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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/>.
*/
/**
* Optimiser component that turns subsequent assignments to variable declarations
* and assignments.
*/
#include <libyul/optimiser/SSATransform.h>
#include <libyul/optimiser/NameCollector.h>
#include <libyul/optimiser/NameDispenser.h>
#include <libyul/AsmData.h>
#include <libdevcore/CommonData.h>
using namespace std;
using namespace dev;
using namespace langutil;
using namespace dev::yul;
using namespace dev::solidity;
void SSATransform::operator()(Identifier& _identifier)
{
if (m_currentVariableValues.count(_identifier.name))
_identifier.name = m_currentVariableValues[_identifier.name];
}
void SSATransform::operator()(ForLoop& _for)
{
// This will clear the current value in case of a reassignment inside the
// init part, although the new variable would still be in scope inside the whole loop.
// This small inefficiency is fine if we move the pre part of all for loops out
// of the for loop.
(*this)(_for.pre);
Assignments assignments;
assignments(_for.body);
assignments(_for.post);
for (auto const& var: assignments.names())
m_currentVariableValues.erase(var);
visit(*_for.condition);
(*this)(_for.body);
(*this)(_for.post);
}
void SSATransform::operator()(Block& _block)
{
set<YulString> variablesToClearAtEnd;
// Creates a new variable (and returns its declaration) with value _value
// and replaces _value by a reference to that new variable.
auto replaceByNew = [&](SourceLocation _loc, YulString _varName, YulString _type, shared_ptr<Expression>& _value) -> VariableDeclaration
{
YulString newName = m_nameDispenser.newName(_varName);
m_currentVariableValues[_varName] = newName;
variablesToClearAtEnd.emplace(_varName);
shared_ptr<Expression> v = make_shared<Expression>(Identifier{_loc, newName});
_value.swap(v);
return VariableDeclaration{_loc, {TypedName{_loc, std::move(newName), std::move(_type)}}, std::move(v)};
};
iterateReplacing(
_block.statements,
[&](Statement& _s) -> boost::optional<vector<Statement>>
{
if (_s.type() == typeid(VariableDeclaration))
{
VariableDeclaration& varDecl = boost::get<VariableDeclaration>(_s);
if (varDecl.value)
visit(*varDecl.value);
if (varDecl.variables.size() != 1 || !m_variablesToReplace.count(varDecl.variables.front().name))
return {};
// Replace "let a := v" by "let a_1 := v let a := v"
VariableDeclaration newVarDecl = replaceByNew(
varDecl.location,
varDecl.variables.front().name,
varDecl.variables.front().type,
varDecl.value
);
return vector<Statement>{std::move(newVarDecl), std::move(varDecl)};
}
else if (_s.type() == typeid(Assignment))
{
Assignment& assignment = boost::get<Assignment>(_s);
visit(*assignment.value);
if (assignment.variableNames.size() != 1)
return {};
assertThrow(m_variablesToReplace.count(assignment.variableNames.front().name), OptimizerException, "");
// Replace "a := v" by "let a_1 := v a := v"
VariableDeclaration newVarDecl = replaceByNew(
assignment.location,
assignment.variableNames.front().name,
{}, // TODO determine type
assignment.value
);
return vector<Statement>{std::move(newVarDecl), std::move(assignment)};
}
else
visit(_s);
return {};
}
);
for (auto const& var: variablesToClearAtEnd)
m_currentVariableValues.erase(var);
}
void SSATransform::run(Block& _ast, NameDispenser& _nameDispenser)
{
Assignments assignments;
assignments(_ast);
SSATransform{_nameDispenser, assignments.names()}(_ast);
}
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