConstantOptimiser.h>
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#include <libyul/optimiser/ASTCopier.h>
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#include <libyul/optimiser/Metrics.h>
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#include <libyul/AsmData.h>
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#include <libyul/AsmPrinter.h>
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#include <libyul/Utilities.h>
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#include <libyul/AsmParser.h>
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#include <libdevcore/CommonData.h>
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using namespace std;
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using namespace dev;
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using namespace yul;
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using Representation = ConstantOptimiser::Representation;
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void ConstantOptimiser::visit(Expression& _e)
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{
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if (_e.type() == typeid(Literal))
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{
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Literal const& literal = boost::get<Literal>(_e);
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if (literal.kind != LiteralKind::Number)
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return;
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if (
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Expression const* repr =
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RepresentationFinder(m_dialect, m_meter, locationOf(_e), m_cache)
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.tryFindRepresentation(valueOfLiteral(literal))
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)
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_e = ASTCopier{}.translate(*repr);
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}
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else
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ASTModifier::visit(_e);
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}
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Expression const* RepresentationFinder::tryFindRepresentation(dev::u256 const& _value)
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{
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if (_value < 0x10000)
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return nullptr;
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Representation const& repr = findRepresentation(_value);
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if (repr.expression->type() == typeid(Literal))
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return nullptr;
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else
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return repr.expression.get();
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}
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Representation const& RepresentationFinder::findRepresentation(dev::u256 const& _value)
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{
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if (m_cache.count(_value))
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return m_cache.at(_value);
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Representation routine = represent(_value);
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if (dev::bytesRequired(~_value) < dev::bytesRequired(_value))
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// Negated is shorter to represent
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routine = min(move(routine), represent("not"_yulstring, findRepresentation(~_value)));
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// Decompose value into a * 2**k + b where abs(b) << 2**k
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for (unsigned bits = 255; bits > 8 && m_maxSteps > 0; --bits)
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{
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unsigned gapDetector = unsigned((_value >> (bits - 8)) & 0x1ff);
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if (gapDetector != 0xff && gapDetector != 0x100)
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continue;
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u256 powerOfTwo = u256(1) << bits;
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u256 upperPart = _value >> bits;
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bigint lowerPart = _value & (powerOfTwo - 1);
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if ((powerOfTwo - lowerPart) < lowerPart)
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{
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lowerPart = lowerPart - powerOfTwo; // make it negative
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upperPart++;
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}
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if (upperPart == 0)
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continue;
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if (abs(lowerPart) >= (powerOfTwo >> 8))
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continue;
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Representation newRoutine;
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if (m_dialect.evmVersion().hasBitwiseShifting())
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newRoutine = represent("shl"_yulstring, represent(bits), findRepresentation(upperPart));
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else
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{
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newRoutine = represent("exp"_yulstring, represent(2), represent(bits));
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if (upperPart != 1)
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newRoutine = represent("mul"_yulstring, findRepresentation(upperPart), newRoutine);
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}
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if (newRoutine.cost >= routine.cost)
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continue;
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if (lowerPart > 0)
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newRoutine = represent("add"_yulstring, newRoutine, findRepresentation(u256(abs(lowerPart))));
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else if (lowerPart < 0)
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newRoutine = represent("sub"_yulstring, newRoutine, findRepresentation(u256(abs(lowerPart))));
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if (m_maxSteps > 0)
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m_maxSteps--;
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routine = min(move(routine), move(newRoutine));
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}
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return m_cache[_value] = move(routine);
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}
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Representation RepresentationFinder::represent(dev::u256 const& _value) const
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{
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Representation repr;
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repr.expression = make_unique<Expression>(Literal{m_location, LiteralKind::Number, YulString{formatNumber(_value)}, {}});
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repr.cost = m_meter.costs(*repr.expression);
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return repr;
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}
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Representation RepresentationFinder::represent(
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YulString _instruction,
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Representation const& _argument
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) const
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{
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Representation repr;
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repr.expression = make_unique<Expression>(FunctionCall{
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m_location,
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Identifier{m_location, _instruction},
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{ASTCopier{}.translate(*_argument.expression)}
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});
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repr.cost = _argument.cost + m_meter.instructionCosts(*m_dialect.builtin(_instruction)->instruction);
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return repr;
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}
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Representation RepresentationFinder::represent(
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YulString _instruction,
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Representation const& _arg1,
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Representation const& _arg2
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) const
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{
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Representation repr;
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repr.expression = make_unique<Expression>(FunctionCall{
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m_location,
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Identifier{m_location, _instruction},
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{ASTCopier{}.translate(*_arg1.expression), ASTCopier{}.translate(*_arg2.expression)}
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});
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repr.cost = m_meter.instructionCosts(*m_dialect.builtin(_instruction)->instruction) + _arg1.cost + _arg2.cost;
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return repr;
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}
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Representation RepresentationFinder::min(Representation _a, Representation _b)
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{
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if (_a.cost <= _b.cost)
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return _a;
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else
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return _b;
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}
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@@ -0,0 +1,108 @@
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/*
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This file is part of solidity.
