Use WebAssembly bulk memory opcodes for memcpy/memset?

[TerrorJack]

WebAssembly bulk memory opcodes have shipped for major browsers for some time. Does it make sense to use that for memcpy/memset functions in wasi-libc? If there are no objections in principle, I'd like to try opening a PR for this.

[sunfishcode]

That sounds great!

It appears bulk-memory is supported in all the engines tracked in the roadmap, and according to this bulk memory was standardized in February.

Could you write the code guarded with #ifdef __wasm_bulk_memory__? I expect we'll enable it by default, but that way if someone wants to make a custom build of wasi-libc without it, they can pass -mno-bulk-memory to clang and build their own.

[kripken]

I'd recommend measuring the effect of this. At least at some point it was the case that not all browsers optimized these operations very well. (But it is a win for size, of course.)