Partial revert for "[wasm] Implement ref.as_non_null"

This reverts unreviewed changes that were accidentally added to
commit 8fbbfdc.

Original change's description:
> [wasm] Implement ref.as_non_null
>
> Bug: 474940922
> Change-Id: I20f142ba41d3efa88872ae0dfa308170a8c0ff11
> Reviewed-on: https://chrome-internal-review.googlesource.com/c/v8/fuzzilli/+/8956716
> Commit-Queue: Matthias Liedtke <mliedtke@google.com>
> Auto-Submit: Matthias Liedtke <mliedtke@google.com>
> Reviewed-by: Leon Bettscheider <bettscheider@google.com>

Bug: 474940922
Change-Id: I5a8d7cc465384c304908502d0447cc3b6c9be6ef
Reviewed-on: https://chrome-internal-review.googlesource.com/c/v8/fuzzilli/+/9347522
Reviewed-by: Leon Bettscheider <bettscheider@google.com>
Commit-Queue: Leon Bettscheider <bettscheider@google.com>
Auto-Submit: Matthias Liedtke <mliedtke@google.com>

Author: Liedtke

Sources/Fuzzilli/Base/ProgramBuilder.swift

@@ -5549,15 +5549,6 @@ public class ProgramBuilder {
                                         }
                                     }
                                 ),
-                                (
-                                    .wasmRefExtern(),
-                                    {
-                                        let i31 = self.wasmRefI31(
-                                            self.consti32(
-                                                Int32(truncatingIfNeeded: self.b.randomInt())))
-                                        return self.wasmExternConvertAny(i31)
-                                    }
-                                ),
                             ]
                             // Note that for a type like eqref there are multiple valid options.
                             let options = allOptions.filter { $0.0.Is(type) }.map { $0.1 }
@@ -5587,15 +5578,6 @@ public class ProgramBuilder {
                                 return wasmStructNewDefault(
                                     structType: b.jsTyper.getWasmTypeDef(for: type))
                             }
-                            if abstractSuper == .WasmFunc {
-                                let signatureType = b.type(of: b.jsTyper.getWasmTypeDef(for: type))
-                                if let f = b.findVariable(satisfying: {
-                                    b.type(of: $0).wasmFunctionDef?.signatureType
-                                        == signatureType
-                                }) {
-                                    return wasmRefFunc(f)
-                                }
-                            }
                         }
                         if nullable {
                             return wasmRefNull(typeDef: b.jsTyper.getWasmTypeDef(for: type))

Tests/FuzzilliTests/WasmTests.swift

@@ -281,8 +281,9 @@ class WasmFoundationTests: XCTestCase {
                     nullable
                         || (
                             // Non-nullable heap types unsupported for these types.
-                            // TODO(mliedtke): Extend for ref func, extend for exnref once we can generate them.
-                            heapType != .WasmFunc && heapType != .WasmExn
+                            // TODO(mliedtke): Extend for ref extern, extend for ref func once we
+                            // have ref.func.
+                            heapType != .WasmFunc && heapType != .WasmExtern && heapType != .WasmExn
                             // Bottom null-types must be nullable.
                             && !heapType.isBottom())
                 }.map { ILType.wasmRef($0.0, nullability: $0.1) }
@@ -293,9 +294,6 @@ class WasmFoundationTests: XCTestCase {
                 }.map { b.type(of: $0.0).wasmTypeDefinition!.getReferenceTypeTo(nullability: $0.1) }
 
             b.buildWasmModule { wasmModule in
-                // Add a dummy function so that ref.func has something to pick.
-                wasmModule.addWasmFunction(with: [] => []) { _, _, _ in [] }
-
                 // Test multiple times. Note that this will lead to a huge test case (but will be
                 // significantly faster than invoking the JS engine many times).
                 for _ in 0..<10 {