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

src/compiler/int64-lowering.cc

 // Copyright 2014 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/diamond.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/machine-operator.h"
@@ skipping 760 matching lines @@
         Node* high_node = GetReplacementHigh(node);
         for (int i = 0; i < node->op()->ValueInputCount(); i++) {
           low_node->ReplaceInput(i, GetReplacementLow(node->InputAt(i)));
           high_node->ReplaceInput(i, GetReplacementHigh(node->InputAt(i)));
         }
       } else {
         DefaultLowering(node);
       }
       break;
     }
+    case IrOpcode::kWord64ReverseBytes: {
+      DCHECK(machine()->Word32ReverseBytes().IsSupported());

[titzer, 2016/07/29 18:21:53]

Can you remove this DCHECK? E.g. the optional operator's .op() method will fail
if it is not supported below.

+      Node* input = node->InputAt(0);
+      ReplaceNode(node, graph()->NewNode(machine()->Word32ReverseBytes().op(),
+                                         GetReplacementHigh(input)),
+                  graph()->NewNode(machine()->Word32ReverseBytes().op(),
+                                   GetReplacementLow(input)));
+      break;
+    }
 
     default: { DefaultLowering(node); }
   }
 }  // NOLINT(readability/fn_size)
 
 void Int64Lowering::LowerComparison(Node* node, const Operator* high_word_op,
                                     const Operator* low_word_op) {
   DCHECK(node->InputCount() == 2);
   Node* left = node->InputAt(0);
   Node* right = node->InputAt(1);
@@ skipping 75 matching lines @@
                     common()->Phi(MachineRepresentation::kWord32, value_count),
                     value_count + 1, inputs_low, false),
                 graph()->NewNode(
                     common()->Phi(MachineRepresentation::kWord32, value_count),
                     value_count + 1, inputs_high, false));
   }
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8