1 files changed, 71 insertions, 0 deletions
diff --git a/libyul/optimiser/CommonSubexpressionEliminator.cpp b/libyul/optimiser/CommonSubexpressionEliminator.cpp
new file mode 100644
index 00000000..23d15cad
--- /dev/null
+++ b/libyul/optimiser/CommonSubexpressionEliminator.cpp
@@ -0,0 +1,71 @@
+/*(
+	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 replaces expressions known to be the current value of a variable
+ * in scope by a reference to that variable.
+ */
+
+#include <libyul/optimiser/CommonSubexpressionEliminator.h>
+
+#include <libyul/optimiser/Metrics.h>
+#include <libyul/optimiser/SyntacticalEquality.h>
+#include <libyul/Exceptions.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::yul;
+
+void CommonSubexpressionEliminator::visit(Expression& _e)
+{
+	// We visit the inner expression first to first simplify inner expressions,
+	// which hopefully allows more matches.
+	// Note that the DataFlowAnalyzer itself only has code for visiting Statements,
+	// so this basically invokes the AST walker directly and thus post-visiting
+	// is also fine with regards to data flow analysis.
+	DataFlowAnalyzer::visit(_e);
+
+	if (_e.type() == typeid(Identifier))
+	{
+		Identifier& identifier = boost::get<Identifier>(_e);
+		string const& name = identifier.name;
+		if (m_value.count(name))
+		{
+			assertThrow(m_value.at(name), OptimizerException, "");
+			if (m_value.at(name)->type() == typeid(Identifier))
+			{
+				string const& value = boost::get<Identifier>(*m_value.at(name)).name;
+				if (inScope(value))
+					_e = Identifier{locationOf(_e), value};
+			}
+		}
+	}
+	else
+	{
+		// TODO this search is rather inefficient.
+		for (auto const& var: m_value)
+		{
+			assertThrow(var.second, OptimizerException, "");
+			if (SyntacticalEqualityChecker::equal(_e, *var.second))
+			{
+				_e = Identifier{locationOf(_e), var.first};
+				break;
+			}
+		}
+	}
+}