mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
130 lines
4.0 KiB
C++
130 lines
4.0 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 removes unused variables and functions.
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*/
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#include <libyul/optimiser/UnusedPruner.h>
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#include <libyul/optimiser/NameCollector.h>
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#include <libyul/optimiser/Semantics.h>
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#include <libyul/optimiser/Utilities.h>
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#include <libyul/Exceptions.h>
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#include <libsolidity/inlineasm/AsmData.h>
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#include <boost/algorithm/cxx11/none_of.hpp>
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using namespace std;
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using namespace dev;
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using namespace dev::yul;
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UnusedPruner::UnusedPruner(Block& _ast, set<YulString> const& _externallyUsedFunctions)
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{
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ReferencesCounter counter;
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counter(_ast);
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m_references = counter.references();
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for (auto const& f: _externallyUsedFunctions)
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++m_references[f];
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}
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void UnusedPruner::operator()(Block& _block)
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{
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for (auto&& statement: _block.statements)
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if (statement.type() == typeid(FunctionDefinition))
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{
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FunctionDefinition& funDef = boost::get<FunctionDefinition>(statement);
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if (!used(funDef.name))
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{
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subtractReferences(ReferencesCounter::countReferences(funDef.body));
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statement = Block{std::move(funDef.location), {}};
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}
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}
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else if (statement.type() == typeid(VariableDeclaration))
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{
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VariableDeclaration& varDecl = boost::get<VariableDeclaration>(statement);
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// Multi-variable declarations are special. We can only remove it
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// if all vairables are unused and the right-hand-side is either
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// movable or it return a single value. In the latter case, we
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// replace `let a := f()` by `pop(f())` (in pure Yul, this will be
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// `drop(f())`).
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if (boost::algorithm::none_of(
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varDecl.variables,
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[=](TypedName const& _typedName) { return used(_typedName.name); }
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))
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{
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if (!varDecl.value)
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statement = Block{std::move(varDecl.location), {}};
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else if (MovableChecker(*varDecl.value).movable())
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{
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subtractReferences(ReferencesCounter::countReferences(*varDecl.value));
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statement = Block{std::move(varDecl.location), {}};
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}
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else if (varDecl.variables.size() == 1)
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// In pure Yul, this should be replaced by a function call to `drop`
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// instead of `pop`.
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statement = ExpressionStatement{varDecl.location, FunctionalInstruction{
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varDecl.location,
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solidity::Instruction::POP,
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{*std::move(varDecl.value)}
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}};
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}
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}
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else if (statement.type() == typeid(ExpressionStatement))
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{
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ExpressionStatement& exprStmt = boost::get<ExpressionStatement>(statement);
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if (MovableChecker(exprStmt.expression).movable())
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{
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// pop(x) should be movable!
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subtractReferences(ReferencesCounter::countReferences(exprStmt.expression));
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statement = Block{std::move(exprStmt.location), {}};
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}
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}
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removeEmptyBlocks(_block);
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ASTModifier::operator()(_block);
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}
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void UnusedPruner::runUntilStabilised(Block& _ast, set<YulString> const& _externallyUsedFunctions)
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{
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while (true)
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{
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UnusedPruner pruner(_ast, _externallyUsedFunctions);
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pruner(_ast);
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if (!pruner.shouldRunAgain())
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return;
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}
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}
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bool UnusedPruner::used(YulString _name) const
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{
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return m_references.count(_name) && m_references.at(_name) > 0;
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}
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void UnusedPruner::subtractReferences(map<YulString, size_t> const& _subtrahend)
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{
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for (auto const& ref: _subtrahend)
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{
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assertThrow(m_references.count(ref.first), OptimizerException, "");
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assertThrow(m_references.at(ref.first) >= ref.second, OptimizerException, "");
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m_references[ref.first] -= ref.second;
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m_shouldRunAgain = true;
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}
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}
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