[moring]

> some implementation even needs LLVM to perform optimizations. I'd say if this is the case, we must've chosen the wrong model.

Why? Optimizing machine-independent code for a particular machine is part of the "core business" of LLVM, up to the point where a sufficiently capable bytecode/optimizer becomes comparable to LLVM.

OTOH, if the main argument here is the size/speed/other weight of LLVM, then of course the host machine that wants to run WASM only needs a tiny subet of LLVM: no frontend, single backend, only a subset of optimization passes... There is also a tradeoff to make to leave optimization passes out that actually improve the code a bit but are too heavy for the host machine.

[xuejie]

There's nothing wrong with LLVM itself, my point is we could've picked a lower level model which don't need a complicated setup like LLVM. Or one that you can direct shipped optimized compiled result of LLVM, that will be a much better world

[ptx]

Doesn't ARM code emulated on x86 (and vice versa) perform even worse than WebAssembly? Isn't that essentially what you would get with a lower-level "optimized compiled result of LLVM"?

[xuejie]

Does the fact that ARM is a bad choice disproves all other choices other than WASM? I'm not sure this is a good argument here. Lower-level bytecodes are more flourishing than just ARM.

[ptx]

I imagine it's more difficult to translate efficiently between two different low-level instruction sets (such as ARM, MIPS, x86, PowerPC, etc.) than to translate something slightly higher-level to the various low-level target instruction sets. Emulating ARM on x86 is usually slow (see the Android emulator) as is the reverse (see Windows 10 on ARM) and PowerPC on x86 (Apple's Rosetta) didn't seem particularly fast either.

Do you have an example in mind of a lower-level instruction set that can be efficiently translated to different real-world ISAs?

[afiori]

I believe that you are looking at wasm with a different priorities than intended. The two fundamental properties are that it must be fully portable and fully secure by default (as in any insecurity needs to be explicitly and statically declared in the bytecode).

Performance comes only after those two. LLVM as far as I know, has a completely different order of priorities.

[xuejie]

Personally I don't see why we cannot get all three.