[Feature Request] Add Wasm Relaxed SIMD support and integer dot product instructions for ONNX Runtime Web

[jing-bao]

Describe the feature request

Wasm Relaxed SIMD includes integer dot product instructions, which will map to VNNI instructions on X86-64 platforms with AVX-VNNI (on ARM maybe SDOT, but I haven't tested), and can greatly improve the QGemm performance. And there may be more optimizations in the future if Relaxed SIMD is supported.

I have some local patches to add Wasm Relaxed SIMD build and VNNI dispatch for QGemmU8X8 to MLAS, and they improve Segment Anything Model performance to ~1.15x. Are such modifications welcome?

Describe scenario use case

Many Web models are quantized, and can benefit from the integer dot product instructions.

[fs-eire]

Hi @jing-bao, it is definitely welcome if you can help contributing to MLAS to support relaxed SIMD for WebAssembly!

I have a question regarding the Relaxed SIMD support: if the browser/Nodejs version does not support Relexed SIMD, will it just failed to load the WebAssembly or there is still a chance to fallback to old code?