I really like what you are doing here, the state of inline assembly is a similar travesty to the state of guided codegen/autovec.

On concern I have is how this maps to ARM64 syntax, because ARM64 is massively overloading all mnemonics.

For example:

    ld1d z0.h, p0/z, [x1, x2, lsl 3]
    ld1d z0.h, p0/z, [x1, z0.h, lsl 3]

Have extremely different performance characteristics, yet would map to the same code:

    ld1d dst, p0/z, [base + idx<<3]

Imo this makes reading the assembly quite bothersome. I'm already not a fan of ARM64 doing the mnemonic overloading, but at least you can figure out the operation by looking at the same line further to the right.

Also, maybe I missed it, but how are you dealing with things like the /z modifier, pre/post-increment load/store and load pair? Or things like TBL/ST4/LD4?

Oh and how are the types going to work for RVV, where the type can't be determined at compile-time in all situations?