Bug 268848 – [Wasm-GC] Fix br_on_cast issue on BBQ

• Status: RESOLVED
• Resolution: FIXED
• Component: WebAssembly

[Asumu Takikawa]

There's a bug in the handling of `br_on_cast` on the BBQJIT tier. Test case:

```
diff --git a/JSTests/wasm/gc/br_on_cast.js b/JSTests/wasm/gc/br_on_cast.js
index dbf465442c6b..f62897236627 100644
--- a/JSTests/wasm/gc/br_on_cast.js
+++ b/JSTests/wasm/gc/br_on_cast.js
@@ -116,6 +116,22 @@ function testBrOnCast() {
     assert.eq(m.exports.f1(), 1);
     assert.eq(m.exports.f2(), 0);
   }
+
+  {
+    let m = instantiate(`
+      (module
+        (type (struct))
+        (type (struct (field (ref null 0))))
+        (global (ref 1) (struct.new 1 (struct.new 0)))
+        (func (export "f") (param) (result structref)
+          (block $exit (result structref)
+            (struct.get 1 0
+               (br_on_cast_fail $exit structref (ref 1)
+                 (global.get 0)))))
+      )
+    `);
+    m.exports.f();
+  }
 }
 
 testBrOnCastValidation();
```

The test runs fine in LLInt and OMG tiers though. I think it has to do with register allocation or the stack handling in BBQ (which is generally trickier than in those tiers, especially for this instruction).

[Asumu Takikawa]

Pull request: https://github.com/WebKit/WebKit/pull/24016

[Radar WebKit Bug Importer]

<rdar://problem/122902355>

[EWS]

Committed 275920@main (d8ada2256e9e): <https://commits.webkit.org/275920@main>

Reviewed commits have been landed. Closing PR #24016 and removing active labels.