RFR 8014911 - Use SUPPORTS_NATIVE_CX8 to help C++ compiler elide code

[David Holmes]

On 19/09/2013 2:41 PM, David Holmes wrote:
> On 19/09/2013 2:39 AM, BILL PITTORE wrote:
>> Would like a review for this simple fix that leverages the macro
>> 'SUPPORTS_NATIVE_CX8' that was added in hotspot revision:
>> changeset:   4611:6b388e7d4905
>> parent:      4547:e01e02a9fcb6
>> user:        bpittore
>> date:        Tue May 07 10:19:33 2013 -0400
>> summary:     8013633: Cleanup platform ifdefs in unsafe.cpp
>>
>> SUPPORTS_NATIVE_CX8 is defined in globalDefinitions_<arch>.hpp based on
>> whether the platform supports 64bit cmpxchg natively. This change uses
>> the define to force the supports_cx8() function to return hard-coded
>> 'true' value. GCC and other compilers will then optimize code that uses
>> supports_cx8() function call by removing the actual reference to
>> _supports_cx8 variable as well as eliminating code for the
>> !supports_cx8() case.
>> Webrev is here: http://cr.openjdk.java.net/~bpittore/8014911/webrev.00/
>
> Can't we also delete the field itself?

To answer my own question ...

Yes _but_ then we'd have to make all the platform specific code that 
sets _supports_cx8 conditional on SUPPORTS_NATIVE_CX8 as well. That's 
unnecessarily intrusive.

David


> David
>
>> thanks,
>> bill
>>