> One thing a lot of people do not seem to realize is compilers do not use the full instruction set. They use a subset and this subset is what has to be fast.

> One thing a lot of people do not seem to realize is compilers do not use the full instruction set. They use a subset and this subset is what has to be fast. That’s a self-fulfilling prophecy. Compiler writers won’t use the instructions that are (relatively) slow. If, tomorrow, Intel makes ‘add’ slow, compilers will eventually start compiling addition as negation + subtraction (and AMD will become more popular) That’s what makes hardware designers unhappy sometimes. If they ship a shiny faster CPU that requires a large overhaul of compilers, it can take time for compiler writers to catch up. Hardware designers shouldn’t (only) aim for getting closer to the local optimum of where compiler writers are, but also for the higher peaks of where they could be.