[turbofan] Machine operators are globally shared singletons.

src/compiler/simplified-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_SIMPLIFIED_LOWERING_H_
 #define V8_COMPILER_SIMPLIFIED_LOWERING_H_
 
 #include "src/compiler/js-graph.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node.h"
 #include "src/compiler/simplified-operator.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class SimplifiedLowering {
  public:
-  explicit SimplifiedLowering(JSGraph* jsgraph)
-      : jsgraph_(jsgraph), machine_(jsgraph->zone()) {}
+  explicit SimplifiedLowering(JSGraph* jsgraph) : jsgraph_(jsgraph) {}
   virtual ~SimplifiedLowering() {}
 
   void LowerAllNodes();
 
   // TODO(titzer): These are exposed for direct testing. Use a friend class.
   void DoLoadField(Node* node);
   void DoStoreField(Node* node);
   void DoLoadElement(Node* node);
   void DoStoreElement(Node* node);
   void DoStringAdd(Node* node);
@@ skipping 19 matching lines @@
   Graph* graph() { return jsgraph()->graph(); }
   CommonOperatorBuilder* common() { return jsgraph()->common(); }
   MachineOperatorBuilder* machine() { return &machine_; }
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMPLIFIED_LOWERING_H_