mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
202 lines
6.8 KiB
C++
202 lines
6.8 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 <libyul/ASTForward.h>
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#include <liblangutil/SourceLocation.h>
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#include <libsolutil/Common.h>
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#include <libsolutil/Numeric.h>
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#include <list>
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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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* In case f has return parameters that are moved to memory, fewer variables are returned and the return values read
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* from memory instead. Assume the third return parameter of f (i.e. c) has to be moved to memory:
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* let a, b, c, d := f()
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* then it is replaced by
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* let _1, _2, _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 := mload(<memory offset of third return parameter of f>)
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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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* Function arguments are moved at the beginning of a function body:
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* If a1 is in the map, replace
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* function f(a1, a2, ..., a17)
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* {
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* ...
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* sstore(a1, a17)
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* }
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* by
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* function f(a1, a2, ..., a17)
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* {
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* mstore(<memory offset for a1>, a1)
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* ...
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* sstore(mload(<memory offset for a1>, a17)
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* }
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* This relies on the code transform popping arguments that are no longer used, if they are on the stack top.
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*
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* Functions with only one return argument that has to be moved are encapsulated in a wrapper function as follows:
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* Suppose b and r need to be moved in:
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* function f(a, b) -> r
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* {
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* ...body of f...
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* r := b
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* ...body of f continued...
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* }
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* then replace by:
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* function f(a, b) -> r
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* {
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* mstore(<memory offset of b>, b)
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* mstore(<memory offset of r>, 0)
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* f_1(a)
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* r := mload(<memory offset of r>)
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* }
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* function f_1(a)
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* {
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* ...body of f...
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* mstore(<memory offset of r>, mload(<memory offset of b>))
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* ...body of f continued...
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* }
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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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using ASTModifier::visit;
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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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/// @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()(TypedName const& _variable) const;
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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()(Identifier const& _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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struct FunctionMoveInfo
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{
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std::vector<std::optional<YulString>> returnVariableSlots;
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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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std::map<YulString, std::vector<TypedName>> _functionReturnVariables
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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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/// Map from function names to the return variables of the function with that name.
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std::map<YulString, std::vector<TypedName>> m_functionReturnVariables;
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/// List of functions generated while running this step that are to be appended to the code in the end.
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std::list<Statement> m_newFunctionDefinitions;
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};
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}
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