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