[wasm] Initial commit for the Int64Reducer.

src/compiler/int64-lowering.h

+// 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.
+
+#ifndef V8_COMPILER_INT64_REDUCER_H_
+#define V8_COMPILER_INT64_REDUCER_H_
+
+#include "src/compiler/common-operator.h"
+#include "src/compiler/graph.h"
+#include "src/compiler/machine-operator.h"
+#include "src/compiler/node-marker.h"
+#include "src/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class Int64Lowering {
+ public:
+  Int64Lowering(Graph* graph, MachineOperatorBuilder* machine,
+                CommonOperatorBuilder* common, Zone* zone);
+
+  void ReduceGraph();
+  Graph* graph() const { return graph_; }
+  MachineOperatorBuilder* machine() const { return machine_; }
+  CommonOperatorBuilder* common() const { return common_; }
+
+ private:
+  enum class State : uint8_t { kUnvisited, kOnStack, kInputsPushed, kVisited };
+
+  struct Replacement {
+    Node* low;
+    Node* high;
+  };
+
+  void ReduceTop();
+  void ReduceNode(Node* node);
+
+  Graph* const graph_;
+  MachineOperatorBuilder* machine_;
+  CommonOperatorBuilder* common_;
+  NodeMarker<State> state_;
+  ZoneStack<Node*> stack_;
+  Replacement* replacements_;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_INT64_REDUCER_H_