[compiler] [wasm] Introduce Word32/64ReverseBytes as TF Optional Opcode

test/unittests/compiler/int64-lowering-unittest.cc

 // Copyright 2016 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.
 
 #include "src/compiler/int64-lowering.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node.h"
 
@@ skipping 801 matching lines @@
 
 TEST_F(Int64LoweringTest, I64PhiFloat64) {
   TestPhi(this, MachineRepresentation::kFloat64, Float32Constant(1.5),
           Float32Constant(2.5));
 }
 
 TEST_F(Int64LoweringTest, I64PhiWord32) {
   TestPhi(this, MachineRepresentation::kWord32, Float32Constant(1),
           Float32Constant(2));
 }
+
+TEST_F(Int64LoweringTest, I64ReverseBytes) {
+  LowerGraph(graph()->NewNode(machine()->Word64ReverseBytes().placeholder(),
+                              Int64Constant(value(0))),
+             MachineRepresentation::kWord64);
+  EXPECT_THAT(
+      graph()->end()->InputAt(1),
+      IsReturn2(IsWord32ReverseBytes(IsInt32Constant(high_word_value(0))),
+                IsWord32ReverseBytes(IsInt32Constant(low_word_value(0))),
+                start(), start()));
+}
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8