I see some fingerprinting potential here

[dead-claudia]

trafficstars

Most Intel-based processors nowadays have 256-bit support, while most ARM processors don't. There's likely other concerns, too, like with low-end phones that may lack NEON support.

[sampsyo]

FWIW, I think CPU fingerprinting is inevitable, even in fixed-length SIMD (https://github.com/WebAssembly/simd). I agree that's not great, but maybe we should try to focus here on potential problems relative to that existing SIMD proposal?