so it means NAVI is still GCN (despite RDNA moniker) and next gen is the real next gen slated for 2020 as AMD Earning Calls roadmap shows. Thanks
If this were a CPU architecture like x86-64, being listed as the same class of machine target for a compiler would go a very long way towards saying it's a member of the same overall architecture or a close derivative.
x86 would be viewed holistically as a combination of instruction formats, behaviors, and properties the vendors and industry have either spelled out or have over time committed to upholding.
That level of definition and abstraction from the implementation is why some wildly different microarchitectures from Athlon, Pentium, Pentium Pro, P4, Zen, and Core are still counted under the same overall umbrella of x86 even though for practical reasons there are architectural shifts like the various modes and corner cases between cores and vendors that make compatibility less than perfect.
GPUs and GCN as an example of them are messier. At an ISA level, AMD has made changes many times that would be problematic for CPUs. In part, it's because GPUs often have intervening compilation and software layers that allow for less than ironclad adherence. What GCN is would be a complicated question. The LLVM changes, for example, reflect a more CU and compute shader focused view of the GPU overall. GPUs are themselves not as tightly defined as CPUs, as the basic operation of a GPU runs through many processors and cores versus the architected single pipeline of a CPU.
Also GCN has committed to various behaviors or features within the scope of the CUs that many CPU architectures would not. Whether that's a side effect of marketing or a choice made purposefully, it increases the list of things that might then be considered architectural changes.
We also don't have all the information yet about what has been changed, so significant alterations might be disclosed. The question about how many changes is enough is at least a little arbitrary and usually a judgement call, and as the vendor AMD has more judgement over it than I do.
The more changes there are, the more I think it would be clearly justified, but I don't think there's any absolute arbiter over these matters and the situation has started out murky.
I'd be delighted if AMD took the opportunity to outline what they consider the set of design-defining elements of GCN, so that we could get closer to the heart of the matter. Although one side effect of not being rigorous all along is that it's possible that AMD could have generated one or more counterexamples for some of them, which would weaken the credibility of the model put forward now.
didn´t they said the same about Polaris and then Vega ? I recall some Bridgman talk about how they rebuild every block in Polaris to get different lego....
That's part of the distinction between architecture and implementation. IP blocks can be different, and every new process means reimplementing things as well. That's where there's usually a defined set of outcomes and behaviors that the implementation is supposed to adhere to that helps categorize things.
