alt Hacker NewsYou can’t really conditionally compute something in hardware. The hard to do the computation exists and is wired up always.
The conditional jump is a great example actually. Typically this would be implemented by having one block compute PC+<instruction size> and another block compute the jump target and then choosing between the two using a mux
That is one way of implementing such conditionals in hardware, but it's just one aspect of the computation. First, we can both agree that in the next clock cycle, a single instruction will be executed, not both instructions that could result after the jump - so clearly the hardware doesn't always do both things.
Secondly, if we think about the instruction decoding itself, it should become pretty clear that even if the hardware of course always exists and is always going to output something, that's not equivalent to saying it will compute all options. If the next instruction is `add ax, bx`, the hardware is not going to compute both ax + bx and ax - bx and ax & bx and ax | bx and so on, and then choose which result to feed back to ax through a mux. Instead, the ALU is constructed of logic gates which evaluate a single logical expression that assigns each output bit to a logical combination of the input bits and the control signal.