mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
133 lines
4.4 KiB
C++
133 lines
4.4 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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* Optimisation stage that moves Yul variables from stack to memory.
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*/
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#pragma once
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#include <libyul/optimiser/ASTWalker.h>
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#include <libyul/optimiser/OptimiserStep.h>
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#include <libsolutil/Common.h>
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namespace solidity::yul
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{
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/**
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* Optimisation stage that moves Yul variables from stack to memory.
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* It takes a map from functions names and variable names to memory offsets.
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* It then transforms the AST as follows:
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*
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* Single variable declarations are replaced by mstore's as follows:
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* If a is in the map, replace
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* let a
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* by
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* mstore(<memory offset for a>, 0)
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* respectively, replace
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* let a := expr
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* by
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* mstore(<memory offset for a>, expr)
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*
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* In a multi-variable declaration, variables to be moved are replaced by fresh variables and then moved to memory:
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* If b and d are in the map, replace
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* let a, b, c, d := f()
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* by
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* let _1, _2, _3, _4 := f()
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* mstore(<memory offset for d>, _4)
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* mstore(<memory offset for b>, _2)
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* let c := _3
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* let a := _1
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*
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* Assignments to single variables are replaced by mstore's:
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* If a is in the map, replace
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* a := expr
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* by
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* mstore(<memory offset for a>, expr)
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*
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* Assignments to multiple variables are split up similarly to multi-variable declarations:
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* If b and d are in the map, replace
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* a, b, c, d := f()
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* by
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* let _1, _2, _3, _4 := f()
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* mstore(<memory offset for d>, _4)
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* mstore(<memory offset for b>, _2)
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* c := _3
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* a := _1
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*
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* Replace all references to a variable ``a`` in the map by ``mload(<memory offset for a>)``.
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*
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* If a visited function has arguments or return parameters that are contained in the map,
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* the entire function is skipped (no local variables in the function will be moved at all).
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*
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* Prerequisite: Disambiguator, ForLoopInitRewriter, FunctionHoister.
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*/
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class StackToMemoryMover: ASTModifier
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{
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public:
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/**
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* Runs the stack to memory mover.
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* @param _reservedMemory Is the amount of previously reserved memory,
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* i.e. the lowest memory offset to which variables can be moved.
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* @param _memorySlots A map from variables to a slot in memory. Based on the slot a unique offset in the memory range
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* between _reservedMemory and _reservedMemory + 32 * _numRequiredSlots is calculated for each
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* variable.
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* @param _numRequiredSlots The number of slots required in total. The maximum value that may occur in @a _memorySlots.
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*/
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static void run(
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OptimiserStepContext& _context,
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u256 _reservedMemory,
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std::map<YulString, uint64_t> const& _memorySlots,
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uint64_t _numRequiredSlots,
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Block& _block
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);
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using ASTModifier::operator();
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void operator()(FunctionDefinition& _functionDefinition) override;
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void operator()(Block& _block) override;
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void visit(Expression& _expression) override;
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private:
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class VariableMemoryOffsetTracker
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{
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public:
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VariableMemoryOffsetTracker(
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u256 _reservedMemory,
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std::map<YulString, uint64_t> const& _memorySlots,
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uint64_t _numRequiredSlots
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): m_reservedMemory(_reservedMemory), m_memorySlots(_memorySlots), m_numRequiredSlots(_numRequiredSlots)
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{}
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/// @returns a YulString containing the memory offset to be assigned to @a _variable as number literal
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/// or std::nullopt if the variable should not be moved.
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std::optional<YulString> operator()(YulString _variable) const;
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private:
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u256 m_reservedMemory;
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std::map<YulString, uint64_t> const& m_memorySlots;
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uint64_t m_numRequiredSlots = 0;
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};
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StackToMemoryMover(
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OptimiserStepContext& _context,
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VariableMemoryOffsetTracker const& _memoryOffsetTracker
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);
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OptimiserStepContext& m_context;
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VariableMemoryOffsetTracker const& m_memoryOffsetTracker;
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NameDispenser& m_nameDispenser;
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};
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}
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