Add extism_load_v128/extism_store_v128

[zshipko]

We could improve load/store performance by adding extism_load_v128, extism_input_load_v128 and extism_store_v128

[OLUWAMUYIWA]

This looks interesting. I'll take it up

[zshipko]

@OLUWAMUYIWA Great! Last time I looked into it I had some issues getting Rust to reliably generate v128 values when compiling to wasm, so I think the first step would be to figure out if it's even possible to reliably use v128 in Rust, then we could try to add these.

These new functions would be in the kernel where debugging can get kinda tricky, so it makes sense to do as much as you can on a test project before moving some of the code into the kernel.

This also has a larger effects on the PDKs and stuff, so we would need to consider how to roll this out, but since it has the potential to provide significant performance improvements it is definitely worth exploring.

[OLUWAMUYIWA]

Thanks for the heads up, @zshipko!

[chrisdickinson]

It struck me that we could possibly achieve this by writing the v128 functions in WAT in a separate module, then using wasm-merge to combine that with the Rust kernel. I'm not sure what effect this would have on kernel verification efforts, though!

[zshipko]

That's a good idea! I don't think it would really cause any issues with the verification work.