Nominal Types in WebAssembly
It was supposed to solve the problem of: some computers run x86, some arm, we need something that is equivalent, but portable across different cpus
What business is it for WebAssembly to know about complex types? What x86 instructions is there for `(type $t (struct i32))` ? Or doing garbage collection.
We would be better off standardizing on a subset of x86 and writing translators to arm etc. Or standardize on arm and translate to x86.
We know it can work. Apple did it with rosetta. Microsoft did it with Prism. I don't think WebAssembly implementation generate faster code than rosetta or prism.
QEMU did it simply (albeit slowly).
WebAssembly is becoming another JVM. It's not simple. It's not fast. It's not easy to use.
But now we're stuck with it and the only path is to add and add and add.
My emulators here have roughly the same performance as the same code compiled as native executable (e.g. within around 5%) - this is mostly integer bit twiddling code. Unless you hand-optimize your code beyond what portable C provides (like manually tuned SIMD intrinsics), WASM code pretty much runs at native speed these days:
Not disagreeing with you, but here’s an article from Akamai about how using WASM can minimize cold startup time for serverless functions.
https://www.akamai.com/blog/developers/build-serverless-func...
> Friends, as I am sure is abundantly clear, this is a troll post :)
He is showing S-expressions ? That is its' syntax ? I am intrigued now.
i32.const 27512
i32.load
local.tee $var1
if
i32.const 27404
i32.load
local.get $var1
call_indirect (param i32)
end
To see what a complete WASM blob looks like in WAT format you can go here: https://floooh.github.io/sokol-html5/clear-sapp.html, open the browser devtools, go to the 'Sources' tab and click the `clear-sapp.wasm` file).
(i32.add
(i32.const 0)
(i32.const 1))
> IIRC early pre-release-versions of WASM were entirely built from S-expressions and as a 'pure stack machine' (I may remember wrong though).
Yes, the S-expressions predate WebAssembly even being a stack machine. Originally the design was that it encoded an AST, so the folded S-expression format was the only option.
There was a lot of discussion back in the day (before my time) about creating a better text format, but no one could agree on what it should be, so they just defaulted to the S-expression idea and focused on getting WebAssembly out the door.
I know this is meant to be silly, and I am no expert, but I kinda do like this syntax. Its like shaking the struct and seeing what falls out.
This blog post mentions that you can kind of emulate nominal types by putting all your types in one rec group, but then it brushes that off as inferior to using exceptions. (Which is hilarious! Good work, Andy.) What it doesn’t make clear is that people actually use this rec group trick in practice. There are two ways to do it: you can put literally all your types in one rec group, or you can emit minimal rec groups with additional “brand types” that serve no purpose but to ensure the groups have different structures. The former solution is better for code size when the entire application is one module, but the latter solution is better if there are multiple modules involved. You don’t want to repeat every type definition in every module, and using smaller rec groups lets you define only the types that are (transitively) used in each module.
The Binaryen optimizer has to ensure that it does not accidentally give distinct types the same structural identity because that would generally be observable by casts. Most of its type optimizations therefore put all the types in one rec group. However, it does have a type merging optimization that takes the casts into account[0]. That optimization is fun because it reuses the DFA minimization code from the original equirecursive type system we were experimenting with for Wasm GC. We also have a rec group minimization optimization[1] that creates minimal rec groups (by finding strongly connected components of the type definition graph), then ensures the types remain distinct first by using different permutations of the types within a rec group and then only as necessary by adding brand types.
[0]: https://github.com/WebAssembly/binaryen/blob/main/src/passes...
[1]: https://github.com/WebAssembly/binaryen/blob/main/src/passes...