solidity/libyul/optimiser/Rematerialiser.h
2019-09-24 14:52:01 +02:00

107 lines
2.9 KiB
C++

/*
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/>.
*/
/**
* Optimisation stage that replaces variables by their most recently assigned expressions.
*/
#pragma once
#include <libyul/optimiser/DataFlowAnalyzer.h>
#include <libyul/optimiser/OptimiserStep.h>
namespace yul
{
/**
* Optimisation stage that replaces variables by their most recently assigned expressions,
* but only if the expression is movable and one of the following holds:
* - the variable is referenced exactly once
* - the value is extremely cheap ("cost" of zero like ``caller()``)
* - the variable is referenced at most 5 times and the value is rather cheap
* ("cost" of at most 1 like a constant up to 0xff)
*
* Prerequisite: Disambiguator, ForLoopInitRewriter.
*/
class Rematerialiser: public DataFlowAnalyzer
{
public:
static constexpr char const* name{"Rematerialiser"};
static void run(
OptimiserStepContext& _context,
Block& _ast
) { run(_context.dialect, _ast); }
static void run(
Dialect const& _dialect,
Block& _ast,
std::set<YulString> _varsToAlwaysRematerialize = {}
);
static void run(
Dialect const& _dialect,
FunctionDefinition& _function,
std::set<YulString> _varsToAlwaysRematerialize = {}
);
protected:
Rematerialiser(
Dialect const& _dialect,
Block& _ast,
std::set<YulString> _varsToAlwaysRematerialize = {}
);
Rematerialiser(
Dialect const& _dialect,
FunctionDefinition& _function,
std::set<YulString> _varsToAlwaysRematerialize = {}
);
using ASTModifier::visit;
void visit(Expression& _e) override;
std::map<YulString, size_t> m_referenceCounts;
std::set<YulString> m_varsToAlwaysRematerialize;
};
/**
* If a variable is referenced that is known to have a literal
* value at that point, replace it by a literal.
*
* This is mostly used so that other components do not have to rely
* on the data flow analyzer.
*
* Prerequisite: Disambiguator, ForLoopInitRewriter.
*/
class LiteralRematerialiser: public DataFlowAnalyzer
{
public:
static constexpr char const* name{"LiteralRematerialiser"};
static void run(
OptimiserStepContext& _context,
Block& _ast
) { LiteralRematerialiser{_context.dialect}(_ast); }
using ASTModifier::visit;
void visit(Expression& _e) override;
private:
LiteralRematerialiser(Dialect const& _dialect):
DataFlowAnalyzer(_dialect)
{}
};
}