Instruction Orders

Which dependences need to be respected?

Type	Needs to be respected?
Program Order	No
Data (RAW) Dependence	Yes
Control Dependence	No
Name Dependences	WAR: No WAW: No

You’ll notice that RAW is the only one you truly have to respect because it is data dependence and affects program correctness.

Removing Name Dependences

These dependences only occur because we have a finite number of architectural registers. They are called ‘name’ dependences because we have to write to the same named register.

If we went to get rid of this type of dependence, we could possibly map registers to a different space. The tradeoff in this case is you have to maintain the mappings of each register and instruction and do bookkeeping.

Subtleties in Write-Back

At the architectural level, it should not be possible to observe whether the processor is in-order or out-of-order. This must hold even in the presence of an exception or interrupt.

We need to be able to provide precise exceptions and precise interrupts.