An unexpected perf feature

I wasn't commenting whether it was a good design. I don't know, as I haven't used it. I was just saying Itanium marked the point when Intel went back to sticking to the knitting - in other words trying to design a new architecture whose sole goal was to run programs fast. If you say they failed despite having that explicit goal then that's a shame.

As I recall the Itanium tried to improve it's speed in a RISC like way - ie by keeping things simple on the hardware side and offloading decisions to the compiler. In the Itanium's case those decisions were about parallelism.

I think it's pretty clear now tuning the machine language to whatever hardware is available at the time is a mistake when you are going for speed. It might work when the hardware is first designed, but then the transistor budget doubles and all those neat optimisations don't much so much sense anymore, but you are welded to them because there are hardwired into the instruction set. Instead the route we have gone down is to implement a virtual CPU, rather like the JVM. The real CPU then compiles the instruction set on the fly into something that can be run fast with todays transistor budget. With tomorrows transistor budget it might be complied into something different.

The x86 instruction set is actually good pretty in this scenario - better than ARM. It's compact, and each instruction gives lots of opportunities to execute bits of it in parallel. If this is true, then Intel ending up with an architecture that can run fast is just dumb luck, as they weren't planning for it 30 years ago. Now that I think about it, the VAX instruction set would probably be even better again.