Yul Optimizer: Remove dead code

libyul/optimiser/DeadCodeEliminator.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/>.
+*/
+/**
+ * Optimisation stage that removes unused variables and functions.
+ */
+
+#pragma once
+
+#include <libyul/optimiser/ASTWalker.h>
+#include <libyul/YulString.h>
+
+#include <map>
+#include <set>
+
+namespace yul
+{
+
+/**
+ * Optimisation stage that removes unreachable code
+ *
+ * Unreachable code is any code within a block which is preceded by a
+ * return, invalid, break, continue, selfdestruct or revert.
+ *
+ * Function definitions are retained as they might be called by earlier
+ * code and thus are considered reachable.
+ *
+ */
+class DeadCodeEliminator: public ASTModifier
+{
+public:
+	using ASTModifier::operator();
+	void operator()(Block& _block) override;
+};
+
+}