Dart SIMD use case.

Hello!

I just wanted to briefly share some use cases for this in the Dart world.

We are working on adding better SIMD support to the dart2wasm compiler in Dart.

One of the use cases we can't support right now is an efficient SIMD based scan.

To be able to efficiently scan through a byte stream (or a string to implement the memchr equivalent in Dart called indexOf) using SIMD we'd need to have the ability to reinterpret parts of the backing storage as appropriate types that allow us to cheaply treat a chunk of it as a SIMD type.

Here's some more Dart use cases from another perspective from @osa1 in https://github.com/WebAssembly/gc/issues/395#issuecomment-1630391803

An 8x unrolled SIMD based scan can achieve 120GB/s on a modern mac using NEON. It would be great if use cases like these could be opened up with this proposal. Experiments show that we are at least an order of magnitude away from being able to reach those numbers with wasm gc.

Start with the issue text and the linked WebAssembly GC discussion to understand the Dart dart2wasm SIMD scan use case and the proposed multibyte array access behavior. No repository files or tests are named, and completion criteria are not defined; the issue would need a concrete proposal or acceptance criterion before implementation can begin.