Revert of Remove register index/code indirection

src/x64/code-stubs-x64.h

 // Copyright 2011 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_CODE_STUBS_X64_H_
 #define V8_X64_CODE_STUBS_X64_H_
 
 namespace v8 {
 namespace internal {
 
@@ skipping 276 matching lines @@
     Register scratch0_orig_;
     Register object_;
     Register address_;
     Register scratch0_;
     Register scratch1_;
     // Third scratch register is always rcx.
 
     Register GetRegThatIsNotRcxOr(Register r1,
                                   Register r2,
                                   Register r3) {
-      for (int i = 0; i < Register::kNumRegisters; i++) {
-        Register candidate = Register::from_code(i);
-        if (candidate.IsAllocatable()) {
-          if (candidate.is(rcx)) continue;
-          if (candidate.is(r1)) continue;
-          if (candidate.is(r2)) continue;
-          if (candidate.is(r3)) continue;
-          return candidate;
-        }
+      for (int i = 0; i < Register::NumAllocatableRegisters(); i++) {
+        Register candidate = Register::FromAllocationIndex(i);
+        if (candidate.is(rcx)) continue;
+        if (candidate.is(r1)) continue;
+        if (candidate.is(r2)) continue;
+        if (candidate.is(r3)) continue;
+        return candidate;
       }
       UNREACHABLE();
       return no_reg;
     }
     friend class RecordWriteStub;
   };
 
   enum OnNoNeedToInformIncrementalMarker {
     kReturnOnNoNeedToInformIncrementalMarker,
     kUpdateRememberedSetOnNoNeedToInformIncrementalMarker
@@ skipping 42 matching lines @@
   Label slow_;
   RegisterAllocation regs_;
 
   DISALLOW_COPY_AND_ASSIGN(RecordWriteStub);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_CODE_STUBS_X64_H_