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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 undoes what the ExpressionSplitter did, i.e.
* it more or less inlines variable declarations.
*/
#pragma once
#include <libyul/ASTDataForward.h>
#include <libyul/optimiser/ASTWalker.h>
#include <map>
namespace dev
{
namespace yul
{
class NameCollector;
/**
* Optimiser component that modifies an AST in place, turning sequences
* of variable declarations into complex expressions, if the variables
* are declared in the right order. This component does the opposite
* of ExpressionSplitter.
* Since the order of opcode or function evaluation is unchanged,
* this transformation does not need to care about conflicting opcodes.
*
* Code of the form
*
* let a1 := mload(y)
* let a2 := mul(x, 4)
* sstore(a2, a1)
*
* is transformed into
*
* sstore(mul(x, 4), mload(y))
*
* The transformation is not applied to loop conditions, because those are
* evaluated with each loop.
*
* The component can be applied to sub-blocks of the AST, you do not
* need to pass a full AST.
*
* Prerequisites: Disambiguator
*
* Implementation note: We visit the AST, modifying it in place.
* The class starts counting references and will only replace variables
* that have exactly one reference. It keeps a "latest statement pointer"
* which always points to the statement right before the current statement.
* Any function call or opcode will reset this pointer. If an identifier
* is encountered that was declared in the "latest statement", it is replaced
* by the value of the declaration, the "latest statement" is replaced
* by an empty block and the pointer is decremented.
* A block also resets the latest statement pointer.
*/
class ExpressionJoiner: public ASTModifier
{
public:
static void run(Block& _ast);
private:
explicit ExpressionJoiner(Block& _ast);
void operator()(Block& _block) override;
void operator()(FunctionalInstruction&) override;
void operator()(FunctionCall&) override;
using ASTModifier::visit;
void visit(Expression& _e) override;
void handleArguments(std::vector<Expression>& _arguments);
void decrementLatestStatementPointer();
void resetLatestStatementPointer();
Statement* latestStatement();
bool isLatestStatementVarDeclJoinable(Identifier const& _identifier);
private:
Block* m_currentBlock = nullptr; ///< Pointer to current block holding the statement being visited.
size_t m_latestStatementInBlock = 0; ///< Offset to m_currentBlock's statements of the last visited statement.
std::map<YulString, size_t> m_references; ///< Holds reference counts to all variable declarations in current block.
};
}
}
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