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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 undoes what the ExpressionSplitter did, i.e.
+ * it more or less inlines variable declarations.
+ */
+#pragma once
+
+#include <libyul/ASTDataForward.h>
+
+#include <libyul/optimiser/ASTWalker.h>
+
+#include <map>
+
+namespace dev
+{
+namespace julia
+{
+
+class NameCollector;
+
+
+/**
+ * Optimiser component that modifies an AST in place, turning sequences
+ * of variable declarations into complex expressions, if the variables
+ * are declared in the right order. This component does the opposite
+ * of ExpressionSplitter.
+ * Since the order of opcode or function evaluation is unchanged,
+ * this transformation does not need to care about conflicting opcodes.
+ *
+ * Code of the form
+ *
+ * let a1 := mload(y)
+ * let a2 := mul(x, 4)
+ * sstore(a2, a1)
+ *
+ * is transformed into
+ *
+ * sstore(mul(x, 4), mload(y))
+ *
+ * The transformation is not applied to loop conditions, because those are
+ * evaluated with each loop.
+ *
+ * The component can be applied to sub-blocks of the AST, you do not
+ * need to pass a full AST.
+ *
+ * Prerequisites: Disambiguator
+ *
+ * Implementation note: We visit the AST, modifying it in place.
+ * The class starts counting references and will only replace variables
+ * that have exactly one reference. It keeps a "latest statement pointer"
+ * which always points to the statement right before the current statement.
+ * Any function call or opcode will reset this pointer. If an identifier
+ * is encountered that was declared in the "latest statement", it is replaced
+ * by the value of the declaration, the "latest statement" is replaced
+ * by an empty block and the pointer is decremented.
+ * A block also resets the latest statement pointer.
+ */
+class ExpressionJoiner: public ASTModifier
+{
+public:
+	virtual void operator()(FunctionalInstruction&) override;
+	virtual void operator()(FunctionCall&) override;
+	virtual void operator()(If&) override;
+	virtual void operator()(Switch&) override;
+	virtual void operator()(Block& _block) override;
+
+	using ASTModifier::visit;
+	virtual void visit(Expression& _e) override;
+
+	static void run(Block& _ast);
+private:
+	explicit ExpressionJoiner(Block& _ast);
+
+	void handleArguments(std::vector<Expression>& _arguments);
+
+	void decrementLatestStatementPointer();
+	void resetLatestStatementPointer();
+	Statement* latestStatement();
+	bool isLatestStatementVarDeclOf(Identifier const& _identifier);
+
+	Block* m_currentBlock = nullptr;
+	size_t m_latestStatementInBlock = 0;
+	std::map<std::string, size_t> m_references;
+};
+
+}
+}