1. A method, in a data processing system, for optimizing code execution, comprising: associating, in the code of a program, an instruction with a kill data object intrinsic specifying a data object of the instruction; compiling the code of the program, wherein compiling the code of the program comprises performing an optimization operation for reordering instructions in a program flow of the code; and restricting reordering of instructions in the program flow of the code that operate on the data object such that the instructions are not moved across a point in the program flow of the program where the data object is specified as having been killed by the kill data object intrinsic.