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