Bug 254178 – [Wasm-GC] Air assertion failure when casting to nullref

• Component: WebAssembly
• Status: RESOLVED FIXED

[Tim Chevalier]

An existing test, https://searchfox.org/wubkat/source/JSTests/wasm/gc/casts.js , fails in the wasm-simd, wasm-bbq, and wasm-air configurations when running the run-jsc-stress-tests script. I'm not sure why the test isn't being run with these configurations in CI.

The output is:
```
wasm.yaml/wasm/gc/casts.js.wasm-simd: ASSERTION FAILED: isSubtype(src.type(), dst.type())
wasm.yaml/wasm/gc/casts.js.wasm-simd: /home/tjc/WebKit/Source/JavaScriptCore/wasm/WasmAirIRGenerator64.cpp(701) : void JSC::Wasm::AirIRGenerator64::emitMove(const JSC::Wasm::TypedTmp&, const JSC::Wasm::TypedTmp&)
```

and the specific test case causing the error is the first one in `testNullCasts()`:

```
        (func (param arrayref) (result nullref)
          (ref.cast none (local.get 0)))
```

I'll submit a PR.

[EWS]

Committed 261935@main (bd06994b39e7): <https://commits.webkit.org/261935@main>

Reviewed commits have been landed. Closing PR #11730 and removing active labels.

[Radar WebKit Bug Importer]

<rdar://problem/107021321>