The Contract

This contract is between the programmer and the system. The system consists of the compiler that generates machine code, the processor that executes the machine code and includes the different caches that store the state of the program. Each of the participants wants to optimise its part. For example, the compiler uses registers or modifies loops; the processor performs out of order execution or branch prediction; the caches applies prefetching of instructions or buffering of values. The result is - in the good case - a well-defined executable, that is fully optimised for the hardware platform. To be precise, there is not only a single contract, but a fine-grained set of contracts. Or to say it differently: the weaker the rules are that the programmer has to follow, the more potential there is for the system to generate a highly optimised executable.

There is a rule of thumb. The stronger the contract, the fewer liberties for the system to generate an optimised executable...