[diamondlovesyou]

I don't think scalable vectors is particularly useful feature, especially compared to what compilers have to go though to support it. It's much more useful to be able to do "more powerful" things with existing vector widths at hardware speeds (or perhaps just make the existing stuff faster than it is) than to be able to go wider. Scalable vectors also doesn't solve the ISA problem: don't break existing processors.

[evancox100]

Of course they are free to add new "more powerful" instructions to SVE at any time, just like Intel could for AVX, etc.

Also, I think it is supposed to be easier for compilers to autovectorize SVE than, say, neon. Whether that's the case in practice I don't know. Is there something specific you see that makes it more difficult than with SIMD-style, fixed operation width instructions? Or you are referring to something else with "compiler support"?