2 files changed, 111 insertions, 0 deletions
diff --git a/libyul/optimiser/SSAValueTracker.cpp b/libyul/optimiser/SSAValueTracker.cpp
new file mode 100644
index 00000000..a1291d67
--- /dev/null
+++ b/libyul/optimiser/SSAValueTracker.cpp
@@ -0,0 +1,53 @@
+/*
+	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/>.
+*/
+/**
+ * Component that collects variables that are never assigned to and their
+ * initial values.
+ */
+
+#include <libyul/optimiser/SSAValueTracker.h>
+
+#include <libsolidity/inlineasm/AsmData.h>
+
+using namespace std;
+using namespace dev;
+using namespace dev::yul;
+
+void SSAValueTracker::operator()(Assignment const& _assignment)
+{
+	for (auto const& var: _assignment.variableNames)
+		m_values.erase(var.name);
+}
+
+void SSAValueTracker::operator()(VariableDeclaration const& _varDecl)
+{
+	if (_varDecl.variables.size() == 1)
+		setValue(_varDecl.variables.front().name, _varDecl.value.get());
+	else
+		for (auto const& var: _varDecl.variables)
+			setValue(var.name, nullptr);
+}
+
+void SSAValueTracker::setValue(string const& _name, Expression const* _value)
+{
+	assertThrow(
+		m_values.count(_name) == 0,
+		OptimizerException,
+		"Source needs to be disambiguated."
+	);
+	m_values[_name] = _value;
+}
diff --git a/libyul/optimiser/SSAValueTracker.h b/libyul/optimiser/SSAValueTracker.h
new file mode 100644
index 00000000..8c39a98e
--- /dev/null
+++ b/libyul/optimiser/SSAValueTracker.h
@@ -0,0 +1,58 @@
+/*
+	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/>.
+*/
+/**
+ * Component that collects variables that are never assigned to and their
+ * initial values.
+ */
+
+#pragma once
+
+#include <libyul/optimiser/ASTWalker.h>
+
+#include <string>
+#include <map>
+#include <set>
+
+namespace dev
+{
+namespace yul
+{
+
+/**
+ * Class that walks the AST and stores the initial value of each variable
+ * that is never assigned to.
+ *
+ * Prerequisite: Disambiguator
+ */
+class SSAValueTracker: public ASTWalker
+{
+public:
+	using ASTWalker::operator();
+	virtual void operator()(VariableDeclaration const& _varDecl) override;
+	virtual void operator()(Assignment const& _assignment) override;
+
+	std::map<std::string, Expression const*> const& values() const { return m_values; }
+	Expression const* value(std::string const& _name) const { return m_values.at(_name); }
+
+private:
+	void setValue(std::string const& _name, Expression const* _value);
+
+	std::map<std::string, Expression const*> m_values;
+};
+
+}
+}