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diff --git a/libyul/optimiser/ExpressionSplitter.h b/libyul/optimiser/ExpressionSplitter.h
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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 complex expressions into multiple variable
+ * declarations.
+ */
+#pragma once
+
+#include <libyul/ASTDataForward.h>
+
+#include <libyul/optimiser/ASTWalker.h>
+#include <libyul/optimiser/NameDispenser.h>
+
+#include <vector>
+
+namespace dev
+{
+namespace julia
+{
+
+class NameCollector;
+
+
+/**
+ * Optimiser component that modifies an AST in place, turning complex
+ * expressions into simple expressions and multiple variable declarations.
+ *
+ * Code of the form
+ *
+ * sstore(mul(x, 4), mload(y))
+ *
+ * is transformed into
+ *
+ * let a1 := mload(y)
+ * let a2 := mul(x, 4)
+ * sstore(a2, a1)
+ *
+ * The transformation is not applied to loop conditions, because the loop control flow
+ * does not allow "outlining" the inner expressions in all cases.
+ *
+ * The final program should be in a form such that with the exception of a loop condition,
+ * function calls can only appear in the right-hand side of a variable declaration,
+ * assignments or expression statements and all arguments have to be constants or variables.
+ */
+class ExpressionSplitter: public ASTModifier
+{
+public:
+	explicit ExpressionSplitter(NameDispenser& _nameDispenser):
+		m_nameDispenser(_nameDispenser)
+	{ }
+
+	virtual void operator()(FunctionalInstruction&) override;
+	virtual void operator()(FunctionCall&) override;
+	virtual void operator()(If&) override;
+	virtual void operator()(Switch&) override;
+	virtual void operator()(ForLoop&) override;
+	virtual void operator()(Block& _block) override;
+
+private:
+	/// Replaces the expression by a variable if it is a function call or functional
+	/// instruction. The declaration of the variable is appended to m_statementsToPrefix.
+	/// Recurses via visit().
+	void outlineExpression(Expression& _expr);
+
+	/// List of statements that should go in front of the currently visited AST element,
+	/// at the statement level.
+	std::vector<Statement> m_statementsToPrefix;
+	NameDispenser& m_nameDispenser;
+};
+
+}
+}