1. Role of instruction sets

Processor instruction sets comprise all the machine instructions that enable the processor to execute a program. They therefore play a dual interface role:

• Machine instructions are a minimum static language defining the operations to be performed by the hardware;

• machine instructions are the target of a compiler, i.e. they form the interface between high-level programming languages and the machine language.

At the same time, the apparent architecture as seen by the compiler must be capable of evolving over time, while respecting constraints so that it can be executed by different hardware architectures.