An apparatus for selectively executing different versions of executable code for the same source code, wherein the different versions are optimized in different ways, comprising: a receiving mechanism configured to receive an executable code module which includes two or more versions of executable code for the same source code, wherein the two or more versions are optimized in different ways; and an execution mechanism configured to execute the executable code module, wherein while executing the executable code module, the execution mechanism is configured to: evaluate a test condition; and to execute a specific version of the executable code based on the outcome of the evaluation, whereby the executable is optimized for the test condition.
