[YulOpt] Implement loop-invariant code motion

libyul/optimiser/SSAValueTracker.cpp

@@ -49,6 +49,16 @@ void SSAValueTracker::operator()(VariableDeclaration const& _varDecl)
 		setValue(_varDecl.variables.front().name, _varDecl.value.get());
 }
 
+set<YulString> SSAValueTracker::ssaVariables(Block const& _ast)
+{
+	SSAValueTracker t;
+	t(_ast);
+	set<YulString> ssaVars;
+	for (auto const& value: t.values())
+		ssaVars.insert(value.first);
+	return ssaVars;
+}
+
 void SSAValueTracker::setValue(YulString _name, Expression const* _value)
 {
 	assertThrow(