I don't agree with what you are saying about Zen borrowing anything significant from BD. There's a video out there where David Kanter is asked about that and he seemed to struggle to come up with much other than the branch predictor (?), not sure. I'll try to find the video. If anything I'd think Zen borrowed some from the Cat Cores and maybe a bit from K10, but I think it was just mostly fresh stuff.
Around 39:00 he is asked about what came from BD, and can't come up with anything. Says ALU's then walks that back and says microcode. Then goes on about planar to FinFet and saying they basically had to redo it all anyway. I take that as basically saying nothing much if anything was taking from BD/XV.
Zen1 has few significant things from BD, like dual cluster FPU concept (
two 64-bit FPUs with ability to handle 128-bit AVX as well, in Zen uplifted to 128-bit to be able handle 256-bit AVX2), also SMU and separated INT and FPU. Dozer was bad due to very weak designed back-end (2xALUs) but concept itself was pretty innovative. As Keller said, they took the good things from both DB and Jaguar uarchs. Don't forget that speaking about BD legacy in Zen publicly was not good idea at that time. They needed to attract investors to great product, not to scare them with BD resurrection. IMHO that's why he spoke very vague in this topic.
I'm still having trouble trying to follow your K12 timeline. As
@moinmoin pointed out it was on their roadmap alongside Zen (Though not in that image as it's ARM only).
As moinmoin mentioned their first ARM CPU AMD A1100 based on Cortex A57 was delayed two years (2014->2016). High priority project Zen was delayed half year. Side project as K12 with all those challenges (bigger engine, new ISA) was probably delayed much more, probably at least one year more than Zen. I remember there was rumor about K12 was taped out in the same time as Zen however it doesn't make sense. It could be tape out of delayed A1100 as we know today. So K12 would reach market probably between 2018-2019.
Here begins the Zen 3 thing. AMD had half finished new K12 uarch with bigger engine in 2015 and Zen 3 development began about the same time. Here starts the questions:
- was AMD rich enough to waste 3 years of engineering work on K12? IMHO no.
- was good things developed for K12 used in Zen 3 design? IMHO yes, same way they used BD stuff for Zen.
- is Zen 3 reworked K12 to x86? IMHO Probably not, but it depends on how much ""bigger" the K12 engine was.
- does it make sense to build Zen 3 on similar 4xALU K12 engine like Zen1/2 just little bigger? Probably not.
- does it make sense to build Zen 3 on bigger 6xALU K12 engine? Probably yes.
EDIT: @Olsan: You're right. BD had 2x pipes of 128-bit FMAC, Excavator 3x pipes and Zen 4x pipes. So in fact Zen FPU is even more similar to BD/XV than I thought.