[wasm] Support externref returns in the generic wrapper

Externref does not need a translation from WebAssembly to JavaScript.
The return value can therefore just be forwarded to JavaScript.

R=thibaudm@chromium.org

Bug: v8:12565
Change-Id: I3b3ae37578c2793f6c09d1345f4ee555b40c853d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3404779Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78721}

src/builtins/x64/builtins-x64.cc

@@ -3544,6 +3544,11 @@ void Builtins::Generate_GenericJSToWasmWrapper(MacroAssembler* masm) {
   __ cmpq(valuetype, Immediate(wasm::kWasmF64.raw_bit_field()));
   __ j(equal, &return_kWasmF64);
 
+  // All types that are not SIMD are reference types.
+  __ cmpq(valuetype, Immediate(wasm::kWasmS128.raw_bit_field()));
+  // References can be passed to JavaScript as is.
+  __ j(not_equal, &return_done);
+
   __ int3();
 
   __ bind(&return_kWasmI32);

src/wasm/function-compiler.cc

@@ -175,10 +175,14 @@ bool UseGenericWrapper(const FunctionSig* sig) {
   if (sig->returns().size() > 1) {
     return false;
   }
-  if (sig->returns().size() == 1 && sig->GetReturn(0).kind() != kI32 &&
-      sig->GetReturn(0).kind() != kI64 && sig->GetReturn(0).kind() != kF32 &&
-      sig->GetReturn(0).kind() != kF64) {
-    return false;
+  if (sig->returns().size() == 1) {
+    ValueType ret = sig->GetReturn(0);
+    if (ret.kind() == kS128) return false;
+    if (ret.is_reference()) {
+      if (ret.heap_representation() != wasm::HeapType::kExtern) {
+        return false;
+      }
+    }
   }
   for (ValueType type : sig->parameters()) {
     if (type.kind() != kI32 && type.kind() != kI64 && type.kind() != kF32 &&