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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/>.
*/
/**
* Base class to perform data flow analysis during AST walks.
* Tracks assignments and is used as base class for both Rematerialiser and
* Common Subexpression Eliminator.
*/
#include <libyul/optimiser/DataFlowAnalyzer.h>
#include <libyul/optimiser/NameCollector.h>
#include <libyul/optimiser/Semantics.h>
#include <libyul/Exceptions.h>
#include <libsolidity/inlineasm/AsmData.h>
#include <libdevcore/CommonData.h>
#include <boost/range/adaptor/reversed.hpp>
using namespace std;
using namespace dev;
using namespace dev::yul;
void DataFlowAnalyzer::operator()(Assignment& _assignment)
{
set<YulString> names;
for (auto const& var: _assignment.variableNames)
names.emplace(var.name);
assertThrow(_assignment.value, OptimizerException, "");
visit(*_assignment.value);
handleAssignment(names, _assignment.value.get());
}
void DataFlowAnalyzer::operator()(VariableDeclaration& _varDecl)
{
set<YulString> names;
for (auto const& var: _varDecl.variables)
names.emplace(var.name);
m_variableScopes.back().variables += names;
if (_varDecl.value)
visit(*_varDecl.value);
handleAssignment(names, _varDecl.value.get());
}
void DataFlowAnalyzer::operator()(If& _if)
{
ASTModifier::operator()(_if);
Assignments assignments;
assignments(_if.body);
clearValues(assignments.names());
}
void DataFlowAnalyzer::operator()(Switch& _switch)
{
visit(*_switch.expression);
set<YulString> assignedVariables;
for (auto& _case: _switch.cases)
{
(*this)(_case.body);
Assignments assignments;
assignments(_case.body);
assignedVariables += assignments.names();
// This is a little too destructive, we could retain the old values.
clearValues(assignments.names());
}
clearValues(assignedVariables);
}
void DataFlowAnalyzer::operator()(FunctionDefinition& _fun)
{
// Save all information. We might rather reinstantiate this class,
// but this could be difficult if it is subclassed.
map<YulString, Expression const*> value;
map<YulString, set<YulString>> references;
map<YulString, set<YulString>> referencedBy;
m_value.swap(value);
m_references.swap(references);
m_referencedBy.swap(referencedBy);
pushScope(true);
for (auto const& parameter: _fun.parameters)
m_variableScopes.back().variables.emplace(parameter.name);
for (auto const& var: _fun.returnVariables)
m_variableScopes.back().variables.emplace(var.name);
ASTModifier::operator()(_fun);
popScope();
m_value.swap(value);
m_references.swap(references);
m_referencedBy.swap(referencedBy);
}
void DataFlowAnalyzer::operator()(ForLoop& _for)
{
// Special scope handling of the pre block.
pushScope(false);
for (auto& statement: _for.pre.statements)
visit(statement);
Assignments assignments;
assignments(_for.body);
assignments(_for.post);
clearValues(assignments.names());
visit(*_for.condition);
(*this)(_for.body);
(*this)(_for.post);
clearValues(assignments.names());
popScope();
}
void DataFlowAnalyzer::operator()(Block& _block)
{
size_t numScopes = m_variableScopes.size();
pushScope(false);
ASTModifier::operator()(_block);
popScope();
assertThrow(numScopes == m_variableScopes.size(), OptimizerException, "");
}
void DataFlowAnalyzer::handleAssignment(set<YulString> const& _variables, Expression* _value)
{
clearValues(_variables);
MovableChecker movableChecker;
if (_value)
movableChecker.visit(*_value);
if (_variables.size() == 1)
{
YulString name = *_variables.begin();
// Expression has to be movable and cannot contain a reference
// to the variable that will be assigned to.
if (_value && movableChecker.movable() && !movableChecker.referencedVariables().count(name))
m_value[name] = _value;
}
auto const& referencedVariables = movableChecker.referencedVariables();
for (auto const& name: _variables)
{
m_references[name] = referencedVariables;
for (auto const& ref: referencedVariables)
m_referencedBy[ref].emplace(name);
}
}
void DataFlowAnalyzer::pushScope(bool _functionScope)
{
m_variableScopes.emplace_back(_functionScope);
}
void DataFlowAnalyzer::popScope()
{
clearValues(std::move(m_variableScopes.back().variables));
m_variableScopes.pop_back();
}
void DataFlowAnalyzer::clearValues(set<YulString> _variables)
{
// All variables that reference variables to be cleared also have to be
// cleared, but not recursively, since only the value of the original
// variables changes. Example:
// let a := 1
// let b := a
// let c := b
// let a := 2
// add(b, c)
// In the last line, we can replace c by b, but not b by a.
//
// This cannot be easily tested since the substitutions will be done
// one by one on the fly, and the last line will just be add(1, 1)
// Clear variables that reference variables to be cleared.
for (auto const& name: _variables)
for (auto const& ref: m_referencedBy[name])
_variables.emplace(ref);
// Clear the value and update the reference relation.
for (auto const& name: _variables)
m_value.erase(name);
for (auto const& name: _variables)
{
for (auto const& ref: m_references[name])
m_referencedBy[ref].erase(name);
m_references[name].clear();
}
}
bool DataFlowAnalyzer::inScope(YulString _variableName) const
{
for (auto const& scope: m_variableScopes | boost::adaptors::reversed)
{
if (scope.variables.count(_variableName))
return true;
if (scope.isFunction)
return false;
}
return false;
}
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