[stubs] Optimize LoadGlobalViaContextStub and StoreGlobalViaContextStub.

src/x64/macro-assembler-x64.h

 // Copyright 2012 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_X64_MACRO_ASSEMBLER_X64_H_
 #define V8_X64_MACRO_ASSEMBLER_X64_H_
 
 #include "src/assembler.h"
 #include "src/bailout-reason.h"
 #include "src/base/flags.h"
@@ skipping 1550 matching lines @@
                             int offset) {
   return Operand(object, index, scale, offset - kHeapObjectTag);
 }
 
 
 inline Operand ContextOperand(Register context, int index) {
   return Operand(context, Context::SlotOffset(index));
 }
 
 
+inline Operand ContextOperand(Register context, Register index) {
+  return Operand(context, index, times_pointer_size, Context::SlotOffset(0));
+}
+
+
 inline Operand GlobalObjectOperand() {
   return ContextOperand(rsi, Context::GLOBAL_OBJECT_INDEX);
 }
 
 
 // Provides access to exit frame stack space (not GCed).
 inline Operand StackSpaceOperand(int index) {
 #ifdef _WIN64
   const int kShaddowSpace = 4;
   return Operand(rsp, (index + kShaddowSpace) * kPointerSize);
@@ skipping 24 matching lines @@
     masm->popfq();                                                           \
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_