Understanding subtyping matching

[CharlieTap]

Hello,

I'm running into a problem when testing my runtime against the wasm test suite, specifically this test:

gc/test/core/gc/ref_test.wast

Line 276 in e5af649

(br_if $l (ref.test (ref $t1) (table.get (i32.const 0))))

I'm currently matching these two types as I've made the following assumptions:

• Both references are non null
• Reference 1 is a reference to the abstract heap type struct
• Reference 2 is a defined type which when expanded is a composite type struct

Looking at the matching logic from the reference interpreter it would appear that these should match:

gc/interpreter/valid/match.ml

Line 78 in e5af649

| DefHT dt, t ->

So I'm guessing maybe Reference 1 should not be a abstract heap type of struct? I get this after substituting the reference type embedded in the instruction 🤔

Somewhere I'm going wrong and I feel like I should be comparing two defined types and thus would be not matching because the structs don't match

[tlively]

Reference 1 is also a defined type, not the abstract heap type struct. (type $t0 (sub (struct))) is a defined struct type with zero fields.

[CharlieTap]

Thank you, I think its my type_of_ref equivalent function should be more complex for the Function, Array and Struct scenarios.

For anyone looking at this in the future, the logic for these branches appears:

Struct and Arrays

gc/interpreter/runtime/aggr.ml

Line 59 in e5af649

let type_of_ref' = !Value.type_of_ref' in

Functions

gc/interpreter/runtime/instance.ml

Line 43 in e5af649

let type_of_ref' = !Value.type_of_ref' in