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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/>.
*/
/**
* Optimiser component that turns complex expressions into multiple variable
* declarations.
*/
#pragma once
#include <libyul/AsmDataForward.h>
#include <libyul/optimiser/ASTWalker.h>
#include <libyul/optimiser/NameDispenser.h>
#include <vector>
namespace yul
{
class NameCollector;
/**
* Optimiser component that modifies an AST in place, turning complex
* expressions into simple expressions and multiple variable declarations.
*
* Code of the form
*
* sstore(mul(x, 4), mload(y))
*
* is transformed into
*
* let a1 := mload(y)
* let a2 := mul(x, 4)
* sstore(a2, a1)
*
* The transformation is not applied to loop conditions, because the loop control flow
* does not allow "outlining" the inner expressions in all cases.
*
* The final program should be in a form such that with the exception of a loop condition,
* function calls can only appear in the right-hand side of a variable declaration,
* assignments or expression statements and all arguments have to be constants or variables.
*/
class ExpressionSplitter: public ASTModifier
{
public:
explicit ExpressionSplitter(NameDispenser& _nameDispenser):
m_nameDispenser(_nameDispenser)
{ }
void operator()(FunctionalInstruction&) override;
void operator()(FunctionCall&) override;
void operator()(If&) override;
void operator()(Switch&) override;
void operator()(ForLoop&) override;
void operator()(Block& _block) override;
private:
/// Replaces the expression by a variable if it is a function call or functional
/// instruction. The declaration of the variable is appended to m_statementsToPrefix.
/// Recurses via visit().
void outlineExpression(Expression& _expr);
/// List of statements that should go in front of the currently visited AST element,
/// at the statement level.
std::vector<Statement> m_statementsToPrefix;
NameDispenser& m_nameDispenser;
};
}
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