1. A method, comprising: loading an executable program comprising a sequence of machine instructions compiled according to a source instruction set architecture (source ISA) for execution by a target instruction set architecture (target ISA)-based hardware execution unit, the loading including mapping a compiler built-in helper function (“helper function”) in the executable program to a target ISA machine instruction; and executing the loaded program, the executing comprising replacing the helper function with the target ISA machine instruction to which the helper function was mapped and executing the target ISA machine instruction.