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Some of SSE is required as part of the x86_64 ABI, and also new versions of Windows (infamously, now) add required CPU extensions so software will often base its requirements on that. And SSE4x is ubiquitous enough (99% of PCs) that some software/games will just require it and simply crash if it can't use those instructions.

It looks like many Linux distros require x86-64-v2 from 2008 and they're preparing to move to v3 from 2013. At this rate they'll never support a level with expired patents. https://en.wikipedia.org/wiki/X86-64#Microarchitecture_level...

Considering there are no meaningful patent-free x86 CPUs in the wild, why should they?

It's just the default optimization level for those distros. If patent-free x86 CPUs become relevant, compiling another set of binaries would be trivial. Until then it doesn't make any sense to kneecap the >99% of x86 deployments by deliberately refusing to use faster and more efficient instructions.

> Considering there are no meaningful patent-free x86 CPUs in the wild, why should they?

Open core; no ME.

That's a fair point. I guess a bigger problem is that a patent-free x86 processor couldn't run any supported version of Windows.

That's the last thing I would want to do.

No, often any fallback would be unusuably slow anyway.