To defend of 6xALU back end - Apple A12 Vortex core has 6xALU and has massive 1.76x IPC INT increase over Intel Xeon SkylakeX:

Code:

SPEC2006 INT
The Xeon turbos to 3.8 GHz while the A12 “turbos” to 2.5 GHz.

Xeon 8176 Apple A12

400.perlbench 46.4 45.38
401.bzip2 25.0 28.54
403.gcc 31.0 44.56
429.mcf 40.6 49.92
445.gobmk 27.6 38.54
456.hmmer 35.6 44.04
458.sjeng 30.8 36.60
462.libquantum 86.2 113.40
464.h264ref 64.5 66.59
471.omnetpp 37.9 35.73
473.astar 24.7 27.25
483.xalancbmk 63.7 57.03

The most powerful beast CPU on the world in term of INT IPC is running in your cellphone wiht TDP 4.2 Watts. HPC server CPU running @3.8 GHz outperformed by cellphone CPU running @2.5GHz by +12%. Pretty amazing.

+50% ALUs (4->6) deliver +76% IPC over Skylake .... with no SMT at all. Were you worry about utilizing 6xALU? Apple did it. Zen is internaly RISC processor as ARM is, so it's achievable.

SMT4 is not necessary however, Jim Keller knows Alpha EV8 SMT4 design for 20 years. And when you design new CPU because of increased ALUs, you need also new front-end, you can adopt also SMT4. Zen3 might be Jim's the big Zen CPU when he come back to AMD. Assuming that Zen1 was little Zen compromised-but-fast-developed design to avoid AMD's bankruptcy. But I might be wrong.

There is also rumors that ARM is working on desktop/server ARM CPU (and desktop ARM GPU). CPU with probably 6xALUs to keep up with Apple. Intel and AMD have to deliver 6xALU CPU very soon otherwise they are gonna be outperformed by any China company who buy ARM license. I assume they already start working on it when they analyzed Apple A12 Vortex CPU. Well no, 6xALUs brought A11 at 2017. So it's being while already.

Conclusion: I assume that Zen3 might be the first 6xALU x86 CPU just because it is inevitable and Jim Keller had opportunity to do that.

(src)

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