[clang] [llvm] [WebAssembly] Represent reference types as TargetExtType (PR #203165)

[Hood Chatham via llvm-commits]

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@@ -2839,6 +2840,43 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     return CGF.authPointerToPointerCast(Result, E->getType(), DestTy);
   }
   case CK_AddressSpaceConversion: {
+    llvm::Type *DestLTy = ConvertType(DestTy);
+    // WebAssembly reference types are opaque target extension types so an
+    // "address space conversion" involving them is not a real pointer cast.
+    auto IsWasmFuncref = [](llvm::Type *T) {
+      auto *TET = dyn_cast<llvm::TargetExtType>(T);
+      return TET && TET->getName() == "wasm.funcref";
+    };
+    bool SrcIsFuncref = IsWasmFuncref(ConvertType(E->getType()));
+    bool DestIsFuncref = IsWasmFuncref(DestLTy);
+    if (SrcIsFuncref && DestIsFuncref) {
+      // funcref -> funcref (e.g. between differently-typed funcrefs) is the
+      // identity on the opaque reference value.
+      return Visit(E);
+    }
+    if (SrcIsFuncref && !DestIsFuncref) {
+      // funcref -> pointer: use wasm_funcref_to_ptr. This will probably crash
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hoodmane wrote:

For now let's not do that. I think for it to work correctly we need a stack of funcrefs, and it's just not worth it.

https://github.com/llvm/llvm-project/pull/203165