[turbofan] Use load/store indexes as 64-bit registers on arm64.

src/compiler/arm64/code-generator-arm64.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/code-generator.h"
 
 #include "src/arm64/macro-assembler-arm64.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
@@ skipping 82 matching lines @@
       case kMode_Operand2_R_LSL_I:
       case kMode_Operand2_R_LSR_I:
       case kMode_Operand2_R_ASR_I:
       case kMode_Operand2_R_ROR_I:
         break;
       case kMode_MRI:
         *first_index += 2;
         return MemOperand(InputRegister(index + 0), InputInt32(index + 1));
       case kMode_MRR:
         *first_index += 2;
-        return MemOperand(InputRegister(index + 0), InputRegister(index + 1),
-                          SXTW);
+        return MemOperand(InputRegister(index + 0), InputRegister(index + 1));
     }
     UNREACHABLE();
     return MemOperand(no_reg);
   }
 
   MemOperand MemoryOperand() {
     int index = 0;
     return MemoryOperand(&index);
   }
 
@@ skipping 906 matching lines @@
     }
   }
   MarkLazyDeoptSite();
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8