Implement lazy function generation using function generation queue

libsolidity/codegen/MultiUseYulFunctionCollector.h

@@ -41,10 +41,15 @@ public:
 	std::string createFunction(std::string const& _name, std::function<std::string()> const& _creator);
 
 	/// @returns concatenation of all generated functions.
+	/// Guarantees that the order of functions in the generated code is deterministic and
+	/// platform-independent.
 	/// Clears the internal list, i.e. calling it again will result in an
 	/// empty return value.
 	std::string requestedFunctions();
 
+	/// @returns true IFF a function with the specified name has already been collected.
+	bool contains(std::string const& _name) const { return m_requestedFunctions.count(_name) > 0; }
+
 private:
 	/// Map from function name to code for a multi-use function.
 	std::map<std::string, std::string> m_requestedFunctions;