Reference types crash wasm-opt‘s asyncify pass

[surma]

(module
  (type (;0;) (func))
  (type (;1;) (func (result externref)))
  (import "gl" "createProgram" (func $src/asc/gl/createProgram (type 1)))
  (func $src/asc/lemonsoda/init (type 0)
    call $src/asc/gl/createProgram
    drop
  )
  (export "init" (func $src/asc/lemonsoda/init))
)

$ wat2wasm --enable-reference-types test.wat -o test.wasm
$ wasm-opt --asyncify --enable-reference-types test.wasm -o test2.wasm
invalid type
UNREACHABLE executed at /tmp/binaryen-20210320-71286-1g5tfwr/binaryen-version_100/src/wasm/wasm-type.cpp:488!
[1]    56081 abort      wasm-opt --asyncify --enable-reference-types test.wasm -o test2.wasm

[surma]

It seems to be specifically about using externref in imported functions. Both an externref parameter and return type will trigger this error, but not for an exported function.

[martianboy]

FWIW, this is not limited to externref, it happens for all reference types since they can't be stored on memory.
Just out of curiosity, @kripken would this entail setting the reftype value on a table and store the index instead?

[surma]

@martianboy Ah of course! That makes a lot of sense.

Since the reference types proposal also allows having multiple tables, it seems like your idea with the table is a really good one.

[martianboy]

@surma Right, although this cannot happen yet in Binaryen, as it still doesn't have table operations and typed tables. But it shouldn't be too difficult to support reference types in Asyncify after those are done. I may still be missing something though.

[kripken]

I think that's correct @martianboy & @surma. Yes, the issue is writing references to linear memory. Instead we would need to create a new table in asyncify, and use that to spill values using table.get/table.set, etc., so as mentioned above we'd need support for those features.

[martianboy]

Thanks for confirmation, @kripken. I'm in the middle of adding types to tables and element segments and after that I was planning to add table operations. I can see if I can fix Asyncify next. :)

[kripken]

Sounds great @martianboy ! I hope that's pretty straightforward when you get to it (only nontrivial part might be to have two "stack pointers"), let me know if you have questions I can help with.

[surma]

Not to be that impatient dude on GH, but curious if there are any updates on this?

[martianboy]

@surma So I'm "almost" done with implementation of table instructions which was a prerequisite. My guess is that I will be able to get to Asyncify in about 10 days. Sorry for the wait. :)

[surma]

Oh please, don’t apologize! I’m just curious! Very excited to see this :)

[surma]

Hey @martianboy, just wanted to gently ask if you had any time to get to this? 🙇‍♂️

[alexdoesh]

@kripken looks like the problem is still exists, can we elaborate a little bit more on how it should be solved, I'd be happy to spend time for this. any real blockers, or just a matter of implementation?