Hacker News Reader

Comment by airforce1 | Hacker News Reader

In my experience it is pretty difficult to make WASM faster than JS unless your JS is really crappy and inefficient to begin with. LLVM-generated WASM is your best bet to surpass vanilla JS, but even then it's not a guarantee, especially when you add js interop overhead in. It sort of depends on the specific thing you are doing.

I've found that as of 2025, Go's WASM generator isn't as good as LLVM and it has been very difficult for me to even get parity with vanilla JS performance. There is supposedly a way to use a subset of go with llvm for faster wasm, but I haven't tried it (https://tinygo.org/).

I'm hoping that Microsoft might eventually use some of their wasm chops to improve GO's native wasm compiler. Their .NET wasm compiler is pretty darn good, especially if you enable AOT.

View on HN

I think the Wasm backends for both Golang and LLVM have yet to support the Wasm GC extension, which would likely be needed for anything like real parity with JS. The present approach is effectively including a full GC implementation alongside your actual Golang code and running that within the Wasm linear memory array, which is not a very sensible approach.

Yeah. If I remember it correctly, you need to compile the GC to run on WASM if the GC extension is not supported.

The GC extension is supported within browsers and other WASM runtimes these days - it's effectively part of the standard. Compiler developers are dropping the ball.

The Wasm GC currently doesn't support the functionality needed by both Go and C#. (Interior pointers, for instance)

I'm hoping that a later version makes this possible.

The major roadblocks for WasmGC in Golang at the moment are (A) Go expects a non-moving GC which WasmGC is not obligated to provide; and (B) WasmGC does not support interior pointers, which Go requires.

https://github.com/golang/go/issues/63904#issuecomment-22536...

These are no different than the issues you'd have in any language that compiles to WasmGC, because the new GC'd types are (AIUI) completely unrelated to the linear "heap" of ordinary WASM - they are pointed to via separate "reference" types that are not 'pointers' as normally understood. That whole part of the backend has to be reworked anyway, no matter what your source language is.

Go exposes raw pointers to the programmer, so from your description i think those semantics are too rudimentary to implement Go's semantics, there would need to be a WasmGC 2.0 to make this work.

It sounds like it would be a great fit for e.g. Lua though.

I don't think Go supports any pointer arithmetic out-of-the-box? What it has in the base language is effectively references.

It does, via unsafe package, yes it does look ugly, that is on purpose.

    item := *(*int)(unsafe.Pointer(uintptr(start) + size*uintptr(i)))

A random example taken from Internet.

That's not the base language, it's an unsafe superset. There's no reason why a Wasm-GC backend for Golang should be expected to support that by default.

If it is part of the language reference it is part of the language.

Usually when language reference books used to be printed, or we used ISO languages, what is there on paper, is the language.

We are only discussing semantics, if it is hardcoded primitives, or made available via the standard library, specially in case of blessed packages like unsafe which aren't fully implemented, rather magical types for the compiler.

Hence why the only thing you will see here is mostly documentation, https://github.com/golang/go/blob/master/src/unsafe/unsafe.g...

Which is nothing new since the 1960's that there are systems languages with some way to mark code unsafe, the C linage of languages are the ones that decided to ignore this approach.

The standard library uses unsafe for syscalls, for higher-performance primitives like strings.Builder, etc, so it's support is mandatory to run any non-trivial Go program

Somehow I don't think Wasm-GC is going to support bare metal syscalls anytime soon. That stuff all has to be rewritten anyway if you want to target WASM.

It's not just system calls. E.g. reflection package uses unsafe too: https://github.com/golang/go/blob/master/src/reflect/value.g... . Many packages from Go standard library use unsafe one way or the other, so it's not fair to say that unsafe package is separate from the rest of the language

For a while the GOOS=nacl port and the Google App Engine ports of Go disallowed unsafe pointer manipulation too, so there is some precedent. Throughout some of the ecosystem you can see pieces of "nounsafe" build tag support (e.g. in easyjson).

Most programming languages that offer unsafe, either as language keyword, or meta package (unsafe/SYSTEM/UNSAFE whatever the name), have similar option, that doesn't make it less of a feature.

It also has an address-of operator, you can take the address of the middle of a large array.

I suppose that would be possible with fat-pointers that are reference+offset.

You can get a pointer inside a struct ("interior pointers") without pointer arithmetic.

> the Wasm GC extension, which would likely be needed for anything like real parity with JS

Well, for languages that use a GC. People who are writing WASM that exceeds JS in speed are typically doing it in Rust or C++.

I did some perf benchmarks a few years ago on some JS code vs C code compiled to WASM using clang and running on V8 vs the same C code compiled to x64 using clang.

The few cases that performed significantly better than the JS version (like >2x speed) were integer-heavy math and tail-call optimized recursive code, some cases were slower than the JS version.

What I was surprised was that the JS version had similar performance to the x64 version with -O3 in some of my benchmakrs (like float64 performance).

This was a while ago though when WASM support had just landed in browsers, so probably things got better now.

Apparently not good enough, given the decision to use Go.

Reply on news.ycombinator.com