[wasm] Implement polymorphic checking, matching the reference interpreter.

src/wasm/wasm-opcodes.h

Index: src/wasm/wasm-opcodes.h
diff --git a/src/wasm/wasm-opcodes.h b/src/wasm/wasm-opcodes.h
index 69773d59ca182da91a66bb30e062b8fff59dbeb6..a3c322c43fff9065f91823753393247f49ebcbbe 100644
--- a/src/wasm/wasm-opcodes.h
+++ b/src/wasm/wasm-opcodes.h
@@ -36,8 +36,7 @@ const ValueType kWasmI64 = MachineRepresentation::kWord64;
 const ValueType kWasmF32 = MachineRepresentation::kFloat32;
 const ValueType kWasmF64 = MachineRepresentation::kFloat64;
 const ValueType kWasmS128 = MachineRepresentation::kSimd128;
-// We use kTagged here because kNone is already used by kWasmStmt.
-const ValueType kWasmEnd = MachineRepresentation::kTagged;
+const ValueType kWasmVar = MachineRepresentation::kTagged;
 
 typedef Signature<ValueType> FunctionSig;
 std::ostream& operator<<(std::ostream& os, const FunctionSig& function);
@@ -649,10 +648,9 @@ class V8_EXPORT_PRIVATE WasmOpcodes {
         return 's';
       case kWasmStmt:
         return 'v';
-      case kWasmEnd:
-        return 'x';
+      case kWasmVar:
+        return '*';
       default:
-        UNREACHABLE();
         return '?';
     }
   }
@@ -671,8 +669,8 @@ class V8_EXPORT_PRIVATE WasmOpcodes {
         return "s128";
       case kWasmStmt:
         return "<stmt>";
-      case kWasmEnd:
-        return "<end>";
+      case kWasmVar:
+        return "<var>";
       default:
         return "<unknown>";
     }