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diff --git a/libyul/optimiser/RedundantAssignEliminator.cpp b/libyul/optimiser/RedundantAssignEliminator.cpp
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+++ b/libyul/optimiser/RedundantAssignEliminator.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 removes assignments to variables that are not used
+ * until they go out of scope or are re-assigned.
+ */
+
+#include <libyul/optimiser/RedundantAssignEliminator.h>
+
+#include <libyul/optimiser/Semantics.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+#include <libdevcore/CommonData.h>
+
+#include <boost/range/algorithm_ext/erase.hpp>
+
+using namespace std;
+using namespace dev;
+using namespace dev::yul;
+using namespace dev::solidity;
+
+void RedundantAssignEliminator::operator()(Identifier const& _identifier)
+{
+	changeUndecidedTo(_identifier.name, State::Used);
+}
+
+void RedundantAssignEliminator::operator()(VariableDeclaration const& _variableDeclaration)
+{
+	ASTWalker::operator()(_variableDeclaration);
+
+	for (auto const& var: _variableDeclaration.variables)
+		m_declaredVariables.emplace(var.name);
+}
+
+void RedundantAssignEliminator::operator()(Assignment const& _assignment)
+{
+	visit(*_assignment.value);
+	for (auto const& var: _assignment.variableNames)
+		changeUndecidedTo(var.name, State::Unused);
+
+	if (_assignment.variableNames.size() == 1)
+		// Default-construct it in "Undecided" state if it does not yet exist.
+		m_assignments[_assignment.variableNames.front().name][&_assignment];
+}
+
+void RedundantAssignEliminator::operator()(If const& _if)
+{
+	visit(*_if.condition);
+
+	RedundantAssignEliminator branch{*this};
+	branch(_if.body);
+
+	join(branch);
+}
+
+void RedundantAssignEliminator::operator()(Switch const& _switch)
+{
+	visit(*_switch.expression);
+
+	bool hasDefault = false;
+	vector<RedundantAssignEliminator> branches;
+	for (auto const& c: _switch.cases)
+	{
+		if (!c.value)
+			hasDefault = true;
+		branches.emplace_back(*this);
+		branches.back()(c.body);
+	}
+
+	if (hasDefault)
+	{
+		*this = std::move(branches.back());
+		branches.pop_back();
+	}
+	for (auto& branch: branches)
+		join(branch);
+}
+
+void RedundantAssignEliminator::operator()(FunctionDefinition const& _functionDefinition)
+{
+	(*this)(_functionDefinition.body);
+
+	for (auto const& param: _functionDefinition.parameters)
+	{
+		changeUndecidedTo(param.name, State::Unused);
+		finalize(param.name);
+	}
+	for (auto const& retParam: _functionDefinition.returnVariables)
+	{
+		changeUndecidedTo(retParam.name, State::Used);
+		finalize(retParam.name);
+	}
+}
+
+void RedundantAssignEliminator::operator()(ForLoop const& _forLoop)
+{
+	// This will set all variables that are declared in this
+	// block to "unused" when it is destroyed.
+	BlockScope scope(*this);
+
+	// We need to visit the statements directly because of the
+	// scoping rules.
+	walkVector(_forLoop.pre.statements);
+
+	// We just run the loop twice to account for the
+	// back edge.
+	// There need not be more runs because we only have three different states.
+
+	visit(*_forLoop.condition);
+
+	RedundantAssignEliminator zeroRuns{*this};
+
+	(*this)(_forLoop.body);
+	(*this)(_forLoop.post);
+
+	visit(*_forLoop.condition);
+
+	RedundantAssignEliminator oneRun{*this};
+
+	(*this)(_forLoop.body);
+	(*this)(_forLoop.post);
+
+	visit(*_forLoop.condition);
+
+	// Order does not matter because "max" is commutative and associative.
+	join(oneRun);
+	join(zeroRuns);
+}
+
+void RedundantAssignEliminator::operator()(Block const& _block)
+{
+	// This will set all variables that are declared in this
+	// block to "unused" when it is destroyed.
+	BlockScope scope(*this);
+
+	ASTWalker::operator()(_block);
+}
+
+void RedundantAssignEliminator::run(Block& _ast)
+{
+	RedundantAssignEliminator rae;
+	rae(_ast);
+
+	AssignmentRemover remover{rae.m_assignmentsToRemove};
+	remover(_ast);
+}
+
+template <class K, class V, class F>
+void joinMap(std::map<K, V>& _a, std::map<K, V>&& _b, F _conflictSolver)
+{
+	// TODO Perhaps it is better to just create a sorted list
+	// and then use insert(begin, end)
+
+	auto ita = _a.begin();
+	auto aend = _a.end();
+	auto itb = _b.begin();
+	auto bend = _b.end();
+
+	for (; itb != bend; ++ita)
+	{
+		if (ita == aend)
+			ita = _a.insert(ita, std::move(*itb++));
+		else if (ita->first < itb->first)
+			continue;
+		else if (itb->first < ita->first)
+			ita = _a.insert(ita, std::move(*itb++));
+		else
+		{
+			_conflictSolver(ita->second, std::move(itb->second));
+			++itb;
+		}
+	}
+}
+
+void RedundantAssignEliminator::join(RedundantAssignEliminator& _other)
+{
+	m_assignmentsToRemove.insert(begin(_other.m_assignmentsToRemove), end(_other.m_assignmentsToRemove));
+
+	joinMap(m_assignments, std::move(_other.m_assignments), [](
+		map<Assignment const*, State>& _assignmentHere,
+		map<Assignment const*, State>&& _assignmentThere
+	)
+	{
+		return joinMap(_assignmentHere, std::move(_assignmentThere), State::join);
+	});
+}
+
+void RedundantAssignEliminator::changeUndecidedTo(YulString _variable, RedundantAssignEliminator::State _newState)
+{
+	for (auto& assignment: m_assignments[_variable])
+		if (assignment.second == State{State::Undecided})
+			assignment.second = _newState;
+}
+
+void RedundantAssignEliminator::finalize(YulString _variable)
+{
+	for (auto& assignment: m_assignments[_variable])
+	{
+		assertThrow(assignment.second != State::Undecided, OptimizerException, "");
+		if (assignment.second == State{State::Unused} && MovableChecker{*assignment.first->value}.movable())
+			// TODO the only point where we actually need this
+			// to be a set is for the for loop
+			m_assignmentsToRemove.insert(assignment.first);
+	}
+	m_assignments.erase(_variable);
+}
+
+void AssignmentRemover::operator()(Block& _block)
+{
+	boost::range::remove_erase_if(_block.statements, [=](Statement const& _statement) -> bool {
+		return _statement.type() == typeid(Assignment) && m_toRemove.count(&boost::get<Assignment>(_statement));
+	});
+
+	ASTModifier::operator()(_block);
+}