mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
100 lines
3.2 KiB
C++
100 lines
3.2 KiB
C++
/*
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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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* Optimiser component that undoes what the ExpressionSplitter did, i.e.
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* it more or less inlines variable declarations.
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*/
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#pragma once
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#include <libyul/AsmDataForward.h>
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#include <libyul/optimiser/ASTWalker.h>
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#include <map>
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namespace yul
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{
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class NameCollector;
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struct OptimiserStepContext;
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/**
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* Optimiser component that modifies an AST in place, turning sequences
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* of variable declarations into complex expressions, if the variables
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* are declared in the right order. This component does the opposite
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* of ExpressionSplitter.
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* Since the order of opcode or function evaluation is unchanged,
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* this transformation does not need to care about conflicting opcodes.
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*
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* Code of the form
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*
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* let a1 := mload(y)
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* let a2 := mul(x, 4)
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* sstore(a2, a1)
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*
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* is transformed into
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*
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* sstore(mul(x, 4), mload(y))
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*
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* The transformation is not applied to loop conditions, because those are
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* evaluated with each loop.
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*
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* The component can be applied to sub-blocks of the AST, you do not
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* need to pass a full AST.
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*
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* Prerequisites: Disambiguator
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*
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* Implementation note: We visit the AST, modifying it in place.
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* The class starts counting references and will only replace variables
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* that have exactly one reference. It keeps a "latest statement pointer"
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* which always points to the statement right before the current statement.
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* Any function call or opcode will reset this pointer. If an identifier
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* is encountered that was declared in the "latest statement", it is replaced
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* by the value of the declaration, the "latest statement" is replaced
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* by an empty block and the pointer is decremented.
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* A block also resets the latest statement pointer.
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*/
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class ExpressionJoiner: public ASTModifier
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{
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public:
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static constexpr char const* name{"ExpressionJoiner"};
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static void run(OptimiserStepContext&, Block& _ast);
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private:
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explicit ExpressionJoiner(Block& _ast);
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void operator()(Block& _block) override;
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void operator()(FunctionCall&) override;
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using ASTModifier::visit;
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void visit(Expression& _e) override;
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void handleArguments(std::vector<Expression>& _arguments);
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void decrementLatestStatementPointer();
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void resetLatestStatementPointer();
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Statement* latestStatement();
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bool isLatestStatementVarDeclJoinable(Identifier const& _identifier);
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private:
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Block* m_currentBlock = nullptr; ///< Pointer to current block holding the statement being visited.
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size_t m_latestStatementInBlock = 0; ///< Offset to m_currentBlock's statements of the last visited statement.
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std::map<YulString, size_t> m_references; ///< Holds reference counts to all variable declarations in current block.
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};
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}
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