University of Johannesburg

Keywords • Combinatorial optimisation • Compilers (Computer programs) • Scheduling The topic for this dissertation is the optimisation of computer programs, as they are being compiled, using discrete optimisation techniques. The techniques introduced aim to optimise the runtime performance of programs executing on certain types of processors. A very important component of this dissertation is the movement of complexity from the processor to the compiler. Therefore both computer architecture and compilers are important supporting topics. The data output of the compiler is processed using information about the processor to produce execution information which is the goal of this disserta-tion. Concepts related to instruction level parallelism are covered in two parts. The first part discusses implicit parallelism, where parallel instruction scheduling is performed by the processor. The second part discusses explicit parallelism, where the compiler schedules the instructions. Explicit parallelism is attractive because it allows processor design to be simplified resulting in multiple benefits. Scheduling the instructions to execute while adhering to resource limitations is the area of focus for the rest of the dissertation. In order to find optimal schedules the problem is modelled as a mathematical program. Expressing instructions, instruction dependencies and resource limitations as a mathematical program are discussed in detail with several algorithms being introduced. Several aspects prevent the mathematical programs from being solved in their initial state, therefore additional techniques are introduced. A heuristic algorithm is introduced for scheduling instructions in a resource limited environment. The primary use of this heuristic is to reduce the computational complexity of the problem. However, this heuristic algorithm can be used to generate good schedules on its own. i ii Finally information regarding a practical implementation of a compiler that implements the introduced techniques is introduced as well as experimental results. The experimental results are generated from a series of test programs illustrating the complete process and the computational complexity of the algorithms employed.