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

src/wasm/wasm-opcodes.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_WASM_OPCODES_H_
 #define V8_WASM_OPCODES_H_
 
 #include "src/globals.h"
 #include "src/machine-type.h"
 #include "src/runtime/runtime.h"
@@ skipping 18 matching lines @@
 
 // We reuse the internal machine type to represent WebAssembly types.
 // A typedef improves readability without adding a whole new type system.
 typedef MachineRepresentation ValueType;
 const ValueType kWasmStmt = MachineRepresentation::kNone;
 const ValueType kWasmI32 = MachineRepresentation::kWord32;
 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);
 
 typedef Vector<const char> WasmName;
 
 typedef int WasmCodePosition;
 const WasmCodePosition kNoCodePosition = -1;
 
 // Control expressions and blocks.
@@ skipping 591 matching lines @@
       case kWasmI64:
         return 'l';
       case kWasmF32:
         return 'f';
       case kWasmF64:
         return 'd';
       case kWasmS128:
         return 's';
       case kWasmStmt:
         return 'v';
-      case kWasmEnd:
-        return 'x';
+      case kWasmVar:
+        return '*';
       default:
-        UNREACHABLE();
         return '?';
     }
   }
 
   static const char* TypeName(ValueType type) {
     switch (type) {
       case kWasmI32:
         return "i32";
       case kWasmI64:
         return "i64";
       case kWasmF32:
         return "f32";
       case kWasmF64:
         return "f64";
       case kWasmS128:
         return "s128";
       case kWasmStmt:
         return "<stmt>";
-      case kWasmEnd:
-        return "<end>";
+      case kWasmVar:
+        return "<var>";
       default:
         return "<unknown>";
     }
   }
 };
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_OPCODES_H_