1. A method for implementation in a processor-based system, comprising: selecting a first subset of instructions, wherein each instruction in the first subset is the earliest in program order of instructions associated with a corresponding one of a plurality of sub-matrices of a matrix having a plurality of matrix entries, each matrix entry indicating the program order of one pair of instructions that are eligible for execution; and selecting, from the first subset of instructions, the instruction that is earliest in program order based on matrix entries associated with the first subset of instructions.