Also, I don’t think executing both sides of a branch ever took off on any mainstream CPUs (unless Itanium counts). It wastes power to spend half your execution units on things that won’t be committed, why not use them on the other hyperthread instead?
That part I am sure off. I will double check with a friend of mine of of curiosity, but one thing to note is that the execution units are processing branches up to the point when branch is evaluated, then the false path is dropped.
Back then the speed was trumping the power draw. I am not sure what are the priorities today.
In terms of hyperthread, i don't think you can safely execute instructions of both siblings due to possible shared cache mem clashes. But I am guessing now. Its been a while since I have been working that low level to remember the details.
Modern CPUs speculate hundreds of instructions ahead, and with just a dozen branches you can have a few thousand different paths. It makes more sense to speculate down one path with very high accuracy.
I think a lot of folks get mixed up with GPU and/or SIMD architecture, where you execute both sides of the branch out of necessity: Some of the lanes need to go one way and some the other, so you have to do both.
not to mention that you burn a lot more power.