solidity/libyul/optimiser/UnusedPruner.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 removes unused variables and functions.
*/
#pragma once
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#include <libyul/optimiser/ASTWalker.h>
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#include <libyul/optimiser/OptimiserStep.h>
#include <libyul/YulString.h>
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#include <map>
#include <set>
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namespace solidity::yul
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{
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struct Dialect;
struct SideEffects;
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/**
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* Optimisation stage that removes unused variables and functions and also
* removes side-effect-free expression statements.
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*
* If msize is used, we cannot remove any statements that access memory.
* Because of that, the Unused Pruner should only be invoked on full ASTs,
* such that it can check for the presence of msize itself, or
* the `_allowMSizeOptimization` needs to be passed.
*
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* Note that this does not remove circular references.
*
* Prerequisite: Disambiguator
*/
class UnusedPruner: public ASTModifier
{
public:
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static constexpr char const* name{"UnusedPruner"};
static void run(OptimiserStepContext& _context, Block& _ast) {
UnusedPruner::runUntilStabilisedOnFullAST(_context.dialect, _ast, _context.reservedIdentifiers);
}
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using ASTModifier::operator();
void operator()(Block& _block) override;
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// @returns true iff the code changed in the previous run.
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bool shouldRunAgain() const { return m_shouldRunAgain; }
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// Run the pruner until the code does not change anymore.
static void runUntilStabilised(
Dialect const& _dialect,
Block& _ast,
bool _allowMSizeOptimization,
std::map<YulString, SideEffects> const* _functionSideEffects = nullptr,
std::set<YulString> const& _externallyUsedFunctions = {}
);
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static void run(
Dialect const& _dialect,
Block& _ast,
std::set<YulString> const& _externallyUsedFunctions = {}
)
{
runUntilStabilisedOnFullAST(_dialect, _ast, _externallyUsedFunctions);
}
/// Run the pruner until the code does not change anymore.
/// The provided block has to be a full AST.
/// The pruner itself determines if msize is used and which user-defined functions
/// are side-effect free.
static void runUntilStabilisedOnFullAST(
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Dialect const& _dialect,
Block& _ast,
std::set<YulString> const& _externallyUsedFunctions = {}
);
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// Run the pruner until the code does not change anymore.
// Only run on the given function.
// @param _allowMSizeOptimization if true, allows to remove instructions
// whose only side-effect is a potential change of the return value of
// the msize instruction.
static void runUntilStabilised(
Dialect const& _dialect,
FunctionDefinition& _functionDefinition,
bool _allowMSizeOptimization,
std::set<YulString> const& _externallyUsedFunctions = {}
);
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private:
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UnusedPruner(
Dialect const& _dialect,
Block& _ast,
bool _allowMSizeOptimization,
std::map<YulString, SideEffects> const* _functionSideEffects = nullptr,
std::set<YulString> const& _externallyUsedFunctions = {}
);
UnusedPruner(
Dialect const& _dialect,
FunctionDefinition& _function,
bool _allowMSizeOptimization,
std::set<YulString> const& _externallyUsedFunctions = {}
);
bool used(YulString _name) const;
void subtractReferences(std::map<YulString, size_t> const& _subtrahend);
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Dialect const& m_dialect;
bool m_allowMSizeOptimization = false;
std::map<YulString, SideEffects> const* m_functionSideEffects = nullptr;
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bool m_shouldRunAgain = false;
std::map<YulString, size_t> m_references;
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};
}