1. A method in a data processing system for processing expressions, the method comprising: responsive to receiving expressions, identifying parameters for the expressions to form a set of identified parameters; identifying each type of execution unit that can execute the instructions needed to process the expressions using the set of identified parameters, wherein a set of identified execution unit types is formed; selecting an execution unit type from the set of identified execution unit types to meet a performance goal; and generating the instructions for the execution unit type to process the expressions.