1. An article of manufacture providing a code preparation environment embodied on one or more machine-readable storage media, comprising: instructions, stored in at least one machine-readable medium and executable by at least one processing unit, that: determine whether code units with caller-callee relationships have overlapping memory mappings between at least one caller code unit of the code units and at least one corresponding callee code unit called by the at least one caller code unit within a computer system that executes the code units by checking whether a boundary of a memory range of the at least one caller code unit falls within a memory range of the at least one corresponding callee code unit or a boundary of the memory range of the at least one corresponding callee code unit falls within the memory range of the at least one caller code unit; generates and utilizes a call graph representing the caller-callee relationships; and instruments the code units to at least reduce those of the code units that have overlapping memory mappings between the at least one caller code unit and the corresponding callee code unit called by the at least one caller code unit, the instrumenting including tightly packing one or more of code units that are called frequently and code units that execute concurrently into memory.