solidity/libyul/optimiser/SSAReverser.h

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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/>.
*/
// SPDX-License-Identifier: GPL-3.0
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#pragma once
#include <libyul/optimiser/ASTWalker.h>
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#include <libyul/optimiser/OptimiserStep.h>
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namespace solidity::yul
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{
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class AssignmentCounter;
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/**
* Reverses the SSA transformation.
*
* In particular, the SSA transform will rewrite
*
* a := E
*
* to
*
* let a_1 := E
* a := a_1
*
* To undo this kind of transformation, the SSAReverser changes this back to
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*
* a := E
* let a_1 := a
*
* In the special case
* let a := E
* a := a
*
* the redundant assignment "a := a" is removed.
*
*
* Secondly, the SSA transform will rewrite
*
* let a := E
* to
*
* let a_1 := E
* let a := a_1
*
* To undo this kind of transformation, the SSAReverser changes this back to
*
* let a := E
* let a_1 := a
*
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* After that the CSE can replace references of a_1 by references to a,
* after which the unused pruner can remove the declaration of a_1.
*
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* Prerequisites: Disambiguator
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*
*/
class SSAReverser: public ASTModifier
{
public:
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static constexpr char const* name{"SSAReverser"};
static void run(OptimiserStepContext& _context, Block& _ast);
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using ASTModifier::operator();
void operator()(Block& _block) override;
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private:
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explicit SSAReverser(AssignmentCounter const& _assignmentCounter): m_assignmentCounter(_assignmentCounter) {}
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AssignmentCounter const& m_assignmentCounter;
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};
}