solidity/libyul/optimiser/SSATransform.cpp

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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>
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#include <libdevcore/CommonData.h>
using namespace std;
using namespace dev;
using namespace langutil;
using namespace yul;
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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;
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// Creates a new variable and stores it in the current variable value map.
auto newVariable = [&](YulString _varName) -> YulString
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{
YulString newName = m_nameDispenser.newName(_varName);
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m_currentVariableValues[_varName] = newName;
variablesToClearAtEnd.emplace(_varName);
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return newName;
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};
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);
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bool needToReplaceSome = false;
for (auto const& var: varDecl.variables)
if (m_variablesToReplace.count(var.name))
needToReplaceSome = true;
if (!needToReplaceSome)
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return {};
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// Replace "let a := v" by "let a_1 := v let a := a_1"
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// Replace "let a, b := v" by "let a_1, b_1 := v let a := a_1 let b := b_2"
auto loc = varDecl.location;
vector<Statement> statements;
statements.emplace_back(VariableDeclaration{loc, {}, std::move(varDecl.value)});
TypedNameList newVariables;
for (auto const& var: varDecl.variables)
{
YulString newName = newVariable(var.name);
YulString oldName = var.name;
newVariables.emplace_back(TypedName{loc, newName, {}});
statements.emplace_back(VariableDeclaration{
loc,
{TypedName{loc, oldName, {}}},
make_unique<Expression>(Identifier{loc, newName})
});
}
boost::get<VariableDeclaration>(statements.front()).variables = std::move(newVariables);
return { std::move(statements) };
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}
else if (_s.type() == typeid(Assignment))
{
Assignment& assignment = boost::get<Assignment>(_s);
visit(*assignment.value);
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for (auto const& var: assignment.variableNames)
assertThrow(m_variablesToReplace.count(var.name), OptimizerException, "");
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// Replace "a := v" by "let a_1 := v a := v"
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// Replace "a, b := v" by "let a_1, b_1 := v a := a_1 b := b_2"
auto loc = assignment.location;
vector<Statement> statements;
statements.emplace_back(VariableDeclaration{loc, {}, std::move(assignment.value)});
TypedNameList newVariables;
for (auto const& var: assignment.variableNames)
{
YulString newName = newVariable(var.name);
YulString oldName = var.name;
newVariables.emplace_back(TypedName{loc, newName, {}});
statements.emplace_back(Assignment{
loc,
{Identifier{loc, oldName}},
make_unique<Expression>(Identifier{loc, newName})
});
}
boost::get<VariableDeclaration>(statements.front()).variables = std::move(newVariables);
return { std::move(statements) };
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}
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);
}