Formal modelling and transformations of processor instruction sets

Instruction sets of modern processors contain hundreds of instructions defined on a relatively small set of datapath components and distinguished by their codes and the order in which they activate these components. Optimal design of an instruction set for a particular combination of available hardware components and software requirements is crucial for system performance and is a challenging task involving a lot of heuristics and high-level design decisions. The overall design process is significantly complicated by inefficient representation of instructions, which are usually described individually despite the fact that they share a lot of common behavioural patterns. This paper presents a new methodology for compact graph representation of processor instruction sets, which gives the designer a new high-level perspective for reasoning on large sets of instructions without having to look at each of them individually. This opens the way for various transformation and optimisation procedures, which are formally defined and explained on several examples, as well as practically evaluated on an FPGA platform.