Update x64 RecordWrite comment. When the offset is zero the index...

src/x64/macro-assembler-x64.h

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 83 matching lines @@
   template <typename LabelType>
   void InNewSpace(Register object,
                   Register scratch,
                   Condition cc,
                   LabelType* branch);
 
   // For page containing |object| mark region covering [object+offset]
   // dirty. |object| is the object being stored into, |value| is the
   // object being stored. If |offset| is zero, then the |scratch|
   // register contains the array index into the elements array
-  // represented as a Smi. All registers are clobbered by the
-  // operation. RecordWrite filters out smis so it does not update the
-  // write barrier if the value is a smi.
+  // represented as an untagged 32-bit integer. All registers are
+  // clobbered by the operation. RecordWrite filters out smis so it
+  // does not update the write barrier if the value is a smi.
   void RecordWrite(Register object,
                    int offset,
                    Register value,
                    Register scratch);
 
   // For page containing |object| mark region covering [address]
   // dirty. |object| is the object being stored into, |value| is the
   // object being stored. All registers are clobbered by the
   // operation.  RecordWrite filters out smis so it does not update
   // the write barrier if the value is a smi.
   void RecordWrite(Register object,
                    Register address,
                    Register value);
 
   // For page containing |object| mark region covering [object+offset] dirty.
   // The value is known to not be a smi.
   // object is the object being stored into, value is the object being stored.
   // If offset is zero, then the scratch register contains the array index into
-  // the elements array represented as a Smi.
+  // the elements array represented as an untagged 32-bit integer.
   // All registers are clobbered by the operation.
   void RecordWriteNonSmi(Register object,
                          int offset,
                          Register value,
                          Register scratch);
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
   // ---------------------------------------------------------------------------
   // Debugger Support
 
@@ skipping 1554 matching lines @@
       Jump(adaptor, RelocInfo::CODE_TARGET);
     }
     bind(&invoke);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_