Is Webassembly compilation a look-up table?

Question

My understanding is that Webassembly is basically a set of machine code instructions that all supported processors have in common, i.e. it contains commands like "pop register 2', but not specialized commands specific to only a few processors, e.g. Intel MMX commands.

It seems to me that, given programs limited to these common commands, compiling them is merely a matter of looking up the local equivalent machine code for each listed Wasm code, which would explain how "streaming compilation" is possible.

Is this description accurate, grossly oversimplified, or flat out wrong?

Answer 1

Is WebAssembly compilation a look-up table?

No.

My understanding is that Webassembly is basically a set of machine code instructions that all supported processors have in common

No, it is not. WebAssembly has a simple instruction set that is assembly-like in some ways (bitwise operators, load, store, simple maths), however, in other ways it is not at all like assembly language. It supports functions, structured control flow - in the future it will support reference types, etc ...

It seems to me that, given programs limited to these common commands, compiling them is merely a matter of looking up the local equivalent machine code for each listed WASM code, which would explain how "streaming compilation" is possible.

The 'streaming compilation' works because the binary format of WebAssembly precedes each section, function body etc ... is preceded with its length. This makes it easy to split it into 'chunks' which are compiled across different threads.

Is this description accurate, grossly oversimplified, or flat out wrong?

Perhaps a bit of each? ;-)

You can find out much more about the design goals of WebAssembly on the 'Design Rationale' page on the website:

https://webassembly.org/docs/rationale/