[Custom Descriptors] OptimizeInstructions: Optimize trapping in descriptor operations

[kripken]

No description provided.

[tlively]

It looks like we don't do skipNonNullCast on a ref.cast_desc descriptor, either, although we do already have trapOnNull. We don't have either for br_on_cast_desc{_fail}.

[kripken]

It looks like we don't do skipNonNullCast on a ref.cast_desc descriptor, either, although we do already have trapOnNull.

Is that valid? ref.cast_desc can succeed on a null descriptor, I think, if it is a nullable cast and the input is null?

[tlively]

No, it always traps on a null descriptor no matter what.

[kripken]

I don't see that in wasm-interpreter.h. Am I missing it, or is that a bug?

[tlively]

It's there in doDescCast:

    auto expected = desc.getSingleValue().getGCData();
    if (!expected) {
      trap("null descriptor");
    }

[kripken]

Sorry, I somehow read that twice and missed it...

[kripken]

Ok, added those too.