Yul Optimizer: Remove dead code

libyul/optimiser/DeadCodeEliminator.cpp

@@ -0,0 +1,94 @@
+/*
+	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 unreachable code.
+ */
+
+#include <libyul/optimiser/DeadCodeEliminator.h>
+#include <libyul/AsmData.h>
+
+#include <libevmasm/SemanticInformation.h>
+#include <libevmasm/AssemblyItem.h>
+
+#include <algorithm>
+
+using namespace std;
+using namespace dev;
+using namespace yul;
+
+namespace
+{
+bool isTerminating(yul::ExpressionStatement const& _exprStmnt)
+{
+	if (_exprStmnt.expression.type() != typeid(FunctionalInstruction))
+		return false;
+
+	auto const& funcInstr = boost::get<FunctionalInstruction>(_exprStmnt.expression);
+
+	return eth::SemanticInformation::terminatesControlFlow(funcInstr.instruction);
+}
+
+/// Returns an iterator to the first terminating statement or
+/// `_block.statements.end()()` when none was found
+auto findFirstTerminatingStatement(Block& _block)
+{
+	return find_if(
+		_block.statements.begin(),
+		_block.statements.end(),
+		[](Statement const& _stmnt)
+		{
+			if (
+				_stmnt.type() == typeid(ExpressionStatement) &&
+				isTerminating(boost::get<ExpressionStatement>(_stmnt))
+			)
+				return true;
+			else if (_stmnt.type() == typeid(Break))
+				return true;
+			else if (_stmnt.type() == typeid(Continue))
+				return true;
+
+			return false;
+		}
+	);
+}
+}
+
+void DeadCodeEliminator::operator()(Block& _block)
+{
+	auto& statements = _block.statements;
+
+	auto firstTerminatingStatment = findFirstTerminatingStatement(_block);
+
+	if (
+		firstTerminatingStatment != statements.end() &&
+		firstTerminatingStatment + 1 != statements.end()
+	)
+		statements.erase(
+			std::remove_if(
+				firstTerminatingStatment + 1,
+				statements.end(),
+				[] (Statement const& _s)
+				{
+					return _s.type() != typeid(yul::FunctionDefinition);
+				}
+			),
+			statements.end()
+		);
+
+	ASTModifier::operator()(_block);
+}
+