Advanced Micro Devices Inc (AMD)

[HailMary]

So, 4 HT threads would not require twice as much register space.

That is correct, but they would require a whole bunch of other things be duplicated or partitioned. The instruction TLB, reorder buffers, various queues, etc.

I think a 4 way HT core would be too complex for too little gain. I doubt we'll see this from either Intel or AMD. AMD seems to even say they are not going to do a HT core at all in favor of multiple cores. It may be for AMD's microarchitecture the benefits of HT are very small. Higher IPC cores will be able to utilize HT less. Long pipeline cores with lower IPC like P4, however, have more waste in the execution units that the 2nd thread can use.