Generic CPU discussion

I will give this a go.

"Are there systematic ways you could simplify the x86 architecture and instruction code without making the binaries incompatible?" :

Nope. I think there's a contradiction in the question, or it depends upon what you are keeping constant when you 'simplify'. If you simplify the instruction codes then you will get to binary incompatibility. That is, prior binaries will not run for some instructions on the simplified encoding. As for the architecture, that's already been done while keeping binary compatibility on executables. For instance, microcode is an 'inner' layer with respect to the 'outer' layer of instruction encoding. It makes a CISC be implemented by a RISC. RISC and CISC are in truth arbitrary/relative terms for regions on a spectrum of universal machine designs.

"Or alternatively once you had it built recompile from source code?" :

Alan Turing would say yes¹, in that any universal machine² can mimic any other universal machine - in it's sequence of outputs for a given sequence of inputs - with the rider that it may do that mimicry in a different time frame and/or with a different amount of storage. Generically speed and storage are tradeable one for the other.

"Or might a compiler using a subset of the IC produce a more efficient binary?" :

Probably not in general as per the speed/storage trade. It kind of depends on what you mean by more efficient. Faster ie. fewer total cycles? Smaller footprint when stored? What are the constraints?

ASIDE : These concerns will be examined more closely in the near future, as I think we have approached the end of Moore's law : which used to solve any efficiency problem simply by waiting for faster silicon to be manufactured. The masking of silicon features is well into the UV realm and any (much) further reduction in wavelength will begin to impose upon the lattice substrate etc.

Cheers, Mike.

1. See ON COMPUTABLE NUMBERS, WITH AN APPLICATION TO THE ENTSCHEIDUNGSPROBLEM which is more than a bit dense in parts. But it is the underlying seminal work for modern computing devices and algorithms. See also the works of John von Neumann.

2. See Part 1 of the above paper, that part which is titled "Computing machines". 

In my opinion, from a 3950x, a reasonable upgrade would be a 24 or 32 core CPU. 5950x is great, but does not provide that much computing power compared to a 3950x in multithreaded workloads. 10-15% uplift does not justify the extra cost. If anyone has a 8 or 12 core CPU on AM4 platform, then yes, 5950x is the ultimate way to go.