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solidity is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
|
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(at your option) any later version.
|
||||
|
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solidity is distributed in the hope that it will be useful,
|
||||
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||||
GNU General Public License for more details.
|
||||
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You should have received a copy of the GNU General Public License
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along with solidity. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* Optimisation stage that replaces constants by expressions that compute them.
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*/
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#pragma once
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#include <libyul/optimiser/ASTWalker.h>
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#include <libyul/YulString.h>
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#include <libyul/Dialect.h>
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#include <libyul/backends/evm/EVMDialect.h>
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#include <libyul/AsmData.h>
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#include <liblangutil/SourceLocation.h>
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#include <libdevcore/Common.h>
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#include <tuple>
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#include <map>
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#include <memory>
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namespace yul
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{
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struct Dialect;
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class GasMeter;
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/**
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* Optimisation stage that replaces constants by expressions that compute them.
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*
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* Prerequisite: None
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*/
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class ConstantOptimiser: public ASTModifier
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{
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public:
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ConstantOptimiser(EVMDialect const& _dialect, GasMeter const& _meter):
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m_dialect(_dialect),
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m_meter(_meter)
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{}
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void visit(Expression& _e) override;
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struct Representation
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{
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std::unique_ptr<Expression> expression;
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size_t cost = size_t(-1);
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};
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private:
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EVMDialect const& m_dialect;
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GasMeter const& m_meter;
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std::map<dev::u256, Representation> m_cache;
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};
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class RepresentationFinder
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{
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public:
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using Representation = ConstantOptimiser::Representation;
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RepresentationFinder(
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EVMDialect const& _dialect,
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GasMeter const& _meter,
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langutil::SourceLocation _location,
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std::map<dev::u256, Representation>& _cache
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):
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m_dialect(_dialect),
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m_meter(_meter),
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m_location(std::move(_location)),
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m_cache(_cache)
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{}
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/// @returns a cheaper representation for the number than its representation
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/// as a literal or nullptr otherwise.
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Expression const* tryFindRepresentation(dev::u256 const& _value);
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private:
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/// Recursively try to find the cheapest representation of the given number,
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/// literal if necessary.
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Representation const& findRepresentation(dev::u256 const& _value);
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Representation represent(dev::u256 const& _value) const;
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Representation represent(YulString _instruction, Representation const& _arg) const;
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Representation represent(YulString _instruction, Representation const& _arg1, Representation const& _arg2) const;
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Representation min(Representation _a, Representation _b);
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EVMDialect const& m_dialect;
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GasMeter const& m_meter;
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langutil::SourceLocation m_location;
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/// Counter for the complexity of optimization, will stop when it reaches zero.
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size_t m_maxSteps = 10000;
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std::map<dev::u256, Representation>& m_cache;
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};
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}
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@@ -24,6 +24,7 @@
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#include <libyul/optimiser/VarDeclInitializer.h>
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#include <libyul/optimiser/BlockFlattener.h>
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#include <libyul/optimiser/ControlFlowSimplifier.h>
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#include <libyul/optimiser/ConstantOptimiser.h>
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#include <libyul/optimiser/DeadCodeEliminator.h>
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#include <libyul/optimiser/FunctionGrouper.h>
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#include <libyul/optimiser/FunctionHoister.h>
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@@ -59,6 +60,7 @@ using namespace yul;
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void OptimiserSuite::run(
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Dialect const& _dialect,
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GasMeter const& _meter,
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Block& _ast,
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AsmAnalysisInfo const& _analysisInfo,
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bool _optimizeStackAllocation,
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@@ -206,6 +208,8 @@ void OptimiserSuite::run(
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ControlFlowSimplifier{_dialect}(ast);
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FunctionGrouper{}(ast);
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ConstantOptimiser{dynamic_cast<EVMDialect const&>(_dialect), _meter}(ast);
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VarNameCleaner{ast, _dialect, reservedIdentifiers}(ast);
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yul::AsmAnalyzer::analyzeStrictAssertCorrect(_dialect, ast);
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@@ -31,6 +31,7 @@ namespace yul
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struct AsmAnalysisInfo;
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struct Dialect;
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class GasMeter;
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/**
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* Optimiser suite that combines all steps and also provides the settings for the heuristics
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@@ -40,6 +41,7 @@ class OptimiserSuite
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public:
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static void run(
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Dialect const& _dialect,
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GasMeter const& _meter,
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Block& _ast,
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AsmAnalysisInfo const& _analysisInfo,
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bool _optimizeStackAllocation,
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