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Diffstat (limited to 'libyul/optimiser/DataFlowAnalyzer.cpp')
| -rw-r--r-- | libyul/optimiser/DataFlowAnalyzer.cpp | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/libyul/optimiser/DataFlowAnalyzer.cpp b/libyul/optimiser/DataFlowAnalyzer.cpp new file mode 100644 index 00000000..ca1e5153 --- /dev/null +++ b/libyul/optimiser/DataFlowAnalyzer.cpp @@ -0,0 +1,193 @@ +/*( + 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<string> names; + for (auto const& var: _assignment.variableNames) + names.insert(var.name); + assertThrow(_assignment.value, OptimizerException, ""); + visit(*_assignment.value); + handleAssignment(names, _assignment.value.get()); +} + +void DataFlowAnalyzer::operator()(VariableDeclaration& _varDecl) +{ + set<string> names; + for (auto const& var: _varDecl.variables) + names.insert(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<string> 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) +{ + m_variableScopes.emplace_back(true); + for (auto const& parameter: _fun.parameters) + m_variableScopes.back().variables.insert(parameter.name); + for (auto const& var: _fun.returnVariables) + m_variableScopes.back().variables.insert(var.name); + ASTModifier::operator()(_fun); + m_variableScopes.pop_back(); +} + +void DataFlowAnalyzer::operator()(ForLoop& _for) +{ + // Special scope handling of the pre block. + m_variableScopes.emplace_back(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()); + + m_variableScopes.pop_back(); +} + +void DataFlowAnalyzer::operator()(Block& _block) +{ + size_t numScopes = m_variableScopes.size(); + m_variableScopes.emplace_back(false); + ASTModifier::operator()(_block); + m_variableScopes.pop_back(); + assertThrow(numScopes == m_variableScopes.size(), OptimizerException, ""); +} + +void DataFlowAnalyzer::handleAssignment(set<string> const& _variables, Expression* _value) +{ + clearValues(_variables); + + MovableChecker movableChecker; + if (_value) + movableChecker.visit(*_value); + if (_variables.size() == 1) + { + string const& 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].insert(name); + } +} + +void DataFlowAnalyzer::clearValues(set<string> const& _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) + + set<string> variables = _variables; + // Clear variables that reference variables to be cleared. + for (auto const& name: variables) + for (auto const& ref: m_referencedBy[name]) + variables.insert(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(string const& _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; +} |