solidity/libyul/optimiser/Metrics.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/>.
*/
// SPDX-License-Identifier: GPL-3.0
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/**
* Module providing metrics for the optimizer.
*/
#pragma once
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#include <libyul/optimiser/ASTWalker.h>
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#include <liblangutil/EVMVersion.h>
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namespace solidity::yul
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{
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struct Dialect;
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struct EVMDialect;
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/**
* Weights to be assigned to specific yul statements and expressions by a metric.
*
* The default values are meant to reflect specifically the number of AST nodes.
*
* The following AST elements have a default cost of zero (because the cleanup phase would
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* remove them anyway or they are just wrappers around something else that will be counted instead):
* - expression statement (only the expression inside has a cost)
* - block (only the statements inside have a cost)
* - variable references
* - variable declarations (only the right hand side has a cost)
* - assignments (only the value has a cost)
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* - literal zeros (we optimistically assume they can be copied from somewhere else)
*
* Each statement incurs and additional cost of one
* per jump/branch. This means if, break and continue statements have a cost of 2,
* switch statements have a cost of 1 plus the number of cases times two,
* and for loops cost 3.
*/
struct CodeWeights
{
// Statements
size_t expressionStatementCost = 0;
size_t assignmentCost = 0;
size_t variableDeclarationCost = 0;
size_t functionDefinitionCost = 1;
size_t ifCost = 2;
size_t switchCost = 1;
size_t caseCost = 2;
size_t forLoopCost = 3;
size_t breakCost = 2;
size_t continueCost = 2;
size_t leaveCost = 2;
size_t blockCost = 0;
// Expressions
size_t functionCallCost = 1;
size_t identifierCost = 0;
size_t literalCost = 1;
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size_t literalZeroCost = 0;
size_t costOf(Statement const& _statement) const;
size_t costOf(Expression const& _expression) const;
};
/**
* Metric for the size of code.
* Ignores function definitions while traversing the AST by default.
* If you want to know the size of a function, you have to invoke this on its body.
*
* The cost of each statement and expression type is configurable via CodeWeights.
*/
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class CodeSize: public ASTWalker
{
public:
static size_t codeSize(Statement const& _statement, CodeWeights const& _weights = {});
static size_t codeSize(Expression const& _expression, CodeWeights const& _weights = {});
static size_t codeSize(Block const& _block, CodeWeights const& _weights = {});
static size_t codeSizeIncludingFunctions(Block const& _block, CodeWeights const& _weights = {});
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private:
CodeSize(bool _ignoreFunctions = true, CodeWeights const& _weights = {}):
m_ignoreFunctions(_ignoreFunctions),
m_weights(_weights) {}
void visit(Statement const& _statement) override;
void visit(Expression const& _expression) override;
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private:
bool m_ignoreFunctions;
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size_t m_size = 0;
CodeWeights m_weights;
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};
/**
* Very rough cost that takes the size and execution cost of code into account.
* The cost per AST element is one, except for literals where it is the byte size.
* Function calls cost 50. Instructions cost 0 for 3 or less gas (same as DUP),
* 2 for up to 10 and 50 otherwise.
*/
class CodeCost: public ASTWalker
{
public:
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static size_t codeCost(Dialect const& _dialect, Expression const& _expression);
private:
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CodeCost(Dialect const& _dialect): m_dialect(_dialect) {}
void operator()(FunctionCall const& _funCall) override;
void operator()(Literal const& _literal) override;
void visit(Statement const& _statement) override;
void visit(Expression const& _expression) override;
private:
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void addInstructionCost(evmasm::Instruction _instruction);
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Dialect const& m_dialect;
size_t m_cost = 0;
};
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/**
* Counts the number of assignments to every variable.
* Only works after running the Disambiguator.
*/
class AssignmentCounter: public ASTWalker
{
public:
using ASTWalker::operator();
void operator()(Assignment const& _assignment) override;
std::size_t assignmentCount(YulString _name) const;
private:
std::map<YulString, size_t> m_assignmentCounters;
};
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}